Research On Ammonia-Based Wet Flue Gas Desulfurization And Simultaneous Desulfurization And Denitrification Combined With Ozone Oxidation

The ammonia-based wet flue gas desulfurization technology has been widely used in China due to its high SO2removal efficiency and recovery of ammonium sulfate as byproduct in good quality, it is a good technology which can be up to the requirements of environment protection and circular economy. The ammonia-based WFGD can realize simultaneous desulfurization and denitrification if the ozone oxidation technology is used with it, the new technology has great potential in research and application for the reason that it can remove SO2and NOx and recover ammonium sulfate and ammonium nitrate at the same time. In this paper, experiments were conducted to study the process of oxidation and catalytic oxidation of ammonium sulfite. A self-made bubbling reactor was used to make systematic study on ammonia-based WFGD process, the mechanism of ammonium sulfite oxidation was discussed according to experiment results. The decomposition rules of ozone and the oxidation behavior of ozone on main pollutants in flue gas were explored, an investigation on the process of simultaneous absorption of SO2and NOx into ammonia was also studied in bubbling reactor.The kinetics of ammonium sulfite intrinsic oxidation in high purity water were studied in an intermittent airtight homogeneous reactor, the reaction orders of reactants and the apparent activation energy were determined. The kinetics of ammonium sulfite macroscopical oxidation were studied in an aeration stirring reactor, the kinetics equations were established and the diffusion of oxygen is the controlling step in the oxidation of ammonium sulfite. The kinetics of ammonium sulfite intrinsic oxidation by different catalysts were studied in an intermittent airtight homogeneous reactor, ferrous chloride was selected as the best catalyst in the end. The kinetics of ammonium sulfite macroscopical oxidation catalyzed by ferrous chloride were studied in an aeration stirring reactor, the results showed that the reaction orders of ammonium sulfite and ferrous chloride are1.0and0.4, the apparent activation energy is29.87kJ/mol.The ammonia-based WFGD process was studied both in the absence and appearance of catalyst by bubbling reactor. The experiment results showed that the bubbling reactor has good ability of impact resistance to the changes of flue gas amount and sulfur dioxide concentration, the higher flue gas amount and oxygen content and lower dioxide concentration are favorable to the recovery of ammonium sulfate. The catalyst decreased the absorption capacity, the increase of catalyst concentration could shorten the duration in high desulfurization efficiency. The changes of pH could be divided into three stages including slow decline stage, rapid decline stage and slow decline-again stage, the dividing points were7.0and4.0. The desulfurization efficiency was over99%when pH was greater than4.0, the removal efficiency decreased rapidly when the pH was lower than4.0.Experiment was carried out to study the decomposition rules of ozone and the oxidation behavior of ozone on sulfur dioxide and nitric oxide. The results indicated that temperature is the main factor which influences the ozone decomposition, the ozone concentration had little impact on ozone decomposition. The dosage of ozone was the most critical factor which effects the oxidation of nitric oxide by ozone, other factors such as concentrations of nitric oxide and sulfur dioxide, residence time and oxygen content of flue gas had not obvious influence on the effect of nitric oxidation. The oxidation rate of nitric oxide always kept at more than90%as long as controlling the molar ratio between ozone and nitric oxide over1.0.The simultaneous absorption process of sulfur dioxide and nitrogen oxides was studied in bubbling reactor. The results showed that the desulfurization efficiency stabilize at99%under different operating conditions, the denitrification efficiency increased as the increase of ozone dosage and sulfur dioxide concentration, the denitrification efficiency decreased as the increase of nitric oxide concentration and flue gas oxygen content. More flue gas amount, ozone dosage and flue gas oxygen content were beneficial for by-products recycling. The changes of pH could be divided into three stages including slow decline stage, rapid decline stage and slow decline-again stage, the dividing points were8.5and4.0. The desulfurization and denitrification efficiency stabilized at a high level, when pH was greater than4.0, the removal efficiency of sulfur dioxide and nitric oxide decreased rapidly when the pH was lower than4.0.