Fluid handling – Systems – Tank with internally extending flow guide – pipe or conduit
Patent
1998-12-30
2000-08-08
Rivell, John
Fluid handling
Systems
Tank with internally extending flow guide, pipe or conduit
162 17, 162 52, 162246, D21C 706
Patent
active
060986581
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND AND SUMMARY OF THE INVENTION
The present invention relates to a method and apparatus for filling a pulp tower. The invention is especially well applicable in the wood processing industry to filling high consistency pulp towers and corresponding storage towers containing fiber suspension.
Pulp towers used in the wood processing industry are, as know, most commonly tanks containing high-consistency pulp, the consistency being 10-20%, although pulp at a lower consistency is also used occasionally. These tanks are used for example for storing pulp or as blow tanks of some apparatus, i.e. for example for storing pulp which comes in batches from batch digesters, the pulp being then used as a uniform flow in the subsequent treatment apparatus. In other words, it is characteristic of towers according to the invention that the level thereof varies to a great extent, although they most commonly have an optimum level, and the intention is to keep the surface of the pulp at this level.
Several different arrangements for filling pulp towers of the above-mentioned type are known from the prior art. One of the oldest methods known is pumping the pulp to the top of the tower, wherefrom it is allowed to drop down more or less directly. If the pulp is allowed to drop directly onto the pulp below, it goes without saying that the pulp dropping from high above permeates the surface of the pulp in the tower and penetrates deep down into the old pulp. There are several drawbacks to this. For the first, if a dilution of the pulp is performed in the lower portion of the tower, as is very often the case, the pulp fed to the tower may permeate as far as to the dilution zone. This results in the pulp discharging uncontrollably to the dilution zone and the dilution not being as uniform as would be required for the apparatus following the tower. Another problem is that the pulp, when permeating into the old pulp, is drifted closer to the discharge opening of the tower than the pulp already present in the tower, whereby the content of the tower does not change uniformly, but part of the pulp passes out of the tower within some minutes, whereas another part may have to stay in the tower even as long as several weeks. This, in turn, brings about more problems. For the first, it is impossible to even imagine that pulp staying in a tower for days or even weeks could be of the same quality as fresh pulp. For the second, a complete change of stock in towers like this may take days and at least several hours, the pulp discharged from the tower being thus a mixture of old and new pulp of this time span. Depending on the following object of use of the pulp, this "intermediate pulp" may in the worst case be totally unusable. Furthermore, the old pulp staying longer in the tower and the new pulp permeating deeper into the tower, liquid is gradually filtered from the surface of the pulp layer, whereby the surface layer hardens and gets thus damaged more easily. Finally, energy consumption may also be mentioned as a problem, at least from the point of view of our invention, since pumping the whole production volume of a pulp mill, i.e. about 1,000 tons of pulp per day, to the height of 20-30 meters, only to be dropped down to the height of about 3-10 meters, can be regarded as wasting of pumping energy. In other words, the pumping energy that would be really needed is most often less than half of the energy now used.
It is of course possible (U.S. Pat. No. 3,964,962) to discharge the pulp onto a distributing device, for example onto a rotating plate arranged in the upper portion of the tower, by means of which plate the pulp is distributed more uniformly all over the cross-section of the tower. Part of said problems may be solved in this way, but pumping energy is still consumed to the same extent as before, and in addition, the arrangement of distributing devices of pulp in the upper portion of the tower results in both complicated structures and great energy consumption. As the distributing device decomposes the pulp flow into drops, o
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Ahlstrom Pumput Oy
Rivell John
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