基于热分析动力学的烧结用焦炭颗粒燃烧数值模拟

Numerical simulation on combustion characteristics of sintering used coal char particle based on thermo-gravimetric kinetic analysis

基于烟气循环烧结中氧体积分数降低抑制了燃料燃烧,焦炭细化可显著改善整体燃烧效率,是烧结工艺极具潜力的节能增产措施,采用缩核模型,模拟贫氧率和粒度对焦炭颗粒燃烧特性的影响。焦炭的着火温度ti、不完全燃烧系数κ、燃烧反应焓ΔH等燃烧特性参数采用热重实验确定,焦炭燃烧的本征活化能E和指前因子A通过Flynn-Wall-Ozawa（FWO）法计算。研究结果表明：空气气氛中,焦炭颗粒的ti约为550℃,κ为1.128～1.333,对应的ΔH则为28.810～31.640 MJ/kg,E约为137.156 k J/mol;ti基本上不随实验条件变化,κ随着氧体积分数的降低显著增大,E则略减小;焦炭颗粒的最高燃烧温度约为1 560 K,燃烧速率随着灰层厚度的增加逐渐降低;当颗粒粒度增大或氧体积分数降低时,燃烧效率显著下降,且前者影响更大;考虑采用烟气循环,当焦炭细化效率达到1.33时,可保证整体燃烧效率不比传统烧结的低。

In flue gas recirculation sintering technology, the reduction of oxygen content in the recirculated flue gas significantly inhibits the combustion characteristics of the coal char, and refining coke can significantly accelerate coke combustion rate with the increase of the surface area, which can effectively save energy. The influence of oxygen contents（oxygen-lean） and particle sizes on combustion characteristics of the sintering used coal char particle was numerically simulated. The unreacted-core shrinking model was employed. The ignition temperature ti, incomplete combustion coefficient κ and reaction enthalpy ΔH of the coal char were determined by thermo-gravimetric technology, while the intrinsic activation energy E and pre-exponential factor A were calculated in different heating rates with Flynn-Wall-Ozawa（FWO） method. The results show that ti of coal char is about 550 ℃ in air atmosphere; κ increases from 1.128 to 1.333 when heating rate increases, while ΔH decreases from 28.810 k J/kg to 31.640 MJ/kg, respectively, E is about 137.156 k J/mol. ti hardly changes with the change of experimental conditions, while κ significantly increaseswith the decrease of oxygen volume fraction, and E shows the opposite trend. In the numerical simulation, the maximum temperature of char particle in combustion process is 1 560 K. During combustion, ash layer thickness gradually increases, resulting in decrease of the reaction rate of particle. The combustion efficiency decreases significantly when particle size increases or the oxygen content decreases, on which the effect of the former is more obvious. The refining efficiency of coal char is suggested to be 1.33,when flue gas recirculation sintering technology is applied, aiming at a consistent overall combustion efficiency compared to the conventional sintering process.