Gas stream purification method utilizing electrically driven oxygen ion transport

Abstract

A method of purifying a gas stream by removing oxygen from the gas stream in which the gas stream is introduced into a series of electrically driven oxygen separation zones that separate the oxygen from the gas stream. Each of the electrically driven oxygen separation zones has an electrolyte that conducts oxygen ions upon the application of the voltage to electrodes sandwiching the electrolyte. The voltage applied to each of the electrodes of the separation zones is selected such that an ionic current induced in the electrolyte within a particular zone that is no greater than a limiting current. When voltage is applied in such manner, the electrical power that is consumed is reduced over the power that would otherwise be consumed had a constant voltage been applied to all zones. The gas stream can be a crude argon stream obtained from a crude argon column or a crude nitrogen stream obtained from a pressure swing adsorption unit or a polymeric membrane unit.

1 . A method of purifying a gas stream by removing oxygen from said gas stream, said method comprising: 
 introducing said gas stream into a series of electrically driven oxygen separation zones operating an elevated temperature to separate the oxygen from the gas stream, thereby to produce a purified gas stream;    each of the electrically driven oxygen separation zones having an electrolyte and cathode and anode assemblies for applying a voltage to the electrolyte that such that the oxygen ions are transported through the electrolyte and emerge therefrom to recombine into elemental oxygen, thereby to separate the oxygen from the gas stream;    the oxygen being separated from the gas stream at a successively lower partial pressure due to the separation of the oxygen within successive electrically driven oxygen separation zones;    each of the electrically driven oxygen separation zones being capable of separating the oxygen as an increasing function of the voltage applied to the cathode and anode assemblies up to a level that induces an oxygen ion current that approaches a limiting oxygen ion current within the electrically driven oxygen separation zones at which a further increase in the voltage fails to produce an increase in oxygen separation, the limiting oxygen ion current limit being a function of the successively lower partial pressure such that the voltage applied decreases for each of the successive electrically driven oxygen separation zones; and    applying the voltage to each of the electrically driven oxygen separation zones in an amount selected such that the oxygen ion current approaches the limiting oxygen ion current applicable thereto.    
   
   
       2 . The method of  claim 1 , wherein the gas stream is a crude argon stream that is formed by vaporizing a crude liquid argon stream withdrawn from a crude argon column of a cryogenic air separation plant and containing the oxygen in a range of between about 0.1 percent and about 3 percent by volume.  
   
   
       3 . The method of  claim 1 , wherein the gas stream is a crude argon stream that is formed by vaporizing a crude liquid argon stream withdrawn from a crude argon column of a cryogenic air separation plant and containing the oxygen in a range of between about 0.5 percent and about 2 percent by volume.  
   
   
       4 . The method of  claim 1 , wherein the gas stream is a crude nitrogen stream withdrawn from a pressure swing adsorption apparatus or a membrane separation apparatus and containing between about 0.05 percent and about 2 percent by volume oxygen.  
   
   
       5 . The method of  claim 1 , wherein the gas stream is a crude nitrogen stream withdrawn from a pressure swing adsorption apparatus or a membrane separation apparatus and containing between about 0.1 percent and about 1 percent by volume oxygen.  
   
   
       6 . The method of  claim 1 , wherein the gas stream is a crude nitrogen stream withdrawn from a pressure swing adsorption apparatus or a membrane separation apparatus and containing between about 0.15 percent and about 0.5 percent by volume oxygen.  
   
   
       7 . The method of  claim 2  or  claim 4 , wherein the oxygen ion current is between about 80 percent and about 99.9 percent of the limiting oxygen ion current.  
   
   
       8 . The method of  claim 7 , wherein the oxygen ion current is at least about 95 percent of the limiting oxygen ion current.  
   
   
       9 . The method of  claim 2  or  claim 4 , wherein the electrolyte is fabricated from YSZ and the elevated temperature is in a range of between about 600° C. and about 900° C.  
   
   
       10 . The method of  claim 2  or  claim 4 , wherein the range is between about 650° C. and about 800° C.  
   
   
       11 . The method of  claim 3  or  claim 6 , wherein the range is between about 700° C. and about 800° C.  
   
   
       12 . The method of  claim 2  or  claim 4 , wherein: 
 the electrically driven oxygen separation zones are separated; and    the electrolyte of an initial of the electrically driven oxygen separation zones is fabricated from 8YSZ and subsequent of the electrically driven oxygen separation zones are fabricated from 6 YSZ or 3YSZ.    
   
   
       13 . The method of  claim 2 , wherein: 
 a crude liquid argon stream is vaporized through indirect heat exchange with an air stream, thereby to liquefy the air stream and thereby to form the crude argon gas stream to be purified;    the crude argon gas stream is heated through indirect heat exchange with the purified gas stream; and    the purified gas stream is liquefied through indirect heat exchange with a liquid air stream.    
   
   
       14 . The method of  claim 2 , wherein: 
 a crude liquid argon stream, the purified gas stream and a liquid nitrogen stream are subjected to indirect heat exchange, thereby to vaporize the crude liquid argon stream to form the crude argon stream to be purified, to vaporize the liquid nitrogen stream and to liquefy the purified gas stream;    the crude argon stream is heated through further indirect heat exchange with the purified gas stream prior to the purified gas stream engaging in the heat exchange involving the purified gas stream and the crude liquid argon stream stream; and    further pressure is imparted to the crude argon stream to raise the pressure thereof above that of the purified gas stream by a blower.    
   
   
       15 . The method of  claim 2 , wherein: 
 the crude liquid argon stream is vaporized and the product stream is liquefied in a main heat exchanger of the cryogenic air separation plant; and    the crude argon stream is heated through indirect heat exchange with the purified gas stream prior to liquefaction of the purified gas stream within the main heat exchanger.    
   
   
       16 . The method  claim 15 , wherein a compressed and purified air stream to be rectified in the cryogenic air separation plant is cooled within the main heat exchanger and oxygen and nitrogen product streams of the cryogenic air separation plant are warmed within the main heat exchanger.  
   
   
       17 . The method of  claim 4 , wherein the gas stream and the purified gas stream are subject to indirect heat exchange to heat the gas stream and cool the purified gas stream.  
   
   
       18 . The method of  claim 4  or  claim 17 , wherein during start-up or maintenance of the electrically driven oxygen separation unit, the pressure swing adsorption unit or the membrane separation unit is operated at a lower capacity to produce the crude nitrogen stream at a higher purity than operations conducted at full capacity.  
   
   
       19 . The method of  claim 1  or  claim 2  or  claim 4  or  claim 13  or  claim 14  or  claim 15  or  claim 17 , wherein the oxygen separated from the gas stream is extracted from the electrically driven oxygen separator with a purge stream formed from part of the gas stream.  
   
   
       20 . The method of  claim 1  or  claim 2  or  claim 4  or  claim 13  or  claim 14  or  claim 15  or  claim 17  wherein the oxygen separated from the gas stream is extracted from the electrically driven oxygen separators with a purge stream.