Numerical Simulation of Pulverized Coal Combustion using Computational Fluid Dynamics (CFD)

In the past, the use of pulverized coal burners has not been prevalent in small and medium-sized enterprises where a large amount of thermal energy is used in the production process. The use of pulverized fuel has several advantages over conventional solid fuels; it has better combustion efficiency than lump fuel. Furthermore, since the transport and handling of pulverized fuel must be in a closed system at all times, the use of pulverized fuel can significantly reduce the environmental impact from dust particle dispersion during handling and storage of conventional solid fuel. The aim of this research is to numerically model and analyze the combustion characteristics of pulverized coal with smaller than 74 µm in diameter within a symmetrical axial 2D combustion chamber model comprising 25% primary air volume, 65% secondary air volume and 10% tertiary air volume, which is the initial proportion used during experiments. The mixture between the primary air and pulverized coal is sprayed into the burner to mix with the secondary air under the effect of swirl flow. The governing equation for the turbulence flow analysis in the combustion chamber is the standard k-ε turbulence flow model. For the analysis of particle motion and volatile emissions including devolatilization and heterogeneous reaction, the Discrete Particle Model (DPM) will be used. For homogeneous reaction, the eddy-dissipation model which assumes that the intensity of chemical reaction occurs according to the fast kinetic assumption so that the reaction rate is controlled by turbulent flow intensity.  In addition, the discrete ordinate model will be used to for  radiation heat transfer. Ansys Fluent will be used as a primary tool in this study. Using Computational Fluid Dynamics (CFD) simulation, this work will calculate the internal temperature of burner at the heat rate of 300 kW. The flowrate of primary air, secondary air, and tertiary air will be adjusted. The results of this study will be used as a body of knowledge for further analysis and study of the combustion characteristics of pulverized coal in the future.

When the accurate CFD model for pulverized fuel is verified, it can then be applied to study the combustion of alternative fuels as coal replacement to reduce coal consumption.  In this case, biomass is identified as a suitable replacement of coal because it shares several similarities to coal. However, each type of biomass has a variety of fuel composition, therefore, it is necessary to perform a detailed investigation in computer simulation before practical use. They are many types of biomass, each of which has different composition and properties. The study of combustion behavior by experimental methods in actual pulverized burner requires a lot of resources and efforts. Therefore, the study of combustion characteristics by computer modeling using Computational Fluid Dynamics (CFD) is important and could significantly contribute to the rapid development of pulverized burner technology.