FI96043C - Method and apparatus for treating pulp - Google Patents

Description

96043

Method and apparatus for handling pulp

The present invention relates to a method and apparatus for treating pulp. The method and device according to the invention are suitable for use in the wood processing industry both in connection with batch cooking and, in some cases, also in connection with cooking. More particularly, the invention relates to the treatment of pulp when unloading pulp from a digester.

10 When unloading the pulp from the batch digester for further processing, e.g. for washing and sorting, this is done using the so-called a dozer tower, which is a tank about 2-3 times the volume of the digester, from which the pulp is further pumped in a steady stream for the next processing steps 15 diluted to a suitable consistency. Depending on the nature of the batch cooking process, the digester is emptied from time to time into the buffer tower, whereby the surface level of the tower reaches its maximum. During cooking, the surface height of the dozer tower, in turn, drops to its minimum value. The tower is thus used for both temporary storage of the pulp and dilution of the pulp. There are two basic types of dozer towers: flat-bottomed and conical-bottomed. As its name implies, the base of a flat-bottomed tower is flat in diameter, either substantially equal to or smaller than the diameter of the tower. The latter in the case-25 sa that the tower so-called. the dilution zone is separated from the top of the tower by a conical or equivalent contraction. The dilution zone of a flat-bottomed tower is usually equipped with one or more agitators located substantially horizontally. The conical base of the tower 30 is likewise conical, as the name implies. It is usually equipped with a vertical agitator to mix the diluent into the pulp.

For the treatment following the dozer tower, i.e. the washing of the pulp, it is essential that the consistency of the pulp to be unloaded from the tower is as constant as possible between the emptying of the digester and the emptying of the kitchen. In practice, however, it has been found in 2 96043 that it is almost impossible to obtain mass removal from a dozer tower at a uniform consistency. For example, in a factory recently opened in Finland, a supplier of batch cooking equipment was in great difficulty trying to standardize the consistency of the pulp to be removed from the pusher tower.

In researching this, we have found that there are two reasons for the variability in mass consistency. First, when discharging the pulp from the digester to the dozer tower, it is a common belief 10 that the pulp remains on top of the pulp already in the tower, causing the medium-thick column of pulp in the tower to flow down at a constant rate with the mass flow pumped. However, experiments have shown that the butt stream from the digester, due to its speed of movement, penetrates the tower to a depth of several meters. In this case, at the beginning and end of the buffer discharge, the clearly dilute mass flowing from the digester in the worst case penetrates directly to the dilution zone at the bottom of the tower, immediately causing a strong change in consistency in the mass to be removed, no further control measures can be eliminated. the original adjustment margin is not even understood to take into account. Another reason for the fluctuation in consistency may be that if no penetration occurs, this dilute or correspondingly thicker mass remains flooded in the storage zone of the tower and from there enters the dilution zone when the tower is dismantled, causing a strong change in consistency. Namely, it has been found that when discharging a conventional batch digester at both the beginning and the end of the butt 30, almost only lye with a consistency of virtually zero flows from the digester. Correspondingly, in the middle stages of the butt, the pulp is discharged from the digester at a consistency of up to 12 to 13%, which differs greatly in properties from the mass at an average butt density of 35 to 9%. Such highly fluctuating consistency places great demands on the runnability and adjustability of the scrubber following the dozer tower.

Il 96043 3

The method and apparatus according to the present invention have solved the problems described above, e.g. arranging a mass butt in the tower eccentrically on one side of the tower and further arranging two or more chambers connected in series in one way or another on the bottom of the tower. It is essential that the mass butt in the tower hits the area of the chamber from which the mass is not removed from the tower. Preferably, each of said chambers is provided with a diluting mixer. Furthermore, the chambers are preferably connected to each other so that the flow of the diluted mass from one chamber to another is controlled, whereby the variations in the consistency of the mass during both the filling of the tower, i.e. the butt and the discharge of the dozer tower, can be controlled. Other advantages of the device and method according to the invention include e.g. the fact that the height of the dozer tower can possibly be reduced somewhat, as well as the volume of the entire tower, because the butt joint does not have to be placed very high for fear of a through-bull.

Other features of the method and device according to the invention will become apparent from the appended claims.

