AHO, Tuomo (Ryydynkatu 19, Tampere, FI-33400, FI)
KESSELI, Harri (Kimpikatu 2, Tampere, FI-33400, FI)
AHO, Tuomo (Ryydynkatu 19, Tampere, FI-33400, FI)
| CLAIMS 1. A method for controlling reject handling in a pulping process which has a pulper (1) for the preparation of a fibre pulp suspension and a rag- ger (2) for the removal of reject from the pulper (1) in the form of a ragger rope (4), characterised by measuring at least one property of the ragger rope (4) of the ragger (2) and/or at least one effect caused by the ragger rope (4) on the ragger (2) and/or the rate of travel of the ragger rope (4) and/or at least one property of the operation of the ragger (2), and adjusting the rate of travel of the ragger rope (4) and/or the rotation rate of the pulper (1) rotor and/or the amount of raw material of the fibre pulp suspension being fed into the pulper (1) on the basis of the measured ragger rope (4) property and/or effect of the ragger rope (4) on the ragger (2) and/or rate of travel of the ragger rope (4) and/or property of the operation of the ragger (2). 2. A method as claimed in claim 1, characterised in that when measuring at least one property of the ragger rope (4) of the ragger (2), the thickness (T) and/or weight (W) and/or length (L) and/or stiffness and/or elasticity of the ragger rope (4) is measured. 3. A method as claimed in claim 1 or 2, characterised in that when measuring at least one effect caused by the ragger rope (4) on the ragger (2), the compression stress directed by the ragger rope (4) on the front part of the ragger (2) frame structure (11) and/or the tensile stress directed by the ragger rope (4) on the back part of the ragger (2) frame structure (11) and/or the oscillation or vibration (V) caused by the ragger rope (4) on the ragger (2) frame structure (11) is measured. 4. A method as claimed in any one of the preceding claims, characterised in that when measuring at least one property of the ragger (2) operation, the torsional moment (TM) of the drawing roll (5) of the ragger (2) is measured. 5. A method as claimed in any one of the preceding claims, characterised by decreasing the ragger rope (4) rate of travel when the ragger rope (4) is light or thin, or when the vibration (V) caused by the ragger rope (4) on the ragger (4) frame structure (11) is minor. 6. A method as claimed in any one of claims 1 to 4, character- is e d by increasing the ragger rope (4) rate of travel when the ragger rope (4) is heavy or thick, or when the vibration (V) caused by the ragger rope (4) on the ragger (2) frame structure (11) is strong. , 7. Equipment for controlling reject handling in a pulping process which has a pulper (1) for the preparation of a fibre pulp suspension and a ragger (2) for the removal of reject from the pulper (1) in the form of a ragger rope (4), characterised in that the equipment contains one or more measuring elements (9, 12, 13, 14, 16) for measuring at least one property of the ragger rope (4) of the ragger (2) and/or at least one effect caused by the ragger rope (4) on the ragger (2) and/or the rate of travel of the ragger rope (4) and/or at least one property (TM) of the operation of the ragger (2), and that the equipment contains at least one control unit (10) for adjusting the ragger rope (4) rate of travel and/or rotation rate of the pulper (1) rotor and/or the amount of raw material of the fibre pulp suspension being fed into the pulper (1) on the basis of the measured property of the ragger rope (4) and/or effect caused by the ragger rope (4) on the ragger (2) and/or ragger rope rate of travel and/or property of the ragger (2) operation. 8. Equipment as claimed in claim 7, characterised in that the at least one measuring element (9, 12, 13, 17) measuring the property of the ragger rope (4) and belonging to the equipment is arranged to measure the thickness (T) and/or weight (W) and/or length (L) and/or stiffness and/or elasticity of the ragger rope (4). 9. Equipment as claimed in claim 7 or 8, characterised in that the one or more measuring element (12, 13, 14) belonging to the equipment for measuring the effect caused by the ragger rope (4) on the ragger (2) is arranged to measure the compression stress directed by the ragger rope (4) to the front part of the ragger (2) frame structure (11) and/or the tensile stress directed by the ragger rope (4) to the back part of the ragger (2) frame structure (11) and/or the oscillation or vibration (V) caused by the ragger rope (4) on the ragger (2) frame structure (11). 10. Equipment as claimed in any one of claims 7 to 9, characterised in that the measuring element (16) for measuring the operational property of the ragger (2) is arranged to measure the torsional moment (TM) of the drawing roll (5) of the ragger (2). 11. Equipment as claimed in any one of claims 7 to 10, character i s e d in that the control unit (10) is arranged to decrease the ragger rope (4) rate of travel when the ragger rope (4) is light or thin or when the vibration (V) caused by the ragger rope (4) on the ragger (4) frame structure (11) is minor. 12. Equipment as claimed in any one of claims 7 to 10, characterised in that the control unit (10) is arranged to increase the ragger rope (4) rate of travel when the ragger rope (4) is heavy or thick or when the vibration (V) caused by the ragger rope (4) on the ragger (4) frame structure is strong. |
BACKGROUND OF THE INVENTION
[0001] The invention relates to a method for controlling reject handling in a pulping process which has a pulper for the preparation of a fibre pulp suspension and a ragger for the removal of reject from the pulper in the form of a ragger rope.
