Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – Charging and/or discharging fibrous material
Patent
1995-10-05
1998-04-07
Czaja, Donald E.
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
Charging and/or discharging fibrous material
162243, 162246, 3661691, D21C 708
Patent
active
057360057
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a scraper device, preferably a bottom scraper arranged at the bottom of a continuous digester for pulp production, the purpose of the scraper being to ensure an even feeding-out from a container.
In the text which follows reference is made only to a bottom scraper arranged at the bottom of a continuous digester for pulp production. However, the person skilled in the art will realise that the invention is not limited to this illustrative use.
PRIOR ART AND PROBLEMS
It has long been known to use a scraper device at the bottom of a continuous digester in order to ensure a continuous feeding-out of pulp from the digester. The scraper device consists of a number of scraper arms which are arranged on the shaft disposed vertically for the operation. The movement of the arms in the pulp suspension counteracts bridge formation and channelling and other undesirable effects, as a result of which a continuous feeding-out of pulp having the desired properties is ensured.
From an early stage, the above mentioned shaft for operating the said scraper arms has been used for adding liquid in the lower part of the digester. Liquid has in this case been added by making the whole shaft hollow and introducing the liquid by this route. Liquid was added in the first place in order to wash the pulp. Later, this bore has also been used to add liquid in order to dilute the pulp for the purpose of ensuring the feeding-out, which is sometimes found to be necessary in conjunction with exceptionally large digesters.
This known solution, with a continuous bore in the drive shaft, results in a number of disadvantages. Because the liquid is supplied to the bore at the lower end, it has not been possible to drive the shaft directly, and, instead, an intermediate transmission, normally a gear transmission, has been necessary. Such a transmission is not only expensive to purchase and expensive to install, but also requires relatively extensive maintenance.
In addition, in the case of a shaft with a continuous bore, bearing problems have been experienced when the liquid which is added through the pipe exceeds a certain temperature since this has led to carbonization and the like which adversely affects the useful life of the bearing.
Perhaps the most serious problem is, however, the sealing problem, associated with sealing between the medium inside the vessel, usually pulp, and the atmospheric pressure at which the lower part of the shaft is situated. A stuffing box is normally used for this sealing. On account of the position of this stuffing box, the entire digester must be emptied in order to be able to replace the box. To empty a digester is both costly and difficult. This sealing is thus an extremely critical component in a conventionally designed digester. Due to the fact that at the one end it is sealed directly against a pulp suspension, its operating conditions are in addition exceptionally arduous.
SOLUTION AND ADVANTAGES
An object of the present invention is to propose a scraper device which remedies at least some of the above mentioned problems. This object is achieved by means of a scraper device according to the invention, preferably a bottom scraper arranged, at a continuous digester for pulp production, which scraper comprises at least one scraper arm (12), preferably arranged with shovel members (13), which scraper arm (12) is arranged at a first end of a rotatable shaft (6), a drive device (15) for driving the said shaft (6), an axially extending bore (8) inside the said shaft (6) for supply of liquid, and a sealing means (3, 4, 5, 14) for sealing between the atmosphere and the medium in which the said scraper arm (12) is intended to rotate, the said bore (8) extends along only a limited part of the said shaft (6) in the said first end of the shaft (6) at which the said scraper arm (12) is arranged, and the said bore (8) communicates with at least one liquid supply channel (1), which opens out into a preferably annular space (16).
The above features are known from U.S. P
REFERENCES:
patent: 4056429 (1977-11-01), Richter et al.
patent: 4236961 (1980-12-01), Green
patent: 5271672 (1993-12-01), Peck
Drawing 1-2225-90R2 by Kamyr Inc., Glenn Falls, NY.
Drawing 0-2225-18R15 by Kamyr, Inc., Glenn Falls, NY.
Czaja Donald E.
Kananen Ronald P.
Kvaerner Pulping Technologies Aktiebolag
Nguyen Dean T.
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