Patent Application
20200248962
The present invention relates generally to systems and methods for cooling or liquefying gases and, more particularly, to a mixed refrigerant system and method for cooling or liquefying gases.
Natural gas and other gases are liquefied for storage and transport. Liquefaction reduces the volume of the gas and is typically carried out by chilling the gas through indirect heat exchange in one or more refrigeration cycles. The refrigeration cycles are costly because of the complexity of the equipment and the performance efficiency of the cycle. There is a need, therefore, for gas cooling and/or liquefaction systems that lower equipment cost and that are less complex, more efficient, and less expensive to operate.
Liquefying natural gas, which is primarily methane, typically requires cooling the gas stream to approximately −160° C. to −170° C. and then letting down the pressure to approximately atmospheric. Typical temperature-enthalpy curves for liquefying gaseous methane, have three regions along an S-shaped curve. As the gas is cooled, at temperatures above about −75° C. the gas is de-superheating; and at temperatures below about −90° C. the liquid is subcooling. Between these temperatures, a relatively flat region is observed in which the gas is condensing into liquid.
Refrigeration processes supply the requisite cooling for liquefying natural gas, and the most efficient of these have heating curves that closely approach the cooling curves for natural gas, ideally to within a few degrees throughout the entire temperature range. However, because the cooling curves feature an S-shaped profile and a large temperature range, such refrigeration processes are difficult to design. Pure component refrigerant processes, because of their flat vaporization curves, work best in the two-phase region. Multi-component refrigerant processes, on the other hand, have sloping vaporization curves and are more appropriate for the de-superheating and subcooling regions. Both types of processes, and hybrids of the two, have been developed for liquefying natural gas
Cascaded, multilevel, pure component refrigeration cycles were initially used with refrigerants such as propylene, ethylene, methane, and nitrogen. With enough levels, such cycles can generate a net heating curve that approximates the cooling curves shown in
However, as the number of levels increases, additional compressor trains are required, which undesirably adds to the mechanical complexity. Further, such processes are thermodynamically inefficient because the pure component refrigerants vaporize at constant temperature instead of following the natural gas cooling curve, and the refrigeration valve irreversibly flashes the liquid into vapor. For these reasons, mixed refrigerant processes have become popular to reduce capital costs and energy consumption and to improve operability.
U.S. Pat. No. 5,746,066 to Manley describes a cascaded, multilevel, mixed refrigerant process for ethylene recovery, which eliminates the thermodynamic inefficiencies of the cascaded multilevel pure component process. This is because the refrigerants vaporize at rising temperatures following the gas cooling curve, and the liquid refrigerant is subcooled before flashing thus reducing thermodynamic irreversibility. Mechanical complexity is somewhat reduced because fewer refrigerant cycles are required compared to pure refrigerant processes. See, e.g., U.S. Pat. No. 4,525,185 to Newton; U.S. Pat. No. 4,545,795 to Liu et al.; U.S. Pat. No. 4,689,063 to Paradowski et al.; and U.S. Pat. No. 6,041,619 to Fischer et al.; and U.S. Patent Application Publication Nos. 2007/0227185 to Stone et al. and 2007/0283718 to Hulsey et al.
The cascaded, multilevel, mixed refrigerant process is among the most efficient known, but a simpler, more efficient process, which can be more easily operated, is desirable.
A single mixed refrigerant process, which requires only one compressor for refrigeration and which further reduces the mechanical complexity has been developed. See, e.g., U.S. Pat. No. 4,033,735 to Swenson. However, for primarily two reasons, this process consumes somewhat more power than the cascaded, multilevel, mixed refrigerant processes discussed above.
First, it is difficult, if not impossible, to find a single mixed refrigerant composition that generates a net heating curve that closely approximates the typical natural gas cooling curve. Such a refrigerant requires a range of relatively high and low boiling components, whose boiling temperatures are thermodynamically constrained by the phase equilibrium. Higher boiling components are further limited in order to avoid their freezing out at low temperatures. The undesirable result is that relatively large temperature differences necessarily occur at several points in the cooling process, which is inefficient in the context of power consumption.
Second, in single mixed refrigerant processes, all of the refrigerant components are carried to the lowest temperature even though the higher boiling components provide refrigeration only at the warmer end of the process. The undesirable result is that energy must be expended to cool and reheat those components that are “inert” at the lower temperatures. This is not the case with either the cascaded, multilevel, pure component refrigeration process or the cascaded, multilevel, mixed refrigerant process.
