Transcript Slide 1
Chemical &
Biological
Engineering
Microbubbles:
an energy-efficient way to accelerate biofuel
production
Will Zimmerman
Professor of Biochemical Dynamical Systems
Chemical and Biological Engineering, University of Sheffield
with Dr Hemaka Bandulasena and Dr Jaime Lozano-Parada,
with Mr Kezhen Ying and Mr James Hanotu
and special thanks to Professor Vaclav Tesar, Dr Buddhi Hewakandamby, and
Mr Olu Omotowa (all formerly University of Sheffield researchers).
‘Engineering from Molecules’
Outline
• Why and how microbubbles?
• ALB concept
• Performance studies
• Steel stack gas trials
• Advantages for microbial and mammalian cell ALBs
• Ozone plasma microreactor in the lab (oxidation,
lysing cells)
• Prototype designs
Chemical &
Biological
Engineering
‘Engineering from Molecules’
‘Engineering from Molecules’
Why microbubbles?
Steep mass transfer
enhancement.
Nine fundamental processes intensified including
• Faster mass transfer -- roughly proportional to the
inverse of the diameter
• Flotation separations -- small bubbles attach to
particle / droplet and the whole floc rises
Chemical &
Biological
Engineering
‘Engineering from Molecules’
‘Engineering from Molecules’
The Fluidic oscillator
What is it?
No moving part, Self-excited Fluidic Amplifier.
Outlets
Inlet
Mid Ports
Linked by a feedback Loop
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‘Engineering from Molecules’
Fluidic oscillator makes microbubbles!
Same Diffuser
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Engineering
• 20 micron sized bubbles from 20 micron sized pores
• Rise / injection rates of 10-4 to 10-1 m/s without
coalescence: uniform spacing/size
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Gas Inlet
Relatively large coalescent and
fast rising bubbles
Production of Mono-dispersed
Uniformly spaced, non-coalescent
Microbubbles
Gas Inlet
Oscillatory Flow
Conventional Continuous Flow
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Engineering
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Bubble size
distribution
Fine mist of bubbles rising from
Micropore Technologies
Metallic membrane diffuser
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Engineering
Median: 47 microns
Standard deviation: 20 microns
20 micron sized pores
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‘Engineering from Molecules’
Energetics from pilot plant
Current draw with varying volumetric
flowrate and feedback loop length
Suprafilt layout for 30m^3/h
Master-slave amplifier system
for fluidic oscillator
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Engineering
Oscillatory flow draws less power than
steady flow at the same throughput!
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‘Engineering from Molecules’
Air lift loop bioreactor design
Schematic diagram of an internal ALB with
draught tube configured with a tailor made
grooved nozzle bank fed from the two
outlets of the fluidic oscillator.
The microbubble generator is required to
achieve nearly monodisperse, uniformly
spaced, non-coalescent small bubbles of
the scale of the drilled apertures.
Chemical &
Biological
Engineering
• Journal article has won the 2009
IChemE Moulton Medal for best
publication in all their journals.
• Designed for biofuels production
• First use: microalgae growth
• Current TSB / Corus / Suprafilt grant on
carbon sequestration feasibility study on
steel stack gas feed to produce
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‘Engineeringmicroalgae.
from Molecules’
Construction
Top with lid
Inner view:
Heat transfer
coils separating
riser /downcomer.
Folded
perforated
Plate m-bubble
generator.
Replaced by
Suprafilt 9inch diffuser
Body / side view
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Engineering
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‘Engineering from Molecules’
Growing algae in the lab
Dunaliella salina
Internal of the ALB
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Engineering
The gas separator section links the riser to the
downcomer at the top, permitting gas disengagement
and recirculation of fluid. Consequently, this drives a
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flow from the top of the riser to
the bottom.
‘Engineering from Molecules’
Gas Dissolution
7.4
7.3
7.2
7.1
7
6.9
6.8
6.7
6.6
6.5
6.4
6.3
Day 3
Fluidic Oscillator
Fluidic Oscillator
Day 7
Without Fluidic
Oscillator
pH
Without F.O.
