Patent Application
20240068745
Not applicable.
The present invention relates to the field of natural gas liquefaction. More particularly, the invention relates to a method of heavy hydrocarbon removal and liquefying natural gas using a closed-loop refrigeration system.
A renewed push and demand for using cleaner, cheaper, and locally supplied fuels for transportation and peak-shaving applications has led to natural gas becoming a widely used source for clean fuel. In order to more easily and safely transport and store natural gas, liquefaction processes are performed to convert natural gas to liquefied natural gas (LNG). This in conjunction with the shale gas boom in the United States, has created a boost in building infrastructure for both the domestic natural gas processing capacity and the construction of LNG export terminals. A surge in liquefaction projects, such as these, has stimulated the development of more efficient and innovative LNG liquefaction technologies, which in turn have dramatically lowered the cost of LNG production and provided significant economic savings for consumers.
Currently, there are several methods for liquefying natural gas in practice. Many existing methods and technologies can be relatively inefficient and more expensive due to their process designs, mechanical designs, or their configurations of major equipment. As such, a growth in the development of competitive small-scale liquefaction technologies has occurred in the industry to provide the most efficient, scalable, and flexible modular designs that are best positioned to meet the growing demand for fuels in shipping and trucking industries, as well as the demand for the larger LNG plants used for LNG export.
Consequently, there is a need in the art for an optimized small-scale method and refrigeration system capable of more efficiently producing a liquefied natural gas product at a desired capacity using a minimum amount of equipment and a modularized design to reduce construction costs. The optimized method and refrigeration system need to be both robust and operationally flexible in order to handle variations in feed gas composition and flow rate, while still requiring minimal capital outlay and operating at the lowest possible cost.
These and other needs in the art are addressed in one embodiment by a natural gas liquefaction method comprising: introducing a natural gas stream into a natural gas liquefaction system, wherein the natural gas liquefaction system comprises a natural gas (NG)-to-liquefied natural gas (LNG) portion and a closed-loop refrigeration portion comprising a closed-loop single mixed refrigerant system, wherein the NG-to-LNG portion and the closed-loop refrigeration portion are joined by a heat exchanger; passing the natural gas stream through the NG-to-LNG portion to provide a liquified natural gas stream and a vaporized natural gas liquids stream; and circulating a mixed refrigerant (MR) composition through the closed-loop single mixed refrigerant system to provide cooling to the NG-to-LNG portion.
These and other needs in the art are addressed in one embodiment by a natural gas liquefaction method comprising: introducing a natural gas stream in a natural gas liquefaction system, wherein the natural gas liquefaction system comprises an NG-to-LNG portion and a closed-loop refrigeration portion comprising a closed-loop gaseous nitrogen expansion refrigeration system, wherein the NG-to-LNG portion and the closed-loop refrigeration portion are joined by a heat exchanger; passing the natural gas stream through the NG-to-LNG portion to provide a liquified natural gas stream and a vaporized natural gas liquids stream; and circulating a nitrogen refrigerant through the closed-loop gaseous nitrogen expansion refrigerant system to provide cooling to the NG-to-LNG portion.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter that form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiments disclosed may be readily utilized as a basis for modifying or designing other embodiments for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent embodiments do not depart from the spirit and scope of the invention as set forth in the appended claims.
For a detailed description of the preferred embodiments of the invention, reference will now be made to the accompanying drawings in which:
In embodiments, NG-to-LNG portion 100 may be configured to accept natural gas streams at any pressure, including both high pressures and low pressures.
