Inaugural US-EU-China Thermophysics Conference-Renewable Energy 2009 (UECTC 2009 Proceedings)
Renewable Energy Applications
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Numerical investigation of coal∕biomass co-firing is presented in this study. Co-combustion of biomass and coal is a complex problem that involves gas and particle phases, along with the effect of the turbulence on the chemical reactions. The transport equations for the continuous phase (gas) and discrete phase (spherical particles) are solved respectively in the Eulerian and Lagrangian frame of reference. The mathematical models used for co-pulverized coal∕biomass particles combustion consist of models for turbulent flow (RNG k-ε model); gas phase combustion (mixture fractions∕PDF model); particles dispersion by turbulent flow (stochastic tracking model); coal∕biomass particles devolatilization (two competing rates Kobayashi model); heterogeneous char reaction (kinetics∕diffusion limited rate model); and radiation (P-1 radiation model). Drayton coal was used in this study. The coal was blended with 5 to 10% pine sawdust (thermal basis) for co-firing. The effect of the percentage of biomass blended with coal on the gas temperature, particle devolatization and burnout, and pollutant emissions is presented in this paper. The results show a reduction of gas temperature, NO mass fraction and CO2 mole fraction for pine sawdust∕coal co-combustion compared to coal combustion. This reduction depends on the proportion of biomass (pine sawdust) blended with coal. Drayton coal + 10% pine sawdust co-firing shows a reduction of 5.2% of the gas temperature, 14.8% of CO2 mole fraction and 49.5% of NO mass fraction compared to Drayton coal combustion. Better devolatization and burnout of solid particles are also obtained when pine sawdust was blended with coal.