U.S. patent application number 14/942176 was filed with the patent office on 2016-07-21 for filter-press with integrated rf heating.
The applicant listed for this patent is Daniel J. Simpson. Invention is credited to Ferdinand Kogler, Daniel J. Simpson.
Application Number | 20160206976 14/942176 |
Document ID | / |
Family ID | 42164240 |
Filed Date | 2016-07-21 |
United States Patent
Application |
20160206976 |
Kind Code |
A1 |
Simpson; Daniel J. ; et
al. |
July 21, 2016 |
Filter-Press with Integrated RF Heating
Abstract
A method of separating a mixture of liquid and insoluble solids
in a filter press may comprise: pumping the mixture into a chamber
between two filter plates in the filter press to form a filter
cake, wherein the chamber is lined by filter cloths, and wherein,
during the pumping, filtrate is forced through the filter cloths
and out of the chamber; heating the filter cake in the chamber,
wherein, during the heating, filtrate is forced through the filter
cloths and out of the chamber, and wherein the heating is by radio
frequency irradiation of the filter cake in the chamber; and
releasing dried filter cake from the chamber. A filter press system
for separating a mixture of liquid and insoluble solids may
comprise: a frame; a plurality of filter plates configured to form
a stack of parallel plates, each of the plurality of filter plates
being movably attached to the frame, the plurality of filter plates
further being configured to form a multiplicity of chambers, each
of the multiplicity of chambers being lined by filter cloths,
wherein the plurality of filter plates, the multiplicity of
chambers and the filter cloths are configured to allow filtrate to
escape from the chambers while retaining solids from the mixture to
form a filter cake; and a radio frequency heater, for directly
heating the filter cake in the multiplicity of chambers. The radio
frequency heating may include microwave heating, or dielectric
heating by lower frequency radio waves in the range of 1 to 100
MHz.
Inventors: |
Simpson; Daniel J.; (Rio
Vista, CA) ; Kogler; Ferdinand; (Rio Vista,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Simpson; Daniel J. |
Rio Vista |
CA |
US |
|
|
Family ID: |
42164240 |
Appl. No.: |
14/942176 |
Filed: |
November 16, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14025686 |
Sep 12, 2013 |
9186605 |
|
|
14942176 |
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|
12590150 |
Nov 2, 2009 |
8535542 |
|
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14025686 |
|
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|
61197996 |
Oct 31, 2008 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B01D 25/164 20130101;
B01D 25/215 20130101; B01D 25/164 20130101; B01D 25/284 20130101;
B01D 25/285 20130101; B01D 25/215 20130101; B01D 25/322 20130101;
B01D 25/284 20130101 |
International
Class: |
B01D 25/28 20060101
B01D025/28; B01D 25/32 20060101 B01D025/32 |
Claims
1. A method of separating a mixture of liquid and insoluble solids
in a filter press, said method comprising: pumping said mixture
into a chamber between two filter plates in said filter press to
form a filter cake, wherein said chamber is lined by filter cloths,
and wherein, during said pumping, filtrate is forced through said
filter cloths and out of said chamber; heating said filter cake in
said chamber, wherein, during said heating, filtrate is forced
through said filter cloths and out of said chamber; and releasing
dried filter cake from said chamber; wherein said heating is by
radio frequency irradiation of said filter cake in said
chamber.
2. A method as in claim 1, wherein said radio frequency irradiation
is microwave irradiation.
3. A method as in claim 2, wherein said microwave irradiation is at
a frequency between 300 and 3000 MHz.
4. A method as in claim 1, wherein said radio frequency irradiation
is applied by a system including parallel electrode plates
configured (1) with the planes of said parallel electrode plates
roughly orthogonally to the planes of each of said plurality of
filter plates, (2) in close proximity to the outer surface of said
plurality of filter plates, and (3) on either side of said
plurality of filter plates.
5. A method as in claim 4, wherein said radio frequency irradiation
is at a frequency between 1 and 100 MHz.
6. A method as in claim 1, further comprising, during said heating,
vacuum pumping said chamber.
7. A method as in claim 1, further comprising squeezing said filter
cake in said chamber.
8. A method as in claim 7, wherein each of said plurality of filter
plates includes an envelope, said envelope being inflatable by a
fluid, and wherein said squeezing includes inflating said envelopes
with said fluid.
9. A method as in claim 8, wherein said fluid is steam.
10. A method as in claim 8, wherein said fluid is compressed
air.
11. A method as in claim 1, wherein said filtrate forced through
said filter cloths and out of said chamber during said heating
includes filtrate vapor.
12. A method as in claim 1, wherein said filtrate is water and said
dried filter cake contains less than 10% water by weight.
