Cross-flow filtering process for separating fluid from a free-fl

Details Cross-flow filtering process for separating fluid from a free-fl Cross-flow filtering process for separating fluid from a free-fl

1997-01-16

1999-09-28

Fortuna, Ana

Liquid purification or separation

Processes

Liquid/liquid solvent or colloidal extraction or diffusing...

210636, 210 97, 2102572, 2101952, 210 962, 210740, 210741, B01D 6100

Patent

active

059582448

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The invention relates to a cross-flow filtration method for separating liquid from a flowable medium, wherein a material stream to be filtered contains parts to be separated and is moved in as a retentate through at least one module containing porous membranes and a filtrate is separated therefrom, as well as to an installation for performing the method.


BACKGROUND OF THE INVENTION

A method of this type is already known from EP-B1-0 427 099 (W. Muller). It achieves the purpose of obtaining a predetermined degree of thickening of the retentate in an operationally assured and simple manner. This micro-filtration method, in which the material stream to be filtered passes under pressure in a circuit through a micro-filtration module with membranes, over which the stream passes tangentially with continuous addition and removal of concentrate, operates by measuring the velocity and pressure drop in the retentate stream. The concentration of a turbid material is calculated from these measured values and the concentrate output is adjusted in case of deviations from a set value.
The aim in connection with such membrane filtrations in the form of ultra-filtration or micro-filtration is to thicken the retentate in the course of the thickening process to obtain the highest possible proportion of wet sludge. By means of this it is possible to reduce the costs for subsequent drying and disposal of the retentate. The degree of retentate thickening which can be achieved depends essentially on the highest viscosity at which the retentate can still be passed through the membrane modules of the installation used. To achieve high viscosity, it has been known up to now to keep at low levels the number of modules in each series (during each pass) and the velocity of the retentate over the membranes. However, a reduction of the number of modules per pass reduces the output of the installation and thus decreases it efficiency.


SUMMARY OF THE INVENTION

It is therefore the object of the invention to recite a method and an installation for the separation of liquids from a flowable medium, which make it possible to separate more liquids in comparison with known methods and in this way to obtain higher proportions of wet sludge in the retentate.
In accordance with the invention the object of the invention is attained by means of a method of the type mentioned at the outset by admixing a gaseous medium to the retentate. Various practical embodiments of this method ensue from the claims. Installations for the advantageous execution of the method in a filtration installation are also recited in the claims.
Tests with an installation in accordance with the invention have shown that it is possible to provide thickening of up to 90 to 95% parts of wet sludge by doubling the customary number of filtration modules per pass. With increased proportions of wet sludge, this is assumed to be the result of a reduction in the viscosity of the retentate because of the admixture of air. The novel method permits the employment of a larger number of filtration modules in series per pass and thus more efficient installations. Because of the larger proportions of wet sludge in the retentate there is an energy savings during final drying. In addition, the lowering of the viscosity of the retentate brings a reduction in the membrane wear. The mentioned advantages also occur during juice separation from fruit mash in membrane installations known per se, if the mash with all solid parts is directly filtered by means of the cross-flow method, while omitting the squeezing process.


BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention are described in detail in the following description and the drawing figures. Shown are in:
FIG. 1, a diagram of an installation in accordance with the invention for separating liquid from a medium, with different devices for admixing air with the medium;
FIG. 2, the admixture of air with the surface of a retentate in a batch tank,
FIG. 3, the admixture of air with the retentate i

REFERENCES:
patent: 3120489 (1964-02-01), Hoch
patent: 3472765 (1969-10-01), Budd et al.
patent: 3992301 (1976-11-01), Shippey et al.
patent: 4069155 (1978-01-01), Tsusimoto et al.
patent: 5112489 (1992-05-01), Hartmann
patent: 5254253 (1993-10-01), Behmann
patent: 5271830 (1993-12-01), Faivre et al.

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