| Municipal solid waste(MSW)is known as a misplaced resource and a never-ending urban mineral deposit.With the development of economy and large-scale urbanization,the production of urban MSW is increasing day by day.At present,the incineration-based MSW energy utilization treatment mode has been founded in large and medium-sized cities in China,but the MSW treatment mode in some remote plateau low-oxygen areas in China is still immature,and the treatment mode in large and medium-sized cities is difficult to copy directly,which is due to the special geographical environment and living habits in the plateau low-oxygen areas,resulting in the unclear characteristics of MSW emissions,and it is difficult to effectively explore the MSW energy utilization and treatment mode.This not only causes a large amount of resource loss,but also poses a great threat to the fragile ecological environment of the plateau region.Therefore,this paper takes Lhasa as an example to clarify the emission characteristics of MSW in the plateau low-oxygen region,analyze its energy distribution,and explore the energy conversion pattern of MSW in the plateau low-oxygen environment.In this thesis,the daily per capita waste production method was used to estimate the MSW emissions in each district and county of Lhasa city,analyze the physical composition and chemical properties of MSW in each district and county,and study the weight loss characteristics of MSW by using thermogravimetric analysis.The potential energy distribution of MSW in Lhasa was evaluated by analyzing the emission,physicochemical properties and other characteristics of MSW in Lhasa,and the energy distribution spectrum was plotted.The thermal transformation characteristics of typical components of MSW in the low oxygen environment of plateau were explored and compared with the transformation law of MSW in plain areas,which provided a theoretical basis for the energy utilization of MSW in the low oxygen area of plateau.The study shows that:(1)Municipal waste emissions in Lhasa are small and scattered,relatively concentrated in localised areas and high in organic matter.The physical composition of MSW discharged in urban areas is complex,while the composition in suburban counties is more homogeneous and mainly consists of food waste.The moisture content of food waste in urban areas is about70-85%,which is significantly higher than that of 45-55%in suburban areas,while the moisture content of other MSW components is generally lower to about 15%,which is conducive to energy utilization.The thermal weight loss of typical components of MSW,such as paper,wood,textile and plastic,is mainly concentrated in the range of 300-600℃,with the largest weight loss rate in the range of 370-450℃,and the weight loss process is basically completed when the temperature reaches 650℃.(2)The distribution of total potential energy and potential energy per unit area of MSW in Lhasa showed a decreasing pattern from the central urban area to the suburban areas.The theoretical and actual values of total potential energy in urban areas are 1.2×10~8-2.08×10~9MJ and 1.48×10~8-2.57×10~9MJ,respectively,with the largest value in Chengguan District,where the theoretical and measured values are above 2.0×10~9MJ,while the theoretical and measured values of total MSW potential energy in suburban counties are 6.95×10~7-1.37×10~8MJ and1.13×10~8-2.01×10~8MJ,respectively.The theoretical and measured values of potential energy per unit area in urban areas are 87.7-3981 k J/m~2and 108-4458 k J/m~2,respectively,while the measured and theoretical values in most of the outer suburban areas(except Qushui County)are lower than 50 k J/m~2.Compared with the theoretical and measured values of mass energy per unit of dry basis,the theoretical and measured values of mass energy per unit of wet basis in urban areas decreased by 7000-9000 k J/kg and 7000-10000 k J/kg,respectively,and in suburban counties decreased by 4000-6000 k J/kg and 6000-8000 k J/kg,respectively.(3)The energy conversion to pyrolysis gas was 88%,61%,83%,100%and 93%for paper,wood,textile,plastic and simulated actual MSW,respectively,after pyrolysis at 650℃,plus a small amount of energy conversion to pyrolysis oil and residue state.The energy conversion rate to gasification gas and direct use of paper,wood,textile,plastic and simulated actual MSW,after gasification and incineration at 450℃in the low oxygen region of the plateau,were 90%,72%,78%,100%,88%and 90%,78%,85%,100%,92%,respectively,compared with 5%-10%lower than those in the plains.The results of regional distribution of energy conversion of MSW in Lhasa show that the conversion rate of energy conversion of MSW to gasification gas after gasification at 450℃in areas other than Mozhugongka County can reach more than 90%,and the utilization rate of energy release after incineration at450℃in all areas can reach more than 90%.Among them,the gasification gas produced by the gasification process needs to be used twice,but the amount of air required through incineration is large and the heat loss is large,so the MSW in the low oxygen environment of the plateau is suitable for treatment of MSW by gasification-assisted secondary air inlet incineration at 450℃. |
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