Bohlender, Lukas

Dercho, Stefan

Stapf, Dieter

Tavakkol, Salar

Vogt, Jonas

Zeller, Michael

Zhang, Feichi

Zirwes, Thorsten

English

KITopen

KIT – The Research University in the Helmholtz Association www.kit.eduInstitute for Technical Chemistry (ITC)An assessment of fluidized bed dynamics with CPFD simulationsF. Zhang, S. Tavakkol, S. Dercho, L. Bohlender, T. Zirwes, M. Zeller, J. Vogt, D. Stapf31. Deutscher Flammentag27.-28. Sept. 2023TU BerlinFeichi Zhang | An assessment of fluidized bed dynamics with CPFD simulations Institut für Technische Chemie18.12.20232 Motivation Simulation method Numerical setups Results Fluidization behavior Effect of gas temperature Effect of up-scaling SummaryOutlineFeichi Zhang | An assessment of fluidized bed dynamics with CPFD simulations Institut für Technische ChemieChemical recycling of plastic wastes ~350 Mt plastic waste per year worldwide 22% mismanaged, 9% recycled Chemical recycling of plastic wastes Contaminated/mixed plastics Challenges Process design, efficiency, product yield, scale-up, economic viability Fluidized bed technology Enhanced, homogeneous heating Potential for scale-up Simulation of lab-scale fludized bed Model validation, hydrodynamics https://www.oecd.org/environment/plastic-pollution-is-growing-relentlessly-as-waste-management-and-recycling-fall-short.htmPyrolysis: Degradation of polymers at high temperature and oxygen-free environment into short-chain hydrocarbonsMismanaged 22% Landfilled 49% incinerated 19% recycledPolymer-isationPyrolysisEthylenePolyethylene (PE)Feichi Zhang | An assessment of fluidized bed dynamics with CPFD simulations Institut für Technische Chemie18.12.202343D simulations of cold-mode fluidized bed𝑑𝑅 = 5 cm Numerical setups Cylindrical reactor Bed material: quartz sand Fluidizing agent: N2 PSD: 𝑑mean = 2.3 mm Diameter: 𝑑𝑅 = 3, 5, 10 cm Gas temperature: 𝑇𝐺 = 25 and 500 °C OpenFOAM-v2206 Grid resolution: 1 mm No. parcels: up to 32 mil.Feichi Zhang | An assessment of fluidized bed dynamics with CPFD simulations Institut für Technische Chemie18.12.20235Ԧ𝑆𝑢Continuous phase – gasBalance of momentum(Navier-Stokes equations)Disperse phase – particleConservation of momentum(Newton‘s 2nd law)Ԧ𝐹𝑏 Ԧ𝐹𝑑Ԧ𝐹𝑔Ԧ𝐹𝑃𝑃Ԧ𝐹𝑃𝑊𝑚𝑃, 𝜌𝑃, 𝑢𝑃Computational particle fluid dynamics (CPFD)𝜕(𝛼𝑔𝜌𝑔𝑢𝑔)𝜕𝑡+ 𝛻 𝛼𝑔𝜌𝑔𝑢𝑔𝑢𝑔= −𝛻𝑝 + 𝛻 𝛼𝑔 Ԧ𝜏𝑒𝑓𝑓 + 𝛼𝑔𝜌𝑔 