Liquid purification or separation – With means to add treating material – Spaced along flow path
Patent
1986-03-31
1987-12-01
Hruskoci, Peter
Liquid purification or separation
With means to add treating material
Spaced along flow path
210202, 210208, 210519, 210521, B01D 2108
Patent
active
047102918
DESCRIPTION:
BRIEF SUMMARY
The invention relates to rapid clarification of water charged with fine material in suspension.
Water to be clarified by the method of the invention generally occurs at the outlet from an industrial process, and is intended, for example, either for further industrial use or else for rejection into the public water system. However, these indications are not restrictive in any way. Although the following description refers to practical examples in which the method is implemented with waste water from the minerals industry, the method may naturally be applied to clarifying liquids with a wide variety of charges.
Heretofore, generally used methods have required relatively long periods of time to separate and sediment out solid particles in suspension and to obtain a liquid or water which is sufficiently clarified to meet the standards laid down. This arises because the settling speed does not exceed a few meters per hour. As a result it has been necessary to use separator equipment which is expensive, and of large size and volume.
It is known that in order to increase the rate at which solid particles settle it is necessary to link up the particles in suspension by adding a small quantity of additive to the cloudy liquid suitable for initiating the flocculation phenomenon. This phenomenon enables the solid particles to come together to form agglomerates or flakes of considerably greater size than the particles from which they are built up, but having an apparent density which is less than that of the solids from which they are built up.
Generally, after flocculation, the liquid and its charge of flakes of different sizes and densities is conveyed to a settling zone containing a higher concentration of flakes, thereby accelerating the increase in flake size and consequently increasing the settling speed. The flakes which have settled in the lower portion of the settling zone are concentrated and they are removed (generally continuously, but sometimes in a discontinuous manner) in the form of a sludge which is more or less concentrated depending on a suitably determined average flow rate. The clarified liquid is removed at the same time from the top of the settling device from which it merely overflows. This is the case of apparatus providing both clarification and solid settling in a single compartment, i.e. in a single stage.
It is also known that the two functions of clarifying the liquid and concentrating the solid can be obtained more rapidly by separating the functions so that they take place in distinct parts of the apparatus. The apparatus is then said to have two stages. The stages may be superposed with the clarification stage being above the concentration stage, or they may be concentric, or they may be side-by-side.
However, in order to obtain the greatest effect on the speed at which the liquid is clarified and the solids are concentrated, it is necessary to control all of the hydraulic movements within the various portions of the apparatus so as to form flakes which are as dense as possible, with the size of the agglomerates being sufficiently high, e.g. having a size of 1 mm to 10 mm, and containing practically no fine material in non-flocculated suspension.
It is known that the flocculation phenomenon as initiated by flocculation additives forms agglomerates whose mechanical cohesion is low, and that hydraulic movements in the clarification zone may have both advantageous and disadvantageous effects simultaneously on the structure and the physical characteristics of the agglomerates.
Speeds which are too high in some portions of the apparatus destroy the flakes already formed and form flakes having too wide a range of sizes including many very fine agglomerates which settle poorly. Speeds which are too slow in other portions of the apparatus enable flakes to form which are too big and which agglomerate with one another. These flakes then form continuous layers of low permeability which slow down the passage of the liquid to be clarified. Instability phenomena then occur with some zones being form
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Alsthom
Hruskoci Peter
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