US3587731A

US3587731A - Plural refrigerant tray type heat exchanger

Info

Publication number: US3587731A
Application number: US752118A
Authority: US
Inventors: George E Hays
Original assignee: Phillips Petroleum Co
Current assignee: Phillips Petroleum Co
Priority date: 1968-07-22
Filing date: 1968-07-22
Publication date: 1971-06-28
Anticipated expiration: 1988-06-28

Abstract

A CORE TYPE HEAT EXCHANGER COMPRISING A PLURALITY OF PARALLEL, CONTIGUOUS AND SEPARATE PASSAGEWAYS POSITIONED IN AN INSULATED SHELL AND ARRANGED ONE ABOVE THE OTHER WITH THE BOTTOM OF ONE PASSAGEWAY CONSTITUTING THE TOP OF THE PASSAGEWAY IMMEDIATELY BELOW WHEREIN MEANS ARE PROVIDED FOR INTRODUCING REFRIGERANTS AT DIFFERENT TEMPERATURE LEVELS INTO PASSAGEWAYS IN COUNTERCURRENT FLOW RELATIONSHIP WITH RESPECT TO THE PROCESS STREAM BEING COOLED AT LOCI IN THE HEAT

EXCHANGER CORRESPONDING TO THE TEMPERATURE LEVEL OF THE INDIVIDUAL REFRIGERANTS.

Description

United States Patent [72] Inventor George E. Hays Bartlesville, Okla. [21] Appl. No. 752,118 [22] Filed July 22, 1968 [45] Patented June 28, 1971 [73] Assignee Phillips Petroleum Company Continuation of application Ser. No. 510,269, Nov. 29, 1965, now abandoned.

[54] PLURAL REFRIGERANT TRAY TYPE HEAT EXCHANGER 10 Claims, 4 Drawing Figs.

[52] 0.8. CI 165/140, 62/13, 62/40, 165/166, 208/340 [51] Int. Cl. F2811 9/00 [50] Field of Search 165/140, 141, 166; 62/13, 40, 36

[56] References Cited UNITED STATES PATENTS 2,660,038 1 1/1953 Pool 62/13 c m; -14o' 2s PSIA Primary Examiner-Albert W. Davis, Jr. Attorney-Young and Quigg ABSTRACT: A core type heat exchanger comprising a plurality of parallel, contiguous and separate passageways positioned in an insulated shell and arranged one above the other with the bottom of one passageway constituting the top of the passageway immediately below wherein means are provided for introducing refrigerants at different temperature levels into passageways in countercurrent flow relationship with respect to the process stream being cooled at loci in the heat exchanger corresponding to the temperature levels of the individual refrigerants.

CH4 130F e00 PSIA PATENTEU JUH28|97I 3587.731

I sum 2 0F 4 FUEL GAS Baa/kg INVIEN'I'OR G. E. H AYS A T TORNEYS PLURAL REFRIGERANT TRAY TYPE HEAT EXCHANGER This application is a continuation of copending application Ser. No. 510,269, filed Nov. 29, 1965, and now abandoned.

This invention relates to the liquefaction of a gas. In one' aspect it relates to an improvement in the heat exchange steps in a refrigeration system for gas liquefaction. In another aspect this invention relates to a method and means for heat exchanging a plurality of refrigerants at different temperature levels with a process stream in a unitary heat exchanger. In another aspect this invention relates to a method for modifying a heat exchanger so as to accommodate a plurality of refrigerants at different temperature levels.

In the liquefaction of gases such as natural gas, methane, nitrogen, oxygen and the like, by low temperature refrigeration to produce liquid gas for storage or transport or for the recovery of gaseous helium from liquefied natural gas, it is of utmost importance to obtain maximum efliciency of the refrigeration cycle in order to keep power and equipment costs at a minimum.

According to the present invention, the refrigerant in a refrigeration system is expanded to at least two pressure levels and passed in parallel, indirect heat exchange relationship with the process gas stream in a unitary, multistream heat exchanger. Parallel heat exchange relationship means that the refrigerant expanded to the highest pressure is passed in countercurrent flow heat exchange relationship with the warm process gas stream; and the refrigerant expanded to the lowest pressure level is heat exchanged with the process gas effluent from the first heat exchange step in a second heat exchange step and is then passed in heat exchange relationship with the process gas in the first heat exchange steps. Thus the refrigerant vapors exit the heat exchanger at substantially the same temperature but at different pressure levels so that the sensible heat of the refrigerant vapors, as well as the latent heat of vaporization of the refrigerant is utilized in cooling the process gas stream. It has heretofore been necessary to use at least two heat exchangers to accomplish such parallel heat exchange of a process stream with a plurality of refrigerants at different temperature levels. According to the method and means of the present invention it is now possible to introduce each of a plurality of refrigerants into a multistream heat exchanger at the locus in the path of heat exchange corresponding to the temperature level of each refrigerant.

