US2301839A - Ejector refrigeration - Google Patents

Description

Nov. 10, 1942. L. T. WORK ETAL 2,301,839.

EJECTOR REFRIGERATION Filed Aug. 28, 1937 2 Sheets-Sheet 1 =MOLAL RATIO OF TWO COMPONENT T0 SELF-ENTRAINMENT m Y I SECONDARY rLuws M A STEAM I8 METHANOL 52 azs l., o ETHANOL. 46 BENZENE T8 mmmesrurusue m n? a MAXIMUM waves 0 S no use 200 ii,

. 0 0 MOLECULAR WEIGHT OF PRIMARY FLUID INVENTORS'.

Patented Nov. 10, 1942 EJEQTOR. REFRIGERATION Lincoln T.

Work, New York, N. Y., and Vincent W.

Haedrich, Wilmington, Del.

Application August 28, 1937. Serial No.161,510

11 Claims.

This invention relates to an ejector refrigeration process.

An object of this invention is to obtain greater heat efficiency in the operation of an ejector refrigeration process than is now obtainable in similar processes known to the art.

Another object of this invention is to provide an ejector refrigeration process which may be operated at low cost per unit of refrigeration.

Other objects and advantages of the invention will be in part apparent and in part pointed out in the following description.

These objects are attained by providing in the well known ejector refrigeration process an advantageous combination of secondary or evaporator fluid with primary or boiler fluid. The results attainable by the process may be obtained or may be augmented by providing in the process a step whereby the zone into which the ejector discharges is kept at a low pressure to increase the efliciency of operation. Numerous specific examples embodying the principles of this invention will be given hereinafter.

The ejector refrigeration process as known includes essentially aspirating vapors from above a confined body of secondary fluid by employing an ejector, the suction side of which is in communication with the vapors .of the secondary fluid. Removal of vapors of the secondary fluid permits further evaporation of the fluid which abstracts heat from the medium confining the fluid to produce refrigeration. The ejector is operated by passing vapors of a primary fluid through the jet of the ejector to an exhaust or discharge zone, the passage of the primary va- I ejector, mingled with the vapors of the primary fluid and discharged from the ejector.

Known processes'have usually employed water as the secondary fluid and steam as the primary fluid, or ammonia as both refrigerant and. propellant. We call such processes wherein the same fluid is used in both the evaporator as secondary fluid and in the boiler as primary fluid self-entrainment processes. Sometimes the known processes have used a primary fluid differing from the secondary fluid, and such processes we call two-component processes. We have discovered that an ejector does not operate at maximum efiiciency using a self-entrainment process and that, of the two-component processes known to us, none yields optimum efficiency or closely approaches it when using secondary fluids of relatively high molecular weight, while some actually yield a lower emciency than if a corresponding self-entrainment process were employed.

When we compare the efficiency of a two-component process with the efllciency of a self-entrainment process, we do so on the basis of the same secondary fluid in both instances- We have found that great improvement over self-entrainment is to be gained when using a secondary fluid of low molecular weight together with a properly selected primary fluid. Greatest efliciency is to be obtained by selecting a secondary fluid having a molecular weight of about or less and a primary fluid having a molecular weight of from 1.25 times that of the secondary fluid to a value of about 131.

The nature of the two fluids chosen may also be such that at the temperature of condensation existing in a confined exhaust zone the vapor pressure of the mixed condensate is lower than the vapor pressure of the secondary fluid alone at the same, temperature. In this way, efliciency is increased over a' corresponding self-entrainment process. Also auxiliary scrubber fluids may be used in a conflned exhaust zone which lower the effective vapor pressure of the mixed condensate and scrubber fluid to increase efilciency.

In the drawings,

Fig. 1 is a graph illustrating the appropriate combinations of boiler and evaporator fluids which may be used to secure the advantages of the invention, and Figs. 2 to 4 are diagrams showing apparatus suitable for carrying out the process of this invention.

