Note: Descriptions are shown in the official language in which they were submitted.
~185993
VAPOR COMPRESSION DISTILLATION APPARATUS
FIELD OF THE INVENTION
The present invention relates generally to heat exchangers and more
particularly to improvements in heat exchangers useful in vapor compression
5 distillation systems, and to systems using the heat exchangers.
BACKGROUND OF THE INVENTION
Vapor compression distillation is a process that may be used in the
purification of contaminated water. Briefly, contaminated water is heated in
the heat exchanger and removed from the system as steam. The steam is
10 then compressed, increasing its vapor pressure and its temperature. Next,
the steam is passed through the heat exchanger, where it transfers its heat
to the liquid. This process is generally recognized as thermo-dynamically
efficient. The evaporation section generally entails the use of a shell and
tube type heat exchanger. These are normally accepted as having maximum
15 heat transfer values, and as a result have had little or no variation in their
design or performance.
However, it is clear that there are still improvements that could be
made to further increase efficiency. This is becoming increasingly
important, as efforts to reduce environmental pollution by purifying
20 contaminated waters are expanding.
The present invention is therefore concerned with improvements in
the apparatus used in vapor compression distillation.
SUMMARY OF THE INVENTION
According to one aspect of the invention, there is provided a heat
25 exchanger of the shell and tube type, comprising first and second manifolds,
tubes connecting the manifolds for passing a first fluid therebetween, and a
shell having an inlet and an outlet, said shell surrounding the tubes for
confining a flow of a second fluid from the inlet to the outlet for heat
~186993
exchange with the first fluid, said heat exchanger including means for
creating turbulence in the flow of the second fluid as it passes around the
tubes and through the shell.
When used in a vapor compression distillation apparatus, the first fluid
5 is the liquid to be distilled, and the second fluid is the compressed vapor
(steam).
The means for creating turbulence in the flow of the second fluid may
comprise from one to several foraminous screens placed between adjacent
tubes in the shell, each extending across the shell. The foraminous screens
10 act as vortex-drag induction plates in that they will create turbulence in the
flow of the second fluid. The turbulence will also increase the impingement
upon the tubes of the heat exchanger, which will dramatically increase the
heat transfer efficiency or "U" value of the unit. The plates also cause
vortices to form that in turn cause the steam to condense.
According to another aspect of the invention, there is provided a heat
exchanger of the shell and tube type, comprising two manifolds, tubes
connecting the manifolds for passing a first fluid therebetween, and a shell
having an inlet and an outlet, said shell surrounding the tubes for confining a
flow of a second fluid from the inlet to the outlet for heat exchange with the
20 first fluid, said heat exchanger including baffle means for deflecting the flow
of the second fluid from a direct path from the inlet to the outlet of the shellinto a sinuous path.
The baffles may comprise a plurality of spaced apart baffle plates,
each extending across the shell between adjacent tubes in the shell.
25 Diverting the flow of the second fluid creates a longer path for the second
fluid to exchange its heat of vaporization with the first liquid fluid in the
tubes, thereby increasing the condensation efficiency of the second fluid.
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According to a further aspect of the invention, there is provided a
heat exchanger of the shell and tube type, comprising top and bottom
manifolds, tubes connecting the manifolds for passing a liquid first fluid
therebetween, and a shell having an inlet and an outlet, said shell
5 surrounding the tubes for confining a flow of a gaseous second fluid from
the inlet to the outlet for heat exchange with the first fluid, said heat
exchanger including sparging means for injecting bubbles of gaseous second
fluid into the bottom manifold to pass through the liquid first fluid passing
through the tubes.
This steam injection will agitate the flow of the first fluid in the tubes,
thereby increasing its turbulence as it passes through the tubes. These
bubbles will also have a scrubbing effect on the internal tube wall, thereby
reducing scaling and increasing heat exchange efficiency by fifteen percent.
