Experimental Study On Reuse Of Waste SCR Catalyst

At present, most of China’s coal-fired power plants have been installed SCR system to meet the increasingly stringent emission standards for nitrogen oxides. Catalysts, which are the core of SCR system, has been online operation in large-scale. However, as the time passing by, inactivation is inevitable for SCR catalysts in the actual application process due to sintering, pore blockage and toxic elements enrichment. The service life of the catalyst is generally 3 years, and then be replaced. China will face a large number of waste catalyst to be treated, and it has been listed as the hazardous waste, so the disposal of the waste catalyst will become the inevitable problem of thermal power industry. First, this paper study the pickling process of the waste catalyst (with K element, for example) and then, use the clean catalyst as a raw feed material for new catalyst production or for materials recovery, in order to improve the waste catalyst recycling value. The main results are shown as following:1. Through the research of the type selection of acid pickling solution and the pickling condition, the effect of acetic acid on activity recovery and element cleaning was found. With these condition of the concentration of acetic acid is 0.05mol/L, the pickling time is 40min and at normal atmospheric temperature, the removal rate of K is 80% and without W and V loss. On the basis of acid pickling, the catalyst was used as raw material for new catalyst production, and the catalyst activity was found to be inhibited.2. Experimental study on alkaline leaching condition and leaching kinetics of sodium hydroxide was carried out. The experimental results show that with the conditions of concentration of sodium hydroxide is 7.5mol/L, the leaching temperature is 100％℃, and the ratio of L/S mass is 5, the leaching efficiency of V2O5 and WO3 can reach 93.48% and 91.68% respectively. The leaching kinetics showed that when the concentration of sodium hydroxide is 0.5-7.5mol/L and temperature is 30-100℃, the diffusion through the catalyst is the rate-controlling process during the leaching reaction, and improve the leaching temperature will promote V2O5 and WO3 leaching efficiency.3. The purification experiment by controlling the pH value of the solution and the enrichment of vanadium and tungsten by calcium salt were investigated. It is found that the precipitation rate of aluminum and silicon increases with the decrease of pH value, however, with the decrease of pH value, the precipitation of vanadium and tungsten in solution occurs due to the adsorption of colloid. When the pH value is about 9.5, the precipitation rates of Al and Si are 100% and 88.34%, respectively, and the loss rate of vanadium and tungsten is less than 10%, which is 9.07% and 4.55%, respectively. The optimal operation conditions of the enrichment of vanadium and tungsten by calcium salt are as followed:the addition of CaCl2 is 19.64, the temperature is 90℃, the time is 30min. with these conditions, the precipitation rates of V and W are 99.89% and 98.9%, respectively...