Design of a Moderate Speed-High Capacity Centrifugal Compressor With Application to PSA and VPSA Air Separation Processes

Abstract

The performance of the PSA (Pressure Swing Adsorption) or VPSA (Vacuum Pressure Swing Adsorption) cycle in an oxygen air separation process is significantly dependent upon the working capacity and working selectivity afforded by the adsorbent. These parameters in turn are dependent on the adsorption pressures employed in the VPSA cycle. Despite the increasing demand for increased capacity and pressure in VPSA air separation plants, they have conventionally used rotary-type positive displacement blowers as the process machinery. These blowers, while most adapted to the oscillating nature of the pressure swing cycles, have increasing high cost per capacity at higher capacities and become very inefficient as the cycle pressures are increased. A new low cost and more efficient process machinery solution is introduced through the use of a moderate speed direct coupled integrated feed and vacuum centrifugal compressor with inlet guide vanes to achieve high efficiencies during the varying operating conditions of the VPSA cycle. In this paper the fundamentals of a VPSA cycle as it applies to a centrifugal compressor operation is presented. A model of the design and predicted performance of a feed and vacuum VPSA centrifugal compressor is presented. A discussion of the proposed design in comparison to a conventional blower is presented. The model and predictions indeed show the superiority of the new design concept to the conventional process machinery equipment in terms of power savings and capacity increase. This new design however requires a feedback control system for the inlet guide vanes.