US2286618A - Refrigerating process - Google Patents

Description

June 16, 1942. N. H. HILLER, JR 2,286,618

REFRIGERATING PROCESS Filed Nov. 5, 1959 5 Sheets-Sheet 1 d NICOLAI H. HILLER'JR. INVENTOR BY @fiq/(u,

ATTORNEYS June 6, 1942- N. H. HILLER, JR'

REFRIGERATING PROCESS Filed Nov. 3, 1939 3 Sheets-Sheet 2 NICOLAI H.HILLER JR.

1 ENTOR m '0 SE l m ATTORNEYS June 16, 1942.

' N. H. HILLER, JR

REFRIGERATING PROCESS Filed Nov. 3; 1939 a She ets-Sheet 3 NICOLAI HHILLER JR. INVENTOR ATTORNEYS Patented June 16, 1 942 REFRIGERATING PROCESS Nicolai H. Hiller, Jr., Bronxville, N. Y., assignor,

by mesne assignments, to The Texas Company, a corporation of Delaware Application November 3, 1939, Serial No. 302,660

1 Claim.

This invention relates to refrigerating systems and more particularly to a method and apparatus for continuously cooling and dehumidifying a gas or air. The principal object of the invention is to produce continuously a cold, neutral gas or air which is clean and which has a minimum moisture content. Another object is to provide chemical means for continuously defrosting the equipment used in cooling the gas, and a still further object is to provide means for regenerating or concentrating the chemical used in defrosting so as to eliminate waste thereof.

This is a continuation in part of my co-pending application serial No. 160,942 filed August 26, 1937.

Several methods of.defrosting cooling equipment have been used in the past but most of these are unsatisfactory for various reasons. When using hot ammonia vapor, such procedure requires the use of two sets of cooling coils or other equipment so that one set can remain in use while the other is being defrosted in order to produce a continuous supply of cold gas or air. This involves a double investment for cooling equipment and also presents a problem of disposing of the melted frost in an, atmosphere likely to be below freezing, without affecting the operation of the companion cooling unit. It has also been proposed to defrost the equipfiient by heat supplied, for instance, by electric heating elements disposed in the stream of gas to be cooled. It is thus necessary to cut off the circulation of brine or other cooling medium and to defrost the unit by means of the warmed gas or air blowing against the frosted elements. This requires considerable time and consequently causes an abrupt rise in temperature of the space being cooled, or else the investment necessary for double or twin cooling units, as was mentioned in regard to the use of hot ammonia vapor. Other methods of supplying heat for defrosting, such as the use of steam coils, also involve additional expensive equipment and many operating difficulties.

In accordance with the present invention, the cooling coils and equipment are prevented from becoming frosted by means of a spray of a hytermed the defrosting. solution is regenerated or concentrated to permit continuous use.

In carrying out the invention in connection with the cooling of a room or space, such as may be used for observing the reaction of various substances to low temperatures or in treating processes such as the solvent dewaxing of hydrocarbon oils, the room is refrigerated by the provision of internal circulation of air over suitable cooling or chilling units, the cooled air being returned to the room and a portion of the foul air beingdisplaced continuously by fresh air, chilled and dehumidified. and introduced into the main chilling unit. The cooling coils and other equipment are continuously submitted to a cold spray of a defrosting solution such, for example, as a mixtureof water and ethylene glycol in proper proportionsserving to prevent the formation of frost on the equipment and also to absorb moisture from the air passing therethrough. In the course of use the defrosting solution, because of its hygroscopic character, absorbs moisture and this continuesuntil the spray solution has become so dilute that it is no longer hy roscopic at the working temperature; Such a solution is denoted as being spent. A spray solution which obtain as to cause the defrosting solution to be completely spent. In order to maintain the defrosting solution at its optimum efiiciency it is desirable that the partly spent solution be continuously regenerated by removing therefrom sufficient water to maintain the solution within a groscopic aqueous solution of a neutral inherently hygroscopic compound, said usolution to be of a predetermined concentration. Suitable hygroscopic compounds include ethylene glycol, di-- ethylene glycol, propylene glycol or di-ethylene particular range of concentrations. This may be effected by subjecting the partly spent defrosting solution in whole or in part to distillation or to any other suitable operation for the removal of water. By' this system a continuous supply of cold,'dehumidified air or other gas is thus made available either for cooling a room or for other purposes. Furthermore, since the defrosting solution is continuously regenerated without appreciable loss of the contained hygroscopic compound the process isrelatively inexpensive in op eration,

