FI66660B - FREQUENCY MECHANISM FOR FRAME MECHANICAL MASS - Google Patents

Description

1 66660

The present invention relates to a method according to the preamble of claim 5. The invention also relates to an apparatus for applying this method.

Pulp is traditionally sorted or purified as a very dilute aqueous fiber mixture. Several methods are known, the most common of which currently in use is the so-called vortex cleaning sorting. This vortex cleaning sort is based on the different density difference of the particles suspended in water, but above all the so-called a form factor difference that affects the flow resistance of particles in the medium in different ways.

The conventional stone grinding process for which the vortex cleaning sorting plant was originally developed produces a relatively large number of sticks, fiber bundles and other unwanted particles.

Now, later, with the generalization of other types of mechanical pulp production - which pulps are produced in the so-called with plate mills and commonly referred to as, for example, thermo-pulp pulps, pulp pulps, chemitherm-pulp pulps or combinations thereof - in the manufacture of these considerably smaller amounts of said fibrous bundles, sticks and the like are formed. However, the total amount of pulp to be treated is the same as in previous stone grinding processes. Therefore, milling processes also require the same equipment investment and energy use as previous grinding processes for vortex cleaning plants, although the amount of unwanted particles to be removed is considerably smaller in mass than in previous processes.

Now, new tread processes have become 35 mostly 2-stage, and the use of multi-stage processes can also be imagined. The number of steps of 2,66660 contributes to the increasing purity of the final pulp. However, already the so-called. in the first milling step, a large portion of the fibers are made fibrillated and in their final desired shape. Typically, in one or more subsequent steps, there is a further reduction in stick content and fiber bundles as they become fibers and further fibrillation of the fibers obtained in the previous milling step, but also unwanted breakage and formation of short fibers.

In principle, it is possible to build a hierre plant with several stages and which does not require a sorting plant at all. However, this has the disadvantage that the investment required is large, the disruptions of the 15 processes that occur in the first stage are typically amplified in the subsequent stages, and the management of the process becomes even more difficult. In addition, the more stages in the plant through which the material has to pass, the more the long fiber fraction is destroyed. For example, typical new thermo-milling plants have developed in the direction of grinding under pressure, after which the fibers are separated from the generated steam and the steam is typically used as pure steam in the drying section of a paper machine.

We have now found that the separation of the fibers, fiber bundles and sticks can also be carried out in the gas phase, preferably in steam, contrary to previous practice.

30 This separation of steam and fiber is usually carried out in steam-phase cyclones, in which the so-called complete separation of steam and fiber. A typical complete separation is of the order of magnitude that there are only a few tens or hundreds of milligrams of 35 fibers left in a ton of steam. Now, when examining various separation devices 3 66660, we have found that this separation can also be made from the imperfect as desired.

Furthermore, we have found that this distinction can be made to your adjustment.

5 This means that lighter, already fibrillated fiber particles ,. The shape coefficient of the particles is such that the coefficient of resistance to surface friction becomes high, is made indistinguishable from steam, while undesired particles which are sticks, fiber bundles or heavier particles can be distinguished from this.

According to the invention, this is achieved, for example, by using a separating device in which the pressure difference is not used as the driving force, as in conventional cyclones, but in which the separation is based on mechanical centrifugal force. When such a separation device is applied in the gas phase between the grinding steps, only the undesired particles which need further processing can be fed to the next grinding step and the acceptable fibers 20 can be recovered without further grinding.

More specifically, the method according to the invention is characterized by what is set forth in the characterizing part of claim 1.

The apparatus according to the invention, in turn, is characterized by what is set forth in the characterizing part of the claim.

The invention provides considerable advantages. Thus, energy consumption can be saved because the mass flow to subsequent refiners is substantially reduced, and the breakage of fibers that have already reached the desired degree of refining can be minimized.

Also, the process of the invention no longer necessarily requires the following typical water-phase separation, and consumes a minimum amount of water. In applying such a process, no sorting water is required at all to produce the 66660 pulp, but the approved fiber fractions can be recovered, dried and packaged into the pulp as such without conventional sorting in the aqueous stage.

The invention will now be examined in more detail with the aid of the accompanying drawings.

. Figure 1 schematically shows an embodiment of an apparatus according to the invention, in which the fibers 10 are sorted in the gas phase before the 2nd grinding step.

Figure 2 schematically shows an embodiment of the apparatus according to the invention, in which the fibers are sorted after the grinding step and the unapproved fraction is returned to the feed of the grinder.

The process according to the invention is carried out e.g.

in principle as follows:

In the solution according to Figure 1, the pre-washed wood chips are fed in a continuous stream through the line 1 to the shut-off feeder 2 and further to the evaporation chamber 3.

From this, the chip stream is led through the vertical channel 5 of the shut-off feeder and the feeder 6 to the I-stage refiner 7.

From this, the pulp is fed along line 8 to a separator 9, from which the accepted fibers are removed via line 10 directly to the final fiber separation cyclone 16. Non-25 accepted fibers are in turn transferred via line 11 and feeder 13 to a stage II refiner 14. through the conduit 17, while the separated fibers 30 are fed through a pressure-maintaining feeder 18 connected to the lower end of the cyclone 16 as a finished pulp out of the tube 19.

The solution according to Figure 2 differs from that according to Figure 1 in that it lacks a stage II refiner.

For this reason, the non-approved fibers are returned from the lower end of the separator 9 via line 12 and feeder 6 to a single 66660 5 refiner 7 (corresponding to the I-stage refiner 7 of Figure 1) for further recycling. According to the solution of Figure 1, the pulp is fed along line 8 to a separator 9, from which the accepted fibers are removed 5 via line 10 to a cyclone 16.

