Blade Disk Turbine Research Articles

Power consumption and oxygen transfer optimization for C5 sugar acid production in a gas-liquid stirred tank bioreactor using CFD-Taguchi method

Power consumption and oxygen transfer are considered the two most important direct indexes, affecting the effective and cost-efficient C5 sugar acid fermentation from C5 sugar. In this work, an effective optimization approach combining computational fluid dynamics (CFD) modeling and the Taguchi method, was presented to evaluate C5 sugar acid fermentation in a gas-liquid stirred tank bioreactor. Three most critical control factors of impeller type (Rushton turbine (RT), concaved blade disc turbine (CBDT), and four wide-blade hydrofoil impeller pumping down (WHd)), agitation speed and aeration rate involved three levels, were quantitatively studied by numerical simulation based on a validated CFD model. Results indicated that, the WHd impeller gave the best energy-saving performance, the CBDT impeller gave the best oxygen transfer performance, while the RT impeller was the most balanced one. The agitation speed contributed most to both the power consumption and oxygen transfer, while exerting minor impact on compromise indexes. The aeration rate had little contribution to power consumption and oxygen transfer, while deserving more attention when energy efficiency and trade-off optimization are considered. These findings can be used as guidelines to achieve efficient and economical C5 sugar acid production.

Multiphase Stirred Tank Bioreactors – New Geometrical Concepts and Scale‐up Approaches

AbstractMainly with respect to biotechnological cases, current developments in the field of impeller geometries and findings for multistage configurations with a specific view on aerated stirred tanks are reviewed. Although often the first choice, in the given case the 6‐straight blade disc turbine is usually not the best option. Furthermore, quantities usable for scale‐up, specifically applicable in this field are discussed. Only quantities taking local conditions into account appear to be able to actually compare different stirrer types and scales.

Gas dispersion and solid suspension in a three-phase stirred tank with triple impellers

The hydrodynamics is still not fully understood in the three-phase stirred tank equipped with multi-impeller due to the intensive interaction between phases. In this work, the solid critical suspension speed ( N JSG ), relative power demand (RPD) and overall gas holdup ( ε G ) were measured in an air–water–glass beads stirred tank equipped with multi-impeller, which consists of a parabolic blade disk turbine below two down-pumping hydrofoils. Results show that either the N JSG or the specific power consumption increases when increasing the volumetric solid concentration or superficial gas velocity. RPD changes less than 10% when solid volumetric concentration ranges from 0 to 15%. ε G decreases with the increase of solid concentration, and increases with the increase of both superficial gas velocity and the total specific power consumption. The quantitative correlations of N JSG , RPD and ε G were regressed as the function of superficial gas velocity, specific power consumption, Froude number and gas flow number, in order to provide the reference in the design of such three-phase stirred tank with similar multi-impellers. • Just-suspension speed, RPD and gas holdup with triple impeller were measured. • Superficial gas velocity significantly affects the suspension speed. • Overall gas holdup is evidently affected by the solid.

Process optimization in a stirred tank bioreactor based on CFD-Taguchi method: A case study

Cleaner aerobic fermentation with high efficiency is of great significance to microbial production. In an aerobic fermentation process, gas holdup and power consumption are main indexes for its performance evaluation. Based on CFD-Taguchi method, effects of control factors of impeller type, gas flow rate and agitation speed on gas holdup and power consumption were studied, by taking pullulan fermentation of Aureobasidium pullulans in a stirred tank bioreactor as a case study. Innovatively, three representative viscosity stages and their corresponding viscosities were defined according to viscosity change during fermentation, so as to quantitatively optimize the fermentation process. By range analysis and analysis of variance, effects of control factors and their significant levels on fermentation performance were obtained so as to optimize the fermentation system. All control factors were significant at low viscosity stage, and insignificant at stages of medium and high viscosity except for gas flow rate at high viscosity stage (p < 0.05). Impeller of bent blade disc turbine had the highest comprehensive evaluation index during the fermentation process, with the optimal agitation speed and gas flow rate 400 rpm and 7.8 L/min at low viscosity stage, and 400 rpm and 7.8 L/min at stages of medium and high viscosity.

