Query: SCR SO3

title: Effect of Na2SO4 Poisoned SCR Catalyst on SO3 Generation Characteristics
abstract: In order to study the effect of Na2SO4 poisoned SCR catalyst (V2O5 WO3 /TiO2 catalyst) on SO3 generation characteristicsshax the Na2SO4 poisoned SCR catalysts with w(Na) of 3% Na2SO4 was prepared by the wet impregnation methodshax and the physicochemical properties of the catalyst were characterized by N2 physical adsorption/desorptionshax XRD (X ray diffraction)shax SEM scanning electron microscope) and XPS (X ray photoelectron spectroscopy) The results showed that: (1) As the reaction temperature increasedshax the SO3 generation rate of all catalysts gradually increased. When the temperature increased to 490 degCshax the SO3 generation rate was 0 85% for the SCR catalyst. Howevershax the SO3 generation rateincreased to 1 36% for the 3% Na2SO4 poisoned SCR catalyst. The presence of SO4 2 caused an increase in the number of V O S bondsshax thereby promoting SO3 generation. 2) Increasing the inlet r SO2 )shax the SO3 generation rate tended to decrease. When the inlet r(SO2) was 1 000 mg/mshax the SO3 generation rate of the 3% Na2SO4 poisoned SCR catalyst was 1 02%shax while the SCR catalyst was only 0 60% The effect of r(SO2) on the SO3 generation rate mainly depended on the temperature and the number of active sites of the catalyst. (3) The results of N2 physical adsorption/desorptionshax XRD and SEM showed that compared with the SCR catalystshax Na2SO4 accumulated on the surface of the Na2SO4 poisoned SCR catalyst. Cracks and macropores appearedshax while the specific surface area and pore volume of the catalyst decreased. These changes were unfavorable to the catalytic performance of the catalyst. XPS results showed that the addition of Na2SO4 increased the surface chemisorption of oxygen and reduced the w(V) /w(V ratio in the active component. The above results suggested that the SO3 generation rate of the Na2SO4 poisoned SCR catalyst greatly increased as compared with the SCR catalyst.

title: Influenced factors study and evaluation for SO2/SO3 conversion rate in SCR process
abstract: SO3 generated in coal fired boiler and selective catalytic reduction (SCR) process has become a significant problem due to its adverse effects on boiler facilities and air environment. The factors influenced conversion rate of SO2 to SO3 (SO2/SO3) during SCR process were studied and evaluated, which included the effects of flue gas composition and SCR catalyst components on the conversion of SO2/SO3. SO3 was trapped by the condensation and isopropanol absorption method, and SO42 concentration was detected by spectrophotometer. The results showed that a certain concentration of NH3 in the flue gas significantly promoted the conversion rate, but when NH3 and NO coexisted, NO inhibited the catalytic action of NH3, while NO itself and O2 had small effect on the conversion rate. Besides, the conversion rate of SO2 increased with the increase of Ti and V content in the catalyst, and SiO2 and BaO abated the catalytic oxidation of SO2, while WO3 promoted the formation of SO3.

title: Reversible and irreversible deactivation of Cu CHA NH3 SCR catalysts by SO2 and SO3
abstract: Sulfur oxides are a common source for the deactivation of Cu exchanged CHA zeolite based catalysts used for NOx reduction in diesel exhausts by selective catalytic reduction with NH3 (NH3 SCR) Since water and possible formation of SO3 affect the deactivation of Cu CHA catalysts, the deactivation in the presence of SO2 or a mixture of SO2 and SO3 was studied by measuring the SCR activity in wet and dry gas at 200 and 550 degC. The estimated S content in the catalysts before and after 4 h regeneration at 550 degC in NO, NH3, O2 and H2O was related to the deactivation. The deactivation can be divided into two parts: a reversible deactivation that is restored by the regeneration treatment, and an irreversible part. The irreversible deactivation does not affect the activation energy for NH3 SCR and display a 1:1 correlation with the S content, consistent with deactivation by Cu sulfate formation. The reversible deactivation results in a lower activation energy and a deactivation that is larger than expected from the S content. The presence of SO3 at 200 degC leads to higher reversible and irreversible deactivation, but has no significant impact at 550 degC. Furthermore, the irreversible deactivation is always higher when exposed at 200 degC than at 550 degC, and in wet conditions, compared to a dry feed. The deactivation is predominantly reversible, making regeneration at 550 degC a realistic approach to handle S poisoning in exhaust systems.

