Study On Preparation Of Ozone By Plasma And Simultaneous Desulfurization And Denitrification

In recent years,great achievements have been made in air pollution control in China.However,coal-fired pollutants are still the main source of air pollution.The flue gas released from coal combustion contains large amounts of NO_X and SO₂,which are seriously destructive to the natural environment and human physical and mental health.The traditional desulfurization and denitrification technology mainly operate in series between the single denitrification unit and the single desulfurization unit,which suffers many disadvantages of catalyst deactivation,large occupation area,equipment corrosion and complicated system.To get over these shortcomings,simultaneous desulfurization and denitrification based on wet desulfurization technology has been favored by researchers.In this paper,the simultaneous removal of NO_X and SO₂ via ammonia absorption based on pre-ozonation were studied.Firstly,the process and mechanism of preparation of O₃ by dielectric barrier discharge（DBD）microplasma technology were studied.Then,the effects and mechanisms of various factors on NO pre-ozonation and absorption of ammonia during simultaneous desulfurization and denitrification were explored.The discharge gap,discharge length,discharge power and residence time in DBD reactor had different effects on O₃ concentration and energy efficiency.With sinusoidal AC power supply,the maximum O₃ concentration achieved under optimized conditions was 120.6 g/Nm³,and the corresponding energy efficiency was89.9 g/（k W·h）.Additionally,with the pulsed modulation power supply,the O₃concentration and energy efficiency can reach 128.8 g/Nm³ and 119.5 g/（k W·h）,respectively,which is basically close to the minimum energy consumption for industrial ozone production.The coexistence of N₂,Ar and water vapor in O₂ was not conducive to the formation of O₃,among which water vapor had the greatest effect,while Ar had the least.The optical emission spectroscopy（OES）diagnostics was used to monitor the discharge process in different discharge atmospheres,and the mechanism of O₃ synthesis was proposed.Fe₂O₃ and Cr₂O₃ were formed on the surface of stainless steel electrodes by oxygen plasma oxidation,which promoted the formation of O₃.In the study of simultaneous desulfurization and denitrification,the products of NO oxidation by O₃ varied with the change of MR（O₃/NO）;the change of pre-oxidation temperature,SO₂ concentration,water vapor content and sampling position had negligible insignificant impact on NO conversion.Increasing the concentration of ammonia and SO₂ can promote the absorption of NO_X,while the increased absorbent temperature and O₂ content had adverse effects.The change of solution p H had substantial influence on the absorption of NO_X.Since the buffer pair formed by CO₂ in the solution kept the absorbent weak alkaline all the time,the removal efficiency of NO_X was only 60%at lower absorbent temperature（25℃）with the coexistence of CO₂.Raising the absorbent temperature to 60℃,the removal efficiency of NO_X increased to 89.2%.Both the addition of Na₂S₂O₃ and urea can boost the NO_X removal efficiency at lower absorbent temperature（25℃）.But the advantage of adding Na₂S₂O₃ became less evident at higher absorbent temperature and coexistence of CO₂.In all experiments,the absorption of SO₂ in ammonia was quite nice,the removal efficiency was always above 99%,and was basically not affected by the above factors.The above results laid a foundation for the integration of coal-fired flue gas desulfurization and denitrification.