Flexible asu for variable energy cost

Abstract

A process for the production of at least liquid oxygen and/or liquid nitrogen in cryogenic rectification. During a first period, during which electrical power prices are low, a process stream utilized by the ASU is liquefied and stored. During a second period, during which electrical prices high, at least a portion of the stored, liquefied process stream is withdrawn and introduced into the ASU. Wherein the MAC has a discharge pressure of greater than 10 bara during the first period, a first molar flowrate (LF) and a first pressure (LP) during the first period, a second molar flowrate (HF) and a second pressure (HP) during the second period. Wherein C=(LF/HF)/(LP/HP). And wherein second molar flowrate (HF) is <90% of first molar flowrate (LF) and C is between 0.9 and 1.05.

What is claimed is: 
     
         1 . A process for the production of at least liquid oxygen and/or liquid nitrogen in the cryogenic rectification of feed air, comprising an air separation unit and a main air compressor, the process comprising:
 during a first period, during which electrical power prices are below a first predetermined threshold, a process stream utilized by the air separation unit is liquefied and stored at least a part of the time of this period,   during a second period, during which electrical prices are at, or above a second predetermined threshold, at least a portion of the stored, liquefied process stream is withdrawn and introduced into the air separation unit at least a part of the time of this period,   
       wherein the main air compressor has a discharge pressure of greater than 10 bara during the first period,
 wherein the main air compressor has a first molar flowrate (LF) and a first pressure (LP) during the first period, 
 wherein the main air compressor has a second molar flowrate (HF) and a second pressure (HP) during the second period, 
 wherein C=(LF/HF)/(LP/HP), and 
 wherein second molar flowrate (HF) is <90% of first molar flowrate (LF) and C is between 0.9 and 1.05. 
 
     
     
         2 . The process of  claim 1 , wherein second molar flowrate (HF) is <80% of first molar flowrate (LF) and C is between 0.8 and 1.15. 
     
     
         3 . The process of  claim 1 , wherein the first predetermined threshold is approximately equal to the second predetermined threshold. 
     
     
         4 . The process of  claim 1 , wherein the process stream that is liquefied and stored in at least a portion of the first period and withdrawn and introduced into the air separation unit in the second period, is liquid air. 
     
     
         5 . The process of  claim 4 , wherein the air separation unit produces a mass flowrate of liquid oxygen and a mass flowrate of liquid nitrogen, and
 wherein the combined mass flowrate of the liquid oxygen and the mass flowrate of liquid nitrogen of the first period and the second period are approximately equal at least a portion of the time.   
     
     
         6 . The process of  claim 1 , wherein the air separation unit further comprises one or more rotating devices selected from the group consisting of a booster air compressor, recycle compressor, refrigeration compressor and expanders, and
 wherein none of the rotating devices are stopped when transitioning from the first period to the second period.   
     
     
         7 . A process for the production of at least liquid oxygen and/or liquid nitrogen in the cryogenic rectification of feed air, comprising an air separation unit and a main air compressor, and an auxiliary compressor the process comprising:
 during a first period, during which electrical power prices are below a first predetermined threshold, a process stream utilized by the air separation unit is liquefied and stored at least a part of the time of this period,   during a second period, during which electrical prices are at, or above a second predetermined threshold, at least a portion of the stored, liquefied process stream is introduced into the air separation unit at least a part of the time of this period,   
       wherein the auxiliary compressor has a pressure ratio of greater than 6 during the first period,
 wherein the auxiliary compressor has a first molar flowrate (LF) and a first pressure ratio (LPR) during the first period, 
 wherein the auxiliary compressor has a second molar flowrate (HF) and a second pressure ratio (HPR) during the second period, 
 wherein CR=(LF/HF)/(LPR/HPR), and 
 wherein second molar flowrate (HF) is <90% of first molar flowrate (LF) and CR is between 0.9 and 1.05. 
 
     
     
         8 . The process of  claim 7 , wherein second molar flowrate (HF) is <80% of first molar flowrate (LF) and CR is between 0.8 and 1.15. 
     
     
         9 . The process of  claim 7 . wherein the first predetermined threshold is approximately equal to the second predetermined threshold. 
     
     
         10 . The process of  claim 7 , wherein the process stream that is liquefied and stored in at least a portion of the first period and withdrawn and introduced into the air separation unit in the second period, is liquid air. 
     
     
         11 . The process of  claim 10 , wherein the air separation unit produces a mass flowrate of liquid oxygen and a mass flowrate of liquid nitrogen, and
 wherein the combined mass flowrate of the liquid oxygen and the mass flowrate of liquid nitrogen of the first period and the second period are approximately equal at least a portion of the time.   
     
     
         12 . The process of  claim 7 . wherein the air separation unit further comprises one or more rotating devices selected from the group consisting of a booster air compressor, recycle compressor, refrigeration compressor and expanders, and
 wherein none of the rotating devices are stopped when transitioning from the first period to the second period.   
     
     
         13 . A process for the production of at least gaseous oxygen in the cryogenic rectification of feed air, comprising an air separation unit and a main air compressor; the process comprising:
 during a first period; during which electrical power prices are below a first predetermined threshold, a process stream utilized by the air separation unit is liquefied and stored at least a part of the time of this period.   during a second period, during which electrical prices are at, or above a second predetermined threshold, at least a portion of the stored, liquefied process stream is introduced into the air separation unit at least a part of the time of this period,   
       wherein the main air compressor has a discharge pressure of greater than 10 bara during the first period,
 wherein the main air compressor has a first molar flowrate (LF) and a first pressure (LP) during the first period, 
 wherein the main air compressor has a second molar flowrate (HF) and a second pressure (HP) during the second period, 
 wherein C=(LF/HF)/(LP/HP), and 
 wherein second molar flowrate (HF) is <90% of first molar flowrate (LF) and C is between 0.9 and 1.05. 
 
     
     
         14 . The process of  claim 13 , wherein second molar flowrate (HF) is <80% of first molar flowrate (LF) and C is between 0.8 and 1.15. 
     
     
         15 . The process of  claim 13 , wherein the first predetermined threshold is approximately equal to the second predetermined threshold. 
     
     
         16 . The process of  claim 13 , wherein the process stream that is liquefied and stored in at least a portion of the first period and withdrawn and introduced into the air separation unit in the second period, is liquid air. 
     
     
         17 . The process of  claim 16 , wherein the air separation unit produces a mass flowrate of gaseous oxygen and/or a mass flowrate of gaseous nitrogen, and,
 wherein the combined mass flowrate of the gaseous oxygen and/or the mass flowrate of gaseous nitrogen of the first period and the second period are approximately equal at least a portion of the time.   
     
     
         18 . The process of  claim 17 , wherein the air separation unit further comprises one or more rotating devices selected from the group consisting of a booster air compressor, recycle compressor, refrigeration compressor and expanders, and
 wherein none of the rotating devices are stopped when transitioning from the first period to the second period.