AN APPARATUS FOR WASHING AND DEWATERING PULP

Technical Field

The present invention relates to an apparatus for washing and dewatering pulp, especially cellulose-containing pulp, comprising two rotatable press rolls having a permeable outer surface, between which the pulp is pressed, and a casing comprising a vat in which the press rolls are installed. The vat partly encloses the outer surface of each press roll and the vat comprises a first side vat segment which partly encloses the outer surface of the first press roll and a second side vat segment which partly encloses the outer surface of the second press roll. The casing comprises a first side casing member provided with the first side vat segment, and a second side casing member provided with the second side vat segment, at least the first side casing member being pivotable about a rotation axis for providing access to the first press roll.

Background of the Invention When producing cellulose-based products, a roll press is frequently used for washing and dewatering the cellulose-based pulp. The pulp is passed between two co-operating press rolls installed in the roll press, the press rolls having a perforated outer surface, a so called mantle surface, whereby the outer surface is permeable to liquid pressed out of the pulp, and the pulp is pressed in the roll nip, or the press nip, between the press rolls, whereby liquid is pressed out of the pulp. The roll press also includes one or more washing zones prior to the press nip. One example of such a roll press is disclosed in US 3,980,518, where the central axes of the press rolls are lying in substantially the same horizontal plane, and the pulp is passing the press nip between the press rolls in a vertical direction, from below upwards.

The above-mentioned roll presses comprise a vat in which the two press rolls are installed and partially enclosed. The vat limits the accessibility to the press roll, especially if the vat encloses a large portion of the circumference of the perforated outer surface of the press roll. The accessibility to the press roll is nec- essary for performing maintenance work, cleaning the press roll and the press nip, e.g. clearing plugs and removing pulp jammed on the perforated outer surface or in proximity to the press roll, or for changing press rolls. US 5 063 840 discloses several previously known solutions of providing accessibility to the press rolls and

the press nip. In one known solution, the vat is provided with a number of small- sized vat access doors. In another known solution, a bottom door is provided, and the nip wedge, which converges towards the press nip, is an integral part of the bottom door. The bottom door is supported by a hoist cylinder and is movable in a vertical direction. However, the access provided by these previously known solutions is limited, and said doors do not provide sufficient working room for clearing plugs. To overcome these drawbacks, US 5 063 840 suggests a solution where the vat is equipped with a bottom door having a nip wedge as an integral part, which bottom door is pivotally mounted by means of a hinge, whereby the acces- sibility is increased.

The use of a vat having pivotable vat segments is also disclosed in US 6 311 849 which describes an apparatus for dewatering and washing pulp, comprising two press rolls, between which the pulp is passed, the rotation axes of the press rolls lying on a horizontal plane. The vat of this apparatus comprises two upper pivotable vat segments which can be folded upwards for providing better accessibility when performing maintenance work, especially when changing rolls. In this apparatus, the pulp is distributed on the press roll at the lowest position of the circumference of the outer surface.

Further, EP 1 035 250 describes an apparatus for washing and dewatering pulp comprising two filter drums installed in a vat and arranged to rotate in opposite directions to create a press nip. The filter drums are installed in a vat which comprises two pivotable upper vat segments for providing access to the filter drums. A gap is formed between the vat and the outer surface of the filter drums, in which gap the pulp is fed while being pressed and washed. However, there are still further installations and arrangements associated with the roll press, especially stationary external equipment adjacent to the roll press, which are bulky and impairs the accessibility when performing maintenance work, especially when making inspections, changing press rolls, removing plugs, and cleaning the perforated outer surface or the region in proximity to the outer surface of the press roll, or the press nip.

The Object of the Invention

The object of the present invention is thus to provide an apparatus for washing and dewatering pulp which provides an improved accessibility when performing maintenance work.

Summary of the Invention

The above mentioned object is achieved by providing an apparatus as defined in the enclosed independent claim.

In prior art roll presses, the pulp distribution device is stationary mounted adjacent to the press roll, and when the pivotable side casing member is in an opened position, the stationary pulp distribution device limits the accessibility when performing maintenance work, such as inspection, the exchange of press rolls, removal of plugs, and the cleaning the permeable outer surface or the region in proximity to the outer surface of the press roll, or the press nip. By mounting the pulp distribution device on the side casing member, the pulp distribution device is automatically moved away from the press roll when opening the side casing member, whereby an improved accessibility to the different parts of the apparatus is provided, a larger portion of the outer surface of the first press roll is uncovered when the side casing member is opened, and the above-mentioned maintenance work is radically facilitated. Advantageously, the axes of rotation of the press rolls are in substantially the same horizontal plane.

