Field of the invention

This invention relates to a washing arrangement of the type comprising a drum, preferably a compartmented drum, for washing and dewatering cellulose pulp.

Background of the invention and prior art

All fiber lines include some type of washing arrangement in order to separate the digestion liquor from the pulp. Later on in the process a washing arrangement is provided to separate bleaching liquors after bleaching stages. There exist several different types of washing arrangements operating according to different principles.

One type of washing arrangement is the drum washer where the pulp is dewatered on a rotary filter drum after the addition of washing liquid, which displaces the liquor remaining on the pulp web after preceding processing stages, for example a digestion or bleaching stage. The static pressure causes the displaced liquor to pass through a perforated metal sheet mounted on the rotary drum. A further development of the original drum washer is the pressurized displacement washer where the filtrate at overpressure is caused to pass through the metal sheet. The increased pressure difference effects an improved displacement of the pulp. In the pressurized

displacement washer the increased pressure difference can cause the pulp web to deposit itself harder on the metal sheet of the drum and at times must be removed by some kind of auxiliary means. The pulp web, for example, then can be loosened by means of liquid or air.

According to a known design of a pressurized displacement washer, the drum is provided with compartments, in which the pulp places itself in the form of rectangles in axial direction of the drum against the metal sheet. The compartmentalization of the drum ensures that the pulp cake does not break up and starts moving, but instead maintains the form brought about at the deposition of the pulp. The compartments consist of bars placed axially along the entire axle of the drum, which bars are the walls of the compartments. The perforated metal sheet, on which the pulp deposits, is located spaced from the drum, so that filtrate channels are formed in the space between the drum and the sheet. In a drum washer a plurality of different washing stages can be carried out, with separate addition of washing liquid to the different stages, and also recycling of filtrate from one stage as washing liquid to another stage.

In order to maintain maximum washing effectiveness, it is preferred that washing liquid intended for a specific washing stage is not transported to a later washing stage.

Washing liquid intended for a washing stage later in the process is cleaner than the washing liquid used in a preceding washing stage. A difference in pressure between the stages causes added washing liquid to tend to move to the lower pressure and therefore it is often desirable to have the same or similar pressure in adjacent washing zones. In order to be able to separate different washing stages as well as forming stages and discharging stages, the respective zones are sealed by axial seals, which are placed between the compartment walls of the rotary drum and the surrounding pressure-bearing casing. Thus, the function of the longitudinal seals is of outmost importance, e.g. in order to ensure that washing liquid intended for a specific washing step is not moved to a later washing step.

Furthermore, washing effectiveness also depends on the washing zone area. Basically, a larger washing zone enables more pulp to be washed under given circumstances. In a washing arrangement, the washing zones cannot be extended since the forming zone and discharge zone requires a certain size (see Fig. 2) in order to secure a proper function of the washing arrangement.

Nevertheless, there is need of washing arrangements that are capable of, inter alia, providing improved washing effectiveness.

Summary of the invention

By the invention as defined in the claims an increased washing effectiveness and a higher capacity can be obtained. The present invention may also provide for maintained washing effectiveness but in a physically smaller washing apparatus or arrangement.

According to an aspect of the present invention, there is provided a washing

arrangement for washing and dewatering cellulose pulp, comprising a rotary drum with a plurality of external compartments on the drum for the pulp to be washed, which compartments are defined by axial compartment walls distributed along the circumference of the drum, a stationary cylindrical casing enclosing the drum, whereby a ring-shaped space is defined between the casing and the drum. The ring-shaped space by means of longitudinal seals in the axial direction of the drum is divided into a forming zone for forming the pulp in the compartments of the drum, at least one washing zone for washing the pulp at overpressure, and a discharge zone for feeding out the washed pulp. At least one washing liquid applicator is arranged to supply washing liquid into a washing zone. The at least one washing liquid applicator comprises at least one liquid passage for directing the washing liquid to the washing zone and a longitudinal seal, wherein the at least one liquid passage is arranged in the longitudinal seal.

