Imperforate bowl: centrifugal separators – Rotatable bowl – Including driven material-moving means therein
Patent
1988-01-04
1989-05-09
Simone, Timothy F.
Imperforate bowl: centrifugal separators
Rotatable bowl
Including driven material-moving means therein
494 43, B04B 120, B04B 304
Patent
active
048285412
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to a decanter centrifuge comprising an axially symmetrical bowl and a conveyor screw journalled therein.
Such a decanter centrifuge is employed for separating a slurry supplied to the interior of the bowl into a solids phase and one or more liquid phases. This is obtained by rotating the entire centrifuge at a high number of revolutions and rotating at the same time the conveyor at a low number of revolutions relative to the bowl.
The separating effect of the centrifuge and its capacity or throughput depend, on one hand, on the magnitude of the field of gravitation generated by the centrifugal force in the separating space of the bowl, i.e. on the number of revolutions and the inner diameter of the bowl and, on the other hand, on the length of the separating space.
A factor of decisive importance for the maximum allowable number of revolutions is the flexural rigidity of the conveyor radially supported at both ends of the bowl because the flexural rigidity determines the critical number of revolutions of the conveyor.
This fact has hitherto implied that the .lambda.-value of a given centrifuge--the .lambda.-value being defined as the ratio between the length and the inner diameter of the separating space--has not in practice exceeded values of about 5.
In cases where a large field of gravitation and a large capacity have been required, the resulting centrifuges have been excessively large and expensive. This relates to the fact that a straight geometrically enlargement of a given decanter centrifuge has caused the costs of manufacture to increase by the cube of the scale ratio, while the capacity only increases by the square of the scale ratio.
In view of the fact that, inversely, a capacity increase proportional to the extension is obtained simply by increasing the length of the centrifuge--without a corresponding rise in price--it is obvious to aim at producing decanters having .lambda.-values exceeding said approx. 5.
SUMMARY OF THE INVENTION
This is now made possible by a decanter centrifuge according to the invention which differs from the prior art centrifuges in that the average density of the conveyor, i.e. the ratio between its total weight and the volume it displaces, is smaller than the density of the lighter liquid phase of the actual slurry, and in that at least one end of the conveyor in operation is unsupported in the radial direction in relation to the bowl.
The invention will now be described in more detail with reference to the drawings in which
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematical longitudinal section through a decanter centrifuge according to the invention, in operation, and
FIG. 2 is a section as FIG. 1, but through a second embodiment of a centrifuge according to the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The decanter centrifuge 1 illustrated in FIG. 1 consists by and large of a horizontal, axially symmetrical bowl 2 with a cylindrical section 3 and a conical section 4. The bowl 2 includes an elongated conveyor screw 5 with a central body portion 6 and surrounded by a continuous screw flight 7. The bowl is at its ends rotatably supported in bearings 8 and 9, respectively, and is driven via a gear 10--for example an epicyclic gear--ensuring in a known manner that bowl 2 and conveyor 5 in operation rotate relative to each other.
The suspension to be separated is supplied through an inlet 11 in the form of an inlet tube 12 and extending coaxially with the axis of rotation of the centrifuge through a central passage 13 provided in conveyor body 6. The tube 12 ends in a transverse, radial passage 14 discharging into the separating space 15 of the centrifuge. The liquid level in operation is illustrated in dotted lines 16 and solid lines 17. After separation in space 15 solids are discharged through apertures 18 while liquid is discharged through an annular outlet 19.
Conveyor 5 is by and large constructed as a hollow body with closed cavities 20 and 21 and is so dimensioned that the average densi
REFERENCES:
patent: 2679974 (1954-06-01), Gooch
patent: 3148145 (1964-09-01), Reed
patent: 3802621 (1974-04-01), Merzenich
patent: 3854658 (1974-12-01), Probstmeyer
patent: 4209128 (1980-06-01), Lyons
patent: 4298159 (1981-11-01), Epper et al.
patent: 4714456 (1987-12-01), Bender et al.
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