Strategies of Coping with Deactivation of NH3-SCR Catalysts Due to Biomass Firing

Abstract

Firing of biomass can lead to rapid deactivation of the vanadia-based NH3-SCR catalyst, which reduces NOx to harmless N2. The deactivation is mostly due to the high potassium content in biomasses, which results in submicron aerosols containing mostly KCl and K2SO4. The main mode of deactivation is neutralization of the catalyst’s acid sites. Four ways of dealing with high potassium contents were identified: (1) potassium removal by adsorption, (2) tail-end placement of the SCR unit, (3) coating SCR monoliths with a protective layer, and (4) intrinsically potassium tolerant catalysts. Addition of alumino silicates, often in the form of coal fly ash, is an industrially proven method of removing K aerosols from flue gases. Tail-end placement of the SCR unit was also reported to result in acceptable catalyst stability; however, flue-gas reheating after the flue gas desulfurization is, at present, unavoidable due to the lack of sulfur and water tolerant low temperature catalysts. Coating the shaped catalysts with thin layers of, e.g., MgO or sepiolite reduces the K uptake by hindering the diffusion of K+ into the catalyst pore system. Intrinsically potassium tolerant catalysts typically contain a high number of acid sites. This can be achieved by, e.g., using zeolites as support, replacing WO3 with heteropoly acids, and by preparing highly loaded, high surface area, very active V2O5/TiO2 catalyst using a special sol-gel method.

Strategy and Technical Progress of Recycling of Spent Vanadium–Titanium-Based Selective Catalytic Reduction Catalysts

“…Globally, fossil fuels, such as natural gas, oil, and coal, are the primary energy source required by national industries. Nitrogen oxides (NO x ) emitted in significant quantities during the combustion of fossil fuels cause environmental pollution such as acid rain, the greenhouse effect, and photochemical smog and even harm human health. − Figure (a) is a schematic diagram of the different pathways of NO x pollution in the environmental system . Coal-fired power plants are considered one of the significant sources of anthropogenic NO x emissions to the atmosphere. , China is a sizable coal-consuming country.…”

Combined Effect of a Catalytic Reduction Device with Waste Frying Oil-Based Biodiesel on NOx Emissions of Diesel Engines

“…To address this challenge, Sala et al, 2017 [23] in an experiment preheated and evaporated the urea solution before injecting it into the engine exhaust gas. In addition, while using biodiesel with SCR technology, because of the high concentration of impurities (potassium in the biodiesel), the catalyst [mostly V 2 O 5 -WO 3 /TiO 2 (VWT) vanadium/titanium-based] has been observed to be deactivated due to the neutralization of the catalyst's acid sites by the high basicity content of the potassium, thus decreasing the adsorption of NH 3 (Kröcher, 2018 [22]; Schill and Fehrmann, 2018 [24]). Several studies have considered using SCR technology alongside biodiesel blends to further investigate and reduce the NO x emission from diesel engines.…”

Selective Catalytic Reduction of NOx

“…To this end, Sala et al have developed an automated sampling and analysis system to probe the NO x and NH 3 concentration profiles of a passenger car SCR catalytic converter indirectly from the downstream side of the converter [2].Regarding stationary SCR applications, firing of biomass is a special challenge due to the high concentration of impurities and particularly potassium contained in this type of fuel, deactivating the used vanadia-titania-based catalysts. Schill and Fehrmann reviewed different strategies for SCR systems to cope with the high potassium loading from biomass with a focus on intrinsically potassium-resistant SCR catalysts [3]. Such catalysts can be prepared by coating vanadia-titania systems with thin protective layers of, for example, magnesia or sepiolite, using zeolites as support, replacing tungsta with heteropoly acids, and preparation methods to achieve unusual high surface areas.Zhao, Mao, and Dong have worked on ways to improve vanadia-titania systems and achieved good low-temperature activity combined with water and sulfur tolerance, when adding manganesia and ceria [4].…”

“…Regarding stationary SCR applications, firing of biomass is a special challenge due to the high concentration of impurities and particularly potassium contained in this type of fuel, deactivating the used vanadia-titania-based catalysts. Schill and Fehrmann reviewed different strategies for SCR systems to cope with the high potassium loading from biomass with a focus on intrinsically potassium-resistant SCR catalysts [3]. Such catalysts can be prepared by coating vanadia-titania systems with thin protective layers of, for example, magnesia or sepiolite, using zeolites as support, replacing tungsta with heteropoly acids, and preparation methods to achieve unusual high surface areas.…”