| With the development of human modern society,energy demand has gradually increased,pollution caused by coal-fired power generation has become more and more serious,and the harm of heavy metal pollution has gradually emerged.At present,man-made mercury pollution has existed in the ecological cycle for a long time,directly causing damage to the ecology and the human body.As the largest mercury emission source,coal-fired power plants have invested in many commercial low-mercury emission equipment and coordinated control systems in recent years.Among them,the fly ash flue injection mercury removal system has the most excellent effect.Bromination coupled mechanically modified fly ash adsorbent has both high specific surface area and bromination characteristics.After modifying the original fly ash in situ,it is injected into the flue to absorb most of the mercury in the flue gas,which is highly efficient,cheap and easy to obtain make it have unlimited application prospects.Coal-fired fly ash is widely used in building materials and other fields.For fly ash that has adsorbed mercury,it is not clear what the secondary release characteristics of the enriched mercury are.Therefore,it is imminent and far-reaching to understand the secondary release mechanism and form of mercury adsorption by fly ash,and how to limit the secondary release of mercury if the release is obvious.In this thesis,fly ash is used as the main adsorbent,three laboratory modification methods including brominated coupling mechanical modification are selected to modify it,and commercial granular activated carbon with high efficiency adsorption is selected for comparison.The adsorption experiment was carried out in a fixed bed mercury adsorption system at room temperature to compare and analyze the adsorption effects of various adsorbents;then the desorption experiment was carried out at different temperatures to study the effect of mercury in the adsorbent in the secondary thermal processing environment of fly ash.Release and thermal stability;through the improved BCR continuous extraction experiment,the water environment desorption experiment was carried out on the adsorbent,and the secondary release of different forms of mercury and the adsorption stability of the water environment were studied.In addition,this thesis uses SEM,XPS and other equipment to characterize the fly ash samples and discuss the adsorption-desorption mechanism in order to improve the adsorption stability of the modified fly ash.Studies have shown that after the fixed bed mercury adsorption experiment,the bromination coupled ball milling modified fly ash showed an excellent instantaneous adsorption effect,which is very suitable for the flue injection mercury removal system of power plants,thanks to the combination of bromination and ball mill The modification method.Compared with other modification methods,the bromination coupling ball milling modification improves the physical and chemical adsorption performance of fly ash,and has a stronger mercury capture ability.After adsorption,it can also be directly collected by a dust collector for secondary use.Under higher temperature conditions,the release of mercury will increase as the temperature rises.In the temperature range of 150-350 ℃,the mercury in the fly ash adsorbent escapes faster,until it is completely released at 800℃.In the case of long-term heating at low temperature and storage at room temperature,fly ash mercury has a very small amount of release,and the fixing effect is ideal.Therefore,the use of fly ash in road paving and mine backfilling is difficult to cause secondary mercury pollution.In the improved BCR continuous extraction experiment,the mercury in the adsorbent is not easy to escape in water and weak acid environment,and oxidation and reduction extraction are likely to cause the secondary release of mercury. |
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