Combustion and NOₓ emissions of biomass-derived syngas under various gasification conditions utilizing oxygen-enriched-air and steam

The purpose of this study is to investigate the NOₓ emissions from combustion of syngas derived from gasification of three different biomass feedstock (i.e., pine, maple–oak mixture, and seed corn) at different oxygen-enriched-air and steam conditions. Three different oxygen-enriched-air and steam conditions were tested for each feedstock, thus resulting in nine different sets of syngas. The biomass-derived syngas was burned in an industrial burner that was integrated into the gasification system. The gasifier and burner are rated at 800kW and 879kW thermal, respectively. For each set of biomass-derived syngas, NOₓ emissions were measured at different burner operating conditions including various heat rates and equivalence ratios using emission analyzers with chemiluminescence technology. All the combustion test conditions are in the lean mixture ranges in order to avoid the peak temperature limitation of both the burner and combustion chamber. Results show that NOₓ emissions using syngas obtained from woody feedstock decrease almost linearly as the combustion mixture becomes leaner and the heat rate decreases. When compared to natural gas, syngas from both woody feedstock generates higher NOₓ emissions even when the heat rates are comparable, indicating that fuel NOₓ formation is highly important in biomass-derived syngas combustion. In contrast to syngas from woody feedstock, syngas from seed corn results in peak NOₓ emissions before NOₓ decreases with leaner conditions. The trend is observed for all fuel flow rates and all oxygen-enriched-air and steam conditions of seed corn-derived syngas. Among the three feedstock, seed corn has the highest nitrogen content which yields the highest ammonia concentration in syngas, which, in turn, results in the highest NOₓ emissions for all test conditions. Overall, the NOₓ emissions from seed corn-derived syngas combustion are approximately in the range of 450–900ppm higher compared to those from wood-derived syngas combustion.