WO1987006961A1

WO1987006961A1 - Method and device for slushing papermaking pulp

Info

Publication number: WO1987006961A1
Application number: PCT/SE1987/000191
Authority: WO
Inventors: Hjalmar Sten Ingemar Bystedt; Jan-Olof Gunnar Sehlin
Original assignee: Sunds Defibrator Aktiebolag
Priority date: 1986-05-15
Filing date: 1987-04-15
Publication date: 1987-11-19
Also published as: NZ220107A; AU7399887A; SE8602223D0; SE463029B; SE8602223L

Abstract

Flash dried and compressed papermaking pulp is slushed by means of a rotor (4), the shell surface of which is provided with slushing members (12). A press (5) presses the bales against the shell surface. Means (9) for the supply of liquid are located directly before the press (5). The slushing is carried out so that the fibers in the papermaking pulp are exposed and thereafter are removed from the rotor (4).

Description

Method and device for slushing papermaking pulp

This invention relates to a method and a device for slush¬ ing bales of flash dried and compressed papermaking pulp-.

At present papermaking pulps often are dried by being brought in flake state into contact with hot gases and not, as it previously was the case, by being dried in the form of a sheet web against heated cylinder surfaces or by means of hot air. With the flash drying technique, the procedures both at the mechanical dewatering and at the drying are considerably faster, and the pulp assumes a different nature. This implies, that the pulp is more difficult to re-wet and to slush for papermaking, possibly due to the fact that the fibre surface is made hydrophobic at the drying.

As a result thereof, the energy consumption for slushing is higher for flash dried pulps than for web dried ones, and the paper has a lower tensile strength and bursting strength. The present invention has the object to elim¬ inate these drawbacks and to propose a simple and effective method and device for slushing flash dried pulps accord¬ ing to a new principle.

Among the pulps, which are flash dried and, thus, can be treated according to the invention, can be mentioned sulphite and sulphate pulps, CTMP, TMP, groundwood pulp and other pulp types from different raw materials, for example softwood and hardwood, annual plants etc.

At the manufacture of flash dried pulp, the dried flakes are compressed at high pressure to a bale, which thereby becomes very compact and hard. The flakes possibly can be compressed to thin layers, which thereafter are assembled to a bale.

Conventionally, this bale is slushed in the paper mill in a pu-lper with the addition of water and at intensive agitation. The defibrering, however, obtained hereby is not complete. To be able to slush entire bales of flash dried pulp in this way, large pulpers with generous dimensions and high motor effects are required. In small paper mills, therefore, it is necessary first to divide the bales by hand which, of course, is complicated and labour demanding.

Another way of slushing bale pulp is by using a teasing cylinder, which is provided with sharp teeth, which tear off pulp from the bale while it is pressed against the cylinder. The resulting product is in the form of pulp flakes con¬ stituting bundles of a great number of fibres.

The slushing of the pulp flakes is thereafter continued in a pulper with the addition of water and at agitation. The slushing is made easier in this way, but the system is made more complicated.

The present invention implies a simplified system for the slushing of flash dried pulp, at which the -slushing is effected in that a pulp bale is pressed against the shell surface, of a rotor provided with slushing members. The slushing is carried out so completely,that the indiv-' idual fibres are exposed. It was simultaneously found by surprise that the strength properties of the paper made of the pulp slushed according to the invention were improved compared with paper made of pulp slushed in a conventional way.

It is possible,according to the invention, in connection with the defibering also to subject the individual fibres to a limited mechanical working, whereby the development of the strength properties of the pulp is favoured addit¬ ionally. The characterizing features of the invention become apparent from the attached claims.

The invention is described in greater detail in the foll¬ owing, with reference to the accompanying drawings show¬ ing an embodiment thereof. In the drawings, Fig. 1 is a cross-section through a device according to the invention, Fig. 2 is a longitudinal section along II-II in Fig. 1, Fig. 3 shows on an enlarged scale the profile of the shell surface of the rotor in Fig. 1, and Figs. 4-9 are diagrams showing the results of trial runs.

The device according to the embodiment shown comprises a rotatable axlέ 1 supported in bearings 2 and driven by a motor 3. On the axle 1 a rotor 4 is attached, the shell surface of which preferably is cylindric. In conn¬ ection to the rotor 4 a press 5 is located, which comprises a shaft 6 and a pressing plate 7, which is movable by means of an hydraulic or pneumatic press cylinder 8. Other pressing means known per se, of course, also can be used, for example screws, chains etc.

Directly before the press 5, seen in the rotation direction of the rotor, liquid supply means 9 are located. After the press 5 flushing-away members 10 are located. The rotor 4 is enclosed by a casing 11 for collecting the material and discharging it to subsequent processing steps.

The embodiment shown has a vertical shaft 6. The shaft, however, also can be arranged inclined or horizontally. Several shafts can be connected to the same rotor.

The shell surface of the rotor 4 is provided with slushing members 12, which form a relief pattern on the surface. Said members 12 consist of elevations with a height of 0,1 - 1,0 mm, preferably 0,2 - 0,5 mm, with a division of 0,5 - 10 mm, preferably 1,5 - 5 mm.

