Air separation method and apparatus

Abstract

Provided is an air separation method and apparatus in which consumed power source can be reduced when oxygen is collected in a three-column process, including: a first separation step in which feed air is separated into high pressure nitrogen gas and high pressure oxygen-enriched liquid air; a second separation step in which a high pressure oxygen-enriched liquid air is separated into medium pressure nitrogen gas, and medium pressure oxygen-enriched liquid air; a first indirect heat exchange step in which a medium pressure nitrogen gas is condensed and a low pressure oxygen-enriched liquid air is vaporized by indirect heat exchange; and a third separation step in which a low pressure oxygen-enriched air is separated into low pressure nitrogen gas and low pressure liquid oxygen.

1 . An air separation method for cryogenically liquefying and separating feed air to collect product oxygen comprising:
 a first separation step in which compressed, purified and cooled feed air is cryogenically distilled to be separated into high pressure nitrogen gas and high pressure oxygen-enriched liquid air;   a second separation step in which the high pressure oxygen-enriched liquid air is cryogenically distilled after reducing pressure to be separated into medium pressure nitrogen gas, and medium pressure oxygen-enriched liquid air;   a first indirect heat exchange step in which indirect heat exchange is performed between low pressure oxygen-enriched liquid air which is the medium pressure oxygen-enriched liquid air whose pressure is reduced and the medium pressure nitrogen gas, and the medium pressure nitrogen gas is condensed to obtain a medium pressure liquid nitrogen, and at the same time, the low pressure oxygen-enriched liquid air is vaporized to obtain low pressure oxygen-enriched air;   a third separation step in which the low pressure oxygen-enriched air is cryogenically distilled to be separated into low pressure nitrogen gas and low pressure liquid oxygen;   a second indirect heat exchange step in which indirect heat exchange is performed between the high pressure nitrogen gas and the low pressure liquid oxygen, and the high pressure nitrogen gas is condensed to obtain high pressure liquid nitrogen, and at the same time, the low pressure liquid oxygen is vaporized to obtain low pressure oxygen gas;   a third indirect heat exchange step in which indirect heat exchange is performed between high pressure nitrogen-enriched air in an intermediate stage in the first separation step and the medium pressure oxygen-enriched liquid air, and the high pressure nitrogen-enriched air is condensed to obtain high pressure nitrogen-enriched liquid air, and at the same time, the medium pressure oxygen-enriched liquid air is vaporized to obtain medium pressure oxygen-enriched air; and   a product gas collecting step in which the low pressure oxygen gas and/or the low pressure liquid oxygen is/are collected as a product oxygen gas after heat recovery.   
     
     
         2 . An air separation method for cryogenically liquefying and separating feed air to collect product oxygen comprising:
 a first separation step in which compressed, purified and cooled feed air is cryogenically distilled to be separated into high pressure nitrogen gas and high pressure oxygen-enriched liquid air;   a second separation step in which the high pressure oxygen-enriched liquid air is cryogenically distilled after reducing pressure to be separated into medium pressure nitrogen gas, and medium pressure oxygen-enriched liquid air;   a third separation step in which low pressure oxygen-enriched liquid air which is the medium pressure oxygen-enriched liquid air whose pressure is reduced is cryogenically distilled to be separated into low pressure nitrogen gas and low pressure liquid oxygen;   a first indirect heat exchange step in which indirect heat exchange is performed between the medium pressure nitrogen gas, and low pressure oxygen-enriched refluxed liquid air in an intermediate stage in the third separation step, and the medium pressure nitrogen gas is condensed to obtain a medium pressure liquid nitrogen, and at the same time, the low pressure oxygen-enriched refluxed liquid air is vaporized to obtain low pressure oxygen-enriched vaporized air;   a second indirect heat exchange step in which indirect heat exchange is performed between the high pressure nitrogen gas and the low pressure liquid oxygen, and the high pressure nitrogen gas is condensed to obtain high pressure liquid nitrogen, and at the same time, the low pressure liquid oxygen is vaporized to obtain low pressure oxygen gas;   a third indirect heat exchange step in which indirect heat exchange is performed between high pressure nitrogen-enriched air in an intermediate stage in the first separation step and the medium pressure oxygen-enriched liquid air, and the high pressure nitrogen-enriched air is condensed to obtain high pressure nitrogen-enriched liquid air, and at the same time, the medium pressure oxygen-enriched liquid air is vaporized to obtain medium pressure oxygen-enriched air; and   a product gas collecting step in which the low pressure oxygen gas and/or the low pressure liquid oxygen is/are collected as a product oxygen gas after heat recovery.   
     