In the following, the method and apparatus according to the invention will be explained in more detail with reference to the accompanying figures, in which Fig. 1a shows a prior art dozer tower in a schematic side sectional view, Figs. Ib and 1e show two different construction alternatives of the prior art. Fig. 2b shows a schematic top view of a dozer tower according to a preferred embodiment 35 of the invention, Fig. 2c shows a schematic side view of another preferred embodiment of the invention. Figures 3a to 3g show a detail of a detail of a dozer tower according to the invention in a schematic view from above. alternative embodiments, and Figure 4 shows a side view of a mixer preferably used in a dozer tower according to the invention.

The prior art dozer tower 10 of Figures 1a-c consists of a substantially cylindrical tower top portion 12, a conically downwardly tapering intermediate portion 14 and a cylindrical dilution portion 16. A fitting 18 is provided in the top wall of the tower for discharging the digester to the dozer tower 10. The height of one of the 18, measured from the bottom of the tower, is of the order of 5 to 15 m, depending on the size of the tower. The dilution section 16 of the Tor-20 is provided with a mixer 20, by which the medium-thick mass (10 to 14%) discharged from the digester is diluted to a washing consistency, i.e. usually in the range of 2 to 6% by means of a diluent fed from the compound 22. In the embodiment of the figure, opposite the mixer 20 to the tower dilution part 25, a manifold 24 is arranged, by which this flow of the mixer 20 is distributed to rotate in the dilution part 16 two semicircular paths or also at least partially vertically, in some cases rounding or beveling

Figure 1a shows how the pulp M fed from the joint 18 to the tower 10 penetrates directly through the pulp layer in the tower into the dilution part 16 of the tower 10 with the consequences 35 described above. In addition, it is otherwise worth noting that the residence time of the pulp in the buffer tower 10 varies greatly if the new pulp to be discharged from the digester penetrates below the pulp 5,96043 already in the tower. Then part of the mass is removed from the tower immediately after it enters the tower, another part of the mass standing in the tower for even more butts.

5 Figure 1a also shows in broken lines how a pooled mass and / or lye accumulates in the storage zone of the tower, depending on the digestion stage of the digester in case the mass speed of the mass is not sufficient to cause penetration. As the pond 10 described by the dashed lines descends into the dilution zone, it causes a strong fluctuation in consistency which is practically impossible to correct by conventional means of dilution control.

Figure Ib shows how the dilution section 16 of the tower is provided with a dilute pulp outlet 26 located on the opposite side of the tower with respect to the buffer M penetrating the dilution section 16. Fig. 1a, on the other hand, shows, as a mainly warning example, a completely incorrectly designed dozer tower 20, in which the outlet connection 26 'is located next to the penetrated butt M. With such a structure, it is quite possible to unload undiluted mass from the tower. Namely, it is possible that the butt penetrating the mixing section is channeled directly into the outlet connection without; 25 no diluent can be mixed into it.

i

Figures 2a and b show a dozer tower according to a preferred embodiment of the invention, the basic structure of which corresponds to the prior art tower of Figure 1. However, the basic structure of the tower 30 may differ greatly from that shown in the figure, as the solution according to the invention is not very significantly dependent on the basic structure of the tower. Essential to the dozer tower according to the invention is that the tower is provided at least at the height of its dilution part 160 with one or more partitions 162 (for clarity only a tower with one partition is shown in the figure), in which a suitably located opening 164 is arranged. a flow path from which the mass can flow from one chamber of the dilution section to another. The first chamber 166 of the dilution section, upper in Figure 2b, is intended to receive the butt M coming from the digester.

The chamber 166 is provided with at least one mixer 168, which is preferably a mixer with a supply of diluent as described in FI patent application 902486.

Of course, it is also possible to use a mixer according to the prior art, to which the diluent is fed from the side 10 of the mixer via a separate supply pipe. Through the opening 164, the diluted pulp in the chamber 166 can be discharged in a controlled manner into the second chamber 170 of the dilution section 160, which is provided not only with at least one mixer 172, preferably a mixer 168, but also with a dilute pulp discharge connection 174. Preferably, the discharge connection 174 is provided with a means or device for determining the consistency of the pulp, according to the impulses of which the amount of diluent to be mixed by the mixer 20 172 (preferably fed through the mixer) is adjusted. The tower of Fig. 2b is further provided, just like Fig. Ib, with a divider 176, at the tip of which a partition wall 162 is attached at one end. In this embodiment, the manifold directs the pulp in chambers 166 and 170 to rotate more smoothly in each chamber. In a solution according to an alternative embodiment, not shown in the figures, the flow generated by the agitator (s) of one or more chambers can be directed to rotate vertically in the chamber, whereby the flow in question achieves a few advantages over horizontal circulating flow.

