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.
Optimizing SCR Catalyst Design and Performance for Coal-Fired Boilers
The design of an SCR system for a coal-fired application is a challenge due to particulate, catalyst poisons, and So2 in the flue gas. Our experience show that coalfired SCRs are successful when the system impact and catalyst deterioration factors are understood and specific countermeasure are implemented in system and catalyst design There are several factors that the system and catalyst must consider in order to assure success. They include: type of boiler, required performance, fuel and ash analysis, ash loading, type of SCR, inlet conditions, Catalyst deactivation mechanisms and impact on down stream equipment. This paper explains each system and catalyst deterioration factor that we have experienced. For each factor, it presents the specific countermeasure that has resulted in successful SCR systems. Also, it discusses the design of improved catalyst derived from our experience. Finally, two case studies illustrate the impact of optimized design.
An FT-IR study of ammonia adsorption and oxidation over anatase-supported metal oxides
Abstract The adsorption and the oxidation of ammonia over sub-monolayer TiO2-anatase supported chromium, manganese, iron, cobalt, nickel and copper oxides, has been investigated using FT-IR spectroscopy. These materials are models of catalysts active in the Selective Catalytic Reduction of NOx by ammonia (SCR process) and in the Selective Catalytic Oxidation of ammonia to dinitrogen (SCO process). For comparison, the adsorption of ammonia and hydrazine over the TiO2-anatase support has also been studied. CrOx TiO2 adsorbs ammonia both in a co-ordinated form over Lewis acid sites and in a protonated form over Bronsted acid sites, involving high-valence chromium (chromyl species). However, simple outgassing at r.t. causes the desorption of ammonia from Bronsted acid sites showing that they are very weak. All other catalysts do not present any Bronsted acidity. Co-ordinated ammonia gives rise to several oxidation products over Fe2O3 TiO2, CrOx TiO2, CoOx TiO2 and CuO TiO2, among which hydrazine is likely present. Other species have been tentatively identified as imido species, NH, nitroxyl species, HNO, and nitrogen anions,N−2. NiOx TiO2 and MnOx TiO2 appear to be even more active in ammonia oxidation, because the adsorbed species disappeared completely at lower temperature (473 K) than in the other cases. However, possibly just due to their excessive activity, no adsorbed species different from co-ordinated ammonia can be found in significant amounts over these surfaces. Based on these data, the mechanism of the SCR and SCO processes over these catalytic materials is discussed. In particular, it is concluded that Bronsted acidity is not a requirement for SCR and SCO activity.