Numerical Simulation Of Mild-Oxyfuel Combustion Of Pulverized Coal With Different Excess Oxygen Coefficient And Particle Size

The MILD-Oxyfuel combustion of pulverized coal combines oxyfuel combustion technology and MILD combustion technology, to achieve the aims of capturing carbon dioxide, reducing NOx production and improving combustion efficiency and combustion stability. This paper studied the impact on MILD-Oxyfuel combustion of pulverized coal with different excess oxygen coefficient and different pulverized coal particle sizes by using CFD software, to provide theoretical reference for practical industrial applications of this new combustion technology.The 0.3MW vertical coal combustion furnace, which located in the State Key Laboratory of Coal Combustion of Huazhong University of Science and Technology, is for the numerical simulation and experimental studies. Experiments of MILD combustion of pulverized coal and conventional combustion of pulverized coal were done on 0.3MW pulverized coal combustion furnace. The furnace temperature distribution and NOx-emissions in the flue gas were measured on two conditions. At the same time numerical simulation for MILD combustion of pulverized coal and conventional combustion of pulverized coal was carried out by using CFD software. Comparing the results of the simulation and the experimental measurements, it shows that the temperature distribution and the NOx-emissions is similar. For conventional pulverized coal combustion,NOx-emissions difference of 12%; for MILD pulverized coal combustion, NOx-emissions difference of 5.9%. It shows that simulation calculation method is accurate.First numerical simulation of conventional pulverized coal combustion, coal MILD combustion and coal MILD-Oxyfuel combustion were carried out, and the furnace temperature distribution, CO distribution, NOx-emissions of the three combustion mode were compared. It shows that the change rules are similar to the reports of related literature,which shows simulation calculation method of MILD-Oxyfuel combustion of pulverized coal is accurate. CFD was used to research the impact on MILD-Oxyfuel combustion of pulverized coal with excess oxygen coefficient from 1.05 to 1.20, under different oxygen concentration from 21%, 25% to 29%. The results show that as excess oxygen coefficient decreases, the maximum temperature in the furnace is lower, no matter how much oxygen concentration is. Under 21% and 25% oxygen concentration, the temperature distributionand reactants in the furnace are more uniform with the case of oxygen coefficient of 1.10,while under 29% oxygen concentration, with the case of excess oxygen coefficient of 1.05.When oxygen concentration is higher than 25%, the coal can be burn out with four cases,from 1.20 to 1.05. As the oxygen concentration increases, the overall temperature increases.Under the same oxygen concentration, NOx-emissions decrease with excess oxygen coefficient. Under the same excess oxygen coefficient, NOx-emissions decrease with oxygen concentration.The impact on MILD-Oxyfuel combustion of pulverized coal with different pulverized coal particle size was also studied. The results show that when coal particle size is smaller,the furnace radial temperature distribution is more uniform; when coal particle size is bigger, the furnace axial temperature distribution is more uniform. When coal particle size is from 110?m to 200?m, the CO distribution in the furnace is most uniform, as well as the temperature distribution. With the decrease of the particle size of pulverized coal,NOx-emissions decrease gradually, which caused by a reduction of the specific surface area with the particle size of pulverized coal decreased, thus increasing the devolatilization rate and reducing the ignition delay, thereby enhancing the NOx local reducing atmosphere. But as the exception, when coal particle size is 110?m, NOx-emissions is the minimum.