TECHNICAL FIELD

This invention relates generally to refrigeration.

BACKGROUND ART

A thermoacoustic engine is a device that employs a tube containing hot and cold end heat exchangers thermally linked by a stack of parallel plates or by a regenerator matrix to convert thermal energy to acoustic or pressure energy. The work of the acoustic energy can be used to produce mechanical work, electricity or refrigeration. The thermal energy provided to the thermoacoustic engine is typically not fully used in the thermoacoustic engine to generate the acoustic energy. A system for gainfully employing the remnant thermal energy from a thermoacoustic engine, such as to produce refrigeration, would be highly desirable.

Accordingly, it is an object of this invention to provide a system for employing remnant thermal energy from a thermoacoustic engine to generate refrigeration.

SUMMARY OF THE INVENTION

The above and other objects, which will become apparent to those skilled in the art upon a reading of this disclosure, are attained by the present invention, one aspect of which is:

A method for generating refrigeration comprising:

(A) producing a hot fluid and using a first portion of the heat of the hot fluid to produce acoustic energy;

(B) providing a high pressure heat pump solution comprising refrigerant and absorbent, and using a second portion of the heat of the hot fluid to warm the high pressure heat pump solution and to separate the high pressure heat pump solution into refrigerant fluid and absorbent fluid;

(C) expanding the refrigerant fluid to generate refrigeration and providing refrigeration from the refrigerant fluid to a heat load;

(D) mixing the resulting refrigerant fluid with absorbent fluid to produce reconstituted heat pump solution; and

(E) increasing the pressure of the reconstituted heat pump solution to produce said high pressure heat pump solution.

Another aspect of the invention is:

Apparatus for generating refrigeration comprising:

(A) a thermoacoustic engine, a refrigerant generator, means for passing a hot fluid to the thermoacoustic engine, and means for passing the hot fluid from the thermoacoustic engine to the refrigerant generator;

(B) an expansion device and means for passing refrigerant fluid from the refrigerant generator to the expansion device;

(C) a heat exchanger and means for passing refrigerant fluid from the expansion device to the heat exchanger;

(D) an absorber, means for passing refrigerant fluid from the heat exchanger to the absorber, and means for passing absorbent fluid from the refrigerant generator to the absorber; and

(E) a compression device, means for passing fluid from the absorber to the compression device, and means for passing fluid from the compression device to the refrigerant generator.

BRIEF DESCRIPTION OF DRAWING

The sole FIGURE is a schematic representation of one preferred embodiment of the refrigeration system of this invention.

DETAILED DESCRIPTION

The invention will be described in detail with reference to the Drawing. Referring now to the FIGURE, fuel

14

and oxidant

15

are provided into combustion zone

10

wherein they are combusted. The fuel may be any suitable fuel. Preferably the fuel is a gaseous fuel such as methane, propane or natural gas. The oxidant may be air, oxygen-enriched air, or commercial oxygen having an oxygen purity of 99.5 mole percent or more. If desired, a process fluid

13

may also be provided into combustion zone

10

to absorb, either by direct or indirect heat exchange, heat from the hot combustion reaction products resulting from the combustion of fuel

14

and oxidant

15

. Combustion reaction exhaust is removed from combustion zone

10

in exhaust stream

17

. Examples of fluids which may be used as the process fluid

13

in the practice of this invention include water or steam, liquid metals, helium, air, nitrogen and flue gas.

Hot fluid is withdrawn from combustion zone

10

in stream

16

. The hot fluid may comprise combustion reaction products from the combustion of fuel

14

and oxidant

15

and/or may comprise heated process fluid

13

. The hot fluid in stream

16

has considerable thermal energy and typically has a temperature within the range of from 400° C. to 1000° C. Any other suitable method for producing a hot fluid

16

may also be used in the practice of this invention.

Hot fluid

16

is provided to thermoacoustic engine

20

wherein a first portion of the heat or thermal energy contained in hot fluid

16

is used to generate acoustic or pressure pulse energy. Thermoacoustic engines and their operation are known. A good description of thermoacoustic engines may be found at Physics Today, “Thermoacoustic Engines and Refrigerators”, Gregory W. Swift, pp. 22-27, July 1995. The acoustic energy or acoustic work produced by thermoacoustic engine

20

, represented by arrow

70

in the FIGURE, may be used to generate electricity by being provided to a generator, such as a linear generator, or may be used to generate refrigeration by being provided to an acoustic refrigerator such as a pulse tube refrigerator, or may be converted to shaft work by mechanical means.

The hot fluid exiting thermoacoustic engine

20

in stream

22

, now at a lower temperature than that of stream

16

and typically within the range of from 300° C. to 700° C., is passed to refrigerant generator

41

. Also passed into refrigerant generator

41

is high pressure heat pump solution

54

which typically is at a pressure within the range of from 20 to 500 pounds per square inch absolute (psia). The heat pump solution comprises refrigerant and absorbent. Typically high pressure heat pump solution

54

comprises from 20 to 80 weight percent refrigerant and from 80 to 20 weight percent absorbent. Among the refrigerants which may be used in the practice of this invention one can name ammonia, water and methanol. Among the absorbents which may be used in the practice of this invention one can name water, lithium bromide, lithium nitrite, potassium nitrite, sodium nitrite, and sodium thiocyanate.

