|其他摘要||Recently, the annual production of municipal solid waste (MSW) increases sharply, which leads to serious environmental problems. Much more attention has been paid on the disposal of MSW through incineration due to its harmlessness, volume reduction and recycling. However, incineration has high capital investment, low combustion efficiency and high pollutants emission. Compared to that, co-firing MSW with coal gangue in the existing coal gangue CFB boiler, which has high combustion efficiency, broad fuel adaptability and complete pollutants removal equipment, may utilize MSW with low capital cost, high efficiency and less pollutions. Besides, MSW has high volatile content and can be ignited easily, which may improve the ignition and combustion characteristics of coal gangue. Hence, co-combustion of coal gangue and MSW is a highly potential way for collaborative utilization of coal gangue and MSW.
However, there is a big difference in combustion characteristics between coal gangue and MSW. Besides, MSW has high chlorine content, which may give a risk of HCl emission. Hence, the co-combustion of coal gangue and MSW is investigated from four aspects including the co-combustion characteristics，combustion kinetics, the hydrogen chloride emission characteristics and the hydrogen chloride emission control.
(1) The combustion characteristics of coal gangue, MSW and their various blends were investigated by the Thermogravimetric Analyzer-Differential Scanning calorimeter (TGA-DSC). The results show that the MSW blending can decreases the volatile release temperature and ignition temperature significantly and improve coal gangue ignition characteristic. The comprehensive combustion characteristic parameter decreased firstly and then increased with the increasing of MSW blending ratio. When the MSW blending ratio is above 30 wt.%, the combustion characteristic of co-fuels changes obviously compared to coal gangue. There are different interactions between coal gangue and MSW during co-combustion. During volatile release and combustion stage, there is inhibiting interaction between coal gangue and MSW due to the mix and the lack of air, when the MSW blending ratio was lower than 30 wt.%. While, during the fixed carbon combustion stage, MSW may promote the initial combustion of fixed carbon, when the MSW blending ratio is larger than 20 wt.%.
(2) The first order model and Coats-Redfern method are adopted to investigate the blending of MSW on the thermal reactivity of coal gangue. The results investigated that the activation energy for the devolatilization stage increased with the increasing of MSW blending ratio, while the opposite for fixed carbon combustion stage, which improve the thermal reactivity during fixed carbon combustion stage for co-fuels.
(3) The high-temperature tube furnace combustion system is adopted to investigate the hydrogen chloride emission rules for the co-combustion of coal gangue with PVC, NaCl and MSW. The results show that the chlorine in PVC can be inhibited to be released by coal gangue during co-firing, while that in NaCl can be promoted to be released. Besides, the inhibition and promotion effects decrease with the increasing of MSW blending ratio. During co-combustion of coal gangue and MSW, HCl is promoted to be released and the HCl concentration in flue gas increases.
(4) Based on the above research results, the effect of CaCO3 addition on the controlling of HCl emission was analyzed. It can be found that the chlorine retention increased firstly and then decreases with the increasing of combustion temperature. The best combustion temperature for controlling HCl emission by CaCO3 is 700 oC, where there is the largest chlorine retention 32.62 %. The chlorine retention increased with the increasing Ca/(S+0.5Cl) molar ratio. However, when the Ca/(S+0.5Cl) molar ratio reached 12:1, the improvement of chlorine retention ratio by CaCO3 is not significant.|