U.S. patent number 3,854,301 [Application Number 05/152,332] was granted by the patent office on 1974-12-17 for cryogenic absorption cycles.
Invention is credited to Ellis P. Cytryn.
United States Patent |
3,854,301 |
Cytryn |
December 17, 1974 |
CRYOGENIC ABSORPTION CYCLES
Abstract
For the development of power and/or the production of cryogenic
fluids, e.g., oxygen, absorption refrigeration cycles are employed.
For example, one process comprises the steps of absorbing a
refrigerant vapor in a liquid absorbent, increasing the pressure on
resultant mixture of said refrigerant and said absorbent,
distilling and rectifying the mixture into substantially pure
refrigerant vapor and pure absorbent, reducing the pressure on
resultant pure liquid absorbent and returning the latter to the
absorbing step, cooling and condensing the refrigerant vapor to the
liquid state, reducing the pressure upon the liquid refrigerant to
below the triple point of the refrigerant to produce solid
refrigerant, sublimating the solid refrigerant to the vapor state,
and passing resultant refrigerant vapor to the absorbing step at a
rate that maintains the pressure below the triple point.
Inventors: |
Cytryn; Ellis P. (Marlton,
NJ) |
Family
ID: |
22542472 |
Appl.
No.: |
05/152,332 |
Filed: |
June 11, 1971 |
Current U.S.
Class: |
62/101; 62/112;
62/467; 203/DIG.17; 60/645; 62/335; 62/476; 62/629 |
Current CPC
Class: |
F25J
1/0225 (20130101); F25J 1/0035 (20130101); F25J
1/0012 (20130101); F25J 3/04278 (20130101); F25B
15/00 (20130101); Y02B 30/62 (20130101); Y02A
30/277 (20180101); Y10S 203/18 (20130101); F25J
2260/30 (20130101); F25J 2270/906 (20130101); Y02A
30/27 (20180101) |
Current International
Class: |
F25J
1/00 (20060101); F25B 15/00 (20060101); F25J
1/02 (20060101); F25b 015/00 () |
Field of
Search: |
;62/46,101,102,112,467,476 ;60/36 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
refrigeration and Air Conditioning, W. F. Stoecker, McGraw-Hill,
1958, p. 37..
|
Primary Examiner: O'Dea; William F.
Assistant Examiner: Ferguson; Peter D.
Attorney, Agent or Firm: Millen, Raptes & White
Claims
What is claimed is:
1. A refrigeration process comprising the steps of:
absorbing a refrigerant vapor in a liquid absorbent;
increasing the pressure on resultant mixture of said refrigerant
and said absorbent;
distilling and rectifying the mixture into substantially pure
refrigerant vapor and pure absorbent;
reducing the pressure on resultant pure liquid absorbent and
returning the latter to the absorbing step;
cooling and condensing the refrigerant vapor to the liquid
state;
reducing the pressure upon the liquid refrigerant to below the
triple point of the refrigerant to produce solid refrigerant;
sublimating the solid refrigerant to the vapor state; and
passing resultant refrigerant vapor to the absorbing step at a rate
that maintains the pressure below the triple point.
2. A process according to claim 1 wherein prior to the sublimating
step the liquid refrigerant is passed through a porous plate and
solid refrigerant is formed in said plate.
3. A process according to claim 2 wherein the porous plate is
heated to sublimate the refrigerant.
4. A process according to claim 1 wherein the passage of the
refrigerant from the sublimation step to the absorbing step is
induced by mechanical means.
5. A process according to claim 1 in which the pressure on the
liquid absorbent is reduced by passing said liquid absorbent
through a turbine, thereby recovering energy therefrom.
6. A process according to claim 1 in which the refrigerant is
selected from the group consisting of nitrogen, hydrogen, neon,
helium and hydrocarbon having a saturation pressure between that of
butane and methane; and the absorbent is a liquid having a freezing
point below the temperature of the process and selected from the
group consisting of a hydrocarbon liquid and an inorganic
liquid.
7. A process according to claim 1 wherein the refrigerant is
methane and the absorbent is selected from ethane and propane.
8. A process according to claim 1 wherein the cooling and
condensing of the refrigerant is conducted in heat exchange with a
separate absorbent refrigeration cycle.
9. A process according to claim 1 wherein the heat for distilling
and rectifying the mixture is supplied by heat exchange with a
separate absorbent refrigeration cycle.
10. A process for the recovery of energy and refrigeration
comprising the steps of:
absorbing a refrigerant vapor in a liquid absorbent;
increasing the pressure on the resultant mixture of refrigerant and
absorbent;
distilling and rectifying the mixture into substantially pure
refrigerant vapor and pure absorbent;
heating the refrigerant vapor from the distillation step by
indirect heat exchange with absorbent from the distillation step,
to simultaneously increase the temperature of the vapor refrigerant
and reduce the temperature and pressure of the liquid
absorbent;
recovering energy from the refrigerant vapor by reducing its
temperature and pressure;
condensing the vaporous refrigerant to the liquid state;
recovering the energy of the liquid refrigerant by reducing its
pressure and temperature;
evaporating the liquid refrigerant under reduced pressure; and
returning the absorbent and the refrigerant to the absorbing step.
Description
This invention relates to improvements in industrial processes for
the development of power and the production of useful industrial
products, such as liquid air, liquid oxygen, liquid nitrogen and
the development of cryogenic temperatures and is based upon new
arrangements and cycles of absorption refrigeration.
BACKGROUND OF THE INVENTION
Since the development of the steam engine in the Seventeenth
Century, the common source of energy for man's use has been the
combustion of fossils fuels at high temperatures. This burning of
fossils fuel in either a furnace or in an internal combustion
engine has resulted in the pollution of the atmosphere with both
the products of combustion and with heat, and the removal of heat
in the development of power has resulted in the thermal pollution
of large bodies of water. In a high temperature energy system, such
as the steam turbine, the working fluid water is first evaporated
at high pressure and then expanded in the turbine and finally
condensed to liquid at temperatures above the ambient temperature.
The heat rejected is usually discharged into a river or lake. The
use of water as the working fluid introduces the exceedingly high
heat of vaporization of water. This heat of vaporization is energy
of which a large part is lost in the system. Because the prior
processes can utilize only a small fraction of the heat supplied by
the burning of fuel, the net result is that our environment is
subjected to a serious thermal pollution.
