Method for optimizing refining energy during the refining operation of a fiber composition

Abstract

The present invention relates to a method for optimizing the refining energy supplied to a fiber composition during refining operation in a refiner, the refiner comprising at least two refining discs which are separated from each other by an adjustable gap. The present invention also relates to a refining system suitable for implementing such a method.

Description

Technical Field

[0001] The present invention relates to a method for optimizing the refining energy supplied to a fiber composition during a refining operation of a refiner, and a refining system suitable for implementing such a method. Background Art

[0002] In the field of papermaking technology, it is known and currently practiced to refine a cellulose fiber composition that is intended to subsequently form a paper sheet or a cardboard sheet in order to modify certain properties of the sheet.

[0003] Refining involves subjecting the fibers to a mechanical treatment that combines mechanical compression and shear. In particular, when this refining is carried out in the presence of mineral fillers, it makes it possible to increase the retention rate of these fillers in the paper sheet without altering the mechanical properties of the paper, and in particular without altering the tensile or tear strength of the paper.

[0004] Refining is generally carried out between two parallel refining discs facing each other, which are spaced apart from each other by an adjustable distance commonly referred to as a "gap". These two discs generally include a rotating disc (or rotor) and a fixed disc (stator). They are generally made of a metal alloy and include protrusions and depressions for guiding the fiber composition when there is a fiber composition between the discs.

[0005] Refining can be carried out by (one or more) passes of the fiber composition between these discs. It can also be carried out by (one or more) passes through a series of pairs of discs (for example, 2 to 6 pairs of discs), and these pairs of discs can have the same gap or a decreasing gap.

[0006] EP 3839134 relates to a method for refining a fiber composition. The method involves measuring the vibration of a refiner during a refining operation and adjusting the refiner gap according to the measured vibration value. The method does not control the refining energy.

[0007] WO 86 / 06770 relates to a method for controlling the preparation of mechanical pulp in a refiner process. According to this method, due to the relationship between the vibration and wear of the refiner discs, the properties of the pulp can be predicted.

[0008] One of the main concerns remains the control of the energy consumption of the refiner required for the refining operation.

[0009] During the refining operation, the physico-chemical characteristics of the fiber composition vary according to the refining time and the number of passes of the fiber composition between the discs of the refiner or between a series of discs of the refiner. These characteristics are, in particular, the consistency or density of the fiber composition, and the rheology of the fiber composition, i.e. the flow properties of the fiber composition according to the mechanical strain imposed on it by the refiner.

[0010] The modification of the physico-chemical characteristics of the composition is due to the phenomena imposed on the fibers during refining. The fibers actually undergo compressive and shear forces, which may cause their fibrillation. In this case, the fibers then have a wrinkled appearance. In addition, the fibers can also be cut during refining so that their length can decrease with each pass between the refiners.

[0011] Thus, it can be simply said that the further the refining progresses, the more fluid the fiber composition in the gap becomes.

[0012] Therefore, it can be understood that if all the operating parameters of the refiner (especially the spacing between the discs) are kept constant during refining, the refining energy supplied by the refiner to the fiber composition tends to decrease over time.

[0013] To illustrate the subject and specifically depict the energy phenomena involved, Figure 1 a graph is shown. It generally shows the variation of the refining energy and the gap G according to the number of passes (or number of cycles) Np of the fiber composition between the refiner discs.

[0014] Generally, the refining energy, also known as "specific energy", corresponds to the amount of energy required by the refiner to refine one ton of fiber composition per hour. Therefore, it is expressed in kilowatt-hours per ton of fiber (kWh / t).

[0015] The first curve E relates to the specific energy measured in real time or discretely during the refining operation, which is the energy supplied by the refiner to the fiber composition during the refining operation.

[0016] The second curve Ei shows the specific energy corresponding to the optimal energy, which enables the work suitable for their refining to be supplied to the fibers in a way without energy loss during the refining period.

[0017] The third curve Cs shows the refining energy setpoint that the refiner, selected and set by the operator, must comply with. Generally, the operator reduces the energy setpoint in a stepwise manner during the refining operation.

[0018] Finally, the gap G corresponds to the distance between the discs and can generally be expressed in micrometers (μm).

[0019] From this graph, it can be observed that at the start of the method, the operator sets the energy setpoint Cs to a first setpoint value Cs1 (shown as a dashed line). Thus, the specific energy will tend towards and, if possible, reach this setpoint value. To maintain a relatively constant specific energy E1 close to the setpoint value Cs1, the gap decreases with the cycles according to a predefined sequence.