In Fig. 1, the abscissa represents the molecular weight of the primary fluid, while each of the solid curves terminating at the right in dotted lines represents a secondary fluid of a given molecular weight. The ordinate is a fraction expressing the ratio of the number of mols of a given secondary fluid entrained in unit time by a primary fluid to the number of mols of the same secondary fluid entrained in unit time under like conditions of operation when the secondary fluid is also used as primary fluid. In other words, it is the molal ratio of entrainment of two-component operation with respect to corresponding self-entrainment operation. The dotted line intersecting the curves is thelocus of maximum entrainment improvement, and the molecular weight of a primary fluid which will give optimum efficiency with a given secondary fluid corresponds to the intersection of this curve of maxima with the solid curve for said secondary fluid. The molecular weight of the primary fluid is read off of the horizontal scale. For example, the curve of maxima intersects the steam curve at a horizontal scale reading of about 60. Thus, the ideal primary fluid for use with steam as secondary fluid should have a molecular weight of about 60. Propyl alcohol with a molecular weight of 60.09 satisfies this requirement.

In using secondary fluids having a molecular weight of 50 or less great improvement in entrainment efliciency, which means a corresponding improvement in refrigeration in the ejector refrigeration process, may be obtained by selecting as a substance for aspirating said secondary fluid a primary fluid having a molecular weight at least 1.25 times the molecular weight of the secondary fluid and not greater than 131.

We have found that the invention is independent of specific ejector design, and the efliciency improvements may be obtained irrespective of the ejector used.

Factors such as boiling points of fluids, latent heats, vapor pressure, miscibility of the fnixed vapors from the ejector when condensed, etc., will be considered by the skilled engineer in the selection of particular primary and secondary fluids.

The following examples are given by way of illustration. They are not to be considered as limiting the scope of the invention defined in the appended claims.

Type 1.--Simp1e systems taking advantage of favorable molecular weight ratios.

Examination of the efliciency diagram in Fig. 1 shows that for a given set of pressure relations, water may best be entrained by a fluid of molecular weight 60; methanol by a fluid of molecular weight '78; and ethanol by a. fluid of molecular weight 100. It further shows that the greatest improvement can be had by a light molecular weight fluid such as water, or ammonia, Unfortunately, pressure conditions cannot be rigidly duplicated with different fluids operating at. the same desired temperature: however, some improvement may be effected, as will appear from consideration of two cases of this type as follows:

(a) Separable after condensation. The following boiler fluids butane (molecular Weight 58), pentane ('72), butanol (74), benzene (78), methylene chloride (85), toluene (92), chloroform (119) butyl ether (130), and diphenyl (154) may be used with water (18) or with aqua ammonia (1'7-18), depending upon the vapor pressure curve of the boiler fluid as shown later, with an improvement from to 70% over analogous conditions of operation of the steam-steam or aqua ammonia self-entrainment systems. In order to operate this type of system the boiler fluid is evaporated and passed through a jet to entrain the evaporated fluid as it vaporizes. The two fluids are separated after condensation and returned to their respective chambers.

(b) Miscible after condensation. In this case the boiler fluid and the evaporator fluid are dis-- solved in each other after condensation. A marked improvement may be had if the vapor pressure of the boiler fluid at condenser temperature is appreciably lower than that of the refrigerant, because dilution of the refrigerant by the boiler fluid will then give a reduction in vapor pressure of the refrigerant mixture with a resulting favorable compression ratio and a correspondingly better entrainment ratio. This type,

however, presents the problem of external separation which can be performed by distillation. salting out, freezing, or the like.' The following cases are illustrative of suitable molecular weight ratios for improved conditions:

Boiler fluid Evaporator fluid Improve I ment in entrainment based on Name M. W. Name M. W. M. W.

ratio only Benzene 78 Methanol 32 35 Ethylene glycoL--. 62 18 65 N-propylalcohol 60 18 65 Diphenyl 154 58 12 Aqueous methyl 3i Aqua ammom 17 50 amino. Water 18 do 17 15 Diethyl amine 73 Methyl amine 31 35 Cargo): tetrachlo- 154 Methyl chloride... 5O 15 n e. Ethanol 46 Aqua ammonia 17 Aqueous ethyl 45 ,do 17 70 amine.