SUMMARY OF THE INVENTION
The present invention offers techniques which permit the reduction
of polluting effect of the prior process for converting heat into
power, as these techniques utilize heat which has been wasted. One
embodiment of the present invention begins with air at ambient
temperature and pressure and liquifies the air at subatmospheric
pressure and temperature and recovers the energy from the air. As a
feature of this process the air can be heated during the process by
what is now considered to be waste heat, and the energy of this
waste heat recovered. The present invention teaches the recovery of
useful work from waste heat and from solar energy.
This invention is based upon the employment of one or more
absorption refrigeration cycles, so arranged that energy may be
recovered from the cycle and allows the production of cryogenic
temperatures and the production of useful products. This invention
is directed to utilization primarily of cycles in which the
refrigerant is highly or completely soluble in the absorbent, such
as, but not limited to the use of a hydrocarbon, such as methane,
in solution of a higher boiling hydrocarbon, such as ethane or
propane. Other combinations such as ethane in solution in propane
or propane in butane are illustrative. Further examples of useful
combinations are solutions of nitrogen in methane, or ethane, or
hydrogen in methane. Any hydrocarbon whose saturation pressure and
temperature relationships are between that of methane and butane is
acceptable. It is apparent that substituted hydrocarbons such as
the halogenated hydrocarbons can be used. In order to secure the
maximum differences in temperatures, this invention contemplates
the employment of a cascade operation having a series of absorption
refrigeration cycles using different refrigerants, such as the use
of ethane or propane in the first cycle, ethane or methane in the
second cycle, and methane or nitrogen in final cycle. If even lower
temperatures are desired, additional cycles using neon, hydrogen or
helium as the refrigerants may be employed in lower temperature
cycles.
It is thus an object of this invention to provide a system in which
very low cryogenic temperatures can be obtained with the energy for
the system being derived from waste heat.
It is a further object of the invention to recover the latent
energy from low temperature heat sources such as waste heat from
power plants or from solar energy.
It is a further object of this invention to recover pure gases from
air using low grade heat as the source of the energy needed to
separate the pure gas from air.
It is a further object of this invention to recover pure water from
saline and impure waters using an absorption refrigeration cycle to
supply the energy to separate the pure water from the brine.
It is a further object of this invention to recover energy from
fluids which are being liquified.
It is a further object of this invention to produce a low
temperature process in which the refrigerant is sublimed.
It is still a further object of this invention to provide an
evaporator-sublimator which has a porous partition.
It is a further object of the invention to provide a power system
which can be utilized for the propulsion of vehicles in which the
amount of heat discharged is substantially reduced and in which the
efficiency is materially increased.
Further objects and advantages of the present invention will become
apparent upon further study of the specification and claims.
BRIEF DESCRIPTION OF THE DRAWINGS
The more specific objects and advantages of this invention will be
more readily apparent from the ensuing description wherein
reference is made to the accompanying drawings illustrating the
preferred embodiments of the invention.
In the drawings,
FIGS. I to X and XV to XVII are schematic flow sheets illustrating
the principal features of the various embodiments.
FIG. I shows the basic absorption refrigeration cycle in a
simplified form in which an evaporator-sublimator is used.
FIG. II shows an embodiment of the absorption refrigeration cycle
of the basic system in which energy is recovered by the cycle.
FIG. III shows another embodiment of the basic system in which
energy is recovered.
FIG. IV is another embodiment of the absorption refrigeration cycle
which permits the recovery of thermal energy from the system.
FIG. V shows an embodiment of the invention in which two absorption
refrigeration cycles are connected in a cascade manner and in which
mechanical energy is recovered in each cycle.
FIG. VI shows an embodiment of the invention in which air is
liquified and energy is recovered.
FIG. VII shows a further embodiment in which a gas is liquified and
in which energy is recovered.
FIG. VIII shows a system for recovering energy from low temperature
source by the use of air as a pressure medium.
FIG. IX shows a system similar to FIG. VII in which two turbines
are employed.
FIG. X illustrates an embodiment of the invention in which the
refrigeration cycle is combined with a saline water distillation
system.
FIG. XI is cross-sectional view through an evaporator-sublimator of
this invention.
FIG. XII is a cross-sectional view of another embodiment of an
evaporator-sublimator of this invention.
FIG. XIII is a chart showing the conditions during a power recovery
cycle of this invention.
FIG. XIV is a cross-sectional view of flash distillation vessel of
this invention.
FIGS. XV and XVI are illustrations of this invention in which the
power generated is used as a propulsive force.
FIG. XVII shows the invention as applied to liquefaction of
gases.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 illustrates the basic refrigeration cycle employed by this
invention. In this Figure and throughout the description of this
specification only the basic elements of the system are described.
Auxiliary equipment common to refrigeration systems is omitted from
the drawing and from the description to facilitate the
understanding of the principles of the invention.
The present invention employs a basic absorption system which
includes the step of evaporating the refrigerant in a heat sink by
the removal of heat from another body, followed by the absorption
of the refrigerant in an absorbent to form a liquid solution. The
solution is transferred to another place and heated to separate the
refrigerant from the absorbent followed by the condensation and
return of the refrigerant to the evaporator. The system preferably
is operated with the separator and condenser at a higher pressure
than the absorber. While it is possible to introduce a third fluid
to the refrigerant and absorbent solution to produce transfer of
the fluids by diffusion without the requirements for mechanical
energy inputs, this invention contemplates a continuous system in
which mechanical energy is used to transfer the solution of
refrigerant in absorbent from the zones of lower pressure to the
zones of higher pressure. This energy can be recovered, at least in
part from the absorbent and the refrigerant as they move from the
zones of higher pressure to the zones of lower pressure. In order
that substantial refrigerating effects are obtained and that there
be available substantial recovery of energy, it is contemplated to
have substantial difference in pressure between these zones.
In FIG. I, the evaporator-sublimator 1 is connected by a conduit
with the absorber 2. This conduit may be provided with means to
produce a lower pressure in the evaporator-sublimator 1 than in the
absorber 2. The provision of such means is particularly desirable
when the refrigerant is present as a solid in the
evaporator-sublimator and the pressure is below the triple point,
and when it is desirable to increase the solubility of the
refrigerant in the absorbent.