[0020] In fact, as previously mentioned, the refining of the fiber composition results in a modification of the physical and chemical properties of the fiber composition, in particular a modification of its consistency and flow (i.e., the rheology of the fiber composition). To keep the specific energy level at the level of the setpoint, it is therefore necessary to adapt the gap to the changes in the rheology of the composition and thus pull the disks towards each other, which results in a decrease in the gap G after the adoption of a new energy setpoint. Reference can be made to the variation of curve G between time 0 and cycle 10.

[0021] To avoid disk collision, the operator lowers the setpoint to a second setpoint value Cs2 at cycle 10. This results in a sudden increase in the gap because the disks are then exerting too much strain on the composition relative to the rheology of the composition at that time, so the disks are quickly pulled apart from each other to lower the specific energy.

[0022] Between cycle 10 and cycle 20, the modification of the rheology of the composition results in a regular decrease in the gap G to maintain a relatively constant specific energy E close to the setpoint value Cs2.

[0023] This scenario is implemented until the specific energy reaches a lower threshold at which the operator knows that the fiber has been sufficiently refined. Then the refining is stopped.

[0024] In this way, the setpoint energy Cs is gradually decreased in a stepped form, thus making it possible to approach the desired specific energy Ei.

[0025] The setpoint energy Cs is obtained empirically by trial and error, by repeating the method a large number of times and by adjusting the parameters accordingly, and this is the case for each type of fiber composition.

[0026] In fact, the desired energy curve Ei depends on a large number of parameters, including the characteristics of the fiber, the consistency of the composition, and generally the rheology of the composition, etc.

[0027] Based on this analysis, two ways can be envisaged.

[0028] The first way, called the conservative way, consists in defining a stepped curve of the energy setpoint using conservative parameters before starting the refining. However, this means a long refining time because it is necessary to completely avoid disk collision, so a safety margin needs to be provided by choosing the energy setpoint stages.

[0029] A second way, called the aggressive way, consists of defining a step curve of the energy setpoint to obtain a short refining time. However, for certain sets of input parameters, this may cause disk collisions because the optimal motion law of the disk is unique for each set of input parameters.

[0030] Therefore, neither of these two ways is optimal.

[0031] Therefore, in order to obtain the optimal motion law of the disk, continuous manual monitoring is required. The main drawback is that this solution requires the presence of a qualified operator, which results in high production costs. In addition, it may also reduce production efficiency in cases where the operator has to spend time on this task instead of on other tasks that may require their expertise. Summary of the Invention

[0032] An object of the present invention is to provide a method for optimizing the refining energy supplied to a fiber composition by a refiner during a refining operation, so as to overcome the previous drawbacks.

[0033] The fiber composition comprises water and fibers, advantageously water and cellulose fibers. The fiber composition may also comprise mineral fillers. Those skilled in the art will be able to adjust the mass ratio between the cellulose fibers and the mineral fillers. They will also be able to adjust the concentration of the cellulose fibers and the mineral fillers in the composition (especially in water).

[0034] In particular, the present invention aims to provide such a method that enables the optimization of the refining energy supplied by a refiner to a fiber composition according to the physico-chemical characteristics of the fiber composition and according to the changes in these physico-chemical characteristics during the refining operation, and to perform this optimization in an automatic manner without the need for an operator to specifically manage the energy and / or set the gap during the refining operation.

[0035] In the method according to the present invention, "energy" or "refining energy" refers to the specific energy of the refiner, which depends on the amount of fibers because it is expressed in kilowatt-hours per ton of fibers. The method according to the present invention can optimize the specific energy by continuously adjusting the gap between the refiner disks.

[0036] To this end, the present invention provides a method for optimizing the refining energy supplied to a fiber composition by a refiner during a refining operation, wherein the refiner comprises at least two refining disks that are separated from each other by an adjustable gap.

[0037] The main feature of the method is that it comprises the following steps:

[0038] a) Set an initial refining energy setpoint,

[0039] b) Measure the vibration of the refiner to obtain a corresponding vibration signal depending on the clearance,

[0040] c) Compare at least one characteristic of the vibration signal with a determined maximum value and / or minimum value to:

[0041] c1) If the characteristic of the vibration signal is below the maximum value, the method restarts from step b),

[0042] c2) If the characteristic of the vibration signal is higher than or equal to the maximum value, automatically reduce the initial refining energy setpoint to a lower setpoint value and automatically increase the clearance so that the refining energy tends towards the lower setpoint value, and / or

[0043] c3) If the characteristic of the vibration signal is higher than the minimum value, the method restarts from step b),

[0044] c4) If the characteristic of the vibration signal is lower than or equal to the minimum value, automatically increase the initial refining energy setpoint to a higher setpoint value and automatically reduce the clearance so that the refining energy tends towards the higher setpoint value.