Within refrigerant generator

41

the high pressure heat pump solution is heated by indirect heat exchange with intermediate temperature hot fluid

22

. Thus a second portion of the heat or thermal energy of the hot fluid is used to warm the high pressure heat pump solution. The heating of the high pressure heat pump solution serves to desorb some of the refrigerant out from the absorbent. Resulting desorbed refrigerant fluid is withdrawn from refrigerant generator

41

in stream

42

and remaining absorbent fluid, typically comprising from 10 to 60 weight percent refrigerant and from 40 to 90 weight percent absorbent, is withdrawn from refrigerant generator

41

in stream

55

. The spent process fluid is withdrawn from refrigerant generator

41

in stream

36

. In a closed system stream

36

may be recycled to hot fluid generator or combustion zone

10

as stream

13

.

Refrigerant in stream

42

is passed to cooler

43

wherein it is cooled by indirect heat exchange with coolant such as cooling water. In the embodiment of the invention illustrated in the FIGURE, cooling water

29

is provided in stream

30

to cooler

43

to cool the high pressure refrigerant fluid, emerging therefrom as warmed cooling water

71

. Another portion of cooling water

29

is provided in stream

32

to provide cooling to thermoacoustic engine

20

, emerging therefrom as warmed cooling water

72

.

Cooled high pressure refrigerant fluid, generally entirely in the vapor phase, is withdrawn from cooler

43

in stream

44

and passed to an expansion device, typically a Joule-Thomson valve

45

or a throttle valve. The refrigerant fluid is expanded by passage through the expansion device thereby generating refrigeration, and is passed out from the expansion device as refrigeration bearing refrigerant fluid

46

which typically has a pressure within the range of from 10 to 200 psia and has a temperature within the range of from −40° C. to 15° C. Generally the refrigeration bearing refrigerant fluid in stream

46

is in two phases, a liquid phase and a vapor phase. Refrigeration bearing refrigerant fluid

46

is provided to heat exchanger or evaporator

47

wherein it is warmed and the liquid portion vaporized by indirect heat exchange with a heat load thereby providing refrigeration to the heat load. In the embodiment of the invention illustrated in the FIGURE, the heat load is a fluid stream

73

provided to heat exchanger

47

which emerges therefrom as refrigerated fluid in stream

74

. The refrigerated fluid may be used in any suitable application, such as for example, for food freezing, industrial cooling or air conditioning.

The warmed refrigerant fluid from heat exchanger

47

is passed in stream

48

to absorber

49

. Absorbent fluid in stream

55

is cooled in secondary heat exchanger

53

, passed in stream

56

to valve

57

and then as stream

58

into absorber

49

wherein it mixes with refrigerant fluid provided therein in stream

48

to produce reconstituted heat pump solution wherein the refrigerant fluid in vapor form is absorbed by the absorbent. The heat of absorption is removed by indirect heat exchange with cooling fluid, typically water, which is provided to absorber

49

in stream

75

and removed therefrom in stream

76

.

The reconstituted heat pump solution is withdrawn from absorber

49

in stream

50

and increased in pressure by passage through a compression device, such as liquid pump

51

, to a pressure within the range of from 20 to 500 psia to form high pressure heat pump solution

52

. The high pressure heat pump solution

52

is warmed in secondary heat exchanger

53

by indirect heat exchange with the aforesaid cooling absorbent fluid in stream

55

. The resulting high pressure heat pump solution is withdrawn from heat exchanger

53

as stream

54

for passage to refrigerant generator

41

and the absorbent heat pump refrigeration cycle begins anew.

A simulation of the refrigeration system of this invention was carried out in accord with the embodiment illustrated in the FIGURE, and the results of the simulation are presented in Table 1. The numerals in Table 1 correspond to those of the FIGURE. In the saturated conditions were assumed for streams

44

,

48

,

54

and

55

and pressure drops were neglected. The flows were based on the production of one ton of refrigeration. The heat pump solution comprised water as the refrigerant and a lithium bromide-water mixture as the absorbent. The example of the invention reported in Table 1 is provided for illustrative purposes and is not intended to be limiting.

TABLE 1

Mix, x

Temp

Flow, m

Press. P

Lb LiBr/lb

Stream

° C.

Lb/(hr) (ton)

psia

mix

22

104

15.78

17.2

—

36

104

15.78

17.2

—

41

93

—

24.1

—

42

93

0.198

24.1

0.00

44

38

0.198

24.1

0.00

46

4

0.198

3.1

0.00

48

4

0.198

3.1

0.00

50

38

2.580

3.1

0.60

52

48

2.580

24.1

0.60

54

82

2.580

24.1

0.60

55

93

2.380

24.1

0.65

56

56

2.380

24.1

0.65

58

2.380

3.1

0.65

Although the invention has been described in detail with reference to a certain preferred embodiment, those skilled in the art will recognize that there are other embodiments of the invention within the spirit and the scope of the claims.