To mitigate this second inefficiency and also address the first, numerous solutions have been developed that separate a heavier fraction from a single mixed refrigerant, use the heavier fraction at the higher temperature levels of refrigeration, and then recombine the heavier fraction with the lighter fraction for subsequent compression. See, e.g., U.S. Pat. No. 2,041,725 to Podbielniak; U.S. Pat. No. 3,364,685 to Perret; U.S. Pat. No. 4,057,972 to Sarsten; U.S. Pat. No. 4,274,849 to Garrier et al.; U.S. Pat. No. 4,901,533 to Fan et al.; U.S. Pat. No. 5,644,931 to Ueno et al.; U.S. Pat. No. 5,813,250 to Ueno et al; U.S. Pat. No. 6,065,305 to Arman et al.; and U.S. Pat. No. 6,347,531 to Roberts et al.; and U.S. Patent Application Publication No. 2009/0205366 to Schmidt. With careful design, these processes can improve energy efficiency even though the recombining of streams not at equilibrium is thermodynamically inefficient. This is because the light and heavy fractions are separated at high pressure and then recombined at low pressure so that they may be compressed together in a single compressor. Generally, when streams are separated at equilibrium, separately processed, and then recombined at non-equilibrium conditions, a thermodynamic loss occurs, which ultimately increases power consumption.
Therefore the number of such separations should be minimized. All of these processes use simple vapor/liquid equilibrium at various places in the refrigeration process to separate a heavier fraction from a lighter one.
Simple one-stage vapor/liquid equilibrium separation, however, doesn't concentrate the fractions as much as using multiple equilibrium stages with reflux. Greater concentration allows greater precision in isolating a composition that provides refrigeration over a specific range of temperatures. This enhances the process ability to follow the typical gas cooling curves. U.S. Pat. No. 4,586,942 to Gauthier and U.S. Pat. No. 6,334,334 to Stockmann et al. (the latter marketed by Linde as the LIMUM®3 process) describe how fractionation may be employed in the above ambient compressor train to further concentrate the separated fractions used for refrigeration in different temperature zones and thus improve the overall process thermodynamic efficiency. A second reason for concentrating the fractions and reducing their temperature range of vaporization is to ensure that they are completely vaporized when they leave the refrigerated part of the process. This fully utilizes the latent heat of the refrigerant and precludes the entrainment of liquids into downstream compressors. For this same reason heavy fraction liquids are normally re-injected into the lighter fraction of the refrigerant as part of the process. Fractionation of the heavy fractions reduces flashing upon re-injection and improves the mechanical distribution of the two phase fluids.
As illustrated by U.S. Patent Application Publication No. 2007/0227185 to Stone et al., it is known to remove partially vaporized refrigeration streams from the refrigerated portion of the process. Stone et al. does this for mechanical (and not thermodynamic) reasons and in the context of a cascaded, multilevel, mixed refrigerant process that requires two separate mixed refrigerants. The partially vaporized refrigeration streams are completely vaporized upon recombination with their previously separated vapor fractions immediately prior to compression.
Multi-stream, mixed refrigerant systems are known in which simple equilibrium separation of a heavy fraction was found to significantly improve the mixed refrigerant process efficiency if that heavy fraction isn't entirely vaporized as it leaves the primary heat exchanger. See, e.g., U.S. Patent Application Publication No. 2011/0226008 to Gushanas et al. Liquid refrigerant, if present at the compressor suction, must be separated beforehand and sometimes pumped to a higher pressure. When the liquid refrigerant is mixed with the vaporized lighter fraction of the refrigerant, the compressor suction gas is cooled, which further reduces the power required. Heavy components of the refrigerant are kept out of the cold end of the heat exchanger, which reduces the possibility of refrigerant freezing. Also, equilibrium separation of the heavy fraction during an intermediate stage reduces the load on the second or higher stage compressor(s), which improves process efficiency. Use of the heavy fraction in an independent pre-cool refrigeration loop can result in a near closure of the heating/cooling curves at the warm end of the heat exchanger, which results in more efficient refrigeration.