The resolution of the mechanical separation device 9 used in the process of the invention can be influenced by adjusting the rotational speed so that only non-approved fiber bundles and sticks are re-ground, either to the previous refiner 7 (Fig. 3) or the next refiner 14 (Fig. 2), while the approved fibers can be removed process.

There may, of course, be several subsequent grinding steps, as well as intermediate separators.

The following examples illustrate the method and apparatus of the invention.

Table 1 shows the properties of the pulp after stages I and II. From this table it can be seen that the coarse mass fraction retained by 28 mesh of 28 mesh was 51.2% after Phase I and 17.5% after Phase II · It is also observed that the number of sticks after Phase I was 6.22%, After phase II only 0.28%.

The results presented relate to measurements obtained on two production lines A and B.

25 TABLE 1 grinder stick (28 (48 omirä- phase CFS figure mesh me sh (200 (200 energy consumption (ml) ^ ino-flfraino- $ foaino - $ ^ ino-7Qfoaino-%)) (kWh / t) 30 A / I 348 6.22 51.2 13.6 3.2 24.2 1,400 A / II 76 0.28 17.5 20.5 8.6 33.2 800 • EVI 352 5.53 50.7 13 .6 3.1 24.4 1,350 tulle 103 0.80 44.9 13.5 4.0 28.2 700 35 It is further observed from Table 1 that the amount of very 6,66660 finely divided material passing through the 200 mesh wire was 24 , 2% after stage I and 33.2% after stage II In general, it can be considered that this increase in the amount of very fine material 5 is undesirable.

The same experiment was performed on another grinding line. where the fibers larger than 28 mesh were 50.7% after phase I and 44.9% after phase II »and at the same time 24.4% went through the 200 mesh wire after phase I and 28.2% after phase II. the amount of fiber.

In the same experiment, the number of sticks after stage I was 5.53 and after stage II was 0.8. With this refining line, it can be seen that most of the material had been ground to almost sufficient fineness already in stage I and the operation of the second stage 15 can be considered largely useless for the whole material. In this case, where stage I operated so favorably and stage II relatively so unfavorably, but stage II consumed 35% of the total energy consumption, it is found that by applying the fraction of fibers and sticks between stages, significant energy and capital savings are achieved, Typically in a thermal mill there is either the same number of Phase II refiners as the Phase I refiners or two Phase I refiners feed one Phase II-25 refiner. If such a plant is reconstructed with gas-phase sorting after the I-stages, it is easily achieved that the 4, 5 or 6 I-phase refiner feeds only one or two phase II refiners after the gas-phase sorting.

30 It is observed that capital savings can be in the order of 20-30% and energy regulation in the order of '30 - 35%.

It should be noted that it has been found experimentally that if the coarse pulp fraction is 33 ... 67% and preferably 35 about 50% of the total amount of material to be fractionated, an economically and technically advantageous operating range is achieved.

Claims (10)

A method for producing a hot mill from a cellulosic raw material, such as wood chips, according to which the raw material is passed to a pretreatment sieve (3), e.g. ), in which the raw material 10 is defibered, the fibrous material obtained by grinding is finally passed in the direction of the process to a separation cyclone (16) or the like, in which steam is removed and the finished fibrous material 15 is discharged, characterized in that the steam from the first refiner (7) the fibrous material is divided in the vapor phase at a pressure of 100 to 500 kPa in a separator 20 (9) into two fractions, namely a first fraction comprising acceptable fibers and a second fraction containing coarse fibers, sticks and fiber bundles, the first fraction being passed directly to a separation cyclone (16) the fraction is fed to at least one refiner (7; 14) for further grinding. A method according to claim 1, wherein a single-stage grinding is applied, characterized in that the second fraction is recycled from the separation device (9) back to the sole grinder (7) for re-grinding (Fig. 2). A method according to claim 1, wherein multi-stage grinding is used, characterized in that the second fraction is passed from the separating device (9) to at least one subsequent refiner (14) for further grinding. Method according to Claim 1, characterized in that a mechanical sorter (9) based on centrifugal force is used as the separating device. Method according to Claim 4, characterized in that a differential pressure cyclone-type separating device is used. Apparatus for applying a method according to claim 1 for producing a hot mill from a cellulosic material, the apparatus comprising a pretreatment vessel (3), at least one refiner (7; 14), , for removing the separation cyclone (16) or similar steam, for feeding the ground fibrous material of the first supply line (8, 10) from the grinder (7) to the separation cyclone (16), and for discharging the finished pulp from the separation cyclone (16) to the supply line (8). 10) a centrifugal pressure separator (9) connected between the at least one refiner 25 (7) and the separation cyclone (16), adapted to divide the steam-moving fibrous material into two fractions, namely a first fraction comprising 30 acceptable fibers and coarse fibers, a second fraction containing fiber bundles, and a second supply line (11; 1 2) feeding the second fraction to at least one refiner (7; 14) for 35 new grindings. 9 66660 Apparatus according to claim 6, comprising a single refiner (7), characterized by a feed line (12) connecting the separating device (9) and the refiner (7) to effect recirculation of the second fraction (Figure 2). 7 66660 Apparatus according to claim 6, comprising at least two refiners (7; 1 * 0), characterized by a separating device (9) and at least one subsequent refiner (1 * 0) connecting a supply line 10 (11) for feeding a second fraction to said next refiner (1). * 0 (Figure 1). Apparatus according to Claim 6, characterized in that the separating device is a mechanically-produced centrifugal separating device (9), the centrifugal force of which can be adjusted by means of a layer speed. Apparatus according to claim 6, characterized in that the separating device is a differential pressure cyclone-type separating device comprising one or more cyclones connected in parallel or in series to achieve the desired separating efficiency. 10 66660