Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – Vacuum treatment
Patent
1996-02-09
1999-03-02
Silverman, Stanley S.
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
Vacuum treatment
95247, 95266, 96195, D21D 526, C02F 120
Patent
active
058765603
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method and arrangement for removing gas from a fibre/liquid suspension in a fibre treatment line in a pulp mill, which line includes at least one stage in which the fibre/liquid suspension is treated and/or stored in a large container before being conveyed for further treatment.
2. Description of the Prior Art
It is commonly known that gas bubbles in fibre/liquid suspensions, whether the bubbles occur as free bubbles in the liquid between the fibers or as bubbles bound to the fibers, can lead to problems in different phases of the fibre treatment process. The nature of the problems varies in different parts of the fibre treatment line in the pulp mill, such as interruptions in the flow of the suspension through valves, screens, and so forth, and fibre flocculation, foaming, dewatering problems, and so forth. Also, in a subsequent paper-making machine, the occurrence of gas bubbles in the suspension can cause problems.
The gas in question can, for example, be air, oxygen, and the like. In general it is a question of various gas mixtures
The problem has been addressed in different ways in the prior art. For example, it is known to remove the gas from pumps which transport the suspension between the various treatment stations of the fibre treatment line. However, the capacity of these pumps to remove gas is limited, and this is particularly so when the pump is intended to transport very large flows of fibre/liquid suspension. It is also known to remove gases from large containers in the fibre treatment line, in which containers the fibre/liquid suspension is stored for a long period in order to be stirred and homogenized, for example, or subjected to another treatment. However, the subatmospheric pressure which is needed in such a container in order to achieve the desired degassing requires that the walls of the container be strengthened to such an extent that the overall construction becomes very expensive, which is an obvious disadvantage.
SUMMARY OF THE INVENTION
An object of the invention is to provide a method and an arrangement for removing gas, efficiently and by relatively simple means, from a fibre/liquid suspension in a fibre treatment line in a pulp mill, which line includes at least one stage in which the fibre/liquid suspension is treated and/or stored in a large container before being conveyed onward for further treatment. According to the invention, the fibre/liquid suspension is conveyed to a large container via a vessel which with its lower part communicates with the large container and has a significantly smaller horizontal sectional area than the large container, but extends upwards above the level of the fibre/liquid suspension in the large container, with gas being removed from the fibre/liquid suspension in the area of the upper part of the smaller vessel by means of the area being subjected to a sub-atmospheric pressure. As a result of the significantly smaller horizontal sectional area, important design advantages are achieved from a strength point of view, as compared with dimensioning the large container to take account of the subatmospheric pressure chosen for the gas removal.
The internal horizontal cross-sectional area of the smaller vessel is preferably at least less than 1/10 of the corresponding area in the large container, preferably less than 1/20.
The level of the fibre/liquid suspension in the large container is preferably kept essentially constant, while the level of the fibre/liquid suspension in the smaller vessel is kept at a higher level than the level in the large container by means of being sucked up by the subatmospheric pressure in the area. The liquid column represented by the difference in level corresponds essentially to the subatmospheric pressure in the area in the smaller vessel. The subatmospheric pressure can amount to a water column of between 0.5 and 2 m, preferably to a water column of between 0.8 and 1.8 m, and expediently to a water column of between 1 and 1.5 m.
When
REFERENCES:
patent: 2571219 (1951-10-01), De Cew
patent: 4198266 (1980-04-01), Kirk et al.
patent: 4684442 (1987-08-01), Meredith et al.
patent: 5217575 (1993-06-01), Backlund
Gustavsson Lennart
Svaneg.ang.rd Bo
Kvaerner Pulping Technologies Aktiebolag
Nguyen Dean T.
Silverman Stanley S.
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