METHOD FOR OPERATING A PULPER FOR PRODUCING A SUSPENSION, IN PARTICULAR A FIBROUS SUSPENSION

Abstract

A method for operating a screening device for cleaning a fibrous suspension includes the steps of: providing that the screening device includes a housing, a rotor arranged in the housing, and a screen; feeding the fibrous suspension and a rinsing water to the screening device; passing a portion of the fibrous suspension through the screen; discharging the portion of the fibrous suspension passing through the screen via an accepted stock discharge; and regulating, depending on a power consumption of a rotor drive, at least one of an inflow into the screening device and a cycle duration.

Claims

1. A method for operating a screening device for cleaning a fibrous suspension, the method comprising the steps of: providing that the screening device includes a housing, a rotor arranged in the housing, and a screen; feeding the fibrous suspension and a rinsing water to the screening device; passing a portion of the fibrous suspension through the screen; discharging the portion of the fibrous suspension passing through the screen via an accepted stock discharge; and regulating, depending on a power consumption of a rotor drive, at least one of an inflow into the screening device and a cycle duration.

2. The method for operating the screening device according to claim 1, wherein the cycle duration of at least one subsequent cycle is regulated depending on the power consumption of the rotor drive.

3. The method for operating a screening device according to claim 2, wherein the at least one subsequent cycle is at least one of a throughput cycle, a post-dissolving cycle, a rinse cycle, and a discharge cycle.

4. The method for operating the screening device according to claim 1, wherein, if the power consumption of the rotor drive exceeds a predetermined limit valueat least at a start of a subsequent rinse cyclean inflow of the rinsing water is reduced compared to a maximum possible inflow of the rinsing water.

5. The method for operating the screening device according to claim 1, wherein a cycle duration of at least one of a throughput cycle and a rinse cycle is regulated depending on a flow of an accepted stock.

6. The method for operating the screening device according to claim 1, wherein at least one of an inlet pressure and a differential pressure is considered for a pressure of the accepted stock discharge when regulating a subsequent cycle duration.

7. The method for operating the screening device according to claim 1, wherein a plurality of system-specific limit values are read in or are manually entered or are stored during a start-up.

8. The method for operating the screening device according to claim 7, wherein a maximum system-specific accepted stock flow will be stored or is stored.

9. The method for operating the screening device according to claim 8, wherein at least one of a factory default and a basic setting is stored in a control unit, and wherein an operation without adaptive control is possible with the factory default and the basic setting.

10. The method for operating the screening device according to claim 8, wherein, if the power consumption of the rotor drive is outside a stored power range, an operation is continued based on data from a basic setting or a factory default until a recorded operating data is again within a stored standard range.

11. The method for operating the screening device according to claim 8, wherein, if the power consumption of the rotor drive is outside a stored power range in a throughput cycle, an operation is continued based on data from a basic setting or a factory default until a recorded operating data is again within a stored standard range.

12. The method for operating the screening device according to claim 8, wherein, if an operating parameter is outside a stored standard range, the method is continued by reverting to a predetermined number of cycles, and a plurality of the operating parameter used for the predetermined number of cycles are adaptively adjusted.

13. A method for operating a system, the method comprising the steps of: providing that the system includes a first screening device, a second screening device, and a pulper, the first screening device configured for being cyclically operated and thus for being operated in a plurality of cycles, the second screening device configured for being cyclically operated and thus for being operated in a plurality of cycles, the second screening device being arranged in parallel to the first screening device; and coordinating the plurality of cycles of the first screening device and the plurality of cycles of the second screening device with each other for utilizing at least one peripheral equipment of a line of the system, in that at least one of (a) at least one of a plurality of rinse cycles is at least one of (i) extended and (ii) shortened from a plurality of currently ongoing sequences and (b) at least a throughput cycle is shortened.

