Influence Of Ca-Based Compounds On SCR Activity Of V₂O₅-WO₃/TiO₂ Catalyst

Nitrogen oxides ?NOX?, one of the major air pollutants, is heavily harmful to the human health, agricultural production and natural ecological environment. Government has launchedNO_x emission reduction plan since 2010. NO_x mainly comes from the coal-fired combustion, which accounts for about 60% of the total emission. In recent years, NO_x emission from biomass-fired boiler increase continually. Selective catalytic reduction ?SCR? of NOX by NH₃ with V₂O₅/TiO₂ as the basic catalyst has been widely used in industry due to its high activity and N₂ selectivity. Since the usual operating temperature is around 400 ? to prevent the deactivation caused by the deposited sulfur ammonium salt, vanadium titanium based catalyst bed is usually placed before the filter, which causes the catalyst runs under the condition of high temperature and high ash. Hence, blocking, washing and chemical etching of the catalyst caused by the dust is inevitable. The data indicates the flue gas including alkali, alkaline earth metals, phosphorus and arsenic may lead to catalyst deactivation due to poisoning. In order to alleviate catalyst poisoning, improve the catalytic performance and prolong its service life, it's necessary to know the poisoning mechanism of different dust. In view of current research on mechanism of alkaline earth metal poisoning is less at home and abroad, especially lacking the influence of SO₂, CO₂ and water vapor on the alkaline earth metal poisoning, this article chose CaCl₂, CaCO₃ and CaO as alkaline earth metal representatives to do some detailed study in this aspect. In addition, this paper also compared the differences between impregnation method ?marked Imp? and solid diffusion method ?marked Dif? to simulate actual operation situation of the SCR catalyst.The main conclusions are drawn as follows:1. When CaCl₂/V is increasing, the NO_x removal efficiency of SCR catalyst appears a decreasing trend, because CaCl₂ can reduce the oxidation ability and surface acidity of the catalyst; The smaller the poisoning components, the deeper the poisoning degree.2. With the same Ca/V, the poisoning degree of two methods is:diffusion menthod> impregnation menthod. The two poisoning methods lead to different CaCl₂ distribution levels wahile diffusion poisoningcatalyst has obvious agglomeration.3. With the same Ca/V, the poisoning degree of three different components is as follows:CaCl₂> CaCO₃> CaO, the components ?CaCl₂, CaCO₃ and CaO? all can weaken the surface acidity, while the interaction between Cl- and V causes the losses of the active component.4. Both CO₂ and SO₂ can improve the efficiency of the SCR catalyst by strengthening the surface acidity and increasing the content of active oxygen. To some extent, the exist of Ca can weaken the effect of CO₂.