Distribution Of Toxic Heavy-metal Elements In The Combustion Products Of Of Large-scale Coal-fired Power Plants In Shaanxi Province

Coal is a major source of energy in Shanxi Province.However,the combustion products of the coal-fired power plants with heavy-metal elements are harmful to environment and human health.The magnitude of the hazard is determined by the distribution of certain heavy-metal elements.Therefore,it is of great theoretical and practical importance to investigate the distribution of toxic heavy-metal elements in the combustion products of of large-scale coal-fired power plants in Shaanxi Province.In the present thesis,samples of raw coal and combustion products from coal-fired power plants with the installed capacity larger than 300 MW in Shaanxi Province are collected.The concentration of Mercury,Arsenic,Cadmium,Lead and Chromium in the raw coal,fly ash,slag,desulfurization gypsum,desulfurization wastewater and effluent from coal are determined by the measurements of microwave digestion,atomic fluorescence spectrometry,activated carbon adsorption and thermal cracking.The distribution of those heavy-metal elements in different combustion products is investigated.Moreover,the effects of different environmental treatments on the distributions as well as the influnces of different types of coal are analyzed.The main conclusions obtained in the present study include:(1)The enrichment of Mercury is not obvious in the slag but rather strong in the fly ash.The coal with higher ash content will increase the adsorption of Mercury as more condensation nuclei can be formed.Consequently,it will enhance the removal efficiency of Mercury by dust collector.(2)The environmental treatment process of SCR+WFGD+ESP has higher mercury removal efficiency than the process of SNCR+LIFAC+ESP.The one with highest removal efficiency of Mercury is the dust removal system,and followed by desulfurization system.The removal efficiency of Mercury by dust removal system is twice that of the desulfurization system.(3)The concentration of all heavy-metal elements in Shenmu coal is the lowest.The Lead content is the highest in Binchang coal,Huating coal and Hancheng coal.TheArsenic content is the highest in Hancheng coal.The Chromium content is the highest in Binchang coal and Hancheng coal.The Cadmium content in Hancheng coal is the highest.(4)The boiling temperature of Chromium and its compounds is higher than that of other heavy-metal elements,and is higher than the temperature of typical coal-fired boiler.Therefore,Chromium is more easily concentrated in the slag(or bottom ash).