Mutual Transformation Mechanism Of Calcium Sulfate And Calcium Sulfide At High Temperature In Different Reacting Atmosphere

In this article, the oxidation mechanism of calcium sulfide and the decomposition mechanism of calcium sulfate was discussed in detail with large amounts of theory analysis and mechanism research, so that a full understanding of the staged desulfurization mechanism in PCC boilers can be taken. In addition, a two stage desulfurization industrial test on W shape PCC boiler was taken.Firstly, the decomposition mechanism under different oxidizing, inert and reduceing atmosphere was studied in detail and the decomposition reaction kinetics was studied using Freeman-Caroll method. In addition, Methylene blue spectrophotometric method and the simultaneous generation of calcium sulfide and calcium oxide was adopted to take a deep research of the decomposition mechanism of the decomposition mechanism under carbon monoxide atmosphere with different concentration, moreover the decomposition reaction type and the ultimate content of calcium sulfide in reaction product was analyzed.Secondly, the possibility of calcium sulfide generation in CaO-SO2-CO system was studied using FACT software. Afterwards a fixed bed quartz reactor system, Rosemounte gas analyzer and Methylene blue spectrophotometric method were used to take a deep research on the dedulfurization reaction and the transformation from CaCC<3 to CaS under fuel-rich condition.Thirdly, the solid-solid reaction of calcium sulfide and calcium sulfate, controlling step of the oxidation reaction of calcium sulfide and the decomposition reaction of calcium sulfate, was studied in detail. The solid-solid reaction kinetics was studied using Freeman-Caroll method. In addition, some kinetics parameters were used to study the superiority between different reactions: the solid-solid reaction, the decomposition reaction of calcium sulfate and the oxidation reaction of calcium sulfide with carbon dioxide. Moreover the influence of calcium sulfide content and calcium sulfate content on reaction rate of solid-solid reaction was also analyzed.Afterwards, the oxidation reaction of calcium sulfide under different reaction temperature and O2 with different concentration was studied using Quantitative Analysis Method for infrared spectroscopy and Methylene blue spectrophotometric method. With the quantitative analysis results of calcium sulfide and the amount of SO2 released , the phase composition of reaction product and the distribution of different kinds of sulfur in gas phase, solid phase were analyzed in detail. In addition, unreacted core model was applied in studying the chemical reaction rate constant and solid state diffusivity.Moreover, a new kind of staged desulfurization method was put forward considering the characteristic oxidizing and reducing conditions in pulverized coal fired boilers. The 'W shape flame experimental combustion furnace was used and the dynamic concentration of various compositions of flue gas in the combustor, including SO2 and H2S, was measured. It was foundthat when the sorbents was mixed up with the pulverized coal with a molar ratio Ca/S=2 and transmitted into the furnace by the first air, the sulfur removal efficiency was 41.2%. When the two-stage calcium injection process with a molar ratio Ca/S=3 was used, the sulfur removal efficiency could be greatly improved to 71.2%.At last, the oxidation reaction of CaS with CO2 was discussed in detail. The different reaction type of CaS under different CO2 concentration and the influence of CO2 concentration, reaction temperature on CaS oxidation reaction was studied thoroughly. In addition, the oxidation reaction of CaS in O2/CO2 atmosphere was studied to elucidating the reaction rate of CaS in O2 and CO2 atmosphere.