It is also important to pay attention to the stability when choosing denitrification catalysts, while the characteristics of different chemical agents are different, such as physical properties, hot spots, melting points, electrical conductivity, etc., are different, and for chemical properties, they are also different.

The coal used in China's thermal power plants is constrained by China's coal resources and fuel supply policies, and the quality of coal combustion is usually poor, and the content of harmful impurities such as ash and sulfur in coal combustion is generally high. Therefore, alkali metals, alkaline earth metals and arsenic in the fuel when using SCR denitration catalyst, as well as water vapor, fly ash, sulfur and ammonium sulfide produced after combustion all have an impact on the use of denitration catalyst. These components enter the active point of denitration catalyst by diffusion and occupy the active point of denitration catalyst, and the denitration catalyst will be gradually passivated, and the activity of denitration catalyst decreases with the operation time. NOx reduction efficiency decreases, ammonia consumption increases, ammonia escape increases, and SCR denitrification system operation cost will rise due to the influence of harmful elements.
1 Influence of alkali metals

The contact between alkali metal and denitration catalyst surface will reduce the activity of denitration catalyst. The deposition of alkali metals on the denitration catalyst results in a much less acidic denitration catalyst surface and a stronger K neutralization effect for the same molar concentration of K compared to Na. K preferentially coordinates to either the OH root on the or, K20 is generated with the reaction and K interferes with the formation of NH4+, the ammonia active intermediate species, resulting in passivation of the denitration catalyst. Avoiding the condensation of water vapor on the surface of denitration catalyst reduces the effect on denitration catalyst activity due to the accumulation of alkali metals on the surface of denitration catalyst.

2 Effect of alkaline earth metals

The poisoning of denitration catalyst by alkaline earth metals is mainly caused by the reaction generation of free CaO in fly ash and adsorbed on the surface of denitration catalyst, which causes scaling on the surface of denitration catalyst and can obscure the surface of denitration catalyst, thus preventing the diffusion of reactants into the denitration catalyst. By appropriately increasing the blowing frequency, the deposition of fly ash on the denitration catalyst can be reduced, and reducing the deposition of CaO on the surface of the denitration catalyst is an effective means to slow down the poisoning of the denitration catalyst

3 Effect of arsenic

Arsenic (As) originates from coal and is present in the flue gas in volatile form dispersed into the denitration catalyst and solidified in the active and inactive regions, and also adsorbed on the fly ash particles (in the form of oxides). The process of arsenic poisoning will result in restricted diffusion of the reactant gas within the denitration catalyst and disruption of the channels. As poisoning of the denitrification catalyst, especially in the liquid slagging furnace and fly ash recirculation processes, can lead to enrichment of arsenic in the recirculation process. In the form of oxide as an example, its poisoning effect is attributed to its alkalinity. It leads to the substitution of OH roots by As-OH (arsenate distributed on the surface). The arsenic poisoning of denitrification catalysts results in a reduction of denitrification catalyst activity as ammonia is not readily adsorbed to the active sites of the poisoned denitrification catalysts.

The denitrification catalyst surface can be made inactive to arsenic during use, and the purpose of adsorption protection can be achieved by controlling the acidity of the denitrification catalyst surface so that the surface of the denitrification catalyst does not adsorb arsenic oxide; another method is to improve the active site and obtain a stable denitrification catalyst surface by high temperature calcination, mainly in the form of mixed oxides of vanadium and molybdenum, so that the location of As adsorption does not affect the active site of SCR

Anhui Yuanchen Environmental Technology Co., Ltd ("Yuanchen Technology") is a high-tech enterprise integrating R&D, production and sales of dust removal bags and denitrification catalysts. The dust bags (mainly PPS, PTFE, P84 and composite series filter materials) and SCR denitrification catalysts have been widely used in cement, steel, glass kilns, waste incineration power generation, biomass power generation, non-ferrous metal smelting and other industries. In the future, Yuanchen Technology will be guided by "becoming the guardian of global ecological environment", always rooted in environmental protection, and insist on the great cause of guarding the blue sky and white clouds. Leveraging on the national ecological civilization construction pattern, we will continue to deepen technology, optimize management, strengthen brand, refine industry, solidify advantages, and create synergistic value for industry through comprehensive and integrated governance and services. http://www.yckjgf.com/