According to another aspect of the present invention, there is provided a method for washing and dewatering cellulose pulp in a washing arrangement comprising a rotary drum with a plurality of external compartments on the drum for the pulp to be washed, which compartments are defined by axial compartment walls distributed along the circumference of the drum, a stationary cylindrical casing enclosing the drum, whereby a ring-shaped space is defined between the casing and the drum, and where the ring- shaped space by means of longitudinal seals in the axial direction of the drum is divided into a forming zone for forming the pulp in the compartments of the drum, at least one washing zone for washing the pulp at overpressure, and a discharge zone for feeding out the washed pulp. The method comprises supplying washing liquid into a washing zone using at least one washing liquid applicator, directing the washing liquid to the washing zone using at least one liquid passage of the washing liquid applicator, and directing the washing liquid to the washing zone through the longitudinal seal.

The present invention provides increased washing effectiveness and a higher capacity and thus achieves several advantages in comparison to the known art. For example, the integrated longitudinal sealing and liquid supply increases the effective washing zone since more compartments are located within a washing zone at a given point of time, and, thus more compartments are used for washing pulp in the washing zone at a given point of time.

In the prior art solutions, the penetration of washing liquid into and through the pulp is the area between the longitudinal seal and the washing inlet is impaired. This "dead" area may be about 5 degrees, which corresponds to 4 - 5 percent of the total washing area in a washing zone. By integrating the liquid supply into the longitudinal sealing it is possible to utilize the "dead" area for washing and thereby increase the effective washing area in a washing zone.

The present invention may alternatively provide for maintained washing effectiveness in a physically smaller washing apparatus or arrangement having a smaller washing drum and, hence, a smaller available area for the washing zones. In other words, it is possible to maintain the washing effectiveness at the same time as the washing drum is made smaller in comparison to a prior art drum.

According to an embodiment of the present invention, the at least one liquid passage communicates with at least one aperture or orifice arranged in the at least one longitudinal seal, wherein washing liquid is supplied into the washing zone via the at least one aperture.

According to another embodiment of the present invention, a number of apertures are arranged in the at least one longitudinal seal and are distributed along the seal in the longitudinal direction, for example, substantially along a row.

According to an embodiment of the present invention, more than one aperture is arranged in a radial direction. In other alternatives of the invention, the apertures are distributed in a longitudinal direction in a pattern such as a zig-zag like pattern, or in double rows or in any other pattern.

According to alternatives of the invention, the apertures are shaped as circular, elliptical, rectangular, square-like, or in any other form.

According to embodiments of the invention, the longitudinal seal may be axially movable relative the drum or may be substantially fixed relative the drum. In both embodiments, the longitudinal seal is arranged with a distance to the outer periphery of the drum or a slot between the seal and the outer periphery of the drum. In

embodiments, the distance or slot is 0 - 10 mm, or preferably between 2 - 8 mm. Restricting members may be used, by means of which it is possible to restrict to a desired extent excess motion of the sealing element inwards towards the drum, such that a distance of desired size, for example in the range of less than 1 or 2 or 3 mm, always remains between the seal and the drum. Adjustment member may be used and operated so that the seal is pressed with a desired even force against the drum, whereby a separate motion restriction would not be needed.

In a further embodiment of the present invention, at least one aperture is arranged to supply washing liquid substantially in a circumferential direction of the drum.

In another embodiment of the present invention, at least one aperture is arranged to supply washing liquid substantially in a radial direction of the drum or in a direction with an angle to the pulp mat between 10 and 80 degrees, or preferably, between 20 and 70 degrees.

