The Effects of Radiative Heat Transfer on the Flame Structures of Pulverized Coal Combustion

本研究旨在阐明辐射换热对煤粉燃烧火焰结构的影响。采用严格的辐射处理，建立了一个描述含有惰性颗粒悬浮物的燃烧混合物火焰的一维模型的数值模型。同时进行了实验研究，以证实数值分析的结果。结果可分为以下三大类：1。利用颗粒悬浮液可燃气体燃烧系统的一维模型，揭示了悬浮颗粒对可燃气体燃烧系统的两大影响。一种是利用颗粒的热容抑制燃烧，另一种是利用基于辐射传热的能量再循环增强燃烧。当加载比较小时，后一种效果优于前一种效果；当加载比较大时，后一种效果相反。并定量地阐明了颗粒的辐射特性。对生成物和反应物之间能量循环燃烧系统的热力学方面进行了广泛的讨论，提出了一个新的特征温度——“绝热极限火焰温度”。这个温度的概念是非常重要的，特别是当考虑到可用的能量和燃烧系统的效率。结果还表明，存在与绝热极限火焰温度相对应的理论最大可用能量。在考虑颗粒/壁面、壁面/壁面辐射换热以及颗粒间辐射交换的气固两相体系中，对火焰结构和燃烧速度进行了进一步的研究。结果表明，颗粒对壁面、壁面对壁面的辐射换热和壁面对气体的对流换热是增强燃烧能量循环的重要途径。少

This study is aimed at clarifying the effects of radiative heat transfer on the on the flame structures of pulverized coal combustion. Using a strict treatment of radiation, a numerical model is developed describing a one-dimensional model of a flame involving a burning mixture with inert particle suspensions. Experimental studies have been also executed simultaneously to confirm the results of numerical analyses. The results are classified into following three large groups.1. Using the one dimensional model of a combustion system of a combustible gas mixture with particle suspension, it is disclosed that the suspended particles have two major effects. One is the suppression of combustion by the heat capacity of particles, and the other is the combustion augmentation by the energy recirculation based on radiative heat transfer. The latter effect is superior to the former one when the loading ratio is small and vice versa when it becomes large. The effects of the particle diameter and t … More he radiative properties of the particle have been clarified quantitatively.2. The thermodynamic aspect of the combustion system with energy recirculation between products and reactants is discussed extensively, and a new characteristic temperature, the "adiabatic limit flame temperature", has been proposed. The concept of this temperature is very important, especially when considering the available energy and the efficiency of combustion systems. It is also shown that there exists the theoretical maximum of the available energy corresponding to the adiabatic limit flame temperature.3. A farther study has been made on the flame structure and burning velocity in a gas-solid two- phase system where particle/wall and wall/wall radiative heat transfers have been taken into account as well as the radiative exchange between particles. The result shows that the important route of energy recirculation for combustion augmentation is the particle to wall and wall to wall radiative heat transfers and the wall to gas convective heat transfer. Less