8.4
8.2
8
7.8
7.6
7.4
7.2
7
6.8
6.6
6.4
6.2
0
15
30
45
7.8
Day 10
7.6
Fluidic Oscillator
Without F.O.
7.4
7.2
7
6.8
6.6
6.4
0
Chemical &
Biological
Engineering
15
30
45
0
60
60
7.4
7.3
7.2
7.1
7
6.9
6.8
6.7
6.6
6.5
6.4
6.3
15
30
45
Time (minutes)
Day 11
60
Fluidic Oscillator
Without F.O.
0
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15
30
45
60
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Biomass Concentration
Algal biomass / bioenergy production (~30% extra biomass from
CO2 microbubble dosing for only 1 hour per day).
Chlorophyll Content
(μg/ml)
4.00
3.50
With Fluidic Oscillator
3.00
2.50
Without Fluidic Oscillator
2.00
1.50
1.00
0.50
0.00
1
2
3
4
5
7
8
9
10
11
Time (days)
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Engineering
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‘Engineering from Molecules’
Algal bioreactor challenge and market
AIMS
- To investigate the feasibility of growing microalgae using
CO2 rich steel plant exhaust gas
- To investigate the performance of an airlift loop
bioreactor (ALB) with microbubble technology
Potential markets
• Carbon capture in biomass (worst case: fertilizers!)
• Integrated waste management
• Nutraceuticals (food additives)
• Fish and animal feed
• Bioplastics and other organic / fine chemical co-products
• Biofuels
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Engineering
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Methodology
This photobioreactor is designed to facilitate high algal growth within a short period of time by
improving its transport processes. For best possible carbon capture and biofuel production, high
biomass concentrations are preferred.
Airlift loop
effect
Challenges in Algal Cultivation
• Carbon dioxide supply
• Oxygen removal
• Light limitation
• Mixing
• Contamination
Volume = 2m3
( 1.5m X 1.3m X 1m )
Key design features
• CO2 dissolution and O2 stripping is substantially improved by microbubbels.
• Air lift loop design promotes vertical mixing of algae – keeps all algae suspended in the
reactor while bringing them to lighted surfaces regularly.
• Designed as a closed system to avoid contamination.
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‘Engineering from Molecules’
Field trials
• Corus: steel plant algal culture
• Aecom: separation/harvesting
• Oxyfuel integration with CLCC.
Approximately
1 cubic metre
cube design with
0.8 m2 square
ceramic microporous
diffusers.
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‘Engineering from Molecules’
Key Findings/results
Two trials were carried out with Dunaliella salina using power plant exhaust gas as the
carbon source. Second trial was run for three weeks with improved operating conditions
compared to the first trail, which was only run for two weeks.
Supra-exponential growth
Field trial 2
Dry biomass % increase
4000.00%
Field trial 1
3500.00%
3000.00%
2500.00%
2000.00%
1500.00%
1000.00%
500.00%
0.00%
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
Time (d)
Inlet and outlet CO2 and O2
concentrations were measured by FTIR.
The difference between red curves
CO uptake
shows
while the
2
difference between blue curves shows
O2 stripping rate.
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‘Engineering from Molecules’
Probing operation
29th of April
25
Bioreactor switched off
Stoppage
Stoppage
Concentration, (%)
20
Flow rate = 80 l/min
Leakage in inlet
15
10
Bioreactor switched on
5
0
10:33
11:45
12:57
14:09
15:21
16:33
Time, (hh:mm)
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Engineering
Carbon dioxide CO2
Oxygen (O2)
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‘Engineering from Molecules’
Pseudosteady operation
5th of May 2010
25
Bioreactor switched on
Bioreactor switched off
CO2 Inlet = 23.00%
Concentration (%)
20
15
10
5
O2 Inlet = 4.95%
4 h operation
0
10:48
12:00
13:12
14:24
Time, (hh:mm)
Chemical &
Biological
Engineering
Carbon dioxide CO2
Oxygen (O2)
‘Engineering from Molecules’
‘Engineering from Molecules’
Next Steps
• Installing microbubble generators in algal bioreactor
company’s pilot plants and other types of bioreactors.