In a further embodiment of the present invention, a first liquid passage communicates with at least one aperture arranged to supply washing liquid substantially in a radial direction of the drum or in a direction with an angle to the pulp mat between 10 and 80 degrees, or preferably, between 20 and 70 degrees and a second liquid passage communicates with at least one aperture arranged to supply washing liquid

substantially a circumferential direction of the drum and/or a radial direction of the drum or in a direction with an angle to the pulp mat between 10 and 80 degrees, or preferably, between 20 and 70 degrees. By having two separate liquid passages for supplying the washing liquid it is possible to, for example, have different pressures in the different passages. In one embodiment, the first liquid passage is arranged to supply washing liquid upstream in a rotational direction and is operated to supply washing liquid at a higher pressures than the pressure in the washing zone upstream the longitudinal seal. The second liquid passage may, in this embodiment, be operated to supply washing liquid at lower pressure than the first liquid passage and at substantially the same pressure as in the washing zone downstream in a rotational direction. The washing liquid supplied from the second liquid passage is supplied downstream the first liquid passage. By supplying washing liquid locally at a higher pressure it is possible to control direction of flow between washing zones and to obtain an earlier displacement.

According to a further embodiment of the present invention, at least one aperture is arranged to supply washing liquid substantially in a circumferential direction of the drum and at least one aperture is arranged to supply washing liquid substantially in a radial direction of the drum or in a direction with an angle to the pulp mat between 10 and 80 degrees, or preferably, between 20 and 70 degrees.

According to embodiments of the present invention, a number of apertures are arranged in the at least one longitudinal seal and are distributed along the seal in a circumferential direction.

According to embodiments of the present invention, a number of apertures are arranged in the at least one longitudinal seal and are distributed along the seal in the longitudinal direction and in the circumferential direction.

Further advantageous embodiments of the present invention and further advantages of the present invention will emerge from the detailed description of the embodiments.

Description of the drawings

The invention is described in greater detail in the following, with reference to the Figures.

Fig. 1 shows schematically a washing arrangement with two washing zones and countercurrent recycling of filtrate according to known art.

Fig. 2 shows schematically the washing arrangement in Fig. 1 in a view seen from the end wall of a washing arrangement of the type compartmented drum.

Fig. 3 shows schematically a washing arrangement with two washing zones and countercurrent recycling of filtrate according to the present invention.

Fig. 4 shows schematically the washing arrangement in Fig. 3 in a view seen from the end wall of a washing arrangement of the type compartmented drum.

Fig. 5 shows schematically a washing arrangement according to another embodiment of the present invention in a view seen from the end wall of a washing arrangement of the type compartmented drum. Fig. 6a shows schematically a cross sectional view of a washing applicator according to an embodiment of the present invention.

Fig. 6b shows schematically a cross sectional view of a washing applicator according to another embodiment of the present invention.

Fig. 6c shows schematically a cross sectional view of a washing applicator according to a further embodiment of the present invention.

Fig. 6d shows schematically a cross sectional view of a washing applicator according to another embodiment of the present invention.

Fig. 6e shows schematically a cross sectional view of a washing applicator according to yet another embodiment of the present invention.

Fig. 7 shows schematically a washing arrangement according to a further embodiment of the present invention in a view seen from the end wall of a washing arrangement of the type compartmented drum.

Fig. 8 shows schematically a cross sectional view of a washing applicator according to a further embodiment of the present invention.

Detailed description of preferred embodiments

In Fig. 1 is shown an outline diagram illustrating the filtrate flow according to known art at a countercurrent displacement washer with two washing stages. The pulp enters a forming zone 1 with associated filtrate collection 11. The pulp is moved to a first washing zone 2 with associated filtrate collection 21. In the first washing zone washing liquid is supplied in the washing liquid applicator 22. The pulp arrives then at a second washing zone 3, with associated filtrate collection 31 and washing liquid applicator 25. The washing arrangement terminates with a discharge zone 4, to which no washing liquid is added. The discharge zone has an associated filtrate collection 41. The first portion of the discharge zone acts as a pulp concentration increasing zone. Washing liquid to the second washing zone 3 is supplied via the washing liquid applicator 25. The filtrate from the filtrate collection 31 of the second washing zone is recycled to the washing liquid applicator 22 and is used as washing liquid for the first washing zone 2. Fig. 2 shows the washing arrangement in Fig. 1 according to prior art, seen from the end wall of the drum. The washing arrangement 100 comprises a rotary drum 5 with a plurality of external compartments 6 on the drum for the pulp to be washed, which compartments are defined by axial compartment walls 7 distributed along the circumference of the drum, a stationary cylindrical casing 8 enclosing the drum, whereby a ring-shaped space 9 is defined between the casing and the drum and where the ring-shaped space by means of longitudinal seals 15, 16, 17, 18 in the axial direction of the drum is divided into annular zones; a forming zone 1 for forming the pulp in the compartments of the drum, at least one washing zone 2, 3 for washing the pulp at overpressure and a discharge zone 4 for feeding out the washed pulp. The pulp enters the forming zone 1 and is then moved on the rotary drum 5 to the first washing zone 2. Washing liquid is supplied via the inlet 10a. The first washing zone 2 is defined by a first axial seal 15 in the front portion of the first washing zone 2 and a second axial seal 16 in the rear portion of the first washing zone. In the second washing zone 3, washing liquid is supplied via an inlet 10b. The second washing zone 3 is defined by the second axial seal 16 and a third axial seal 17. The discharge zone 4 is defined by the third axial seal 17 and a fourth axial seal 18.

