Research On ClO₂ Gas Phase Oxidative Desulfurization And Denitrification Process And Its Application

With China’s increasing emphasis on the atmospheric environment,traditional desulfurization and denitration processes have been unable to meet the country’s new requirements for flue gas treatment.According to the characteristics and treatment requirements of exhaust gas from small and medium-size industrial boilers,the commonly used liquid-phase oxidation absorption process is improved,and the ClO₂ gas-phase oxidation combined with sodium-alkali liquid absorption desulfurization and denitration is adopted to treat the exhaust gas.Through laboratory research,the gas-phase oxidation efficiency,NOx removal effect,influencing factors,and optimal process conditions were investigated;the feasibility of desulfurization liquid reuse denitration and the mechanism of desulfurization and denitrification were explored.Subsequently,the actual desulfurization and denitrification effect was verified through the application on industrial boiler exhaust gas treatment.The main research contents and results are as follows:（1）Under laboratory conditions,the effect of NaOH solution on the removal of SO₂ was first investigated.NaOH concentration and absorption temperature are confirmed to be the main factors affecting the removal rate.The removal rate decreases with the increase of NaOH concentration,or decreases with the increase of the absorption temperature.The desulfurization rate of 4～10 g/L NaOH solution for 990 ppm SO₂ gas can reach 98.28%-99.80%at room temperature,and 0.1mol/L（4g/L）NaOH solution can still achieve 94.34%of desulfurization rate at 40℃.It can be seen that NaOH is an excellent desulfurizing agent.（2）The oxidation efficiency of ClO₂ to NO under gas phase conditions was studied.The molar ratio:[ClO₂]/[NO]of gas phase reaction is verified an important factor affecting the efficiency of NO oxidation;the NO oxidation rate increases with the increase of[ClO₂]/[NO].The optimal[ClO₂]/[NO]obtained under the experimental conditions is 1.01;the NO oxidation rate is able to reach 94.1%;and the main oxidation product is NO₂.The higher NO oxidation rate lays the foundation for the improvement of the denitration efficiency of the alkaline solution absorption method.（3）The removal effects of several sodium-alkali denitration solutions on ClO₂/NO reaction products were investigated.Among them,the denitration effect of NaOH solution is not ideal;the denitration rate can only reach 66.33%under the best conditions.The denitration effect of Na₂SO₃ solution is better than NaOH solution,and the maximum denitration rate can reach 93.59%.The NaOH+Na₂SO₃ composite solution has better denitrification effect than the previous two used alone,and the denitration rate is less affected by various factors than the NaOH or Na₂SO₃ denitration solution used alone.At room temperature and in a wider[ClO₂]/[NO]range（0.52～1.01）,the denitration rate is more than97%.At 40°C and 1.0 of[ClO₂]/[NO],the composite solution with the economical concentration of 0.06mol/L NaOH and 0.015mol/L Na₂SO₃ can also possess a denitration rate of more than 96%.It can be seen that the NaOH+Na₂SO₃ composite solution is more suitable for the removal of NO oxidation products,which also provides ideas for the disposal and utilization of desulfurization product SO₃^2-.In addition,NO₂^-in the absorption solution was confirmed to be inhibitory to the absorption of NO_x.Therefore,it needs to be disposed in time according to the denitration effect in engineering applications,so as to ensure the denitration effect.（4）The feasibility and mechanism of denitration of sodium-alkali desulfurization solution were studied.The main desulfurization product of sodium-alkali solution is sulfite.From the point of view of concentration and yield of desulfurization products,and from the denitration effect of the composite absorption solution,the sodium-alkali desulfurization solution has reuse value.By measuring the composition and concentration of the products before and after denitration of the simulated sodium-alkali desulfurization solution,it is concluded that the main products of denitration of sodium-alkali desulfurization solution are NO₂^-and NO₃^-,and mainly NO₂^-.Result show that the denitration process of the sodium-alkali solution containing sulfite is mainly that of reduction denitration.（5）Combined with the improvement of ultra-low emission flue gas treatment process of enterprise’s 30t/h industrial coal-fired boiler,the ClO₂ gas phase oxidation denitration link was introduced in the original process.At the same time,the spray absorption and dust removal system was optimized,and the desulfurization and denitration waste liquid pre-treatment was added.After this improvement,the removal rates of particulate matter,SO₂ and NOx by the system can reach 99.86%,99.61%and 97.43%,respectively.The emission concentrations of particulate matter,SO₂ and NOx decreased from 11 mg/m³,8 mg/m³ and120 mg/m³ before the improvement to 2.3～3.1 mg/m³,2.6～4.6 mg/m³,and 7.1～8.6 mg/m³.The system achieved ultra-low emissions,with the most significant improvement in denitration efficiency.The cost of the flue gas treatment agent is￥65.06/10000m³,of which￥24.52 is the cost of newly added oxidants.The additional desulfurization and denitrification waste liquid pretreatment devices enable the initial detoxification of desulfurization and denitrification products such as acid,alkali and nitrite in the waste liquid,clarified water be re-used,and subsequent treatment costs be reduced,which has the effect of saving water and reducing emissions.