Numerical and experimental investigations into combustion of a single biomass particle

This paper presents numerical and experimental investigations of combustion of a single biomass particle. The Implicit Continuous-fluid Eulerian (ICE) method combined with particle mass and energy conservation equations was used for an unsteady 1-dimensional numerical simulation of single biomass particle combustion. The single biomass particle was treated as a Lagrange discrete particle which served as a supplementary boundary condition of a permeable rigid wall which makes possible the flow of gas species into or out the computational domain. The mass fluxes of individual gas species describing devolatilization and biomass char combustion and particle temperature being the solution of the particle mass and energy conservation equations were applied to define the boundary conditions in the ICE method which describes a multispecies chemically reactive unsteady compressible flow around the particle. To define the gas velocity and density, the unsteady mass and momentum equations have been combined each other like usually made in projection methods to get the Helmholtz equation which together with appropriate boundary conditions define gas pressure. Considering the spherical symmetry of the system assumed for the numerical simulation, the time-dependent 1-dimensional energy and species mass conservation equations and the pressure Helmholtz equation can be efficiently solved by use of the tridiagonal matrix algorithm (TDMA). The combustion process has been also experimentally investigated in an electrically heated up reactor through which the flow of hot gases up to temperature of 1223 K is possible. Heating up, devolatilization, ignition and combustion of volatiles in a laminar diffusion flame around the particle and biomass char combustion are phenomena which occurred and have been recorded by a high speed camera during the whole combustion process. The particle temperature has been measured by a thermocouple on which the particle was placed. Experimental investigations of combustion have been performed for the single willow particle having the diameter around 1 mm burning in air at temperature of 923 K. Numerical results have been compared with the experimental ones. The numerical results, i.e. the particle temperature, gas species concentrations and other, correctly reflect the whole combustion process experimentally observed