[0002] The invention further relates to equipment for controlling reject handling in a pulping process which has a pulper for the preparation of a fibre pulp suspension and a ragger for the removal of reject from the pulper in the form of a ragger rope.
[0003] In the initial step of preparing the fibre pulp suspension for use in the preparation of paper and board, for instance, it is possible to use pulping as part of the process. The purpose of pulping is to defibrate the fibre material being fed into the pulper and to mix it with the water being fed into the pulper to form a fibre pulp suspension. Generally, the fibre material may for instance be cellulose or recycled fibre material or fibre-content material from a paper or board mill.
[0004] When using recycled fibre material, a great deal of impurities, such as plastic and metal pieces, sand, and glass, typically enter the pulper with the recycled fibre. In low-consistency pulpers, it is possible to use a ragger to remove elongated plastic material and metal wires. A ragger usually has a drawing roll and a press roll pressing toward the drawing roll, by means of which the ragger rope or reject rope or rope made up of elongated plastic materials, plastic film pieces, metal wires, and other reject material that has intertwined in the pulper is pulled out of the pulper. The ragger rope pulled out of the pulper by the ragger is cut with a cutter positioned after the ragger into suitable pieces for further processing the ragger rope. Publications US 2005/0115690 A1 , US 3 844 488 and US 4 592 513 disclose systems related to pulping, in which a ragger rope is used to remove impurities from the system.
[0005] However, malfunctions, such as breaking of the ragger rope, often occur in raggers. The breaking of the ragger rope may for instance take place when the thickness of the ragger rope and, therefore, also its weight increases too much while the speed of the ragger rope is too low in comparison with the amount of reject being removed. The breaking of the ragger rope may also take place when the ragger rope is thin, in which case the pull directed to the ragger rope may break it. Occasionally, ragger malfunctions are also caused by the thickness of the ragger rope increasing so much that the rope is difficult to remove or too big for the size of the ragger.
[0006] Controlling the operation of a ragger is today based on controlling the ragger rope speed set by the user or operator. The speed of the ragger rope may be monitored through a camera used to monitor the operation of the ragger or through inspections at the ragger. These currently used control methods cannot in practice react to the continuously present variations in the raw material, which means that the removal of reject from the pulper is disturbed. Poor reject removal also causes malfunctions in the secondary pulper belonging to the pulping system and in the reject pump as well as a stronger than usual wear of the pulper rotor and screen plate.
BRIEF DESCRIPTION OF THE INVENTION
[0007] It is an object of this invention to provide a novel and improved method of controlling reject handling in the form of a ragger rope.
[0008] The method of the invention is characterised by measuring at least one property of the ragger rope and/or at least one effect caused by the ragger rope on the ragger and/or the rate of travel of the ragger rope and/or at least one property of the operation of the ragger, and by adjusting the rate of travel of the ragger rope and/or the rotation rate of the pulper rotor and/or the amount of raw material of the fibre pulp suspension being fed into the pulper on the basis of the measured ragger rope property and/or effect of the ragger rope on the ragger and/or the rate of travel of the ragger rope and/or the property of the operation of the ragger.
