Laboratory-to-Pilot Fluidization Scaling Study with Eulerian Multiphase CFD Model

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2 Ari Vepsäläinen LTY Heterogeneous Mass Transfer Characteristics in Char Combustion at Fluidized Beds Laboratory-to-Pilot Fluidization Scaling Study with Eulerian Multiphase CFD Model Research program on sustainable energy SusEn Multiphase fluidized bed processes in sustainable energy technologies

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4 FIELD OF RESEARCH

5 Near Future Actions I will start by presenting four themes for intruducing different concepts and separate sub-research fields.. 1) Cluster/Particle Scales 2) 3 Fluidized Bed Models 3) Challenge of Sherwood Heterogeneous mass transfer in fluidized Beds 4) Art of Scaling Fluid dynamics Mr. Horio 5) Char combustion modelling approach and model applied here A simple kinetic model, but interesting backgrounds.. Mid Term Execution Plan.. Let s continue by going getting familiar with FB Models and see what they can do and tell us about heterogeneous characterisitcs of fluidized beds A. Transient Eulerian CFD B. Steady-state 1D 1-phase C. Steady-state 1D 2-phase model

6 1.Cluster/Particle Scales & 2. FB Models

7 3. Challenge of Sherwood..Local Bubble of thought.... Analysis: 1. How different Models consider heterogeneous Mass transfer? 2. Usually expressed with dimensionless relationship with Reynolds number What is mass transfer resistance in FB? Scale: tests in lab scale Local / bed average Fluidization Mode Versatility of available Models 1d, 1.5d, 2d, 3d Steady, quasi-steady, transient, dynamic Phases: dispersed / bubble & emulsion Included in reaction rate / mass transfer model

8 Lappeenrantalainen Ajatuskupla 4. Art of Scaling of Fluid dynamics.. Analysis: How different Models consider? 1. Scale-up: tests in lab scale 2. Local / bed average phenomenon 3. Fluidization Mode Mr. Horio s Approach [1]:

9 Lappeenrantalainen Ajatuskupla 4. Art of Scaling of Fluid dynamics Can we do it.. With CFD?.. Analysis: How different Models consider? 1. Scale-up: tests in lab scale 2. Local / bed average phenomenon 3. Fluidization Mode

10 Lappeenrantalainen Ajatuskupla 4. Art of Scaling of Fluid dynamics Can we do it.. With CFD?.. Analysis: How different Models consider? 1. Scale-up: tests in lab scale 2. Local / bed average phenomenon 3. Fluidization Mode

11 Lappeenrantalainen Ajatuskupla 4. Art of Scaling of Fluid dynamics How about.. Fluidization Regime Map.. Analysis: How different Models consider? 1. Scale-up: tests in lab scale 2. Local / bed average phenomenon 3. Fluidization Mode

12 5. Char Combustion Model at it s simplest form To be able to just consider, focus and analyze transient heterogeneous mass limitation.... Let us consider only ONE chemical reaction: Combustion Regime Kinetics with Arrhenius: CFD: Kinetically controlled Suitable for fine porous coal char 1D Models: additional mass transfer resistances: o Convection-Diffusion + intra-emulsion mixing o Bubble emulsion phase mass transfer Char particle o One particle size: 0.4mm (lab) & 1.25mm (Pilot) o Constant density: 1000kg/m3

13 .. And then Models, your turn.., first.. 2D Eulerian CFD Model - transiently Similar approach as presented by my colleague Shah et al. [22] Eulerian 3-phase CFD model The modeling approach: the kinetic theory of granular flow. Shah et al. (2012): mesh and time step effects on cluster resolution and solid density profiles in pilot scale CFB riser.

14 2D Eulerian CFD Model Governing equations

15 2D Eulerian CFD Model Pilot, 3.5m/s, mesh: 0.5cm*0.5 cm 10 seconds of fluidization (~10 hours)

16 2D Eulerian CFD Model Focusing to dense bed region 1. Bubble size & rising velocity 2. Reaction regimes 3. Frequency of fluctuations.. Emulsion/Bubble interchange Extreme lateral gas velocity gradients low velocity at dense regions, high at bubbles Oxygen-char contact near grid

17 ..Response from 2D Eulerian CFD Model: Char-Oxygen Contact Efficiency One Way of saying it.. Straigthforward way Scaling of mass transfer limitation on reaction rate Based on averaged CFD results e.g. Oxygen continuity equation in 2- phase model:

18 2D Eulerian CFD Model.. Fluidization Characteristics..Cluster frequency analysis..

19 Steady-state 1D 2-phase Model

20 Steady-state 1D 2-phase Model Phase characteristics

21 Steady-state 1D 2-phase Model

22 Steady-state 1D 2-phase Model Phase mass transfer coefficient kl [1/s] Pilot reactor - phase mass transfer analysis:

23 ..last, but not least.. Steady-state 1D 1-phase Model

24 Steady-state 1D 1-phase Model..giving Sherwood.. and showing dimensionless relationship with Reynolds number Vepsäläinen et al. (2012)

25 SHAH ANALOGY One extra possibility.. Dimensionless relationship between Phase Drag & Heterogeneous Mass Transfer Can this kind of relationship be established? If YES, by just CFD modeling fluid dynamics, mass transfer could be estimated.. Just for Fun? Nice to know Note: Combination of solid and gas phase momentum equation [Kallio]:

26 Let s Sum it Up Themes 1) Fluid dynamic Scaling (Horio) Lab-to-Pilot interpreting test results based with proper understanding of fluid dynamics 2) Characteristics of FB Models: Eulerian transient 2D CFD, Two steady-state 1D models: 1 - & 2-phase 3) Challenge of Sherwood Number 4) Eulerian CFD Validation: Heterogeneous mass transfer can be predicted on certain accuracy with proper modelling technique Results 3 Ways of presenting mass transfer limitation in heterogeneous reactions 3 FB Models Lots of Modeling Experience..

27 .. Ja jottei homma näyttäisi täysin itse keksityltä..

28 References

29 ACKNOWLEDGEMENT The authors would like to acknowledge the financial support for this research from the Academy of Finland under grant Special thanks also to Fortum Oyj. The author would like to express his thanks to Prof. Dr. Timo Hyppanen for his valuable inspiration and contribution to this work. Research program on sustainable energy SusEn Multiphase fluidized bed processes in sustainable energy technologies

30 See you at th International FBC Conference