[0045] The present invention is based on the control and optimization of the refining energy (specific energy) for refining a fibrous composition by using the measurement of the vibration of a refiner.

[0046] To this end, the method according to the invention establishes a direct link between the vibration of the refiner and the specific energy.

[0047] This direct link enables the adjustment of the specific energy during the refining operation to be as close as possible to the desired energy ( Figure 1 curve Ei). Thus, for the same refining duration, the total amount of energy required to refine the fibrous composition is reduced. In other words, for the same amount of energy used, the refining time is reduced. Therefore, the number of refining disc pairs and / or the number of refining cycles can be reduced.

[0048] More specifically, as mentioned above, the further the refining progresses, the more fluid the fibrous composition becomes. Therefore, in order to maintain effective refining, i.e., in order to maintain a specific energy value sufficient to effectively refine the fibers (this specific energy value is usually set at a setpoint), it is necessary to pull the discs (of the same pair) towards each other, which results in a reduction in the clearance.

[0049] Pulling the discs towards each other causes the discs to start resonating with each other. In particular, this phenomenon causes a modification of the vibration signal through an increase in the harmonic amplitude of the frequency characteristics of the refiner body and the discs of the refiner.

[0050] The present invention uses this resonance phenomenon by measuring the vibration of the refiner (preferably in real time (continuously)) at regular intervals to detect resonance. When resonance is reached, the energy setpoint is lowered. Then, the disks are displaced to pull away from each other so that the measured energy tends to or even reaches the new, lowered energy setpoint. Thus, it leaves the resonance region. It is a top-down adjustment.

[0051] The present invention also provides a bottom-up adjustment. When the vibration of the refiner becomes too low, this means that the disk spacing is too far to supply the optimal specific energy to the composition. Then, the energy setpoint is increased, which causes the disks to be pulled towards each other so that the measured energy tends to or even reaches the new, increased setpoint. Then, the resonance region is approached.

[0052] Repeating these steps during refining results in a stepwise and automatic overall reduction of the specific energy, and it approaches as closely as possible the desired energy ( Figure 1 the curve Ei). Due to the measurement of the refiner vibration, the specific energy is thus optimized. Of course, in the case of a bottom-up adjustment, a local increase in the specific energy can be observed, which is caused by the increase in the energy setpoint.

[0053] Furthermore, until the disks start to resonate, the displacement profile and displacement speed of the disks between two consecutive energy setpoints depend on the characteristics of the fibrous composition (i.e., depend on the physical properties of the fibrous composition including its rheology), and depend on the chemical properties of the fibrous composition (i.e., depend on the characteristics of the fibers). Now, the characteristics of the fibrous composition change over time, and particularly between two consecutive energy setpoints. Thus, the method according to the present invention enables the optimization of the specific energy based on the vibration of the refiner, according to the physico-chemical characteristics of the fibrous composition and the changes in these physico-chemical characteristics during the refining operation, and to perform this optimization precisely and automatically without the need for operator monitoring. The present invention does not require knowledge or measurement of the viscosity of the fibrous composition.

[0054] As will be seen in the rest of this document, an energy change profile according to the number of passes is thus obtained, and this energy change profile is different according to the characteristics of the fibrous composition being refined.

[0055] For information, it is specified that "vibration" designates the mechanical oscillatory movement of molecules around a stable equilibrium position. The measurement of vibration is carried out by converting the mechanical oscillation into an electrical oscillation by means of a transducer (such as an electromagnetic sensor, an electric sensor, an electrostatic sensor or also a piezoelectric sensor (advantageously an accelerometer or a microphone)). One or more sensors can be used. In the case of multiple sensors, these sensors are advantageously sensors of the same type, such as accelerometers.

[0056] Since sound is a mechanical vibration of a fluid, the term "vibration" includes not only waves propagating in the elements (solid media) forming the refiner, but also waves propagating in the air (fluid medium) surrounding the refiner, i.e., "sound waves", regardless of whether they belong to the audible spectrum, the infrasonic spectrum or the ultrasonic spectrum.

