WO2024079026A1

WO2024079026A1 - Method for operating a pulper for producing a suspension, in particular a fibrous suspension

Info

Publication number: WO2024079026A1
Application number: PCT/EP2023/077858
Authority: WO
Inventors: Wolfgang Müller; Pantelis Zafeiropoulos
Original assignee: Voith Patent Gmbh
Priority date: 2022-10-13
Filing date: 2023-10-09
Publication date: 2024-04-18
Also published as: DE102022126745A1

Abstract

The invention relates to a method for operating a screen device (50, 250) for cleaning a fibrous suspension with a rotor (58), arranged in a housing (51, 251) of the screen device (50, 250), and a screen (57), wherein fibrous suspension and rinsing water are fed to the screen device (50), and that proportion of the fibrous suspension which passes through the screen (57) is discharged via an accepted stock discharge (67, 267), wherein an inflow into the screen device (50, 250) and/or a cycle time duration are/is regulated in a manner which is dependent on the power consumption (162) of the rotor drive (59, 259).

Description

Method for operating a pulper for producing a suspension, in particular a fiber suspension

The invention relates to a method for operating a screening device for cleaning a fiber suspension according to the preamble of claim 1 and to an arrangement with a screening device for carrying out the method.

Digitalization makes it possible to control and regulate processes more precisely. This can involve increased computing capacity and AI. Voith already has a number of specific applications, which are listed below.

OnEfficiency.BreakProtect uses a unique Kl algorithm to automatically detect a wide variety of causes of breakage in paper production. This allows countermeasures to be defined early on for each specific type of breakage and ensures stable, cost-efficient production.

OnEfficiency.DIP optimizes an existing DIP line towards constant DIP quality at minimal costs. The existing flotation is supplemented by additional actuators and new sensors are installed to monitor the quality parameters. The DIP quality fluctuations caused by incoming raw materials or production changes are reduced by dynamic adjustment of the losses during washing/flotation and by real-time optimization of the bleaching chemical dosing.

The Valmet company has promoted an application for better refiner quality under the name “Fiber Furnish Control”.

Pulpers are used in particular in the field of fibre extraction from waste paper. Waste paper and water are fed into a pulper to produce a fibre suspension. The qualities of the waste paper can vary. The patent application DE 10 2021 103 233 describes a process for optical detection of waste paper quality is described. Depending on the recorded properties of the waste paper, control of process parameters such as the addition of water is provided.

A discontinuously operated pulper is first filled with water, then the waste paper or pulp is added and dissolved there. The fiber suspension is then pumped out and processed further. The dissolving time also depends on the quality of the waste paper fed into the pulper.

There are also continuously operating pulpers, which are continuously fed with waste paper and water. The resulting fiber suspension then passes through a screen to an accepts discharge. In such pulpers, impurities are removed from the pulper via a discharge provided above the screen plate. The stock density of normal pulpers is around 3 to 6%.

Sieving devices are used to clean fiber suspensions with a high impurity content. A sieving device is known, for example, from EP 2104766 A1. This sieving device has an asymmetrical housing. A sieve is arranged in an upper area of the housing. A rotor is assigned to the sieve, which keeps the sieve free of contaminants. In addition, the supplied suspension is set in rotation. Accepted material is discharged from the top of the housing and above the suspension feed in relation to the vertical direction. In the lower part of the housing there is an outlet opening for impurities leading diagonally downwards. Such sieving devices are used in particular to process, for example, the contaminated suspension coming from the pulper. In particular, this sieving device is also suitable for a fiber suspension that comes from a discontinuously operated pulper without passing through a sieve, as described above. The sieving device described here is operated cyclically. The throughput cycle, the post-dissolving cycle (if applicable, also known as “slushing”), the rinsing cycle and the discharge cycle run cyclically. During the flow cycle, fiber suspension is fed to the screening device and the accepts discharge is opened.

A post-dissolving cycle is a cycle in which no more suspension is added and the rinsing process has not yet started. The suspension present in the sieve device is treated in the sieve device.

During the rinsing cycle, no more fiber suspension is introduced into the screening device and rinsing water is introduced into the screening device. This allows dissolved fibers to be rinsed out of the screening device as acceptable material.

In the discharge cycle, a contaminant discharge is opened and contaminants are discharged from the screening device as rejects.