In embodiments, treated high-pressure natural gas stream 102, being free of contaminants, may enter a first pass A1 of a main heat exchanger 500 and exit as a cooled high-pressure natural gas stream 105. Main heat exchanger 500 may be a brazed aluminum heat exchanger (BAHX) with minimum stream temperature approaches as low as 3° F. Further, main heat exchanger 500 may comprise a warm-end and a cold-end which may correspond to temperature within the heat exchanger, the highest temperatures being at the top of the warm-end and the lowest temperatures being at the bottom of the cold-end. In embodiments, first pass A1 may be a natural gas path disposed within main heat exchanger 500 beginning at the top of the warm-end and ending at a point below the top of the warm-end and above the cold-end. As such, treated high-pressure natural gas stream 102 may be cooled and/or partially-condensed by main heat exchanger 500 as it travels through first pass A1. In embodiments, the resulting cooled high-pressure natural gas stream 105 may have a reduced temperature between about −25° F. and about 10° F.
In embodiments, due to the high-pressure value of cooled high-pressure natural gas stream 105, the stream may enter a first pressure reduction device 305 and exit as a cold partially-condensed natural gas stream 116. In embodiments, first pressure reduction device 305 may be a pressure let-down valve or a natural gas expander system capable of reducing the pressure of cooled high-pressure natural gas stream 105 to an optimal pressure between about 400 psig and about 600 psig. In embodiments in which first pressure reduction device 305 may be a natural gas expander system, the natural gas expander system may be equipped with a vapor/liquid separator at its inlet (not illustrated) in order to prevent any potential liquid from entering the natural gas expander system. Further, first pressure reduction device 305 may be an optional component of NG-to-LNG portion 100, particularly when high-pressure natural gas stream 101 is already at the optimal pressure. In addition to reaching the optimal pressure, the resulting cold partially-condensed natural gas stream 116 may reach an optimal temperature between about −120° F. to about −80° F. upon exiting first pressure reduction device 305. In embodiments, this combination of optimal pressure and optimal temperature for stream 116 may allow for effective removal of heavy hydrocarbons in a vapor/liquid separator or a rectification column disposed within the natural gas liquefaction system, and thus may further prevent freezing and/or damage from occurring in the system.
In embodiments, pressure-increased natural gas stream 104, which is at the optimal pressure, may enter FGFT system 302 and exit as a treated pressure-increased natural gas stream 106. Similarly to above, FGFT system 302 may remove acid gases (e.g. carbon dioxide and hydrogen sulfide), water, and other contaminants (e.g. mercury) from pressure-increased natural gas stream 104. Removal of such components may further prevent freezing and/or damage from occurring in the natural gas liquefaction system. In embodiments, treated pressure-increased natural gas stream 106, which is free of certain contaminants, may comprise less than about 50 ppmv of carbon dioxide concentration, less than about 0.5 to about 1.0 ppmv of water concentration, and less than about 0.01 μg/Nm3 of mercury.
In embodiments, treated pressure-increased natural gas stream 106, being at the optimal pressure and free of contaminants, may enter first pass A1 of main heat exchanger 500 and exit as cold partially-condensed natural gas stream 116. In embodiments, as set forth above, first pass A1 may be a natural gas path disposed within main heat exchanger 500 beginning at the top of the warm-end and ending at a point below the top of the warm-end and above the cold-end. As such, treated pressure-increased natural gas stream 106 may be cooled by main heat exchanger 500 as it travels through first pass A1. In embodiments, the resulting cold partially-condensed natural gas stream 116 may reach the optimal temperature between about −120° F. to about −80° F. Again, this combination of optimal pressure and optimal temperature for stream 116 may allow for effective removal of heavy hydrocarbons in a vapor/liquid separator or a rectification column disposed within the natural gas liquefaction system, and thus may further prevent freezing and/or damage from occurring in the system.
