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, mapleaoak 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 800 kW and 879 kW 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 450a900 ppm higher compared to those from wood-derived syngas combustion.