PRODUCTION OF CHLORINE-FREE COAL CO-FIRING FUEL FROM MUNICIPAL SOLID WASTE BY HYDROTHERMAL TREATMENT

摘要

The usage of waste derived fuel for coal co-firing fuel is still hindered by its low energy density and high chlorine content, especially in the plastic-impregnated municipal solid waste (MSW). A hydrothermal treatment is developed to convert the MSW into solid fuel by employing a commercial scale system of about 1 ton capacity, applying saturated steam at about 2 MPa for about 60 minutes holding time. It was shown that the product has better uniformity, higher density and better drying performance compared to MSW with the heating value of about 20 MJ/kg (dry base), which is similar to that of low-rank sub-bituminous coal, and therefore sufficient to be used as co-firing fuel with coal.The results from the experiments also showed that at such processing condition, up to 80% of the organic chlorine in the MSW was converted into inorganic, water-soluble chlorine, which is beneficial to the usage of plastic-impregnated MSW as co-firing fuel due to the simpler chlorine removal process. Further small-scale experiments using PVC in laboratory autoclave showed that the phenomenon occurred depends on processing temperature, mixing process and air presence. It was shown that the operating temperature of about 220 ℃ is the critical dechlorination temperature.Mass and energy balance calculations of the hydrothermal treatment were conducted to find the optimum operating condition for MSW. The energy requirement for the hydrothermal treatment was as low as one-eighth of the energy content in the product, and the required energy to produce solid fuel from MSW was 0.8 MJ/kg MSW. It can be concluded that the hydrothermal treatment can be employed to convert plastic-impregnated MSW into a chlorine-free solid fuel for co-combustion with coal.