The absorber 2 receives the vapor from the evaporator-sublimator
and also receives absorbent from the regenerator 3. The absorber 2
can be provided with known means for effecting contact between the
vapor and the liquid. The pressure in the absorber will be
maintained below the saturation pressure for the refrigerant in the
absorbent. The solution which is a mixture of the refrigerant and
absorbent is transferred by the pump 4 to the regenerator 3.
As the refrigerant and absorbent used in the preferred embodiments
of this invention may have close boiling points, it is generally
necessary to have a distillation process embodying a rectification
system to separate the substantially pure refrigerant from the
relatively pure absorbent. While it is generally contemplated to
employ a rectification column, there are some combinations of
refrigerant and absorbent which can be separated by simple
distillation.
The regenerator or separator 3 includes a rectification column 8
having a cooling coil 10 to provide the necessary reflux for
separation. This column can be of any well-known construction and
can be either a plate column or a packed column. The regenerator
will also be provided with a heating coil 9. This coil will
ordinarily supply the major part of the heat used in the process
and will generally reach the highest temperature in the cycle.
In accordance with good distillation practice, the solution of
refrigerant and absorbent will be introduced into the column at an
optimized point. The composition of the mixture introduced at the
point will approximate the composition of the mixture in the column
at the point of introduction. The preferred mode of heating the
mixture of the refrigerant and absorbent before it is introduced
into the column will be described later.
The column 8 will produce a vapor stream of substantially separated
refrigerant at the top of the column and a stream of liquid
absorbent relatively free from refrigerant from the bottom of the
regenerator 3. The absorbent which is hot and under high pressure
is returned to the absorber prior to which it must be reduced in
temperature and pressure to substantially the temperature and
pressure in the absorber. The pressure may be reduced by passing
the liquid through the turbine 7 which will recover part of the
energy imparted by the pump 4. The liquid absorbent may be cooled,
at least in part, by heat exchange with the solution which is being
fed to the column 8. The heat exchanger 6 is shown provided with
coils or the like for effecting this exchange of heat. When the
amount of heat in the liquid absorbent is greater than that which
can be absorbed by the solution, the absorbent can be cooled by
other means.
The substantially pure vapor discharged from the top of the column
is passed through the line 11 to the condenser 12. As the vapor in
condenser 12 is under substantially higher pressure than exists in
the evaporator, it can be condensed to a liquid at a higher
temperature than exists in the evaporator-sublimator 1 or the
absorber 2. The condenser 12 will cool the refrigerant to a
temperature below its condensation point at the pressure existing
in the condenser. This will discharge a portion of the heat from
the system.
The condensed refrigerant is passed as a liquid through the
pressure reducing means 13. This can be a simple pressure reducing
valve or orifice. However, it is preferred to use a device which
will recover at least some of the energy available upon the release
of pressure. This device will normally take the form of a turbine
of known construction, but any other form of device which will
recover the energy can be used. It is to be understood that
whenever the term "turbine" is used to described a means for
recovering energy by pressure reduction, any similar expansion
engine is included.
The evaporator-sublimator 1 is provided with a heat exchange means
14, which supplies the heat necessary to vaporize the refrigerant
and is cooled to approach the lowest point in the cycle. The
evaporator-sublimator 1 is preferably of the construction shown in
more detail in FIGS. XI and XII, and will be described later. This
evaporator-sublimator is designed to permit the conversion of the
refrigerant to vapors by either sublimation or evaporation. The
liquid refrigerant from the pressure reduction means 13 is fed into
the first compartment 15 of the evaporator-sublimator 1. This
compartment is separated from the vapor section 17 by a porous
plate 18 through which passes the heat exchange means 14. The
liquid in compartment 15 is at a slightly higher pressure than
exists in the vapor section 17, and thereby oozes through the
porous partition.
When the pressure in the compartment 17 is below the triple point,
the refrigerant will freeze as it is passed through the porous
partition. The frozen refrigerant will thus block the pores in the
plate and prevent further flow. The heat exchange means 14 will
then supply the heat necessary to sublime the refrigerant. At this
stage the heat exchanger 14 constitutes the heat sink of the
process. This manner of operation requires that the pressure in the
vapor section be below the triple point for the refrigerant. To
maintain this pressure may require the positive removal of vapor
from the section 17 by mechanical means.
If the pressure of the refrigerant in the section 17 is not below
the triple point of the refrigerant, the liquid refrigerant will
ooze through the porous plate and be evaporated by the heat from
the heat exchange 14.
The evaporator-sublimator 1, the absorber 2, the regenerator 3, the
column 8, and the condenser 12, are provided with suitable heat
exchange means 14, 5, 9, 10 and 16, respectively. The heat
exchanger 14 will supply the heat necessary to vaporize the liquid
refrigerant and will cool the fluid circulating therein to the
lowest temperature in the system. The heat exchangers 5, 10 and 16
will abstract heat from the system.
As this invention prefers the use of refrigerants of the class of
methane, ethane, nitrogen, neon, hydrogen and helium with
absorbents selected from the lower boiling hydrocarbons and lower
boiling point inorganic fluids, the heat of solution in absorber 2
will be relatively small and the amount of heat removed by heat
exchanger 5 will be a minimum and in some instances the heat
exchanger 5 may be omitted.
Since the refrigerants employed in the present invention have
relatively low boiling points, the highest temperature necessary in
the regenerator 3 can be relatively low and can be supplied with
waste heat or by solar heat. The temperature of condensation
selected in the highest temperature cycle can be selected according
to the needs of the process and the cooling medium available. In
some instances, water at ambient temperature can be used, and in
others the heat can be rejected through a suitable heat exchanger
directly to the ambient atmosphere.
FIG. II shows another embodiment of the cycle shown in FIG. I which
permits the conversion of some of the thermal energy within the
absorption refrigeration system to mechanical energy. In this
modification, the gaseous refrigerant discharging from the column
208 of the regenerator 203, is first compressed then heated and
expanded to recover part of the energy. The gas leaving the column
208 is fed to a compressor 226 through the conduit 211 of a
suitable type. The compressed vapor is passed through the heat
exchanger 219 where the vapors are heated. All or part of this heat
may be supplied by passing the relatively pure absorbent from the
regenerator 203 through the heat exchange elements of the exchanger
219. The exchanger may also supply heat from external sources.
The heated and compressed gaseous refrigerant is then expanded
through the turbine 220 to convert the thermal energy to mechanical
energy. The cooled refrigerant at lower pressure is then passed to
the condenser 212 where it is cooled to condensation point. The
liquid is then passed through the pressure reduction means 213 and
fed into the evaporator-sublimator 201. The vapors from the
evaporator-sublimator 201 are passed by mechanical inducement in
pump 205 to the absorber 202 and mixed with absorbent which has
passed through the heat exchangers 219 and 206 and turbine 207. The
solution from the absorber 202 is pumped by pump means 204 through
the heat exchanger 206 to the column 208.
