DETAILED DESCRIPTION OF THE INVENTION

[0055] The invention as described herein eliminates selected distributor fins, collector fins, headers, nozzles, and manifolds from plate-and-fin core-type heat exchangers typically used for low temperature gas processing. In the various embodiments of the invention, these distributor fins, collector fins, headers, nozzles, and manifolds are eliminated at the feed stream inlet, the processed stream outlet, or both the feed stream inlet and the processed stream outlet of the heat exchanger. The invention can be utilized for cooling a fluid stream (i.e., a gas or a liquid stream) without phase change, or alternatively for partially or totally condensing a gas stream.

[0056] A first embodiment of the invention is illustrated in FIG. 1. Heat exchanger 1 is a typical plate-and-fin core-type heat exchanger as earlier described, and usually is installed in a generally vertical orientation inside pressure vessel 3. A portion of the flow passageways in the heat exchanger can be utilized for condensing service, and these passageways form a feed circuit through which the uncondensed feed gas and condensate flow cocurrently. The flow passageways are oriented such that the uncondensed feed gas and condensate flow cocurrently in a generally downward direction, i.e., in a vertical downward direction or in a downward direction which deviates from vertical wherein the flow passageways operate such that the condensate flows downward by the force of gravity. The generally downward direction is preferably vertical but can deviate from the vertical as long as the deviation does not adversely affect the downward cocurrent flow of uncondensed feed gas and condensate through the exchanger and the transfer of heat from the uncondensed feed gas and condensate.

[0057] The bulk flow of vapor and liquid is generally parallel to the axes of the flow passageways. The feed circuit heat transfer fin section extends to bottom 5 of heat exchanger 1, and the feed circuit is open at bottom 5 and is in full flow communication with the interior of pressure vessel 3. The term “open” means that the end of the exchanger has no collector fins or headers associated with it, and therefore fluid can flow unimpeded without restriction from the end of each flow channel. Thus in FIG. 1 both vapor 7 and condensed liquid 9 flow unimpeded from the exchanger core without restriction, and the full fluid-handling capacity of the core therefore can be utilized.

[0058] A stream of mixed feed gas 11 enters inlet 13 of pressure vessel 3, flows through manifolds 17 and 19, and flows through header 21 through distributor fins (not shown) into the feed circuit of heat exchanger 1. The distributor fins are located at the entrance to the core and function to direct fluid from the header into the main flow passageways in the body of the core. The distributor fins can be considered as part of the plate-and-fin heat exchanger core. Manifold 17, manifold 19, and header 21 are generically described as fluid transfer means to transfer fluid from inlet 13 to the end of heat exchanger 1.

[0059] The feed gas flows downward in this embodiment and is partially condensed therein by refrigeration provided in adjacent flow channels as described below. Condensate 9 drains freely from the feed circuit at the bottom of the core and collects in the bottom of vessel 3, from which liquid product stream 23 is withdrawn through vessel outlet 25. Uncondensed vapor 7 exits exchanger 1 via vessel outlet 27 to provide vapor product stream 29. This arrangement eliminates the need for a separator drum to separate the condensed liquid from the uncondensed vapor portion of the cooled feed.

[0060] Vapor product stream 29 is enriched in the lower boiling, more volatile components in the feed gas mixture and liquid product 23 is enriched in the higher boiling, less volatile components in the feed gas mixture. The feed gas mixture contains more volatile components and less volatile components, and the mixture typically contains two or more components selected from the group consisting of hydrogen, helium, carbon monoxide, carbon dioxide, nitrogen, argon, oxygen, and C, to C₆ hydrocarbons. Feed gas mixtures can include cracked gas, refinery and petrochemical plant offgases, synthesis gas, natural gas, and air.

[0061] Typical refrigerant stream 31 is introduced via vessel inlet 33, manifolds 35 and 37, header 39, and distributor fins (not shown) into a refrigerant circuit which comprises a group of flow channels in the core of heat exchanger 1. Refrigerant flows upward through the refrigerant circuit in heat exchanger 1 while warming and/or vaporizing to provide indirect cooling to the condensing vapor in the feed circuit described earlier. Warmed refrigerant is withdrawn from the heat exchanger through collector fins (not shown), header 41, manifolds 43 and 45, and outlet 47 to provide warmed refrigerant stream 49.

