TURBULENT FLOW IN STIRRED TANKS: SCALE-UP COMPUTATIONS FOR VESSEL HYDRODYNAMICS

A numeric model for turbulent flow was used to compute the flow patterns in Rushton turbine agitated vessels. The cases considered cover two orders of magnitude for the three different scaling criteria of constant impeller Reynolds number, power input per unit mass, and impeller tip speed. The constant power input scale-up criteria maintains the turbulence levels throughout the vessel during scale-up. The circulation times, however, increase with vessel size for this scaling criteria. The other scaling criteria of constant impeller tip speed and impeller Reyonds number lead to decreasing turbulence levels in the tank along with further increases in circulation times.     

Model-based scale-up strategy for mycelial fermentation processes

With the aid of a mathematical model describing the interrelationships between mycelial morphology, mycelial growth and product formation, rheology, mass transfer, and environmental conditions, a new scale-up strategy has been developed, simulating the bioreactor performance at different agitation speeds. The simulations have shown that there is an optimum agitation speed, yielding maximum product formation that is different from the conventional scale-up results based on constant P_g/V_T, k_L a and N_I D_I. It has also been shown in the simulations that the product formation scaled up by means of conventional methods is considerably lower than the simulated maximum or is close to the maximum but requiring a higher energy consumption. This indicates that model-based scale-up could be a more accurate and efficient method for scaling up complex systems such as mycelial fermentation processes.     

A modified three-phase multistage fluid bed model by considering axial dispersion in bubble side

ABSTRACT

The previously published multistage three-phase model (proposed by El-Halwaghi and El-Rifai) has been improved by considering axial dispersion in the bubble phase. Comparing the predicted results of the developed model with the different experimental data available in the literature showed a close agreement on both axial concentration profile and overall conversions. The presented model is found to be valid over a wider range of operating conditions as compared to the original model. At high reaction rates where the shortcomings of the hydrodynamic model come to light as well as at high superficial gas velocities where the reactant concentration in the bubble side is critical in reactor performances, the developed model gives obviously better results. It has also been shown that the proposed model is attractive in scale-up procedure. The effects of enlargement of bed diameter on reactor performances could be predicted by the presented model more reasonably.     

集中式全空气空调系统该如何发展

回顾了家用空调和多联机空调系统的发展过程,认为集中式全空气空调系统的规模化生产是发展的必然趋势,其关键是实现规格化、模块化、系列化。提出了可实现规模化生产的全空气空调系统的模式。该系统可通过优化系统组合,取消二次回风,实现能量的最佳利用和回收,具有系统简洁、安装维护简便,可靠性高等优点。     

增强型聚醚砜超滤干膜的研制及中试放大

本文报道了聚醚砜超滤干膜的试制和中试放大的研究情况，分析了溶剂、致孔剂及聚合物分子量和粘度对膜性能的影响，并进行了成膜条件和膜干燥温度的变化对膜性能改善的对比试验，简单揭示了膜的微观结构及膜的耐溶剂特性，最后着重介绍了超滤膜的中试放大、连续化、机械化的制备情况，以及将膜装入５ｍ＾２膜面积的超滤器上的运行结果。     

Development of a pilot-scale microfiltration harvest for the isolation of physostigmine from Streptomyces griseofuscus broth

