U.S. patent application number 10/464173 was filed with the patent office on 2004-01-15 for apparatus and method for cleaning pipelines, tubing and membranes using two-phase flow.
Invention is credited to Labib, Mohamed Emam, Lai, Chung-Yue, Tabani, Yacoob.
Application Number | 20040007255 10/464173 |
Document ID | / |
Family ID | 33539000 |
Filed Date | 2004-01-15 |
United States Patent
Application |
20040007255 |
Kind Code |
A1 |
Labib, Mohamed Emam ; et
al. |
January 15, 2004 |
Apparatus and method for cleaning pipelines, tubing and membranes
using two-phase flow
Abstract
An apparatus and method for cleaning passageways and the like
with a two-phase mixture of gas under pressure and an aqueous
cleaning solution. The two-phase cleaning mixture is generated in a
module and is passed out of the module at a predetermined rate that
determines droplet size, velocity and droplet density at the
pipeline surface to be cleaned. The droplets impact the walls of
the passageway to be cleaned, thereby fragmenting, eroding and
removing contaminants in said passageway. These are then flushed
out of the passageway by the two-phase flow. The flow of cleaning
solution can be steady or pulsed. The apparatus and process include
a clean-in-place system that is useful in food, beverage,
pharmaceutical and similar process industries.
Inventors: |
Labib, Mohamed Emam;
(Princeton, NJ) ; Lai, Chung-Yue; (Lawrenceville,
NJ) ; Tabani, Yacoob; (Basking Ridge, NJ) |
Correspondence
Address: |
Birgit E. Morris, Esq.
16 Indian Head Road
Morristown
NJ
07960
US
|
Family ID: |
33539000 |
Appl. No.: |
10/464173 |
Filed: |
June 18, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10464173 |
Jun 18, 2003 |
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10091201 |
Mar 5, 2002 |
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10091201 |
Mar 5, 2002 |
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09466714 |
Dec 17, 1999 |
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6454871 |
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09466714 |
Dec 17, 1999 |
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08880062 |
Jun 20, 1997 |
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5892462 |
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Current U.S.
Class: |
134/30 ;
134/166C; 134/22.12; 134/26; 134/94.1 |
Current CPC
Class: |
B08B 9/0327 20130101;
B08B 9/032 20130101; G01C 5/005 20130101; B01D 65/02 20130101; B08B
9/0328 20130101; C11D 11/0041 20130101; C23G 1/00 20130101; C11D
3/48 20130101; A61L 2/18 20130101; B01D 65/022 20130101; B01D
2321/28 20130101; A61B 90/70 20160201; B08B 2209/022 20130101; A61B
2090/701 20160201; A61M 1/169 20130101; B08B 9/0326 20130101; C11D
3/044 20130101; C11D 3/3956 20130101; A61L 2/22 20130101; C23G 5/00
20130101; B01D 2321/04 20130101; B01D 2321/185 20130101; A61M
1/1682 20140204 |
Class at
Publication: |
134/30 ;
134/22.12; 134/26; 134/94.1; 134/166.00C |
International
Class: |
B08B 009/00 |
Claims
We claim:
1. An apparatus for cleaning pipes, tubing and membranes
comprising: a module have a gas inlet and a liquid inlet wherein a
two phase flow of gas and liquid is stored, and an outlet for
passing the resultant two phase flow into one or more pipes, tubing
or membranes to be cleaned; an air or gas source for supplying said
gas to said module; one or more holding tanks for liquid connected
to said module; a first pumping means for supplying said liquid at
a predetermined rate to said module; a second pumping means for
supplying gas under pressure to said module; a mist separator
connected to said module that collects said two phase flow,
separates the gas and the liquid and passes them through separate
outlets.
2. An apparatus according to claim 1 wherein said two phase flow
has a gas to liquid ratio between about 50:1 to 15,000:1.
3. An apparatus according to claim 1 further including a
backflushing line connected to one or more valves to supply
pressurized liquid at a predetermined rate.
4. An apparatus according to claim 1 further comprising one or more
holding tanks for supplying sanitizing solutions to aid module
through one or more valves that deliver said sanitizing solution at
a predetermined rate.
5. An apparatus according to claim 1 further comprising one or more
holding tanks for supplying rinse solution to said module through
one or more valves that deliver said rinse solution at a
predetermined rate.
6. An apparatus according to claim 5 further comprising one or more
valves and lines from said module to the lines being cleaned at a
predetermined rate.
7. An apparatus according to claim 1 further comprising a
controller connected to said apparatus for delivering cleaning
solution, gas, rinse solution and sanitizer solution to said module
at a predetermined rate and for a predetermined time, in any
sequence.
8. An apparatus according to claim 1 further comprising a nozzle
that generates droplets of a predetermined size to said module.
9. A method of cleaning pipes, tubing and membranes comprising
mixing air under pressure and an aqueous cleaning solution having a
pH of 1.0 to 14.0 in an enclosed module at a predetermined rate so
as to obtain a gas to liquid ratio of between 50:1 and 15,000:1,
thereby creating a two-phase flow of gas and liquid; passing said
mixture to one or more lines to be cleaned; backflushing said lines
with the cleaning liquid under pressure; flushing said lines with a
sanitizing solution; rinsing said lines with an aqueous solution;
and drying said lines.
10. A method according to claim 9 wherein said two-phase mixture is
formed using a nozzle that generates droplets in the liquid between
25 and 400 microns in size.
11. A method according to claim 9 wherein said gas and liquid pass
along said pipes at a velocity of from 10 meters per second to 200
meters per second.
12. A method according to claim 9 wherein said gas and liquid is
pulsed.
Description
[0001] This invention is a continuation-in-part of Ser. No.
10/091,201 filed Mar. 5, 2002, which is a continuation-in-part of
Ser. No. 09/466,714 filed Dec. 17, 1999, now U.S. Pat. No.
6,454,871 issued Sep. 24, 2002; which is a continuation-in-part of
application Ser. No. 08/880,062 filed Jun. 23, 1997, now U.S. Pat.
No. 6,027,572.
[0002] This invention relates to apparatus and method for removing
contaminants adhered to a lumen surface. More particularly this
invention relates to apparatus and method for cleaning passageways,
pipelines, tubing and membranes of adherent contaminants.
BACKGROUND OF THE INVENTION
[0003] In order to achieve effective cleaning and removal of
adhered substances or contaminants, including biofilm, proteins,
carbohydrates, lipids, milk residues, deposits of food, beverages,
contaminants of pharmaceuticals, including bio-pharmaceuticals and
the like from equipment, piping and membrane surfaces, the adhesion
forces between such contaminants and the surface to be cleaned must
be overcome by the action of the cleaning process. To achieve good
cleaning of such adhered residue or contaminants, the shear
stresses generated by the cleaning process must be higher than the
adhesive strength of the adhered contaminants to the surface to be
cleaned. The simplest form of adhesion is due to van der Waals
forces of attraction between the contaminant and the surface.
[0004] However, during actual industrial processing, other surface
forces, such as electrostatic forces of attraction, acid-base
interactions, hydrophobic forces, entanglement of contaminant
molecules with roughness features of the substrate, or combinations
of the above, are usually present between the surface of equipment
or pipes and the contaminants to be removed. In these cases, the
adhesion forces can become too high to be overcome with a simple
circulation or flushing of cleaning liquids in the passageways, and
thus cleaning cannot be achieved with such conventional means. When
the contaminant is insoluble in the liquid employed in the cleaning
operation, detachment of the contaminant from the surface and its
subsequent flushing out from the pipeline, tubing and/or passageway
are necessary to achieve good cleaning.
[0005] The physical nature of contaminants at a surface determines
the extent and level of cleaning difficulty. The contaminant may be
present on the surface as discrete particles or as layers of
particles, in separate domains or areas covered by the contaminant.
In the most difficult case, a continuous layer, as in the case of
biofilm, food and dairy residues is present. Many cases of interest
to the present invention relate to contaminants that are not
soluble in the liquid or solution used in the cleaning process. The
present invention is directed to cases when contaminants are mostly
insoluble in the liquid used for a cleaning operation, when
overcoming adhesion plays a considerable role in the cleaning
process.
[0006] The conventional way to clean a pipeline, tubing or a
passageway is to pass or circulate a liquid through the passageway.
When the contaminant is present as discrete particles, or separate
domains adhering to the surface, particle detachment, or
contaminant domain detachment, by fluid (gas or liquid) flow must
be achieved in order to clean the surface of the passageway. To
achieve contaminant detachment, mechanical forces or shear stresses
must be able to reach the contaminated surface. The ability to
bring sufficient shear stress to the contaminated surface is a
difficult task because of the fundamental limitations arising from
the presence of a liquid boundary layer at the surface. The effect
of the boundary layer on the ability to detach contaminants and
clean surfaces of pipelines, tubing and passageways will be further
explained below.
[0007] If the contaminant is present as discrete particles, and
when there are several layers in the contaminant domain, it is
possible to remove individual particles from the topmost layer of
the contaminant domain. The removed particles then can be entrained
and removed from the pipeline or passageway. It is possible that a
whole section of the layer can be removed and entrained in a
flowing fluid by a process called "denudation." However, the
contaminant layer may be left behind at the surface if the forces
generated by the flow condition are not sufficient to detach the
entire contaminant, especially with the limitation imposed by the
presence of a liquid boundary layer at the surface. This is the
case with conventional liquid circulation cleaning methods.
Further, if the flow conditions are not sufficient to carry the
detached contaminant out of the pipeline or passageway, the
detached contaminants can deposit back onto the surface, and
re-attach to the surface, or become entrapped in the boundary layer
of the liquid near the surface. Therefore, it is necessary in order
to achieve cleaning to provide flow conditions to transport the
detached contaminants outside of the pipeline, tubing or
passageway.
[0008] The conventional way to decrease the adhesive strength of a
contaminant adhering to a surface is to use surfactants in the
cleaning solution. Surfactant molecule may transport to the gap
between the particle and the surface, and adsorb in the gap. The
adsorption of surfactants increases the separation distance between
the particle and the surface to be cleaned, and thus achieves a
decrease in the adhesion strength of the particle to the surface,
and thereby enhances detachment and transfer of the solid into the
flowing fluid. The degree of detachment from the surface depends on
the contact area between the contaminant and the surface to be
cleaned. In the case of discrete particles attached to the surface,
the contact area is small and detachment is possible. As the
contact area between contaminant and surface increases, the total
adhesion force become too large for liquid flow to achieve
contaminant detachment, even in the presence of surfactants and
conventional liquid flow rates. The most difficult contaminant to
remove is when the contaminant covers most or even the entire
surface to be cleaned, as in the case of biofilm, or a completely
coated surface of food residues or other contaminants that are
numerous in industrial processing, including pharmaceutical and
biopharmaceutical residues.
[0009] When the contaminant covers the entire surface of a
passageway, such as in the case of biofilm, milk or protein
residues, and when the thickness of the contaminant layer is large,
it is difficult for the surfactant to reach the interface between
the contaminants and the surface, and therefore the adhesive
strength remains high for cleaning with conventional liquid
circulation, even if the cleaning solution includes surfactants and
other cleaning ingredients. Furthermore, in the case of liquid
circulation at 5 feet/sec, as in the conventional clean-in-place
(hereinafter C-I-P) cleaning method, the shear stresses created at
the surface are too small to detach biofilm or protein layers. This
is due to the presence of thick boundary layers and other complex
limitations due to fluid dynamics, and due to the difficulty of
transfer of shear forces to the surface to be cleaned. This
normally leads to lengthy cleaning times and to the use of high pH
fluids, such as caustic and other harsh chemicals.
[0010] The final result is always insufficient for good and
efficient cleaning. The use of liquid flow also demands large
amounts of cleaning liquids, rinse water and other liquids used in
the process of CIP cleaning. The result of such limitation is both
economic and environmental, including loss of production time, the
cost of expensive chemicals, and consumption of large amounts of
water for rinsing operations, in addition to the cost of
neutralization and discharge of the waste generated from such
cleaning operations. Cleaning processes may in some cases produce
more waste to discharge than the production operation itself, a
scenario common in food, pharmaceuticals, biopharmaceuticals and
other industrial processes.
[0011] The contact area between biofilm and tubing, pipeline or
passageway surfaces that carry water or other processing liquids,
is very large, since it almost covers the entire lumen surface as
compared to the small contact area of a discrete particle attached
to the surface. Correspondingly, the adhesion force of biofilm, or
other similar contaminants that cover most or the entire lumen
surface of a passageway, becomes very large. In order to achieve
detachment and removal of biofilm or similar substances, the
contaminant needs to be fragmented to create cracks or holes in the
continuous S contaminant layer so that surfactant diffusion to the
interface between the contaminant and the surface of a passageway
becomes possible.
[0012] Fragmentation of biofilm and like contaminants is believed
to be necessary to allow surfactant diffusion and adsorption at the
interface between the biofilm and the surface. The latter process
is important for decreasing the adhesive strength of the biofilm to
the lumen surface (interior surface) of a passageway. Otherwise,
the adhesive strength of biofilm to solid surfaces such as glass,
metal or plastic, as measured by many investigators, ranges from 50
to 120 Pascals, which is too high for conventional liquid
circulation to overcome, even in the presence of surfactants.
Therefore, fragmentation and crack formation of biofilm and like
contaminant layers is needed to allow the decrease of the adhesion
forces between biofilm and a surface to a level that is amenable to
cleaning and provides sufficient shear stresses created by the flow
conditions used in cleaning operations. This fragmentation and
crack formation is almost impossible to achieve with conventional
liquid circulation which is too slow for many applications.
SUMMARY OF THE INVENTION
[0013] In accordance with the present invention, two phase flow of
a gas and a liquid is generated and creates droplets of liquid that
are formed and re-formed along the length of pipelines, tubing or
passageways. The high velocities and controlled liquid to gas ratio
of the flow, as well as the composition of the cleaning solution,
provide conditions such that the liquid boundary layer is thin or
non-existent. Droplets form and re-form continually, impacting the
lumen surface to be cleaned. In the particularly difficult case of
a highly adherent biofilm, droplet impact of the biofilm results in
inertial hydrodynamic erosion of the biofilm layer that results in
biofilm fragmentation and in the creation of cracks in the biofilm
that allow surfactant molecules to diffuse and transport into the
interface between the biofilm and the lumen surface of the
pipeline, tubing or passageway. Using the two-phase flow of the
present invention, the droplets that impact the surface are
optimized with respect to size and velocity by the key flow
parameters including; gas and liquid velocity, gas to liquid ratio,
cleaning composition, surface tension equilibrium and dynamic
surface tension properties of the cleaning solution, also taking
into account the wetting properties of the lumen surface to be
cleaned.
[0014] The droplets created by the two phase flow of this invention
achieve biofilm fragmentation and detachment, and the biofilm
fragments that are detached from the surface bounce back into the
gas:liquid flow along with the droplets and become incorporated
into the moving two-phase flow as it travels along the pipeline,
tubing or passageway. Biofilm fragments can then be entrained in
the air stream, or with the liquid fraction of the two-phase flow.
Thus the detached biofilm is swept along and flushed out of the
passageway during this cleaning process.
[0015] The embodiments of the invention include apparatus and
process for cleaning, rinsing and sanitizing/disinfecting tubing,
pipelines, passageways including hollow membranes and other
equipment. The combination of the apparatus and cleaning process
according to the invention further includes a clean-in-place
(hereinafter C-I-P) systems for use in food, beverage,
pharmaceutical and other industries.
BRIEF DESCRIPTION OF THE DRAWING
[0016] FIG. 1 is a schematic view of an apparatus for carrying out
the present cleaning method.
[0017] FIG. 2A illustrates a cross sectional view of a two-phase
generating module with a nozzle used to form a two-phase flow
including droplets.
[0018] FIG. 2B illustrates a cross sectional view of another
embodiment used to create a two-phase flow including droplets.
[0019] FIG. 2C illustrates a cross sectional view of a two-phase
generating module to create two-phase flow including droplets using
a T-connection.
