The invention relates to a method for observing incidents in an end part area of a pulp dryer, a pulp dryer and use of a monitoring member according to the preambles of the independent claims presented below.

In a pulp dryer, a web formed of pulp, i.e. a pulp web, is conveyed along a multi- layered path by floating it on an air- cushion formed by blow nozzles. The blow nozzles are arranged in several superposed, typically horizontal nozzle levels having almost the length of the pulp dryer. The pulp web is typically brought into the pulp dryer through its first end, the so-called wet end. Then the pulp web is conveyed on the uppermost nozzle level of the pulp dryer to the second end of the device. In the ends of the device there are typically turn rolls, over which the pulp web is turned each time to the next, lower nozzle level. When the pulp web is brought to the lowest nozzle level of the pulp dryer, the pulp web is removed from the pulp dryer, typically through the second end of the pulp dryer. The pulp dryer typically has 15-30 nozzle levels, and the length of the pulp web inside the pulp dryer may be up to one kilometre. The gas blown from the blow nozzles is typically hot air, the blow air generally having a temperature of 120-170 °C. When entering the pulp dryer, the pulp web typically has a dry solids content of 48-54 %. The dry solids content of the pulp web leaving the pulp dryer is typically 85-95 %, most commonly approximately 90 %. The pulp web may have a width of 12 m, typically 3-10 m. The pulp web is typically conveyed at a speed of 140-220 m/min in the pulp dryer.

A typical prior art pulp dryer thus comprises an actual drying section, where the pulp web is dried by air floatation drying with hot air jets or the like, and at least one, usually several recirculation fans arranged adjacent to the actual drying section, with which recirculation fans moist air is removed from the actual drying section, and with which heated air is blown as drying air into the actual drying section, and heating devices, with which the removed moist air is heated before it is returned as drying air into the actual drying section. Pulp dryer typically has, in both its end parts, several superposed rows of access doors, which rows comprise a number of adjacent access doors. The access doors are closed during normal operation of the pulp dryer, and during maintenance, such as after a web break, the access doors may be opened. Via an access door, it is possible to perform operations for example at the turn rolls. Pulp dryers typically have, in both end parts, a moving maintenance bridge having the width of the entire dryer, on which maintenance bridge a process operator may work, and from which he may be connected to and in contact with the inner parts of the pulp dryer when one or more rows of access doors are opened.

Web break situations are often problematic, since locating a web break inside a pulp dryer is difficult. In practice the process operators are forced to look for the disturbance point by opening several access doors in different rows and examining visually the inner part of the pulp dryer and turn rolls. Corresponding problems occur also in tail threading situations when a narrow pulp web or threading tail breaks. In current pulp dryers it is also practically impossible to predict possible problems during tail threading. One object of the present invention is to reduce or even completely eliminate the above-mentioned problems appearing in the prior art.

One object of the present invention is to provide a method, with which monitoring of incidents, for example locating a web break, in an end part area of a pulp dryer may be performed from the outside of the pulp dryer without opening the access doors.

Another object of the present invention is a pulp dryer, where the monitoring of incidents in the end part area of the pulp dryer is easy and occurs in real-time.

One object of the present invention is additionally to provide at least to some extent a prediction for possible disturbance situations during tail threading. The above-mentioned disadvantages are eliminated or reduced, and the above- mentioned objects are attained with the present invention, which is characterised by what is defined in the characterising parts of the independent claims presented hereafter.

Some preferred embodiments according to the invention are disclosed in the dependent claims presented hereafter.

A typical method for observing incidents in an end part area of a pulp dryer, especially in connection with tail threading or web break, comprises

- arranging at least one machine vision unit in connection with a first end part of the pulp dryer,

- directing the machine vision unit toward the inner part of the pulp dryer,

- monitoring the incidents in the end part area of the pulp dryer with the machine vision unit, and

- delivering monitoring data obtained from the machine vision unit to outside the pulp dryer.