title: The Role of SO3 Poisoning in CU/SSZ 13 NH3 SCR Catalysts
abstract: To reveal the role of SO3 poisoning in Cu/SSZ 13 NH3 SCR catalysts, fresh and sulfated Cu/SSZ 13 catalysts were prepared in the presence or absence of SO3 flux. The deactivation mechanism is probed by the changes of structural, copper species, and selective catalytic reduction (SCR) activity. The variations concentrate on the changes of copper species as the Chabazite (CHA) framework of Cu/SSZ 13 catalysts could keep intact at high ratios of SO3/SOx. The thermal gravimetric analyzer (TGA) results reveal that the copper sulfate formed during sulfation and the amounts of sulfate species increased with an increase in the SO3/SOx ratio. In contrast to the changing trend of copper sulfate, temperature program reduction (H2 TPR) and electron paramagnetic resonance (EPR) results manifest that, since the number of active copper ions declines with an increase of the SO3/SOx ratio, the active sites transform to these inactive species during sulfation. Due to the combination of NH3 SCR activity and the kinetic tests, it is shown that the decreased number of active sites is responsible for the declined SCR activity at low temperature. As Cu/SSZ 13 catalysts show excellent acid resistance ability, our study reveals that the Cu/SSZ 13 catalyst is a good candidate for NOx elimination, especially when SO3 exists.

title: Nature of SO3 poisoning on Cu/SAPO 34 SCR catalysts
abstract: To reveal the nature of SO3 poisoning of Cu/SAPO 34 selective catalytic reduction (SCR) catalysts, CHA structure, copper species, and NOx conversion were probed. The Cu/SAPO 34 catalyst was treated with different ratios of SO3 to SOx (0, 6, 13, and 20% at 250 degC. The breakage of Si O(H) Al bonds takes place and leads to aluminum sulfate formation upon SOx sulfation. More isolated Cu2+ transform to copper sulfate with an increment of the SO3/SOx ratio. Catalysts poisoned with SOx show lower NOx conversion at 150 300 degC, the reason for which is a reduced number of isolated Cu2+ sites, as their turnover frequencies (TOFs) are identical. The loss of isolated Cu2+ and Si O(H) Al bonds is responsible for the inferior activity above 300 degC. The presence of SO3 cannot be ignored because of the irreversible reaction with Cu/SAPO 34 when diesel oxidation catalysts are applied upstream of the SCR.

title: Sulfur poisoning of Copper BEA zeolite in SCR. Effect of SO2/SO3 ratio

title: Experimental study on the removal of SO3 from coal fired flue gas by alkaline sorbent
abstract: Selective Catalytic Reduction (SCR) system can efficiently remove NOx in coal fired power plant, while raise SO3 concentration in the flue gas. Alkaline sorbent injection is a major approach to remove SO3. Experiments were conducted to study the SO3 absorption performance of alkaline sorbent. The SO3 absorption performance of the three alkaline sorbents was Na2CO3 Ca(OH)2 Mg(OH)2. The ratio of SO3 absorption rate to SO2 absorption rate for Na2CO3 increased with the increasing temperature. The key parameters on the SO3 absorption performance of Na2CO3 were studied. The SO3 absorption by Na2CO3 was increased by 72.7% with increasing temperature from 150 degC to 300 degC, and the temperature had little influence on SO3 absorption above 300 degC. The increasing SO3 concentration and decreasing particle size of Na2CO3 enhanced SO3 absorption. However, when the average particle diameter was less than 50 mm, the SO3 absorption was no longer significantly increased. The increasing CO2 concentration slightly reduced the SO3 absorption. After adding vapor into the flue gas, the SO3 absorption was obviously increased below 300 degC. The SO3 absorption variation above 300 degC was similar to the condition without vapor. When reaction temperature was 300 degC or above and reaction time was less than 20 min, external diffusion became the control step for SO3 absorption. On the basis of external diffusion control model, the mass transfer coefficient slightly increased from 1.68 x 10 3 m/s to 1.75 x 10 3 m/s when the reaction temperature increased from 300 degC to 400 degC.

