FI122950B - Pulp tank and pulp unloading procedure - Google Patents

Description

FIELD OF THE INVENTION The present invention relates to a pulp container, the lower portion of which is provided with devices for mixing and removing pulp from the container. The invention also relates to a method for discharging pulp from a pulp container.

BACKGROUND OF THE INVENTION

Particularly in the wood processing industry, which includes both pulp production and paper and board production, the pulps used are stored and processed in various pulp containers, pulp towers and waste towers. In mass towers, the consistency of the mass is typically about 8-12% by weight, while in waste towers and other intermediate tanks, the consistency of the mass varies by about 3% upwards. Generally, mass towers and wreck towers are cylindrical with a cylindrical lower part, so-called. mixing or dilution space, having a smaller cross-sectional area than the top of the tower storage space. In the dilution mode of the mass towers, the pulp is diluted before being pumped forward to subsequent process steps. The mass is diluted to a consistency of about 3-5%, whereby the mass can be pumped with a conventional centrifugal pump. Dilution is accomplished by feeding either pure water or filtrate from a suitable process step to the bottom of the tower and mixing the dilution water with separate mixers provided in the dilution space of the Tor-25 n. There are usually 1-3 mixers, depending on the size of the mass tower. Dilution water is usually led to the lower part of the tower. It is not necessary to dilute the pulp if the pulp is already at the desired consistency, then the pulp is only mixed at the bottom of the tower. The mixing and dilution of the pulp can also be carried out in containers other than the pulp towers described above.

The construction and design of the base of the mass towers, wreck towers, and various reservoirs used for the storage and handling of pulp 35 are due to a variety of factors. However, all types of mass towers and tanks are characterized by the fact that uniform mass consistency is almost impossible to achieve when unloading towers or other mass tanks. One reason for this is that the consistency of the pulp entering the pulp container, for example the pulp tower, varies greatly and the thick pulp flows unevenly down the tower and the pulp cannot be uniformly mixed at the bottom of the tower before the pulp is fed to the subsequent process steps.

The current arrangements for mixing and diluting the pulp at the bottom of the pulp tanks, especially the pulp tower, before transferring pulp from the pulp tower to other process steps, require several separate mixers to ensure uniform dilution water mixing and pulping consistency. However, using separate mixers increases the cost of energy. Since the pulp cannot be mixed sufficiently uniformly in the pulp tower, the pulp must be diluted and / or mixed in separate tanks after the pulp tower to smooth out pulp consistency variations before the pulp is passed through the process. Mass consistency fluctuations also have an effect on e.g. the quality of the paper or board being manufactured.

Brief Description of the Invention

It is an object of the present invention to provide a novel solution for discharging pulp from pulp containers, in particular from a pulp tower, which allows simplification of the pulp container structure by removing separate stirrers from the lower part of the pulp container. The invention also makes it possible to reduce the volume of mixing space of mass towers. It is a further object of the invention to provide a process for removing pulp from a pulp container, thereby minimizing the consistency and flow variations of the pulp to be discharged.

In order to accomplish this purpose, the pulp container according to the invention is mainly characterized in that the lower part of the container, so-called. the mixing space is tapered downward in cross-sectional area, and the mixing space is provided with a mixing member disposed on the drive shaft of the pulp removal pump 35.

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Mass container means any container in which mass is stored or handled. The pulp container according to the invention is preferably a pulp tower, which means a pulp container having a storage space at its upper part narrowing at its lower part and below which is a mixing space having a smaller cross-sectional area.

Correspondingly, the method according to the invention is characterized in that the pulp is removed from the base of the pulp container by means of a pump on the drive shaft of which a mixing member is provided.

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The pulp container according to the invention is divided at least into a so-called upper container. storage space and lower so-called. a mixing chamber in which the pulp is mixed before being discharged from the pulp container. In a pulp tower according to the invention, separate mixers, so called, are not required to mix and dilute the pulp to a uniform consistency before removing pulp from the pulp tower. in the mixing space at the bottom of the tower, such as prior art mass towers. In the pulp tank according to the invention, the dilution water is mixed with the pulp in the mixing chamber of the bottom of the tank by a mixing element connected to the drive shaft of the drain pump 20. The energy savings are significant compared to prior art pulp tanks and pulp towers, where dilution water is mixed with pulp by separate mixers and discharged from the tank or tower by a separate pump. Alternatively, the dilution water is not added to the pulp mixing space at the bottom of the pulp tank, but only 25 pulps are mixed at the pulp tank mixing stage to achieve a uniform mass.

