WO2009053530A1

WO2009053530A1 - A pulp container and a method for discharging pulp from a pulp container

Info

Publication number: WO2009053530A1
Application number: PCT/FI2008/050590
Authority: WO
Inventors: Raimo Pitkänen
Original assignee: Upm-Kymmene Corporation
Priority date: 2007-10-26
Filing date: 2008-10-22
Publication date: 2009-04-30
Also published as: FI20075757A0; FI20075757A; FI122950B

Abstract

A pulp container (1) whose lower part, the so-called mixing space (6), has a downwards tapering cross section and the mixing space (6) is equipped with a mixing means (10) arranged on the drive shaft of a pulp discharge pump (9). The invention also relates to a method for discharging a pulp silo.

Description

A PULP CONTAINER AND A METHOD FOR DISCHARGING PULP FROM A PULP CONTAINER

Field of the invention

The invention relates to a pulp container, whose lower part is equipped with devices for mixing pulp and discharging it from the container. The invention also relates to a method for discharging pulp from a pulp container.

Background of the invention

Pulp to be used particularly in wood-processing industry, comprising both the manufacture of chemical pulp and the manufacture of paper and cardboard, is stored and processed in various pulp containers, pulp silos and broke towers. In pulp silos, the consistency of pulp is typically about 8 to 12%; in broke towers and other intermediate containers, the consistency of pulp varies from about 3% upwards. Normally, pulp silos and broke towers are cylindrical, and their cylindrical lower part, the so-called mixing or diluting space, is smaller in its cross- section than the upper part of the silo or tower, the so-called storage space. In the diluting space of pulp silos, pulp is diluted before it is pumped forward to the next process steps. The pulp is diluted to a consistency of about 3 to 5%, wherein the pulp can be pumped by a conventional centrifugal pump. The dilution is carried out by supplying either fresh water or filtered liquor from a suitable process step into the lower part of the silo, and by mixing the dilution water with the pulp by separate mixers provided in the dilution space of the silo. There are normally 1 to 3 mixers, depending on the size of the pulp silo. The dilu- tion water is normally led into the lower part of the silo. The dilution of the pulp is not necessary, if the pulp already has the desired consistency; in this case, the pulp is only mixed in the lower part of the silo. Mixing and dilution of the pulp can also be performed in other kinds of containers than the above-described pulp silos.

The structures and the design of the lower parts of pulp silos, broke towers and various containers used for the storage and processing of pulp vary from each other, due to a number of factors. However, it is typical of all kinds of pulp silos and containers that it is almost impossible to achieve a uniform pulp consistency when discharging pulp silos or other pulp containers. One reason for this is the fact that the con- sistency of the pulp entering the pulp container, for example a pulp silo, varies to a great extent, and high-consistency pulp will run irregularly downwards in the silo and the pulp cannot be mixed evenly in the lower part of the silo before the pulp is led forward to the next process steps.

The arrangements currently used for mixing and diluting pulp in the lower part of pulp containers, particularly a pulp silo, before the pulp is transferred from the pulp silo to other process steps, require several separate mixers to secure that the dilution water is evenly mixed into the pulp and the consistency of the pulp can be stabilized. However, the application of separate mixers raises the energy costs. Because the pulp cannot be mixed sufficiently evenly in the pulp silo, the pulp must be diluted and/or mixed further in separate containers after the pulp silo, so that the variations in the consistency of the pulp can be levelled out before the pulp is led forward in the process. The variations in the consistency of the pulp also affect, among other things, the quality of the paper or cardboard to be manufactured.

Brief summary of the invention

It is an aim of the present invention to present a novel solution for discharging pulp from pulp containers, particularly a pulp silo, which makes it possible to simplify the structure of pulp containers by eliminating separate mixers from the mixing space in the lower part of the pulp container. The invention also makes it possible to reduce the vol- ume of the mixing space in the pulp silos. Furthermore, it is an aim of the invention to present a method for discharging pulp from a pulp container, by which method the variations in the consistency and flow of the pulp to be discharged can be minimized.