It is 'an object of this invention to provide a method and means for increasing the efficiency of heat exchange and refrigeration in the liquefaction of a gas by introducing refrigerants at different temperature levels into a multistream heat exchanger into the path of heat exchange with the process stream corresponding to the temperature level of each refrigerant. It is also an object of this invention to modify a core type heat exchanger so as to allow the introduction of heat exchange fluids into said heat exchanger at the various points along the path of heat exchange. Other objects, aspects and advantages of the invention will be apparent to one skilled in the art upon studying the disclosure, including the detailed description of the invention, and the appended drawing wherein:

FIG. 1 is a schematic flow diagram of a preferred embodiment of the invention as utilized in a system for the liquefaction of natural gas;

FIG. 2 is a perspective view of a core type heat exchanger showing the location of the exits and entrances of the refrigerants and process streams;

FIG. 3 is a perspective view of the core of a core type heat exchanger with the manifolds removed so as to show the entry points for the refrigerants and process streams; and

FIG. 4 is a view of the opposite side of the core of FIG. 3 showing the exits of the refrigerants.

In the embodiment shown in FIG. 1 of the drawing, natural gas from which water, gasoline components and CO have been removed is passed through conduit at about 600 pounds per square inch absolute (p.s.i.a.) to a first heat exchanger 11 which is a multistream heat exchanger of the core type shown in greater detail in FIGS. 2, 3 and 4. Propane is compressed to about 150 p.s.i.a. in compressor 14 and passed via conduit 15 to a water cooler 16 where the propane is condensed with F. water and then passed to a surge tank 17. Liquid propane is removed from surge tank 17 and passed via conduit 18 and flashed through valve 19 into flash chamber 21 maintained at about 40 F. and about 80 p.s.i.a. Liquid propane at about 40 F. is passed from flash tank 21 via conduit 22 into heat exchanger 11 at the locus of heat exchanger 11 where the temperature is about 40 F. and the 80 p.s.i.a. vapors removed from heat exchanger 11 are passed to the high compression stage 23 of propane compressor 14 via conduit 24. Vapors from flash tank 21 are removed via conduit 25 and also passed to high stage compression via conduit 24.

Liquid propane is removed from surge tank 17 and passed via conduit 26 and flash valve 27 to flash tank 28 where the temperature is maintained at about 10 F. and a pressure of about 45 p.s.i.a. Liquid is removed from flash tank 28 via conduit 29 and passed into heat exchanger 11 at the point where the temperature in the heat exchanger is about 10F. The 45 p.s.i.a. vapor is removed from heat exchanger 11 and then passed via conduit 33 to the intermediate stage of compression 34 of propane compressor 14. Vapor from flash tank 28 is passed via conduit 31 to conduit 33.

Liquid propane from surge tank 17 is passed via conduit 35 and flash valve 36 to flash tank 37 where the temperature is maintained at about 30 F. at a pressure of about p.s.i.a. Liquid from flash tank 37 are passed via conduit 38 into the cold end of heat exchanger 11 and the 20 p.s.i.a. vapors removed from heat exchanger 11 are passed to the low compression stage 45 of compressor 14 via conduit 44. Vapors from flash tank 37 are passed via conduit 39 to conduit 44. A portion of the liquid from flash tank 37 is passed via conduit 47 through heat exchanger 48 in indirect heat exchange with ethylene in conduit 49 and thence via

conduits

50 and 39 to conduit 44.

