Research On Poisoning Mechanism Of SCR Catalyst In Power Plant

Air pollution caused by massive emissions of nitrogen oxides, has become the constraints of social and economic development, and attracts widespread attention of the whole society. In order to ensure the NOx emissions standards, coal-fired power plant as the main emission source of nitrogen oxides in China, already widely use the flue gas de-nitration technology. Among them, the selective catalytic reduction(SCR) is the mainstream technology of flue gas de-nitration technology in coal-fired power plant at home and abroad. SCR catalysts are the core of the flue gas de-nitration system in coal-fired power plant, and the main influencing factors of SCR system’s de-nitration efficiency and economic benefits. Poisoning is inevitable in the de-nitration process of SCR catalyst, it is closely related to the composition of flue gas. Thus, research on the catalyst poisoning mechanism in coal-fired power plant has important practical significance and economic value.The main work of this article is, taking the SCR catalysts of a certain power plant in Beijing as the research object, on the basis of the active track detection through a set of catalyst activity detecting device, we test characteristics, micro structure and chemical composition of the catalyst by some detection means, analyze the reason for catalyst deactivation, make an experimental study on catalyst poisoning main factors’ poisoning mechanism, we make a conclusion as follows:1.The congestion is the main reason for activity decline of SCR catalyst in the power plant. This is mainly due to the long running in flue gas, which has a higher dust content.2.As poisoning is also the important reason for reduction of catalyst activity in the very power plant. A small amount of As contained in coal will generate As2O3 at high temperature, As2O3 molecular is so small that it is easy to enter the catalyst pores, and block these pores, so that the active sites of the catalyst is covered, the flue gas can not reach the active sites to react, the catalyst activity is also decreased.3.The presence of K, Na and Ca is the main cause of catalyst poisoning to the power plant, they will be deposited on the surface of catalyst, plug some pores of the catalyst, and even can be united with some acid sites. This can reduce the effective contact area between catalyst and flue gas, available active sites is decreased. The final result is catalyst poisoning and lower catalytic activity.4.SO2 has two opposite effects on SCR catalysts: on the one hand, SO2 will compete active sites with NH3, decrease concentration of NH3,which can reach the active sites; on the other hand, SO2 can promote the formation of SO42- on the surface of the catalyst, strengthen the acidity of acidic sites on the catalyst’ surface, thus the activity of de-nitration catalyst is increased.5.H2 O has two kinds of effects on catalysts: on the one hand, H2 O can condense on the surface of the catalyst, the alkali soluble salt are more likely to stay on the surface of the catalyst, and then produce toxic effects on catalyst; On the other hand, the water vapor condenses in the catalyst micro-pores, they can make a damage on micro-porous structure of the catalyst after be heated.