US2456386A - Cascade refrigeration unit with controls therefor - Google Patents

Description

Dec. 14, 1948. COOPER 2,456,386

CASCADE REFRIGERATION UNIT WITH GONTI ROLS THEREFOR Filed May 7, 1946 5 I4 17 /e 12c 2% I /5 29 v 22a 22 22 FIG. i.

FIG. 2

INVENTOR.

HOWELL 0'. COOPER Patented Dec. 14, 194e OFFICE REFRIGERATION UNIT WITH CONTROLS THEREFOR Howell C. Cooper, Sewlokley, Pa. Application May 1, 1946', Serial No. comes 2 Claims. (01. 62 115) This invention relates to low temperature refrigeration, such as employed for liquefaction of natural or other gases, of the type including means providing a plurality of refrigerant circuits in cascade relation wherein the refrigerants of ad- Jacent circuits have change of state by heat exchange therebetween, each circuit having-pump means for compression and circulation of its refrigerant.

As an object, the invention contemplates employment of positive displacement pump means, and a single motor means arranged for common drive and consequent interconnection of the pump means, with fixed speed relation therebetween, for coordinate operation of the circuits as a unit.

. 2 one responsive to a decrease in the rate of circulation in another, so as to maintain a balance between circuits and therefore maintain'operation of the complete unit. I

Specifically. for the purpose the invention contemplates bypass means about the compressor 'means of a given circuit.

and preferably about only the first stage thereof, together with automatic by-pass control to provide recirculation responsive to refrigerant pressure ahead of the corresponding compressor means.

Further objects and advantages of the invention will be apparent from the following descrip- An example of such arrangement includes a -multi-cy1inder internal combustion engine and a number of compressors driven thereby for the purpose, each compressor having positive drive directly from the engine crankshaft as by a connecting rod from one of the engine cranirs. Such engine-compressor unit is well known in the art as an angle compressor" wherein, typically, the engine cylinders are vertically disposed and the compressor cylinders horizontally disposed, all having positive interconnection through a single crankshaft common to both engine and compressor parts. One or more of the compressor units may consist of a plurality of cylinders disposed in tandem and operating'in staged relation with each other; and this invention further contemplates employment of one of such compressor units for each of the refrigerant circuits.

It will be apparent that by such arrangement, operation of the engine will cause coincident operation of all of the refrigerant circuim as a refrigeration unit, and this invention has for its principal general object, the provision or such complete unit, including properly interreiating the capacities of the respective refrigerant circuits thereof.

The advantages of such arrangement will be apparent, among which are that structurally the assembly may ice-very compact, operation of the,

complete liquefaction system follows mere operation of the engine, and "as to capacity a single unit of relatively slight capacity in the aria-say for liquefaction of a million cubic feet of natural as per day-may be perfected, and multiples of such units be employed where greater capacity is desired.

This invention, as a further object, provides means for automatically maintaining interrelai tion of the efiective capacities of the circuits, by reducing the edectiveness of the pump means of tion taken in connection with the accompanying drawings wherein: a k

Fig. 1 is a simplified flow sheet indicating the principal elements of a cascade refrigeration unit embodying the invention, and

Fig. 2 is a conventionalized plan view illustrating the structural disposition of parts indicated in Fig. l.

With reference now to the drawings, i indicates a product condenser wherein gas to be liquefied enters as indicated at A, and leaves the condenser as a liquid as indicated at B. The product gas to be liquefied may be natural gas consisting principally of methane. and the unit herein disclosed is suitable for producing the refrigeration necessary for liquefaction of such product; but it will be understood that the refrigeration might be employed for other purposes or for liquefaction of other gases.

The condenser l is served by a methane circuit whereby liquid methane is produced and boiled as a refrigerant in the condenser E for condensation of the product gas as a refrigerate.

The methane circuit includes pump means generally designated at 2 and as here indicated consisting of three stage compressor means ta, 2b,

and 20 respectively, with associated interstage coolers 2d and 2e, and afterstage cooler 21; con denser means 3, accumulator t, flash tank and the condenser i In this circuit, the methane leaves the condenser i, as a gas at low pressure in the order of 17 lbs. is compressed to 600 lbs. in the compressor 2, is liquefied in the condenser is, and regasified inthe condenser i. In the flash tank 5 a portion of the methane is allowed to regasify by reduction of its pressure and such regasified portion is returned to the compressor 2 after the first stage thereof by a connection 6 having a back pressure valve 7 set to maintain 62 lbs. The

only, and by way of example only, and all are expressed in pounds per square inch absolute.

The condenser l is served by an ethylene circuit whereby the ethylene acts as a refrigerant to iiquefy the methane in the condenser I as its rei'rlgerate. The ethylene circuit includes pump means generally designated at 12 and as here indicated consisting of two stage compressor means Ma and I2!) respectively, with associated interstage cooler I and after stage cooler lid; condenser means it, accumulator l4. flash tank II, and the condenser 3.

In this circuit the ethylene leaves the condenser 8 as a gas, is compressed to 855 lbs. in the compressor i2. liquefied in the condenser it, and regasified in the condenser 3. In its flash tank ll iii a portion of the ethylene is allowed to regasity by reduction of its pressure and such regasifled portion is returned to the compressor l2 after the first stage thereof by a connection it having a back pressure valve ll set at 82 lbs.

The condenser i3 is served by an ammonia circult wherein the ammonia acts as a refrigerant to liquefy the ethylene in the condenser 13. The ammonia circuit includes pump means generally designated at 22 and as here indicated consisting of two stage compressor means 22a and 22b with assooiated interstage cooler 22c and after cooler 22d, condenser means 23, accumulator 2t, flash tank 26. and the condenser l3.