[0057] According to the invention, monitoring the vibration allows the specific energy to be optimized so that the refiner is always at its highest possible energy limit (i.e., its highest screeching sound).

[0058] According to other aspects, the method according to the invention exhibits the following different characteristics individually or according to their technically possible combinations:

[0059] - After performing step c2) or step c4), the method is repeated at least once starting from step b), and the initial refining energy set point is accordingly replaced by the lower set point or the higher set point;

[0060] - The characteristics of the vibration signal include the acceleration of the refiner;

[0061] - The acceleration is measured by calculating the real-time average value of a parameterizable number of acceleration values measured within a time interval preferably in the range from 0.5 seconds to 5 seconds, more preferably in the range from 1 second to 3 seconds;

[0062] - The parameterizable number of acceleration values is in the range from 10 to 500, preferably in the range from 50 to 300, more preferably in the range from 100 to 300;

[0063] - The lower set point of step c2) or the higher set point of step c4) remains constant for a time interval of at least 5 seconds, preferably at least 10 seconds, more preferably at least 20 seconds (advantageously less than 60 minutes), regardless of the vibration measured during the time interval.

[0064] The invention relies on the acceleration of the refiner.

[0065] Preferably, the acceleration is measured by calculating the real-time average value of a parameterizable number of acceleration values measured within a time interval. Thus, measuring the acceleration does not depend on the number of times above the maximum value or below the minimum value.

[0066] The invention also relates to a refining system for implementing the foregoing method. Thus, it is a refining system for optimizing the refining energy supplied to the fiber composition during the refining operation of the refining system.

[0067] The main features of the system include:

[0068] - A refining machine, which is provided with at least two refining discs, and the at least two refining discs are separated from each other by an adjustable gap.

[0069] - A vibration sensor, which is configured to measure the vibration of the refining machine and output a corresponding vibration signal, and the vibration signal depends on the gap.

[0070] - A control system, which is configured to receive the vibration signal of the vibration sensor according to the foregoing method, compare at least one characteristic of the vibration signal with a determined maximum value or minimum value, and control the refining machine.

[0071] According to other aspects, the system according to the present invention has the following different features individually or in accordance with their technically possible combinations:

[0072] - The vibration sensor includes an accelerometer (or a microphone), and the characteristic of the vibration signal includes the acceleration of the refining machine measured by the accelerometer (or the microphone).

[0073] - The control system is configured to measure the acceleration by calculating the real-time average value of a parameterizable number of acceleration values measured by the accelerometer (or the microphone) within a time interval ranging from 0.5 seconds to 5 seconds, preferably from 1 second to 3 seconds.

[0074] - The parameterizable number of acceleration values ranges from 10 to 500, preferably from 50 to 300, more preferably from 100 to 300.

[0075] - The control system is configured to keep the lower set point in step c2) or the higher set point in step c4) constant within a time interval of at least 5 seconds, preferably at least 10 seconds, more preferably at least 20 seconds (advantageously less than 60 minutes), regardless of the vibration measured during the time interval. Description of the Drawings

[0076] Other advantages and features of the present invention will become apparent when reading the following description given as an illustrative and non-limiting example in conjunction with the following drawings:

[0077] Figure 1 is a graph according to the prior art, which illustrates the change of the specific energy and gap of a pair of discs of a refining machine according to the number of refining cycles.

[0078] Figure 2 shows a flowchart for illustrating different steps of the optimization method of the refining energy according to the present invention.

[0079] Figure 3A measurement signal showing the acceleration of the refiner during the refining operation.

[0080] Figure 4 Shows a plurality of graphs A to F according to the present invention, which illustrate the variation of the refining energy according to the number of refining cycles for a plurality of refining operations for different fiber compositions. Detailed description

[0081] The present invention relates to a method for optimizing the refining energy supplied to a fiber composition by a refiner during a refining operation, and a refining system suitable for implementing such a method.

[0082] The refining system includes a refiner.

[0083] The refiner is provided with at least two refining disks separated from each other by an adjustable gap. This means that the disks can move relative to each other and can be pulled towards or away from each other. Generally, in a pair of disks, a single disk in the pair can be movable (rotor), while the other disk remains fixed (stator). The centers of the disks are on the same axis as the axis of the refiner. One of the disks is usually located on the opening part (i.e., the door) of the refiner, which allows for easy rearrangement or replacement of the disks.

[0084] According to the desired type of refining, several pairs of disks can be provided arranged in series or in parallel. Those skilled in the art will know how to optimize the number of disks and their arrangement to obtain the desired refining performance.