[0009] The equipment of the invention is characterised in that the equipment comprises one or more measuring elements for measuring at least one property of the ragger rope and/or at least one effect caused by the ragger rope on the ragger and/or the rate of travel of the ragger rope and/or at least one property of the operation of the ragger and that the equipment comprises at least one control unit for adjusting the rate of travel of the ragger rope and/or the rotation rate of the pulper rotor and/or the amount of raw material of the fibre pulp suspension being fed into the pulper on the basis of the measured ragger rope property and/or effect of the ragger rope on the ragger and/or the rate of travel of the ragger rope and/or the property of the operation of the rag- ger.
[0010] The method for controlling reject handling in a pulping process having a pulper for the preparation of a fibre pulp suspension and a ragger for the removal of reject from the pulper in the form of a ragger rope measures at least one property of the ragger rope and/or at least one effect of the ragger rope caused on the ragger and/or the rate of travel of the ragger rope and/or at least one property of the operation of the ragger, and adjusts the rate of travel of the ragger rope and/or the operation of the pulping on the basis of the measured ragger rope property and/or effect of the ragger rope caused on the ragger and/or rate or travel of the ragger rope and/or property of the operation of the ragger. When adjusting the pulping operation, it is possible to adjust for instance the rotation rate of the pulper rotor and/or the amount of raw material of the fibre pulp suspension being fed into the pulper.
[0011] Due to the solution, the rate of travel of the ragger rope or the pulping operation may be controlled in a simple, controlled manner taking into consideration the impurities of the raw material. Due to the solution, breaking of the ragger rope may be reduced, thus reducing disturbances in the removal of reject from the pulper and in the operation of the rest of the pulper section. Further, due to the solution, it is possible to control the adjustment of the physical properties of the ragger rope, such as its diameter, weight, and length, in such a manner that an even and trouble-free removal of the ragger rope from the pulper may be achieved.
[0012] According to an embodiment, the weight of the ragger rope is measured by measuring the effect of the ragger rope on the ragger. By measuring the effect of the ragger rope on the ragger, it is possible to measure for instance the compression stress caused by the ragger rope on the front part of the frame structure of the ragger or the tensile stress caused by the ragger rope on the back part of the frame structure of the ragger, whereby the required measuring instruments are very simple and easily maintained or replaced.
BRIEF DESCRIPTION OF THE FIGURES
[0013] Some embodiments of the invention are described in greater detail in the attached figure that is a partly sectional schematic side represen- tation of a pulper, ragger, cutter, and equipment for controlling the operation of the ragger and pulping.
[0014] In the figure, some embodiments of the invention are shown simplified for the sake of clarity.
DETAILED DESCRIPTION OF THE INVENTION
[0015] The figure is a partly sectional schematic side representation of a pulper 1, ragger 2, cutter 3, and equipment for controlling the ragger 2. In the pulper 1 , fibre material fed into the pulper is defibrated with a rotor (not shown for the sake of clarity) and mixed with water fed into the pulper to form a fibre pulp suspension. Especially when using recycled fibre material, a great deal of impurities, such as pieces of plastic and metal, sand and glass, enter the pulper 1 with the recycled fibre material. As a result of the rotating movement of the pulp in the pulper, elongated plastic material, pieces of plastic film, and metal wires tend to intertwine or attach to each other to, thus, form a ragger rope 4 or reject rope 4 or rope 4. Other reject material, such as sand or glass, is also attached or intertwined to the thus formed ragger rope 4. This ragger rope 4 is fed from the pulper 1 to the ragger 2 having a drawing roll 5 that is rotated by a very schematically presented motor 6. The ragger 2 often also includes a press roll 15 that presses toward the drawing roll 5 and acts as a counterpart for the drawing roll 5. The task of the ragger 2 is to pull the ragger rope 4 out of the pulper 1 and, thus, prevent the reject material in the ragger rope 4 from moving on in the pulping process. After the ragger 2, there is typically a cutter 3 to which the ragger rope 4 is guided and where the ragger rope 4 is cut into suitably sized pieces with a cutting blade 7. The pieces of the ragger rope 4 are, in turn, led away from the cutter 3 through a reject port 8 for further processing. The pulper 1 is typically a low-consistency pulper in which the consistency of the fibre pulp suspension being defibrated is typically approximately 5% or less, since in high fibre pulp suspension consistencies the formation of the ragger rope 4 abates or does not take place. The general structure and operating principle of the system formed by the pulper 1 , ragger 2, and cutter 3 is generally known to a person skilled in the art, and they are not discussed herein in more detail.