In the operation of these systems the boiler fluid is passed through the jet to entrain the anol may be separated by water washing, the

water remaining in the evaporator until the methanol had largely distilled and then'returning the water to the condenser to efl'ect a separation. One system in particular stands out and that is the case of the amines. By using as a boiler fluid an aqueous solution of methyl amine or ethyl amine and a more volatile evaporator fluid, such as aqua ammonia, it becomes possible to condense the mixture, including such water as may. pass over; to place the condensate first in the evaporator for removal of ammonia, and then into the boiler for removal of amine. After the amine has been stripped in the boiler, the water may .be moved to the condenser to act as an absorbing fluid, thereby lowering the vapor pressure and effecting a material improvement in the efliciency of the system. While an absorbing action takes place with the ammonia and amines in water, the actual conditions do not give scrubber benefits because in this case we convey the ammonia water from the condenser to the evaporator and it quickly becomes depleted in ammonia, making it necessary to utilize a greater pressure difference between the entrainment pressure and the exhaust pressure than is the case with pure fluid. One more s; stem of particular interest is the steam-aqua ammonia system which may be operated in very much the same manner as the amine system; namely, that the aqua ammonia from the condenser is passed to the evaporator for reduction in ammonia content and is .then passed to the boiler for evaporation primarily as water.

Fig. 2 represents diagrammatically an apparatus for carrying out the process of the ammoniaamine system. The boiler I, heated by burner I 0, contains an aqueous solution of an amine. Vapors of the amine are boiled off from the solution and pass under pressure through conduit 5 to the ejector 4. Conduit 5 is provided with a valve 4|. These amine vapors serve to operate the ejector to create a vacuum in the line I [leading'from the evaporator 2 to the suction side of the ejector. Line llv is provided with a valve 43.

The evaporator contains an aqueous solution oi ammonia plus some amine in solution; and the more highly volatile ammonia evaporates from the solution to produce a chilling effect therein. The mixed vapors of ammonia and amine pass from the ejector through the conduit 6 to the scrubber-condenser 3 where they come in contact with lean liquid taken from the boiler I through conduit 9, provided with valve 42, and cooled in heat-interchangeri2 before introducing it into the scrubber-condenser 3. This cooled boiler liquid serves to condense and absorb the mixed amine vapors in the scrubber-condenser, and to form a solution of these vapors. This solution is passed through pipe I to the evaporator where the more volatile ammonia is vaporized to produce cooling. The liquid in the evaporator contains a proportion of amine, and some of this amine-containing evaporator fluid is passed to the boiler through pipe 8, where it is stripped of its amine content. These amine vapors are recycled through the ejector, as has been described. Heat interchanger I2 serves to preheat the cool liquid going from evaporator to boiler through line 8, and, at the same time, to cool the boiler liquid going to the scrubber condenser through line 9. Suitable liquid pumps 44 and II are provided to move liquid through line I, from scrubber condenser 3 to evaporator 2, and through line 8, from evaporator 2 to boiler I, respectively.

Type 2.-Systems taking advantage of low con densation pressures as well as favorable molecular weight ratios.

(a) Simple absorber.In the case of the steam-steam system, a scrubber fluid may be passed into the condenser so that the condenser water will be dissolved in it to form a solution with lower vapor pressure. Washing the condenser with ethylene glycol, or with strong salt solution, will attain 'this objective.

Still greater improvement may be made under other conditions. The absorber fluid may be reconcentrated by evaporation in a spray toweror in a boiler, for re-use as an absorbent. If a substance such, for instance, as isobutyric acid is used as absorber fluid, the two phases (i. e., boiler fluid and absorber fluid) are miscible at condenser temperature and are separable by the use of a limited amount of cooling, e. g., to 35-40 F., into isobutyric acid-rich and waterrich layers. The scheme is particularly useful where the boiler fluid separates as a liquid of low vapor pressure and the scrubber liquid need only reduce the vapor pressure of the evaporator 'fluid. Many other schemes may be conceived, as where water is used to scrub ammonia or amine.