To achieve this aim, the pulp container according to the invention is primarily characterized in that the lower part of the container, the so- called mixing space, has a downwards tapering cross-section, and the mixing space is equipped with a mixing means arranged on the drive shaft of the pulp discharging pump.

The pulp container refers to all containers in which pulp is stored or processed. The pulp container according to the invention is preferably a pulp silo, which means a pulp silo in which the storage space of the upper part tapes in its lower part, and underneath which there is a mixing space with a smaller cross-section.

The method according to the invention, in turn, is characterized in that the pulp is discharged from the bottom of the pulp container with a pump whose drive shaft is equipped with a mixing means.

The pulp container according to the invention is divided into at least an upper so-called storage space and a lower so-called mixing space, in which the pulp is mixed before the pulp is discharged from the pulp container. In the pulp silo of the invention for mixing and diluting pulp to a uniform consistency before the pulp is discharged from the pulp silo, no separate mixers are needed in the so-called mixing space in the lower part of the silo, as in the pulp silos of prior art. In the pulp container according to the invention, the dilution water is admixed into the pulp in the mixing space in the lower part of the container by a mixing means connected to the drive shaft of the discharge pump. Energy savings are significant in comparison with pulp containers and pulp silos of prior art, in which the dilution water is admixed to the pulp by means of separate mixers and is discharged from the container or silo by means of a separate pump. Alternatively, no dilution water is admixed to the pulp in the mixing space of the lower part of the pulp silo, but the pulp is only mixed in the mixing space of the pulp silo in order to produce homogenous pulp.

It is an aim of the invention to provide a controlled unit in the mixing space of the lower part of the pulp container by simplifying the mixing and by altering the design of the mixing space so that the pulp has a uniform consistency and flows smoothly when it is discharged from the silo. The mixing means according to the invention, connected to the pulp discharge pump, is preferably placed on the side wall of the mix- ing space of the pulp container. However, the discharge pump and the mixing means connected to its drive shaft may also have other possible locations in the mixing space, provided that a controlled pulp flow pattern is obtained. The mixing space of the pulp container according to the invention is designed in such a way that the admixing of dilution water into the pulp is efficient, and a controlled flow pattern is achieved in the mixing space of the container by means of a mixer connected to the drive shaft of the pump. The lower part in the containers, the so- called mixing space, is designed in such a way that it has a smaller cross-section than the rest of the container, and the cross-section tapers downwards. Furthermore, the opening between the mixing space and the storage space is designed in such a way that the pulp can flow/run freely from the upper storage space to the lower mixing space, and it has no abrupt angles affecting the pulp flows. In the pulp silo according to the invention, the mixing is brought as close to the storage part of the pulp silo as possible, wherein the mixing also extends to the storage part. A similar design is also implemented in other pulp containers applying the mixing means according to the invention, connected to the drive shaft of the pulp discharge pump.

By the solution according to the invention, the necessary mixing space can be reduced, resulting in reduced energy consumption and thereby also in reduced costs. The solution for mixing pulp according to the invention will level off particularly the problems caused by variations in the consistency of pulp entering the pulp silo, because the design of the silo secures that high-consistency pulp cannot fall down from the upper storage space of the silo into the mixing space, but the pulp runs smoothly into the mixing space. The design of the pulp silo according to the invention prevents the formation of a vault between the diluted pulp in the lower part and the undiluted pulp in the upper part of the silo, which vault could fall down into the lower part of the silo and cause a significant surge in the consistency of the pulp to be discharged from the silo.

The pulp container according to the invention can be used in all kinds of pulp containers and pulp silos in wood-processing industry, including broke towers and bleaching towers. The pulp container or silo accord- ing to the invention, and the method for discharging a silo, can also be applied in the production of chemical pulp. The pulp containers and pulp silos according to the invention are suitable for the processing and storage of both chemical and mechanical pulp. The structure is par- ticularly applicable for pulp of medium or low consistency, varying in the range from 3 to 15%.