According to an advantageous embodiment of the apparatus according to the present invention, the apparatus comprises an inlet device for receiving pulp to the apparatus, at least one flow channel for transporting pulp from the inlet device to the first pulp distribution device is mounted to the first side casing member, and at least one flow channel for transporting pulp from the inlet device to the second pulp distribution device is mounted to the second side casing member.

Hereby, the amount of stationary pipes of the external pulp feeding system associated with prior art apparatus, which provides the apparatus with pulp, and surrounds the apparatus and thereby limits the access to the press rolls, is reduced, and the bulkiness of the external stationary pulp feeding system surrounding the apparatus is consequently reduced. Especially the external stationary pipes connected to each pulp distribution device can be excluded. By this reduc-

tion of the external stationary pipe arrangement, the accessibility when performing maintenance work of the above-mentioned kind is further improved. When installing a prior art roll press, the external pipe arrangement for feeding pulp to the apparatus is mounted on site where the plant is located, and the pipe arrangement is often custom-made to be adapted to the environmental condition at the plant. This installation work is time consuming and generates costs. By integrating the arrangement for transporting pulp from the inlet device to the pulp distribution device in the pivotable side casing member, the amount of work for mounting the external pipe arrangement is minimized, and time and money is saved. Further, by providing the apparatus with one inlet device which distributes pulp to all flow channels, the number of connection points of the apparatus to the external pulp supply can be reduced, since only the inlet device needs to be connected to the external pulp supply, instead of connecting each pulp distribution device to the pulp supply, which facilitates the installation on site. Advantageously, the inlet device is provided with only one inlet for connection to the external pulp supply. Thus, the present invention also contributes to standardization with regard to the plant and the pulp supply system, which facilitates the installation of the apparatus. Advantageously, the apparatus comprises a stationary base unit positioned substantially below the first and second press rolls, which base unit houses the inlet device.

According to an advantageous embodiment of the apparatus according to the present invention, the inlet device comprises an outlet means for each flow channel, which outlet means is located in the base unit and is connectable to the flow channel when the side casing member is in a closed and operating position, and the apparatus comprises sealing means for sealing the passage, from the outlet means to the flow channel, between the outlet means and the flow channel. Hereby, a leak proof path for the pulp from the inlet device to the pulp distribution device is provided, although the inlet device is stationary and the pulp from the inlet device to the pulp distribution device is guided via the movable side casing member through the flow channel.

According to a further advantageous embodiment of the apparatus according to the present invention, the apparatus comprises a flow meter for measuring the flow of pulp in the flow channel, the outlet means comprises valve means for controlling the flow of pulp to the flow channel, and the apparatus comprises a

control device for controlling the valve means based on the input of the flow meter. Hereby, an individual flow control of the pulp flow of each flow channel is provided, which is especially advantageous when the side casing member comprises several flow channels distributed one after the other along the longitudinal extension 5 of the press roll, which is an advantageous embodiment of the apparatus according to the present invention.

Further advantageous embodiments of the apparatus according to the present invention emerge from the dependent claims and the detailed description of preferred embodiments.

i o Brief Description of the Drawings

The present invention will now be described, for exemplary purposes, in more detail by way of embodiments and with reference to the enclosed drawings, in which:

Fig. 1 is a schematic side view of an embodiment of the apparatus 15 according to the present invention, and

Fig 2 is a schematic bottom view of the embodiment of Fig. 1.

Detailed Description of Preferred Embodiments

Fig. 1 shows an embodiment of the apparatus for washing and dewatering cellulose-containing pulp according to the present invention. The apparatus has a 20 substantially symmetric configuration with regard to a symmetry plane 101 , and in Fig. 1 , the left side of the apparatus, i.e. to the left of the symmetry plane 101 , illustrates the apparatus in an opened position, whereas the right side of the apparatus, i.e. to the right of the symmetry plane 101 , illustrates the apparatus in a closed and operating position. The apparatus comprises a first rotatable press roll 25 102 on the left side of the apparatus and a second rotatable press roll 104 on the right side of the apparatus, each press roll 102, 104 having a permeable outer surface 106, 108. The outer surface 106, 108 is perforated, i.e. provided with apertures, whereby the outer surface 106, 108 is permeable to filtrate pressed out of the pulp. The shape of the apertures is normally circular, but any shape is possi- 30 ble. The press rolls 102, 104 comprise a number of filtrate channels radially inwards of the outer surface 106, 108 to lead evacuated filtrate away. The two press rolls defines a press nip 112 between them, in which press nip the pulp is pressed, and are arranged to rotate in opposite directions, the left press roll 102 being ar-

