WO2017060046A1

WO2017060046A1 - Method and system for determining the hydraulic/mechanical loading of cellulose webs

Info

Publication number: WO2017060046A1
Application number: PCT/EP2016/071550
Authority: WO
Inventors: Helmuth HARRER; Thomas Kefer; Christoph SPIELMANN
Original assignee: Andritz Ag
Priority date: 2015-10-05
Filing date: 2016-09-13
Publication date: 2017-04-13
Also published as: UY36933A

Abstract

The invention relates to a method for assessing the hydraulic/mechanical loading of a cellulose web during production. The method is primarily characterized in that, by means of an optical system, a measured variable is formed which describes the level of unevenness or the depths of the furrows in the cellulose web. The invention further relates to a system for carrying out the method, in which an optical system comprising an illumination device (19), a camera (17), and a control system is provided. By using such a method and such a system, the causes of breaks and delaminations of cellulose webs can be detected at an early time and can be counteracted accordingly in order to prevent breaks or delaminations.

Description

METHOD AND APPENDIX FOR DETERMINING THE

HYDRAULIC / MECHANICAL TREATMENT OF PULLEYS

The invention relates to a method and a system for assessing the

Hydraulic / mechanical loading of a pulp web during production in a pulp drying plant consisting of a web formation part, a press part and a thermal drying plant, with the aim of predicting and avoiding web break.

Pulp is a raw material among other things for the paper industry and is produced on plants with up to several thousand tons per day. The investment volume for these plants can amount to several hundred million euros.

The production process is similar to papermaking. After recovering the pulp fibers in a cooking process, a pulp suspension is sprayed onto screens or transport felts. The pulp is now transported and dewatered along the machine at speeds of up to 300 m / min on the wire or between sieves and felts. During transport, the pulp continuously loses water. In the course of the wet part (forming and pressing zone) of the production machine, the pulp passes through several dewatering and

Press stages with the aim of continuously reducing the water content. While in the forming zone usually gentle drainage elements by means of surface load

(volumetric displacement in wedge-shaped elements, gravitational and / or vacuum-assisted dewatering tables by means of perforated plates or strips), the pressing stages consist of roller pairs which form a gap through which the pulp is transported under high pressure.

Rollers are often used to improve drainage performance

Vacuum suction, radial bores and / or executed with grooves in the circumferential direction.

After the pulp has passed through the pressing stages another takes place

Reduction of the dry content by thermal drying. After reaching a predetermined final dry content typically 90% - 95%, but also about it, the pulp web is cut into sheets, stacked and pressed into bales. In contrast to papermaking, the surface texture is the

Zellstoffbahn of subordinate importance .. The most important optimization criterion in pulp production is to achieve the highest possible production capacity in compliance with the Endtrockengehaltes a given plant without that the pulp web breaks or splits into layers (delamination) and the web breaks. Tears thus lead to an unwanted and costly

Interrupting production.

The basic strength of a pulp web in terms of demolition and delamination is largely determined by the type of wood, fiber texture, basis weight, the

Production speed, machine settings, added chemicals and condition of drainage elements as well as felts and sieves. These parameters are difficult to determine during the production process, variable and provide no immediate indication of impending demolition due to reduced web strength or delamination.

In the dewatering elements, the pulp web is often loaded too high hydraulically and thereby destroyed. Above all, when passing through a press nip, the pulp web is subjected to adjustable line pressures which lead to a pressure gradient in the production direction and force the water out of the gap. With increasing production speed and increasing

Line pressure, for example, increases this pressure gradient on the inlet side of the gap and leads to ever greater flow velocities of the water and forces on the fibers within the pulp web.

Depending on the basic strength and fiber composition of the pulp web, weaker binding fibers are washed away by the flow and re-accumulate at points of lower compressive forces. There are channels between increasingly dense fiber accumulations in which the flow rate is additionally increased and favors the further leaching of fibers.

These resulting vulnerabilities are increasing with increasing

Production speed and increasing line pressures increasingly pronounced and are seen as the actual cause of web tear, demolition and delamination.

Weak spots in the pulp web are also caused by unclean

Edge trimming eg due to wear of the water jet nozzles as well as through Air pockets due to intake air due to wear on seals. Both weakens the pulp web and leads to tears, in particular in the edge region and as a result of more frequent breaks in the pulp web.

Depending on the basic strength of the pulp web and on the condition of the pulp web

Production machine, these weaknesses form at higher or lower production speeds and line pressures and therefore form a largely independent of other parameters overall criterion for the load on the pulp web.

