High Efficiency Flue Gas Desulfurization And Denitrification Technology Based On Wet Oxidation And Non-Thermal Plasma Dry Methods

Sulphur dioxide?SO₂?and nitrogen oxides?NOx?from coal combustion are the main atmospheric pollutants in China.The control of SO₂ and NOx emissions are important for economy,politics,and environment sustainable development.At present,limestone-gypsum and selective catalytic reduction?SCR?are the main desulfurization and denitrification technologies,but these methods are difficult to meet the growing environmental requirements,because of the problems including large area,high investment,harsh operating conditions,high operating costs,low system stability,and secondary pollutants.Therefore,a simple,economical and environmentally friendly desulfurization and denitrification technology is needed for air pollution control.The wet oxidation method and non-thermal plasma?NTP?dry method are two of the most promising desulfurization and denitrification methods.The wet oxidation method has the characteristics of high removal efficiency of SO₂ and NO₂,while the NTP dry method has the advantages of simple process,no secondary pollution and simultaneous removal of many pollutants.Threedesulfurizationanddenitrificationtechnologiesincluding254nm-UVC/Na₂S₂O₈ wet process,DBD-NPC dry process and the combination of Na₂S₂O₈and DBD-NPC dry-wet process were proposed in this study.The effects of various factors on NO and SO₂ removal were studied in a self-made simulated flue gas system.The flue gas analyzer,ionization chromatography,and mass spectrometry were used to study the reaction path,reaction mechanism,and products.The results show that the combination of Na₂S₂O₈ and DBD-NPC can remove NO and SO₂ efficiently.Finally,the by-products can be converted into valuable substances by ion exchange resin.The main results are as follows:?1?A 254 nm-UVC ultraviolet photocatalytic Na₂S₂O₈ wet desulfurization and denitrification system was set up.The experiments of single and simultaneous desulfurization and denitrification were carried out at atmospheric pressure.The results show that 254 nm-UVC can obviously activate the reaction with Na₂S₂O₈ participates.The conditions of ultraviolet irradiation intensity,Na₂S₂O₈ concentration,solution temperature,O₂ concentration,and solution height can promote NO removal.Ultraviolet irradiation can weaken the negative effect of inlet gas flow rate and initial NO concentration on NO removal.At the same time,the removal efficiency of SO₂ and NO can reach 95%and 70%respectively,and SO₂ can promote NO removal.Ion chromatography analysis shows that NO and SO₂ are converted into NO₃^-,SO₄^2-,respectively.The concentrations of SO₄^2-and NO₃^-after photocatalysis are much higher than that without photocatalysis.The calculated value of ion concentrations are consistent with the measured value and the data are reliable.?2?A DBD-NPC dry desulfurization and denitrification system was set up.The process of desulfurization and denitrification was investigated at room temperature and pressure with five aspects:discharge reaction system,electrode condition,reaction condition,additive,and energy density.The reaction path,reaction products,and reaction mechanism were also studied.The results show that the increase of applied current can promote the removal of NO and reduce the formation of NO₂ and N₂O;the increasing of NO concentration can not only reduce the removal rate of NO,but also reduce the formation rate of NO₂;O₂,CO₂,and H₂O inhibit the NO removal in a decreasing order;adding methanol and ethanol can significantly improve the NO removal efficiency without secondary pollutants of CO and NO₂.NO_X?NO,NO₂?is mainly reduced to N₂.Unlike NO removal,O₂ and H₂O promoted SO₂ removal.At the condition of SO₂ and NO coexistence,the removal of SO₂ is in competition with that of NO.?3?The method of combining methanol-assisted DBD-NPC with Na₂S₂O₈ wet process was proposed and studied,both NO and SO₂ can be removed efficiently,and the industrial application of this method was also discussed.Finally,the by-product sodium sulfate was converted into sodium bicarbonate and ammonium sulfate by introducing recyclable anion and cation exchange resin.This study can provide an experimental and theoretical basis for industrial application of high efficiency desulfurization and denitrification technology.