[0020] FIG. 3 is a cross sectional view of a membrane system with
backflushing means to be used with the two-phase flow.
[0021] FIG. 4 is a cross sectional view of a pipe distribution
network that can be cleaned using two-phase flow.
[0022] FIG. 5 is a cross sectional view of an adapter used to
separate feeding channels from permeate channels of membranes
during two-phase flow cleaning.
[0023] FIG. 6A is a photomicrograph of a lumen surface of a pipe
prior to cleaning.
[0024] FIG. 6B of a photomicrograph of a lumen surface of a pipe
after cleaning with the present two-phase method.
[0025] FIG. 7A is a graph of bacteria count in CFU/ml collected
over several weeks prior to two-phase cleaning.
[0026] FIG. 7B is a graph of bacteria count in CFU/ml as monitored
for some days after two-phase cleaning.
DETAILED DESCRIPTION OF THE INVENTION
[0027] The term "passageway", as used herein, includes, inter alia,
pipelines, tubing and hollow membranes.
[0028] According to the two-phase flow cleaning method of the
present invention, droplet size plays an important role in the
cleaning process since the inertial impact of the droplet is
tangible, and become very significant at the optimal droplet size,
between 30 to 200 microns. Droplets that are too small have
inertial impact forces that are too low to achieve fragmentation
and detachment of biofilm and like contaminants from the lumen of
passageways. The larger the droplet, the larger is its kinetic
energy, and the larger is biofilm fragmentation for example.
However, in the two-phase flow of this invention, the optimal
droplet size is determined by the flow conditions and parameters
mentioned above. The two-phase flow of the present invention
optimizes droplet size without compromising the main flow
attributes needed to cover the entire lumen surface and length of
the passageway to be cleaned; and at the same time ensure that the
liquid boundary layer is either very thin or discontinuous. The
purpose of the latter condition is to keep the contaminant bare
such that the droplets directly or nearly directly impact the
contaminants, causing their fragmentation, erosion and detachment.
Droplets that are too small are not effective for cleaning and thus
can be entrained in the gas phase without impacting the lumen
surface of the passageway. On the other hand, very large droplets,
e.g., those that are >200 microns in size are difficult to
create and re-suspend (in the gas flow) in an efficient manner.
[0029] In accordance with the present invention, the best droplet
sizes are in the range between 30 and 200 microns, and preferably
they are about 50-150 microns. Again, as the droplets leave the
surface, biofilm fragments become attached to them, and as this
process continues, more and more of the biofilm is eroded from the
lumen surface of the passageway. As holes and cracks in the film
are created by this process, surfactant molecules and small ions
diffuse to the interface and lower the adhesion of the biofilm to
the surface. As a result, as the cleaning proceeds, the remaining
biofilm becomes easier to detach and remove by the fast moving
two-phase flow.
[0030] Complete coverage of the lumen surface of a passageway with
droplets along the entire surface area and length ensures the
complete removal of biofilm and like contaminants from various
passageways having varying diameters. According to the present
invention, passageway diameters from 150 microns to more that 12 cm
can be cleaned with the present two-phase flow system, including
cleaning of diverse contaminants ranging from biofilm to protein
layers to dairy and food residues, spores, blood residues and the
like.
[0031] According to this invention, the conditions needed to remove
biofilm and other adherent substances, such as dairy or milk
residues, blood clots, protein layers, and foulants such as those
encountered in membranes used in waste water treatment, with the
two-phase flow system from the lumen of passageways include: an
initial droplet formation device at the beginning of the passageway
that creates droplets of between about 25 to 200 microns but up to
400 microns. This is done by adjusting the liquid to gas ratio, gas
and liquid flow rates, solution chemistry and droplet break-up
properties of the cleaning solution so that a sustained droplet
formation and re-formation takes place along the entire length and
lumen surface area of the passageway. Under proper conditions,
passageways having a large length:diameter (hereinafter L/D), such
as a diameter of from about 1 mm to about 10 cm, and a length up to
100-300 meters can be cleaned in accordance with the invention.
[0032] In addition, and simultaneously, a condition of complete
coverage of the surface with droplet impact needs to be achieved,
along with creation of droplets of more or less uniform size, so as
to create a sufficient localized shear and other mechanical
stresses when they impact the surface of the passageway. Therefore,
droplet impact should be made sufficient for the destruction of any
section of biofilm remaining at the surface. Further, the process
must be applied for a sufficient time sp that complete removal of
the biofilm fragments, or like contaminants, is completed from the
entire lumen surface of the passageway being cleaned. Again, in
order to ensure that the inlet of the passageway, especially one
with a large L/D, is cleaned, the droplets must be injected into
the passageway with the aid of a nozzle into the air stream near
the entrance of the passageway. In addition, the average droplet
size must remain in the range between 30 to 200 microns, preferably
between about 50 -150 microns, because large droplets will have
small penetration depth, and thus can experience problems due to
gravity and other effects.
[0033] Further, according to the present invention, the flow
condition must be made to cover the entire circumference of the
lumen of the passageway so that the lumen surface receives uniform
coverage and uniform droplet impact during the cleaning. This
condition must be satisfied for horizontal, vertical and positions
in between, since piping systems in industrial processes have
various orientations and arrangements. To achieve this condition,
the two-phase flow velocity, and the liquid fraction of the
two-phase flow mixture must be adjusted to create these coverage
conditions. Therefore, a minimum gas velocity must be used and the
gas velocity and the liquid to gas ratio must be adjusted for
different diameter passageways and surface wetting conditions of
the lumen surface to be cleaned. Further, according to this
invention, the surface of the contaminant must be bare, or almost
bare, of a liquid layer so that droplet impact achieves the most
effective fragmentation of the contaminant layer and thus effects
cleaning of the lumen of the passageway.
[0034] We believe that the most favorable condition for cleaning is
a special form of the annular mist regime in two-phase flow or
other regimes in its vicinity that satisfy droplet formation and
instability of the boundary layer, one where droplet formation,
droplet deposition and droplet impact at the lumen surface is
maximized for the purpose of cleaning, but where the liquid
boundary layer thickness is minimal, and preferably where the
surface of the passageway is not entirely covered by a thick liquid
film. The condition favorable for cleaning according to the present
invention is distinct from the well-known annular film flow, where
the lumen of the passageway is covered with a continuous liquid
film, and where droplet formation is kept to minimum. The latter
flow regime is not efficient for cleaning since the droplet
formation and impact is inadequate. In the present invention,
extensive droplet formation and droplet impact are required for
fragmentation of biofilm and like contaminants. Droplet impact
creates a localized shear. This localized shear has been estimated
to be 100 to 1000 times more than the bulk shear generated during
liquid circulation at about 5 feet/sec, as is present in
conventional C-I-P systems.
[0035] In the stratified flow regime, only the bottom of the tubing
or passageway is in contact with the liquid, while the top portion
of the lumen is bare of cleaning liquid. Therefore, the cleaning in
this case is worse than cleaning with liquid circulation only.
Also, other two-phase flow regimes, including bubble flow, slug
flow and others that completely cover the lumen surface, are not
very different from a liquid circulating regime. The main function
of air in the above flow regimes, where the liquid is the major
phase, is to increase the velocity of the liquid in the passageway;
however, the shear stress generated is still defined by the bulk
shear due to liquid flow. Thus the magnitude of the shear stress is
too low to remove highly adherent contaminants such as biofilm and
the like, and the liquid boundary layer remains thick enough to
hamper removal of surface contaminants. The two-phase flow of the
present invention is thus different in mechanism and in the
magnitude of shear stresses generated due to droplet impact.
Further, there are additional surface forces that assist in
cleaning during two-phase flow according to this invention due to
pulling of droplets from liquid domains formed from droplet
coalescence during the formation and re-formation of droplets along
the length of the passageway. As droplets are pulled away from the
surface, they exert other types of forces (other than droplet
impact) due to surface tension forces and other complex surface
phenomena during the two-phase cleaning, and these forces are
important in increasing cleaning efficiency.
[0036] We have shown that a two-phase flow regime that creates and
sustains high velocity droplets can fragment and remove biofilm in
several applications. In the optimal regime for cleaning we
identified that droplet formation, droplet deposition and then
droplet re-formation are necessary for cleaning. Droplet formation
and re-formation as well as droplet deposition density at the lumen
surface to be cleaned should be kept at a condition optimal for
cleaning, while simultaneously ensuring that wetting and de-wetting
dynamics at the surface are favorable for cleaning and preventing
formation of a thick boundary layer. We found, using a clear or
transparent tubing with the aid of a microscope, that the optimal
cleaning condition occurs when gas velocity and the liquid:gas
ratio are adjusted so that droplet formation becomes optimal, and
when the droplet deposition rate is maximized. This ensures that
the droplets impact the bare surface of biofilm, for example. When
droplet deposition does not form a continuous liquid film on the
lumen surface, fragmentation and cleaning can take place.
Therefore, the correct regime is different from the annular flow
regime, where liquid flow forms a film along the walls of the
passageway and the gas flows near the center, as described in the
prior art. In addition, we have found that the presence of
surfactants and the wettability of the passageway surface
significantly affect the physical form of the liquid that is
created by droplet impact and deposition. Surfactants were found to
aid the process of wetting and de-wetting at the lumen surface of
the passageway in a way so as to achieve the condition of droplet
formation, a thin boundary layer, bare areas of surface, and impact
shear stresses in this cleaning process.
[0037] A critical sub-process during the cleaning of passageways
with high L/D is the re-formation of droplets after they impact the
lumen surface along the length of the passageway. As droplets
impact the surface, droplets that land nearby each other coalesce
to minimize their surface energy, and to form a liquid domain that
is then, either fully or partially, ripped off by the gas flow to
form new droplets. The flow conditions of the present invention do
not allow the liquid to accumulate, or to form a continuous thick
film on the lumen surface, but rather to facilitate the dispersion
of the coalesced droplets very quickly and re-form other droplets
that are then carried by the flow.
[0038] Droplet breakup at the interface during two-phase flow
cleaning may take place by one or more modes, depending on the
cleaning solution surface chemistry, static and dynamic surface
tension and wetting, viscosity and flow conditions, particle gas
velocity and liquid-to-gas ratio; also the wetting properties of
the surface to be cleaned plays an important part in this process.
The known modes of liquid breakup include either "bag breakup" or
"ligament breakup", or a combination of the two, and even more
complex forms.
[0039] In the case of "bag breakup" the gas may flatten a body of a
liquid, created by coalesced droplets at the surface, to form a
bag-shaped body of liquid with thin walls. These then burst as the
liquid wall becomes very thin, to form new droplets that travel
with the flow, and can impact another location downstream at the
surface and thus achieve cleaning.
[0040] In the case of "ligament breakup", the same sequence of
breakup is achieved but the body of the liquid domain is in the
form of a ligament which then breaks up into individual droplets
that become a part of the flowing two-phase flow, i.e., they travel
downstream, impact the surface at another location, and the process
is repeated until the liquid exits the passageway. It is possible
to have a combination of the two modes or mechanism of droplet
re-formation taking place during the cleaning process with the
two-phase flow, depending on the conditions of surface chemistry,
of surface and cleaning solutions, dynamic and static surface
tension, dynamics of the wetting and de-wetting processes, liquid
viscosity, the flow conditions and the like.
[0041] Irrespective of the exact detailed mechanism of droplet
re-formation, the two-phase flow of the present invention should
sustain the formation and re-formation of droplets over the entire
length of the passageway, even in the case of a very long pipeline
(>300 feet in some cases). Fortunately, since the velocity of
the gas increases as the gas expands as it travels downstream to
the open end of the passageway due to a pressure drop (passageway
volume is constant), the formation and re-formation of droplets and
their velocity increases towards the open end of the passageway.
This feature is important with respect to being able to sustain an
active two-phase flow optimal for the cleaning of the lumen of long
passageways with a high L/D. In fact, we discovered that the
cleaning towards the outlet end of pipelines is usually easier to
accomplish compared to the front end, due to the increase in
droplet velocity as the flow travels to the open end for the
reasons described above.
[0042] Furthermore, we have also found that the cleaning efficiency
at the front end of the passageway must have optimal two-phase flow
conditions with sufficient droplet impact and droplet formation and
re-formation (velocity, liquid to gas ratio, liquid surface
tension, etc.) to ensure that the front end of the passageway is
properly cleaned. According to the present invention, we found that
if the flow is adjusted for cleaning of the front section of a long
passageway (where the two-phase flow is injected), the other open
end of the passageway will always receive higher velocity droplets
and thus the cleaning of the entire passageway can be achieved.
[0043] The velocity change between the inlet and outlet of
passageways during two-phase flow cleaning is provided in the
examples below. It is important to adjust the liquid:gas ratio at
the entrance of a passageway so that, when the gas expands
downstream, an optimal liquid:gas ratio still remains in the
optimal range for cleaning, i.e., is sufficient to generate enough
droplet deposition density within the size range needed to clean
the section near the outlet of the passageway.
[0044] Yet another important feature of the invention is the size
of the droplets that are formed in the two-phase flow, and
consideration of the change in gas velocity as the two-phase flow
travels from the entrance to the outlet of the passageway. If the
droplets become too small towards the end of the passageway, a
larger fraction becomes entrapped in the gas and thus not enough
droplet impact density is achieved, resulting in a less than
optimal cleaning towards the outlet end of the passageway. In such
case, it is possible to overcome the above limitation by adjusting
the gas:liquid ratio at the entrance of the passageway, or at a
location along the length of the passageway, so that the optimal
gas:liquid ratio needed for cleaning is achieved for the entire
length of the passageway. It is clear that these conditions can be
varied to clean different passageway types for different
applications by using the ranges and conditions as exemplified
below.
[0045] Further, in order to achieve cleaning according to this
invention, the two-phase flow must produce uniform droplet
deposition along the entire surface of the passageway as the flow
travels from inlet to outlet, and the droplet impact on the surface
of the contaminant must create sufficient shear and other
mechanical stresses so as to destroy any section of the biofilm or
the contaminant present on the surface of the passageway. The above
conditions must be capable of achieving fragmentation of the
biofilm or the contaminant layer, and ultimately achieve the
detachment and removal of the entire layer from the lumen surface
of the passageway. Droplet deposition density onto the lumen
surface to be cleaned is an important variable that controls the
efficiency of the cleaning process, and this is directly related to
droplet size, flow conditions and the liquid fraction of the
two-phase mixture. Droplet size is a function of the cross section
(diameter), of the passageway, the liquid mass flux in
kg/m.sup.2.sec, the gas mass flux in kg/m.sup.2.sec, the surface
tension and, to some extent, the viscosity/rheology of the liquid.
Therefore a superficial gas velocity in excess of 10 meters/sec
covers the effective range of cleaning, and is preferably between
20 and 100 meters/sec near the inlet of the passageway to be
cleaned; the velocity of the gas increases as it travels though the
passageway towards the outlet end.
[0046] Furthermore, we have found that droplet dimensions differ
with the cross section of the passageway, with the gas velocity and
the liquid mass flux. The latter may have to be varied by
experimentation in order to obtain effective droplet size, droplet
velocity, droplet deposition density, and at the same time ensure
that the surface of the pipeline is not flooded with a liquid
layer, or forms a film that could mask or shield the biofilm or the
contaminant present from direct or close direct impact by the
droplets. By manipulating the above parameters, one can achieve the
proper conditions for cleaning.
[0047] The condition at the lumen surface of the passageway during
cleaning with the two-phase flow of this invention is very
important to achieving effective cleaning. The wetting properties
of the surface to be cleaned also play an important role in the
cleaning process, especially with respect to the nature of the
liquid that accumulates as droplets impact the surface and coalesce
on the lumen surface during the two-phase flow cleaning. If the
surface has a low contact angle (the surface is wettable), the
liquid that accumulates as the result of droplet coalescence will
tend to spread out to cover a larger area compared to a surface
with a high contact angle with the cleaning liquid. Furthermore,
this spreading is a complex process, especially because it is
transient in nature, and at the same time is subjected to the
dynamic conditions of the two-phase flow. These events last only
tens of a millisecond and they cannot be readily explained with
equilibrium wetting knowledge as is known in the field of surface
chemistry. Visual observation shows that a complex process
involving a very dynamic spreading process at the surface during
the cleaning with the present methods. It is important to adjust
the conditions to avoid forming thick or continuous liquid films at
the surface during the cleaning with the two-phase process. These
parameters in many cases require controlling the flow conditions
and can be visually seen using a transparent section of the
passageway.
