Production of an air product in an air separation plant with cold storage unit

Abstract

A method for producing an air product in an air separation plant. Feed air is cooled at least in a main air compressor and is fed into a distillation column system. A fluid storage unit and a cold accumulator are used. In a first operating mode, fluid is stored in the fluid storage unit and the cold accumulator is heated. In a third operating mode, fluid is released and the cold accumulator is cooled, and in a second operating mode, fluid is neither stored nor released.

1 . A process for producing an air product in an air separation plant in which feed air, which is altogether compressed in a main air compressor and thereafter partly recompressed in a booster air compressor, is cooled down and subsequently entirely or partially fed into a distillation column system, the process comprising,
 in a first operating mode
 feeding the feed air in a first air feeding amount into the distillation column system, and in this system using the feed air to produce a liquid intermediate product in a first amount of intermediate product, 
 of the first amount of intermediate product, storing at least one fraction in a liquid form in a storage amount in a liquid storage unit, 
 warming up a further fraction of the first amount of intermediate product or of another amount of liquid intermediate product under pressure in a first amount of product in the main heat exchanger and providing it as the air product and allowing a cold storage unit with at least one cold store to be flowed through by a first process stream, the cold store being warmed up and the first process stream being cooled down, and 
   in a second operating mode
 feeding the feed air in a second air feeding amount into the distillation column system and in this system using the feed air to produce a liquid intermediate product in a second amount of intermediate product, 
 the cold storage unit not being flowed through, 
   in a third operating mode
 feeding the feed air in a third air feeding amount into the distillation column system and in this system once again using the feed air to produce a liquid intermediate product in a third amount of intermediate product, the first air feeding amount being greater than the third air feeding amount, 
 removing the liquid intermediate product stored in the first operating mode in a removal amount from the liquid storage unit and combining it with the third amount of intermediate product to form a total amount, which is warmed up under pressure in the main heat exchanger in a third amount of product and provided as the air product, and 
 allowing the cold storage unit to be flowed through by a second process stream, the cold store being cooled down, the second process stream being warmed up. 
   
     
     
         2 . The process as claimed in  claim 1 , in which the part of the feed air that is recompressed in the booster air compressor is recompressed there in a booster air compressor amount, the booster air compressor amount being greater in the first operating mode than in the third operating mode. 
     
     
         3 . The process as claimed in  claim 2 , in which, at least in the first operating mode, part of the booster air compressor amount is cooled down in a turbine stream amount to a temperature level that lies above the liquefaction temperature of nitrogen, and is expanded in an expansion machine, and in which part of the booster air compressor amount is cooled down in a throttle stream amount to a temperature level that lies below the liquefaction temperature of nitrogen, and is expanded. 
     
     
         4 . The process as claimed in  claim 3 , in which the sum of the turbine stream amount and the throttle stream amount is greater in the first operating mode than in the third operating mode. 
     
     
         5 . The process as claimed in  claim 3 , in which, after expansion, the throttle stream amount and the turbine stream amount are fed into the distillation column system as part of the air feeding amount. 
     
     
         6 . The process as claimed in  claim 1 , in which part of the feed air that is not compressed in the booster air compressor is expanded by way of an expansion turbine into a low-pressure column of the distillation column system of the air separation plant. 
     
     
         7 . The process as claimed in  claim 1 , in which a fraction of a cryogenic gas product removed from the distillation column system, not in the form of the first and/or third amount of intermediate product, is passed through the cold storage unit in the cryogenic state in the third operating mode to cool the unit down. 
     
     
         8 . The process as claimed in  claim 7 , in which the cryogenic gas product is warmed up completely in the main heat exchanger, a fraction of the warmed-up gas product subsequently being passed through the cold storage unit to warm the unit up. 
     
     
         9 . The process as claimed in  claim 1 , in which in the first operating mode part of the feed air is passed through the cold storage unit for cooling-down purposes and part through at least one portion of the main heat exchanger. 
     
     
         10 . The process as claimed in  claim 1 , in which in the third operating mode the entire feed air is passed through at least one portion of the main heat exchanger and cooled down therein, a fraction of the cooled-down feed air being used thereafter for cooling down the cold storage unit. 
     
     
         11 . The process as claimed in  claim 1 , in which in the third operating mode the entire feed air is passed through at least one portion of the main heat exchanger. 
     
     
         12 . An air separation plant for producing an air product, which is designed for compressing feed air altogether in a main air compressor and thereafter partly recompressing it in a booster air compressor and cooling the feed air down and subsequently entirely or partially feeding it into a distillation column system, said plant being provided with means that are designed for
 in a first operating mode
 feeding the feed air in a first air feeding amount into the distillation column system, and in this system using the feed air to produce a liquid intermediate product in a first amount of intermediate product, and 
 of the first amount of intermediate product, storing at least one fraction in a liquid form in a storage amount in a liquid storage unit, 
   warming up a further fraction of the first amount of intermediate product or of another amount of liquid intermediate product under pressure in a first amount of product in the main heat exchanger and providing it as the air product and
 allowing a cold storage unit with at least one cold store to be flowed through by a first process stream and warmed up, the first process stream being cooled down, and 
   in a second operating mode
 feeding the feed air in a second air feeding amount into the distillation column system and in this system using the feed air to produce a liquid intermediate product in a second amount of intermediate product, 
 the cold storage unit not being flowed through, 
   in a third operating mode
 feeding the feed air in a third air feeding amount into the distillation column system and in this system once again using the feed air to produce a liquid intermediate product in a third amount of intermediate product, the first air feeding amount being greater than the third air feeding amount, 
 removing the liquid intermediate product stored in the first operating mode in a removal amount from the liquid storage unit and combining it with the third amount of intermediate product to form a total amount and warming it up under pressure in the main heat exchanger in a third amount of product and providing it as the air product, and 
 allowing the cold storage to be flowed through by a second process stream and cooled down, the second process stream being warmed up.