[0062] Refrigerant 31 can be a cold process fluid which is warmed to provide sensible and/or latent heat for cooling and condensing the feed gas. Alternatively, a liquid refrigerant can be used which vaporizes while flowing through the refrigerant circuit. The liquid refrigerant can flow downward if desired. Typical refrigerants can be selected from C₁ to C₃ hydrocarbons, ammonia, fluorocarbons, chlorofluorocarbons, and mixed refrigerants which are recirculated through a closed-loop refrigeration circuit. More than one refrigerant circuit can be used if desired, which would require additional header and distributor/collector systems at the top and bottom of heat exchanger 1.

[0063] Additional heat exchangers can be installed in parallel with heat exchanger 1 in pressure vessel 3 if desired. An additional heat exchanger 51, for example, is shown in FIG. 1 and operates in parallel with heat exchanger 1. Feed gas 11 is introduced into the feed circuit of heat exchanger 51 via inlet 13, manifold 17, manifold 53, distributor header 55, and distributor fins (not shown). Uncondensed vapor 59 and condensate 61 flow from the bottom of exchanger 51 in a similar manner to the flows from heat exchanger 1. Refrigerant 31 for heat exchanger 51 enters via inlet 33, manifolds 35 and 55, and distributor header 57 and fins. Warmed refrigerant is withdrawn from heat exchanger 51 via collector fins and header 63, manifolds 65 and 45, and outlet 47.

[0064] Typical operating temperatures and pressures range from +100° F. to 400° F. for feed and refrigerants, 100 to 1500 psia for the feed, and 2 to 1500 psia for refrigerants.

[0065] When parallel heat exchanger cores are used, inlet and outlet lines can be manifolded inside pressure vessel 3 as shown to reduce the number of pipes passing through the vessel shell, although this is not necessary. Refrigerant drums, which may be used for ethylene, propylene, or similar thermosiphon-type refrigerant circuits, or for distributing two-phase refrigerant streams into the heat exchanger cores, can be located inside or outside the pressure vessel as desired. The pressure vessel can be externally insulated, similar to a distillation column, so that no cold box is required, particularly where operating temperatures are above about −250° F.

[0066] Alternatively, it may be desirable to have the feed gas 11 enter and/or leave the sides, rather than the ends, of heat exchangers 1 and 51 (not shown). In this case, distributor and/or collector fins would be required at one or both ends of the core to distribute flow into and/or collect flow from the cores. The corresponding distributors or collectors would be open to the interior of pressure vessel 3 on the side of the core to permit feed gas to enter and/or leave the core. Headers, nozzles and manifolds would not be required for the open sides of the cores.

[0067] While the heat exchanger as described above is utilized for condensing flow, the heat exchanger alternatively can be utilized to cool a fluid (either gas or liquid) without phase change. For example, a superheated gas stream can be cooled to a temperature above its dew point, while a liquid at or below its bubble point can be subcooled to a temperature further below its bubble point. In this alternative, the axis of the heat exchanger and the flow direction of the fluid being cooled (which is generally parallel to the axis of the exchanger) can be vertical, horizontal, or between vertical and horizontal. Thus the fluid being cooled can flow in any desired direction.

[0068] An alternative embodiment is shown in FIG. 2 which can be used when the feed gas is to be cooled or partially condensed in an upward flow direction, or when it is desirable to remove the vapor and liquid portions of the cooled and partially condensed gas as a mixed stream rather than as separate vapor and liquid streams. In this arrangement, feed gas 11 is introduced via inlet 201 of pressure vessel 203, and feed gas 205 flows into the open ends of heat exchangers 207 and 209. The gas condenses as it flows upward with the resulting condensate, and the two-phase vapor/liquid stream is withdrawn via collector fins and headers 211 and 213, manifolds 215, 217, and 219, and outlet 221 to provide final vapor/liquid product 223. Headers 211 and 213 and manifolds 215, 217, and 219 are generically described as fluid transfer means to transfer fluid from the ends of heat exchangers 207 and 209 to outlet 221. The refrigerant in this alternative embodiment can be provided as described earlier for the embodiment of FIG. 1.

