SE463821B - PROCEDURE TO REDUCE ENERGY CONSUMPTION BY REFINING A MIXTURE OR SUSPENSION OF FIBER MATERIAL - Google Patents

Description

463 821 Although there are refiners where both grinding surfaces are movable to achieve a desired relative movement in the grinding gap, in the following only refiners will be considered here as an example only a fixed part called a stator, and an adjacent part called a stator IOÉOI '.

A first energy-saving measure consists in that the grinding process is carried out with a drastically reduced grinding frequency by keeping the rotating part speed substantially equal to before but with a drastically reduced number of cutting elements on the grinding surfaces.

As a second measure, partly to compensate for the lower grinding frequency, at the same time the volume has been increased, i.e. the residence time of the fibrous material between the grinding elements.

Since with a disc refiner with only radially directed grinding gap due to centrifugal forces acting on the fibrous material at given speeds it is limited with respect to the diameter of the grinding zone, it is instead possible to increase the grinding zone volume by making the grinding gap cylindrical or slightly conical. In this way, the diameter can be kept within reasonable limits while the length of the mold zone is increased.

As a third measure, also to partially compensate for the lower milling frequency, to reduce energy consumption, as much as possible of the steam generated in the milling gap is removed already while the steam is in the milling gap to improve the availability of the milling surfaces on the fibrous material and thus increase fiber. the residence time of the material in the grinding zone itself. 463 821 Much research and development work has been done on the actual design of the grinding members, which in modern machines are usually made replaceable, as they are exposed to great stresses and wear. Canadian patent CA 901857 shows examples of disc-shaped as well as conical grinding segments with different patterns with respect to grooves or bars in order to achieve as efficient grinding as possible. Another pattern is shown in US patent US 3,815,834 for disc refiner, from which it is clear that the grooves at the smaller disc diameter have a relatively large distance and that the distance becomes smaller and smaller the further out towards the periphery of the disc. Grinding frequency refers to the rotor speed per second multiplied by the number of grooves at the periphery of the grinding surfaces. Rotor speeds of 1500 - 1000 revolutions per minute can be considered normal, which gives frequencies in the order of 6000 - 20000 Hz. Through the invention it has been found that the energy consumption can be reduced considerably, in favorable cases to less than half, if the frequency is reduced to about 300 - 800 Hz by reducing the number of cutting elements of the rotor and stator from the usual 400 - 600 to 20 - 30 while maintaining the rotor. .

To compensate for the above-mentioned reduced frequency, it is necessary to increase the volume, i.e. the residence time between the grinding elements by building the refiner cylindrical or preferably slightly conical. In this case, it is possible to increase the path of the fibrous material through the refiner, i.e. along the conical surface, to a greater extent than would be possible with a disc refiner, since, as mentioned, it is not desired to increase the diameter of the grinding zone too much. 465 821 According to the invention, in order to further extend the residence time in the refiner, generated steam is drawn continuously and along substantially the entire length of the rotor. In this case, the steam separation should be made as complete as possible in order to reduce the compressibility of the chip-fiber-water-steam mixture, which helps to effectively direct the applied shear forces to the chips and fiber.

Being able to extract steam efficiently from the malzone in refiners has long been a problem in the industry. However, an example is shown in Canadian patent CA 1079559, where the grinding segments, in addition to grooves, are provided with openings which lead steam and accompanying fibrous material from the grinding gap to the back of the grinding segments themselves.

According to the present invention, most of the steam produced in the grinding gap is led away from the grinding zone and is also purified from the main part of any accompanying fibrous material. Thereafter, the steam is led away from the refiner separately from the fibrous material outlet through one or more steam outlets. The amount of steam is then regulated by maintaining a suitable pressure difference between the steam outlet and the fibrous material outlet.

Claims (2)

463 821 PATENT CLAIMS A method for reducing energy consumption when refining a mixture or suspension of fibrous material, eg moist wood chips in a refiner with inlet and outlet for fibrous material, in which the material passes through a grinding gap between relative to each other with a speed of 1000 rpm - 1500 rpm variable grinding surfaces with a conical or cylindrical shape, the grinding frequency being 6000 Hz - 20000 Hz, characterized in that a) the grinding process is carried out with a drastically reduced grinding frequency to about 300 Hz - 800 Hz by a reduced number of cutting elements on the grinding surfaces, maintaining the grinding speed at approx. rpm - 1500 rpm b) the grinding process is carried out with an increased residence time of the fibrous material in the grinding gap to compensate for the number of grinding pulses lost by the frequency reduction, and c) steam released from the fibrous material is continuously removed in radial direction from the grinding gap. 2. A method according to claim 1, characterized in that the steam removed from the grinding gap within the refiner is freed from substantially all of the steam material following the steam.