13. A method as in claim 12, wherein said dried filter cake
contains less than 1% water by weight.
14. A method as in claim 1, wherein said filter press comprises a
plurality of said filter plates and a multiplicity of said
chambers.
15. A method as in claim 14, wherein said plurality is N and said
multiplicity is M, M is equal to N-1, and N and M are integers.
16. A method of separating a mixture of liquid and insoluble solids
in a filter press including a plurality of filter plates, said
method comprising: pumping said mixture into a multiplicity of
chambers to form a filter cake, each of said multiplicity of
chambers being between adjacent filter plates of said plurality of
filter plates, each of said multiplicity of chambers being lined by
filter cloths, wherein, during said pumping, filtrate is forced
through said filter cloths and out of said multiplicity of
chambers; heating said filter cake in said multiplicity of
chambers, wherein, during said heating, filtrate is forced through
said filter cloths and out of said multiplicity of chambers; and
releasing dried filter cake from said multiplicity of chambers;
wherein said heating is by radio frequency irradiation of said
filter cake in said chambers.
17. A method as in claim 16, wherein said plurality is N and said
multiplicity is M, M is equal to N-1, and N and M are integers.
18. A filter press system for separating a mixture of liquid and
insoluble solids, said filter press system comprising: a frame; a
plurality of filter plates configured to form a stack of parallel
plates, each of said plurality of filter plates being movably
attached to said frame, said plurality of filter plates further
being configured to form a multiplicity of chambers, each of said
multiplicity of chambers being formed by adjacent filter plates of
said plurality of filter plates, each of said multiplicity of
chambers being lined by filter cloths, wherein said plurality of
filter plates, said multiplicity of chambers and said filter cloths
are configured to allow filtrate to escape from said chambers while
retaining solids from said mixture to form a filter cake; and a
radio frequency heater, for directly heating said filter cake in
said multiplicity of chambers.
19. A filter press system as in claim 18, wherein said radio
frequency heater comprises parallel electrode plates attached to
said frame and electrically coupled to a radio frequency generator,
said parallel electrode plates being configured with the planes of
said parallel electrode plates roughly orthogonally to the planes
of each of said plurality of filter plates, and in close proximity
to the outer surface and on either side of said plurality of filter
plates.
20. A filter press system as in claim 19, wherein said parallel
electrode plates include multiple pairs of parallel electrode
plates.
21. A filter press system as in claim 20, wherein each of said
multiple pairs of parallel electrode plates is coupled to a
separate radio frequency generator.
22. A filter press system as in claim 18, wherein said radio
frequency heater comprises a microwave antenna positioned in an
aperture extending centrally through said plurality of filter
plates, said microwave antenna being roughly orthogonal to the
planes of each of said plurality of filter plates.
23. A filter press system as in claim 22, wherein said microwave
antenna is configured to be retractable from said aperture
extending centrally through said plurality of filter plates.
24. A filter press system as in claim 18, wherein said radio
frequency heater comprises multiple microwave antennae embedded in
a plurality of filter plates.
25. A filter press system has in claim 24, wherein said multiple
microwave antennae are embedded in every P.sup.th of said plurality
of filter plates, P being an integer greater than 1.
26. A filter press system as in claim 18, wherein said radio
frequency heater comprises multiple microwave horns positioned on
the surface of said plurality of filter plates and configured to
direct microwave radiation into said chambers.
27. A filter press system as in claim 18, further comprising a
radio frequency screen in close proximity to the surface of said
plurality of filter plates for absorbing radio frequency radiation
emanating from said filter press.
28. A filter press system as in claim 18, wherein said plurality of
filter plates are made of plastics.
29. A filter press system as in claim 18, wherein said frame is
nonmetallic.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 14/025,686 filed Sep. 12, 2013, which is a continuation of U.S.
application Ser. No. 12/590,150 filed Nov. 2, 2009 (now U.S. Pat.
No. 8,535,542), which claims the benefit of U.S. Provisional
Application Ser. No. 61/197,996 filed Oct. 31, 2008, all
incorporated by reference in their entirety herein.
FIELD OF THE INVENTION
[0002] The invention relates to a filter-press and more
specifically to a filter-press with integrated microwave/radio
frequency heating and vacuum drying.
BACKGROUND OF THE INVENTION
[0003] Filter presses are used for dewatering/drying materials such
as slurries. Part of the process may involve heating the material
held in the filter press in chambers between the filter plates
while apply a vacuum to remove water vapor and other volatile
substances. Currently, heating of the material is accomplished by
heat transfer through filter plates, from steam channels within the
filter plates. The filter plates are made of plastic, which limits
the temperature of the steam to ensure that the filter plates do
not soften too much. There is a need for more efficient ways of
heating the material held between the filter plates. There is a
need to increase the temperature of the material held between the
plates, or to deposit more energy per unit volume within the
material, so as to increase the throughput of a filter press,
without jeopardizing the integrity of the filter plates.