A typical pulp dryer according to the invention is suitable for drying a pulp web or the like, and comprises

- a number of drying levels, whereby an individual drying level comprises a number of drying groups for drying and supporting the web to be dried,

- a first end part, where a roll tower is arranged, which comprises several superposed parallel turn rolls, whereby

at least one machine vision unit is arranged in connection with the first end part, which machine vision unit is directed to monitor the end part area of the pulp dryer.

Typically according to the invention a monitoring member is used for monitoring the end part area of the pulp dryer, which monitoring member is a machine vision unit.

Now it has surprisingly been found that by arranging in connection with the end part of the pulp dryer at least one machine vision unit, which is directed to monitor incidents in the end part area of the pulp dryer inside the pulp dryer, and by delivering monitoring data obtained from the machine vision unit to outside the pulp dryer, reliable information regarding the incidents at the end part area of the pulp dryer may easily and simply be obtained. The process operators are for example able to monitor incidents at the turn rolls of the pulp dryer from a monitor in a control room at a distance from the pulp dryer. For example, a web break during tail threading or a cut off of the threading tail may easily be located based on the monitoring data obtained from the machine vision unit, because the occurrence of the web break may be limited between any two superposed turn rolls. A normal tail threading situation may thus be observed at the first turn roll, while for example the narrow end of the pulp web or the threading tail is no longer observed at the subsequent turn roll. Thus time is saved in locating the disturbance point, whereby the disturbance incident itself also usually is shorter. The invention may also be used to predict to some extent possible future disturbance situations, for example if the narrow end of the pulp web is observed to wander on the turn rolls toward the outer edge of the roll, whereby there is a danger that it may "collide" with the edge of the pulp dryer. When possible disturbance situations may be assessed in advance, it is also possible to take anticipatory measures, by which the emergence of the disturbance situation may possibly be completely prevented.

The machine vision unit is arranged in connection with the first end part of the pulp dryer, for example in the end wall of the pulp dryer or in connection with the ceiling structures of the pulp dryer, and it is directed to monitor incidents in the inner part of the pulp dryer.

According to one preferred embodiment of the invention, the machine vision unit is a process camera. The process camera functioning as a machine vision unit may for example be a digital matrix CCD camera, a high speed camera or a pinhole camera. The machine vision unit may comprise a protective casing, wherein a cooling and/or cleaning system is arranged for cooling and/or cleaning functions. The machine vision unit may be cooled and/or cleaned by arranging through the protective casing of the machine vision unit an air flow, which cools the parts of the machine vision unit. In the protective casing of the machine vision unit may, if necessary or alternatively, be arranged also a cleaning system, with which the imaging opening or lens of the machine vision unit may be cleaned, such as washed, blown or wiped clean, when necessary or at predetermined time intervals. In practice any existing process camera or process imaging unit, which can withstand the conditions prevailing inside the pulp dryer in its end part, is suitable for use in the present invention. Such process cameras and process imaging units are known as such to a person skilled in the art. If necessary, separate lighting units, such as lamps, lights or the like, may be arranged in the end part of the pulp dryer, inside the pulp dryer, for improving the illumination in the end part area of the pulp dryer. The use of separate lighting units is however not necessary for the invention. In one embodiment the lighting unit, such as lamp, may be integrated in connection with the machine vision unit.

The used machine vision unit preferably has a wide imaging area, typically the height of the imaging area is > 1 m and the width is > 2 m. In this context the imaging area means the area, from which the machine vision unit is able to observe objects, phenomena and incidents. In one preferred embodiment of the invention the incidents of at least one, preferably several superposed and parallel turn rolls located in the end part of the pulp dryer are monitored with one machine vision unit. In connection with the first end part may be arranged 1-5, preferably 3-4 machine vision units, each of which is directed to monitor at least one, preferably several turn rolls. Each machine vision unit thus monitors a certain end part area of the pulp dryer inside the pulp dryer, preferably more than one turn roll located in the end part of the pulp dryer. When the total number of machine vision units remains relatively low, the investment costs may also be kept at a low level and simultaneously a comprehensive total monitoring area may still be achieved in the end part area of the pulp dryer.

