Study On Mathematical Model Of Mass Transfer Absorption And Oxidation Of +4 Sulful In Ammonia Desulfurization By Spray Tower

A series of physical and chemical reactions will be triggered when the sulfur dioxide?SO₂?entered the atmosphere,not only caused the direct harm like haze and acid rain to the environment,but also the indirect harm to the environment was also quite serious,the resulting economic losses should not be underestimated.Although the country's control efforts was increased and the emission standards were more stringent about the emissions of SO₂,but the total emissions of SO₂ still exceeded 18 million tons/year.The ammonia as a high chemical activity of alkaline substances was used to be as absorbent to absorb SO₂ in flue gas in the ammonia desulfurization,not only the SO₂ can be removed in the flue gas,but also the by-product of ammonium sulfate-an efficient fertilizer was produced in the desulfurization at the same time,and the recovery and utilization of sulfur resources was achieved.At present,the engineering design and operation about the spray tower of ammonia desulfurization in China were mainly depends on flow simulation and control the relevant parameters for experience to achieve,it was difficult to achieve the optimal combination of economy and technology,and the probability of the occurrence of the escape of aerosol in the desulfurization process will be increased.Therefore,this paper combined with the characteristics of ammonia desulfurization process,the mass transfer of SO₂,the absorption of SO₂ and the process of +4 sulfide oxidation of ammonia desulfurization in the spray tower was studied,and the relevant mathematical model was established.The mass transfer coefficient was an very important design parameter of absorption tower in the ammonia desulfurization.Therefore,the technical characteristics of the ammonia desulfurization by spray tower was considered,it has combined with the calculation of liquid droplet and liquid film movement on the wall of spray tower,the experimental research of the absorption and mass transfer process of SO₂ under different flue gas flow rate,pH value and liquid gas ratio were carried out.On thisbasis,the mass transfer rate of SO₂ under different conditions was simulated by nonlinear fitting,and the expression of gas phase mass transfer coefficient of SO₂ absorption in ammonia desulfurization was obtained.The mass transfer coefficient could reflect the mass transfer rate of unit mass transfer interface,which was more suitable than the mass transfer coefficient by numbers related formula and volumetric mass transfer coefficient.The absorption of SO₂ was one of the main reaction processes in the ammonia desulfurization,it was satisfied the conservation of the ion charge and the conservation of the material.Based on this basic principle,the gas-liquid equilibrium and the characteristics of chemical reaction of ammonia desulfurization were combined,the dynamic balance function relationship between the SO₂ equilibrium concentration y* at gas-liquid interface and the concentration of hydrogen ion H+ was constructed,and the mathematical model of SO₂ absorption process in the ammonia desulfurization was established.The removal rate of SO₂ under different slurry pH value,liquid gas ratio and flue gas flow rate was calculated by the established mathematical model,and the measured values and the calculated values were compared.The oxidation of +4?S?IV??was the key to realize the recovery and utilization of sulfur resources and improve the economic benefits of ammonia desulfurization.Based on the former research of oxidation kinetics of S?IV??+4 valence sulfur?in our research group,according to the characteristics of ammonia desulfurization process,the spray tower holding tank was regarded as continuous mixed bubbling oxidation reaction device,the +4 valence sulfur oxidation model was established,and the change rule of oxidation ratio about the S?IV?with total sulfur concentration,pH value,oxidation air quantity,residence time and other parameters in the holding tank were revealed by the mathematical model of the oxidation of S?IV?,and the measured values and the calculated values were compared.Characteristics of ammonia desulfurization process were combined,and the three processes of gas liquid two phase mass transfer,absorption of SO₂ and oxidation of+4 sulfur were studied in the ammonia desulfurization,the mathematical model wasestablished to accurately reflect the mechanism of ammonia desulfurization process,it was provided a theoretical reference for the design and operation of ammonia desulfurization by spray tower.