Fig. 2c shows a solution according to another preferred embodiment of the invention, which differs from the solution of Fig. 2b 35 in that the dilution part is divided into four chambers by two cross-partitions which, in the embodiment of the figure, are placed at right angles to each other. Of course, it is possible that the dilution portion would be divided into several chambers and / or that the angle between the partitions would deviate from the shown right angle and / or that the chambers would not be of the same size as shown. For example, the chambers comprising the discharge opening of the diluted pulp could, if desired, be either smaller or larger than the chambers receiving the butt. Thus, in Fig. 2c, the dilution part 260 of the dozer tower is divided by partitions 261-264 into four chambers 265-268. At least one stirrer 269 is arranged in each chamber for diluting the mass 10, which is preferably already in accordance with the device described in the above-mentioned FI patent application 902486. Chambers 266 and 267 are provided with pulp outlet connections 270 for discharging diluted pulp from the dozer tower. In the solution of the figure, the chambers of the dilution part 260 15, the so-called the discharge chambers, 266 and 267, from which the pulp is removed from the tower, are arranged in parallel. Similarly, the chambers, the so-called the butt chambers, 265 and 268, into which the pulp is discharged from the digester, or, if desired, from the digesters, are located in parallel. The partitions 263 and 264 located between the butt shells and the discharge chambers are provided with openings or the like 271, which may be one or more for each wall between the chambers. The operation of such a four-chamber dozer tower is exactly in line with the operation of the tower described in Figures 2a and b.

25

Of course, it is also possible to arrange the chambers crosswise (Fig. 2d) so that the discharge chambers 366 and 367 from which the pulp is removed are on opposite sides of the tower, and the butch chambers 365 and 368 into which the pulp is discharged from the digester (s) are between them. Other differences which are by no means intended to be used solely in the solution shown in this figure, but also in other solutions applying the principles of the invention where applicable, are that in a preferred embodiment each wall 381 to 384 of the dilution part 360 is provided with one or more orifices 371 to allow mass flow from the butt chamber (s) to the discharge chamber (s). Preferably, said openings 371, as well as the openings otherwise described in the previous embodiments, can be provided with an adjustable or merely openable and closable flap, with which the flow between the chambers can thus be regulated.

In other words, in the solution of Figure 2d it is possible to regulate the co-operation of the chambers, if necessary e.g. such that the mass to be buffered into the chamber 365 is allowed to discharge into both discharge chambers 366 and 367. Respectively, for example, the chamber 368 can be completely closed with respect to the partitions 383 and 384, if desired. Further, Figure 2d shows how each corner of each chamber is rounded so that the mass cannot accumulate and store there.

15

With regard to the term used in the text above in the partition wall, i.e. in practice the flow path enabling the mass flow between the chambers, this term must be understood in its broadest possible sense. In contrast, the septum of the so-called soot may be provided with one or more (Fig. 3a) actual openings, which may be of any shape and located at any point in the septum. It can thus be practically in the middle of the wall or between the wall and the bottom or wall of the tower (Fig.

: 25 3b). It may also be an elongate slit (Fig. 3c, 3d) which may extend to the entire height of the septum (Fig. 3d). Likewise, it can also be a recess at the top of the partition (Fig. 3e). At its widest, the flow connection between the chambers can be arranged, for example, over the upper edge of the partition (Fig. 3f).

It is also possible to provide a connection between the chambers by means of a connecting pipe (Fig. 3g), which may be equipped with a control / shut-off valve and from which the consistency can also be measured in order to optimize the mixing process. As for the size of the orifice, if any, it naturally depends on the size of the dozer tower, the production volume, the number of butt chambers, the number of orifices, the consistency of the mass transferred through the orifice, etc. Thus, only an approximate and relatively wide range can be given. telual area 0.1 - 2 m2 '

Although in all the above figures the height of the partition wall 5 has been shown to be practically the same as that of the narrower zone of the lower end of the dozer tower, the so-called the height of the dilution part, it may deviate greatly from it. First, it is quite possible that the tower structure is not described above, but is either conical-bottomed or practically constant in diameter over its entire height.

