Construction And Application Of The Detection Method Of SO₃ In Coal-fired Power Plant Flue Gas After SCR Calalyst

With the Ministry of Environmental Protection attaching importance to energy-saving emission reduction. The state has issued the 《thermal power plant air pollutant emission standards》. known as the most stringent emission standards in history. With the improvement of coal fired power plant desulphurization facilities, the governance effect of SO2 is becoming more and more obvious, and now the nitrogen oxide is becoming the first acid gas pollution. During "the Twelfth five-year Plan", the nitrogen oxide emission has became the focus of environmental protection work, and the selective catalytic reduction method denitration technology （SCR） has been currently applied in coal-fired power plant flue gas denitration technology due to the characteristics of its high denitration efficiency and the mature technology. However, the existing SCR catalyst has some inevitable defects:high investment and operating expenses, the production of SO₃. and high design requirements. The harm of SO₃ formation and emission to the environment has gradually attracted people’s attention. SO₃ easily combines with water droplet in the flue and then causes corrosion problems, health problem and the reduction of boiler efficiency. However SO₃ is hard to be measured accurately, So it’s important to carry out research on high accuracy SO;, detection technology.In this paper, a method for the determination of the SO₃ is proposed. The accuracy and precision of the test method are studied. The flue gas after SCR catalyst is simulated and tested and the main results are as follows:（1） The measurement of SO₄^2- concentration in flue gas is using thorium barium complex spectrophotometry, the method of thoron dosage is 0.20 mL. BaCl2 using liquid dosage is 0.32 mL. the wavelength is 530 nm.The determination of absorbance should be completed within 50 minites after liquid putting in. SO4 standard curve equation is y=-0.0091x+0.9219. among them:y as the absorbance;x is the amount of SO42-, μg. R3 is 0.9995. the linear correlation is very significant.and the SO42- measuring range is 5～40 μg/mL. the detection limit of 4.44 μg/mL.The precision and accuracy can meet the requirements of environmental monitoring analysis.（2） In this paper I taked the catalyst samples of a company in Tianjin as an example, to detect SO₃ of flue gas by the spectrophotometric method on the power plant flue gas simulation device.The measurement results was on the high side.then through analysis of the reason I think the interference of the result is SO2 and NOx.The next step is to modifying SO42- standard curve and improving the sampling method.