WO2012008909A1

WO2012008909A1 - A method of drying a cellulose pulp web and an arrangement for drying such a web

Info

Publication number: WO2012008909A1
Application number: PCT/SE2011/050943
Authority: WO
Inventors: Roland Kampris; Tommy Fransson
Original assignee: Andritz Technology And Asset Management Gmbh
Priority date: 2010-07-14
Filing date: 2011-07-11
Publication date: 2012-01-19
Also published as: FI20135022A7; CL2012002226A1; SE535179C2; CN102713055A; SE1050791A1; BR112012019093A2; BR112012019093B1; FI128244B

Abstract

An arrangement (20) for drying cellulose pulp comprises a drying box (22), a web position control unit (24), which is operative for controlling the lateral position of a web (44) of cellulose pulp dried in the drying box (22), and a web forwarding device (28), which is operative for forwarding the web (44) of pulp through the drying box (22) and through the web position control unit (24). The web position control unit (24) comprises a guide roller (54) arrangement comprising at least one guide roller (60, 62) and is operative for delivering a pulp web (44), the lateral position of which has been controlled, at an angle of -45° to +45° to the horizontal plane.

Description

A METHOD OF DRYING A CELLULOSE PULP WEB AND AN ARRANGEMENT FOR DRYING SUCH A WEB

Field of the Invention

The present invention relates to an arrangement for drying cellulose pulp, the arrangement comprising a drying box, a web position control unit, which is operative for controlling the lateral position of a web of cellulose pulp dried in the drying box, and a web forwarding device, which is operative for forwarding the web of pulp through the drying box and through the web position control unit.

The present invention further relates to a method of drying a cellulose pulp in an arrangement of the above referenced type.

Background of the Invention

Cellulose pulp is often dried in a convective type of dryer operating in accordance with the air borne web principle. An example of such a dryer is described in WO 2009/154549. Hot air is blown onto a web of cellulose pulp by means of upper blow boxes and lower blow boxes. The air blown by the blow boxes transfer heat to the web to dry it, and also keeps the web floating above the lower blow boxes. Hot air is supplied to the blow boxes by means of a circulation air system comprising fans and steam radiators heating the drying air. A complete cellulose pulp dryer is illustrated in WO 99/36615.

A mill producing cellulose pulp requires a very large space, such space requirement not only increasing the investment cost of the mill, but also makes the mill less effective since both personnel, equipment and the cellulose pulp as such needs to be transported over long distances internally in the mill. Summary of the Invention

An object of the present invention is to provide an arrangement for drying of a cellulose pulp web, the arrangement being more space efficient than the prior art arrangements.

This object is achieved by means of an arrangement for drying cellulose pulp, the arrangement comprising a drying box, a web position control unit, which is operative for controlling the lateral position of a web of cellulose pulp dried in the drying box, and a web forwarding device, which is operative for forwarding the web of pulp through the drying box and through the web position control unit, wherein the web position control unit is arranged upstream, as seen with respect to the direction of forwarding the web, of the web forwarding device, and comprises a guide roller arrangement comprising at least one guide roller and being operative for delivering a web of pulp, the lateral position of which has been controlled, at an angle of -45° to +45° to the horizontal plane.

An advantage of this arrangement is that the arrangement can be made quite low, such that other devices, including broke transfer devices for removing pieces of pulp from the drying box, can be conveniently integrated with the arrangement. According to one embodiment, the guide roller arrangement is operative for delivering a web of pulp, the lateral position of which has been controlled, at an angle of -30° to +30° to the horizontal plane. An advantage of this embodiment is that a further reduction of the height of the arrangement is enabled. According to a further embodiment, the guide roller arrangement is operative for delivering a web of pulp, the lateral position of which has been controlled, at an angle of -15° to +15° to the horizontal plane.

According to one embodiment the guide roller arrangement comprises a first guide roller and a second guide roller, with the second guide roller being located downstream of the first guide roller as seen in the direction of forwarding the web. An advantage of this embodiment is that efficient control of the lateral position of the web can be achieved also in situations where the web both enters and leaves the guide roller arrangement at a low angle, such as -30° to +30°, to the horizontal plane. According to one embodiment the guide roller arrangement is arranged inside a housing of the drying box. An advantage of this

embodiment is that the total length of the arrangement can be reduced, since some of the space required for the web position control unit, in particular in the longitudinal direction, as seen along the arrangement, is integrated in the drying box.

According to a further embodiment the drying box comprises at least one deck comprising blow boxes being operative for blowing a gas towards the web, the guide roller arrangement being arranged in said deck. An advantage of this embodiment is that a particularly short total length of the arrangement can be achieved.

According to one embodiment blow boxes are arranged in said at least one deck both upstream and downstream of said guide roller arrangement. An advantage of this embodiment is that the guide roller arrangement can be integrated anywhere along the deck, such as a deck of a drying zone or of a cooling zone, while still maintaining most of the drying or cooling capacity, as the case may be, of that deck.

According to one embodiment said deck is included in a cooling zone of the drying box, said cooling zone being operative for cooling the dried web. An advantage of this embodiment is that the temperature is normally rather low in the cooling zone, which means that sensitive devices, such as electronics and control devices, associated with the guide roller arrangement are not exposed to excessive temperatures.

According to one embodiment the drying box comprises at least one column of turning rolls around which the web of pulp may be turned when being forwarded between decks included in the drying box, the guide roller arrangement being arranged below said column of turning rolls. An advantage of this embodiment is that the guide roller arrangement can be installed in a part of the drying box where it causes minimum reduction of the capacity of a cooling zone or of a drying zone, as the case may be.

According to one embodiment at least a portion of a free distance needed for the web downstream of the guide roller arrangement is arranged inside a housing of the drying box. An advantage of this embodiment is that the total length of the arrangement can be reduced, without having to compromise with the free length that is desired for a proper function of the web position control unit.

According to one embodiment the guide roller arrangement is arranged downstream of the drying box, as seen in the direction of forwarding the web. An advantage of this embodiment is that the drying box need not be modified, causing minimum influence on the drying and cooling efficiency of the drying box.