[0048] Also, according to this invention, the presence of a
surfactant in the cleaning liquid plays an important role with
respect to droplet formation, droplet size and the nature of the
liquid domains that accumulate on the surface during the two-phase
cleaning. Specifically this is relevant with respect to issues
related to the dynamic surface tension properties of the cleaning
liquid. Equilibrium surface tension of a surfactant solution is the
value of surface tension (dynes/cm) that is measured when
surfactant molecules accumulate at the liquid/water interface and
are in equilibrium with surfactant molecules in the bulk solution.
This is usually measured by the conventional "ring method" or other
techniques as known in the prior art; these methods usually require
several minutes to obtain a measurement. Therefore, equilibrium
surface tension is measured when the liquid/water interface is at
equilibrium and it is independent of the diffusion rates of
surfactant molecules from the bulk of the liquid to a newly created
air/water interface. Most surfactant suppliers only specify static
or equilibrium surface tension values in the information bulletins
they provide to their users.
[0049] On the other hand, dynamic surface tension describes the
surface tension behavior as a function of time, usually in time
scale from zero to about 100-200 milliseconds, or longer. This is
usually presented as a plot of dynamic surface tension (mN/m)
versus surface age in milliseconds. For many surfactants, it takes
sometimes seconds or minutes for the surface tension values to
reach their equilibrium values. On the other hand, dynamic surface
tension depends on the diffusion rates of surfactant molecules to
reach the newly created interface, as is the case of dynamic
processes such as the formation of new droplets or the spreading of
liquid droplets after they impact the surface, such as the case
during the two-phase flow process of the present invention. We
found that the dynamic surface tension behavior of the cleaning
solution is important for droplet break up, droplet formation,
droplet re-formation, and physical spreading of the liquid on the
surface to be cleaned. In the present invention, we found that pure
water only, having a surface tension of 72 mN/m, is difficult to
use in some applications due to the difficulty of forming droplets
during the two-phase flow cleaning process, and it is possible to
use water only except when the gas velocity used is very high. In
the case of water alone, we observed that water tends to segregate
into slug and such slugs move alone followed by periods with only
gas flowing in the passageway; this mode of two-phase flow was
found to be unfavorable for cleaning. However, when a surfactant is
used in the cleaning solution, droplet formation and re-formation
becomes possible, and the behavior of the liquid deposited at the
surface to be cleaned tends to satisfy the conditions required for
cleaning, i.e., the liquid domains become smaller, and re-disperse
very readily.
[0050] We found that the use of proper surfactants ensures ready
formation of the two-phase flow with droplets at reasonable
velocities, and that the surface of the passageway to be cleaned is
not covered with a continuous liquid film and where the contaminant
surface remains more or less bare, so that impact of the liquid
droplets effects fragmentation and removal of the biofilm or
contaminant. It is thus important to select surfactants with
certain properties of dynamic surface tension and dynamic wetting
and de-wetting properties.
[0051] Examples of surfactants that do not foam in the two-phase
cleaning liquid are set forth below in the Examples. It is also
possible to add a de-foaming agent to solve a foaming problem, if
necessary. However, it is important to consider several parameters
to arrive at the proper choice of a successful surfactant for
two0-phase cleaning, including: dynamic and static surface tension
properties; the dynamics of wetting and de-wetting; foaming and
foaming dynamics.
[0052] The selection of an optimal cleaning solution for two-phase
cleaning also includes the pH, chelating capacity, and
oxidation-reduction properties. Therefore the present invention
includes th4e use of those surfactants and cvomposition, in
combination with the two-phase fluid dynamic parameters and the
nature of surface processes, as described in the present
invention.
[0053] The following parameters illustrate conditions that were
found to achieve 99.6% removal of bacterial cells and a biofilm
matrix;
[0054] Inlet velocity, 104 feet/second
[0055] Two-phase cleaning time, 20 min.
[0056] Rinsing time, 10 min.
[0057] Air volume, 27.4 SCFM
[0058] Liquid-to-gas ratio: inlet, 1/4000 and outlet, 1/14000
[0059] Cleaning solution is alkaline with a pH of 11.5
[0060] Visual observation of the two phase flow that was found to
be effective in removing biofilm revealed that optimal biofilm
removal took place when the two phase flow mixture flowing in the
passageway contained liquid droplets that continually impacted the
lumen surface of the pipeline. Further, the optimal removal was
achieved when part of the lumen surface was not covered by a liquid
film, and when surface de-wetting was accomplished by adjusting the
gas to liquid ratio and the gas velocities in the ranges indicated
above. It is important to note that when we use passageways having
different internal diameters. Adjustment of the gas:liquid ratio is
required to achieve the two-phase flow condition that provides
liquid droplets that impact the lumen surface and prevent the
formation of a liquid film on the surface of the passageways.
[0061] Further, the two-phase flow apparatus and method are
applicable for performing cleaning followed by rinsing and
sanitizing steps. These steps can be used either together, or in
any combination, as required for the purposes of various processes.
The apparatus and method set forth herein, and their variations,
should be considered as a means to deliver chemical cleaning
agents, sanitizing agents and rinsing liquids to passageways, as
employed in industrial processes.
[0062] During a sanitizing step using the two-phase flow process,
the gas:liquid ratio may be the same or different from that used in
cleaning or rinsing steps. The nature and behavior of the two-phase
flow at the surface or a passageway that achieves effective
sanitization was found to be somewhat different compared to the
cleaning step. During a sanitizing step, the lumen surface using
the two-phase flow process, droplet impact forces are not as
critical as during the cleaning step, and the nature of the
two-phase flow at the surface requires a different set of
manipulations. The two-phase flow condition in this case needs to
ensure that the entire surface of the passageway is covered with
the sanitizing solution for a set period of time to accomplish
disinfection. A slightly lower gas:liquid ratio would be expected
to perform better sanitization.
[0063] An apparatus 100 suitable for carrying out the methods of
the invention is shown in FIG. 1.
[0064] A passageway to be cleaned 400 is connected to a two-phase
flow generating module 12 connected in turn to an air source 10 and
a holding tank for cleaning solution 14. The passageway to be
cleaned 400 is directly connected to an inlet adapter 56 and an
outlet adapter 58.
[0065] A pipe 142 is used to inlet the air-fluid mixture through
inlet adapter 56. A pipe 170 feeds a backflushing liquid into the
passageway 400 via an inlet adapter 80. When backflushing is
complete, the mixture exits through the outlet adapter 58 via the
pipe 144.
[0066] The two-phase generating module 12 is used to combine the
pressurized air from air source 10 and a pre-defined amount of
liquid from the holding tank 14 to generate droplets that are
carried along with the air stream and delivered to the passageway
to be cleaned 400. The two-phase generating module 12 includes an
air inlet pipe segment 136, and a liquid inlet pipe 214. The
two-phase generating module 12 also includes a two-phase mixture
outlet pipe 138. The two-phase generating module 12 mixes
pressurized air and a pre-defined amount of liquid for generating
droplets that are carried along with the air stream to perform
cleaning, rinsing or sanitizing of the passageway to be cleaned
400. The two-phase generating module 12 includes an air inlet port
134 that is connected to pipe segment 136, and a liquid inlet port
that is connected with pipe segment 214. A P-type fine atomization
nozzle 13 such as those manufactured by Bete Fog Nozzle, Inc. is
installed at the liquid inlet of the module 12 to generate liquid
droplets in the range between 25 and 400 microns in diameter.
Selection of the nozzle 13 and droplet range may depend on the
nature of the passageway to be cleaned and other factors. The
two-phase generating module 12 also includes a two-phase mixture
outlet that is connected with pipe segment 138. A typical design of
the two-phase generating module using a nozzle to break up the
liquid in the form of droplets is shown in FIG. 2A.
[0067] A second type of two-phase generating module is shown in
FIG. 2B where the nozzle is replaced by an orifice 31. This type of
design is used in some cases especially when the passageway to be
cleaned is small or complex in shape, or when the passageway is
narrow and it is possible to create the requisite two-phase flow
with droplets without the aid of a nozzle at the entrance of the
system to be cleaned. The main function of the orifice in this case
is to provide a fixed amount of liquid to mix with air for
generating a two-phase mixture with a known gas to liquid ratio.
The two-phase generating module 12 using orifice 31 is usually
equipped with a long section of tubing (expansion section), to
allow the liquid-gas mixture enough time to form droplets in the
air stream and to reach some sort of steady state before entering
to the passageway to be cleaned 400.
[0068] Yet another version of the two-phase generating module 12 is
shown in FIG. 2C where liquid is introduced into the air stream
through a T-connection. Again, this type of design is usually
accompanied with a long pipe or tubing section to allow enough time
for the liquid to break up into droplets, as per the requisite of
the two-phase cleaning method, before entering the passageway to be
cleaned 400.
[0069] Air is supplied via air source 10 and directed to the inlet
of the two-phase generating module 12 via pipe segments 126, 128,
130, 132, 134 and 136 through valve 46. Air flow is regulated by an
air regulator 42, and monitored by a pressure gage 44, a pressure
transducer 48 and a flow meter 50. These instruments provide a
feedback loop to a controller 600.
[0070] The holding tank 14 is provided by first pumping means 30
via pipe segments 199, 198, 200, 202, 204, 205, 210, 212 and 214
through valves 84 and 76 at a pre-defined liquid pumping rate.
Liquid pressure is monitored by a liquid pressure transducer 74. A
return loop via pipe segments 209, 194, 192 and 193 through the
manual valve 88 serves as a pressure adjustment means to maintain
the desired pressure range necessary for operating the nozzle 13 in
the two-phase generating module 12 during the cleaning period in
order to avoid back pressure to other parts of the apparatus. The
cleaning solution is then atomized/dispersed at the nozzle 13 and
mixed with air to generate the two-phase cleaning mixture which is
then directed to the inlet adapter 56 connected with the passageway
to be cleaned 400 via pipe segments 138, 140, and 142 through valve
54. Thermocouple 52 is employed to measure the two-phase mixture
temperature before entering the passageway to be cleaned 400. The
two-phase exhaust leaving outlet adapter 58 connected to the
passageway to be cleaned 400 is then directed to mist separator 500
via pipe segments 144, 146, 148 and 150 through valve 62. The
exhaust pressure is monitored at pressure transducer 60. The liquid
phase is then separated from the two-phase mixture inside the mist
separator 500 and discharged via pipe 152 through valve 64, and gas
is discharged via a ventilation duct 154. In this process the
desired mixture temperature is controlled by the liquid heater 15
and air heater 11, and is monitored by the thermocouple 52 with a
feedback loop to the controller 600.
[0071] If a second cleaning solution (such as an acidic solution)
is required or desired in the second cleaning process, the cleaning
solution is contained in a second cleaning solution holding tank
16. This cleaning solution is then supplied to the liquid inlet of
the two phase generating module 12 by the first pumping means 30
via pipe segments 191, 190, 200, 202, 204, 205, 210, 212, and 214
through valves 84 and 76 at a pre-defined liquid flow rate. The
liquid pressure is always monitored by the liquid pressure
transducer 74. A return loop via pipe segments 209, 194, 188 and
189 through the manual valve 92 is used to serve as a pressure
adjustment means to maintain the desired pressure range necessary
for operating the nozzle 13 in the two-phase generating module 12.
The cleaning solution is then atomized at the nozzle 13 and mixed
with air to generate two-phase cleaning mixture which is then
directed to the inlet adapter 56 which is connected with the
passageway to be cleaned 400 via pipe segments 138, 140, and 142
through valve 54. A thermocouple 52 is employed to measure the
two-phase mixture temperature before entering the passageway to be
cleaned 400. The two-phase exhaust leaving outlet adapter 58, which
is connected to the passageway to be cleaned 400, is directed to
the mist separator 500 via pipe segments 144, 146, 148 and 150
through valve 62. The exhaust pressure is monitored with pressure
transducer 60. The liquid phase is then separated from the
two-phase mixture inside the mist separator 500 and discharged via
pipe 152 through valve 64. A gas is discharged via a ventilation
duct 154. In this process the desired mixture temperature is
controlled by liquid heater 17 and the air heater 11 and monitored
by the thermocouple 52.
[0072] Sanitizers can also be used after the cleaning step in many
C-I-P operations. In this case, a sanitizer holding tank 18 is used
to supply the sanitizing liquid. The sanitizer contained in the
sanitizer holding tank 18 is supplied to the liquid inlet of the
two phase generating module 12 by a second pumping means 32 via
pipe segments 180, 182, 186, 187, 208 205, 210, 212 and 214 through
valves 101 and 76 at a pre-defined liquid rate. Liquid pressure is
monitored by the liquid pressure transducer 74. A return loop via
pipe segments 184 and 185 through the manual valve 94 is used to
serve as a pressure adjustment means to maintain a desired pressure
range necessary for operating the nozzle 13 in the two-phase
generating module 12. The sanitizing liquid is then atomized at the
nozzle 13 and mixed with air to generate a two-phase sanitizing
mixture which is then directed to the inlet adapter 56 which is
connected with the passageway to be cleaned 400 via pipe segments
138, 140, and 142 through valve 54. A thermocouple 52 is employed
to measure the temperature of the two-phase mixture before entering
the passageway to be cleaned 400. The two-phase exhaust leaving the
outlet adapter 58, which is connected to the system to be cleaned
400, is directed to the mist separator 500 via pipe segments 144,
146, 148 and 150 through valve 62. The exhaust pressure is
monitored by pressure transducer 60. The liquid phase is then
separated from the two-phase mixture inside the mist separator 500
and discharged via a pipe 152 through a valve 64 and air is
discharged via a ventilation duct 154. In this process the desired
two-phase mixture temperature is controlled by a liquid heater 19
and the air heater 11 and monitored by the thermocouple 52.
[0073] Sometimes water is mixed with air for rinsing purposes. In
these cases, rinse water holding tank 20 is used to supply rinse
water/liquid. Water is supplied to the liquid inlet of the
two-phase generating module 12 by the third pumping means 34 via
pipe segments 172, 174, 178, 206, 208, 209, 205, 210, 212 and 214
through valves 98 and 76. The liquid pressure transducer 74 is used
to monitor water pressure. A return loop via pipe segments 176 and
177 through manual valve 96 is used to serve as a pressure
adjustment means to maintain the desired pressure range necessary
for operating the nozzle 13 in the two-phase generating module 12.
Water is then atomized at the nozzle 13 and mixed with air to
generate a two-phase rinsing mixture which is then directed to the
inlet adapter 56 which is connected with the passageway to be
cleaned 400 via pipe segments 138, 140 and 142 through valve 54.
The thermocouple 52 is employed to measure the temperature of the
two-phase mixture before entering the passageway to be cleaned. The
two-phase exhaust leaving outlet adapter 58, which is connected to
the passageway to be cleaned 400, is directed to the mist separator
500 via pipe segments 144, 146, 148 and 150 through valve 62. The
exhaust pressure is monitored at pressure transducer 60. The liquid
phase is then separated from the two-phase mixture inside the mist
separator 500 and discharged via the pipe 152 through the valve 64,
and gas or air is discharged via the ventilation duct 154. In this
process the desired mixture temperature is controlled by a liquid
heater 21 and an air heater 11 and monitored by the thermocouple
52.