“Cold vapor” separation has been used to fractionate high pressure vapor into liquid and vapor streams. See, e.g., U.S. Pat. No. 6,334,334 to Stockmann et al., discussed above; “State of the Art LNG Technology in China”, Lange, M., 5th Asia LNG Summit, Oct. 14, 2010; “Cryogenic Mixed Refrigerant Processes”, International Cryogenics Monograph Series, Venkatarathnam, G., Springer, pp 199-205; and “Efficiency of Mid Scale LNG Processes Under Different Operating Conditions”, Bauer, H., Linde Engineering. In another process, marketed by Air Products as the AP-SMR™ LNG process, a “warm”, mixed refrigerant vapor is separated into cold mixed refrigerant liquid and vapor streams. See, e.g., “Innovations in Natural Gas Liquefaction Technology for Future LNG Plants and Floating LNG Facilities”, International Gas Union Research Conference 2011, Bukowski, J. et al. In these processes, the thus-separated cold liquid is used as the middle temperature refrigerant by itself and remains separate from the thus-separated cold vapor prior to joining a common return stream. The cold liquid and vapor streams, together with the rest of the returning refrigerants, are recombined via cascade and exit together from the bottom of the heat exchanger.
In the vapor separation systems discussed above, the warm temperature refrigeration used to partially condense the liquid in the cold vapor separator is produced by the liquid from the high-pressure accumulator. This requires higher pressure and less than ideal temperatures, both of which undesirably consume more power during operation.
Another process that uses cold vapor separation, albeit in a multi-stage, mixed refrigerant system, is described in GB Pat. No. 2,326,464 to Costain Oil. In this system, vapor from a separate reflux heat exchanger is partially condensed and separated into liquid and vapor streams. The thus-separated liquid and vapor streams are cooled and separately flashed before rejoining in a low-pressure return stream. Then, before exiting the main heat exchanger, the low-pressure return stream is combined with a subcooled and flashed liquid from the aforementioned reflux heat exchanger and then further combined with a subcooled and flashed liquid provided by a separation drum set between the compressor stages. In this system, the “cold vapor” separated liquid and the liquid from the aforementioned reflux heat exchanger are not combined prior to joining the low-pressure return stream. That is, they remain separate before independently joining up with the low-pressure return stream.
Power consumption can be significantly reduced by, inter alia, mixing a liquid obtained from a high pressure accumulator with the cold vapor separated liquid prior to their joining a return stream.
It is desirable to provide a mixed gas system and method for cooling or liquefying a gas that addresses at least some of the above issues and improves efficiency.
There are several aspects of the present subject matter which may be embodied separately or together in the methods, devices and systems described and claimed below. These aspects may be employed alone or in combination with other aspects of the subject matter described herein, and the description of these aspects together is not intended to preclude the use of these aspects separately or the claiming of such aspects separately or in different combinations as set forth in the claims appended hereto.
In one aspect, a system for cooling a gas with a mixed refrigerant is provided and includes a main heat exchanger including a warm end and a cold end with a feed stream cooling passage extending therebetween, with the feed stream cooling passage being adapted to receive a feed stream at the warm end and to convey a cooled product stream out of the cold end. The main heat exchanger also includes a high pressure vapor cooling passage, a high pressure liquid cooling passage, a cold separator vapor cooling passage, a cold separator liquid cooling passage and a refrigeration passage.
The system also includes a mixed refrigerant compressor system including a compressor first section having an inlet in fluid communication with an outlet of the refrigeration passage and an outlet. A first section cooler has an inlet in fluid communication with the outlet of the compressor first section and an outlet. An interstage separation device has an inlet in fluid communication with the outlet of the first section cooler and a liquid outlet and a vapor outlet. A compressor second section has an inlet in fluid communication with the vapor outlet of the interstage separation device and an outlet. A second section cooler has an inlet in fluid communication with the outlet of the compressor second section and an outlet. A high pressure separation device has an inlet in fluid communication with the outlet of the second section cooler and a liquid outlet and a vapor outlet.
