SYSTEM AND METHOD FOR PRECOOLING A HYDROGEN FEED STREAM WITH CONCURRENT NITROGEN LIQUEFACTION

Abstract

A system and process for precooling of a hydrogen feed stream with concurrent nitrogen liquefaction is disclosed. The disclosed hydrogen precooling refrigeration system and associated methods employ two centrifugal hydrogen compressors, including a centrifugal hydrogen cold compressor and a centrifugal hydrogen low pressure compressor.

Claims

1. A refrigeration system for precooling of one or more hydrogen feed streams in a hydrogen liquefaction system, the refrigeration system comprising: one or more centrifugal compressors to compress at least one of the one or more hydrogen feed streams to a pressure in a range of 40 bar (a) and 70 bar (a); a first heat exchanger or a set of first heat exchange cores configured to precool the one or more hydrogen feed streams, and cool a high pressure nitrogen refrigerant stream; a warm turbine/expander configured to receive a first diverted portion of the high pressure nitrogen refrigerant stream and expand the first diverted portion of the high pressure nitrogen refrigerant stream to yield a warm exhaust stream; a cold turbine/expander configured to receive a second diverted portion of the high pressure nitrogen refrigerant stream and expand the second diverted portion of the high pressure nitrogen refrigerant stream to yield a cold exhaust stream; an expansion valve disposed in the refrigeration circuit configured for expanding a third portion of the high pressure nitrogen refrigerant stream to yield a two-phase nitrogen stream; a phase separator disposed in fluid communication with the expansion valve and configured to receive the two-phase nitrogen stream and separate the two-phase nitrogen stream into a nitrogen liquid and a gaseous nitrogen stream; a second heat exchanger or a set of second heat exchange cores configured to receive the cooled hydrogen feed stream from the first heat exchanger or the set of first heat exchange cores and further precool the one or more hydrogen feed streams to a temperature of about 80 Kelvin or lower via indirect heat exchange with all or a portion of the liquid nitrogen stream received from the phase separator; wherein the hydrogen feed stream is precooled in the first heat exchanger or a set of first heat exchange cores via indirect heat exchange with the warm exhaust stream, the cold exhaust stream, and the gaseous nitrogen stream from the phase separator; wherein at least one of the one or more centrifugal compressors is a hydrogen cold compressor configured to compress a hydrogen stream taken from the first heat exchanger or the set of first heat exchange cores.

2. The refrigeration system of claim 1, wherein the hydrogen cold compressor is configured to compress a diverted hydrogen stream taken from the first heat exchanger or the set of first heat exchange cores at a temperature in a range of 150 Kelvin to 185 Kelvin.

3. The refrigeration system of claim 1, wherein the hydrogen cold compressor is configured to compress a diverted hydrogen stream taken from the first heat exchanger or the set of first heat exchange cores at a medium pressure in a range of 2 bar (a) to 9 bar (a).

4. The refrigeration system of claim 1, wherein another of the one or more centrifugal compressors is a low pressure hydrogen compressor configured to compress a low pressure hydrogen stream exiting the first heat exchanger or the set of first heat exchange cores at an ambient temperature to a medium pressure in a range of 2 bar (a) to 9 bar (a) to yield a further compressed hydrogen return stream.

5. The refrigeration system of claim 4, wherein the hydrogen cold compressor is configured to compress a diverted hydrogen stream taken from the first heat exchanger or the set of first heat exchange cores and wherein the diverted hydrogen stream is a mixture of a medium pressure hydrogen return stream warmed in the first heat exchanger or the set of first heat exchange cores and the further compressed hydrogen return stream that is re-cooled in the first heat exchanger or the set of first heat exchange cores.

6. The refrigeration system of claim 1, further comprising: a nitrogen feed compressor configured to compress the warmed gaseous nitrogen stream exiting the first heat exchanger or the set of first heat exchange cores; a nitrogen recycle compressor configured to compress the compressed gaseous nitrogen stream and a nitrogen recycle stream to form a further compressed nitrogen refrigerant stream; and a warm booster compressor and a cold booster compressor configured to still further compress the further compressed nitrogen refrigerant stream and form the high pressure nitrogen refrigerant stream.

7. The refrigeration system of claim 6, wherein the warm booster compressor and the cold booster compressor are arranged in parallel.

8. The refrigeration system of claim 1, wherein a portion of the liquid nitrogen stream from the phase separator is taken as a liquid nitrogen product stream.

