Behavior of combustion process in the fuel bed on the grate, is characterized by different thermochemical conversion stages, each with significantly different temperatures, and the reacting conditions. This simple analysis of combustion processes taking place on the grate is a useful information for understanding of the paths of pollutants formation and destruction as well. The large fixed bed reactor was used for obtaining the experimental results of straw combustion. The fixed bed reactor contains a column of biomass fuel that is ignited at the top and with air entering through the grate from the bottom, measurements are performed while the ignition front proceeds downwards. The influence of inlet air flow velocity and temperature, moisture content in the fuel and oxygen concentration in the inlet air on combustion parameters such as ignition front velocity (kg/(m2·s)), temperature, and gas species concentration during combustion is presented based on measurements of in-bed temperatures along the bed and different gas compounds (O2, CO2, CO and NO) over the bed. A 1-D transient heterogeneous model was used for straw combustion in a fixed bed. The processes included in the model comprise: moisture evaporation, biomass pyrolysis, heterogeneous reaction of char forming CO and CO2, homogeneous reactions of CO, H2, CH4, CxHy and tar, heat and mass transfer between the gas and solid phases. The model provided detailed structure of the ignition flame front, gas species... [to full text]