Gas-Solid Flow,Combustion Characteristics,and Gas Emissions in a 75 t/h CFB Boiler Based on the CPFD Method

A 3D simulation using Computational Particle Fluid Dynamics（CPFD） methods was used to calculate coal combustion in a 75 t/h industrial-scale circulating fluidized bed（CFB） boiler.Combustion characteristics,gas-solid flow characteristics,and gaseous pollutant emissions of CFB boilers from combustion ignition to stable operation were systematically evaluated in this study.Results show that the temperature distribution is relatively uniform throughout the boiler.As the combustion process unfolds within the boiler,the gas composition curve strikingly portrays the inverse correlation between CO2 and O2 concentrations.As the combustion reaction progresses,it becomes evident that the concentration of CO2 progressively increases,while the concentration of O2 concurrently decreases.This inverse relationship underscores the fundamental combustion reaction,where carbon-based fuels react with oxygen to produce carbon dioxide and release energy.Furthermore,a comprehensive analysis has revealed that,from ignition to stable combustion,both nitric oxide（NO） and sulfur dioxide（SO2） emissions exhibit a declining trend.This reduction in pollutant generation is attributed to the improvement in combustion efficiency.More complete combustion leads to lower levels of unburned hydrocarbons,which are prone to NO formation.Similarly,the sulfur content in the fuel is more efficiently oxidized to sulfur trioxide（SO3） or bound in sulfates,reducing SO2 emissions.At steady state in the simulation,the SO2 mass flow rate varies significantly with the furnace height,gradually increasing from 0.07 kg·s-1 at 4 m at the bottom of the furnace to a peak of 0.078 kg·s-1 at 8 m in the center,and then decreasing to 0.06 kg·s-1 at 20m at the top of the furnace.