| Waste incineration technology is the mainstream urban domestic waste treatment method.The secondary pollution caused by waste incineration,especially the discharge of persistent toxic substances,has attracted great attention.In this paper,the domestic garbage in Lhasa was used as the experimental raw material,and the physical and chemical analysis and the analysis of heavy metal elements were carried out according to the standard provisions of"Sampling and Physical Analysis Method of Urban Domestic Waste"（CJ/T313-2009）through the pretreatment of samples and the preparation of experimental samples.Field investigation was carried out on the domestic waste incineration power plant in Lhasa,and samples of fly ash,slag and flue gas were collected,and heavy metal content was analyzed.Finally,combined with the heavy metal content in the flue gas,the composition of flue gas and the distribution characteristics of heavy metals in the incineration plant were simulated using the Computational Fluid Dynamics（CFD）simulation software Fluent.The main research contents and conclusions are as follows:（1）The physical components of domestic waste in Lhasa vary greatly in different functional areas,and the physical components are mainly paper,plastic rubber,plants,ash and slag.Plant waste mainly exists in the commercial area（39.74%）,metal waste mainly exists in the mixed area（15.19%）,glass waste mainly exists in the mixed area（13.29%）,plastic（rubber）waste in each functional area The proportion is very large,and waste paper waste mainly exists in the business area（23.72%）.Among them,the proportion of paper,plastic rubber,glass and metal components is generally higher than that of inland cities.（2）The moisture content and calorific value of domestic waste in Lhasa urban area are significantly different with different functional areas.The ash content of the end-mixing area of domestic waste（landfill）in Lhasa is between 12.43%and 54.30%.After calculation,the ash content of each functional area is between 8.92%and 46.00%.The ash value is closely related to the composition（inorganic matter content）of domestic waste.（3）The calorific value of domestic waste varies greatly in each functional area,and the calorific value of waste is expressed as special area>business area>cleaning area>residential area>commercial area.The domestic waste in Lhasa has reached the calorific value limit of 5000 k J/kg required for incineration,which is suitable for incineration treatment.（4）The concentrations of heavy metals Cu,Pb,Cr,Hg and Cd in Lhasa municipal solid waste were 13.551 mg/kg,6.761 mg/kg,163.038mg/kg,0.008 mg/kg and 2.234 mg/kg,respectively.Compared with inland cities,the heavy metal content of domestic waste in Lhasa is relatively low,and the risk of regional environmental pollution is relatively small.In general,the garbage in Lhasa is mainly composed of paper,plastic,rubber,animals and plants,and heavy metals have relatively little environmental pollution.（5）Through the detection of heavy metals in the flue gas of domestic waste incineration,the results show that the content of Hg in the flue gas of domestic waste incineration in Lhasa in 2020 is 2.31×10-2 mg/m~3,and neither Pb nor Cd is detected;the content of Pb in 2021 is 5×10-2mg/m~3,the content of Hg is 2.5×10-2 mg/m~3,and the concentration of other heavy metal elements is extremely low.In contrast,the content of Hg is extremely high,but it does not exceed the emission limit of the"Standard for Pollution Control of Domestic Waste Incineration"（GB18485-2014）,and the toxicity and pollution of Pb are far less harmful to human health and the surrounding environment than Hg.The Hg content was large and stable for two consecutive years from 2020 to 2021.The content of heavy metals in the slag produced by the Lhasa waste incineration power plant is very low.Studies have shown that:the dust,glass,ceramics,metals and other toxic and harmful substances in the domestic waste contribute to the content of barium,copper,zinc and lead in the slag.In particular,the content of barium and zinc elements exceeds the national average;plastic waste incineration contributes greatly to the content of nickel and chromium in the slag;while the content of these elements in the slag of the Lhasa waste incineration plant is very low,which should be This is because there is currently no large-scale industrial and mining industry in Tibet.（6）Through the CFD fluid dynamics simulation technology,combined with the mathematical and physical model,modeling and simulation of the actual operation of the plateau waste incineration flue gas emission characteristics distribution.Under normal combustion conditions,the combustion temperature is above 850℃,and the exhaust gas temperature of the waste heat boiler is 190℃～210℃.The flue gas discharge temperature does not change much in the chimney,combined with the small change in the water vapor emission in the chimney,it can be concluded that because the chimney itself has a thermal insulation effect,the flue gas discharge temperature at the chimney discharge outlet is not much different from that in the chimney;but in the same The temperature above the flue gas on the isosurface of the longitudinal section is much greater than that below.There is no obvious change in the water vapor content on the same longitudinal isosurface at the flue gas discharge outlet,but the water vapor content on the same horizontal isosurface changes greatly,probably because the flue gas temperature varies with the outside temperature at a distance of 150m from the chimney discharge outlet.drop,so that part of the water vapor liquefies into water droplets and falls,resulting in a decrease in the water vapor content.Large-sized particles and smaller-sized particles are more likely to settle due to the action of gravity;only large-sized particles fall at a distance of 80m from the flue gas discharge outlet.Some large-sized particles have a downward trend at 20m from the chimney,which may be delayed due to the external wind speed and the internal impact force of the chimney.Due to its large molecular weight and strong gas convection,mercury emissions diffuse with the flow trend of wind speed and air volume.It is easy to draw from the mercury isosurface velocity vector diagram and the content map that the velocity and content of mercury are the largest in the chimney or near the chimney,which deserves the most attention. |
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