Correlation For kLa Research Articles

Modeling and Simulation of an Industrial Trickle-Bed Reactor for Benzene Hydrogenation: Model Validation against Plant Data

A heterogeneous three-phase reactor model is used to simulate an industrial trickle-bed reactor for benzene hydrogenation, and simulated temperature profiles are compared to actual plant data. The agreement of model predictions with measured data is excellent. Analysis of the results shows that the process is limited by gas−liquid mass transfer of hydrogen. The simulation results show high sensitivity toward the liquid film mass transfer coefficient kLa. Some correlations for kLa are tested, and their validity is evaluated. The estimated values of kLa and kGa are comparable to measured values from a bench-scale reactor reported in the literature.

Surfactant Effects on Aeration Performance of Stirred Tank Reactors

AbstractThe effect of surfactants on aeration performance in stirred tank reactors (STR) at high rates of foaming is studied. The volumetric oxygen transfer coefficient (kLa) and foaming activity estimated as foaming height (Hf) were determined. Biotechnology of lipopeptide biosurfactants from aerobic organisms, e.g., Bacillus subtilis were addressed. Using model solutions of known foam‐generating properties, high‐molecular weight surfactin and low‐molecular weight sodium dodecyl sulphate (SDS), as well as impellers of different types, with flat and fluid‐foil blades, clues on the concentration dependence of STR oxygen transfer and foaming as well as options for foam reduction in the presence of biosurfactant were sought. In response to a two‐fold decrease of surface tension by surfactin, kLa values decreased up to 30 % but remained within the range expected for the mixing system in water; the experiments with SDS showing stronger dependence on surfactant concentration and surface tension. Mixing of surfactant media by a standard six‐blade disc turbine (RT) imposed rate limitations on gassing. A low‐shear impeller Narcissus (NS) could be used to avoid bulk foam outflow, while preserving kLa values that remained unchanged. The ‘power per unit volume' correlation of kLa in stirred tanks is tested in the presence of surfactin.

Packing Characteristics for Mass Transfer in a Rotating Packed Bed

This work investigated the mass transfer of a rotating packed bed (RPB) with emphasis on the effects of the packing's size, shape, material, and surface property. Experimental results show that there is no obvious relationship between at and kLa. Among the various shapes of the packings, the mass transfer coefficients of Raschig rings and Intalox saddles are lower than those of the others, while the kLa of the wire meshes is the highest. As to materials, the mass transfer coefficients are similar for acrylic, glass, ceramic, and stainless steel beads. Besides, the kLa values of the hydrophobically treated packings are 8−27% lower than those of the original glass and ceramic packings. A modified correlation of kLa, which includes the effects of various packings, is proposed based on our RPB experimental results. Further, this correlation can also reasonably estimate most of the kLa data in the Higee literature.

Power Consumption and Gas-Liquid Mass Transfer Volumetric Coefficient in an Agitated Vessel with Pitched Wire-Gauze Blade Impeller under Aeration.

Power consumption in a baffled agitated vessel with pitched wire-gauze blade impeller is measured over a wide range of Reynolds number in turbulent flow region, where the power consumption decreases with decreasing the wire-gauze blade angle. The power consumption without aeration is well correlated with the baffled condition parameter (BW/D)nb0.8. The rotational speed to occur the gross circulation of gas NR increased with the decrease of a blade angle θ for the upflow condition. In the operating conditions of the gross circulation flow of the gas back into the impeller (N > NR) and the turbulent flow (Red > 200), the power consumption under aeration at the standard baffled condition Npg is correlated with the modified equation by the blade angle θ, which was reduced to the power correlation for the wire-gauze impeller (θ = π/2). In the range of the rotational speed of N > NR the power number under aeration is almost independent of the impeller position and the liquid flow direction through the impeller.The measured gas-liquid mass transfer volumetric coefficient for the pitched wire-gauze blade impeller kLa coincides well with the correlation of kLa for the wire-gauze impeller in lower viscosity liquid, whereas the former is smaller than the latter in higher viscosity liquid because of the lost of the wire-gauze blade effect.

Measurement of Gas-Liquid Mass Transfer in an Agitated Vessel. A Comparison between Different Impellers.

Measurement of mass transfer rate was carried out in an agitated vessel with gas sparging. The performance of mass transfer of several commonly used impellers (i.e. Lightnin A315 and A310, 45° pitched blade turbine, concave blade turbine, Rushton turbine, and Rushton turbine with holes) were examined systematically under the same fluid and tank conditions. A dynamic gassing-out method was used to measure the mass transfer rate of oxygen from gas to the de-ionised water. The variation of the dissolved oxygen concentration of the water was measured by a polarographic dissolved oxygen probe (ORION PCM800). The present data shows reasonable agreement with that in previous publications such as those of Linek et al. (1987), Hickman (1988), Warmoeskerken and Smith (1989), Martin et al. (1994), and Chen and Chen (1999). All the data collected here shows that van’t Riet’s (1979) expression, i.e.: kLa = α(P/V)0.4Us0.5 represents reasonably, well (to within ± 30%) the correlation of kLa with specific power P/V and superficial gas velocity Us. However, the present data seem to indicate that the radial flow impellers provide slightly higher (17%) mass transfer rate than the axial flow impellers.

Effect of water on the solubilities and mass transfer coefficients of gases in a heavy fraction of fischer‐tropsch products

AbstractThe effects of water on the solubilities, C*, and volumetric mass transfer coefficients, kLa, for CO, H2, CH4 and CO2 in a heavy fraction of Fischer‐Tropsch liquid were examined at elevated pressures and temperatures at different mixing power inputs. For these gases, higher solubilities were measured in the hydrocarbon mixture saturated with water than those obtained in the hydrocarbon free of water. The kLa values for the four gases were slightly affected by the presence of dissolved water in the hydrocarbon mixture; and they were strongly dependent on the power input per unit liquid volume. Two empirical correlations for kLa as a function of turbine speed and pressure are proposed.

Oxygen Mass Transfer Coefficient (KLa) as Scale-Up Criterion in Brine Shrimp Culture

Correlations were developed for the overall oxygen mass transfer coefficient (KLa) of air agitated system in two types of container geometries; a) cylindri-conical tank and b) oblong-shaped center-partitioned raceway. For each container type, three geometrically similar sizes were investigated with scale ratio of approximately 1:2:3.5. The correlations for KLa in terms of operating and design parameters were shown to involve the Froude and Reynolds numbers. These correlations were subsequently used to provide the scaling equations to define the operating parameters in different sizes of containers for the culture of brine shrimp. The high correlation coefficient obtained for the relationship between total brine shrimp biomass production and the overall mass transfer coefficient applicable to different sizes of both the cylindri-conical tank and the raceway indicates that the overall oxygen mass transfer coefficient is an effective scale-up criterion in brine shrimp culture.