[0085] The refining system further includes at least one vibration sensor configured to measure the vibration of the refiner and output a vibration signal of the refiner.

[0086] For this purpose, one or more vibration sensors can be used to make the vibration measurement more accurate. The (one or more) sensors can be arranged at different positions of the refiner, such as on the refiner body and / or on the refiner motor. According to a specific embodiment, the refiner does not include any vibration sensors on the refining disks.

[0087] According to other specific embodiments, the refiner does not include any vibration sensors on the refiner door. Generally, sensors on the refiner door allow detection of vibrations parallel to the axis of the refiner. According to this embodiment, the vibration sensors are not along the axis.

[0088] According to a preferred embodiment, the refiner includes vibration sensors on its body. The vibration sensors are preferably positioned so as to allow detection of vibrations perpendicular to the axis of the refiner.

[0089] Preferably, at least two vibration sensors are used, where the first sensor is located on the refiner body and the second sensor is located on the refiner motor.

[0090] According to a preferred embodiment, the vibration sensor includes an accelerometer (or microphone) configured to measure the acceleration of the refiner and output the electrical signal characteristics of the acceleration of the refiner.

[0091] Alternatively, the vibration sensor may include a microphone configured to measure the sound vibration caused by the vibration of the refiner and output the electrical signal characteristics of the sound vibration.

[0092] The refining system further includes a control system configured to control at least one of the elements of the refiner, and the elements of the refiner include at least one of the refining disks.

[0093] As further explained in detail in the remainder of this document, the control system is configured to receive the vibration signal of the vibration sensor as an input, compare at least one characteristic of the vibration signal with a determined maximum or minimum value, and control at least one of the disks to modify the gap accordingly.

[0094] The refining system preferably includes at least one computing device configured to calculate the refining energy (i.e., specific energy). The computing device is connected to a plurality of sensors, and the computing device receives data for calculating the specific energy from these sensors, such as the flow rate of the fiber composition, the rotational speeds of the motor and the disk, or also the gap.

[0095] The computing system can calculate the specific energy in real time (i.e., continuously) or discretely at a determined moment.

[0096] The computing device can be integrated into the control system or be different from the control system.

[0097] The refining system further includes a memory that can store data related to the operation of the refining system. These data particularly include one or more specific energy set points. These data can be recorded by the manufacturer during system manufacture and / or by the operator before or during the refining operation.

[0098] The memory can be integrated into the control system or be different from the control system.

[0099] Now reference will be made to Figure 2 、 Figure 3 and Figure 4 to describe the method for optimizing the refining energy according to the present invention. This method is based on the implementation of the refining system just described.

[0100] The method is started by starting the refining system, which is fed with a fiber composition stream.

[0101] Preferably, the refining energy is measured from the beginning of the refining and throughout the refining operation. This measurement is performed by the computing device.

[0102] The rotational speeds of the fiber assembly stream and the motor and disc of the refiner are preferably kept constant throughout the refining operation. This allows for the variation of a small number of parameters, enabling better control of the specific energy over time, apart from obvious reasons of convenience and industrial limitations.

[0103] At step a), an initial refining energy (or initial specific energy) set point, denoted as Cs1, is set.

[0104] Step b) includes measuring the vibration of the refiner to obtain a corresponding vibration signal. The vibration signal depends on the gap, with the closer the discs are to each other, the stronger the vibration signal. In practice, this measurement is carried out by a vibration sensor that receives the refiner vibration as input and outputs a corresponding vibration signal. The vibration signal is then transmitted to the control system.

[0105] The vibration signal can then be processed by a system provided for signal processing. For example, the signal is filtered over a given frequency interval.

[0106] The control system receives the vibration signal as input. At step c), the control system compares at least one characteristic Cq of the vibration signal with a determined maximum value V max or minimum value V min for comparison.

[0107] In Figure 2 's flowchart, these conditions are denoted as: "Cq≥V max ?" and "Cq≤V min ?"

[0108] In practice, the maximum value V max and the minimum value V min depend on the settings of the refining system. Therefore, the maximum value V max and the minimum value V min are determined by the operator through experience during different refining trials and recorded by the operator in the memory of the refining system. The operator can modify them before or during the refining operation.

[0109] At the end of the comparison, if the characteristic Cq of the vibration signal is lower than the maximum value V max , or higher than the minimum value V min , then the previous condition (N) is not satisfied. Then, the method is repeated starting from the measurement step b). This alternative is referred to as c1) or c3) in Figure 2 's flowchart.

