Numerical Investigation of the Effect of CO₂/H₂O Composition in Oxidizer on Flow Field and Combustion Behavior of Oxy-pulverized Coal Combustion

Oxy-coal combustion is the most promising technology for the reduction of greenhouse gases from pulverized coal-fired power plants. Oxy-coal combustion employs recirculated flue gas mainly consisting of CO₂ and water vapor as a diluent. Thus, the pulverized coal particles are surrounded and burned under steam rich atmosphere. The addition of H₂O would have a significant impact on the combustion characteristics of oxy-coal combustion. The chemical and physical properties of steam are different than the CO₂, replacement of CO₂ with steam will alter heat capacity, gasification, and radiation properties considerably. The present article numerically compares ideal dry recycle oxy-coal combustion (0% H₂O) with wet recycle oxy-coal (10-50% H₂O) and oxy-steam combustion (H₂O replaces whole CO₂ from oxidant) in terms of flow field, temperature distribution, oxidizer distribution, radiative heat transfer, char consumption, and species concentration. Higher flame temperatures under enriched steam oxy-coal combustion cases were found due to lower volume heat capacity of H₂O than CO₂. Steam enrichment also enhanced char gasification reaction, which has affected temperature distribution and incident radiation profile inside the combustion chamber. Peak temperature obtained under oxy-steam case is around 10% higher than ideal dry recycle case (0% H₂O) and 2-5% higher than the wet oxy-coal combustion cases having 50-10% H₂O in the oxidizer.