Ethylene is compressed to about 300 p.s.i.a. in ethylene compressor 114 and passed via conduit 49 to heat exchanger 48 where it is condensed by heat exchange with liquid propane and then passed to surge tank 117 at about -20 F. and about 300 p.s.i.a. Liquid ethylene is removed from surge tank 117 via conduit 118 and flashed through valve 119 into flash tank 121 at about 90 F. and about 80 p.s.i.a. Liquid from flash tank 121 is passed via conduit 122 into heat exchanger 111 at the locus in heat exchanger 111 where the temperature is about 90 F. The 80 p.s.i.a. vapors removed from heat exchanger 111 are passed via conduit 124 to high stage of compression 123 of ethylene compressor 114. Vapor from flash tank 121 is passed via conduit 125 to conduit 124. Liquid ethylene from flash tank 117 is also passed via conduit 126 and flash valve 127 to flash tank 128 at about F. and about 30 p.s.i.a. Liquid ethylene is removed from flash tank 128 and passed via conduit 129 to heat exchanger 111 at the locus of the heat exchanger where the temperature in the heat exchanger is about l35F. The 30 p.s.i.a. vapors from heat exchanger 111 are passed via conduit 132 to the intermediate stage of ethylene compression 133 of ethylene compressor 114. Vapors removed from flash tank 128 are passed via conduit 131 to conduit 132.

Liquid ethylene from surge tank 117 is also passed via conduit 135 and flash valve 136 to flash tank 137 at about -l40 F. and about 25 p.s.i.a. Liquid is passed from flash tank 137 via conduit 138 into the cold end of heat exchanger 111. The 25 p.s.i.a. vapors from heat exchanger 111 are passed via conduit l44-to the low stage of compression of ethylene compressor 11'4. Liquid ethylene from flash tank 137 is also passed via conduit 147 through heat exchanger 148 in indirect heat exchange with methane in conduit 149. Ethylene vapors from heat exchanger '148 are passed via conduit 15 0 along with vapors from flash tank 137 and conduit 139 to conduit 144.

Methane is compressed in compressor 214 to about 540 p.s.i.a., passed via conduit 149 and methane condenser 148 to surge tank 217 at about 1 30 F. and about 530 p.s.i.a. Liquid methane from surge tank 217 is passed via conduit 218 and flash valve 219 to flash tank 221 at about l75 F. and about 215 p.s.i.a. Liquid from flash tank 221 is passed via conduit 222 into heat exchanger 211 at the locus of heat exchanger 211 where the temperature is about l75 F. The 2 l5 p.s.i.a. vapors from heat exchanger 211 are passed via conduit 224 to the low stage of compression 223 of methane compressor 214. Vapors from flash tank 221 are passed via conduit 225 to conduit 224. The liquid is also passed from surge tank 217 via conduit 226 and flash valve 227 to flash tank 228 at about 2l0 F. and about 85 p.s.i.a. Liquid from flash tank 228 is passed via conduit 229 into heat exchanger 211 at the locus where the temperature in heat exchanger 211 is about 2l0 F. The 85 p.s.i.a. vapor removed from heat exchanger 211 is passed via conduit 232 to the intermediate stage of compression 233 of methane compressor 214. Vapor from flash tank 228 is passed via conduit 231 to conduit 232.

Liquid methane from surge tank 217 is also passed via conduit 235 and flash valve 236 to flash tank 237 at about 240 F. and a pressure of about 30 p.s.i.a. Liquid from flash tank 237 is passed via conduit 238 into the cold end of heat exchanger 211. The 30 p.s.i.a. vapors from heat exchanger 211 are passed via conduit 244 into the low stage of compression 245 of methane compressor 214. Vapors from flash tank 237 are passed via conduit 239 into conduit 244.

The natural gas stream removed from the cold end of heat exchanger "211 via conduit is flashed in valve 300 and passed into flash tank 301 at about p.s.i.a. (about atmospheric pressure) and a temperature of about 258 F. Vapors removed from product tank 301 via conduit 302 are passed in countercurrent flow relationship to the natural gas in conduit 10 through heat exchangers 211, 111 and 11 and removed from the warm end of heat exchanger 11 and passed to fuel gas supply. or other disposition. Liquid natural gas product is removedas needed via conduit 303.

The heat exchangers 11, 111 and 211 are shown in greater detail in FIGS. 2, 3, and 4 wherein heat exchanger 111 is taken as exemplary. in FIG. 2 the low pressure ethylene in conduit 138 at a temperature of about -l40 F. passes into manifold 138 a and thence into passageway A of heat exchanger 111 at the cold end thereof. Ethylene at a temperature of about 1 35 F. passes via conduit 129 into manifold 129a and thence into passageways G and L of heat exchanger 11] at the point in heat exchanger 1 11 where the temperature of each of the streams is about 135 F. Ethylene at about 90 F. passes via conduit 122 into manifold 122a and thence into passageways E and K of heat exchanger 111. The entry points of the various streams are shown in FIG. 3.

The refrigerants are removed from the warm end of the heat exchanger as illustrated in FIG. 4. The outlet manifolds 122b, 12% and l38b are shown in FIG. 2.

