Numerical Simulation On A 2008t/h Tangentially Fired Pulverized-Coal Boiler

Currently tangentially fired pulverized-coal boilers are used widely for power stations in China, accounting for.80% in the installed gross capacity. Because of the fuel variability, some problems frequently happen such as combustion instability, over-temperature and coking, which seriously affect the safety and economy for the boilers. The traditional test methods not only spend a lot of manpower, material resources and financial resources, but also depend on the accumulated experience in debugging, which is of some blindness. However, by analyzing the numerical simulation, people may predict the process of coal combustion in furnace to provide the evidence for safety and economic operation of the boiler.In this thesis the computational domain is limited from the dry bottom hopper to the platen. By Paving the author meshes the primary combustion in order to ensure the direction consistency in the grid and the velocity and reduce the false diffusion to the maximum extent. In simulation the planten-divided superheater and rear-platen superheater are added. In view of their impacts on the flow and the heat transfer, the reasonable models are built according to the actual operating parameters.The thesis takes 2080t/h tangentially fired boiler in Shanxi Yuncheng belonging to Shanxi Datang Power Company as the object. By numerical simulation methods, the author analyzes the aerodynamic field and temperature field under the original condition. The result shows that the mesh method, physical model, the parameter set are reasonable after compared with the characteristics of tangentially fired boilers and their thermodynamic calculation results.On these bases, the effects of excess air coefficients, loads and air distribution methods are studied. The simulation results show that with the increase of the excess air coefficients, the furnace flame centre moves down. The temperature in the primary combustion zone rises, and the flue-gas velocity at the exit speeds up. NOx production rises due to the increased oxygen in the furnace. As the boiler load increases, the flow speed in the primary combustion zone obviously accelerates, the furnace flame centre moves to both sides, and the amount of NOx goes up. If the speeds of the secondary air G and the over-fire air are changed, the excess air coefficient rises from 1.2 to 1.22. The furnace flame centre moves down and the residual rotation is weakened.The numerical simulation is used to guide the practical operation. The operation results collected shows that the ratio of the water flow for desuperheating reduces from 2.85 to 2.55 in the left-right sides. The over-temperature points on the planten-divided superheater decrease from 4 to 2, and the water flow for desuperheating reduces to 105.9t/h. So the safety and economy for the boiler is improved. The practice shows that the numerical simulation method used for guiding the combustion adjustment is effective.