Operation of integrated gasification combined cycle power generation systems at part load

A method of operating an integrated gas turbine/air separation system at part load which comprises compressing a first stream of air in a gas turbine air compressor, combusting at least a portion of the resulting compressed air with a fuel in a gas turbine combustor to form hot combustion products, expanding the hot combustion products in a gas turbine expander which drives the compressor, separating air into nitrogen-rich and oxygen-rich products in a cryogenic air separation unit wherein feed air to the air separation unit is provided at least in part by compressing a second stream of air in a main air compressor, wherein the integrated gas turbine/air separation system is operated at part load such that

• (a) when the gas turbine air compressor supplies compressed air at a given operating pressure which is greater than a minimum air separation unit feed pressure, the air separation unit is operated at a feed pressure essentially equal to the given operating pressure and the feed air is provided to the air separation unit in part by the main air compressor and in part by an additional portion of compressed air from the gas turbine air compressor;
• and
• (b) when the gas turbine air compressor supplies compressed air at a given operating pressure which is essentially equal to or less than the minimum air separation unit feed pressure, the air separation unit is operated at a feed pressure essentially equal to the minimum air separation unit feed pressure and the feed air to the air separation unit is provided by the main air compressor without additional compressed air from the gas turbine air compressor.