Interactions of Hcn with No in Pressurized Oxy-Combustion

Abstract

Pressurized oxy-combustion (POC) is considered to be one of the most promising CO2 capture technologies in coal-fired power plants. The knowledge of NOx concentration in the flue gas of pressurized combustion system is very important for an appropriate design of the carbon capture process. NOx final emissions in POC depend on the reburn reactions of NO that entered through the recycled flue gases. HCN is the main intermediate during this process, and thus, it may interact with NO significantly. The current study aims to assess the gas-phase interactions of HCN and NO in a CO2 atmosphere, which is customary to pressurized oxy-combustion conditions. Kinetic modeling study of the oxidation of HCN in the presence of NO has been performed under POC condition and in the 973-1473K temperature range. The influence of the stoichiometry, pressure, H2O concentration and NO inlet concentration are analyzed. The results show that the HCN-NO interaction reduces both HCN and NO, and that the interaction increases as pressure increases when the temperature is high, whereas the opposite is true in low-temperature regions. The effect of stoichiometric parameters also strongly depends on temperature but follows the opposite trend compared with the effect of pressure. These differences are contributed to the suppressive effect on O2 decomposition and the positive effect on H2O decomposition at elevated pressures. An optimal temperature for NO reduction is shifted to lower temperature with the pressure and H2O concentration. The analysis of the total fixed nitrogen (TFN) indicates that for an actual boiler (5%O2), the temperature should be controlled at 1373K, 1223K, 1173K and 1173K, respectively, as the pressure increasing from 1atm to 15atm. Finally, a 21-spcies and 69-steps reduced chemistry is developed and validated to accurately predict the interaction of HCN with NO at elevated pressures.

Keywords: HCN, NO, kinetic mechanism, interaction, pressurized oxy-combustion