Active gas regenerative liquefier system and method

Abstract

The present invention provides an active gas regenerative liquefier (AGRL) for efficiently cooling and liquefying a process stream based on the combination of several active gas regenerative refrigerator (AGRR) stages configured to sequentially cool and liquefy the process stream, e.g. natural gas or hydrogen. In specific embodiments, the individual AGRR stages include heat exchangers, dual active regenerators, and a compressor/expander assembly, configured to recover a portion of the work of compression of a refrigerant by simultaneously expanding a refrigerant in one portion of the device while compressing the refrigerant in another portion to effect cooling of a heat transfer fluid, and ultimately the process stream.

1 . An active gas regenerative liquefier (AGRL), comprising at least a first active gas regenerative refrigerator (AGRR) stage and a second AGRR stage, the first AGRR stage configured to receive and cool a process stream, and deliver the process stream to the second AGRR stage, wherein the first and second AGRR stages have means for heat rejection to a common heat sink. 
   
   
       2 . The AGRL of  claim 1 , in which the second AGRR stage and any subsequent AGRR stage is configured to successively receive and cool the process stream. 
   
   
       3 . The AGRL of  claim 2 , further comprising at least a third AGRR stage for the liquefaction of natural gas. 
   
   
       4 . The AGRL of  claim 2 , further comprising at least a third AGRR stage, wherein the first through third AGRR stages have respective cold reservoirs at temperatures of about 220 K, 164 K, and 123 K, respectively. 
   
   
       5 . The AGRL of  claim 2 , further comprising at least a third, a fourth, a fifth, and a sixth AGRR stage for the liquefaction of hydrogen. 
   
   
       6 . The AGRL of  claim 2 , further comprising at least a third, a fourth, a fifth, and a sixth AGRR stage, wherein the first through sixth AGRR stages have respective cold reservoirs at temperatures of about 192 K, 120 K, 76 K, 48 K, 32 K, and 20 K, respectively. 
   
   
       7 . The AGRL of  claim 2  in which the process stream is hydrogen gas, further comprising at least one ortho to para converter located between any two sequential AGRR stages. 
   
   
       8 . An active gas regenerative liquefier (AGRL), comprising:
 at least one active gas regenerative refrigerator (AGRR) stage, said AGRR stage comprising at least two active regenerators, means for heat rejection to a common heat sink near room temperature, and means to provide work to compress a refrigerant and simultaneously recover work from expansion of the refrigerant;   said AGRR stage configured to receive and cool a process stream to the point of liquefaction, and deliver the liquefied process stream to a storage vessel.   
   
   
       9 . The AGRL of  claim 2 , in which the AGRR stage comprises:
 a first active regenerator and a second active regenerator, the first active regenerator and the second active regenerator each comprising an array of tubes, wherein at least one passive micro-regenerator is located at an entrance of each of said tubes, said tubes containing a refrigerant;   a compressor/expander assembly, said assembly comprising a manifold having a first portion and a second portion, a first piston in said first portion of said manifold, and a second piston in said second portion of said manifold, said array of tubes of the first active regenerator being connected to said first portion of said manifold and said array of tubes of the second active regenerator being connected to said second portion of said manifold, said manifold also containing the refrigerant, said pistons being configured to separately periodically compress and expand the refrigerant to thereby increase or decrease the temperature of the refrigerant in said tubes;   means to drive the pistons such that one piston compresses the refrigerant in one portion of said manifold while the other piston expands the refrigerant in the other portion of said manifold, thereby enabling work recovery from expansion to offset work required for compression;   means to circulate a heat transfer fluid between the process stream and the heat sink, said heat transfer fluid circulating past the first active regenerator and the second active regenerator in order to accept heat from or transfer heat to said active regenerators;   at least a first process stream heat exchanger for exchanging heat from said process stream to said heat transfer fluid; and   at least a first heat rejection exchanger for exchanging heat from said heat transfer fluid to said heat sink.   
   
   
       10 . The AGRL of  claim 9 , in which the means to circulate the heat transfer fluid is coupled in phase with the means to drive the pistons, such that the heat transfer fluid circulates along a first flow path while the refrigerant in the first portion of the manifold is expanded and along a second flow path while the refrigerant in the second portion of the manifold is expanded. 
   
   
       11 . The AGRL of  claim 10 , further comprising:
 a second process stream heat exchanger, a second heat rejection exchanger, a first valve connecting the first process stream heat exchanger, the second process stream heat exchanger, and the process stream, and a second valve connecting the first heat rejection exchanger, the second heat rejection exchanger, and the heat sink;   where said means to circulate the heat transfer fluid comprises a circulator that directs the heat transfer fluid in an oscillatory manner along the first flow path in which the heat transfer fluid flows sequentially through the first active regenerator, the first process stream heat exchanger, the second process stream heat exchanger, the second active regenerator, and the second heat rejection exchanger and along the second flow path sequentially through the second active regenerator, the second process stream heat exchanger, the first process stream heat exchanger, the first active regenerator, and the first heat rejection exchanger;   said first valve configured to direct the process stream through the first process stream heat exchanger when the heat transfer fluid flows along the first flow path and to direct the process stream through the second process stream heat exchanger when the heat transfer fluid flows along the second flow path;   said second valve configured to direct a cooling fluid through the second heat rejection exchanger when the heat transfer fluid flows along the first flow path and to direct the cooling fluid through the first heat rejection exchanger when the heat transfer fluid flows along the second flow path.   
   
