The Formation Mechanism And Regulation Of Hydrogen Sulfate In The Process Of The SCR Denitration

In order to control NO_x emission, the thermal power plant air pollutants emission standards?GB132323-2011? shows that control of NO_x emissions in coal-fired power plants is 100 mg/m3. Through NH₃ or urea as the reducing agent of selective catalytic reduction?SCR? is one of the most effective technology to reduce nitrogen oxides. V₂O₅ content in the commercial SCR catalyst is usually in 0⁴%. Because in the process of flue gas denitration, V₂O₅ catalysts react in the catalytic reduction of NO_x and at the same time, also make part of SO₂?0.75%¹.5%? in flue gas oxidation into SO₃, which reacts with SCR denitration process incomplete reaction of ammonia in a certain condition to produce ammonium bisulfate?ABS?, ABS can deposit on the surface of the catalyst and the downstream equipment and pipeline of the SCR reactor to cause clogging, corrosion and resistance rising. But because it is difficult to research the formation of ABS, currently, there is little discussion of the formation mechanism, the factors influencing the formation of ABS is also a lack of domestic detailed understanding, because of the obstacle in knowledge and technical barriers of foreign denitration companies, many electric power enterprises blindly implement air preheaters, and catalyst premature deactivation happens repeatedly, and denitration efficiency declines etc., which bring huge economic losses, and affect the electric power enterprises to promote energy saving and emission reduction. Especially due to the NO_x control is gradually severe, SCR often run at low load conditions, while the minimum operating te mperature of SCR depends on the dew point of ABS, so it is very important to explore th e formation law and dew point of ABS.In this paper, on the basis of studying the formation mechanism of ABS, utilize ABS formation test-bed designed by ourselves to research on the rules of the formation of ABS, it is concluded that the formation of ABS is a function of temperature and concentration. The formation temperature range of ABS is between 220 and 261 ?, the specific formation temperature is related to the concentrations of NH3 and H₂SO₄. The greater concentration of the product, the higher the formation temperature of ABS. About the reaction features between ABS and air preheater of fly ash, characterization results show that the particle size increased obviously. It turns out that the morphology characteristics of fly ash appears to change after they are ABS-doped. Test results show that in ABS-doped samples, Fe₂?SO₄?₃ and Na₂SO₄ are detected in addition to the original mineral phases in the original fly ash samples. Specific resistance test result shows that ABS-doping will reduce the resistivity of fly ash and enhance the ability of electrical precipitator to capture fly ash. XPS analysis shows that Na₂O in the fly ash reacts with ABS to form Na₂SO₄ in ABS-doped samples. Through analyzing the corrosion rate by static weight loss experiment and by using potentiodynamic polarization curve, the conclusions can been gotten as follows: the corrosion process of carbon steel and stainless steel respectively in different concentrations of ABS and sulfuric acid solution was similar, which indicates that ABS has the characteristics of acid and highly corrosive, and its corrosion mechanism is similar to sulfur ic acid. The element compositions and their combined-state of surface corrosion product film of carbon steel and stainless steel are analyzed through the methods of SEM/EDS and XPS, which have been soaked in the two concentrations solution of ABS for two months, finally it is determined that the types of corrosion products are Fe₂O₃, FeOOH, Fe₃O₄, iron sulfate, etc.In conclusion, this paper studies the prevention and control of ABS generated in coal-fired power plant, relieving the problem of air preheater clogging due to ABS deposition in denitration units, which has important theoretical significance and application value to ensure that the stable operation of denitration units, improve the operation rate of denitration facilities, reduce acid rain and emissions of fog precursor.