The function of the seals is of outmost importance, e.g. in order to ensure that washing liquid intended for a specific washing step is not moved to a later washing step, especially when, under normal conditions, there exists a difference in pressure between different washing steps.

Each seal 15, 16, 17, 18 has a width which is somewhat larger than the distance between two adjacent compartment walls. Accordingly, the compartment walls will pass the seal one by one when the drum rotates and the position of the seal is such that in every movement it "covers" either one or two compartment walls. Furthermore, the seal, as seen in an axial direction, e.g. can extend principally along the whole drum. Alternatively, the drum may have two or more seals in an axial direction.

With reference to Fig. 3 and 4, an embodiment of a washing arrangement according to the present invention will be discussed. Like or similar parts shown in Fig. 2 will be denoted with the same reference numerals also in Fig. 3. In Fig. 3 is shown an outline diagram illustrating the filtrate flow according to an embodiment of the present invention at a countercurrent displacement washer with two washing stages. It should be noted that this illustrated washer comprises one integrated sealing and washing supply. According to the invention, a washer may comprise more than one integrated sealing and washing supply, as shown in Fig. 5. The pulp enters a forming zone 1 with associated filtrate collection 1 1. The pulp is moved to a first washing zone 2 with associated filtrate collection 21. In the first washing zone washing liquid is supplied in the washing liquid applicator 22. The pulp arrives then at a second washing zone 203, with associated filtrate collection 31 and washing liquid applicator 25. The washing arrangement terminates with a discharge zone 4, to which no washing liquid is added. The discharge zone has an associated filtrate collection 41. The first portion of the discharge zone acts as a pulp concentration increasing zone. Washing liquid to the second washing zone 203 is supplied via the washing liquid applicator 225 integrated in the longitudinal sealing between zone 2 and 203, as will be shown in more detail in Fig. 4. The filtrate from the filtrate collection 31 of the second washing zone 203 is recycled to the washing liquid applicator 22 and is used as washing liquid for the first washing zone 2.

Fig. 4 shows the washing arrangement in Fig. 3 according to an embodiment of the present invention, seen from the end wall of the drum. The washing arrangement 200 comprises a rotary drum 5 with a plurality of external compartments 6 on the drum for the pulp to be washed, which compartments are defined by axial compartment walls 7 distributed along the circumference of the drum, a stationary cylindrical casing 8 enclosing the drum, whereby a ring-shaped space 9 is defined between the casing and the drum and where the ring-shaped space by means of longitudinal seals 15, 216, 17, 18 in the axial direction of the drum is divided into annular zones; a forming zone 1 for forming the pulp in the compartments of the drum, at least one washing zone 2, 203 for washing the pulp at overpressure and a discharge zone 4 for feeding out the washed pulp. The pulp enters the forming zone 1 and is then moved on the rotary drum 5 to the first washing zone 2. Washing liquid is supplied via the inlet 10a. The first washing zone 2 is defined by a first axial seal 15 in the front portion of the first washing zone 2 and a second axial seal 216 in the rear portion of the first washing zone.