Referring to the embodiment illustrated in FIG. III, the pure
absorbent from the regenerator 303 is passed through the heat
exchange means 319 and supplies part of the heat to the refrigerant
which has been compressed by pump 326. The partially cooled
absorbent then is passed to the heat exchanger 306 and then through
the turbine 307 to the absorber 302. As the absorbent has been
partially cooled before arriving at the heat exchanger 306, it
supplies only a part of the heat necessary for conditioning the
mixture or solution of refrigerant and absorbent to be fed into the
column. Additional heat can be supplied to the mixture by cooling
the vapors in the heat exchange means 327.
The heat for the separation of the mixture is supplied by the heat
exchange means 309, and the refrigerant is vaporized by the heat
supplied in the evaporator-sublimator 301 by the heat exchange
means 314. Heat is removed from the condenser by the heat exchange
means 316, and the absorber by heat exchange means 305. It is to be
understood that the area of heat exchange surfaces in the
regenerator 303, the condenser 312, the heater 306, the cooler 323,
the absorber 302, and the heater 319, will be selected to give the
transfer appropriate to steady operation.
The features which are specifically shown in FIGS. I, II and III
can be combined or modified by the features of each other and can
be used in connection with auxiliary equipment as is well-known in
the art.
FIG. IV illustrates a cycle which is an embodiment of the basic
cycle and which is designed to produce very low temperatures in
single cycle. This arrangement materially reduces the amount of
energy required to generate a given refrigerating effect. In this
example the values are given for a cycle using methane as the
refrigerant and propane as the absorbent.
In a specific operation of FIG. IV, the evaporator-sublimator 401
is supplied with about 0.45 pounds of methane per second at a
temperature of about 163.degree. R. and discharges the vapors at
about 135.degree. R. at a pressure of 0.1354 psia. The vapors are
passed to the absorber 402 and are mixed with about 1.1 pounds per
second of propane having a temperature of about 154.5.degree. R.
The pressure in the absorber 402 is about 0.0967 psia. The solution
of methane in propane is discharged from the absorber at the rate
of about 1.6 pounds per second and at a temperature of about
153.degree. R. The solution passes to a heat exchanger
corresponding to the heat exchanger 6 of FIG. I. In FIG. IV this
heat exchanger has two sections 406 and 406'. The solution enters
the section 406' and is heated by indirect heat exchanges with two
separate sources of heat. One source of heat is the stream of
propane returning from the regenerator 403 to the absorber. This
stream is supplied at the rate of about 1.14 pounds per second at a
temperature of about 159.degree. R. The other source of heat is the
condensed methane from condenser 412 which has a temperature of
about 229.degree. R. and is passed through the heat exchanger at
the rate of 0.45 pounds per second. Simultaneously, a minor stream
of the condensed methane from condenser 412 is introduced into the
solution of methane and propane in the heat exchanger section 406'
by turbine 425. This stream is supplied at the rate of 0.19 pounds
per second. The solution is discharged from the heat exchanger 406'
at the rate of 1.79 pounds per second at a temperature of
155.degree. R. The solution is then heated in heat exchanger
section 406 to about 374.degree. R, by the stream of propane
returning to the absorber. The solution is pressurized by the pumps
404 and 404' to a pressure of about 600 psia and is introduced into
column 408 of the regenerator or separator 403. The regenerator 403
is heated by the coil 409 which received a heating medium at
658.degree. R. The separated propane leaves the regenerator at a
weight of 1.144 pounds per second at a temperature of 653.degree.
R. Before entering the heat exchanger 406, the stream of propane is
cooled by passing through heat exchangers 427 and 428. The stream
of propane is cooled by fluid passing through coils 421 and 422 to
a temperature of about 449.degree. R. The methane leaves the top of
the column 408 at the rate of about 5.47 pounds per second and is
transferred to heat exchanger 419 where the methane is cooled by
fluid in the coil 420. The methane leaving the column 408 is at
about 340.degree. R. and is cooled to 336.degree. R. in the heat
exchanger 419. A major amount of the methane amounting to about
4.82 pounds per second is returned to the column 408 where it
serves as reflux. The minor portion of the methane amounting to
about 0.64 pounds per second is transferred to the condenser 412.
In condenser 412, the methane is cooled and liquified to a
temperature about 229.degree. R. and the stream is passed to the
heat exchanger 406'. The major portion of the condensate amounting
to 0.45 pounds per second passes through the coil 426 and is passed
through the pressure reducing means 413 into the absorber 401. A
minor portion of the condensed methane is passed through turbine
425 into contact with the solution in the heat exchanger 406' and
mixed therewith.
The mode of operation as described for FIG. IV presents a specific
manner in which the present invention may be applied. While
relative quantities and temperatures given are considered as merely
illustrative of a single operation, it should be noted that this
operation requires only the addition of mechanical energy to
operate the pumps 404 and 404'. In this example, the heat supplied
was at 658.degree. R. or 199.degree. F. which would be normally
considered as waste heat. In this example, the heat supplied is
such that Q= about 229 in the regenerator and the heat supplied to
the evaporator is such that Q=100. Also in the example, the heat is
removed in the exchangers 427 and 428 amounts to such that Q=164
and the amount removed by exchanger 419 amounts to such that Q=
about 50 and the heat removed in the condenser is such that Q=124.
From these values, it will be appreciated that in the cycle a
cooling effect of about one half of the heat supplied is obtained
at a temperature of 135.degree. R. or -324.degree. F. with the use
of waste heat and minor amount of mechanical energy.
The quantities of refrigerant, absorbent and temperatures may be
varied to suit specific problems without departing from the
invention.
FIG. V illustrated one manner in which it contemplated to arrange
two absorption refrigerating cycles of this invention, in a cascade
manner so as to utilize maximum percentage of the energy supplied
to the system. The Figure also illustrates how energy can be
recovered in a cascade system. In each of the cycles shown in this
Figure, the vapors of refrigerant are passed from the respective
evaporator-sublimators 501 and 501' to the corresponding absorbers
502 and 502' and are there mixed with the returning absorbent. The
separate solutions of refrigerant and absorbent are pumped by pumps
504 and 504' through the respective heat exchangers 506 and 506'.