ranged to rotate in counter clockwise direction and the right press roll 104 being arranged to rotate in clockwise direction. In this embodiment, the axes of rotation of the press rolls 102, 104 are in substantially the same horizontal plane, and the apparatus is arranged to feed the pulp through the press nip 112 in a substantially vertical direction from below upwards. However, other positions of the press rolls 102, 104 in relation to each other are possible, and the pulp can be fed through the press nip 112 in other directions. The press rolls 102, 104 are adjustable in relation to each other, whereby the press nip 112 is adjustable.

The apparatus comprises a casing which includes a vat 114, 116, 118, in which the press rolls 102, 104 are installed, the vat 114, 116, 118 partly enclosing the outer surface 106, 108 of each press roll 102, 104, whereby a gap 124 for each press roll 102, 104 is defined, limited by the vat 114, 116, 118 and the outer surface 106, 108 of the respective press roll 102, 104. The vat 114, 116, 118 comprises a first side vat segment 114 which partly encloses the outer surface 106 of the first press roll 102, and a second side vat segment 116 which partly encloses the outer surface 108 of the second press roll 104.

Said casing comprises a first side casing member 115 which extends between the ends of the first press roll 102 and to which the first side vat segment 114 is mounted, and a second side casing member 117 which extends between the ends of the second press roll 104 and to which the second side vat segment 116 is mounted. The side vat segment 114, 116 can be mounted to the side casing member 115, 117 in different ways, or the side vat segment 114, 116 can be integrally formed with its side casing member 115, 117. The side casing members 115, 117, together with their side vat segments 114, 116, are pivotable about an axle 121 , 123 forming a rotation axis 121 , 123, and movable between a closed position and an opened position for providing access to the press rolls 102, 104. In Fig. 1 , on the left side of the apparatus, the first side casing member 115 is in an opened position, whereby access to the press roll 102 is provided, whereas on the right side of the apparatus, the second side casing member 117 is in a closed and operating position.

Further, the vat 114, 116, 118 comprises a central vat segment 118 partly enclosing the outer surface 106, 108 of the press rolls 102, 104 between the press nip 112 and the side vat segments 114, 116. The central vat segment 118 is movable in a substantially vertical direction for providing additional accessibility to the

region in proximity to the press nip 112. In Fig. 1 , on the left side of the apparatus, the central vat segment 118 is shown in an opened position, whereas on the right side of the apparatus, the central vat segment 118 is shown in a closed and operating position. As mentioned above, a gap 124 is formed between the vat 114, 116, 118 and the outer surface 106, 108 of the press rolls 102, 104. In Fig. 1 , only the right side of the apparatus illustrated the apparatus in a closed and operating position, and thus, only the gap 124 with regard to the second press roll 104 and the vat 116, 118 is shown, whereas the gap with regard to the first press roll 102 and the vat 114, 118 is not present in Fig. 1. However, when the left side of the apparatus is in a corresponding closed and operating position, a corresponding gap is provided between the first press roll 102 and the vat 114, 118.

The apparatus comprises a first pulp distribution device 126 for distributing pulp on the first press roll 102 and a second pulp distribution device 128 for dis- tributing pulp on the second press roll 104. The pulp distribution devices 126, 128 are arranged to distribute pulp to the gap 124 along the whole length of each press roll 102, 104. The pulp distributed on the outer surface 106, 108 of the press roll 102, 104 forms a mat on the press rolls 102, 104. From the pulp distribution devices 126, 128 to the press nip 112, the pulp is fed in the gap 124 in the direction of rotation of the press rolls 102, 104 while being pressed, or pressed and washed.