[0004] Radio frequency heating is used to dry a wide range of
products including food products, ceramic powders and filter cakes.
Radio frequency heating, also referred to as dielectric heating,
occurs due to dielectric losses in a material exposed to a changing
electric field. An apparatus for dielectric heating at lower
frequencies may include parallel metal plates with a changing
potential difference applied at a frequency somewhere in the range
of 1 to 100 megahertz; particular frequencies that have been set
aside by the United States FCC for dielectric heating are 13.56,
27.12 and 40.68 MHz. Material is placed or moved between the
parallel plates in order to be heated. Microwave heating of
materials is a sub-category of dielectric heating within a
frequency range of 300 to 3000 MHz. As a reference point,
conventional microwave ovens generally operate at 2.45 GHz.
Microwave sources are well known in the prior art. When using
dielectric heating, metal objects or components within the
irradiated volume may be undesirable, particularly when the metal
causes reflection of the radio frequency energy and/or damaging
electrical discharges.
[0005] The present invention provides a breakthrough by integrating
radio frequency heating directly into a filter press.
SUMMARY OF THE INVENTION
[0006] This invention is the integration of radio frequency heating
into a filter press system to assist in the separation of liquids
and insoluble solids for a wide range of mixtures including
slurries, sludges, tailings, oil deposits, food products,
pharmaceuticals, etc. The separation of liquids and insoluble
solids includes dewatering/drying. The separated liquid and solids
are generally referred to as filtrate and filter cake,
respectively.
[0007] Radio frequency heating provides a potentially very
efficient method of directly heating the filter cake within the
filter press. This may be achieved by choosing a radio frequency
for which the filter cake has strong absorption of the radio
frequency energy and fabricating the filter press out of materials
with weak radio frequency absorption at the chosen frequency.
Direct heating of the filter cake also has the advantage of
removing the need for indirect heating. (Indirect heating of the
filter cake by passing steam through the filter plates can result
in thermal problems for plastic filter plates, such as softening.)
For example, for dewatering, there are frequencies for which water
is strongly absorbing and for which plastics materials/polymers,
out of which filter plates may be made, are weakly absorbing.
[0008] According to aspects of the invention, a method of
separating a mixture of liquid and insoluble solids in a filter
press comprises: pumping said mixture into a chamber between two
filter plates in the filter press to form a filter cake, wherein
the chamber is lined by filter cloths, and wherein, during the
pumping, filtrate is forced through the filter cloths and out of
the chamber; heating the filter cake in the chamber, wherein,
during the heating, filtrate is forced through the filter cloths
and out of the chamber; and releasing dried filter cake from the
chamber; wherein the heating is by radio frequency irradiation of
the filter cake in the chamber.
[0009] The radio frequency heating may include microwave heating.
The microwave heating may be by at least one microwave antenna
embedded in at least one of the filter plates. The microwave
antenna may be a monopole, a dipole, a wave guide, a linear
structure, a helical structure, etc. A filter press contains a
multiplicity of filter plates. The antennas may be configured in
the filter plate(s) to optimize the heating of the filter cake in
the chambers between the filter plates. The antennas may be
embedded in every Pth filter plate in the filter press, where P is
an integer greater than or equal to 2, or greater than or equal to
10, for example. Alternatively, the filter plates may be configured
with an aperture in the center, the microwave heating may be by at
least one microwave antenna positioned in the apertures through the
middle of the filter plates, and the microwave antenna is removable
from the aperture allowing for the filter plates to be removed from
the filter press. In another alternative, microwave heating may be
by microwave horns positioned externally, but in close proximity
to, the filter press.
[0010] Furthermore, the radio frequency heating may include
dielectric heating by lower frequency radio waves in the range of 1
to 100 MHz, and the radio frequency irradiation is applied by a
system including parallel electrode plates configured (1) with the
planes of the parallel electrode plates roughly orthogonally to the
planes of each of the plurality of filter plates, (2) in close
proximity to the outer surface of the plurality of filter plates,
and (3) on either side of the plurality of filter plates.
[0011] In general, microwave frequencies may be well suited for
small filter presses and the lower frequencies may be well suited
for large filter presses. This is due to the lower frequencies
being more penetrating within the filter press. In general, small
filter presses are used for high value products such as foodstuffs
and pharmaceuticals, for example, and large filter presses are used
for high volume processes. The use of radio frequency has a further
advantage in that it is effective in destroying biological growths,
pathogens and viruses.