In each of the cycles of this Figure a further refinement of the
utilization of energy is shown in that, instead of passing directly
from the heat exchangers 506 and 506' to the midpoints of the
columns 508 and 508' of the regenerators 503 and 503', the
solutions are passed through the heat exchange coils in condensers
512 and 512' and then lead into the columns 508 and 508'. The
vapors from the columns 508 and 508' are passed through their
respective heat exchangers 520 and 520'. The vapors are heated in
these exchangers by heating fluid supplied to coils 524 and 524'.
While the connection is not shown on the drawing for passing the
returning absorbent from the regenerators 503 and 503'to the heat
exchangers 520 and 520', it is to be understood that a portion, at
least of the heat supplied to the vapors, may be derived from these
sources as shown in FIG. III. The separate streams of vapors heated
in exchangers 520 and 520' are expanded by passing them through the
corresponding turbines 523 and 523'. The vapors from the turbines
are then fed to the condensers 512 and 512' respectively and the
energy in the liquid refrigerant recovered in the pressure reducing
means 513 and 513' and the liquids passed to the
evaporator-sublimators 501 and 501'.
In FIG. V the two cycles are shown as being in heat exchange
relation by having a heat transfer means 530 removing heat from
condenser 512 and supplying the same heat to the regenerator 503'.
Another heat transfer means 531 is shown for removing heat from the
condenser 512' and absorber 502' and supplying this heat to the
evaporator 501.
The turbines 507 and 507' perform the same functions as the
corresponding parts in FIG. I, as do the heat exchangers 505, 509,
510 and 510'.
While the cascade arrangement is illustrated with only two cycles,
three, four or more cycles can be constructed and connected in the
manner shown. The first cycle of a series could employ ethane as
the refrigerant, the second could use methane, and subsequent
cycles could employ nitrogen, neon, hydrogen and helium as
refrigerants. The number of cycles and the refrigerant will be
selected according to the needs of the system.
As shown by the several Figures of the drawing, the available heat
in one portion of the system can be transferred to another location
in the same cycle where the difference in temperature is sufficient
to effect a worthwhile heat exchange. The area of the heat exchange
surfaces will be selected to give the desired transfer of heat. The
individual features may be combined whenever a significant saving
of heat or energy will be effected.
FIG. VI illustrates a generic arrangement for the liquification of
a gas such as air, using the heat sink of an individual cycle or a
plurality of cycles to remove the heat from the air. In this
Figure, the details of the refrigeration cycles have been omitted
and are indicated merely by the cooling coils in the heat
exchangers 642 and 644.
Atmospheric air enters through a conduit 640 and is passed through
the turbine 641 into a region of lower pressure and is passed
through the heat exhangers 642 and 644 of the absorption
refrigeration cycle. The cooling of the air is provided by
substantially isentropic expansion in the turbine and by heat
exchange with the heat sinks of the refrigeration evaporators in
the heat exchangers 642 and 644, where the air is condensed to
liquid. The system may be provided with known means to remove water
vapor and carbon dioxide, to avoid fouling of the heat exchanger
surfaces.
The liquid air is discharged from the heat exchanger 644 into
conduit 645 and may be drawn off as a product by conduit 646.
Alternatively, the liquid air may be fed to separator 647, which
may be of known construction, e.g., a rectification column which
will separate the liquid air into its components. Frequently, only
nitrogen and oxygen will be separated, but the invention
contemplates the recovery of the minor constituent gases of the
atmosphere, e.g., argon, neon, helium, krypton, hydrogen xenon,
ozone and radon, if desirable. The carbon dioxide in the air may
also be recovered in the process.
The oxygen and nitrogen may be drawn off at 648 and 649, if
desired, to use the separated element as such and may be supplied
to other processes. The liquid air from conduit 645 may be passed
to pump 661 where the fluid is pressurized and then passed to coil
651. Similarly, the oxygen passes to pump 662 and coil 652, and the
nitrogen to pump 663 and coil 653 of heat exchanger 650. The
respective streams can then be passed, if desired, to turbines 657,
658 or 659 respectively. The product may be recovered by vessel
660. In the event that oxygen is being passed through the turbine
658, it may be desirable to mix the oxygen with a fuel which is
introduced through conduit 656 and to ignite the mixture before the
combustion gas is passed through the turbine 658.
This Figure illustrates the many ways in which the absorption
refrigeration system can be used commercially to recover energy and
to supply liquid, air, oxygen, nitrogen, or the rare gases to
industrial processes. Since the process of refrigeration as
described in this specification does not require the consumption of
large amounts of energy, it provides these materials in an
economical manner.
In FIG. VI, the heat exchanger 650 may also serve to transfer heat
between two or more of the streams. As for instance the coil 651
which receives liquid air may serve to further cool other streams,
or may be further cooled by the other streams. The coil 654 is
indicated as a separate heat exchange means for an independent heat
transfer medium to supply heat to or to remove heat from the
exchanger 650, and may serve to transfer heat between the liquid
air, the nitrogen or oxygen and the absorption refrigeration cycle.
There may be a plurality of these means as desired. The vessel 660
into which the gases are individually collected may serve as a heat
sink for the absorption refrigeration system or as an independent
cooling means.
FIG. VII illustrates the basic system for recovering energy using a
low temperature in the cycle with air as the energy transfer medium
with liquifaction of the air. In this cycle the lowest temperature
will be substantially the temperature of liquid air, and the
highest temperature normally contemplated is that available from
waste heat. While it is preferred to use waste heat as the source
of the highest temperature in the cycle, it is clear that if the
conditions are feasible the air can be heated to a higher
temperature by the combustion of fuel. In the preferred form the
cascade absorption refrigeration system is used to produce the low
temperatures in the cycle. A cascade refrigeration system as
illustrated in FIG. V is indicated by the block 770 in the drawing.
This system is provided with heat transfer means 771 to remove heat
from the energy producing system. While only a single means 771 is
indicated in the drawing it is to be understood that this means may
be composed of a plurality of separate connections for transferring
heat at different temperatures between the systems.
