| This paper takes a 330MW subcritical front wall opposed-fired pulverized coal boiler as the research object.Due to the problems of coal quality deviation,high coal consumption and high nitrogen oxide generation,it is faced with multiple comprehensive transformations in the whole process.From the perspective of pulverized coal fineness,this paper proposes to reduce the pulverized coal fineness through the modification of a dynamic pulverized coal separator,in order to improve the combustion process of pulverized coal,and assist in reducing the generation of NOx,and at the same time explore the separation process of the pulverized system by changing the fineness,The influence of the pyrolysis of pulverized coal and the combustion reaction of volatile matter,the combustion process in the furnace,etc.First of all,through the numerical simulation of the separation performance of the design structure of the dynamic separator to be modified,the change trend of R90 and R200 under different loads and different speed conditions is obtained,which is the field modification and commissioning of the separator.The later variable working condition adjustment provides a reference.The simulation results show that the rotor speed reaches 80r/min,which can reduce the pulverized coal fineness R90 to below 15%and R200 to below 1%to meet the fineness requirements of low-load combustion.After the transformation,the fineness test was carried out on the spot,and the results were basically consistent with the simulation results.Secondly,using Chemkin,through the PFR plug-type reactor model,the temperature and volatile concentration,which are not easy to control in the experiment,but are closely related to NOx generation,are used as controllable variables to perform variable-condition simulations.The influence trend of the combustion of pulverized coal with different temperatures,different excess air coefficients and different volatile concentrations to produce NOx.The results show that when the release of volatile matter fluctuates between 90-100%and the temperature is 1300-1450℃,the more release of volatile matter,the less amount of NOx produced.Using the sensitivity analysis of the chemical kinetic method,the main reaction pathways of the two gas-phase precursors of fuel NOx,HCN and NH3,were obtained to construct a volatile reaction model suitable for the combustion process simulation in this paper.Finally,using the constructed volatile reaction path combined with the EDC model to simulate the gas phase combustion reaction,while considering the coke surface reaction,the Fluent simulated the combustion of different fineness coal in a single swirl burner and a large furnace.The NOx generation situation was also compared with the field test data of the furnace.The simulation results of a single burner show that the 30μm particle size coal ignites the fastest,the recirculation zone is the most stable,the outlet NO concentration is the lowest,and the surface heterogeneous reduction reaction rate is the fastest,which is 1.85 times the surface reaction rate of 60μm particle size coal.The simulation results of the large furnace show that the temperature peak in the furnace is higher when the pulverized coal is coarser and the position in the furnace is higher;when the pulverized coal fineness R90 is reduced from 22%by 14.2%,the mass concentration of NO produced in the furnace is reduced from 330.94mg/Nm3 to 275.19mg/Nm3.Comparing the field test results,we can see that the dynamic separator rotor frequency is increased by 8 Hz,the carbon content of fly ash is reduced by 45.55%,and the NOx concentration at the outlet of the economizer is reduced by 18%.The increase in exhaust rate also effectively reduces the formation of nitrogen oxides. |
PDF Full Text Request