| The limestone-gypsum wet flue gas desulfurization process is an important process for controlling sulfur dioxide emissions in thermal power plants in China,and the oxidation rate of calcium sulfite is an important technical index in this process.At present,only simple acid-base control is performed on the slurry oxidation rate in domestic practical engineering applications,but a single pH indicator cannot reflect the internal oxidation state of the slurry.Unstable oxidation rate will cause many problems,such as excessive energy consumption of oxidation fan,excessive sulfite standard,system scaling,and poor quality of gypsum.Therefore,the use of multiple indicators to scientifically and effectively control the mandatory oxidation of the desulfurization system to ensure a high oxidation rate of calcium sulfite is of great significance to the energy saving and consumption reduction of the power plant desulfurization system.Through experimental research and simulation,this paper sets Dissolved Oxygen(DO)and Oxidation Reduction Potential(ORP)as control indicators.The regulation mechanism of dual indicators in the oxidation process of desulfurization slurry was explored.The relationship model of DO-SO3---ORP in the slurry was established.The influence and control factors of DO and ORP were analyzed.Which provides theoretical guidance to the economic,stable and efficient operation of desulfurization system.By setting up a static oxidation experiment table,the characteristics of the SO32-oxidation rate and its rate of change with time,pH,DO and ORP with time were studied under different calcium sulfite concentrations.Revealed the changing law of pH value,DO and ORP and the changing law of calcium sulfite oxidation rate and its changing rate under different sulfite concentration conditions:as the concentration of calcium sulfite keeps decreasing,the pH value keeps decreasing.Under different concentration conditions,the changes of DO and ORP can be basically divided into four stages:a significant rising stage,the first stable stage,a short-term rising stage and a final stable stage.The effect of initial concentration on the concentration of SO3-,SO4-and SO5-was explored through numerical simulation,and the regulation mechanism of oxidation process was revealed.After SO3 opening the oxidation reaction chain,SO4-and SO5-begin to dominate the oxidation reaction.In this paper,based on the use of quasi-steady state analysis to simplify the reaction rate,a dimensionless number(Dp number)characterizing the relative magnitude of mass transfer and intrinsic reaction rate is constructed to determine the reaction control zone during the reaction process:Between 0 and 0.15 is the reaction control zone,between 0.15 and 0.4 is the joint mass transfer and reaction control zone,and above 0.4 is the mass transfer control zone.By setting up a dynamic oxidation experiment table,the effects of different oxidation air volume and different SO2 concentration DO and ORP on the oxidation rate were explored,and a specific control plan was made for the operation of the 150MW unit:under the condition that the slurry ORP value was positive Next,when the dissolved oxygen content in the slurry was maintained at 2.25 mg/L and the residence time of the circulating slurry was within 5 minutes,the desulfurized gypsum reached the standard for second-level desulfurized gypsum.The contribution of various factors(slurry temperature,oxidizing air volume and inlet SO2 concentration)at different stages of the desulfurization cycle slurry oxidation process to the DO and ORP of the desulfurization slurry system and the influence of various factors on DO and ORP were studied.It is concluded that temperature is the main factor affecting the change of ORP,and the amount of oxidizing air is the main factor affecting the change of DO.In a power plant in Shandong Province,We use DO as the measurement index to carry out field tests.According to the mechanism test results,we kept the slurry DO not less than 2.25mg/L,controlled the oxidation fan in different frequency ranges,recorded the real-time data of DO,and detected the internal oxidation state of the slurry.The test results show that the desulfurization efficiency changes less than 0.1%,and the change of DO has no effect on the desulfurization efficiency.The practical feasibility of DO indicating the oxidation state of the slurry is verified.The oxidation control using DO as the control index can bring huge economic benefits to the power plant,and the empirical values based on the DO indicating the oxidation state of the slurry are obtained,and the optimized operation of oxidation fan in the desulfurization system is realized. |
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