The heat exchanger, which is shown diagrammatically, is supplied
with a gas, usually air, which is condensed by the cooling effect
of the transfer means to a liquid. While air is usually the gas
employed, nitrogen or other gases can be used to avoid the risk of
combustion and oxidation. The liquid air from the heat exchanger
772 is passed to the pump 773 which increases the pressure on the
liquid. The change in pressure is usual quite significant. The
liquid at the higher pressure is circulated through the heat
exchangers 774 and 775 and converted to gas at high pressure and
temperature and then is expanded through the turbine 776. The air
leaving the turbine is cooled in heat exchanger 774 by heat
exchange with the liquid air from the pump 773. The cooled air is
then fed to the condenser or heat exchanger 772 completing the
cycle.
This Figure shows a simplified energy recovery system, in which
energy in the form of heat is supplied to the system by the heat
exchanger 775, which roughly corresponds to the boiler of a
conventional steam power system, and which converts the liquid air
to hot gas at high pressure. The hot compressed air is expanded
through the turbine and cooled by the liquid air from the
condenser, which corresponds to the condenser of a steam system.
The pump 773 corresponds to the injector on a steam boiler system.
Since the lowest temperature in the proposed system is near
absolute zero the efficiency of the system is high. The maximum
efficienty of a steam system is low since the temperature of
condensation is high. As pointed out above, while the invention
contemplates the use of waste heat, the air may be heated in heater
775 by heat from any source.
FIG. VIII illustrates a more developed system for recovering
energy. This Figure employs the basic energy system set forth in
FIG. VII. In this Figure, the absorption refrigeration system is
indicated by the block 870. This absorption refrigeration system
can be like the one shown in FIG. V but the details of the system
have been omitted for the purpose of clarity. The refrigeration
system is shown as removing heat from the energy recovery system by
the heat transfer means 871 associated with the condenser or heat
exchanger 872. The liquid gas which will be, hence forth referred
for convenience as liquid air, is passed from the condenser 872 to
the first pump 873 which increases the pressure of liquid air to
about 50 psia. The pressurized liquid air is passed through the
heat exchangers 874 and 874' and is heated by the air leaving the
turbines. The liquid air is then pressurized by the pump 873' to a
very high pressure such as 3500 psia., and is fed to the heat
exchanger 874". In this heater, the liquid air is vaporized and
converted into gas at high pressure and much higher temperature.
The hot gas is further heated in heat exchanger 875 and introduced
into the turbine 876. The air as discharged from turbine 876 is
reheated to about the original high temperature by the reheater
875' and is expanded through a second turbine 876'. The gas at
lower pressure and temperature is reheated to about the original
high temperature in reheater 875" and is expanded through the third
turbine 876". The air is then passed through the heat exchanger
874" and to the condenser 872 after passing through the cooler 890
and the heat exchangers 874 and 874'.
As an example, this system can be arranged to circulate air at the
rate of one pound per second through the cycle. If the pressure in
the condenser is maintained at atmospheric pressure, the
temperature in the condenser will be about 142.degree. R. The
liquid air is pressurized to about 50 psia. and passed through heat
exchangers 874' and 874 and the temperature raised to about
165.degree. R. The pump 873 raises the pressure to about 3,500
psia. and the temperature is raised to about 202.degree. R. The
liquid air is passed through the heaters 874 and 875 and is
converted to gas at 700.degree. R. (240.degree. F.). The hot air is
cooled in passing through the turbine 876 to 437.degree. R. and the
pressure is reduced to about 565 psia. In the heater 875', the air
is returned to the temperature of 700.degree. R. In turbine 876',
the temperature is dropped to 473.degree. R. and the pressure to
about 91 psia. In the heater 875', the air is reheated to about
700.degree. R. The expansion in turbine 876" drops the temperature
of the air to 473.degree. R. and the pressure to atmospheric. The
air is cooled in the heat exchangers 890, 874, 874' and 874" before
being condensed to liquid at 142.degree. R.
The values set forth in this cycle are illustrated by the chart
shown in FIG. XIV. The points on the diagram are identified as
follows: 1, indicates the condition of the liquid air leaving the
condenser 872; 2, the condition of the liquid air leaving the pump
873; 3, 4 and 5, the condition of the liquid air leaving the heat
exchanger 874, 874' and 875'; 6, the condition of the air leaving
the pump 873'; 7, the condition of the air leaving the heater 875
and entering the turbine 876; 8, the condition of the air
discharged from the first turbine 876; 9, the condition of the air
leaving the reheater 875' and entering the second turbine 876'; 10,
the condition of the gas as discharged from the second turbine; 11,
the condition of the air leaving the second reheater 875" and
entering the third turbine 876"; 12, the condition of the air as
discharged from the third turbine; 13, 14, 15 and 16, the condition
of the air as it is cooled and returned to the condenser at point
1.
The liquid air flowing from the condenser 872 is pressurized by the
pump 873 (point 2 on the chart) and is returned in indirect heat
exchange in heater 874 to absorb part of the latent heat of the
condensing air. This transfer of energy is possible with air, as
air is essentially a binary mixture of oxygen and nitrogen, and the
dew point temperature is approximately 5.5.degree. F. higher than
its bubble point. The heat exchanger 874 warms the liquid air to
slightly below its saturation point (point 4 on the chart). The
liquid is pressurized by pump 873' to the pressure at turbine inlet
(point 8 on the chart). The liquid at high pressure is vaporized in
the heat exchanger 875. In this heat exchanger, the highest
temperature in the cycle is reached. The temperature shown can
readily be reached by employing low quality thermal energy, such as
waste heat. Nothing in this disclosure should be construed as
preventing the use of higher temperatures which can be obtained
from other heat sources.
The system shown, when supplied with air at the rate of one pound
per second, would produce about two hundred horsepower in excess of
that required to operate the pumps 873 and 873', subject to the
limitation of the efficiencies of the turbines and losses in the
system.
FIG. IX illustrates another embodiment of the invention for the
recovery of energy, preferably using the absorption refrigeration
system as a means for establishing the necessary temperature
differential. In this Figure 970 indicates an absorption
refrigeration system and 971 indicates a heat transfer means for
transfering heat from the power recovery system to the heat sink of
the refrigeration cycle. This system includes a condenser 972 for
liquifying a gas such as air. The liquid air is pressurized by the
pump 973 and is heated by the heat exchanger 974. The heating
medium is the air being cooled and condensed. The pressurized and
heated liquid air is vaporized in the heat exchanger 975 and is
introduced into the turbine 976 and then reheated in reheater 975'
and passed into turbine 976'. This turbine discharges the air at
the pressure of the condenser.
