| Selective catalytic reduction(SCR)as one of technologies abating NOx in flue gas is currently the most widely used control of NO,emission technology.Catalysts are critical to selective catalytic reduction of NO.and affecting the NO,removal efficiency of the SCR system.At present the commonly used commercial SCR catalysts are V2O5-WO3/TiO2honeycomb catalyst and the lifetime is generally 3 years.With the increasingly strict environmental policy in China,the capacity of the denitrification unit with SCR system in coal-fired power plants will continue to increase.However,when the used SCR catalysts activity can't meet the denitrification requirement,they have to be overall replaced.As the replaced SCR catalyst contains many toxic constituents and comes with a great amount,it may pose an enormous challenge to environmental protection.Therefore,it is necessary to carry out a feasible way to regenerate the waste catalysts.In this paper,the deactivation mechanism was studied for the commercial SCR catalysts after 30000 hours of practical operation.In addition,different renewable liquids are performed benefit for the used catalysts.The main conclusions are as follows:(1)Comparing the used catalysts after 30000 hours of practical operation with that of the fresh catalysts,the resultshowed that the denitration activity of the usedcatalyst decreased by 30.9%and BET surface area decreased by25.0%.The deposition of alkali metals,arsenic compounds and sulfates may be the main cause for the drop of activity.The potassium content increased by 192.8%,the sodium content increased by 115.4%,the sulfate content increased by 245.0%,and despositions of arsenic appeared.(2)The effects of ammonium sulfate,dilute sulfuric acid,calcium hydroxide solution(pH=9.0)and citric acid on the regeneration of used catalysts were investigated.It was found that ammonium sulfate,dilute sulfuric acid,calcium hydroxide solution(pH=9.0)had better effect on the regeneration.The three kinds of solution will increase the V5+ content ratio and chemical adsorption oxygen content concentration ratio.After regenerated by 0.5M dilute sulfuric acid,the denitration efficiency of the used catalysts increased to 72.3%at 350?.After regenerated by calcium hydroxide solution,the BET surface area of the used catalysts increased by 59.5%while the part of the arsenic and sulfate deposition were removed.(3)The performance and surface properties of commercial SCR catalysts(20000 hours)which were continuously flushed up to 336 hours by high temperature water vapor(due to rupture of the economizer shell)were investigated.It was found that the denitration activity of the SCR catalysts was still as high as 91.4%after high temperature water vapor treatment.The high temperature water vapor removes the alkali metal and soluble sulphate from the surface of the catalyst so that the covered active sites exposed again.The proportion of surface chemical adsorption oxygen on the catalysts surface increased at the same time.The used commercial SCR catalysts can be regenerated cost-effectively in situ with high temperature water vapor. |
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