Kinetic modeling study on the potential of staged combustion in gas turbines for the reduction of nitrogen oxide emissions from biomass IGCC plants

The potential for reduction of nitrogen oxides in gas turbine combustors wa s studied by detailed chemical kinetic modeling under ideal flow conditions . The investigation focused on turbines burning biomass-derived gasificatio n gas from an air-blown integrated gasification combined cycle plant. The a im was to give detailed information about the parameters that favor reducti on of NOx emissions, providing a solid background for designing an air-stag ed, low-NOx gas turbine. The potential and limitations of the detailed chem ical kinetic modeling as a predictive tool for simulating the process were discussed. Instantaneous, delayed, and back-streamed air/fuel mixing models were tested to study the effect of mixing on the emissions. Predictions sh owed that the nitrogen chemistry was mainly affected by temperature and pre ssure: low temperatures of about 900-1000 degrees C and high pressures of a bout 10-20 bar favored fuel nitrogen conversion to N-2. At atmospheric pres sure, an increase in the number of air addition stages increased the conver sion to N-2, but at higher pressure the reduction was more efficient with t hree-stage addition than with either one- or six-stage addition. The conver sion efficiency of NH3 to N-2 increased with the inlet NH3 concentration, b ut the final NOx emission calculated in ppm(v) increased as well. NOx emiss ion often was higher when HCN replaced ammonia in the gasification gas. The main paths for fuel-NH3 conversion to NOx and N-2 were predicted to occur via intermediate formation of amino radicals (NHi). Another important conve rsion path to N-x was shown to proceed via a H2NO intermediate. Models acco unting for delayed mixing led to more realistic predictions, showing the ef fect of CH4 in the gasification on increased NOx emission by means of its C Hi radicals.