城市污泥用作水泥行业替代燃料的可行性分析

Feasibility analysis of the municipal sludge taken as an alternative fuel for cement industry

采用X射线荧光光谱仪、全自动数显量热仪和原子吸收分光光度计等检测手段测定3种不同来源的干化城市污泥及煤粉的成分、热值和重金属毒性,对比分析了污泥用作水泥工业部分替代燃料的可能性,通过热重（TG）试验研究了污泥掺比对混合燃料燃烧效果的影响。结果表明：3种干燥污泥发热量较高,最高可达16.02 MJ/kg,且主要成分与煤粉相似,均为CaO、SO3、Al2O3和SiO2,比例之和超过65%,可部分替代水泥生产燃料;污泥灼烧后,剩余灰分中重金属质量比满足GB 50295—2008《水泥工厂设计规范》标准限制,不会对水泥熟料产生影响;干燥污泥的加入可促进煤的燃尽,混合燃料TG曲线随污泥比例增加向低温段移动;部分混合燃料固定碳燃烧阶段放热量低于5 000 J/g,污泥掺量以不超过40%为宜。

The present paper is inclined to introduce an analysis of the feasibility of the municipal sludge to be used as an alternative fuel to the cement-preparation industry by testing the calorific value and the heavy metal content of the sewage sludge from the 3different sources and the traditional fuel coal via the X-ray fluorescence spectrum,digital calorimeter and the atomic absorption spectrophotometer,to study the impact of the sewage sludge rates on the combustion process of the mixed flows.For the 3 kinds of the dry sewage sludge and coal,the results of our experiment demonstrate that the main chemical components should be of high content concentration rates but of a bit difference with the 4 main components（Ca O,SO3,Al2O3,SiO2）being at least over 65%.As a matter of fact,though the ash in the sewage sludge is low,yet,the calorific value should be found so high as to 16.02MJ/kg.In spite of the fact that the content and the variety of the heavy metals in the residual ash can be found in a little difference with that of the coal ash,yet the experimental results prove to be conformed with and to the permissible data specified in the national standard（GB 50295—2008）,which shouldn’t be made affecting the cement clinker.Therefore,the sludge remains feasible to be used as fuel partially in the cement-making industry.Besides,since it is prone to form and result in fouling and slagging,the fluidized bed material is also prone to get agglomerated with the other problems likely to take place in the combustion process in the boiler because of its higher rates of alkali metal residence,whose highest content rate of Ca O may be so high as up to 42.332 1%,though there may exist a certain limit on the amount of admixture.Furthermore,the TG and DSC results show that there may also exist obvious gap between the combustion of the different mixed fuels and the sludge or coal.For example,during the sample combustion,neither the stages of volatile volatilization nor the combustion of the residue volatile with the fixed carbon in the burning-out stage should be taken as the main combustion process.What is more,addition of the dry sludge can promote the coal burnout,when the TG curve moves to the low temperature zone with an increase of the sludge.Therefore,for a certain mixed fuel combustion,the fixed carbon in the later stage should be expected to produce considerably lower heat productivity,which should not have been preferably expected to go beyond 40%.