Up-pumping Pitched Blade Turbine Research Articles

Kinetic analysis of dual impellers on methane hydrate formation

Abstract This study investigates the effects of types of impellers and baffles on methane hydrate formation. Induction time, water conversion to hydrates (hydrate yield), hydrate formation rate and hydrate productivity are components that were estimated. The initial hydrate formation rate is generally higher with the use of Ruston turbine (RT) with higher values 28.93 × 10−8 mol/s in RT/RT with full baffle (FB) experiment, but the decline rate of hydrate formation was also high compared to up-pumping pitched blade turbine (PBTU). Power consumption is higher also in RT/RT and PBT/RT with higher value 392,000 W in PBT/RT with no baffle (NB) experiment compared to PBT/PBT and RT/PBT experiments respectively. Induction time values are higher in RT/RT experiments compared to PBT/PBT ones. Hydrate yield is always smaller when there is no baffle in all four groups of experiments while the higher values exist in experiments with full baffle. It should be noticed that PBT is the same with PBTU, since all experiments with mixed flow have upward trending.

Kinetic Analysis of Methane-Propane Hydrate Formation by the Use of Different Impellers.

In the present study, the effect of different kinds of impellers with different baffles or no baffle was investigated. Up-pumping pitched blade turbine (PBTU) and Rushton turbine (RT) were the two types of impellers tested. The reactor was equipped with different designs of baffles: full, half and surface baffles, or no baffles. Single (PBTU or RT) and dual (PBTU/PBTU or RT/RT) use of impellers with full (FB), half (HB), surface (SB), and no baffle (NB) combinations formed two sets of 16 experiments. The first group of experiments was close to the equilibrium line (P = 26.5 bars and T = 8.5 °C), and the second group was deep in the equilibrium line (P = 24.5 bars and T = 2 °C). There was estimation of rate of hydrate formation, induction time, hydrate productivity, overall power consumption, split fraction, and separation factor. In both single and dual impellers, the results showed that RT experiments are better compared to PBTU in the rate of hydrate formation. The induction time is almost the same because we are deep in the equilibrium line while, hydrate productivity values are higher in PBTU compared to RT experiments. As a general view, RT experiments consume more energy compared to PBTU experiments.

The Effect of Experimental Conditions on Methane (95%)–Propane (5%) Hydrate Formation

In the present study, the effect of different kinds of impellers with different baffles or no baffle was investigated. Up-pumping pitched blade turbine (PBTU) and Rushton turbine (RT) were the two types of impellers tested. The reactor was equipped with different designs of baffles: full, half and surface baffles or no baffles. Single (PBTU or RT) and dual (PBTU/PBTU or RT/RT) use of impellers with full (FB), half (HB), surface (SB) and no baffle (NB) combinations formed two sets of 16 experiments. There was estimation of rate of hydrate formation, induction time, hydrate productivity, overall power consumption, split fraction and separation factor. In both single and dual impellers, the results showed that RT experiments are better compared to PBTU in rate of hydrate formation. The induction time is almost the same since we are deep in the equilibrium line while hydrate productivity values are higher in PBTU compared to RT experiments. As general view RT experiments consume more energy compared to PBTU experiments.

Using PLIF/PIV techniques to investigate the reactive mixing in stirred tank reactors with Rushton and pitched blade turbines

Planar laser induced fluorescence (PLIF) technique was used to investigate concentration profiles and reaction progress of a turbulent reactive mixing process in a baffled stirred tank reactor. Rushton turbine, up-pumping pitched blade turbine (PBTU), and down-pumping pitched blade turbine (PBTD) were used to study the effect of mixing on the fast Fenton reaction progress. For determining the reaction progress, a criterion was developed, which was based on obtaining the number of mixed pixels with a defined uniformity percentage for the entire reactor area. It was found that impeller type, impeller clearance, and reactant injection location significantly altered concentration profiles and reaction progress. The reaction time scale along with the micro- and macromixing time scales were determined and it was concluded that the system performance was controlled by macromixing in the tank. Mean velocity field of the impellers was obtained by particle image velocimetry (PIV) technique and reasonably validated the concentration distribution results of PLIF technique.

PEPT measurements of solid–liquid flow field and spatial phase distribution in concentrated monodisperse stirred suspensions

The technique of positron emission particle tracking (PEPT) has been used to determine the two-phase flow field and spatial phase distribution in a stirred vessel containing coarse glass particles suspended in water. The Lagrangian flow data provided by PEPT have been converted to give a detailed Eulerian description of the two-phase flow generated by a pitched blade turbine (PBT) operating in up-pumping or down-pumping mode. For the first time, it has been possible to determine the full 3D velocity and concentration fields of both the liquid and the solid phase within an opaque dense slurry of this type containing up to 40 wt% solids. The detailed PEPT measurements have also enabled the solids mass balance and the mass continuity of the two phases to be accurately verified throughout the vessel. The data show that the pumping effectiveness of the PBT is unaffected at moderate solid fractions, but is considerably reduced at high fractions and even more so in the up-pumping mode. A uniformity index based on the variance of the local solids concentration in the vessel shows that, overall, a down-pumping PBT achieves a significantly better homogeneity than an up-pumping PBT.

