Air separation unit feed flow control in an igcc power generation system

Abstract

A cryogenic air separation system which is subject to periods of significant changes in product demand is controlled during such periods to minimize the impact of transient operation on product purity. The feed air is introduced directly into the higher pressure column of a distillation system having at least two columns, and nitrogen-rich and oxygen-rich vapor products are withdrawn from the lower pressure column. The flow rate of the nitrogen-rich vapor product is controlled as a function of the feed air flow rate by a feed air flow controller which controls the suction pressure of the nitrogen product compressor. The set point of the flow controller is manipulated as a function of the composition of the oxygen-enriched vapor product. A nitrogen-rich liquid is withdrawn from the higher-pressure column and introduced into the lower-pressure column as reflux. An inventory of this liquid is maintained in a holdup tank for storage or withdrawal during periods of transient operation. A feedforward control system increases or decreases the flow rates of the nitrogen-rich vapor product, the oxygen-rich vapor product, and the nitrogen-rich liquid during periods of increasing or decreasing product demand by manipulation of the set points of the feed air, the oxygen-rich vapor product, and the nitrogen-rich liquid flow controllers.