煤焦表面加压多组分扩散控制反应机制的研究

For coal char conversion at high temperature in humid air-flow and oxy-fuel in coal-fired boiler power generation，industrial furnace,and coal gasifier,CO is substantially produced on char surface by multicomponent heterogeneous reactions and is controlled by diffusion, which distinguishes from the regime of chemical kinetics. It is the key factors of influence on the accurate prediction that chemical kinetics models are coupled with velocity field, temperature field and concentration field in the process of coal char conversion. Char particles formed from different coal rank, under conditions of P=0.1-4MPa，T≤1800K, mixtures which consist of different concentration of O2,CO2 and H2O flow in 2D direction around cylinder char-rod or char flat plate at relative velocity of pulverized coal in entrained flow, the boundary layers of velocity field, temperature field and concentration field, ratio CO/CO2， attached and detached flame, the condition of which reaction rate changes abruptly and prediction model of characteristic parameters such as reaction rate, burn-off time and burn-off extent is studied. With the aid of computational simulation and experiment, variable is separated from complex factors and the effect of every factor and models are verified .The objects are to discover the law of interaction between combustion and gasification at high pressure and high temperature in multicomponent system, and set up the prediction model of characteristic parameters and improve the precision of prediction so as to design and control of coal char conversion process.

在湿空气和富氧条件下,燃煤电站锅炉、工业炉和高压煤气化炉中，煤焦高温燃烧气化，不同于化学动力学阶段，固相反应以CO生成为主的多组分反应，化学动力学过程耦合了较强的扩散控制过程，动力学模型和颗粒边界层的速度场、温度场和浓度场信息一直是研究的难点。采用不同煤阶的煤焦颗粒，在冻结和非冻结气相反应条件下，压力0.1-4MPa，终温 1800K，不同浓度比的O2、CO2和H2O混合气，以载流煤粉颗粒相对速度流过二维煤焦圆柱棒或平板，研究煤焦表面边界层、CO/CO2比、附着和离析火焰的生成规律，反应速率突跃条件及主要特征参数（反应速率、反应时间和转化率）的预测模型。借助数值实验和物理试验相结合的方法，获得单因素和多因素的作用机制，以检验预测模型的正确性。揭示高温高压多组分流动条件下煤焦燃烧气化的耦合规律及转变温度；建立对应条件下的特征参数计算模型；为煤的燃烧气化设计、预测与控制奠定理

固体燃料在常压和加压下动力学控制区的本征反应机制、扩散控制区的质量传递规律对加压煤气化、舰船稠油加压燃烧和火驱稠油开采具有重要的理论和应用价值。. 研究项目揭示了煤、焦在空气、O2/ CO2和O2/H2O气氛下动力学控制区煤的官能团能量态与反应机理；建立了本征反应动力学模型；基于本征动力学模型、能量守恒和Semenov TET 着火理论，提出了利用热流法得到动力学控制区的煤粉着火温度的方法，得到了加压和常压下的着火规律；并能更准确预测载流煤粉着火温度。.通过激光横向大剪切干涉法测定了燃烧反应中扩散控制区各主要二元组分对的扩散系数。CO2-O2 加压水平扩散实验，靠近扩散室下壁面处，CO2 浓度分布、层流边界层及流场的分布呈抛物型，流动的等势线与等浓度线重合，壁面对CO2 气体附壁层流的剪切效应明显。同样地，在靠近上壁面O2势流线和浓度场分布也呈抛物型。随着过程的继续， CO2 沿底部向前层流运动并发生分子扩散，其过程可以用二维层流扩散运动方程描述。CH4-O2 加压垂直扩散过程是在震荡中进行的，这说明分子的自重对分子扩散过程的影响很大；扩散进行较长时间之后，扩散方向大体为一维纵向，水平方向浓度分布相对均匀。. 研究表明，常压下化学动力区、化学-扩散区、扩散控制区的临界温度分别为1360K 和1600K，而在加压工况下，临界温度分别为1200K 和1400K，压力促进了扩散控制机制的提前形成。