| The removal of mercury pollutants from coal-fired power stations mainly focuses on three stages:before,during and after combustion.In comparison,the post-combustion flue gas mercury removal technology has good stability,high control efficiency and strong adjustability.At present,most ultra-low emission units in China use the existing air-pollutant control devices(APCDs)for coordinated mercury removal.The test results show that mercury emission can meet the requirements of China’s emission standards.However,in order to meet more stringent emission standards in the future,it is still necessary to apply specialized mercury removal technologies based on the existing collaborative control of APCDs.In this thesis,taking the 1000MW ultra-supercritical ultra-low emission#2 coal-fired unit of Xuzhou Power Plant of State Energy Group as an example,the modification of fly ash adsorption technology of mercury pollutants in flue gas is adopted to carry out special mercury removal technology transformation.The operation results show that the mercury emission can be effectively controlled by combining with the existing APCDs,and the goal of deep mercury removal can be achieved.The research results have demonstrative significance and important reference value for the application of modified fly ash mercury removal technology in practical engineering in the future.The main research work and conclusions are as follows.(1)Analyze and master the mercury removal mechanism of fly ash from coal burning,mechanically modify and chemically modify the fly ash from the ash hopper of electrostatic precipitator of power plant,improve the adsorption capacity,and prepare the adsorbent specially used for removing flue gas mercury.(2)Complete the synergistic mercury removal effect test of existing APCDs,and the results show that:Mercury concentration in flue gas at the entrance of denitration system was 19.78μg/Nm~3,that before air preheater was 18.56μg/Nm~3,that at the outlet of electrostatic precipitator was 9.92μg/Nm~3,and that at the outlet of desulfurization system(chimney entrance)was 2.89μg/Nm~3.The removal efficiency of mercury from flue gas by electric dust removal(ESP)is 46.55%,that by wet desulfurization(WFGD)is 70.87%,and that by SCR-WFGD is 85.39%.(3)Design and develop the modified fly ash injection system,which mainly includes the modification system and the conveying system.It can realize the quantitative,continuous and uniform transportation of fly ash sorbent,and the system output can be continuously adjustable to meet the requirements of different load conditions of coal-fired units.(4)Complete the online modification of adsorbent and special mercury removal modification by direct injection method,and conduct the flue gas mercury removal test for 1000MW ultra-supercritical coal-fired unit.The experimental results show that the combined action of APCDs and fly ash injection equipment in coal-fired power plant can effectively control mercury emission.After spraying modified fly ash,the removal efficiency of mercury by ESP and WFGD is 69.61%and 70.37%,respectively,and the additional mercury removal efficiencies are 33.12%and-0.71%,respectively.The total removal efficiency of mercury by SCR-WFGD is 91.84%,and the additional efficiency is 7.02%,and the mercury concentration at flue gas outlet is reduced from 2.89μg/Nm~3 to 1.52μg/m~3.There are 32 figures,12 tables and 105 references in this paper. |
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