U.S. patent application number 12/392723 was filed with the patent office on 2010-08-26 for sludge heat exchanger.
This patent application is currently assigned to Komax Systems, Inc.. Invention is credited to Richard F. Carlson.
Application Number | 20100212872 12/392723 |
Document ID | / |
Family ID | 42629921 |
Filed Date | 2010-08-26 |
United States Patent
Application |
20100212872 |
Kind Code |
A1 |
Carlson; Richard F. |
August 26, 2010 |
SLUDGE HEAT EXCHANGER
Abstract
A heat exchanger for transferring heat energy from a heated
liquid at a first temperature to sludge at a second temperature.
The heat exchanger includes a first conduit for receiving a stream
of sludge which houses a plurality of mixing elements. The mixing
elements are characterized as having no edges perpendicular to the
longitudinal axis of the conduit and are sized and positioned
within the conduit such that at any plane passing perpendicularly
to the longitudinal axis at least 75% of the circumference of the
conduit being free of any mixing elements and no mixing elements
are in contact with one another resulting in an open region of
travel for sludge passing through the conduit.
Inventors: |
Carlson; Richard F.;
(Wilmington, CA) |
Correspondence
Address: |
Bay Area Technology Law Group;Suite 404
500 Sansome Street,
San Francisco
CA
94111
US
|
Assignee: |
Komax Systems, Inc.
|
Family ID: |
42629921 |
Appl. No.: |
12/392723 |
Filed: |
February 25, 2009 |
Current U.S.
Class: |
165/109.1 |
Current CPC
Class: |
F28D 2021/0098 20130101;
F28D 7/106 20130101; B01F 2005/0636 20130101; F28F 13/12 20130101;
F28F 9/26 20130101; B01F 5/0617 20130101; F28D 2021/0052
20130101 |
Class at
Publication: |
165/109.1 |
International
Class: |
F28F 13/12 20060101
F28F013/12 |
Claims
1. A heat exchanger for transferring heat energy from a heated
liquid at a first temperature to sludge at a second temperature,
said heat exchanger comprising a first conduit for receiving a
stream of sludge, said first conduit having a length, substantially
circular circumference, a longitudinal axis through said length and
being open at both ends thereof, said first conduit housing a
plurality of mixing elements, said mixing elements having no edges
perpendicular to said longitudinal axis and are sized and
positioned within said conduit such that at any plane passing
perpendicularly to said longitudinal axis, at least 75% of the
circumference of said conduit is free of any mixing elements and no
mixing elements are in contact with one another resulting in an
open region of travel for sludge passing through said first conduit
along its longitudinal axis and a second conduit in the form of a
sleeve having a longitudinal axis substantially coincident with the
longitudinal axis of said first conduit and defining an annular
space open at both ends for receiving and discharging said heated
liquid.
2. The heat exchanger of claim 1 wherein said mixing elements are
provided in said first conduit in complementary pairs, wherein
adjacent mixing elements cause fluid passing within said first
conduit to rotate in opposite directions.
3. The heat exchanger of claim 1 wherein each mixing element
located within said first conduit is seated at an angle between
approximately 30.degree. to 45.degree. to its longitudinal
axis.
4. The heat exchanger of claim 1 wherein said mixing elements are
in the form of primarily circular segments wherein each mixing
element is characterized as being widest in profile at its midpoint
and narrowest at its longitudinal end points.
5. The heat exchanger of claim 4 wherein each mixing element is of
a height equal to approximately D/10 and a radius of approximately
D/2 wherein D is the diameter of said first conduit.
6. The heat exchanger of claim 1 wherein said mixing elements are
sized and positioned within said first conduit such that such first
conduit is capable of passing therethrough solid matter contained
within said sludge having a diameter of at least 75% of the
diameter of said first conduit.
7. The heat exchanger of claim 1 wherein said heated liquid is
water.
8. The heat exchanger of claim 2 wherein a plurality of mixing
elements are located in said annular space.