Fig.3 illustrates one form of apparatus suitable for carrying ou a scrubbing process in he condenser whereby to lower the pressure therein. In Fig, 13, I3 represents a boiler, M an evaporator, and 15 a scrubber-condenser. An aqueous solution of ethylene glycol, for example, is used in the boiler. Under the influence of heat supplied by burner l6, water principally is evaporated from the boiler, and this steam passes by w"y of pipe I! to the ejector l8 to operate the,;,-

same. The loss of water from the liquid in the water from the evaporator ll through pipe 20 which leads from the evaporator to the suction side of the ejector. The liquid used in the evaporator is water in this case. The concentrated glycol entering the scrubber is diluted therein by the water vapor entering through pipe 2|. The diluted glycol is conducted back to the boiler through conduit 22. The rich glycol passing from boiler l3 through line l9 and the lean glycol returning to the boiler through line 22 are passed in heat exchange relationship through heat interchanger 23. Lines [1, 20 and i9 are provided with valves 46, 41 and 49, respectively. A pump 48 is provided in line 22.

An ofi-take 24, provided with valve 25, is used to bleed excess water from the system in the form of steam, while make up water is supplied tothe evaporator through pipe 26 from a source of water, not shown. Or the steam taken 01! at 24 may be condensed, cooled, and reintroduced into the evaporator through pipe 26.

(b) Simple absorber in which boiler fluid serves as absorbent. Taking the case of isobutyric acid cited above, it would beuneconomical to reject the water containing isobutyric acid-- hence the isobutyric acid-rich layer may, be returned to the boiler. In this case there is a favorable molecular weight ratio, as some of the isobutyric acid distills, making the boiler fluid heavier in effective molecular weight. The residual isobutyric acid, low in water content, may be passed to the condenser for dilution of the condensate. Obviously, little is to be gained in this way by adding a diluted condensate to the evaporator, for thenthe evaporator fluid would be lowered in vapor pressure and an unfavorable pressure ratio would develop,

( Special absorbent for separation of two.

'two components are miscible on condensation,

but they may be separated by the use of a salt solution such as potassium chloride. The salt layer containing water and some propyl alcohol is sent to'theievaporator while the propyl alcohol containing some water is sent to the boiler. Both boiler and evaporator fluids may be returned to the condensate to utilize their saltvalues for separation.

(e) Separation by distillation utilizing heat of the distillation. In certain systems such as pyridine-methanol 'where molecular weight ratios are favorable, the condensate may best be separated by distillation. It is sent to a high-pressure boiler from w'hich'the vapor is conveyed to a high-pressure condensing coil within the ystem boiler. The vapor is condensed there under high pressure, causing boiling of the primary fluid and is itself then cooled for admission to the evaporator. The residue in the still boiler is transferred to the system boiler where it flash evaporates and is boiled away to cause the ejector to operate. This type of condensation also utilizes the values of reduced vapor pressure bcyond the jet.

Special comb nation systems Numerous combinations of systems may be used. The following types will illustrate and present system desirable from the molecular weight point of view.

(a) High boiling heavy boiler fluid condensation heat to cause boiling.

As an adjunct to the ammonia absorption system.

In this system there is usually a residual pressure of 30-40 lbs/sq. in. after the ammonia is evaporated and before it passes to the absorber. We utilize a portion of this ammonia for a special absorber and pass the other portion through an ejector where it causes evaporation of the ammonia from this special absorption step. The ammonia is then merged to go to the absorber which feeds the regular boiler. In this way the residual ammonia adds up to about 50 percent of the capacity of the absorption system.

The apparatus, diagrammatically illustrated in Fig. 4, shows a refrigerator using the principles of the present invention in connection with an ammonia absorption system.