In embodiments, as illustrated in
In embodiments, liquid product stream 113, having high levels of heavy hydrocarbon components and a low temperature between about −120° F. to about −80° F., may enter a second pass A2 of main heat exchanger 500 and exit as a vaporized natural gas liquid (NGL) stream 114. In embodiments, liquid product stream 113 may be routed to main heat exchanger 500 by a level control valve 313. Level control valve 313 may be any level control valve suitable for monitoring and responding to the level, volume, and/or height of liquid product stream 113, thereby enabling an appropriate amount of the stream to be directed toward second pass A2. In embodiments, second pass A2 may be a natural gas liquid path disposed within main heat exchanger 500 beginning at a point above the bottom of the cold-end below the warm-end and ending at the top of the warm-end. As such, liquid product stream 113 may provide cooling to the warm passes disposed within main heat exchanger 500, while simultaneously being warmed and vaporized as it travels through second pass A2. In embodiments, the resulting vaporized NGL stream 114, having been warmed to a temperature close to any warm streams entering the warm-end of main heat exchanger 500, may be fully or partially vaporized. In embodiments, streams entering the warm-end of main heat exchanger 500 may be any temperature greater than those at the cold-end of main heat exchanger 500. After vaporization, vaporized NGL stream 114 may be routed out of the natural gas liquefaction system and sent for further treatments as needed. Treatments may include, without limitation, NGL separation, LPG separation, or any combinations thereof.
In embodiments, vapor product stream 107, having low level contents of heavy hydrocarbons and a low temperature between about −120° F. to about −80° F., may enter a third pass A3 of main heat exchanger 500 and exit as a warmed vapor product stream 108. Third pass A3 may be a natural gas path disposed within main heat exchanger 500 beginning at a point below the top of the warm-end and above the cold-end and ending at the top of the warm-end. As such, vapor product stream 107 may provide cooling to the warm passes disposed within main heat exchanger 500, while simultaneously being warmed as it travels through third pass A3. In embodiments, the resulting warmed vapor product stream 108 may have an increased temperature close to any warm streams entering the warm-end of main heat exchanger 500. This temperature increase may prepare warmed vapor product stream 108 for entry into a second pressure booster device 309, which may then exit as a compressed vapor stream 109. In embodiments, second pressure booster device 309 may be a single stage or a multi-stage booster compressor system with a cooler at each compressor stage discharge, capable of increasing the pressure of warmed vapor product stream 108 to a pressure between about 800 psig and about 1100 psig. This pressure increase may significantly increase the energy efficiency of the natural gas liquefaction system. In embodiments, compressed vapor stream 109, having an increased pressure, may enter a cooling device 310 and exit as a de-superheated compressed vapor stream 110. Cooling device 310 may be any standard vapor cooling system capable of lowering the temperature of compressed vapor stream 109. In embodiments, the temperature of de-superheated compressed vapor stream 110 may be dependent upon the cooling medium of cooling device 310. For example, if the cooling medium is ambient air, the temperature of de-superheated compressed vapor stream 110 may be between about 80° F. and about 120° F. Lowering the temperature of compressed vapor stream 109 before entry into main heat exchanger 500 may minimized the amount of energy needed to liquefy the stream.
In embodiments in which high-pressure natural gas stream 101 may be fed into the natural gas liquefaction system, as illustrated in
In embodiments, de-superheated compressed vapor stream 110, having an increased pressure between about 800 psig and about 1100 psig and a temperature between about 80° F. to about 120° F., may enter a fourth pass A4 of main heat exchanger 500 and exit as a liquefied natural gas stream 111. Fourth pass A4 may be a natural gas path disposed within main heat exchanger 500 beginning at the top of the warm-end and ending at the bottom of the cold-end. As such, de-superheated compressed vapor stream 110 may be further cooled by main heat exchanger 500 as it travels through fourth pass A4. In embodiments, fourth pass A4 may be cooled by the cold natural gas passes A3 and A2, and refrigerant passes disposed within main heat exchanger 500. The resulting liquefied natural gas stream 111 may have a final temperature between about −250° F. to about −265° F., allowing for complete liquefaction of de-superheated compressed vapor stream 110. Due to its high pressure between about 800 psig and about 1100 psig, liquefied natural gas stream 111, may enter a first flow control valve 312 and exit as a pressure-reduced liquefied natural gas stream 112. First flow control valve 312 may be any flow control valve suitable for regulating the flow or pressure of liquefied natural gas stream 111. In embodiments, pressure-reduced liquefied natural gas stream 112 may have a decreased pressure between about 1 psig and about 20 psig, which may be a suitable pressure for storing pressure-reduced liquefied natural gas stream 112 in LNG storage tank 317 as well as for transporting pressure-reduced liquefied natural gas stream 112 in LNG storage tank 317.