[0012] The structural components of the filter press, such as the
frame, may be non-metallic. The filter plates may be surrounded by
a radio frequency screening material, so as to reduce radio
frequency radiation outside of the filter press.
[0013] According to further aspects of the invention, a filter
press system for separating a mixture of liquid and insoluble
solids comprises: a frame; a plurality of filter plates configured
to form a stack of parallel plates, each of the plurality of filter
plates being movably attached to the frame, the plurality of filter
plates further being configured to form a multiplicity of chambers,
each of the multiplicity of chambers being formed by adjacent
filter plates of the plurality of filter plates, each of the
multiplicity of chambers being lined by filter cloths, wherein the
plurality of filter plates, the multiplicity of chambers and the
filter cloths are configured to allow filtrate to escape from the
chambers while retaining solids from the mixture to form a filter
cake; and a radio frequency heater, for directly heating the filter
cake in the multiplicity of chambers. Furthermore, the radio
frequency heater may comprise parallel electrode plates attached to
the frame and electrically coupled to a radio frequency generator,
the parallel electrode plates being configured with the planes of
the parallel electrode plates roughly orthogonally to the planes of
each of the plurality of filter plates, and in close proximity to
the outer surface and on either side of the plurality of filter
plates.
[0014] According to further aspects of the invention, a filter
press comprises: a multiplicity of filter plates formed of a
plastics material/polymer, each of the filter plates having a
flange on a first side and a flat surface on the second side, the
flange having a rectangular cross-section, whereby, when the flange
of a first plate is brought into contact with the flat surface of
an adjacent second plate and pressure is applied, a seal is formed
between the first and second plates.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] These and other aspects and features of the present
invention will become apparent to those ordinarily skilled in the
art upon review of the following description of specific
embodiments of the invention in conjunction with the accompanying
figures, wherein:
[0016] FIG. 1 is a schematic of a filter press system;
[0017] FIG. 2 is a schematic of a filter press system including
radio frequency heating, according to aspects of the present
invention;
[0018] FIGS. 3A-3D are a representation of a process for separating
a mixture of liquid and insoluble solids using a filter press,
according to some embodiments of the present invention;
[0019] FIG. 4 is a process flow for separating a mixture of liquid
and insoluble solids using a filter press, according to some
embodiments of the present invention;
[0020] FIG. 5 is a top view representation of a filter press with
integrated microwave heating using microwave horns, according to
some embodiments of the present invention;
[0021] FIG. 6 is a plan view of a filter plate with microwave
antennas, according to some embodiments of the present
invention;
[0022] FIG. 7 is a cross-section of the filter plate of FIG. 6,
showing part of one antenna, transducer and cable, according to
some embodiments of the present invention;
[0023] FIG. 8 is a top view representation of a stack of filter
plates in a filter press with a microwave antenna through the
center of all of the plates, according to some embodiments of the
present invention;
[0024] FIG. 9 shows a single filter plate from the stack shown in
FIG. 8, showing the position of the microwave antenna, according to
some embodiments of the present invention;
[0025] FIG. 10 shows a filter press with integrated radio frequency
heating using parallel plate electrodes, according to some
embodiments of the present invention;
[0026] FIG. 11 shows a cross section through the filter press shown
in FIG. 11, showing the position of the parallel plate electrodes,
according to some embodiments of the present invention;
[0027] FIG. 12 is a cross-section of the filter plate of FIG. 11
showing detail of the sealing flanges, according to some
embodiments of the present invention; and
[0028] FIG. 13 shows a cross section through the plate of FIG. 11,
showing drainage holes and the retention of the filter cloth,
according to some embodiments of the present invention.
DETAILED DESCRIPTION
[0029] The present invention will now be described in detail with
reference to the drawings, which are provided as illustrative
examples of the invention so as to enable those skilled in the art
to practice the invention. Notably, the figures and examples below
are not meant to limit the scope of the present invention to a
single embodiment, but other embodiments are possible by way of
interchange of some or all of the described or illustrated
elements. Moreover, where certain elements of the present invention
can be partially or fully implemented using known components, only
those portions of such known components that are necessary for an
understanding of the present invention will be described, and
detailed descriptions of other portions of such known components
will be omitted so as not to obscure the invention. In the present
specification, an embodiment showing a singular component should
not be considered limiting; rather, the invention is intended to
encompass other embodiments including a plurality of the same
component, and vice-versa, unless explicitly stated otherwise
herein. Moreover, applicants do not intend for any term in the
specification or claims to be ascribed an uncommon or special
meaning unless explicitly set forth as such. Further, the present
invention encompasses present and future known equivalents to the
known components referred to herein by way of illustration.
