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  • 11
    Electronic Resource
    Electronic Resource
    Interpretation of gas residence time distributions in large airlift tower loop reactors (1994)
    Springer
    Bioprocess engineering 11 (1994), S. 153-159 
    Details
    ISSN: 0178-515X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    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)
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00518737
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  • 12
    Electronic Resource
    Electronic Resource
    Automatic control of the specific growth rate in fed-batch cultivation processes based on an exhaust gas analysis (1996)
    Springer
    Bioprocess engineering 15 (1996), S. 145-150 
    Details
    ISSN: 0178-515X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract  A new simple strategy for a reliable and robust automatic control of the specific growth rate in fed-batch cultivation processes is presented. Its advantages over model supported control is that the algorithm only needs a minimum of information about the process. Moreover, it is independent of the specific microorganism, the cultivation phase and the biomass level. Also, only a minimum of soft- and hardware is required. Hence, the approach is attractive for industrial production processes that do not have specialized instrumentation. Its accuracy is comparable with model supported control and thus sufficient for most industrial applications. Simulations and experimental tests of the technique performed for the example of a fed-batch cultivation of E. coli demonstrate a good controller performance for various cultivation conditions and process disturbances. Preferred applications will be production systems where the productivity is critically dependent on the growth rate, e.g. in recombinant protein or antibiotic productions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00369618
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  • 13
    Electronic Resource
    Electronic Resource
    Model based design of a biochemical cultivation process (1998)
    Springer
    Bioprocess engineering 18 (1998), S. 227-234 
    Details
    ISSN: 0178-515X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract In this paper a simple design procedure is used to enhance the performance of a biotechnical cultivation process. A model supported approach is proposed. It starts with a simple classical process model obtained from literature data, which is used to design the first experiment. Then, the main procedure is an iteration of (i) improving the model making use of the deviations between the experimental data and the data predicted by the model, (ii) of designing the next experiment by determining the optimal control profiles from the current model, and (iii) of executing that designed experiment. Important for the success of the procedure is that the model development is oriented at the process performance. The procedure is demonstrated at the simple practical example of a laboratory-scale fed-batch cultivation of Escherichia coli.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004490050435
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  • 14
    Electronic Resource
    Electronic Resource
    Model based calculation of substrate/inducer feed-rate profiles in fed-batch processes for recombinant protein production (1999)
    Springer
    Biotechnology techniques 13 (1999), S. 37-42 
    Details
    ISSN: 1573-6784
    Keywords: fed-batch cultivation ; recombinant protein ; E. coli ; model based optimization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract A model-based feed-rate profile optimization problem is discussed for the fed-batch recombinant protein production. Two optimization procedures, an evolutionary programming technique and a simplified method using the dynamic programming concept, are discussed and compared. Modeling as well as experimental results are presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008887514011
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  • 15
    Electronic Resource
    Electronic Resource
    Model-based design of biochemical processes: simulation studies and experimental tests (1997)
    Springer
    Biotechnology letters 19 (1997), S. 1043-1047 
    Details
    ISSN: 1573-6776
    Source: Springer Online Journal Archives 1860-2000
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract A simple design procedure is proposed that can be used to enhance the performance of a biological cultivation process. The model-supported method starts with a simple model. This is used to design first experiment, i.e., to calculate such a control profile that improves the process performance. The results of the experiment are then used to update the model and subsequently the control profiles. The procedure was first tested at simulated Saccharomyces cerevisiae and Penicillum chrysogenum cultivation processes and then practically applied to optimize an E.coli cultivation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018415921489
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  • 16
    Electronic Resource
    Electronic Resource
    Characterization of a pilot plant airlift tower loop reactor: III. Evaluation of local properties of the dispersed gas phase during yeast cultivation and in model media (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 56-64 
    Details
    ISSN: 0006-3592
    Keywords: bioreactor ; tower loop bioreactor ; yeast ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The local properties of the dispersed gas phase (gasholdup, bubble diamater, and bubble velocity) were measured and evaluated at different positions in the riser and downcomer of a pilot plant reactor and, for comparison, in a laboratory reactor. These were described in Parts I and II of this series of articles during yeast cultivation and with model media. In the riser of the pilot plant reactor, the local gas holdup and bubble velocities varied only slightly in axial direction. The gas holdup increased considerably, while the bubble velocity increased only slightly with aeration rate. The bubble size diminished with increasing distance from the aerator in the riser, since the primary bubble size was larger than the equilibrium bubble size. In the downcomer, the mean bubble size was smaller than in the riser. The mean bubble size varied only slightly, the bubble velocity was accelerated, and the gas holdup decreased from top to bottom in the downcomer. In pilot plant at constant aeration rate, the properties of the dispersed phase were nearly constant during the batch cultivation, i.e., they depended only slightly on the cell concentration. In the laboratory reactor, the mean bubble sizes were much larger than in the pilot plant reactor. In the laboratory reactor, the bubble velocities in the riser and downcomer increased, and the mean gas holdup and bubble diameter in the downcomer remained constant as the aeration rate was increased.