According to one embodiment the web is forwarded directly from the guide roller arrangement to the web forwarding device, the path of the web being changed less than +/-10" in a vertical direction between the guide roller arrangement and the web forwarding device. An advantage of this

embodiment is that the total length of the arrangement is minimized when the web is forwarded directly from the web position control unit to the web forwarding device.

According to one embodiment the drying box, the web position control unit, and the web forwarding device are all mounted directly on a common machine room floor. An advantage of this embodiment is that the

arrangement can be made low, as seen in a vertical direction, which saves structural steel, and makes maintenance and supervision easier.

Another object of the present invention is to provide a method for drying a cellulose pulp web, the method being more space efficient than the prior art method.

This object is achieved by means of a method of drying a cellulose pulp in an arrangement comprising a drying box, a web position control unit, which is operative for controlling the lateral position of a web of cellulose pulp dried in the drying box, and a web forwarding device, which is operative for forwarding the web of pulp through the drying box and through the web position control unit, the method comprising

forwarding the dried web to a guide roller arrangement being included in the web position control unit and comprising at least one guide roller,

controlling the lateral position of the web by means of the guide roller arrangement , and delivering the web from the guide roller arrangement at an angle of -45° to +45° to the horizontal plane.

An advantage of this method is that the web is forwarded in a quite low manner downstream of the drying box, such that other process steps, including applying traction force to the web, measuring the properties of the dried web, removing pieces of pulp from the drying box at unintentional stops, etc, can be made to occur at a low vertical level, just above a machine room floor, making inspection and maintenance easier. According to one

embodiment a pulp web, the lateral position of which has been controlled, is delivered from the guide roller arrangement at an angle of -30° to +30° to the horizontal plane. An advantage of this embodiment is that other process steps can be performed at an even lower vertical level. According to a further embodiment, a pulp web, the lateral position of which has been controlled, is delivered from the guide roller arrangement at an angle of -15° to +15° to the horizontal plane.

According to one embodiment the method further comprises forwarding the web, after having passed the guide roller arrangement, along a free distance, along which the path of the web being changed less than +/-10" in a vertical direction, at least a portion of said free distance being located inside a housing of the drying box. An advantage of this embodiment is that the process steps occurring in the arrangement can be made to occur along a short total length, reducing investment and maintenance costs.

According to one embodiment the method further comprises forwarding the web directly from the guide roller arrangement to the web forwarding device, the path of the web being changed less than +/-10" in a vertical direction when being forwarded from the guide roller arrangement to the web forwarding device. An advantage of this embodiment is that the total length of the arrangement is further reduced.

Further objects and features of the present invention will be apparent from the description and the claims. Brief description of the Drawings

The invention will now be described in more detail with reference to the appended drawings in which:

Fig. 1 is a schematic side view, and illustrates an arrangement for drying cellulose pulp in accordance with prior art.

Fig. 2a is a schematic side view, and illustrates an arrangement for drying cellulose pulp in accordance with a first embodiment of the present invention.

Fig. 2b is an enlarged side view, and illustrates the area Mb of Fig. 2a. Fig. 2c is a top view, illustrating a web position control unit illustrated in

Fig. 2a.

Fig. 2d is an enlarged side view, similar to that of Fig. 2b, and illustrates an optional roller.

Fig. 3a is a schematic side view, and illustrates an arrangement for drying cellulose pulp in accordance with a second embodiment.

Fig. 3b is an enlarged side view, and illustrates the area 1Mb of Fig. 3a.

Fig. 4a is a schematic side view, and illustrates an arrangement for drying cellulose pulp in accordance with a third embodiment.

Fig. 4b is an enlarged side view, and illustrates the area IVb of Fig. 4a. Fig. 5 is an enlarged side view and illustrates an arrangement for drying cellulose pulp in accordance with a fourth embodiment.

Description of preferred embodiments

Fig. 1 illustrates a prior art arrangement 1 for drying cellulose pulp. The arrangement 1 comprises a drying box 2 in which a web 3 of cellulose pulp is dried. The drying box 2 could be similar to the drying box illustrated in

WO 99/36615. The dried cellulose pulp web 3 leaves the drying box 2 and is forwarded to a web position control roll 4. The web position control roll 4 controls the lateral position of the web. After the roll 4, the web 3 is forwarded vertically upwards to a roll 5. The vertical distance H from the web position control roll 4 to the roll 5 should be at least 0.5 times the width of the web 3, to avoid wrinkling of the web. The web 3 is then forwarded through a measurement station 6 analysing the properties, such as moisture content, basis weight, any presence of spots of dirt and brightness, of the web 3. A web pulling nip 7 is arranged after the measurement station 6 to pull the web 3 through the drying box 2, and the rolls 4, 5. The web 3 is then transferred to a cutter 8 for being cut to suitable lengths for being baled for transport.

Alternatively, the dried pulp may be collected on a so-called pope reeler on which a reel of dried pulp is formed. A broke transfer device 9 is operative for transferring pieces of web getting stuck inside the drying box 2 at

unintentional stops from the drying box 2 to a pulp pit 10, in which the pieces of pulp may be dissolved and utilized for producing a new pulp web.

Fig. 2a illustrates an arrangement 20 for drying cellulose pulp in accordance with a first embodiment of the present invention. Fig. 2b illustrates an enlargement of the area Mb of Fig. 2a. The arrangement 20 comprises a drying box 22, a web position control unit 24, a measurement station 26, a web forwarding device 28, a cutter 30, and a broke transfer device 32.

