Process and apparatus for thickening of solid liquid mixtures by

Details Process and apparatus for thickening of solid liquid mixtures by Process and apparatus for thickening of solid liquid mixtures by

1995-07-26

1997-12-02

Fortuna, Ana

Liquid purification or separation

Processes

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

210641, 210651, 2101952, 210 86, 210 87, B01D 600

Patent

active

056932294

DESCRIPTION:

BRIEF SUMMARY
The invention relates to a process for thickening solid/fluid mixtures by means of membrane technology using an apparatus with membrane modules having a retentate circuit, as well as to a device for carrying out this process.
At this time, there are no known special apparatuses for the thickening of retentates which are produced in ultrafiltration or microfiltration. When clarifying fruit juices by means of filtration technologies of this kind, thickening states of up to approximately 50 vol % wet pulp content are achieved in the retentate residues, measured in the centrifuge test. That is, in the centrifuge these residues still give off at least 50 vol % of fluid. Retentates of this kind are still fluid and must be further processed especially for disposal by means of vacuum rotary filters.
Vacuum rotary filters are precoated filters, and for filtration they require diatomaceous earth, which has to be procured and then disposed of once again. Disposing of retentate via the sewer is hardly possible anymore, and so the retentate must be thickened and put in a waste dump or incinerated. In both cases, the lowest possible water content in the retentate is truly very significant economically. Only membrane apparatuses which are especially equipped for this purpose seem practical, if further thickening of the residue over and above the 50 vol % mentioned is to be attained. Similar problems also occur in other uses of membrane technology outside the realm of fruit juice.
The JOURNAL OF FOOD SCIENCE, Vol. 51, No. 3, 1986, pp. 559-563 discloses an apparatus, which has metal membrane ultrafiltration with a single pass, for improved apple juice production yield. Juice production yields of up to 85% were reached with it, but apparatuses of this kind with single passes do not seem practical for a thickening of retentates on a large scale.
The object of the invention, therefore, is to indicate a process for thickening solid/fluid mixtures by means of membrane technology and a device to carry it out.
According to the invention, by using an apparatus with membrane modules having a retentate circuit, this object is attained in that the retentate feed stream in the membrane modules is kept virtually constant in a first step with a membrane apparatus, which is operated in the batch mode, or quasi-continually, until as a result of the thickening process of the retentate, the inflow pressure into the membrane modules exceeds a predetermined desired value; in that in a second step, the inflow pressure is kept constant by reducing the retentate feed stream until a desired value of thickening of the retentate is achieved; and in that in a third step, the thickened retentate is removed from the circuit.
An apparatus for carrying out this process is distinguished by at least one volumetrically feeding pump in the retentate circuit, which pump is equipped with a device for changing the feed capacity.
Further characteristics and advantageous embodiments of the invention can be inferred from the claims.


BRIEF DESCRIPTION OF DRAWINGS

Exemplary embodiments of the invention are explained in the following description and in the drawing figures. Shown are:
FIG. 1, a schematic representation of a multi-step thickening apparatus according to the invention, with a flow divider,
FIG. 2, a schematic representation of a multi-step thickening apparatus according to the invention, with a plurality of pumps for retentate recirculation,
FIG. 3, a schematic representation of a multi-step thickening apparatus according to the invention, for products with coarse solid contents,
FIG. 4, a schematic representation of a single-step thickening apparatus according to the invention,
FIG. 5, a schematic representation of a single-step thickening apparatus according to the invention for quasi-continual operation, having a closed retentate circuit without a batch vessel,
and
FIG. 5a, a time diagram of the retentate outflow F4 and of the product inflow F1 in an apparatus according to FIG. 5.


DETAILED DESCRIPTION

FIG. 1 schematically represents two filtrat

REFERENCES:
patent: 4581236 (1986-04-01), Bandel et al.
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patent: 5171767 (1992-12-01), Buckley et al.
patent: 5395516 (1995-03-01), Gray
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