The sections which go to make up the refrigerator core, il-

lustrated as A through L, are generally rectangular in shape with the bottom plate of one section or passageway constituting the top of the passageway immediately below and containing a corrugated metal sheet with the corrugations in contact with the top and bottom of the passageway so as to attain maximum heat transfer from and across the passageway. The sections or passageways are sealed around the periphery except for the entrance and exits. The corrugations are positioned in the passageways so that the flow of gases is parallel with the corrugations. Where the flow of refrigerant enters and exits the heat exchanger it is normal to the direction of the corrugations and therefore at those locations the corrugations are removed to allow unrestricted gas flow to and from the heat exchanger. As shown in FIG. 3, the gas stream 10 flows in a first direction through corrugated passageways, B, D, F, H, and J, while the first refrigerant 302 flows in the opposite direction through passageways, C and I, intermediate and contiguous with the passageways in which the gas is flowing. One

or more

other refrigerants

122, 129 and 138 are introduced at spaced points intermediate the length of heat exchanger 111 and flow cocurrently with the first refrigerant and countercurrent to the gas through passageways, A, E, G, K and L, contiguous with gas passageways.

If the composition of the gas to be refrigerated is known and constant, the proper position for entry of the various temperature level refrigerants into the heat exchanger can be calculated. If the composition of the gas to be refrigerated is unknown or if desired for other reasons, thermocouples can be placed at intervals in the heat exchanger to determine the proper locations for entry of the refrigerants at the different temperatures.

Any natural gas feed stream will normally contain compounds heavier than methane and as a result such compounds will condense at some temperature warmer than F. at 600 p.s.i.a. This will move the refrigeration load to a warmer temperature and thus reduce the compression requirements for the refrigerants operating at the colder temperature. The natural gas feed stream will often be obtained as the effluent from a natural gasoline plant and will have the heavier hydrocarbons as well as the water and CO removed. In the Example used in the description of FIG. 1 the natural gas stream had been dehydrated to l00 F. dew point and contained less than 0.02 mol per cent CO If a wet gas stream is to be refrigerated for liquefaction of natural gas, provision should be made to withdraw compounds such as benzene and CO which will solidify at the low temperatures contemplated. Such liquidation can be tapped off from the heat exchangers at appropriate points of temperature and pressure.

Propane, ethylene and methane have been chosen as the refrigerants in the cascaded system of the specific embodiment of the invention described because these refrigerants are particularly applicable to the temperatures and pressures selected; however, other refrigerants such as ammonia, freons and the like can be utilized if desired. Hydrocarbons will often be preferred as refrigerants because of their availability in connection with natural gas liquefaction and because of the wide range of hydrocarbons available for use as refrigerants.

In FIG. 1 the vapor from the various tanks is bypassed around the heat exchangers in order to decrease the load on the heat exchangers; however, if it is desired to utilize the sensible heat of the refrigerant vapors and if the heat exchanger has sufficient capacity to handle these vapors, the vapor stream can be joined with the liquid refrigerant passing into the heat exchanger. If a combined liquid and vapor stream is introduced into the heat exchanger, it may be desirable to utilize a liquid-vapor distributor such as described in US. Pat. No. 3,158,010 issued Nov. 24, 1964.

FIG. 1 shows parallel expansion of the three refrigerants into the three lower-pressure flash tanks, i.e., liquid propane from tank 17 is passed in parallel through

flash valves

19, 27, and 36 into

respective tanks

21, 28, and 37. It is sometimes desirable to use series expansion, i.e., some of the liquid from tank 21 is flashed into tank 28 and some of the liquid from tank 28 is flashed into tank 37. Liquid ethylene may be similarly flashed from tank 117 into tank 121, then into tank 128, and finally into tank 137. Methane refrigerant may be similarly flashed.

Iclaim:

1. A heat exchanger comprising:

an insulated shell;

a plurality of coextensive parallel contiguous and separate passageways for a gas stream flowing in a first direction and a first refrigerant and plural further refrigerants flowing in the opposite direction, passageways for the first refrigerant being intermediate passageways for the gas stream, contiguous passageways having common plates forming the boundary therebetween corrugated sheet metal members positioned between and contacting the common plates, first refrigerant and gas stream flowing in contiguous coextensive passageways; and

means to introduce the plural further refrigerants at different temperatures at plural spaced points intermediate the length of the exchanger for flow countercurrent with said gas stream and cocurrent with said first "refrigerant through other of said passageways contiguous with at least one of said first refrigerant and said gas stream, at least one path of each of the plural refrigerants being intermediate the gas stream, the corrugated sheet metal members being interrupted at said plural spaced points to allow unrestricted flow of each said plural further refrigerant into the respective passageway.

