Study on Mid-temperature SCR DeNO x Catalyst under High SO 2 and
1B INTRODUCTION Chinese main energy resource is coal and fire power plant is the primary producer of NOx. With the rapid development of economy, the environmental damage caused by coal-fired becomes more serious. The multiplex acid rain is mainly caused by the emission of SO2 and NOx of coal fire power plants and cement kilns. The Emission Standard of Air Pollutants for Coal-fired Plants implemented at 1st Jan, 2004, has greatly prompted the development of DeNOx industry and the DeNOx industry is becoming a highlight of environmental protecting industry. The SCR technology (Selective Catalytic Reduction) is the most efficient method to control the emission of NOx, which has been widely used in coal-fired plants of developed countries. However, in domestic, the commercial application of DeNOx has just stepped out. The constitutes of coals in China vary drastically, and many coals contain high SO2, high CaO, high ash, and contains of arsenic changes greatly. It is greatly different from the east area coal of America.[1] So far, our country SCR DeNOx equipment have applied alien technology entirely and what’s more, We are short of the experience of pattern selection and operating of catalysts. The core technology of SCR is the systemic design to maintain uniform distribution of smoke and fly ash in reactor. It reported that (NH4)2SO4 and CaSO4 in smoke poisoned catalysts of SCR and reduced the efficiency of DeNOx. Aiming at high SO2 and high CaO ash in coals of China, this paper develops the DeNOx experiments of Mid-temperature SCR catalyst in high SO2 and high CaO condition. The research is a great help for the pattern selection of catalyst in domestic DeNOx industry of coal fired plants.
Sulfuric acid formation over ammonium sulfate loaded V2O5–WO3/TiO2 catalysts by DeNOx reaction with NOx
Abstract Operating the SCR DeNO x reactor at temperatures below 200 °C results in a considerable saving in operating costs. Plant experience shows that on the catalysts in these second generation DeNO x plants, even for flue gases with SO 2 concentration below 10 mg/m 3 , over 1–2 years operating time sizeable quantities of ammonium sulfates accumulate. Ammonium sulfates deposited on V 2 O 5 –WO 3 /TiO 2 catalysts react with NO x to nitrogen and sulfuric acid. Second-order rate constants of this reaction for temperatures of 170 °C have been derived. It could be shown that the sulfuric acid formed on the catalyst is displaced by water vapour and desorbs resulting in gas phase concentrations of up to 6.5 mg acid/m 3 flue gas. Plant equipment downstream of the ammonium sulfate containing low temperature DeNO x catalysts has to be protected against the corrosive action of the sulfuric acid in the flue gases leaving the DeNO x reactor.
Vanadia-Titania Catalysts for Selective Catalytic Reduction of Nitric-Oxide by Ammonia
The reaction mechanism and catalytic cycle for the selective catalytic reduction of nitric oxide by ammonia over vanadia/titania catalysts has been elucidated by in situ on-line FTIR studies under steady-state conditions. Under all reaction conditions, a large concentration of ammonia is adsorbed on both Lewis and Bronsted acid sites, whereas no significant amounts of adsorbed NO are adsorbed. The catalytic activity is found to be related to the ammonia adsorbed on the Bronsted acid sites associated with V5+OH. Surface VO groups are involved in activation of the adsorbed ammonia and are also found to play an important role in the catalytic cycle. The activation involves a transfer or a partial transfer of a hydrogen and reduced V-OH groups are produced. The V5+O surface species are regenerated by oxidation. The results, therefore, show that the catalytic cycle consists of both acid-base and redox reactions. The ammonia adsorption is observed to be a fast equilibrated step under all the conditions studied but the other catalytically significant steps may shift depending on the reaction conditions. At high O2 partial pressures, the rate is mainly determined by the concentration of Bronsted acid sites and the NO partial pressure, whereas at low O2 partial pressures, surface reoxidation is slow and the rate becomes dependent on the concentration of V5+O groups.