In the second washing zone 203, washing liquid is supplied via a washing liquid applicator 225 according to the present invention. The washing liquid applicator 225 includes a longitudinal sealing 216 comprising an inlet channel 210. The second washing zone 203 is defined by the second axial seal 216 and a third axial seal 17. The discharge zone 4 is defined by the third axial seal 17 and a fourth axial seal 18.

According to embodiments of the invention, the longitudinal sealing 216 is arranged with a distance 28 to compartments 6 or a slot between the seal and the compartments 6. In embodiments, the distance or slot is 0 - 10 mm, or preferably between 2 - 8 mm.

Alternatively, as shown in Fig. 7, the washing arrangement 700 is a one stage washer. This embodiment comprises a forming zone 1 for forming the pulp in the compartments of the drum, one washing zone 703 for washing the pulp at overpressure and a discharge zone 4 for feeding out the washed pulp. The pulp enters the forming zone 1 and is then moved on the rotary drum 5 to the washing zone 703. Washing liquid is supplied via the inlet 210. The washing zone 703 is defined by a first axial seal 216 in the front portion of the washing zone 703 and a second axial seal 17 in the rear portion of the washing zone.

Washing liquid is supplied via a washing liquid applicator 225 according to the present invention. The washing liquid applicator 225 includes a longitudinal sealing 216 comprising an inlet channel 210.

According to embodiments of the invention, the longitudinal sealing 216 is arranged with a distance 28 to compartments 6 or a slot between the seal and the compartments 6. In embodiments, the distance or slot is 0 - 10 mm, or preferably between 2 - 8 mm.

Fig. 5 shows a washing arrangement according to another embodiment of the present invention, seen from the end wall of the drum. The washing arrangement 300 comprises a rotary drum 5 with a plurality of external compartments 6 on the drum for the pulp to be washed, which compartments are defined by axial compartment walls 7 distributed along the circumference of the drum, a stationary cylindrical casing 8 enclosing the drum, whereby a ring-shaped space 9 is defined between the casing and the drum and where the ring-shaped space by means of longitudinal seals 215, 216, 17, 18 in the axial direction of the drum is divided into annular zones; a forming zone 1 for forming the pulp in the compartments of the drum, at least one washing zone 202, 203 for washing the pulp at overpressure and a discharge zone 4 for feeding out the washed pulp. The pulp enters the forming zone 1 and is then moved on the rotary drum 5 to the first washing zone 202.

In the first washing zone 202 washing liquid is supplied via a first washing liquid applicator 225 according to the present invention. The washing liquid applicator 225 includes a longitudinal sealing 215 comprising an inlet channel 210. The first washing zone 202 is defined by the first axial seal 215 in the front portion of the first washing zone 202 and a second axial seal 216 in the rear portion of the first washing zone. In the second washing zone 203, washing liquid is supplied via a second washing liquid applicator 225 according to the present invention. The washing liquid applicator 225 includes a longitudinal sealing 216 comprising an inlet channel or liquid channel or passage 210. The second washing zone 203 is defined by the second axial seal 216 and a third axial seal 17. The discharge zone 4 is defined by the third axial seal 17 and a fourth axial seal 18.

According to embodiments of the invention, the longitudinal sealing 216 is arranged with a distance 28 to compartments 6 or a slot between the seal and the compartments 6. In embodiments, the distance or slot is 0 - 10 mm, or preferably between 2 - 8 mm.

In Fig. 6a, a cross-sectional view of an embodiment of the washing liquid applicator 225 according to the present invention is shown. In this embodiment of the present invention, the at least one aperture 218 is arranged to supply washing liquid substantially in a circumferential or rotational direction of the drum 5.

According to another embodiment of the present invention, a number of apertures are arranged in the at least one longitudinal seal and are distributed along the seal in the longitudinal direction, for example, substantially along a row.

According to an embodiment of the present invention, more than one aperture is arranged in a radial direction. In other alternatives of the invention, the apertures are distributed in a longitudinal direction in a pattern such as a zig-zag like pattern, or in double rows or in any other pattern.

