Yang Yao Bin, Swithenbank Jim
School of Energy and Power Engineering, Xian Jiaotong University, Xian 710049, PR China.
Waste Manag. 2008;28(8):1290-300. doi: 10.1016/j.wasman.2007.04.012. Epub 2007 Aug 13.
Packed bed combustion is still the most common way to burn municipal solid wastes. In this paper, a dispersion model for particle mixing, mainly caused by the movement of the grate in a moving-burning bed, has been proposed and transport equations for the continuity, momentum, species, and energy conservation are described. Particle-mixing coefficients obtained from model tests range from 2.0x10(-6) to 3.0x10(-5)m2/s. A numerical solution is sought to simulate the combustion behaviour of a full-scale 12-tonne-per-h waste incineration furnace at different levels of bed mixing. It is found that an increase in mixing causes a slight delay in the bed ignition but greatly enhances the combustion processes during the main combustion period in the bed. A medium-level mixing produces a combustion profile that is positioned more at the central part of the combustion chamber, and any leftover combustible gases (mainly CO) enter directly into the most intensive turbulence area created by the opposing secondary-air jets and thus are consumed quickly. Generally, the specific arrangement of the impinging secondary-air jets dumps most of the non-uniformity in temperature and CO into the gas flow coming from the bed-top, while medium-level mixing results in the lowest CO emission at the furnace exit and the highest combustion efficiency in the bed.
固定床燃烧仍然是焚烧城市固体废物最常用的方式。本文提出了一种主要由移动燃烧床中炉排运动引起的颗粒混合扩散模型，并描述了连续性、动量、组分和能量守恒的传输方程。模型试验得到的颗粒混合系数范围为2.0×10⁻⁶至3.0×10⁻⁵m²/s。寻求数值解以模拟一台每小时处理12吨垃圾的全尺寸垃圾焚烧炉在不同床层混合水平下的燃烧行为。研究发现，混合程度的增加会使床层着火稍有延迟，但会大大增强床层主燃烧期的燃烧过程。中等程度的混合产生的燃烧分布更位于燃烧室的中部，任何剩余的可燃气体（主要是一氧化碳）直接进入由反向二次风射流产生的最强烈湍流区域，从而迅速被消耗。一般来说，撞击式二次风射流的特定布置将大部分温度和一氧化碳的不均匀性排入来自床顶的气流中，而中等程度的混合导致炉排出口处一氧化碳排放最低，床层燃烧效率最高。
