Gas residence time distribution in stirred tank bioreactors

Residence time distributions of gas phase have been measured in fermentation broths and in simulated media of low as well as high viscosity (1 × 10^?3 ? 0.5 Pas) using a step-function-Helium-tracer technique. On the basis of these, simple mathematical models have been developed and their parameters are qualitatively correlated with operating conditions. It was shown that even in low viscosity Newtonian fluids, gas phase does not behave as well mixed. Differences between gas flow patterns in low and high viscosity fluids, already reported in literature, have been verified.     

Effect of flow pattern on cellulase deactivation in stirred tank bioreactors

In biochemical process industries, the dynamic environment within the bioreactor and in the purification equipment is known to affect the enzyme activity and yield of enzyme production. This has drawn our attention to examine the effect of various flow parameters on the deactivation behavior of enzyme in stirred tank reactor. In the present work, cellulase deactivation was investigated in 0.1,0.3 and 0.57 m i.d. stirred vessels with single and dual impeller. Enzyme solution was subjected to hydrodynamic stress using various types of impeller and impeller combinations over a wide range of power consumption (). The effects of tank diameter, impeller diameter, blade width, blade angle and number of blades were studied on the extent of deactivation. The results have been compared with the previously published literature. Attempts have been made to relate the extent of deactivation with the flow pattern (maximum and average value of turbulent energy dissipation rate, average shear rate and average turbulent normal stress). The extent of cellulase deactivation has been found to correlate well with the average turbulent normal stress within the stirred vessel.     

The stirred tank forced

We examine the response of a continuous stirred tank reactor (CSTR), in which a simple irreversible reaction A → B occurs, to periodic variations of the coolant temperature. The amplitude and the frequency of the forcing are used as control parameters. The remaining operating conditions are chosen so that the unforced CSTR exhibits a single stable oscillation; this means that for small forcing amplitudes the system behaves like a typical forced oscillator: its response consists of alternating entrainment and quasi-periodicity. As the forcing amplitude grows, more characteristic traits of the CSTR and the particular forcing variable become apparent, and a complicated picture develops, involving the co-existence of multiple periodic, quasi-periodic and even chaotic oscillations, period doublings and global bifurcations. We track several of these traits numerically, placing special emphasis on the mechanisms by which such features branch out from the well-defined low-amplitude region. Several algorithms based on shooting methods for boundary value problems are used in this task, and some appropriate ways of tackling the simple initial value problem of simulation are also employed. In particular, the need for efficient algorithms to tackle global bifurcations is stressed. Such algorithms seem to be indispensable tools in the systematic study of the forced CSTR and, more generally, of periodically forced oscillators.The qualitative traits discovered for the forced CSTR are compared with other known results for model systems, and several questions present themselves as possible subjects of further research, both for the CSTR and for a wide class of periodically forced and/or coupled reactor models.     

Turbulence parameters in a stirred tank

Mean and fluctuating radial velocities have been measured in the inipeller stream of a baffled, turbine-agitated cylindrical tank. Auto-correlation functions, energy spectra and amplitude probabilitv density functions of the radial velocity fluctuations were also obtained. In the vicinity of the impeller, the motion is distinctly periodic, with a time scale corresponding to n_bN/60, where n_b is the number of turbine blades and N is the rpm. The amplitude of the periodic component was found to decrease with radial distance from the inipeller tip and was used to correct the measured turbulence intensities.     

Study on macro-instability in stirred tank

Macro-instability(MI)is an important natural phenomenon affecting the mixing performance in stirred tank significantly,which results from movement and evolution of large eddies.Factors associated with MI frequency in mixing operation and energy dissipation related to MI were reviewed.Flow pattern in turbulent regime contains many coherent structures,which have much energy vortices and may result in flow field MI.Adjustment of coherent structure and controlling MI may contribute to energy saving and good mixing performance.Controlling methods for MI was prospected.     

偏心搅拌反应器内的液相混合行为

利用先进的无干扰流场测试手段——平面激光诱导荧光技术(PLIF),对斜叶桨搅拌反应器内的液相混合过程进行高精度定量可视化。对比了中心搅拌和3种不同偏心率下的偏心搅拌混合行为,引入参数混合均匀度和均匀混合时间定量描述测量平面的示踪剂浓度分布。研究发现,偏心搅拌过程由于破坏了流场的对称性,比中心搅拌能更快达到均匀混合。反应器内局部混合存在差异,偏心搅拌中不同监测点达到均匀混合时间差异较小,体现了偏心搅拌在液相混合中的优势。     

搅拌气升式生物反应器的研究进展

搅拌气升式反应器作为一种新型高效的生物反应器,因为其独特的优势而越来越受到重视,具有良好的研究和应用前景.概述了搅拌气升式反应器的国内外研究进展,着重评述了搅拌气升式反应器相比于传统机械搅拌式反应器和气升式反应器的所体现出的优点,详细介绍和分析了该新型反应器的基本结构、流体力学性质及相关的重要表征参数,并对其在生物发酵和化工行业中的应用和发展进行了回顾和展望.     

