Research On Dioxin Emission And Behavior From A Cement Kiln Co-processing MSW

With the rapid development of economy and urbanization of China, the production of MSW (Municipal Solid Waste) increases fast. How to deal with it becomes a big problem and it draws more and more attention in China. The technology of co-processing MSW with cement kiln reduces the adverse effect of MSW to the surrounding environment. It has the advantages of volume reduction, pollution reduction and resource utilization. This study was based on a cement kiln in Hubei province with clinker capacity of4500t/d. A lot of research work was conducted and several valuable conclusions were drawn as following:1. To recognize the characteristics of MSW and RDF (Refuse Derived Fuel) which were collected from Wuxue city and Chibi city, a lot of basic tests were done, such as industry analysis, elemental analysis, moisture content, calorific value, physical composition, chlorine content, heavy metal and so on. These tests helped us have comprehensive understanding about the MSW and RDF;2. RDF was used as alternative fuel. The feeding rate of RDF was8-12t/h. The average level of dioxin emitting to the atmosphere was0.0765ng I-TEQ/m3in normal operation, while it was0.0967ng I-TEQ/m3in co-processing RDF. There was no remarkable difference in emissions between with and without RDF addition in this study. Both of them were under the standard of0.1ng I-TEQ/m3. The input dioxin level of C1(the first stage of cyclone-type vessel) was0.3991ng I-TEQ/m3, while0.2172ng I-TEQ/m3of the output. It reduced45.58%of the dioxins, mainly because of the adsorption characteristic of raw meal;3. The dioxin level of recycling bag ash was0.0473ng I-TEQ/g, and the level of raw meal out of the mill was0.0697ng I-TEQ/g in co-processing RDF. After investigated the dioxin levels of three different kinds of particle size (PM<2.5, PM2.5-10, PM>10),we found that the dioxin level increased with the particle size decreasing. Did thermal desorption experiments of the recycling bag ash at350℃in different atmosphere, it demonstrated that part of the dioxins in particle phase transferred to gaseous phase while the total dioxins remained nearly the same;4. The dioxin level of combustion gas decreased from0.92ng I-TEQ/g RDF when combusting only RDF to0.31ng I-TEQ/g RDF when combusting RDF with raw meal. On the other hand, after the combustion gas of RDF flowed through the raw meal, the dioxin reduced remarkably. We believed that the alkaline atmosphere in the cement kiln had a good inhibition effect on dioxin formation and emission.