[0030] This invention is the integration of radio frequency heating
into a filter press system to assist in the separation of liquids
and insoluble solids for a wide range of mixtures including
slurries, sludges, tailings, oil deposits, food products,
pharmaceuticals, etc. The separation of liquids and insoluble
solids includes dewatering/drying. The separated liquid and solids
are generally referred to as filtrate and filter cake,
respectively. The invention may include incorporating radio
frequency heating into filter presses, including the filter presses
described herein and similar filter press machines. Furthermore,
radio frequency heating may be incorporated in other filter presses
according to the teaching and principles of the present
invention.
[0031] Radio frequency heating, also referred to as dielectric
heating, occurs due to dielectric losses in a material exposed to a
changing electric field. An apparatus for dielectric heating at
lower frequencies may include parallel metal plates with a changing
potential difference applied at a frequency somewhere in the range
of 1 to 100 megahertz; particular frequencies that have been set
aside by the United States FCC for dielectric heating are 13.56,
27.12 and 40.68 Hz. Material is placed or moved between the
parallel plates in order to be heated. Microwave heating of
materials is a sub-category of dielectric heating within a
frequency range of approximately 300 to 3000 MHz. A variety of
radio frequency sources and apparatuses are described herein.
However, other radio frequency sources and apparatuses operating
within the frequency range from 1 MHz to 3 GHz may be used
according to the principles and teaching of the present
invention.
[0032] Radio frequency heating provides a potentially very
efficient method of directly heating the filter cake within the
filter press. This may be achieved by choosing a radio frequency
for which the filter cake has strong absorption of the radio
frequency energy and fabricating the filter press out of materials
with weak radio frequency absorption at the chosen frequency.
Direct heating of the filter cake also has the advantage of
removing the need for indirect heating. (Indirect heating of the
filter cake by passing steam through the filter plates can result
in thermal problems for plastic filter plates such as softening.)
For example, for dewatering, there are frequencies for which water
is strongly absorbing and for which plastics materials/polymers,
out of which filter plates may be made, is weakly absorbing.
[0033] FIG. 1 shows a schematic of a filter press system which is
representative of those manufactured and installed worldwide by
DES, Inc., DryVac Canada, Ltd. and affiliated companies. FIG. 1
shows a filter press 10 for processing a slurry 20 to produce a
filtrate 22 and a dry filter cake 24. The dry filter cake is
released from the filter press as indicated by the large arrows, as
described in more detail below, and is collected in a tray, on a
conveyor belt below the filter press, or in any other removal
device. In this example, a slurry is described as being fed into
the filter press for separation, however, a wide range of mixtures
of liquid and insoluble solids may be separated using this system.
The filter press system includes: an air compressor 30 for forcing
air through the cake in the filter press to remove filtrate; a
vacuum source 40 connected to a knock out pot/condenser 42 and then
to the filter press 10 through a valve 44; and a boiler 50 for
generating steam connected in a closed circuit to the filter press
10 and a condensate return pump 52--the direction of flow for the
steam into the filter press and the condensate out of the filter
press is indicated by the arrows. The vacuum source 40 is used to
apply a vacuum to the filter cake in the filter press to remove
filtrate (as either a liquid or a vapor). Note that the valve 44 is
used to isolate either or both the air compressor 30 and/or the
vacuum source 40 depending on what is required in a particular
processing step in the filter press. The knock out pot part of 42
is basically a low velocity flow part of the vacuum line where
filtrate may be collected; the condenser part of 42 condenses any
filtrate present in vapor form. The boiler 50 produces steam, at
approximately 15 psi, for heating the filter press 10 and/or
inflating envelopes in the filter plates in the filter press, as
described in more detail below.
[0034] FIG. 2 shows a schematic of a filter press system including
radio frequency heating, according to some embodiments of the
present invention. FIG. 2 shows an example of the radio frequency
heating-radio frequency sources 70, such as microwave sources,
generate radio waves shown propagating into the filter press 10
where the filter cake absorbs some of the radio frequency energy
and heats up. Other than the radio frequency heating, the system of
FIG. 2 operates very similarly to the system of FIG. 1. Comparing
FIGS. 1 & 2, it is seen that in FIG. 2 the steam supply has
been replaced by an air compressor 60. Heating using radio
frequency may be more efficient than using steam, and therefore
removes the need for steam. However steam may be used in
combination with radio frequency heating, if desired. Regarding
inflation of the envelopes in the filter plates, compressed air
alone may be used,
[0035] As is well known in the art, filter presses include a stack
of filter plates, the filter plates are covered by filter cloths,
and each pair of filter plates defines a chamber lined with filter
cloths into which slurry or other material is fed for dewatering or
similar processing. Generally, there will be a stack of N filter
plates in a filter press, and M chambers between the plates, where
M=N-1 and M and N are integers. Details of filter plates which are
representative of those manufactured and installed worldwide by
DES, Inc., DryVac Canada, Ltd. and affiliated companies are
provided below and in FIGS. 5-13. Filter plates are also described
in U.S. Pat. Nos. 5,672,272 and 6,149,806 to William Baer,
incorporated by reference in their entirety herein.