In one embodiment at least two, preferably several machine vision units, such as cameras, are arranged in connection with the first end part of the pulp dryer, at a distance from each other in the height direction of the end part. In one preferred embodiment the machine vision units are arranged in connection with the end part so that machine vision units, which are adjacent to each other in the vertical direction, are placed on their own imaginary vertical lines. The machine vision units are thus preferably arranged in connection with the end part so that in the vertical direction the first machine vision unit is placed at a first distance from the side edge of the end part of the pulp dryer and the second machine vision unit is arranged at a second distance from the side edge of the end part of the pulp dryer, the first and second distances being different from each other. When using several machine vision units, they are thus not preferably all placed on the same vertical line, but they are placed in different points in the cross direction of the end part of the pulp dryer. Thus a maximal imaging area may be ensured. In one embodiment of the invention each machine vision unit is placed on its own imaginary vertical line. At least one reflecting member, such as a mirror, may also be arranged in connection with the first end part of the pulp dryer, for expanding the imaging area of the machine vision unit, i.e. for maximising the monitoring area of the machine vision unit in connection with the end part. The web arriving at or leaving the turn roll in the end part of the pulp dryer may be monitored with the aid of the reflecting member. The reflecting member is placed and directed so that it reflects incidents on a certain turn roll or on certain turn rolls to the imaging area of the machine vision unit. The reflecting member may for example be placed beneath the rotating axis of the turn roll, preferably beneath the lower edge of the turn roll, whereby information about incidents on the lower part of the turn roll are obtained with the reflecting member. Normally it is difficult to obtain information visually about incidents on the lower part of the turn roll, but with the aid of this embodiment even this problem may be solved. The reflecting member may also be placed so that the floating of the pulp web in the immediate vicinity of the end part of the pulp dryer may be evaluated with its aid, i.e. the distance of the pulp web from the lower nozzles of the drying group of the drying level near the turn roll. With the aid of a reflecting member more than one turn roll may easily be monitored and observed, even if the imaging area of the machine vision unit would be narrow, or incidents on even more turn rolls may be monitored with a machine vision unit with a wide imaging area. If the reflecting member is a mirror, it may be cut in a suitable manner to reflect and turn the incidents occurring on the turn roll to a desired direction. Cleaning member may, if necessary, be arranged in connection with the reflecting member, for cleaning the reflecting member when necessary or at predetermined time intervals. With the aid of the cleaning member the reflecting member may be washed, blown or mechanically wiped or brushed clean, either when needed or at predetermined time intervals.

In one embodiment at least two, preferably several reflecting members are arranged in connection with the first end part of the pulp dryer, at a distance from each other in the height direction of the end part. Typically there may be for example 1-10 reflecting members. In one preferred embodiment the reflecting members are arranged in connection with the end part so that reflecting members, which are adjacent to each other in the vertical direction, are placed on their own imaginary vertical lines. The reflecting members are thus preferably arranged in connection with the end part so that the first reflecting member in the vertical direction is placed at a first distance from the side edge of the end part of the pulp dryer and the second reflecting member is arranged at a second distance from the side edge of the end part of the pulp dryer, the first and second distance being different from each other. When using several reflecting members, they are thus not preferably all placed on the same vertical line, but they are placed in different points in the cross direction of the end part of the pulp dryer. Thus a maximal imaging area may be ensured. In one embodiment of the invention each reflecting member is placed on its own imaginary vertical line.

In one embodiment of the invention the machine vision unit is in functional connection with a central unit and delivers monitoring data to it from the end part area of the pulp dryer. The central unit may be, for example, a separate or inseparable part of the monitoring and control system of the pulp dryer. Monitoring data obtained from a machine vision unit or several machine vision units may be used for adjusting other monitoring and/or control parameters of the pulp dryer. The monitoring data obtained from the machine vision unit may be used to adjust for example a device for guiding the web in the cross direction, such as a guide roll, or a distance adjuster of the turn rolls in the roll towers. In one embodiment of the invention the floating of the pulp web on the drying nozzles of the drying group of the drying level situated next to the end part of the pulp dryer is evaluated with the aid of the monitoring data delivered from the machine vision unit.