Due to fluctuations in the impurity content in the fiber suspension, high mechanical and/or process-related stresses occur again and again. This often results in alarm messages. Due to the frequency of such alarm messages, such alarm messages are often acknowledged without any concrete action being taken to intervene in the process and without the cause of the alarm being checked. In addition, intervention is only possible to a limited extent due to the inertia of the system and is difficult due to the large number of influencing factors.

The invention is based on the object of improving a method for operating a screening device. In particular, the occurrence of overloads should be avoided, or at least reduced. In particular, the occurrence of alarm messages should be reduced without this leading to an overload of the device. The object is achieved by the method having the features according to claim 1. The arrangement for achieving the object comprises the features of claim 14. Further advantageous features are mentioned in the dependent claims.

To solve the problem, a method for operating a screening device for cleaning a fiber suspension is provided. The screening device has a rotor arranged in a housing of the screening device and a screen arranged in the housing. Fiber suspension and rinsing water can be fed to the screening device. The portion of the fiber suspension that passes through the screen is discharged via an accepts discharge. Depending on the power consumption of the rotor drive, an inflow into the screening device and/or a cycle time duration is regulated or controlled. The regulation and control can relate to a power consumption of the rotor in a previous cycle. This allows the inertia of the system to be taken into account on the one hand and continuous regulation or control during operation of the screening device to be ensured on the other.

In an advantageous embodiment, it is provided that the cycle time is regulated for at least one cycle of a subsequent cycle sequence depending on the power consumption of the rotor drive. A cycle sequence comprises at least one run-through cycle, rinsing cycle, discharge cycle. Optionally, a post-dissolving cycle can be carried out between the run-through cycle and the rinsing cycle. The provision of a post-dissolving cycle can be provided in particular depending on the outflow of accepted material during the run-through cycle.

In one embodiment of the method, it is provided that if the power consumption of the rotor drive exceeds a predetermined limit, the inflow of flushing water is reduced at least at the beginning of a subsequent flushing cycle compared to a maximum possible inflow of flushing water. This can prevent overloading of the rotor drive. As a result, frequently occurring alarm messages can be prevented. Especially at the beginning of the flushing cycle, the application of flushing water can prevent a further increase in the flow of flushing water. the power consumption of the rotor of the screening device. It has been shown that a moderate addition of rinsing water, especially at the beginning of the rinsing cycle, can have a significant influence on the maximum power consumption of the rotor in a cycle sequence.

In one embodiment of the method for operating a screening device, it is provided that, additionally or alternatively, a cycle time duration of the throughput cycle and/or the rinsing cycle is regulated depending on the flow rate of accepted material and/or an optional post-dissolving cycle is provided. The duration of the post-dissolving cycle can also be regulated depending on the flow rate of accepted material, in particular during the throughput cycle or the post-dissolving cycle. Alternatively, when the post-dissolving cycle is activated, the post-dissolving cycle can be carried out with a predetermined duration.

In one embodiment of the method for operating a screening device, it is provided that an inlet pressure and/or a differential pressure to the pressure of the accepted material discharge is taken into account when controlling a subsequent cycle time. This allows conclusions to be drawn about the suspension present in the screening device and its quality. Depending on the suspension quality and suspension quantity present in the screening device, this can be taken into account when controlling the screening device.

In one variant of the method for operating a screening device, it is provided that system-specific limit values are read in or manually entered or stored during commissioning. This makes it possible to access these values. For example, it can be provided that in the event of contradictory measurement data, this stored data is used. When this data is used, the device is operated in basic mode. This is not a dynamically adaptive mode. During the application of this basic mode, the stored system-specific limit values are not adjusted. However, a Adaptive adjustment of the stored limit values during dynamic operation should be provided.

In one embodiment of the method for operating a screening device, a maximum system-specific acceptable material flow is stored. This ensures that faults can be detected and remedied using stored procedures.

In one embodiment of the method for operating a screening device, a factory setting and/or a basic setting is stored in the control system, whereby operation without adaptive control is possible with the factory setting and the basic setting. However, this means that the efficiency of the device is lower than when operating with adaptive control.

In one embodiment of the method for operating a screening device, it is provided that if the power consumption of the rotor drive is outside a stored power range, in particular in the run-through cycle, the operation is continued on the basis of data from a basic setting or factory setting until the recorded operating data are again within the stored standard range.