[0074] In addition to the two-phase rinsing step discussed above,
rinsing can also be accomplished by circulating water continuously
through the passageway to be cleaned 400. In this step, a water
source is supplied from the water holding tank 28 to the inlet
adapter 56 which is connected to the system to be cleaned by the
sixth pumping means 40 via pipe segments 231, 230, 234, 246, 250,
270, 272, 140 and 142 through valves 114, 106 and 54. The water
flow rate is monitored using a flow meter 120. Instead of using the
water from water holding tank 28, water can also be supplied from
an outside source to the water holding tank 28 via pipe segments
254 and 252 through a valve 124. After passing through the
passageway to be cleaned 400, the rinse water is directed to the
adapter 58 and to the mist separator 500 via pipe segments 144,
146, 148, and 150 through valve 62. The rinse water inside the mist
separator 500 is then discharged via a pipe segment 152 through
valve 64. In many cases, warm or hot water can enhance cleaning
results and thus controlling the rinse water temperature becomes
important in the control of the process. This can be achieved by
using a heater and its controller 29 inside the water holding tank
28.
[0075] Rinsing with water is enhanced by applying intermittent air
pulsation can increase rinsing effectiveness. This step is achieved
by applying a continuous supply of water as described above and
intermittently introduces pressurized air to the rinse water
stream. Air is supplied from the air source 10 to the valve 54 to
push the rinse water through the passageway to be cleaned 400 via
pipe segments 126, 128, 130, 132, 134, 136, 138, 140 and 142
through valve 46 and the two-phase generating module 12. The air is
regulated by the regulator 42 and monitored by pressure gage 44,
pressure transducer 48 and flow meter 50. During this process,
valves 70 and 76 are closed to avoid any back pressure to other
parts of the apparatus. The pulsation pattern is controlled by the
valve 46 which is electronically controlled by the controller 600.
A typical pattern of the pulsation is to open the valve 46 for
about 3-6 seconds after every 6-10 seconds. With the automatic
control from the controller 600, other pulsation patterns can be
easily achieved.
[0076] Re-circulation of the cleaning solution, sanitizer or rinse
water through the passageway to be cleaned 400 for a period of time
with a desired liquid temperature is an important step for soaking
or rinsing the internal surfaces of passageways or equipment in
processing industries. In this step, liquids are circulated through
the system to be cleaned with a continuous liquid phase. When the
first cleaning solution, which may be a basic solution, is applied
for recirculation purposes, the cleaning solution contained in the
cleaning solution holding tank 14 is pumped to the inlet adapter 56
by the fourth pumping means 36 via pipe segments 227, 226, 228,
266, 268, 270, 272, 140 and 142 through the valves 87, 102 and 54.
The liquid flow rate is monitored by the flow meter 120 and the
temperature of the liquid is monitored by the thermocouple 52.
After passing through the passageway to be cleaned 400, the
cleaning solution leaves the system to be cleaned at the outlet
adapter 58 and is directed to the cleaning solution recirculating
tank 22 via pipe segments 144, 146, 148, 264, 262, 260, and 261
through valves 62 and 116. The liquid pressure transducer 60 is
used to monitor the liquid pressure during the process. This
process is continued until the liquid level in the cleaning
solution recirculating tank 22 reaches about 80%, when the
circulation process does not consume more fresh cleaning solution
from the cleaning solution holding tank 14. At this moment, valve
87 is closed and valve 108 is opened so that the cleaning solution
retained in the cleaning solution recirculating tank 22 is
connected to the above mentioned recirculation loop via pipe
segments 241, 240 and 236 through the valve 108. The recirculation
process is then continued for a period of time depending on rinsing
or soaking requirements for each cleaning process/protocol. The
desired liquid temperature is controlled by a heater 15 before the
valve 87 is closed and by a heater 23 throughout the entire
recirculation process.
[0077] When the second cleaning solution (here referred as acidic
solution) is required for recirculation purposes, the cleaning
solution contained in the cleaning solution holding tank 16 is
pumped to the inlet adapter 56 by the fourth pumping means 36 via
pipe segments 223, 222, 224, 228, 266, 268, 270, 272, 140 and 142
through valves 91, 102, and 54. The liquid flow rate is monitored
by the flow meter 120 and the temperature of the liquid is
monitored by the thermocouple 52. After passing through the
passageway to be cleaned 400, the cleaning solution exits at the
outlet adapter 58 and is directed to the cleaning solution
recirculating tank 24 via pipe segments 144, 146, 148, 264, 262,
258, and 259 through valves 62 and 118. A liquid pressure
transducer 60 is used to monitor the liquid pressure during the
process. This process is continued until the liquid level in the
cleaning solution holding tank 24 reaches about 80% when the
circulation process does not consume more fresh cleaning solution
from the cleaning solution holding tank 16. The valve 91 is closed
and valve 110 is opened so that the cleaning solution retained in
the cleaning solution recirculating tank 24 is connected to the
above mentioned recirculation loop via pipe segments 239, 238 and
236 through valve 110. The desired liquid temperature is controlled
by heater 17 before valve 91 is closed and by heater 25 throughout
the entire recirculation process.
[0078] When a sanitizer is required for recirculation purposes, the
sanitizer solution contained in the sanitizer holding tank 18 is
pumped to inlet adapter 56 by the fifth pumping means 38 via pipe
segments 217, 216, 218, 220, 242, 250, 270, 272, 140 and 142
through valves 95, 102 and 54. The liquid flow rate is monitored by
flow meter 120 and the liquid temperature is monitored by the
thermocouple 52. After passing through the passageway to be cleaned
400, the sanitizer exits the passageway at outlet adapter 58 and is
directed to the sanitizer recirculating tank 26 via pipe segments
144, 146, 148, 264, 263 and 256 through valves 62 and 122. The
liquid pressure transducer 60 is used to monitor the liquid
pressure during the process. This process is continued until the
liquid level in the sanitizer recirculating tank 26 reaches about
80% when the circulation process does not consume more fresh
sanitizer from the sanitizer solution holding tank 18. The valve 95
is then closed and the valve 112 is opened so that the sanitizer
retained in the sanitizer recirculation tank 26 is connected to the
above mentioned recirculation loop via pipe segments 233 and 232
through the valve 112. The recirculation process is then continued
for a period of time depending on rinsing and soaking requirements
of each sanitizing case. A desired liquid temperature is controlled
by heater 19 before valve 95 is closed and by the heater 27
throughout the entire recirculation process.
[0079] Backflushing is an important option of the two-phase
cleaning apparatus 100, used particularly to clean tubular and
hollow fiber membranes where backflushing is often required, for
instance for ultrafiltration and microfiltration separation
membranes. Backflushing usually involves the use of either a
cleaning solution or water in liquid phase, or in the form of the
two-phase mixtures in other cases. In this step, a second liquid
inlet adapter 80 is used to connect the backflushing fluid to the
product port of the membrane to be cleaned, as shown in FIG. 3.
When the backflushing is in the form of a cleaning solution in a
liquid phase or foam mixture, the cleaning solution in the cleaning
solution holding tank 14 is delivered to inlet adapter 80 by the
first pumping means 30 via pipe segments 199, 198, 200, 202, 204,
205, 168, and 170 through valves 86, 84 and 78. Meanwhile air is
supplied from the air source 10 via pipe segments 158, 160, 162,
164, and 166 to pipe 210 to pressurize the liquid that is held
inside the housing of the membrane to be cleaned 400. Air in this
case is regulated by the regulator 66 and monitored by the pressure
gage 68 and pressure transducer 72. A liquid return loop via pipe
segments 209, 194, 192, and 193 through the manual valve 88 is used
to adjust the liquid pressure within a range that can be sustained
by the membrane housing. Any permeate generated during this
backflushing operation is directed to the mist separator 500 via
pipe segments 144, 146, 148, and 150 through valve 62. The liquid
collected inside the mist separator 500 is then discharged via pipe
segment 152 through valve 64. This process can be performed at the
desired liquid and air pressures depending on the specifications of
the membrane to be cleaned.
[0080] If an air stream is introduced to the lumen of tubular or
hollow fiber membranes during back flushing, a two-phase flow can
be formed in situ and can be used to clean the lumen side of the
membrane and thus enhance overall cleaning. This in situ two-phase
generation step is achieved in apparatus 100 by introducing air to
the inlet adapter 56 which is connected to the inlet of the
membrane to be cleaned 400 via pipe segments 126, 128, 130, 132,
134, 136, 138, 140 and 142 through valves 46 and 54 and the
two-phase generating module 12. Air in this case is regulated by
the regulator 66 and monitored by the pressure transducer 72. With
two-phase flow generated in situ, the mist separator 500 is
collecting two-phase exhaust rather than liquid phase only. Liquid
is separated from the two-phase exhaust inside the mist separator
500 and discharged via pipe segment 152 through valve 64 and air is
discharged via pipe segment 154.
[0081] If a second cleaning solution in the form of a liquid phase
or as a foam mixture is needed for backflushing purposes, the
cleaning solution in the cleaning solution holding tank 16 is
delivered to the inlet adapter 80 by first pumping means 30 via
pipe segments 191, 190, 200, 202, 204, 205, 168, and 170 through
valves 90, 84, and 78. Meanwhile air is supplied from the air
source 10 via pipe segments 158, 160, 162, 164, and 166 to pipe 210
for use to pressurize the liquid that is held inside the membrane
housing. Air in this path is regulated by the regulator 66 and
monitored by the pressure gage 68 and the pressure transducer 72. A
liquid return loop via pipe segments 209, 194, 188 and 189 through
manual valve 92 is used to adjust the liquid pressure within a
range that can be sustained by the membrane housings. Any permeate
liquid formed inside the membrane lumen during the backflushing
step is directed to the mist separator 500 via pipe segments 144,
146, 148, and 150 through valve 62. The liquid collected inside the
mist separator 500 is then discharged via pipe segment 152 through
valve 64. This process can be performed under certain desired
liquid and air pressures, depending on the specification of the
membrane to be cleaned.
[0082] As discussed above, if an air stream is introduced to the
lumens of the tubular or hollow fiber membranes by backflushing, a
two-phase flow can be created in situ inside the lumen of the
membrane to enhance the cleaning surface of the membrane. This step
is again done by introducing air to inlet adapter 56 via pipe
segments 126, 128, 130, 132, 134, 136, 138, 140, and 142 through
valves 46 and 54 and the two phase generating module 12. Air in
this path is regulated by regulator 66 and monitored by pressure
transducer 72. With the two-phase generated in situ, the mist
separator 500 is collecting two-phase exhaust rather than liquid
phase only. Liquid is separated from the two-phase exhaust inside
the mist separator and discharged via pipe segment 152 through
valve 64 and air is discharged via pipe segment 154.
[0083] If a sanitizer is used in the backflushing process as
required for pharmaceutical and medical facilities, the sanitizer
in the sanitizer holding tank 18 is delivered to inlet adapter 80
by the second pumping means 32 via pipe segments 180, 182, 186,
187, 208, 209, 205, 168 and 170 through valves 100 and 78,
meanwhile air is supplied from the air source 10 via pipe segments
158, 160, 162, 164, and 166 to pipe 210 for use to pressurize the
liquid that is held inside of the membranes. Air in this path is
regulated by the regulator 66 and monitored by the pressure gage 68
and pressure transducer 72. A liquid return loop via pipe segments
184 and 185 through manual valve 94 is used to adjust liquid
pressure within a range that can be sustained by tubular membrane
housing. Any permeate liquid generated during backflushing into the
lumens of the membrane is directed to mist separator 500 via pipe
segments 144, 146, 148, and 150 through valve 62. The liquid
collected inside a mist separator 500 is then discharged via pipe
segment 152 through valve 64. This process can be performed under
certain desired liquid and air pressures depending on the
specifications of membrane housing design.
[0084] As discussed above, the backflushing process can be used to
supply liquid to the lumen side of the membrane and a two-phase
flow can be generated in situ when mixed with air directed to the
lumen side from the air source 10. This step is done by introducing
air to the inlet adapter which is connected to the inlet of the
membrane to be cleaned via pipe segments 126, 128, 130, 132, 134,
136, 138, 140, and 142 through valves 46 and 54 and the two-phase
generating module 12. Air in this pass is regulated by the
regulator 66 and monitored by the pressure transducer 72. With the
two phase mixture generated in situ, the mist separator 500 is
collecting two-phase exhaust rather than liquid phase only. Liquid
is separated from the two-phase exhaust inside the mist separator
500 and discharged via pipe segment 152 through valve 64 and air is
discharged via pipe segment 154.
[0085] If water is to be used in the backflushing process during
membrane cleaning processes, water in the holding tank 20 is
delivered to inlet adapter 80 by the third pumping means 34 via
pipe segments 172, 174, 178, 206, 208, 209, 205, 168 and 170
through valves 98 and 78. Meanwhile and simultaneously, air is
supplied from the air source 10 via pipe segments 158, 160, 162,
164 and 166 to the pipe 210 for use to pressurize the liquid that
is held inside the housing of the membrane. Air in this path is
regulated by the regulator 66 and monitored by the pressure gage 68
and the pressure transducer 72. A liquid return loop via pipe
segments 176 and 178 through a manual valve 98 is used to adjust
the liquid pressure within a range that can be sustained by the
membrane. Any permeate liquid created inside the lumen of the
membrane is directed to the mist separator 500 via pipe segments
144, 146, 148, and 150 through the valve 62. The liquid collected
inside the mist separator 500 is then discharged via pipe segment
152 through valve 64. This process can be performed under certain
desired liquid and air pressures depending on the specifications of
the membrane to be cleaned.
[0086] As discussed above, a two-phase flow can be created, in
situ, in the membrane lumen by mixing the backflushing liquid with
air from the air source 10. The gas to liquid ratio in this case is
adjusted by controlling the backflushing liquid and air pressures.
This step is done by introducing air to the inlet adapter which is
connected to the inlet of the membrane to be cleaned via pipe
segments 126, 128, 130, 132, 134, 136, 138, 140, and 142 through
valves 46 and 54 and the two phase generating module 12. Air in
this path is regulated by the regulator 66 and monitored by the
pressure transducer 72. With the two-phase flow generated in situ
in this case, the mist separator 500 is collecting two-phase
exhaust rather than liquid phase only. Liquid is separated from the
two-phase exhaust inside the mist separator 500 and discharged via
pipe segment 152 through valve 64; air is discharged via pipe
segment 154.
[0087] The drying step is an important part of the apparatus 100.
It allows dry air that is heated to a desired temperature by heater
and controller 11 to pass through the internal surfaces of the
passageway to be cleaned 400. Drying is usually performed after the
cleaning, sanitizing and rinsing steps to prevent bacterial growth
or biofilm formation. Drying is done by introducing dry air at the
desired temperature from the air source 10 to the adapter that is
connected with the inlet of the object to be cleaned via pipe
segments 126, 128, 130, 132, 134, 136, 138, 140 and 142 through
valves 46 and 54 and the two-phase generating module 12. Air is
regulated by the regulator 42 and monitored by the pressure gage
44, pressure transducer 48 and the flow meter 50. The air
temperature is also monitored by the thermocouple 52. The air
leaving the system to be cleaned at the adapter 58 is directed to
the mist separator 500 via pipe segments 144, 146, 148, 150 through
the valve 62. The transducer 60 is used to monitor the pressure of
the exhaust. Air is then discharged via pipe segment 154 from the
mist separator 500. Any liquid collected during the drying process
is discharged via the pipe segment 152 through the valve 64.
[0088] The controller unit 600 is a PLC-operated controller. It is
programmed to operate all control valves, pumps, heaters and their
controllers, pressure transducers, and flow meters in accordance
with a designed operating sequence to carry out all the function
discussed above. All the components that are connected to the
controller 600 are displayed in FIG. 1 with an electrical contact
symbol.
[0089] Valve 82 and pipe segment 156 provides means for collecting
water or liquid samples during each step of the process to monitor
the quality of the rinse water, the cleaning agent concentration,
and the sanitizing agent concentration. The collected samples are
used to monitor pH, conductivity, surfactant concentration, and
sanitizer concentration such as bleach, peroxy-acids, iodine or
others. The liquid temperature is normally monitored at the
thermocouple 52.
[0090] In another variation of the apparatus, liquids discharging
from the mist separator 500 through the valve 64 can be connected
through a pipe 196 to the manifold 263 and also recirculated back
to the corresponding tank or pump to be fed again to the system to
be cleaned.
[0091] FIGS. 2A, 2B and 2C illustrate alternate equipment used to
create a two-phase flow.
