Abstract
Nitrogen dioxide is one of the most dangerous air pollutants, because its high concentration in air can be directly harmful to human health. It is also responsible for photochemical smog and acid rains. One of the most commonly used techniques to tackle this problem in large combustion plants is selective catalytic reduction (SCR). Commercial SCR installations are often equipped with a V2O5−WO3/TiO2 catalyst. In power plants which utilize a solid fuel boiler, catalysts are exposed to unfavorable conditions. In the paper, factors responsible for deactivation of such a catalyst are comprehensively reviewed where different types of deactivation mechanism, like mechanical, chemical or thermal mechanisms, are separately described. The paper presents the impact of sulfur trioxide and ammonia slip on the catalyst deactivation as well as the problem of ammonium bisulfate formation. The latter is one of the crucial factors influencing the loss of catalytic activity. The majority of issues with fast catalyst deactivation occur when the catalyst work in off-design conditions, in particular in too high or too low temperatures.
Highlights
Fossil fuel power plants are subjected to increasingly rigorous NOx emission limits
Power plant operators may consider closing NH3 injection if the actual temperature of the flue gas is lower than the minimum safe temperature, as operating the selective catalytic reduction (SCR) reactor below the ammonium bisulfates (ABS) dew point can be seriously damaging for catalyst activity
According to Khutan et al [113], temperature of the transition can be decreased by vanadium doping, which might be unfavorable for SCR catalysts containing both anatase TiO2 and V2 O5
Summary
Fossil fuel power plants are subjected to increasingly rigorous NOx emission limits. In Europe there are still plenty of coal-fired power generation units that produce significant amounts of nitrogen oxides. 85, 100 and 150 mg/Nm3 [1] These limits favor utilization of SCR technology for medium and large existing units, as well as for all newly built ones. According to Zheng et al [3], the rate of deactivation of V2 O5 −WO3 /TiO2 catalyst installed on a straw-fired boiler can be as high as. There are two main factors that are responsible for SCR catalyst deactivation—flue gas physical parameters and flue gas composition. The former is derived from various process parameters, boiler construction, as well as boiler load. This paper gives detailed overview of the commercial V2 O5 −WO3 /TiO2 catalysts used in DeNOx process in industrial boilers, with focus on the mechanisms of its deactivation. The authors describe the effect of boiler operation conditions on the overall catalyst performance
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