FI120743B - Method for Sorting Pulp and Sorting Pulp - Google Patents

Description

The present invention relates to a method for sorting a pulp and a pulp screener. The method comprises screening the pulp cellulosic fibrous fiber 5 so that it does not contain large particles, for example bundles of fibers. The cellulosic fibrous mass to be sorted forms a mixture with a substantially gaseous medium, such as steam or air. The splitter is a device for carrying out the above method.

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The state of the art is described below with reference to Figure 1, which shows various pulp screeners according to US 4,606,789.

The method disclosed in US 4,606,789 has at least one fiber mass separator which separates the acceptable fiber mass from heavier bodies, e.g. sticks. The sorption force is high-pressure steam produced in the refiner, with which the pulverized fiber passes and is conveyed at high speed to the sorter.

The publication also discloses three different alternatives for the separation vessel as shown in Figure 1: a) Fiber pulp is introduced into the sorter 22 along the pipe 20, whereby. t> acceptable fiber mass exits the sorting fluid; * / 25 through the spout 68 along the conduit 24 and the rejected fraction is removed ···· * through the outlet screw 28 through the conduit 30.

B) The pulp is introduced into the sorbent 70 through tubes 20 at its upper end into a closed cylinder 72. The fibers exit the cylinder through 30 open lower ends. At a given distance, the underside of the cylinder is an upwardly tapered cone 74 which is coaxial with the cylinder 72. The cone guides the pulp to the side and the acceptable pulp exits through the outlet pipe 76 and the rejected fraction through the outlet screw 28 through the pipe 30.

V-l 35 (c) Fiber pulp is introduced into the sorter 80 through tubes 78. Sort by · * ··. Iija is based on the fact that heavier particles fall closer to the mouth of the feed pipe 78 than lighter particles. At the bottom of the sorter are feed screws 82 and 84, which are separated by a partition 86.

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The German patent application DE 2012797 discloses a centrifugal force strainer, corresponding to Finnish patent 55128. In addition, methods are known for directing a mass flow into a cyclone where the separation of fibers takes place. Such a solution is presented e.g. juicy-10 sussa US 4,309,283.

Problems of the known methods are the low consistency used in sorting, about 1%. In addition, long, flexible fibers easily pass by the wreck fraction. This is a particular problem in the TMP process 15 (thermomechanical pulp), which produces a relatively high amount of long fibers compared to other mechanical pulping processes.

The method of the invention is intended to avoid the disadvantages of the prior art. Thus, the process of the invention is characterized in that the pulp is sorted at a consistency of at least 10%. The sorting of the method according to the invention is carried out by a strainer, characterized in that it is a cylindrical chamber having a diameter to length ratio of 1-10.

The method and apparatus of the invention provide a plurality of · · · -; benefits. The process operates at high consistency, requiring less water pumping and water circulation. At the same time, the sorting method • · V ·: also simplifies. The quality of the pulp is improved because the screener effectively separates the coarse coarse fibers into the wreck fraction and the: T: 30 flexible fibers go into the acceptable pulp. The resin remains finely divided because it is unable to spread on the fiber surface due to its high consistency.

* • · * v 1 The screener is simple and does not contain moving parts, so manufacturing and V ·: 35 maintenance costs are low. The size of the screen is small because it is sorted at high speed. Due to the small size of the sorter ···:: ··· ♦ 3 the manufacturing costs are low. The separator can use the steam generated in the refiner as a sorting force, so separate power sources may not be needed.

The sorting of the pulp takes place at a consistency of at least 10%, more preferably at least 20%, and most preferably at least 40%. On the other hand, the material to be sorted must have a consistency of not more than 90%, more preferably no more than 80% and most preferably no more than 60%. The consistency of 10 refers to the percentage by weight of pulp in a mixture of pulp and water. In the process of the invention, water is in a vaporized form.

The method for sorting the pulp and the pulp sorter are described in more detail below with reference to the accompanying drawings, in which Figure 2 shows a cross-sectional view of the screen, Figure 3 shows a flow diagram of pulp during screening Figures 6a and 7a show a top view of the screen and Figures 4b, 5b, 6b and 7b show a side view of the corresponding screen, and Figure 8 shows the sorters connected in series.

As shown in Figure 2, the screen is formed by a cylindrical chamber 1 having a diameter to length ratio of 1-10. The length of the jacket refers to the perpendicular distance between the side walls 6 and 7 of the cylindrical chamber. A typical chamber 1 has a diameter of about 1 m and a sheath length of 0.2 m.

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For feed mass, the sorter has a feed point. The feed S is fed tangentially from the refiner 2 via the feed pipe 3 to the chamber 1, where the pulp gets swirling motion due to the pressure drop. Spi- • · * *. (In the case of a rotationally rotating mass flow, the mass of the middle passage * *. * ·: 35 is greater than at the sides, whereby the accepted mass enters the middle of the collector * "** · and the rejected mass is in or near the inner periphery of the screen. sorting is based on the mass, size and surface area of the wood fibers.

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For approved and rejected pulp, the screen has discharge points. According to Figure 3, the approved mass A is removed from the center of the cylinder along the outlet pipe 4 and the rejected mass R is removed from the periphery of the cylinder 5 along the outlet pipe 5. The rejected pulp R is refined in the refiner 2, from where it is returned to the screen 1 via the feed pipe 3. The inlet and outlet pipes may be mounted in different positions along the length of the cylinder casing, or there may be several inlet and outlet pipes.

