Large Eddy Simulation Of Pulverized Coal Jet Combustion And Flame Propagation

In the situation of global energy shortage and the increasingly serious problem ofenvironmental pollution, energy saving and environmental protection has become theimportant issues faced by all countries. Improving the generating and utilizingefficiency of traditional energy is one of the most important means to alleviate theenergy shortage and environmental pollution problems. How to improve the energy’sutilizing efficiency and combustion stability plays a very important role in ourcontinuous development as a coal-producing country. In China, pulverized coalcombustion boilers are widely used in thermal power plants, and the pulverized coal isfed by the burners arranged on the furnace of the boiler in combustion process, therefore,deep insight of pulverized coal jet combustion is the foundation for the optimizeddesign and operation of efficient and clean combustion equipments.Pulverized coal jet combustion is a very complex physical and chemical process,involving the phenomenon of volatilization discharging, coal combustion, radiation heattransfer, gas-solid two-phase flow and gas turbulent combustion. At present, the detailedinformation of pulverized coal jet combustion process is still not clear. With the rapiddevelopment of computational fluid dynamics, computational combustion, hardwareand software technologies of modern computer, much precise numerical simulation ofcoal jet combustion has become possible.In order to find an efficient simulation method for gas-solid turbulent combustion,this thesis focuses on the pulverized coal combustion process with typical horizontal jetas the research object. Based on the open code CFD package OpenFOAM, the largeeddy simulation method (LES) is used to predict the instantaneous temperature field,pressure field, velocity vector field and species concentration field. For Gas-particletwo-phase flow model, the Euler-Lagrangian particle trajectory model with the PSICmethod is used to solve the interaction between two phases. The semi-empiricalRosin-Rammler formula, one-equation eddy viscosity model, double-volatile reactionsmodel, dynamic-diffusion limited rate surface reaction model and EBU-Arrheniusmodel are chosen as the particle size distribution model, sub-grid turbulent model,volatilization discharging model, coal combustion model and gas turbulent combustionmodel, respectively, and the P-1model is used for the simulation of furnace radiationheat transfer. In order to verify the validity and advancement of LES method and models used inthis thesis, the simulation results are compared with the experimental data and theresults of Reynolds-averaged methods (RANS). Based on large eddy simulation method,combustion with different inlet velocities are simulated to get an optimal value, undersuch a condition that a good combustion kinetic filed can be established. Furthermore,using the optimal jet velocity, combustion process with different coal particle diametersand volatile content are simulated to investigate their effects on combustion intensityand stability. The results can provide a theoretical basis for the flame stability study andsystem optimization design of pulverized coal jet combustion and this modeling methodcan be used in other more complex combustion research.