Experimental Study On Mass Transfer Reaction Kinetics Of Na₂S₂O₈ Wet Oxidation NO Of Ship Exhaust Gas

SO₂,NO_x and other polluting gases emitted by ships have caused serious harm to the atmospheric environment and human health.The Na₂S₂O₈ wet washing technology based on NO oxidation and SO₂ removal is an effective emission control technology of marine diesel engine,in which the efficient oxidation of NO is the key of the process.The oxidation efficiency of NO can be improved by activating Na₂S₂O₈ or forming a composite oxidation system with other oxidants.However,there is still a lack of research on the mass transfer parameters and mass transfer reaction kinetics of NO in the absorption process of Na₂S₂O₈ solution.In view of the above problems,the main influencing factors,mass transfer parameters and mass transfer reaction kinetics were systematically studied in a bubbling reactor in the process of NO oxidation by Na₂S₂O₈ solution.Firstly,the mass transfer reaction kinetics test system of Na₂S₂O₈ wet oxidation of NO was established,and the effects of gas liquid contact time,solution temperature,Na₂S₂O₈ concentration,initial "NO concentration and flue gas velocity on NO removal rate were explored.Combined with liquid products,the reaction path of NO oxidation was analyzed.The results show that the removal rate of NO increases with the increase of gas liquid contact time,solution temperature and Na₂S₂O₈ concentration,and decreases with the increase of initial NO concentration and flue gas velocity.When the temperature is 60℃,Na₂S₂O₈ concentration is 0.2 mol/L,flue gas flow is 0.8 L/min and initial NO concentration is 1200 mg/m3,the removal rate of NO reaches the highest,and the highest removal rate is 42%.Combined with the analysis of liquid phase products,it can be concluded that NO in flue gas is oxidized to NO2 and nitrite in the liquid phase first,and then about 1/3 of it is finally oxidized to nitrate.Secondly,taking the CO₂ absorption system of alkali solution 0.5 mol/LNa₂CO3-0.5 mol/L NaHCO₃（0.002～0.008 mol/L NaAsO₂ as catalyst）as the experimental research system of gasliquid mass transfer reaction,the liquid-phase mass transfer coefficients kNO,L and gas-liquid specific phase boundary area aNO,L in the process of NO absorption in Na₂S₂O₈ solution were indirectly measured by Danckwerts plotting method.And the gas-phase mass transfer coefficients kNO,G in the process of NO absorption were indirectly measured by CO₂ absorption system by alkali solution 0.02～0.08 mol/LNaOH.The results show that under the experimental conditions,the values of kNO,L are about 3.5-15×10-4 m/s,the values of aNO,L are about 30-170 m²/m³,and the values of kNO,G are about 1.6-5.2×10-5 m/s.Finally,the mass transfer reaction kinetics in the process of NO absorption is studied.The mass transfer process in the process of Na₂S₂O₈ wet oxidation of NO is analyzed.The NO absorption rate equation is obtained according to the mass transfer reaction differential equation.And the variation law of chemical reaction rate constant of NO and the of "Hatta number" are calculated.The results show that the absorption process of NO in Na₂S₂O₈ solution is affected by both mass transfer rate and chemical reaction rate,and conforms to the basic law of double film theory,.The absorption rate equation of NO is（?） and the value of chemical reaction rate constant of NO is between 0.14-6.66×109s-1,and the value of Hatta number is between 0.89-3.29×103.It can be concluded that the process of NO removal by Na₂S₂O₈ wet oxidation belongs to rapid pseudo first order reaction,and the mass transfer rate is the main control step affecting the whole absorption process.