[0016] The figure further shows a measuring device 9 of the ragger rope 4 thickness T arranged to optically monitor the ragger rope 4. The measuring device 9 may comprise software or other necessary means for determin- ing the value of the ragger rope 4 thickness T on the basis of the optical monitoring of the ragger rope 4. The measuring device 9 thus forms a measuring element that generates a measuring signal, on the basis of which the thickness of the ragger rope 4 may be determined. The value of the ragger rope 4 thickness T is transferred to a control unit 10 that, on the basis of the value, controls the rotating rate of the ragger 2 drawing roll 5 and, consequently, the rate of travel of the ragger rope 4 by adjusting the operation of the motor 6 or a frequency converter possibly controlling it by means of a control signal CS. Alternatively, the measuring device 9 may transfer to the control unit 10 only the one or more measuring signals it has measured, on the basis of which the control unit 10 with its software or other means may determine the thickness T of the ragger rope 4.
[0017] The measurement of the ragger rope thickness may for instance be based on known computer vision sensors and related systems in which a picture is taken of the ragger rope and its thickness is calculated on the basis of the outlines formed by the ragger rope in the picture. An example of another useful solution for the measurement of the ragger rope thickness is to use photocells, several of which may be placed side by side, and to measure to what extent the ragger rope overshadows the travel of light in the measuring. These measurements may naturally also be made in two different directions, whereby the dimension of the ragger rope in its other direction is also verified.
[0018] Computer vision sensors and related systems may also be used to measure the rate of travel of the ragger rope 4. The rate of travel is determined for example by comparing pictures taken at specific intervals and by measuring the progress of a picture or a detail thereof from consecutive pictures during a period of time. The adjustment of the ragger rope rate of travel may also be implemented on the basis of such a measuring arrangement. The rate of travel of the ragger rope is proportional to the rotating rate of the drawing roll 5 of the ragger 2, so instead of the ragger rope rate of travel, it is possible to determine the rotating rate of the drawing roll that may be considered a property of the ragger 2 operation and measured using for instance a device for measuring the rotating rate located in the motor 6. In addition to the ragger 2 rate of travel, it is generally also necessary to measure another quantity, such as a property of the ragger rope 4, for instance the diameter, that is, thickness, of the ragger rope 4 or the weight of the ragger rope 4, in which case these measuring results, when transmitted to the control system, form together an adjustment base for adjusting the rate of travel of the ragger rope 4, for instance.
[0019] When the thickness T of the ragger rope 4 increases or is great, it is possible to increase the rotation rate of the ragger 2 drawing roll 5 and thus also the rate of travel of the ragger rope 4 from the pulper 1 to the ragger 2 with the intention of pulling the ragger rope 4 faster out of the pulper
1 , thereby to reduce the thickness of the ragger rope 4 and to prevent the breaking of the ragger rope 4 due to its too great a thickness and, consequently, also its too great a weight. If the ragger rope 4 becomes thinner or is thin, the rate of travel of the ragger rope 4 may be slowed down by slowing down the rotation rate of the ragger 2 drawing roll 5 with the intention of obtaining a thicker and, therefore, more pull-resistant ragger rope 4 to, thus, avoid the breaking of the ragger rope 4 and a disturbance in reject removal.