Effect of zoning on mixing and mass transfer in dual agitated gassed vessels

Gas–liquid multi-phase processes are widely used for processes that require reactions. To increase productivity in these reactions one potential method is to increase the gas flow rate into the vessel. This means that it is important to understand how these reactors perform at high gas flow rates, which can create problems such as zones within the vessel. This paper investigates the mixing performance and the mass transfer in dual agitated systems at high gas flow rates. Two configurations have been compared a 6 blade disk turbine (Rushton turbine) below either a 6 Mixed flow Up-pumping or down-pumping agitator. Zoning has been identified by Electrical Resistance Tomography which affects the mixing time within the vessel, with increasing agitation rate potentially increasing the mixing times at high gas flow rates. At these high gas flow rates the zoning also affects the mass transfer meaning that it is not constant within the whole vessel. However, dividing the vessel into the key zones allows the mass transfer rate to be predicted with a single equation.

Asymmetric Blade Disc Turbine for High Aeration Rate in a Fermenter

Asymmetric Blade Disc Turbine for High Aeration Rate in a Fermenter

Gas–liquid mixing in dual agitated vessels in the heterogeneous regime

Gas–liquid multi-phase processes are widely used for reactions such as oxidation and hydrogenation. There is a trend for such processes to increase the productivity of the reactions, one method of which is to increase the gas flow rate into the vessel. This means that it is important to understand how these reactors perform as high gas flow rates occurs well into the heterogeneous regime. This paper investigates the mixing performance for the dual axial radial agitated vessel of 0.61m in diameter. 6 blade disk turbine (Rushton turbine) below a 6 Mixed flow Up-pumping and down-pumping have been studied at very high superficial gas velocities to understand the flow regimes operating at industrial conditions. Electrical resistance tomography have been used to produce the 3D images using Matlab, along with analysing the mixing parameters such as Power characteristics, gas hold-up and dynamic gas disengagement. Minimal difference between the two configurations have been reported in terms of gas hold-up, however with the choice of upward and downward pumping impeller power characteristics show significant difference at very high gas flow rates. Also at these high superficial gas velocities, this report introduces a 3rd bubble class, as seen in dynamic gas disengagement experiments, which corresponds to very large slugs of gas.

Corrosion of carbon steel in two phase flow (CO2 gas-CaCO3 solution) controlled by sacrificial anode

Corrosion tests of carbon steel (CS) in two phase flow of gas-liquid (CO2 gas-CaCO3 solution) were carried out using electrochemical polarization technique. The effects of different operating parameters such as temperature, agitation speed, gas flow rate, and time were investigated. Flat blade disc turbine mixer was used to simulate the two phase flow conditions. Cathodic protection was used to protect carbon steel in the salt solution-CO2 mixture by using zinc as a sacrificial anode under different operating conditions. The corrosion rate (CR) represented by limiting current density (iL) in two phase mixture decreased with the increase in agitation speed depending on the flow rate of CO2, temperature, and time. In general, increasing the CO2 gas flow rate caused a clear decrease in the CR especially under agitation conditions. Increasing the temperature caused a considerable increase in the corrosion rate. Good corrosion protection percent was attained which reached up to 85%. In addition, the variations of corrosion potential with time for both metals (CS and Zn) were determined as well as the loss in weigh for each metal.

Energy efficiency of a deep hollow bladed impeller for mixing viscoplastic fluids in a cylindrical vessel

The energy efficiency of a deep hollow blade disk turbine in unbaffled mixing vessel is determined in this article via numerical simulations. The vessel is filled with xanthan gum solutions, which ...