The high pressure vapor cooling passage of the heat exchanger has an inlet in fluid communication with the vapor outlet of the high pressure separation device and a cold vapor separator has an inlet in fluid communication with an outlet of the high pressure vapor cooling passage, where the cold vapor separator has a liquid outlet and a vapor outlet. The cold separator liquid cooling passage of the heat exchanger has an inlet in fluid communication with the liquid outlet of the cold vapor separator and an outlet in fluid communication with the refrigeration passage. The low pressure liquid cooling passage of the heat exchanger has an inlet in fluid communication with the liquid outlet of the interstage separation device. A first expansion device has an inlet in communication with an outlet of the low pressure liquid cooling passage and an outlet in fluid communication with the refrigeration passage. The high pressure liquid cooling passage of the heat exchanger has an inlet in fluid communication with the liquid outlet of the high pressure separation device and an outlet in fluid communication with the refrigeration passage. The cold separator vapor cooling passage of the heat exchanger has an inlet in fluid communication with the vapor outlet of the cold vapor separator. A second expansion device having an inlet in fluid communication with an outlet of the cold separator vapor cooling passage and an outlet in fluid communication with an inlet of the refrigeration passage.
In another aspect, a system for cooling a gas with a mixed refrigerant includes a main heat exchanger including a warm end and a cold end with a feed stream cooling passage extending therebetween. The feed stream cooling passage is adapted to receive a feed stream at the warm end and to convey a cooled product stream out of the cold end. The main heat exchanger also includes a high pressure vapor cooling passage, a high pressure liquid cooling passage, a cold separator vapor cooling passage, a cold separator liquid cooling passage and a refrigeration passage.
The system also includes a mixed refrigerant compressor system including a compressor first section having an inlet in fluid communication with an outlet of the refrigeration passage and an outlet. A first section cooler has an inlet in fluid communication with the outlet of the compressor first section and an outlet. An interstage separation device has an inlet in fluid communication with the outlet of the first section cooler and a vapor outlet. A compressor second section has an inlet in fluid communication with the vapor outlet of the interstage separation device and an outlet. A second section cooler has an inlet in fluid communication with the outlet of the compressor second section and an outlet. A high pressure separation device has an inlet in fluid communication with the outlet of the second section cooler and a liquid outlet and a vapor outlet.
The high pressure vapor cooling passage of the heat exchanger has an inlet in fluid communication with the vapor outlet of the high pressure separation device. A cold vapor separator has an inlet in fluid communication with an outlet of the high pressure vapor cooling passage, where the cold vapor separator has a liquid outlet and a vapor outlet. The cold separator liquid cooling passage of the heat exchanger has an inlet in fluid communication with the liquid outlet of the cold vapor separator and an outlet in fluid communication with the refrigeration passage. The high pressure liquid cooling passage of the heat exchanger has an inlet in fluid communication with the liquid outlet of the high pressure separation device and an outlet in fluid communication with the refrigeration passage. The cold separator vapor cooling passage of the heat exchanger has an inlet in fluid communication with the vapor outlet of the cold vapor separator. An expansion device has an inlet in fluid communication with an outlet of the cold separator vapor cooling passage and an outlet in fluid communication with an inlet of the refrigeration passage.
In yet another aspect, a compressor system for providing mixed refrigerant to a heat exchanger for cooling a gas is provided and includes a compressor first section having a suction inlet adapted to receive a mixed refrigerant from a heat exchanger and an outlet. A first section cooler has an inlet in fluid communication with the outlet of the compressor first section and an outlet. An interstage separation device has an inlet in fluid communication with the outlet of the first section after-cooler and a vapor outlet. A compressor second section has a suction inlet in fluid communication with the vapor outlet of the interstage separation device and an outlet. A second section cooler has an inlet in fluid communication with the outlet of the compressor second section and an outlet. A high pressure separation device has an inlet in fluid communication with the outlet of the second section cooler and a vapor outlet and a liquid outlet, with the vapor outlet adapted to provide a high pressure mixed refrigerant vapor stream to the heat exchanger and said liquid outlet adapted to provide a high pressure mixed refrigerant liquid stream to the heat exchanger. A high pressure recycle expansion device has an inlet in fluid communication with the high pressure separation device and an outlet in fluid communication with the interstage separation device.