In one variant of the method for operating a screening device, if an operating parameter is outside a stored standard range, the method is continued using a predetermined number of cycles and the operating parameters used are adaptively adjusted for these cycles. The aim of this is to ensure that basic operation without adaptive control is not used every time there is a deviation from the standard range. However, if this does not allow operation within the stored standard ranges within the predetermined number of cycles, the system switches to basic operation. This can prevent permanent or excessive overloading of the device. In a method for operating a system with at least a first cyclically operated screening device and a second cyclically operated screening device arranged in parallel, a pulper, it is provided that the cycles of at least two screening devices are coordinated with one another for the use of peripheral devices, such as a downstream sorting drum, of the system. Coordination takes place by extending at least one of the rinsing cycles from the currently ongoing sequences and/or shortening at least one of the throughput cycles. This allows peripheral devices to be used optimally and does not have to be provided separately for each screening device. For example, a pump for supplying fiber suspension can be accessed jointly. It is also possible to supply rinsing water to two screening devices using one pump.

In one embodiment of the method for operating a system with a pulper and at least one screening device, fiber suspension is returned to the pulper. It is intended that the consistency and amount of fiber suspension returned to the pulper are taken into account in order to achieve a constant stock density in the pulper. In particular, depending on the consistency and inflow of the fiber suspension returned to the pulper, control of the supply of dilution water can be provided. This can minimize fluctuations in the stock density of the fiber suspension leaving the pulper. In particular, this makes it possible to maintain a predetermined stock density range more precisely, whereby subsequent processing and cleaning of the fiber suspension can be better tailored to the fiber consistency. For example, a predetermined stock density consistency of +/- 0.2% absolute percent can be maintained.

Arrangement with a pulper and at least one screening device, wherein a control valve is arranged in the supply of rinsing water to the screening device. The control valve is provided for a controlled supply of rinsing water into the screening device. This allows a supply of rinsing water, in particular during rinsing cycle. This regulated supply of rinsing water can prevent overloading of the rotor drive, or at least reduce it. The control valve makes it possible to continuously increase the amount of rinsing water supplied.

In the rinsing cycle and discharge cycle, the supply of fiber suspension is interrupted. Rinsing water is fed to the screening device in a targeted manner. The rinsing water initially rinses out more fibers. It has been found that this phase in particular is very susceptible to overloads. Not only the required drive power for the fiber suspension with enriched impurities, but also the supplied rinsing water inflow affects the rotor. Although the rinsing water serves to dilute the fiber suspension present in the screening device and it could be assumed that fibers can now flow through the screen more easily, it has been shown that, surprisingly, overload situations occur precisely at these times. An overload situation can be avoided by reducing the initial rinsing water inflow. Additional exposure of the rotor to rinsing water can be reduced. Acceptable material can flow through the screen, even if it is possibly partially covered by impurities. This can reduce the peak load on the rotor drive and also the overall load on the drive in the rinsing cycle.

The duration of the rinsing cycle can be adaptively extended and the amount of rinsing water per rinsing cycle, preferably with a deviation of +/- 10% from a predetermined amount of rinsing water, can still be kept constant in the rinsing cycle. This means that a good yield of fiber can be achieved by adapting the rinsing cycle. Quantities are given in cubic meters. When we talk about a flow, such as inflow, throughflow or outflow, we mean volume per time, often given in liters per minute.

In a discharge cycle following the rinsing cycle, rinsing water flows in at a predetermined maximum inflow. This reduces the Sieve device remaining suspension with concentrated impurities from the

The rejects discharge is closed

In one design variant, the duration of the discharge cycle is adapted depending on the power consumption of the rotor. This can improve the discharge of impurities. On the other hand, the discharge cycle should only last as long as noticeably impurities are being discharged. For example, if the rotor's power consumption falls below a predetermined level, this can be used as an indication that the screening device has been sufficiently cleaned of impurities.

In some applications, it has proven advantageous to allow the duration of the cycles to vary within a predetermined time frame depending on at least the parameter of the rotor's power consumption. This can prevent the system from remaining in an operating step when the operating data is incorrect.

The better the removal of impurities, the more efficient the subsequent cycle can be. This means that the drive power of the rotor can be reduced because impurities do not remain in the screening device for an unnecessarily long time. In addition, there is the positive effect that the impurities are exposed to the rotor for a shorter time, which prevents them from being rubbed off by the rotor, or at least reduces this.

