Method for compressing an incoming feed air stream in a cryogenic air separation plant

A method for compression of an incoming feed air stream to a cryogenic air separation plant, the method comprising the steps of:

• (a) compressing the incoming feed air stream in a lower pressure multi-stage compressor of a common air compression train driven directly by a double ended first variable speed electric motor assembly configured to operate at speeds of between 5000 rpm and 9000 rpm, wherein the lower pressure multi-stage compressor further comprises a first compression stage or first compressor unit directly and rigidly coupled to one end of the double ended first variable speed electric motor assembly, and a second compression stage or second compressor unit directly and rigidly coupled to the other end of the double ended electric motor assembly, with the first compression stage or first compressor unit and the second compression stage or second compressor unit arranged in series and driven directly by the double ended first variable speed electric motor assembly, wherein the first compression stage or first compressor unit is configured to receive and compress the incoming feed air stream and produce a first compressed air stream and the second compression stage or second compressor unit is configured to receive and further compress the first compressed air stream to produce a second compressed air stream;
• (b) further compressing the second compressed feed air stream in one or more higher pressure compressors of the common air compression train to produce the final compressed feed air stream, wherein the one or more higher pressure compressors are directly and rigidly coupled to a second variable speed electric motor assembly and driven by the second variable speed electric motor assembly configured to operate at speeds suitable for the cryogenic air separation plant;
• (c) purifying the final compressed feed air stream to remove impurities and produce a compressed and purified feed air stream;
• (d) splitting the compressed and purified feed air stream into two or more portions in a split functional air compression train, the two or more portions including a turbine air stream moving through a turbine air circuit and a boiler air stream moving through a boiler air circuit;
• (e) further compressing the boiler air stream in one or more additional compressor units disposed in the boiler air circuit;
• (f) further compressing the turbine air stream in one or more additional compressor units disposed in the turbine air circuit;
• (g) directing the further compressed boiler air stream and the further compressed turbine air stream to a primary heat exchanger configured to cool the boiler air stream and turbine air stream to temperatures suitable for rectification in a distillation column system of the cryogenic air separation plant;
• (h) expanding the further compressed and cooled turbine air stream in a turbo-expander;
• (i) directing the further compressed and cooled boiler air stream and the expanded turbine air stream to a distillation column system of the cryogenic air separation plant to produce liquid and gaseous products;
• and
• (j) adjusting the speed of the first variable speed electric motor assembly in response to changes in operating conditions of the cryogenic air separation plant and a measured flow rate of air in the incoming feed air stream and thereafter adjusting the speed of the second variable speed electric motor assembly in response to changes in the speed of the first variable speed electric motor assembly and a discharge pressure, the discharge pressure selected from the group consisting of a measured pressure in the turbine air circuit, a measured pressure in the boiler air circuit, or a measured pressure in the common air compression train;
• and
• wherein the ratio of the speed of the first variable speed-electric motor assembly to the speed of the second variable speed electric motor assembly before the adjustment in step (j) is different than the ratio of the speed of the first variable speed-electric motor assembly to the speed of the second variable speed electric motor assembly after said adjustments in step (j).