Research On Low Temperature SCR De-Nox Catalyst With Sulfur And Water-Resistance

Nitrogen oxides?NO_x?are the main air pollutants involved in photochemical smog and other environmental problems.In this paper,NO_x in non-electric industrial boilers?furnaces?with flue gas temperature lower than 300^? is used as the treatment object.Selective catalytic reduction?SCR?is the main control technology for the removal of NO_x.Based on the laboratory research,the low temperature denitration performance over V₂O₅-WO₃-TiO₂ catalyst was optimized.By adding different compounds such as A,D,E,G,L,Q,R,Z?Because the catalyst formula needed to be kept confidential,the 8 letters of A,D,E,G,L,Q,R,Z were all code symbols of different elements?and ammonia to improve the NO conversion and sulfur-resistance and water-resistance performance of catalysts,and catalyst was applied to the non-electric industry flue gas denitration treatment project.The characterization methods of BET,SEM,XRF,XRD,FT-IR,TG and H₂-TPR were used to analyse the effects of metal compounds and nonmetal compounds on the physicochemicalproperties,SCRreactivityandsulfur-resistanceand water-resistance of catalysts.At first,the physicochemical properties of industrial grade TiO₂ and its catalysts from different manufacturers were compared.The optimum loading of V₂O₅ was 3wt%.When the reaction temperature was 160^?,the NO conversion of 3%V₂O₅-WO₃-TiO₂ catalyst was 93.7%,the selectivity of N₂ was more than 98%and SO₂ oxidation was less than 1%.In the range of 110³20^?,NO conversion of catalyst increased with the increasing of the O₂ volume fraction,and decreased with the increasing of the NO inlet concentration,but the NO_x removal amount gradually increased.When n?NH₃?/n?NO??1,the optimal NO conversion of catalyst was approximately equal to the corresponding percentage of n?NH₃?/n?NO?.When n?NH₃?/n?NO?>1,the activity was barely improved.With the increase of space velocity,the high activity temperature range of catalyst was narrowed,and NO conversion of catalyst decreased in varying degrees.Under the condition of 240^?,the denitration performance of 3%V₂O₅-WO₃-TiO₂ catalyst was tested 258 h containing 0.035%SO₂ and 15%H₂O in the flue gas.The effect of H₂O alone on the catalyst was smaller and the deactivation rate was 0.12%·h^-1,when SO₂ and H₂O existed simultaneously,the deactivation rate increased to 0.27%·h^-1.With the increase of regeneration temperature?350⁵00 ^??and regeneration frequency,the deactivation rate gradually increased.Layered filling could reduce the negative effect of SO₂ and H₂O on NO conversion of catalyst.As the flue gas passed through the catalyst bed from top to bottom,the upper catalyst first touched the SO₂ and H₂O,which leaded to the most serious deactivation.At the same time,it protected the latter two layers catalysts,slowed down the overall deactivation rate and prolonged the service life of catalysts.Combined with the characterization results,the catalyst inhibited the decomposition of NH₄HSO₄ and promoted the deposition of?NH₄?₂SO₄and NH₄HSO₄ on catalyst surface and pores.After the reaction,the morphology of catalyst became blurred and the surface was covered with irregular flocs.Specific surface area,pore volume and active components decreased in different degrees,which accelerating the deactivation of catalyst.Secondly,the addition of different compounds such as A,D,E,G,L,Q,R,Z and ammonia water widened the low-temperature and high-activity temperature range of catalyst,and greatly improved the sulfur-resistance and water-resistance of catalysts.In the case of 150^?,the denitration performance order of catalysts was 3wt%A-V₂O₅-WO₃-TiO₂?98.1%?>1.5 wt%R-V₂O₅-WO₃-TiO₂?97.8%?>pH=10-V₂O₅-WO₃-TiO₂?96.7%?>0.2 wt%Q-V₂O₅-WO₃-TiO₂?93.5%?>3 wt%E-V₂O₅-WO₃-TiO₂?93.1%?>0.025 wt%G-V₂O₅-WO₃-TiO₂?92.8%?>1.75 wt%D-V₂O₅-WO₃-TiO₂?91.8%?>0.25 wt%Z-V₂O₅-WO₃-TiO₂?90.3%?>0.0075 wt%L-V₂O₅-WO₃-TiO₂?89.0%?>V₂O₅-WO₃-TiO₂?82.7%?,in which the NO conversions over 3 wt%A-V₂O₅-WO₃-TiO₂,1.5 wt%R-V₂O₅-WO₃-TiO₂ and pH=10-V₂O₅-WO₃-TiO₂ catalysts were more than 95%.Under 240^? condition after catalyst layered filling,when the reaction gas contained 15%H₂O,the water-resistance order of catalysts was as follows:0.25 wt%Z-V₂O₅-WO₃-TiO₂>pH=10-V₂O₅-WO₃-TiO₂>3wt%A-V₂O₅-WO₃-TiO₂>1.75wt%D-V₂O₅-WO₃-TiO₂>3 wt%E-V₂O₅-WO₃-TiO₂>0.0075 wt%L-V₂O₅-WO₃-TiO₂>0.025 wt%G-V₂O₅-WO₃-TiO₂>0.2 wt%Q-V₂O₅-WO₃-TiO₂>1.5 wt%R-V₂O₅-WO₃-TiO₂>V₂O₅-WO₃-TiO₂.When 0.035%SO₂ and 15%H₂O existed simultaneously in reaction gas,the sulfur-resistance and water-resistance of catalysts were ranked as:1.75 wt%D-V₂O₅-WO₃-TiO₂>pH=10-V₂O₅-WO₃-TiO₂>0.025wt%G-V₂O₅-WO₃-TiO₂>0.25 wt%Z-V₂O₅-WO₃-TiO₂>1.5 wt%R-V₂O₅-WO₃-TiO₂>3 wt%E-V₂O₅-WO₃-TiO₂>3 wt%A-V₂O₅-WO₃-TiO₂>0.2wt%Q-V₂O₅-WO₃-TiO₂>0.0075 wt%L-V₂O₅-WO₃-TiO₂>V₂O₅-WO₃-TiO₂.Results showed that pH=10-V₂O₅-WO₃-TiO₂ catalyst had the best denitration performance.Meanwhile,the influence of SO₂ and H₂O on denitration performance of catalysts was summarized.The paper also focused on the sulfur-resistance and water-resistance and on-line heat regeneration performance of 3 wt%A-V₂O₅-WO₃-TiO₂ and 1.5 wt%R-V₂O₅-WO₃-TiO₂ catalysts after layered filling.The results showed that the 3 wt%A-V₂O₅-WO₃-TiO₂ catalyst was tested in the reaction gas containing SO₂ and H₂O for 482 h,its sulfur-resistance and water-resistance performance was better than the catalyst without A.With the increase of regeneration temperature and regeneration frequency,the deactivation rate of catalyst gradually increased.Because of the loss and sulfated of active components,the catalyst was irreversibly poisoned.In the same way,the 1.5 wt%R-V₂O₅-WO₃-TiO₂ catalyst was tested in reaction gas containing SO₂ and H₂O for 1500 h,its sulfur-resistance and water-resistance performance was significantly better than the catalyst without R ions.With the increase of regeneration frequency at 350^?,the deactivation rates of catalysts were maintained at 0.074⁰.077%·h^-1,and they were not significantly increased when compared with the deactivation rate before non-regeneration(0.054%·h^-1),which indicating that the catalyst had good thermal regeneration performance.Adding appropriate amount of R^- slowed down the formation of side reaction products,and enhanced the catalyst's ability to resist poisoning.