Characterization Of Atmospheric Mercury Emissions From Coal-fired Power Plant And Cement Plant

Because of the bioaccumulation, neurological toxicity and high volatility of mercury, it's harmful to the global humans, especially children and pregnant women, and the United Nations Environment Programme (UNEP) called for signing the international instruments of limiting global atmospheric mercury emissions, moreover, it is expected to make into legal documents in the second half year of 2013. According to UNEP, the United States Environmental Protection Agency and foreign scholars, China is one big country of the global atmospheric mercury emissions, the main sources of atmospheric mercury emissions are coal-fired power plants, lead and zinc smelters, cement plants and so on, so China is facing great diplomatic pressure in mercury emissions. For this reason, a further research of the typical characteristics of atmospheric mercury emissions sources and emission rules, the precise understanding and mastering of atmospheric mercury emission detailed lists and emission rules, then guide the development of the mercury pollution control laws and regulations and control the emission of atmospheric mercury effectively. It is undoubtedly important in theoretical and practical.This paper chooses the 2 main types of units and four coal-fired cement plants, makes use of the U.S. EPA method 30B to test the characteristics of the flue gas mercury emissions, and collect and test the samples of coal, ash, slag and other solid. The main conclusions are as follows:1. The mercury of coal-fired power plants mainly come from the release by coal combustion, and almost 100% of mercury in coal released into the flue gas, the main destination is to the precipitator ash, gypsum, and stack emissions into the atmosphere, the main conclusions are as follows: a) A coal-fired generating unit is 300MW Pulverized to low nitrogen plus burners, flue gas purification equipment have selective catalytic reduction, electrostatic precipitators and limestone wet FGD system; During the testing period, the average mercury concentration of the coal-fired generating unit is 0.0484mg/kg, the total gaseous mercury concentrations in the flue gas were:before ESP is 4.73μg/m3, after ESP (before WFGD) is 4.31μg/m3, after WFGD is 2.45μg/m3. The concentration of atmospheric mercury emissions performance of A coal-fired generating unit is 3.8μg/Kwh.b) Test of mercury concentration in liquid, solid and gas samples of A coal-fired unit, combining with the working conditions during the test, the mass balance of the mercury reached 79.6%. Unit A draw material flow analysis of mercury:coal-fired take into 98.5% of the mercury, followed by desulfurization process water 1.2%, limestone 0.3%; 36.7% of the main destination of mercury is gypsum, bottom ash of ESP take away 25% of it,17.6% of the mercury emit into the atmosphere with the flue gas, waste slag and sulfur, respectively take away 0.1% and 0.2% of the mercury. With the ESP of A coal-fired unit, mercury efficiency of collaborative removal is 25%(emission factor is 75%), emission factor of selective catalytic reduction+ESP+wet FGD systems of gaseous mercury is 17.8%.c) B coal-fired unit is 300MW pulverized, flue gas purification equipment have ESP and wet FGD system. The first test period, the average mercury concentration of the coal is 0.103mg/kg, the total gaseous mercury concentration is 3.60μg/m3 after the WFGD, during the first test period, emission factors of gaseous mercury of ESP+wet FGD system is 21.7%. During the second test, the average mercury concentration in coal is 0.062mg/kg, total gaseous mercury concentration(in flue gas) is 3.06μg/m3 after WFGD, during the second test, emissions factor of gaseous mercury of flue gas purification equipment is 32.7%. The average emission factor of gaseous mercury of ESP+wet FGD system of B coal-fired unit is 27.2%.2. According to efficiency of this test of the coal-fired power plant flue gas purification equipment and mercury removal, and combining with the situation of our country's thermal power in 2008. According to the average mercury concentration of the coal is 0.19mg/kg, this paper estimate the mercury emissions of gas fired power plant in 2008 is 124.3 tons.3. The mercury of cement plant mainly come from coal combustion and the heat of raw material. Because the ingredients of coal combustion and raw materials of cement plants are different, mercury emission factors of each cement plant are different. The average mercury content in kiln ash of the four cement plants'dust bag is up to 8.33mg/kg in the test. It shows the bag filter remove large amount of mercury. The emission of gaseous mercury of cement production of cement plants with shaft kilns and bag filters is 3.6mg/t of cement, the gaseous mercury emission of 3 plants'cement unit production with rotary kilns and bag filters, respectively, is 3.3,12,8.7mg Hg/t cement, the average gaseous mercury emission of unit cement production of rotary kilns with bag filters is 8.0 mg Hg/t cement. 4. According to the development of cement plants in China, it estimates the current situation of our country's plants. With the emission factors of cement plants, it shows the mercury emission of China's cement plants is 20.6 tons in 2008.