Process and Device for Obtaining Liquid Nitrogen by Low Temperature Air Fractionation

Abstract

A device for obtaining liquid nitrogen by low-temperature air fractionation in a distillation column system for nitrogen-oxygen separation includes a high-pressure column; a low-pressure column; a high-pressure column top condenser which is constructed as a condenser-evaporator and comprises a liquefaction compartment and an evaporation compartment; a low-pressure column top condenser which is constructed as a condenser-evaporator and comprises a liquefaction compartment and an evaporation compartment. A throttle stream is formed by one part of a purified feed air that is liquefied or pseudoliquefied in a main heat exchanger. The throttle stream is expanded, and at least some of the expanded throttle stream is introduced as refrigerant stream into the evaporation compartment of the high-pressure column top condenser.

1 . Process for obtaining liquid nitrogen by low-temperature air fractionation in a distillation column system for nitrogen-oxygen separation which comprises two distillation columns, namely a high-pressure column, a low-pressure column, and a single high-pressure column top condenser for liquefying overhead gas of the high-pressure column, which high-pressure column top condenser is constructed as a condenser-evaporator and comprises a liquefaction compartment and a single evaporation compartment, said process comprising:
 compressing feed air to a first pressure in a main air compressor and purifying the feed air;   liquefying or pseudoliquefying a throttle stream, which is formed by one part of the purified feed air, in a main heat exchanger at a second pressure which is higher than the first pressure;   expanding the liquefied or pseudoliquefied throttle stream;   introducing at least some of the expanded throttle stream as a refrigerant stream into the evaporation compartment of the high-pressure column top condenser;   introducing at least some of an overhead gas of the high-pressure column into the liquefaction compartment of the high-pressure column top condenser;   introducing at least some of the overhead nitrogen of the low-pressure column into a liquefaction compartment of a low-pressure column top condenser;   introducing an oxygen-enriched liquid from a bottom region of the low-pressure column into an evaporation compartment of the low-pressure column top condenser; and   generating a nitrogen product in the low-pressure column and removing at least of the nitrogen product as a liquid product.   
     
     
         2 . Process according to  claim 1 , wherein the refrigerant stream is introduced directly into the evaporation compartment of the high-pressure column top condenser immediately downstream of the expansion of the throttle stream. 
     
     
         3 . Process according to  claim 1 , wherein at least some of the expanded throttle stream is subjected to a phase separation and the refrigerant stream is formed by at least some of the liquid phase from the phase separation, wherein the phase separation is performed at an intermediate point of the high-pressure column. 
     
     
         4 . Process according to  claim 1 , wherein:
 the purified feed air is at least in part mixed with a return stream to form a circuit stream;   the circuit stream is compressed in a circuit compressor to an intermediate pressure which is higher than the first pressure;   a first turbine stream, which is formed by a first part of the circuit stream downstream of the circuit compressor, is work-producingly expanded in a first expansion machine;   a second turbine stream, which is formed by a second part of the circuit stream downstream of the circuit compressor, is work-producingly expanded in a second expansion machine; and   at least some of the work-producingly expanded first turbine stream and/or at least some of the work-producingly expanded second turbine stream is recirculated as return stream to the circuit stream.   
     
     
         5 . Process according to  claim 4 , wherein:
 at least some of the circuit stream compressed to the intermediate pressure is compressed in two series-connected recompressors to a high pressure which is higher than the intermediate pressure;   the first expansion machine is mechanically coupled to one of the two recompressors; and   the second expansion machine is mechanically coupled to the other of the two recompressors.   
     
     
         6 . Process according to  claim 5 , wherein at least some of the circuit stream compressed to the intermediate pressure is compressed in two series-connected recompressors to a high pressure which is higher about the same as the second pressure. 
     
     
         7 . Process according to  claim 1 , wherein all of the cold used in the high-pressure column top condenser is made available by the refrigerant stream. 
     
     
         8 . Process according to  claim 1 , wherein vapor generated in the evaporation compartment of the high-pressure column top condenser is introduced into the low-pressure column at the bottom thereof. 
     
     
         9 . Process according to  claim 1 , wherein neither the high-pressure column nor the low-pressure column comprises a reboiler for generating ascending vapor from a liquid of the corresponding column. 
     
     
         10 . Process according to  claim 1 , wherein a fraction remaining liquid from the evaporation compartment of the high-pressure column top condenser is introduced into the evaporation compartment of the low-pressure column top condenser. 
     
     
         11 . Process according to  claim 1 , wherein at least some of the liquid obtained in the liquefaction compartment of the high-pressure column top condenser is introduced into the low-pressure column. 
     