[0092] FIG. 2A illustrates generating droplets using a nozzle 13. A
gas inlet pipe 136 and a liquid pipe 214 mix the two phases in the
two-phase generating module 12. The two-phase flow exits in pipe
138.
[0093] FIG. 2B illustrates generating droplets using a liquid
delivery orifice 31, which is at an angle with respect to the gas
inlet pipe 136. After mixing the air and liquid, the mixture again
exits in pipe 138.
[0094] FIG. 2C illustrates generating droplets using a T
arrangement of the liquid inlet pipe 214 which is about
perpendicular with the gas inlet pipe 136. The two-phase mixture
exits through pipe 138.
[0095] FIG. 3 illustrates a system 400 that can be used to
backflush the liquid-air mixture.
[0096] A pipe 142 is used to inlet the air-fluid mixture through
inlet adapter 56. A pipe 170 feeds a backflushing liquid into the
passageway 400 via an inlet adapter 80. When backflushing is
complete, the mixture exits through the outlet adapter 58 via the
pipe 144.
[0097] FIG. 4 illustrates a pipe distribution network 400 to be
cleaned. Air and liquid in a pipe 142 are combined in an inlet
adapter 56 and flows through pipe 402 to be cleaned through a
bifurcation valve 404. This valve 404 in turn connects to two pipes
to be cleaned, 406 and 408/In turn, pipe 408 flows through a second
bifurcation valve 410 to clean pipes 412 and 414. The mixture exits
through outlet adapter 58 via a pipe 144.
[0098] FIG. 5 is a cross sectional view of an adapter used to clean
membrane channels using two phase flow cleaning.
[0099] The invention will be further described in the following
Examples. However, the invention is not meant to be limited by the
details described therein. In the Examples, the apparatus parts
refer to FIG. 1.
EXAMPLE 1
[0100] This example describes apparatus and process for removing
biofilm, contaminants and debris from passageways that carry pure
water or bicarbonate dialysate solution as used in dialysis center
water systems, pharmaceutical plants or industrial operations that
require the use of pure water distribution systems. To simulate the
above water distribution systems, we constructed a water system
that allowed us to grow biofilm on the lumen surface of long tubing
having a range of internal diameters by circulating water or other
liquids suitable for biofilm growth. In this example, the
passageway to be cleaned was constructed from PVC tubing and pipes
having internal diameters from 0.25 inch to 1 inch, and having
lengths from 100 to 300 feet. This arrangement provides pipelines
and tubing with a length to diameter (L/D) ratio between 1,000 and
15,000. The tubing and pipe used to construct this arrangement were
made from clear PVC to allow us to observe the two-phase flow at
any section along the pipe. This pipe arrangement is referred to as
a pipe system hereafter.
[0101] After allowing biofilm to grow for several weeks, we
subjected these simulated pipes to two-phase cleaning for five or
ten minutes, and measured both water quality (CFU/ml) and biofilm
density (CFU/cm.sup.2) before and after the two-phase flow
cleaning. SEM was also used to evaluate biofilm before and after
the application of the two-phase flow cleaning for one set of
experiments. All the cleaning was done with a two-phase mixture
where the liquid phase contained sodium hydroxide to a pH about
11.5 or higher. This solution is safe and is currently recommended
for cleaning dialysis water systems. A high pH condition lowers the
adhesive strength of biofilm to PVC tubing surfaces, and
facilitates its removal with the two-phase dynamics.
[0102] Part A
[0103] The above pipeline system was connected as the passageway to
be cleaned 400 in apparatus 100. The inlet of the pipeline system
was connected to an inlet adapter 56 and its outlet was connected
to an outlet adapter 58. Cleaning of the pipeline system was
performed using a two phase flow mixture generated inside the two
phase generating module 12 by supplying air from air source 10
through line segments 126, 128, 130, 132, 134 and 136 which connect
to the inlet of the two phase generating module 12. The air flow
rate was controlled by pressure regulator 42 and air flow meter 50
and monitored by pressure gauge 44 and pressure transducer 48. The
cleaning solution used to form the two phase flow mixture was
supplied from cleaning solution holding tank 14 through a valve 86
using first pumping means 30 through line segments 199, 198, 200,
202, 204, 210, 212 and 214 leading to the liquid inlet of the
two-phase generating module 12. The liquid flow rate was controlled
by adjusting the first pumping means 30 and was monitored by
pressure transducer 74. During cleaning, air was supplied to the
inlet of the two phase generating module 12 by opening a valve 46,
and the cleaning solution was supplied at the required flow rate by
first pumping means 30 by opening valves 84 and 76. The liquid was
supplied to the two-phase generating module 12 via a nozzle P-type
Fine Atomization Nozzle made by Bete Fog Nozzle, Inc. of
Greenfield, Mass. This nozzle provides droplet sizes in the range
of 25 to 400 microns. When the liquid droplets are mixed with air
inside the two-phase generating module 12, they form a two phase
flow that was directed to the pipeline system by opening valve 54
through the inlet adapter 56. The two-phase flow passes through the
pipeline system 400 and exits through the outlet adapter 58 to a
mist separator 500 through line segments 144, 146, 148 and 150 by
opening a valve 62. The discharged two-phase flow mixture is
separated into a gas stream that is vented through an outlet 154
and the liquid phase is discharged through line segment 152 through
a valve 64. After the cleaning step, the pipe system 400 was rinsed
with a two-phase flow mixture consisting of water and air, supplied
through the two-phase generating module 12. The air supplied to the
two-phase generating module 12, was supplied in the same way as
described above for the cleaning step. Rinse water was supplied
from rinse water holding tank 20 and pumped through a third pumping
means 34 via line segments 172, 174, 178, 206, 208, 209, 210, 212
and 204, which connects to the liquid inlet of the two-phase
generating module 12. The two phase flow generated in the two phase
generating module 12 is directed to the pipeline system 400 for
rinsing, and discharged through the outlet 58 to the mist separator
500, where the air and water are separately discharged through
ports 154 and 152 respectively. During rinsing, the same air
pressure was used as in the cleaning step, and the rinse water flow
rate was between 15 to 200 ml/min. During rinsing, the optimal time
was about 10 minutes and was determined by monitoring the pH and
specific conductivity of the rinse liquid by withdrawing rinse
liquid from the test port 82. Rinsing was continued until the rinse
liquid had the same pH and specific conductivity as the water
supplied from the rinse water holding tank 20.
[0104] Part B
[0105] Rinsing was done using a continuous flow of pure water from
a pure water source 254 or the rinsing water recirculating tank 28
via a sixth pumping means 40 through line segments 231, 230, 234,
242, 246, 250, 270 and 272 through a valve 54 and the inlet adapter
56. The rinse solution was discharged through the outlet adapter 58
via line segments 144, 146, 148 and 152 through a valve 62.
[0106] Part C
[0107] In another experiment, the rinsing was done using a pulsing
mode. In this case, a continuous supply of water from the water
source 254 or the rinse water recirculating tank 28 was delivered
by the sixth pumping means 40 through line segments 231, 230, 234,
242, 246, 250, 270 and 272 through the valve 54 and the inlet
adapter 56. In this rinsing mode, the air was supplied
intermittently for 3 seconds after every six seconds of a
continuous liquid flow, by opening valve 46 with the aid of the
control system 600. The rinse time in these cases was again
determined by the same method, by measuring the pH and the specific
conductivity of the rinse solution from the sampling port 82. The
discharge of rinse liquid in this case was the same as described
above.
[0108] The cleaning parameters used to remove biofilm from the
pipeline system 400 were: a) the inlet air pressure to the two
phase generating module 12 was regulated at 30-50 psig; b) the
cleaning solution flow rate to the inlet of the two phase
generating module 12 was 15-100 ml/min; c) the estimated velocity
at the inlet of pipeline system 400 was in the range of 48-104
ft/sec; d) the estimated exit velocity at the adapter 58 was in the
range of 114-390 ft/sec; and e) the liquid to gas ratio used to
clean pipeline system 400 was in the range of 1/800 to 1/14000.
[0109] The results of biofilm removal from 0.25 and 0.5 inch
diameter tubing, each 100 feet long, are set forth in Table 1
below:
1TABLE 1 Ve- Liquid/Air Biofilm Cleaning locity Ratio D Age Time
(ft/s) (volumetric) CFU/cm.sup.2 Tubing (in) L/D (weeks) (min) In
Out In Out Pre Post S2 0.25 4800 2 5 75 345 1/860 1/4000 890 <10
S3 0.25 4800 2 10 75 345 1/860 1/4000 -- <10 B1 0.50 2400 2 10
48 114 1/1400 1/3300 550 30 S4 0.25 4000 4 10 72 360 1/800 1/4100
1.8 .times. 10.sup.5 <1 S5 0.25 4800 4 5 90 390 1/1000 1/4400
1.8 .times. 10.sup.5 <1 B2 0.50 2400 4 10 69 186 1/2000 1/5400
6.2 .times. 10.sup.5 <10
[0110] These results show that water in contact with a
biofilm-laden surface before cleaning can have over one million
CFU/ml in the case of two week old biofilm. After either 5 or 10
minutes of two-phase cleaning, both the surface of the tubing and
distilled water stored in the tubing demonstrate that effective
cleaning gas been achieved.
[0111] The results further show that during 4 weeks of exposure to
tap water, the biofilm density has increased to the order of
100,000 CFU/cm.sup.2.
[0112] After cleaning, the biofilm density was reduced to almost
zero, and the bacterial counts reflect this.
[0113] The above microbiology results have been supported by SEMs
on the surface of the tubing before and after cleaning--see FIGS.
6A & 6B. It is clear from the SEM of FIG. 6A that a mature
biofilm with extensive polysaccharide matrix has formed at the
surface of the tubing. Two-phase flow cleaning achieves significant
removal of the biofilm along with its associated matrix, as shown
in FIG. 6B.
EXAMPLE 2
[0114] This example describes the process for removing biofilm and
residues from tubing that carry carbonated water or beverages such
as those used in soda fountain and beverage dispensing
machines.
[0115] A flow of water was maintained through a 3/8 inch internal
diameter plastic tubing having a length of 50 feet (L/D=1600) for
three months to simulate soda fountain conditions in the field. A
thick biofilm formed on the tubing during this period of time.
[0116] The tubing was cleaned using the apparatus of FIG. 1 and an
alkaline cleaning agent including 0.1% of Tergitol-1X surfactant
having a pH of 11.5 for five minutes. The liquid to gas ratio was
1:1800 and the pressure was 45 psig. Air velocities at the inlet
and the outlet of the tube were 50 ft/sec and 250 ft/sec,
respectively.
[0117] Complete removal of the biofilm from the entire length of
the tubing was obtained, as measured by standard microbiology
methods. Thus the shear stress of the two-phase flow was high
enough to overcome the biofilm adhesion having an adhesive strength
of about 100 Pascals. This tubing arrangement is referred to as
soda or beverage line and was cleaned by apparatus 100 as in
Example 1.
[0118] The cleaning conditions that were found to completely remove
biofilm from soda and beverage line were: a) air pressure, 40-50
psig; b) liquid to gas ratio, 1/1400 to 1/7300; c) gas velocities,
70-360 ft/sec; d) the cleaning solution used to create the two
phase flow included a non-ionic surfactant like Tergitol-1X made by
Dow Chemical Co and it had a pH between 10.5-13.0; e) cleaning
time, 10 min; f) rinsing time, 5 min.
[0119] The CFU/cm.sup.2 showed an initial count of
1.8.times.10.sup.5 CFU/cm.sup.2 before cleaning and <1
CFU/cm.sup.2 after the two phase cleaning performed as described
above. SEM micrographs confirmed the effective removal of biofilm
including the polysaccharide matrix from the soda and beverage line
used in this example. Furthermore, the use of a high pH cleaning
solution in the above range was found to be essential to remove
biofilm from soda or beverage lines. We found that cleaning
solutions in the acid pH range were ineffective to remove biofilm
within a reasonable period of time.
EXAMPLE 3
[0120] This example illustrates the use of apparatus 100 and the
two-phase process to remove biofilm and residue from small tubing
having an internal diameter between 1.2 to 2 mm and lengths up to 5
meters, with a range of L/D from 2500 to 4000. In this case, the
object to be cleaned includes a network of lines as depicted in
FIG. 4. This network of lines is referred to as a distribution
network in this example and illustrates the use of apparatus 100 in
cleaning a network of lines where there is branching and more than
one line in the distribution network.
[0121] Referring to FIG. 4, the distribution network has a common
inlet line 402, a 3-way valve 404 when the line 402 divides into
two lines 406 and 408. Line 408 has a 3-way valve 410, which then
splits into two lines 412 and 414. This network of lines became
contaminated with biofilm and residues due to the flow of water or
like liquids. This kind of arrangement is common in industrial
applications such as food and beverage processing, and in medical
devices such as in dental chairs and dialysis machines.
[0122] A network of lines used in a dental chair in use for 11
years was cleaned using apparatus 100. A base line bacterial count
was performed for a period of seven weeks. The network was found to
be highly contaminated with mature biofilm. The bacterial level in
water passing through this line had a range between
10.sup.6-10.sup.7 CFU/ml. This network was cleaned with the
two-phase flow process using apparatus 100 as follows:
[0123] The inlet of the distribution network 400 shown in FIG. 1
was connected to inlet adapter 56 which directs the two phase flow
mixture through the distribution network. The outlet of lines 406,
412, and 414 are collectively connected to outlet adapter 58 for
the purpose of discharging the two-phase flow through the mist
separator 500. The two-phase flow delivered to the adapter 56 is
formed using the same arrangement as described in Example 1 with
the aid of controller 600. In this network, the following steps
were used to clean, rinse and sanitize. The two-phase flow
conditions used in this example were: a) air pressure, 40-80 psig;
b) liquid to gas ratio, 1/1500; and c)
cleaning/sanitizing/disinfecting solution flow rate, 5 to 10
ml/min.
[0124] Step 1--Air purge: The distribution network was first purged
with air supplied from the air source 10 through the regulator 42
and the control valve 46 for 30 seconds. The discharged mixture was
directed to the mist separator as described in Example 1.
[0125] Step 2--Two phase cleaning/sanitization/disinfection: a) Two
phase flow was created in the two phase generating module 12 and
delivered through the inlet adapter 56 to clean lines 402 and 406
together for 90 seconds via the control valve 404; b) The two phase
flow from the inlet adapter 56 was used to clean lines 402, 408 and
412 via control valves 404 and 410 for 90 seconds; c) The two phase
flow from the inlet adapter 56 was used to clean lines 402, 408 and
414 via control valves 404 and 410 for 90 seconds. The
cleaning/sanitizing/disinfecting solution included a mixture of a
non-ionic surfactant and a biocide. The pH was 10.5-13.0.
[0126] Step 3--Rinsing with pulsation: The rinsing was performed in
the pulsing mode as described in Example 1--Part C as follows: Pure
rinse water was supplied from rinse water source 254, or rinsing
water recirculating tank 28, through line segments 230, 234, 242,
246, 250, 270 and 272 via valve 54 to inlet adapter 56 in a
continuous mode. During rinsing, air was injected intermittently
for 3 seconds after every 6 seconds. The lines were rinsed in the
same sequence as in the cleaning step described above.
[0127] Step 4--Rinsing with continuous water flow: Rinsing in this
step was performed with a continuous flow of water supplied from
the rinse water source 254 or rinsing water recirculating tank 28
through the sixth pumping means 40 without the use of air. In this
step all the lines were rinsed together by opening the valves 404
and 410 for 120 seconds.
[0128] The quality of rinse water was tested by collecting water
samples through port 82 by measuring pH, specific conductivity and
surfactant concentration.
[0129] Step 5--Purging and drying: In this step, the network
distribution system was purged with air supplied from the air
source 10 through the adapter 56 for 60 seconds. This step
minimizes biofilm growth during periods of non-use of the
tubing.
[0130] The use of this cleaning and sanitizing mechanism achieved
complete removal of biofilm as shown by SEM analysis and bacterial
counts taken for over a period of 3 months. The results are shown
in FIGS. 7A and 7B.
