Mechanism And Kinetics Of Fe(?) EDTA Absorption-Mn Powder Reduction For Flue Gas Denitrification

Nitrogen oxides?NO_x?is the main atmospheric pollutants,mainly derived from boiler flue gas emissions.In recent years,NO_x has drawn governmental and public attention.SCR and SNCR technology can meet the emission standard of boiler flue gas of power plant in China,but it need high cost and complicated process.Today,complex method for flue gas denitrification is a kind of high efficiency technology with simple process equipment,which can meet the national technical requirements for the deep treatment of flue gas from coal-fired boilers.Fe?II?EDTA is a highly effective complexation absorber for NO,and many processes have been studied to utilize the Fe?II?EDTA to enhance the denitrification efficiency of existing processes.In this paper,based on the process of Fe?II?EDTA complexation and absorption NO,the kinetic parameters of self-made bubbling reactor were studied,then the solid-liquid reaction between Mn powder and Fe?II?EDTA-NO was analyzed,finally proposed a recovery process of manganese ions in solution.In this paper,the process of Fe?II?EDTA absorbed NO in a self-made bubbling reactor was studied,and the effects of temperature and flow rate on complex absorption were investigated.The results show that the removal efficiency of NO decreases with increasing temperature and flow rate.According to the surface renewal theory,the liquid phase mass transfer coefficient?k_L?and the specific phase boundary area?a?in the self-made bubbling reactor were determined.The relationship between the liquid phase mass transfer coefficient and the flow rate and temperature can be expressed.Similarly,the relationship between the phase boundary area and the flow rate and temperature can be expressed.The enhancement factor of experimental determination and theoretical calculation were obtained,the relative error was controlled at±1.61%.The reduction of Fe?II?EDTA-NO by Mn powder was studied by using the shrinking core model.The effects of manganese powder particle size,Fe?II?EDTA-NO concentration,manganese powder concentration,stirring speed and reaction temperature on solid-liquid reaction were investigated.The efficiency expression of Fe?II?EDTA-NO reduced by manganese powder can be written.From the reaction image and activation energy calculation,it is concluded that the reaction rate of Mn powder to reduce Fe?II?EDTA-NO is mainly controlled by chemical reaction,not by membrane diffusion,and the activation energy of the reaction is 43.00 kJ/mol.A part of manganese ions(Mn²⁺)in the denitrification waste liquid was recovered by a precipitation reaction between ammonium hydrogen carbonate?NH₄HCO₃?and Mn²⁺to form the rhodochrosite?MnCO₃?.The experimental results showed that the equilibrium time of the carbonization precipitation reaction was about 90 min,and the concentration of Mn²⁺in the solution dropped from 8.51 mM to 4.51 mM,and the recovery efficiency reached 45%.The carbonization efficiency of Mn²⁺also increased with the increase of pH,temperature and the concentration of NH₄HCO₃.According to Arrhenius and Eyring-Polanyi equations,the analysis was performed with the change of Mn²⁺concentration at different temperatures.The value of activation energy?E_a?of the Mn²⁺carbonized precipitate is 17.25 kJ/mol,the enthalpy of activation??H^??of the reaction is 14.55 kJ/mol,and the entropy of activation??S^??is-252.07 J/?k mol?.It indicates that both reactants binding in the transition state occurs,and the temperature increase is favorable for the progress of the carbonization precipitation.The manganese content in the rhodochrosite recovered after the experimental conditions reached 42.7%,indicating that the product reached the industrial first-class product standard.