Study On The Mercury Captured By Mechanochemical And Bromide Surface Modification Of Coal Fly Ash

China is rich in coal resources and coal-fired power generation accounts for about 70% of China's total.However,coal-fired power plants are deemed to be one of the main anthropogenic mercury pollution emission sources which can do great harm to production and living of human beings.Therefore,it is very urgent to carry out research on China's annual mercury emissions.Many research about the control of the mercury emission from coal-fired power plant showed that activated carbon injection technology is proved to be an efficient method.However,due to the high cost of activated carbon injection and not conductive to the utilization of the fly ash,the technonlogy is difficult to be widely adopted.In recent years,numerous studies show that fly ash adsorption on the removal of mercury has good effects.This article sumarized the adsorption theories and progress about fly ash.Based on these knowledge,this thesis proposes combining mechanochemical and bromide modified methods to improve the mercury adsorption performance.The fly ash was subjected to ball milling,i.e.,a mechanochemical modification method,and addition of bromide compounds.Adsorption experiments of this fly ash samples were conducted in the fixed-bed apparatus to evalute the mercucy adsorption capacity.In order to achieve this objective,Malvern laser particle size analyzer,scanning electron micrographs(SEMs),thermo gravimetric(TG)and ion chromatography(IC)analysis were employed to analysis the samples.This article shows that the fly ash samples have more improved significantly by mercury adsorption capacity through grinding and bromide modified.The results show that mercury capture capacity increased with increasing grinding time,up to 50 minutes,however it cannot be improved more with additional grinding beyond 50 minutes.Results from the mercury adsorption test show that the mechanochemical processing technique coupled with the addition of bromide compounds improves mercury adsorption performance for fly ash.Improvements in capture performance are contributed by both physical and chemical factors.Results show that increasing the grinding time produced smaller particles,higher surface area and more unburned carbon was exposed,which leads to better mercury adsorption.The temperature that produces highest oxidation of unburned carbon in fly ash decreases with increasing grinding time,suggesting the enhanced thermal activity of carbon in fly ash after the mechanical treatment.Analysis of bromine loading ratio shows that addition of bromide improves Hg~0 oxidation and capture capacity even at the low temperature.The first on-line modified fly ash unit has been installed on site for the 300 MW coal fired power plant in China as results of this study.