[0020] The figure further shows a compression stress measuring element 12 located in the frame structure 11 of the ragger 2, in the front part of the frame structure, that is, on the pulper 1 side thereof. The compression stress measuring element 12 may in itself be a measuring member or comprise a measuring member, such as a strain gauge or power rating device, that is arranged to measure the compression effect or compression stress caused by the ragger rope 4 on the front part of the ragger 2 frame structure 11 , that is, on the pulper 1 side thereof; the effect or stress representing the weight W of the ragger rope 4. The ragger rope 4 causes a compression effect or compression stress on the front part of the ragger 2 frame structure, because the ragger rope 4 supports itself on the front part of the ragger 4 frame structure 11 or on a part in connection therewith, when it travels from the pulper 1 to the ragger 2. The greater the weight of the ragger rope 4, the greater the compression effect directed to the front part of the frame structure 11 of the ragger
2. The compression stress measuring element 12 may comprise software or other necessary means for determining the weight W of the ragger rope 4 and for transmitting it to the control unit 10. Alternatively, the compression stress measuring element 12 may transmit to the control unit 10 only the measured signal representing the compression effect, on the basis of which the control unit 10 determines the weight W value of the ragger rope 4 and controls the rotation rate of the ragger 2 drawing roll 5 by adjusting the operation of the motor 6, or the frequency converter possibly controlling it, by means of a control signal CS, thus adjusting the rate of travel of the ragger rope 4 from the pulper
I to the ragger 2.
[0021] The figure further shows a tensile stress measuring element 13 located in the back part of the ragger 2 frame structure 11 , that is, to a part opposite to the pulper 1. The tensile stress measuring element 13 may in itself be a measuring member or comprise a measuring member, such as a strain gauge, that is arranged to measure the tensile effect or tensile stress caused by the ragger rope 4 on the back part of the ragger 2 frame structure 11 , which represents the weight W of the ragger rope 4. The ragger rope 4 causes a tensile stress effect on the back part of the ragger 2 frame structure, because the ragger rope 4 supports itself on the back part of the ragger 4 frame structure
I I or on a part in connection therewith, when it travels from the pulper 1 to the ragger 2. The greater the weight W of the ragger rope 4, the greater the tensile stress effect directed to the back part of the frame structure 11 of the ragger 2. The tensile stress measuring element 13 may comprise software or other necessary means for determining the weight W of the ragger rope 4 and for transmitting it to the control unit 10. Alternatively, the tensile stress measuring element 13 may transmit to the control unit 10 only the measured signal representing the tensile stress effect, on the basis of which the control unit 10 determines the weight W value of the ragger rope 4 and controls the rotation rate of the ragger 2 drawing roll 5 by adjusting the operation of the motor 6, or the frequency converter possibly controlling it, by means of a control signal CS, thus adjusting the rate of travel of the ragger rope 4 from the pulper 1 to the ragger 2.
[0022] When the weight W of the ragger rope 4 increases or is great, it is possible to increase the rotation rate of the ragger 2 drawing roll 5 with the intention of pulling the ragger rope 4 faster out of the pulper 1 , thereby to reduce the weight of the ragger rope 4 and its effect on the ragger 2 and, thus, to prevent the breaking of the ragger rope 4 due to its too great a weight. If the ragger rope 4 becomes lighter or is light, the rotating rate of the ragger 2 drawing roll 5 and, thus, the rate of travel of the ragger rope 4 may be slowed down with the intention of obtaining a heavier and, therefore, more pull- resistant ragger rope 4 to, thus, avoid the breaking of the ragger rope 4.
[0023] The weight of the ragger rope may also be measured by directing the ragger rope 4 to the ragger 2 over a roll system, curved plate, or pipe to which weighing of the ragger rope 4 is combined using for instance a spring balance or some other measuring element suitable for weight measurement.
[0024] One way of determining the weight W of the ragger rope 4 is to arrange the measurement of the torsional moment of the ragger rope drawing roll 5, from which the weight of the ragger rope may be calculated. The torsional moment TM, which may also be considered a property of the ragger operation, may be measured for instance by measuring the power of the motor driving the drawing roll and by calculating the torsional moment of the drawing roil on the basis of the motor power consumption. The torsional moment may also be measured by means of a torsional moment measuring device arrange- able between the ragger rope drawing roll and its driving device and shown schematically in the figure and indicated by reference number 16.