[0110] Conversely, if the characteristic Cq of the vibration signal is greater than or equal to the maximum value V max , or less than or equal to the minimum value V min, the previous condition (O) is satisfied.

[0111] Satisfying the condition Cq ≥ V max means that the refiner has started to resonate and means that the discs are very close to each other. Then, the control system automatically reduces the specific energy setpoint Cs1 to a lower setpoint value Cs2. In order for the specific energy to tend towards the lower setpoint value and then stabilize near that value, the control system automatically controls the discs to pull them apart, thereby increasing the gap Ef. Thereby, the refiner leaves the resonant state. This alternative is Figure 2 referred to as c2) in the flowchart of

[0112] Incidentally, steps c) and c2) make it possible to avoid collisions of the refiner discs and do so regardless of the current energy setpoint. This means that a very high initial energy setpoint can be selected to maximize the refining efficiency without worrying about accidents caused by collisions of the discs.

[0113] Satisfying the condition Cq ≤ V min means that the vibration is very low, which indicates that the discs are too far apart to provide sufficient energy for effective fiber refining. Then, the control system automatically increases the specific energy setpoint Cs1 to a higher setpoint value Cs2. In order for the specific energy to tend towards the higher setpoint value and then stabilize near that value, the control system automatically controls the discs to bring them closer to each other, thereby reducing the gap Ef. This alternative is Figure 2 referred to as c4) in the flowchart of

[0114] According to a preferred embodiment, the characteristic Cq of the vibration signal includes the acceleration of the refiner. Such acceleration is typically expressed in g, where 1g is approximately equal to 9.82 m / s 2 . Then, by comparing the acceleration value with the maximum acceleration value V max and the minimum acceleration value V min the comparison c) and the alternatives c2) and c4) are performed using the acceleration value.

[0115] The acceleration used can be the root mean square value of the amplitude of the vibration signal filtered over a determined frequency range. The determined frequency range can be, for example, in the range from 4 kHz to 10 kHz.

[0116] Preferably, the acceleration is measured by calculating the real-time average value of a parameterizable number of acceleration values measured within a given time interval. This is then referred to as the moving average or sliding average. This means that the average value is continuously modified by continuously considering the new acceleration values used for the calculation of the average and discarding the old acceleration values.

[0117] The time interval for calculating the average acceleration is advantageously in the range from 0.5 s to 5 s, preferably in the range from 1 s to 3 s.

[0118] Furthermore, the parameterizable number of acceleration values is advantageously in the range from 10 to 500, preferably in the range from 50 to 300, more preferably in the range from 100 to 300.

[0119] At the end of step c2) or step c4), the method is preferably repeated at least once starting from step b) to optimize the specific energy during the entire refining operation. In this case, depending on the result of comparing step c), the new specific energy setpoint Cs2 may be automatically modified to a lower or higher setpoint Cs3, and so on in successive iterations of the method.

[0120] Preferably, the lower or higher setpoint Cs2 respectively produced by step c2) or step c4) is kept constant for a time interval of at least 5 s (preferably at least 10 s, more preferably at least 20 s (advantageously less than 60 minutes)), regardless of the vibrations measured during said time interval. This makes it possible to properly stabilize the system energy at the new setpoint value and avoid any energy losses.

[0121] Optionally, after step c) (i.e., sub-step c2) and sub-step c4)) there may be a step d), according to which the measuring device makes a measurement of the average length of the fibers of the fiber composition. Depending on the needs of the operator, it may be a number, weight or length average.

[0122] If the average length L of the fibers is greater than the minimum length L min , the refining continues. Conversely, if the average length of the fibers is less than or equal to the minimum length L min , the refining stops.

[0123] Figure 3 A graph is illustrated showing the vibration signal measured by the sensor and transmitted by the sensor to the control system. Here, the characteristic of the vibration signal that is measured and subsequently compared is the acceleration, denoted as Ac (expressed in g) plotted on the ordinate.

[0124] The left-hand signal relates to the first reactor, and the maximum acceleration value of the first reactor is set to 5 g (1 g = 9.80665 m / s 2)。The computing device determines the average value of the acceleration in real time based on the amplitude of the signal. When the average value is greater than or equal to the maximum value of 5g, the control system reduces the setpoint value to a new lower setpoint value (e.g., 4.5g), and sends a control command to the disks to pull them away from each other, thereby increasing the gap and then reducing the specific energy. The control system adjusts the gap such that the specific energy tends to or even reaches the new lower setpoint value. Thus, the specific energy is controlled in a top-down manner.