The pulp silo according to the invention, and the method for discharging the same, also make it possible to simplify the pulp processing systems in paper and cardboard machines, because by the solution according to the invention, the pulp has a uniform consistency and constitutes a homogeneous continuous flow when it is pumped from the pulp silo forward to the next process steps, and no more intermediate containers will be needed for adjusting the consistency of the pulp in the pulp processing system. Thus, the arrangement makes it possible to simplify the whole pulp processing system.

Brief description of the drawings

In the following, the invention will be described in more detail with reference to the appended drawings, in which

Fig. 1 shows an arrangement of prior art for mixing and diluting pulp in the lower part of a pulp silo and for discharging pulp from the pulp silo,

Fig. 2 shows an arrangement according to the invention for discharging pulp from a pulp silo,

Fig. 3 shows an arrangement according to the invention for discharging pulp from a pulp container, and

Figs. 4a and 4b show, by way of example, a design for the mixing space of a pulp silo according to the invention. Detailed description of the invention

Figure 1 shows an arrangement of prior art for diluting pulp in the lower part of a pulp silo and for discharging pulp from the pulp silo. The pulp silo 1 can be divided roughly into two parts: an upper so-called storage space 5 and a lower so-called mixing space 6. The storage space 5 is cylindrical, tapering in its lower part, and underneath it there is a cylindrical mixing space 6 whose cross-sectional area is smaller than that of the storage space. The angle A between the side wall of the mixing space 6 and the bottom level C of the storage space 5 is 90°. The pulp 2 entering the pulp tower is normally led into the pulp silo 1 from the upper part of the silo, from where the pulp runs via the storage part 5 into the mixing space 6. In the mixing space 6, if necessary, dilution water 3 can be admixed to the pulp 2 by means of separate mixers 7 placed on the walls of the mixing space 6. There are normally 1 to 3 mixers. The dilution water is normally led to the suction side of the mixers, and alternatively also to the suction side of the pump, into the so- called discharge pipe of the silo. The diluted pulp flow 4 is pumped by the discharge pump 8 forward to the next process steps.

Figure 2 shows an example arrangement according to the invention for discharging pulp as a continuous and uniform volume flow from the pulp silo. The pulp silo 1 is divided into at least a storage space 5 and a mixing space 6. The storage space 5 is cylindrical, tapering in its lower part, and underneath it there is a cylindrical mixing space 6 whose cross-sectional area is smaller than that of the storage space. The pulp 2 entering the pulp silo is primarily supplied into the pulp silo from the upper part of the silo, from where the pulp 2 runs down to the lower part of the silo, into the so-called mixing space 6. The angle A between the side wall of the mixing space 6 and the bottom level C of the storage space 5 is selected so that the pulp can flow as smoothly as possible from the storage space into the mixing space, without forming an abrupt angle protruding inwards. If necessary, the dilution water 3 is led into the mixing space 6. The pulp is mixed to a homogeneous state, and possible diluting water is admixed to the pulp 2 by a mixing means 10 connected to the drive shaft of the discharge pump 9. By means of the pulp discharge pump 9, the pulp is led forward to the next process steps.

Figure 3 shows, by way of example, a solution according to the inven- tion for mixing pulp and discharging it from a pulp container. The pulp container shown in Fig. 3 differs from the pulp silo of Fig. 2 in that the container does not comprise a reduction in the lower part of the storage space 5 of the pulp silo, but the container of Fig. 3 tapers directly into the mixing space 6. Dilution water 3 can be introduced into the mixing space 6, if necessary, and the pulp is mixed by a mixing means 10 connected to the drive shaft of the discharge pump 9.