14. A method for operating a system, the method comprising the steps of: providing that the system includes a pulper and a screening device, the method including a first method for operating the screening device for cleaning a fibrous suspension, the first method including the steps of: providing that the screening device includes a housing, a rotor arranged in the housing, and a screen; feeding the fibrous suspension and a rinsing water to the screening device; passing a portion of the fibrous suspension through the screen; discharging the portion of the fibrous suspension passing through the screen via an accepted stock discharge; and regulating, depending on a power consumption of a rotor drive, at least one of an inflow into the screening device and a cycle duration; and returning the fibrous suspension to the pulper.

15. The method for operating the system according to claim 14, wherein a consistency and a volume of the fibrous suspension returned to the pulper is considered for provision of a stock density consistency within a predetermined stock density range of an accepted pulp stock.

16. The method for operating the system according to claim 14, wherein a consistency and a volume of the fibrous suspension returned to the pulper is considered for preparation of a stock density consistency in the pulper.

17. A system including a pulper, the system comprising: at least one screening device; and a control unit, which is configured for carrying out a method for operating the at least one screening device for cleaning a fibrous suspension, the method including the steps of: providing that the at least one screening device includes a housing, a rotor arranged in the housing, and a screen; feeding the fibrous suspension and a rinsing water to the at least one screening device; passing a portion of the fibrous suspension through the screen; discharging the portion of the fibrous suspension passing through the screen via an accepted stock discharge; and regulating, depending on a power consumption of a rotor drive, at least one of an inflow into the at least one screening device and a cycle duration; an infeed for a rinsing water to the at least one screening device; and a control valve, which is arranged in the infeed for the rinsing water to the at least one screening device.

18. The system according to claim 17, wherein the control valve is configured for being actuated depending at least on the power consumption-which is detectedof the rotor drive.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0054] The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:

[0055] FIG. 1 is a schematic representation of a system according to the invention;

[0056] FIG. 2 is a schematic representation of a system according to the invention with continuously operated pulper;

[0057] FIG. 3 is a schematic representation of a system according to the invention with two screening devices arranged in parallel;

[0058] FIG. 4 is a schematic representation of a control system;

[0059] FIG. 5 is a schematic representation of measurement operating curves: [0060] a) Drive power, pump [0061] b) Accepted stock discharge [0062] c) Drive power, rotor of screening device 50 [0063] d) Volume of supplied dilution-/washing water.

[0064] Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate at least one embodiment of the invention, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.

DETAILED DESCRIPTION OF THE INVENTION

[0065] FIGS. 1, 2 and 3 present examples of arrangements 1 for the production of a fibrous suspension. The problem with fiber extraction from wastepaper consists in removing as much of the contaminants as possible. However, removal of fibers associated with the removal of contaminants should be kept to a minimum.

[0066] Paper stockalso referred to as wastepaper and shown here as balesis fed to a pulper 20 via a conveyor 11. In pulper 20, for example, wastepaper as the paper stock is mixed with water and converted into a fibrous suspension. For this purpose, dilution water is fed to pulper 20 via a controllable water supply 10 and infeed 15. In addition, pulper 20 is further supplied with a suspension classified as accepted stock from a screening device 50 and post-screening device 70 downstream of pulper 20. Screening device 50 and post-screening device 70 will be discussed in detail later.

[0067] In its bottom region, pulper 20 is equipped with a screen 29 through which part of the suspension can pass into the annular space. A rotor 25 is arranged above screen 29 by way of which the paper stock/water mixture is caused to rotate on the one hand and on the other hand keeps screen 29 free. Rotor 25 is driven by drive 27. The fibrous suspension which has passed through screen 25 is discharged via an accepted stock discharge 21. The portion of suspension produced in pulper 20 which is discharged via contaminant discharge 23 is directed into a storage tank 30 which is equipped with a contaminant outlet 31. Coarse heavy dirt contained in the introduced fibrous suspension can be separated in storage tank 30. Ideally, the suspension is diluted to 3.5% in collection tank 30 for more effective separation of heavy particles. The coarse heavy dirt sinks down into collection tank 30 and is discharged directly through an automatically controlled trash discharge with a contaminant outlet 31. Additional dilution water may be added to the trash discharge to improve fiber backwashing.

