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MFIX Overview

MFIX Overview. M. Syamlal, Fluent, Inc. Federal Energy Technology Center Morgantown , WV 26507-0880. Outline. Multiphase Theory Validation Studies Bubbling Fluidized Bed Circulating Fluidized Bed Turbulent Gas-solids Jet Carbonizer Gasifier Application. Multiphase Theory.

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MFIX Overview

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  1. MFIX Overview M. Syamlal, Fluent, Inc. Federal Energy Technology Center Morgantown , WV 26507-0880

  2. Outline • Multiphase Theory • Validation Studies • Bubbling Fluidized Bed • Circulating Fluidized Bed • Turbulent Gas-solids Jet • Carbonizer • Gasifier Application

  3. Multiphase Theory

  4. Multiphase Formulation • Two Phases • Three phases Fluid Solids Fluid Char Solids - 1 Solids - 2 Coal

  5. Multiphase Formulation • Details of flow field and particle interaction have been averaged out. • Account for the information lost due to averaging -constitutive equations • Constitutive equations specify how the phases interact with themselves and with each other1 1. Drew and Lahey (1993)

  6. Continuity Equation

  7. Momentum Equation • Interaction within the phase - stresses • collisions, sliding or rolling friction • electrostatic, van der Waals, capillary

  8. Momentum Equation Interaction between phases - interphase forces

  9. Momentum Equation Interactions with rest of the universe - body forces

  10. Energy Balance originates from a work term for e changes

  11. Energy Balance Viscous dissipation

  12. Energy Balance Energy sources; e.g..., radiation

  13. Energy Balance heat conduction

  14. Energy Balance Interphase heat transfer

  15. Energy Balance Energy transfer with mass transfer

  16. Species Mass Balance • Multiphase chemical reactions are described by tracking chemical species in each of the phases

  17. Validation Studies

  18. Fluidized Bed with Jet • Gidaspow (1994)1 • 500 & 800 mm sand (2610 kg/m3) • Jet velocities: 3.5, 5.77, 9.88 m/s • 2D bed with a central jet • 0.39 m width x 0.58 m height • 124 x 108 cells a 1. Sec.7.8.1; Syamlal (1997)

  19. Bubble Size and Shape Gidaspow (1994) Fig. 7.10

  20. Bubble Size and Shape Gidaspow (1994) Fig. 7.11

  21. Voidage Contourstime average 3.55 m/s 5.77 m/s Data - Gidaspow, Lin, and Seo (1983)

  22. Centerline Voidagetime average Data -- Gidaspow and Ettehadieh (1983)

  23. Bubble Rise Velocity Rowe and Partridge (1962), Davidson and Harrison (1963), Syamlal and O’Brien (1989)

  24. Uniform Fluidization • Halow and Nicoletti (1992) • 700 mm plastic (1460 kg/m3) • Uniform flow 1.04 Umf -air • 3D cylindrical bed • 0.15 m diameter x 0.25 m height • 30 x 100 x 16 cells a

  25. Bubble PropertiesAverage of 9 bubbles Data -- Halow and Nicoletti (1992)

  26. Bubble Rise Velocity Data -- Halow and Nicoletti (1992)

  27. Gas + solids Solids Gas Circulating Fluidized Bed • Bader, Findlay, and Knowlton (1988) • 76 mm FCC catalyst (1714 kg/m3) • Solids flux: 98 and 147 kg/m2.s • Vg0 : 3.7 - 9.1 m/s • 0.305 m dia x 12.20 m height • 2-D, cyl., 12 x 240 cells O’Brien and Syamlal (1993)

  28. Pressure Drop Across CFB Data -- Bader et al. (1988)

  29. Solids Distribution in Riser Data -- Bader et al. (1988)

  30. Carbonizer Model • Froehlich et al. (1994) • 550 mm coal and sorbent particles • 1207 K, 1034 kPa • axisymmetric cylindrical coordinates • Flows (kg/s): coal- 0.044; sorb- 0.01; air - 0.1; N2- 0.028; Steam - 0.007 • 0.36 max dia x 10.36 m height • 16 x 132 cells Product gas Coal, sorbent, air and steam a Syamlal et al. (1996)

  31. Carbonizer Chemistry H2O CO + H2O WCO2 + H2 Ash coal CO2 + H2O + CO + CH4 + H2 +Tar sorbent Moisture CaO CaCO3 CO2 Volatile Matter CaMg(CO3)2 O2 MgO CO2 + H2O Fixed Carbon H2 O2 O2 CO CH4 CO2 + H2O + CO + CH4 + H2 + Fixed Carbon CO2 CO2 H2O H2 + CO

  32. Temperature Distribution Syamlal et al. (1996)

  33. SynGas Composition Syamlal et al. (1996)

  34. Gasifier Application

  35. PyGASJ Gasifier air • Novel gasifier1;1200 K, 4130 kPa • 2120 mm coal and sorbent • axisymmetric cylindrical coordinates • Flows (kg/s): coal+sorb- 1.8; air: pyro - 2.6, top - 0.9, grate- 2.9 • 2.0 max dia x 8.2 m height • 39 x 165 cells fuel gas ash air + Steam air+coal a 1. Sadowski (1992)

  36. Gas Temperature • Scale: Red - Blue 300 - 1500 K • Upper Zone Flame (~1800 K) • Stable flame at the riser bottom (~1600 K)

  37. Coal Mass Fraction • Scale: Red - Blue 0.0 - 0.05 g/cc • Coal conversion to char completes in the pyrolyzer

  38. CO Mass Fraction • Scale: Red - Blue 0.0 - 0.2 • CO and CH4 concentrations are low in hot regions • Nonuniform CO distribution in the packed bed

  39. Tar Mass Fraction • Scale: Red - Blue 0.0 - 0.003 • Coal devolatilization is completed 20 ft above the inlet • Tar cracking is completed in the pyrolyzer

  40. Other Results • Information on gas and solids flow patterns • Cannot maintain a tall coflow bed • No regions where coal agglomerate Char particles Sticky coal particle (350-500o C)

  41. It is far better to foresee even without certainty than not to foresee at all. - Henri Poincare

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