Modeling the Rate of Batch-Mode Thermal Degradation of Polyethylene Suspended in an Oven
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ORIGINAL PAPER
Modeling the Rate of Batch-Mode Thermal Degradation of Polyethylene Suspended in an Oven Q. Balme1 · M.T. Rozaini1 · F. Marias3 · F. Lemont2 · P. Charvin1 · J. Sedan1 Received: 12 February 2020 / Accepted: 6 November 2020 © Springer Nature B.V. 2020
Abstract This study presents dynamic modeling of the thermal degradation of polyethylene (PE) in an oxidizing atmosphere. The purpose of the work is to calculate the degradation rate of samples placed in a macro-thermobalance. The model is composed of two coupled sub-models: the first one describes the processes occurring in the condensed phase (where termal degradation of PE in lighter molecule occurs) while the second one accounts for the processes occurring in the gaseous phase. The condensed phase model allows for the evaluation of the rate at which combustible gas is produced by PE pyrolysis and the gas phase model computes the gaseous oxidation of the products of pyrolyse and subsequent heat flux transferred back to the sample. This second model relies on the use CFD (Ansys Fluent) where turbulent combustion of octane (which is supposed to be the product of PE Pyrolysis) is accounted for thanks to eddy dissipation approximation. The effect of the filling height in the sample crucible containing the polyethylene is studied. The experimental results from macro TGA (MTGA) and from the mathematical model are compared. Three different behaviors associated to crucible filling height are highlighted. For small ones, kinetics of pyrolysis is the overall limiting phenomenon, whereas heat transfer to the sample is the limiting one for high filling heights. Both experimental and numerical findings show that the position of the flame in the vincity of the crucible (inside or outside and surrounding it) is the key parameter in polyethylene’s degradation rate. Graphic Abstract
Keywords Combustion · Polyethylene · Macro TGA · Pyrolysis · Thermal degradation · CFD Extended author information available on the last page of the article
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Waste and Biomass Valorization
Statement of Novelty Combustion of loads of polyethylene in a Macro TGA, with samples up to 65 g, is investigated with the aim to highlight the influence of the shape and filling rate of the crucible on the overall degradation rate. The analysis is performed using both experimental results and numerical ones resulting from dynamic modelling of the physical and chemical phenomena occurring during the transcient emptying of the crucible. This dynamic modelling, which relies on the coupling between a home-made model and CFD with non-stationary boundaries, constitutes a novelty.
Introduction Many studies examining pyrolysis [1–8], torrefaction [9, 10] or gasification [5, 11, 12] of household waste or biomass rely on the use of a macro Thermogravimetric Analyser (MTGA). These devices measure, simply and reliably, the rate at which a compound (possibly multi-constituent) decomposes under the effect of heat. Macro TGA is not often used when the thermal degradation is performed
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