Study On Chlorinated Liquid Waste Oxidation At High Temperature

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.