System and Method for Turndown of a Hydrogen Precooling and/or Hydrogen Liquefaction System

Abstract

A highly efficient refrigeration system and process for precooling/liquefaction of a hydrogen feed stream and method of turndown of such system is disclosed. The disclosed refrigeration system and associated methods employ a reverse Brayton refrigeration cycle using a nitrogen based refrigerant and a fully integrated three pinion bridge (BriM) machine operatively coupling at least two turbine/expanders and at least four nitrogen refrigerant compression stages. Turndown of the hydrogen precooling and liquefaction process requires removal of nitrogen refrigerant from the refrigeration recycle loop by retaining liquid nitrogen in the phase separator, which is sized to accommodate the bulk of the nitrogen refrigerant used in the refrigeration circuit.

What is claimed is: 
     
         1 . A method for turndown of a nitrogen-based refrigeration system in a hydrogen precooling or hydrogen liquefaction system comprising the steps of:
 (a) receiving a hydrogen feed stream at a prescribed volumetric flow;   (b) cooling the hydrogen feed stream in a first heat exchanger or first set of heat exchanger cores via indirect heat exchange with a low pressure gaseous recycle stream and a medium pressure gaseous recycle stream to yield a cooled, hydrogen feed stream;   (c) cooling a high pressure nitrogen refrigerant stream in the first heat exchanger or first set of heat exchanger cores and diverting a first portion of the high pressure nitrogen refrigerant stream from within the first heat exchanger or 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 that forms a part of the medium pressure gaseous recycle stream at a temperature colder than the first diverted stream;   (e) diverting a second portion of the high pressure nitrogen refrigerant stream from within the first heat exchanger or 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 that forms another part of the medium pressure gaseous recycle stream at a temperature colder than the second diverted stream;   (g) recycling the medium pressure gaseous recycle stream through the first heat exchanger or first set of heat exchanger cores to cool the high pressure nitrogen refrigerant stream and the hydrogen feed stream;   (h) expanding the remaining portion of the of the high pressure nitrogen refrigerant stream in an expansion valve to yield a two-phase nitrogen stream;   (i) separating the two-phase nitrogen stream in a phase separator to yield a liquid nitrogen stream and the low pressure gaseous recycle stream;   (j) recycling the low pressure gaseous recycle stream through the first heat exchanger or first set of heat exchanger cores to cool the high pressure nitrogen refrigerant stream and the hydrogen feed stream; and
 wherein, in a first operating mode, the method further comprises the steps of: (k) directing a prescribed volumetric flow of the liquid nitrogen from the phase separator to the second heat exchanger or second set of heat exchanger cores; and (l) precooling the cooled, hydrogen feed stream in a second heat exchanger or second set of heat exchanger cores via indirect heat exchange with the liquid nitrogen to yield a precooled hydrogen feed stream at a temperature of less than or equal to 80 Kelvin; and 
 wherein, in a second operating mode, the method further comprises the steps of: (m) restricting the flow of the hydrogen feed stream to the first heat exchanger or first set of heat exchanger cores such that the flow is less than the prescribed volumetric flow of the hydrogen feed stream to the first heat exchanger or first set of heat exchanger cores; (n) restricting the flow of liquid nitrogen from the phase separator to the second heat exchanger or second set of heat exchanger cores via a control valve; (o) retaining a remaining portion of the liquid nitrogen in the phase separator; and (p) precooling the cooled, hydrogen feed stream in a second heat exchanger or second set of heat exchanger cores via indirect heat exchange with the restricted flow of liquid nitrogen to yield a precooled hydrogen feed stream at a temperature of less than or equal to 80 Kelvin. 
   
     
     
         2 . The method of  claim 1 , wherein the phase separator is configured to be capable of holding greater than 70% of the nitrogen refrigerant used in the refrigeration circuit. 
     
     
         3 . The method of  claim 1 , wherein in a third operating mode, the method further comprises the steps of: (m) increasing the flow of the hydrogen feed stream to the first heat exchanger or first set of heat exchanger cores such that the flow is greater than the flow of the hydrogen feed stream to the first heat exchanger or first set of heat exchanger cores in the second operating mode but less than the prescribed volumetric flow; (n) releasing additional flow of liquid nitrogen from the phase separator to the second heat exchanger or second set of heat exchanger cores via the control valve; and (p) precooling the cooled, hydrogen feed stream in a second heat exchanger or second set of heat exchanger cores via indirect heat exchange with the increasing flow of liquid nitrogen to yield a precooled hydrogen feed stream at a temperature of less than or equal to 80 Kelvin. 
     
     
         4 . The method of  claim 1 , further comprising the steps of:
 (q) compressing the recycled low pressure stream in a nitrogen feed compressor;   (r) mixing the compressed, recycled low pressure stream with the recycled medium pressure stream to form a mixed recycle stream; and   (s) further compressing the mixed recycle stream in a plurality of further compression stages; and
 wherein the plurality of further compression stages comprises at least four further compression stages and the at least four further compression stages together with the warm turbine/expander and cold turbine/expander are operatively coupled to an integral gear machine having at least three pinions. 
   
