Hydrocyclone

Details Hydrocyclone Hydrocyclone

1984-09-06

1986-04-08

Spitzer, Robert

Liquid purification or separation

Tangential flow or centrifugal fluid action

209211, B04C 504, B01D 2126

Patent

active

045811423

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to a cyclone separator, preferably of the type used for separation of solid particles from a liquid medium. Such separators are often termed hydrocyclones.
A short account of hydrocyclones is inter alia given in the "Encyclopedia of Chemical Technology", 2nd. edition, volume 4 (pp 747-748).
Theoretically, a free vortex will exist in such a cyclone, resulting in large shear forces being developed in the sedimentation zone. Hence such cyclones are not well suited for separation of flocculated matters or solid particles which easily are broken up.
However, such cyclones are well suited for removal of fine particles at low or medium concentrations. Due to the shear forces existing in the vortex in a hydrocyclone, it is not only the centrifugal force which causes separation, but the form of the particles also exerts a certain effect. Hydrocyclones have hence been used in the wood pulp industry to cause a certain separation of fibres of different lengths.
Normally, a hydrocyclone comprises a rotatable symmetrical, elongated hollow body which under operation is arranged, vertically, and the upper part of which is provided with at least one tangential inlet through which the liquid to be treated at high velocity is introduced, the rotation of the body causing the formation of a vortex in the hydrocyclone.
In the upper part of the hydrocyclone a central opening exists, the cross-sectional area of which is larger than the total cross-sectional area of the inlet openings. Through the central upper outlet opening the injected liquid is passed and is fully or partly devoid of solid particles.
In the lowest part of the hydrocyclone there is provided a central outlet opening, the cross-sectional area of which is less than the cross-sectional area of the inlet opening which opening serves as an outlet for a minor part of the injected liquid which is enriched with respect to the solid matter.
The rotatable, symmetrical hollow body can be designed approximately conical along its entire length, as shown in U.S. Pat. No. 2,920,761, or be designed with a cylindrical upper part and a conical lower part, as shown in Norwegian Patent No. 144 128. In order to adapt hydrocyclones to different purposes, and in order to improve their efficiency, several modifications of hydrocyclones have been proposed. For instance, they may be modified with respect to the inlet for the liquid to be treated, as shown in the above-mentioned Norwegian patent, or by modifying the outlet for the liquid portion enriched with solid matter, as shown in U.S. Pat. No. 4,309,238.
Special designs for the outlet for the accept liquid are shown in U.S. Pat. No. 4,259,180 and French Patent No. 1,518,253.
Different variations of hydrocyclones are mentioned in the U.S. Pat. Nos. 4,265,470, 4,280,902, 4,305,825 and 4,267,048, as well as in U.S. Pat. No. 4,272,260, which deals with a cyclone for separation of solid particles from gases. Common features of known cyclone separators and hydrocyclones, as described in the above-mentioned patents, are that the outlet for the accept liquid consists of a central tube and the outlet opening is normally positioned below the level of the injected liquid.
In order that the liquid shall be able to flow through the central outlet as an overflow, a substantial part of the volume of the cyclone will be occupied by rotating liquid layers. Due to the turning tendency at the lower conical inner wall of the hydrocyclone, turbulence will occur in the rotating liquid body disturbing the flow pattern, in turn resulting in decreased efficiency. Due to the passage of the rotating liquid to and through the central outlet, a substantial part of the supplied kinetic energy will be lost as a consequence of friction losses. This occurs because the leaving overflow can have only a rotational energy corresponding to the rotational velocity and the cross-section of inertia of the overflow.
The angular velocity of the overflow to and through the central opening cannot be greater than the velocity of the liquid in the re

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