| Purposes and ImportanceThe present status of municipal solid waste (MSW) treatment of China was analyzed, the advantages and disadvantages of all treatment methods of MSW were compared, and the method of co-firing of coal and refuse derived fuel (RDF) was proposed.The purposes of this research were to add RDF to existing fluidized bed combustors for co-firing, this treatment method of MSW could save lot of capital cost for building new incinerators. Besides, some small-scale coal-fired power plants, which were shutdown according to the government policy, could be relived after being retrofitted by choosing the way for co-firing coal and RDF.Fluidized bed combustor was chosen due to some advantages, for example, wider range fuels, lower NOX emission and lower cost for SOT retention etc.There are some differences between coal combustion and co-firing coal with RDF, because of their different particle sizes, different caloric values, different shapes and different compositions. When coal and RDF are co-fired, harmful acid gases HC1 and SO2 are emitted. Therefore, it's necessary to study the simultaneously removal of HC1 and SO2.Summary and ProcessTwo sets of fluidized bed apparatuses were set up, one made of plexiglass and another made of stainless steel. They had the same dimensions with an inner diameter of 150mm. The combustor system includes fluidized bed reactor, air system, feeding system, power system and cyclone scrubber etc.To co-fire coal and RDF more efficiently, a new type internally circulating fluidized bed (ICFB) was developed. The internal circulation was achieved by a non-uniformed distributor plate. The central area of plate had a lower opening area ratio, behaving moving bed; and the annular area of plate had a higher opening area ratio, behaving fluidized bed. The characteristic of internal circulation was studied in plexiglass fluidized bed, and co-combustion of coal and RDF was completed in both bubbling fluidized bed combustor and ICFB combustor,Two kinds of RDFs were co-fired with coal, the effects of RDF/coal proportion, excess air ratio, Ca/S molecular ratio and bed temperatures on the removal acid gases (SO2 and HC1) were studied. Concentrations of O2, CO2, H2O, CO, CH4, SO2, HC1, NO, NO2, N2O and HCN in flue gas were measured by online FTIR spectrometer and online gas analyzer. Fly ash and bottom ash were analyzed by XRD and SEM. The material balance was calculated. The distribution of Cl and S was analyzed.The reactions between acid gases and sorbents (limestone and CaO) were studied in TGA by either isothermal or non-isothermal methods. Kinetics parameters and thermodynamic parameters were calculated. According to the composition of flue gas, individual reacting gas or parts reacting gases were grouped to react with CaO, so as to identify the reaction mechanism.The combination technology of TGA with gas analyzer was successfullyused, continuous weight changes and gas compositions were simultaneously analyzed, this combination provided a proof of chemical reaction mechanism.Coal with high contents of chlorine was combusted in a bench scale fluidized bed combustor for simultaneously removal of SO2 and HCI. The emissions of SO2 and HCI was studied, and the effects of Ca/S molecular ratio, excess air ratio and bed temperatures on the removal of acid gases were also studied.A newly formula of theoretical air amount for co-firing coal and RDF was deduced, which was different from all published ones due to either Cl being included or every parameter having clear meaning. The formula fitted the calculation for any proportion of coal and RDF.Mainly ResultsThe temperature changes by vertical direction indicates that the more RDF added the higher the temperature in freeboard was, which means that RDF mainly burned in freeboard zone.Within the temperature range of 750℃~900℃, with the increase of bed temperature, the emissions of acid gases increased; With the increase of Ca/S, the SO2 retention increased, but HCI retention was not obvious. The expe...
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