US2408802A

US2408802A - Absorption refrigeration cycle

Info

Publication number: US2408802A
Application number: US313858A
Authority: US
Inventors: Glen W Miller; Edward L Kells; Delmar H Larsen
Original assignee: Individual
Current assignee: Individual
Priority date: 1940-01-15
Filing date: 1940-01-15
Publication date: 1946-10-08
Anticipated expiration: 1963-10-08

Description

Oct. 8,1946. e; w. MILLER EI 'AL 2,408,802

ABSORPTION REFRIGERATION CYCLE 2 Sheet s-Sheet 1 Filed Jan. 15, 1940 ATTORNEY 1946- e. w. MILLER El'AL I 2,408,802

, ABSORPTION REFRIGERATION CYCLE Filed Jan. 15, 1940 2 Sheets-Sheet 2 WEN R ATTORNEY Patented Oct. 8, 1946 ABSORPTION REFRIGERATION CYCLE Glen W. Miller, Glendale, Edward L. Kells, Montrose, and Delmar H. Larsen, Los Angeles,

Calif.

Application January 15, 1940, Serial No. 313,858

9 Claims. (Cl. 62-119) This invention relates to the art of absorption refrigeration, and embodies a new and useful type of absorption cycle using new combinations of absorbent and refrigerant.

One of the objects of the invention is to provide a new cycle in that low boiler temperatures are thereby made possible.

Another object is to provide ameans of using refrigerant-solvent combinations otherwise unutilizable because of relatively high solvent Volatility.

Another object is to disclose several novel retion. These are illustrated in the accompanyingv drawings where- Figure 1 is a diagrammatic drawing of the cycle in which the transfer of fluid is effected by an internally energized pump.

Figure 2 discloses the invention as applied to a three fluid, or diffusion absorption cycle.

In absorption refrigeration systems, the refrigerating effect is produced by the evaporation of a liquid refrigerant by allowing it to expand from a pressure greater than its vapor pressure at cooling water temperature to a pressure less than its vapor pressure at the refrigerating temperature. In order to re-cycle the refrigerant, it is absorbed into a liquid of high solvent power; thus dissolved, it is pumped to the higher pressure and driven from the solvent by heat. The function of the solvent is thus to reduce to a minimum the mechanical work necessary in bridging the low and high pressure sides of this system, since the volume of the refrigerant as pumped is reduced. The remainder of the necessary energy used to drive the refrigerant from this solution can then I ammonia and water boiling points differ by 240 I deg. F. However, by the method of refrigeration which we disclose herein, it is possible to use combinations of refrigerants and solvents wherein the difference in boiling points is much less than 240 deg. F. and which difierence may be as low as 91 deg. F. and is preferably not more than deg. F. In order to utilize these combinations efficiently, it is necessary when heat is applied to the refrigerant-solvent combination to secure a separation into a relatively pure solvent return and a relatively pure refrigerant return, This is accomplished by the substitution of a fractionating tower for the usual boiler and analyzer, wherein the solution passes preferably into the fractionating tower at a point wherein the liquid present in the fractionating tower has approximately the same composition and temperature as the solution from the absorber and applying heat to the solvent.

It has always been recognized that a really effective solvent should be quite non-volatile with respect to the refrigerant in order that the separation of the two by the applied heat may be as complete as possible. For example, the combination of ammonia with water is commonly used; water with sulphuric acid; and gaseous chlorofluorohydrocarbons with high boiling organic solvents of the plasticizer type are combinations which have also been employed. In all of these, there exists a sufiicientlylarge difference in volatilities that simple heating suffices to drive enough refrigerant in a relatively pure state from the refrigerant-solvent elllux of the absorber to continue the operation of the cycle.

