FI60042B - METHOD OF INSPECTION OF BLEACHING CHEMICALS IN FIBER MASS WITH MASSAGE CONCENTRATION - Google Patents

Description

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Patent- och registerstyrelsen '' Anattkan utlagd odt utUkrift · »pubikend 31 · 07.8l (32) (33) (31) Pyydetty atuolkeut — Baginl prloritet 13 * 06.72

Sweden-Sweden (SE) 7776/72 (71) Defibrator Aktiebolag, Box 27 073 »S-102 51 Stockholm 27, Sweden-Sweden (SE) (72) Arne Johan Arthur Asplund, Lidingö, Rolf Bertil Reinhall, Lidingö,

Per Johan Ingemar Ahrel, Frövi, Sweden-Sweden (SE) (7 * 0 Oy Kolster Ab (5I *) Method for mixing bleaching chemicals into fiber pulp at high pulp concentrations

The present invention relates to a process by which bleaching chemicals can be efficiently mixed and distributed to individual fibers in a cellulose pulp during fiber breakage and / or grinding in so-called pressurized refiners or pressure refiners at elevated pressure and temperature.

It is generally known to use certain oxidizing and reducing agents as bleaching agents for pulps intended for use with lighter grades of paper. Examples of such chemicals which, when added to the fibrous mass, have a whiteness-improving effect are various types of peroxides as well as various salts, e.g. sulfuric acid, sulphite and bisulphite and hydrosulphites. These bleaches are relatively expensive, and it is well known that the power and efficiency of the bleaching process increase significantly if it can occur at a high pulp mass concentration, i.e., when less water is present. In order to obtain this beneficial effect without the need for overdosing of chemicals due to distribution difficulties, it is essential that chemicals added to a high bulk density pulp be rapidly and efficiently distributed in the same proportions to each individual fiber in the pulp suspension. According to this, it is known to use, for example, fast-running plate refractors as a mixing device, in which case the chemicals are fed before passing through the fiber suspension or through or during the passing of the mixing plates.

In addition to plate refiners, several other agitator granules are used for this purpose, with slower or faster rotating agitator arms operating in a high-density pulp. What these mixers have in common, however, is that the purely mechanical treatment which causes the added chemicals to disperse and distribute has a similar effect on the fibers contained in the pulp suspension and thus alters the so-called grinding state of the spawn, which may be more desirable in such a context.

The power requirement in the mechanical echoing process is also high, but nevertheless the mixing efficiency is relatively low. Therefore, when using previously known devices, it has been necessary to overdose the amount of chemicals added in order to compensate for the effect of the lack of instantaneous mixing.

According to the invention, the mixing of the necessary chemicals is preferably combined with the production of the pulp itself.

In the accompanying drawing, Figure 1 shows, in connection with a pressure refiner, a side view and a partially vertical section of an apparatus for carrying out the method according to the invention.

Figure 2 shows a section of the throttling point on a larger scale.

The device comprises a so-called pressurized refiner, which operates at elevated pressure and elevated temperature according to the Defibrator method, whereby the release of the fibers takes place at a temperature of more than 100, the lignocellulosic middle lamella holding the fiber together softens and plasticizes more and more. The separation of the fibers can then take place, saving considerable force at the same time as the individual fiber can be separated without damage. This process of mass production thus requires in itself a completely special device, i.e. a plate refiner operating at elevated pressure.

The fibrous material, which is not, for example, in one or more stages of the defibrator, broken in the form of chips, is fed to the melt or through a so-called chamber feeder 10 to a heater 12. To this steam is led via a line 14 fitted with a valve for the steam used by the valve 20 and the gases leaving the ground pulp, respectively. The cash register settles down in the preheater and then heats up quickly to the intended treatment temperature, e.g. between 120 and 170 ° C, depending on the steam pressure and temperature. At the bottom of the preheater 12 is a screw feeder 22 driven by a sprocket 24 with a motor (not shown) which conveys the heated mass through a duct 26 to a refiner 28 provided with two grinding plates 30, 32 inside in a known manner. The refiner may be of the species disclosed in Swedish Patent 3,60042,179,557. Grinding disc 32 is driven by motor 34 »

The ground mass exits via Line 38, which is fitted with a throttling point 40 embodying the invention. in the next pipeline. This phenomenon, known per se, is used according to the present invention for efficient mixing of bleaching chemicals into the pulp prepared in a pressure refiner.

In this embodiment, the throttling point 40 is provided with a fixed throttle nozzle 41 »through which the pulp is blown out to the next conveying line 43» which opens into a receiving cyclone 44 »where the steam accompanying the fiber suspension is separated. The separated pulp is fed to the lower storage tank 45 at the lower end of the cyclone, where the fiber, with or without the addition of water, is prepared for the desired delay time for the final reaction with the chemicals added at the throttle point 40.

The choke nozzle 41 is provided with one or more radial inlet passages 42 through which bleaching chemicals are dispensed in liquid form, such as an aqueous solution, into the steam-containing fiber stream passing through the choke nozzle.

The fiber fed from the pressure refiner to the throttling point usually has a concentration of 40 to 70 fs. As it passes through the choke nozzle, the fiber suddenly passes from a relatively high pressure maintained in the pressure refiner to a substantially lower pressure in the area downstream of the choke nozzle. The steam following the fiber then undergoes approximately adiabatic expansion with subsequent temperature drops, at the same time as some of the moisture in the accompanying fiber changes to the vapor form.

Thus, the fed pulp dries partially as it passes through the throttling point 41 to an even higher concentration. The expansion of the steam then causes a very strong vortex flow after the next outlet line 43. This vortex flow also passes to the fibrous particles accompanying the steam and in this case the This device for mixing chemicals has the following advantages: 1. Mixing can take place at a pulp concentration of 4,60042, which is considerably higher than is possible without damage to the fiber to be treated by previously known mechanical mixing devices. 2. Due to the fact that fiber particles with a dry content of more than 50 can be effectively coated with bleaching chemicals, they can be allowed to react with the surface layer of the fiber without any significant dilution of the water accompanying the fiber particles. The desired chemical concentration can thus be maintained with a smaller amount of added chemicals than has been the case so far.

The invention is not limited to the example described above, but can be modified in the broadest sense. Among other things, the throttling point can be provided with an adjustable throttle nozzle, in the form of a plug, ball valve or other device, by means of which the flow area can be regulated. Chemicals may also be added immediately before or after the throttle point 40 in the region of the vortex flow of the fibers. Further, additional processing machines can be placed between the throttling point 40 and the receiving cyclone 44 to provide the fiber suspension with the desired quality properties.