Thus, it can be seen that the height of the septum is determined in relation to the shape and volume of each tower in relation to the volume of the pus. The height of the partition wall can only be given a very wide range, with a minimum height of about 0.5 * 15 the diameter of the dozer tower and a maximum height of 0.9 * the height of the dozer tower. In our current understanding, the latter dimension comes into question only if the butt in the tower takes place in the bottom area of the butt chamber and the discharge into the unloading chamber over said high partition.

20

It is characteristic of the operation of the device according to the invention described above that the unloading of the digester is directed to a part of the tower from which the butt cannot be channeled directly to the pulp outlet. In the solution described, it is treated in such a way that 25. the butt is guided by one or more partitions * · - into a chamber of the dilution part divided, so-called to the butt chamber, from which the pulp is not removed directly to the process, but is discharged into the so-called second dilution chamber. through the discharge chamber in a controlled manner. In this case, even the penetrating butt M cannot affect the consistency of the pulp to be removed from the butt tower so much and quickly that the supply of diluent to the second chamber would not have time to adjust with the change in consistency. Thus, by means of a partition, the pulp is taken to the outlet of the dozer tower in two passes; a portion flowing directly from above and a portion from an opening in the 35 partitions. Since the consistency of the pulp coming directly from above is substantially more uniform than the consistency of the pulp coming from the pus-on side of the tower through the partition opening, it is preferable to take most of the dilutable pulp from above and only a small part of the pus-side chamber. This operation is also capable of equalizing the consistency 5 of the pulp fed to the butt-side chamber, because the mixer in the chamber mixes the pulp entering the chamber and, when the chamber is large enough, both the the consistency naturally evens out.

In the dozer tower according to the invention, it is most advantageous to use a diluting mixer according to Fig. 4, which gives a better mixing result than prior art mixers, because the dilution water is led to a shrink-wrapped jacket around the shaft, from which the liquid can be discharged . In this case, the diluent also cannot "escape" directly to the discharge connection located at the bottom or side wall of the tank, but must first mix with the medium in the tank. Due to the direction of flow of the diluent in the direction of the propeller flow, the same mixing result is obtained with lower energy consumption.

The device of Figure 4 is characterized in that the diluent nozzle water is fed tangentially to the jacket, increasing its helical velocity toward the jacket discharge end, and as it discharges from the jacket, the diluent forms a conical fluid jet easily propelled by the propeller into the pulp. If the direction of rotation of the spiral • flow of diluent is the same as the direction of rotation of the propeller, the energy consumption and mixing efficiency are at a minimum. If a more efficient mixing effect is desired, the supply of diluent to the jacket can be arranged in the opposite direction, whereby the helical flow 35 rotates against the direction of rotation of the propeller and the energy consumption of the mixing is correspondingly increased. Also, no sudden pressure shocks can be applied to the agitator blades 96043 11 because the diluent is directed to the center of the propeller, from where it spreads in a uniformly conical jet to the mixing zone of the propeller. When the jacket is always filled with liquid, the medium 5 cannot escape into the seal, whereby the service life of the seal is significantly extended. In addition, the diluent supply cone forms a streamlined flow surface for the medium outside the jacket, thereby reducing the pressure difference and the power requirement of the mixer, respectively.

10

According to Figure 4, the agitator consists essentially of a drive 32, a gear 34, a shaft 36, a shaft bearing 38 and a seal 40 and a propeller 42 attached to the end of the shaft 36. Although the bearing and seal are shown in Figure 4 in connection with or at least it is possible to bring the propeller in the immediate vicinity inside the cylindrical tube, thus minimizing the bending stresses on the shaft. The agitator is attached to the outside of the tank 20 from its gear 34 by a substantially cylindrical spacer 44 and a flange 46 therein to a flange 50 in the wall of the tank 48. Inside the tank 50, a jacket 52 is preferably attached to the same flange 50, thus enclosing the shaft 36. 38, 40 and the propeller 42. However, the end of the jacket 52 on the propeller 42 side is open to such an extent that fluid flowing inside the jacket, preferably tangentially connected to the jacket 52, can discharge through the center of the propeller 42 into the reservoir 30 48, i.e. the buffer or discharge chamber. The tubes 54 are passed through the wall of the tank 48 to the outside of the tank, from which the desired diluent is pumped into the tube 54.