The above-mentioned mixing means 10 connected to the discharge pump is preferably placed on the side wall of the mixing space 6. The discharge pump 9 and the mixing means 10 connected to its drive shaft can also be placed in other possible locations in the mixing space 6 of the pulp container or pulp silo, provided that a controlled pattern of the flow of the pulp in the mixing space 6 is obtained. For example, the discharge pump 9 and the mixing means 10 connected to its drive shaft may be placed on the bottom of the mixing space 6 instead of the side wall. The angle of the mixing means 10 in relation to the walls of the mixing space 6 may vary, depending on the design of the mixing space as well as the consistency and quality of the pulp. Preferably, the shaft of the mixing means is perpendicular to the side wall of the mixing space in which the mixing means is located.

For mixing the pulp and discharging it from the pulp container, a pump is applied, whose drive shaft is equipped with a mixing means. The rotational speed of the mixer depends on the volume of the mixing space, because the pulp flow rate must be sufficiently high so that the pulp running downwards from the upper part of the container or silo and having an uneven consistency can be mixed to a uniform consistency in the mixing space of the container or silo. The mixing means is brought as close to the storage part of the container or silo as possible, wherein variations in the consistency can be minimized. Thanks to the uniform flow pattern, efficient mixing and the design of the lower part of the pulp silo, problems caused particularly by fluctuations in the con- sistency of the pulp entering the pulp silo can be minimized, because the pulp cannot fall down into the mixing part of the silo and cause significant momentary surges in the consistency. As a result, the pulp can also be pumped in a uniform volume flow from the pulp silo forward, because pressure fluctuations caused by falling down of the pulp cannot occur.

The pulp discharge pump used is preferably a centrifugal pump whose drive shaft is equipped with a mixing means. The combined mixing element and pump provide a pulp consistency and a volume flow which remain as constant as possible. Furthermore, the pump can be equipped with a gas outlet.

The consistency of the pulp in the pulp containers or in the storage space of a pulp silo varies from about 3 to 15%; preferably, the consistency of the pulp is about 8 to 12%. The consistency of the pulp may be less than 6% in the storage space of the silo, wherein any separate dilution is no longer needed in the mixing space, for example in the case of broke towers. In this case, however, the pulp is mixed in the mixing space, so that the consistency of the pulp flow to be discharged will be as constant as possible. A low consistency in the storage space of the silo is possible, for example, in the case of broke towers.

If necessary, the pulp can be diluted by means of a dilution water flow introduced into the mixing space. The dilution water inlets are preferably placed on the side walls of the mixing space. The dilution water used is either fresh water or filtered liquor from a process step. The dilution water is preferably led into the suction side of the mixing means. The pulp is preferably diluted to a consistency of about 3 to 6% in the lower part of the pulp silo, after which the pulp is pumped out of the silo.

In the pulp silo according to the invention, the storage space 5 is preferably cylindrical, tapering in its lower part, and underneath it there is a mixing space having a flat bottom and a smaller cross-sectional area. A container does not necessarily comprise a reduction between the storage space and the mixing space that exists in a pulp silo. The mixing space in a container or silo is downwards tapering, having at least one inclined side wall. Alternatively, the mixing space may be a downwards tapering cone with a flat bottom.

The interface between the storage space and the mixing space of the pulp silo is designed so that it does not comprise an abrupt inwards protruding angle which would disturb the pulp flow from the storage part into the mixing space. The angle A between the side walls of the mixing space 6 and the bottom level C of the storage space 5 is selected so that the pulp can flow as smoothly as possible from the storage space into the mixing space. The size of the angle A depends on the angle at which the lower part of the storage space is tapering. Preferably, the angle A of at least one side wall of the mixing space is about ±15° from the angle B, at which the storage part is tapering, but still such that the mixing space is downwards tapering. The angle A is advantageously between 30 and 60° for at least one side wall of the mixing space, preferably between 30 and 45°. In a corresponding manner, in other containers with no tapering of the lower part of the storage space, the interface between the mixing space and the storage space is designed so that the pulp can flow smoothly into the mixing space.