The visual appearance of the pulp web thus changes at

increasing load from a smooth structure to an uneven, nodular structure with different depths depending on the load, up to cracks and holes in the pulp web.

The object of the invention is to detect the degree of unevenness or depth of the furrows, the unevenness of the edge trimming and the number of thin spots and in particular cracks in the edge area by measurement and the

Production speed or other influencing variables to regulate so that a predetermined setpoint of these variables is maintained as possible and thus the maximum production capacity of the plant is achieved under the given boundary conditions.

The invention is characterized in that an optical system simultaneously detects a plurality of parameters and forms therefrom measurement variables which describe the state of the pulp web, in particular the degree of unevenness or the depths of furrows with regard to the strength of the pulp web.

A favorable development of the invention is characterized in that both parameters of the pulp web and the edge of the pulp web are detected simultaneously. This allows several influencing parameters to be recorded simultaneously with one measuring device.

An advantageous embodiment of the invention is characterized in that the measurement of the parameters by the optical system takes place after a press part before the thermal drying plant. This allows prompt reactions to changes in the railway structure. A favorable embodiment of the invention is characterized in that the pulp web illuminated from the top and with a camera the

Intensity distribution of the translucent light is detected as transmitted light on the underside.

An advantageous development of the invention is characterized in that the measured variable for describing the unevenness of the pulp web through the

Intensity difference of the translucent light between light and dark areas is formed, and also for determining the intensity difference, the standard deviation of the intensity of the average over a certain area can be formed as a measure.

A favorable development of the invention is characterized in that additionally local peak values of the intensity are taken into account, the intensity preferably being normalized to the mean value before the brightness differences are calculated.

An advantageous embodiment of the invention is characterized in that one or more laser lines are projected onto the pulp web at a certain angle, wherein the deviation of the projected laser line or lines from the straight line determined by the camera is used as a measure of the unevenness of the pulp web.

A favorable embodiment of the invention is characterized in that the determination of the degree of unevenness is carried out in a time-sequential, traversing across the width of the pulp web.

An alternative embodiment of the invention is characterized in that the determination of the degree of unevenness parallel in time through several

juxtaposed optical systems, in particular camera systems, is performed.

The invention also relates to a system for the evaluation of

Hydraulic / mechanical loading of a pulp web during production in a pulp drying plant consisting of a web formation part. This is characterized in that an optical system consisting of a

Lighting device, a camera and a control system is provided, which is arranged after a press part in front of the thermal drying plant. An advantageous development of the invention is characterized in that the illumination on the upper side and the camera are arranged on the underside of the pulp web. Thus, the camera can always work in the area that is not affected by the steam of the web. A favorable embodiment of the invention is characterized in that in addition to the illumination device, a laser unit is provided. Thus, on the one hand, the unevenness of the pulp web can be detected, on the other hand, the position of the optical system for the measurement can be set optimally.

An advantageous development of the invention is characterized in that a fork-shaped device is provided, wherein the pulp web runs between the two arms of the fork and advantageously the fork-shaped device in the vertical and horizontal directions can be moved.

To avoid web break or delamination is primarily the

Production speed reduced if a previously set set value for the unevenness of the pulp web is exceeded.

Advantageously, by changing other process parameters empirically, the production speed can not reduce the influence of these

Parameters are determined on the unevenness of the pulp web (model). In consequence, a model-based controller first uses those parameters, taking into account the process engineering limits for the control, which do not reduce the production speed. So it is possible to build up a knowledge of experience and / or rules and to automatically categorize typical manifestations in the pictures. The categories can either be defined as a rule or automatically formed by learning behavior. A combination is also conceivable.

The visual appearance of the pulp web thus changes at

increasing load from a smooth structure 8, 11 to an uneven nodular structure 10,13 with different depth depending on the load, up to holes and tears 16 in the pulp web.

Analogously, the detection of the parameters described above takes place after the last pressing stage 5, since only then no further significant mechanical stresses are to be expected, which is the strength of the pulp web reduce. Recording after drying 3 proves to be unfavorable since the parameters can only be determined after a delay of several minutes.

Immediately after the last pressing stage 5, the pulp web is due to the design obliquely upward 7 and after a deflection perpendicular 6 up to the dryer 3 out. The vertical part 6 of the pulp web is dense on both sides

surrounded by rising vapor and unsuitable for visual inspection.