   
       12 . The AGRL of  claim 10 , in which the means to circulate the heat transfer fluid comprises a plurality of valves configured to direct the flow of the heat transfer fluid alternately along the first flow path in which the heat transfer fluid passes sequentially through the first active regenerator, the process stream heat exchanger, the second active regenerator, and the heat rejection exchanger, and the second flow path in which the heat transfer fluid passes sequentially through the second active regenerator, the process stream heat exchanger, the first active regenerator, and the heat rejection exchanger. 
   
   
       13 . The AGRL of  claim 12 , in which a first valve is positioned between the first active regenerator and the heat rejection exchanger, a second valve is positioned between the first active regenerator and the process stream heat exchanger, a third valve is positioned between the second active regenerator and the heat rejection exchanger, and a fourth valve is positioned between the second active regenerator and the process stream heat exchanger. 
   
   
       14 . The AGRL of  claim 12 , in which the valves maintain continuous counterflow of the heat transfer fluid in the process stream heat exchanger and the heat rejection exchanger with periodic heat transfer fluid flow from the first and the second active regenerators. 
   
   
       15 . The AGRL of  claim 9 , wherein the tubes of each active regenerator are arranged in a plurality of layers with temperatures in the tubes spanning from a cold temperature in a bottom layer to a hot temperature in a top layer, such that the first piston performs distributed work as a function of the temperature in the tubes during compression of the refrigerant and the second piston simultaneously recovers distributed work as a function of the temperature in the tubes during expansion of the refrigerant. 
   
   
       16 . The AGRL of  claim 9 , wherein the passive micro-regenerator comprises spheres with a diameter less than the diameter of the entrance of the tube and with a thermal mass several times greater than the thermal mass of the refrigerant. 
   
   
       17 . The AGRL of  claim 9 , wherein the passive micro-regenerator comprises screens with a diameter approximately equal to the diameter of the entrance of the tube and with a thermal mass several times greater than the thermal mass of the refrigerant. 
   
   
       18 . The AGRL of  claim 9 , in which the temperature differences between the heat transfer fluid and the refrigerant within the active regenerators are 2 K or less. 
   
   
       19 . The AGRL of  claim 9 , in which the temperature differences between the heat transfer fluid and a cooling fluid in the heat rejection exchanger, and between the heat transfer fluid and the process stream in the process stream heat exchanger are 10's of K or less. 
   
   
       20 . A natural gas liquefier, comprising at least three active gas regenerative refrigerator (AGRR) stages situated and configured to receive and sequentially cool a natural gas process stream. 
   
   
       21 . A hydrogen liquefier, comprising at least six active gas regenerative refrigerator (AGRR) stages situated and configured to receive and sequentially cool a hydrogen process stream and an ortho to para converter situated between each of the AGRR stages. 
   
   
       22 . A method of liquefying a process stream of gas, comprising the steps of:
 A. Cooling a heat transfer fluid by passing it through a first active regenerator in which a refrigerant has been cooled by expanding said refrigerant;   B. Circulating said heat transfer fluid through a process stream heat exchanger for exchanging heat from the process stream to the heat transfer fluid;   C. Passing said heat transfer fluid through a second active regenerator in which a refrigerant has been heated by compression of said refrigerant;   D. Circulating said heat transfer fluid through a heat rejection exchanger for exchanging heat from said heat transfer fluid to a heat sink;   E. Repeating steps A-D multiple times in a first stage of refrigeration to cool said process stream to a first temperature; and   F. Repeating steps A-D multiple times in at least one subsequent stage of refrigeration to further cool said process stream to successively lower temperatures until liquefaction occurs.   
   
   
       23 . The method of  claim 22 , in which expansion of the refrigerant in step A is simultaneous with compression of the refrigerant in step C, such that a distributed work of compression of the refrigerant is offset by a distributed work of expansion of the refrigerant. 
   
   
       24 . A method of making a highly efficient liquefier, comprising the steps of
 A. providing at least one stage of refrigeration, said stage comprising a first active regenerator, a second active regenerator, and a refrigerant;   B. providing means to input work via compression of the refrigerant, said input work distributed over a first temperature span in the first active regenerator of each stage;   C. providing means to recover work via expansion of the refrigerant, said recovered work distributed over a second temperature span in the second active regenerator of each stage, said second temperature span being lower than said first temperature span;   D. providing means to couple said means for work input and said means for work recovery enabling the work input to be offset by the work recovered;   E. maintaining small temperature differences wherever heat transfer occurs; and   F. simultaneously optimizing heat transfer, pressure drops, and longitudinal conduction, friction losses, and other parasitic heat leaks in the liquefier operation.   
   
   
       25 . The method of  claim 24 , in which the first and the second temperature spans range from near cryogenic temperatures to near room temperature and in which the means to input and recover work are accomplished by polytropic temperature changes of the refrigerant from distributed compression or expansion. 
   
   
       26 . The method of  claim 25 , wherein the distributed compression or expansion of the refrigerant causes temperature changes of between 15 K and 20 K. 
   
   
       27 . The method of  claim 24 , wherein the means to couple means for work input and said means for work recovery comprises a resonant piston compressor/expander in a common cylinder.