In yet another aspect, a method of cooling a gas in a heat exchanger having a warm end and a cold end using a mixed refrigerant includes compressing and cooling a mixed refrigerant using first and last compression and cooling cycles, separating the mixed refrigerant after the first and last compression and cooling cycles so that a high pressure liquid stream and a high pressure vapor stream are formed, cooling and separating the high pressure vapor stream using the heat exchanger and a cold separator so that a cold separator vapor stream and a cold separator liquid stream are formed, cooling and expanding the cold separator vapor stream so that an expanded cold temperature stream is formed, cooling the cold separator liquid stream so that a subcooled cold separator stream is formed, equilibrating and separating the mixed refrigerant between the first and last compression and cooling cycles so that a low pressure liquid stream is formed, cooling and expanding the low pressure liquid stream so that an expanded low pressure stream is formed and subcooling the high pressure liquid stream so that a subcooled high pressure stream is formed. The subcooled cold separator stream and the subcooled high pressure stream are expanded to form an expanded cold separator stream and an expanded high pressure stream or mixed and then expanded to form a middle temperature stream. The expanded streams or middle temperature stream are or is combined with the expanded low pressure stream and the expanded cold temperature stream to form a primary refrigeration stream. A stream of gas is passed through the heat exchanger in countercurrent heat exchange with the primary refrigeration stream so that the gas is cooled.
It should be noted that while the embodiments are illustrated and described below in terms of liquefying natural gas to produce liquid natural gas, the invention may be used to liquefy or cool other types of fluids.
It should also be noted herein that the passages and streams described in the embodiments below are sometimes both referred to by the same element number set out in the figures. Also, as used herein, and as known in the art, a heat exchanger is that device or an area in the device wherein indirect heat exchange occurs between two or more streams at different temperatures, or between a stream and the environment. As used herein, the terms “communication”, “communicating”, and the like generally refer to fluid communication unless otherwise specified. And although two fluids in communication may exchange heat upon mixing, such an exchange would not be considered to be the same as heat exchange in a heat exchanger, although such an exchange can take place in a heat exchanger. A heat exchange system can include those items though not specifically described are generally known in the art to be part of, or associated with, a heat exchanger, such as expansion devices, flash valves, and the like. As used herein, the term “reducing the pressure of” does not involve a phase change, while the term “flashing” or “flashed” does involve a phase change, including even a partial phase change. As used herein, the terms, “high”, “middle”, “warm” and the like are relative to comparable streams, as is customary in the art and illustrated by U.S. patent application Ser. No. 12/726,142, filed Mar. 17, 2010, and U.S. patent application Ser. No. 14/218,949, filed Mar. 18, 2014, the contents of each of which are hereby incorporated by reference. The contents of U.S. Pat. No. 6,333,445, issued Dec. 25, 2001, are also hereby incorporated by reference.
A first embodiment of a mixed refrigerant system and method is illustrated in
The heat exchange system includes a multi-stream heat exchanger, indicated in general at 100, having a warm end 101 and a cold end 102. The heat exchanger receives a high pressure natural gas feed stream 5 that is liquefied in feed stream cooling passage 103, which is made up of feed stream cooling passage 105 and treated feed stream cooling passage 120, via removal of heat via heat exchange with refrigeration streams in the heat exchanger. As a result, a stream 20 of liquid natural gas (LNG) product is produced. The multi-stream design of the heat exchanger allows for convenient and energy-efficient integration of several streams into a single exchanger. Suitable heat exchangers may be purchased from Chart Energy & Chemicals, Inc. of The Woodlands, Tex. The plate and fin multi-stream heat exchanger available from Chart Energy & Chemicals, Inc. offers the further advantage of being physically compact.
As will be explained in greater detail below, the system of
The removal of heat is accomplished in the heat exchanger 100 of the heat exchange system 70 (and other heat exchange systems described herein) using a single mixed refrigerant that is processed and reconditioned using the MR compressor system 50 (and other MR compressor systems described herein). As an example only, the mixed refrigerant may include two or more C1-C5 hydrocarbons and optionally N2. Furthermore, the mixed refrigerant may include two or more of methane, ethane, ethylene, propane, propylene, isobutane, n-butane, isobutene, butylene, n-pentane, isopentane, N2, or a combination thereof. More detailed exemplary refrigerant compositions (along with stream temperature and pressures), which are not intended to be limiting, are presented in U.S. patent application Ser. No. 14/218,949, filed Mar. 18, 2014.
The heat exchange system 70 includes a cold vapor separator 200, a mid-temperature standpipe 300 and a cold temperature standpipe 400 that receive mixed refrigerant from, and return mixed refrigerant to, the heat exchanger 100.
The MR compressor system includes a suction drum 600, a multi-stage compressor 700, an interstage separation device or drum 800 and a high pressure separation device 900. While accumulation or separation drums are illustrated for devices 200, 300, 400, 600, 800 and 900, alternative separation devices may be used, including, but not limited to, another type of vessel, a cyclonic separator, a distillation unit, a coalescing separator or mesh or vane type mist eliminator.
