烟气催化脱硫反应器化学反应的数值模拟

Numerical Simulation of Chemical Reaction of Catalytic Desulfurization Reactor for Flue Gas

烟气催化脱硫反应器主要通过在含有脱硫催化剂的填料表面发生脱硫反应,实现降低出口烟气的SO2浓度,使之达到排放标准。为了准确预测脱硫率,需要探明脱硫反应器的主要结构和操作参数对其的影响。借助于ANSYS软件,利用脱硫有效容积逐渐减少的稳态计算方法,模拟反应器内的非稳态流动和催化氧化反应,可以探明烟气SO2浓度、空速和填料高度对脱硫率的影响,找到反应器脱硫率随时间变化及出口SO2浓度随时间变化的规律,并通过流动模拟数据和实验结果的对比修正适合催化脱硫的计算模型。研究结果表明:在脱硫催化剂加热阶段对脱硫速率的影响较大,会使脱硫率降低;进口烟气SO2浓度的增加会使反应器脱硫率下降、出口SO2浓度增大;空速对脱硫率有较大的影响,过高或过低的空塔气速均不利于脱硫系统的运行;催化剂床层高度越高,脱硫率越高。因此,考虑到实际工业操作中烟气加热催化剂阶段的影响,对反应速率常数表达式进行温度修正,所得的结果可与工业试验数据很好的吻合;将实际工况中反应表面的减少简化为反应空间的减少,并将床层划分为若干个子空间,采用逐渐减少计算域催化反应总空间容积进行非稳态流动和化学反应模拟是可行的;为了达到较高的脱硫率,空速在0.2~0.3 m/s的范围内选取较为合适;催化剂填料床层高度适宜的范围为1 600~1 800 mm。这些为工程设计提供了重要的依据。

The lower outlet SO2 concentration of flue gas and emission standards were achieved mainly through the desulfurization reaction occurred on the surface of the carriers of catalyst in desulfurization reactor. The effects of important structural and operational parameters of the desulfurization reactor on desulfurization percent need to be clearly investigated to predict the desulfurization percent accurately. Based on the finite element software ANSYS,the unsteady flow and catalytic oxidation reaction in the reactor were simulated,the effects of SO2 concentration,empty tower gas velocity and the catalyst packing bed height on the desulfurization percent were investigated by means of a method of reducing effective reaction volume. The regularities of desulfurization percent and outlet concentration of SO2 vs. time were also studied. By comparing the simulated data with the experimental results,the mathematical model of reaction rate for the catalytic desulfurization was corrected. The results showed that the desulfurization percent became lower during heating of the carriers of catalyst,both the desulfurization percent and SO2 outlet concentration of the reactor would decreased with the increasing inlet concentration of SO2, the effect of the space velocity on the desulfurization percent was great,the operation of the desulfurization system became abnormal at too high or too low space velocity and the desulfurization percent increased with the increasing catalyst packing bed height. Therefore,the reaction rate constant could be corrected based on the changing operation temperature during heating stage of hot flue gas with the good agreement with the industrial data. It is feasible in simulating the unsteady flow and chemical reaction that the unsteady model could be simplified by gradually reducing the total reaction volume of computational domain instead of reducing reaction surface area. The high desulfurization percent could be obtained when the space velocity is in the range from 0.2 to 0.3 m/s. Besides,it is suitable that the catalyst packing bed height ranges from 1 600 to 1 800 ram. The results could provide important basis for engineering design of catalytic desulfurization reactor.