Optimization of Dual-Impeller Configurations in a Gas–Liquid Stirred Tank Based on Computational Fluid Dynamics and Multiobjective Evolutionary Algorithm

An optimization strategy combining computational fluid dynamics (CFD) with multiobjective evolutionary algorithm (MOEA) for dual-impeller design in an aerated tank was proposed to maximize the overall effective gas holdup and minimize the power consumption with six geometrical variables. The nondominated sorting genetic algorithm-II (NSGA-II) was applied to construct a Pareto front from numerous design points with greatly reduced computation. The measurement of local gas holdup and power consumption by dual electric conductivity probe and torque sensor was utilized to verify the CFD model and evaluate the optimal design. The optimal design with a pitched concave blade disk turbine as the lower impeller and a down-pumping pitched blade turbine as the upper impeller exhibited the best gas dispersion performance with efficient energy savings. This approach has the potential to greatly enhance the efficiency of industrial stirred reactors.

CFD investigation of Schizochytrium sp. impeller configurations on cell growth and docosahexaenoic acid synthesis.

Effects of impeller configurations on docosahexaenoic acid production and flow characteristics were investigated by Schizochytrium sp. in a 15L bioreactor. 6-straight blade disc turbine (6-SBDT), 6-arrowy-blade disc turbine (6-ABDT) and down-pumping propeller (DPP) were combined to form different impeller configurations. Simulated results showed that configuration SSA consisting of upper two 6-SBDT and one bottom 6-ABDT possessed the worst oxygen supply capacity. But it obtained the highest DHA percentage of 48.17% and DHA yield of 21.42g/L, indicating that it was beneficial for DHA synthesis and converting glucose to biomass and lipids. Configuration SAS consisting of one middle 6-ABDT and two 6-SBDT provided better mixing capacity, which resulted in the maximum glucose consumption rate of 2.86g/Lh and the highest biomass of 108.09g/L. This study would improve insight into understanding the relationship between flow field and the physiology of Schizochytrium sp. for the scale-up of industrial DHA production.

Influence of impeller diameter on overall gas dispersion properties in a sparged multi-impeller stirred tank

The impeller configuration with a six parabolic blade disk turbine below two down-pumping hydrofoil propellers, identified as PDT+2CBY, was used in this study. The effect of the impeller diameter D, ranging from 0.30T to 0.40T (T as the tank diameter), on gas dispersion in a stirred tank of 0.48m diameter was investigated by experimental and CFD simulation methods. Power consumption and total gas holdup were measured for the same impeller configuration PDT+2CBY with four different D/T. Results show that with D/T increases from 0.30 to 0.40, the relative power demand (RPD) in a gas–liquid system decreases slightly. At low superficial gas velocity VS of 0.0078m·s−1, the gas holdup increases evidently with the increase of D/T. However, at high superficial gas velocity, the system with D/T=0.33 gets a good balance between the gas recirculation and liquid shearing rate, which resulted in the highest gas holdup among four different D/T. CFD simulation based on the two-fluid model along with the Population Balance Model (PBM) was used to investigate the effect of impeller diameter on the gas dispersion. The power consumption and total gas holdup predicted by CFD simulation were in reasonable agreement with the experimental data.

Influence of impeller diameter on local gas dispersion properties in a sparged multi-impeller stirred tank

Vertical distributions of local void fraction and bubble size in air–water dispersion system were measured with a dual conductivity probe in a fully baffled dished base stirred vessel with the diameter T of 0.48m, holding 0.134m3 liquid. The impeller combination with a six parabolic blade disk turbine below two down-pumping hydrofoil propellers, identified as PDT+2CBY, was used in this study. The effects of the impeller diameter D, ranging from 0.30T to 0.40T (corresponding to D/T from 0.30 to 0.40), on the local void fraction and bubble size were investigated by both experimental and CFD simulation methods. At low superficial gas velocity VS of 0.0077m·s−1, there is no obvious difference in the local void fraction distribution for all systems with different D/T. However, at high superficial gas velocity, the system with a D/T of 0.30 leads to higher local void fraction than systems with other D/T. There is no significant variation in the axial distribution of the Sauter mean bubble size for all the systems with different D/T at the same gas superficial velocity. CFD simulation based on the two-fluid model along with the population balance model (PBM) was used to investigate the effect of the impeller diameter on the gas–liquid flows. The local void fraction predicted by the numerical simulation approach was in reasonable agreement with the experimental data.