This Figure shows an arrangement generally corresponding to the
system of FIG. VIII, but in which the construction has been
simplified. This Figure shows an arrangement which will allow a
substantial recovery of power with a lower plant investment. The
actual selection of the number of turbines and the number of
reheaters will depend upon an economic balance between the cost of
equipment and the value of the power drived.
FIG. X illustrates the recovery of pure water by the use of a low
grade heat source. In the production of water from saline water or
impure water, one of the major problems has been the cost of the
power required to vaporize the water. Another problem has been the
scaling of the water in the heating vessels. The utilization of the
absorption refrigeration systems of this invention will overcome
some of these previous difficulities.
In FIG. X the evaporator of the absorption refrigeration system is
indicated as 1001, the refrigerant absorber as 1002, the pump for
the solution of refrigerant and absorbent as 1004, the regenerator
as 1003 and the column as 1008. The vapors of the refrigerant are
passed to the heater 1019 and are heated by indirect heat exchange
with the absorbent from the regenerator 1003. The heated vapors are
then expanded through the turbine 1020, to recover energy and to
cool the vapors. The vapors are condensed in condenser 1012 and the
liquid refrigerant is passed through the pressure reduction means
1013 to the evaporator 1001. The refrigeration system thus far
disclosed is similar to that shown in FIG. IV.
The condenser 1012 includes a heat exchanger element 1021 through
which is passed the water to be distilled. The refrigerant and the
pressure of condensation are selected so that the heat of the
condensing vapors heats the water to be distilled. The warmed water
is then passed to the heat exchange element 1006' in the heat
exchanger 1006, and the water is further heated by the absorbent
returning to the absorber 1002 from the regenerator 1003.
The hot water is then fed into the distillation system. The
distillation system comprises a series of flash chambers which
utilize the latent heat in the water to vaporize a portion of the
water. The hot water is introduced in the first flash chamber 1080,
and a portion of the water flashed into steam. The steam is fed
through the heat exchange means 1082 in the second flash chamber
1081 and is condensed. The water from the first flash chamber is
fed to the second chamber 1081 which is at a lower pressure. A
second quantity of water flashes into steam. While only two flash
chambers are shown, it is to be understood that the number of flash
chambers may be selected according to the design criteria of such
distillation systems.
The vapors from the final flash chamber and the condensate from the
heat exchanger 1082 are fed into the condensing chamber 1083. This
chamber is cooled by heat exchange element 1084 through which is
circulated a heat exchanger medium which also is passed through the
element 1014 of the evaporator 1001. The non-condensible gases in
the saline water are removed from the distillation system by the
ejector 1086. The evaporator 1001 which is heated by the condensing
water vapor in the condenser 1083, will maintain a minimum pressure
and temperature in the water vapor condenser. The unevaporated
water or waste brine from the final distillation stage is
discharged through the heat exchange means 1087 in the refrigerant
condenser 1012 or through the heat exchange means 1088 in the
refrigerant absorber 1002, to remove the heat of these elements. In
a like manner, the distilled water is passed through the heat
exchanger means 1089 in the refrigerant condenser 1012 or through
the heat exchange means 1091 in the absorber 1002 or through
both.
FIG. X demonstrates the application of absorption refrigeration
system of this invention using a low temperature heat source to
produce energy and to perform useful chemical engineering unit
process operations. While this example shows the application of the
process of this invention to the distillation of water, it is
apparent that other liquids could be distilled in a similar manner.
Furthermore, the temperature differential available from the
absorption refrigeration cycles of this invention can be used in
other unit processes requiring temperature changes. For example,
water could be purified by freezing rather than by distillation.
The invention could also be used to dehydrate materials as by
freeze drying since the invention can produce both low temperature
and low pressure.
FIG. XI shows the construction of a preferred form of the
evaporator-sublimator of this invention. The figure is a cross
section through the vessel constituting the evaporator-sublimator.
The vessel is normally provided with insulation about the walls.
The interior of the vessel is divided into a liquid receiving
section 1101 and a vapor section 1103 with a porous plate 1102
separating the section from each other. The liquid to be vaporized
is introduced into the section 1101 by the pipe 1104. The vapor is
removed from section 1103 by the pipe 1105. This pipe is designed
to maintain the pressure in the section 1103 at a desired level.
The pipe 1105 may include a fan, if necessary, to maintain the
desired pressure.
The porous plate 1102 which serves as a partition, is formed of an
open cell material such as porous brick or stone or metal which
will permit the slow passage of the liquid through the partition.
The partition includes a heat exchange means 1114 which will supply
the heat necessary to vaporize the liquid. This heat exchange means
serves as the heat sink in the refrigeration cycle.
The evaporator-sublimator is operated as a sublimating means by
establishing a pressure in the section 1103 which is below the
triple point of the refrigerant. Under these conditions, the
refrigerant, as it passes through the partition 1102, will freeze
in the passages and block further flow of liquid. The heat exchange
means 1114 will supply heat to sublimate the refrigerant. As the
refrigerant is evaporated, more liquid refrigerants will pass into
the plate and be frozen. Thus, the passage for the liquid is
automatically limited to the rate at which the frozen material is
sublimed by the heat.
When the pressure in the chamber is above the triple point of
refrigerant, the liquid will ooze through the plate and be heated
by the heat exchange means and will evaporate into the chamber
1102. This will occur before the system has reached the triple
point pressure at the time the system is being started up or the
system can be operated under these conditions as desired.
FIG. XII is another embodiment of the evaporator-sublimator. In
this Figure, the liquid chamber is designated as 1201, the vapor
chamber as 1203 and the porous plate as 1202. The liquid is
supplied by pipe 1204 and the vapor removed by pipe 1205. This
embodiment differs from that shown in FIG. XI by having the feed
pipe 1204 pass through the vapor section 1203. This pipe includes
the heat exchange means 1207 in the vapor section. This permits the
liquid refrigerant to be further cooled before entering the chamber
1201. This construction assures a rapid stabilization of conditions
to enable the operation of the evaporator-sublimator as a
sublimator. The heat sink is designated by the heat exchange means
1214.