The drying box 22 comprises a housing 34. Inside the housing 34 a drying zone 36 and a cooling zone 38 are arranged. The drying zone 36 comprises a number of drying decks 40, each such deck 40 comprising a number of upper blow boxes 42 and lower blow boxes 43 that are arranged for blowing a hot drying gas towards a cellulose pulp web 44. Typically, a drying box 22 may comprise 10 to 50 drying decks 40 arranged one above the other, although Fig. 2a in the interest of maintaining clarity of illustration only illustrates the lower portion of the drying box 22. The lower blow boxes 43 are operative for keeping the web 44 in a "floating" condition, such that the web 44 becomes airborne during the drying process. Typically air of a temperature of 80 to 250°C is utilized for the drying process. The cellulose pulp entering the drying box 22, from an upstream web forming station, not shown in Fig. 2a, typically has a dry solids content of 40-60 % by weight, and the cellulose pulp web leaving the drying box 22 has a dry solids content of typically 85-95 % by weight. The cellulose pulp web 44 leaving the drying box 22 typically has a basis weight of 800 to 1500 g/m², when measured at a moisture content of 0.1 1 kg water per kg dry substance, and a thickness of 0.8 to 3 mm. The cooling zone 38 comprises at least one cooling deck 46, in Fig. 2a two such cooling decks 46 are illustrated, each such deck 46 comprising a number of upper blow boxes 47 and lower blow boxes 48 that are arranged for blowing a cooling gas towards the cellulose pulp web 44. The lower blow boxes 48 are operative for keeping the web 44 in a "floating" condition, such that the web 44 becomes airborne during the cooling process. Typically, air of a temperature of 15 to 40°C is utilized as a cooling gas for the cooling process. An isolated wall 49 separates the drying zone 36 from the cooling zone 38.

At a first end 50 of the housing 34 a first column of turnings rolls 51 is arranged, and at a second end 52 of the housing 34 a second column of turning rolls 53 is arranged. The web 44 is turned around the turning rolls 51 , 53 when being transferred from one deck 40, 46 to another deck 40, 46 and when being transferred from the drying zone 36 to the cooling zone 38.

The web position control unit 24 comprises a guide roller arrangement

54, two cameras 56, of which only one is visible in Fig. 2a, and two light sources 58, of which only one is visible in Fig. 2a. The guide roller

arrangement 54, the cameras 56, and the two light sources 58 are arranged inside the housing 34, and in fact inside the cooling zone 38. In accordance with an alternative embodiment, the web position control unit 24 could be arranged with only one camera 56 and only one light source 58, since it is sometimes enough to keep track on just one of the lateral sides of the web 44.

Fig. 2b illustrates the web position control unit 24 in more detail. The guide roller arrangement 54 comprises a first guide roller 60 and a second guide roller 62. The direction of forwarding the web 44 is indicated by an arrow T. The web 44 is forwarded above the first roller 60 and below the second roller 62. The upper end of the first roller 60 is located at a higher level than the lower end of the second roller 62, meaning that the web 44 will make two turns, firstly downwards when passing the first roller 60, and secondly upwards when passing the second roller 62, as illustrated in Fig. 2b. The first and second rollers 60, 62 are mounted on a roller rack 64. The roller rack 64 is mounted on a foundation 66 in such a manner that the roller rack 64 may slide on the foundation 66 along an arc, having a central axis A. The web 44 leaves the guide roller arrangement 54 at an angle B to the horizontal plane of about +5° as illustrated in Fig. 2b, i.e., at an angle of 5° above the horizontal plane. Typically, the angle B would be from -45° to + 45°, i.e., the web 44 would leave the guide roller arrangement 54 at an angle B in the range of from 45° below the horizontal plane, to 45° above the horizontal plane. More often the angle B would be in the range of -30° to +30°, or even in the range of -15° to +15°.

Cameras 56 and light sources 58 are typically located a short distance, typically 0.2 to 1 m, downstream of second roller 62.

Fig. 2c illustrates the web position control unit 24 as seen from above. Arrows S indicate how the roller rack 64 may slide on the foundation 66 illustrated in Fig. 2b, such sliding movement occurring along a horizontal arc having its centre in the axis A. The sliding of the roller rack 64 on the foundation, and along the arc having its centre in axis A, influences the position of the web 44. The direction of forwarding the web 44 is indicated by an arrow T in Fig 2c. The rollers 60, 62 are provided with motors 67, 68 that are utilized during start up of the drying process, by forwarding a narrow "tail" of pulp there through. When the pulp drying process is in normal operation motors 67, 68 are inactive.

If the roller rack 64 is slid to the left as seen in the direction T of forwarding the web 44, i.e., upwards in the illustration of Fig. 2c, the web 44 is forced to the left. If the roller rack 64 is slid to the right as seen in the direction T of forwarding the web 44, i.e., downwards in the illustration of Fig. 2c, the web 44 is forced to the right. The two cameras 56, one camera 56 being arranged on each lateral side of the web 44, as illustrated in Fig. 2c, and above the web 44, as illustrated in Fig. 2b, registers an amount of light passing by the web 44 from the respective light source 58 arranged vertically below the respective camera 56, and below the web 44, as illustrated in Fig. 2b and 2c. The two cameras 56 are connected to a control system 70, illustrated in Fig. 2c. The control system 70 analyses signals from cameras 56, and determines, based on such signals, whether or not it is necessary to adjust the lateral position of the web 44. If such adjustment is necessary, control system 70 sends a signal to servomotor 72 to make roller rack 64 slide to the left or to the right, as the case may be, to adjust the lateral position of the web 44. A control system of this type is available from Fife Corporation, Oklahoma city, USA.

Fig. 2a illustrates a free distance FD being the distance from the second roller 62 of the roller arrangement 54 to a support roller 74. The free distance FD is preferably at least 0.5 times the width W, illustrated in Fig. 2c, of the web 44. As can be seen from a reference to Fig. 2a, most of the free distance FD is located inside the actual housing 34 of the drying box 22, and a substantial portion of the free distance FD is located inside the actual cooling zone 38. As illustrated in Fig. 2b, upper and lower blow boxes 47, 48 may even be arranged downstream of guide roller arrangement 54. The fact that a substantial portion of the free distance FD is located inside the housing 34 makes it possible to design an arrangement 20 for drying a very wide cellulose pulp web, such as a pulp web 44 having a width W of 8-20 meters, without substantially increasing the total length of the arrangement 20, compared to a prior art arrangement drying a pulp web of a lower width. Of course the present arrangement 20 can be utilized also for drying a pulp web 44 of lower width, such as a width W of 2 to 8 meters, in which case a very compact and short arrangement is obtained. In addition to the free distance FD between the second guide roller 62 of the guide roller arrangement 54 to a support roller 74, it is also preferable that there is another free distance located upstream of the first guide roller 60 of the guide roller arrangement 54. Hence, there is preferably another free distance located between the lowest turning roll 51 and the first guide roller 60, said another free distance being preferably at least equal to the width W of the web 44.

