Removal Of NO_x From Flue Gas By Surface Discharge Ozonation Combined With NaOH-Na₂SO₃ Absorption Process

The widely used technology for coal-fired flue gas treatment at present is the combination of wet desulfurization and SCR/SNCR.These methods always need complex equipment and covers an area with larger scale,and there also have the problem of secondary pollution.In addition,the removal rate of NO_x is lower than SO₂.To solve these problems,we use the method which combined ozone oxidation with reducing alkali solution absorption process to improve the removal rate of NO_x.To explore the removal mechanism of NO_x,we use the surface discharge non-thermal plasma as the source of O₃ to make NO oxidized to NO₂.Then we use NaOH-Na2SO₃ solution as absorbent to implement the removal of NO₂ through the absorption process.Finally,the main reaction during NO₂ removal process has been discovered by analyzing the calculation results.In this paper,we investigate the results of NO oxidation and NO₂ removal.The effect of reaction conditions and removal mechanism of NO₂ also been investigated.The main contents and results are as follows:?1?The surface discharge reactor use a stainless steel spring as the high voltage electrode,and we investigate the influence of screw ring spacing and line diameter on O₃ output.Finally,we determine the screw ring spacing and line diameter of 5 mm and 1 mm respectively.?2?We investigated the O₃ output,oxidation rate and removal rate of NO under the condition of different discharge voltage.When the voltage increase from 2.4 kV to 3.0 kV,there have a rapidly growth of O₃ production.When the voltage is higher than 3.0 kV,the production of O₃ begin to decrease slowly.When the molar ratio of O₃ and NO is 1.1 at 2.6 kV,the removal rate of NO is 91% and remain stable during the increase of O₃/NO molar ratio.The conversion rate of NO to NO₂ is 85% at 2.6 kV,and it will have a rapidly decrease with the increasing of voltage.?3?The increase of moisture content in simulated flue gas makes NO oxidation rate declined,and the effect is obvious within the scope of the discharge voltage if 2.5 2.8 kV.The increase of residence time have little influence on NO conversion rate.The presence of SO₂ makes NO conversion rate declined.?4?The absorption liquid in this experiment is a mixed solution of NaOH and Na2SO₃,and the mass fraction of them is 0.1% and 1%,respectively.The removal rate of NO₂ is 97%.The mass fraction of NaOH has less effect on NO₂ removal,but a larger mass fraction of Na2SO₃ will makes the NO₂ removal rate maintaining stability after a rising process.The removal rate of NO₂ increase with the increasing of pH value,and decrease with the increasing of absorption liquid temperature and oxygen content of simulated flue gas.The reaction mechanism of absorption process include the reaction of NO₂ soluble in water and react with SO₃2-ions.The reaction products and calculation results indicate that the remove of NO₂ mainly through the reaction with SO₃^2-.