| China’s coal-fired power stations have been fully upgraded with ultra-low emissions,and sulfur dioxide,nitrogen oxide and soot have been significantly reduced.The change rules,emission characteristics and control of unconventional pollutant such as SO3 Hg and As under ultra-low emission conditions have become hot research hotspot in the field of air pollutant control.Based on the typical ultralow emission coal-fired power station,the test of SO3,Hg and As in flue gas have been carried out,and the migration characteristics and the collaborative removal of SO3,Hg and As have been investigated.The emissions of SO3,Hg and As have been estimated.The method 8 released by U.S.Environmental Protection Agency(USEPA)was used for sampling and measuring the sulfur trioxide concentrations in flue gas,fly ash and bottom ash.The conclusions are as follows:(1)SO3 accounted for 0.46%of total sulfur dioxide in the flue gas before selective catalytic reduction(SCR)and the SO2-to-SO3 conversion rate in the SCR is 0.58%.The concentration of gaseous SO3 is significantly reduced,and gaseous SO3 is converted to 74.33%into ash as flue gas through the air preheater.(2)The particulate SO3 was removed in low temperature electrostatic precipitator(LT-ESP).The content of sulfur trioxide in fine ash is 1.38 times of that in coarse ash.The total removal efficiency of SO3 by ultra-low emission pollutants control devices is 48.45%.and the atmospheric emission concentration of SO3 is 1.5 mg/Nm3.(2)The SO3 coal-specific emission factor is 17.13 mg/kg and the electricity-specific emission factor is 4.41 mg/kW.h in the ULE power plant.Based on the test data,the SO3 emitted to the atmosphere from the 660MW coal-fired power station is 11.77t/a.The total SO3 emitted to the atmosphere from coal-fired power stations in China was estimated to be 48,100 tons in 2021.The comparative test of Hg detection methods was carried out,the data from 30B were consistent with the Hg-CEMS test data,and the test results of Hg concentration of OH method were lower than 30B.The modified activated carbon adsorption tube based on 30B is developed.The technical indexes such as breakthrough test and analytical bias meet the requirements of USEPA 30B.The USEPA 30B and OH method were used for sampling and measuring Hg in coal,flue gas,fly ash and bottom ash gypsum and wastewater from ultra-low emission coal-fired power stations.The conclusions are as follows:(1)Mercury is the form of Hg0 before SCR in the flue gas of 660MW ultra-low emission F coal-fired power station.About 20.98%Hg0 are oxidized in flue gas out of SCR.Total Hg removal of the LT-ESP is 84.4%and the concentration of Hg0 and Hg2+ in the outlet flue gas is the lowest,when the outlet flue gas temperature of the low temperature economizer is 90℃.(2)Hg content of fuel coal in coal-fired power stations of 20 provinces and autonomous regions have been analyzed,and the average value is 88.54μg/kg,which is lower than the average Hg content in coal of China.Testing Six typical ultra-low emission coal-fired power stations,The mercury removal rate is between 75.45～99.67%.The mercury emitted to atmosphere is between 0.82～0.95μg/Nm3.(3)The Hg coal-specific emission factor is 1.42～9.79μg/kg,and the electricity-specific emission factor is 0.49～3.30μg/kW.h form six ultra-low emission coal-fired power stations.The total Hg emitted to the atmosphere from coal-fired power stations in China was estimated to be 4.27 tons in 2021.After the ultra-low emission transformation of A coal-fired power station,the emission factor of Hg has been significantly reduced by more than 70%.The method 29 released by USEPA was used for sampling and measuring the As concentrations in coal,flue gas,fly ash and bottom ash gypsum and wastewater from the 300MW ultra-low emission coal-fired power station.The conclusions are as follows:(1)The volatile ratio of Arsenic after combustion is 99.01%,most of As remain in ash during coal combustion.Particulate As in flue gas reaches 99.98%out of SCR,and most of particulate As was removed in LT-ESP.The removal rate is LT-ESP>WFGD>SCR,99.94%,75.44%,5.15%,respectively.The Ultra-low emission pollutants control devices reduced the atmospheric emission of As.The As emitted to atmosphere is 0.28μg/Nm3.(2)According to the test data,The As coal-specific emission factor is 2.24μg/kg,and the electricity-specific emission factor is 0.79μg/kW.h form the 300MW coal-fired power station and the As atmospheric emission in 2021 is 1.06kg/a.The total As emitted to the atmosphere from coal-fired power stations in China was estimated to be 482.80 kg in 2021. |
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