The apparatus usually employed to separate the refrigerant from the solvent-refrigerant mixture consists of a container wherein heat may be supplied to the introduced mixture, whereby some of the refrigerant therein is driven off. Often a few entrainment plates, comprising what is known as the analyzer, are placed above the boiler, and sometimes a so-called dephlegmater, a partial condenser, is placed above the analyzer. However, these last two devices serve principally to enrich the refrigerant, and have only a relatively small enriching efiect upon the solventrefrigerant mixture in the boiler, which is generally drawn off for re-cycling from the same container which it enters from the absorber.

It has generally been considered that the re frigerant and solvent must differ greatly in volatility in order that the former may be readily driven off from the latter in the still, as has been mentioned. For example, the boiling points (at atmospheric pressure) of ammonia and water differ by 240 deg. F. This great difference enables the ammonia driven ofi to be relatively anhydrous, but if ammonia-free water were desired to issue from the boiler, it would require for the usual cooling water temperature available, a boiler temperature in the neighborhood of 390 deg. F. Accordingly, in the usual ammoniawater absorption machine, the solvent returned to the absorber contains in the neighborhood of 20% ammonia. The present invention comprises, aside from features mentioned hereinafter, a means of securing both low boiler temperatures and pure solvent return, in that a solvent is chosen having a boiling point (at atmospheric pressure) not to exceed by more than 150 deg. F. that of the refrigerant, and in that both refrigerant and solvent are obtained in a relatively pure state by the substitution of a fractionating tower for the usual boiler and analyzer. It is also highly desirable that the low side pressurethat is, the pressure prevailing in the absorberbe not excessively low, say not less than lit/sq. in. abs., as otherwise in practice it becomes virtually impossible to maintain'the system free from air filtered in through leaks in the system. To be sure, so-called-difiusion machines have been constructed which employ an inert gas to build up the-total pressure in the low pressure side of the apparatus, but many complications are thereby introduced which'make it highly desirable from a practical standpoint to dispense with the use of-an-inert gas whenever possible.

Intwo fluid absorption machines a pump is commonlyemployed to circulate th refrigerant rich'solventfromthe absorber through the heat exchangers against the pressure in the separating means. To cause such a circulation requires that thepump impress upon the refrigerant rich liquid from the absorber a pressure substantially greater than the pressure in the separating'means'. This pump is driven by external energy, such as an electrically operated motor. Such a pump, however, has the disadvantage of complex packing glands which may leak-and also it requires high grade energy to drive it. There is much to be gained in making the machine self -contained and independentof this external-source of energy. This is done in somemachines by th introduction of a third fluid to balance the pressure throughout, the refrigerant expanding and'condensing due to differences in partial pressure. In other machines automatic valve systems operate at intervals toequalize-thepressure in part of the system, thus allowinganaccumulation of the refrigerantrich solvent to fiowby gravity into-the separating means. Three fluid machines have not, as yet, proven very efiicient and machines with equalizers lose due to wasted refrigerant richvapor for pressure equalizing.

Wepropose to, utilize a pump which is energized-by vapor fromthe separating means and which operates whenever a quantity of refrigerantrich solvent liquor from the absorber has accumulated. flhiseliminates the necessity of an external source of energy, gives continuous operation and rids the machine ofpany packing glands. Used in a machine with a customary generator as the separating means this device should be slightly less eflicient than the pressure equalizing devices but affords great advantages in allowing the use of an adequate heat exchanger between the absorber and separating means. However the vapor driving the pump, just as the vapor needed to equalize the pressures, would be largely refrigerant vapor, or at least the vapor that ordinarily goes to the rectifier and thus much refrigerant would be returned to the absorber without being expanded in the evaporator and usefully absorbing heat. If, however, as is proposed'here, suchaproposed pump is used in connection with a fractionating tower, it is apparent that substantially pure solvent vapor is available near the base of the tower and can be used to drive the pump. This vapor can then be exhausted into the absorber without a loss of refrigerant, the only loss being the heat necessary to do the pumping and a, slight increase in the heat abstracted by the cooling coil in the absorber. It is also apparent that this solvent can then perform its normal function. This would cause a slight decrease in the efliciency, but it would be only a fraction of the loss caused by using vapor which contained considerable refrigerant and .would of course be operatively much cheaper than an externally energized pump, as in general heat energy is the cheapest available.