It has proven to be advantageous that the increase in the flow of flushing water in the flushing cycle is adaptive and dependent on the current load, only as long as the maximum power consumption is below a predetermined maximum upper limit. If this upper limit is exceeded, the rotor drive is overloaded. By not supplying the maximum amount of flushing water, overload situations in the rotor drive can be prevented, or at least their occurrence can be reduced and the overload reduced. For example, the flow of rinse water in the rinse cycle can be reduced from a predetermined limit value compared to the maximum flow of rinse water during the first 5 seconds, or a maximum of the first 20 seconds. This limit value is below the maximum upper limit value. This is intended to prevent the maximum upper limit value from being exceeded.

It has been found to be advantageous that when the inflow of rinsing water is reduced, the inflow is reduced to a minimum of 20% of the maximum inflow of rinsing water in the rinsing cycle. In an advantageous operating variant, the amount of rinsing water remains as predetermined. This extends the rinsing cycle and a constant amount of rinsing water is used to rinse out fibers. This means that fibers can still be rinsed out and an overload of the rotor drive can be counteracted.

In one embodiment, it can be provided that flushing is carried out adaptively and predictively from the current impurity load based on the drive power of the rotor until a predetermined lower limit of the power consumption is reached. This ensures that a large proportion of the impurities have been flushed out. This again provides a good starting point and thus filling capacity of the screening device for subsequent cleaning of fiber suspension in the flow cycle and the following cycles.

Adaptive here means adjusting. It is an adaptation based on the detected operating parameters.

A predictive setpoint adjustment and its control are considered predictive. In particular, the previous cycles 1 to 50 can be used. It can be provided that, depending on the power consumption at the end of the discharge cycle above a lower limit, the length of the subsequent or the subsequent new cycle of the fiber suspension input is shortened. The drive power of the rotor at the end of the discharge cycle gives an indication of remaining impurities. This impurity can be traced back to a high impurity load of the fiber suspension fed to the screening device. However, a high impurity load can also have accumulated in the screening device due to a long previous cycle.

The ability to react dynamically to the impurity load can increase the efficiency of the screening device. If there is a low impurity load in the fiber suspension fed into the flow cycle, the flow cycles can be extended without risking overloading the rotor drive.

On the other hand, the cycle times can be shortened if the impurity load is high. This can be recognized by the speed at which the rotor drive power increases. Impurities are then removed more frequently and overloading of the rotor drive is counteracted, which has a positive effect on the service life of the screening device.

If the accepted material is to be fed back into the pulper, the more frequent discharge of impurities in the screening device can also ensure that the impurity load in the pulper is broken down more quickly. This results in less shredding in the pulper. Shredding would mean that the shredded impurities would become an increased burden in subsequent cleaning process stages and could potentially have a negative impact on the final accepted material quality.

In one process variant, it is planned that, depending on the power consumption at the end of the discharge cycle, the amount and also the inflow of fed fiber suspension is reduced. This means that the new impurity input per time interval as well as the total amount of fiber suspension fed in this cycle and the associated impurity in the screening device at the end of the throughput time can be reduced. This is a particularly effective way of counteracting overload situations.

According to the invention, the arrangement with a sieve device is characterized in that the arrangement has an adjustable valve in the flushing water supply for adjusting the inflow of flushing water. This makes it possible to dynamically regulate the inflow of flushing water. The drive power of the rotor drive can be recorded by a control system. To avoid overload situations, it is now possible to use the control valve to reduce the inflow of flushing water depending on the drive power of the rotor. Characteristic curves can be stored in the control system or even taught in.

In a variant in which a pulper is installed upstream of the screening device, the control system is designed to reduce the supply of material to the pulper after a predetermined number of cycles with a power consumption of the rotor of the screening device exceeding a limit value stored in the control system. This counteracts an overload of the fiber processing. The speed of processing waste paper to be processed into an acceptable material can thus be adapted to the quality of the waste paper fed to the pulper.

By means of a computer program product, an existing plant can be retrofitted with a pulper and at least one subsequent cyclically operated screening device for carrying out the process according to one of the previously described inventive processes. This can increase the efficiency of old plants.

Further advantageous features of the invention are explained using embodiments with reference to the drawings. Fig. 1 schematic representation of a system according to the invention

Fig. 2 schematic representation of a plant according to the invention with continuously operated pulper

Fig. 3 schematic representation of a system according to the invention with two screening devices arranged in parallel

Fig. 4 Schematic representation of a control system Fig. 5 Operational measurement curves in schematic representation a) Drive power of pump b) Acceptable material discharge c) Drive power of rotor of the screening device 50 d) Volume of the dilution-wash water supplied

Figures 1, 2 and 3 show examples of systems 1 for producing a fiber suspension. The problem with fiber extraction from waste paper is to remove as many impurities as possible. However, the removal of fibers associated with the removal of impurities should be kept to a minimum.