[0069] The flow passageways are oriented such that the cocurrent flow of uncondensed feed gas and condensate is in a generally upward direction, i.e., in a vertical upward direction or in an upward direction which is between vertical and horizontal. The flow passageways deviate sufficiently from the horizontal such that the condensate flows upward by entrainment in the upward-flowing gas. Preferably, the flow is in a generally upward direction, which means that the flow is preferably vertically upward but can deviate from the vertical as long as the deviation does not adversely affect the upward cocurrent flow of uncondensed feed gas and entrained condensate through the exchanger and/or the transfer of heat from the uncondensed feed gas and condensate to the refrigerant. The refrigerant can flow upward as shown using a vaporizing fluid, or downward using a gaseous refrigerant, to maintain an adequate temperature difference between the feed and the refrigerant.

[0070] In the embodiments of FIGS. 1 and 2, heat exchangers 1 and 209 are open at the bottom and have a header and manifolds at the top of the exchanger. In an alternative embodiment (not shown), the heat exchanger is open at the top and has a header and manifolds at the bottom. Fluid flow in this alternative embodiment can be either upward or downward, and can be either single-phase or condensing flow as described above.

[0071] Another alternative embodiment of the invention is shown in FIG. 3 which illustrates the use of two heat exchangers in parallel, although single or more than two heat exchangers can be used if desired. In this embodiment, heat exchangers 301 and 303 are installed in pressure vessel 305, and seal means 307 (shown schematically) is installed between the heat exchanger and pressure vessel walls to segregate the vessel interior into upper section 309 and lower section 311 which are not in flow communication. Seal means 307 can be installed at any appropriate axial location between the upper and lower ends of heat exchangers 301 and 303. Seal means 307 can be any type of seal known in the art for segregating the upper and lower sections of the vessel against a low gas pressure differential, for example, 1 to 10 psi. Seal means 307 could be integrated with a core or piping support member.

[0072] The use of seal means 307 eliminates the need for feed distributor fins, headers, and manifolds at the top of the heat exchangers and processed gas collector fins, headers, and manifolds at the bottom of the heat exchangers. Thus the flow passageways or channels are open at both ends. The term “open” means that the end of the exchanger has no distributor fins, collector fins, or headers associated with it, and therefore fluid can flow unimpeded without restriction into and out of the ends of the flow channels. The heat transfer fins in the flow passageways can be continuous from the top to the bottom of the core, with no distributor or collector fins at either end. The bottom end of each feed channel is in flow communication with lower section 311 of pressure vessel 305, and the upper end of each feed channel is in flow communication with upper section 309 of the pressure vessel. The refrigerant circuits can be similar to those described in FIG. 1.

[0073] A portion of the flow passageways in the heat exchanger can be utilized for condensing service, and these passageways form a feed circuit through which the uncondensed feed gas and condensate flow cocurrently. The flow passageways are oriented such that the uncondensed feed gas and condensate flow cocurrently in a generally downward direction, i.e., in a vertical downward direction or in a downward direction which deviates from vertical wherein the flow passageways operate such that the condensate flows downward by the force of gravity. The generally downward direction is preferably vertical but can deviate from the vertical as long as the deviation does not adversely affect the downward cocurrent flow of uncondensed feed gas and condensate through the exchanger and/or the transfer of heat from the uncondensed feed gas and condensate to the refrigerant.

[0074] In this embodiment, feed gas stream 313 flows through vessel inlet 315, and interior feed gas 317 flows into upper section 309 of vessel 305 and then downward through the feed channels of heat exchangers 301 and 303. Condensation occurs as the gas and condensate flow downward through the feed channels, liquid 319 flows from the open ends of heat exchangers 301 and 303, and liquid 321 collects in the bottom of the vessel. Liquid product 323 is withdrawn via outlet 325 and uncondensed vapor 327 flows directly from the open feed channels at the lower ends of the heat exchangers and is withdrawn via vessel outlet 329 to provide vapor product 331.

