The Impact Of Ultra-low Emission Technology On Mercury Emission From Coal-fired Power Plant

Mercury is a persistent heavy metal pollutant that can be transmitted over long distances and lead to biological lesions.With the rapid economic development,China has become one of the largest global mercury emitters.On December 11,2015,the National Development and Reform Commission,the Ministry of Environmental Protection and the Energy Bureau jointly issued the document“Full implementation of the ultra-low emission and energy-saving retrofit program for coal-fired power plants”.By 2020,all coal-fired power plants with transformation conditions in China should strive to achieve the standard of ultra-low emissions?ie,the concentration of smoke,dust,sulfur dioxide,and nitrogen oxide should not be higher than 10,35,and50 mg/m³ at a reference oxygen content of 6%?.At this background,ultra-low emission reforms were implemented at all power plants.After the ultra-low emission reform,the operating conditions of pollution control devices have undergone major changes.In this paper,a field test of a coal-fired is unit taken to study the impact of Ultra-low Emission modification on the mercury emission characteristics of coal-fired units,through mercury removal efficiency of flue gas purification equipment to establish emission factors of various forms of mercury in coal-fired units,and estimating mercury emissions from coal-fired units.This article will provide a strong technical support for the reform of collaborative mercury pollution control for ultra-low-emissions from coal-fired units.Mercury is highly enriched in fly ash after combustion of coal at high temperature in the furnace.In the flue gas behind the boiler,the gaseous mercury mainly exists in the form of elemental mercury and oxidized mercury.When flue gas flows through the pollution control equipment,mutual transformation took place between the gaseous mercury.The test results showed that the oxidation rate of Hg⁰by the newly added SCR system in the reformation of Ultra-low Emission is 49.42%;Particular mercury can be effectively removed by ESP,and its was 19.57%;WFGD can remove oxidized mercury efficiently with the removal efficiency of 86.31%;WESP can further remove the remaining oxidized mercury and the removal efficiency was 34.12%.After Ultra-low Emission modification,the SCR+ESP+WFGD+WESP pollutant treatment system was formed.The total mercury removal efficiency was increased to 54.38%from 14.3%.After the Ultra-low Emission,the Hg⁰ accounted for92.96%of the total emission,Hg²⁺only accounted for 7.04%of the total emission.Therefore,in order to improve the mercury removal efficiency of the system,it is necessary to further convert Hg⁰,which is relatively difficult to remove,to relatively easy-to-handle Hg²⁺.According to the test results,the mercury emission factors of Hg⁰,Hg²⁺and Hg^P which are treated by SCR+ESP+WFGD+WESP combined pollutant control devices were 0.495,0.066 and 0,respectively,and the total mercury emission factor was0.456;By using the measured mercury emission factors,the average daily mercury emission of the test unit was 0.226kg,and the average annual mercury emission was0.083t.