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[0001] Plate-and-fin or core-type heat exchangers are widely used in the process industries for the exchange of heat between fluid mixtures, particularly those which contain components with sub-ambient boiling points. These well-known heat exchangers are typically constructed with parallel plates separated by fins wherein the plates and fins are brazed together to form an integrated assembly of alternating flow channels. The most widely-used material for fabrication of these exchangers is aluminum.
[0002] The characteristic operating feature of core-type heat exchangers is the cooling of a first fluid stream, which flows through a first group of flow channels or passageways, by indirect heat transfer with a second fluid stream, which is warmed in another group of flow channels. The first and second fluid streams generally flow through alternating channels in order to maximize the effective heat transfer area of the exchanger. Additional fluid streams can be warmed and/or cooled in adjacent channels in the same heat exchanger, and thus core-type exchangers can transfer heat among multiple fluid streams.
[0003] In a typical application, a gas is cooled and condensed by indirect heat transfer with a warming fluid such as a vaporizing liquid process stream or refrigerant. In the condensation mode of operation, a feed gas mixture is cooled and partially condensed within a group of flow channels by indirect heat transfer with one or more refrigerants or colder fluids flowing in adjacent alternating flow channels.
[0004] An important requirement for the efficient operation of plate-and-fin core-type heat exchangers is the proper distribution of each process stream into the heat exchanger so that the stream flows uniformly through each of the desired flow channels. This is accomplished by the use of feed distributor fins, headers, and nozzles which are joined to the inlet of the heat exchanger assembly. In addition, similar collector fins, headers, and nozzles are required to withdraw the process streams evenly from the outlet end of the heat exchanger. These distributor and collector devices are complex and expensive. When multiple, parallel heat exchangers are required, complex and expensive manifolding also is required to distribute flow to and collect flow from the parallel heat exchangers. Dome headers eliminate the distributor fins or collector fins. However, these 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.
[0005] Because these heat exchangers often are used in the processing of low-boiling gas mixtures, the resulting low-temperature operation typically requires the use of cold boxes to contain the heat exchangers, phase separators, and associated piping.
[0006] Low-temperature gas processing plants, which utilize the complex heat exchange equipment described above, are highly capital-intensive. There is an ongoing need to reduce the capital cost and equipment complexity of these plants, while retaining high operating efficiency. The invention described below and defined by the claims which follow meets this need by reducing or eliminating the use of complex feed gas distributors and collectors, and optionally by eliminating the need for cold boxes to contain the heat exchangers and associated piping.
[0007] A first embodiment of the invention is a system for cooling a fluid feed stream which comprises:
[0008] (a) a pressure vessel having an interior and an exterior;
[0009] (b) a heat exchanger installed in the interior of the pressure vessel, wherein the heat exchanger comprises a group of flow passageways which has a first end and a second end, wherein at least one of the first end and the second end is open and in flow communication with the interior of the pressure vessel;
[0010] (c) inlet piping means for introducing the fluid feed stream into the interior of the pressure vessel;
[0011] (d) outlet piping means for withdrawing from the interior of the pressure vessel at least a portion of the cooled fluid stream;
[0012] (e) cooling means for indirectly cooling the group of flow passageways to cool the fluid feed stream therein to form a cooled fluid stream; and
[0013] (f) fluid transfer means for transferring the fluid feed stream from the inlet piping means into the group of flow passageways at one end thereof or for transferring a cooled fluid stream from one end of the group of flow passageways to the outlet piping means.
[0014] In this first embodiment, the heat exchanger can be constructed in a plate-and-fin configuration.
[0015] The system described above can further comprise
[0016] (g) an additional pressure vessel having an interior and an exterior;
[0017] (h) a heat exchanger installed in the interior of the additional pressure vessel, wherein the heat exchanger comprises a group of flow passageways which has a first end and a second end, wherein at least one of the first end and the second end is open and in flow communication with the interior of the additional pressure vessel;
[0018] (i) inlet piping means for introducing an intermediate fluid stream into the interior of the additional pressure vessel;
[0019] (j) cooling means for indirectly cooling the group of flow passageways to cool the intermediate fluid stream therein to form an additional cooled fluid stream;
[0020] (k) outlet piping means for withdrawing from the interior of the additional pressure vessel at least a portion of the additional cooled fluid stream; and
[0021] (l) fluid transfer means for transferring the fluid feed stream from the inlet piping means into the group of flow passageways at one end thereof or for transferring a cooled fluid stream from one end of the group of flow passageways to the outlet piping means.