9. A heat exchanger for transferring heat energy from a heated
liquid to sludge, said heat exchanger comprising a plurality of
inner conduits for receiving a stream of sludge, said plurality of
inner conduits each having a length, substantially circular
circumference, longitudinal axis through said length and each being
connected to one another to provide a continuous path for said
sludge whereby an entry is provided in an upstream most first inner
conduit for said sludge and an exist is provided for said sludge in
a downstream most inner conduit, each such inner conduit housing a
plurality of mixing elements having no edges perpendicular to said
longitudinal axis and are sized and positioned within each said
inner conduit such that at any plane passing perpendicularly to
said longitudinal axis, at least 75% of the circumference of said
inner conduit is free of any mixing element and no mixing elements
are in contact with one another resulting in an open region of
travel for sludge passing through each of said inner conduits along
its longitudinal axis and a plurality of outer conduits in the form
of interconnected sleeves each having a longitudinal axis
substantially coincident with the longitudinal axis of the inner
conduit to which it surrounds thus defining a continuous annular
space open at both ends for receiving and discharging said heated
liquid.
10. The heat exchanger of claim 9 wherein said mixing elements are
provided in said first conduit in complementary pairs, wherein
adjacent mixing elements cause fluid passing within said first
conduit to rotate in opposite directions.
11. The heat exchanger of claim 9 wherein each mixing element
located within said first conduit is seated at an angle between
approximately 30.degree. to 45.degree. to its longitudinal
axis.
12. The heat exchanger of claim 9 wherein said mixing elements are
primarily in the form of circular segments wherein each mixing
element is characterized as being widest in profile at its midpoint
and narrowest at its longitudinal end points.
13. The heat exchanger of claim 12 wherein each mixing element is
of a height equal to approximately D/10 and a radius of
approximately D/2 wherein D is the diameter of said first
conduit.
14. The heat exchanger of claim 12 wherein said mixing elements are
sized and positioned within said first conduit such that said first
conduit is capable of passing therethrough solid matter contained
within said sludge having a diameter of at least 75% of the
diameter of said first conduit.
15. The heat exchanger of claim 9 wherein said heated liquid is
water.
16. The heat exchanger of claim 9 wherein plurality of mixing
elements are located in said annular space.
Description
TECHNICAL FIELD OF THE INVENTION
[0001] The present invention is directed to a heat exchanger for
transferring heat energy from a heated liquid at a first
temperature to sludge at a second temperature. The heat exchanger
includes a conduit containing non-clogging motionless mixing
elements to optimize heat transfer while preventing clogging of
sludge within the apparatus.
BACKGROUND OF THE INVENTION
[0002] Virtually every municipality has a waste water treatment
system which is employed to remove nutrients such as nitrogen and
phosphorus from waste water as well as to destroy pathogens and
viruses which are found within waste sludge. Heating municipal
sludge to 135.degree. F. in a digester for 15 days or longer kills
such pathogens. The sludge is then classified as class A sludge
which may be used as commercial fertilizer for farms instead of
burying it in landfills. Interestingly, the conversion of waste to
class A sludge is mandatory in many jurisdictions such as the state
of California; a standard which has prevailed in Europe for many
years.
[0003] Most wastewater systems involve batch processing of sludge.
Primary and secondary treatments zones ate employed as are are
clarifiers and separators. It is common to have purified effluent
discharge into streams or lakes while sludge drawn from a clarifier
is oftentimes returned to the head of the activated sludge system
and mixed with influent wastewater as a continuous process. As
such, it is highly advantageous to have a mixer located within
treatment zones and particularly within the heat exchanger to not
only maximize the efficiency of the waste water treatment system,
but also optimize the transfer of heat energy from a heating
liquid, such as water, to the sludge and resulting digester.
[0004] Although there are various types of sludge, most can be
characterized physically as including a high percentage of solids
and stringy material. As such, there are basically two varieties of
heat exchanger's which have been employed in this arena. The first
involves a pipe with a hot water jacket. Such a configuration has
the advantage of having an open six inch diameter or larger piping
which eliminates plugging. However, such a heat exchanger assembly
requires enormous floor space as it must be large due to the low
heat transfer characteristics of the configuration. Multiple
sections of jacketed piping must be used to achieve the requisite
temperature increase. This results in higher installation costs
than those involved in employing a spiral type of heat
exchanger.
[0005] The spiral type of heat exchanger involves providing a
spiraling passage for sludge and a spiraling passage for hot water.