Fig. 2a further illustrates how the pulp web 44, after having passed through the web position control unit 24 and the support roller 74 arranged downstream thereof, as seen with reference to the direction of forwarding the pulp web 44, is forwarded to the measurement station 26. The measurement station 26 includes a measurement beam 76 being supported by a

measurement rack 78 and comprising one or several measurement devices, such as moisture measurement devices, brightness measurement devices, basis weight measurement devices etc. The measurement beam 76 measures those various properties of the web 44 being passed through the station 26. The measurement rack 78 is, same as with the housing 34 of the drying box 22 and the web position control unit 24, mounted directly on a machine room floor 80. By "mounted directly on a machine room floor" is meant that no intermediate stands, vibration dampers, etc of a height of more than about 1 m are arranged between the machine room floor 80 and the respective rack 78, drying box 22, etc.

The web 44 is forwarded further to the web forwarding device 28. The web forwarding device 28 comprises a nip roller 82 and a drive roller 84 arranged vertically above each other and forming between them a nip 86 through which the web 44 is forwarded. The drive roller 84 is driven by a motor (not shown) and apply a traction force to the web 44, forcing the web through the drying box 22, the web position control unit 24 and the

measurement station 26. The rollers 82, 84 are arranged in a drive roller rack 88, which is mounted directly on the machine room floor 80.

The web 44 is further forwarded, above a pulp pit 90, from the web forwarding device 28 to the cutter 30 for being cut to sheets suitable for being baled. As alternative to being cut and then baled, the dried pulp may be collected on a so-called pope reeler on which a reel of dried pulp is formed.

The broke transfer device 32 is operated when an operation problem has occurred and pieces of pulp has gotten stuck inside the housing 34. The broke transfer device 32 comprises a pulp forwarding slide 92 which extends from the drive roller rack 88 to a lift 94 which can be moved vertically along the housing 34, as indicated by an arrow V. The pulp forwarding slide 92 is mounted on a slide stretching roller 96. The slide stretching roller 96 makes it possible to adapt the length of the pulp forwarding slide 92 to the present position of the lift 94, such that the slide 92 is always in a stretched condition when in use. When pulp pieces has gotten stuck inside the housing 34 an operator directs the lift 94 to be in line with that deck 40 at which pulp pieces have been stuck. The operator takes out pulp pieces from the deck 40 in question, puts the pulp pieces on pulp forwarding slide 92, and allows the pulp pieces to glide along slide 92, such that the pulp pieces fall into the pulp pit 90, as indicated by an arrow P. It could be noted that during such pulp cleaning procedure, there is no web 44 extending from the web forwarding device 28 to the cutter 30, giving a free passage for the pulp pieces to pass from the slide 92 and down into the pulp pit 90, in which the pieces of pulp are dissolved and utilized for producing a new pulp web.

The fact that the pulp web 44 leaves the second roller 62 of the guide roller arrangement 54 at an angle B of -45° to +45° to the horizontal plane, as illustrated with reference to Fig. 2b, makes it possible to arrange the measurement rack 78 and the drive roller rack 88 directly on the machine room floor 80. Thanks to this fact, the pulp forwarding slide 92 will slope from the lift 94 towards the pulp pit 90 also when the lift 94 is moved to the lower decks 40 of the drying box 22. This is, as illustrated in Fig. 1 , not possible in the prior art, where measurement station 6 and web pulling station 7 are located high above the ground, mounted on a separate stand, making it difficult in the prior art to transport pulp pieces removed from lower decks to the pulp pit 10. Returning to Fig. 2a, a vertical distance D between the machine room floor 80 and the web 44 is preferably less than 2 m, all the way from the guide roller arrangement 54 to the web forwarding device 28.

Fig. 2d is a schematic and enlarged side view, similar to that of Fig. 2b, and illustrates an optional third guide roller 63 added to the web position control unit 24. A guide roller arrangement 54 is arranged in a similar manner as described hereinbefore with reference to Figs. 2a-2c, and comprises a first guide roller 60, a second guide roller 62, and the third guide roller 63, which is arranged downstream of the second guide roller 62, as seen in the direction of forwarding the web 44, indicated by arrow T. The first, second and third guide rollers 60, 62, 63 are arranged, in this order as seen in the direction of forwarding the web 44, on a common roller rack 65. The roller rack 65 is mounted on a foundation 69 in such a manner that the roller rack 65 may slide horizontally on the foundation 69 along a horizontal arc, in a similar manner as described hereinbefore with reference to Figs. 2b and 2c concerning the roller rack 64 sliding on the foundation 66, in order to control the lateral position of the web 44. Upon controlling the lateral position of the web 44 all three rollers 60, 62 and 63 move together, since they are mounted on the common roller rack 65. As can be seen from Fig. 2d, the web 44 leaves second guide roller 62 at an angle of about 30° to the horizontal plane. Optional third guide roller 63, located downstream of roller 62, breaks the path of web 44, such that web 44 travels along a substantially horizontal path downstream of roller 63. The vertical level of web 44 is substantially the same downstream of third guide roller 63 as upstream of first guide roller 60.

Optional third guide roller 63 may be utilized in such cases where there is a desire to have the web 44 leaving guide roller arrangement 54 along a substantially horizontal path, i.e., at an angle to the horizontal plane of about 0°.

Fig. 3a illustrates an arrangement 120 for drying cellulose pulp in accordance with a second embodiment of the present invention. Fig. 3b illustrates an enlargement of the area 1Mb of Fig. 3a. Those parts of the arrangement 120 that are similar to the parts of arrangement 20 described hereinbefore with reference to Figs. 2a-2c have been given the same reference numbers and are not described in detail. The arrangement 120 comprises a drying box 122, a web position control unit 124, a measurement station 26, a web forwarding device 28, a cutter 30, and a broke transfer device 32.

The drying box 122 comprises a housing 134. Inside the housing 134 a drying zone 36 and a cooling zone 138 are arranged. The drying zone 36 comprises a number of drying decks 40 that are similar to those described hereinbefore with reference to Fig. 2a.