The first pulp distribution device 126 is mounted on the first side casing member 115, and the second pulp distribution device 128 is mounted on the second side casing member 117, whereby each pulp distribution device 126, 128 is moved away from the respective press roll 102, 104 when its side casing member 115, 117 is opened and moved away from the respective press roll 102, 104, providing an improved accessibility. Herein, the pulp distribution device 126, 128 comprise a forming unit 130, 132 for forming the pulp prior to distribution on the press roll 102, 104. However, other kinds of pulp distribution devices are possible, such as pulp distribution screws etc. The pulp distribution device 126, 128 can also comprise several separate pulp distribution units distributed one after the other along the longitudinal extension of the press roll 102, 104.

Further, the apparatus is provided with an inlet device 134 for receiving pulp to the apparatus, and several flow channels 136, 138 for transporting pulp from the inlet device 134 to the pulp distribution devices 126, 128, which flow

channels 136, 138 are mounted to and integrated with the side casing members 115, 117. Herein, the flow channels are in the form of pipes having a substantially circular cross-section, however, other designs are possible. The inlet device 134 is housed in a stationary base unit 140 positioned substantially below the first and second press rolls 102, 104. The inlet device includes an inlet 142 for connection to an external pulp supply, and an outlet means 344, 144 for each flow channel 136, 138 which outlet means 344, 144 is located in the base unit 140 and is con- nectable to its flow channel 136, 138 when the side casing member 115, 117 is in a closed position. The apparatus has sealing means for sealing the passage, from the outlet means 344, 144 to the flow channel 136, 138, between the outlet means 344, 144 and the flow channel 136, 138. The apparatus is provided with a flow meter 346, 146 for measuring the flow rate of the pulp flow in the flow channel 136, 138, and the outlet means 344, 144 comprises a valve 348, 148 for controlling the flow of pulp to the flow channel 136, 138. The apparatus comprises a con- trol device 150 for controlling the valve 348, 148 based on the input of the flow meter 346, 146. Further, each side casing member 115, 117 is pivotally attached to the base unit 140, and each side casing member 115, 117 is also connected to the base unit 140 via a respective hydraulic cylinder 178, 179 for controlling the movement of the respective side casing member 115, 117. The central vat seg- ment 118 is also movably attached to the base unit 140 via a hydraulic cylinder 119 for controlling the movement of the central vat segment 118.

The apparatus also includes a pulp transport screw 152, which for example can be in the form of a pulp disintegrating screw or a shredder screw, towards which the pulp which has been pressed in the press nip 112 is conveyed. The pulp transport screw 152 extends parallelly to the longitudinal axes of the press rolls 102, 104, and is arranged to disintegrate the pulp and transport the pulp axially away from the press for further processing. Each press roll 102, 104 is provided with a respective doctor bar 154, 156, and each doctor bar 154, 156 is provided at the bottom thereof with a respective doctor blade 158, 160 for scraping the outer surface 106, 108 of the respective press roll 102, 104.

The apparatus comprises two sets of arms 162, 164 (only one set shown in Fig. 1 ). Each set comprising a first arm 162 and a second arm 164, where the first side casing member 115 is provided with the first arm 162 and the second side casing member 117 is provided with the second arm 164. Each arm 162, 164

is provided with a locking means 170, 172, in the form of a recess, adapted to be detachably attached to a complementary locking means 174, 176, in the form of a bolt, for locking the side casing member 115, 117 in its closed position. Said complementary locking means 174, 176 are pivotally anchored to a stationary central member 166 of the apparatus, which central member 166 is positioned above the press rolls 102, 104. The stationary central member 166 is positioned above the pulp transport screw 152. Alternatively, the attachment members 162, 164 are directly attachable to each other.

Fig. 2 is a bottom view of the embodiment of Fig. 1. Each side casing member 115, 117 comprises several flow channels 136, 138 distributed one after the other along the longitudinal extension of the press roll 102, 104. Each flow channel 136, 138 is connected to the inlet device 134 via its own outlet means 144, 344 included in the inlet device 134. Each outlet means 144, 344 comprises the valve 148, 348 for controlling the flow of pulp to the flow channel 136, 138, and each flow channel 136, 138 is provided with flow meter 146, 346. Further, the inlet device 134 comprises a distribution channel 302, which extends along the longitudinal extension of at least one of the press rolls 102, 104, for distributing pulp to every flow channel 136, 138 via the outlet means 144, 344. The inlet 142 of the inlet device 134 for connection to an external pulp supply is centrally positioned between the ends of the distribution channel 302.