No details of the proposed pump are included as it is obvious that a common pump of the double piston, duplex boiler feed type would operate and that numerous developments of this type and the diaphragm types could be used. Thus the novelty does not reside in the pump but in the means employed in supplying energy thereto.

There follows a list of refrigerant-solvent combinations which not only meet the requirements specified above, but which are individually new in themselves, and have been moreover chosen to represent combinations highly useful from the practical standpoints of temperatures and pressures involved and chemical stability. There is given for-each combination the difference in boiling points, the condenser and evaporator pressures, maximum boiler temperatures, and theoretical minimum energy ratios (ratio of total heat input to total useful refrigerating effect, both in. heat units, vallowing a.20% stack loss in heat input to boiler).

Table I S l e R 32 3:; Refrigerant Solvent BS 122 Bf it g 31922? g-l 1 atmos. '1' atmos Ftcond.

F. F. F. F. 1 Freon 12, C012]? Carrene, CHaCli..- 103.7 21.7 125.4 233 2.10 2 d0. Freon 113, CzClgF; 118 -21. 7 139. 7- 265 l. 85 3 do D-48, CzHzClzw 1 18 21. 7 139.7 263 2.00 5 Methyl chloride, CHgCl. Carlene, CHzClz... r 103.7 11 114. 7 220 2. 30 6.. .do Freon 113, CzChF: 118 .11 129 253 1. 72 7 do D-48 118 11 129 2 55 1.80 8 do 133 11 144 265 1. 73 9. Freon 114, CCl2F4. d 133 42 V 91 197 5. 65 1o. o C01. 170 42 12$ 235 2.83 l1 ..(l0 Trichloro ethylene, 166 42 12 1 218 2.85

CQHC I I 4 13 Freon 21, CHCIzF CCh 170 48 122 225 2.40 14 do Trichloro ethylene, 166 48' 118 213 2.35

C2HC13. 16 Ethyl chloride, CzH5C1. C014 h... 1'70 54 116 218 2.67 17 do Trichloro ethylene, 166 54 112 299 2.50

C2HC13. Freon 11, 00131? "(10,. 166 74. 7 91.3 188 4.0 21 SO, Acetone C3H6O 154 14 255 1.50 22 -.do Methylacetate, CzHaOz. .135 .14 121 248 1.43

It is to be noted that those combinations shown above which comprise for both refrigerant and solvent halogenated hydro-carbons having fewer than three hydrogen atoms and at least one fluorine atom are particularly desirable for use because of low toxicity and great chemical stability. Such compounds are in use as refrigerants, but we propose to use them as well for solvents. h I

In the disclosure and claims of this application, the terms 11-48 and D-60 refer, respectively, to the trans and cis forms of dichloroethylene. They are known as such commercially'since their boiling points on the centigrade scale are, respectively, 48 and 60", although their chemical formulae are the same.

The manner of use of these novel combinations may be seen by reference to the figures and .to the explanations thereof which follow,

In Figure 1 the evaporator receives the liquid refrigerant, which evaporates at the low pressure, thereby absorbing heat from the medium to be cooled in coil H or from the surrounding medium. Arrow I2 indicates heat input to the cycle. From the evaporator the gas is conducted by pipe may again by suitable means be taken up by the solution from the absorber. It is understood that heat may also be conserved at other points in the system where desirable and possible. The refrigerant-rich gas is carried from the tower l9 by means of the pipe 29 to the condenser 30, cooled-to condensation by the coil 3l or the sur rounding medium, and the arrow 32 indicates heat out of the cycle. The liquid from the con-' denser is piped to the evaporator H] by the pipe 33, in which there is interposed a flow controlling means 34. The entry of the solvent into the absorber is regulated by the flow controlling means 35. I

The pump 36 may be a well known unequal area double-piston duplex pump which is actuated by solvent vapor through pipe 31 emitting I from the point 38 in the tower I9, which point is i3 to the absorber [4, which is of a suitable type with means of introducing solvent therein through the pipe l5 and the rose I6. In the absorber the refrigerant vapor is absorbed into the solvent. A fin tube coil I! represents means to remove the heat in the solvent and the heat produced by the absorption of the refrigerant into the solvent. Arrow l8 shows that at this point heat is being taken out of the cycle.