[0025] The figure further shows a vibration measuring element 14 located in the front part of the ragger 2 frame structure 11, that is, on the pulper 1 side part. The vibration measuring element 14 may in itself be a measuring member or comprise a measuring member, such as an acceleration sensor, that is arranged to measure the oscillation or vibration V caused by the ragger rope 4 on the ragger 2 frame structure 11. The vibration caused by the ragger rope 4 on the ragger 11 frame structure is due to the vibration of the ragger rope 4, which in turn is caused by the ragger rope 4 coming close to the pulper 1 rotor. The closer to the pulper 1 rotor the ragger rope 4 is, the stronger is the oscillation of the ragger rope and the stronger is the vibration V caused by the ragger rope 4 on the ragger 2 frame structure 11. The vibration measuring element 14 may comprise software or other necessary means for determining the value representing the vibration V and for transmitting it to the control unit 10. Alternatively, the vibration measuring element 14 may transmit to the control unit 10 only the measured signal representing vibration, on the basis of which the control unit 10 may adjust the rate of travel of the ragger rope 4 from the pulper 1 to the ragger 2 by controlling the rotation rate of the ragger 2 drawing roll 5 by adjusting the operation of the motor 6 or a frequency converter possibly controlling it by means of a control signal CS.
[0026] When the vibration of the ragger 2 frame structure 11 increases or is strong, the rotation rate of the ragger 2 drawing roll 5 is increased with the intention of pulling the ragger rope 4 faster out of the pulper 1 and thus further away from the pulper 1 rotor, thus shortening the length of the ragger rope 4 and avoiding the breaking of the ragger rope 4. If the vibration of the ragger 2 frame structure 11 is very slight or minor, the rotation rate of the ragger 2 drawing roll 5 may be decreased with the intention of enhancing the formation of the ragger rope 4 and thus reject removal from the pulper 1.
[0027] The length L of the ragger rope 4 may also be considered a property of the ragger rope 4. The length L of the ragger rope may be determined for instance with a length measuring element 17 that may be located on the bottom of the pulper 1 and that on the basis of capacitance, for instance, measures the length L of the ragger rope 4 through the bottom of the pulper 1 , and on the basis of the length, the rate of travel of the ragger rope 4, for example, may be adjusted. The length L of the ragger rope 4 may also be determined by means of the weight W, average diameter D, and density p of the ragger rope 5 with the formula
wherein the weight W of the ragger rope 4 may be determined by the methods described above, for instance, and the average diameter D may be determined on the basis of the above-mentioned measurement of the thickness T of the ragger rope 4. The density value of a ragger rope with an approximately similar diameter removed earlier from the pulper may, in turn, be used as the value of the ragger rope 4 density p. Instead of the density value, it is also possible to experimentally define one or more coefficiencies depending on the ragger rope diameter, in which case by multiplying the quotient of the square of the ragger rope weight and diameter with the coefficient, it is possible to determine the length L of the ragger rope 4.
[0028] The stiffness or elasticity of the ragger rope or a combination thereof may also be measured as its property for the purpose of determining the rate of travel of the ragger rope. The implementation may comprise a pusher, for instance, in which a force acting in the transverse direction is directed to the ragger rope and an offset, bend, or flex of the ragger rope caused by the force is measured, and, on the basis of the measuring result or a combination of measuring results, the rate of travel of the ragger rope or the operation of the pulper is set by means of the control system in such a manner that the ragger rope does not break. The control system may be set to interpret the ragger rope as stiff, when the offset or bend caused by the transverse-direction force is small, and to set a high rate of travel for the ragger rope. Correspondingly, the control system may be set to interpret the ragger rope as elastic, when the offset or bend caused by the transverse-direction force is big, and to set a low rate of travel for the ragger rope. Further, if the system measures a small ragger rope transverse offset, but a big ragger rope flex, in which case the pusher pushes into the ragger rope and moves it only relatively slightly in the transverse direction, then the system may be set to adjust either a high ragger rope rate of travel or a low ragger rope rate of travel depending on the material being processed in the pulper. The presented pusher-based measuring arrangement for ragger rope stiffness, bending or elasticity may be arranged to take place at a press roll 15, for example, or as a separate measuring arrangement.