title: Formation, transformation, measurement, and control of SO3 in coal fired power plants
abstract: The formation and emission of sulfur trioxide (SO3) in coal fired power plants has received increasing attention due to its adverse effects on the operation of plant and environment. With the wide application of selective catalytic reduction (SCR) systems, the problem caused by SO3 has become severe, especially when high sulfur coal is burned. Emission regulations of SO3 for coal fired power plants, which promote the development of SO3 measurement and control technologies, have been set in some countries and regions. In this paper, recent advances in the formation, transformation, measurement, and control mechanism and technologies of SO3 in coal fired power plants were summarized. The formation mechanisms of SO3 in boiler and SCR systems and its form transition and corresponding effects on the performance of power plants were analyzed. Different SO3 test standards and methods were compared, and online SO3 monitor based on isopropanol absorption method were developed. Various SO3 control technologies, including simultaneous and specific removal technology, were summarized. Low low temperature and wet electrostatic precipitators could remove up to 90% SO3/H2SO4 aerosol, and the removal efficiency of SO3 in wet flue gas desulfurization can be enhanced to 80% by absorber optimization and inlet flue gas temperature decrease. For power plants that burn high sulfur coal, the injection of alkaline sorbent before the SCR or air preheater system can remove more than 90% of SO3 to decrease the formation of NH4HSO4 and the pressure drop in the air preheater. High SO3 removal technology and strategies for different scenarios were proposed to meet different SO3 emission requirements in the future.

title: Influence of geometrical parameters of honeycomb commercial SCR DeNOx catalysts on DeNOx activity, mercury oxidation and SO2/SO3 conversion
abstract: A systematic study on the influence of geometrical parameters (pitch and wall thickness) of commercial high dust honeycomb SCR DeNOx catalysts on DeNOx activity, mercury oxidation and SO 2 /SO 3 conversion is described. All catalysts had an identical chemical composition of 0.6 wt. V 2 O 5 The study was conducted in a laboratory micro reactor and a technical scale bench reactor and focuses on the effect of different honeycomb geometrical parameters on the reactions at the catalysts. The combined variation of pitch and wall thickness showed lower DeNOx activity at catalysts with larger channel openings. This indicates mass transfer limitations when the flow regimes are developed in the catalyst's channels due to the relatively fast reaction kinetics of the DeNOx reaction. Results showed that the SO 2 /SO 3 conversion is linearly dependent on catalysts wall thickness. Mercury oxidation increased slightly linear with increasing wall thickness of the catalyst, indicating that the reaction takes also place in the catalysts bulk because of its slow chemical reaction kinetics in contrast to DeNOx reaction being controlled by diffusion. The importance of flue gas HCl concentration on mercury oxidation was pointed out. Additionally, research on the co influence of DeNOx reaction and SO 2 /SO 3 conversion was performed. A strong inhibition of SO 2 /SO 3 conversion by flue gas ammonia was shown. However, DeNOx activity is enhanced by conditioning with SO 2 due to superior acidity of active sites. Summarising the results, due to the drawback of elevated SO 2 /SO 3 conversion, higher risk of channel blocking and material costs, increasing wall thickness cannot be considered a reasonable strategy to enhance mercury oxidation by SCR catalysts.

title: Study on competitive absorption of SO3 and SO2 by calcium hydroxide
abstract: Alkaline injection is an effective way to control the emission of high concentration SO3 caused by the use of high sulfur coal and selective catalytic reduction (SCR) but its performance is affected by the competitive absorption of SO2. A fixed bed reactor was used to study the competitive absorption of SO3 and SO2 by Ca(OH)2. The dynamic absorption curves in different atmospheres were obtained, the intermediate products were characterized, and the competitive absorption mechanism was discussed. The absorption of SO3 and SO2 consists of the chemical kinetics controlled and product layer diffusion controlled stages. In the chemical kinetics controlled stage, the SO3 and SO2 removal efficiencies were around 90% and 55% at first and then decreased; the SO3 selectivity was around 0.1 at first and then increased. In the product layer diffusion controlled stage, the SO3 removal efficiency gradually decreased but kept greater than 10% while the SO2 removal efficiency deceased to zero; the SO3 selectivity continued to increase and reached 0.31 at most when SO2 absorption ceased. There existed significant competition between SO3 and SO2 absorption. The increasing SO3 concentration promoted the SO3 absorption and the increasing SO2 concentration decreased it. The absorption of SO3 increased the intensity of the SO 4 2 band, decrease the intensity of the SO 3 2 band, and made the product layer more compact. The possibility of SO3 reacting with the components (CaSO3, CaSO4 and CaCO3) on the reacted Ca(OH)2 surface was analyzed. Ionic diffusion was proposed as the main mechanism of the continuous SO3 absorption after the formation of a dense product layer.