The usual ammonia absorption system comprises a primary evaporator 21, a primary absorber 28, and a boiler 29. ,In operation of this known system, liquid ammonia is vaporized in the primary evaporator 21 to produce cooling; the vapors of ammonia are then passed to the primary absorber 28, where they are dissolved in a solvent, usually water. The resulting solution of water is then conducted, through line 54 provided with pump 55, to the boiler 29. In boiler 29 the solution of ammonia is fractionated into a depleted boiler liquid and ammonia gas; the latter is withdrawn from boiler 29 through conduit 56, is cooled and condensed in ammonia condenser 51, and thence passed through line 58 to primary evaporator 21. The depleted boiler liquid is with- 'drawn from the boiler through line 59, is cooled in cooler 60, and thence passed through line 6| to primary evaporator 21 to undergo smother cycle.

As an adjunct to this system, we provide a secondary absorber 30, a secondary evaporator 3|, and an ejector 32 to obtain an additional cooling eflect from the ammonia gas from the primary evaporator, which gas usually leaves the evaporator under a pressure of 30-40 lbs/sq. in.

Gaseous ammonia under pressure' is present in conduit 33 leading from the primary evaporator. This ammonia is split into two portions which are led into pipes 34 and 35 which are provided with valves 50 and 5|, respectively. Pipe 34 conveys a portion of the gas into the secondary absorber 30 wherein it forms a solution of ammonia (preferably a water solution). This solution is then transferred by pipe 36 to the secondary evaporator 3| through cooler 31, which is used to cool the solution when necessary. Pipe 38, provided with valve 52, connects the secondary evaporator to the suction side of the ejector 32, which is operated by that portion of the gaseous ammonia conducted through pipe 35 from the primary evaporator. In the secondary evaporator the aqueous solution of ammonia is caused to give up the greater proportion of its ammonia which is carried through pipe 38 to the ejector where it merges with the ammonia actuating the ejector. Thus, cooling is produced in the evaporator, which is added to the cooling produced by the primary evaporator resulting in an increased output for the system as a whole. Depleted solvent from the secondary evaporator is recycled to the secondary absorber through duct 39 provided with pump 53.

The gaseous ammonia from the ejector is led through pipe 40 to the primary absorber 28 where it is taken up in the absorbing liquid, fractionated in the boiler 29, andreturned to the primary evaporator, as has been described above in connection with the explanation of the usual ammonia absorption system.

We claim:

1. The process of refrigerating which comprises passing vapors of a primary fluid under pressure direct to a condenser through an ejector having its suction side communicating with a confined body of secondary fluid having a molecular weight of less than about 50, said primary fluid having a molecular weight at least 1.25 times that of said secondary fluid and not greater than 131, and thereby aspirating vapors of said secondary fluid to effect evaporative cooling in said body of secondary fluid, condensing the mixed vapors from the ejector in said condenser, said secondary fluid having a vapor pressure at the temperature of condensation greater than the vapor pressure of the condensed mixed vapors at the same temperature.

2. The process of refrigerating which comprises passing vapors of a primary fluid under pressure to a condenser through an ejector having its suction side communicating with a confined body of secondary fluid having a molecular weight of less than about 50, said primary fluid having a molecular weight at least 1.25 times that of said secondary fluid and not greater than 131, and thereby aspirating vapors of said secondary fluid to effect evaporative cooling in said body of secondary fluid, and condensing the mixed Vapors from the ejector in the condenser in the presence of an absorber fluid which, in admixture with the condensed mixed vapors from the ejector has a vapor pressure, at the temperature of condensation, lower than the vapor pressure of the secondary fluid alone at the same temperature.

3. The process of refrigerating which comprises generating vapors in a boiler from a primary fluid comprising an aqueous solution of an aliphatic amine having a molecular weight less than 50, passing the vapors of said primary fluid, under pressure, to a condenser through an ejector having its suction side communicating with an evaporator containing a secondary fluid comprising an aqueous solution of ammonia, thereby aspirating vapors of said secondary fluid to effect evaporative cooling in said body of secondary fluid, withdrawing a portion of fluid from the boiler and condensing the mixed vapors from the ejector in said condenser, in the presence of said fluid Withdrawn from the boiler, augmenting the secondary fluid by additions of condensate from the condenser, and augmenting the primary fluid by additions of fluid from the evaporator.