Paper stock, also referred to as waste paper, shown here as waste paper bales 13, is fed to a pulper 20 via a conveyor belt 11. Pulpers 20 are also referred to below as pulpers 20. In the pulper 20, for example, waste paper as paper stock is mixed with water and converted into a fiber suspension. For this purpose, dilution water is fed to the pulper 20 via an adjustable water supply 10 and the feed 15. In addition, suspension classified as acceptable stock is fed to the pulper 20 from a screening device 50 and a re-sorting device 70 connected downstream of the pulper 20. The screening device 50 and the re-sorting device 70 will be discussed in more detail later.

The pulper 20 is equipped with a screen 29 in its bottom area, through which part of the suspension can enter the annular space. Above the screen 29 is a rotor 25 is arranged, which on the one hand sets the paper stock-water mixture in rotation and on the other hand keeps the screen 29 free. The rotor 25 is driven by the drive 27. The fiber suspension that has passed through the screen 25 is discharged via an accepts discharge 21. The portion of the suspension produced in the pulper 20 that is discharged via an impurities discharge 23 is led into a collecting container 30 with an impurities outlet 31. In the collecting container 30, coarse heavy dirt contained in the introduced fiber suspension can be separated. In the collecting container 30, the suspension is ideally diluted to 3.5% for more effective heavy particle separation. The coarse heavy dirt sinks in the collecting container 30 and is separated directly through an automatically controlled dirt lock with impurities outlet 31. It can be provided that additional dilution water is added to the dirt lock for better fiber backwashing.

In the upper area of the collecting container, a discharge 33 for suspension is provided. Fiber suspension is removed from this upper area of the collecting container 30. This fiber suspension is fed by means of a pump 40 for further treatment via a line and a feed 52 to the screening device 50 with the housing 51. The pump 40 is a special pump for fiber suspensions loaded with impurities. This pump 40 can pump the impurity suspension from the pulper into the screening device 50 largely without clogging and reliably. This pump 40 is designed with a large nozzle diameter and a free-flow impeller for clogging-free pumping of fiber suspensions with a high impurity content. In particular, the impeller can be optimized for particularly high resistance by armoring. A drive 45 with a frequency converter enables an optimized pump speed for discontinuous pumping operation. As a result, the volume flow delivered by the pump 40, also referred to as flow, can be regulated, preferably continuously regulated.

The accepted material from the collecting container is fed into the downstream screening device 50 for further processing. This is a cyclically operated Sieving device. A sieve 57 is provided in the housing. A rotor 58 is arranged in front of the sieve 57. The rotor 58 causes the fiber suspension introduced into the housing 51 of the sieving device to rotate in front of the sieve 57. The rotor is driven by a drive 59. A portion of the supplied fiber suspension passes through the sieve 57 and is discharged from the sieving device via an accepted material discharge 67. Figure 5 shows a graphic representation of the discharge of the accepted material discharged from the sieving device over time. Figure 5 also shows a graphic representation of the power consumption of the rotor drive 59 over time.

There is a cycle for feeding fiber suspension, also referred to as a flow cycle. In the flow cycle 117, fiber suspension is fed to the screening device 50. The suspension is set in rotation by the rotor 58. The rotor 58 is arranged in front of a screen 57. Dissolved fibers pass through the screen 57. There is a differential pressure that promotes the outflow of dissolved fibers through the screen 57. The accepted material discharge 67 for the outflow of the accepted material with the switching valve 69, see Figure 4, is open. The impurity discharge 66 with the switching valve 56, see Figure 4, is closed. As a result, impurities are concentrated in the fiber suspension in the screening device 50 in front of the screen 57.

For increased processing of this suspension in the screening device 50, the supply of fiber suspension can be interrupted. The switching valve 53, see Figure 4, is provided for this purpose. The suspension in the screening device 50 is processed by the movement in the screening device 50. The valve 56 of the impurity discharge 66 remains closed and the accepted material discharge is open. The movement of the suspension can loosen fiber clumps present in the suspension. The loosened fibers can pass through the screen and flow out via the accepted material discharge 67. This cycle is also referred to as the post-dissolving cycle 119.

