Kinetics Of Oxidation Process In Wet Flue Gas Desulfurization Technology

The power generation in China is mostly generated by coal-fired plant. As the coals resources containing high quantity of ash and sulfur, the pollution of sulfur dioxide, which produced by coal-fired power plant, becomes severe nowadays. The flue gas desulfurization (FGD) is an effective way to control the emitted sulfur dioxide. The wet FGD process is the most extensively used technology for desulfurization. In that technology, the oxidation ratio of calcium bisulfite determines the removal ratio of SO₂ in the flue gas. So the study of oxidation is of significance.Aim at the typical 300 MW FGD absorber, the simulant device has been set up, based on similarity principle. The similarity ratio of the device was set to 10:1. So its inside diameter was 1.2 m and height was 1.2 m. The device also has been equipped with a dial type air jet to make air uniformity in the slurry. The results of simulations and experiments indicated that, the simulant device is of preferable mass transfer performance. So the device could be used in the experimental research of the oxidation process.The uncatalyzed oxidation experiments have been executed in the simulant device. The bisulfite was obtained by the reaction of analytic calcium oxide, distilled water and sulfur dioxide. The optimal experimental conditions, have been gained by orthogonal experiments, which the bisulfite concentration was 0.01 mol·L^-1, the pH was 3.5, the temperature of slurry was 55℃, the oxygen partial pressure was 60.8 kPa and the stir speed was 0.01 mol·L^-1. The uncatalyzed oxidation experimental results indicated that the reaction order of bisulfite was 1, the reaction order of dissolved oxygen was 0 and the activation energy was 71.43kJ·mol^-1. The rate determine step of uncatalyzed oxidation was the secondary ionization of bisulfite.The oxidation process which was catalyzed by manganese or ferrous ion has been researched. The manganese catalyzed experiments indicated that, the reaction order of manganese ion was 0.5, the bisulfite was 1 and the dissolved oxygen was 0. The activation energy was 40.72 kJ·mol^-1. The rate determine step of manganese catalyzed oxidation was the generation of free radical initiated by manganese ion. The ferrous catalyzed experiments indicated that, the reaction order of ferrous ion was 0.5, the bisulfite was 1 and the dissolved oxygen was 0. The activation energy was 54.52 kJ·mol^-1. The rate determine step of ferrous catalyzed oxidation was the generation of free radical initiated by ferrous ion.The catalyzed oxidation experiments have been executed first time when manganese and ferrous ion existed simultaneously. The manganese-ferrous catalyzed experiments indicated that, the reaction order of manganese ion was 0.25, the ferrous ion was 0.25, the bisulfite was 1 and the dissolved oxygen was 0. The activation energy was 43.73 kJ·mol^-1. The rate determine step of manganese-ferrous catalyzed oxidation was the generation of free radical initiated by manganese ion and ferrous ion. It agreed the parallel reaction mechanism.The dynamic model of oxidation process has been established, based on the experimental results. The main expression was as follows:The calculation results indicated that the model could preferably explain the oxidation process. The results also indicated that, the activation energy of uncatalyzed oxidation, manganese catalyzed oxidation, ferrous catalyzed oxidation and manganese-ferrous catalyzed oxidation were 73.08kJ·mol^-1, 42.11kJ·mol^-1, 53.85kJ·mol^-1 and 44.80kJ·mol^-1 respectively. The relative errors between these calculation results and the experimental results were 2.32 %, 3.40 %, 1.22 % and 2.46% respectively.The crystallization process of desulfurization gypsum has been researched experimentally. The results indicated that, the optimal residence time was eight hours. Besides, the impurities could change the crystal form, which might be related to the crystal plane absorbing the impurities. The last, the stir speed could change the crystal form. That was because descending the stir speed could reduce the calcium bisulfate concentration in one hand, in another hand the low stir speed could make the grow speed of crystal plane differently.The originality innovations of the thesis are as follows. (1) The simulant device has been set up aim at the typical 300 MW FGD absorber. Based on the device, the catalyzed oxidation experiments have been executed first time when manganese and ferrous ion existed simultaneously. (2) The oxidation process which was catalyzed by manganese or ferrous ion has been systemically researched. The rate determine step of manganese catalyzed oxidation has been obtained the first time, which was the generation of free radical initiated by manganese ion or ferrous ion. (3) The dynamics model of oxidation process has been established. The main expression of it was as follows:...