Numerical Analysis of the Combustion of Gases Generated during Biomass Carbonization

The paper deals with the analysis of the combustion of volatiles evolved during thermolysis (thermal treatment) of biomass feedstock. The process is tailored to produce charcoal (biochar), heat and electricity and the whole system consists of a carbonizer, afterburning chamber and steam recovery boiler. In order to maintain safe operation of the carbonizer the process temperature has to be maintained at an acceptable level and thus the majority of gases evolved during biomass processing have to be combusted outside in the afterburning chamber. In this paper the combustion of those gases in a specially-designed combustion chamber was investigated numerically. The calculation results indicated that the production of the biochar has to be carried out with tight integration and management of the heat produced from the combustion of the volatiles and the emission of CO and methane may be maintained at a low level by optimization of the combustion process. The most promising effects were achieved in cases C4 and C5 where the gas was fed tangentially into the afterburning chamber. The calculation results were then used for the design and manufacture of a pilot reactor—from which the parameters and operational data will be presented and discussed in a separate paper.

The rate of stationary wave of filtration combustion of gases in the same fields of temperature and concentration

Combustion of hydrogen-methane-air mixtures of gases in an inert porous medium is considered when the temperature fields of the medium end the concentration of the missing component of the mixture are similar. The relationship between the functions of temperature and concentration, as well as the equation for the numerical calculation of the temperature distribution, are obtained. Numerical calculations were made for different compositions of the hydrogen-methane-air mixture of gases and their effects on the wave velocity were determined. Dependences of the wave velocity, the equilibrium temperature, the characteristic size of the combustion zone, and the diffusion coefficient of the missing component on the gas injection rate are studied.

Computational Analysis of a Fixed Bed Thermal Oxidizer for Solid Wastes Disposal

Combustion control techniques have become a legal requirement to minimize pollution in municipal solid waste incinerators. Typically, incinerator destruction of pollutants is achieved when 2-second gas residence time at 8500 Celsius and about 6% O2 are guaranteed at exit. Performance of a fixed bed (two-stage) thermal oxidizer for solid waste is analyzed numerically using computational fluid dynamics (CFD) technique. The CFD analysis provides three-dimensional view of thermal and gas flow field inside the thermal oxidizer chamber. Localized zones of temperature and species concentration were analyzed and provided critical information for understanding the thermo-chemical processes taking place during incineration leading into design optimization and the operation strategy of the thermal oxidizer. Based on the CFD results, the original design of the thermal oxidizer was modified to optimize the flow characteristics and the residence time in the secondary chamber thereby achieving complete combustion of gases emanating from the lower chamber, hence less emissions of CO.