The post-dissolving cycle 119 or the run-through cycle 117 is followed by a rinsing cycle 127. In the rinsing cycle 127, a supply of rinsing water provided. The rinsing water is provided by the water supply 10. The inflow into the screening device 50 takes place via a control valve 65. The inflow can be regulated by the control valve 65. The inflow 152 of rinsing water can be regulated depending on the power consumption 162 of the rotor. Depending on the drive power of the rotor 58 of the screening device 50 before the rinsing cycle 127, the inflow of rinsing water is initially throttled. This prevents or at least reduces an overload of the rotor drive.

The supplied rinse water flow could also be controlled via an adjustable drive of the pump 60 for the rinse water supply. During this cycle, fiber suspension is increasingly rinsed out via an accepts discharge 67.

The rinsing cycle 127 is followed by a discharge cycle 137. The suspension with the concentrated impurities is discharged from the housing 51 of the screening device 50. For this purpose, the impurity discharge 66, valve 56, is opened. The cycles of the run-through cycle and the rinsing cycle can overlap or be carried out purely serially. The length of the respective cycle can be changed by a control 100 and thus adapted to the respective degree of contamination or the paper quality of the waste paper. The fraction of acceptable material extracted by the screening device 50 is fed back to the pulper 20 via a feed 17. The fraction of impurities extracted in the screening device 50 is fed to a re-sorting device 70.

In the re-sorting device 70, further washing out of fibers still present in the impurities is provided. Here, the re-sorting device 70 comprises a screen drum and a dilution water supply 75. By rotating the drum, the introduced fraction is set in rotation and also moved axially. Fibers pass through openings in the drums together with rinsing water to an accepts discharge 73 and are fed from the re-sorting device 70 to the pulper 20 via a feed 19. The material that does not pass through the screen The remaining portion is removed as impurities via an impurity removal device 76. The inflow of rinsing water can also be regulated in the re-sorting device 70. In particular, the amount of rinsing water can be regulated depending on the drive power of the drum in order to avoid overloading the drum drive.

In the arrangement 1 shown in Figure 2, the fiber suspension produced in the pulper 20 is cyclically fed directly to a downstream screening device 50. The accepted material from the screening device 50 is fed to a large collecting container 68 and the impurities separated by the screening device 50 are fed via a pump 40 to a collecting container 30 with an impurity outlet 31. From the collecting container 30, suspension can be continuously fed to a re-sorting device 70 via a feed 71 via an outlet 33. This re-sorting device 70 corresponds to the re-sorting device 70 described with reference to Figure 1. Here, the accepted material extracted by the re-sorting device 70 is fed to the pulper 20 via the accepted material discharge 73. The portion not remaining as accepted material in the re-sorting device 70 is discharged via a impurity discharge 76.

Figure 3 shows a further variant of a system for fiber processing. This system differs from the system shown in Figure 1 in that two screening devices 50, 250 are arranged parallel to one another. The functioning of the screening devices 50, 250 does not differ from the functioning of the screening device 50 from Figure 1. The second screening device also has a housing 251, a supply for suspension 252, a drive 259, a supply for rinsing water 261, an impurity discharge 266 and an acceptable material discharge 267. For efficient operation, the cycles of the two screening devices are coordinated with one another. Only one pump 40 is provided, through which fiber suspension is supplied to the first screening device 50 or the second screening device 250. A common supply of rinsing water is also provided. The impurities from the screening devices are fed to a re-sorting device 70. Figure 4 shows a more detailed version of a controller 100 for a screening device 50. The controller 100 controls the motor 45 of the pump 40. A pump controller 140 is provided for this purpose. The pump controller 140 outputs a target value and an actual value of the drive frequency of the pump and a drive power 144. The aim is to ensure maximum flow in the flow cycle without overloading the drive, under changing boundary conditions such as pre-pressure and impurity content. Here, the supply of suspension to the screening device 50 is regulated via the pump 40. A controller 150 for the water pump 60 is provided for the supply of rinsing water and the inflow of rinsing water. The valve 65 provided in the water supply 61 can be controlled via this controller. The valve 65 is an adjustable valve. The inflow of supplied rinsing water can be regulated or controlled by this valve 65. The control 150 of the flushing water pump 60 includes a target value of a delivery capacity and a base value of the delivery capacity of the water pump 60. In addition, the current drive power is recorded.

To control the pump 60 of the rinsing water and to control the rinsing water flow and quantity in the respective cycle, in particular during the rinsing cycle, values of the drive power 117 of the drive 59 of the rotor 58 of the screening device 50 are included. The control as a function of the drive power of the rotor 58 is described in more detail with reference to Figures 4 and 5.