Intensified biogas purification in a stirred tank

The present study aims at intensifying the absorption of carbon dioxide in aqueous phases. For this purpose, a second immiscible liquid phase is used to improve the mass transfer of carbon dioxide in water. Absorption measurements are carried out in a stirred cell by online infrared monitoring of the output carbon dioxide concentration. As dispersed phase, 1-octanol shows an improvement in mass transfer whereas colza oil retards it. Toluene has no significant effect in the range of concentrations investigated. Mass transfer coefficients are determined using a chemical method. Nevertheless, the variety of behaviors could not be explained simply by solubility or variation of mass transfer coefficients. In order to understand the complex gas–liquid–liquid interactions and deduce the mass transfer mechanism between these three phases, surface and interface tension measurements and direct observation of bubbles and droplets are also carried out.     

Dynamic properties of a continuous stirred tank biofilm bioreactor for aerobic processes

A dynamic analysis of a continuous stirred tank bioreactor with biofilm was performed. The existence of gas, liquid, and biofilm were taken into account. The proposed heterogeneous model of such bioreactor takes into account dynamic biofilm growth and interphase transfer of substrates and biomass for a double‐substrate aerobic process. Simulations were performed to investigate the influence of important process parameters, i.e., toxic substrate concentration in the feed stream, detachment rate coefficient, mean residence time of the liquid and aeration intensity, on dynamic properties of the bioreactor. Dynamic behavior at conditions of anoxia of microorganisms were shown. A method was proposed to reduce bioreactor start‐up time significantly. The paper presents a mathematical model of the bioreactor that uses a discrete model of biofilm growth based on the theory of cellular automata. Dynamics of the bioreactor based on the continuous and discrete biofilm model was compared. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1818–1829, 2017     

Minimum tank volumes for CFST bioreactors in series

The primary reactor type currently used in the production of microorganisms or microbial products is the stirred tank reactor (STR). If operated on a continuous flow basis (CFSTR) they become similar in performance to the primary reactor configuration used in most of the chemical industry. In this work, microbial kinetics are considered in the design of CFSTRs in series. An equation is derived to predict the minimum possible total residence time to achieve any desired substrate conversion. The equation permits the use of a wide variety of growth kinetic models and is applied here to Monod, substrate inhibition and product inhibition cases. For the majority of cases, it is found that three optimally designed CFSTRs in series provide close to the minimum possible residence time for any desired substrate conversion. A comparison to the use of a PFR is made for cases of both no-recycle and biomass recycle to the CFSTR train. It is found that three CFSTRs, which are not equi-volume, provide the same required total mean residence time as a PFR for Monod kinetics, but are significantly superior (i.e., less total volume required) to a PFR for substrate-inhibited growth.     

超声场下搅拌槽内微观混合

以醋酸锌、氯乙酸乙酯和氢氧化钠的平行反应为研究体系,考察了较高物料浓度时超声场下搅拌槽内的微观混合情况。结果表明:搅拌和超声波振荡对微观混合有明显的强化作用,在不同超声功率下,存在搅拌速率N对微观混合影响的临界搅拌速率Nc。当N>Nc时,搅拌速率对微观混合的影响可以忽略;N相似文献   

Pattern formation in interacting continuous stirred tank reactors

The dynamic behavior of coupled continuous stirred tank reactors in which the nonisothermal Langmuir-Hinshelwood type reactions occur, exhibits several types of pattern formation. The regular and irregular multipeak patterns are detected for the endothermic reaction of a Langmuir-Hinshelwood type when the heat communication between the neighboring cells is larger than the mass interaction. These observations may imply the possible existence of spatial structure in a matrix of catalysis, the non-uniform distribution of concentration and temperature in packed bed reactors, and corrugated propagating fronts in combustion problems.     

