Sewage treatment plant for thickening a solid-liquid suspension

Details Sewage treatment plant for thickening a solid-liquid suspension Sewage treatment plant for thickening a solid-liquid suspension

1999-06-11

2001-07-24

Upton, Christopher (Department: 1724)

Liquid purification or separation

Structural installation

Flume stream type

C210S413000, C210S433100, C210S499000

Reexamination Certificate

active

06264834

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to improvements made to plant for thickening a sold-liquid suspension by drainage.
BACKGROUND OF THE INVENTION
FR-A-2,581,559 describes a treatment plant for thickening a solid-liquid suspension, which operates continuously, placed at the delivery side of the sludge feed pump. This plant comprises a flat and stationary drainage or thickening grating, onto which the sludge that is to be thickened is continuously delivered, this sludge being constantly scraped by a scraping system with flexible blades. The sludge concentration increases gradually as it progresses along the grating zone.
This known plant, intended more specifically for thickening sludge from sewage works can be used either for final thickening, for example for an agricultural use of the sludge, or for pre-thickening, upstream of a dewatering plant.
Although, in general, this type of plant is satisfactory as it allows a broad range of sludge concentrations to be thickened, it does, however, have the drawback of operating with relatively low hydraulic flow rates, in particular in the case of low-concentration solid-liquid suspensions, that is to say ones which have concentrations of below 5 g/l. It is, incidentally, for this very reason that this known thickening plant is generally fed from a construction or an intermediate device whose function is to raise the concentration of the solid-liquid suspension fed to the plant.
Furthermore, this known plant is equipped with a grating made up of a number of large cross-section strips, the gaps percentage of which is of the order of 25%. This characteristic contributes to the hydraulic limitations of this type of plant.
BRIEF SUMMARY OF THE INVETNION
Starting out from this state of the art, the present invention proposes to make improvements with a view, in particular, to significantly increasing the permissible hydraulic flow rates and to do so in particular for low-concentration solid-liquid suspensions.
The invention also makes it possible to do away with any intermediate construction or device intended, in plants according to the state of the prior art, to raise the concentration of the solid-liquid suspension fed to the plant.
Likewise, the improved plant according to the invention makes it possible to get around variations in the quality and concentration of solid-liquid suspensions generated by the intermediate constructions and devices. The operating parameters for the plant (supply of reagents, washing sequences, etc.) can be optimized given that it is fed with a solid-liquid suspension of stable concentration, for example a water-sludge suspension from an aeration tank.
In consequence, the present invention relates to a plant intended for separating solids and liquids under gravity, particularly for sludge from sewage works, comprising a flat and stationary thickening or drainage grating onto which the sludge is continuously conveyed, this sludge being constantly scraped by a scraping system with flexible blades. The grating is made up of a number of strips, the spacings of which vary along their lengths, the characteristics of the spacings between the strips of the grating and their variations being defined on the basis of the nature of the solid-liquid suspension to be thickened, of its concentration, of the feed rate of the plant.
According to the present invention, the variation in spacing between the strips of the grating may be continuous or discontinuous between the inlet and the outlet of the plant.
According to another feature of the invention, the thickening grating may be inclined, with an upwards slope between the inlet and the outlet of the plant, it being possible for this slope to be between 1 and 40°, preferably between 2 and 15°.
According to the present invention, it is also possible to use a grating in which the strips have a small cross section so as to further and significantly increase the gaps percentage. This feature, combined with the feature relating to the choice of the size of the spacing between the strips of the drainage grating makes it possible, according to the invention, to obtain a drainage grating which has a gaps percentage in excess of 30% and which may be as high as 50%.
Other features and advantages of the present invention will emerge from the description given hereafter with reference to the appended drawings, which illustrate some entirely non-limiting embodiments thereof.


REFERENCES:
patent: 3332556 (1967-07-01), Hirs
patent: 3865727 (1975-02-01), Broling et al.
patent: 4247397 (1981-01-01), Dobosi
patent: 4277339 (1981-07-01), Quin
patent: 4666602 (1987-05-01), Hartzeh
patent: 5795467 (1998-08-01), Schloss et al.
patent: 3920196 (1991-01-01), None
patent: 2581559 (1986-11-01), None
Translation of DE 3920196.

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