The controller 100 can dynamically adjust the duration of individual cycles and adjust the amount of suspension and rinsing water added per time.

The control 110 records the run cycle 117. The run cycle is the time period in which fiber suspension is fed to the screening device 50. A base value of a time period for a run cycle is specified and a target value of a time period of a run cycle is specified adaptively and predictively. An adaptive predictive specification is a specification that changes depending on parameters adaptive predictive presetting. An adaptive predictive control can be based on stored characteristics or it can be provided by an adaptive learning control. If no values or characteristics are available initially, an initial learning is required. A self-learning adjustment of basic values as well as target values can then be provided.

Different basic values/initial values can also be stored in the control system for predetermined grades of waste paper. The duration of the cycles and inflows of rinsing water and suspension are controlled by the control system 100. A determined target value is provided for the individual cycles by the control system. In particular, the power consumption of the rotor drive 58 of the screening device is included. It can be provided that the duration of the flow cycle is controlled depending on the minimum power consumption of the rotor in the rinsing cycle. In addition, it can be provided that the quality and/or the amount of accepted material discharged is also included. An adjustment of a flow cycle in the range 15 see. to 150 see., preferably in the range 60 to 120 see., has proven to be a suitable control range. With the same structure, 50 see. was specified as the duration for the flow cycle in static operation. Here, the increase in efficiency through dynamic operation is evident. In case of inconsistent measured values, the values from static operation can be used to initially continue operation.

The control 120 is provided for regulating the rinsing cycle 127. In the rinsing cycle 120, rinsing water is fed into the screening device with the aim of rinsing or washing out fibers from the suspension enriched with impurities located in front of the screen. No more fiber suspension is fed through the pump 40. The switching valve 53 is or will be closed. The valve 69 for removing the accepted material is still open. The control provides for regulating the rinsing cycle 127. There is an actual rinsing time and a basic value for a rinsing time is stored. In addition to the duration of the rinsing cycle, the flow of rinsing water fed in is also regulated depending on the power consumption of the drive 59 of the rotor 58. For the rotor drive, the control 160 is provided. The rinsing cycle can also be referred to as a washing cycle. In this cycle, fibers are increasingly washed out of the suspension present in the screening device by means of the supplied rinsing water. No suspension is supplied to the screening device 50.

To regulate the inflow of rinsing water, a control 150 is assigned to the drive of the pump 60. In the control of the pump, a maximum value 154 is provided for the rinsing water. An inflow of rinsing water can be increased from an initially low value to the maximum value in the course of a cycle, as shown in Fig. 5. A base value is stored for the duration of the rinsing cycle 127 and the discharge cycle 137. A duration of 15 see. to 50 see. has proven to be a suitable dynamic range for the rinsing cycle 127. In comparison, a duration of 15 see. is provided for in static operation. By extending the duration, a good yield of fibers can be achieved.

The rinsing cycle is followed by a discharge cycle 137. The discharge cycle 137 is regulated by the control 130 for the discharge cycle. The control valve 65 is open during the discharge cycle 137. The valve 56 for the discharge of impurities is or will be opened and the valve 69 for the removal of acceptable materials is closed. The supply of fiber suspension is prevented by the valve 53. In the discharge cycle 137, a maximum inflow of rinsing water is supplied to the screening device in order to achieve a thorough rinsing of the suspension enriched with impurities. In dynamic operation, time periods in the range of 15 to 35 seconds are stored in the control. In static operation, 35 seconds is stored as a predetermined constant time. Since the impurities are conveyed out of the screening device in the discharge cycle 137, this cycle is also frequently referred to as a reject cycle.

If the drive power of the rotor 58 in the discharge cycle 137 and also in the subsequent run cycle 117 does not fall below a predetermined lower limit value, arrow in Figure 5, the control then shortens the run cycle 117 in the next newly starting run cycle 117. In the next cycle, the subsequent discharge cycle and thus the time for reject discharge is extended. Due to the inertia of the screening device 50, immediate intervention in a run-through cycle 17 that has already begun is not yet possible with the screening devices 50 currently available. However, if the drive power 162 of the rotor 58 exceeds a predetermined limit, an alarm is issued.

Figure 5 shows examples of temporal progressions. The inflow of fiber suspension 112 and the outflow of accepted material 114, the power consumption 162 of the drive of the rotor 58 and the inflow of rinsing water 152 are shown in relation to one another and over time. A reduced inflow 158 of rinsing water can be seen from the temporal progression of the inflow of rinsing water. The maximum inflow of rinsing water 154 is supplied in the discharge cycle 137. The cycles such as the run-through cycle 117, post-pulling cycle 119, rinsing cycle 127 and discharge cycle 137 are entered.