The object of the invention is to provide a controlled entity for the mixing space of the lower part of the mass container by simplifying the mixing and changing the design of the mixing space so that the mass can be discharged from the container in a uniform consistency and flow. Preferably, the mixing member of the invention connected to a degassing pump is located on the sidewall of the mixing chamber of the mass container. However, the outlet pump and the mixing member connected to its drive shaft may also be located in the mixing space at other possible locations so that the pulp flow pattern is controlled. The mixing space of the pulp container according to the invention is designed such that the mixing of the dilution water with the pulp is effective and a controlled flow pattern in the mixing space of the pump is obtained by a mixer connected to the pump drive shaft. Bottom of the tanks the mixing chamber is shaped such that it has a smaller cross-sectional area than the rest of the container and narrows the cross-sectional area 5 downwards. In addition, the opening between the mixing space and the storage space is shaped so that the mass can flow / flow freely from the upper storage space to the lower mixing space and has no sharp angles to influence the mass flows. In the mass tower according to the invention, the mixing is brought as close as possible to the storage part of the mass tower 10, whereby the mixing also extends to the storage part. A similar design has also been realized in other pulp tanks using a mixing member according to the invention connected to the drive shaft of the pulp removal pump.

The solution according to the invention reduces the required mixing volume, as a result of which the energy consumption is reduced and thus also the costs are reduced. The solution for mixing the pulp according to the invention alleviates the problems caused by the consistency of the pulp entering the pulp tower, in particular, because the design of the tower ensures that the thick pulp does not collapse from the upper storage space of the tower to the mixing space. The design of the mass tower according to the invention prevents the formation of a vault between the diluted mass of the base member and the undiluted mass of the upper part of the tower, which can collapse into the base of the tower 25 and cause considerable oscillation in consistency.

The pulp container of the invention can be used in the wood processing industry in all types of pulp containers and pulp towers including wreck towers and bleach towers. The pulp container or tower of the invention and the method of disassembling the container can also be used in pulp production. The pulp tanks and pulp towers of the invention are suitable for handling and storing both chemical and mechanical pulps. The structure is particularly suitable for medium and low consistency mas-35 marshes with a consistency of between 3% and 15%.

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The pulp tower of the invention and the method of dismantling it also make it possible to simplify pulp handling systems for paper and board machines because the solution of the invention allows the pulp to be pumped at a constant consistency and continuous flow from the pulp The arrangement thus enables the whole mass processing system to be simplified.

10 Brief Description of the Figures

In the following, the invention will be explained in more detail with reference to the accompanying drawings, in which Figure 1 shows a prior art arrangement for mixing and diluting pulp at the bottom of a pulp tower, and deploying pulp from a pulp tower; , and Figures 4a and 4b show, by way of example, the design of a mixing space for a mass tower according to the invention.

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DETAILED DESCRIPTION OF THE INVENTION

Figure 1 shows a prior art arrangement for diluting the mass in the lower part of the mass tower and for discharging mass from the mas-30 channel. The mass tower 1 can be roughly divided into two parts: the upper so-called. storage space 5 and lower so-called. to the mixing space 6. The storage space 5 is cylindrical, tapering at its lower part, and below it is a cylindrical mixing space 6 having a smaller cross-sectional area than the storage space. The angle A between the side wall of the mixing chamber 6 and the bottom plane C of the storage room 5 is 90 °. Mass entering the pulp tower 2 is led to pulp tower 1, generally from the top of the tower, from where the pulp flows through the storage portion 5 to mixing space 6. Mixing water 6 may be mixed with pulp 2 by separate mixers 7 on walls of tower mixing space 6. There are usually 1-3 mixers. The dilution water is generally directed to the suction side of the mixers 7 and, alternatively, 5 also to the suction side of the pump 8. tower outlet pipe. The diluted mass flow 4 is pumped by the outlet pump 8 to the subsequent process steps.