It is to be understood that the suction drum 600 may be omitted in embodiments that use compressors that do not require a suction drum for their inlets. A non-limiting example of such a compressor is a screw compressor.
The functionality and additional components of the MR compressor system 50 and heat exchange system 70 will now be described.
The compressor first section 701 includes a compressed fluid outlet for providing a compressed suction drum MR vapor stream 710 to first section cooler 710C so that cooled compressed suction drum MR stream 720 is provided to interstage separation device or drum 800. The stream 720 travels to the interstage separation device or drum 800 and the resulting low pressure MR vapor stream 855 is provided to the compressor second section 702. The compressor second section 702 provides a compressed high pressure MR vapor stream 730 to the second section cooler 730C. As a result, a high pressure MR stream 740 that is at least partially condensed travels to high pressure separation device 900.
It is to be understood that, in the present and following embodiments, there could be one or more additional intermediate compression/compressor and cooling/cooler sections between the first compression and cooling section and the second compression and cooling section so that the compressor second section and the second section cooler are the last compressor section and the last section cooler. It should be further understood that while the compressors 701 and 702 are illustrated and described as different sections of a multi-stage compressor, the compressors 701 and 702 may instead be separate compressors including two or more compressors.
The high pressure separation device 900 equilibrates and separates the MR stream 740 into a high pressure MR vapor stream 955 and a high pressure MR liquid stream 975, which is preferably a mid-boiling refrigerant liquid stream.
In an alternative embodiment of the MR compressor system, indicated in general at 52 in
Furthermore, MR compressor system 52 may optionally provide a high pressure MR recycle liquid stream 980 from high pressure separation device 900 to an expansion device 980E so that a high pressure MR recycle mixed phase stream 990 is provided to interstage drum 800 so that streams 720 and 990 are combined and equilibrated. Recycling liquid from the high pressure separation device 900 to the interstage drum 800 keeps the pump 880P running under conditions which the interstage drum would otherwise not receive a sufficient supply of cool liquid, such as when warm ambient temperatures exist (i.e. on a hot day). Opening the device 980E eliminates the necessity of shutting the pump 880P off until sufficient liquid is collected, and thus keeps a constant composition of refrigerant flowing to the high pressure separation device 900. As examples only, stream 980 may have a pressure of 600 psig and a temperature of 100° F., while stream 990 may have a pressure of 200 psig and a temperature of 60° F.
In another alternative embodiment of the MR compressor system, indicated in general at 54 in
As further illustrated in
In a simplified, alternative embodiment of the MR compressor system, indicated in general at 56 of
The compressor first section 701 includes a compressed fluid outlet for providing a compressed suction drum MR vapor stream 710 to first section cooler 710C so that cooled compressed suction drum MR stream 720 is provided to interstage drum 800. The stream 720 travels to the interstage drum 800 and the resulting low pressure MR vapor stream 855 is provided to the compressor second section 702. The compressor second section 702 provides a compressed high pressure MR vapor stream 730 to the second section cooler 730C. As a result, a high pressure MR stream 740 that is at least partially condensed travels to high pressure separation device 900.
The high pressure separation device 900 separates the MR stream 740 into a high pressure MR vapor stream 955 and a high pressure MR liquid stream 975, which is preferably a mid-boiling refrigerant liquid stream.
In an alternative embodiment of the MR compressor system, indicated in general at 58 in
Otherwise, the MR compressor system 58 of
The heat exchange system 70 of
The feed stream cooling passage 103 includes a pre-treatment feed stream cooling passage 105, having an inlet at the warm end of heat exchanger 100, and a treated feed stream cooling passage 120 having a product outlet at the cold end through which product 20 exits. The pre-treatment feed stream cooling passage 105 has an outlet that joins feed fluid outlet 10 while treated feed stream cooling passage 120 has an inlet in communication with feed fluid inlet 15. Feed fluid outlet and inlet 10 and 15 are provided for external feed treatment (125 in
In an alternative embodiment of the heat exchange system, indicated in general at 72 in
The heat exchanger includes a refrigeration passage, indicated in general at 170 in
The combination of the middle temperature refrigerant streams and the cold temperature refrigerant stream forms a middle temperature zone or region in the heat exchanger generally from the point at which they combine and downstream from there in the direction of the refrigerant flow toward the primary refrigeration passage outlet.
