Nitrogen producing cryogenic air separation unit with excess air circuit

Abstract

A nitrogen producing cryogenic air separation unit with an excess air circuit is provided. The nitrogen producing cryogenic air separation unit is capable of producing high pressure gaseous nitrogen without the use of a nitrogen product compressors and is also capable of producing high rates of liquid nitrogen without adding additional compression stages in the main air compressor and/or without a nitrogen recycle compressor.

What is claimed is: 
     
         1 . A nitrogen producing air separation unit configured to receive an incoming feed air stream and produce a high pressure gaseous nitrogen product and a liquid nitrogen product, and further configured to be capable of taking more than 30% of the nitrogen product as liquid nitrogen product, wherein the nitrogen producing air separation unit comprises: a main air compression and purification system; a heat exchanger; a distillation column system having at least one nitrogen column and at least one nitrogen condenser configured to operate at a pressure of about 8 bar(a) or higher; and a nitrogen liquefaction system, the nitrogen producing air separation unit characterized by:
 an excess air stream diverted from the incoming feed air stream at a location downstream of the main air compression and purification system;   one or more excess air compressors configured to further compress the excess air stream to a pressure greater than about 24 bar(a), wherein a first portion of the further compressed excess air stream is directed to a nitrogen column;   an excess air expander configured to expand a second portion of the further compressed excess air stream to produce an excess air exhaust stream; and   a waste and excess air expander configured to receive a vapor stream from the nitrogen condenser and the excess air exhaust stream and expand the vapor stream from the nitrogen condenser and the excess air exhaust stream to produce a waste exhaust stream;   wherein the waste exhaust stream is configured to be warmed in the heat exchanger against one or more portions of the compressed, purified air stream to produce a warmed exhaust stream.   
     
     
         2 . The nitrogen producing air separation unit of  claim 1  wherein the one or more excess air compressors further comprise a motor driven booster compressor configured to receive and further compress the excess air stream and one or more booster compressors driven by the waste and excess air expander and excess air expander. 
     
     
         3 . The nitrogen producing air separation unit of  claim 2  wherein one or more excess air compressors configured to further compress the excess air stream to a pressure between about 34 bar(a) and 55 bar(a). 
     
     
         4 . The nitrogen producing air separation unit of  claim 1  wherein the one or more excess air compressors further comprise a first booster compressor operatively coupled to and driven by the waste and excess air expander and a second booster compressor arranged in series with the first booster compressor, the second booster compressor operatively coupled to and driven by the excess air expander. 
     
     
         5 . The nitrogen producing air separation unit of  claim 4  wherein one or more excess air booster compressors configured to further compress the excess air stream to a pressure between about 24 bar(a) and 35 bar(a). 
     
     
         6 . The nitrogen producing air separation unit of  claim 1  further comprising a generator operatively coupled to the waste and excess air expander. 
     
     
         7 . The nitrogen producing air separation unit of  claim 1  further comprising a feed air booster compressor downstream of the main air compression and purification system and configured to further compress the incoming feed air, the feed air booster compressor operatively coupled to and driven by the waste and excess air expander. 
     
     
         8 . The nitrogen producing air separation unit of  claim 7  wherein the one or more excess air booster compressors further comprise a first booster compressor configured to receive and further compress the excess air stream and a second booster compressor arranged in series with the first booster compressor, the second booster compressor operatively coupled to and driven by the excess air expander. 
     
     
         9 . The nitrogen producing air separation unit of  claim 1  further comprising a bridge machine operatively coupled to the one or more excess air booster compressors, the waste and excess air expander and the excess air expander. 
     
     
         10 . The nitrogen producing air separation unit of  claim 1  wherein the at least one nitrogen column comprises one nitrogen column and the at least one nitrogen condenser comprises one nitrogen condenser. 
     
     
         11 . The nitrogen producing air separation unit of  claim 1  wherein the at least one nitrogen column comprises two nitrogen columns and the at least one nitrogen condenser comprises one nitrogen condensers. 
     
     
         12 . The nitrogen producing air separation unit of  claim 1  wherein the at least one nitrogen column comprises two nitrogen columns and the at least one nitrogen condenser comprises two nitrogen condensers. 
     