In certain embodiments, as illustrated in
In embodiments, closed-loop refrigeration portion 200 may be configured to provide cooling to the natural gas passes disposed within main heat exchanger 500, particularly to first pass A1 which cools treated high-pressure natural gas stream 102 as illustrated in
Beginning at the top of the warm-end of main heat exchanger 500, a vapor MR stream 201, which may be an MR composition in a vapor state, may enter an MR multi-stage compressor system 400 and exit as four separate product streams: a third vapor MR product stream 211 and a first, second, and third liquid MR product stream 217, 218, and 219. In embodiments, MR multi-stage compressor system 400 may comprise a suction scrubber 402 and any number of compression stages so as to effectively increase the pressure of vapor MR stream 201 to a desired pressure between about 450 psig to about 650 psig. Suction scrubber 402 may be any inlet gas scrubber suitable for knocking liquids out to protect the compressor system, and further may maintain a pressure between about 25 psig and about 50 psig. As illustrated in
When entering MR multi-stage compressor system 400, vapor MR stream 201 may enter suction scrubber 402 and exit as a scrubbed vapor MR stream 202. Scrubbed vapor MR stream 202, which has been freed of excess liquids, may enter first stage pressure booster device 403 and exit as a pressure-increased vapor MR stream 203. Pressure-increased vapor MR stream 203, which has been increased in pressure, may enter first stage discharge cooler 404 and exit as a partially-condensed vapor MR stream 204. Partially-condensed vapor MR stream 204, which has been cooled and partially condensed, may enter first stage discharge separator 405 and exit as two separate product streams: a first vapor MR product stream 205 and first liquid MR product stream 217. In embodiments, first vapor MR product stream 205 may remain within MR multi-stage compressor system 400, while first liquid MR product stream 217 may exit MR multi-stage compressor system 400.
In embodiments, first vapor MR product stream 205 may enter second stage pressure booster device 406 and exit as a pressure-increased first vapor MR product stream 206. Pressure-increased first vapor MR product stream 206, which has been increased in pressure, may enter second stage discharge cooler 407 and exit as a partially-condensed first vapor MR product stream 207. Partially-condensed first vapor MR product stream 207, which has been cooled and partially condensed, may enter second stage discharge separator 408 and exit as two separate product streams: a second vapor MR product stream 208 and second liquid MR product stream 218. In embodiments, second vapor MR product stream 208 may remain within MR multi-stage compressor system 400, while second liquid MR product stream 218 may exit MR multi-stage compressor system 400.
In embodiments, second vapor MR product stream 208 may enter third stage pressure booster device 409 and exit as a pressure-increased second vapor MR product stream 209. Pressure-increased second vapor MR product stream 209, which has been increased in pressure, may enter third stage discharge cooler 410 and exit as a partially-condensed second vapor MR product stream 210. Partially-condensed second vapor MR product stream 210, which has been cooled and partially condensed, may enter third stage discharge separator 411 and exit as two separate product streams: third vapor MR product stream 211 and third liquid MR product stream 219. In embodiments, both third vapor MR product stream 211 and third liquid MR product stream 219 may exit MR multi-stage compressor system 400.
