生活垃圾气化过程含氯污染物迁移转化机制及炉内协同脱氯方法研究

Incineration is one of the most preferable municipal solid waste (MSW) treatment methods in recent years. However, due to the existence of chlorine, MSW incineration has raised the possibility to cause some serious environmental problems. Hydrogen chloride (HCl), which is easily formed during incineration, contributes to corrosion in the equipment; besides, it also acts as a chlorine source promoting the low-temperature heterogeneous formation of dioxins. Therefore, research on the formation and reduction of chlorinated contaminants is of great significance. Compared with incineration, MSW gasification technology has showed great advantages on emission reduction and energy efficiency improvement. Meanwhile, it is found that the optimum working temperature range of waste gasification overlaps with the temperature window of dechlorinate sorbents, which increases the potential operation conditions for the removal of chlorinated contaminants during gasification reaction process. Regarding the fact, in this project, the utilization of in-bed dechlorinate sorbents to decrease chlorinated contaminants at the gasifier has been proposed. In this way, the concentration of HCl in flue gas can be reduced effectively and thus to inhibit the formation of dioxins simultaneously. The objectives of this project are to obtain the migration and transformation of chlorine element as well as the formation pathways of chlorinated emissions during MSW gasification; to understand dechlorinate mechanism by adding in-bed sorbents; and to grasp the effect of dechlorinates on the reduction of dioxins emissions.

城市生活垃圾由于其较高的氯元素含量，在焚烧过程中容易形成HCl气体导致受热面高温腐蚀等问题；同时，HCl在烟气降温过程中为二恶英等持久性有机污染物的低温异相合成阶段提供了氯源，促进了其生成与排放。因此，降低垃圾热处理过程中的含氯污染物生成与排放具有重要意义。垃圾气化技术在污染物减排与提高能量效率方面具有很大的优势。研究发现垃圾气化的最佳工况温度与脱氯吸收剂的最佳反应温度窗口重合，为气化反应炉内脱氯提供了适宜的温度条件。因此，本项目创新性提出在气化炉内添加吸收剂，实现反应过程中含氯污染物高效脱除，有效降低烟气中HCl含量，减少二恶英氯源，达到污染物减排、发电效率提升的目标。本项目研究目标包括：了解垃圾气化过程中氯元素的迁移转化规律和含氯污染物的生成与排放机制，获得不同气化反应器炉内添加吸收剂脱除含氯污染物反应机理，掌握炉内脱氯对二恶英类有机污染物减排机理。

垃圾焚烧过程产生的HCl气体会造成设备高温腐蚀并参与二恶英的生成，开展相关研究具有理论意义和应用价值。本项目创新性地提出炉内加入钙基添加剂在垃圾热解气化过程中脱除HCl，探索炉内钙基添加剂对垃圾热解气化过程中含氯污染物（HCl、氯苯、二恶英）排放规律的影响，主要研究内容和结果如下：. 1 掌握了垃圾中不同含氯组分热转化过程中氯元素的转化特性。研究表明，无机氯源NaCl中的氯元素在热转化过程中主要以NaCl的形式存在于固相产物中，有机氯源(如PVC)中的氯元素在热转化过程中主要以HCl的形式存在于气相产物中。有机氯源是生活垃圾热处置过程产生HCl的主要来源。. 2 垃圾热解气化过程中钙基吸收剂能有效降低和控制HCl和含氯污染物的生成和排放，并开展了相关基础研究，主要工作和结论如下：.(1) 炉内钙基添加剂脱除HCl的推荐工况条件为常压下反应温度低于772 ℃（CaCl2熔化温度），钙氯摩尔比2:1，粒径根据炉型进行选择，HCl脱除效率能达到85%以上。相比于CaO，煅烧白云石和Ni/CaO对于HCl气体脱除以及油相产物中氯含量降低的表现更优。生活垃圾热解气化过程中钙基添加剂的脱氯表现优于焚烧过程的表现。.(2) 炉内添加CaO能促进垃圾热解气化过程焦油的分解从而提升了可燃气体的产率，并吸收CO2，HCl等气体，促进水煤气转化反应，提升H2的产率，从而大大的提升可燃气体品质。.(3) 在垃圾热解过程添加CaO、煅烧白云石、Ni/CaO，氯苯总产率分别降低了39%、59%、66%，并通过实验和高斯模拟研究得出还原性气氛有利于氯苯高温降解。.(4) 垃圾热解气化过程二恶英生成量和毒性显著低于焚烧的情况，而添加钙基添加剂能进一步有效降低垃圾热解气化过程中气相产物和油相产物中的二恶英，通过炉内钙基添加剂与垃圾热解气化技术相结合，能有效降低垃圾热处置过程二恶英的排放，二恶英生成量和总毒性分别降低88%和85%以上。. 本研究表明，热解气化和炉内脱氯的结合能有效控制垃圾热转化过程含氯污染物的生成和排放，有望形成新的垃圾热转化和热处置原理和技术，发展传统的焚烧方法和技术。