The method of regenerating or concentrating the solution is an important feature of the invention. In accordance with the invention a system of control is provided so that the used solution can be concentrated between predetermined definite limits, depending upon the temperature room and also an elevation and flow diagram of the apparatus for concentrating the defrosting solution; and

Figure 3 is a freezing point curve for an aqueous solution of ethylene glycol.

Fresh air dehumidifier and chiller As shown in Figure 1, the equipment for dehumidifying and cooling the make-up air, i. e., the fresh air necessary for continuously displacing a predetermined amount of foul air from the room or space to be cooled, is preferably mounted in a box or container Hi the walls of which are suitably heat insulated; A pump or blower l2 draws fresh air at the desired rate through the inlet pipe l4 and exhausts this air through the conduit l6 into the space A which may be termed the first stage of the make-up air cooler. It is to be understood that instead of the blower I! at the inlet of space A, a suction fan or pump may be located at the outlet of space D to be described hereinafter. A suitable filter I8 is preferably mounted in the path of the air issued from the conduit l6 and serves also to straighten out the currents of air so that they will fiow uniformly through the space A. The air passing through space A is washed by. means of cooling water sprays 20 which are fed through the conduit 22, the water being withdrawn bymeans of' conduit 24. This cooling water need not be at a particularly low temperature, 60 F. having been found suitable. The cooling water may be supplied from the cooling system of the plant where the apparatus is to be used or it may be supplied from any suitable separate pump, not shown. These sprays will remove approximately 99% of any dust, dirt, lint, absorbable gas or other impurities and the cooled air should then approximate 65 F, and 100% relative humidity. The cooled air having been washed by the sprays 20 will then enter section B where. it will be further cooled by means of the cold water sprays 25.- The cold water for the sprays 26 is shown as supplied from a cooler such as a direct expansion ammonia cooler 28', the ammonia temperature being held to approximately 33 F. and the cooling water entering the sprays 26 at from 33 to 37 F. The. cooling water collects in the per pound, the condensed moisture having been picked up in the A and B sections.

In space C the air passes through sprays 34 of the defrosting solution which for the purpose of this example is a solution containing 60% ethylene glycol and 40% water. Since ethylene glycol has the ability to absorb large quantities of water-or water vapor, the incoming air to section C will be reduced in temperature to approximately F. The defrosting solution for the sprays 34 is supplied by means of a suitable pump 35 p from a sump tank or reservoir 38 under the ammonia chillers to be described later. An eliminator section 40 at the outlet of the C section removes any entrained partly spent defrosting solution and the chilled air enters the final stage or section D where final chilling brings its temperature down to approximately 30 F. or lower. As the air enters the D section it passes through sprays 42 of defrosting solution supplied from conduit 43 and located at the up-stream side of the direct expansion chilling units 44 receiving a suitable refrigerant such as ammonia through the conduit 45. The continuous wash tion C will collect in the reservoir and will run' by gravity through the conduit 52 to the solution tank 54 in the concentrator shown in Figure 2. Liquid collecting below the eliminator 46 will pass through a conduit 56 into the reservoir 38.