[0075] While the heat exchanger of FIG. 3 as described above is utilized for condensing flow, the heat exchanger alternatively can be utilized to cool a fluid (either gas or liquid) without phase change. For example, a superheated gas stream can be cooled to a temperature above its dew point, while a liquid at or below its bubble point can be subcooled to a temperature further below its bubble point. In this alternative, the axis of the heat exchanger and the flow direction of the fluid being cooled (which is generally parallel to the axis of the exchanger) can be vertical, horizontal, or between vertical and horizontal. Thus the fluid being cooled can flow in any desired direction.

[0076] The advantage of the embodiment of FIG. 3 is that no manifolds, headers, distributor fins, or collector fins are needed at either end of heat exchangers 301 and 303 for feed introduction and product withdrawal. This greatly simplifies the entire heat exchanger assembly and results in reduced capital cost.

[0077] Two or more heat exchanger cores operating in different temperature or pressure ranges can be utilized in series or in parallel by stacking the pressure vessels in a vertical arrangement or by locating the vessels side-by-side. When used in series, the exit gas from a first heat exchanger is fed to a second heat exchanger for further cooling as described below. An internal head can be used inside a single pressure vessel to separate the warmer and colder heat exchangers as shown in the alternative embodiment of FIG. 4. In this embodiment, lower pressure vessel section 401 and upper pressure vessel section 403 are formed by head 405 installed in overall pressure vessel 407. Lower pressure vessel 401 and heat exchangers 409 and 411 installed therein are similar to the system described above for FIG. 3. Upper pressure vessel 403 and heat exchangers 413 and 415 are similar to the system described earlier for FIG. 1.

[0078] Feed gas 417 is processed in heat exchangers 413 and 415 in the same manner as that described earlier for exchangers 1 and 51 for the embodiment of FIG. 1. Intermediate vapor product 419 flows through vessel inlet 421 into upper portion 423 of pressure vessel 401, and is processed in the same manner as that described earlier for the embodiment of FIG. 3. First liquid product 425 is withdrawn via outlet 427. Vapor 429 condenses further in exchangers 409 and 411, which operate with a colder refrigerant than exchangers 413 and 415.

[0079] Additional liquid is condensed and condensate 431 flows out of the bottoms of heat exchangers 409 and 411, and collects in the bottom of vessel 401 as liquid 433. This liquid is withdrawn via outlet 435 to provide second liquid product stream 437, which contains additional higher boiling components. Vapor 439 flows from the bottoms of heat exchangers 409 and 411, and vapor product 441 is withdrawn via outlet 443. This vapor product is enriched in the more volatile components in feed gas 417.

[0080] Refrigerant 445 provides refrigeration to heat exchangers 413 and 415 as described earlier for the operation of heat exchangers 1 and 51 of FIG. 1. Refrigerant 449, which is at a lower temperature than refrigerant 445, provides refrigeration to heat exchangers 409 and 411 as described earlier for the operation of heat exchangers 301 and 303 of FIG. 3. The two sections of vessel 407 can utilize different numbers or sizes of heat exchangers, and the sections may be of different diameters.

[0081] The two vessel sections of FIG. 4 can be operated at different pressures if desired. In this mode of operation, vessel section 403 is operated at a higher pressure than vessel section 401, and uncondensed gas stream 419 is reduced in pressure before being introduced into inlet 421.

[0082] Several alternatives to the embodiment of FIG. 4 are possible. In one alternative, upper section 403 can be similar to bottom section 401, wherein both sections utilize heat exchangers open on both ends with seals to segregate the upper and lower portions of the exchangers. In another alternative, the bottom section 401 would contain heat exchangers identical to those in upper section 403 of FIG. 4. In yet another alternative, heat exchangers 409 and 411, with seal 447, can be located in upper section 403 while heat exchangers 413 and 415, with gas inlet headers and distributor fins, can be located in lower section 401.

