A kinetic evaluation and optimization study on NO_X reduction by reburning under pressurized oxy-combustion

摘要

Pressurized oxy-combustion is an emerging and more efficient technology for carbon capture, utilization, and storage than the first generation (atmospheric) oxy-combustion. NO_X is a major conventional pollutant produced in pressurized oxy-combustion. In pressurized oxy-combustion, the utilization of latent heat from moisture and removal of acid gases (NO_X and SO_X) are mainly conducted in an integrated direct-contact wash column. Recent studies have shown that NO_X particular inlet concentration should be maintained before direct contact wash column to remove NO_X and SO_X efficiently. As a result, minimizing NO_X for environmental reasons, avoiding corrosion in carbon capture, utilization, and storage, and achieving effective NO_X and SO_X removal in direct contact wash columns are crucial. Reburning is a capable and affordable technology for NO_X reduction; however, this process is still less studied at elevated pressure, particularly in pressurized oxy-combustion. In this paper, the kinetic evaluation and optimization study on NO_X reduction by reburning under pressurized oxy-combustion was conducted. First, the most suitable mechanism was selected by comparing the results of different kinetic models with the experimental data in literature at atmospheric and elevated pressures. Based on the validated mechanism, a variety of parameters were studied at high pressure, i.e., comparing the effects of oxy and the air environment, different reburning fuels, residence time, H_2O concentration, CH_4/NO ratio, and equivalence ratio on the NO reduction. The results show that de-NO_X efficiency in an oxy environment is significantly enhanced compared to the air environment. Improvement in the de-NOx efficiency is considerably higher with a pressure increase of up to 10 atm, but the effect is less prominent above 10 atm. The formation of HCN is significantly reduced while the N_2 formation is enhanced as the pressure increases from 1 to 10 atm. The residence time required for the maximum NO reduction decreases as the pressure increases from 1 atm to 15 atm. At the higher pressure, the NO reduction rises prominently when the ratio of CH_4/NO increases from 1 to 2; however, the effect fades after that. At higher pressure, the NO reduction by CH_4 reburning decreases as the H_2O concentration increases from 0 to 35%. The optimum equivalence ratio and high pressure for maximum NO reduction are 1.5 and 10 atm, respectively. This study could provide guidance for designing and optimizing a pressurized reburning process for NO_X reduction in POC systems.