The solution is returned from the bottom of the absorber M to the fractionating tower [9 by means of the pipe 20, wherein there is-interposed pumping means 36, which maybe an unequal area, double diaphragm pump, An ordinary motor driven pump may be substituted. The solution passes through the heat exchanger 22, whereby there is effected a heat exchange between the relatively pure solvent in pipe I5 and the refrigerant-rich solution in pipe 20. The solution heated in this manner passes into the fractionating tower H] at the point 23, which is that point at which the liquid present in the fractionating tower has approximately the same composition, or preferably composition and temperature, as the solution from the absorber. Other points may be chosen, but are less effective.

In the fractionating tower Hi there is mutual contact throughout the length of the fractionatbetween the fractionating section of the tower and the liquid level in the still thereof. The vapor passes from the pump 36 by the pipe 39 to the absorber. The pump 36 is adapted to utilize the pressure difference prevailing between the point 38 and the absorber, and is of sufficient power to force the refrigerant-rich solution from the absorber through the heat exchanger and into the fractionating tower, Check valves 2| and 2! control the flow of the solution. It is evident that there will be more than enough energy available to carry out the transfer of solution from the absorber because the volume of solvent available as vapor can be many times the volume of liquid solvent and refrigerant which must be returned to the tower l9. The solvent vapor is exhausted from the pumping means into the absorber in addition to the bulk of the solvent arriving there directly in the liquid state.

Figure 2 shows in diagrammatic form an absorption'refrigeration system, likewise adapted to ing portion thereof between liquid passing downward and vapor passing upward, whereby the former becomes enriched in solvent and the latter becomes enriched in refrigerant, Liquid for the upper portion of the tower is provided by the partial condenser 24. Heat to the fractionating tower is supplied by suitable means such as the burner 25, which heats the substantially pure solvent which is in liquid form in the bottom of the tower l9.

It will be noted that the solution for the absorber is drawn off from the bottom of the fractionating tower and consists of substantially pure solvent. At the same time the efflux from the top of the tower consists of substantially pure refrigerant. The fractionating portion of the tower I9 is packed with helices or Raschig rings, or the like, or may be provided with bubble plates. These helices or equivalents are indicated by the number 26.

The arrow 28 indicates heat into the cycle and arrow 2'! indicates heat out from the cycle, which the use of the combinations hereinbefore speci fied as forming part of this invention, and in which system an inert gas is used to obviate the necessity of a pumping means. In this system the fractionating tower 40 operates precisely as in the systems shown in Figure 1, with the exception that a vapor lift pump shown at 4| serves to lift the solvent through a riser 42 into a standpipe 43, in order that sufficient head'may be supplied to cause the solvent to flow by gravity through the heat exchanger 44 into the absorber 45. The vapor used to perform the lift returns to the base of the tower just above the liquid level therein through the connecting tube 46. As in the previously described systems, the substan: tially pure refrigerant from the top of the tower passes through the condenser 41, whence it passes through liquid seal 48, into the evaporator 49, wherein evaporation takes place and the gaseous refrigerant passes through the heat exchanger 50 into the absorber 45. From the point at which refrigerant vapor commences to liquefy in the condenser to the liquid level in the absorber, there exists an inert gas, such as for example, helium, the partial pressure of which is everywhere equal to the difference between the partial pressures of the refrigerant (plus that of the solvent) and the total pressure in the system. The inert gas carried to the absorber by the flow of refrigerant vapor thereto is returned to the top of the evaporator 49, circulation taking place because of the difference in density between the refrigerant laden inert gas and the inert gas freed from refrigerant by the solvent in the absorber. A gas heat exchanger 50 serves to lower the temperature of the inert gas returning to the evapo- .6. Theprocess ofabsorption refrigeration comprisingcireulating arefrigerant through an evaporator, absorbing the vaporized refrigerant in a solvent and forming an enriched liquor, introducing the enriched liquor into a fractionating towerfland therein separating the refrigerant and solvent by fractionation, passing liquid solvent from the tower to the absorber in indirect heat exchange with the enriched liquor, and separateset forth.