[0083] In another alternative, an internal head or other arrangement, such as a chimney tray (not shown), can be used inside a single pressure vessel to separate the heat exchangers in sections 401 and 403. In this alternative, the vapor from the upper section can flow by means of the chimney tray directly into the lower section without flowing through external piping required for stream 419 of FIG. 4. The two sections of the pressure vessel can contain the same size or different sizes of heat exchangers, can contain the same or different numbers of heat exchangers, and can be of different diameters if necessary. The feed gas can flow either upward or downward in each of the heat exchangers as described earlier. The feed inlet, the processed gas/liquid outlet, or both the feed inlet and processed gas/liquid outlet of each of the heat exchangers can be open to the interior of the pressure vessel.

[0084] A common feature of all embodiments of the invention described above operating in condensing flow is that condensed liquid and uncondensed vapor flow through the channels of the core-type heat exchangers cocurrently, i.e., in the same direction. Preferably, flow is in a generally downward direction, but upward flow is used in at least one alternative embodiment as described above. When upward flow is used, the heat exchangers must be designed so that the upward gas flow velocity is sufficient to entrain the condensate such that essentially none of the condensate flows in a downward direction.

[0085] As discussed earlier, conventional full dome header distributor and collector devices typically cannot be used on cores larger than about 3 feet by 4 feet in cross section at pressures above about 150 psig. The pressure vessel for the present invention, however, can be designed to operate at any pressure level, preferably in the range of 100 to 1500 psia. The heat exchanger cores can be any size, both in cross-section and in length. Welded-blocks, i.e. two or more cores welded together side-by-side, can be utilized to increase the available cross-section of the heat exchanger cores to a very large size, such as 4 feet by 8 feet or more. Any length of core can be used, and is typically in the range of 5 to 20 feet.

[0086] The pressure vessel can be externally insulated, similar to a distillation column, so that no cold box is required for the heat exchangers. When parallel heat exchanger cores are used, the number of pipes which must pass through the pressure vessel shell can be minimized by manifolding refrigerant stream nozzles inside the pressure vessel. Refrigerant drums can also be located either inside or outside the pressure vessel, as desired.

[0087] In other alternative embodiments, three or more heat exchangers, each operating at progressively colder temperatures, can be installed in series within a single pressure vessel, or in separate vessels, or a combination of stacked and separate pressure vessels. Any combination of feed flow direction and open core ends/sides can be used in each of the heat exchangers. All refrigerant streams entering or leaving the heat exchangers typically would utilize conventional distributors, collectors, headers, and nozzles, which are piped through the vessel shell.

[0088] When two or more heat exchangers are utilized in series in either stacked or separate pressure vessels, one or more of the heat exchangers can be replaced by a dephlegmator. In the dephlegmator, feed gas enters the pressure vessel, flows into the open bottom end of the core and upward through the core. Condensed liquid drains downward, and rectification occurs as the liquid and vapor flow countercurrently in the core. Condensate exits freely from the bottom of the core into the bottom of the vessel for removal. The feed vapor outlet at the top end of the dephlegmator may be either open or closed. All refrigerant streams entering or leaving the dephlegmator typically would utilize conventional distributors, collectors, headers, and nozzles.

[0089] Thus the present invention simplifies the design of plate-and-fin heat exchanger cores which operate in the condensing mode and allows efficient use of the core cross section because no manifolds, distributor fins, and headers are required at the inlet of each feed circuit. In an optional embodiment, vapor collector fins, manifolds, and headers are not required at the outlet of each feed circuit, further simplifying heat exchanger design and operation. The present invention allows operation of plate-and-fin core-type heat exchangers at higher pressures than many prior art systems which require dome headers or similar integrated vessels attached to the heat exchanger feed circuits. In addition, higher throughput is possible because the available fluid handling capacity of each heat exchanger is not reduced by distributors, collectors, headers, nozzles, or manifolds.

[0090] The essential characteristics of the present invention are described completely in the foregoing disclosure. One skilled in the art can understand the invention and make various modifications without departing from the basic spirit of the invention, and without deviating from the scope and equivalents of the claims which follow.