     
         3 . The air separation method according to  claim 1 , wherein, in the third indirect heat exchange step,
 in addition to the high pressure nitrogen-enriched liquid air, a high pressure low purity nitrogen gas in which nitrogen is more concentrated is obtained by performing cryogenic distillation in which, while the high pressure nitrogen-enriched air is flowed upward in same passages of a heat integrated distillation device, condensed liquid is flowed downward, and at the same time,   in addition to the medium pressure oxygen-enriched air, a medium pressure low purity liquid oxygen in which oxygen is more concentrated is obtained by performing cryogenic distillation in which, while the medium pressure oxygen-enriched liquid air is flowed downward in the other passages of the heat integrated distillation device, vaporized gas is flowed upward.   
     
     
         4 . The air separation method according to  claim 1 , wherein, in the third indirect heat exchange step, part of the feed air can be used in place of the high pressure nitrogen-enriched air. 
     
     
         5 . The air separation method according to  claim 1 , wherein the air separation method of the present invention comprises at least one of
 a high pressure nitrogen gas collecting step in which a high pressure nitrogen gas obtained in the first separation step is collected after heat recovery,   a medium pressure nitrogen gas collecting step in which a medium pressure nitrogen gas obtained in the second separation step is collected after heat recovery,   a low pressure nitrogen gas collecting step in which a low pressure nitrogen gas obtained in the third separation step is collected after heat recovery,   a high pressure liquid nitrogen collecting step in which the high pressure liquid nitrogen condensed in the second indirect heat exchange step is collected,   a medium pressure liquid nitrogen collecting step in which the medium pressure liquid nitrogen condensed in the first indirect heat exchange step is collected, and   a low pressure liquid oxygen collecting step in which the low pressure liquid oxygen obtained in the third separation step is collected.   
     
     
         6 . An air separation apparatus for cryogenically liquefying and separating feed air to collect product oxygen comprising:
 a high pressure column in which compressed, purified and cooled feed air is cryogenically distilled to be separated into high pressure nitrogen gas and high pressure oxygen-enriched liquid air;   a medium pressure column in which the high pressure oxygen-enriched liquid air is cryogenically distilled after reducing pressure to be separated into medium pressure nitrogen gas, and medium pressure oxygen-enriched liquid air;   a medium pressure column condenser in which indirect heat exchange is performed between low pressure oxygen-enriched liquid air which is the medium pressure oxygen-enriched liquid air whose pressure is reduced and the medium pressure nitrogen gas, and the medium pressure nitrogen gas is condensed to obtain a medium pressure liquid nitrogen, and at the same time, the low pressure oxygen-enriched liquid air is vaporized to obtain low pressure oxygen-enriched air;   a low pressure column in which the low pressure oxygen-enriched air is cryogenically distilled to be separated into low pressure nitrogen gas and low pressure liquid oxygen;   a main condenser reboiler in which indirect heat exchange is performed between the high pressure nitrogen gas and the low pressure liquid oxygen, and the high pressure nitrogen gas is condensed to obtain high pressure liquid nitrogen, and at the same time, the low pressure liquid oxygen is vaporized to obtain low pressure oxygen gas;   a medium pressure column reboiler in which indirect heat exchange is performed between high pressure nitrogen-enriched air taken out from an intermediate portion in the high pressure column and the medium pressure oxygen-enriched liquid air, and the high pressure nitrogen-enriched air is condensed to obtain high pressure nitrogen-enriched liquid air, and at the same time, the medium pressure oxygen-enriched liquid air is vaporized to obtain medium pressure oxygen-enriched air; and   a product oxygen gas collecting path in which the low pressure oxygen gas and/or the low pressure liquid oxygen is/are collected as a product oxygen gas after heat recovery.   
     