FIG. XIII shows a vapor separator particularly adapted to be used
in the flash distillation chambers of the system shown in FIG. X.
While particularly adapted for this type of system, the separator
can be used in any distillation system benefitted by little or no
entrainment of the distilland in the vapor. In this Figure, 1301
indicates the vessel for receiving the liquid to be distilled
through the pipe 1302 and discharging the vapor through the pipe
1303. In the vessel above the level of the boiling liquid is a
baffle means 1304. This baffle means includes a shaft 1305 which is
mounted for rotation about an axis. A series of turbine blades 1307
are secured in an inclined position to the shaft so that the
passage of vapor towards the outlet pipe 1303 cause the shaft to
rotate. A perforate plate 1306 secured to the shaft above the
turbine blades rotates with the shaft. The plate, preferably in the
form of a fine mesh screen, engages any droplets of liquid and
centrifugally throws them outwardly away from the outlet. While it
is preferred to have the vapors rotate the screen, it would be
possible to use other means for the purpose.
FIGS. XV and XVI illustrate a more specific embodiment of the
cycles shown in FIG. VI. In these Figures, the energy recovery
system is used to provide motive power for a vehicle. The vehicle
may be any vehicle requiring energy for propulsion, such as
aircraft, boats, air-cushioned vehicles as Hovercraft and trains,
railroad cars, road vehicles or tube cars. The power derived can be
used directly as in the thrust of a jet or indirectly by the use of
a driven turbine.
In FIG. XV, the heat sink of an absorption refrigeration system is
indicated by the block 1570. The power generating system receives
air from the atmosphere at 1560. The entrance may be in the form of
a scoop, taking advantage of the vehicles forward motion to
increase the flow of air. The entering air is passed to the
precooler 1571 and is conveyed from there to the turbocompressor
1572. The compressed air passes through the heat exchange means
1573 in the precooler. The compressed air is fed to the turbine
1574 and there expanded. The cooled air is then passed into the
condenser 1577, in which it is further cooled by supplying heat to
the refrigeration cycle, and is condensed to a liquid. The liquid
air is pressurized by the pump 1575 and passed to the heat
exchanger 1576 in the refrigeration cycle. This exchanger heats the
air to vaporize it. The hot pressurized air is fed to the nozzle of
the thrust means 1578. Fuel may also be supplied to the thrust
nozzle through line 1579 and burnt with the air to supply reaction
forces to the vehicle.
Heat exchange connection 1580, 1581 and 1582 transfer heat from the
refrigeration cycle to the precooler, to the condenser, and to the
heater. The precooler will use well-known techniques to free the
air from ice, carbon dioxide and the like and to remove the ice
from the precooler.
The thrust means 1578 may be a jet engine or a rocket nozzle or a
turbojet engine. While it is desirable, in many instances, to use
fuel in the engine, wherever the added heat of combustion or the
polluting effect of combustion is to be avoided, the engine may be
powered solely by the expanding gas.
FIG. XVI illustrates another embodiment of the invention as used
for the propulsion of a vehicle. In this Figure, the air enters the
system at 1660 and is passed to the precooler 1671. The dried
cooled air is fed to the compressor 1672. The compresser gas then
is passed to the heat exchanger 1673 in the precooler and then fed
to the turbine 1674 and is there expanded. The air is condensed in
condenser 1677. The liquid air is passed through the heat exchange
means 1683 in the precooler and is further heated in the heat
exchanger 1684 before being introduced into the propulsion means
1678. The heat exchangers 1681 and 1682 transfer heat to the
refrigeration cycle.
In this example the precooler is not connected with the
refrigeration cycle as shown in the previous figure.
FIG. XVII shows an embodiment of the invention as applied to the
use of gases such as nitrogen, hydrogen, neon and helium as
refrigerants.
FIG. XVII illustrates one absorption refrigeration cycle of a
cascade system. In this Figure, the absorber 1702 feeds the
solution of a gas such as hydrogen in a liquid hydrocarbon to the
pump 1704 and hence to the heat exchanger 1706 and to the column
1708 of the regenerator or separator 1703. The heat necessary to
separate the gas from the absorbent is preferably supplied by the
condenser of another cycle in the cascade arrangement by means
1709. The gas is then supplied to a heat exchanger 1712. This
exchanger is arranged to remove heat from the gas and supply this
heat to an evaporator of another cycle in the cascade system. This
heat exchanger also includes another heat exchange element 1721.
The cooled gas from the heat exchanger 1712 is passed through the
expansion means 1713 into the chamber 1722. This chamber is at
lower pressure than 1712 and a portion of the gas is liquified and
is passed into the evaporator-sublimator 1701. The vapors from the
evaporator-sublimator 1701 and the vapors from the chamber 1722 are
combined and are passed through the heat exchanger element 1721 in
the chamber 1712 and then passed to the absorber 1702.
The vapors separated from the liquid and the vapors from the
evaporator-sublimator thus serve to cool the gas in the chamber
1712.
When hydrogen is the refrigerant, the heat exchanger 1712 may be
cooled by the heat sink of an evaporator-sublimator of another
cycle of the cascade to 94.degree. R. The hydrogen is further
cooled by the heat exchange element 1721 by the hydrogen from the
evaporator and the chamber 1722. The hydrogen is cooled to the
liquefaction by passage through the expansion means 1713. The
liquid hydrogen from chamber 1722 may be passed to the evaporator
1701 in which it may serve as the heat sink in connection with a
cooler cycle for liquifying helium. If liquid hydrogen is desired
as a product, it is withdrawn from the chamber 1722 and make up
hydrogen is supplied to the absorber 1702.
The same cycle is employed to liquify helium with the exception
that liquid hydrogen is employed as the cooling fluid in the
element of the heat exchanger 1712.
A neon cycle can be substantially the same as for hydrogen, and
will include the expansion of neon in the means 1713. It is
desirable to include a cycle in the cascade system, and then the
neon heat sink will be used to cool the hydrogen before
liquefaction.
The several figures of the drawing illustrates preferred
embodiments of the invention. The several embodiments show numerous
ways in which it is contemplated to apply the invention to recover
energy from low temperature heat sources, and to perform chemical
processes and recover valuable products.
From the foregoing description, one skilled in the art can easily
ascertain the essential characteristics of this invention, and can
without department from the spirit and scope thereof, make various
changes and modifications of the invention to adapt it to various
usages and conditions.
* * * * *