Study of design parameters affecting the performance of CO2 purification units in oxy-fuel combustion

Abstract

Oxy-fuel combustion is a promising technology for capturing carbon dioxide (CO2) from power plants by generating a flue gas which is predominantly CO2 and water vapour (which can be removed by condensation and drying). Other diluents (Ar, O2 and N2) and trace contaminants (SO2, SO3, NO, NO2, CO, etc.) will also be present in the oxy-fuel derived CO2-stream and have to be removed prior to transportation and storage. This flue gas composition makes low temperature physical separation a promising technology for CO2 capture. The aim of this paper is to evaluate low temperature processes for producing high purity, high pressure CO2 from oxy-fuel combustion flue gas through simulation and modelling in Aspen HYSYS using different patent applications filed by COSTAIN as basis. The processes are based on phase separation using simple flash units, integrated with the compression process. Excellent energy recovery is achieved by exploiting the cold duty of the process streams to supply the required refrigeration so that the overall power consumption is low.The capture process shows good performance when treating flue gas of high CO2 concentration, with purity of over 98%, recovery rate over 93%, and power consumption of 165kWh/tCO2 captured. For low CO2 concentration (such as with a retrofit), a lower CO2 recovery is obtained (approximately 85%) so that a small amount of further processing, e.g. by a physical solvent would be required to increase the CO2 capture. The effect of design parameters on performance including CO2 product purity, recovery rate and specific power consumption has been assessed. By optimizing process conditions, an optimum or near-optimum design has been generated taking into account the operating constraints of the equipment.