A Review of Numerical Modeling and Experimental Analysis of Combustion in Moving Grate Biomass Combustors

This Review covers the current state-of-the-art literature dealing with numerical modeling and experimental analysis of moving grate biomass combustors. The greatest attention is paid to the modeling of the thermochemical conversion in the fuel bed. Changes in the fuel characteristics are also tracked during the combustion. Such a review can facilitate understanding a more robust model from viewpoints of thermal performance, chemical and physical properties, pollutant emissions, and combustion stability. Different modeling approaches for the moving grate biomass furnaces are introduced, with a focus on the independent fuel bed modeling. Stepwise biomass fuel degradation inside the bed and corresponding individual mathematical models are described, followed by overbed combustion modeling. Numerical methods for the conservation equations of the combustion model are classified, and a general iterative solution algorithm is delivered. Various NOx formation mechanisms from the fuel-bed efflux and the combustion of hot zone gases are detailed, followed by the particle matter originating from inorganic materials. Air-staging, the flue gas recirculation mechanism, and restriction of the maximum flame temperature can significantly reduce the NOx concentration in the flue gases. Industrial biomass combustion systems are addressed in terms of different grate technologies, and a general laboratory-scale biomass reactor is portrayed. For future work, according to the gaps found in the literature, it is recommended that, considering the intensive inhomogeneity of the biomass fuels, the effects of the fuel uncertainties should be considered in the bed modeling. Furthermore, deep investigation of the infrared images captured from biomass combustion can provide a comprehensive tool for the combustion system analysis. More recommendations are given in the conclusion of this Review.