Process and system for controlling a cryogenic air separation unit during rapid changes in production

A cryogenic distillation system having at least one distillation column for separating air into at least oxygen-rich and nitrogen-rich products for an integrated gasifier combined cycle power plant (IGCC) in which purity requirements are maintained during variations in product demand by the IGCC and during variations of feed air pressure comprising:

• reflux flow means for said distillation system for providing reflux flow of nitrogen-rich fluid;
• storage means coupled to said reflux flow means for storing nitrogen-rich fluid;
• and
• means for controlling the reflux flow (1) for removing nitrogen-rich fluid from the reflux flow means and storing said removed nitrogen-rich fluid in said storage means as the product demand and the feed air pressure substantially increases and (2) for adding nitrogen-rich fluid from the storage means to the reflux flow means as the product demand and the feed air pressure substantially decreases.

In a process for the separation of air in a double column cryogenic distillation system having a low pressure column, a high pressure column, and reflux flows from the high pressure column to the low pressure column wherein air is separated into at least oxygen-rich and nitrogen-rich products, the improvement for substantially maintaining purity requirements during variations in product demand and feed air pressure comprising the steps of:

• (a) upon an increase in oxygen product demand, increasing feed air pressure and decreasing flow of nitrogen-rich product from the low pressure column, thereby increasing the pressure in the low pressure column;
• (b) upon a decrease in oxygen product demand, decreasing feed air pressure and increasing flow of nitrogen-rich product from the low pressure column, thereby decreasing the pressure in the low pressure column;
• (c) removing and storing a portion of the nitrogen-rich reflux flow fluid as the product demand increases and the feed air pressure substantially increases;
• and
• (d) adding to the reflux flow a portion of the stored nitrogen-rich fluid as the product demand decreases and the feed air pressure substantially decreases.