Kinetic study and optimization on SNCR process in pressurized oxy-combustion

Pressurized Oxy-combustion is one of the most promising technologies for carbon capture, utilization, and storage (CCUS) of coal utilization. In pressurized oxy-combustion, the removal of acid gas pollutants and the latent heat of moisture condensation are mainly carried out by an integrated direct-contact wash column (DCC). Recent studies have shown that the inlet concentration of NO_x in the column is important for the combined removal of NO_x and SO_x, therefore, it is essential to control the NO_x emissions before the DCC. Selective non-catalytic reduction (SNCR) is a promising and economical technology of NO_x reduction; however, no study has been conducted on SNCR at elevated pressure, especially in pressurized oxy-combustion. In this paper, kinetic modeling is carried out to explore and optimize the NO_x reduction by SNCR in pressurized oxy-combustion. First, the detailed mechanism used in this study is validated by the experimental results in literature. Based on the validation of the detailed mechanism, the effects of different parameters including temperature, oxygen concentration, moisture content, NH₃ concentration, and SO₂ concentrations on the SNCR performance are analyzed at higher pressures in oxy-combustion atmosphere. The modeling results show that by increasing the pressure from 1 atm to 15 atm, the SNCR de-NOx efficiency increased by 2–3%. The width of the optimum temperature window for maximum De-NO_x is broadened from 1250K to 1450K with increasing the pressure from 1 atm to 10 atm. The increase of pressure has no significant effect on thermal de-NOx efficiency with increasing the NH₃/NO ratio. At higher pressure (10 atm) the increase in O₂ concentration from 1 to 20% the de-NOx efficiency decreases almost twice as much as at 1 atm. The increase of SO₂ and moisture contents at high pressure have no significant effect on the de-NOx efficiency. Rate of production (ROP) and sensitivity analysis are performed to determine the dominant reaction paths of de-NO_x in pressurized-oxy SNCR process. This study can provide guidance for the process optimization of de-NO_x by SNCR in pressurized oxy-combustion.