     
         12 . Process according to  claim 1 , wherein a liquid crude oxygen stream from the bottom of the high-pressure column is introduced into the low-pressure column. 
     
     
         13 . Process according to  claim 1 , wherein a fractionation air stream which is formed by a part of the purified feed air is introduced as the throttle stream in the gaseous state into the high-pressure column, and the fractionation air stream comprises at least some of the work-producingly expanded first turbine stream and/or at least some of the work-producingly expanded second turbine stream. 
     
     
         14 . Process according to  claim 13 , wherein the fractionation air stream is introduced as the throttle stream in the gaseous state into a bottom of the high-pressure column. 
     
     
         15 . Process according to  claim 1 , wherein at least 40 mol % of the total amount of the feed air is introduced in the liquid state into the distillation column system for nitrogen-oxygen separation. 
     
     
         16 . Process according to  claim 1 , wherein at least 50 mol % of the total amount of the feed air is introduced in the liquid state into the distillation column system for nitrogen-oxygen separation. 
     
     
         17 . Device for obtaining liquid nitrogen by low-temperature air fractionation, comprising:
 a distillation column system for nitrogen-oxygen separation which comprises a high-pressure column having a single high-pressure column top condenser comprising a liquefaction compartment and a single evaporation compartment, and a low-pressure column;   a main air compressor for compressing feed air to a first pressure;   a purification appliance for purifying feed air compressed to the first pressure;   means for forming a throttle stream by one part of the purified feed air;   a main heat exchanger for liquefying or pseudoliquefying the throttle stream at a second pressure which is higher than the first pressure;   means for expanding the liquefied or pseudoliquefied throttle stream;   means for introducing the expanded throttle stream into the distillation column system for nitrogen-oxygen separation;   means for introducing at least some of the overhead gas of the high-pressure column into the liquefaction compartment of the high-pressure column top condenser;   means for removing as liquid product a nitrogen product generated in the low-pressure column;   means for introducing at least some of the expanded throttle stream as refrigerant stream into the evaporation compartment of the high-pressure column top condenser;   a low-pressure column top condenser comprising a liquefaction compartment and an evaporation compartment;   means for introducing at least some of the overhead nitrogen of the low-pressure column into the liquefaction compartment of the low-pressure column top condenser; and   means for introducing an oxygen-enriched liquid from a lower region of the low-pressure column into the evaporation compartment of the low-pressure column top condenser.   
     
     
         18 . A Process for obtaining liquid nitrogen by low-temperature air fractionation, comprising:
 compressing feed air to a first pressure in a main air compressor and purifying the feed air;   liquefying or pseudoliquefying a throttle stream which is formed by one part of the purified feed air in a main heat exchanger at a second pressure which is higher than the first pressure;   expanding the liquefied or pseudoliquefied throttle stream;   introducing at least some of the expanded throttle stream as a refrigerant stream into an evaporation compartment of a high-pressure column top condenser;   introducing at least some of the overhead gas of the high-pressure column into a liquefaction compartment of the high-pressure column top condenser;   introducing at least some of the overhead nitrogen of a low-pressure column into the liquefaction compartment of a low-pressure column top condenser;   introducing an oxygen-enriched liquid from a bottom region of the low-pressure column into an evaporation compartment of the low-pressure column top condenser; and   generating a nitrogen product in the low-pressure column and removing at least part of the nitrogen product as liquid product.   
     
     
         19 . A device for obtaining liquid nitrogen by low-temperature air fractionation, comprising:
 a distillation column system comprising a high-pressure column having a single high-pressure column top condenser comprising a liquefaction compartment and a single evaporation compartment; and a low-pressure column comprising a low-pressure column top condenser comprising a liquefaction compartment and an evaporation compartment;   a main air compressor for compressing feed air to a first pressure,   a purification appliance for purifying feed air compressed to the first pressure;   a compressor and cooler for forming a throttle stream by one part of the purified feed air;   a main heat exchanger for liquefying or pseudoliquefying the throttle stream at a second pressure which is higher than the first pressure;   a throttling valve for expanding the liquefied or pseudoliquefied throttle stream;   a line for introducing at least some of the expanded throttle stream as a refrigerant stream into the evaporation compartment of the high-pressure column top condenser;   a line for introducing at least some of the overhead gas of the high-pressure column into the liquefaction compartment of the high-pressure column top condenser;   a line for introducing at least some of the overhead nitrogen of the low-pressure column into the liquefaction compartment of the low-pressure column top condenser;   a line for introducing an oxygen-enriched liquid from a lower region of the low-pressure column into the evaporation compartment of the low-pressure column top condenser; and   a line for removing as liquid product a nitrogen product generated in the low-pressure column.