[0125] The right-hand signal relates to the second reactor, and the maximum acceleration value of the second reactor is set to 3g. Similar to the left-hand reactor, when the measured average acceleration is higher than or equal to the maximum value of 3g, the control system reduces the setpoint value to a new lower setpoint value and controls the disks to increase the gap.

[0126] The value of 3g can also be provided independently or in combination with the maximum value of 5g to represent the minimum acceleration value of the left-hand reactor (1). In this case, when the measured average acceleration is less than or equal to the minimum value of 3g, the control system increases the setpoint value to a new higher setpoint value (e.g., 3.5g), and sends a control command to the disks to bring them closer to each other, thereby reducing the gap and then increasing the specific energy. The control system adjusts the gap such that the specific energy tends to or even reaches the new higher setpoint value. Thus, the specific energy is controlled in a bottom-up manner.

[0127] Respectively, of course, the value of 5g can be provided independently or in combination with the minimum value of 3g to represent the maximum acceleration value of the right-hand reactor (2). The operating principle is the same as the foregoing.

[0128] In the case where both the minimum value of 3g and the maximum value of 5g are set, the measured average acceleration is compared with each of these two limit values, and the specific energy is increased or decreased according to its value. Thus, the specific energy is controlled in both a top-down and a bottom-up manner.

[0129] Figure 4 Eight curves with markings (A), (B), (C), (D), (E), (F), (G) and (H) are shown, which illustrate the variation of the specific energy E with the number of passes Np in the refiner for different fiber compositions.

[0130] It is worth noting that these curves all have relatively similar profiles, i.e., the energy decreases with the progress of the refining of the composition. However, the number of stages, the duration of the stages and the energy of each stage vary from one curve to another, and thus the number of stages, the duration of the stages and the energy of each stage vary from one fiber composition to another.

[0131] For example, curve graph (A) includes 8 stages. Comparatively, curve graph (B) only has 7 stages. Similarly, curve graph (G) includes 9 stages. Comparatively, curve graph (H) only has 7 stages.

[0132] In addition, still by way of example, the 23 - kWh / t stage of curve graph (A) lasts for approximately 1 pass, while the 23 - kWh / t stage of curve graph (B) lasts for approximately 3 passes. Similarly, the 17 - kWh / t stage of curve graph (G) lasts for approximately 1 pass, while the 17 - kWh / t stage of curve graph (H) lasts for approximately 5 passes. In addition, the 17 - kWh / t stage is the last stage of curve graph (H) because at this time the fibers have reached their minimum size. In contrast, curve graph (G) also includes a 14 - kWh / t stage and a subsequent 11 - kWh / t stage required to complete the refining.

[0133] This can be explained as follows. The compositions of curve graphs (A) to (H) are different due to the physico - chemical properties of the composition, in particular due to the characteristics of the fibers, the relative amount of fibers in the composition, the length distribution of the fibers, or also due to the consistency of the composition, and due to the presence and characteristics of the fillers incorporated into the composition.

[0134] The differences in these properties have an impact on the rheology of the composition, that is, on its flow properties according to the strain applied during refining.

[0135] In addition, the further the refining progresses, the more the fibers are shortened and sheared, so that the previous properties and rheology are modified.

[0136] Accordingly, the change in specific energy measured over time for one composition is different from that of another composition, resulting in different regulations of said energy by the control system according to the present invention. In practice, the changing profile of the gap during refining varies according to the composition to be refined.

[0137] The method of the present invention takes into account the changes in the physico - chemical properties of the composition and accordingly automatically adjusts the specific energy to be closest to the optimal energy.

[0138] Therefore, the method of the present invention automatically adjusts and optimizes the specific energy according to the physico - chemical properties of the composition to be refined by using the vibration of the refiner as a measurement element.

