Method and System for Membrane-Based Gas Recovery

Abstract

A fast gas is recovered from a feed gas containing a fast gas and at least one slow gas using a gas separation membrane. A controller may control a control valve associated with a partial recycle of a permeate gas from the membrane for combining with the feed gas. A controller may control a control valve associated with the backpressure of a residue gas from the membrane.

What is claimed is: 
     
         1 . A method of recovering a fast gas from a process producing a varying flow rate of an exhaust gas comprising a fast gas and at least one slow gas, said method comprising the steps of:
 providing a plurality of sources of a gas mixture comprising the fast and slow gases;   obtaining a feed gas stream from one or more of the sources, the feed gas stream comprising the fast and slow gases, the feed gas stream having a variable flow rate based upon how many of the plurality of sources are actively producing the gas mixture;   compressing the feed gas stream;   feeding the compressed feed gas to a primary gas separation membrane;   withdrawing from the primary gas separation membrane a primary permeate stream enriched in the fast gas and a primary residue stream deficient in the fast gas;   directing a first portion of the primary permeate stream to the compressor, wherein the first portion is commingled and compressed with the feed gas stream;   withdrawing a remaining portion of the primary permeate stream to provide a product gas;   adjusting a degree to which the primary permeate stream is allocated between the first portion and the remaining portion based upon a recovery of the gas of interest achieved by performance of said method.   
     
     
         2 . The method of  claim 1 , wherein the plurality of sources comprises a plurality of optical fiber cooling towers, the fast gas is Helium, and the slow gas is air. 
     
     
         3 . The method of  claim 1 , wherein the plurality of sources comprises a plurality of Helium furnaces and the fast gas is Helium. 
     
     
         4 . The method of  claim 1 , further comprising the steps of:
 feeding the primary residue stream to a secondary gas separation membrane;   withdrawing from the secondary gas separation membrane a secondary permeate stream and a secondary residue stream; and   directing the secondary permeate stream to the compressor, wherein the secondary permeate stream is compressed with the first portion and the feed gas stream.   
     
     
         5 . The method of  claim 1 , wherein said step of obtaining a feed gas stream comprises the steps of:
 combining exhaust gas streams from one or more of the plurality of sources;   compressing the combined exhaust gas streams;   feeding the compressed combined exhaust gas streams to a secondary gas separation membrane; and   withdrawing from the secondary gas separation membrane a secondary permeate stream enriched in the fast gas and a secondary residue stream deficient in the fast gas, wherein the secondary permeate is the feed gas stream.   
     
     
         6 . The method of  claim 1 , further comprising the steps of:
 providing a control valve in fluid communication with the primary residue stream, the control valve being adapted to selectively adjust a pressure of the primary residue stream;   measuring a purity of the fast gas in the product gas; and   sending a signal to the controller representative of the measured purity, wherein the controller controls the adjustment of the pressure of the primary residue stream based upon the measured purity via the control valve in fluid communication with the primary residue stream.   
     
     
         7 . The method of  claim 1 , further comprising the steps of:
 providing a control valve in fluid communication with the primary permeate stream;   determining a recovery of the fast achieved by performance of said method;   sending a signal to a controller representative of the determined recovery, wherein the controller controls the allocation of the primary permeate stream into the first portion and the remaining portion based upon the signal via the control valve.   
     
     
         8 . The method of  claim 7 , further comprising the steps of:
 providing a control valve in fluid communication with the primary residue stream, the control valve being adapted to selectively adjust a pressure of the primary residue stream;   measuring a purity of the fast gas in the product gas;   sending a signal to a controller representative of the measured purity, wherein the controller controls the adjustment of the primary residue stream pressure based upon the product gas purity signal via the control valve in fluid communication with the primary residue stream.   
     
     
         9 . The method of  claim 7 , wherein:
 a) said step of obtaining a feed gas stream comprises the steps of:
 combining exhaust gas streams from one or more of the plurality of sources; 
 compressing the combined exhaust gas streams; 
 feeding the compressed combined exhaust gas streams to a secondary gas separation membrane; and 
 withdrawing from the secondary gas separation membrane a secondary permeate stream enriched in the fast gas and a secondary residue stream deficient in the fast gas, wherein the secondary permeate is the feed gas stream; and 
   b) said method further comprises the steps of:
 providing a control valve in fluid communication with the secondary residue stream, the control valve being adapted to selectively adjust a pressure of the secondary residue stream; 
 measuring a purity of the fast gas in the product gas; 
 sending a signal to a controller representative of the measured purity, wherein the controller controls the adjustment of the secondary residue stream pressure based upon the product gas purity signal via the control valve in fluid communication with the secondary residue stream. 
   
     
     
         10 . The method of  claim 1 , wherein the fast gas and slow gas are selected from the group consisting of: H 2  and Ne, H 2  and CO 2 , H 2  and CH 4 , H 2  and N 2 , H 2  and O 2 , H 2  and O 2 /N 2 , CO 2 , and N 2 , CO 2  and O 2 , CO 2  and N 2 /O 2 , CO 2  and CH 4 , Ne and N 2 , Ne and O 2 , Ne and N 2 /O 2 , He and N 2 , He and O 2 , He and N 2 /O 2 . 
     
     
         11 . A system for recovering a gas of interest from a process producing a varying flow rate of an exhaust gas, comprising:
 a plurality of sources of an exhaust gas, the exhaust gas comprising a fast gas and a slow gas;   a feed gas conduit in selective fluid communication with the plurality of sources;   a compressor having an inlet in fluid communication with the feed gas conduit and an outlet;   a primary gas separation membrane having an inlet, a permeate outlet and a residue outlet, the inlet of the primary gas separation membrane being in fluid communication with the compressor outlet, the primary gas separation membrane being preferentially permeate to the gas of interest;   a primary permeate conduit in fluid communication with the permeate outlet of the primary gas separation membrane;   a product gas conduit in fluid communication with the primary permeate conduit;   a recycle conduit in fluid communication between the primary permeate conduit and the compressor inlet;   a recycle control valve in fluid communication with the primary permeate conduit, the recycle conduit, and the product gas conduit, the recycle control valve being adapted to adjust a proportion of permeate gas that is allowed to flow from the primary permeate conduit to the recycle conduit versus the product gas conduit; and   a controller adapted to:
 receive a signal from a sensing device that is representative of a recovery of the fast gas that is achieved by operation of said system; and 
 control the proportionate adjustment by the recycle control valve based upon the recovery signal. 
   
     
     
         12 . The system of  claim 11 , further comprising:
 a secondary gas separation membrane having an inlet in fluid communication with the residue outlet of the primary gas separation membrane, a secondary residue outlet, and a secondary permeate outlet; and   a secondary permeate conduit in fluid communication between the permeate outlet of the secondary gas separation membrane the recycle conduit.   
     
     
         13 . The system of  claim 11 , further comprising a secondary gas separation membrane having an inlet in selective fluid communication with the plurality of sources, a secondary residue outlet, and a secondary permeate outlet in fluid communication with the feed gas conduit. 
     
     
         14 . The system of  claim 11 , further comprising:
 a secondary gas separation membrane having an inlet in fluid communication with the residue outlet of the primary gas separation membrane, a secondary residue outlet, and a secondary permeate outlet; and   a secondary permeate conduit in fluid communication between the permeate outlet of the secondary gas separation membrane the recycle conduit, wherein the sources are optical fiber cooling towers and the fast gas is Helium.