[0036] The schematic illustrations of FIGS. 3A-3D and the process
flow of FIG. 4 are used together to describe a method of separating
a mixture of liquid and insoluble solids using a filter press
system, such as the filter press system shown in FIG. 2, according
to some embodiments of the present invention. The illustrations in
FIGS. 3A-3D show a cross-sectional view of a block of three
adjacent filter plates in the filter press for four different
process steps. Each of the filter plates is shown to comprise a
frame 110 around the periphery of the plate, a diaphragm 120 in the
center of the plate, the diaphragm containing a hollow envelope 130
which can be inflated or deflated in order to squeeze the filter
cake 24 which sits in chambers between the filter plates. Filtrate
22 is removed from the filter press through ducts as shown.
[0037] Step 201 includes feeding a mixture of liquid and insoluble
solids into the chambers of a filter press, forming a filter cake
in the chambers. As the mixture is forced into the chambers, some
of the filtrate is lost through filter cloth which lines the
chambers and leaves the filter press through ducts in the filter
plates. This is shown in FIG. 3A--note that the envelopes 130 are
not inflated at this point in the process. Step 202 includes
squeezing the filter cake by inflating the envelopes in the filter
plates, while blowing compressed air through the filter cake. Both
the squeezing and blowing act to remove filtrate from the filter
cake and act together efficiently, although the squeezing and
blowing may be used separately or just one of the squeezing or
blowing may be used. FIG. 3B shows the envelopes 130 partially
inflated, by compressed air, for squeezing the filter cake 24 in
the chambers. Step 203 includes directly heating the filter cake in
the chambers by radio frequency irradiation, while pulling a vacuum
on the filter cake. The envelopes are still inflated by compressed
air. FIG. 3C shows radio frequency heating by radio frequency
irradiation from a radio frequency source 70, such as a microwave
source. The combination of pulling a vacuum on the filter cake 24
in the chambers and the inflation of the envelopes 130 by
compressed air squeezes more filtrate 22 out of the filter cake 24
and reduces the volume of the chambers. Note that the filtrate may
be removed from the filter cake as a vapor or a liquid, depending
on the physical properties of the filtrate and the environmental
conditions in the chamber--specifically temperature and pressure.
Step 204 includes opening the filter press and releasing the dried
filter cake. At this point in the process the radio frequency
heating has been stopped, the vacuum is no longer applied to the
filter cake and the envelopes 130 have been deflated. As shown in
FIG. 3D, the filter plates are separated to allow the dried filter
cake 24 to fall out of the chambers, as shown, and to be
collected.
[0038] FIG. 5 shows a top view of a filter press 310 with
integrated microwave heating using microwave horns 70, according to
some embodiments of the present invention. The filter press 310
includes a stack of filter plates 320 mounted in a press comprising
frame rails 330, on which the filter plates hang, fixed end plates
340 and 342, a movable plate 344, and rods 346 for applying a
compressive force to the movable plate 344 as shown. Application of
a compressive force to the movable plate 344 results in compressing
the stack of filter plates 320. The microwave horns 70 are shown
propagating radio waves into the filter press where the filter cake
in the chambers absorbs the radio frequency energy and heats up.
The microwave horns are arranged around the outside of the stack of
filter plates so as to provide relatively uniform heating of the
filter cake within. Six microwave horns 70 are shown in the figure,
but more or less may be used and arranged differently to achieve
uniform heating of the filter cake in the chambers.
[0039] FIGS. 6 & 7 show plan view and cross-sectional views of
a filter plate 420 with microwave antennae embedded within. Eight
microwave antennae 430 are attached to a transducer 432 each, and
the transducers are attached to a power supply by coaxial cable 434
via a connector 436 on the outside of the filter plate. The
microwave antennae 430 and related components are all embedded
within the plate, but their positions within the plate are
indicated in the plan view of FIG. 6 (with dashed lines). FIG. 7
shows the position of the microwave antennae 430 within the filter
plate 420, between upper 424 and lower 426 parts of the plate 420.