     
     
         5 . The method 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 wherein the warm exhaust stream is at a temperature in the range of 150 Kelvin to 185 Kelvin. 
     
     
         6 . The method of  claim 5 , wherein the second diverted stream is greater than the volume of the first diverted stream and wherein the cold exhaust stream is at a temperature in the range of 85 Kelvin and 105 Kelvin. 
     
     
         7 . The method of  claim 1  further comprising the step of treating the precooled hydrogen feed stream exiting the second heat exchanger or set of second heat exchanger cores with an ortho/para conversion catalyst vessel configured to treat the precooled hydrogen feed stream. 
     
     
         8 . A refrigeration system for precooling of hydrogen and liquefaction of nitrogen, the refrigeration system comprising:
 an integral gear machine comprising a drive assembly, a bull gear, and a plurality of pinions arranged to drive four or more refrigerant compression stages of the refrigeration system and for receiving work produced by the at least two turbine/expanders of the refrigeration system;   a refrigeration circuit configured to circulate a plurality of nitrogen streams including a high pressure nitrogen refrigerant stream and a hydrogen feed stream;   an expansion valve disposed in the refrigeration circuit configured for expanding the high pressure nitrogen refrigerant stream to yield a two-phase nitrogen stream;   a phase separator disposed within the refrigeration circuit and 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 first heat exchanger or set of first heat exchange cores disposed within the refrigeration circuit and configured to cool the hydrogen feed stream and cool the high pressure nitrogen refrigerant stream via indirect heat exchange with exhaust streams from the at least two turbine/expanders and the gaseous nitrogen stream from the phase separator;   a second heat exchanger or set of second heat exchange cores disposed within the refrigeration circuit and configured to receive the cooled hydrogen feed stream from the first heat exchanger or set of first heat exchange cores and precool the cooled hydrogen feed stream to a temperature of about 80 Kelvin or lower via indirect heat exchange with a liquid nitrogen stream received from the phase separator; and   a control valve in fluid communication with the phase separator and configured to control the liquid nitrogen exiting the phase separator to the a second heat exchanger or set of second heat exchange cores in response to the flow of the hydrogen feed stream to the first heat exchanger or set of first heat exchange cores;   wherein the phase separator is sized to hold at least 70% by volume of the nitrogen in the refrigeration system.   
     
     
         9 . A refrigeration system of  claim 8 , wherein:
 the refrigeration circuit is further configured to mix a nitrogen feed stream and a low pressure nitrogen recycle stream to form a nitrogen refrigerant stream and direct the nitrogen refrigerant stream to a nitrogen feed compressor;   wherein the refrigeration circuit is further configured to mix the compressed nitrogen refrigerant stream from the nitrogen feed compressor with a nitrogen recycle stream and direct the mixed stream to a nitrogen recycle compressor; and   wherein the refrigeration circuit is further configured to direct the further compressed nitrogen refrigerant stream to a warm booster compressor and a cold booster compressor to still further compress the nitrogen refrigerant stream and form the high pressure nitrogen refrigerant stream.   
     
     
         10 . The refrigeration system of  claim 9 , further comprising a high pressure hydrogen stream at a pressure of greater than or equal to about 40 bar(a) and that is circulated through the refrigeration circuit and cooled in the first heat exchanger or set of first heat exchange cores to a temperature of about 80 Kelvin. 
     
     
         11 . The refrigeration system of  claim 9 , further comprising one or more hydrogen return streams that are circulated through the refrigeration circuit and the first heat exchanger or set of first heat exchange cores to cool the high pressure nitrogen refrigerant stream and the hydrogen feed stream. 
     
     
         12 . The refrigeration system of  claim 9 , wherein the at least two turbine/expanders further comprise a warm turbine/expander disposed in the refrigeration circuit and configured to receive a first diverted portion of the high pressure nitrogen refrigerant stream and a cold turbine/expander disposed in the refrigeration circuit and configured to receive a second diverted portion of the high pressure nitrogen refrigerant stream. 
     
     
         13 . The refrigeration system of  claim 9 , 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 in the range of 150 Kelvin to 185 Kelvin; and wherein the warm exhaust stream is warmed to ambient temperatures in the first heat exchanger or first set of heat exchanger cores. 
     
     
         14 . The refrigeration system of  claim 13 , 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 in the range of 85 Kelvin and 105 Kelvin; and wherein the cold exhaust stream is warmed to ambient temperatures in the first heat exchanger or first set of heat exchanger cores. 
     
     
         15 . The refrigeration system of  claim 9 , further comprising an ortho/para conversion catalyst vessel configured to treat the precooled hydrogen feed stream exiting the second heat exchanger or set of second heat exchanger cores. 
     
     
         16 . The refrigeration system of  claim 15 , wherein the second heat exchanger or 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.