Liquid purification or separation – Processes – Separating
Patent
1982-03-16
1985-06-04
Fisher, Richard V.
Liquid purification or separation
Processes
Separating
210396, 210397, 210402, 210784, 162259, B01D 3702
Patent
active
045213143
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a method and device for use at the filtering of a suspension, for example bakery yeast mixed with common salt (NaCl) or other active electrolyte according to the cytorrhysis method or at the filtering of other plant cell material with or without salt.
At such method, first the rotary drum filter is pre-coated with filter auxiliary, so-called precoat, for example starch. The filtering of, for example, the yeast suspension mixed with electrolyte is carried out from a trough located below the lowermost point of the rotary filter drum. The washing of the salt out of the filter cake is effected in known manner and the filter cake formed at the filtering process is taken off by a take-off knife.
Examples of the known art in the field with respect to filters here concerned are the so-called Lundin filter or the so-called rapid filter with bottom trough, which are marketed by AB Alfa Laval, Sweden.
Very small changes in the concentration, composition or properties of a product require the most varying contact times between filter surface and suspension in order to obtain a filtering result which is optimum. For this reason, the filtering results with the present filters rarely are at optimum, because the filters in most cases are adjusted at optimum to only one product. The required variation in contact time between the suspension and the active filter surface can vary between a dipping angle of 180.degree., i.e. where half the drum is dipped into the suspension, for example at the filtering of must in wine-cellars, and a dipping angle of 1.degree.-2.degree., for example at the filtering of sediments in yeast in wine-cellars and breweries. This implies that the ratio between dipping zone and drying zone in the first-mentioned case amounts to 1:1 and in the latter case to the magnitude 1:250.
When the suspension level in the trough at conventional bottom trough filters is lowered in order to reduce the contact time, and the take-off knife remains in its original position, a corresponding part of the active filter surface is lost and simultaneously arises there air leakage. The result, this, is reduced filtering capacity. When, instead, the level in the trough is raised, this yields optimum filtering capacity for a very limited number of suspensions. For the majority of suspensions, for example in the ferment industry, the resulting long contact time between filter surface and suspension cannot be utilized for cake formation. The result is also in this case a substantially reduced filtering capacity.
Most of the existing rotary vacuum filters, thus, show the weakness that it is difficult to achieve good balance between coating zone and drying zone, i.e. between the drum portion where cake formation takes place, and the drum portion where the filter cake achieves by degrees maximum dry content.
A problem associated therewith is, that at a trough adjusted to a certain suspension said balance is changed during the filtering process, because the knife is moved relative to the trough and the suspension level.
The present invention solves this problem and offers advantages also in other respects, as will appear from below. 0009he present invention, thus, relates to a method at the filtering of a suspension, for example yeast or other plant cell material on a rotary vacuum filter, beneath which a trough containing the suspension is located. The invention is characterized in that a take-off knife for the filter cake produced by the filtering process is attached to the trough, and the suspension level in the trough is held constant, and that at least the trough portion carrying the take-off knife is moved by a feeding device to the centre of the filter drum while the drum is being rotated.
The invention, further, relates to a device of the kind and having the main characterizing features as defined in claim 5.
The invention is described in greater detail in the following, with reference to the accompanying drawings, in which
FIG. 1 shows schematically, partially by vertical section, a device where t
REFERENCES:
patent: 617367 (1899-01-01), Solvay
patent: 2306074 (1942-12-01), Meyer
patent: 2444466 (1948-07-01), Peterson
patent: 3772144 (1973-11-01), Luthi et al.
patent: 3869389 (1975-03-01), Rokitansky
patent: 3919088 (1975-11-01), Doncer et al.
Eriksson Sven
Lundin Ingvar
Lundin Per O.
Cohen Sharon T.
Fisher Richard V.
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