9. The refrigeration system of claim 1, wherein the first diverted stream is less than or equal to about 40% by volume of the high pressure nitrogen refrigerant stream and is expanded in the warm turbine/expander to yield a warm exhaust stream at a temperature of about 170 Kelvin; and wherein the warm exhaust stream is warmed to ambient temperatures in the first heat exchanger or the first set of heat exchanger cores.

10. The refrigeration system of claim 9, wherein the second diverted stream is greater than the volume of the first diverted stream and is expanded in the cold turbine/expander to yield a cold exhaust stream at a temperature of about 97 Kelvin; and wherein the cold exhaust stream is warmed to ambient temperatures in the first heat exchanger or the first set of heat exchanger cores.

11. The refrigeration system of claim 10, wherein an inlet pressure of the cold turbine/expander and an inlet pressure of the warm turbine/expander are equal and an outlet pressure of the cold turbine/expander and an outlet pressure of the warm turbine/expander are equal.

12. The refrigeration system of claim 1, further comprising an ortho/para conversion catalyst configured to treat the precooled hydrogen feed stream exiting the second heat exchanger or the set of second heat exchanger cores.

13. The refrigeration system of claim 12, wherein the second heat exchanger or the set of second heat exchanger cores is further configured to re-cool the treated precooled hydrogen feed stream to a temperature of about 80 Kelvin.

14. A method of precooling one or more hydrogen feed streams in a hydrogen liquefaction system comprising the steps of: (a) compressing at least one of the one or more hydrogen feed streams in one or more centrifugal compressors to a pressure in a range of 40 bar (a) and 70 bar (a); (b) cooling a high pressure nitrogen refrigerant stream and the one or more hydrogen feed streams in a first heat exchanger or a first set of heat exchanger cores; (c) diverting a first portion of the high pressure nitrogen refrigerant stream from within the first heat exchanger or the first set of heat exchanger cores to yield a first diverted stream; (d) expanding the first diverted stream in a warm turbine/expander to yield a warm exhaust stream; (e) diverting a second portion of the high pressure nitrogen refrigerant stream from within the first heat exchanger or the first set of heat exchanger cores to yield a second diverted stream, wherein the second diverted stream is at a temperature colder than the first diverted stream; (f) expanding the second diverted stream in a cold turbine/expander to yield a cold exhaust stream; (g) expanding a third portion of the high pressure nitrogen refrigerant stream in an expansion valve to yield a two-phase nitrogen stream; (h) separating the two-phase nitrogen stream in a phase separator to yield a liquid nitrogen stream and a gaseous nitrogen stream; and (i) further precooling the one or more hydrogen feed streams in a second heat exchanger or a set of second heat exchanger cores via indirect heat exchange with all or a portion of the liquid nitrogen stream to yield one or more precooled hydrogen feed streams at a temperature of less than or equal to 80 Kelvin; wherein the one or more hydrogen feed streams are precooled in the first heat exchanger or a set of first heat exchange cores via indirect heat exchange with the warm exhaust stream, the cold exhaust stream, and the gaseous nitrogen stream from the phase separator; wherein at least one of the one or more centrifugal compressors is a hydrogen cold compressor configured to compress a hydrogen stream taken from the first heat exchanger or the set of first heat exchange cores.

15. The method of claim 14, wherein the hydrogen cold compressor is configured to compress a diverted hydrogen stream taken from the first heat exchanger or the set of first heat exchange cores at a temperature in a range of 150 Kelvin to 185 Kelvin.

16. The method of claim 14, wherein the hydrogen cold compressor is configured to compress a diverted hydrogen stream taken from the first heat exchanger or the set of first heat exchange cores at a medium pressure in a range of 2 bar (a) to 9 bar (a).

17. The method of claim 14, further comprising a low pressure hydrogen compressor configured to compress a low pressure hydrogen stream exiting the first heat exchanger or the set of first heat exchange cores at an ambient temperature to a medium pressure in a range of 2 bar (a) to 9 bar (a) to yield a further compressed hydrogen return stream.

18. The method of claim 17, wherein the hydrogen cold compressor is configured to compress a diverted hydrogen stream taken from the first heat exchanger or the set of first heat exchange cores and wherein the diverted hydrogen stream is a mixture of a medium pressure hydrogen return stream warmed in the first heat exchanger or the set of first heat exchange cores and the further compressed hydrogen return stream that is re-cooled in the first heat exchanger or the set of first heat exchange cores.

19. The method of claim 14, wherein a portion of the liquid nitrogen stream from the phase separator is taken as a liquid nitrogen product stream.