The cooling zone 138 comprises at least one cooling deck 46, in Fig. 3a two such cooling decks 46 are illustrated, each such deck 46 comprising a number of upper blow boxes 47 and lower blow boxes 48 that are arranged for blowing a cooling gas towards the cellulose pulp web 44.

At a first end 50 of the housing 134 a first column of turnings rolls 51 is arranged, and at a second end 52 of the housing 134 a second column of turning rolls 53 is arranged. The web 44 is turned around the turning rolls 51 , 53 when being transferred from one deck 40, 46 to another deck 40, 46 and when being transferred from the drying zone 36 to the cooling zone 138. The web position control unit 124 comprises a guide roller arrangement 54, two cameras 56, of which only one is visible in Fig. 3a, and a two light sources 58, of which only one is visible in Fig. 3a. The guide roller

arrangement 54 is arranged inside the housing 134, just below the second column of turning rolls 53. The cameras 56 and the light sources 58 are arranged just outside of the housing 134. In accordance with an alternative embodiment, the web position control unit 124 could be arranged with only one camera 56 and only one light source 58, since it is sometimes enough to keep track on just one of the lateral sides of the web 44.

Fig. 3b illustrates the web position control unit 124 in more detail. The guide roller arrangement 54 comprises a first guide roller 60 and a second guide roller 62 and functions in a similar manner as the guide roller

arrangement 54 described hereinbefore with reference to Figs. 2a-2c.

The first roller 60 and the second roller 62 of guide roller arrangement 54 of web position control unit 124 are located at substantially the same horizontal level, meaning that the web 44 will make two turns, firstly

downwards when passing the first roller 60, and secondly upwards when passing the second roller 62, as illustrated in Fig. 3b. The web 44 leaves the guide roller arrangement 54, in the direction of the arrow T, at an angle B to the horizontal plane of about +10° as illustrated in Fig. 3b, i.e., at an angle of 10° above the horizontal plane. Typically, the angle B would be from -45° to +45°, i.e., the web 44 would leave the guide roller arrangement 54 at an angle B in the range of from 45° below to the horizontal plane, to 45° above the horizontal plane. More often the angle B would be in the range of -30° to +30°, or even in the range of -15° to +15°.

In the embodiment illustrated in Fig. 3b the first and second guide rollers 60, 62 are mounted on a roller rack 64 which is mounted on an angled foundation 166. The roller rack 64 is, due to the foundation 166, tilted at an angle which is similar to the angle B, i.e., at an angle of about +10° to the horizontal plane. The roller rack 64 may slide on the foundation 166 along a tilted arc, having a central axis A, the central axis A being tilted about 10° to the vertical plane. Utilizing a tilted foundation 166 may be advantageous to the control of the lateral position of the web 44 when the angle B between the web 44 leaving guide roller arrangement 54 and the horizontal plane is from about 10° to about 45°, or from -10° to about -45°.

Fig. 3a illustrates a free distance FD being the distance from the second roller 62 of guide roller arrangement 54 to a nip 86 of the web forwarding device 28. The web forwarding device 28 comprises a nip roller 82 and a drive roller 84 arranged to generate a traction force to the web 44, forcing the web through the drying box 122, the web position control unit 124 and the measurement station 26. The rollers 82, 84 are arranged in a drive roller rack 88, which is mounted on the machine room floor 80.The free distance FD is preferably at least 0.5 times the width of the web 44. As can be seen from a reference to Fig. 3a, a part of the free distance FD is located inside the actual housing 134, and the rest of the free distance FD is located between the housing 134 and the web forwarding device 28.

As is illustrated in Fig. 3a a support roller 174 is located between the second roller 62 of the guide roller arrangement 54 and the nip 86 of the web forwarding device 28. The support roller 174 stabilizes the web 44 to decrease fluttering of the web 44 upon entry into the measurement station 26, such that reliable measurements are ensured.

Fig. 3b illustrates the support roller 174 in more detail. The support roller 174 is mounted on a support roller rack 175 which is mounted directly on a machine room floor 80, on which also the housing 134 and the guide roller arrangement 54 are mounted. The support roller 174 changes the path of the web 44 to a very limited degree. As illustrated in Fig. 3b, the support roller 174 changes the path, in the vertical direction, of the web 44 by an angle C of about + 3°. Typically, the angle C would be from -10° to + 10°, i.e., the support roller 174 would change the path of the web 44 in the range of from 10° below the path that the web 44 has after the second roller 62, to 10° above the path that the web 44 has after the second roller 62. More often the angle C would be in the range of -5° to +5°. Such a small change of path, i.e., less than 10°, and more often less than 5°, would not induce any web wrinkling, and would not interfere with the required free distance FD, although the support roller 174 is in fact located along the free distance FD, as illustrated in Fig. 3a. According to one embodiment, the support roller 174 could be provided with a very smooth surface, for example a chromium-plated surface, to obtain a minimum friction and, hence, a minimum interference with the web 44. Continuing with Fig. 3a, the measurement station 26 would normally perform most of the measurements on the web 44 in a contact-free, or at least low contact, manner. Hence, the measurement station 26 would not induce any web wrinkling, and would not interfere with the required free distance FD, although the measurement station 26 is in fact located along the free distance FD, as illustrated in Fig. 3a. Hence, the support roller 174 and the measurement station 26 will not result in a negative effect on the free distance FD required between the roller 62 and the nip 86. As long as the path of the web 44 is changed by less than +/-10⁰ in a vertical direction between the guide roller arrangement 54 and the web forwarding device 28, and the web 44 is not forwarded through any nip formed between rollers or similar device substantially restricting the lateral movement of the web 44, such forwarding is defined as a "direct" forwarding of the web 44 from the guide roller arrangement 54 to the web forwarding device 28.

The fact that a portion of the free distance FD is located inside the housing 134, and another portion of the free distance FD is located between the housing 134 and the web forwarding device 28, makes it possible to design an arrangement 120 for drying a very wide cellulose pulp web, such as a pulp web 44 having a width of 8-20 meters, without substantially increasing the total length of the arrangement 120, compared to arrangements drying pulp webs of a lower width. Furthermore, with the arrangement 120 the web position control unit 124 does not interfere with the cooling zone 138 and the upper and lower blow boxes 47, 48 arranged therein, meaning that the cooling effect of the cooling zone 138 will not be impaired by the fact that the web position control unit 124 is partly mounted inside the housing 134 of the drying box 122.

