1. MODELLING DESIGN OF MULTIPHASE BUBBLE-BED REACTORS IN ADVANCED FOOD- INDUSTRY APPLICATIONS … 2/3 J Zahradnik, M Ruzicka 1, J Markos 2, J Teixeira 3, S Generalis 4, N Thomas* 1.Inst Chem Proc Fundamentals Prague 2. Univeristy of Technology, Bratislava 3.University of Minho, Braga 4.Aston University, Birmingham * FRED Ltd – Aston Park, Birmingham B7’4BJ UK Neale@Thomas.net

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3. BIOREACTION ENGINEERING broad consensus asserts columns and loops superior to stirred tanks - simpler designs, no mechanicals, more uniform and lower shear. comparisons for food applications - internal versus external loops by measurements on process enhancement, transport efficiency, transfer / transport correlations in real broths batch citric / gluconic acid with filamentous fungi Aspergillus niger and continuous ethanol production – special / complementary facets of facilities + outcomes fermentation for citric acid by A. niger - initially aqueous increasingly non-Newtonian pseudo-plasticity fermentation for gluconic acid - 3-phase complexity as spherical fungi pellets dispersed in bubbly aqueous liquid. citric acid only for growth conditions - sacharidic nutrient and DO to product and biomass / DO sensitive but not pH gluconic acid for both growth and stationary conditions - both DO and pH sensitive but growth entails sterility and complex media, also two-phase becoming three-phase continuous ethanol production by flocculent yeast – 3-phase system to 30% solid volume fraction with important rheological response

4. fermentation unit implemented and optimised for column and loop scales 10, 33, 200 litres - smaller ones with optional separator. pH, DO, temperature probes – air to inner tube via perforated plate PC logged probes, plus inlet / outlet pressures and outlet O 2 / CO 2 also controlled temperature, flow and pH. 2 x 60 L loop reactors (one internal, one external)

5. A niger fermentations for transport diagnostics with magnetic particle - detector sampled signals comparable to dissolved tracer results. Chem Pap 54, 456 – 466 citric acid fermentations showed no configurational sensitivity to bubble separators Bulgarian Chem Comms 34, 547 data on downcomer holdup, circulation velocity, mixing intensity and gas circulation J Chem Tech Biotech – accepted

6. pulsing strategy optimised for gas hold-up and DO so efficient operation maintained in highly viscous broths Chem Eng Sci 54, 4937 – 4943 stationary fermentation of gluconic acid for DO uptake in bioconversion of glucose to gluconic acid thence by difference estimate biomass growth air rate dependence reflects increased DO and intensified circulation and mixing but … biomass concentration boosts production rate so adverse impact as Michaelis-Menten inhibition is outweighed by pellet activation of bubbles Bioproc Eng – submitted gas-liquid transfer limiting factor in aerobic fermentations, exacerbated by elevated viscosity high biomass densities compounding high oxygen periodic pulsing gas increases DO in citric acid fermentations, attributed to more complete utilisation of oxygen in small foam bubbles

7. ethanol fermentations for transport diagnostics showed mass loading impairment of floc-stabilised cultures so studies were done on … riser gas hold-up, downcomer and riser liquid velocity, circulation and mixing times for superficial gas velocities between 0.03 and 0.17 m/s at solids loading to 30% v/v calcium alginate beads used as solid phase model of yeast cell flocs - riser gas holdup decreased with solids loading, coalescence-induced slip-speed enhancement increased with increasing solids density effects more pronounced in ILR - solids density negligible influence on circulation and solids distribution in the ELR ELR circulation satisfactory at higher solids loading butILR circulation ceased for solids > 30% and for gas velocities < 0.15 m/s - top and bottom bend throttling circulation increased with superficial gas velocity and weak influence of solids loading – no effect on circulation time dependence on superficial gas velocity Biotech Bioeng 64(6), 692-697 mixing time increased slightly with solids fraction but sparger hole diameter had no effect on performance

8. correlational model for GLS 3-phase reactor at high loading of low- density solids using Zuber-Findlay for hold-up plus energy balance for riser superficial velocities Zuber-Findlay factor set to reflect boosted flux uniformity with solids but not for ILR at higher solids with bend throttling non-uniformities

9. model captures main elements - slip-speed increase is attributed to coalescence by bubble-bubble interactions - solids loading de- / in- creased circulation in ILR / ELR Chem Eng Sci 54, 5253-5258 Chem Eng Sci 55, 4961-4972 Favourable comparisons with data < 10% discrepancy for ILR gas hold-up and riser velocity < 15% discrepancy for gas hold-up and downcomer liquid velocity

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