According to a still further aspect of the invention, there is provided a~5 heat exchanger of the shell and tube type, comprising:
two manifolds;
a plurality of rows of parallel tubes connecting the manifolds for
passing a first fluid therebetween;
a shell having an inlet and an outlet, the shell surrounding the tubes
20 for confining a flow of a second fluid from the inlet to the outlet in a
direction across the rows of tubes for heat exchange with the first fluid;
baffle means comprising a plurality of spaced apart baffle plates, each
extending across the shell between adjacent rows of plates in the shell for
deflecting the flow of the second fluid from a direct path across the rows of
25 tubes into a sinuous path having portions thereof extending along the tubes;
vortex-drag induction means comprising a plurality of foraminous
plates, each extending across the shell between adjacent rows of tubes for
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creating turbulence in the flow of the second fluid as it passes around the
tubes and through the shell.
There may be plural rows of tubes between adjacent baffle plates,
with the number of rows of tubes between adjacent baffle plates increasing
5 with spacing from the outlet towards the inlet. Additionally, there may be a
baffle plate or a vortex-drag induction plate between each pair of adjacent
rows of tubes.
According to another aspect of the invention, there is provided a
vapor compression distillation apparatus comprising:
a vessel for containing a liquid to be distilled;
a shell and tube heat exchanger within the vessel, said heat
exchanger comprising:
top and bottom manifolds;
tubes connectin~q the manifolds for passing the liquid to be distilled
1 5 therebetween;
a shell having an inlet and an outlet, said shell surrounding the tubes
for confining a flow of vaporized liquid from the inlet to the outlet for heat
exchange with the liquid in the tubes; and
vortex-drag induction means for creating turbulence in the flow of
vaporized liquid as it passes around the tubes and through the shell;
means for supplying the liquid to be distilled to the vessel;
means for passing the liquid to be distilled into the bottom manifold;
means for releasing vaporized liquid from the top manifold;
means for collecting vapor from the vessel above the liquid therein;
means for compressing the collected vapor;
means for delivering the compressed vapor to the inlet of the heat
exchanger shell; and
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means for collecting condensed vapor from the heat exchanger shell.
In preferred embodiments of the apparatus, the tubes are arranged in
a plurality of rows of parallel tubes connecting the manifolds for passing a
first fluid therebetween. Vortex-drag induction pates extend across the shell
5 between adjacent rows of tubes for creating the turbulence in the flow of
vapor. The heat exchanger includes baffle plates, each extending across the
shell between adjacent rows of plates in the shell for deflecting the flow of
the second fluid from a direct path across the rows of tubes into a sinuous
path having portions thereof extending along the tubes.
10 BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings, which illustrate an exemplary
embodiment of the present invention:
Figure 1 is a schematic illustration of the vapor compression
distillation apparatus;
Figure 2 is an isometric diagram showing the positioning of the baffles
or 'H'-plates in relation to the outer walls of the shell;
Figure 3 is an isometric view showing the positioning of the baffles or
'H'-plates with respect to the tubes;
Figure 4 is a partial isometric view showing the positioning of a vortex
20 drag induction plate with respect to two adjacent tube rows;
Figure 5 is a partial isometric view of the heat exchanger showing the
location of the sparging tubes; and
Figure 6 is a sectional view of the heat exchanger showing the
location of the sparging tubes.
25 DETAILED DESCRIPTION
Referring to the accompanying drawings, and particularly to Figure 1,
there is illustrated a vapor compression distillation apparatus 10. The
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apparatus includes a closed contaminated water vessel or tank 12. The
tank has a contaminated water inlet 14 controlled by a float valve 16 to
maintain a constant liquid level in the tank. Submerged in the liquid is a
heat exchanger 18. The exchanger has a liquid side communicating with~ the liquid in the tank, and a vapor side isolated from the contaminated liquid.
The head space 20 at the top of the vessel 12 is connected via a
steam conduit 22 to a compressor 24. The compressor outlet is coupled by
a steam conduit 26 to the inlet to the vapor side of the heat exchanger. A
conduit 28 from the heat exchanger vapor side outlet leads from the
10 exchanger to a second, external heat exchanger 30 for transferring heat to
the incoming contaminated liquid upstream from the tank 12.