Micromixing characteristics in a gas–liquid–solid stirred tank with settling particles

The parallel-competing iodide–iodate reaction scheme was used to study the micromixing performance in a multi-phase stirred tank of 0.3m diameter. The impeller combination consisted of a half elliptical blade disk turbine below two down-pimping wide-blade hydrofoils, identified as HEDT+2WHD. Nitrogen and glass beads of 100μm diameter and density 2500kg·m−3 were used as the dispersed phases. The micromixing could be improved by sparging gas because of its additional potential energy. Also, micromixing could be improved by the solid particles with high kinetic energy near the impeller tip. In a gas–solid–liquid system, the gas–liquid film vibration with damping, due to the frequent collisions between the bubbles and particles, led to the decrease of the turbulence level in the liquid and caused eventually the deterioration of the micromixing. A Damping Film Dissipation model is formulated to shed light on the above micromixing performances. At last, the micromixing time tm according to the incorporation model varied from 1.9ms to 6.7ms in our experiments.

Micromixing Characteristics in an Aerated Stirred Tank with Half Elliptical Blade Disk Turbine

Abstract The parallel-competing iodide-iodate reaction scheme was used to investigate the micromixing efficiency in an aerated stirred tank of 0.30 m diameter agitated by a half elliptical blade disk turbine. The mean specific energy dissipation rate Pm ranged from 0.5 to 2.2 W/kg, while the superficial gas velocity VS ranged from 0.015 to 0.047 m/s. Four sub-surface feed positions were considered. When the tank is fed just under the liquid surface or in the near-wall region, the micromixing efficiency can be enhanced by introducing gases with superficial gas velocities higher than 0.031 m/s. The effects of gas on the micromixing performance become complicated, while the tank is fed in the impeller discharging region. The increase of gas flow rate does not always have good effects on the micromixing performance. Moreover, the way to feed sulfuric acid can strongly affect the efficiency of the reaction scheme. For a single liquid phase, the micromixing time tm according to the incorporation model varies from 5 × 10−3 to 3 × 10−2 s. The dimensionless local specific energy dissipation rate Φ near the liquid surface is almost independent of Pm, while Φ in the impeller discharging area decreases with increasing Pm.

Numerical Simulation of Multi-Impeller High Intensity Conditioning in Fine Coal Flotation

The numerical simulation of a mixing vessel with three layers of six 45° leaned blade disc turbine impeller was conducted by using the standard k-ε turbulence model and multiple reference frame method (MRF), the velocity field were analyzed. Results show that multi-impeller increases the fluid turbulence zone, strengthens the mixing effect and enhances the function of the axial velocity gradient of conditioning vessel.

PIV Study of Flow in an Aerated Tank with a Hollow Blade Turbine

Liquid phase hydrodynamics in an aerated tank (ID = 0.19 m) stirred by a half elliptical blade disk turbine (HEDT) have been investigated using particle image velocimetry (PIV) under both aerated and unaerated conditions. The effect of the gas flow rate on the aerated mean velocity of the liquid phase, turbulent kinetic energy and turbulent kinetic energy dissipation are discussed, and their comparisons with those under unaerated conditions are also carried out. Under aerated conditions, the presence of gas does not remarkably change the velocity pattern of the liquid phase. When the direction of the liquid flow is the same as the buoyancy, the liquid is accelerated up to 10.4% by bubbles at position of z/T=0.8 and r/T=0.45; while the liquid flow reversely, the liquid is decelerated about 37.5% under the gas flow rate of 0.2 vvm at the position of z/T=0.25 and r/T=0.45. The turbulent kinetic energy in the bulk flow increases after introducing gas phase, and the average turbulent kinetic energy of the upper, middle and lower regions at 0.2 vvm are increased by 37.3%, 37.8% and 142.7%, respectively. Large-eddy PIV approach is carried out to estimate the distribution of the turbulence kinetic energy dissipation. The result shows that the distribution of the turbulent kinetic energy dissipation is similar as those of turbulent kinetic energy.

