Gas separation – Means within gas stream for conducting concentrate to collector
Patent
1991-08-23
1993-06-01
Hart, Charles
Gas separation
Means within gas stream for conducting concentrate to collector
55185, 55204, 55399, 55401, 55415, B01D 1900
Patent
active
052155595
DESCRIPTION:
BRIEF SUMMARY
This invention refers to a device for the separation of fibres and gas.
At the manufacture of mechanical pulp from fibre material the fibres are freed by working the fibre material mechanically. This is carried out normally by refining the material in the form of wood chips in one or more steps. The chips possibly can be preheated and pretreated with chemicals. At the refining, which is carried out at overpressure between two opposed refiner discs rotatable relative to one another, large amounts of heat are developed which causes the liquid following along with the chips to evaporate.
The fibres after their freeing are to be subjected to continuous processing in subsequent steps. Prior thereto the steam developed is separated together with other gases, such as air. The separation normally takes place in a special device of cyclone type, where the fibres are separated from the gas following along by centrifugal action.
The gas discharged from the cyclone is desired to be entirely free of fibres and fibre fragments so as to be applicable to other purposes. This is in practice scarcely possible, because conventional cyclones cannot bring about a complete separation. The steam includes fibre particles, which renders the application field for the separated steam to be restricted. The steam then can be utilized only for preheating the fibre material or be used in a heat exchanger or in some other place where the fibre content is of minor importance. Steam containing fibres, however, can give rise to problems by clogging the conduits.
According to the present invention, the aforesaid problem is solved in that the separation of gas and fibres is close to 100%. The fibres thus are prevented from following along with the gas by means of a screen, which is provided with apertures and rotated at such a speed, that resulting accelerations and forces prevent the fibres from passing through the apertures of the screen.
The invention is described in the following in greater detail by way of two embodiments thereof and with reference to the accompanying drawings.
FIGS. 1 and 2 show two embodiments of the device according to the invention.
FIG. 3 shows in greater detail the design of the perforated screen in FIG. 2.
FIGS. 4 and 5 show two devices used at experimental runs.
FIGS. 6, 7 and 8 are cross-sections of different designs of the screen wall .
The embodiment according to FIG. 1 comprises a cyclone 1 with an inlet 2 for gas and fibres. The inlet is located tangentially so that the separation of the fibres is effected by centrifugal action. The fibre material can be removed through a fibre outlet 3 in the bottom of the cyclone. A screw thread 4 is provided rotatably in the cyclone for scraping down the fibres adhering to the walls. In the upper part a gas outlet 5 is located. In front of the gas outlet a perforated screen is provided, which covers the outlet and is formed as a plane disc 6, which can be rotated at high speed by means of a drive arrangement 7.
Gas and fibres entering through the inlet 2 are separated in the cyclone by centrifugal action, whereby the fibres are taken out downwardly through the fibre outlet 3, and the gas is taken out upwardly through the gas outlet 5. The fibres and fibre fargments, which in spite thereof follow along with the steam toward the gas outlet 5, are prevented from passing out through the outlet by the rotating disc 6. The fibres approaching the disc are thrown outward partially by a border layer nearest to the disc and partially by the edges of the perforations. The gas, however, is passed through so that the separation is substantially 100%. A control device can be arranged for sensing the axial load on the disc, so that a possible clogging of the perforations throttles down the fibre supply.
The cyclone 1 according to FIG. 2 is provided with a discharge means consisting of a screw 8, which feeds out the fibre material in the form of an air-tight plug. A holder-on 9 prevents the plug from being blown out by the pressure in the cyclone. In front of the gas outlet 5 a screen is
REFERENCES:
patent: 3224173 (1965-12-01), Webb
patent: 4162148 (1979-07-01), Furstenberg
patent: 4604109 (1986-08-01), Koslow
Hart Charles
Sunds Defibrator Industries Aktiebolag
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