The device described above operates in such a way that the liquid discharged from the pipe 54 to the jacket 35 into the head 52 flows in a helical flow from the propeller 42 side of the jacket to the tank on the propeller suction side, causing it to be in the center of the propeller stream and disintegrate substantially conically. into a sex fan from which the liquid, due to the turbulence of the flow, mixes optimally with the surrounding medium flow.

5

As can be seen from the above, it has been possible to develop a new and simple solution which effectively eliminates the disadvantages of the prior art, described above by only a few schematic examples, which are in no way intended to limit the scope of the invention as set forth in the appended claims. , which alone define the scope of our application.

Claims (17)

96043 Patent for suction et A method for handling pulp when emptying a digester into a dozer tower and dismantling a dozer tower, characterized in that a) the pulp is unloaded from the digester into the dozer tower, b) the buffer is guided in the tower in a so-called to a buffer chamber, c) mixing the pulp in said buffer chamber, d) discharging the pulp from the buffer chamber to the discharge chamber in a controlled manner, e) diluting and mixing the pulp in the discharge chamber, and f) removing the pulp from the discharge chamber. A method according to claim 1, characterized in that in step a) the pulp is discharged into the bottom part of the dozer tower. Method according to Claim 1 or 2, characterized in that a diluent is mixed into the pulp during step c). A method according to claim 1, 2 or 3, characterized in that in step d) said mass from the dozer chamber 25 is discharged into the discharge chamber among the mass flowing from the top of the dozer tower. A method according to claim 1, 2, 3 or 4, characterized in that step d) is performed via flow paths connecting said chambers. A method according to claim 1, 2, 3 or 4, characterized in that step d) is performed over an opening in a partition separating said chambers, a separate connecting pipe 35 or a partition separating said chambers. 96043 Apparatus for handling pulp, the apparatus comprising a substantially vertical tower (10) provided with a pulp discharge connection from the digester and divided into at least two parts; to the upper so-called. to the storage part 5 (12) and to the lower so-called a dilution section (160; 260; 360), said dilution section being provided with means for diluting (168, 172; 269; 369) and removing (174; 270; 370) the pulp from the tower (10), characterized in that at least part of the tower dilution section (160) ; 260; 360) is divided into two chambers (166, 170; 265, 266, 267, 268; 365, 366, 367, 368) connected in 10 or more separate series. Device according to claim 7, characterized in that at least a part of the dilution part (160; 260; 15 360) of the tower is divided into two or more separate chambers (166, 170; 265, 266, 267, 268; 365, 366, 367) connected in series. , 368) with one or more partitions (162; 261, 262, 263, 264; 381, 382, 383, 384). Device according to claim 7 or 8, characterized in that each chamber (166, 170; 265, 266, 267, 268; 365, 366, 367, 368) is provided with at least one pulp dilution device (168, 172; 269; 369). Device according to claim 8, characterized in that said partition (162; 261, 262, 263, 264; 381, 382, 383, 384) is provided with one or more openings (164; 271; 371) for said partition. to provide series connection. 30 Device according to claim 8, characterized in that said partition (162; 261, 262, 263, 264; 381, 382, 383, 384) is provided with one or more notches, slots or recesses for providing said series connection 3. · 96043 < Device according to claim 8, characterized in that said series connection between the chambers is provided by a connecting pipe. Device according to claim 8, characterized in that the height of said partition (162; 261, 262, 263, 264; 381, 382, 383, 384) varies between 0.5 times the diameter of the dozer tower and 0.9 times the height of the dozer tower. Device according to claim 8, characterized in that said dilution device (168, 172; 269; 369) is a mixer provided with dilution liquid supply devices (52, 54). Apparatus according to claim 14, characterized in that said feed device (52) is a jacket shrinking towards the agitator propeller (42) surrounding the axis of the agitator (168, 172; 269; 369). Apparatus according to claims 14 and 15, characterized in that said feed device (54) is a tube for supplying diluent to the agitator (168, 172; 269; 369) associated with said jacket (52) tangential to the direction of rotation of the propeller (42). 25 Device according to claims 14 and 15, characterized in that said feed device (54) is a tube for supplying diluent to the agitator (168, 172; 269; 369) associated with said jacket (52) tangential to the direction of rotation of the propeller 30 (42) against. 96043