Research On Fuel Gas Production From Catalytic Gasification Of Municipal Solid Wastes

As the social and economic development and urbanization process acceleration, the generation rate and the production of municipal solid waste (MSW) increased rapidly. Traditional disposal processing of municipal solid waste, including landfill, composting, incineration, have drawbacks and secondary pollution. The gasification technology, because of its low emissions, a significant reduction of the capacity and the production of combustible gases, is considered to be the most potential alternative technologies for incineration, and gradually become a new hotspot.Nickel ferrite nanocomposites were prepared by a homogeneous precipitation method and the influences of various processing parameters in preparation process on the yield and mean size of the product were also investigated. Meanwhile, XRD, FTIR and SEM were used to characterize the nanoparticles and precursors. The results indicated that the production prepared at the optimum conditions were NiFe2O4 and NiO nanocomposites, they were uniform in particle size and had a fine crystal phase of cubic spinel structure with a mean size of 52 nm. The optimum conditions for preparing nanocrystalline were as follows: the molar ratio of nickel chloride hexahydrate to iron nitrate nonahydrate was 3:1, the temperature of precipitation reaction was 110℃, the reaction time was 2.0 h, and the calcination temperature was 600℃.The nickel-based catalysts such as Ni-Fe/γ-Al₂O₃, Ni-Co/γ-Al₂O₃, Ni-Ce/γ-Al₂O₃ were prepared by deposition-precipitation (DP) method, and XRD, FTIR and SEM were used to characterize the catalysts. For the purpose of testing and comparing the performance of the catalysts, the catalysts were used to pyrolyze and reforming tar in the product gas which is produced from catalytic gasification of municipal solid waste. The catalytic cracking and gasification experiments were carried out in a fixed bed reactor with municipal solid waste as raw material and using self-made nickel-based catalyst. The effects of catalyst, reactor temperature, steam to municipal solid waste ratio (S/M), particle size of municipal solid waste that influence the characteristics of gas production were discussed, and the yield and composition of the product gas were analyzed to determine the best catalytic gasification process conditions. The experimental results showed that the main component of product gas from MSW gasification were H₂, CO, CH₄ and CO₂, and the nickel-based catalyst could effectively promote tar cracking, improve the gas quality. The catalytic properties of the three kinds of nickel-based catalysts were: Ni-Fe/γ-Al₂O₃ > Ni-Ce/γ-Al₂O₃ > Ni-Co/γ-Al₂O₃, of which Ni-Fe/γ-Al₂O₃ catalyst could reach 99% tar removal rate at 800℃, and the maximum yield of H₂ 56%. The parametric tests indicated that temperature was the most important factor in this process, and higher temperature favored hydrogen production and gas yield. This experimental test has also confirmed that the introduction of steam to MSW gasification was favorable for improving gas quality and hydrogen yield. However, excessive steam would lower gasification temperature and so degrade product gas quality. Focusing on gas yield and quality as well as energy aspects, the optimal value of S/M was found to be 1.33 under the present operating condition. MSW particle size also had influence on gas composition and gas yield; the smaller particles were more favorable for gas quality and H2 yield. Meanwhile, catalytic cracking and gasification of MSW, steam reforming of hydrocarbons were discussed preliminarily, to explore the reaction mechanism of catalytic gasification of municipal solid waste to produce hydrogen-rich gas.