The two channels spiral in from the outside of the periphery of the
system ending and exiting neat the central of the spiral. Such a
configuration is relatively compact and thus results in space
saving over the pipe/water jacket configuration discussed above.
However, the spiral geometry characteristically results in periodic
plugging of its narrow 1 inch.times.30 inch sludge passage
resulting in repeated weekly or monthly maintenance. It is not
uncharacteristic to devote a full day of labor to opening up the
heat exchanger and cleaning out the plugging debris. Despite these
limitations, due to its compact size, spiral type heat exchangers
are used in over 95% of the waste water treatment plant
installations now in service.
[0006] It is thus an object of the present invention to provide the
non-plugging advantages of a jacketed pipe type heat exchanger
while enjoying the relatively compact design of the spiral type
heat exchanger while eliminating plugging and maximizing heat
transfer in mixing of the sludge.
[0007] These and further objects will be more readily apparent when
considering the following disclosure and dependent claims.
SUMMARY OF THE INVENTION
[0008] The present invention is directed to a heat exchanger for
transferring heat energy from a heated liquid at a first
temperature to sludge at a second temperature. The heat exchanger
comprises a first conduit for receiving a stream of sludge, the
first conduit having a length, substantially circular
circumference, a longitudinal axis through said length and being
opened at both ends thereof. The first conduit houses a plurality
of mixing elements which are characterized as having no edges
perpendicular to the longitudinal axis and which are sized and
positioned within the conduit such that at any plane passing
perpendicularly to the longitudinal axis, at least 75% of the
circumference of the conduit is free of any mixing elements and,
further, no mixing elements are in contact with one another
resulting in an open region of travel for sludge passing through
the first conduit along its longitudinal axis. A second conduit is
also provided in the form of a sleeve having a longitudinal axis
coincident with the longitudinal axis of the first conduit defining
an annular space open at both ends for receiving and discharging
heated liquid. As a preferred embodiment, a second set of mixing
elements can be located in the annular space created between the
first conduit and sleeve for enhancing heat transfer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a perspective drawing of the sludge heat exchanger
of the present invention.
[0010] FIG. 2 is a schematic of the sludge heat exchanger of FIG. 1
showing fluid flow paths within such device.
[0011] FIG. 3 is a schematic in partial cut away showing the mixing
elements found within those straight segments of the first conduit
for carrying sludge.
[0012] FIG. 4 is a side, partial cut away view of the conduit of
FIG. 3.
[0013] FIG. 5 is an end plan view of the sludge heat exchanger
taken along cross section 5-5 of FIG. 1.
DETAILED DESCRIPTION OF THE INVENTION
[0014] The heat exchanger of the present invention is shown, in its
preferred configuration, in FIG. 1. Heat exchanger 10 is configured
as a series of straight sections 15 joined to one another by curved
sections 20 producing a continuous serpentine structure. In
operation, sludge is introduced within the heat exchanger at 11
noting that the heat exchanger can be connected to supporting
structure via flange 12 which, in turn, can be functionally
connected to a number of subsidiary devices such as purifiers,
aerators and digesters. A heating liquid, such as water, is
introduced within the heat exchanger at opening 13, again being
connected to a source of, for example, water, via flange 14. The
heating liquid travels through manifold 19 and introduces heating
liquid in a jacket surrounding the conduit carrying sludge In this
regard, the heated sludge exits the heat exchanger 10 at opening 18
while the heating liquid exits the system at exit 17.
[0015] The schematic pathway for the sludge and heating liquid is
shown in FIG. 2. As noted, sludge is introduced to conduit 30 at
opening 11 passing through conduit 30 by schematic pathway 31 to
the remaining conduits, the internal details of which will be
described hereinafter.
[0016] For the sake of simplicity, a single segment of conduit 30
has been selected for discussion. This conduit extends along spaced
arrow 16 (FIG. 1) although the description of the internal elements
of conduit 30 could be applied to the remaining straight sections
of the sludge heat exchanger as well. As noted previously, it is
the intent of the present invention to provide the advantages of a
spiral type heat exchanger in an environment in which sludge having
a high degree of solids and stringy mass which would tend to clog
spiral type heat exchanges of the prior art.