20. The method of claim 14, wherein: the first diverted stream is less than or equal to about 40% by volume of the high pressure nitrogen refrigerant stream and the warm exhaust stream is at a temperature of about 170 Kelvin; the second diverted stream is greater than the volume of the first diverted stream and the cold exhaust stream is at a temperature of about 97 Kelvin; and wherein the warm exhaust stream and the cold exhaust stream are warmed to ambient temperatures in the first heat exchanger or the first set of heat exchanger cores.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0012] It is believed that the claimed invention will be better understood when taken in connection with the accompanying drawings in which FIG. 1 shows a schematic of the process flow diagram for an embodiment of the present system and method for hydrogen precooling.

DETAILED DESCRIPTION

[0013] Turning to FIG. 1, a schematic of the high-level process flow diagram for an embodiment of the present system and method is provided. The illustrated refrigeration systems 10 includes a plurality of compressors, including a nitrogen feed compressor 20, a two-stage nitrogen recycle compressor 25 and two booster compressors, namely a warm booster compressor 30 and a cold booster compressor 35, and one of more hydrogen feed compressors (not shown). The illustrated refrigeration systems 10 further includes a plurality of heat exchangers or heat exchange sections E1, E2, E3, E4, and E5, a warm turbine/expander 50, a cold turbine/expander 55, an expansion valve 60, and a phase separator 70. The hydrogen precooling refrigeration system 10 may also include a compander machine 80 (See FIG. 3) coupled to a motor (not shown) and configured to drive the multiple stages of the nitrogen recycle compressor 25 and the two booster compressors 30, 35. The hydrogen feed compressor (not shown) and the nitrogen feed compressor 20 are preferably driven by separate motors or machines that are not shown.

[0014] The nitrogen feed stream 12 is a purified and compressed gaseous nitrogen stream at a feed pressure preferably at or above 40 bar (a), and more preferably at a pressure in a range of 40 bar (a) and 70 bar (a), most preferably at a pressure of about 55 bar (a). Nitrogen feed 12 is merged with the nitrogen recycle stream 72 and compressed in the nitrogen feed compressor 20 with the resulting compressed nitrogen stream 14 merged with recycle exhaust stream 59 and further compressed in a multi-stage nitrogen recycle compressor 25 to yield a gaseous nitrogen stream 28. The serially compression in feed compressor 20 and in the stages of the recycle compressor 25 may also include appropriate intercooling and/or aftercooling used to offset the temperature increases caused by the heat of compression. Such aftercooling may be accomplished by way of indirect contact with air, cooling water, chilled water or other refrigerating medium or combinations thereof.

[0015] In the embodiment illustrated in FIG. 1, the gaseous nitrogen stream 28 is then preferably split into two parallel streams 32, 36 that are still further compressed in booster compressors 30 and 35, respectively to yield still further compressed nitrogen streams 34, 38 which are recombined into a high pressure nitrogen refrigerant stream 39 at a pressure preferably at about 55 bar (a), and more preferably at a pressure in the range of between about 40 bar (a) and 70 bar (a). In some other embodiments, is may be desirable to have the booster compressors 30, 35 arranged in a series configuration (See FIG. 2) and not split the gaseous nitrogen stream 28.

[0016] The high pressure nitrogen refrigerant stream 39 is then cooled in at least one heat exchange section E1. A first portion of the cooled refrigerant stream 39 is diverted as a first diverted stream 52 and expanded in the warm turbine/expander 50 configured to expand the first diverted stream 52 to generate refrigeration. The first diverted stream 52 is preferably in the range of 20% to 60% and more preferably about 40% by volume of the high pressure nitrogen refrigerant stream 39 and is expanded in the warm turbine/expander 50 down to a pressure in the range of 1.3 bar (a) to 10.0 bar (a). The exhaust stream 54 of the warm turbine/expander is preferably at a temperature in the range of 150 Kelvin to 185 Kelvin and more preferably at about 170 Kelvin and warmed to ambient temperatures the heat exchange sections E2 and E1 while cooling the compressed refrigerant stream 39 and precooling the hydrogen feed stream 40 also traversing the heat exchange sections E2 and E1 recycled to the multi-stage recycle compressor 25.