    Additional Material: 20 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260380108
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  • 17
    Electronic Resource
    Electronic Resource
    Characterization of the two-phase systems in airlift tower-loop bioreactors during the cultivation of E. coli (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 25 (1983), S. 437-450 
    Details
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: During the cultivation of E. coli in an airlift tower-loop bioreactor, the following properties were measured: transverse profiles of Sauter bubble diameter, dS; local relative gas holdup, EG; bubble rise velocity, uBS; local mean velocity, ū turbulence intensity, u′; macrotime scale, TEL; dissipation time scale, τE; power spectrum, E(n); and energy dissipation spectrum D(n) at different distances from the aerator. The influence, distance from the aerator, absence and/or presnece of cells, and batch and/or continuous-culture operation on the behavior of the two-phase system are discussed on the basis of these properties.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260250211
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  • 18
    Electronic Resource
    Electronic Resource
    Characterization of a pilot plant airlift tower loop bioreactor. I: Evaluation of the phase properties with model mediaArticle II of this series was published in 37(10) pp 910-917. (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 43-55 
    Details
    ISSN: 0006-3592
    Keywords: bioreactor ; tower loop bioreactor ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Investigations were carried out in a 9 m high, 4 m3 volume, pilot plant airlift tower loop bioreactor with a draft tube. The reactor was characterized by measuring residence time distributions of the gas phase using pseudostochastic tracer signals and a mass spectrometer and by evaluating the mixing in the liquid phase with single-pulse tracer inputs. The local gas holdup and the bubble size (piercing length) were measured with two-channel electrical conductivity probes. The mean residence times and the intensities of the axial mixing in the riser and downcomer and the circulation times of the phases as well as the fraction of the recirculated gas phase were evaluated. The gas holdup in the riser is nearly uniform along the reactor. In the downcomer, it diminishes from top to bottom. The liquid phase dispersion coefficients, DL, are smaller than those measured in the corresponding bubble columns. In the pilot plant with tap water the following relationship was found: DLr = cwSGn; with c = 203.4; n = 0.5;DLr(cm2 s-1;) and WSG(cm s-1) where DLr is the longitudinal dispersion coefficient in the riser and WSG is the superficial gas velocity. The gas phase dispersion coefficients in the riser of the pilot plant, DGr, are also enlarged with increasing superficial gas velocity, WSG, however, no simple relationship exists. Parameter DGr is the highest in the presence of antifoam agents, intermediate in tap water, and the smallest in ethanol solution.
    Additional Material: 24 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260380107
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  • 19
    Electronic Resource
    Electronic Resource
    Characterization of a pilot plant airlift tower loop bioreactor: II. Evaluation of global mixing properties of the gas phase during yeast cultivation (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 910-917 
    Details
    ISSN: 0006-3592
    Keywords: yeast cultivation ; airlift tower loop reactor ; pseudostochastic tracer signals ; axial mixing ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Saccharomyces cerevisiae was cultivated in a 4-m3 pilot plant airlift tower loop reactor with a draft tube in batch and continuous operations and for comparison in a laboratory airlift tower loop reactor of 0.08 m3 volume. The reactors were characterized during and after the cultivation by measuring the distributions of the residence times of the gas phase with pseudostochastic tracer signals and mass spectrometer and by evaluating the mixing in the liquid phase with a pulse-shaped volatile tracer signal and mass spectrometer as a detector. The mean residence times and the intensities of the axial mixing in the riser and downcomer, the circulation times of the gas phase, and the fraction of the recirculated gas phase were evaluated and compared.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260371003
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  • 20
    Electronic Resource
    Electronic Resource
    Fluid dynamics in bubble column bioreactors: Experiments and numerical simulations (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 52 (1996), S. 248-258 
    Details
    ISSN: 0006-3592
    Keywords: two-phase gas-liquid flow ; bubble columns ; dynamic three-dimensional numerical simulation ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Detailed measurements of multiphase flows that prevail in bioreactors tell us that different transport mechanisms are dominating on different observation scales. The consequence in terms of reactor modeling is that the processes on different scales can be treated independently. A three-dimensional, dynamical model is presented that can be used to describe bubble column bioreactors on the reactor scale. It is based on the Navier-Stokes equation system. On the next smaller scale, the dynamics of the gas phase is described in a Lagrangian way, by tracking many bubble clusters or bubbles simultaneously on their way through the reactor. The model is capable of describing bubble columns of different size and can thus be used for scale-up. Its performance is demonstrated with a production-scale beer fermentor. © 1996 John Wiley & Sons, Inc.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
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