侧进式搅拌釜内气液两相流的数值模拟

采用计算流体力学(CFD)技术对φ1.5 m×1.2 m侧进式气液搅拌釜内气液两相流场进行数值模拟,检验了3种气液分界面边界条件和两种相间曳力模型。通过UDF程序将上述模型分别与欧拉双流体模型和 dispersed k-ε 两相湍流模型进行耦合计算,得到搅拌功率准数、总体气含率和气相分布,并与冷模实验结果进行对比,得到能准确预测的CFD模型。研究结果表明,3种气液界面边界条件下采用标准S-N模型计算所得的功率准数和气体分布误差均较大,而Brucato-Tsuchiya模型的预测结果更接近实验结果;气液界面边界条件对总体气含率的预测影响较大,采用速度进口或脱气边界和Brucato-Tsuchiya模型耦合计算所得的结果误差比压力出口边界明显要小。     

Break-up of a drop in a stirred tank

The drop break-up mechanism was studied in a stirred tank containing two immiscible liquids. The daughter drops formed by break-up of a single drop of known size were recorded photographically. From the experiments at constant agitator speed the following results were obtained. There is a critical drop size under which drops do not break up under given conditions. The break-up frequency increases approximately linearly with increase in drop volume. The number of daughter drops, v, is a random variable with a mean v > 2 which increases with the volume of the mother drop. The relative volume of a daughter drop has a β-distribution.     

Local droplet diameter variation in a stirred tank

The local variation of droplet diameter in a stirred tank was measured in the vicinity of the impeller and at another region. The degree of difference in droplet diameter between regions increases with the impeller speed. A correlation equation between the local difference in droplet diameter and the frequencies of coalescence and circulation of the droplet was derived according to the circulation interaction model. The degree of local difference in droplet diameter was found to be controlled strongly by the ratio of coalescence to circulation frequency.     

Transitional flow in a Rushton turbine stirred tank

The way in which the single phase flow of Newtonian liquids in the vicinity of the impeller in a Rushton turbine stirred tank goes through a laminar‐turbulent transition has been studied in detail experimentally (with Particle Image Velocimetry) as well as computationally. For Reynolds numbers equal to or higher than 6000, the average velocities and velocity fluctuation levels scale well with the impeller tip speed, that is, show Reynolds independent behavior. Surprising flow structures were measured—and confirmed through independent experimental repetitions—at Reynolds numbers around 1300. Upon reducing the Reynolds number from values in the fully turbulent regime, the trailing vortex system behind the impeller blades weakens with the upper vortex weakening much stronger than the lower vortex. Simulations with a variety of methods (direct numerical simulations, transitional turbulence modeling) and software implementations (ANSYS‐Fluent commercial software, lattice‐Boltzmann in‐house software) have only partial success in representing the experimentally observed laminar‐turbulent transition. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3610–3623, 2017     

The quasi-steady-state approximation in continuous stirred tank reactors

The Quasi-steady-state-approximation (QSSA) applied lo continuous stirred tank reactors (CSTR) is examined. The induction period is found to be somewhat longer and the error in the QSSA larger than for batch reactors. This error is usually insignificant except when CSTR conversions are low. An alternative approximation is proposed for this case. The errors in the QSSA are also illustrated for the well known cases of Enzyme and Free-Radical polymerization kinetics.     

Segregated regions in continuous laminar stirred tank reactors

Using visualization techniques, including acid/base reactions and UV fluorescence, we provide experimental evidence of segregated regions (islands) during mixing of viscous Newtonian fluids under laminar flow conditions in continuous stirred tank reactors (CSTRs). The effect of inlet/outlet stream position and Reynolds number on the dynamics of the mixing processes is examined. Numerical experiments in 3-D map were able to capture the main features of the CSTR flow by perturbing a Batch system using an imposed axial flow. Asymmetric flow patterns produced by off-center positioning of inlet and outlet pipes cause a reduction in size of the segregated region, enlarging the chaotic region and leading to more efficient mixing. Under dynamic inlet flow conditions, the laminar steady flow is perturbed, giving rise to an asymmetric flow pattern that is able to destroy toroidal segregated regions. Counter-intuitively, higher agitation speed (higher Re) did not enhance overall mixing efficiency. Faster agitation stabilized the toroidal regions, making it harder to destroy them. In addition, dynamic mixing protocols are investigated to enhance mixing performance. We demonstrate that time-dependent pumping and stirring protocols are able to efficiently destroy long-lasting toroidal regions.     

搅拌反应器内计算流体力学模拟技术进展

综述了计算流体力学(CFD)技术应用在搅拌反应器的进展情况。重点对搅拌反应器内流动场模拟的各种处理方法,包括"黑箱"模型法、内外迭代法、多重参考系法和滑移网格法,进行了介绍与评价,指出了各种方法所具有的特点及存在的问题。阐述了搅拌反应器内CFD技术的发展方向,并就国内的研究现状进行了简单概述。