Ԧ𝑔 + Ԧ𝑆𝑢𝑚𝑝𝑑𝑢𝑝𝑑𝑡= ∑ Ԧ𝐹𝑒𝑥𝑡𝑒𝑟𝑛𝑎𝑙= Ԧ𝐹𝑑 + Ԧ𝐹𝑔 + Ԧ𝐹𝑐 + Ԧ𝐹𝑖Ԧ𝐹𝑑 Euler-Lagrange modeling (4-way coupling) Multiphase particle-in-cell (MPPIC) for modeling collisional forceԦ𝑆𝑢 = −1𝑉𝑐𝑒𝑙𝑙෍𝑖=1𝑛𝑝,𝑐𝑒𝑙𝑙Ԧ𝐹𝑑 Ԧ𝐹𝑐 ∝ 𝛻𝜏𝑝 𝜏𝑝 =𝑝𝑠 ∗ 𝛼𝑝𝛽𝛼𝑝𝑎𝑐𝑘𝑒𝑑 − 𝛼𝑝Feichi Zhang | An assessment of fluidized bed dynamics with CPFD simulations Institut für Technische Chemie18.12.20236ResultsFeichi Zhang | An assessment of fluidized bed dynamics with CPFD simulations Institut für Technische Chemie18.12.20237Fluidization behavior293 g 390 g          488 g𝑢𝑔 = 21 𝑐𝑚/𝑠𝜀 [−]13.6 cm/s    21.2 cm/s     29.7 cm/s𝜀 [−]Bed inventory 𝐦𝐒 ↑ Superficial velocity 𝒖𝒈 ↑𝑚𝑆 = 390 𝑔Feichi Zhang | An assessment of fluidized bed dynamics with CPFD simulations Institut für Technische Chemie12/18/20238Comparison with experiments𝒎𝑺↑ 𝒎𝑺↑ Bed height ℎ𝐵 increases with 𝑚𝑆 and 𝑢𝐺 Pressure drop ∆𝑝 increases with 𝑚𝑆 and remains almost constant with 𝑢𝐺Bed height 𝒉𝑩 Pressure drop ∆𝒑•  Exp.– Sim.Feichi Zhang | An assessment of fluidized bed dynamics with CPFD simulations Institut für Technische Chemie12/18/20239Specific kinetic energy of sand 𝒌𝑺 and bubble frequency 𝒇𝑩 Increase of 𝑘𝑆 with 𝑚𝑆 and 𝑢𝐺 𝑓𝐵 decreases inversely proportionally with 𝑚𝑆Dynamic properties of fluidized bed𝑢𝐺 = 21 cm/s𝐾𝑆 =12෍𝑖=1𝑁𝑝𝑚𝑝,𝑖𝑢𝑝,𝑖2 , 𝑘𝑆= Τ𝐾𝑆 𝑚𝑆𝑚𝑆↑Bubble frequency 𝒇𝑩 [Hz]Kinetic energy of sand 𝒌𝑺 [mJ/kg]𝒖𝑮↑293 g 390 g     488 gFeichi Zhang | An assessment of fluidized bed dynamics with CPFD simulations Institut für Technische Chemie18.12.202310𝑇𝐺 [℃] 25 500𝜌𝐺 [kg/m3] 1.14 0.44𝜐𝐺 [m2/s] 1.6e-5 8e-5ℎ𝐵 [cm] 17.5 19.0p [mbar] 18.9 19.8𝑚𝑆 = 390 g, 𝑢𝐺 = 21 cm/s25 °C 500 °C 25 °C 500 °CGas volume fractionҧ𝜀 [−]Gas velocityത𝑢[𝑚/𝑠]Gas volume fraction𝜀 [−]Impact of gas temperature25 °C 500 °C Increase of gas density and viscosity with 𝑇𝐺 Same fluidization behavior at increased 𝑇𝐺 Slight increase of ℎ𝐵 and ∆𝑝Feichi Zhang | An assessment of fluidized bed dynamics with CPFD simulations Institut für Technische Chemie18.12.202311𝑇𝐺 [℃] 25 500𝑘𝑆 [mJ/kg] 13.6 19.2𝑓𝐵 [Hz] 3.7 4.0 Increase of drag force with 𝑇𝐺 Increase of 𝑘𝑆 by ca. 50% 𝑓𝐵 remains almost constantImpact of gas temperature𝑇𝐺↑αP = 0.5αP = 0.4αP = 0.3αP = 0.2αP – particle volume fractionFeichi Zhang | An assessment of fluidized bed dynamics with CPFD simulations Institut für Technische Chemie Up-scaling at Constant ∆𝑝 and ℎ𝐵 Bubbling fluidization