A. Ahlstrom Corporation

Andritz Oy

Andritz-ahlstrom Oy

Antero Laine

Olavi E Pikka

Risto A Ljokkoi

Harri Qvintus

Sami Siik

Timo Alajaaski

Kalevi Laakso

Kaj Henricson

Pertti Wathen

Markku A Simola

The present invention relates to the thickening of pulp suspensions. A low consistency pulp suspension is fed to a pre-thickener () through an inlet conduit (). A layer of thickened pulp, formed on a filter surface (), is pushed along the filter surface by a cleaning member to the discharge end of the pre-thickener and is discharged through the outlet (). The cleaning member comprises a rotating shaft (), on which shaft at least one screw thread () is fixed so as to leave a free space between the shaft and the screw thread. Essentially non-thickened pulp is allowed to flow through the apparatus via this space.

Method for the controlled thickening of low consistency fiber suspensions

The present invention relates to the thickening of pulp suspensions. A low consistency pulp suspension is fed to a pre-thickener ( ) through an inlet conduit ( ). A layer of thickened pulp, formed on a filter surface ( ), is pushed along the filter surface by a cleaning member to the discharge end of the pre-thickener and is discharged through the outlet ( ). The cleaning member comprises a rotating shaft ( ) on which shaft at least one screw thread ( ) is fixed so as to leave a free space between the shaft and the screw thread. Essentially non-thickened pulp is allowed to flow through the apparatus via this space.

Apparatus for the thickening of fiber suspensions

Chemical pulp is produced by cooking comminuted cellulosic fibrous material (e.g. wood chips) in a continuous digester or batch digesters or produce brown stock, and washing the brown stock in a brown stock washer to produce chemical pulp, oxygen delignifying the chemical pulp at medium consistency, and then screening the oxygen delignified pulp to produce an accept fraction and a shive-containing reject fraction. Drawbacks inherent in the prior art are overcome by directly transporting (i.e. without refining or accessory oxygen delignification) the shive-containing rejects fraction to the main fiber line before oxygen delignification (e.g. to just before a mixer for the oxygen delignification stage, to between the brown stock washer and mixer, to a coarse screen between the digester and the brown stock washer, and/or to a washer for the coarse rejects from the coarse screen). The oxygen delignification stage may include at least two upflow vessels, of different first and second stages, with a mixer before each stage, and at least one of the vessels includes a multiple feeding device. Gas separation can also be practiced in one or all of the oxygen delignification vessels. The screening stage may be provided before or after a washer for washing the oxygen delignified pulp.

Treatment of chemical pulp

A fiber suspension, such as an in a pulp mill, is treated in an manner which minimizes both the investment and the operating costs associated with a screening plant. A single pump has an outlet connected to a knotter and primary and secondary screening states so that the pump provides substantially the sole motive force to the pulp moving it through the knotter and screening stages. The knotter and screening stages are provided in a common housing with the knotter vertically above the screening stages, and the screening stages one above the other. A single motor may be provided to rotate rotatable elements associated with the knotter and screening stages. The knotter may be connected to a knot washer external of the housing by a valved conduit less than two meters in length, and the secondary screening stage can be connected to a tertiary screening stage exterior of the housing by a valved conduit less than two meters long. Rejects from the knot washer and secondary screening stage may be recycled to the pulp inlet, and dilution water may be introduced where necessary.

Method and apparatus for screening fibrous suspensions

Apparatus for treating fiber suspension

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Kotka, Finland

Antero Laine