Fuel-bound nitrogen evolution during biomass gasification

Fuel bound nitrogen (FBN) in biomass can be converted to molecular nitrogen (N{dollar}sb2{dollar}) or gas phase pollutants and pollutant precursors such as ammonia (NH{dollar}sb3{dollar}), hydrogen cyanide (HCN), and oxides of nitrogen (NO{dollar}sb{lcub}rm x{rcub}{dollar}) during high temperature gasification. In order to control nitrogenous pollutant emissions from biomass gasification systems, studies need to be performed to quantify the effects of operational parameters, such as temperature and equivalence ratio on fuel nitrogen evolution during gasification.; In the present study, pyrolysis and gasification of leucaena, sawdust, and several other biomass feedstocks with significantly different nitrogen content were investigated in a bench scale, indirectly-heated, fluidized bed reactor to determine the effect of operating conditions on the partitioning of FBN among gas species. In order to address shortcomings in earlier nitrogen species inventories, a procedure to quantify N{dollar}sb2{dollar} using gas chromatography (GC) was devised. An assay of all major nitrogenous components of the gasification products was performed for the first time, providing a clear accounting of the evolution of FBN.; Since earlier studies have indicated that the partitioning of FBN among gasification products is determined by kinetics rather than equilibrium, a kinetics model, the first one of its kind, was developed to simulate the evolution of FBN during biomass gasification. This model considers 109 elementary chemical reactions and about 30 C, H, O, N species. It was assumed that biomass gasification comprises an initial instantaneous pyrolysis step, that divides the biomass into char and volatiles, followed by heterogeneous and homogeneous reactions between the volatiles, oxidizer(s), and char.; Important findings of this research include: (1) NH{dollar}sb3{dollar} is the dominant nitrogenous gas species produced during pyrolysis of biomass; (2) the majority of FBN is converted to NH{dollar}sb3{dollar} and N{dollar}sb2{dollar} during gasification; relative levels of NH{dollar}sb3{dollar} and N{dollar}sb2{dollar} are determined by thermochemical reactions which are affected strongly by temperature; (3) N{dollar}sb2{dollar} appears to be produced from NH{dollar}sb3{dollar} in the gas phase; (4) good agreement between experimental data and simulation results is obtained when it is assumed in the model that NH{dollar}sb3{dollar} is the sole nitrogenous pyrolysis product.