Compression method and air separation

Abstract

A compression method, a multistage compression system and an air separation method and plant in which a gas is compressed in a series of compression stages to produce a compressed gas and each of the compression stages incorporate a variable speed compressor. In such compression method and system, the compressed air is produced at a pressure that remains stable during both normal operational conditions and during turn down conditions during which the flow rate of the gas is reduced. This reduction is accomplished by reducing the speed of the compressor in an initial compression stage such that the compressor operates at a point along its peak efficiency operating line at which the pressure ratio is directly proportional to the flow rate and such that the lower turn down flow rate is obtained at a reduced pressure which is made up in successive compression stages.

Description

RELATED APPLICATIONS[0001]This application is a continuation-in-part of prior U.S. application Ser. No. 13 / 087,734, filed on Apr. 15, 2011, which is incorporated herein by reference.FIELD OF THE INVENTION[0002]The present invention relates to a method and system for compressing a gas and an air separation method and plant incorporating such method and system in which a gas or air is compressed in a series of compression stages to a higher pressure that is maintained both at normal operating conditions and during turndown operational conditions when a lower flow rate of the gas or air is required. More particularly, the present invention relates to such a method and system and air separation method and plant in which the compression stages have variable speed motors driving compressors and the speed of each of the compressors is adjusted during turndown such that an initial of the compression stages operates at a point along a peak efficiency operating line.BACKGROUND OF THE INVENTIO...

AI Technical Summary

Benefits of technology

[0009]When a multistage compression system is operated in accordance with the present invention, as set forth above, the flow rate is reduced during the turn down operating conditions while allowing the gas to be delivered at the pressure that is obtained during the normal operating conditions. Thus, the method of the present invention allows the multistage compression system to be used in applications where a stable pressure is required under all operational regimes. In addition to the foregoing, the method of the present invention is particularly energy efficient when the multistage compression system is operated during turn down conditions. The reason for this is that the power consumed by a multistage compression system have multiple stages is greatest at the initial compression stage because the volumetric flow rate is greatest in such stage due to the fact that the gas has the lowest density while being compressed in the initial stage. As the gas is successively compressed, the density increases and consequently less power is consumed in subsequent compression stage. However, since the initial compression stage is operated and turned down to a point along its peak efficiency operating line, the power consumed by such stage at turndown is less than would otherwise have been consumed had it not be operating along a point of its peak efficiency operating line. The successive stages will recover the reduction of the pressure in the first stage of compression due to turn down and as such, will very likely not operate along their peak efficiency operating line. However, since the successive stages will consume less power than the initial compression stage, the loss in efficiency will be more than compensated for through operation of the initial stage at its peak efficiency. Consequently, the operation of a compression system in accordance with the present invention enables both a reduced power consumption and the higher pressure level of the normal operating condition to be obtained that would not be possible had the compression stages been turned down at a constant speed ratio.

Problems solved by technology

The successive stages will recover the reduction of the pressure in the first stage of compression due to turn down and as such, will very likely not operate along their peak efficiency operating line.

However, since the successive stages will consume less power than the initial compression stage, the loss in efficiency will be more than compensated for through operation of the initial stage at its peak efficiency.

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