Numerical Simulation Study On Combustion Characteristic And Products Of Biomass Gas Co-Firing In A Coal-Fired Boiler

The power generation technology of biomass gas co-firing with pulverized coal is an efficient and low pollution clean combustion technology which is developed in recent years.Combined with the present development of biomass gas co-firing in a coal-fired boiler at home and abroad,according to the practical and technical problems of co-firing,this paper uses numerical simulation methods to study the process of biomass gas co-firing.The main research contents are as follows:1.Based on the structural characteristic of a 300 MW coal-fired boiler and the theory of biomass gas co-firing with coal,the co-firing model is built.The turbulence model,gas-particle two-phase flow model,the gas phase turbulent combustion model,the devolatilization model,the char combustion model and the radiation model are selected to carry on the mathematical description of the co-firing process of biomass gas co-firing in a coal-fired boiler.2.Gambit is used to mesh the furnace structure of a 300 MW coal-fired boiler,and the boundary conditions are determined.The air field in the furnace under the rated load condition is simulated by the Fluent software,the good flow field distribution in the furnace is acquired.And according to the design conditions of the boiler,the initial and boundary conditions are calculated under different working conditions.3.Compared with the biomass gas co-firing with coal and the pulverized coal combustion,the distribution regularities of the velocity field,the temperature field and the flue gas component field in the furnace under every combustion condition of different temperature biomass gas co-firing in a coal-fired boiler are analyzed.Compared with the pure coal combustion condition,the gas velocity of the burner zone increases by co-firing,and the mole fraction of O₂ and CO at furnace outlet also increases.The mole fraction of CO at furnace outlet decreases gradually.When the co-firing biomass gas temperature changes from300 to 600?,the highest combustion temperature of furnace drops from 1845 K to 1745 K,the mole fraction of O₂ at outlet increases gradually,the mole fraction of CO showes a trend of decline,and the mole fraction of CO₂ increases gradually.4.The distribution regularities of temperature field,velocity field and the flue gas components field in the furnace at different height of the 600 ? biomass gas nozzle are obtained.As height of the biomass gas nozzle increases,at furnace outlet,the temperature increases,the mole fraction of O₂ decreases,the mole fractions of CO and CO₂ keep the samevalue.