Effect of Selective Catalytic Reduction System on Fine Particle Emission Characteristics

Abstract

Based on commercial catalysts (V 2 O 5 −WO 3 /TiO 2 ), the effects of a selective catalytic reduction (SCR) system on the emission characteristics of fine particles were investigated. The size distribution, morphology, element compositions, and chemical compositions of fine particles at the outlet of the SCR system were measured by an electrical low pressure impactor (ELPI), particulate matter (PM 10 /PM 2.5 ) samplers, field emission scanning electron microscopy/energy dispersive spectrometry (FSEM−EDS), X-ray diffraction (XRD), etc. The influences of reaction conditions and flue gas components on fine particle formation were also studied. The results reveal that a large number of fine particles can be generated during the SCR process. These fine particles are mostly in the submicrometer size range and appear to be nonuniform. The main components of these fine particles are ammonium sulfate or ammonium bisulfate. There is a good correlation between the formation of fine particles and the SO 2 oxidation rate. Fine particle number concentration at the outlet of the SCR system increases obviously with the reaction temperature and molar ratio of NH 3 to NO (NSR, normalized stoichiometric ratio). Moreover, the enhancement of SO 2 , H 2 O, and O 2 concentrations in the inlet flue gas would increase the number concentration of the formed fine particles. The effects of the SCR process on the PM 2.5 emission characteristics consist of two aspects. On the one hand, some SO 2 can be oxidized to SO 3 during the SCR process at the function of the catalyst. Then SO 3 would react with NH 3 and H 2 O to form ammonium sulfate and ammonium bisulfate particles, which is a reversible process simultaneous with the deNOx reactions. On the other hand, SO 3 can also react with the escaped NH 3 and H 2 O to form ammonium sulfate and ammonium bisulfate particles after the SCR system.

Effect of selective catalytic reduction on exhaust nonvolatile particle emissions of Euro VI heavy-duty compression ignition vehicles

“…Some studies showed an increase in the nonvolatile PN emissions due to secondary formation of nanoparticles in the SCR system (Czerwinski et al 2015). These particles could be nitrates and sulfates (Amanatidis et al 2014;Bao et al 2016). Thermogravimetric analysis showed that a part of ammonium sulfate and ammonium bisulfate still exists as nonvolatile (solid) particles within the optimal temperature range (300-400 C) of the SCR process, which is also the temperature of the volatile particle removers of the PN systems (Bao et al 2016).…”

“…These particles could be nitrates and sulfates (Amanatidis et al 2014;Bao et al 2016). Thermogravimetric analysis showed that a part of ammonium sulfate and ammonium bisulfate still exists as nonvolatile (solid) particles within the optimal temperature range (300-400 C) of the SCR process, which is also the temperature of the volatile particle removers of the PN systems (Bao et al 2016). Others have also assumed that these nanoparticles originate from isocyanic acid polymerization, urea pyrolysis and urea micro-explosions (Lee et al 2007;Robinson et al 2016).…”

Experimental Research of an Active Solution for Modeling In Situ Activating Selective Catalytic Reduction Catalyst

“…The type of the prepared catalyst samples was ZERONOX1831K, and the catalyst parameters are listed in Table 1. The catalyst adopts TiO 2 as the carrier, and the main active ingredients are V 2 O 5 , WO 3 , and MoO 3 . The fresh and deactivated catalysts were labeled as C and C0, respectively.…”

“…SO 2 , SO 3 , fly ash, and alkali metals contained in the flue gas may decrease the denitrification capacity of the catalyst. SO 3 reacts with NH 3 to form (NH 4 ) 2 SO 4 [2], NH 4 HSO 4 [3], and CaSO 4 [4]. These small particles, with a particle size <10 µm [5], with sticky ammonium sulfate particles, especially ammonium bisulfate, may clog the micropores of the catalyst surface [6,7] and stain and corrode the downstream devices of the SCR, such as the air preheater [8,9].…”

“…The particles can also block the microporous channels on the catalyst surface [13], and the deposition of fly ash on the surface of the catalyst may contaminate and shield the catalyst [14], which may prevent the NO x , NH 3 , and O 2 in the flue gas from reaching the active site of the catalyst [5]. The alkali metal oxide decreases the number of active sites on the catalyst and poisons the catalyst by combining with the active acid sites of V 2 O 5 , which also reduces the ammonia adsorption on the catalyst surface, decreasing the denitrification activity of the catalyst [15][16][17].…”