Co-current solid—liquid extraction with initial concentration profile

Plachco, Florencio P.; Krasuk, J. H.

doi:10.1016/0009-2509(72)85059-0

Cited by 7 publications

(4 citation statements)

References 4 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The extractor comprises a vertical descending screw (1) inserted coaxially into a perforated tube (2). The screw is driven by an electric motor (3) with a gearbox (4) furnishing the necessary number of revolutions. A cylindrical head (6) with a tangential pipe feeds in the liquid phase (7), and a screw bearing (8) is attached by fittings to the lower part of the conical case (5).…”

Section: Methodsmentioning

confidence: 99%

“…[1][2][3] To predict extraction yields, mass-transfer models are added to the transport models, under general, simplified, steady-state operating conditions. 4,5 The present study aims to describe, experimentally and theoretically, the behavior of a new type of countercurrent screw extractor. The apparatus has the advantage of providing reliable conveyance outside the screw through the ascending hydrotransport of a dispersed solid material.…”

Section: Introductionmentioning

confidence: 99%

“…The major difficulty in the scale-up of this design can be attributed to complex solid−liquid transport phenomena. As a whole, convection−dispersion models coupled with experimental measurements of the residence time distributions are used to assess the level of axial mixing. − To predict extraction yields, mass-transfer models are added to the transport models, under general, simplified, steady-state operating conditions. , …”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Modeling of a Screw Solid−Liquid Extractor through Concentration Evolution Experiments

Simeonov

Seikova

Pentchev

et al. 2003

Ind. Eng. Chem. Res.

View full text Add to dashboard Cite

Experimental data and mathematical models are presented for extraction from plants in a continuous countercurrent screw extractor operating with solvent recycling. The working process of the device was analyzed for two kinetically different solid-liquid systems: Geranium macrorhizum L.-water and Nicotiana tabacum L.-water. A dimensionless convection-diffusion model, adapted for the relevant flow configuration, was solved numerically under dynamic conditions. From independent experiments in a periodically stirred vessel and in a continuous screw extractor, the model parameters (effective diffusivity, mass-transfer coefficient, and axial dispersion) were obtained by comparing the model solutions to the experimental data. It was found that, for systems containing dilute solutions at high solvent velocity with an internaldiffusion-controlled process (Bi . 40), a simplified perfect-mixing approximation successfully fits the experimental data for the larger particle sizes studied. IntroductionScrew contactors are extensively used in solvent extraction for chemical, biological, and wood species valorization because of their simple mechanical configuration and reliable exploitation mode. The major difficulty in the scale-up of this design can be attributed to complex solid-liquid transport phenomena. As a whole, convection-dispersion models coupled with experimental measurements of the residence time distributions are used to assess the level of axial mixing. 1-3 To predict extraction yields, mass-transfer models are added to the transport models, under general, simplified, steady-state operating conditions. 4,5The present study aims to describe, experimentally and theoretically, the behavior of a new type of countercurrent screw extractor. The apparatus has the advantage of providing reliable conveyance outside the screw through the ascending hydrotransport of a dispersed solid material. Because the multistage process equipment presents some differences with respect to conventional continuous processing, a mathematical model that can adequately describe the processing is required. The proposed model is based on integration of the differential mass balances that takes into account the coupled processes of internal diffusion, external convection, and axial dispersion.All of the results are compared with the predictions obtained using the standard function derived from the experimental kinetics of the process, 6,7 which gives an approximation of the extraction kinetics under the assumption of perfect mixing for both phases. The use of the standard function allows for an integral description of the internal diffusion resistance without knowledge of the corresponding kinetic parameters. The ability of this standard function to predict the variation in the kinetics for a change in the phase ratio is commonly employed in the case of periodic processes, but no consideration has been given to the accuracy of the approximation for dynamic conditions.

show abstract

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Modeling of a Screw Solid−Liquid Extractor through Concentration Evolution Experiments

Simeonov

Seikova

Pentchev

et al. 2003

Ind. Eng. Chem. Res.

View full text Add to dashboard Cite

show abstract

“…Plachco and Krasuk (1972) have shown that mathematically, the differential equations and boundary conditions for such a system are identical to those for diffusion into a finite atmosphere, for which an analytical solution exists. However, although the set of differential equations and the analogy established by Plachco and Krasuk (1972) were valid, their solutions to the problem appeared somewhat inconsistent with those obtained by others (Crank, 1975;Vergnaud, 1992). Our analysis Downloaded by [University of Sussex Library] at 10:39 24 August 2015 (17) concluded that the analytical expressions in the latter references should be used.…”

Section: No Recirculating Streammentioning

confidence: 95%

Mathematical Modeling of Diffusion-Controlled Pneumatic-Conveying Dryers

1996

Chemical Engineering Communications

View full text Add to dashboard Cite

A mathematical model for a continuous pneumatic-conveying dryer has been developed for removing internally bound moisture from solid particulates. The dryer relies on a recirculating carrier gas stream for entrainment. Drying is carried out by injecting into the gas loop a fresh stream of conditioned drying gas while an equal amount of wet gas is vented out. Because pneumatic-conveying dryers usually employ huge gas velocities, the particulates are well dispersed in the gas. Therefore, for solids absent of surface moisture, the drying kinetics is controlled by intraparticle diffusion. The model developed based on the diffusion mechanism relates the moisture reduction in the solids to various process parameters (diffusivity, partition coefficient, particle size, residence time, solids loading, drying gas usage, and carrier gas recirculating rate), and is fully predictive. Therefore, it can be used to study the effects of these variables.The model was compared with the plant data and found to match the data within ± 15%.

show abstract