[0017] The compressed refrigerant stream 39 continues to cool in heat exchanger section E2 and E3 to a temperature in the range of 150 Kelvin to 185 Kelvin and more preferably at about 176 Kelvin when a second portion of the cooled refrigerant stream 39 is diverted as a second diverted stream 56. The second diverted stream is preferably in the range of about 70% to 95% by volume of remaining cooled refrigerant stream 39 or in the range of between about 35% to 70% of the original high pressure nitrogen refrigerant stream 39. The second diverted stream is expanded in cold turbine/expander 55 configured to expand the second diverted stream 56 to generate additional refrigeration. The exhaust stream 58 of the cold turbine/expander 55 exits the cold turbine/expander at a temperature in the range of 85 Kelvin and 105 Kelvin and more preferably at a temperature of about 97 Kelvin and is warmed to ambient temperatures in heat exchange sections E3, E2, and E1 while cooling the compressed refrigerant stream 39 and also precooling the hydrogen feed stream 40 traversing the same heat exchange sections E3, E2, and E1. The warming exhaust stream 58 from the cold turbine/expander 55 may be merged at some point with exhaust stream 54 of the warm turbine/expander 50 and the warmed streams (or combined warmed stream) is then recycled as recycle stream 59 to the recycle compressor 25.

[0018] The remaining portion or third portion 62 of the high pressure nitrogen refrigerant stream is cooled in heat exchange section E3 and then expanded in a Joule Thomson expansion valve 60 with the resulting two-phase nitrogen stream 64 directed to the phase separator 70. The two-phase nitrogen stream 64 discharged from the Joule Thompson expansion valve 60 is a two-phase mixture in the range of 15% to 25% vapor phase and 85% to 75% liquid phase. The phase separator 70 separates the vapor nitrogen from the liquid nitrogen with the resulting vapor nitrogen stream 72 recycled to the nitrogen feed compressor 20 via heat exchange sections E4, E3, E2, and E1 where it precools the hydrogen feed stream. The resulting liquid nitrogen stream 74 also exits the phase separator 70.

[0019] A first part of the liquid nitrogen stream is optionally taken as liquid nitrogen product stream 76 while a second part of the liquid nitrogen stream 75 is directed to heat exchange section E5 where it is boiled against the cooled hydrogen feed stream to fully precools the hydrogen and yield a precooled hydrogen stream 45. Although not shown, external liquid can also be added to the process at the phase separator 70 if needed. After boiling, the two-phase nitrogen stream 78 leaving heat exchange section E5 is sent back to the phase separator 70. The low pressure vapor stream 72 exiting the phase separator 70 is warmed back to ambient temperatures through warming in heat exchange sections E1, E2, E3, and E4.

[0020] In the present system and method for hydrogen precooling with nitrogen liquefaction, there are multiple distinct hydrogen streams used in the process, including a hydrogen feed stream 40, a low pressure hydrogen return stream 42 that comes from an adjacent hydrogen liquefaction process, a medium pressure hydrogen return stream 43 that also comes from the adjacent hydrogen liquefaction process, and a high pressure hydrogen stream 44. In the present embodiment, the low pressure hydrogen return stream 42 is fully warmed and then compressed in a centrifugal low pressure hydrogen compressor 142, aftercooled in aftercooler 143, and re-cooled in heat exchanger sections E1 and E2 to yield a cold medium pressure return stream 144. The cold medium pressure return stream 144 is combined with the medium pressure return stream 43 that is partially warmed in heat exchanger sections E4 and E3 with the resulting combined cold medium pressure return stream 145 being further compressed in a hydrogen cold compressor 150, which is a centrifugal compressor. The cold compressed stream exiting the centrifugal hydrogen cold compressor 150 forms the high pressure hydrogen stream 44.

[0021] The hydrogen feed stream 40 is a gaseous hydrogen stream that will ultimately become the liquid hydrogen product. The hydrogen feed stream 40 is preferably a purified and compressed gaseous hydrogen stream at a pressure in the range of 10 bar (a) to 40 bar (a) and is substantially free of hydrocarbons and other impurities. This hydrogen feed stream 40 is then further compressed in a hydrogen compressor (not shown) to a pressure preferably in the range of 40 bar (a) to 70 bar (a). In the illustrated embodiment, the hydrogen feed stream 40 is cooled in heat exchanger sections E1, E2, and E3 against the turbine exhaust streams 54, 58, the low pressure nitrogen vapor stream 72 exiting the phase separator 70, and the hydrogen recycle streams (i.e. the further compressed low pressure hydrogen return stream 42 and the medium pressure hydrogen return stream 43).

