Design and evaluation of a novel system for the flue gas compression and purification from the oxy-fuel combustion process

The process of flue gas compression and purification is essential for oxy-fuel combustion, because of its significance in determining the quality of the CO2 product. Based on the difference of dew points between CO2 and acid contaminants, a novel system, which integrated the partial CO2 recirculation with the flue gas purification, was proposed and evaluated in this study. The simulation results confirmed that a CO2 stream with a purity of 99.9% could be achieved, and the distillate after treatment in SO2 and NO absorbers could be directly recycled back to the boiler. The performance of CO2 recovery was enhanced by elevating the condensing pressure to 3.0-4.0 MPa. Besides, there was a critical ratio between the recycled CO2 liquid and the raw flue gas for the abatement of contaminants, which was 11.0 L/m(3). Furthermore, the performances of SO2 and NO removal were investigated. The efficiencies of SO2 and NO abatement could be more than 99% when the reaction pressures were 0.5 MPa and 1.5 MPa separately. Besides, a critical molar ratio of SO2 to NO in the raw feeding flue gas was determined, and the removal of SO2 was restrained when the SO2/NO molar ratio increased over the critical point. As for the NO abatement, the continuous re-oxidation of NO released from the dissociation of HNO2 was dominant in the NO absorber, and the performance of NO removal was dramatically enhanced with the presence of NO pre-oxidation at low reaction pressures.

Automated summary

The process of flue gas compression and purification plays a crucial role in determining the quality of CO2 product in oxy-fuel combustion. A novel system integrating partial CO2 recirculation with flue gas purification was proposed and evaluated, achieving a purity of 99.9% CO2 stream. Enhancing condensing pressure to 3.0-4.0 MPa improved CO2 recovery performance, while critical ratios between recycled CO2 liquid and raw flue gas were identified for efficient contaminant abatement. The efficiencies of SO2 and NO removal exceeded 99%, with critical molar ratios and reactions pressures determining the success of abatement.