Experimental Investigation On Simultaneous Desulfurization And Denitrfication By Wet Scrubbing And Preparation Of Ammonium Persulfate Using The Absorption Solution

The technology of desulfurization and denitrification using urea/ammonia solution has very high desulfurization efficiency and relatively high denitrification efficiency. The content of ammonium sulfate in the circulating absorbent has reached 82%. Prepared high value-added ammonium persulfate from ammonium sulfate in the circulating absorbent of the wet simultaneous desulfurization and denitrification technology using urea/ammonia solution by electrochemical process is a novel method with the bright future, which can realize resource recycling utilization for the wet simultaneous desulfurization and denitrification technology using urea/ammonia solution.The experiment research was carried out in a homemade electrolytic experiment device. The lead plate and the titanium plate was adopted as cathode which has never been reported. The effects of operating parameters(such as the electrobath voltage, the concentration of reactant, catalysts, electrolytic time and so on) on the electrochemical process of preparing ammonium persulfate from ammonium sulfate solution were investigated by experiment in this paper. It was found that the titanium plate could reach high current efficiency and conversion under lower electrochemical process parameters. and the current efficiency reached 60.16% by using titanium plate and was only 52.17% by using lead plate after four hours on the best electrolysis conditions. The results of the above studies indicated that titanium plate was a novel cathode which can replace the lead plate. In addition, considering the composition of the circulating absorbent on the desulfurization and denitrification using urea/ammonia solution, the effects of urea, ammonium chloride, ammonium polyphosphate, ammonium thiocyanate and the mixed additives on the electrochemical performance were researched based on the titanium plate cathode in this paper. It was found that the promotive effect of above four kinds additives on the electrochemical performance of preparing ammonium persulfate from ammonium sulfate solution were ammonium thiocyanate> urea> ammonium polyphosphate> ammonium chloride in turn. Ammonium polyphosphate could improve the current efficiency decline, its current efficiency reached 86.77% when 0.1% urea mixed with 0.25% ammonium polyphosphate, and the electrochemical performance was better than any one of two additives.Due to the residue of electrolytic preparation containing a little ammonium persulfate, it could promote the denitrification efficiency greatly as well. Considering the green and circulation economic utilization of the electrolytic residue which derived from the desulfurization and denitrification residual absorbent using urea/ammonia solution, it was necessary to carry out the related experiment research for denitrification process of the electrolytic residue solution. Moreover, since the denitrification efficiency has reached more than 97% on wet denitrfication using ammonia solution, the influence of SO2 on denitrification process mainly derived from the intermediate product (NH4)2SO3. For above reasons, additives such as the electrolytic product (ammonium persulfate), electrolytic anode additives (ammonium thiocyanate and ammonium polyphosphate) and the mixed additives of them, were screened to investigate the denitrification mechanism for the ammonium sulfite/urea solution. It was found that the denitrification effect of ammonium persulfate was better than that of ammonium thiocyanate, and the reaction mechanism of them were different. Ammonium persulfate was through the oxidation of NO to promote the denitrification process; while promoted the denitrification process by ammonium thiocyanate which was oxidized by oxygen on its own. However the excessive ammonium thiocyanate was disadvantageous, and it may pollute the environment. Therefore, the ammonium thiocyanate was not suitable as the electrolytic and wet denitrification additive. Adding ammonium persulfate could promote the denitrification process in diethanolamine or triethanolamine additives, but because of their higher price, diethanolamine or triethanolamine were not conducive to reduce the denitrification cost. Mixing 0.05% ammonium persulfate with 0.02% ammonium polyphosphate could reach 51% of the denitrification efficiency after 30 minutes, and the mixed additives were better than any one of two additives. Therefore it was feasible and effective to adopt urea and ammonium polyphosphate as electrolytic additive for preparation ammonium persulfate from the circulating absorbent of the wet simultaneous desulfurization and denitrification technology using urea/ammonia solution, and used ammonium persulfate and ammonium polyphosphate as additives of wet desulphurization and denitrfication using urea/ammonia solution, which is a novel technology with wide engineering application foreground and research value.