[0068] An outlet 33 for suspension is provided in the upper region of the storage tank. Fibrous suspension is removed in this upper region of storage tank 30. By way of pump 40, said fibrous suspension is fed via a line and infeed 52 to screening device 50 with housing 51 for further treatment. Pump 40 is a special pump for contaminant-loaded fibrous suspension. Pump 40 can be used to convey the contaminated suspension from the pulper into screening device 50 in a predominantly blockage-free and reliable manner. Pump 40 is designed to have a large nozzle diameter and a non-clog impeller for clog-free pumping of fibrous suspensions with a high proportion of contaminants. In particular, the impeller can be optimized for particularly high resistance by way of hard-facing. Drive 45 with frequency converter facilitates optimized pump speed for discontinuous pump operation. Thus, the volume flowalso referred to as flowconveyed by pump 40 can be regulated, optionally infinitely variably regulated.

[0069] The accepted stock from the storage tank enters downstream screening device 50 for further processing. This is a cyclically operated screening device. A screen 57 is provided in the housing. A rotor 58 is arranged prior to screen 57. Rotor 58 causes the fibrous suspension introduced into housing 51 of the screening device to rotate prior to screen 57. The rotor is driven by a drive 59. A portion of the supplied fibrous suspension passes through screen 57 and is discharged via an accepted stock discharge 67 from the screening device. In FIG. 5 the power consumption of drive 59 of the rotor over time is plotted. Moreover, the power consumption of drive 59 of the rotor over time is also potted in FIG. 5.

[0070] There is a cycle for the supply of fibrous suspension that is also referred to as the throughput cycle. In throughput cycle 117, fibrous suspension is fed to screening device 50. Rotor 58 causes the suspension to rotate. Rotor 58 is arranged prior to screen 57. Dissolved fibers pass through screen 57. A differential pressure is applied, which conveys the outflow of dissolved fibers through screen 57. Accepted stock discharge 67 for the discharge of the accepted stock with switching valve 69 (see FIG. 4) is open. Contaminant discharge 66 with switching valve 56 (see FIG. 4) is closed. As a result, contaminants are concentrated in the fibrous suspension in screening device 50 before screen 57.

[0071] To increase the processing of this suspension in screening device 50, the supply of fibrous suspension can be interrupted. Switching valve 53 (see FIG. 4) is provided for this purpose. The suspension in screening device 50 is processed by the movement in screening device 50. Valve 56 of contaminant discharge 66 is still closed and the accepted stock discharge is open. The movement of the suspension can loosen fiber clumps present in the suspension. The dissolved fibers can pass through the screen and flow off via accepted stock discharge 67. This cycle is also referred to as post-dissolving cycle 119.

[0072] Post-dissolving cycle 119 or throughput cycle 117 is followed by a rinse cycle 127. A supply of rinsing water is provided in rinse cycle 127. The rinsing water is provided by the water supply 10. The inflow into screening device 50 occurs via control valve 65. The inflow into screening device is implemented via a control valve 65. The inflow is adjustable by way of control valve 65. Depending on power consumption 162 of the rotor, inflow 152 of rinsing water can be regulated. The inflow of rinsing water is initially throttled, depending on the drive power of rotor 58 of screening device 50 before rinse cycle 127. Overloading of the rotor drive is thereby prevented or at least reduced.

[0073] Control of the supplied rinsing water inflow could also occur via an adjustable drive of pump 60 for the rinsing water admission. During this cycle, fibrous suspension is increasingly flushed out via an accepted stock discharge 67.