[0017] The sludge-carrying first conduit 30 of the present
invention is shown in the shape of a cylinder provided with
longitudinal axis 37. As shown in FIG. 1, end flanges 12 can be
provided to enable the sludge carrying conduit to be joined with
adjacent conduits for carrying the stream of sludge in employing
the present invention.
[0018] The sludge carrying conduit 30 is provided with mixing
elements 33, 34, 35 and 36 These elements are characterized as
having no edges or surfaces perpendicular to longitudinal axis 37
and are sized so that no such elements are in contact with one
another resulting in an open region of travel 96 for fluids passing
through conduit 30 along its longitudinal axis. Ideally, each
mixing element is seated within the sludge carrying conduit at an
angle between approximately 30.degree. to 45.degree. to said
longitudinal axis. Most importantly, however, the mixing elements
are positioned within the conduit so that at least 75% of the
conduit's circumference in any plane is free of any mixing element.
Obviously, various mixing elements are provided with no points of
contact so that there arc actually no "crotches" provided which
would otherwise result in sludge hangup. In fact, it is the design
objective of the present invention to enable debris having
effective diameters of 75% or more of the conduit diameter to pass
through the conduit without entrainment. Such a geometry is
disclosed and claimed in applicant's U.S. Pat. No. 5,758,967.
Mixers made according to the teachings of the '967 patent have been
tested using flows of 2% to 4% sludge in pipe sizes for 2'' to 8''
in diameters. In no case did plugging occur over a period of more
than six months.
[0019] As previously noted, it is the intent of the present
invention to provide a device which is uniquely adaptable for the
mixing of waste sludge and for enhancing heat transfer throughout a
continuous stream of such material. Sludge is somewhat unique in
its tendency to plug or clog mixing components for material within
the sludge tends to migrate to and accumulate in low pressure or
"dead spots" and long fibers will catch and build up in "crotches".
Both of these effects allow and encourage more material to
accumulate until the sludge carrying conduit finally plugs By
providing spacing 96 and, more importantly, by providing the
placement of mixing elements whereby at least 75% of the conduit
circumference in any plane is clear of any ancillary structure
accomplishes the goals of the present invention. Even the most
problematic components "slide" over the mixing elements without
clogging under both laminar and turbulent flow conditions. Ideally,
the mixing elements are provided as pairs such as 33/34 and 35/36.
Each complimentary pair cause flowing material to rotate above the
axis of the conduit in opposite directions. As further noted, the
four mixing elements are each shown primarily as a circular segment
configuration each of a height approximately D/10 and radius of
D/2, wherein D is the diameter of the conduit. The various mixing
segments or elements are set in a non-opposing fashion at the pipe
wall so as to present to the fluid in any plane normal to the axis
of conduit a non-symmetrical cross-section. This serves to break up
the normal circular symmetry of flow and to substantially reduce
the conduit length necessary to achieve effective mixing. As such,
mixing is accomplished with minimal pressure drop and sludge hang
up.
Experimental Data
[0020] The primary performance limiting factor in both pipe-in-pipe
and shell and tube heat exchangers is that associated with the
internal film coefficient located at the internal surface of the
tube well. It is well known that static mixing elements installed
in the tube or tubes can improve overall heat transfer performance
by a factor of three or more, but such mixing elements, as noted
above, tend to plug. The next performance limiting factor is that
associated with the external film coefficient and is usually much
smaller than the internal film coefficient. The present invention
allows mixing elements 53, 54, 55, and 56 to be installed on the
outside of conduit 30 being installed in the annular space between
conduit 30 and conduit 50 as shown in FIG. 5. Although mixing
elements 53, 54, 55, and 56 are shown being appended to the inner
wall of conduit 50, they could have just as well been appended to
the outer surface of conduit 30 which gives a modest but useful
improvement in the overall heat transfer performance. In order to
test the present design, a heat exchanger was built with a 2'' pipe
in a 3'' shell having an overall length of 60''. Flow rates and
temperatures were measured and the data, inserted into software
made available by Thermal Analysis Systems as to calculate heat
exchange performance. In general, an improvement factor of more
than 3 was obtained. In a typical run enclosed with a core tube
velocity of 4' per second, the pipe-in-pipe result was
.DELTA.T=2.78 while the experimental value was 86.degree. F. giving
an "improvement" factor of 31.
* * * * *