Chemical & Biological Engineering ‘Engineering from Molecules’ Microbubbles: an energy-efficient way to accelerate biofuel production Will Zimmerman Professor

Chemical &BiologicalEngineering

‘Engineering from Molecules’

Microbubbles:an energy-efficient way to accelerate biofuel production

Will Zimmerman Professor of Biochemical Dynamical SystemsChemical and Biological Engineering, University of Sheffield

with Dr Hemaka Bandulasena and Dr Jaime Lozano-Parada, with Mr Kezhen Ying and Mr James Hanotuand special thanks to Professor Vaclav Tesar, Dr Buddhi Hewakandamby, and Mr Olu Omotowa (all formerly University of Sheffield researchers).

Chemical &BiologicalEngineering ‘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



Why microbubbles?

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

Steep mass transferenhancement.



The Fluidic oscillator

Mid Ports

Inlet

Outlets

Linked by a feedback Loop

What is it?

No moving part, Self-excited Fluidic Amplifier.



Fluidic oscillator makes microbubbles!

• 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• Watch the videos!

Same Diffuser



Relatively large coalescent and fast rising bubbles

Production of Mono-dispersedUniformly spaced, non-coalescent Microbubbles

Gas Inlet

Gas Inlet

Conventional Continuous Flow

Oscillatory Flow



Bubble size distribution

Fine mist of bubbles rising fromMicropore Technologies Metallic membrane diffuser

Median: 47 micronsStandard deviation: 20 microns20 micron sized pores



Energetics from pilot plant

Suprafilt layout for 30m^3/h

Master-slave amplifier system for fluidic oscillator

Oscillatory flow draws less power than steady flow at the same throughput!

Current draw with varying volumetric flowrate and feedback loop length



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.

• 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 microalgae.



Construction

Body / side view

Top with lid

Inner view:Heat transfercoils separatingriser /downcomer.

Folded perforated Plate -bubblegenerator.Replaced bySuprafilt 9inch diffuser



Growing algae in the lab

Internal of the ALB

The gas separator section links the riser to the downcomer at the top, permitting gas disengagement and recirculation of fluid. Consequently, this drives a flow from the top of the riser to the bottom.

Dunaliella salina



Gas Dissolution

Day 10

Day 3



Biomass ConcentrationAlgal biomass / bioenergy production (~30% extra biomass from CO2 microbubble dosing for only 1 hour per day).



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



Methodology

Challenges in Algal Cultivation • Carbon dioxide supply• Oxygen removal• Light limitation• Mixing• Contamination

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.

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.

Airlift loop effect

Volume = 2m3

( 1.5m X 1.3m X 1m )



Field trials

• Corus: steel plant algal culture

• Aecom: separation/harvesting

• Oxyfuel integration with CLCC.

Approximately 1 cubic metrecube design with0.8 m2 square ceramic microporousdiffusers.



Key Findings/resultsTwo 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.

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0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Time (d)

Dry

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incr

ease

Field trial 2 Field trial 1

Inlet and outlet CO2 and O2 concentrations were measured by FTIR. The difference between red curves

shows CO2 uptake while the

difference between blue curves shows

O2 stripping rate.

Supra-exponential growth



Probing operation29th of April

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10:33 11:45 12:57 14:09 15:21 16:33

Time, (hh:mm)

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Carbon dioxide CO2 Oxygen (O2)

Bioreactor switched on

Bioreactor switched off

StoppageStoppage

Flow rate = 80 l/min Leakage in inlet



Pseudosteady operation5th of May 2010

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10:48 12:00 13:12 14:24

Time, (hh:mm)

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%)

Carbon dioxide CO2 Oxygen (O2)

CO2 Inlet = 23.00%

O2 Inlet = 4.95%

Bioreactor switched on Bioreactor switched off

4 h operation



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 co-products 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



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

concentration of CO2 emissions from stack gases (ongoing field trials).



Ozone Kills and mineralizes!

Ozone dissolves inwater to producehydroxyl radicals

Hydroxyl radical attacks bacterial cell wall, damages it by ionisation, lyses the cell (death) and finally mineralises the contents.

One ozone molecule kills one bacterium in water!



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).



Plasma discs

• 25 plasma reactors each with treble throughput over first microchip



Dosing lance assembly

Axial view of the old lanceWith 8 or 16 microdisc reactors

New lance = 70 microdisc reactorsQuartz for UV irradiation





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.



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

• Yorkshire Forward, TSB, EPSRC, SUEL

Documents

Chemical & Biological Engineering ‘Engineering from Molecules’ Microbubbles: an energy-efficient way to accelerate biofuel production Will Zimmerman Professor