[0029] The pulping operation may be adjusted for instance by controlling the rotation rate of the pulper 1 rotor by controlling the operation of the motor 18 or a frequency converter possibly controlling it by means of a control signal CS'. By altering the rotation rate of the pulper 1 rotor, it is possible to affect the rate of growth of the ragger rope 4. The pulping operation may also be controlled by adjusting the amount of raw material, that is, typically the recycled fibre material, fed into the pulper 1. This may be done for instance by controlling the rate of a transporter 19 feeding raw material into the pulper 1 through a control signal CS" or by controlling the operation of some other device feeding raw material into the pulper 1 in such a manner that the amount of raw material fed into the pulper 1 may be adjusted. By adjusting the amount of raw material fed into the pulper 1 , it is possible to influence the amount of reject entering the pulper with the raw material and, consequently, the intensity of the formation of the ragger rope.
[0030] The measuring elements presented in this description are all shown in the same figure. However, it is clear that it is possible to use only one of the above-mentioned measuring devices in the solution or that one of the above-mentioned measuring devices or some other measuring device mentioned in the description or some other corresponding measuring device is used in the solution together with one or more above-mentioned measuring devices or some other corresponding measuring device.
[0031] By measuring at least one property of the ragger rope 4 of the ragger 2 and/or at least one effect caused by the ragger rope 4 on the rag- ger 2 and/or the rate of travel of the ragger rope and/or a property of the operation of the ragger, and by adjusting the rate of travel of the ragger rope or the operation of the pulper on the basis of the measurement, the ragger rope 4 is removed from the pulper 1 in a controlled manner, or its formation in the pulper and thus also reject handling may be influenced while taking into consideration the variation of impurities in the raw material. The solution makes it possible to limit for example the thickness, weight and/or length of the ragger rope 4, or to keep the variation in said properties small, and to adjust said properties by altering for instance the removal rate of the ragger rope 4. Thanks to the solution, breakings of the ragger rope 4 may be reduced or avoided altogether and, in addition, variation of the ragger rope thickness, weight, and length may be reduced, thus reducing disturbances in reject removal from the pulper and making reject removal from the pulper even and controlled. When there are less disturbances in reject removal from the pulper, there are also less disturbances in the different steps of the pulping process following the pulper, whereby the solution provides disturbance-reducing multiplicative effects in the operation of the rest of the pulper area.
[0032] In some cases, the features disclosed in this application may be used as such regardless of the other features. On the other hand, the features disclosed in this application may, if necessary, also be combined to form different combinations. Thus, to control reject handling, the adjustments may be based on one measurable quantity only or on several simultaneously measurable quantities. In addition, the adjustments may be implemented by means of controls affecting the rate of travel of the ragger rope or the operation of the pulper only or by adjusting simultaneously both the ragger rope rate of travel and the operation of the pulper.
[0033] The drawings and the related description are intended only to illustrate the idea of the invention. The invention may vary in detail within the scope of the claims. Thus, according to the solution, when measuring at least one property of the ragger rope 4 of the ragger 2, it is possible to measure at least one of the following properties: the thickness T of the ragger rope 4, the weight N of the ragger rope 4, the length L of the ragger rope 4, the stiffness of the ragger rope 4, the elasticity of the ragger rope 4. Further, when measuring at least one effect caused by the ragger rope 4 on the ragger 2, it is possible to measure at least one of the following properties: the compression stress directed by the ragger rope 4 to the front part of the ragger 2 frame structure 11 , the tensile stress directed by the ragger rope 4 to the back part of the ragger frame structure 11 , oscillation or vibration caused by the ragger rope 4 on the ragger 2 frame structure.