• Catalyzing the next generation pilot plant to produce coproducts and biofuels by assembling leading edge unit
operations such as artificial lighting (AAT), dewatering
(UoS), ultrasonic milking (NPL), microwave pyrolysis
(York) and esterification intensification (CSL).
•When could it become commercially viable? Biofuels still
need a large cost reduction. Nutraceuticals? NOW
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Features
From the other experiments,
Microbubbles formed from fluidic oscillation draw 18% less electricity than the same flow
rate of steady flow forming larger bubbles. 1.5-2 bar gauge pressure needed.
3-4 fold better aeration rates with ~300-500 micron bubbles, up to 50 fold larger with 20
micron sized bubbles
Very low shear mixing is possible at low injection rates (rise rate 10-4 m/s )
From the air-lift loop bioreactor performance,
Microbubbles dissolve CO2 faster and therefore increase algal growth.
Microbubbles extract the inhibitor O2 produced by the algae from the liquid so that the
growth curve is wholly exponential.
Algal culture with the fluidic oscillator generated bubbles had ~30% higher yield than
conventionally produced bubbles with only dosing of one hour per day over a two week trial
period.
Bioenergy could become a more attractive option in the recycling of the high
Chemical &
concentration
of CO2 emissions from stack gases (ongoing field trials).‘Engineering from Molecules’
Biological
Engineering
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Ozone Kills and
mineralizes!
Ozone dissolves in
water to produce
hydroxyl radicals
One
ozone
molecule
kills one
bacterium
in water!
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Engineering
Hydroxyl radical attacks bacterial cell
wall, damages it by ionisation, lyses the
cell (death) and finally mineralises the
contents.
‘Engineering from Molecules’
‘Engineering from Molecules’
Microfluidic onchip ozone generation
Our new chip design and associated electronics produce ozone from O2 with key
features:
1. Low power. Our estimates are a ten-fold reduction over conventional ozone
generators.
2. High conversion. The selectivity is double that of conventional reactors (30%
rather than 15% single pass).
3. Recently discovered strong irradiation in UV “killing zone” of ~300 nm.
4. Operation at atmospheric pressure, at room temperature, and at low voltage
(170V, can be mains powered).
Chemical &
Biological
Engineering
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‘Engineering from Molecules’
Plasma discs
• 25 plasma reactors each with treble throughput over
first microchip
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Dosing lance assembly
New lance = 70 microdisc reactors
Quartz for UV irradiation
Axial view of the old lance
With 8 or 16 microdisc reactors
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‘Engineering from Molecules’
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Consequences
• Our low power ozone plasma microreactor can be
inserted into the microporous diffusers to arrange for
ozone dosing on demand in an ALB, for sterilization
or other uses.
• One potential use is providing a non-equilibrium
driving force for biochemical reaction / biomass
growth by breaking down extracellular metabolites
secreted by microorganisms to minerals (CO2, H2O,
nitrates, phosphates etc.) by UV-ozone providing a
strong oxidizing environment in situ.
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‘Engineering from Molecules’
More Acknowledgements
• Corus: Bruce Adderley, Mohammad Zandi and many
more.
• Suprafilt: Graeme Fielden, Jonathan Lord, and
Hannah Nolan
• Micropore Technologies: Mike Stillwell
• HP Technical Ceramics: Tim Wang
• AECOM DB: Brenda Franklin, Ben Courtis, Hadi Tai
• Yorkshire Water: Martin Tillotson, Ilyas Dawood
• UoS: Jim Gilmour, Raman Vaidyanathan, Simon
Butler, Graeme Hitchen, Adrian Lumby, Stuart
Richards,
Clifton Wray, Andy Patrick
Chemical
&
Biological
Engineering
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• Yorkshire Forward, TSB, EPSRC, SUEL
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