MASS TRANSFER IN SYNGAS FERMENTATION BIOREACTORS

Mohsen Karimi & Henrik Ström

Marine Technology and Fluid Dynamics Workshop

March 2020

| 122020-03-16 Marine Technology and Fluid Dynamics Workshop 2

FINAL RESULTS

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5 6 7 8 9 10

Coe

ffici

ent o

f Var

iatio

n, (-

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Time, (s)

Injection

90% mixing

99% mixing

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CONTEXT

Converting syngas (H2, CO, CO2) into fuels using microorganisms

augmented with electrical field to improve selectivity of target

products and increase carbon efficiency.

What is syngas fermentation?

Modeling approach

Macro-scale

Micro-scale

• Tool: ANSYS Fluent

• Target: Mass transfer coefficient

• Tool: OpenFOAM• Target: Sub-gird model to resolve the

mass boundary layer

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MACRO-SCALE𝑘!𝑎 Flow field Mixing time Representation of mixing

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MACRO-SCALEMixing representations 30 probes 5 probes

𝐶𝑜𝑉 =𝜎

𝐶!"#$

𝛾# = 1−Σ 𝐶% − *𝐶% 𝐴%2 �̅�% Σ𝐴%

𝑈!#&/!%$ =𝐶!#& 𝑡 − 𝐶!%$(𝑡)

𝐶!"#$

Δ!#& = max 𝐶!#& −𝐶!"#$, 𝐶!"#$ −𝐶!%$

𝑈 𝑡 = 1−Δ!#& 𝑡Δ!#&(0)

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MACRO-SCALE

rpmExperiments

CFD ̅𝑡" 𝑠𝑡𝑑

300 3.1 0.804 2.1500 1.9 0.141 1.8800 1.2 0.271 1.41

Mixing time:

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MICRO-SCALE

COCO2H2

Problem formulation:

Extremely thin mass boundary layer that should be resolved:

1. Fine mesh

2. Sub-grid scale model

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MICRO-SCALE2D, Half a bubble with axis of symmetry

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MICRO-SCALEScaling boundary layer thickness

𝛿 ∝1𝑆𝑐

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MICRO-SCALEIdea of sub-grid model

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MICRO-SCALE

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CONCLUDING REMARKS• Modeling mass transfer for syngas fermentation bioreactor

o Macro-scale:

§ Flow characteristics by mixing time

§ Volumetric mass transfer coefficient (ongoing)

o Micro-scale

§ Resolving the mass boundary layer utilizing fine mesh

§ Developing sub-grid scale models (ongoing)