Process and apparatus for cryogenic separation of air with mixed gas turbine

Abstract

In this process and apparatus for cryogenic separation of air, the separation column system comprises a high-pressure column, a low-pressure column and a crude argon column. A mixed gas stream produced by mixing gaseous oxygen and a gas stream from the evaporation space of the argon top condenser, is work expanded in a mixed gas turbine.

1 . Process for cryogenic separation of air in a separation column system comprising a high-pressure column, a low-pressure column, a main condenser, which is a condenser-evaporator having a liquefaction space and an evaporation space and brings high-pressure column top and low-pressure column bottom in heat-exchange relationship, and a crude argon column having an argon top condenser, which is a condenser-evaporator having a liquefaction space and an evaporation space, comprising
 compressing a total feed air stream,   cooling the compressed feed air in a main heat exchanger,   introducing at least a portion of the feed air into the high-pressure column,   introducing at least one fraction from the high-pressure column directly or indirectly to the low-pressure column,   introducing an argon transition fraction from the low-pressure column to the crude argon column,   introducing a liquid cooling fraction from the high-pressure column into the evaporation space of the argon top condenser,   withdrawing a gaseous oxygen stream from the low-pressure column,   mixing the gaseous oxygen stream with another gas stream having a higher nitrogen content than the gaseous oxygen stream to form a mixed gas stream,   warming the mixed gas stream in the main heat exchanger,   work expanding the warmed mixed gas stream in an expansion machine and   completely warming the expanded mixed gas stream in the main heat exchanger, wherein   the above stream having a higher nitrogen content is withdrawn from the evaporation space of the argon top condenser.   
     
     
         2 . Process according to  claim 1 , wherein
 a gaseous nitrogen fraction from the low-pressure column is used as a recycle gas,   the recycle gas is warmed in the main heat exchanger,   the warmed recycle gas is compressed in a nitrogen compressor,   the compressed recycle gas is cooled in the main heat exchanger, and withdrawn from the main heat exchanger in gaseous form and   at least a first portion of the cooled recycle gas is introduced either in gaseous form or in liquefied form into the separation column system, in particular into the high-pressure column and/or the low-pressure column.   
     
     
         3 . Process according to  claim 2 , wherein at least a portion of the cooled recycle gas is introduced into the high-pressure column via the liquefaction space of the main condenser. 
     
     
         4 . Process according to  claim 1 , wherein
 the separation column system further comprises a pure argon column,   a crude argon stream is withdrawn from the crude argon column or the argon top condenser,   the crude argon stream is introduced into the pure argon column,   a liquid pure argon stream is withdrawn from the pure argon column,   the liquid pure argon stream is pressurized in liquid state,   the pressurized pure argon stream is warmed in the main heat exchanger and   finally recovered as a pressurized argon product.   
     
     
         5 . Process according to  claim 1 , wherein the crude argon column is split into a first part and a second part, the argon top condenser being arranged on the top of the second part, whereby a gas fraction from the top of the first part is introduced into the bottom of the second part and at least a first portion of the bottom liquid of the second part is introduced into the top of the first part. 
     
     
         6 . Process according to  claim 5 , wherein
 the separation column system further comprises a pure oxygen column,   a liquid fraction from the crude argon column is introduced into the top of the pure oxygen column and   a liquid pure oxygen fraction is withdrawn from the bottom of the pure oxygen column.   
     
     
         7 . Process according to  claim 6 , wherein the pure oxygen column is arranged immediately below a methane rejection column having just a single bottom/top plate between each other. 
     
     
         8 . Process according to  claim 6 , wherein the pure oxygen column
 has a bottom reboiler, which is a condenser-evaporator having a liquefaction space and an evaporation space.   
     
     
         9 . Process according to  claim 2 , wherein a second portion of the cooled recycle gas is introduced into the liquefaction space of the pure oxygen column bottom reboiler. 
     
     
         10 . Process according to  claim 1 , wherein, at least temporarily, an argon-oxygen mixture is withdrawn from the crude argon column via an intermediate gas outlet and the argon-oxygen mixture is warmed in the main heat exchanger. 
     
     
         11 . Process according to  claim 1 , wherein
 the low-pressure column is split into a bottom part and a top part,   a gaseous connection stream is withdrawn from the top of the bottom section   the gaseous connection stream is introduced into the bottom of the top section,   a liquid connection stream is withdrawn from the bottom of the top section and   the liquid connection stream is introduced into the top of the bottom section.   
     
     
         12 . Process according to  claim 1 , wherein
 a portion of the top gas of the high-pressure column is warmed in the main heat exchanger and   the warmed gas is withdrawn as a pressurized gaseous nitrogen product.   
     
     
         13 . Process according to  claim 1 , characterized in that
 a top gas from the low-pressure column is warmed in the main heat exchanger,   the warmed gas is compressed in a nitrogen compressor and   the compressed gas is withdrawn as a pressurized gaseous nitrogen product, in particular by admixing it the warmed top gas from the high-pressure column.   
     
     
         14 . Process according to  claim 1 , characterized in that the cooled recycle gas is introduced into the high-pressure column in gaseous form. 
     
     
         15 . Apparatus for cryogenic separation of air comprising a separation column system comprising a high-pressure column, a low-pressure column, a main condenser, which is a condenser-evaporator having a liquefaction space and an evaporation space and is configured to bring high-pressure column top and low-pressure column bottom in heat-exchange relationship, and a crude argon column having an argon top condenser, which is a condenser-evaporator having a liquefaction space and an evaporation space, and further comprising
 a main air compressor for compressing a total feed air stream,   a main heat exchanger for cooling the compressed feed air,   a main air compressor for compressing a total feed air stream,   a main heat exchanger for cooling the compressed feed air,   means for introducing at least a portion of the feed air into the high-pressure column,   means introducing at least one fraction from the high-pressure column directly or indirectly to the low-pressure column,   an argon transition line for introducing an argon transition fraction from the low-pressure column to the crude argon column,   means for introducing a liquid cooling fraction from the high-pressure column into the evaporation space of the argon top condenser,   means for withdrawing a gaseous oxygen stream from the low-pressure column,   means for mixing the gaseous oxygen stream with another gas stream having a higher nitrogen content than the gaseous oxygen stream to form a mixed gas stream,   means for introducing the mixed gas stream into the main heat exchanger for warming,   an expansion machine for work expanding the warmed mixed gas stream and   means for completely warming the expanded mixed gas stream in the main heat exchanger,   wherein   means for mixing the gaseous oxygen stream with another gas stream having a higher nitrogen content are connected to the evaporation space of the argon top condenser.