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It is also possible for a screen drum with slots to be mounted inside the screen and rotated at a suitable speed, for example 3000 rpm. It may not be necessary to rotate it, but may be driven by the steam supplied to the screen 15.

Figures 4-7 show some possible screening structures. The diameter of the feed pipe 3 and / or outlet pipe 5 may be smaller (Figures 5 and 7) or equal (Figures 4 and 6) than the length of the cylindrical sheath of the screen 1. The feed pipe 3 and / or outlet pipe 5 may be arranged differently with respect to each other, as shown in Figures 4-7.

The separator can be positioned so that the cylindrical portion of the chamber is ..... either vertical or horizontal. The screen can be used to sort all types of grain: *. 25 cellulosic fibrous pulp, but particularly advantageous in a · ··· * manufacturing process such as TMP, which produces a relatively long fiber pulp.

V: The pulp is fed to the screen either by a separate power source, such as compressed air, or by utilizing a refiner outlet pressure, which is normally 3.5-4.0 bar. The pulp leaving the grinder is: T: a mixture of steam and fibers with a consistency of 40-60%.

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The mixture is accelerated to a speed, preferably 200- * ·· '* · 35,800 m / s, by appropriately selecting the diameter of the feed pipe 3 or by adding suitable nozzles to the feed pipe to control the flow. With such a no- *. ···; at the fin, coarse particles drift to the edges of the sorting cylinder and flexible, supple fibers in the center.

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As shown in Fig. 8, several screeners 1 can be placed in succession, whereby the accepted mass of the next stage is returned to the feed of the previous stage. Thus, the rejected mass R becomes strictly separated from the approved 5 mass A and only the mass which really needs refining is returned to the refiner 2.

«1 • · · t · * · • 1 · •» · • · · • 1 • · • «1 • ·· t 1 · 1 •» 4 t • * · · · · · · «« t · T 1 »t« M »1 't ·» • · · • 1 «· • 1 • · 1 • · * ·» t1 «• 1 6

Example.

Thermomechanical pulp 5 (TMP) having a fiber length of 1.46 mm and a length of 0.299 mg / m was fed to the screen at different pressures. The following results were obtained (fiber length and length by mass from an authorized mass):

Input Pressure Rejection Ratio Fiber Length Length Weight (bar) _j%] _ (mm) _ (mg / m) _ 1.0 _50_089_010_ 2.0 _60_1j23_011_ 2.5 | 62 1.29 10.26 10

Refractory Ratio refers to the ratio of rejected pulp solids flow rate to feed pulp solids flow. Length pulp refers to the ratio of pulp to pulp length in mg / m.

The results show that as the feed pressure increases, the average length of the approved fibers increases, so that the admissible mass increases with relatively higher lengths of feed pressure. At the same time, however, the rejection ratio increases, with a greater proportion of the mass going to the rejected mass as the pressure increases. However, the acceptable pulp length-20 pulp increases and the screener is thus capable of separating non-very fine fibers into the acceptable pulp.

It is obvious that the method for sorting the cellulosic fibrous pulp and the fibrous pulp screener can also be implemented in other ways within the scope of the claims. There may be only one removal point for acceptable mass · · · \ .. m. Inside the cylindrical sheath of the screen, there may be, for example, guides that direct the rejected pulp to the outlet. There may also be abrasive surfaces on the inside of the sheath, which contribute to disintegrating the fiber bundles that have drifted to the inside of the sheath. The main point is that the cellulosic v: 30 pulp is sorted at high consistency and is carried out by a screener having a diameter greater than or equal to its shell length.

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Claims (7)

A method for sorting cellulosic fibrous pulp, wherein the cellulosic fibrous pulp to be sorted forms a mixture with a substantially gaseous medium, such as steam or air, and wherein the cellulosic pulp to be sorted is a screen, which is a cylindrical 10-chamber chamber with a diameter to jacket ratio of 1-10. Method according to Claim 1, characterized in that the flow rate of the cellulosic fibrous pulp is adjusted to a suitable value and the pulp is fed to the screen (1). 15 Method according to claim 1 or 2, characterized in that the cellulosic pulp is fed tangentially to the screen (1) by the outlet pressure of the refiner (2). Method according to claim 3, characterized in that the approved mass (A) is removed from the center of the cylindrical chamber and the hy -: ** mass (R) is removed from the periphery of the cylindrical chamber and the conductor:. either re-grinding or wrecking. ···· • · · * · ·. · * '· 25 A method according to any one of the preceding claims, characterized in that a plurality of screeners (1) are connected in series such that: -: The accepted mass (A) of the Y stage is fed to the input of the previous stage. : to work. ·· ·: *. · * 30 6. A screener for sorting cellulosic fibrous pulp, which screener contains only solid parts, and which screener comprises a tangential feed point for inlet pulp, an acceptable point of discharge. ···. for the collection of sanitary and for the collection of the rejected mass at the outlet "T *, characterized in that the strainer is a cylindrical chamber having a ratio of hal: V 35 to the length of the diaper of 1-10. • · A strainer according to claim 6, characterized in that there is an outlet at the center of the cylindrical chamber for collecting acceptable mass and an outlet 5 at the periphery of the cylindrical chamber for collecting rejected mass. M · • · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · ··· · · · · · · · · · · · · · · · · · · · · · · · · · · · · ···