A pilot-scale microfiltration harvest was developed for the isolation of physostigmine from a mycelial fermentation broth. Complete permeation for this extracellular secondary metabolite was obtained during initial laboratory screening with a variety of crossflow filtration membranes but poor filtration flux made process feasibility uncertain. Modification of the fermentation medium improved fluxes from 10–20 dm³ m^?2 h^?1 to 60–80 dm³ m^?2 h^?1 which significantly reduced membrane area requirements, making the process feasible for larger scale implementation. A commercially-available ceramic membrane with 0·2 μm pores was employed for the scale-up of this step to the pilot plant; this membrane was found to provide flux similar to that of polymeric membranes and had superior regeneration characteristics. Optimum performance at bench scale was obtained using 70 kPa transmembrane pressure and 4·0 m s^?1 crossflow velocity. The mycelial broth had a very high suspended solids concentration (30% (v/v)) which limited us to a two-fold concentration before starting the diafiltration washes. The process was scaled-up to the 200–400 dm³ scale, with good reproducibility and excellent membrane regenerability observed in a series of five experiments. An increase in membrane loading did result in a decreased average flux at the larger scale (47·6 dm³ m^?2 h^?1), which indicated the importance of this parameter. A centrifugal pump was substituted for a positive displacement pump upon scale-up and performed well if provided with the appropriate suction head. Scale-up in general was straightforward, provided proper attention was given to the hydraulic design of the system.     

Enhancing the recovery and concentration of polyphenols from camu-camu (Myrciaria dubia H.B.K. McVaugh) by aqueous two-phase flotation and scale-up process

In this study, polyphenols obtained from camu-camu pulp residue were recovered and concentrated from aqueous two-phase flotation (ATPF) by evaluating different operating conditions, such as solvent type, pH, ammonium sulfate concentration, flotation time, air flow, and volumetric ratio. Under optimal conditions, the polyethylene glycol 400/ammonium sulfate ATPF system showed an efficiency of 81.02% and a concentration coefficient two times higher than traditional aqueous two-phase extraction. Experiments were also carried out on a semi-pilot scale, using an apparatus with a 2.5-L working volume. The results showed that the semi-pilot system was comparable to the smaller scale system.     

Hydrodynamics in rectangular air-lift reactors: Scale-up and the scale-up and the influence of gas-liquid separator design

Experiments were conducted on air-lift reactors with different liquid volumes, aspect ratios, and gas-liquid separator configurations, with constant downcomer to riser cross-sectional area ratio and riser/downcomer height. Reactor performance was highly dependent on the gas-liquid separator design. By changing the latter, the mode of operation could be changed from that of a concentric tube reactor (with gas recirculation) to an external loop reactor (without gas recirculation). Liquid velocity and overall gas hold-up data were correlated to the power per liquid volume and “Disengagement Ratio”, a geometric parameter describing the separator's configuration. During scale-up, similar gas hold-ups and liquid velocities were found in laboratory and pilot reactors. A modified air-lift reactor with an enlarged channel for a gas-liquid separator also was studied.     

硝酸氧化法处理BI有机废水工艺放大试验

以含己酸过氧化氢（HPOCaP）的酸性废水（BI废水）为原料、醋酸钴作分解反应的催化剂、浓硝酸作氧化剂制取己二酸的小试（间歇操作）技术条件为依据,完成了间歇操作改连续操作及放大试验过程工艺研究,为进一步工业化生产设计奠定了基础.己二酸产率约为8.4wt%.     

往复振动筛板萃取塔放的大设计模型

对往复振动筛板萃取塔（RPEC）塔内的传质过程进行了理论分析，并在此基础上，从单液滴传质模型出发，应用数学统计方法建立了RPEC放大设计模型，即进行放大设计时应遵循通量、塔板间距、振幅和频率不变的原则计算表观传质单元高度H_OXP.采用林可霉素-正丁醇-酸水物系对塔径100 mm的RPEC实验塔研究表明：真实传质单元高度H_OX与体系物性、表观速度、输入能量（振幅A×频率f）有关，而与塔径无关，且不受轴向混合的影响，模型较好地预测了H_OX随输入能量的增加而减小，而通量的变化则对其影响较小;分散传质单元高度H_OXD是塔径D、输入能量、通量U_s和体系物性的函数，实验结果表明模型较好地描述了输入能量和通量增加强化传质起主导作用，有效降低分散传质单元高度H_OXD的传质过程部分，而不能描述轴向混合起主导作用部分.应用放大设计模型对直径325 mm的RPEC放大设计结果验证模型的预测误差在20％以内.