regime Increase of 𝑚𝑆 with 𝑑𝑅: 𝑚𝑆 ∝ 𝑑𝑅2 Simulation setups Same resolution for gas phase (1 mm) Proportionally increased No. of Lagrange parcels with 𝑚𝑆18.12.202312𝑢𝐺∗𝑑𝑃∗𝑢𝐺∗ = 𝑢𝐺3 𝜌𝑔2𝜇𝑔 𝜌𝑠 − 𝜌𝑔 𝑔𝑑𝑃∗ = 𝑑𝑃3 𝜌𝑔 𝜌𝑠 − 𝜌𝑔 𝑔𝜇𝑔2𝑑𝑅 3 cm 5 cm 10 cm𝑚𝑆 140 g 390 g 1600 g𝑢𝐺 21 cm/s 21 cm/s 21 cm/s𝑁𝑃 2.9 mil. 8.0 mil. 32.0 mil.Regime diagram for gas-solid fluidized bed according to Grace𝑢𝐺∗ = 0.30𝑑𝑝∗ = 10.24Impact of scale-up: setupsGrace JR, Contacting modes and behaviour classification of gas–solid and other two-phase suspensions.1986 Feichi Zhang | An assessment of fluidized bed dynamics with CPFD simulations Institut für Technische Chemie18.12.2023133 cm 5 cm 10 cmGas volume fractionIso-surface 𝜶𝒈 = 0.65𝜀 [−]Impact of scale-up: bubble formationFeichi Zhang | An assessment of fluidized bed dynamics with CPFD simulations Institut für Technische Chemie18.12.202314𝑑𝑅 [cm] 3 5 10ℎ𝐵 [cm] 18.0 17.5 17.4p [mbar] 21.0 20.2 20.0ത𝑘𝑆 [mJ/kg] 18.8 19.6 19.3𝑓𝐵 [Hz] 2 3.2 3.83 cm 5 cm 10 cm ത𝑢[𝑚/𝑠]3 cm 5 cm 10 cmҧ𝜀 [−]Impact of scale-up: dynamic properties Increased bubble-to-wall distance Enhanced bubble formation Multiple arrays of rising bubbles at 𝑑𝑅 = 10 cm Specific kinetic energy remains constant  Bubble frequency increasesTime-mean Streamwise velocityInner recirculation of sand particlestwo arrays of rising bubbles𝑚𝑆↑ℎ𝐵, p ≈ const.𝑘𝑆 ≈ const.Time-mean gas volume fraction𝑓𝐵↑Feichi Zhang | An assessment of fluidized bed dynamics with CPFD simulations Institut für Technische Chemie18.12.202315 Simulation of cold-mode fluidized bed 𝑘𝑆 increases with 𝑚𝑆 and 𝑢𝐺 𝑓𝐵 decreases with 𝑚𝑆 and remains constant with 𝑢𝐺 𝑘𝑆 increases at elevated gas temperature, while 𝑓𝐵 ≈ const. Up-scaling leads to enhanced bubble formation and an increase of 𝑓𝐵 while 𝑘𝑆 ≈ const. Importance of 𝑘𝑆 and 𝑓𝐵 for characterizing hydrodynamic behaviors of fluidized bedOutlookMixing of plastic particles, contact heat transfer, pyrolysis reactionsCorrelation of 𝑘𝑆 and 𝑓𝐵 with heating rate and pyrolysis reactionSummaryThank you for your attention! Particle-resolved simulationPlastic pyrolysis in fluidized bed

An assessment of fluidized bed dynamics with CPFD simulations

https://publikationen.bibliothek.kit.edu/1000165896/151901774

An assessment of fluidized bed dynamics with CPFD simulations

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