The central unit may comprise a memory unit and/or analysis means for analysing the monitoring data. Monitoring data delivered from a machine vision unit or several machine vision units may be stored in the memory unit of the central unit. When a web break or other disturbance occurs, the monitoring data stored in the memory unit may be used for locating the disturbance point and/or for ascertaining the cause of the disturbance. Thus information can better than before be obtained about causes leading to web breaks or other process disturbances, whereby their occurrence may be actively prevented. In one embodiment of the invention monitoring data delivered to the central unit and/or stored in its memory unit is analysed with analysing means, and operating parameters of the pulp dryer are changed based on the obtained analysis data. Different existing and suitable image analysing programs and methods may be used as analysing means. By analysing the monitoring data it is maybe also possible to predict future disturbances, and prevent a possible disturbance by changing the operating parameters of the pulp dryer.

The invention is described in more detail below with reference to the enclosed schematic drawings, in which

Figure 1 shows an end part area of a pulp dryer according to one embodiment of the invention seen from the side,

Figure 2 shows an end part of a pulp dryer according to one embodiment of the invention seen in the machine direction,

Figure 3 shows an end part area of a pulp dryer according to one embodiment of the invention seen from the side, Figure 4 shows an end part area of a pulp dryer according to one embodiment of the invention seen from the side. Figure 1 shows one embodiment of the invention seen from the side of a pulp dryer. A number of access doors 3, 3' are arranged in the end wall 2 of the pulp dryer 1. Typically two access doors 3, 3' are arranged for each turn roll 4, 4', which access doors are in Figure 1 shown opened. The turn rolls 4, 4' are arranged parallel and superposed, and their purpose is to turn the pulp web 5 from one drying level to the next. In the end wall 2 of the pulp dryer 1 is arranged a camera 6, with which incidents in connection with the turn rolls 4, 4' may be observed. The wide imaging area of the camera 6, due to which the camera 6 observes incidents on the turn rolls 4, 4', is shown with lines A and B. Figure 2 shows an end part of a pulp dryer according to one embodiment of the invention seen in the machine direction. A number of turn rolls 4, 4', 4" are arranged in the end part of the pulp dryer 1 , which turn rolls are arranged parallel on top of each other. Machine vision units 7, 7', 7", 7"' are arranged in the end part of the pulp dryer, by means of which machine vision units incidents in connection with the turn rolls 4, 4', 4" of the pulp dryer 1 may be observed. A group of the machine vision units 7, T are arranged in the upper part of the end part of the pulp dryer 1 and a group of the machine vision units 7", 7"' are arranged in the middle part of the end part of the pulp dryer 1. A number of reflecting members 8, 8', 8" are also arranged in the end part of the pulp dryer, for maximising the imaging area of the machine vision units 7, 7', 7", 7"'. With the aid of the reflecting members 8, 8', 8", incidents beneath the central axis of the turn rolls 4, 4', 4" may for example be observed more efficiently. The reflecting members 8, 8', 8" are not placed on the same vertical line, but they are placed diagonally in relation to each other in the vertical direction, at differing distances from the side edge V of the pulp dryer !

Figure 3 shows one embodiment of the invention seen from the side of a pulp dryer. The reflecting members 8, 8', 8", 8"' are arranged in connection with the end wall 2 of the pulp dryer 1 , to reflect incidents beneath the central axis of the turn rolls 4, 4', 4" to the machine vision unit 7.

Figure 4 shows one embodiment of the invention seen from the side of a pulp dryer. Lighting units 9, 9', 9", 9"' are arranged in connection with the end wall 2 of the pulp dryer 1 , to make the illumination more efficient on turn rolls 4, 4', 4" located in the end part of the pulp dryer 1. Incidents in the end part of the pulp dryer 1 , especially incidents occurring on the turn rolls 4, 4', 4", are monitored and observed with a machine vision unit 7 arranged in the upper part 1 ", i.e. ceiling structures, of the pulp dryer 1.

It is apparent to a person skilled in the art that the invention is not limited exclusively to the examples presented above, but that the invention may vary within the scope of the claims presented below.