EXAMPLE 4
[0131] This example describes a process and apparatus for removing
bio burden and pathogens from medical tubing such as those used in
endoscopes, catheters, surgical drainage tubes, respirators,
ventilators and the like. Two 3-meter long plastic tubings having
internal diameters of 1.1 mm and 4 mm respectively, were
contaminated with Bacillus subtilis spores in British soil (i.e. 10
ml of Bovine serum, 10 ml of saline solution and 6 grams of dry
milk powder) at a level of 1.6.times.10.sup.6 CFU/tubing and were
allowed to dry overnight to ensure that the soil became highly
adherent to the lumen surface of the tubing. These contaminated
tubings were separately connected to apparatus 100 through the
inlet adapter 56 and the outlet adapter 58. Two phase flow was
generated in the two phase generating module 12 by supplying air
from the air source 10 to the gas inlet of the two phase generating
module 12 as described in Example 1. An alkaline cleaning solution
(pH=11.5) and a non-ionic surfactant, Tergitol-1X, was supplied
from the cleaning solution holding tank 14 through the first
pumping means 30 to the two-phase generating module 12 for 10
minutes. The entire process was controlled with the aid of the
controller 600.
[0132] The process parameters used in this example were: a) gas
pressure; 20-30 psig; b) liquid to gas ratio between 1/600 to
1/800; c) gas inlet velocities in the range of 100 to 200 ft/sec;
d) temperature of the two-phase mixture, 45.degree. C.
[0133] The tubes were then rinsed using two-phase flow for 5
minutes, as described in Example 1. The tubing were then extracted
three times with 50 ml Peptone-tween to recover any remaining
organisms as per accepted good laboratory practice (GLP) industry
protocols. The eluted samples were then cultured to enumerate CFU
per tubing. The results of this test showed that the above cleaning
achieved complete removal of the Bacillus spores, a 6.2 log
reduction (99.999%). The results are shown in Table 2 II.
2 TABLE II Counts after Percent Log Channel Exposure (CFU)
Reduction Reduction Large dia. tube <1 <99.999% 6.2 Small
dia. tube <1 <99.999% 6.2
EXAMPLE 5
[0134] This example describes cleaning an endoscope having a
complex network of channels as in FIG. 4. All the internal channels
of two Pentax gastroscopes Model EG-2901 were inoculated with
2.times.10.sup.6 Bacillus subtilis spores dispersed in British
soil. The concentration of spores in British soil was
10.sup.9/ml.
[0135] Cleaning was done using the apparatus 100 by connecting the
inlets of endoscope internal channels to the inlet adapter 56 and
by confining the outlet to the outlet adapter 58. Cleaning and
rinsing were done as described in Example 1. The endoscope was
cleaned and rinsed according to the following process steps
(protocol):
[0136] a) Two phase cleaning: Pressure: 20-30 psig; liquid to gas
ratio, 1/600-1/800; velocities, 100-200 ft/sec; temperature,
45.degree. C.; cleaning time, 10 min.
[0137] b) Rinsing with pulsation: Pressure, 20-30 psig;
temperature, 25.degree. C.; rinsing time, continuous water flow for
5 minutes followed by intermittent air flow for 3 seconds after
every 6 seconds;
[0138] c) Drying: Pressure, 20-30 psig; temperature, 45.degree. C.;
drying time, 2 min.
[0139] The individual channels of the two endoscopes used in this
example were then extracted three times with 50 ml Peptone-tween
and cultured according to industry standards. The results of this
test are shown in Table III. It is clear that the process and the
apparatus of this invention are capable of achieving high log
reduction by the two phase flow cleaning method.
3TABLE III Corrected counts after exposure to two-phase flow
process Percent Log Channel (CFU/channel) Reduction Reduction
Endoscope #1 1.0 >99.999% 6.2 Air/water channel Endoscope #1
15.1 >99.99% 5.0 Suction/biopsy channel Endoscope #2 3.0
>99.99% 5.7 Air/water channel Endoscope #2 <1 >99.999% 6.2
Suction/biopsy channel
EXAMPLE 6
[0140] This example describes cleaning of tubing contaminated with
mature biofilm and illustrates the importance of adjusting the
liquid to gas.
[0141] A 1.4 mm internal diameter tubing having a length of 24
inches (L/D=435) was covered with a highly adherent biofilm on its
interior surface and cut in three equal sections, designated as A,
B and C.
[0142] Section A was used as a Control. It was cleaned by scraping
the biofilm with a scalpel and found to contain a total of
2.5.times.10.sup.8 CFU.
[0143] Section B was cleaned in a slug flow regime by mixing air
and a cleaning solution containing 0.15% Tergitol-1X, 1% of SPT and
0.18% of sodium silicate at a liquid to air ratio of 1:1 to 1:10
for ten minutes. The inlet air pressure was 60 psig.
[0144] A total of 2.5.times.10.sup.8 CFU was found, indicating that
the cleaning using the slug flow regime at the above liquid to air
ratio was not effective to remove biofilm.
[0145] Section C was cleaned with the same cleaning solution with
two phase flow according to the method and apparatus of this
invention. A two phase flow mixture with a liquid to gas ratio of
1:920 was applied for 10 minutes at 60 psig air pressure.
[0146] A total of 800 CFU was found, indicating that the present
method is effective to remove highly adherent biofilm.
[0147] A comparison of the cleaning results performed at a high gas
to liquid ratio with those performed at a low gas to liquid ratio
(slug flow) demonstrates that the apparatus and method of this
invention achieve effective removal of highly adherent biofilm or
residues.
EXAMPLE 7
[0148] This example describes the apparatus and process for
cleaning tubular membrane filters either individually or in series
according to this invention. The cleaning solution contained an
amphoteric surfactant and potassium hydroxide and had a pH of
12.8.
[0149] A rather large tubular filter having a length of about 6
feet including 8 individual tubes connected in series, an overall
flow length of 48 feet, having a flow path with a total of seven
return bends of 180 degrees each, available from the Zenon
Environmental Co. of Ontario, Canada, was used as an ultrafilter
during a wastewater treatment operation. The tubular membrane was
Zenon MT-100 having a molecular weight cut-off of about 100,000.
The inside diameter of the tube was about 0.8 inch.
[0150] Waste water was supplied to the inside of this tube and
clean water was extracted from the outside. During cleaning, the
air supply pressure ranged from 40-80 psig. The flow rate of air
was 120 standard cubic feet per minute. The velocity of the air was
calculated to range from about 40 m/s near the inlet to about 175
m/s near the outlet. The Reynolds number of flow of air in these
tubes was 225,000.
[0151] The filter was treated by a controlled synthetic wastewater
until its flux decreased to 39% of its as-manufactured value. The
filter was then cleaned by the two-phase cleaning method using
several steps, including both acidic and alkaline cleaning liquids.
Using an air to liquid ratio of 200:1, and an alkaline surfactant
for 3 minutes, the flux recovered to 64% of its initial value.
Applying the two-phase flow for another 2 minutes improved the flux
to 81% of its initial value. A slight further improvement in the
flux values was realized when the direction of the two-phase flow
was reversed.
[0152] These results show that a total of five minutes cleaning of
a tubular filter using two-phase flow is sufficient to restore the
flux values and compares favorably with conventional cleaning
requiring a much longer period of time.
[0153] This experiment also illustrates the re-formation of the
mixed-phase flow condition after a sharp change of direction. At
each return bend it can be expected that there might be some
disturbance of the mixed-phase flow condition, such as coalescence
of droplets, but the successful cleaning results show that there is
rapid re-formation of the mixed-phase flow condition after a flow
irregularity, such as a bend.
EXAMPLE 8
[0154] Using the same type of filter and cleaning solution as in
Example 7, the filter was fouled by a controlled wastewater to the
point where its flux level dropped to 35% of its initial value.
Cleaning was performed and then stopped, while the flux was
measured briefly using the controlled wastewater. Cleaning was
resumed, and this was repeated several times until it became
apparent that no further improvement was obtained. After three
intervals of such cleaning, all at the same mixed-phase flow
conditions, the flux level reached a plateau of about 74% of the
baseline and no further improvement was obtained. To obtain further
improvement, soaking was initiated because both the surface and
pore structure of the tubular membrane had become fouled. For a
period of time, the passageway was filled with foam which was
stationary, and pressure continued to be applied in the same
direction as normal operation of the filter. This allows the
cleaning solution to reach deeper into the pores. This hold and
soak cycle lasted 2 minutes, and was followed by the application of
two-phase flow for 15 seconds to remove any newly-dislodged
residue. The soaking brought a further improvement up to 95% of the
baseline value.
EXAMPLE 9
[0155] Three additional filters were cleaned using the cleaning
solution of Example 7. Two of them had been fouled by normal use
until the flux was about 40% of its initial value, and one had been
fouled by normal use until the flux was only 4% of its initial
value. The cleaning cycle included several minutes each of
two-phase flow and a holding period, with internal pressure under
static conditions. A light backflushing was then performed using
the liquid cleaning solution pressurized on the permeate side to
several psi.
[0156] For the most heavily fouled filter, a further treatment was
performed using an acidic two-phase flow cleaning for three
minutes, followed by an alkaline two-phase flow cleaning for three
minutes. The first two filters were restored essentially to 100% of
their initial flux, and the last was restored to about 95% of its
initial specified flux.
EXAMPLE 10
[0157] This example describes the cleaning of C-I-P piping systems
including tubing, fittings, valves, pumps and other equipment used
in C-I-P systems of dairy, food, beverage, cosmetics,
pharmaceutical and similar process industries. The piping system
used in this example included over 200 feet of sanitizing stainless
steel pipe with an internal diameter of 2.0 inch. This pipeline
system was arranged with several bends and turns to simulate a
typical dairy, beverage or pharmaceutical pipeline system used in
industry. The pipeline system had numerous test sections placed at
different locations within the piping system that could be removed
for inspection to determine the cleaning, rinsing and sanitizing
efficiency and then replaced back into the piping system for
regular operation. To generate a two-phase flow for cleaning this
pipeline system, a special compressor with 450 SCFM capacity was
used as the air source. This air source was capable of supplying
air flow at pressures over 30 psig and could be regulated at any
pressure through a pressure regulator. The two-phase flow used to
perform cleaning, rinsing and sanitizing this pipeline system was
generated by using a special two phase generating module including
the arrangement of air and liquid delivery design as shown in FIG.
2A and using the apparatus of FIG. 1.
[0158] The nozzle used to generate droplets for the two phase flow
used in cleaning, rinsing, and sanitizing the pipeline was designed
to supply liquid droplets in the range between 25 to 400 microns
using three different pumps. The process steps for performing the
entire cleaning, rinsing and sanitizing cycles were controlled.
First, initial testing to determine gas and two-phase flow
velocities at the inlet and outlet of the piping system was
performed. Water was supplied at different flow rates to the
two-phase generating module 12 through the third pumping means 34.
Air was regulated using a pressure regulator 42 and a flow meter 50
to cover an air pressure range between 10 to over 30 psig. The two
phase flow delivered to the piping system through the inlet adapter
56 was controlled to provide two phase flow having pressures
between 12-32 psig and liquid flow rates ranging from 0 to 1.2 gpm.
The air and liquid flow rates used in this experiment covered gas
to liquid ratios between 900:1 to 27,000:1.
[0159] The type of flow going through the pipeline system was
observed through transparent sections within the pipeline system.
It was found that two phase flow mixtures applicable for cleaning,
rinsing and sanitizing the pipeline system can have liquid to gas
ratios between 1:1000 to 1:6000. The gas flow rate was determined
in these experiments using the flow meter 50.
[0160] These sets of experiments showed that the inlet velocities
to the passageway system 400 is in the range between 63-110 ft/sec
depending on the pressure and the gas to liquid ratio used. Outlet
two-phase velocities of the piping system was between 114 to 350
ft/sec.
[0161] These experiments provided the conditions to generate
two-phase flow with a known gas to liquid ratio, velocity,
appropriate setting of first, second, and third pumping means and
pressure regulators. These parameters were input into the PLC
program of controller 600. During these experiments, the two phase
flow mixture exiting the pipeline system was discharged through the
mist separator 500 via the outlet adapter 58 and line segments 144,
146, 148 and 152.
[0162] Standardized residues and soiling methods were selected for
the pipe surfaces to be cleaned and for the removable test panels.
Raw milk was applied and dried according to specific industry
protocols. These soiling protocols were previously determined to
constitute a severe challenge for cleaning with fully flooded
conventional C-I-P cycles using conventional chemistries and
current cleaning protocols in the dairy industry.
[0163] The method of inspection and surface analysis to objectively
determine the nature and extent of residue removal were selected
based on extensive prior experience and validation. Initial needs
to rank relative cleaning performance were satisfied by visual and
qualitative evaluation. Relative ranking from 0-10 was used, 10
being clean, 0 being heavily soiled. Baseline cleaning performance
data was generated by preparing the milk residues and soiling of
pipe and test panels and then executing conventional C-I-P cycles
chosen to be representative of industry practice. A set of test
panels from these runs were used as controls to determine the
cleaning efficiency.
[0164] As a control, a conventional fully flooded CIP cycle was
used to establish a baseline to be used to compare the efficiency
of cleaning, rinsing and sanitizing pipeline systems as
follows:
[0165] Step 1--Preflushing the line with water: Time, 3 min; vol.
of water used, 90 gallons; temperature, ambient.
[0166] Step 2--Drain 1: Time, 0.5 min.
[0167] Step 3--Cleaning step: Time, 12 min; vol. of water used, 90
gallons; vol. of cleaning sol. Used, 60 gallons; chemistry,
alkaline with hypochlorite bleach; temperature, 150.degree. F.
[0168] Step 4--Drain 2: Time, 0.5 min.
[0169] Step 5--Rinse: Time, 3 min; vol. of water used, 90 gallons;
temperature, ambient
[0170] Step 6--Drain 3: Time, 0.5 min.
[0171] Step 7--Sanitizing: Time, 2 min; vol. of water used, 90
gallons; sanitizing solution vol., 60 gallons; chemistry, peracetic
acid based; temperature, ambient.
[0172] Step 8--Drain: Time, 0.5 min.
[0173] Thus this fully flooded C-I-P cycle takes 22 minutes,
consumes 360 gallons of water and 120 gallons of cleaning chemicals
and sanitizers. The test panels placed at different locations (30
feet apart) were inspected and were rated between 3 and 5 on the
cleaning efficiency scale, i.e., the panels still showed some
remaining residues and had hazy spots.
[0174] Several tests to perform the two-phase flow cleaning of the
pipeline system using apparatus 100 were performed to determine the
range of effective operating conditions to clean milk residues. The
following experiments were performed:
[0175] Test Series 1
[0176] Multiple tests were performed to determine the cleaning
efficiency of the pipeline system contaminated with dried milk
residues as described above. In this series of tests, the effect of
air pressure and gas to liquid ratio on cleaning efficiency was
evaluated. Air pressure to form the two-phase flow was in the range
between 8-32 psig; gas to liquid ratio was adjusted between 1400:1
to 15,000:1. To achieve these conditions, the air flow rate was
measured by the flow meter 50 at different pressures. The liquid
flow rates were varied between 0.12 to 2.0 gpm by adjusting the
first pumping means 30 with the aid of controller 600. Again, test
sections were installed and removed to determine cleaning
efficiency using the 0-10 scale as described above.
[0177] In further experiments, the inlet air pressure was kept
constant at 12 psig using the air source 10 and the regulator 42 of
apparatus 100. The cleaning liquid level was varied between 0.12 to
1.2 gpm, giving rise to gas to liquid ratios between 12,000:1 to
900:1, respectively. The cleaning time in all cases was kept
constant at 5 minutes. Cleaning efficiency results were measured by
inspecting the test sections as described above. The results of
these experiments showed that a gas to liquid ratio between 2,000:1
to 6,000:1 achieve effective cleaning (cleaning scale=6-7) at an
air pressure of about 12 psig.