     
         7 . An air separation apparatus for cryogenically liquefying and separating feed air to collect product oxygen comprising:
 a high pressure column in which compressed, purified and cooled feed air is cryogenically distilled to be separated into high pressure nitrogen gas and high pressure oxygen-enriched liquid air;   a medium pressure column in which the high pressure oxygen-enriched liquid air is cryogenically distilled after reducing pressure to be separated into medium pressure nitrogen gas, and medium pressure oxygen-enriched liquid air;   a low pressure column in which low pressure oxygen-enriched liquid air which is the medium pressure oxygen-enriched liquid air whose pressure is reduced is cryogenically distilled to be separated into low pressure nitrogen gas and low pressure liquid oxygen;   a medium pressure nitrogen condenser in which indirect heat exchange is performed between the medium pressure nitrogen gas, and low pressure oxygen-enriched refluxed liquid air descending at an intermediate portion of the low pressure column, and the medium pressure nitrogen gas is condensed to obtain medium pressure liquid nitrogen, and at the same time, the low pressure oxygen-enriched refluxed liquid air is vaporized to obtain low pressure oxygen-enriched vaporized air;   a main condenser reboiler in which indirect heat exchange is performed between the high pressure nitrogen gas and the low pressure liquid oxygen, and the high pressure nitrogen gas is condensed to obtain high pressure liquid nitrogen, and at the same time, the low pressure liquid oxygen is vaporized to obtain low pressure oxygen gas;   a medium pressure column reboiler in which indirect heat exchange is performed between high pressure nitrogen-enriched air taken out from an intermediate portion of the high pressure column and the medium pressure oxygen-enriched liquid air, and the high pressure nitrogen-enriched air is condensed to obtain high pressure nitrogen-enriched liquid air, and at the same time, the medium pressure oxygen-enriched liquid air is vaporized to obtain medium pressure oxygen-enriched air; and   a product gas collecting path in which the low pressure oxygen gas and/or the low pressure liquid oxygen is/are collected as a product oxygen gas after heat recovery.   
     
     
         8 . The air separation apparatus according to  claim 6 , wherein a heat integrated distillation device in which
 in addition to the high pressure nitrogen-enriched liquid air, a high pressure low purity nitrogen gas in which nitrogen is more concentrated is obtained by performing cryogenic distillation in which, while part of the high pressure nitrogen-enriched air is flowed upward in same passages of a heat integrated distillation device, condensed liquid is flowed downward, and at the same time,   in addition to the medium pressure oxygen-enriched air, a medium pressure low purity liquid oxygen in which oxygen is more concentrated is obtained by performing cryogenic distillation in which, while the medium pressure oxygen-enriched liquid air is flowed downward in the other passage, vaporized gas is flowed upward is used.   
     
     
         9 . The air separation apparatus according to  claim 6 , wherein part of the feed air is used in place of the high pressure nitrogen-enriched air. 
     
     
         10 . The air separation apparatus according to  claim 6 , comprising at least one of
 a high pressure nitrogen gas collecting path in which a high pressure nitrogen gas obtained in the high pressure column is collected after heat recovery,   a medium pressure nitrogen gas collecting path in which a medium pressure nitrogen gas obtained in the medium pressure column is collected after heat recovery,   a low pressure nitrogen gas collecting path in which a low pressure nitrogen gas obtained in the low pressure column is collected after heat recovery,   a high pressure liquid nitrogen collecting path in which the high pressure liquid nitrogen condensed in the main condenser reboiler is collected,   a medium pressure liquid nitrogen collecting path in which the medium pressure liquid nitrogen condensed in the medium pressure column condenser is collected, and   a low pressure liquid oxygen collecting path in which the low pressure liquid oxygen obtained in the low pressure column is collected.   
     
     
         11 . The air separation method according to  claim 2 , wherein, in the third indirect heat exchange step,
 in addition to the high pressure nitrogen-enriched liquid air, a high pressure low purity nitrogen gas in which nitrogen is more concentrated is obtained by performing cryogenic distillation in which, while the high pressure nitrogen-enriched air is flowed upward in same passages of a heat integrated distillation device, condensed liquid is flowed downward, and at the same time,   in addition to the medium pressure oxygen-enriched air, a medium pressure low purity liquid oxygen in which oxygen is more concentrated is obtained by performing cryogenic distillation in which, while the medium pressure oxygen-enriched liquid air is flowed downward in the other passages of the heat integrated distillation device, vaporized gas is flowed upward.   
     
     
         12 . The air separation method according to  claim 2 , wherein, in the third indirect heat exchange step, part of the feed air can be used in place of the high pressure nitrogen-enriched air. 
     
     
         13 . The air separation method according to  claim 3 , wherein, in the third indirect heat exchange step, part of the feed air can be used in place of the high pressure nitrogen-enriched air. 
     