Effects of the Blade Shape on the Trailing Vortices in Liquid Flow Generated by Disc Turbines

Particle image velocimetry technique was used to analyze the trailing vortices and elucidate their relationship with turbulence properties in a stirred tank of 0.48 m diameter, agitated by four different disc turbines, including Rushton turbine, concaved blade disk turbine, half elliptical blade disk turbine, and parabolic blade disk turbine. Phase-averaged and phase-resolved flow fields near the impeller blades were measured and the structure of trailing vortices was studied in detail. The location, size and strength of vortices were determined by the simplified λ 2-criterion and the results showed that the blade shape had great effect on the trailing vortex characteristics. The larger curvature resulted in longer residence time of the vortex at the impeller tip, bigger distance between the upper and lower vortices and longer vortex life, also leads to smaller and stronger vortices. In addition, the turbulent kinetic energy and turbulent energy dissipation in the discharge flow were determined and discussed. High turbulent kinetic energy and turbulent energy dissipation regions were located between the upper and lower vortices and moved along with them. Although restricted to single phase flow, the presented results are essential for reliable design and scale-up of stirred tank with disc turbines.

An Investigation of Heat Transfer in a Mechanically Agitated Vessel

The objective of this study is to optimize experimental conditions of agitating a non-Newtonian liquid using experimental design methodology. The measurements of the temperatures have been carried out in a jacketed vessel equipped with Turbine impellers. The rheological properties of aqueous solutions of carboxymethylcellulose sodium salt had been studied using shear stress/shear rate data. The results of the experimental studies, concerning the effect of the diameter of the impeller, the impeller speed and baffled or unbaffled vessel on the overall heat transfer coefficient have been approximated in the form of equations. Based on the optimization criterion, an agitated vessel equipped with Flat Blade Disc Turbine (FBDT) of diameter ratio d/D = 0.6 and baffles is proposed as the most advantageous for heat transfer processes.

Particle Image Velocimetry Study of Flow Patterns and Mixing Characteristics in Multiple Impeller Stirred Tank

The flow generated in a stirred tank of 0.48 m diameter, agitated by three impellers of 0.19 m diameter, including one half-elliptical blade disc turbine (HEDT) below and two up-pumping wide-blade hydrofoils (WHU), were investigated by using 360° ensemble-averaged particle image velocimetry (PIV) technique. The flow characteristics for seven impeller combinations with different impeller spacings were investigated. Results show that global circulation patterns in the stirred tank are strongly dependent on the impeller spacing. Three types of flow patterns were observed, including five, four, and three circulation loops in the flow field, by changing the spacing between the bottom and the middle impellers (C1), the spacing between the middle and the top impellers (C2), and the submersion depth of the top impeller (C3). While the clearance (ΔC) of the bottom impeller is equal to 0.4T, the five circulation loops flow pattern occurs when C1 = 0.48T, C2 = 0.48T, and C3 = 0.4T, and the four circulation loops flow pattern occurs when C1 = 0.48T, C2 = 0.4T, and C3 = 0.4T, and the three circulation loops flow pattern occurs when C1 = 0.48T, C2 = 0.4T, C3 = 0.32T. The mixing efficiency defined based on the mixing time and the power consumption were also discussed and the results show that less circulation loops could lead to higher mixing efficiency, but the mixing efficiency does not solely increase with the decreasing of the circulation loops.