Numerical Simulation Of Combustion Processes In 600MW Ultra Supercriticle Wall-Tangentially Fired Boilers

Wall-tangential firing is a new tangentially fired approach. Based on the platform of CFD software Fluent 6.3, the combustion processes in 600MW wall-tangentil bitumite-fired and lignite-fired boiler were simulated separately. In the simulation, we adopted general simulation models. The Realizable k- two equations turbulent model was used to simulate the turbulence. The stochastic tracking model was applied to analyze the gas-solid flow field. The P-1 model was applied to simulate radiation. Two competing reaction model was used to simulate the devolatilization process. Probability Density Function (PDF) was used to model the combustion of volatile. Diffusion-kinetics model was used to simulate char combustion.In the first part, air dynamic field, temprature field, the distribution of different species in the boiler, distribution of heat flux to wall, the influence of SOFA ratios on the production of NOx and deviation of temperature at the outlet of the furnace were simulated in the wall tangential bitumite-fired boiler. The result shows, the tangential circle is entirely formed, and large enough. The high temperature zone is concentrated in the neighbourhood of water wall. Low temperature zone doesn't exist in the furnace, and burnout ratio is quite high. The concentration of oxygen in the main combustion zone is quite low, and it is consumed entirely quite close to the nozzles, in addition, concentration of carbon monoxide is quite high, both are favorable for lowering the production of NOx. The key for organizing air staged low NOx combustion is that char combust under the condition of lean oxygen in main combustion zone. The concentration of oxygen in SOFA zone shouldn't be too high, so the key for low NOx technique is the optimization of oxygen ratios between main combustion zone and SOFA zone. The temperature in the furnace along the height tends to be more even with the increase of the SOFA ratio. The concentration of NO isn't monotonically reduced with the increase of SOFA ratio. The emission of NOx is the lowest when the ratio of SOFA is 25%. The deviation at the outlet of the furnace reaches its maxmum 60K when the ratio of SOFA is 15%, so the deviation is not quite large. Heat flux to the water wall has three different distributions which are in the form of V, W and U. In the second part, the non-premixed combustion which accounts for the detailed pyrolysis product was adopted. From the comparision with the simulation method which doesn't account for water in coal, we can draw the conclusion that the gradient of temperature of the primary air is lowered as well as the gradient of oxygen. The extent of high temperature in the cross section of the main combustion zone is reduced. Water in coal has important influence on the attenuation of the primary air. From the comparision with the thermal calculation, we can get that the traditional fuel definition method is in accordance with thermal calculation. The comparision of the simulation in 3# boiler of Yuan Baoshan with experiment shows, experiment is in accordance with simulation, which proves the reliable of the simulation.In the third part, new method in the second part was used to simulate the lignite combustion, and the results show that the circle is entirely formed, large enough. The water has influence in the beginning stage of coal combustion, but large high temperature zone can still ensure the burnout of coal. Horizental staged combustion can decrease the concentration of NO by 10% at the outlet of the furnace. With the increase of the primary velocity, the distance of ignition increases, which is unfavorable for the ignition of coal, furthermore, the decrease of average temperature is unfavorable for the burnout. NO concentration at the outlet of the furnace increases. Low primary ratio is the priority choice. Wall-tangentiallly fired boiler can control the tangential circle effectively. When reduce the tangential circle, the extent of high temperature is enlarged, so combustion becomes more concentrated and the temperature at the outlet of the furnace increases. The velocity in the neighbourhood of water wall decreases.