Figure 2 illustrates, by way of example, an arrangement 10 for discharging pulp out of a pulp tower in a continuous and uniform volume flow. The mass tower 1 is divided at least into a storage space 5 and a mixing space 6. The storage space 5 is cylindrical which tapers at its lower part and below it is a mixing space 6 having a smaller cross-sectional area and a narrower cross-sectional area 15. The mass 2 entering the mass tower is generally led to the mass tower from the top of the tower, from where the mass 2 flows down to the lower part of the tower, so-called. to the mixing chamber 6. The angle A between the side wall of the mixing chamber 6 and the bottom plane C of the storage chamber 5 is selected so that the mass flows as smoothly as possible from the storage chamber to the mixing chamber 20 and does not form a steep inward projection. If necessary, the dilution water 3 is led to the mixing chamber 6. The mass is mixed uniformly and any dilution water is mixed with the mass 2 by means of a mixing member 10 connected to the drive shaft of the exhaust pump 9. By means of the pulping pump 9, the pulp is passed to the following process steps.

Figure 3 illustrates, by way of example, a solution according to the invention for mixing and venting the pulp out of the pulp container. The mass container shown in Figure 3 differs from the mass tower of Figure 2 in that the container does not have a contraction at the bottom of the mass storage chamber 5, but the container of .

The aforesaid mixing element 10 connected to the outlet pump is preferably located on the side wall of the mixing chamber 6. The discharge pump 9 and the mixing element 10 connected to its drive shaft 35 7 can also be located in the mixing space 6 of the pulp tank or the pulp tower at other possible positions so that the mass flow pattern in the mixing space 6 is controlled. For example, the outlet pump 9 and the mixing member 105 connected to its drive shaft may be located at the bottom of the mixing chamber 6 instead of the side wall. The angle of the mixing member 10 relative to the walls of the mixing chamber 6 may vary depending on the design of the mixing chamber and the consistency and quality of the pulp. Preferably, the axis of the mixing member is perpendicular to the side wall of the mixing chamber in which the mixing member is located.

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A pump is provided for mixing and unloading the pulp from the pulp container, the shaft of which is provided with a mixing element. The speed of rotation of the mixer depends on the volume of the mixing space, since the mass flow rate must be high enough to allow the uneven consistency mass flowing down from the top 15 of the tank or tower to be blended to a uniform consistency in the tank or tower mixing space. The mixing member is brought as close as possible to the storage section of the tank or tower, thereby minimizing consistency variations. The benefits of a smooth flow pattern, efficient mixing, and design of the mass tower bottom 20, especially the consistency fluctuations of the mass entering the mass tower, can be minimized because the mass cannot collapse into the mixing section of the tower and cause great instantaneous fluctuations. As a result, the mass can also be pumped at a constant volume flow from the mass tower, since the pressure fluctuations due to the collapse of the mass cannot occur.

The centrifugal pump is preferably used as a pulp removal pump, with a mixing member arranged on the drive shaft. The combined mixing element 30 and pump provide pulp consistency and volume flow that are as constant as possible. In addition, the pump can be combined with degassing.

The consistency of the pulp in the pulp tanks or in the storage tower 35 of the pulp varies from about 3 to 15%, preferably from about 8 to 12%. The consistency of the pulp may be less than 6% in the storage space of the tower, whereby separate dilution in the mixing space is no longer required, for example in the case of wreck towers. However, in this case, the pulp is mixed in a mixing chamber to achieve a constant consistency of the pulverized land flow. Low consistency in the storage space of the tower is possible, for example in the case of wreck towers.

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The pulp may be diluted, if necessary, with a dilution water flow to the tank mixing chamber. The dilution water connections are preferably located on the side walls of the mixing chamber. Dilution water is either pure water or a filtrate from a process step. The dilution water is preferably supplied to the suction side of the mixing member. The mass is preferably diluted to about 3-6% consistency at the bottom of the mass tower, after which the mass is pumped out of the tower.

In a mass tower according to the invention, the storage space 5 is preferably 15 cylindrical, tapering at its lower part and below it is a flat-bottomed mixing space with a lower cross-sectional area. The container may not have a shrinkage in the mass tower between the storage space and the mixing space. The tank or tower mixing space is downwardly tapered with at least one side wall inclined. Alternatively, the mixing chamber 20 may be a downwardly tapered cone which is flat.