Main, chilling unit In Figure 2 the room or space 58 to be cooled is shown as having suitably heat-insulated walls 69 and as containing in its upper portion the main chilling unit indicated generally as 82. This unit which may either be horizontally disposed, as shown, or arranged vertically, comprises a series of chambers connected together and having an inlet opening .64 at one end and an outlet opening 86 in which an exhaust fan 68 is positioned. The fan or blower $8 in drawin air through the unit causes air from the room to enter at 66 together with a predetermined amount of fresh dehumidified and cooled air from the conduit it-connected to the unit shown in Figure 1. The air from the room, together with the fresh make-up air, first passes through v sprays 10 of defrosting solution supplied from a tray 30 and 'is recirculated by means of the pump 32. Although the water cooler 28 is shown as being arranged externally 'of the housing IE, it is to be understood that this unit may be mounted entirely within the housing at any convenient location. An "eliminator 33 at the outlet of section B removes all of the entrained moisture from the air, thus permitting air of approximately 39 F. and 100% relative humidity to enter the section or third stage C. It is to be understood that the "eliminator may be any suitable device through which the air must pass and which will collect andremove the moisture entrained therein. The moisture content of the air entering space C will have been reduced from approximately 100 grains per pound to 35 grains sump or reservoir 12 by means of a suitable pump 14, these sprays being disposed at the upstream side of the direct expansion chilling unit-I5, this unit being supplied with a suitable refrigerant such. as ammonia through conduit 16 and the ammonia being exhausted through conduit 78. The air then passes through another defrosting solution spray and then through the second ammonia chilling unit 82.

As was brought out in connection with the apparatus disclosed in Figure 1, the defrosting solutionspray in passing continuously over the chilling units I5 and 82 prevents the formation of any frost or ice on these units while at the same time the chemical absorbs a considerable amount of moisture from the air. The cold air then passes through an eliminator section 84 Such 'second control: means may suitably com prise a valve in the'steam line l26, controlled by a thermostatic actuating; device having its heatresponsive element inf-contact with .the liquid in thetankllli- The partly spent defrosting solution returning from-the freshair chiller-shown in Figure 1" through conduit 52'and from the main chilling,

unit 62 through conduit aapasses' through a heat exchanger 96 and thence to the partly spent solution tank '54,'previously mentioned, thistank being equipped with a suitable liquid level gauge 08 and safety valve I00. The partly spent deconduit 52 from the unit shown in Figure 1.2 De- Y frosting solution is suppliedto the reservoir," from a branch 90 of a conduit 92 to which latter conduitthe conduit 43 shown in Figure 1 isconnected. A suitable float-controlled valve 93 at the outlet of the branch conduit maintains the level of the'defrosting solution at the desired height in the reservoir 12. The various chambers of'the unit-are shown as providedwith electriclights 9 4 and with sight openings or port holes 85 through which the operation of the unit may be observed.

Defrosting solution concentrator Aqueous solutions of the inherently hyroscopic compounds. the use of which is contemplated in the practice of thisinvention, yield curves of the general shape of the eutectic curve such as the example shownin Figure 3 which is control I I8 is arranged so. that when there is ina freezing point curve of ethylene glycol water 4 solutions. In general the curve shows. that the freezing point of the pure solvent alone is at a higher temperature, than a certain mixture of the solvent and water. For instance, as shown in Figure 3, pure ethylene glycol freezes at approximately plus 8 F. whereas a mixture of 60% ethylene glycol and 40% water freezes at approximately minus 56 F. At any temperature above minus 56 F. there is a -certain'range of ethylene glycol concentration at which a solution will remain in its fluid state. Thus at minus frosting 'solutionis drawn from the reservoir 54 bymeans of a suitable pump. I02 and passes through a heater I04 and thence through'a conduit I06, having valve-controlled branches I08 and H0, to an extraction tower II2 which may be of the bubble tray or rocktype. The tower H2 is mounted on top of a heating tank I14; the solution passing downwardly-througli'the tower and into the tank 'II4 where it is maintained substantially at the level II6 by means of a float.

control II8, the latter being connected to the heating'tank by means of conduits I and I22. A heating coil I24 inthe tank II4 issupplied preferably by steam enteringat I26, the condensate leaving the coil through trap I28. The float sufficient solution in the. heating. tank 4 to reach thelevel I 'I6, the solution -which is continuously withdrawn from the tank bymeans of the pump I is by-passed from conduit I32 through the connection I34 and back tothe tank 30 F. any solution ranging from 46 to 86% ethylene glycol will be fluid and any concentrations below 46% or over 86% will be slushy or solid at this temperature. In order to maintain a frost free chilling coil at minus 30F. it would be necessary to hold the defrosting solution in the range just given by means of a suitable concentrator or'regenerator which would remove the excess water absorbed. in the chilling unit and-- maintain the proper concentration.