Claims

1. An optimization method for optimizing the refining energy supplied to a fiber composition during a refining operation by a refiner, the refiner including at least two refining disks separated from each other by an adjustable gap, the method comprising the following steps: a) Setting an initial refining energy setpoint, b) Measuring the vibration of the refiner to obtain a corresponding vibration signal, the vibration signal depending on the gap, c) Comparing at least one characteristic of the vibration signal with a determined maximum value and / or minimum value to: c1) If the characteristic of the vibration signal is lower than the maximum value, the method restarts from step b), c2) If the characteristic of the vibration signal is higher than or equal to the maximum value, automatically reducing the initial refining energy setpoint to a lower setpoint value and automatically increasing the gap such that the refining energy tends towards the lower setpoint value, and / or c3) If the characteristic of the vibration signal is higher than the minimum value, the method restarts from step b), c4) If the characteristic of the vibration signal is lower than or equal to the minimum value, automatically increasing the initial refining energy setpoint to a higher setpoint value and automatically reducing the gap such that the refining energy tends towards the higher setpoint value, wherein the lower setpoint of step c2) or the higher setpoint of step c4) remains constant for at least 5 seconds regardless of the vibration measured during the time interval, wherein the characteristic of the vibration signal includes the acceleration of the refiner.

2. The method according to claim 1, wherein The lower setpoint of step c2) or the higher setpoint of step c4) remains constant for at least 10 seconds regardless of the vibration measured during the time interval.

3. The method according to claim 1, wherein The lower setpoint of step c2) or the higher setpoint of step c4) remains constant for at least 20 seconds regardless of the vibration measured during the time interval.

4. The method according to any one of claims 1 to 3, wherein after performing step c2) or step c4), the method is repeated at least once starting from step b), and the initial refining energy setpoint is correspondingly replaced by the lower setpoint or the higher setpoint.

5. The method according to any one of claims 1 to 3, wherein The acceleration is measured by calculating a real-time average of a parameterizable number of acceleration values measured in a time interval ranging from 0.5 seconds to 5 seconds.

6. The method according to any one of claims 1 to 3, wherein, The acceleration is measured by calculating a real-time average of a parameterizable number of acceleration values measured in a time interval ranging from 1 second to 3 seconds.

7. The method according to claim 5, wherein The parameterizable number of acceleration values ranges from 10 to 500.

8. The method according to claim 5, wherein The parameterizable number of acceleration values ranges from 50 to 300.

9. The method according to claim 5, wherein, The parameterizable number of acceleration values ranges from 100 to 300.

10. The method according to any one of claims 1 to 3, wherein: - After performing step c2) or step c4), repeat the method at least once starting from step b), with the initial refining energy set point being correspondingly replaced by the lower set point or the higher set point; - Measure the acceleration by calculating the real-time average value of a parameterizable number of acceleration values measured within a time interval in the range from 0.5 seconds to 5 seconds; and - The parameterizable number of acceleration values is in the range from 10 to 500.

11. A refining system for optimizing the refining energy supplied to a fiber composition during a refining operation of the refining system, characterized in that, The refining system comprises: - A refiner provided with at least two refining discs, the at least two refining discs being separated from each other by an adjustable gap, - A vibration sensor configured to measure the vibration of the refiner and output a corresponding vibration signal depending on the gap, - A control system configured to receive the vibration signal of the vibration sensor, compare at least one characteristic of the vibration signal with a determined maximum or minimum value according to the method of any one of claims 1 to 10, and control the refiner, wherein the vibration sensor comprises an accelerometer or a microphone, and the characteristic of the vibration signal comprises the acceleration of the refiner measured by the accelerometer or the microphone, wherein the control system is configured to keep the lower set point of step c2) or the higher set point of step c4) constant within a time interval of at least 5 seconds, regardless of the vibration measured during the time interval.

12. The refining system according to claim 11, wherein, The control system is configured to keep the lower set point of step c2) or the higher set point of step c4) constant within a time interval of at least 10 seconds, regardless of the vibration measured during the time interval.

13. The refining system according to claim 11, wherein, The control system is configured to keep the lower set point of step c2) or the higher set point of step c4) constant within a time interval of at least 20 seconds, regardless of the vibration measured during the time interval.

14. The refining system according to any one of claims 11 to 13, wherein The control system is configured to measure the acceleration by calculating the real-time average value of a parameterizable number of acceleration values measured by the accelerometer or the microphone within a time interval in the range from 0.5 seconds to 5 seconds.

15. The refining system according to any one of claims 11 to 13, wherein, The control system is configured to measure the acceleration by calculating the real-time average value of a parameterizable number of acceleration values measured by the accelerometer or the microphone within a time interval in the range from 1 second to 3 seconds.

16. The refining system according to claim 14, wherein, The parameterizable number of acceleration values is in the range from 10 to 500.

17. The refining system according to claim 14, wherein, The parameterizable number of acceleration values is in the range from 50 to 300.

18. The refining system according to claim 14, wherein The parameterizable number of acceleration values is in the range from 100 to 300.

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