[0074] Rinse cycle 127 is followed by discharge cycle 137. The suspension with the concentrated contaminants is discharged from housing 51 of screening device 50. For this purpose, contaminant discharge 66, valve 56, is opened. The throughput cycle and rinse cycle can overlap or can merely be executed in series. The length of the respective cycle can be changed by a control unit 100 and can thereby be adapted to the respective level of contamination or paper quality of the wastepaper. The fraction of accepted stock extracted by screening device 50 is returned back to pulper 20 via supply 17. The fraction of contaminants extracted in screening device 50 is fed to a post-screening device 70.

[0075] Additional washing out of fibers still present in the contaminants is provided in post-screening device 70. Here, post-screening device 70 includes a screen drum and a dilution water supply 75. Due to rotation of the drum the introduced fraction is caused to rotate and also to move axially. Fibers pass through openings in the drums together with rinsing water to an accepted stock discharge 73 and are fed via infeed 19 from post-screening device 70 to pulper 20. The portion that does not pass through the screen is discharged as contaminants via a contaminant discharge 76. The inflow of rinsing water can also be regulated at post-screening 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.

[0076] In arrangement 1 shown in FIG. 2, fibrous suspension produced in pulper 20 is fed directly cyclically to a downstream screening device 50. The accepted stock of screening device 50 is fed to a large storage tank 68 and the contaminants that are separated from screening device 50 are directed via a pump 40 to a storage tank 30 which is equipped with a contaminant outlet 31. Via an outlet 33, suspension can be continuously fed from storage tank 30 to a post-screening device 70 via infeed 71. This post-screening device 70 is consistent with post-screening device 70 described in connection with FIG. 1. Here, the accepted stock extracted by post-screening device 70 is fed to pulper 20 via accepted stock discharge 73. The portion that does not remain as accepted stock in post-screening device 70 is discharged via a contaminant discharge 76.

[0077] FIG. 3 presents an additional variation of a system for fiber preparation. This system differs from the system shown in FIG. 1 in that two screening devices 50 are arranged in parallel relative to each other. The operating principle of screening devices 50 and 250 does not differ from the operating principle of screening device 50 described in FIG. 1. The second screening device also has a housing 251, an infeed for suspension 252, a drive 259, an infeed for rinsing water 261, a contaminant discharge 266 and an accepted stock discharge 267. The cycles of the two screening devices are coordinated with each other for more efficient operation. Only one pump 40 is provided by way of which fibrous suspension is fed to first screening device 50 or second screening device 250. Thus, a common supply of rinsing water is also provided. The contaminants from the screening devices are fed to a post-screening device 70.

[0078] FIG. 4 shows one version of a control unit 100 for a screening device 50 in more detail. On the one hand, control unit 100 controls motor 45 of pump 40. A pump control unit 140 is provided for this purpose. Pump control unit 140 issues a setpoint value and an actual value of the drive frequency of the pump and a drive power 144. The objective is to ensure a maximum flow in the throughput cycle without overloading the drive at changing boundary conditions such as admission pressure and contaminant content. The supply of suspension to screening device 50 is hereby controlled via pump 40. A control unit 150 is provided for water pump 60 for the supply of rinsing water and the inflow of rinsing water. Via this control unit, valve 65 provided in water supply 61 can be controlled. Valve 65 is an adjustable valve. Valve 65 can be used to regulate or control the inflow of supplied rinsing water. Control unit 150 of pump 60 of the rinsing water includes a setpoint of a delivery rate and a basic value of the delivery rate of water pump 60. In addition, the current drive power is recorded.

[0079] For control of pump 60 of the rinsing water and control of the rinsing water flow and the volume in the respective cyclein particular during the rinse cyclevalues of drive power 117 of drive 59 of rotor 58 of screening device 50 are also considered. FIGS. 4 and 5 describe the control scheme in more detail depending on the drive power of rotor 58.

[0080] Control unit 100 can be used to dynamically adjust the duration of individual cycles and the volume of suspension and rinsing water delivered per time.