To this end a suitable method and an apparatus have been devised which will automatically maintain a proper concentration as demanded by the process, and at the same time eliminate entirely the loss of defrosting material such as ethylene glycol which would normally accompany concentration in an open receptacle. The

apparatus consists of a refluxed fractionation column and a reboiler, the temperatures of both of which are maintained at .a predetermined level by means of suitable control, preferably automatic. Because of the small amount of cooling required to hold the temperature at thetop of the tower at the boiling point of water,

a closed reflux cooling. coil is employed, the

amount of cooling fluid'being controlled bya.

temperature controller, in the vapor line. Since the concentration of the ethylene glycol in the reboiler at the bottom of the tower is determined by the temperature therein, a secondmeans of control is incorporated in the reboiler Structure.

' through conduit 43 to through conduit I36. When the liquid reaches the level II6, the float control II8 closesa valve I38 in the connection I84, and the concentrated solution is then forcedby pump. I30 past a check valve I40 and through a suitable cooler I42 into a defrosting solution storage tank I44.

Thedefrosting solution in the storage tank I44 is maintained under a positive pressureby The tank I44 .is provided with a liquid level gauge I anda safety valve I52. The defrosting solution passes from the tank I44 through conduit I54 and then through thepreviously mentioned heat exchanger 96 to the conduit 32 from which, as has been previously described, part passes through conduit'90 into the reservoir 12 while the remaining portion passes the sprays 42 shown in Figure 1.

Referring again to thetower 2, a cooling coil I56 serves to control the temperature in the upper end of the tower, this-coil being supplied 1 preferably by cold water from a conduit I58. By

. leave the upper end of the tower II2 throughmeans of the cooling coil I56 the temperature at the top of the tower is maintained substantially at the boiling point of water. The water vapors duct' I60 and .then pass downwardly through a cooler I62 from which they are led to a suitable condenser I64, the cold water for which is supplied from-a conduit I66. A thermostat I66 in the duct I60 actuates a valve I10 in the cold water line I56, as is shown diagrammatically by dotted line I12, for controlling the temperature in the upper portion of the tower II2. A valved by-pass I12 is preferably connected around the valve I10 so that the cold water entering the' cooling coll I56 may be manually controlled -if desired. It is to be understood that the tower' II2 maybe of thebubble tray type or it may be means of compressed air supplied from aconduit I46 containing a suitable reducing valve .I48..

in the form of a rock towerpacked with suitable material such as Raschig rings.

It is believed that the operation will be clear from the foregoing description. However, in summarizing, the main cooling unit 62 continuously draws in air from the room 58, cooling this air and forcing it back into the room, through the outlet 66. A supply of fresh air which has been partially cooled and dehumidified by means of the apparatus shown in Figure 1 also. enters the main cooling unit 62 through conduit 48 in order to make up for the portion of foul air which is continuously discharged at 86. The defrosting solution which is supplied to the main cooling unit 62 and also to the fresh air cooler and dehumidifier is withdrawn and part of the water removed by means of the heating tank H4 and the tower H2 and is then recirculated without substantial loss.

Although certain more or less definite temperatures and volumes have been mentioned, it is to be understood that this is a specific adaptation of the invention and that these figures may vary greatly from those given without departing from the scope of the invention.

The invention has been described in one adaptation as applied to the cooling of air for a room which may be used for testing or other purposes, but it is to be understood that the air' which is cooled and dehumidified in accordance with the invention may be used for other purposes such, for instance, as the refrigeration or freezing of foods.

Obviously many modifications and variations of' the invention as before set forth may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated by the appended claim.

I claim:

A cyclic process for cooling and dehumidifying a gas adapted to produce a cold dehumidifled gas for direct contact frost-free refrigerationat temperatures at least as low as 30 F., which comprises contacting said gas with a spray of aqueous ethylene glycol solution, and with cooling surfaces maintained at a temperature below -30 F. and covered with a film of said aqueous ethylene glycol solution resulting from the action of said spray, causing the aqueous ethylene glycol solution flowing from said cooling surfaces to be recycled to said spray, maintaining the concentration of said aqueous ethylene glycol solution at said spray within the range of

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