In this circuit the ammonia leaves its condenser l3, is compressed in its compressor 22 to 250 lbs., liquefied in condenser 23, and regaslfled in the condenser it generally as in the other circuits, a return connection 2 controlled by valve 21 set at 67 lbs. being provided also generally as before.

The ammonia condenser 23 is served by water not indicated in the drawing but which water is employed to liquefy the ammonia as its refrigerate.

What has thus far been described is generally old and well known in the art, wherein it is known as cascade refrigeration and is employed for high capacity attainment of low temperatures.

According to this invention and as indicated in Fig. 2, all of the compressor cylinders of the pump means of the several circuits are driven in fixed speed relation by a single engine 30, here indicated as having eight cylinders vertically disposed in line, the compressors having their drive directly from the engine crankshaft by connection thereto, and being horizontally disposed.

By this arrangement it will be apparent that operation of the engine will cause simultaneous operation of all of the compressor elements, for coordinate operation of all of the refrigerant circuits as a unit.

Obviously for this purpose the parts, and particularly the compressor parts, are so proportioned that the effective capacities of the circuits and particularly the rates of circulation therein are suitably interrelated, each circuit designedly serving and being served without insumciency or excess of the amount of refrigerant circulating.

However, in operationsuch balance between circuits is upsettable by many contingencies such as leaky packing, a broken valve, change in water temperature, etc. I

According to this invention provision is made for automatically interrelating the effective oapacities of the circuits, bydecreasing the rate of circulation in one to balance a decrease in that of another. To this end for each circuit I provide by-pass means about the first stage of its compressor, and control flow in the by-pass responsive to pressure ahead of the by-pass stage, to automatically maintain the pressure of the refrigerant after its gasiflcation and particularly before compression thereof. Thus in the methane circuit 1 provide a by-pass connection 8 about the first compressor stage 2a, controlled by a balance diaphragm valve 8 responsive to suction pressure ahead of the compressor 2. Similarly, in the ethylene circuit I provide a by-pass it about the first compressor stage 12a controlled by a balance valve l8 responsive to pressure ahead .of the compressor l2; and in the ammonia circuit I provide a by-pass 28 about the first compressor stage 22a controlled by a balance valve :3 responsive to pressure ahead of the compressor Upon the basis of the pressures mentioned hereinbefore. each of the by-pass balance control valves 8, l9, and 29 may be set to maintain a suction pressure differential of 16 lbs. ahead of its compressor, by control of its first stage bypass.

For each circuit, control of its by-pass provides control of its efiective capacity by control of the rate of circulation of its refrigerant, opening of the by-pass decreasing the amount circulated.

For each refrigerant, control of its pressure by its balance valve effects control of its temperature at the inlet of the condenser in which it boils as a refrigerant, and therefore effects control of the anmount of refrigerate which is condensed there- The result is that in each circuit, a decrease in rate of circulation of its refrigerant will automatically follow a decrease in circulation rate in any other circuit, to maintain the entire cascade series of circuits in balance; 7

For example, consider the ethylene circuit, as aflected by a decrease in the methane circuit. Less methane delivered to the condenser 3 will cause a decrease in the ethylene pressure at the ethylene outlet of the condenser 8. This will cause opening of the ethylene balance valve is, and operation of the ethylene by-pass to correspondingly reduce ethylene circulation.

Again, consider the methane circuit, as affected by a decrease in the ethylene circuit. Less ethylene delivered to the condenser 3 will cause a decrease in the amount of methane condensed and therefore rise in methane pressure at the 'outlet of the condenser i. This will cause opening of the methane by-pass valve 9 to reduce methane circulation.

Similarly, by automatic adjustment of rate of circulation, and thus of effective capacity, of any circuit, following a decrease in either of its ad- Jacent circuits, the entire cascade system is maintained in balance as a unit, without any variation in relative rates of drive of its various compressor elements.

I claim:

1. In refrigeration means including a plurality oi refrigerant circuits in cascade relation wherein the refrigerants of adjacent circuits have change of state by heat exchange therebetween, each circuit having positive displacement pump means for compression and circulation of its refrigerant, motor means arranged for common drive of said pump means with fixed speed relation therebetween, one of said circuits providing, for its refrigerant, circulation in sequence through multistage compressor means, and condenser means wherein the refrigerant is liquefied, flash tank means wherein a portion of the refrigerant is regasified, a connection providing return of said refrigerant portion to said compressor means between stages thereof, and condenser means wherein the refrigerant remainder boils: by-pass means associated with a compressor stage ahead of said connection to provide recirculation in said stage and arranged to be responsive to refrigerant pressure ahead or said compressor means.

2. In refrigeration means including a plurality of refrigerant circuits in cascade relation wherein the refrigerants of adjacent circuits have change of state by heat exchange therebetween, each circuit having positive displacement pump means for compression and circulation of its refrigerant, motor means arranged for common drive of said pump means with fixed speed relation therebetween, one of said circuits providing, for its refrigerant, circulation in sequence through multistage compressor means, and condenser means wherein the refrigerant is liquefied, flash tank means wherein a portion of the refrigerant is regasified. a connection providing return of back pressure valve means arranged to control flow in said connection responsive to refrigerant pressure in said flash tank means.

HOWELL c. COOPER.

REFERENCES CITED The following references are of record in the file of this patentr UNITED STATES PATENTS 20 Number Name Date 1,808,494 Carney et al. June 2, 1931 2,304,999 Gonzaley Dec. 15, 1942 2,363,273

Waterfill Nov. 21, 1944

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