One dimensional mathematical model for packed bed biomass combustion using MATLAB

Abstract

Packed bed biomass combustion is widely used thermal conversion process which contributes major portion of energy fulfillment around the globe. This process is usually involving higher operation cost due to low efficiency and high emissions. Hence there is a huge room for improvements in the process and needs to be optimized as well as modernized. This thesis presents two-phase one-dimensional mathematical model with MATLAB solver which can be used for diagnosis and optimization of packed bed combustion process under low computing resources and less cost. The mathematical model uses the discretized equations to develop the ordinary differential equations which are solved using implicit method. Free-board region is not taken into account. Only the biomass bed is considered here to solve the combustion system by applying conservation equations into gas and solid phase separately. The main model is consisting with different sub models with subjected to four stages of combustion as drying, pyrolysis, Char oxidization and char combustion. The biomass batch is initially ignited by continuous preheated gas inlet and higher gas flow rate. Radiation heat transfer is assumed to be negligible due to high temperature gas flow at the inlet. Combustion is occurred in batch wise. Particle diameter and bed porosity is considered with a mean value for the simplicity of the model. The developed model is used to find the solid temperature profile and generation of CO2 and CO gases. By using walking column approach, industrial moving grate furnace was represented and required optimum grater length for a particular mass flow rate can be calculated with the fixed bed simulation results.