FIG. 7 is shown with the upper 424 and lower 426 parts of the plate
separated, for ease of illustration; however, the upper 424 and
lower 426 parts are attached, flush to each other, to make the
filter plate 420. Since the microwave antennas 430 are embedded
within the plate, which is made of a plastic material, they are
therefore isolated from the filter cake and filtrate within the
filter press. Filter plates 420 containing microwave antennas 430
may be included perhaps every other plate in the stack of filter
plates in the press, perhaps every 10.sup.th plate in the stack--to
generalize, every P.sup.th plate in the stack where P is an integer
greater than 1. The number of filter plates 420 with microwave
antennas 430 and the configuration of the microwave antennas will
be optimized to heat the filter cake contained within the chambers
between adjacent plates. Furthermore, the number of microwave
antennas 430 will be governed by the size of the chambers and the
power rating of the transducers.
[0040] FIGS. 6 also shows the handles 622 which are used to place
the filter plate 420 on frame rails 330 and may also be used to
move the plates along the frame rails. (See FIG. 11 for a good
illustration of a filter plate positioned on a frame rail 330.)
Filter cloths 628 are shown on both sides of the filter plate 420
in the cross-section of FIG. 7. The filter cloth 628 actually
covers the interior area of the filter plate 420; however the
filter cloth is not shown in FIGS. 6 in order to more clearly show
other features. (FIG. 11 shows the position of the filter cloth 628
in the central area of the filter plate and FIG. 13 shows in more
detail how the filter cloth is attached to the filter plate.)
[0041] FIG. 8 shows a top view of a filter press 510 with
integrated microwave heating using an antenna 530 positioned
centrally within the stack of filter plates, according to some
embodiments of the present invention. The filter press 510 includes
a stack of filter plates 520 with a microwave antenna 530
positioned centrally with the stack. The position of the microwave
antenna 530 within the stack is indicated in the top view of FIG. 8
(with dashed lines). The microwave antenna 530 is attached to a
transducer 532 and a coaxial cable 534, which is connected to a
power supply. FIG. 9 shows the filter plate 520 with the centrally
placed microwave antennae 530. A sealing flange 521 is required in
the center of the filter plate 520 to accommodate the microwave
antennae 530. Similar sealing flanges are described in detail in
U.S. Pat. No. 6,149,806 to William Baer, incorporated by reference
in its entirety herein. However, in the present invention, instead
of having a central feed, the sealing flange 521 must provide a
vacuum tight seal to isolate the central volume in which the
microwave antenna 530 is placed. The microwave antenna 530 may be
inserted in a tube which runs through the center of the stack of
filter plates in the filter press. The microwave antenna 530 (and
its tube, if used) most be removable from the stack so as to permit
removal of individual filter plates.
[0042] Combinations of microwave antennas/sources such as those
shown in FIGS. 5-9 are also envisaged. Furthermore, microwave
sources are not limited to those disclosed above, but may include
microwave antennas such as monopoles, dipoles, wave guides, linear
structures, helical structures, etc.
[0043] FIG. 9 also shows the receiving ports and the filtrate ports
which are situated around the periphery of the filter plate 520.
These ports are apertures which extend completely through the
filter plate and connect with the corresponding ports on the
neighboring filter plates in the stack. The mixture of liquid and
insoluble solids, such as slurry, is delivered through feed ports
640. The example shown in FIG. 9 is referred to as a side feed
port. The configuration of the ports may be changed to provide top
delivery, if desired. Delivery slots 641 are machined into the
filter plate to allow the mixture to get from the feed port into
the filter cloth lined chamber formed between adjacent filter
plates. Steam ports 642 are for delivering steam into the envelope
in the middle of the filter plate, and condensate ports 644 are for
draining condensate from the envelope. (The envelope 130/660 is
shown in FIGS. 3A-3D and 12.) Alternatively, ports 642 and 644 may
be used for inflating/deflating the envelope using compressed
air--when steam is not being used. Ports 646, which include all of
the unlabeled ports around the periphery of the filter plate, are
used to connect to either compressed air during the blowing of air
through the filter cake, or to vacuum when the filter cake is being
heated. (See FIGS. 2 and 4.)
[0044] FIG. 10 shows a top view of a filter press 610 with
integrated radio frequency heating using parallel plate electrodes
630, according to some embodiments of the present invention. The
filter press 610 includes a stack of filter plates 620 and pairs of
parallel plate electrodes 630 positioned outside the stack. The
position of the electrodes 630 is indicated by the arrows--the
electrodes 630 are actually positioned under the frame rails 330,
which is more clearly shown in FIG. 11. Each pair of electrodes 630
may be connected to its own radio frequency generator or a single
radio frequency generator may be used for multiple pairs. The
number of pairs of electrodes may be varied depending on factors
such as the size of the filter press, materials limitations for the
electrodes, load limitations of radio frequency generators, etc.