In the obliquely upward leading portion 7, the top of the pulp web 18 is covered by dense vapor mist, which also does not allow optical inspection with sufficient accuracy. At the bottom, the vapor rises in particular at the edges upwards and thus forms in the edge region a zone which is sufficiently free of condensing vapor to allow an optical inspection of the surface with the required resolutions <0.2 mm.

The inspection of the weak points in the pulp web is carried out by

Camera system in transmitted light in the same way as the visual inspection in the laboratory. The invention describes a device in combination with a selected position on the plant which makes it possible under the described environmental conditions to determine the above-described weak spots of the pulp web in operation in comparable quality as in the laboratory.

The camera 17 is at the edge, below the pulp web at an angle

ascending part 7 of the pulp web 18 mounted. The lighting 19 is mounted on top of the pulp web 8. While the development of steam in the area above the pulp web has a positive effect on a uniform illuminance, mounting the camera at a considerable distance below the pulp web prevents condensation of moisture on the lens.

The image section is selected so that the web edge 15 can be seen and its position in the image can be measured. The edge 15 differs by a dark brightness value from the very bright area outside the pulp web. The deviation of the edge line 15 from the straight line shows the quality of the

Edge trimming with small deviations corresponding to a clean cut. On the underside of the pulp web, one or more laser lines 14 are projected onto the pulp web. The laser 20 is mounted at a certain angle to the camera 17, so that the deviation of the line from the straight line

Surface roughness can be calculated. Weaknesses of the pulp web show in transmitted light as lighter areas where the brightness is a measure of the weakening of the pulp web. According to their nature, the bright areas are classified as cracks (elongated thin objects) or bubbles (large area objects) and counted. All sizes described enter together

State image of the pulp web, which is closely correlated with the probability of demolition.

The position of the pulp web changes operationally in the vertical direction as well as in the horizontal direction. To compensate for these movements is the

Device automatically movable in these two directions. The vertical adjustability ensures that the camera and the laser are always in focus and that the illumination intensity remains constant due to the constant distance to the pulp web. The horizontal adjustability ensures that the web edge is always visible and the average brightness changes due to unequal coverage. The invention will now be described by way of example with reference to the drawings, in which:

1 shows the scheme of a pulp drying production plant,

2 shows the surface of a pulp web with different unevenness in transmitted light,

3 the surface of a cellulosic web with different unevenness when irradiated with a line laser,

Fig. 4 is a camera image of a pulp web with edge region and

Fig. 5 represent an inventive arrangement for determining the unevennesses in the transmitted light.

Fig. 1 shows the scheme of a Zellstofftrocknungsanange, in which a

Pulp suspension is fed via a headbox onto a sieve 4. It can be a fourdrinier with or without Top Former, as shown, but also a twin wire, in which the pulp suspension between two screens in a first wedge-shaped dewatering zone is abandoned. In the wet part 1 then follow several pressing stages 2, which as shown may have a common felt 4 or as separate presses with separate felts for each

Pressing can be formed. After the wet end 1 then follows a Thermal Drying Stage 3. The transition of the pulp web 18 in the dryer 3 takes place in a free train in the obliquely upwardly leading section 7 and after a deflection in a vertically upwardly leading part 6. Subsequently, the pulp web with a usual final dry content of approx. 90% - 95% cut into leaves, stacked and pressed into bales, the bales then being transported to the paper mills or other pulp-processing consumers for further processing.

Fig. 2 shows the different unevenness viewed with a transmitted light method, i. Lighting unit and camera are arranged on different sides of the pulp web. Depending on the composition and the

Strain on the pulp web in the presses (press nips 5) creates weak spots which can lead to undesired breaks or delamination of the web layers. Again, the visual appearance of a smooth changes

Surface 8 virtually without weaknesses over incipient unevenness 9 to an uneven nodular structure 10 with load-dependent furrows. Subsequently, holes or cracks in the pulp web occur. These vulnerabilities are the root cause of web breaks and delamination.

Fig. 3 shows this situation when using a line laser. For this purpose, one (shown here) or several laser lines are projected onto the pulp web with a suitable optical system. The deviation from the straight line is then a measure of the unevenness of the pulp web. It can be seen here with a smooth surface 11 practically a straight line, at beginning irregularities 12 a slightly wavy line and deep grooves 13 a jagged line. The standard deviation or a rating of the peak values can be used as a measure of the deviation from the straight line.