[0022] The hydrogen feed stream 40 is further cooled in heat exchanger section E4 against the low pressure nitrogen vapor stream 72 exiting the phase separator 70 and the hydrogen recycle streams and then still further cooled in heat exchanger section E5 against a liquid nitrogen stream 75 exiting the phase separator 70. Upon exiting E5, the cooled hydrogen feed stream 45 is directed to an ortho/para conversion vessel 46 filled with catalyst. The cooled hydrogen stream 45 will warm slightly in the catalyst filled vessel 46, so the catalyst treated stream 47 it is returned to heat exchange section E5 where it is re-cooled to a temperature of about 80 Kelvin and then directed as a precooled hydrogen stream 98 to the hydrogen liquefaction section of the hydrogen liquefaction system or plant. The final heat exchange passage 49 in heat exchange section E5 may also be optionally filled with an ortho/para conversion catalyst. Alternate contemplated embodiments may utilize ortho/para conversion catalysts in heat exchange passages within heat exchange sections E3 and E4 to reduce or minimize the need for the ortho/para conversion vessel 46.

[0023] As indicated above, the high pressure hydrogen stream 44 is preferably at a pressure in the range of 40 bar (a) to 70 bar (a) and more preferably at a pressure of about 55 bar (a). The high pressure hydrogen stream 44 is directed to and through heat exchange sections E1, E2, E3, E4, and E5 where it is cooled to a temperature of about 80 Kelvin. This high pressure hydrogen stream 44 is not contacted with ortho/para conversion catalyst since the high pressure hydrogen stream 44 is to be used for refrigeration in the adjacent hydrogen liquefaction process and recycled.

[0024] Advantageously, the present embodiment uses two centrifugal compressors including centrifugal low pressure hydrogen compressor 142 and centrifugal hydrogen cold compressor 150. The centrifugal low pressure hydrogen compressor 142 is a centrifugal compressor machine that can operate at ambient temperatures. The low pressure hydrogen stream warmed to ambient temperatures is routed to the centrifugal low pressure hydrogen compressor 142 where it is further compressed to a medium pressure in a range of 2 bar (a) to 9 bar (a). The discharge stream from the centrifugal low pressure hydrogen compressor 142 is cooled in heat exchanger 143 against cooling water and then further cooled in heat exchanger sections E1 and E2 within the cold box to a temperature in a range of 150 Kelvin to 185 Kelvin and more preferably at a temperature of about 165 Kelvin. The resulting cold medium pressure return stream 144 is then mixed or combined with a partially warmed medium pressure hydrogen return stream 43.

[0025] The centrifugal compression of the combined cold medium pressure return stream 145 in centrifugal hydrogen cold compressor 150 is enabled by removing or diverting the medium pressure hydrogen return stream 43 from the cold box also at a temperature in a range of 150 Kelvin to 185 Kelvin and more preferably at a temperature of about 165 Kelvin. The removed or diverted cold hydrogen gas is then combined with cold medium pressure return stream 144 and fed to the centrifugal hydrogen cold compressor 150 that is arranged without intercoolers or aftercoolers. This cold hydrogen gas is compressed to a pressure in the range of 40 bar (a) to 70 bar (a) and more preferably at a pressure of about 55 bar (a). The discharge temperature of the stream exiting the centrifugal hydrogen cold compressor 150 is near ambient temperature. The compressed hydrogen stream is then returned as the high pressure hydrogen stream 44 to the cold box where it is pre-cooled in heat exchangers sections E1, E2, E3, E4 and E5 as described above. The precooled high pressure hydrogen stream 99 exiting the cold box is then directed to the liquefaction section of the hydrogen liquefaction system or plant.

[0026] One drawback of the presents system and method is the increased power and increased nitrogen refrigerant required of the hydrogen liquefaction system and method because the heat of compression from the hydrogen cold compressor must be removed by the precooler refrigeration circuit. Specifically, the nitrogen recycle flows as well as the warm turbine flow in the nitrogen precooling refrigeration circuit must be increased significantly as the precooling refrigeration circuit must now adsorb the heat of compression from the centrifugal hydrogen cold compressor 150.

[0027] Notwithstanding this drawback, the major advantages of the present system and method for hydrogen precooling include a nearly 50% reduction in capital costs for the hydrogen compressors, namely the centrifugal hydrogen cold compressor 150 and the centrifugal low pressure hydrogen compressor 142. In addition, the maintenance requirements and costs of the centrifugal hydrogen cold compressor 150 and the centrifugal low pressure hydrogen compressor 142 are reduced significantly with compared to the maintenance requirements and costs of similar reciprocal compression machines.

[0028] While the present system and method for precooling hydrogen in a hydrogen liquefaction system has been described with reference to a preferred embodiment, it is understood that numerous additions, changes, and omissions can be made without departing from the spirit and scope of the present invention as set forth in the appended claims.