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Notes: Abstract The behaviour of dispersed gas in large aerated stirred tank reactors is modelled by means of a Markov-process, which distinguishes between small recirculation bubbles with “stagnant gas” content, large rising bubbles with “active gas” content and exchange of stagnant and active gas contents, the “gas exchange” region at the impeller. The measurements of the gas residence time distributions (RTDs) in an 1.5 m3 aerated stirred tank reactor with water and Penicillium chrysogenum cultivation medium are interpreted by this model.

Notes: Abstract In a 60 l airlift tower reactor with outer loop fluiddynamical measurements were carried out in presence of three motionless mixer modules (Type SMV, Sulzer) in water, 0.6%, 0.9% and 1.2% CMC solutions. The global mixing properties were determined in the liquid and gas phases by tracers. Detailed local measurements revealed differences of local flow patterns and mixing properties in the unhindered riser and in the immediate wake of the mixer module. The local liquid velocities were measured by the pseudorandom heat pulse technique. The local bubble velocities were determined by the ultrasound Doppler technique. The dependence of liquid velocity, gas velocity and gas holdup on the superficial gas velocity were determined. The radial profiles of the mean liquid velocities and their standard deviations were evaluated in water and CMC solutions upstream and downstream of the motionless mixer modules. The radial profiles of the mean large-bubble velocities and mean small-bubble velocities and their standard deviations were determined as well. The influence of the presence of the motionless mixers in the riser on these properties was evaluated.

Notes: Abstract Gas-residence time distribution (RTD) response curves measured in a 23 m high pilot plant airlift tower loop reactor, which consisted of a riser, a special downcomer construction and at the top of the riser a large head. The measurements were evaluated by means of a deterministic dispersion model, which yielded the following particular parameters for the riser, downcomer and the head: Gas-Bo numbers, gas-mean residence times, gas holdups, liquid velocities, gas and liquid circulation times as well as a fraction of the large and small bubbles in a model medium (water) and during cultivation of baker's yeast.

Notes: Abstract  The behaviour of dispersed gas in large aerated stirred tank reactors is modelled by means of a Markov-process, which distinguishes between small recirculation bubbles with “stagnant gas” content, large rising bubbles with “active gas” content and exchange of stagnant and active gas contents,the “gas exchange” region at the impeller. The measurementsof the gas residence time distributions (RTDs) in an 1.5 m3 aerated stirred tank reactor with water and Penicillium chrysogenum cultivation medium are interpreted by this model. List of symbols CPR CO2 production rate OTR oxygen transfer rate PRS pseudo random signal RTD residence time distribution V gas volume α recirculation coefficient τ mean gas residence time Indices act active gas ex gas exchange stagn stagnant gas tot total gas

Notes: Abstract  The gas-residence time distribution (RTD) response curves measured in a 23 m high pilot plant airlift tower loop reactor, which consisted of a riser, a special downcomer construction and at the top of the riser a large head. The measurements were evaluated by means of a deterministic dispersion model, which yielded the following particular parameters for the riser, downcomer and the head: Gas–Bo numbers, gas-mean residence times, gas holdups, liquid velocities, gas and liquid circulation times as well as a fraction of the large and small bubbles in a model medium (water) and during cultivation of baker’s yeast. List of symbols A cross section Bo Bodenstein number Bo d (=l d w G,d/D d) Bo h (=l h w G,h/D h) Bo r (=l r w G,r/D r) D longitudinal dispersion coefficient E gas holdup E(t) RTD-density function L, l length parameter q fraction of the gas throughput which is not recirculated (approximately equal to fraction of the large bubbles) r fraction of the throughput which is recirculated (approximately equal to the fraction of the small bubbles) t c circulation time t cL liquid circulation time t * c,L liquid circulation time calculated from the measured w Ld in the downcomer V h hydrodynamical calculated gas–liquid volume V h d (=V d+0.75/2V k) V h k =(0.25V k) V h r =(V r+0.75/2V k) V L liquid volume V G dispersed gas volume V * G gas throughput at the gas distributor (given in m3/h) under standard conditions, 1 bar and 25°C) V * G,d gas throughput in downcomer (=V * Gα) V * G,h gas throughput in head (=V * G) V * G,r gas throughput in riser (V * G (1+α) w G gas velocity w G,rel relative gas velocity with respect to the liquid velocity w L w G,d gas velocity in the downcomer (=w G,rel−w Ld) w G,h gas velocity in the head (=w G,rel) (since w Lh=0) w G,r gas velocity in the riser (=w G,rel+w Lr) w L liquid velocity w L,d liquid velocity in the downcomer measured with mass flow meter w SG ⋅ w SL superficial gas and liquid velocities μ first moment of the response curve τ mean residence time Indices d downcomer G gas phase h head L liquid phase r riser h hydrodynamic (upper position)

Notes: Abstract  In a 60 l airlift tower reactor with outer loop fluiddynamical measurements were carried out in presence of three motionless mixer modules (Type SMV, Sulzer) in water, 0.6%, 0.9% and 1.2% CMC solutions. The global mixing properties were determined in the liquid and gas phases by tracers. Detailed local measurements revealed differences of local flow patterns and mixing properties in the unhindered riser and in the immediate wake of the mixer module. The local liquid velocities were measured by the pseudorandom heat pulse technique. The local bubble velocities were determined by the ultrasound Doppler technique. The dependence of liquid velocity, gas velocity and gas holdup on the superficial gas velocity were determined. The radial profiles of the mean liquid velocities and their standard deviations were evaluated in water and CMC solutions upstream and downstream of the motionless mixer modules. The radial profiles of the mean large-bubble velocities and mean small-bubble velocities and their standard deviations were determined as well. The influence of the presence of the motionless mixers in the riser on these properties was evaluated. List of Symbols Bo L w L L/D L , liquid Bo number Bo G w G L/D G , gas Bo number c tracer concentration CMC carboxymelthylcellulose D G gas dispersion coefficient D 1 local liquid dispersion coefficient D L liquid dispersion coefficient D r riser diameter d distance between transmitter and detector of the heat pulse probe E G gas holdup HBV horizontal bubble velocity HLBV horizontal large-bubble velocity HSBV horizontal small-bubble velocity L length of the column l relative distance of the detector position from the tracer injection with respect to L LBV large-bubble velocity n number of circulations OHBV overall horizontal bubble velocity OVBV overall vertical bubble velocity P power input Pe 1 w 1 d/D 1, local liquid Peclet number SBV small-bubble-velocity V L liquid volume VBV vertical bubble velocity VLBV vertical large-bubble velocity VSBV vertical small-bubble velocity w G gas velocity w 1 local liquid velocity w L liquid velocity w SG superficial gas velocity w SL superficial liquid velocity τ mean residence time of the liquid in the riser