     
         13 . A nitrogen producing air separation unit configured to receive an incoming feed air stream and produce a high pressure gaseous nitrogen product and a liquid nitrogen product, and further configured to be capable of taking more than about 30% of the nitrogen product as liquid nitrogen product, wherein the nitrogen producing air separation unit comprises: a main air compression and purification system; a heat exchanger; a distillation column system having a nitrogen column and a nitrogen condenser configured to operate at a pressure of 8 bar(a) or higher; and a nitrogen liquefaction system, the nitrogen producing air separation unit characterized by:
 an excess air stream diverted from the incoming feed air stream at a location downstream of the main air compression and purification system;   a booster compressor configured to receive a vapor stream from the nitrogen condenser that has been warmed and to further compress the warmed vapor stream;   an excess air expander configured to receive the warmed, further compressed vapor stream and the excess air stream and to expand the warmed, further compressed vapor stream from the nitrogen condenser and the excess air stream to produce a waste exhaust stream; and   a nitrogen recycle circuit comprising one or more nitrogen recycle compressors and a nitrogen recycle turbo-expander, the one or more nitrogen recycle compressor stages configured to further compress a nitrogen recycle stream comprised of a diverted portion of the high pressure gaseous nitrogen product and a warmed nitrogen exhaust stream to produce a further compressed nitrogen recycle stream and wherein a first portion of the further compressed nitrogen recycle stream is directed to the nitrogen column and a second portion of the further compressed nitrogen recycle stream is directed to the nitrogen recycle turbo-expander configured to expand the second portion of the further compressed nitrogen recycle stream to produce a nitrogen exhaust stream;   wherein the waste exhaust stream is configured to be warmed in the heat exchanger against the incoming feed air stream and the excess air stream to produce a warmed waste exhaust stream and the nitrogen exhaust stream from the nitrogen recycle turbo-expander is configured to be warmed in the heat exchanger against the incoming feed air stream and the excess air stream to produce the warmed nitrogen exhaust stream.   
     
     
         14 . A method of providing supplemental refrigeration in a nitrogen producing air separation unit, wherein the nitrogen producing air separation unit is configured to receive an incoming feed air stream and produce a high pressure gaseous nitrogen product without a nitrogen product compressor and a liquid nitrogen product, the method comprises the steps of:
 compressing the incoming feed air stream in a main air compressor to produce a compressed feed air stream;   purifying the compressed feed air stream in a pre-purification unit to produce a compressed, purified air stream;   splitting the compressed, purified air stream into an excess air stream and a compressed, purified feed air stream;   cooling compressed, purified feed air stream in a heat exchanger to produce a fully cooled feed air stream that is directed to a distillation column system;   further compressing the excess air stream in one or more excess air booster compressors to a pressure greater than about 24 bar(a);   cooling a first portion of the further compressed excess air stream in a heat exchanger to produce a liquid air stream that is directed to a distillation column system;   expanding a second portion of the further compressed excess air stream in an excess air expander to produce an excess air exhaust stream;   combining the excess air exhaust stream with a waste stream from the distillation column system to produce a combined excess air and waste stream;   expanding the combined excess air and waste stream in a waste and excess air expander to produce waste exhaust stream; and   warming the waste exhaust stream in the heat exchanger to provide supplemental refrigeration to cool the first portion of the further compressed excess air stream and cool the fully cooled feed air stream while producing a warmed waste exhaust stream.   
     
     
         15 . The method of providing supplemental refrigeration in a nitrogen producing air separation unit of  claim 14 , wherein the distillation column system further comprises at least one nitrogen column and at least one nitrogen condenser. 
     
     
         16 . The method of providing supplemental refrigeration in a nitrogen producing air separation unit of  claim 15 , wherein the distillation column system further comprises two nitrogen columns and at least one nitrogen condenser. 
     
     
         17 . The method of providing supplemental refrigeration in a nitrogen producing air separation unit of  claim 15 , wherein the distillation column system further comprises a lower pressure nitrogen column and a higher pressure nitrogen column and two nitrogen condensers. 
     
     
         18 . The method of providing supplemental refrigeration in a nitrogen producing air separation unit of  claim 15 , wherein the waste stream from the distillation column system is a vapor stream from a nitrogen condenser of the distillation column system. 
     
     
         19 . The method of providing supplemental refrigeration in a nitrogen producing air separation unit of  claim 15 , wherein the waste stream from the distillation column system is a warmed vapor stream from a nitrogen condenser of the distillation column system.