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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 Chemical & Biological Engineering ‘Engineering from Molecules’ ‘Engineering from Molecules’ Fluidic oscillator makes microbubbles! Same Diffuser Chemical & Biological 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 ‘Engineering from Molecules’ • Watch the videos! ‘Engineering from Molecules’ 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 Chemical & Biological Engineering ‘Engineering from Molecules’ ‘Engineering from Molecules’ Bubble size distribution Fine mist of bubbles rising from Micropore Technologies Metallic membrane diffuser Chemical & Biological Engineering Median: 47 microns Standard deviation: 20 microns 20 micron sized pores ‘Engineering from Molecules’ ‘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 Chemical & Biological Engineering Oscillatory flow draws less power than steady flow at the same throughput! ‘Engineering from Molecules’ ‘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 ‘Engineering from Molecules’ ‘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 Chemical & Biological Engineering ‘Engineering from Molecules’ ‘Engineering from Molecules’ Growing algae in the lab Dunaliella salina Internal of the ALB Chemical & Biological 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 ‘Engineering from Molecules’ 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 ‘Engineering from Molecules’ 15 30 45 60 ‘Engineering from Molecules’ 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) Chemical & Biological Engineering ‘Engineering from Molecules’ ‘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 Chemical & Biological Engineering ‘Engineering from Molecules’ ‘Engineering from Molecules’ 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. Chemical & Biological Engineering ‘Engineering from Molecules’ ‘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. Chemical & Biological Engineering ‘Engineering from Molecules’ ‘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. Chemical & Biological Engineering ‘Engineering from Molecules’ ‘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) Chemical & Biological Engineering Carbon dioxide CO2 Oxygen (O2) ‘Engineering from Molecules’ ‘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 Chemical & Biological Engineering ‘Engineering from Molecules’ ‘Engineering from Molecules’ 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 ‘Engineering from Molecules’ Ozone Kills and mineralizes! Ozone dissolves in water to produce hydroxyl radicals One ozone molecule kills one bacterium in water! Chemical & Biological 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 ‘Engineering from Molecules’ ‘Engineering from Molecules’ Plasma discs • 25 plasma reactors each with treble throughput over first microchip Chemical & Biological Engineering ‘Engineering from Molecules’ ‘Engineering from Molecules’ Dosing lance assembly New lance = 70 microdisc reactors Quartz for UV irradiation Axial view of the old lance With 8 or 16 microdisc reactors Chemical & Biological Engineering ‘Engineering from Molecules’ ‘Engineering from Molecules’ Chemical & Biological Engineering ‘Engineering from Molecules’ ‘Engineering from Molecules’ 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. Chemical & Biological Engineering ‘Engineering from Molecules’ ‘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 ‘Engineering from Molecules’ • Yorkshire Forward, TSB, EPSRC, SUEL ‘Engineering from Molecules’