| The selective catalytic reduction(SCR)denitrification technology,which shows high denitrification efficiency and good selectivity,is currently the most mature denitrification technology,therefore widely used in the nitrogen oxides(NOx)emission control of stationary sources and mobile sources.The core of this technology is the SCR catalyst.In the actual operation,the catalyst could be deactivated due to poisoning,sintering,abrasion,or blockage,which leads to a significant decrease in denitrification efficiency and an increase in the SO2 oxidation rate.When the catalyst can not meet the overall denitrification performance requirements of the SCR system,the catalyst has to be replaced,and the replaced catalyst should be recycled or disposed according to the type of inactivation and the extent of damage.Based on the above two cases,this paper studied the recycling of commercial SCR denitrification catalyst with typical waste SCR catalyst and arsenic poisoned SCR catalyst respectively.For the waste SCR catalyst,some researchers proposed that it could be recycled with the conventional regeneration method,which contains cleaning of toxic substances and reloading of active components.The denitrification efficiency of the required catalyst could be recovered successfully.However,the conventional recycling of the waste SCR denitrification catalyst will result in a high SO2 oxidation ratio of the recycled catalyst.Based on this fact,a novel recycling technique,including acid washing,acid leaching under reduction condition and active components loading,was proposed to control the SO2 oxidation ratio of the recycled catalyst.Experiments were performed to determine the components,denitrification efficiency and SO2 oxidation ratio of the catalysts obtained in different recycling steps,as well as to characterize these catalysts.The results indicated that the denitrification efficiency and SO2 oxidation ratio of the fresh catalyst,waste catalyst,conventional recycled catalyst and novel recycled catalyst were 99.0%and 0.43%,77.0%and 0.46%,94.2%and 0.80%,99.3%and 0.48%,respectively.Through novel recycling method,both denitrification efficiency and SO2 oxidation ratio of the recycled catalyst were well recovered.The characterization results suggested that the highly polymerized vanadium species on the surface of the waste catalyst could not be removed by using conventional recycling method.Whereas,novel recycling method was effective for removing these vanadium species,and replacing them with highly dispersed vanadium species,resulting in reduction of SO2 oxidation ratio of the recycled catalyst.For the arsenic poisoned SCR catalyst,the conventional recycling technology is alkali washing(strong base),thermal reduction(high temperature).While there might be some serious problems,such as secondary poisoning,a large number of active components dissolved or high temperature sintering during processing.Based on this fact,a novel recycling technique,including alkali washing,thermal reduction and oxidizing calcinating,was proposed to eliminate the rsenic species absorbed on the surface of the catalyst and then to restore its activity.The arsenic content and the denitrification efficiency of the catalysts obtained in different recycling steps were investigated,and the catalysts were characterized by several kinds of characterization.The results showed that the arsenic content and the denitrification efficiency of the fresh catalyst,arsenic poisoned catalyst and recycled catalyst were 0.00%and 95.5%,1.96%and 72.9%,0.11%and 92.7%,respectively.Based on the method proposed in this study,the surface arsenic species of the poisoned catalyst were almost removed,and the denitrification efficiency was basically restored to the level of the fresh catalyst.The characterization results showed that the arsenic species could be removed,and the surface structure and physicochemical properties of the acquired catalysts were improved,so the denitrification efficiency could be effectively recovered. |
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