Method for obtaining an air product, and air separation plant

Abstract

An air product is produced in an air separation plant having a heat exchanger, an expansion/compression unit, a rectification unit, liquid storage, cold storage and an air compressor. The air supplied to the rectification unit is conducted through the main air compressor at a pressure level at least 3 bar above the highest operation pressure for the rectification unit. Cryogenic liquids are produced in a first production amount by a first operating mode, a lower second production amount by a second operating mode and a higher third production amount by a third operating mode. Cryogenic liquid is stored in the liquid storage in the third operating mode and removed from storage in the second operating mode. Cryogenic liquid is evaporated in different amounts in each operating mode, which amounts differ by no more than 10%.

1 . Method for producing an air product in an air separation plant having a heat exchanger unit, an expansion/compression unit, a rectification unit, a liquid storage unit, a cold storage unit and a main air compressor, the method comprising:
 all of the air supplied to the rectification unit is conducted through the main air compressor and, there, is firstly compressed to a pressure level which lies at least 3 bar above the highest pressure level at which the rectification unit is operated,   one or more cryogenic liquids is or are produced in a first production amount in a first operating mode, in a second production amount in a second operating mode and in a third production amount in a third operating mode in the rectification unit using the air conducted through the main air compressor, wherein the second production amount is lower than the first production amount and the third production amount is higher than the first production amount,   the one or more cryogenic liquids is or are put into storage in the liquid storage unit in a putting-into-storage amount, which corresponds to a partial amount of the third production amount, in the third operating mode, and said one or more cryogenic liquids is or are removed from storage in the liquid storage unit, in a removing-from-storage amount, in the second operating mode,   the one or more cryogenic liquids is or are evaporated and/or pseudo-evaporated in a first evaporation amount in the first operating mode, in a second evaporation amount in the second operating mode and in a third evaporation amount in the third operating mode, wherein the first evaporation amount corresponds to the first production amount, the second evaporation amount corresponds to the second production amount plus the removing-from-storage amount, and the third evaporation amount corresponds to the third production amount minus the putting-into-storage amount, wherein the first, the second and the third evaporation amount differ from one another by no more than 10%, and,   using the air conducted through the main air compressor, in the second operating mode, a cryogenic fluid stream is formed, using which the cold storage unit is cooled and which is thereby heated, and in the third operating mode, a hot fluid stream is formed, using which the cold storage unit is heated and which is thereby cooled.   
     
     
         2 . Method according to  claim 1 , wherein
 a part of the air conducted through the main air compressor and compressed there is expanded to a pressure level which corresponds at least to the highest pressure level at which the rectification unit is operated, and in which method the cryogenic fluid stream and the hot fluid stream are formed from a part of the expanded air, wherein the part of the expanded air for forming the cryogenic fluid stream is, after the expansion, conducted unheated through the cold storage unit and is heated in the heat exchanger unit to form the hot fluid stream and is subsequently conducted through the cold storage unit, and/or   a rectification unit with a high-pressure column and a low-pressure column is used, wherein a gas mixture which comprises a nitrogen content of 0.5 to 5 mole percent is extracted from the low-pressure column, and in which method the cryogenic fluid stream and the hot fluid stream are formed from a part of the gas mixture extracted from the low-pressure column, wherein said part is used unheated to form the cryogenic fluid stream and is heated in the heat exchanger unit to form the hot fluid stream, and/or   a further part of the air conducted through the main air compressor and compressed there is subsequently compressed further and cooled in the heat exchanger unit, and in which method the cryogenic fluid stream and the hot fluid stream are formed from a part of the further compressed air that has been cooled in the heat exchanger unit, wherein said part is used unheated to form the cryogenic fluid stream and is heated in the heat exchanger unit to form the hot fluid stream.   
     
     
         3 . Method according to  claim 1 , in which method the cryogenic fluid stream is formed from a part of the one or more cryogenic liquids that is or are evaporated or pseudo-evaporated in the second operating mode, before the evaporation thereof, and in which method the hot fluid stream is formed from a part of the one or more cryogenic liquids that is or are evaporated or pseudo-evaporated in the third operating mode, after the evaporation thereof. 
     
     
         4 . Method according to  claim 2 , in which a part of the hot fluid stream, after the cooling thereof in the cold storage unit, is heated in the heat exchanger unit. 
     
     
         5 . Method according to  claim 1 , in which the cold storage unit has first cold storage means and second cold storage means, wherein in each case a first part of the cryogenic fluid stream and of the hot fluid stream is conducted through the first cold storage means, and a second part is conducted through the second cold storage means. 
     
     
         6 . Method according to  claim 5 , in which the second part of the hot fluid stream and of the cryogenic fluid stream is conducted in each case through a section of a main heat exchanger of the heat exchanger unit before and/or after being conducted through the second cold storage means. 
     
     
         7 . Method according to  claim 1 , in which the one or more cryogenic liquids comprise(s) a nitrogen-rich and/or an argon-rich and/or an oxygen-rich liquid and/or liquid air. 
     
     
         8 . Air separation plant having a heat exchanger unit, comprising an expansion/compression unit, a rectification unit, a liquid storage unit, a cold storage unit and a main air compressor, which air separation plant has means which are designed
 to conduct all of the air supplied to the rectification unit through the main air compressor and, there, to firstly compress said air to a pressure level which lies at least 3 bar above the highest pressure level at which the rectification unit is operated,   to produce one or more cryogenic liquids in a first production amount in a first operating mode, in a second production amount in a second operating mode and in a third production amount in a third operating mode in the rectification unit using the air conducted through the main air compressor, wherein the second production amount is lower than the first production amount and the third production amount is higher than the first production amount,   to put the one or more cryogenic liquids into storage in the liquid storage unit in a putting-into-storage amount, which corresponds to a partial amount of the third production amount, in the third operating mode, and to remove said one or more cryogenic liquids from storage in the liquid storage unit, in a removing-from-storage amount, in the second operating mode,   to evaporate and/or pseudo-evaporate the one or more cryogenic liquids in a first evaporation amount in the first operating mode, in a second evaporation amount in the second operating mode and in a third evaporation amount in the third operating mode, wherein the first evaporation amount corresponds to the first production amount, the second evaporation amount corresponds to the second production amount plus the removing-from-storage amount, and the third evaporation amount corresponds to the third production amount minus the putting-into-storage amount, wherein the first, the second and the third evaporation amount differ from one another by no more than 10%, and,   using the air conducted through the main air compressor, to form, in the second operating mode, a cryogenic fluid stream using which the cold storage unit is cooled and which is thereby heated, and to form, in the third operating mode, a hot fluid stream using which the cold storage unit is heated and which is thereby cooled.