Modelling and numerical simulation of isothermal oxidation of an individual magnetite pellet based on computational flui
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ORIGINAL PAPER
Modelling and numerical simulation of isothermal oxidation of an individual magnetite pellet based on computational fluid dynamics Zhou Pu1
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Feng Zhou1 • Yue Sun1 • Ming Zhang1 • Bo-quan Li1
Received: 29 April 2020 / Revised: 12 July 2020 / Accepted: 13 July 2020 China Iron and Steel Research Institute Group 2020
Abstract A mathematical model based on the computational fluid dynamics method, heat and mass transfer in porous media and the unreacted shrinking core model for the oxidation reaction of an individual magnetite pellet during preheating was established. The commercial software COMSOL Multiphysics was used to simulate the change in the oxidation degree of the pellet at different temperatures and oxygen concentrations, and the simulated results were compared with the experimental results. The model considered the influence of the exothermic heat of the reaction, and the enthalpy change was added to calculate the heat released by the oxidation. The results show that the oxidation rate on the surface of the pellet is much faster than that of the inside of the pellet. Temperature and oxygen concentration have great influence on the pellet oxidation model. Meanwhile, the exothermic calculation results show that there is a non-isothermal phenomenon inside the pellet, which leads to an increase in temperature inside the single pellet. Under the preheating condition of 873–1273 K (20% oxygen content), the heat released by the pellet oxidation reaction in a chain grate is 7.8 9 106–10.8 9 106 kJ/h, which is very large and needs to be considered in the magnetite pellet oxidation modelling. Keywords Magnetite pellet Oxidation Numerical simulation Unreacted shrinking core model Computational fluid dynamics
1 Introduction In recent years, the iron ore pellet has become a desirable feedstock for ironmaking furnaces all over the world due to the fact that the pellets have the advantages such as high iron content, uniform granularity, high porosity, high strength, good reducibility under 1373 K, and the suitability for storage [1–3]. At present, shaft furnace, graterotary kiln and belt-type roasting machine are the main equipment for pelletising production. Among them, the grate-rotary kiln process has the outstanding characteristics of strong applicability to raw materials, diversified fuels, low amount of high temperature resistant special alloy steel, more uniform product pellet quality, and easy to
& Bo-quan Li [email protected] 1
Department of Instrumentation Science and Technology, Jiangsu University, Zhenjiang 212013, Jiangsu, China
achieve large-scale. In the grate-rotary kiln pelletising process, high grade magnetite concentrate is used as the main raw materials for production and made into green pellets with moisture. The wet green pellets are loaded on a travelling grate with a bed height of 20–23 cm. This bed of wet green pellets is transported through the drying zones, updraft drying (UDD) and downdraft drying (DDD). After
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