[0022] The system described above can further comprise piping means connecting the outlet piping means of (d) with the inlet piping means of (i) such that at least a portion of the cooled fluid stream withdrawn from the pressure vessel can provide the intermediate fluid stream to the additional pressure vessel.
[0023] The cooling means of (e) described above can comprise
[0024] (1) one or more additional groups of flow passageways in the heat exchanger wherein each additional group of flow passageways has a first end and a second end, and wherein each additional group of flow passageways is in indirect heat transfer communication with the group of flow passageways of (b);
[0025] (2) inlet piping means for introducing refrigerant into the interior of the pressure vessel;
[0026] (3) outlet piping means for withdrawing warmed refrigerant from the interior of the pressure vessel;
[0027] (4) inlet distributor means for distributing the refrigerant from the inlet piping into the first end of the additional group of flow passageways; and
[0028] (5) outlet collector means for collecting the warmed refrigerant from the second end of the additional group of flow passageways and directing warmed refrigerant into the outlet piping means.
[0029] In a first alternative of the system described in the first embodiment above, the first end of the flow passageways can be an upper end and the second end of the flow passageways can be a lower end, and the lower end can be open and in flow communication with a lower region in the interior of the pressure vessel. In this first alternative, the heat exchanger can be constructed in a plate-and-fin configuration.
[0030] The fluid transfer means described in (l) above can comprise outlet manifold means and outlet header means for transferring a cooled fluid stream from the upper end of the group of flow passageways to the outlet piping. The inlet piping means can be connected to a lower end of the pressure vessel and the outlet piping means can be connected to an upper end of the pressure vessel such that fluid can flow through the group of flow passageways in a generally upward direction. In this case, the fluid transfer means comprises inlet manifold means and inlet header means for transferring the fluid feed stream from the inlet piping into the upper end of the group of flow passageways.
[0031] Alternatively, the inlet piping means can be connected to an upper end of the pressure vessel and the outlet piping means can be connected to a lower end of the pressure vessel such that fluid can flow through the group of flow passageways in a generally downward direction. In this case, the fluid flowing generally downward through the group of flow passageways can be a gas which can condense therein to form a vapor and a liquid which flow into the lower end of the pressure vessel, wherein the outlet piping means of (d) is used for withdrawing vapor from the lower end of the pressure vessel, and wherein the system includes additional outlet piping means used for withdrawing liquid from the lower end of the pressure vessel.
[0032] In this first alternative of the first embodiment, the system can further comprise
[0033] (g) an additional pressure vessel having an interior and an exterior;
[0034] (h) a heat exchanger installed in the interior of the additional pressure vessel, wherein the heat exchanger comprises a group of flow passageways which has a first end and a second end, wherein at least one of the first end and the second end is open and in flow communication with the interior of the additional pressure vessel;
[0035] (i) inlet piping means for introducing an intermediate fluid stream into the interior of the additional pressure vessel;
[0036] (j) inlet fluid transfer means for transferring the intermediate fluid stream from the inlet piping means into the group of flow passageways at one end thereof;
[0037] (k) cooling means for indirectly cooling the group of flow passageways to cool the intermediate fluid stream therein to form an additional cooled fluid stream; and
[0038] (l) outlet piping means for withdrawing from the interior of the pressure vessel at least a portion of the additional cooled fluid stream.
[0039] The system can further comprise piping means connecting the outlet piping means of (d) with the inlet piping means of (i) such that at least a portion of the vapor withdrawn from the pressure vessel can provide the intermediate fluid stream to the additional pressure vessel. This heat exchanger in the additional pressure vessel can be constructed in a plate-and-fin configuration.