In embodiments, third vapor MR product stream 211, having the desired pressure between about 450 psig and about 650 psig, may enter a fifth pass B1 of main heat exchanger 500 and exit as a liquefied MR stream 212. Fifth pass B1 may be an MR path disposed within main heat exchanger 500 beginning at the top of the warm-end and ending at the bottom of the cold-end. As such, third vapor MR product stream 211 may be cooled and completely condensed in main heat exchanger 500 as it travels through fifth pass B1. In embodiments, fifth pass B1 may be cooled by refrigerant passes disposed within main heat exchanger 500. The resulting liquefied MR stream 212 may have a temperature between about −270° F. to about −250° F., allowing for complete liquefaction of third vapor MR product stream 211. Further, liquefied MR stream 212 may maintain the same or similar pressure value as that of third vapor MR product stream 211. Due to the high-pressure value of liquefied MR stream 212, the stream may enter a second pressure reduction device 413 and exit as a first cold two-phase MR stream 213. In embodiments, second pressure reduction device 413 may be a standard control valve system capable of reducing the pressure of liquefied MR stream 212 to a pressure that may be about 5 psig to about 10 psig higher than the pressure maintained at suction scrubber 402. This pressure reduction may create a Joule-Thompson effect that lowers the pressure and temperature of liquefied MR stream 212 and produces first cold two-phase MR stream 213 that contains both liquid and vapor.
In embodiments, first cold two-phase MR stream 213, having a temperature value between about −270° F. and about −250° F. and a pressure value between about 35 psig and about 60 psig, may enter a cold MR distribution separator 414 and exit as two separate cold product streams: a cold vapor MR product stream 214 and a cold liquid MR product stream 215. Cold MR distribution separator 414 may be any standard vapor/liquid flash separation vessel selected and maintained at a certain pressure and temperature similar to that of first cold two-phase MR stream 213. In embodiments, both cold vapor MR product stream 214 and cold liquid MR product stream 215 may be routed to a first mixing device 416 disposed inside the cold-end of main heat exchanger 500. First mixing device 416 may recombine and mix the vapor and liquid streams 214 and 215 to create a vapor/liquid mixture 216, and may further distribute the mixture evenly throughout a sixth pass B2 of main heat exchanger 500. In embodiments, sixth pass B2 may be an MR path disposed within main heat exchanger 500 connecting first mixing device 416 and a second mixing device 429, such that vapor/liquid mixture 216 enters second mixing device 429. Further, sixth pass B2 may comprise finned-channels in which vapor/liquid mixture 216 is evenly distributed through to provide cooling for warm passes disposed within main heat exchanger 500, particularly for fourth pass A4 and fifth pass B1, while simultaneously being warmed as it travels through sixth pass B2.
Referring once again to first, second, and third liquid MR product streams 217, 218, and 219, each exiting MR multi-stage compressor system 400 after separation, may each undergo similar processes. In embodiments, streams 217, 218, and 219 may enter a seventh pass B3, an eighth pass B4, and a nineth pass B5 of main heat exchanger 500 and exit as a subcooled first, second, and third liquid MR product stream 220, 221, and 222, respectively. Passes B3, B4 and B5 may be MR paths disposed within main heat exchanger 500, each beginning at different points along the top of the warm-end and ending at different points below the top of the warm-end and above the cold-end. As such, first, second, and third liquid MR product streams 217, 218, and 219, may be subcooled by main heat exchanger 500 as the streams travel through passes B3, B4 and B5. In embodiments, the resulting subcooled first, second, and third liquid MR product streams 220, 221, and 222 may have temperature values between about −50° F. to about −10° F. Lowering the temperature of first, second, and third liquid MR product streams 217, 218, and 219 may reduce vapor flash after undergoing pressure reduction, which may in turn provide more refrigeration when the liquid is vaporizing.