     
         14 . The air separation method according to  claim 2 , wherein the air separation method of the present invention comprises at least one of
 a high pressure nitrogen gas collecting step in which a high pressure nitrogen gas obtained in the first separation step is collected after heat recovery,   a medium pressure nitrogen gas collecting step in which a medium pressure nitrogen gas obtained in the second separation step is collected after heat recovery,   a low pressure nitrogen gas collecting step in which a low pressure nitrogen gas obtained in the third separation step is collected after heat recovery,   a high pressure liquid nitrogen collecting step in which the high pressure liquid nitrogen condensed in the second indirect heat exchange step is collected,   a medium pressure liquid nitrogen collecting step in which the medium pressure liquid nitrogen condensed in the first indirect heat exchange step is collected, and   a low pressure liquid oxygen collecting step in which the low pressure liquid oxygen obtained in the third separation step is collected.   
     
     
         15 . The air separation method according to  claim 3 , wherein the air separation method of the present invention comprises at least one of
 a high pressure nitrogen gas collecting step in which a high pressure nitrogen gas obtained in the first separation step is collected after heat recovery,   a medium pressure nitrogen gas collecting step in which a medium pressure nitrogen gas obtained in the second separation step is collected after heat recovery,   a low pressure nitrogen gas collecting step in which a low pressure nitrogen gas obtained in the third separation step is collected after heat recovery,   a high pressure liquid nitrogen collecting step in which the high pressure liquid nitrogen condensed in the second indirect heat exchange step is collected,   a medium pressure liquid nitrogen collecting step in which the medium pressure liquid nitrogen condensed in the first indirect heat exchange step is collected, and   a low pressure liquid oxygen collecting step in which the low pressure liquid oxygen obtained in the third separation step is collected.   
     
     
         16 . The air separation apparatus according to  claim 7 , wherein a heat integrated distillation device in which
 in addition to the high pressure nitrogen-enriched liquid air, a high pressure low purity nitrogen gas in which nitrogen is more concentrated is obtained by performing cryogenic distillation in which, while part of the high pressure nitrogen-enriched air is flowed upward in same passages of a heat integrated distillation device, condensed liquid is flowed downward, and at the same time,   in addition to the medium pressure oxygen-enriched air, a medium pressure low purity liquid oxygen in which oxygen is more concentrated is obtained by performing cryogenic distillation in which, while the medium pressure oxygen-enriched liquid air is flowed downward in the other passage, vaporized gas is flowed upward is used.   
     
     
         17 . The air separation apparatus according to  claim 7 , wherein part of the feed air is used in place of the high pressure nitrogen-enriched air. 
     
     
         18 . The air separation apparatus according to  claim 8 , wherein part of the feed air is used in place of the high pressure nitrogen-enriched air. 
     
     
         19 . The air separation apparatus according to  claim 7 , comprising at least one of
 a high pressure nitrogen gas collecting path in which a high pressure nitrogen gas obtained in the high pressure column is collected after heat recovery,   a medium pressure nitrogen gas collecting path in which a medium pressure nitrogen gas obtained in the medium pressure column is collected after heat recovery,   a low pressure nitrogen gas collecting path in which a low pressure nitrogen gas obtained in the low pressure column is collected after heat recovery,   a high pressure liquid nitrogen collecting path in which the high pressure liquid nitrogen condensed in the main condenser reboiler is collected,   a medium pressure liquid nitrogen collecting path in which the medium pressure liquid nitrogen condensed in the medium pressure column condenser is collected, and   a low pressure liquid oxygen collecting path in which the low pressure liquid oxygen obtained in the low pressure column is collected.   
     
     
         20 . The air separation apparatus according to  claim 8 , comprising at least one of
 a high pressure nitrogen gas collecting path in which a high pressure nitrogen gas obtained in the high pressure column is collected after heat recovery,   a medium pressure nitrogen gas collecting path in which a medium pressure nitrogen gas obtained in the medium pressure column is collected after heat recovery,   a low pressure nitrogen gas collecting path in which a low pressure nitrogen gas obtained in the low pressure column is collected after heat recovery,   a high pressure liquid nitrogen collecting path in which the high pressure liquid nitrogen condensed in the main condenser reboiler is collected,   a medium pressure liquid nitrogen collecting path in which the medium pressure liquid nitrogen condensed in the medium pressure column condenser is collected, and   a low pressure liquid oxygen collecting path in which the low pressure liquid oxygen obtained in the low pressure column is collected.