[0178] The results of this series of tests showed that air
pressures between 8 to 32 psig, gas to liquid ratios between 1400:1
to about 6,000:1 and cleaning times between 5 to 10 minutes
produced high cleaning efficiency rated between 7-9 on the 0-10
scale as described above. Based on these experiments, air pressure
of about 10 psig or more, and gas to liquid ratios between 1,400:1
to 6,000:1 appear to provide effective cleaning of the pipeline
system. The use of alkaline cleaning solution including a
hypochlorite salt, as conventionally practiced in dairy C-I-P
cleaning, appears to provide additional advantages when used in the
two-phase cleaning at the conditions described above. The two phase
mixture inlet velocity range optimal for cleaning this system was
between 60 to 100 ft/sec, preferably above 70 ft/sec.
[0179] Test Series 2
[0180] A comprehensive testing was performed to determine the
practical ranges for using the two-phase flow method and apparatus
100 to perform cleaning, rinsing and sanitizing of pipeline systems
used in dairy, food, beverage and pharmaceutical processing. The
following process steps were identified as a guideline:
[0181] Step 1--Air purge: Time, 0.5 min.
[0182] Step 2--Two phase pre-flushing/pre-cleaning: Time, 4 min;
liquid flow rate=1.2 gpm; gas pressure=12-15 psig; gas to liquid
ratio about 1,000:1; chemical, alkaline cleaner with hypochlorite
bleach; temperature, ambient.
[0183] Step 3--Two-phase flow cleaning cycle: Time, 5 min; liquid
flow rate, 0.22 gpm; gas pressure, 12-15 psig; gas to liquid ratio
about 1400:1-7,000:1; chemical, alkaline cleaning solution with
bleach; temperature, ambient.
[0184] Step 4--Two-phase rinsing: Time, 3 min; pressure, 12-15
psig; gas to liquid ratio about 1,000:1; liquid flow rate, 1.2 gpm;
temperature, ambient.
[0185] Step 5--Air purge: Time, 0.5 min.
[0186] Step 6--Two phase sanitizing: Time, 3 min; pressure, 12-15
psig; gas to liquid ratio about 1,000:1; liquid flow rate, 1.2 gpm;
sanitizing chemical, peracetic acid based sanitizer;
temperature=ambient.
[0187] Test results of several runs according to the above process
achieved equivalent or better cleaning results compared to
conventional fully flooded C-I-P systems. The cleaning efficiency
scale of two phase cleaning ranged between 7-9 as compared to 3-5
for fully flooded C-I-P cleaning however.
[0188] The results of this example demonstrate that two phase flow
cleaning is effective and practical for applications in dairy
pipeline cleaning and similar pipeline systems. The use of
apparatus 100 and the process outlined above achieved 25-40%
savings of time, over 95% savings of water, over 90% savings of
cleaning chemical solution and considerable savings in sanitizing
solutions.
EXAMPLE 11
[0189] In this example, we describe methods and apparatus for
removing old biofilm from a fluid distribution system consisting of
pipes, tubing, valves and connections. Examples of such
distribution systems include, but are not limited to, modern water
systems, dental chair water circuits, dialysis machines, such as
those used in hemodialysis, respirator and ventilation tubes, such
as those used in hospitals where biofilm is known to quickly grow
and cause infection, water coolers, beverage dispensing systems and
multiple other applications in the food, beverage and
pharmaceutical industries and the like. This example specifically
pertains to the water circuit in dental chairs and includes a study
that elapsed over a nine-month period. Eight dental chairs were
equipped with apparatus 100 and the dental chair waterlines were
connected as the passageway to be cleaned 400 in apparatus 100 as
shown in FIG. 1. The dental units used in the study were 11 years
old and were supplied with municipal water during this period,
without changing their tubing. The dental unit waterline circuits
were covered with old and mature biofilm, with the presence of
extensive layers of inorganic scale at the surface of the tubing
due to the hardness of the water supply. These dental units had to
be cleaned to remove the old biofilm, as well as the heavy
inorganic scale, in order to bring them into compliance with the
200 CFU/ml level, as recommended by the American Dental Association
(ADA) for dental water quality.
[0190] First, the units were connected to adapters 56 and 58, using
the arrangement and treatment described in Example 3. To perform
the initial treatment, the unit was treated with a two-phase flow
mixture with a high pH composition containing sodium hypochlorite
bleach according to the following composition: 5 wt. % sodium
meta-silicate, 0.5% Tergitol-1X. The treatment was done for 10
minutes and covered all the lines in the dental chair. The
bioburden in dental treatment water was reduced from 10.sup.7 to
about 10.sup.3 CFU/ml.
[0191] The dental units were then cleaned daily with the two-phase
flow process using apparatus 100 as described in Example 3, and the
CFU/ml was monitored daily. After two weeks of monitoring,
bacterial counts in some dental units remained high, around
10.sup.3 CFU/ml. Upon SEM examination of the surface of the dental
tubing, it was discovered that a heavy layer of inorganic scale was
present on the surface and needed to be removed to achieve complete
removal of old biofilm from the entire surface of the water circuit
of non-complying dental units.
[0192] To remove scale, the two-phase flow process was used as
described in Examples 3, except using a de-scaling solution having
the following composition: 3% hydroxyacetic acid and amphoteric
surfactant, pH 1-2. After treating the water circuit of dental
chairs with multiple two-phase cleaning cycles using the de-scaling
agent defined above as the liquid phase, complete removal of the
inorganic scale was achieved as per SEM examination. Then the units
were brought into compliance with the 200 CFU/ml level recommended
by ADA. This low bacterial level was maintained by performing a
daily cleaning with the two-phase flow process as described in
Example 3.
[0193] We discovered that the use of the two-phase flow process
combined with the alkaline compositions having a high pH in the
presence and absence of hypochlorite bleach to be effective in
removing old or highly adherent biofilm.
[0194] To arrive at this composition, a series of liquid
compositions were made covering pH ranges from 2 to 13.5 and
applied using the two phase flow cleaning process to dental tubing
extracted from the 11-year old dental units mentioned above. We
discovered that compositions based on the above formula having a pH
of less than 10.0, and applied with the two-phase flow process do
not achieve removal of biofilm matrix using SEM and optical
microscopy examination. Compositions having an acid pH were found
to be very ineffective in removing biofilm from tubing surfaces.
However, as the pH of the cleaning solution was increased to above
10, some matrix removal was observed; but some highly adhering
biofilm spots remained on the surface of the tubing even when the
cleaning was performed with high two-phase flow velocity of about
100 ft/sec. Increasing the pH of the above composition by
increasing the level of sodium meta-silicate or NaOH to above 12.5
was needed to achieve complete removal of the very old biofilm with
the two-phase flow process, carried on only for about 5-10 minutes.
This high pH level may be essential in ionizing the hydroxyl groups
of sugar moieties of the polysaccharide matrix, thus resulting in
lowering adhesion to the surface of tubing during the two-phase
flow cleaning. Therefore, a combination of high-pH liquids applied
in the form of two phase flow, at velocities above 100 ft/sec, was
necessary to remove highly adhering biofilm from tubing or pipes.
This result was further confirmed by the results of Example 10 in
cleaning dairy pipeline systems and of Example 1 in cleaning
dialysis center piping systems.
[0195] In this example, the removal of old biofilm and inorganic
scale requires the application of two-phase flow cleaning,
preferably alternating acid compositions and alkaline compositions
with high pH (preferably >12.5) to remove adhering biofilm. This
procedure can be repeated several times (2 to 10 times) until all
biofilm and scale are removed. The number of times this treatment
is required depends on the condition of the surface and the
adhesion of biofilm and inorganic scale. The use of highly alkaline
liquid compositions with hypochlorite bleach was beneficial in this
case to remove mature biofilm. The addition of some two-phase flow
cleaning cycles where the cleaning solution included acid
de-scaling agents was important in the cases where scale is
present. This was also the case in cleaning dairy pipelines where
calcium scale deposits are known to form during milk flow. This
example demonstrates the process and compositions needed to treat
and control highly adhering biofilm in fluid distribution
systems.
EXAMPLE 12
[0196] This example describes the apparatus and processes for
cleaning and sanitizing the surfaces of tubing, pipelines,
membranes and equipments. The example relates to the use of
apparatus 100 and the two-phase process to clean, disinfect,
sanitize and sterilize the surfaces of passageways of the
above-listed applications, and similar passageways that are complex
or have high L/D ratio. Two parts of this example illustrate two
important cases including applying a sanitizer as a part of the
entire two-phase cleaning, rinsing and disinfecting process.
[0197] Part A
[0198] This example pertains to cleaning and sanitizing the
internal channels of endoscopes, which constitute a network of
internal tubing having bifurcation and connections, as described in
Example 5. A surrogate endoscope was manufactured from clear
plastic tubing including a suction channel, an air channel and a
water channel, similar to the arrangement used in gastrointestinal
endoscopes made by the Pentax Company. The clear tubing was used to
define the two-phase flow that is optimal in cleaning and
sanitizing internal channels of this network of tubing. Visual
observations were made either with the naked eye or with the aid of
an optical microscope. Gas:liquid ratio, liquid composition and
two-phase flow velocities were varied using apparatus 100 with the
aid of a controller 600. Observations were made and results
collected for several experiments.
[0199] In cleaning experiments, the transparent surrogate endoscope
was contaminated with Hucker's soil (peanut butter, 10 g; butter,
10 g; flour, 10 g; lard, 10 g; dehydrated egg yolk, 10 g (or two
fresh eggs); evaporated milk, 15 ml; distilled water, 50 ml;
Higgins India ink, 4 ml; International printers ink solution (A646
diluted one to one with 10 drops boiled Linseed oil), 20 drops);
Normal saline, 3 ml; dehydrated blood, 1 g) and allowed to dry for
periods ranging from two hours to overnight. The endoscope was then
connected to inlet adapter 56 and outlet adapter 58 of apparatus
100, as described in Example 5.
[0200] Two-phase cleaning was done using the following conditions:
liquid to gas ratio--1/600 to 1/800; gas velocities: 100 to 200
ft/sec; gas pressure 20-30 psig; cleaning time, 10 min.
[0201] Judging by the removal efficiency of black-stained Hucker's
soil, we found that the creation of liquid droplets in the
two-phase cleaning was important to the quick and efficient
cleaning of the internal channels of the endoscope. Three
parameters were found to be important for a successful two-phase
cleaning process: a) the gas:liquid ratio, b) the two-phase
velocity and c) the nature of the two-phase flow distribution
inside the lumen of the channels. If the condition of high velocity
is satisfied (above 70-150 ft/sec), full coverage of the entire
channel surface by dynamic impact of droplets was found to depend
on the gas:liquid ratio, liquid composition, surface tension and
wetting properties of the channel surface, including the residue
that is deposited over it. Optimal cleaning results were obtained
when the two-phase flow produced high-velocity droplets covering
the entire surface of the channel along its full length.
[0202] When the surface of the channel had areas that were not
covered with a liquid film, while other areas were experiencing
droplet impact, the cleaning proceeded fast and with high
efficiency. In this case, it was apparent that parts of the surface
were impacted by droplets and other parts were not wetted by the
liquid in a somewhat uniform distribution. It was evident from
these experiments that de-wetting processes were taking place
during the two-phase cleaning process (especially in the presence
of a surfactant); and it appears that this de-wetting process plays
an important role in the two phase cleaning. This optimal
distribution of droplets over the surface of channels and the
presence of areas not covered by liquid were a function of the
gas:liquid ratio, two-phase flow velocity and liquid composition
(including type of added surfactant and/or solvent), and, to some
extent, on the mode and rate of introducing the liquid when forming
the two-phase flow at the inlet of the channels.
[0203] If the gas:liquid ratio was too high, the flow in the
channels resembled that of "rivulet" flow (liquid moved in the form
of a streak without providing full coverage of channel surface),
and poor cleaning was observed for this flow condition. On the
other hand, when the gas/liquid ratio was too low, surface flooding
took place and the surface of the channel was covered with a liquid
film. The optimal gas:liquid ratio that provided good cleaning was
between 600/1 and 800/1 at a velocity range of 100-200 ft/sec, for
the case of endoscope channels. Further, we have discovered that
different gas:liquid ratios, within this range, need to be somewhat
tailored to the cleaning of the narrow air:water channel or to the
wider suction channel.
[0204] Furthermore, in this example we found that the liquid
composition plays a critical part in the behavior of the two-phase
flow at the surface of the tube or channel during cleaning, even if
such liquid is delivered to give the same gas/liquid ratio. A
composition containing sodium tripolyphosphate, 2%; sodium
carbonate, 0.6%; Tergitol-1X, 0.15% and sodium meta-silicate,
0.13%, was found to give reasonable two-phase behavior at the
surface of the channels when applied at the flow conditions
provided above. However, a higher surfactant concentration (to
about 0.3 to 0.5%) led to excessive surface wetting of the channel
surface and hampered the removal of Hucker's soil. In addition, it
was found that the type of surfactant alters the behavior of the
two-phase flow at the surface of the channel during cleaning.
[0205] For example, when surfactants Tego Betaine ZF, made by
Goldschmidt Chemical Corporation, Surfactants XTJ 504 (or 597),
made by the Huntsman Company, or sodium dodecyl sulfate were used,
instead of Tergitol (1X or 2X) surfactant, excessive surface
wetting and foaming were encountered, and this resulted in a
significant decrease in the effectiveness of the cleaning. It is
thus important to select the type of surfactant, its level and its
wetting and de-wetting dynamic properties at the surface of the
tube or channel. In addition, we also found that the addition of
alcohols, such as isopropanol or the like, in the cleaning
solution, causes excessive surface wetting, and again hampers the
cleaning of the Hucker's soil when using the two-phase flow
process. These factors demonstrate the importance of the above
parameters in achieving effective cleaning.
[0206] Part B
[0207] This example addresses the use of sanitizers to achieve
disinfection with the two-phase flow process after the conclusion
of the cleaning step as described in the examples. In some
applications, when the amount of liquid sanitizers such as bleach,
peroxyacids, iodine and the like is very large, the use of the
two-phase flow method to sanitize the surface after cleaning is
preferred, in order to reduce the amount of sanitizers used. This
is clearly demonstrated in Example 10, where effective sanitization
could be accomplished at a high gas:liquid ratio, which translates
to a very small fraction of sanitizer volume compared to fully
flooded C-I-P systems.
[0208] We found it is best to apply the sanitization step at the
conclusion of the cleaning step according to the two-phase flow
process. When the cleaning is performed with the two-phase flow
process, the surface to be sanitized will be practically free of
microorganisms, and the demand for employing high sanitizer
concentrations, or using long exposure times, will be reduced.
[0209] In one case, the pipeline system used was the same as
discussed in Example 1. The sanitizing step was performed with an
alkaline hypochlorite bleach solution applied in the two-phase flow
mode, at a gas/liquid ratio between 600/1 and 800/1 for 5 to 10
minutes. Culture results of the surface showed no viable count,
i.e., zero CFU/cm.sup.2. In this example, only about 1-2%
sanitizing solution was used to perform the two-phase sanitizing
step with results similar to those obtained in fully flooded liquid
C-I-P system.
[0210] This same experiment was repeated but using peracetic acid
solution (0.1-0.2%) as the liquid fraction of the two-phase
mixture; similar results were also achieved (0 CFU/cm.sup.2). In
the above cases, the sanitizing step was run using apparatus 100
and the gas:liquid ratio was adjusted within the range defined in
Example 1.
EXAMPLE 13
[0211] Cleaning apparatus 100 and the two-phase cleaning process
were used to perform clean-in-place (C-I-P) operations of reverse
osmosis (RO) membrane elements, part of a wastewater system, with
noted success. In this case, the system to be cleaned 400 consisted
of a single 4 inch RO pressure vessel (made by Osmonics
Corporation) having two spiral wound RO elements (FilmTec
TW30-2540) connected in series. The above RO pressure vessel was
piped with a feed inlet, a permeate outlet for purified water and a
concentrate outlet.
