Oxygen supply for oxycoal CO2 capture

Abstract

The oxygen requirements for oxycoal combustion in a coal-fired power station are unusual in several respects. The amount of oxygen required is large, for instance a 500 MWe power plant will require around 10,000 tonnes per day of oxygen. The oxygen purity is low and the pressure required is essentially atmospheric pressure. There is no demand for any significant quantity of co-products, such as argon or nitrogen. The parasitic nature of the power means that high efficiency is important but the large scale means that capital cost should also be minimised. These factors open up new possibilities to optimise the process cycle and machinery configuration to minimise the power consumption of the air separation unit without compromising the requirement for low cost. This paper presents the results of a study to develop Air Products’ air separation unit (ASU) offerings for oxycoal CO2 capture projects. A scalable “reference plant” concept is described to match particular sizes of power generation equipment, taking into account factors such as safety, reliability, operating flexibility, efficiency, and of course low capital cost. We describe the selection of a process cycle to exploit the low purity requirements as well as the options for compression machinery and drivers as the scale of the plant increases and the sizes of referenced equipment limit the possibilities. We also explore integration with other elements of the oxycoal system, such as preheating condensate or heating and expanding pressurised nitrogen. Finally, the advantages and disadvantages of different execution strategies for air separation unit projects are discussed, as well as alternative commercial models for the supply of oxygen.