Introduction

1. Fuel-nitrogen Chemistry in Fuel-NOx Formation during Low-grade Fuel (Coal, Biomass) Firing/Cofiring Chunyang Wu, Brad Damstedt, Robert Marsh, Larry Baxter, and Dale Tree ACERC, Brigham Young University, Provo, UT, 84602 Research Layout Introduction The relation between fuel-nitrogen functional groups and the fuel-NOx precursors (HCN and NH3) is still inconclusive for industrial-scale low-grade fuel combustion. Coal fuel-NOx precursors were proven to be HCN, because its fuel-nitrogen predominantly resides in the form of heterocyclic unsaturated compounds (e.g. pyrrolic and pyridinic derivatives).However, because of the complexity of biomass family, the available fuel-nitrogen functional groups data are limited. This study is aimed to reveal the type of fuel-nitrogen indirectly by quantifying the fuel-NOx precursors, HCN and NH3, during devolatilization in a simulated low-NOx burner so as to evaluate the feasibility of the effective coal fuel-NOx reduction device. Assumption In contrast to herbal-type biomass, the fuel-nitrogen in wood-type biomass is too little to characterize. Based on the data from herbal-biomass and nitrogen metabolism in plants, it is presumed all nitrogen in wood-type biomass exists in the form of amine and amides. So, the fuel-NOx precursor for these fuels is assumed to be NH3 rather than HCN. Dynamics study: Through the comparison of data from CFD and hot-wire anemometer measurement, the dynamics under swirl number of 0, 0.5 and 1.5 of the cold-flow in the Burner Flow Reactor (BFR) has been confidently characterized. Kinetics study: The gas-phase chemistry of HCN and NH3 is compared for biomass firing/cofiring with CHEMKIN. Two of the most widely-used detailed mechanisms---GRImech 3.0 and Kilpinen 97 were selected. Experiment and CFD predictions: Fire/cofire herbal-biomass (straw), wood-biomass (saw-dust), low-rank coal (Black Thunder), higher rank coal (Pittsburgh #8) and their different combinations and measure the nitrogen species(HCN, NH3, and NO) with CO, CO2 and O2 fuel-lean/rich indicators. Swirl = 0 Swirl = 0.5 Velocity Profile: Predicted and Measured; Swirl = 1.5 Swirl = 1.5 Dynamics Study: FLUENT 5.0 was used to predict the velocity field of different swirl numbers in the BFR. The results were compared to the measured flow, which was obtained using a hot-wire anemometer. The results matched surprisingly well. This confirms the ability of using FLUENT 5.0 to model the cold flow in the reactor chamber. Kinetics Study: The 1D CHEMKIN pre-mixed package was used to predict the gas species profiles for different temperatures. Both the GRImech 3.0 and Kilpinen 97 mechanisms were compared to determine the accuracy of prediction of the nitrogen species in the fuel rich region. Kilpinen 97 shows greater accuracy, having the capability to include more nitrogen species than GRImech 3.0. Due to the existence of NH3 in cofiring, added complexity is incurred in determining the fuel nitrogen fate. • Assumptions: • Under fuel-rich conditions, all fuel-carbon is converted to CO2; hydrogen to water; coal sulfur is treated as oxygen; biomass-sulfur is assumed trapped in the ash; biomass-nitrogen is converted to NH3, while coal-nitrogen to HCN. • Inlet conditions: Air feeding rate is fixed, and the fuel feeding rate is calculated based on the #1. Therefore, the inlet gas composition is based on fuel ultimate analysis data. • TNS: the total nitrogen species excluding N2, and it is potentially converted into NOx *With increasing temperature, the difference between the two mechanisms increases. BT-Black Thunder BT/Straw cofiring: straw is 20% energy fraction Straw