| Municipal solid wastes (MSW) do great harm to the environment and the health of humans, and it has resulted in an increasing concern all over the world.The traditional technology to treat MSW is no longer sufficient to meet our need. MSW gasification is a thermochemical process that generates a gaseous, fuel rich product.It has the advantages of higher effect in volume reduction, lower second-step pollution and higher energy recovery.This work takes mixed solid wastes which are made up from typical components of MSW as object of study. The process of mixed solid wastes gasification is investigated by thermogravimetic analysis and the characteristics of gaseous product are carried out in a fixed bed reactor.The results of nonisothermal thermogravimetic analysis show that MSW gasification process can be divided into two stages, the first stage is the yield of volatile components and its gasification and combustion; the second stage is the gasification and combustion of the leftover after pyrolysis. Heating rates affect the process of MSW gasification significantly, the initial temperature Tb, the final temperature Tf and the temperature in the highest mass loss rate Tm increase with the increasing of heating rates, while the ratio of weight loss at each stage remains the same basically. Changing of atmosphere take no effect on the first stage of MSW gasification, but it has big effect on weight loss and reaction velocity of the second stage. Weight loss and reaction velocity in the atmosphere of air or rich oxygen is higher than in poor oxygen.Heating rates take no effect on reaction mechanism, but they can change kinetics parameters E and A. At 10℃/min, in the first stage, the reactions are all controlled by the three-dimensional diffusion model, and in the second stage, the reactions are controlled by phase boundary shrink sphere, chemical reaction (n=1.5) and chemical reaction (n=2) separately in the atmosphere of poor oxygen(10%O2), air(21%O2) and rich oxygen(56%O2).The mechanism equation of first stage is f(α)=3/2(1-α)2/3((1-α))1/3-1]-1, the mechanism equations of second stage art f (α) =3(1-α)(2/3), f(α)= 2(1-α)3/2 and f(α)=(1-α)2 .The kinetics parameters of MSW gasification were obtained indifferent heating rates and atmosphere.The characteristic of MSW gasification are studied in the atmosphere of N2, air and rich oxygen through a series of experiments. The influence of temperature, heating rates and atmosphere are investigated. The variation discipline of gas products(CO,H2,CH4,CO2) in the temperature range of 250-950℃are summarized. In the atmosphere of N2, volume percentage of CO decrease between 250-500℃and increase between 500-950℃with the increasing of heating rates. H2 start to generate after 500℃, and its volume percentage increase between 500-950℃with the increasing of heating rates. With the increasing of volume percentage of oxygen in the atmosphere, volume percentage of CO,H2,CH4 in every temperature spots decrease while CO2 in every temperature spots increase.The instantaneous volume of MSW gasification increase with the increasing of heating rates in the temperature range of 250-650℃.The instantaneous and accumulative total volume of MSW gasification at 10℃/min is the largest in the temperature range of 650-950℃.In conclusion, the technology of MSW gasification has a great expansive prospect because of its environmental and economic benefits. |
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