流化床中煤掺混垃圾燃烧时受热面积灰的研究

Ash Deposition During Co-Combustion of Coals with MSW in AFBC

在利用小型流化床系统研究煤掺混垃圾燃烧时硫对有机污染物排放影响的过程中,发现处于烟气温度338～547℃的对流区域受热面存在积灰,为此对积灰形成过程进行了研究.结果显示,受热面灰沉积量随烟气温度降低而减少;随着混合燃料中垃圾含量及硫含量的增加,灰沉积量也减少.分析发现,沉积物主要由小于5μm的细小颗粒组成,其化学组成中绝大部分为氧化钙,且Ca/S摩尔比明显大于1,因此积灰主要是石灰石床料分解形成的细小氧化钙颗粒沉积所致,而沉积层中的硫酸钙则是沉积的氧化钙进一步反应的结果.燃烧高硫燃料时,由于烟气中SOx的浓度高,使存在于烟气中的粘附性强的氧化钙颗粒减少,进而抑制了积灰的形成.

In the study of emission of organic pollutants during co-combustion of coal with municipal solid waste (MSW) in a bench-scale fluidized bed combustion (FBC) system, it was found that ash deposition occurred in the convection zone where the flue gas temperature was from 338°C to 547°C. In order to understand the process of formation of ash deposition, the character of ash deposition collected by using the probes was investigated. The results show that the amount of ash deposition decreases with the decrease of the flue gas temperature. With the increases of the MSW content or the sulfur content in the fuel filled, the amount of ash deposition also appears to be decreased. And it was found that the deposition mainly comprises the particles smaller than 5 μm. In the chemical composition of the samples studied the contents of calcium oxide are far more than those of others and the mole ratios of Ca/S are obviously larger than 1. Thus the ash deposition is caused by deposit of the fine active lime particles coming from the decomposition of limestone used as the bed material, and the calcium sulphate existing in the deposition is formed through the deposited calcium oxide reacting further. When the fuel with a high sulfur content was filled, the number of particles of calcium oxide that have a strong adherence in the flue gas would be decreased largely because of its reaction with SOx, restricting the formation of the ash deposition.