Fig. 4 shows a camera image of the pulp web with the detection of the edge region. Here, 3 laser lines 14 are shown, with which the surface texture at several positions of the pulp web can be measured simultaneously. Furthermore, the smoothness of the web edge 15 is used here as a parameter, with the lighter surface representing the lighting unit directly. Partial air pockets (blistering) 16 are also present in the marginal area. 16. Extremely irregular edges 15 as well as air pockets 16 can lead to unexpected tears and thus

Lead web breaks. Fig. 5 shows the arrangement of a system for assessing the hydraulic / mechanical load of a pulp web during production and

Determination of unevenness in the transmitted light. Above the pulp web 18, a lighting device 19 is arranged. Below the pulp web 18 is a camera 17 which detects the intensity distribution of the penetrating light. The difference in intensity between light and dark areas then forms a parameter for the unevenness of the pulp web 18. Based on this measured variable and corresponding limit values, a control of the system can then take place in such a way that breaks or delamination of the pulp web are avoided. In addition, a variant of the determination of the unevenness of the web is shown by means of laser 20. For this purpose, one or more lines are projected by means of a suitable optics at a certain angle to the pulp web 18. The

Deviation of the projected line from the straight line is then a measure of the

Irregularities. To improve the informative value, this measurement is combined with a measurement by means of transmitted light method. The laser 20 further serves to determine the exact position of the measuring device 23 in relation to the pulp web 18 and optionally, the position is corrected starting from the measuring signal such that the distances provided are optimally adjusted both in height and transverse to the web running direction. For adjusting the distance of the

Measuring device 23 is a motor 21 and to adapt to the position transverse to the web running direction, a motor 22 is provided.

The invention is not limited by the illustrated examples. Thus, e.g. Also, several cameras arranged side by side can be installed or the camera traversing over the web width can be provided.

Claims

claims

1. A method for assessing the hydraulic / mechanical loading of a pulp web during production in a pulp drying plant consisting of a web formation part, a press part and a thermal drying plant, characterized in that detected by an optical system a plurality of parameters simultaneously and therefrom

Measured variables are formed, which describe the state of the pulp web (18), in particular the degree of unevenness or the depths of furrows with regard to the strength of the pulp web.

2. The method according to claim 1, characterized in that both parameters of the pulp web and the edge (15) of the pulp web are detected simultaneously.

3. The method according to claim 1 or 2, characterized in that the

Measurement of the parameters by the optical system after a press part (2) before the thermal drying plant (3) takes place.

4. The method according to any one of claims 1 to 3, characterized in that the pulp web (18) illuminated from the top (19) and with a camera (17) the intensity distribution of the translucent light is detected as transmitted light on the underside.

5. The method according to claim 4, characterized in that the measured variable for describing the unevenness of the pulp web through the

Difference in intensity of translucent light between bright and dark areas is formed.

6. The method according to claim 4, characterized in that for determining the intensity difference, the standard deviation of the intensity of the mean value over a certain area is formed as a measured variable.

7. The method according to any one of claims 4 to 6, characterized in that in addition local peak values of the intensity are taken into account.

8. The method according to any one of claims 4 to 7, characterized in that prior to the calculation of the brightness differences, the intensity on the

Average is normalized.

9. The method according to any one of claims 1 to 8, characterized in that one or more laser lines (14) at a certain angle to the Cellular web are projected, wherein the determined by the camera (17) deviation of the projected laser line or lines from the line is used as a measure of the unevenness of the pulp web (18).

10. The method according to any one of claims 1 to 10, characterized in that the determination of the degree of unevenness is performed temporally sequentially traversing across the width of the pulp web.

11. The method according to any one of claims 1 to 10, characterized in that the determination of the degree of unevenness parallel in time by a plurality of juxtaposed optical systems, in particular

Camera systems, is performed.

12. System for assessing the hydraulic / mechanical load of a

Cellulose web (18) during production in a pulp drying plant consisting of a web formation part (1, 2, 4), characterized in that an optical system consisting of a lighting device (19), a camera (17) and a control system is provided according to a press part (2) in front of the thermal drying plant (3) is arranged. 3. Plant according to claim 12, characterized in that the illumination (19) on the top and the camera (17) on the underside of

Cellulose web (18) are arranged.

14. Installation according to one of claims 12 to 13, characterized in that in addition to the illumination device, a laser unit (20) is provided.

15. Plant according to one of claims 12 to 14, characterized in that a fork-shaped device (23) is provided, wherein the pulp web (18) extends between the two arms of the fork and advantageously the fork-shaped device (23) in vertical (by means of motor 21) and horizontal (by means of motor 22) direction is movable.