Liquid purification or separation – Tangential flow or centrifugal fluid action
Patent
1994-06-01
1995-08-01
Dawson, Robert A.
Liquid purification or separation
Tangential flow or centrifugal fluid action
210787, 209719, 209720, 209733, 554591, B01D 2120
Patent
active
054377943
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a hydrocyclone for separating a liquid mixture into a heavy fraction and a light fraction, comprising a housing forming an elongated separation chamber with a circumferential wall and two opposed ends, an inlet member for supplying the liquid mixture tangentially into the separation chamber at one end of the latter, an outlet member for discharging separated heavy fraction from the separation chamber at the other end of the latter, and an outlet member for discharging separated light fraction from the separation chamber. The hydrocyclone further comprises means for supplying the liquid mixture to the separation chamber via the inlet member, so that during operation a liquid stream is generated along a helical path having a central axis in the separation chamber, said helical path extending from the inlet member to said outlet member for heavy fraction, and at least one turbulence creating member extending in the separation chamber along the circumferential wall and crossing said path.
In a known hydrocyclone of this kind according to U.S. Pat. No. 4,153,558 there are four turbulence creating members in the form of axial ridges on the circumferential wall. When such a ridge is passed by a liquid stream turbulence is created in a layer of the liquid stream located closest to the circumferential wall, which prevents growth of deposits on the circumferential wall. Unless growth of the deposits is prevented during operation, the deposits might finally clog the outlet member for heavy fraction.
However, the liquid stream will become an inwardly directed component of movement into the separation chamber when the liquid stream passes each ridge, which means that separated light fraction will contain a large amount of heavy components which were supposed to be discharged with separated heavy fraction. This is particularly a drawback when separating liquid mixtures constituted by fibre suspensions, which will be explained more closely in the following.
In the pulp and paper industry hydrocyclones are frequently used for cleaning fibre suspensions from undesired heavy particles. Thus, the fibre suspensions are separated into heavy fractions containing said undesired heavy particles and light fractions containing fibres. A typical hydrocyclone plant for this purpose has hydrocyclones arranged in several stages of hydrocyclones coupled in parallel (normally three or four stages), the hydrocyclone stages being coupled in series with each other. Separated heavy fraction from the first hydrocyclone stage is once more separated in the second hydrocyclone stage, since said heavy fraction also contains fibres, whereafter separated heavy fraction from the second hydrocyclone stage is separated in the third hydrocyclone stage, and so on. In this manner fibres are recovered step by step from created heavy fraction. Light fraction, containing recovered fibres formed in a hydrocyclone stage, is supplied back to the preceding hydrocyclone stage. In this connection it is important that the hydrocyclones, at least in the first hydrocyclone stage, separate efficiently, so that the light fraction contains as few heavy undesired particles as possible.
A problem in connection with separating a fibre suspension by means of a hydrocyclone is that tight mats of fibres can be developed on the circumferential wall of the separation chamber. Heavy undesired particles are easily caught in such mats of fibres, which can result in clogging of the outlet member for heavy fraction. This problem is eliminated by the prior art kind of hydrocyclone described above, whereby the creation of tight mats of fibres on the circumferential wall of the separation chamber is counteracted by said ridges. However, a drawback to the prior art hydrocyclone is that during operation each ridge gives the flowing fibre suspension an inwardly directed component of movement in the separation chamber, whereby an increased share of the undesired heavy particles follows separated light fraction containing fibres.
The object of the present i
REFERENCES:
patent: 4153558 (1979-05-01), Frykhult
patent: 4156485 (1979-05-01), Skardal
Derwent's abstract, No. 49554 E/24, week 8224, Abstract SU, 856560 (Oreless Cons Mat) 25 Oct. 1978.
Celleco Hedmora AB
Dawson Robert A.
Snyder David Reif
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