Study On Flue Gas Wet Desulfurization And Denitrification Process

With the development of industrialization,environmental issues have become the focus of today’s society.The pollutants such as SO_x and NO_x contained in the flue gas cause air pollution to become more serious.Research on low-cost and high-efficiency desulfurization and denitrification technology is urgent.This study introduces the desulfurization and denitrification technology at home and abroad,and makes an objective evaluation of various technologies.Among them,magnesium oxide desulfurization has the advantages of high efficiency,low cost,small footprint,no pollution,and desulfurization by-products can be recycled.It gradually takes the main position of desulfurization technology and has good research value.Firstly,the double membrane theory was used to study the absorption of sulfur dioxide,the digestion of magnesium oxide particles and the liquid phase reaction in the process of magnesium oxide wet desulfurization.Establish a reaction model for the entire desulfurization process and understand its reaction mechanism.The analysis shows that the mass transfer resistance from the sulfur dioxide absorption process mainly comes from the gas film and is controlled by the gas film.During the dissolution of magnesium oxide,the dissolution process is affected by the specific surface area of the solid particles of magnesium oxide and the concentration of magnesium ions ionized by the byproduct magnesium sulfite in the desulfurization slurry.In the liquid phase reaction process,since the magnesium sulfite formed by the reaction has an inhibitory effect on the ionization process of sulfurous acid and magnesium hydroxide,it is necessary to simultaneously control the sulfur dioxide absorption process and the magnesium oxide particle dissolution process.Through the analysis of the reaction mechanism,the desulfurization rate is mainly determined by single factor such as magnesium oxide slurry concentration,flue gas temperature,SO₂ inlet concentration,flue gas flow rate,slurry pH value and liquid-gas ratio（L/G）in the magnesium oxide desulfurization process.The optimum desulfurization conditions were determined:20%magnesium oxide slurry;flue gas temperature 60°C;desulfurization time10 min;SO₂ intake air concentration 1200 mg/m³;slurry pH value was 6;5m³/h;liquid-gas ratio（L/G）is controlled at 5L/m³.Under this condition,the magnesium oxide wet desulfurization efficiency is as high as 99%.Secondly,the gas absorption process was analyzed by the double membrane theory.The analysis showed that the absorption process of nitrogen oxides was controlled by the liquid membrane.The thermodynamic analysis of ammonia and urea denitration showed that the equilibrium partial pressure increased with the increase of temperature in the temperature range of 293.15K-393.15K,the solubility of nitrogen oxides decreased,and the mass transfer rate decreased.Lead to denitrification efficiency is reduced.The thermodynamic analysis shows that after the reaction reaches equilibrium,the partial pressure of nitrogen oxides in the ammonia denitration process is greater than the partial pressure of nitrogen oxides in the denitration process of urea.The denitration effect of ammonia is better than that of urea solution.Through the experiment,the single factor analysis of the denitration process was carried out to study the effects of urea concentration,ammonia concentration,liquid-gas ratio（L/G）,reaction temperature,urea solution pH and initial concentration of NOx on the denitration process.The optimal reaction conditions were determined as follows:The concentration of ammonia is 15%,the concentration of urea is 5%,the reaction temperature is 30°C,the initial concentration of NOx is 800mg/m³,the flow rate of flue gas is 10m³/h,the ratio of liquid to gas（L/G）is 30L/m³,and the pH of urea solution is controlled to 10.Under this condition,the denitration rate reached 50.8%.