This process makes it possible to dynamically adapt the yield of fibers and the amount of cleaned suspension to the quality of the supplied suspension. The duration of the rinsing cycle 127 and the amount of rinse water supplied can be dynamically adapted.

List of reference symbols

Claims

Patent claims

1. Method for operating a screening device (50, 250) for cleaning a fiber suspension with a rotor (58) and sieve (57) arranged in a housing (51, 251) of the screening device (50, 250), wherein fiber suspension and rinsing water are fed to the screening device (50) and the portion of the fiber suspension passed through the sieve (57) is discharged via an accepts discharge (67, 267), characterized in that an inflow into the screening device (50, 250) and/or a cycle time duration is regulated depending on the power consumption (162) of the rotor drive (59, 259).

2. Method for operating a screening device (50, 250) according to claim 1, characterized in that the cycle time duration of at least one subsequent cycle such as run-through cycle (117), post-dissolving cycle (119), rinsing cycle (127) or discharge cycle (137) is regulated as a function of the power consumption (162) of the rotor drive (59, 259).

3. Method for operating a screening device according to claim 1 or 2, characterized in that when the power consumption (162) of the rotor drive (59, 259) exceeds a predetermined limit value, the inflow of rinsing water is reduced at least at the beginning of a subsequent rinsing cycle (127) compared to a maximum possible inflow of rinsing water (154).

4. Method for operating a screening device (50, 250) according to one of the preceding claims, characterized in that additionally or alternatively, a cycle time duration of the flow cycle (117) and/or the rinsing cycle (127) is regulated depending on the flow of accepted material. Experienced in operating a screening device (50, 250) according to one of the preceding claims, characterized in that an inlet pressure and/or a differential pressure for the pressure of the accepts discharge is taken into account when controlling a subsequent cycle time. Experienced in operating a screening device (50, 250) according to one of the preceding claims, characterized in that system-specific limit values are read in or entered manually during commissioning. Experienced in operating a screening device (50, 250) according to claim 6, characterized in that a maximum system-specific accepts flow is or is stored. Experienced in operating a screening device (50) according to one of claims 6 or 7, characterized in that a factory setting and/or a basic setting is stored in the control system (100), wherein operation without adaptive control is possible with the factory setting and the basic setting. experienced for operating a screening device (50, 250) according to one of claims 6 to 8, characterized in that when the power consumption of the rotor drive (59, 259) is outside a stored power range, in particular in the run-through cycle (137), the operation is continued on the basis of data from a basic setting or factory setting until the recorded operating data are again within the stored standard range. Method for operating a screening device (50, 250) according to one of claims 6 to 8, characterized in that if an operating parameter is outside a stored standard range, the method is continued using a predetermined number of cycles and the operating parameters used for the cycles are adaptively adjusted. Method for operating a system with at least a first cyclically operated screening device (50) and a second cyclically operated screening device (250) arranged in parallel, a pulper (20), characterized in that the cycles of the at least two screening devices (50, 250) are coordinated with one another for utilization of peripheral devices (70, 40, 60) of the system (1) by extending at least the rinsing cycle (127) of the currently ongoing sequences and/or shortening at least the throughput cycle (117). Method for operating a plant (1) with a pulper (20) and with at least one screening device (50, 250) according to one of claims 1 to 10, wherein fiber suspension is returned to the pulper (20), characterized in that the consistency and amount of the fiber suspension returned to the pulper (20) is taken into account for the provision of a consistency in a predetermined consistency range of the pulper material. Method for operating a plant (1) with a pulper and with at least one screening device (50, 250) according to one of claims 1 to 10, wherein fiber suspension is returned to the pulper (20), characterized in that that the consistency and quantity of the fiber suspension returned to the pulper (20) is taken into account for the provision of a consistency consistency in the pulper. 14. Plant (1) with a pulper (20) and at least one screening device (50,

250) and a controller (100) for carrying out the method according to one of the preceding claims, characterized in that a control valve (65) is arranged in the supply of rinsing water to the screening device (50, 250), wherein preferably the control valve (65) is a control valve (65) which can be controlled at least as a function of a detected power consumption (162) of the rotor drive (59, 259).

15. Computer program product for providing a method for fiber processing according to a method operated according to one of claims 1 to 12.