The interface between the storage tower and the mixing space of the mass tower is shaped such that it does not have a steep inwardly projecting angle of the tower, which interferes with the mass flow from the storage section to the mixing space. The angle A between the sieve walls of the mixing chamber 6 si-25 and the bottom plane C of the storage chamber 5 is selected so that the mass can flow as smoothly as possible from the storage chamber to the mixing chamber. The magnitude of the angle A depends on the angle at which the lower part of the storage space narrows. Preferably, the angle A of the sidewall of the at least one mixing space is about ± 15 ° from the angle B at which the storage member 30 tapers, but with the mixing space being tapered down. The angle A is preferably between 30 and 60 ° with respect to the sidewall of at least one mixing chamber, most preferably between 30 and 45 °. Correspondingly, in other containers which do not taper the lower part of the storage space, the interface between the mixing space and the storage space is shaped so that the mass 35 can flow evenly into the mixing space.

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The solution of the invention for shaping the bottom of the tanks, which allows a controlled flow pattern and a uniform mass consistency, does not necessarily require the use of a mixer connected to the drive shaft of the outlet pump.

Figures 4a and 4b show, by way of example, the design of a mixing space of a mass tower according to the invention as compared to prior art mass towers. Figure 4a shows the mixing space seen from the side and 4b seen from the front. Angle A depicts the angle between the side wall of the mixing chamber and the bottom plane of the storage space. The bottom part of the mixing chamber of the prior art mass tower has a diameter A1 and the height of the mixing chamber A2, whereby the angle A in this case is 90 °. The bottom of the mixing chamber of the mass tower according to the invention 15 has a diameter B1 and a height B2. The outlet diameter of the mass tower is in the prior art tower A3 and in the tower B3 according to the invention. The dilution connections 3 are located on the walls of the mixing chamber. The mixing chamber according to the invention, shown in Figures 4a and 4b, is a downwardly tapering flat-bottomed space with one wall having a straight wall. The mass outlet with a mixing member connected to the drive shaft of the outlet pump is located on a straight wall side wall.

The volume of the mixing space is not dependent on the volume or height of the storage space of the pulp container or pulp 25, but the mixing space is dimensioned such that the flow pattern of the mixing space is achieved with a single mixer positioned on the drive shaft. The volume of the mixing chamber is also influenced by the diameter of the mixing member.

The mass container or mass tower according to the invention is not limited to the mass container or mass tower designs exemplified above, and the arrangement for removing mass from the mass tower or container is not dependent on their volume and shape, but is applicable to towers and containers of different sizes and designs. 35 The arrangement is also not limited to a particular consistency of the pulp to be treated, but can be used over a wide range of consistency.

Claims (13)

A mass container (1), the lower part of which is provided with means for collecting and removing the mass se-5 from the container, characterized in that the lower part of the container (1), so-called. the mixing chamber (6) is tapered downward in cross-sectional area, and the mixing chamber (6) is provided with a mixing member (10) arranged on the drive shaft of the pulp removal pump (9). Mass container according to Claim 1, characterized in that the mass container (1) is a mass tower. A pulp container according to claim 1 or 2, characterized in that dilution water supply devices (3) are arranged in said mixing space (6). Mass container according to one of the preceding claims, characterized in that the mixing element (10) arranged on the drive shaft of the pulp removal pump (9) is located on the side wall of the mixing chamber (6). 20 A pulp container according to any one of claims 1 to 3, characterized in that the mixing element (10) arranged on the drive shaft of the pulp removal pump (9) is located at the bottom of the mixing space (6). A pulp container according to any one of the preceding claims, characterized in that the mixing space (6) is flat. A pulp container according to any one of the preceding claims, characterized in that at least one sidewall of the mixing chamber (6) is inclined. 30 A bulk container according to any one of the preceding claims, characterized in that the mixing chamber is a tapered taper. A method for discharging pulp from a pulp container (1), wherein the pulp is mixed at the bottom of the container prior to removal from the container (1) by pumping, characterized in that the pulp is removed from the container (1) by a pump (9) the connecting member (10). Process according to claim 9, characterized in that the consistency of the 5 pulps in the container is about 3-15%. Process according to claim 9, characterized in that the consistency of the pulp in the container is about 8-12%. Method according to one of the preceding claims 9 to 11, characterized in that the pulp is diluted in the lower part of the container. Process according to claim 12, characterized in that the pulp is diluted to a consistency of about 3-6%.