Cost Benefit Analysis of Waste Heat to Power Option for Multistage Air Compressor

This paper summarizes results of a study conducted to minimize total cost of ownership of multistage air compressors by integrating it with compact and efficient off-the-shelf organic rankine power cycle units to recover low grade waste heat from inter-stage coolers with subsequent conversion to power. The paper also highlights challenges faced by the integration and provides guidance for future cost and technology targets for key components to make it a commercial scale reality. Various schemes for vaporization of the working fluid including direct and indirect as well as full or partial were explored. Also, in order to better understand interaction between cycle efficiency and capital cost of key components, design as well as operating parameters including evaporator approach temperature, compression stage suction temperature, number of compression stages and cooling water supply temperature were investigated. Configuration, size and hence the cost of evaporator/ inter-stage cooler was found to be one of the major factors governing the overall cost. Impact of various operating modes including turn-down and seasonal variations were also studied. Air flow and final discharge pressure from the multistage air compressor were kept constant throughout the study to facilitate a fair comparison.