4. The process of refrigerating which comprises passing vapors from a primary fluid comprising an aqueous solution of ethylene glycol, under pressure, to a condenser through an ejector having its suction side communicating with a confined body of secondary fluid comprising water, and thereby aspirating vapors from said body of secondary fluid to effect evaporative cooling therein, and contacting the resulting mixed vapors in the condenser with a scrubber fluid comprising ethylene glycol.

5. The process of refrigerating which comprises passing vapors from a body of primary fluid comprising an aqueous solution of ethylene glycol, under pressure, to a condenser through an ejector having its suction side communicating with a confined body of secondary fluid comprising water, thereby aspirating vapors of said secondary fluid to efiect evaporative cooling in said body of secondary fluid, withdrawing a portion of the primary fluid from said body thereof and contacting the vapors from the ejector in the condenser with said withdrawn primary fluid to condense the vapors and to form a solution of the resulting condensate in said withdrawn portion of primary fluid, and returning a portion of the resulting solution to the body of primary fluid.

' 6. The process of refrigerating which comprises passirg vapors from a body of primary fluid comprising an aqueous solution of a substa ce reducing the vapor pressure of water, under ressure, to a condenser through an elector having its suction side communicating with a confined body of secondary fluid comprising water, thereby aspirating vapors of said secondary fluid to efiect evaporative cooling in said body of secondary fluid, withdrawing a portion' of the primary fluid from said body portion thereof and contacting the vapors from the ejector in the condenser with the withdrawn primary fluid to condense said vapors and to form a solution of the resulting condensate in said withdrawn portion of primary fluid, and returning at least a portion of the resulting solution to the body of primary fluid.

'7. The process of refrigerating which comprises removing ammonia vapors in contact with a confined body of liquid ammonia to effect evaporate cooling in said body of liquid ammonia, absorbing part of the ammonia vapors so,

obtained in a solvent to form a solution of ammonia, passing another part of said ammonia vapors, under pressure, to an exhaust space through an ejector having its suction side eommunicating with a confined body of said solution of ammonia, and thereby aspirating vapors from said confined body to efiect evaporative cooling therein.

8. The process of refrigeration which comprises removing ammonia vapors in contact with a confined body of liquid ammonia to efiect evaporative cooling in said body of liquid ammonia, absorbing one part of the ammonia vapors so obtained in a solvent to form a secondary solution of ammonia, passing a second part of said ammonia vapors, under pressure, through an ejector having its suction side communicating with a confined body of said secondary solution of ammonia, thereby aspirating vapors from said secondary solution to effect evaporative cooling therein, and to yield a solution depleted to some extent of ammonia, absorbing further quantities of ammonia, derived from said body of liquid ammonia, in the last mentioned solution to reform said secondary solution, passing the vapors from the ejector to a confined body of primary solvent and dissolving said vapors therein, to yield a primary solution of ammonia, fractionating said primary solution to yield ammonia and a residual primary solvent, condensing the ammonia from the fractionation" step and adding said condensate to said confined body of liquid ammonia, and adding said residual primary solvent to said confined body of primary solvent.

9. The process of refrigeration wherein a confined body of aqueous solution of ammonia as secondary flui is evaporatively cooled by aspirating vapor contact with said body through an ejector actuated by vapor derived from an aqueous solution of an aliphatic amine having a molecular weight of less than as primary fluid.

10. The process of refrigeration wherein a confined body of water as secondary fluid is evaporatively cooled by aspirating vapors in contact with said body through an ejector actuated by vapor derived from a primary fluid selected from the group consisting of propyl alcohol, isobutyric acid and ethylene glycol.

11. The process of regrigeration wherein a confined body of water as secondary fluid is evaporatively cooled by aspirating vapors in contact with said body through an ejector actuated by vapor consisting essentially of ethylene glycol as primary fluid.

LINCOLN T. WORK. VINCENT WM.HAEDRICH.

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