Agitating – Having specified feed means – Liquid injector within mixing chamber
Patent
1997-10-13
1999-07-06
Soohoo, Tony G.
Agitating
Having specified feed means
Liquid injector within mixing chamber
366300, 366301, 162261, 162243, B01F 732
Patent
active
059189789
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process for mixing chemicals into a pulp suspension, preferably in the medium-consistency range, where a rotor is mounted inside a mixing chamber.
2. Description of the Related Art
In addition to the static mixers and so-called high-shear mixers, mixers are also known which make use of the so-called fluidization principle. Such mixers are known, for example, from EP 0 578 284, U.S. Pat. No. 5,279,709 and WO 93/17782. In these mixers, the high-speed rotation of the agitators exerts high shearing stress on the pulp, which then dissolves the pulp mesh and gives the suspension the physical properties of water. Here, a high-speed rotor is mounted in a suitable casing. Due to the relatively large gap between the rotor and the housing, the drive power is much lower compared with high-shear mixers and the individual fibers in the suspension are not destroyed (shortened). Since the dimensions of the housing are small, relatively high throughput rates are achieved and the pulp retention times in the mixer are relatively short as a result. Thus, only brief periods are available for the fluidization process. Particularly when gaseous chemicals are mixed into the pulp, the liquid and the gas separate because of the difference in density. When this happens, the gas moves towards the center of the rotor and is removed there from the mixture of gas and liquid. This effect is exploited by pumps used to convey pulps, particularly in the medium-consistency range, in order to be able to extract the unwanted air at the center of the rotor. Furthermore, mixers are known from U.S. Pat. No. 3,314,660 which can mix different pulps well in one tank. In this case, mixing takes place in a batch process in which the pulps are fed into the tank and then mixed. What is required of a good mixer to mix gaseous chemicals continuously into a pulp suspension is, however, even distribution of the fine bubbles of gas in the pulp. For the reason mentioned above, the mixers known to date do not fulfill the necessary requirements pertaining to even distribution of the chemicals, e.g. ozone, mixed into the pulp.
SUMMARY OF THE INVENTION
The aim of the invention now is to guarantee that chemicals are mixed in evenly, particularly chemicals in gaseous form.
This is achieved by including at least one more rotor and the areas covered by each rotor overlapping. With this arrangement, the number of agitator rotations in the pulp can be doubled while the mixer is running at the same speed.
A further development of the invention is characterized by the center distance of the rotors being selected so that the rotor arms extend almost to the center of at least one other rotor. This design guarantees that the gas cannot escape at the center of a rotor when mixing in chemicals, particularly gaseous chemicals. Due to the rotating movement generated, the undesirable separation of gases at the center of the rotor is prevented, thus permitting even distribution of the chemicals in the pulp suspension.
An advantageous configuration of the invention is characterized by at least the one additional rotor rotating in the opposite direction. Very large shearing forces and turbulences are generated when the rotors rotate in opposite directions, which in turn allow the chemicals added to be mixed well into the pulp and finely distributed, as required.
A favorable further development of the invention is characterized by strips and/or ribs being mounted inside the housing. These exert very high shearing forces on the suspension and generate turbulences, which in turn allow the chemicals added to be mixed well into the pulp and finely distributed, as required.
A favorable configuration of the invention is characterized by the chemicals being mixed into the pulp in the turbulence zone at the mixer inlet area. Since the chemicals are fed directly into the turbulence zone, where fluidization generally takes place as well, mixing efficiency is further improved.
A favorable further development o
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Andritz-Patentverwaltungs-Gesellschaft m.b.H.
Soohoo Tony G.
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