Method and apparatus for maintaining product availability during a disturbance in an air separation unit

Abstract

A method for operating an air separation unit during an unexpected disturbance is provided. The method can include the steps of: determining that a process disturbance has occurred; starting-up a liquid back-up system that is configured to deliver a product gas at a desired product pressure; and introducing compressed air from an air accumulator into the air separation unit at a location that is downstream a main air compressor and upstream a cold box, wherein the compressed air is introduced in an amount that is effective for maintaining nominal operation of the air separation unit during the process disturbance and until the liquid back-up system is delivering the product gas at the desired product pressure.

What is claimed is: 
     
         1 . A method for operating an air separation unit during an unexpected disturbance, the air separation unit having a main air compressor and a cold box, the method comprising the steps of:
 determining that a process disturbance has occurred;   starting-up a liquid back-up system that is configured to deliver a product gas at a desired product pressure; and   introducing compressed air from an air accumulator into the air separation unit at a location that is downstream the main air compressor and upstream the cold box, wherein the compressed air is introduced in an amount that is effective for maintaining nominal operation of the air separation unit during the process disturbance and until the liquid back-up system is delivering the product gas at the desired product pressure.   
     
     
         2 . The method of  claim 1 , wherein the air accumulator is filled with compressed air that was previously compressed in the main air compressor. 
     
     
         3 . The method of  claim 1 , wherein the air separation unit further comprises a second main air compressor. 
     
     
         4 . The method of  claim 1 , wherein the second main air compressor is intentionally turned down during periods of high electricity costs and air from the air accumulator is introduced into the air separation unit in an amount that is effective for maintaining nominal operation of the air separation unit while the second main air compressor is taken off-line. 
     
     
         5 . The method of  claim 1 , wherein the air separation unit further comprises a booster air compressor. 
     
     
         6 . The method of  claim 1 , wherein the process disturbance is selected from the group consisting of a trip of the main air compressor, the booster air compressor, and combinations thereof. 
     
     
         7 . The method of  claim 1 , wherein the process disturbance is determined by a drop in air pressure or process flow rates. 
     
     
         8 . The method of  claim 1 , wherein the air accumulator has an air pressure that is above a discharge pressure of the main air compressor. 
     
     
         9 . The method of  claim 1 , wherein the air accumulator has a capacity that is sufficiently large to allow for operation of the air separation unit for the period of time it takes the liquid back-up system to deliver the product gas at the desired product pressure.