Kinetic modelling of coking coal fluidity development
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Kinetic modelling of coking coal fluidity development M. Sciazko1 · B. Mertas1 · L. Stepien2 Received: 24 July 2019 / Accepted: 21 February 2020 © The Author(s) 2020
Abstract Coal plasticity is a phenomenon directly affecting the creation of coke structure. It is very much a time- and temperaturedependent transformation of the coal matrix, which allows changing the physical phase from solid to liquid-like and again into solid of different properties. The coking process, particularly in a plasticization temperature range, can be considered as a non-isothermal reaction at a constant heating rate. In this work, a macro-kinetics approach is applied that results in effective kinetic parameters, i.e. pre-exponential factor and activation energy. It is postulated in this work that the original content of metaplast (M0) is a part of volatile matter that melts under the effect of temperature. The coal sample can melt steadily with the temperature increase, achieving the maximum fluidity (Fmax) when the total amount of metaplast available turns into the plastic state. Coal behaviour while it is being heated can be described by two mechanisms. Under first one, the coal turns into plastic phase starting at t1 and ending at tmax, where solidification starts. This can be considered as independent reactions model. In the second model, both plasticization and solidification reactions compete over entire range of phenomena. This can be considered as reactions in the series model. The developed models were validated against experimental data of coal fluidity delivering kinetic parameters. Keywords Coking coal pyrolysis · Metaplast content · Fluidity development · Phase transition kinetics
Introduction When coking coal is heated, it becomes soft in the temperature range 385–450 °C. The temperature range within which the coal forms a plastic mass very much depends on its chemical composition. Upon raising the temperature further, the plastic mass begins to harden, producing solidified, porous coke. The plastic state of coal allows trapping of gaseous products released due to the pyrolysis and allocation of plastic mass into the open interparticle spaces. The volume of the trapped gas depends on coal’s properties, particularly on volatile mass released and a plastic mass imperfection caused by the content of insoluble solid particles of coke. The fluidity, on the other hand, is related to its changing viscosity, which is time and temperature dependent. The fluidity measurement is usually measured with a Gieseler * B. Mertas [email protected] 1
Institute for Chemical Processing of Coal, Zamkowa 1, 41‑803 Zabrze, Poland
AGH University of Science and Technology, al. Mickiewicza 30, 30‑059 Kraków, Poland
2
plastometer [1]. In a plastic region, coal particles swell due to the softening and evolution of gaseous components that cause internal pressure to build up in a plastic layer of slot coke-oven charge, eventually generating dangerous wall pressure, also called coking pressure. Uncontrolled increase in this pressure can d
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