2. The apparatus of claim 1 wherein means to introduce the plural further refrigerants comprises a manifold for each of said plural further refrigerants sealed to said shell in open communication with the respective ones of said other passageways 3. The apparatus of claim 2 wherein each plural further refrigerant stream passes through a plurality of passageways and each manifold communicates with the respective plurality of passageways.

4. A unitary heat exchanger comprising an insulated shell;

a plurality of parallel, contiguous and separate passageways positioned in said shell, each contiguous pair of said passageways having a common plate forming a boundary wall therebetween, a plurality of corrugated metal members, each of said plurality of corrugated metal members being positioned in a respective one of said passageways in contact with opposite boundary walls of the respective passageway;

means for passing a process fluid stream to be cooled through the entire length of a first group of at least one of said passageways in a first direction from the inlet end of said first group to the outlet end of said first group;

means for passing a first refrigerant into and through a second group of at least one of said passageways in a second direction opposite to said first direction, the point of introduction of said first refrigerant into said second group being at a first locus intermediate the ends of said first group;

means for introducing a second refrigerant into a third group of at least one of said passageways at a second locus intermediate the inlet end of said first group and said first locus, and passing said second refrigerant through said third group of at least one of said passageways in said second direction;

said passageways of said first, second and third groups being coextensive in length, the corrugated metal members in said second group of passageways being interrupted at said first locus to allow unrestricted flow of said first refrigerant into said second group of passageways, and the corrugated metal members in said third group of passageways, and the corrugated metal members in said third group of passageways being interrupted at said second locus to allow unrestricted flow of said second refrigerant into said third group of passageways.

5. A heat exchanger in accordance with claim 4 further comprising means for introducing a plurality of additional refrigerants at different respective temperatures into additional groups of said passageways at plural spaced points intermediate the ends of said second group for flow in said second direction, each additional refrigerant introduced at a respective one of said plural spaced points having a temperature about the same as the temperature of said first refrigerant at that point.

6. A heat exchanger in accordance with claim 4 wherein each passageway of said second and third groups is contiguous to at least one passageway of said first group, and wherein said first refrigerant is passed through theentire length of said second group.

7. A heat exchanger in accordance with claim 6 wherein each of said corrugated metal members comprises a corrugated sheet metal member.

. A heat exchanger in accordance with claim 7 wherein said first locus is located at a point where the temperature of the first refrigerant entering said second group of passageways is about the same as the temperature of said process fluid stream, wherein said second locus is located at a point where the temperature of said second refrigerant being higher than the entering temperature of said first refrigerant, further comprising means for introducing a third refrigerant at a temperature higher than said entering temperature of said second refrigerant into a fourth group of at least one of said passageways at a third locus intermediate the inlet end of said first group and said second locus wherein the temperature of said first refrigerant is about the same as the entering temperature of said third refrigerant, and passing said third refrigerant through said fourth group of at least one of said passageways in said second direction, each passageway of said fourth group being contiguous to at least one passageway of said first group.

9. A heat exchanger in accordance with claim 8 wherein each of said passageways is rectangular in shape with the bottom plate of one passageway constituting the top of the passageway immediately below and contains at least one corrugated metal sheet member with the corrugations in contact with the top and bottom of the respective passageway so as to attain maximum heat transfer from and across the respective pathway, the corrugated metal sheet members being position in the passageways so that the corrugations are parallel to the flow of fluid.

10. A heat exchanger in accordance with claim 9 wherein said means for passing a process fluid stream comprises manifold means located at the first end of said shell for introducing said process fluid stream into said first group of passageways, and further comprising means located at said first end of said shell for withdrawing said stream of said first refrigerant from said second group of passageways and a stream of said second refrigerant from said third group of passageways.

UNITED STATES PATENT OFFIfE CERTIFICATE OF CORRECTION Patent No. 3,587,731 George E. Hays DBtOdi 'w 1971 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as sham below:

Column 6, line 2h, after "refrigerant" insert entering said third group of passageways is about the same as the temperature of said process fluid stream, the entering temperature of said second refrigerant column 6, line +3, "position" shot read positioned Signed and sealed this 9th day of January 1973.

(SEAL) Attest:

EDWARD M.FLETCHER JR Att ROBERT GOTTSCHALK estlng Officer Commissioner of Patents