A primary MR stream 610, which is vapor or mixed phase, exits the primary refrigeration passage 160 of the heat exchanger 100 and travels to the MR compressor system of any of
The heat exchanger 100 also includes a high pressure vapor cooling passage 195 adapted to receive a high pressure MR vapor stream 955 from any of the MR compressor systems of
The heat exchanger 100 also includes a cold separator vapor cooling passage 127 having an inlet in communication with the cold vapor separator 200 so as to receive the cold separator MR vapor stream 255. The cold separator MR vapor stream is cooled in passage 127 to form condensed cold temperature MR stream 410, which is flashed with expansion device 410E to form expanded cold temperature MR stream 420 which is directed to cold temperature standpipe 400. Expansion device 410E (and as in the case with all “expansion devices” disclosed herein) may be, as non-limiting examples, a valve (such as a Joule Thompson valve), a turbine or a restrictive orifice.
Cold temperature standpipe 400 separates the mixed-phase stream 420 into a cold temperature MR vapor stream 455 and a cold temperature MR liquid stream 475 which enter the inlet of the cold temperature refrigerant passage 140. The vapor and liquid streams 455 and 475 preferably enter the cold temperature refrigerant passage 140 via a header having separate entries for streams 455 and 475. This provides for more even distribution of liquid and vapor within the header.
The cold separator MR liquid stream 275 is cooled in cold separator liquid cooling passage 125 to form subcooled cold separator MR liquid stream 310.
A high pressure liquid cooling passage 197 receives high pressure MR liquid stream 975 from any of the MR compressor systems of
The middle temperature MR streams 355 and 375 are directed to the middle temperature refrigerant inlet 150 of the refrigeration passage where they are mixed with the combined cold temperature MR vapor stream 455 and a cold temperature MR liquid stream 475 and provide refrigeration in the primary refrigeration passage 160. The refrigerant exits the primary refrigeration passage 160 as a vapor phase or mixed phase primary MR stream or refrigerant return stream 610. The return stream 610 may optionally be a superheated vapor refrigerant return stream.
An alternative embodiment of the heat exchange system, indicated in general at 74 in
In another alternative embodiment of the heat exchange system, indicated in general at 76 in
As illustrated in
A further alternative embodiment of a mixed refrigerant system and method is illustrated in
The compressor first section 701 includes a compressed fluid outlet for providing a compressed suction drum MR vapor stream 710 to first section cooler 710C so that cooled compressed suction drum MR stream 720 is provided to interstage drum 800. The stream 720 travels to the interstage drum 800 and the resulting low pressure MR vapor stream 855 is provided to the compressor second section 702. The compressor second section 702 provides a compressed high pressure MR vapor stream 730 to the second section cooler 730C. As a result, a high pressure MR stream 740 that is at least partially condensed travels to high pressure separation device 900.
The high pressure separation device 900 separates the MR stream 740 into a high pressure MR vapor stream 955 and a high pressure MR liquid stream 975, which is preferably a mid-boiling refrigerant liquid stream. A high pressure MR recycle liquid stream 980 branches off of stream 975 and is provided to an expansion device 980E so that a high pressure MR recycle mixed phase stream 990 is provided to interstage drum 800. This keeps the interstage drum 800 from running dry during warm ambient temperatures (i.e. such as on a hot day). As described previously (with respect to
In contrast to the MR compressor system embodiments described above, the interstage drum 800 of MR compressor system 60 includes a liquid outlet for providing a low pressure MR liquid stream 875 that has a high boiling temperature. The low pressure MR liquid stream 875 is received by a low pressure liquid cooling passage 187 of the heat exchanger 100 and is further handled as described below.
An alternative embodiment of the MR compressor system is indicated in general at 62 of
In another alternative embodiment of the MR compressor system, indicated in general at 64 in
Otherwise, the MR compressor system 64 of
The heat exchange system 80 of
As illustrated in
As in the case of the heat exchange system 70 of
In an alternative embodiment of the heat exchange system, indicated in general at 82 in
As in the case of the heat exchange system 70 of
The combination of the middle temperature refrigerant streams and the cold temperature refrigerant stream forms a middle temperature zone or region in the heat exchanger generally from the point at which they combine and downstream from there in the direction of the refrigerant flow toward the primary refrigeration passage outlet.
