Experimental Study On Resource Recycling Utilization Of Absorption Solution From Ammonia-Based Wet Desulfurization And Denitrification

Ammonium-based wet desulfurization and denitrification technology can effectively remove SO₂ and NO_X in the flue gas,and eventually convert the pollutants to ammonium sulfate and ammonium nitrate.The stubbornly high operating cost is still the biggest shortage,which can be reduced in some extent by the profits of recycling by-products.Conventional preparation of mixture salts of ammonium sulfate and ammonium nitrate has many disadvantages,such as high energy consumption,poor quality and low value,which make it less competitive.Therefore,developing a technical scheme which can realize high removal rate of multiple pollutants and resource recycling of valuable by-products without secondary pollution,becomes the direction of exhaust pollutant treatment.Combined with ion-exchange membrane electrolysis,a new green method is developed where the desulfurization and denitrification absorption is used for electrochemical preparation of ammonium persulfate.The oxidizing persulfate can be introduced to the NO removal in flue gas cleaning syatem,making the electrolysis process and desulfurization and denitrification system an organic whole.Meanwhile,the hydrogen produced in cathodic chamber can be comprehensive utilization as clean energy.Furthermore,the remainder solution after crystallization could be coupled with circulation absorption solution,thus improving the denitrification efficiency.Aiming at the new process,the parameters of electrolysis and crystallization was experimentally investigated and then discussed in this study.Firstly,the effect characteristics of electrolyte compositions and concentrations,temperature,current densities,flow rate,electrolytic time and impurities of absorption on current effciency of persulfate production were investigated in a two-compartment electrolytic cell under batch recirculation.The experimental results indicated that urea and ammonia has inhibitory effect on current efficiency,while ammonium sulfite and nitrite existing in anode chamber showed no significant influence on current efficiency.The current efficiency of simulated absorbent solution decreased to 69.88%,which was much lower than86.98%by the pure ammonium sulfate electrolysis process under the optimal condition.Therefore,necessary pretreatments for the absorption solution,which contain the removal of heavy metal ions and urea,the oxidation of sulfite and the adjustment of pH value,must be adopted before entering the electrolysis system.Using the pretreated absorption solution,the anodic current effciency could reach to 85.12%.Secondly,the ammonium persulfate was initially separated and crystallized by using vacuum evaporation crystallization.The optimal process parameters was investigated and determined in a lab-scale crystallizer.The effect of possible impurities of the after electrolytic absorption on the particle size distribution and purity was also examined.The vacuum evaporation experiments show that the better products could be produced by vacuum evaporation crystallization uniformly.The presence of urea could decrease ammonium persulfate particle size.Fly ash can be used as crystal nucleus and inhibit exploding nucleation rate,which is good for large-grained crystal particle.The existence of iron ions inhibit both the growth rate and nucleation rate of the crystal,resulting in much smaller particle size and lower purity.As the content of nitrate increased,the particle size of ammonium persulfate displayed the trend of dropping first and then rising up.Therefore,in order to get high-quality ammonium persulfate crystal,it’s under the necessity of removing the metal ions and controlling the content of fly ash before the electrolysis process.The product that was crystallized by using the simulate absorption after electrolysis met the national standard industrial grade ammonium persulfate.Estimate of economic profits and operating cost of the new process and conventional desulfurization and denitrification technique revealed that there is no much difference of the two methods in investment cost and operation cost.The new recycling process could produce high-value persulfate and hydrogen,and the integrated operation cost of the system is greatly reduced.Therefore,it is a novel environmentally effective technical route for flue gas cleaning,with great prospects for development.