A PIV study of hydrodynamics in gas–liquid high throughput experimentation (HTE) reactors with eccentric impeller configurations

High-throughput experimentation (HTE) is used for the screening of novel catalyst formulations via miniature agitated gas–liquid reactors with vessel volumes of an order of magnitude below the laboratory scale. An investigation of the macroscopic hydrodynamic performance of a miniaturised unbaffled stirred vessel of diameter 45 mm for an air–water system has been carried out at gassing rates of 0.25 and 0.5 vvm (dispersed flow regime) using particle image velocimetry (PIV). Measurements of bubble size and gas hold-up were also made. Eccentric agitation was employed as a means of breaking solid body rotation within the vessel, using a 6-blade, up-pumping pitched blade turbine. The gas phase was introduced via sintered glass panel spargers mounted in the vessel base. Two different configurations were used: firstly where the sparger located directly below the impeller, and secondly where the sparger was located opposite the impeller on the other side of the vessel. Measured distributions of turbulent kinetic energy (TKE) for both gassed configurations were similar and showed significant differences to the ungassed case. Estimates of the gas–liquid interfacial area were at least 2–3 times higher than those found in conventional, lab-scale baffled vessels; this was attributed to the creation of very small bubbles at the sparger ( d 32 ≈ 100 μ m ).

Gas–Liquid Mass Transfer: A Comparison of Down- and Up–pumping Axial Flow Impellers with Radial Impellers

The performance of a down- and up-pumping pitched blade turbine and A315 for gas–liquid dispersion and mass transfer was evaluated and then compared with that of Rushton and Scaba turbines in a small laboratory-scale vessel. The results show that, when the axial flow impellers are operated in the up-pumping mode, the overall performance is largely improved compared with the down-pumping configuration. Compared with the radial turbines, the up-pumping A315 has a high gas handling capacity, equivalent to the Scaba turbine, and is economically much more efficient in terms of mass transfer than both turbines. On the other hand, the up-pumping pitched blade turbine is not as well adapted to such applications. Finally, the axial flow impellers in the down-pumping mode have the lowest performance of all the impellers studied, although the A315 is preferred of the pitched blade turbine.

Surface Feed with Minimum by-Product Formation for Competitive Reactions

Selectivity for several classes of competitive reactions is maximized when the feed is located in a highly turbulent region. The usual practice is to feed close to the impeller with a submerged feed pipe. With submerged feeds, however, many mechanical, metallurgical and/or operational problems must be addressed in detailed engineering design. Surface feed remains an attractive configuration, provided byproduct formation can be suppressed. This study reports several promising configurations for surface feed, all of which achieve high selectivity for the third Bourne reaction. In particular, an up-pumping pitched blade turbine (PBTU) located in the upper third of the tank gives very good results. The up-pumping configuration is robust, with little effect of feed configuration or variations in geometry in the bottom of the tank on the selectivity. There is a maximum impeller speed ( N E ) above which air bubbles are entrained into and remain trapped within the tank. A modified form of the Froude number, Fr = N 2 S/g , can be used to identify this critical point ( Fr crit = N 2 E S/g ). When the PBTU is operated at the critical Froude number ( Fr crit ), byproduct yield is equal to the minimum obtained for a submerged feed.

Modeling turbulent flow in stirred tanks with CFD: the influence of the modeling approach, turbulence model and numerical scheme

Single phase turbulent flow in a tank stirred by a down- and an up-pumping pitched blade turbine has been simulated using computational fluid dynamics. The effect of the modeling approach, discretization scheme and turbulence model on mean velocities, turbulent kinetic energy and global quantities, such as the power and circulation numbers, has been investigated. The results have been validated by laser doppler velocimetry (LDV) data. The stationary and time-dependent modeling approaches were found to have little effect on the turbulent flow, however the choice of the numerical scheme was found to be important, especially for the predicted turbulent kinetic energy. A first-order method was found to highly underestimate LDV data compared with higher order methods. The type of the turbulence model was limited to the k– ε and RNG models due to convergence difficulties encountered with a Reynolds stress model and there was found to be little effect of these models on the mean flow and turbulent kinetic energy. This latter quantity was found to be largely under-predicted in the discharge region of the down-pumping impeller in comparison with LDV data. Better agreement was found for the up-pumping pitched blade turbine. Estimated power numbers were found generally to be in good agreement for the down- and up-pumping data. However, the circulation number tended to be over-predicted by about 30% and 40% for the down- and up-pumping agitators, respectively.

PIV measurements of flow in an aerated tank stirred by a down- and an up-pumping axial flow impeller

Liquid phase hydrodynamics in an aerated tank stirred by a down- and an up-pumping pitched blade turbine have been investigated using particle image velocimetry. The effect of agitator configuration and the gas phase on the mean velocity fields and turbulent quantities in the vessel have been investigated. The global mean gas holdup has also been evaluated for the two pumping conditions. For the gas flow rate used, the presence of gas only slightly alters the liquid flow patterns produced by both the down- and up-pumping configurations and causes a general decrease in the mean liquid velocities. The turbulent kinetic energy in the impeller discharge region was not affected by the presence of gas, but in the bulk of the tank, aeration caused a decrease in this value. Global gas holdup was found to be ∼36% greater for the up-pumping impeller and a large amount of gas was found to be entrained by the primary circulation loop.