A primary MR stream 610 exits the primary refrigeration passage 160 of the heat exchanger 100, travels to the MR compressor system of any of
The heat exchanger 100 also includes a high pressure vapor cooling passage 195 adapted to receive a high pressure MR vapor stream 955 from any of the MR compressor systems of
The heat exchanger 100 also includes a cold separator vapor cooling passage 127 having an inlet in communication with the vapor outlet of the cold vapor separator 200 so as to receive the cold separator MR vapor stream 255. The cold separator MR vapor stream is cooled in passage 127 to form condensed cold temperature MR stream 410, and then flashed with expansion device 410E to form expanded cold temperature MR stream 420 which is directed to cold temperature standpipe 400. Expansion device 410E (and as in the case with all “expansion devices” disclosed herein) may be, as non-limiting examples, a Joule Thompson valve, a turbine or an orifice.
Cold temperature standpipe 400 separates the mixed-phase stream 420 into a cold temperature MR vapor stream 455 and a cold temperature MR liquid stream 475 which enter the inlet of the cold temperature refrigerant passage 140.
The cold separator MR liquid stream 275 is cooled in cold separator liquid cooling passage 125 to form subcooled cold separator MR liquid stream 310.
A high pressure liquid cooling passage 197 receives high pressure MR liquid stream 975 from any of the MR compressor systems of
The middle temperature MR streams 355 and 375 are directed to the middle temperature refrigerant inlet 150 of the refrigeration passage where they are mixed with the combined cold temperature MR vapor stream 455 and a cold temperature MR liquid stream 475 and provide refrigeration in the primary refrigeration passage 160. The refrigerant exits the primary refrigeration passage 160 as a vapor phase or mixed phase primary MR stream or refrigerant return stream 610. The return stream 610 may optionally be a superheated vapor refrigerant return stream.
The heat exchanger 100 also includes a low pressure liquid cooling passage 187 that, as noted above, receives a low pressure MR liquid stream 875, that preferably is high-boiling refrigerant, from the liquid outlet of the interstage separation device or drum 800 of any of the MR compressor systems of
An alternative embodiment of the heat exchange system is indicated in general at 84 in
In another alternative embodiment of the heat exchange system, indicated in general at 86 in
As illustrated in
In alternative embodiments, the expansion device 510E of
In another alternative embodiment illustrated in
In each of the above embodiments, one or more of an external treatment, pre-treatment, post-treatment, integrated treatment, or combination thereof may independently be in communication with the feed stream cooling passage and adapted to treat the feed stream, product stream, or both.
As an example, and noted previously with reference to
An example of a system for external feed treatment, as used with MR compressor system 50 and heat exchange system 70, is indicated in general at 125 in
The external feed treatment 125 may also be combined with any of the MR compressor system and heat exchange system embodiments described above, including MR compressor system 52 and heat exchange system 70, as illustrated in
As illustrated at 22 in
Each of the external treatment, pre-treatment, or post-treatment, may independently include one or more of removing one or more of sulfur, water, CO2, natural gas liquid (NGL), freezing component, ethane, olefin, C6 hydrocarbon, C6+ hydrocarbon, N2, or combination thereof, from the feed stream.
Furthermore, one or more pre-treatment may independently include one or more of desulfurizing, dewatering, removing CO2, removing one or more natural gas liquids (NGL), or a combination thereof in communication with the feed stream cooling passage and adapted to treat the feed stream, product stream, or both.
In addition, one or more external treatment may independently include one or more of removing one or more natural gas liquids (NGL), removing one or more freezing components, removing ethane, removing one or more olefins, removing one or more C6 hydrocarbons, removing one or more C6+ hydrocarbons, in communication with the feed stream cooling passage and adapted to treat the feed stream, product stream, or both.
Each of the above embodiments may also be provided with one or more post-treatments which may include removing N2 from the product and be in communication with the feed stream cooling passage and adapted to treat the feed stream, product stream, or both.
While the preferred embodiments of the invention have been shown and described, it will be apparent to those skilled in the art that changes and modifications may be made therein without departing from the spirit of the invention, the scope of which is defined by the appended claims.
This application is a division of U.S. patent application Ser. No. 15/205,669, filed Jul. 5, 2016, which claims the benefit of U.S. Provisional Application No. 62/190,069, filed Jul. 8, 2015, the contents of both of which are hereby incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 62190069 | Jul 2015 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 15205669 | Jul 2016 | US |
| Child | 16853827 | US |