The arrangement according to the invention for designing the bottom of containers, making a controlled flow pattern and a uniform pulp con- sistency possible, does not necessarily require the use of a mixer connected to the drive shaft of the discharge pump, according to the invention, but the design can also be utilized when one or more separate mixers and a separate pump are used in the mixing space in the lower part of the container.

Figures 4a and 4b show, as an example, the design of a mixing space of a pulp silo according to the invention, compared with pulp silos of prior art. Figure 4a shows the mixing space seen from the side, and Fig. 4b shows it seen from the front. Angle A represents the angle between the side wall of the mixing space and the bottom level of the storage space. In the pulp silo of prior art, the diameter of the lower part of the mixing space is A1 and the height of the mixing space is A2, wherein the angle A is 90° in this case. In the pulp silo according to the invention, the diameter of the lower part is B1 and the height is B2. The diameter of the discharge opening of the pulp silo is A3 in the silo of prior art and B3 in the silo according to the invention. The dilution inlets 3 are arranged on the walls of the mixing space. The mixing space according to the invention, shown in Figs. 4a and 4b, is a downwards tapering space with a flat bottom and one straight wall. The pulp discharge opening, provided with a mixing means connected to the drive shaft of the discharge pump, is placed on the straight 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 silo, but the mixing space is dimensioned so that a controlled flow pattern is obtained in the mixing space by means of one mixer placed on the drive shaft of the pulp discharge pump. The volume of the mixing space is also influenced by the diameter of the mixing means.

The pulp container or pulp silo according to the invention is not limited to the designs for a pulp container or pulp silo presented as examples above, and the arrangement for discharging pulp from the pulp silo or container is not dependent on their volume or shape, but it can be applied in silos and containers of various sizes and having various bottom designs. Furthermore, the arrangement is not limited to a given consistency of the pulp to be processed, but it can be applied in a wide range of consistencies.

Claims

Claims:

1. A pulp container (1) whose lower part is provided with equipment for mixing pulp and for discharging it from the container, characterized in that the lower part of the container (1 ), the so-called mixing space (6), has a downwards tapering cross-section, and the mixing space (6) is equipped with a mixing means (10) arranged on the drive shaft of a pulp discharge pump (9).

2. The pulp container according to claim 1 , characterized in that the pulp container (1 ) is a pulp silo.

3. The pulp container according to claim 1 or 2, characterized in that said mixing space (6) is equipped with means (3) for supplying dilution water.

4. The pulp container according to any of the preceding claims, characterized in that the mixing means (10) arranged on the drive shaft of the pulp discharge pump (9) is placed on the side wall of the mixing space (6).

5. The pulp container according to any of the preceding claims 1 to 3, characterized in that the mixing means (10) arranged on the drive shaft of the pulp discharge pump (9) is placed on the bottom of the mixing space (6).

6. The pulp container according to any of the preceding claims, characterized in that the mixing space (6) has a flat bottom.

7. The pulp container according to any of the preceding claims, characterized in that at least one side wall of the mixing space (6) is inclined.

8. The pulp container according to any of the preceding claims, characterized in that the mixing space (6) is a downwards tapering cone.

9. A method for discharging pulp from a pulp container (1 ), in which method pulp is mixed in the lower part of the container before the pulp is discharged from the container (1 ) by pumping, characterized in that the pulp is discharged from the container (1 ) by a pump (9) whose drive shaft is equipped with a mixing means (10).

10. The method according to claim 9, characterized in that the consistency of the pulp in the container is about 3 to 15%.

11. The method according to claim 9, characterized in that the consistency of the pulp in the container is about 8 to 12%.

12. The method according to any of the preceding claims 9 to 11 , characterized in that the pulp is diluted in the lower part of the con- tainer.

13. The method according to claim 12, characterized in that the pulp is diluted to a consistency of about 3 to 6%.