The following systems may be also used but ly;passmg 23 2 under g f from suffer from the disadvantage of too high a difer r V ng pump fer-ence in boiling point. In some cases they may mg means h emlched quor by Such D even be used without fractionation. sage of the solvent vapor.

Table II Solvent Reirlg. I Max. boiler C bl? Diff. in Energy F. F. F. r. 4 Freon 12, 00121 2., ,D-60, C2H2Clz 133 21.'] 154.7 278 1.85 12 Freon 114,0;OhF Pertbliloro ethylene, 276 42 234 385, 1.95 Freon 21, CHOhF "310.". 27s 48 228 370 1.70 is Ethyl chloride. cursor. do 27c 54 222 352 2.37 Freon l1, OChF .do 276 74. 201.3 320 1. 75

We claim: 7. A process according to claim 6 wherein said 1. As a refrigerant-solvent combination for use refrigerant and solvent differ in boiling points by in absorption refrigeration systems, Freon 2 1 30 l t a b t 150 F, (CHClzF) asthe refrigerantand Trichloro ethyl- A process according, to Claim 6 wherein Said 6116 (0211013) as the Solvent} refrigerant and solvent are halogenated hydro- A Process of absorptlon l'efi'lgeratmn carbons and differ in boiling points by less than prising vaporizing Freon 21 (CIiClzF), absorbabout F. mg Said Freon '21 (CHCIZF) tnchloroethylerte 9. An absorption refrigerating apparatus com- (CzHCla), and separating said Freon 2 1 and mprising, in combination, an evaporator, an abchloroethyletle by fractlonaplon' sorber connected to receive refrigerant therefrom, A machme for absorptlon refngera'tmn i a fractionating tower, means including a conduit pnsmg an evaporator F- Separatmg and a pump for delivering solvent and absorbed means empmymg fractmnanon' pd charge of 40 refrigerant from the absorber to the tower, means Freonl 2i (CHChF) tncmoroethylene for actuating said pump comprising a conduit (CZHC communicating with the fractionating tower ad- The P of absorptionrefngelmtxon jacent thelower end thereof and adapted to depnsmg clrculatmg Freon (CI-I012?) through liver solvent vapor under pressure from the tower an evaporator.and to {m absorber p t the to the absorber, a conduit delivering solvent from vaporized refngerant m Solvent. conslstmg of the tower to the absorber means for producing (CFHCISL pumpmg s01? indirect heat exchange between the solvent i 1' fragttonatmg i ther'eln travelling in said conduit from the tower and the am mg t e re ngerant and ven solvent and refrigerant travelling in the conduit The f i of absorptlon refngemtlon from the absorber to the tower, a condenser, and prlslng vapol'lzmg Freqn 21 (CHCIZF) and means for delivering refrigerant from the upper sorbing the same by trichloroethylene (CZHCIs), end of the tower to the condenser and from the separating the aforesaid refrigerant and absorbon'denser to the evaporator. ent by fractionation, condensing and cooling. said refrigerant, and utilizing the separated andcon- GLEN W. MILLER densed refrigerant vapor for. extractingheat from a refrigerable material.

EDWARD L. KELLS. DELIVIAR LARSEN.