The shell surface possibly also may be provided with coarse channels 13, which extend axially or in the circumferential direction or at an angle therebetween. It can also be imagined that the channels 13 are arranged in a cross pattern. The channels 13 should have a width of 1 - 5 mm, a depth of 1 - mm and a division of 3 - 15 mm.

The shell surface of the rotor 4 should be made of a hard, wear-resistant material, for example steel or grains of tungsten carbide, silicon carbide, aluminium oxiie tield together by a binding agent. The bales to be slushed are fed to the shaft 6 according to known technique. By means of the press cylinder 8 and pressing plate 7 the bales are pressed with adjustable force against the shell surface of the rotor. Liquid, preferably water, is supplied to the rotor shell surface through the liquid supply member 9.

By means of the slushing members 12 the fibres are released from the bale, in that the members 12 give rise to high-frequency pressure pulses. The cavities between the members 12 and channels 13 serve as ducts for the transport ^• of water to the slushing surface and of fibre suspension therefrom. At the same time a certain mechanical working can be obtained, and the degree of working can be influ¬ enced by many factors, see below.

The defibred fibres, suspended in water, thereafter are removed from the rotor, preferably with the help of water from the flush-away members 10. It is, thus, important that the defibred fibres do not followaroundwith the shell surface of the rotor to the slushing zone. The fibre suspension is collected in the casing 11 and dis¬ charged to pulp chests located beneath and to subsequent processing steps. This processing can include beating and possible other further treatment prior to papermaking.

The slushing of the bales and the degree of the limited mechanical working of the fibres are influenced and can be varied by variation of the following parameters.

Material of the shell surface of the rotor Design and location of the slushing members Circumferential speed of the rotor Contact force of the bale against the rotor Liquid supply (pulp concentration) Liquid temperature pH-value of the liquid Chemical content of the liquid Examples

The diagrams in Figs. 4 - 9 show the results of a number of trial runs with bleached pine sulphate pulp, which was flash dried and pressed to bales.

The slushing of the bales was carried out in a device of the kind described above.

Fig. 4 shows how the energy consumption increases with increasing contact force, expressed as specific pressure on the contact surface of the bale. The idling energy has been deducted.

Fig. 5 shows how the freeness-value of the pulp decreases with increasing energy charge.

Figs. 6,7,8 and 9 show the strength properties of the pulp as a function of the freeness-value.

Fig. 6 refers to tensile index, Fig. 7 refers to stretch at break, Fig. 8 refers to burst index, and Fig. 9 refers to tear index. The curves show that the strength and stretch of the pulp initially increase with decreasing freeness down to 500 - 550 CSF. Thereafter the properties deteri¬ orate.

Optimum result, thus, was obtained at a contact pressure of 80 - 140 kPa and an energy charge of 90 - 130 kWh per ton pulp. Other test conditions, of course, can yield other optimum levels.

The test results show a strength development of the pulp similar to that obtained at high-concentration refining, for example in disc refiners, with a rapid development especially of stretch and tear resistance at the beginning of the refining. The energy charge, however, made in the disc refiner is about twice as high, 200 - 300 kWh/ton. The strength development of the pulp according to the invention, thus, can be commenced already at the slushing. This provides a highly favourable starting position for continued strength development by refining prior to the papermaking. The invention, thus, renders it possible with substantially reduced energy consumption to achieve the same strength properties of a papermaking pulp as at conventional slushing and refining.

Alternatively, the strength properties of the papermaking pulp can be improved at the same energy -consumption.

The invention, of course, is not restricted to the embodim¬ ents described above, but can be varied within the scope of the invention idea.

Claims

1. A method of slushing bales of flash dried and compressed papermaking pulp, at which the bales are pressed against the shell surface of a rotor provided with slushing members, c h a r a c t e r i z e d i n that liquid is supplied directly prior to the slushing, that the slushing by means of the rotor is carried out so that the fibres included in the papermaking pulp are exposed, and the exposed! fibres thereafter are removed from the rotor.

2. A method as defined in claim 1, c h a r a c t e r ¬ i z e d i n that the exp'osed . fibres are subjected to limited mechanical working by means of the rotor.

3. A device for slushing bales of flash dried and . compressed papermaking pulp, comprising a rotor (4), the shell surface of which is provided with slushing members (12) and a press (5) co-acting with the shell surface for pressing the bales against the rotor (4), c h a r a c t e r i z e d i n that it comprises means (9) for the supply of liquid to the shell surface directly before the press, that the slushing members (12) consist of elevations with a height of 0,1 - 1,0 mm with a division of 0,5 - 10 mm for effecting exposure of the fibres in the papermaking pulp, and means (10) for flushing the exposed fibres away from the rotor (4).

4. A device as defined in claim 3, c h a r a c t e r - i z e d i n that the shell surface of the rotor (4) also contains coarse channels (13) with a width and depth of 1 - 5 mm.