FI72154C - Method and apparatus for milling lignocellulosic substance to 1 fiber pulp. - Google Patents

Description

1 72154

The present invention relates to a process for preparing a pulp from a lignocellulosic material, including grinding in a steam pressure grinder, wherein the ground fibrous material together with the steam therein is conveyed to the outlet via a pipeline. The invention also relates to an apparatus for grinding a lignocellulosic material into a pulp, the apparatus comprising a container for heating the substance, a conveying screw for conveying the substance to the refiner, and a pipeline and a valve for conveying the ground material from the refiner to the outlet unit.

It is already known to lead the fibers and steam to an expansion tank, cyclone or the like, in which, when expanded, the steam maintains the flow of steam and fibers. However, the reuse of steam thus expanded is most often limited by its low pressure and impurities (fibers and solutes).

The object of the invention is to provide a method and a device which do not have the disadvantages of the known solutions. According to the invention, this is achieved by separating a substantial part of the steam from the fibers in an outlet unit and returning it to the refiner or to a container in communication with the refiner without swelling in between, and to remove the fibers for further processing. The device according to the invention is characterized in that the device has means for squeezing steam from the pulp, as well as means for returning the steam back to the refiner or tank.

Other preferred embodiments of the invention will become apparent from the appended claims.

The invention represents a considerable saving of steam compared to the amount of steam hitherto used to carry out the known cycle when steam and fibers are sucked into the cylinder by means of a piston and the steam contained in this mixture is pressed out of the mixture by the same piston. The extruded steam is returned to the grinder and the fibers are mixed with water to form a pulp.

The method is applicable to all defibering processes in which the defibering of the lignocellulosic material takes place in a state filled with impregnated steam above 100 ° C, usually at a temperature of 130 ° C to 200 ° C with a vapor pressure of 297-1599 kPa.

The invention will now be described with reference to the accompanying drawings, in which Figure 1 shows a device according to the invention, and Figure 2 shows a system in which two devices are connected together.

In Fig. 1, reference numeral 1 shows a storage silo for a lignocellulosic raw material, e.g. wood chips. The chips are fed by means of a screw feeder with a double former 2 into a pressurized container in which the substance is heated. From a source not shown, for example, steam is supplied via a pipeline 18 to the tank 3 to heat the substance. The container 3 communicates via a conveying screw 4 at its lower part with a refining part 20 consisting of a closed housing 5 to which a refining plate 21 and a rotating grinding wheel 6 are rotated by an electric motor 22. The raw material fed by the conveying screw 4 is defibered as it passes between the grinding plates 6 and 21. At the same time, steam flows between the grinding plates into the housing 5.

The material and steam defibered from the housing 5 are led via a pipe 7 to an outlet unit consisting of an inlet valve 8, a cylinder 9, a piston 10, a shut-off flange 11, a screen plate 12, a non-return valve 13 and hydraulic or pneumatic cylinders 14 and 15.

Il 3 72154

One cycle of operation of the output unit takes place as follows: The piston 10 is initially in its extreme position on the right as shown in Figure 1 and the closing flange 11 is vapor-tight by means of a cylinder 14. The non-return valve 13 is closed. Valve 8 opens. As the piston 10 starts to move by means of the cylinder 15 in the figure to the left, it absorbs steam and fibers through the pipe 7 and the valve 8 from the housing 5. When the piston 10 reaches its extreme position in the figure on the left, the valve 8 closes and the piston 10 starts to move to the right. The screen 12 allows steam, but no fibers, through the non-return valve 13 and the flexible pipe 16 into the tank 3.

When the fiber dose in the cylinder 9 has been sealed between the piston 10 and the shut-off flange 11 at a predetermined pressure, the flange 11 moves to its right-hand position in the figure by means of the cylinder 14 and the non-return valve 13 closes. The piston 10 moves to its starting position and pushes the fiber dose out of the cylinder 9. The fiber dose is removed between the piston 10 and the flange 11 by water, compressed air, mechanically or in another suitable manner and mixed with water into a pulp. The flange 11 closes by means of the cylinder 14 and the cycle is at the end.

To minimize the work, it is advisable to connect two or more units together according to Figure 2 to operate alternately so that the suction step of the second unit assists the compression step of the second unit. Several units also compensate for pressure fluctuations in the housing 5.

Another way to reduce the amount of work required is to arrange the pressure in the refiner also in the piston 10, e.g. by enclosing it in a steam-tight cylinder 24, to which steam is introduced from the same source as in the tank 3.

Claims (7)

A process for producing fibrous pulp of lignocellulose-containing substance, which comprises grinding in a powder scanner (20) which starts under meadow pressure, the milled fiber material together with the mead thereof being passed through a conduit (7) to a dispensing unit (23), wherein a substantial portion of the meadow is separated from the fibers of the dispensing unit (23) and returned to the pulverizer (20) or a container (3) staring in conjunction with the pulverizer without expanding the meadow between networks, characterized that the fibers are transported away for post-treatment, and that the fibers and the meadow are sucked with a piston (10) in a tight seal cylinder (24) and with the opposite movement of the piston a substantial part of the meadow is pushed through a sieve plate (12) or the corresponding back the pulverizer (20) or the container (3). 2. A method according to claim 1, characterized in that two or more output units (23, 23 ') are coupled to each other mechanically or hydraulically to operate in pairs, one being in the suction stage while the other being in the compression stage. Apparatus for grinding a lignocellulosic substance into fiber pulp, comprising a container (3) for heating the substance, a transport screw (4) for transporting the substance to a pulverizer (20), and a pipe line (7) and a valve (8) for transporting the ground substance from the pulverizer (20) to the dispensing unit (23), characterized in that the device has means (9, 10, 11, 12) for pressing the meadow from the fiber pulp, and means (13, 16) ) for routing the meadow back to the pulverizer (20) or container (3). 4. Apparatus according to claim 3, characterized in that the means for pressing the meadow from the pulp are constituted by an inlet valve (8) which is connected to the cylinder (9), a piston (9) movable in the cylinder (9), one in the cylinder II.