Experimental Research On Removal Of Dioxin Material From Flue Gas

With the development of economy and the expansion of China's cities, the amount of MSW clean-up has increased year by year. At present in the world, landfill, composting and incineration are the main MSW processing methods Among these three methods, MSW incineration technique has become more and more widely used, because it has advantages in hazard-free treatment, more volume reduction, less area occupying and heat energy recycle. However, due to the complicated matrix, MSW using the incineration technique produces toxic and harmful substances. Dioxin is the most persistent and toxic substance produced after burning, which is regarded as potential threat to human health. It's very difficult and expansive in dealing with dioxin. Instead, highly active absorbent was prepared in this study. The effects of temperature, oxygen content, pH, etc. were investigated using a fixed-bed experimental system. The structure of the product was analyzed by GC-MS. Additionally, the experiments of removal of dioxins type chemicals were carried out in NaClO2 solution. This study has some theoretical meaning and application value for developing the technique of dioxin control.Fly ash and CaO are the main constituents of the modified absorbents, which have the capability of removal 1,2,4-trichlorobenzene. The analysis results of specific surface area and pore structure tests showed that the specific surface area and pore volume of fly ash increased about 10 times after digestion at certain hydrothermal condition by calcium oxide. The sizes of most of the micro pores were in the range of 3-40 nm, which was regarded as the medium pore. The SEM and X-ray energy spectrum analysis showed that:the relative average content of Ca(OH)2 on the absorbents surface was higher than that inside. The additives were dispersed in the absorbent surface evenly.The effects of temperature, inlet 1,2,4-TCB concentration, oxygen content, additive content etc. on the removal efficiency were investigated using a fixed-bed experimental system. The results showed that the absorbents had preferable removal capability of 1,2,4-TCB from flue gas. The result of product analysis showed that 2,6-Bis-[1,1-Dimethylethyl]-4-methyl-Phenol was the major intermediate product in the reaction; CO2 and H2O were the eventual products; Dioxins were not detected by GC/MS. This maybe because the formation routs were blocked off after Cl was absorbed by the highly reactive absorbent, which was decomposed from trichlorobenzene.The experiments of 1,2,4-TCB removal were carried out in NaClO2 solution. The effects of solution concentration, initial pH value, reaction temperature, inlet 1,2,4-TCB concentration etc. on 1,2,4-TCB removal performance were studied in the paper. The results showed that the absorbents had preferable removal capability of 1,2,4-TCB from flue gas.The optimum experimental conditions of removing TCB are the ratio of NaClO2/NaClO in complex absorbent is 2, the reaction temperature is 50℃, and pH of reaction medium is 10. The TCB removal efficiency above 90% was achieved under optimized conditions. There are two steps in this reaction. In the first, Ispo-substitution reaction between TCB and nucleophile reaction might occur in alkaline medium, the product are chlorophenols and 4-methyl-1-pentanol. Then chlorophenols and 4-methyl-1-pentanol would be oxidized by "M" such as ClO2 and ClO2. The result shows that main intermediate products are 4-methyl-1-pentanol and succinic and the end product are H2O and CO2.