Fig. 3a further illustrates how the pulp web 44, after having passed through the web position control unit 124, the support roller 174, the measurement station 26, and the web forwarding device 28, is further forwarded, above a pulp pit 90, from the web forwarding device 28 to the cutter 30 for being cut to sheets suitable for being baled. The broke transfer device 32 is operated in substantially the same manner as described hereinbefore with reference to Fig. 2a, and comprises the same components. The fact that the pulp web 44 leaves the second roller 62 of the guide roller arrangement 54 at an angle B of -45° to +45° to the horizontal plane, as illustrated with reference to Fig. 3b, makes it possible to arrange the measurement rack 78 and the drive roller rack 88 directly on the machine room floor 80. Thanks to this fact, a pulp forwarding slide 92 of the broke transfer device 32 will slope from a lift 94 towards the pulp pit 90 also when the lift 94 is moved to the lower decks 40 of the drying box 122.

Fig. 4a illustrates an arrangement 220 for drying cellulose pulp in accordance with a third embodiment of the present invention. Fig. 4b illustrates an enlargement of the area IVb of Fig. 4a. Those parts of the arrangement 220 that are similar to the parts of arrangement 20 described hereinbefore with reference to Figs. 2a-2c have been given the same reference numbers and are not described in detail. The arrangement 220 comprises a drying box 222, a web position control unit 224, a measurement station 26, a web forwarding device 28, a cutter 30, and a broke transfer device 32.

The drying box 222 comprises a housing 234. Inside the housing 234 a drying zone 36 and a cooling zone 238 are arranged. The drying zone 36 comprises a number of drying decks that are similar to the drying decks 40 described hereinbefore with reference to Fig. 2a.

The cooling zone 238 comprises at least one cooling deck 46, in Fig. 4a two such cooling decks 46 are illustrated, each such deck 46 comprising a number of upper blow boxes 47 and lower blow boxes 48 that are arranged for blowing a cooling gas towards the cellulose pulp web 44.

The housing 234 comprises turning rolls 51 , 53 arranged in a similar manner as described hereinbefore with reference to Fig. 2a.

The web position control unit 224 is arranged just after the housing 234, as seen in the direction T of forwarding the web 44, and comprises a guide roller arrangement 54, two cameras 56, of which only one is visible in Fig. 4a, and a two light sources 58, of which only one is visible in Fig. 4a. Fig. 4b illustrates the web position control unit 224 in more detail. The guide roller arrangement 54 comprises a first guide roller 60 and a second guide roller 62 and functions in a similar manner as the guide roller arrangement 54 described hereinbefore with reference to Figs. 2a-2c.

The web 44 leaves the guide roller arrangement 54, in the direction of the arrow T, at an angle B to the horizontal plane of about +10° as illustrated in Fig. 4b. Typically, the angle B would be from -45° to +45°, i.e., the web 44 would leave the guide roller arrangement 54 at an angle B in the range of from 45° below to the horizontal plane, to 45° above the horizontal plane. More often the angle B would be in the range of -30° to +30°, or even in the range of -15° to +15°.

Fig. 4a illustrates a free distance FD being the distance from the second roller 62 of the guide roller arrangement 54 to a nip 86 of the web forwarding device 28. The web forwarding device 28 comprises a nip roller 82 and a drive roller 84 arranged to generate a drag to the web 44, forcing the web through the drying box 222, the web position control unit 224 and the measurement station 26. The rollers 82, 84 are arranged in a drive roller rack 88, which is mounted directly on the machine room floor 80. The free distance FD is preferably at least 0.5 times the width of the web 44.

As seen from a reference to Fig. 4a, the measurement station 26 is located between the guide roller arrangement 54 and the nip 86, i.e., along the free distance FD. The measurement station 26 would normally perform most of the measurements on the web 44 in a contact-free, or at least low contact, manner. Hence, the measurement station 26 would not induce any web wrinkling, and would not interfere with the required free distance FD, although the measurement station 26 is in fact located along the free distance FD, as illustrated in Fig. 4a.

The fact that the free distance FD is located between the housing 234 and the web forwarding device 28, the measurement station 26 not giving a negative impact on the free distance FD required between the roller 62 and the nip 86, makes it possible to design an arrangement 220 for drying a very wide cellulose pulp web, such as a pulp web 44 having a width W of 8-20 meters, with just a moderate increase in the total length of the arrangement 220, compared to arrangements drying pulp webs of a lower width. With the arrangement 220 the web position control unit 224 does not interfere with the cooling zone 238, meaning that the cooling effect of the cooling zone 238 will not be impaired by the web position control unit 224.

Fig. 4a further illustrates how the pulp web 44, after having passed through the web position control unit 224, the measurement station 26, and the web forwarding device 28, is further forwarded, above a pulp pit 90, from the web forwarding device 28 to the cutter 30 for being cut to sheets suitable for being baled.

The broke transfer device 32 is operated in substantially the same manner as described hereinbefore with reference to Fig. 2a, and comprises the same components. The fact that the pulp web 44 leaves the second roller 62 of the guide roller arrangement 54 at an angle B of -45° to +45° to the horizontal plane, as illustrated with reference to Fig. 4b, makes it possible to arrange the measurement rack 78 and the drive roller rack 88 directly on the machine room floor 80. Thanks to this fact, a pulp forwarding slide 92 of the broke transfer device 32 will slope from a lift 94 towards the pulp pit 90 also when the lift 94 is moved to the lower decks of the drying box 222.

Fig. 5 illustrates an arrangement 320 for drying cellulose pulp in accordance with a fourth embodiment of the present invention. Those parts of the arrangement 320 that are similar to the parts of arrangement 20 described hereinbefore with reference to Figs. 2a-2c have been given the same reference numbers and are not described in detail. The arrangement 320 is illustrated in Fig. 5 in a similar perspective as that of Figs. 2b and 3b. Those parts of the arrangement 320 that are not illustrated in Fig. 5 are similar if not identical to the corresponding parts of the arrangement 20 as illustrated in Fig. 2a.