Furthermore, in some embodiments it is envisaged that a single pair
of plates 630 may be sufficient for a filter press. The placement
of the electrodes 630 is determined by the desire to provide
uniform heating of the filter cake within the chambers in the
filter press, and also by the desire to avoid arcing between the
electrodes 630 and any parts of the filter press. The electrodes
630 may conveniently be attached to the frame rails 330, although
other means of fixing the electrodes in place are clearly
available, such as providing a dedicated frame specifically for
mounting the electrodes. Furthermore, the shape of the electrodes
may be varied as required to improve the uniformity of energy
deposition in the filter cake in the filter press, and also as
required to reduce electrical discharge--by rounding the corners of
the electrodes, for example.
[0045] FIG. 11 is a section along N-N in FIG. 10. The frame rails
330 and electrodes 630 are shown in cross-section; however, for
purposes of clear illustration of certain features, the filter
plate 620 is shown in plan view. The configuration of the frame
rails 330 and electrodes 630 relative to the filter plate 620 is
clearly shown.
[0046] FIGS. 11 and 12 show compression rings/flanges 623 that are
used to form a seal between adjacent filter plates. Each of the
filter plates has a flange on a first side (upper part 624) and a
flat surface on the second side (lower part 626). The flange has a
rectangular cross-section, as shown. When the flange of a first
plate is brought into contact with the flat surface of an adjacent
second plate and pressure is applied, a seal is formed between the
first and second plates. The flanges 623 are also seen to provide
isolation for the different ports around the periphery of the
filter plate, thus ensuring that vacuum ports are isolated from
feed ports, for example. (See also FIG. 9.)
[0047] FIG. 11 also shows the position of the filter cloth 628 in
the central area of the filter plate 620. Note that a clamp 629 is
used to fix the edge of the filter cloth at the bottom of delivery
slot 641, which ensures that the mixture is directed into the
filter cloth lined chamber formed between adjacent filter plates.
(See also FIG. 9 and related discussion.) Furthermore, FIG. 12
shows filter cloths 628 on both sides of the filter plate 620.
(FIG. 13 shows in more detail how the filter cloth is attached to
the filter plate.)
[0048] FIG. 13 shows a cross-sectional representation of the upper
part 624 of filter plate 620. (See also FIG. 11.) The section is
through a compressed air/vacuum port 646 and shows how the port 646
communicates with the chamber in between filter plates through
machined hole 654. Hole 654 may have a circular cross-section in a
plane orthogonal to the plane of the section. Hole 654 allows air
to be forced through the filter cake or allows filtrate to be
vacuumed out of the filtrate. Although not shown, those skilled in
the art will appreciate, after reading the present disclosure, that
a similar configuration may exist at the ports 642 and 644 for
allowing steam or compressed air to inflate the envelope 660. (See
FIGS. 9 & 12.)
[0049] The filter cake is positioned in a chamber in between filter
plates, where the chamber is lined with filter cloths 628. The
section in FIG. 13 shows the filter cloth 628 at the edge of the
chamber and shows how the cloth is kept in position using a vinyl
strap 1301 seated in a "T" shaped slot machined in the filter
plate. The vinyl strap 1301 may be stitched into the edge of the
filter cloth 628. The section also shows features 650 with channels
652 between on the surface of the diaphragm part of the filter
plate. (See also FIGS. 3A-3D.) The channels are arranged so as to
allow any filtrate which is squeezed or vacuumed through the filter
cloth 628 to pass to hole 654 and to vacuum port 646. The filter
plate is similarly configured at each vacuum port 646. (See FIG. 9
for position of ports.)
[0050] The frame rails and other structural components of the
filter press may be formed of carbon fiber and other non-metallic
materials, as required to use radio frequency heating. The stack of
filter plates may be surrounded by a radio frequency screening
material, so as to reduce radio frequency radiation outside of the
filter press, if needed.
[0051] Dewatering using the present invention is capable of
producing dried filter cake containing less than 10% water by
weight, and even less than 1% water by weight.
[0052] In general, microwave frequencies may be well suited for
small filter presses and the lower frequencies may be well suited
for large filter presses. This is due to the lower frequencies
being more penetrating within the filter press. In general, small
filter presses are used for high value products such as foodstuffs
and pharmaceuticals, for example, and large filter presses are used
for high volume processes. The use of radio frequency has a further
advantage in that it is effective in destroying biological growths,
pathogens and viruses.
[0053] Although the present invention has been particularly
described with reference to the preferred embodiments thereof, it
should be readily apparent to those of ordinary skill in the art
that changes and modifications in the form and details may be made
without departing from the spirit and scope of the invention. It is
intended that the appended claims encompass such changes and
modifications.
* * * * *