Method and system for pre-purification of a feed air stream

Abstract

A system and method of pre-purification of a feed gas stream is provided that is particularly suitable for pre-purification of a feed air stream in cryogenic air separation unit. The disclosed pre-purification systems and methods are configured to remove substantially all of the hydrogen, carbon monoxide, water, and carbon dioxide impurities from a feed air stream and is particularly suitable for use in a high purity or ultra-high purity nitrogen plant. The pre-purification systems and methods preferably employ two or more separate layers of hopcalite catalyst with the successive layers of the hopcalite separated by a zeolite adsorbent layer that removes water and carbon dioxide produced in the hopcalite layers.

What is claimed is: 
     
         1 . A method of purifying a feed air stream to reduce the hydrogen and carbon monoxide impurities present in the feed air stream, the method comprising the steps of:
 passing the feed air stream through at least one initial layer of adsorbent configured to remove water and carbon dioxide from the feed air stream and yield a dry feed air stream with less than 10 ppm water and less than 10 ppm of carbon dioxide;   passing the dry feed air stream through a first layer of manganese oxide and copper oxide containing catalyst configured to remove at least some of the carbon monoxide and hydrogen from the dry feed air stream and yield a first intermediate effluent stream;   passing the first intermediate effluent stream through one or more intermediate adsorbent layers disposed downstream of the first layer of manganese oxide and copper oxide containing catalyst, the one or more intermediate absorbent layers configured to remove at least carbon dioxide from the first intermediate effluent stream and yield a second intermediate effluent stream with less than 10 ppm carbon dioxide; and   passing the second intermediate effluent stream through a second layer of manganese oxide and copper oxide containing catalyst disposed downstream of the one or more intermediate absorbent layers and configured to remove at least hydrogen from the second intermediate effluent stream to yield third intermediate effluent stream having less than 20% of the hydrogen concentration in the feed air stream and less than 10% of the carbon monoxide concentration in the feed air stream.   
     
     
         2 . The method of  claim 1 , wherein the third intermediate effluent stream contains less than or equal to 500 ppb hydrogen and less than or equal to 50 ppb carbon monoxide throughout a cycle time of 6.5 hours. 
     
     
         3 . The method of  claim 2 , further comprising the step of passing the third effluent stream through one or more final adsorbent layers configured to remove water and carbon dioxide and yield a purified stream having less than 1 ppm of water and less than 1 ppm of carbon dioxide throughout the cycle time of 6.5 hours. 
     
     
         4 . The method of  claim 3 , wherein the one or more final adsorbent layers further comprise a molecular sieve layer or a layer of alumina or both a molecular sieve layer and a layer of alumina. 
     
     
         5 . The method of  claim 1 , wherein the one or more intermediate adsorbent layers comprise a molecular sieve layer or a layer of alumina or both a molecular sieve layer and a layer of alumina. 
     
     
         6 . The method of  claim 1 , wherein a residence time of the dry feed air stream within the first layer of manganese oxide and copper oxide containing catalyst is less than or equal to 1.5 seconds. 
     
     
         7 . The method of  claim 1 , wherein a residence time of the second intermediate effluent within the second layer of manganese oxide and copper oxide containing catalyst is less than or equal to 1.5 seconds. 
     
     
         8 . The method of  claim 1 , wherein the purified stream comprises greater than or equal to 5 ppb hydrogen and less than or equal to 500 ppb hydrogen. 
     
     
         9 . The method of  claim 1 , wherein the purified stream comprises less than 1 ppb carbon monoxide. 
     
     
         10 . The method of  claim 1 , wherein the at least one initial layer of adsorbent is configured to remove hydrocarbons and nitrous oxide. 
     
     
         11 . The method of  claim 1 , wherein the feed air stream comprises less than 20 ppm hydrogen. 
     
     
         12 . The method of  claim 1 , wherein the feed air stream comprises less than 50 ppm carbon monoxide. 
     
     
         13 . The method of  claim 1 , wherein the dry feed air stream contains less than 10 ppm carbon dioxide. 
     
     
         14 . The method of  claim 1 , wherein the second intermediate effluent contains no more than 10 ppm carbon dioxide. 
     
     
         15 . The method of  claim 1 , wherein the feed air stream is at a pressure greater than or equal to 3 bar(a) and less than or equal to 30 bar(a) and at a temperature greater than or equal to 0° C. and less than or equal to 70° C. 
     
     
         16 . The method of  claim 1 , further comprising the steps of:
 passing the third intermediate effluent stream through a second intermediate adsorbent layer disposed downstream of the second layer of manganese oxide and copper oxide containing catalyst, the second intermediate layer configured to remove carbon dioxide from the third intermediate effluent to yield a fourth intermediate effluent stream; and   passing the fourth intermediate effluent stream through a third layer of manganese oxide and copper oxide containing catalyst configured to remove at least hydrogen from the fourth intermediate effluent stream to yield a fifth intermediate effluent stream.   
     
