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By coupling the heat transfer equation with semi-global chemical reaction kinetic equations, a onedimensional, unsteady mathematical model is developed to describe the pyrolysis of single biomass pellet in the pyrolysis zone of downdraft gasifier. The simulation results in inert atmosphere and pyrolysis zone agree well with the published experimental results. The pyrolysis of biomass pellets in pyrolysis zone is investigated, and the results show that the estimated convective heat transfer coefficient and emissivity coefficient are suitable. The mean pyrolysis time is 15.22%, shorter than that in inert atmosphere, and the pellet pyrolysis process in pyrolysis zone belongs to fast pyrolysis. Among the pyrolysis products, tar yield is the most, gas the second, and char the least. During pyrolysis, the temperature change near the center is contrary to that near the surface. Pyrolysis gradually moves inwards layer by layer. With the increase of pyrolysis temperature and pellet diameter, the total pyrolysis time, tar yield, char yield and gas yield change in different ways. The height of pyrolysis zone is calculated to be 1.51—3.51 times of the characteristic pellet diameter. 相似文献
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工程造价控制是工程建设管理的核心,由于全过程的造价控制贯穿整个项目建设周期,可以较好地实现投资、工期及质量控制目标的有机统一,已成为现代工程管理的重要方式.本文通过分析建设工程项目全过程的构成,针对工程造价全过程控制原则及控制措施进行探讨,以期通过本文的阐述提高建设项目投资控制水平,提高建设项目的经济效益和社会效益,最终促进我国社会主义市场经济的和谐发展. 相似文献
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