Modelling of oxy-pulverized coal combustion to access the influence of steam addition on combustion characteristics

Oxy-coal combustion is identified as the most powerful technology for the reduction of greenhouse gases from pulverized coal-fired power plants. Under oxy-coal combustion, the recirculated flue gas (RFG) is used as diluent that mainly consists of CO2 and water vapor. Thus, the pulverized coal particles are surrounded and burned under steam rich atmosphere. Addition of H2O would considerably affect combustion characteristics of oxy-coal combustion by varying heat capacity, gasification and radiation due to distinct chemical and physical properties of steam than CO2. This article numerically investigates the effect of steam addition on temperature field, oxidizer distribution, radiative heat transfer, char consumption and species concentration. The mole fraction of steam is varied from 0 to 50% at a fixed oxygen mole fraction of 21 vol% to represent various we oxy-coal combustion cases. The oxy-steam variant of oxy-coal combustion obtained by replacing CO2 mole fraction by H2O is also compared with the different we oxy-coal combustion cases. Results revealed higher flame temperature under enriched steam oxy-coal combustion cases 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 we oxy-coal combustion cases having 50-10% H2O in the oxidizer.