垃圾衍生燃料焚烧技术研究

Research on waste derived fuel incineration technology

垃圾衍生燃料广泛应用于干燥工程、水泥制造、供热工程和发电工程等领域。机械炉排焚烧炉存在投资成本高、维护费用高、占地面积大、热损失大等问题;气化焚烧技术仍处于实验室或半工业化阶段,无法实现工业应用;回转窑焚烧要求垃圾热值较高,炉渣指标易超标等,工业应用较少;鉴于流化床锅炉炉膛热容大,炉内混燃剧烈,燃料适应性强等特点,有必要利用其进行垃圾衍生燃料及生物质、固废的焚烧处理工艺研究。笔者从燃烧机理、物料制备与输送等方面入手,通过理论研究、数值模拟、燃烧试验、设备调研、现场试验完成了循环流化床锅炉直接掺烧垃圾关键技术研发、工艺优化和核心部件设计,验证了该技术在大型循环流化床锅炉的应用。结果表明,焚烧处理中,保障焚烧炉温和停留时间(大于2 s),提升炉内湍流度(Re>5 000),可促进垃圾完全、稳定燃烧,促进二噁英分解。提高运行过程中垃圾燃料的燃尽程度,从而减少带到尾部烟道的可燃物含量,可避免未完全燃烧的有机分子在空预器位置发生冷凝而导致积灰及二次燃烧。通过理论分析及试验,最终选择使用气力输送系统将破碎后生物质、固废送入炉内,锅炉接口布置在返料器出口位置,以满足生物质、固废燃烧时间、温度、混合、燃尽等需求。实际运行结果表明:利用300 MW循环流化床锅炉可同时处理生物质200 t/d、固废400 t/d、污泥200 t/d、RDF 50 t/d。烟气中二噁英的排放浓度低于0.001 3 ng/m^3 (标,11%O2),SO2排放均低于12 mg/m^3,NOx排放均低于50 mg/m^3,满足相关标准。该系统1 a可掺烧固体废物12万t,可节约用能量折合标准煤8.55万t,减排CO223.7万t、SO2726.8 t、NOx 632.7 t、灰渣3.35万t,实现了短时间内消纳大量固废,破解秸秆田间直焚、污泥垃圾围城等重要问题。

Refuse derived fuel is widely used in drying engineering,cement manufacturing,heating engineering and power generation engi-neering. The mechanical grate incinerator has the problems of high investment cost,high maintenance cost,large floor area and large heatloss.The gasification incineration technology is still in the laboratory or semi industrial stage,which can not realize the industrial applica-tion.The rotary kiln incineration requires high waste heat value,and the slag index is easy to exceed the standard,so it is rarely used in in-dustry.Therefore,in view of the characteristics of fluidized bed boiler,such as large furnace heat capacity,intense mixed combustion in thefurnace and strong fuel adaptability,it is necessary to study the incineration process of waste derived fuel,biomass and solid waste. Startingfrom the aspects of combustion mechanism,material preparation and transportation,the research and development of key technologies,process optimization and core component design of direct mixed combustion of garbage in CFB boiler were completed through theoretical re-search,numerical simulation,combustion test,equipment research and field test,and the application of this technology in large-scale CFBboiler was verified. The results show that the complete and stable combustion of MSW and the decomposition of dioxin can be promoted by ensuring the incinerator temperature and residence time(more than 2 s) and increasing the turbulence degree(Re>5 000) in the incinera-tor. In order to reduce the content of combustibles brought to the tail flue,it is necessary to improve the burn out of garbage fuel during op-eration,so as to avoid the accumulation of ash and secondary combustion caused by the condensation of incompletely burned organic mole-cules at the position of air preheater. Through theoretical analysis and test,the final choice is to use pneumatic conveying system to sendthe crushed biomass and solid waste into the furnace,and the boiler interface is arranged at the outlet of the feeder to meet the needs of bi-omass and solid waste combustion time,temperature,mixing,burnout,etc. The practical operation results show that the 300 MW CFB boil-er can simultaneously treat 200 t/d biomass,400 t/d solid waste,200 t/d sludge and 50 t/d RDF. The emission concentration of dioxin inthe flue gas is lower than 0.001 3 ng/m^3(standard,11% O2),the emission of SO2 is lower than 12 mg/m^3,and the emission of NOx is lower than 50 mg/m^3,which meets the relevant standards. The system can burn 120 000 tons of solid waste in one year,which can saveenergy equivalent to 85 500 tons of standard coal,and reduce emissions of 237 000 tons of CO2,726.8 tons of SO2,632.7 tons of NOx and33 500 tons of ash. It can dispose a lot of solid waste in a short time,and solve the important problems such as direct burning of straw inthe field,siege of sludge and garbage.