Study On Combustion Characteristic And Numerical Simulation Of Co-firing Biomass With Coal

Compared with biomass directly fired, co-firing biomass with coal in the existing coal-fired power plants can effective utilization of the renewable clean energy, and has the lower cost of construction and reform of the boiler, and makes more efficient combustion of fuel. This paper focused on experiments and numerical simulation research about the combustion characteristic and pollutant emission characteristics of co-firing biomass with coal,and aimed at confirming a suitable blending way on a 300 MW boiler.Firstly, the test of co-firing biomass with coal was performed on the single-burner furnace, and investigated the combustion flame temperature and the routine analysis of combustion products. The result found that the accession of the biomass reduced the ignition temperature of coal and the furnace temperature and decreased the NOX generation, making the fuel burning more completely.With biomass addition increase, the ash melting point temperature gradually decreased, but even when the wood account for 30% of the calorific value of the whole combustion fuel quantity, the ash melting point was still high, so that co-firing had small influence on the boiler burning coking properties. Secondly, the single-burner furnace was modeling and simulating by professional software, and compared the simulation results with the experimental results to determine appropriate numerical simulation models and parameters. At last, the transport equations for the continuous phase(gas) and discrete phase(spherical particle) are solved respectively in the Eulerian and Lagrange frame of reference. The mathematical models used for co-pulverized coal and biomass combustion consist of models for turbulent flow(realizable k-? model); gas phase combustion(mixture fractions/probability density function(PDF) model); particles dispersion by turbulent flow(Lagrange stochastic tracking model); coal particle devolatilization(two-competing rates model); biomass particle devolatilization(single rate model); coal/biomass particles char combustion(diffusion/kinetics model), and radiation(P-1 radiation model).Finally the effects of different biomass mixing ratio and different fuel injection position and different types of biomass on the combustion behavior and NOX emission in a 300 MW industrial boiler were discussed. The simulation results show that with biomass addition increased, the furnace temperature became lower, so that the biomass mixing ratio should not be more than 10%. Three kinds of spray mode was simulated,biomass was injected evenly with coal, the pulverized coal was injected from the lower three layers with the biomass was injected from the upper layer, and biomass was injected from the highest layer of the burner at a slant of 5 degrees,and the third injection mode behaved the best. Comparing the effect of different types of biomass(wood, straw, chaff), the results showed that three temperatures are similar, and wood has the lower NOX emission since its nitrogen content was lower.This article showed the best blending way that sawdust mixing ratio of 10%, and the wood powder was injected into the furnace on the 300 MW tangential boiler from the highest layer of the burner at a slant of 5 degrees, Compared with the original coal-fired boiler, the final spray mode has good economic and environmental benefits with the flame temperature can be guaranteed and the NOX concentration can be decreased 299 mg/m3.The research process and conclusions in this thesis were beneficial to the numerical simulation, test and application of co-firing biomass and coal on large coal-fired boiler in future.