Study Of Deactivation And Regeneration Methods Of De-NO_x Catalyst In Coal-fired Plants

It is inevitable to produce a lot of pollutants in the process of the use of coal,which is one of the most important energy sources in our country.Nitrogen oxides,as one of them,has caused a series of environmental problems,such as acid rain,photochemical smog and some other environmental problems.Statistically,67% of exhausted nitrogen oxides were produced by coal based fossil fuel combustion.Therefore,it is the most important to control the emission of nitrogen oxides from coal fired power plant.Currently,selective catalytic reduction is most widely used in coal fired power plant.Catalyst is the core of SCR technology.At present,V-W-Ti catalyst is most widely used commercial catalysts.It increases costs of power plant due to the high cost of catalysts and replacement because of deactivation after working three to five years.At the same time,the waste catalysts will cause new environmental problems.Therefore,it is very necessary to carry out the analysis of deactivation and regeneration of the catalysts.At present the main regeneration methods include water washing regeneration,pickling regeneration,heat(reduction)regeneration and composite regeneration.In this paper,the reasons for deactivation of the V-W-Ti catalyst were analyzed,and the regeneration studies were carried out on the basis of the results.The main conclusions are as follows:The efficiency of the used catalyst was decreased obviously,and the maximum efficiency of 63.1 % was achieved at 400 degrees,lower than that of the new catalyst,which showed that the used catalyst had been deactivated.The two catalysts were characterized by SEM,N2 adsorption desorption,XRD,XRF,FTIR and so on.The results showed that the crystalform of the used catalyst did not change and was still typical anatase,and the catalyst had not been sinterred.The used catalyst had occurred the pore block,which leaded to the increase of average pore size,decrease of specific surface area and pore volume.At the same time,compared with the new catalyst,the activation of used catalyst had been lost,conversely some toxic elements such as Na,Ka,Ca,Mg and so on had been increased.Also the As element had been found in the used catalyst.Deactivation of used catalyst was mainly caused by the pore block,alkali/alkaline earth metal poisoning and As,the loss of active component.The regeneration process route was established,including water washing,pickling and regeneration impregnation.The effects of washing methods,washing time,acid concentration,acid pickling time,regeneration solution concentration and regeneration time on the regeneration of the catalyst were investigated.The effect of ultrasonic washing was better than that of immersion washing,and 45 minutes was the best cleaning time for ultrasonic washing.The pickling effect was best when the acid concentration is 0.5 mol/L and pickling time is 45 minutes.The regeneration effect was best when regeneration time was 60 minutes and the mass fraction of vanadyl sulfate and ammonium metatungstate were 2 % and 2 %.The denitration efficiency of the regenerated catalysts can regain more than 95 % of its initial activity and reach 91.6 %.