Classifying – separating – and assorting solids – Sifting – With liquid treatment
Patent
1996-02-16
1997-04-22
Dayoan, D. Glenn
Classifying, separating, and assorting solids
Sifting
With liquid treatment
209305, B07B 104
Patent
active
056222670
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method for screening fibre suspension at separate screening stages provided in a single pressure screen, wherein accept from the first screening stage is passed to the second screening stage, and accept from the second screening stage and reject formed in the screening are removed from the pressure screen.
The invention further relates to a pressure screen for screening fibre suspension, comprising a housing, a rotor mounted for rotation within the housing, a first inlet space formed within the housing and defined on one side by a first screen cylinder, a first intermediate space formed on the other side of the first screen cylinder, a second inlet space defined on one side by a second screen cylinder mounted coaxially with the first screen cylinder, a discharge space formed outside the second screen cylinder, and a supply conduit for introducing fibre suspension to be screened into the screen, the first intermediate space communicating with the second inlet space for passing the accept passed through the first screen cylinder to the second screen cylinder, the inlet space being connected to a reject discharge conduit and the discharge space being connected to an accept discharge conduit, and foil blades being connected to the rotor so that they wipe the surface of the screen cylinders on the side of the respective inlet space.
Fibre suspension is treated by screening it before it is introduced into a paper machine or the like in order that various impurities, splinters and other particles deteriorating the quality of the web to be produced could be removed. Normally this takes place by using a screen cylinder having perforations such in shape and size that an accepted fraction, i.e. accept, is able to pass through the perforations as easily as possible, while too large fibres and impurities are not able to pass through. The perforations of the screen cylinder may be round or elongated holes or parallel slits formed in the surface. In practice, in order that the capacity of the screen would remain high enough, the perforations have to be larger than what is actually required by the acceptable size of fibre. As a result, splinters, fibre bundles and other impurities always enter through the screen to some extent, which requires screening at several stages in order that sufficient purity could be obtained. Correspondingly, irrespective of the size of the perforations, some accept is always carried out with the reject, and the reject then has to be screened again for recovering and recycling the accept.
To simplify the screening process and to make it more effective, attempts have been made to provide various screens or filters, where the screening takes place at several different stages. Such devices are described e.g. in Finnish Patent Application 309/67 and Finnish Published Specifications 47789 and 51221.
Finnish Patent Application 309/67 discloses a device comprising two screening units connected functionally one after the other. In the device, suspension to be screened is introduced into the first screen, into the discharge conduit of which accept is passed. Rejected fraction i.e. reject is then diluted by water and passed to the second screening stage, from which accept is again passed into a discharge conduit while reject is discharged through another conduit. This solution requires addition of water to the fibre suspension, which increases the amount of water to be treated later on and calls for extra measures in order that the fibre suspension to be introduced through the head box would have a suitable density.
Finnish Published Specification 47789 in turn discloses a device similarly comprising two screening stages connected in series. The functional interconnection of these stages, however, deviates from that described above. In this solution the fibre suspension to be screened is introduced into the first screening stage and reject is removed from it. Accept is then passed to the second processing stage, from which reject is again removed and accept is passed onwards to
REFERENCES:
patent: 3677402 (1972-07-01), Holz
patent: 3735873 (1973-05-01), Bergstedt
patent: 3785495 (1974-01-01), Holz
patent: 3865243 (1975-02-01), Salminen
patent: 4913806 (1990-04-01), Hillstrom et al.
patent: 4968417 (1990-11-01), hs
Dayoan D. Glenn
Valmet Corporation
LandOfFree
Method and pressure screen for screening fibre suspension does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and pressure screen for screening fibre suspension, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and pressure screen for screening fibre suspension will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-337229