Characterization of hydromechanical stress in aerated stirred tanks up to 40 m3 scale by measurement of maximum stable drop size

Abstract

BackgroundTurbulence intensity, or hydromechanical stress, is a parameter that influences a broad range of processes in the fields of chemical engineering and biotechnology. Fermentation processes are often characterized by high agitation and aeration intensity resulting in high gas void fractions of up to 20% in large scale reactors. Very little experimental data on hydromechanical stress for such operating conditions exists because of the problems associated with measuring hydromechanical stress under aeration and intense agitation.ResultsAn indirect method to quantify hydromechanical stress for aerated operating conditions by the measurement of maximum stable drop size in a break-up controlled dispersion was applied to characterize hydromechanical stress in reactor scales of 50 L, 3 m3 and 40 m3 volume with a broad range of operating conditions and impeller geometries (Rushton turbines). Results for impellers within each scale for the ratio of maximum to specific energy dissipation rate ϕ based on measured values of maximum stable drop size for aerated operating conditions are qualitatively in agreement with results from literature correlations for unaerated operating conditions. Comparison of data in the different scales shows that there is a scale effect that results in higher values for ϕ in larger reactors. This behavior is not covered by the classic theory of turbulent drop dispersion but is in good agreement with the theory of turbulence intermittency. The data for all impeller configurations and all aeration rates for the three scales can be correlated within ±20% when calculated values for ϕ based on the measured values for dmax are used to calculate the maximum local energy dissipation rate. A correlation of the data for all scales and all impeller configurations in the form ϕ = 2.3∙(ϕunaerated)0.34∙(DR)0.543 is suggested that successfully models the influence of scale and impeller geometry on ϕ for aerated operating conditions.ConclusionsThe results show that besides the impeller geometry, also aeration and scale strongly influence hydromechanical stress. Incorporating these effects is beneficial for a successful scale up or scale down of this parameter. This can be done by applying the suggested correlation or by measuring hydromechanical stress with the experimental method used in this study.

Periodic-peristole agitation for process enhancement of butanol fermentation

“…Hydrodynamic characteristic of the fermentation system is one of the external factors responsible for the metabolism rate of cells [ 3 , 4 , 9 ]. It has been discussed for a long time to have large influence on biological process [ 18 ], cell viability, and product titers [ 19 ].…”

“…Nowadays advantages in fluid mechanics enable us to gain a more in-depth insight into the complex effects of agitation processes. Models have been successfully exploited in determining the correlationship between agitation and fermentation process, such as maximum stable (equilibrium) drop size in intermittent turbulence [ 8 , 9 ], hydrodynamic stress [ 10 ], eddy length [ 11 ], and energy dissipation [ 12 ]. At the same time, developments on metabolic flux analysis (MFA) also allows for the systematical elucidation of cellular behaviors [ 13 – 16 ].…”

Characterization of the Metabolic Response of Streptomyces clavuligerus to Shear Stress in Stirred Tanks and Single-Use 2D Rocking Motion Bioreactors for Clavulanic Acid Production

“…In this regard, determination of the k L a in bioreactors is an important parameter when assessing the oxygen mass transfer characteristics in connection with mixing and reactor geometry. In STRs, the increase of k L a implies vigorous stirring to favor mass transfer from gas to liquid phase by increasing the turbulence of the system, thus increasing shear stress on the medium and cells [27,28]. In contrast, wave and rocking-motion reactors are characterized by up to 100-fold lower shear forces compared to STRs [21,22,29] and especially 2D rocking-motion bioreactors provide higher k L a values compared to simple wave systems that are comparable to those obtained in STRs at high stirring speed [23][24][25].…”

Influence of Impeller Geometry on Hydromechanical Stress in Stirred Liquid/Liquid Dispersions

“…for the different operating conditions and impellers apart from the wave-ribbon impellers, which is well in agreement with literature data in the range of 0.56−0.61 for breakup controlled dispersion systems. 2,47,48 It is concluded that in the investigated coalescence inhibited dispersion system, the hydromechanical stress caused by various impellers can be quantified only by examining volume-based drop size distributions. The Sauter mean diameter d 32 , as a volume-based averaged size, emphasizes the changes of the large droplets with the time, the power input, and the impeller type.…”