According to alternatives of the invention, the apertures are shaped as circular, elliptical, rectangular, square-like, or in any other form. In Fig. 6b, a cross-sectional view of another embodiment of the washing liquid applicator according to the present invention is shown. In this embodiment, the washing liquid applicator 325 comprises at least two orifices or apertures 218, 219 that communicate with the liquid channel or passage 217 to supply washing liquid substantially in a circumferential direction of the drum 5 and in a radial direction of the drum 5.

In Fig. 6c, a cross-sectional view of another embodiment of the washing liquid applicator according to the present invention is shown. In this embodiment, the washing liquid applicator 425 comprises at least one aperture 219 that communicates with the liquid passage 217 to supply washing liquid substantially in a radial direction of the drum 5.

In Fig. 6d, a cross-sectional view of another embodiment of the washing liquid applicator according to the present invention is shown. In this embodiment, the washing liquid applicator 525 comprises several apertures 219 that communicate with the liquid passage 217 to supply washing liquid substantially in a radial direction of the drum 5.

In Fig. 6e, a cross-sectional view of another embodiment of the washing liquid applicator according to the present invention is shown. In this embodiment of the washing liquid applicator 625, a liquid passage 217 communicates with at least a first aperture or orifice 219 arranged to supply washing liquid substantially in a radial direction of the drum or in a direction with an angle to the pulp mat between 10 and 80 degrees, or preferably, between 20 and 70 degrees. Further, the liquid passage 217 communicates with at least one second aperture or orifice 218 arranged to supply washing liquid substantially a circumferential direction of the drum. In one embodiment, a space 627 is arranged in the sealing in connection to and in communication with the first aperture or orifice 218. By this arrangement and, for example, by arranging the apertures or orifices with different sizes it is possible to achieve delivery of washing liquid with different pressures in the different apertures or orifices. In this illustrated embodiment, washing liquid is supplied from the first aperture 219 at a pressure P3 being higher than a pressure P ₄ upstream the longitudinal sealing device 216. Washing liquid is supplied from the second aperture or orifice 218 at a pressure Pi being lower than the pressure at which washing liquid is supplied from the first aperture or orifice 219. The pressure Pi is higher or substantially the same as the pressure P2 in the washing zone downstream in a rotational direction. By supplying washing liquid at a locally higher pressure at the first aperture or orifice it is possible to control the direction of flow between different washing zones and also to obtain an earlier displacement.

With reference now to Fig. 8, another embodiments of the washing liquid applicator according to the present invention will be discussed. These embodiments of the integrated washing liquid applicator and longitudinal sealing is arranged to be movable, substantially in a radial direction, relative the drum. All previously shown embodiments of the present invention where the longitudinal seal has been substantially static relative the drum can also be arranged to be movable relative the drum substantially in a radial direction.

The washing liquid applicator comprises a sealing 816 is mounted at least one positioning cylinder 812 for adjusting the radial position of the seal. Via the positioning cylinder 812 the position of the seal in relation to the compartment walls of the drum can be adjusted in a direction R radially according to the arrows in the Figure. The positioning cylinder 812 may be actively controlled or passively in the sense that a counter-pressure is determined manually, for example, by adjusting spring means 820 or a similar device or hydraulically or pneumatically. The active control can be effected by means of, for example, an electrical motor, pneumatically or hydraulically.

The washing liquid is supplied via a liquid passage 817 to the orifice 819 to thereby supply the washing liquid to the compartments 6.

In an embodiment of the present invention, the control can be carried out so that a certain predetermined contact force is not exceeded. At undesired contact between seal and compartment walls of the drum or some other part of the drum, the control is set to rapidly remove the seal in a direction radially outward. At positioning there is a transmitter for each cylinder, so that correct contact force can be determined and, thus, the position can be adjusted for the different parts of a longitudinal seal. The transmitter, for example, can sense load or moment for a correct control of the position. The invention shall not be considered limited to the embodiments illustrated, but can be modified and altered in different ways without departing from the scope of the appended claims. For example, the present invention may also be used with rotary drum with flat surfaces, i.e. drums without compartments.