[0040] The inlet piping means can be connected to an upper end of the additional pressure vessel and the outlet piping means can be connected to a lower end of the additional pressure vessel such that vapor can flow through the group of flow passageways in a generally downward direction. In this case, the vapor flowing generally downward through the group of flow passageways can condense therein to form an uncondensed vapor and a liquid which flow into the lower end of the additional pressure vessel, wherein the outlet piping means of (I) is used for withdrawing the uncondensed vapor from the lower end of the additional pressure vessel, and wherein the system includes additional outlet piping means used for withdrawing liquid from the lower end of the additional pressure vessel.
[0041] In a second alternative of the first embodiment described above, the first end of the flow passageways can be an upper end and the second end of the flow passageways can be a lower end, and wherein the upper end can be open and in flow communication with an upper region in the interior of the pressure vessel. The heat exchanger in the pressure vessel can be constructed in a plate-and-fin configuration. The fluid transfer means can comprise inlet manifold means and inlet header means for transferring the fluid feed stream from the inlet piping into the lower end of the group of flow passageways. In one mode of this second alternative, the inlet piping means can be connected to a lower end of the pressure vessel and the outlet piping means can be connected to an upper end of the pressure vessel such that fluid can flow through the group of flow passageways in a generally upward direction. In this case, the fluid transfer means comprises outlet manifold means and outlet header means for transferring the cooled fluid stream from the lower end of the group of flow passageways to the outlet piping means. In another mode of this second alternative, the inlet piping means can be connected to an upper end of the pressure vessel and the outlet piping means can be connected to a lower end of the pressure vessel such that fluid can flow through the group of flow passageways in a generally downward direction.
[0042] A second embodiment of the invention is a system for cooling a fluid feed stream which comprises:
[0043] (a) a pressure vessel having an interior and an exterior;
[0044] (b) a heat exchanger installed in the interior of the pressure vessel, wherein the heat exchanger comprises a group of flow passageways having a first end and a second end, wherein the first end is open and in flow communication with a first end of the interior of the pressure vessel and the second end is open and in flow communication with a second end of the interior of the pressure vessel;
[0045] (c) cooling means for indirectly cooling the group of flow passageways to cool the fluid feed stream therein to form a cooled fluid stream;
[0046] (d) inlet piping means for introducing the fluid feed stream into the first end of the interior of the pressure vessel;
[0047] (e) outlet piping means for withdrawing at least a portion of the cooled fluid stream from the second end of the interior of the pressure vessel; and
[0048] (f) seal means disposed in the pressure vessel at an axial location between the first and second ends of the group of flow passageways, which seal means isolates the first end of the interior of the pressure vessel from the second end of the interior of the pressure vessel such that the first and second ends of the interior of the pressure vessel are not in flow communication.
[0049] The heat exchanger in this second embodiment can be constructed in a plate-and-fin configuration.
[0050] In one alternative of this second embodiment, the inlet piping means can be connected to a lower end of the pressure vessel and the outlet piping means can be connected to an upper end of the pressure vessel such that fluid can flow through the group of flow passageways in a generally upward direction. In another alternative, the inlet piping means can be connected to an upper end of the pressure vessel and the outlet piping means can be connected to a lower end of the pressure vessel such that fluid can flow through the group of flow passageways in a generally downward direction. In this second alternative, the fluid flowing generally downward through the group of flow passageways can be a gas which can condense therein to form a vapor and a liquid which flow into the lower end of the pressure vessel, wherein the outlet piping means of (e) is used for withdrawing vapor from the lower end of the pressure vessel, and wherein the system includes additional outlet piping means used for withdrawing liquid from the lower end of the pressure vessel.
[0051]
[0052]
[0053]
[0054]
[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
[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
[0058] A stream of mixed feed gas
[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
[0060] Vapor product stream
[0061] Typical refrigerant stream
[0062] Refrigerant
[0063] Additional heat exchangers can be installed in parallel with heat exchanger
[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
[0066] Alternatively, it may be desirable to have the feed gas
[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
[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
[0071] Another alternative embodiment of the invention is shown in
[0072] The use of seal means
[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
[0075] While the heat exchanger of
[0076] The advantage of the embodiment of
[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
[0078] Feed gas
[0079] Additional liquid is condensed and condensate
[0080] Refrigerant
[0081] The two vessel sections of
[0082] Several alternatives to the embodiment of
[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
[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.