In embodiments, subcooled first, second, and third liquid MR product streams 220, 221, and 222, having reduced temperatures and relatively high pressures, may enter a third, fourth, and fifth pressure reduction device 423, 424, and 425, and exit as a second, third, and fourth cold two-phase MR product stream 223, 224, and 225, respectively. Third, fourth, and fifth pressure reduction devices 423, 424, and 425 may be standard control valve systems capable of reducing the pressure of subcooled first, second, and third liquid MR product streams 220, 221, and 222 to a pressure between about 30 psig and about 55 psig. Similarly to liquefied MR stream 212, this pressure reduction of streams 220, 221, and 222 may create a Joule-Thompson effect that lowers the pressure and temperature of streams 220, 221, and 222 and produces second, third, and fourth cold two-phase MR product stream 223, 224, and 225, respectively, containing both liquid and vapor. Second, third, and fourth cold two-phase MR product streams 223, 224, and 225 may be comingled into a combined two-phase stream 226, which will consequently also contain both liquid and vapor.
In embodiments, combined two-phase stream 226, having a temperature value between about −50° F. and about −10° F. and a pressure value between about 30 psig and about 55 psig, may enter a warm MR distribution separator 427 and exit as two separate product streams: a vapor MR product stream 227 and a liquid MR product stream 228. Warm MR distribution separator 427 may be any standard vapor/liquid flash separation vessel deliberately selected and maintained at a certain pressure and temperature similar to that of combined two-phase stream 226. In embodiments, both vapor MR product stream 227 and liquid MR product stream 228 may be routed to second mixing device 429 disposed within main heat exchanger 500. Second mixing device 429 may recombine and mix the vapor and liquid streams 227 and 228 as well as incorporate vapor/liquid mixture 216 to create a comingled MR mixture 229, and may further distribute the mixture evenly throughout a tenth pass B6 of main heat exchanger 500. In embodiments, tenth pass B6 may be an MR path disposed within main heat exchanger 500 connecting second mixing device 429 to a point along the top of the warm-end. Further, similarly to sixth pass B2, tenth pass B6 may comprise finned-channels in which commingled MR mixture 229 is evenly distributed through to provide cooling for warm passes disposed within main heat exchanger 500, particularly for first pass A1, fourth pass A4, fifth pass B1, seventh pass B3, eighth pass B4, and nineth pass B5, while simultaneously being warmed as it travels through tenth pass B6. In embodiments, commingled MR mixture 229 may be partially or fully vaporized upon exiting main heat exchanger 500, at which point commingled MR mixture 229 becomes vapor MR stream 201 and another cycle in the closed-loop mixed refrigeration system may begin.
In embodiments, the nEXP refrigeration system may utilize and circulate a solely nitrogen refrigerant, as opposed to the mixed refrigerant composition used in the closed-loop single mixed refrigerant system. Additionally, the nEXP refrigeration system may comprise a nitrogen refrigeration compander 700. Nitrogen refrigeration compander 700 may be a compact, integrated rotating equipment system, powered by a driver motor 701 (e.g. an electrical motor or gas turbine motor), comprising multiple stages of compressors and expanders to contribute in providing refrigeration to the natural gas liquefaction system. Further, nitrogen refrigeration compander 700 may integrate all stages of nitrogen compressions and expansions into a single bull-gear with a common lubrication system and a common seal gas system. In embodiments, nitrogen refrigeration compander 700 may contribute to a reduction in foot-print design, capital expenditures, and operating expenditures, as well as an increase in system efficiency, reliability, and operability.
An embodiment of nitrogen refrigeration compander 700 that may be utilized in the nEXP refrigeration system may comprise a first and second stage centrifugal compressor 702 and 704 connected via a first pinion 722, a third stage centrifugal compressor 706 and a warm expander 714 connected via a second pinion 724, and a fourth stage centrifugal compressor 708 and a cold expander 715 connected via a third pinion 726. Further, first, second, and third pinions 722, 724, and 726 may comprise a first, second, and third pinion-gear 732, 734, and 736, respectively, which may be geared to a bull-gear 740, held in place by first, second, and third thrust collars 742, 744, and 746, and driven by driver motor 701. Further, pinions 722, 724, and 726 may comprise seals and journal bearings (not illustrated). By this configuration, warm and cold expanders 714 and 715 may be installed at different pinion-gears within nitrogen refrigeration compander 700 so as to provide flexibility to the compander arrangement. For instance, warm and cold expanders 714 and 715 may be mounted to separate pinion-gears so as to allow for different revolution speeds among the expanders, therefore providing an ability to achieve high isentropic efficiency for each expander. This configuration may further reduce the load of the gearing and allow for higher or lower compressor loads than what may be accomplished in standard expander-compressor arrangements in which compressor power may be determined by expander power.