[0212] This single-vessel RO membrane system was integrated into a
pilot plant used to treat a high total suspended solids (TSS), high
total dissolved solids (TDS), salt, protein (whey) and fat laden
dairy wastewater from a dairy plant washdown. This wastewater was
first pretreated using a submerged Kubota FC-25 microfilter (MF),
operated as a bioreactor, to reduce the total suspended solids from
>10,000 ppm to <100 ppm, and to lower the biological oxygen
demand (BOD) of this waste stream. The MF effluent was fed into the
RO vessel described above to produce RO water. The latter RO step
was a single separation stage with 28% recovery and with means for
recirculating the concentrate to a RO feed holding tank. Due to
this configuration, there was a rapid increase in the RO feed
quality, which had a TDS of over 8,000 ppm on the average. The
resulting fouling and scaling in the RO membrane caused significant
reduction of RO flux in a matter of hours to less than 50% of
design specifications of the RO membranes. RO flux, TDS, pH and
temperature data were documented during a three-month study for
this system. In addition, water quality of the micro-filtration
feed, RO pretreated influent and RO products was measured daily
over a period of five weeks.
[0213] Apparatus 100 was used to clean the above RO membranes (two
RO elements connected in series in a single pressure vessel) on a
periodic basis. To connect the RO pressure vessel to apparatus 100
and to allow the application of two-phase CIP cleaning during
normal production of purified water, a special cleaning adapter, as
shown in FIG. 5, was developed to separate the permeate stream from
the rest of the system during the cleaning step.
[0214] The adaptor 415, as shown in FIG. 5, connects the pressure
vessel with the aid of two clamps, 430 and 434. The permeate
channel of the RO spiral element in the pressure vessel becomes
tightly sealed to this adapter through sleeve connector 424, which
separates the permeate channel from the two-phase mixture during
the cleaning cycle. The permeate liquid port 420 is sealed with a
welding joint 436 in a way so as to prevent contact with the
cleaning solution. The RO spiral membrane is designated as 428 and
the body of the adapter is shown as 432.
[0215] During cleaning, the permeate channel is closed with a valve
(not shown) connected to the permeate port 420, which is open
during the filtration operation and is closed during the cleaning
step. The two-phase mixture 422 is created in the two-phase
generating module 12 (FIG. 1) where the liquid fraction is
delivered by the first pumping means 30 to a special nozzle 13, see
FIG. 2A, that delivers liquid droplets in the range of 25 to 400
microns in size to the liquid inlet port 214 of the two-phase
generating module 12. The two-phase flow is generated in the module
12 by propelling the droplets with a gas stream from the gas or air
source 10, as described in Example 1. This two-phase mixture is
directed to the inlet adapter 56, which is connected to the adapter
shown in FIG. 5, to convey such two-phase mixture to the feeding
channels of the RO membrane. The direction of flow is clearly shown
in FIG. 5 where the two-phase flow is directed to inlet 418 through
the adapter 415 and then to the feeding channels of two spiral
wound membrane elements 428 connected in series. The two-phase
exhaust emerging from the end of the feeding channels of the second
membrane element is connected to the outlet adapter 58, and then
discharged though the mist separator 500 as described in Example
1.
[0216] A typical two-phase cleaning cycle of membranes of this type
requires using air pressure in the range of 30 to 50 psig. In the
case of the fouling described above, the air pressure was 50 psig.
The two-phase flow process used in cleaning involved the use of a
two-step cycle. The first step involved two-phase cleaning with an
acid cleaning agent supplied from cleaning solution holding tank
16, and the second step was performed with an alkaline cleaning
solution supplied from cleaning solution holding tank 14. Both were
delivered through first pumping means 30 to the two-phase
generating module 12, see FIG. 1. In each case, the mixture was
delivered to the RO elements via the feed adapter 415. The cleaning
steps with acid and base were carried out for 10 minutes each.
After completing the above two-phase cleaning steps, the RO
elements were rinsed for 10 minutes with the two-phase process by
supplying water from the rinse water holding tank 20 with the aid
of the third pumping means 34. The entire process as described
above was pre-programmed and controlled by the controller 600.
[0217] The data obtained from operating this C-I-P system over a
period of three months indicated that membranes fouled with dairy,
milk and whey residues that were reduced to below 50% of their
normal/clean flux, could be restored and maintained to 80-90% of
design specification using a 10-minute cleaning cycle consuming
only 4 liters of dilute cleaning solution. The results are shown in
Table IV, which shows examples of RO flux data before and after
cleaning for four cases. In order to obtain accurate RO flux
performance results, the temperature of the RO feed water and the
net driving pressure across the RO membrane (indicated by TDS) were
taken into account.
[0218] Cleaning for cases 1 to 3 was performed with the two-phase
flow using an alkaline cleaning solution only; this cleaning
process was sufficient to bring the RO flux back to above 86% of
manufacturer's specifications. However, as inorganic scale builds
up on the membrane surface, thus two-phase alkaline cleaning alone
was not sufficient to remove all foulants.
[0219] In Case 4, two-phase alkaline cleaning only brought the RO
flux performance back to 63% of new performance. However, an
additional two-phase acidic cleaning step, following the alkaline
cleaning step, brought the RO back to 88% of the new performance
flux level. The results are shown in Table IV below, wherein the RO
flux is given in liters per minute, as the manufacturer
specification (Mfr specs)
[0220] In Table IV the RO flux is given as liters per minute, as
the manufacturer specification (Mfr specs).
4TABLE IV RO Flux RO Flux Mfr Cleaning (1 pm) (1 pm) Cleaning specs
Performance Case Before After Solution (1 pm) Recovery 1 2.54 3.19
Alkaline 3.47 92% 2 2.95 2.97 Alkaline 3.47 86% 3 3.38 3.50
Alkaline 3.47 100% 4 1.39 2.18 Alkaline 3.47 63% 3.07 Acid 3.47
88%
[0221] Other configurations of spiral membrane types in pressure
vessels, a different number of elements per pressure vessel, or a
different arrangement of the membranes would all obtain similar
results after treatment.
EXAMPLE 14
[0222] This example relates to cleaning spiral wound membranes of
any type including those used in microfiltration, ultrafiltration,
nanofiltration and reverse osmosis separation processes used in
water treatment, desalination and purification, and in industrial
processing such as dairy, food, beverages, pharmaceutical,
chemical, oil and gas and other industries. The spiral wound
modules in this example were used in municipal water production,
and were fouled with inorganic scale, biofilm, humic substance
(natural organic matter--NOM) and silt as per our microscopic
examination of dissected membrane surfaces. The flux of such
membranes had declined to below acceptable levels and the pressure
drop (between the two ends of the membrane) increased to a level
such that the membranes were rendered unusable.
[0223] Attempts to clean these membranes using a conventional
liquid circulation process with an alkaline cleaning agent for 8
hours followed by additional four hours with acidic cleaning agent
was not successful, i.e., the flux and pressure drop between the
two ends remained below acceptable levels. These membranes were 8
inch RO spirals used for about six months in municipal water
production and were made by Hydranautics, Model number CPA-2. These
RO spiral modules were cleaned with the two-phase process using
apparatus 100 with noted success.
[0224] To perform cleaning, the spiral module was first connected
to adapter 415 of FIG. 5 in order to separate the permeate side
from the feeding side of the membrane during the two-phase
cleaning, as described in detail in Example 13. The spiral element
was then connected to the inlet adapter 56 and the outlet adapter
58 of the passageway to be cleaned 400 of the apparatus 100 as
shown in FIG. 1. For the purpose of cleaning membranes according to
this invention, the spiral elements were connected to apparatus 100
such that the highly fouled end of the module was connected to the
outlet 58 to facilitate contaminant removal from the end where they
were deposited. This arrangement is preferred in order to directly
push the contaminants out of the membrane module to the discharge
end, and at the same time to prevent contaminating the less fouled
portion of the membrane module. The highly fouled end of a spiral
module is normally the end where the liquid feed enters the module
during the separation process.
[0225] The gas source used in this example included a 50-HP
compressor, two air filters and six-240 gallons air tanks to store
the air needed for cleaning purposes. The air was regulated with a
pressure regulator 42 and a pressure gauge 44, and its flow rate
was measured by a flow meter 50. The cleaning process in this
example included application of a two-phase cleaning step using
acid and alkaline cleaning agents as the liquid fraction of the
two-phase mixture. Other steps for soaking the surface of the
membrane for a period of time to condition and weaken the adhesion
of foulants is used before the application of the two-phase
cleaning step. The cleaning protocol employed in this example
included rinsing with water after the conclusion of the two-phase
cleaning steps to restore the function of the membrane as required
for separation processing.
[0226] To perform the cleaning of the spiral elements described
above, air pressure was set at 45 psig using the pressure regulator
42 and the air flow was conveyed to the two-phase generating module
12 as described in the previous examples. Cleaning liquids
(alkaline or acidic) were supplied from cleaning solution holding
tanks 14 and 16 with first pumping means to the liquid inlet 214.
The two-phase generating module in this case was the same as
described in Example 13 and shown in FIG. 2A, with the use of a
nozzle that deliver the liquid at droplet size 25-400 microns. The
use of droplet size distribution in this range or even smaller
(30-200 microns) was found to be important in establishing the
two-phase flow for cleaning spiral wound membranes. The liquid was
fed at rate between 0.1 to 0.2 gallons/minute, using the first
pumping means with the aid of a controller 600 of apparatus 100.
The two-phase mixture formed by the above means was propelled to
enter the feeding channels of the spiral wound membrane. The
two-phase flow with droplets was arranged such that the entire
surface at the entrance of the feeding channels was covered with
droplets, and no flooding conditions were allowed at the entrance
section of the spiral wound membrane. Cleaning was done in both
vertical (from top down) or horizontal directions, as long as the
two-phase velocity was high enough as given in this example. During
cleaning, the two-phase mixture that emerged from the end of the
modules was conveyed to the mist separator 500 for proper discharge
as described in the previous examples.
[0227] Cleaning of spiral membranes in this example was performed
at an inlet air set pressure between 20 to 55 psig and at cleaning
liquid delivery flow rates between 0.052 and 0.3 gallons/minute.
The gas/liquid ratio was in the range of 3000:1 and 30,000:1.
Two-phase flow cleaning time was between 5-15 minutes. Entrance air
velocity that was found to be effective in two-phase cleaning was
about 25-30 feet/second or higher, but over 30 feet in at least in
some portion of the modules is preferred. This ratio may shift
depending on the nature of foulants and their adhesion to the
surface of the membrane.
[0228] To achieve these conditions, sufficient air volume is needed
to reach these velocity values in the feeding channels of spiral
wound membranes. As gas expands inside the membrane feeding
channels when the two-phase flow travels though them, higher
velocities are generated at the highly fouled end of the membrane,
where the two-phase flow exits the membrane. Exit velocities
between 40 to 70 feet/second were estimated from our experiments.
We discovered that two-phase cleaning average velocities between 24
to 30 feet/second to be significant for cleaning spiral wound
membranes. Flux recovery of fouled spiral membranes was not
significant until these velocity values were reached, and cleaning
at below these values produced very little improvement in membrane
flux.
[0229] The nature of the two-phase flow inside spiral wound
membrane channels is more complex to describe due to the presence
of spacers between the channels, but should be similar to the flow
in small tubes such as those described in Examples 3 and 4.
Formation and re-formation of droplets, and generation of high
shear stresses represent the general features of the two-phase flow
for this membrane configuration.
[0230] During cleaning with two-phase flow, we also discovered that
a highly turbid suspension is generated during the first 1-3
minutes of the cleaning process, as judged by collecting the liquid
fraction from port 82. This observation indicated that this
cleaning process is effective in removing solid-particle foulants
such as silt, clay or sand from membrane feeding channels during
the cleaning process. This discovery supports our findings that a
significant improvement in pressure drop values (between the two
ends of the membrane) is accomplished when cleaning is performed
with the two-phase process, as compared with liquid circulation
methods. The shear forces and mass transfer rates achieved in the
feeding channels of the spiral wound membrane during two-phase
cleaning appear to be high enough to efficiently remove types of
foulants that are responsible for the deterioration of the pressure
drop as defined above.
[0231] Five cases were investigated to define the two-phase
conditions needed to recover flux and pressure drop (as defined
above) of fouled 8-inch spiral modules. The 8-inch spiral modules
that were fouled during municipal water production were used in the
experiment. Cleaning was performed using apparatus 100 with the aid
of the adapter 415 (see FIG. 5). The cleaning was performed at the
conditions given in Table 4 to obtain entrance velocity of
two-phase flow of about 30 feet/second. The results showed that
optimal cleaning was achieved at air pressures between 20-50 psig
and preferably about 40-50 psig for this case. The gas:liquid that
gave nearly optimal results was about 4000:1 at the entrance of the
membrane. The two-phase cleaning was performed with an alkaline
cleaning agent at pH 11-12 and had about 0.1% of a non-foaming
non-ionic surfactant (Tergitol 1X--made by the Dow Chemical
Corporation). It was found that prior soaking by circulating the
cleaning agent for 30 to 60 minutes at 40-50.degree. C. to be
beneficial in reducing the time of two-phase cleaning to about 5-10
minutes. The membranes cleaned as above were then rinsed using
two-phase flow with water, and the flux and pressure drop were then
measured. In all the cases tested, the pressure drop decreased from
about 15 psi to <7 psi after the two-phase cleaning. Flux values
before and after the two-phase cleaning are given in Table 6
below.
[0232] A summary of the cleaning conditions are given in Table V
below.
5TABLE V Run Set Pres- Air Pres- sure Velocity Liquid sure* **
(ft/s) Rate Air/Liquid Case (psi) (psi) SCFM In Out (gpm) In Out 1
20 7 394 32.0 47.0 0.052 37900 55690 2 25 10 448 32.0 53.4 0.052
37950 63300 3 30 12 496 32.2 59.0 0.052 38900 70100 4 40 20 510
26.3 60.0 0.3 5358 12450 5 55 26 627 27.3 74.6 0.3 3950 14460 *Set
Pressure is the pressure set at the regulator located at the outlet
of gas storage receiver **Run Pressure is the actual pressure
measured at the inlet of the RO housing during cleaning. The "Out"
condition is at 0 psig.
[0233] Flux improvement on 8-inch RO membrane using the two-phase
cleaning process is shown in Table VI.
6TABLE VI Initial Flux Final Flux RO Filter Serial # (gpm) (gpm)
197761 0.75 3.2 197686 1.2 1.3 197753 1.2 2.8 197702 .about.1.0 3.0
196500 .about.1.0 2.5 197763 .about.1.0 3.5 197763 .about.1.0
2.8
[0234] The results in Table 6 demonstrate that the two-phase
cleaning apparatus and method is effective to restore the flux and
pressure drop in a short cycle of about 5-10 minutes. Pre-soaking
appear to soften the foulants and assist in achieving effective
two-phase cleaning. Improving flux in this case is significant
since application of prior liquid circulation alone over eight
hours was unable to improve the performance of the membrances
tested.
[0235] Cleaning was done in both vertical and horizontal positions
with similar results; however cleaning in the vertical position may
be preferred. In the horizontal position, we discovered that liquid
drainage due to gravity occurs during the two-phase cleaning of
spiral membranes and as a result the gas:liquid ratio becomes
somewhat lower at the bottom of the module compared to the top
cross section. This condition was more pronounced when the
two-phase flow velocity was low and gas:liquid ratios were low;
however, when velocity was increased to the levels given in this
example, more uniform distribution of the two-phase flow in the
membrane was obtained. When the optimal flow condition is achieved,
the orientation of the membrane (vertical or horizontal) does not
appear to affect the cleaning efficiency.
[0236] Based on the results of this example, it is predicted that
frequent cleaning with the two-phase flow is capable of restoring
the flux and maintaining the pressure drop between the two ends of
the membrane at acceptable levels. The frequency of cleaning can
thus be adjusted based on the fluid stream used in the separation
process and the type of residue formed in the internal channels of
the membrane.
[0237] Although the invention has been described in terms of
particular embodiments, the invention is not meant to be limited to
the details set forth above. The invention is only to be limited by
the scope of the appended claims.
* * * * *