Returning to Fig. 5, the arrangement 320 comprises a drying box 322, a web position control unit 324, a measurement station 26, a web forwarding device 28, a cutter (not shown), and a broke transfer device (also not shown). The drying box 322 comprises a housing 334. Inside the housing 334 a drying zone and a cooling zone are arranged in a similar manner as described hereinbefore with reference to Fig. 2a. The web position control unit 324 comprises a guide roller arrangement 354, at least one camera 56 and at least one light source 58. The guide roller arrangement 354 is arranged inside the housing 334, just below a second column of turning rolls 53. The camera 56 and the light source 58 are arranged just outside of the housing 334.

The guide roller arrangement 354 comprises a single guide roller 360 and functions according to a similar principle as the guide roller arrangement 54 described hereinbefore with reference to Fig. 2c, with the single guide roller 360 of guide roller arrangement 354 moving along an arc having its centre in the axis A.

The web 44 is forwarded between blow boxes 47, 48 and enters web position control unit 324 substantially horizontally, makes a turn upwards when passing the single guide roller 360, and leaves the guide roller arrangement 354, in the direction of the arrow T, at an angle B to the horizontal plane of about 30° as illustrated in Fig. 5. Typically, the angle B would be from -45° to +45°, i.e., the web 44 would leave the guide roller arrangement 354 at an angle B in the range of from 45° below to the horizontal plane, to 45° above the horizontal plane. More often the angle B would be in the range of -30° to +30°, or even in the range of -15° to +15°. It will be appreciated that the web 44 would need to make at least some turn around single guide roller 360, and hence encircle single guide roller 360 to some degree, to make it possible for the single guide roller 360 to control the lateral position of web 44. Hence, if the angle B is around 0°, for example in the range of -15° to +15°, it may be suitable to have one or more rollers arranged upstream of single guide roller 360 such that web 44 in such a case is forwarded towards single guide roller 360 at an angle. For example, if angle B is 0°, it would be suitable that the web 44 enters single guide roller 360 at an angle of for example 20-45° to the horizontal plane, such that the web 44 in such a case encircles the single guide roller 360 to a similar degree as illustrated in Fig. 5. With a single guide roller 360 it would be suitable that an angle SG, illustrated in Fig. 5, between web 44 entering single guide roller 360 and web 44 leaving single guide roller 360 is in the range of 100-160°, still being within the above specified range for the angle B. In the embodiment illustrated in Fig. 5 the single guide roller 360 is mounted on a roller rack 364 which is mounted on an angled foundation 366, in a similar manner as described hereinbefore with reference to Fig. 3b.

Returning to Fig. 5, the roller rack 364 is, due to the foundation 366, tilted at an angle which is similar to the angle B, i.e., at an angle of about 30° to the horizontal plane. The roller rack 364 may slide on the foundation 366 along a tilted arc, having a central axis A, the central axis A being tilted at an angle AE of about 60° to the horizontal plane. Utilizing the tilted foundation 366 may be advantageous to the control of the lateral position of the web 44 since the angle B between the web 44 leaving guide roller arrangement 354 and the horizontal plane is 30°, i.e., in the range of about 10° to about 45° as noted hereinbefore with reference to Fig. 3b.

Fig. 5 illustrates how the web 44 is forwarded directly from the guide roller arrangement 354 to the web forwarding device 28, along a free distance FD being the distance from the single guide roller 360 of guide roller arrangement 354 to a nip 86 of the web forwarding device 28. The free distance FD is preferably at least 0.5 times the width of the web 44. As can be seen from a reference to Fig. 5, a part of the free distance FD is located inside the actual housing 334, and the rest of the free distance FD is located between the housing 334 and the web forwarding device 28. The drying box 322, the web position control unit 324, the measurement station 26 and the web forwarding device 28 are all mounted directly on a common machine room floor 80.

The fact that a portion of the free distance FD is located inside the housing 334, and another portion of the free distance FD is located between the housing 334 and the web forwarding device 28, makes the arrangement 320 compact. The fact that the angle B is within the range of -45° to +45° makes the arrangement 320 low, such that a broke transfer device 32 of the type illustrated in Fig. 2a can be conveniently arranged. In accordance with a further alternative embodiment, the guide roller arrangement 354 comprising the single guide roller 360 could be arranged just outside of the housing 334, in a similar manner as the guide roller arrangement 54 of the arrangement 220 illustrated in Figs. 4a and 4b, making the arrangement slightly longer, but still quite low as seen in a vertical direction.

It will be appreciated that numerous variants of the above described embodiments are possible within the scope of the appended claims.

Hereinbefore it has been described, with reference to for example Fig.

2b, that the web 44 is forwarded above the first roller 60 and below the second roller 62 of the guide roller arrangement 54. It will be appreciated that it would be equally possible to forward the web 44 below the first roller 60 and above the second roller 62, after a suitable vertical elevation of the roller rack 64.

Hereinbefore it has been described, with reference to Figs. 2b and 2c, that the roller rack 64 may slide along foundation 66 along an arc having its centre in the vertical axis A. It will be appreciated that roller rack 64 could, as alternative, be moved in another manner to control the lateral position of the web 44. For example, the roller rack 64 could be turned around a vertical axis which is located in one lateral end of the roller rack 64, or a vertical axis which is located at the centre of the roller rack 64 to achieve control of the lateral position of the web. According to a further alternative, the roller rack 64 could be turned around a horizontal axis located at one lateral end of the roller rack 64, or at the centre of the roller rack 64. It would also be possible to control the position of one or more guide rollers 60, 62, 63, 360 independently from the roller rack 64. Hence, control of the lateral position of the web 44 can be achieved in many different manners using at least one guide roller 60, 62, 63, 360, the position of which can be controlled in the vertical and/or horizontal direction.

Hereinbefore it has been described, with reference to Figs. 2a and 2b, that the guide roller arrangement 54 may be installed inside the cooling zone 38 of the drying box 22. It will be appreciated that it in case the drying box does not comprise any cooling zone, the guide roller arrangement 54 could be installed, according to similar principles, in the drying zone of such a drying box.