Referring to
In embodiments, fourth cooled nitrogen stream 609 may be split into two streams, a first split stream 610 and a second split stream 611, before entry into main heat exchanger 500. Each split stream 610 and 611 may have a portion of fourth cooled nitrogen stream 609. In embodiments, first and second split stream 610 and 611 may enter an eleventh pass C1 and a twelfth pass C2 of main heat exchanger 500, and exit as a first and second cooled split stream 612 and 613, respectively. Passes C1 and C2 may be refrigerant paths disposed within main heat exchanger 500, each beginning at different points along the top of the warm-end and ending at different points below the top of the warm-end and above the cold-end. As such, first and second split stream 610 and 611 may be cooled in main heat exchanger 500 as the streams travel through passes C1 and C2. In embodiments, the resulting first cooled split stream 612 may have a temperature value between about −30° F. and about 0° F. and the resulting second cooled split stream 613 may have a temperature value between about −125° F. to about −90° F.
In embodiments, first and second cooled split streams 612 and 613, having reduced temperatures, may enter warm expander 714 and cold expander 715 disposed within nitrogen refrigeration compander 700, and exit as a first and second expanded nitrogen stream 614 and 615, respectively. Warm and cold expanders 714 and 715 may each be a system capable of expanding both first and second cooled split streams 612 and 613 through a near-isentropic process such that the streams may reach low temperatures and low pressures. Further, warm and cold expanders 714 and 715 may provide refrigeration at the warm-end and cold-end of main heat exchanger 500 with their discharge streams 614 and 615 at different temperatures, and therefore the efficiency and operability of main heat exchanger 500 may be improved. Resulting first expanded nitrogen stream 614 may have a low temperature value between about −180° F. and about −150° F. and second expanded nitrogen stream 615 may have a low temperature value between about −270° F. to about −250° F., while both streams have low-pressure values between about 80 psig and about 120 psig.
In embodiments, first and second expanded nitrogen streams 614 and 615, having a decreased temperature and pressure, may enter a thirteenth pass C3 and a fourteenth pass C4 of main heat exchanger 500 and exit as a first and second warmed nitrogen stream 616 and 617. Thirteenth pass C3 may be a refrigerant path disposed within main heat exchanger 500 beginning at a point above the bottom of the cold-end and below the warm-end, and ending at the top of the warm-end. Additionally, fourteenth pass C4 may be a refrigerant path disposed within main heat exchanger 500 beginning at the bottom of the cold-end and ending at the top of the warm-end. In embodiments, both first and second expanded nitrogen streams 614 and 615 may flow in passes C3 and C4 to provide cooling to warm passes disposed within main heat exchanger 500, particularly for first pass A1, fourth pass A4, eleventh pass C1, and twelfth pass C2, while simultaneously being warmed as they travel through their respective passes. The resulting first and second warmed nitrogen streams 616 and 617, after exiting main heat exchanger 500, may be comingled into a single stream which becomes combined warmed nitrogen stream 601 and another cycle in the nEXP refrigeration system may begin.
Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations may be made herein without departing from the spirit and scope of the invention as defined by the appended claims.
This application is a division of U.S. patent application Ser. No. 16/880,419 filed on May 21, 2020, the disclosures of which are herein incorporated by reference in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 16880419 | May 2020 | US |
| Child | 18374918 | US |
