Optimized enriched CO2 recycle oxy-fuel combustion for high ash coals

Oxy-fuel combustion is one of the technologies which enable the economic and efficient carbondioxide (CO2) removal. In the present paper, a new variant to the oxy-coal combustion in a pulverized coal burner is proposed in which CO2-enriched flue gas is used to moderate the flame temperature in conventional oxy-fuel combustion. In this method, a flue gas conditioner is used to remove most of the moisture from the flue gas which results in CO2 enrichment. This gas is recycled back to the furnace to be mixed with pure oxygen from an air separation unit to provide a CO2-rich environment in which the hydrocarbon fuel is burnt. Thermodynamic analysis on a lignite coal-fired power plant shows that, for the same peak flame temperature, the flue gas is significantly richer in CO2 (by up to 80.5% by mass) at the boiler exit. Compared to the conventional exhaust gas recycling, the proposed method is simpler in the sense that one hot-gas particulate cleaning system is eliminated. The volumetric flow rate of the flue gas through the boiler is also reduced. Both these factors make it attractive for high ash coals where particulate cleaning and erosion-related problems are of major concern. Thermodynamic exergy analysis shows that the optimized CO2-enriched flue gas recycled power plant performs better than retrofitted flue gas recycled system.