     
         17 . The method of  claim 16 , wherein the fifth intermediate effluent stream contains less than or equal to 500 ppb hydrogen and less than or equal to 50 ppb carbon monoxide throughout a cycle time of 6.5 hours. 
     
     
         18 . The method of  claim 17 , further comprising the step of passing the fifth intermediate effluent stream through one or more final adsorbent layers configured to remove water and carbon dioxide and yield a purified stream having less than 1 ppm of water and less than 1 ppm of carbon dioxide throughout the cycle time of 6.5 hours. 
     
     
         19 . The method of  claim 18 , wherein the one or more final adsorbent layers further comprise a molecular sieve layer or a layer of alumina or both a molecular sieve layer and a layer of alumina. 
     
     
         20 . The method of  claim 16  wherein the one or more intermediate adsorbent layers is a first intermediate adsorbent layer and the first intermediate adsorbent layer and the second intermediate adsorbent layer each comprise a molecular sieve layer or a layer of alumina. 
     
     
         21 . A pre-purification unit for purifying a feed air stream to reduce the hydrogen and carbon monoxide impurities present in the feed air stream, the pre-purification unit comprising:
 a prepurification vessel having an inlet and an outlet;   one or more initial adsorbent layers disposed in the prepurification vessel proximate the inlet and configured to remove water from the feed air stream and yield a dry feed air stream;   a first layer of manganese oxide and copper oxide containing catalyst disposed downstream of the one or more initial adsorbent layers and configured to remove carbon monoxide and at least some of the hydrogen from the dry feed air stream and yield a first intermediate effluent stream;   one or more intermediate adsorbent layers disposed downstream of the first layer of manganese oxide and copper oxide containing catalyst, the one or more intermediate adsorbent layers configured to remove at least carbon dioxide from the first intermediate effluent stream and yield a second intermediate effluent stream; and   a second layer of manganese oxide and copper oxide containing catalyst disposed downstream of the one or more intermediate adsorbent layers and configured to remove at least hydrogen from the second intermediate effluent stream to yield a third intermediate effluent stream.   
     
     
         22 . The pre-purification unit of  claim 22 , further comprising one or more final layers of adsorbent disposed in the prepurification vessel proximate the outlet and configured to remove water and carbon dioxide from the third intermediate effluent stream yield a purified stream having less than 10 ppm of water and less than 10 ppm of carbon dioxide. 
     
     
         23 . The pre-purification unit of  claim 23 , wherein the one or more final layers of adsorbent comprises a molecular sieve layer or a layer of alumina or both a molecular sieve layer and a layer of alumina. 
     
     
         24 . The pre-purification unit of  claim 22 , wherein the one or more initial adsorbent layers comprise a molecular sieve layer or a layer of alumina or both a molecular sieve layer and a layer of alumina. 
     
     
         25 . The pre-purification unit of  claim 23 , wherein the purified stream comprises greater than or equal to 5 ppb hydrogen and less than or equal to 500 ppb hydrogen. 
     
     
         26 . The pre-purification unit of  claim 23 , wherein the purified stream comprises less than 1 ppb carbon monoxide. 
     
     
         27 . The pre-purification unit of  claim 22 , wherein the one or more initial adsorbent layers are further configured to yield the dry feed air stream with less than 10 ppm of water. 
     
     
         28 . The pre-purification unit of  claim 22 , wherein the first layer of manganese oxide and copper oxide containing catalyst, the one or more intermediate adsorbent layers, and the second layer of manganese oxide and copper oxide containing catalyst are further configured to yield the third intermediate effluent stream with less than 500 ppb hydrogen and less than 50 ppb carbon monoxide. 
     
     
         29 . The pre-purification unit of  claim 22 , wherein the one or more initial adsorbent layers are configured to remove hydrocarbons and nitrous oxide from the feed air stream. 
     
     
         30 . The pre-purification unit of  claim 22 , wherein the one or more initial adsorbent layers are configured to yield the dry feed air stream with less than 10 ppm carbon dioxide. 
     
     
         31 . The pre-purification unit of  claim 22 , wherein the first layer of manganese oxide and copper oxide containing catalyst and the second layer of manganese oxide and copper oxide containing catalyst have different lengths. 
     
     
         32 . The pre-purification unit of  claim 22 , wherein the first layer of manganese oxide and copper oxide containing catalyst has a length greater than the length of the second layer of manganese oxide and copper oxide containing catalyst.