Study On Combustion And Pollutant Emission Of Municipal Solid Waste In Combined Grate And Fluidized Bed Incinerator

The incineration is an effective method to treat municipal solid waste (MSW) for its volume reduction, harmless treatment and energy recovery. It is important to study on the combustion process and pollutant emission in MSW incineration. The experiments and model simulating of MSW combustion and pollutant emission in a combined grate and circulating fluidized bed incinerator (grate-CFBI) have been performed. Through the study, following results are obtained.The analysis of low heating value and ignition temperature of MSW was carried out. The analysis results indicate that the technology of grate-CFBI, that is, to use at first the grate bed to dry out MSW and then to use the fluidized bed to incinerate MSW is very effective for MSW treatment. The drying process of MSW was experimentally investigated in test rigs and in a simulated grate bed respectively. The moisture loss rate and activation energy of typical waste at different temperature were obtained from the experiments. Based on the experimental and theoretical analysis results, the optimized structure of the grate bed of grate-CFBI and its design principle were proposed.The ignition temperature and evolved gas components of typical waste in drying, pyrolysis and oxidization process were experimentally studied by using the thermal gravimetric analysis (TGA). The changing trend of pyrolysis products including alkanes, benzene, et al. and the ignition temperature of MSW ware obtained. In addition, the activation energy and exponential factor of MSW in pyrolysis were analyzed. The obtained kinetic parameters of MSW pyrolysis and the ignition temperatures can be used as the data base in the model simulation of MSW incineration.The experiments of combustion of typical MSW components were performed in an experimental facility. It was found from the experiments that the peak values of CO and CxHy appeared in combustion process of post-drying waste at the grate bed were very high and the secondary air was required for their complete combustion. When MSW incinerated in fluidized bed, the flash vaporization of water and rapid release of volatile matter of MSW induced deflagration combustion, which lead to the pressure and temperature fluctuations in the furnace. With the increase of secondary air flow rate, the emission of CO and NOx decreased.The combustion experiment of raw MSW collected from community and the test carried out in the industrial grate-CFBI of 150t/d (ton per day) and 260t/d grate-CFBI were performed respectively. The results from both the experimental work and the industrial test showed that CO and other combustible gas concentrations along the height of the furnaces were higher and the burnout time of these gases were longer respectively than that in coal fired boilers. The multi-staging air supply was decisive to reduce the original pollutant formation. The experiment and the industrial test also indicated that the pre-drying of waste on the grate bed could not only maintain the stable combustion in furnace and reduce the supplement coal, but also inhibit the deflagration combustion and reduce pollutant emission.A semi-theoretical model for the simulation of MSW combustion and pollutant emission in the grate-CFBI was presented and verified by the experimental and industrial test data. The influence of operation parameters such as the excess air and primary air rate on combustion and pollutant formation was studied by the model simulation. This semi-theoretical simulation model is useful for the design and the operation of the grate-CFBI.