Paper making and fiber liberation – Apparatus – With beating – refining – and/or disintegrating means
Patent
1995-04-26
1997-10-28
Chin, Peter
Paper making and fiber liberation
Apparatus
With beating, refining, and/or disintegrating means
162 55, 162251, 241 21, 241 24, 241 29, 241 68, 241 69, 241 79, 241 791, D21D 500
Patent
active
056814291
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to a mixing device in pulping, which is intended to be placed a the second pulping space, such as a sieving or intermediate tank, basin or the like, for pulping at least at the second stage, the waste matter of the pulping material accumulated on the bottom thereof for discharge. For receiving pre-pulped material, the second pulping space is provided with flow means, such as a tube, channel or the like, preferably periodically by a valve arrangement or the like, in connection with the first pulping space, such as a pre-slusher, pre-pulper or the like for pulping at least at the first stage. The mixing device comprises a mixing means with blades or the like which are arranged to rotate on a primary side of a sieving means, such as a punched plate, screen plate or the like, whereby the pulped material, having passed through the sieving means, is conveyed from a secondary side of the sieving means for further processing via an outlet assembly by a suction effect, such as that caused by gravitation, a pump or the like.
A secondary pulping space to be filled periodically as described above is generally used in the processing of a relatively thick mass, whereby the dry matter content of pre-pulped mass preferably exceeds 10%. This kind of mass is produced e.g. in pre-pulping of waste paper. In multi-stage pulping, it is not necessary to use a sieve plate in the pre-pulper, whereby crude mass can also be transferred to further pulping stages, where the actual sieving is carried out.
Finnish Patent Publication No. 75001 discloses an advanced method with regard to conventional methods, and a device for sieving out impurities mixed in paper pulp. In this method, the mixture is transferred from the pre-pulper, periodically carrying out pulping at the first stage, to a device equipped with a closed pulping space. This pulping space is provided with a sieve plate and a spiral mixer which rotates at a short distance from the surface of the sieve plate. The admitted mass is discharged behind the sieve plate for example by the suction effect of a discharge pump. For diluting the mixture, water is added upon feeding the mixture into the pulping space. The addition of water is continued all the way to washing out the waste pulp, whereby the addition of water is discontinued and the pulping space is discharged of water. Next, the waste pulp, accumulated to the bottom of the pulping stage, is discharged by gravity through a wide opening at the bottom of the pulping space.
For certain parts, the solution described above undoubtedly is advantageous over prior techniques. One advantage is that the described solution can be used to make the pulping space substantially smaller than the pre-pulper, because the whole contents of the pre-pulper do not need to be received in the pulping space at one time. This is based on the fact that the mixer of the pulping space and the discharge pump are set into action when feeding of the mixture from the pre-pulper into the pulping space is started. Another advantage of the presented solution is that the pulping space can be arranged to be filled with water before the mixture is fed thereinto, whereby the mixture can be started with a thin mixture.
The above-described solution entails, however, certain problems. Firstly, the closed construction of the pulping space is risky, particularly in the processing of crude masses. Consequently, upon discontinuing the ventilation of the pulping space, the disadvantages are significant for both the process and the device in question. Furthermore, because of the closed construction and the discharge of waste material through the bottom, the exhausting of the device is not fully reliable. Also, like constructions the prior art by similar principles, waste material is accumulated on the bottom of the device in a way that it hampers the operation of the mixer, possibly eventually breaking the mixer blades. Due to the closed construction, the service and maintenance of the device are also relatively difficult
REFERENCES:
patent: 4604193 (1986-08-01), Lamort
Chin Peter
Valmet Paper Machinery Inc.
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