【作者】 王波；

【导师】 池涌； 严建华； 倪明江；

【作者基本信息】 浙江大学 ， 工程热物理， 2009， 博士

【摘要】 氯代烃类有机溶剂被广泛用于化工等行业中,是工业危险废液的重要组成部份,如二氯甲烷、氯仿和四氯化碳等。对这些危险废液进行安全处置,防止环境污染十分重要。焚烧技术能把有害物质氧化分解为CO和H20等,焚毁率高,是处理含氯危险废液的有效方法之一。但是氯对燃烧过程普遍存在抑制作用,常伴随着CO和COCl2等有害不完全燃烧产物的生成。研究氯代烃高温氧化的基本特性,了解氯对废液燃烧过程抑制作用的机理,寻找控制污染物生成的方法是必要的。本文采用管式流动反应装置对氯在燃烧过程中的抑制作用进行了实验研究,并组建了动力学反应模型,分析了氯对燃烧过程抑制作用的机理。研究结果表明,氯代烃的氧化过程经历了两步,第一步是较快地分解为CO和HCl；第二步是CO在氯的抑制下缓慢氧化。反应物中的碳转化为CO的比例在800℃左右达到最大值。CO的转化率随反应温度的升高而增大,随着氯含量的升高而降低。氯对CO氧化的抑制作用主要通过两个途径实现：一是氯与H结合生成HCl的过程中消耗H,减少OH的生成；二是生成的HCl与OH反应,进一步降低了OH的浓度。温度升高时,通过H+O2=OH+O的速率急剧升高,促进了OH的生成,提高了OH浓度和CO的转化率,削弱了氯对CO氧化的抑制作用。提高反应温度,是促进氯代烃氧化的首选途径。研究发现反应系统中的氯一方面可以促进甲烷等烃类物质分解,另一方面氯和CH4、CH3等含碳分子或基团反应,导致CH3Cl、CH2Cl2和COCl2等有害不完全燃烧产物的生成,抑制反应物中的碳转化为CO2。当CH4等烃类物质的浓度一定时,不完全燃烧产物的浓度随氯含量的增加而增大；当CCl4等氯代烃浓度一定时,提高CH4浓度,降低Cl/H,有利于CCl4分解；但这一过程同时会增大COCl2和CH3Cl等不完全燃烧产物的生成量。温度高于950℃时,这些产物几乎完全分解。在900℃以上,提高CH4浓度,降低C1/H,促进CCl4分解的意义很小,反而会促进氯与含碳分子或基团反应生成有害不完全燃烧产物。在含氯物质高温燃烧过程中,加入辅助燃料主要作用是提高反应温度,并提供H与氯结合生成HCl,减少Cl向其它含氯不完全燃烧产物的迁移。采用辅助燃料-氯代烃两段式燃烧,即先喷入辅助燃料再把含氯物质喷入辅助燃料燃烧产生的高温烟气中,可以消除氯对辅助燃料燃烧的抑制作用,减少氯与含碳分子或基团的反应。和一段式燃烧相比,CO和有机不完全燃烧产物的浓度大幅度下降,有利于控制污染物排放。更多还原

【Abstract】 Chlorinated hydrocarbons are widely used as solvents in chemical industry, such as dichloromethane, chloroform and carbon tetrachloride. They are important components of liquid hazardous wastes. It is important to dispose these wastes and prevent environment pollution. Incineration is one of the effective technologies for chlorinated wastes, in which the toxic components can be oxidized to CO2 and H2O with high destruction and removal efficiency. But the combustion process is usually inhibited by chlorine and toxic products of incomplete combustion (PICs) are formed, such as CO and COCl2. It is necessary to study the combustion characters of chlorinated hydrocarbons and understand the chlorine inhibition mechanism, in order to develop technologies for pollution control.In this paper, the chlorine inhibition phenomenon was studied in tubular flow reactor. Kinetic mechanisms were constructed and kinetic modeling was used to analysis the inhibition mechanism. It is found that chlorinated hydrocarbons are destructed to CO and HCl first, then the CO is slowly oxidized under HCl inhibition. The largest CO concentration is observed at about 800℃. The CO conversion increases with reaction temperature, but decreases with higher chlorine content. The HCl formation reactions slow down the OH production process and the reaction between HCl and OH further decreases the OH concentration, which leads to low CO conversion. Increasing temperatures rapidly accelerates OH formation through the reaction H+O2=OH+O and enhances CO conversion, which is the most effective way to abates the chlorine inhibition effect promotes chlorinated hydrocarbons combustion.The chlorine in the reaction system enhances the destruction of hydrocarbons such as CH4, but the reactions between chlorine and carbonaceous species result in toxic PICs formation, including CH3Cl,CH2Cl2, COCl2 and so on. It also inhibits the conversion of carbon to CO2. When the concentration of hydrocarbons is constant, the production rate of PICs increases with chlorine content. If the mole fraction of chlorinated hydrocarbons is constant, taking CCl4 for example, adding hydrocarbons promotes the chlorinated hydrocarbons destruction process, but the concentration of PICs increases at the same time. At temperatures above 950℃, these PICs are mostly destructed. At temperatures above 900℃, increasing the concentration of hydrocarbons to enhance chlorinated hydrocarbons destruction is meaningless. On the contrary, it promotes the reactions between chlorine and carbonaceous species.In chlorinated hydrocarbons combustion process, the effect of auxiliary fuel is raising reaction temperature and supply hydrogen to form HCl. The auxiliary fuel-chlorinated hydrocarbons two stage combustion is effective for pollution control, in which the auxiliary fuel is combusted first, and then the chlorinated hydrocarbons are injected into the flue gas. This method eliminates the chlorine inhibition effect on auxiliary fuel combustion and decreases the reaction between chlorine and carbonaceous species. The emission of CO and PICs is much lower than that in one stage combustion. It is shown to be an effective method for emission control in chlorinated hydrocarbons incineration.更多还原