- 1.Optimization of a Novel Photobioreactor Design using
Computational Fluid Dynamics Abhinav Soman Department of
Biotechnology VIT University, VelloreYogendra Shastri Department of
Chemical Engineering Indian Institute of Technology Bombay
2. Algal biofuels: Potential fuel option with many challenges
Advantages: Higheryield per unit area Productiveland not required
Compatiblewith fresh and saline water Challenges: Highcost of
cultivation and harvesting Lowyield requiring significant drying 3.
Closed Photobioreactor (PBR) cultivation shows
promiseAttributeOpen-pondPhotobioreactorCostLowHighYieldLowHighContaminationHighLow
Targetyield: 2-3 gm/liters 4. Several bottlenecks exist in using a
photobioreactor (PBR) Expensive to build and maintain High power
consumption Overall efficiency is low Limitations to scalability 5.
PBR design plays a crucial role in its performance Performance
parameters of interest: Lightpenetration Hydrodynamics Mixingand
settlingProposal: Developa novel PBR design Developa computational
fluid dynamics (CFD) model Comparethe performance of the novel
design with conventional design using CFD 6. Two promising designs
Air lift and Flat plate PBR Less photoinhibition, even under high
light intensity Better liquid flow Enhanced gas exchange Better
irradiation cycle Suitable for shear sensitive strainsCourtesy Xu
et al. (2009) Low surface area to volume ratio Strong self shading
for poorly circulated PBRs Scale up not economical 7. Two promising
designs Air lift and Flat plate PBR High surface area to volume
ration Lower accumulation of dissolved oxygen Low power consumption
Good mass transfer capabilityCourtesy Singh and Sharma (2012)
Photoinhibition likely for high intensity radiations Low
photosynthetic efficiency Damage to cells due to high stress 8.
Proposed design combines the airlift and flat plate PBR designs 9.
Proposed design combines the airlift and flat plate PBR
designsOuter body with flat plates for better light intakeCentral
draft tube from an air-lift reactor 10. Circular air/CO2 sparger
located at the base of the draft tubeCentral draft tube Sparger 11.
Baffles were added to maintain flow distribution and consistency
Baffles 12. Top-view of the proposed PBR design Outer reactor with
flat panel surfaceBaffles for flow distribution Inner draft tube
Sparger 13. Rounded corners for the outer body are used 14.
Computational Fluid Dynamics (CFD) simulations Develop a CFD model
for a air-lift PBR design published in literatureValidate the
conventional model results using the CFD modelAdapt the CFD model
for the proposed novel designCompare the simulation results of the
conventional and novel design 15. CFD Model Development and
Validation Air-lift model studied by Luo and AL-Dahan (2011) Outer
tube: Height: 1.13 m Diameter: 0.13 m Inner tube: Height: 1.05 m
Diameter: 0.09 mBoundary Conditions: Inlet : Superficial gas
velocity 1cm/s Incident radiation : 50 W/m2 Outlet : Pressure
outlet Courtesy : Luo and AlDahan (2011)Geometry used for FLUENT
simulation 16. CFD Model Details 3D steady state simulation with
coarse griding Flow Modelling: Eulerian Eulerian multiphase
modelling Turbulence Modelling : Standard k- model with mixture
multiphase model Drag Force : Schiller-Naumann drag correlation
Irradiation simulation: Discrete Ordinates Model (DO) Particle
trajectory tracking : Discrete Phase Modelling (DPM) 17. The
observations reported in Luo and AlDahan (2011) were reproduced
reasonablySlight deviations were probably due to a different drag
model 18. The CFD model was used to simulate the novel design 19.
Dimensions of the novel design were varied to determine the optimal
set of dimensions No.Value1Outer cuboid height (m)1.132 Parameters
varied: Width Height Top clearance Bottom clearancePropertyInner
draft tube height (m) Width (m)1.054Draft tube inner diameter
(m)0.095Side length of the 0.10 outer cuboid casing (m)30.18 20.
Width had a significant impact on the gas holdup 21. Width had a
significant impact on the irradianceGood irradiance history for
small width (2 cm) Particle trapped in the concentric space due to
higher width (6 cm) 22. Optimized design was determined based on
the simulation results PropertyValueOuter cuboid height
(m)1.15Inner draft tube height (m) Width (m)1.05Draft tube inner
diameter (m)0.09Top and bottom clearance (m)0.050.02 23. Irradiance
history and gas hold-up showed desirable values for the optimized
design 24. Contours of gas holdupContours of incident
radiationContours of axial liquid velocityVelocity vectors for Air
25. Conclusions The novel design has better light/dark cycling
patterns for algal cells.A higher superficial gas velocity must be
to achieve higher gas holdup and turbulent kinetic energyAdditional
simulations with algal growth kinetics needed 26. References
Hu-Ping Luo, Muthanna H. Al-Dahhan.(2011). Verification and
validation of CFD simulations for local flow dynamics in a draft
tube airlift bioreactor, Chemical Engineering Science. 66:
907-923.Ling Xu, Pamela J. Weathers, Xue-Rong Xiong, Chun-Zhao Liu.
(2009) Microalgal bioreactors: Challenges and opportunities, Eng.
Life Sci. 3: 178 189.O. Pulz. (2001). Photobioreactors: production
systems for phototrophic microorganisms, Appl Microbiol Biotechnol.
57: 287293.Aditya M. Kunjapur and R. Bruce Eldridge.( 2010),
Photobioreactor Design for Commercial Biofuel Production from
Microalgae, Ind. Eng. Chem. Res. 49: 35163526.R.N. Singh, Shaishav
Sharma.(2012). Development of suitable photobioreactor for algae
production A review, Renewable and Sustainable Energy Reviews,
Volume 16, Issue 4, 2347-2353 27. Thank You ! [email protected]
28. Why Microalgae ?Courtesy: Chisti, 2007 29. Comparison between
the two systemsCourtesy : Xu et al., 2009 30. Air-lift model
studied by Luo and ALDahan (2011) Unstructured tetrahedral mesh was
generated comprising 68864 elementsThe bubble diameter was set
0.005 m (Simcik et al., 2011)Air inlet velocity of 0.38 m/s in the
axial directionAir volume fraction was set to 0.5Simulation was
initialized with 0.01 volume fraction and 0.01 m/s air inlet
velocitySingle wavelength region (400 nm to 700 nm) for DO
modelWater refractive index was set to 1.34 and absorbtion
coefficient was set to 0.3Surface injection was used to inject 44
particles from the inlet surface that mimic the microalgae size (5
m) and neutral buoyancy (998 g/m3) 31. Simulations performed: 32.
Width had a significant impact on the axial liquid velocity 33.
Height variations did not impact the performance much 34. Top
clearance did not impact the performance much 35. Unstructured mesh
36. Outer walls that receive radiation from light source. 37.
Velocity Vectors of liquid
