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Study On The Influence Of Coke And Its Impurities On Pyrolysis Process Of Calcium Sulfate

Posted on:2012-09-04Degree:MasterType:Thesis
Country:ChinaCandidate:R W XuFull Text:PDF
GTID:2121330332474831Subject:Chemical Engineering
Abstract/Summary:PDF Full Text Request
Industrial by-product gypsum is by-produced of the chemical reaction production of calcium sulfate dihydrate as the main component of the product industrial production, with very large output. But most of the industrial by-product gypsum has not been rational used, mainly in the stacking approach, which not only occupies a lot of land, but also pollutes the environment. Therefore, by-produced gypsum's treatment and utilization has become a worldwide problem. Co-production of cement and acid from gypsum can reduce both the gypsum stack, to avoid environmental pollution, and can achieve recycling of sulfur resources, with good prospects of application. However, there are some disadvantages in the traditional system of calcium sulfate through gypsum reduction by coke with co-production of cement, such as low concentration of sulfur dioxide, high energy consumption and investment, low output and poor economic, which restrict the promotion of this process. In this paper, the influence of coke and its impurities on the pyrolysis process of calcium sulfate was systematically studied in the aim of overcoming the shortcomings of this technology.Firstly, thermodynamic calculations of the possible reactions occurring during the reaction of calcium sulfate and carbon were carried out. The results showed that it was most likely to produce calcium sulfide and carbon dioxide by the reaction of calcium sulfate and carbon. And solid-solid reaction between calcium sulfate and calcium sulfide may occurs with production of calcium oxide and sulfur dioxide. Moreover, calcium sulfide and sulfur dioxide can continue to react and produce sulfur elemental calcium sulfate.Thermal analysis method was introduced for studying the reaction process of calcium sulfate and carbon. It's found that with excess calcium sulfate, carbon dioxide and calcium sulfide were produced by the reaction of calcium sulfate with carbon as the temperature increasing. Then solid-solid reaction between calcium sulfate and calcium sulfide occurs with production of calcium oxide and sulfur dioxide; if there is residual calcium sulfate, it will self-decomposed. In addition, there have been some side reactions, mainly the reaction of carbon and carbon dioxide producing carbon monoxide, or the reaction of calcium sulfide and sulfur dioxide producing sulfur elemental and calcium sulfate. Meanwhile, non-isothermal reaction kinetics were calculated about the self-decomposition of calcium sulfate and the reaction of calcium sulfate with carbon, The activation energy for self-decomposition of calcium sulfate is 367.09 kJ·mol-1, and the mechanism function is 1-(1-a) 0.87 with pre-exponential factor A is 2.076×1011S-1. And the activation energy of the reaction of calcium sulfate and carbon is 264.02 kJ·mol-1, and mechanism of function of a3/2, with the preexponential factor A is 8.613×109 S-1. The thesis also studies of influences of impurities in coke such as Fe2O3, SiO2, CaO on the decomposition of calcium sulfate. The results show that:the addition of Fe2O3 will promote the calcium sulfate decomposition; the addition of SiO2 will firstly promote the reaction because of the reaction of calcium sulfate and silicon dioxide, and then hinder the reaction due to the formation of molten calcium silicate wrapping on calcium sulfate; the addition of CaO will slightly hinder the decomposition of calcium sulfate.
Keywords/Search Tags:industrial by-product gypsum, co-production of cement and acid from gypsum, thermodynamics, non-isothermal kinetics
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