Hereinbefore it has been described that the drying box 22 comprises a housing 34 in which drying decks 40, and, optionally, cooling decks 46, are arranged for drying a pulp web in accordance with the air borne web principle. In accordance with this principle the web is forwarded in a horizontal direction between upper and lower blow boxes 42, 43, 47, 48 blowing air towards the web. It will be appreciated that an arrangement for drying cellulose pulp could, as alternative, include a drying box operating in accordance with another principle. One example of such another principle is the so-called vertical web dryer in which the web is forwarded, in a vertical direction, between blow boxes. An example of a dryer operating in accordance with the last-mentioned principle is described in US 6,014,818. As described in that document, upper and lower turning rolls are arranged in a drying box to make the web travel vertically through a number of vertical drying decks, and/or cooling decks between blow boxes, called "jet boxes" in US 6,014,818. A web position control unit 24; 124; 224; 324 of one of the types described in the present document with reference to Figs. 2a to 5 could be arranged inside, or just outside, of the housing of a drying box of a vertical web dryer to control the lateral position of the web leaving the vertical web dryer.

Claims

1 . Arrangement for drying cellulose pulp, the arrangement comprising a drying box (22; 122; 222; 322), a web position control unit (24; 124; 224; 324), which is operative for controlling the lateral position of a web (44) of cellulose pulp dried in the drying box (22; 122; 222; 322), and a web forwarding device (28), which is operative for forwarding the web (44) of pulp through the drying box and through the web position control unit,

c h a r a c t e r i s e d in the web position control unit (24; 124; 224; 324) being arranged upstream, as seen with respect to the direction (T) of forwarding the web (44), of the web forwarding device (28), and comprising a guide roller arrangement (54; 354) comprising at least one guide roller (60, 62, 63; 360) and being operative for delivering a web (44) of pulp, the lateral position of which has been controlled, at an angle (B) of -45° to +45° to the horizontal plane.

2. Arrangement according to claim 1 , wherein the guide roller arrangement (54) comprises a first guide roller (60) and a second guide roller (62), with the second guide roller (62) being located downstream of the first guide roller (60) as seen in the direction (T) of forwarding the web (44).

3. Arrangement according to any one of the preceding claims, wherein the guide roller arrangement (54; 354) is arranged inside a housing (34; 134; 334) of the drying box (22; 122; 222).

4. Arrangement according to any one of the preceding claims, wherein the drying box (22) comprises at least one deck (40; 46) comprising blow boxes (42, 43; 47, 48) being operative for blowing a gas towards the web (44), the guide roller arrangement (54) being arranged in said deck (40; 46).

5. Arrangement according to claim 4, wherein blow boxes (47, 48) are arranged in said at least one deck (46) both upstream and downstream of said guide roller arrangement (54).

6. Arrangement according to any one of claims 4-5, wherein said deck (46) is included in a cooling zone (38) of the drying box (22), said cooling zone (38) being operative for cooling the dried web (44).

7. Arrangement according to any one of the preceding claims, wherein the drying box (122; 322) comprises at least one column of turning rolls (53) around which the web (44) of pulp may be turned when being forwarded between decks (40; 46) included in the drying box (122; 322), the guide roller arrangement (54; 354) being arranged below said column of turning rolls (53).

8. Arrangement according to any one of the preceding claims, wherein at least a portion of a free distance (FD) needed for the web (44) downstream of the guide roller arrangement (54; 354) is arranged inside a housing (34; 134; 334) of the drying box (22; 122; 322).

9. Arrangement according to any one of claims 1 -2, wherein the guide roller arrangement (54) is arranged downstream of the drying box (234), as seen in the direction (T) of forwarding the web (44).

10. Arrangement according to any one of the preceding claims, wherein the web (44) is forwarded directly from the guide roller arrangement (54; 354) to the web forwarding device (28), the path of the web (44) being changed less than +/-10⁰ in a vertical direction between the guide roller arrangement (54; 354) and the web forwarding device (28).

1 1 . Arrangement according to any one of the preceding claims, wherein the drying box (22; 122; 222; 322), the web position control unit (24; 124; 224; 324), and the web forwarding device (28) are all mounted directly on a common machine room floor (80).

12. Arrangement according to any one of the preceding claims, wherein the guide roller arrangement (54; 354) is operative for delivering a web (44) of pulp, the lateral position of which has been controlled, at an angle (B) of -30° to +30° to the horizontal plane.

13. A method of drying a cellulose pulp in an arrangement comprising a drying box (22; 122; 222; 322), a web position control unit (24; 124; 224; 324), which is operative for controlling the lateral position of a web (44) of cellulose pulp dried in the drying box (22; 122; 222; 322), and a web forwarding device (28), which is operative for forwarding the web (44) of pulp through the drying box and through the web position control unit,

c h a r a c t e r i s e d in forwarding the dried pulp web (44) to a guide roller arrangement (54; 354) being included in the web position control unit (24; 124; 224; 324) and comprising at least one guide roller (60, 62, 63; 360),

controlling the lateral position of the web (44) by means of the guide roller arrangement (54; 354), and

delivering the web (44) from the guide roller arrangement (54; 354) at an angle (B) of -45° to +45° to the horizontal plane.

14. A method according to claim 13, further comprising forwarding the web (44), after having passed the guide roller arrangement (54; 354), along a free distance (FD), along which the path of the web (44) being changed less than +/-10" in a vertical direction, at least a portion of said free distance (FD) being located inside a housing (34; 134; 334) of the drying box (22; 122; 322).

15. A method according to any one of claims 13-14, further comprising forwarding the web (44) directly from the guide roller arrangement (54; 354) to the web forwarding device (28), the path of the web (44) being changed less than +/-10" in a vertical direction when being forwarded from the guide roller arrangement (54; 354) to the web forwarding device (28).

16. A method according to any one of claims 13-15, further comprising forwarding the web (44) through the guide roller arrangement (54) which comprises a first guide roller (60) and a second guide roller (62), with the second guide roller (62) being located downstream of the first guide roller (60) as seen in the direction (T) of forwarding the web (44).

17. A method according to any one of claims 13-16, wherein the web (44) is forwarded from the guide roller arrangement (54; 354) to the web forwarding device (28) at a vertical distance (D) of less than 2 m above a machine room floor (80) on which the guide roller arrangement (54; 354) and the web forwarding device (28) are mounted.