A precipitated solids outlet 32 draws off a portion of the
contaminated liquid in the tank along with settled solids. This flow is
passed through the heat exchanger 30 to transfer its heat content to the
15 incoming liquid stream.
An electric heater 33 in the tank 12 is used for initial pre-heating and
periodically to supply make-up heat as required. The system operates
primarily on the energy produced by the compressor.
The heat exchanger 18 is of the shell and tube type. It has a top
20 manifold 34 and a bottom manifold 36, both of which are in open
communication with the interior of tank 12. The tubes 38 joining the
manifolds are vertical and arranged in staggered rows R1 to R 23 across the
shell 40, countin~ from the steam inlet towards the vapor outlet. The vapor
inlet 42 is at one end of the shell, at the top, while the condensate outlet 44
25 is at the opposite end, at the bottom.
Within the shell 40, between adjacent rows of the tubes 14 are four
baffle plates H1 to H4, the locations of which are shown in Figure 2. The
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number of rows of tubes between the baffles increases from the condensate
outlet towards the steam inlet. In the illustrated embodiment, the baffles
are between rows R9 and R10, R14 and R15, R18 and R19 and R21 and
R22. Each of the baffle plates extends from side to side of the shell.
Baffles H1 and H3 extend to the top of the shell and have steam slots 46 in
their bottom edges. Baffles H2 and H4 have steam slots 48 in their top
edges and smaller condensate slots 50 in their bottom edges. The baffles
cause the condensed steam to travel in a sinuous path from the vapor inlet
to the condensate outlet, with portions of the path extending along the
tubes. This creates a longer path for the vapor to exchange its heat of
vaporization with the liquid in the tubes. The positioning of the baffles also
helps to prevent air locks from forming inside the exchanger.
Between adjacent rows of tubes where there is no baffle plate are
vortex-drag induction plates 52. these are foraminous plates formed, in the
illustrated embodiment, of expanded metal mesh. These create turbulence
in the steam and cause vortices that promote condensation of the gaseous
stream. The turbulence creates increased impingement upon the heat
exchanger tubes and a significantly increased heat transfer efficiency or "U"
value of the unit.
Extending the length of the bottom manifold 36 are five sparging
tubes 54. These are connected to the compressor 24 to receive high
pressure steam. Orifices 56 in the sparging tubes discharge the steam into
the manifold to disperse bubbles of vapor into the liquid. This increases the
flow velocity through the tubes 38. The bubbles have a scrubbing effect on
the inside of the tube wall, reducing scaling and increasing heat exchange
efficiency.
In operation, contaminated water is piped from the contaminated
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water source via conduit 58 into the heat exchanger 30 where the
temperature is raised to 210~ F by recovering the heat from the discharging
effluent. The pre-heated liquid is then delivered to the inlet 14 of tank 12.
From the tank, water vapor (steam) is drawn into compressor 24 and is
5 compressed from 1 psi to 4 psi. This increases the temperature of the
vapor by approximately 10~ F. The compressed steam is then delivered to
the heat exchanger 18 where it exchanges its heat of vaporization with the
liquid in the tank 12. The vapor condenses and flows out through conduit
18 to heat exchanger 30 where it exchanges its remaining heat with the
10 incoming liquid stream. The condensate then flows to storage.
Approximately 5% of the incoming liquid flow is discharged through
conduit 32 to remove solids that have precipitated in the vessel 12 as a
result of super-saturation. This flow is passed through a section of heat
exchanger 30 to transfer its heat to the incoming liquid stream.
Since various modifications can be made in my invention as herein
above described, and many apparently widely different embodiments of
same made within the spirit and scope of the claims without departing from
such spirit and scope, it is intended that all matter contained in the
accompanying specification shall be interpreted as illustrative only and not in
20 a limiting sense.