[0081] Control unit 110 records throughput cycle 117. The throughput cycle is the period of time in which the fibrous suspension is fed to screening device 50. A basic value of a time duration for a throughput cycle is specified, and a setpoint value of a time duration of a throughput cycle is adaptively-predictably specified. An adaptive-predictive specification is a predictive presetting that adapts depending on parameters. An adaptive-predictive control can be based on stored characteristic curves, or it can be provided by an adaptive learning control system. If initially no values or characteristic curves are available, then initial teaching is required. Subsequently, a self-learning adjustment of basic values as well as target values can be provided.

[0082] Different basic values/starting values can also be stored in the control system for predetermined grades of wastepaper. The duration of the cycles and inflows of rinsing water and suspension are regulated by control unit 100. A determined setpoint value is provided by the control unit for the individual cycles. Thereby, the power consumption of rotor drive 58 of the screening device is considered, in particular. It may be provided that the duration of the throughput cycle is regulated depending on the minimum power consumption of the rotor in the rinse cycle. It may furthermore be provided that the quality and/or also the volume of the discharged accepted stock are taken into consideration. An adjustment of a throughput cycle in the range of 15 to 150 seconds, optionally in the range of 60 to 120 seconds has proven to be a suitable adjustment range. In an equivalent arrangement, a duration of 50 seconds was specified for the throughput cycle in static operation. Here, the increase in efficiency through dynamic operation is evident. If the measured values are inconsistent, the values from static operation can be used initially to continue operation.

[0083] Control unit 120 is provided for control of rinse cycle 127. In rinse cycle 127, rinsing water is introduced into the screening device with the objective of flushing or washing out fibers from the contaminant-enriched suspension prior to the screen. Fibrous suspension is no longer supplied by pump 40. Switching valve 53 is or will be closed. The control unit regulates rinse cycle 127. An actual rinse time is designated, and a basic value of a rinse time is stored. In addition to the duration of the rinse cycle, the flow of supplied rinsing water is also controlled depending on the consumed or detected power consumption of drive 59 of rotor 58. Control unit 160 is provided for the rotor drive. The rinse cycle can also be referred to as wash cycle. In this cycle, fibers from the suspension present in the screening device are increasingly washed out by way of the supplied rinsing water. No suspension is fed to screening device 50.

[0084] In order to regulate the inflow of rinsing water, a control unit 150 is assigned to the drive of pump 60. A maximum value 154 is provided for the rinsing water in the control unit of the pump. An inflow of rinsing water can be increased from an initially low value to the maximum value over the course of a cycle, as shown in FIG. 5. A basic value is stored for the duration of rinse cycle 127 and discharge cycle 137. A duration of 15 seconds to 50 seconds has proven to be suitable as a dynamic range for rinse cycle 127. In comparison, a duration of 15 seconds is provided for this in a static operation. A good yield of fibers can be achieved by extending this time frame.

[0085] The rinse cycle is followed by a discharge cycle 137. Discharge cycle 137 is regulated by control unit 130 for the discharge cycle. Control valve 65 is open during discharge cycle 137. Valve 56 for the discharge of contaminants is or will be open and valve 69 for the accepted stock discharge is closed. The supply of fibrous suspension through valve 53 is prevented. In discharge cycle 137, a maximum inflow of rinsing water is fed to the screening device in order to achieve effective flushing out of the suspension enriched with impurities. In dynamic operation, time spans in the range of 15 to 35 seconds are stored on the control unit. In static operation 35 seconds are stored as predetermined constant time. Since the contaminants are transported out of the screening device during discharge cycle 137, this cycle is often also referred to as reject cycle.

[0086] If the drive power of rotor 58 does not drop below a predetermined lower limit value during discharge cycle 137 and also starting throughput cycle 117arrow in FIG. 5then the control unit shortens throughput cycle 117 in the next newly starting throughput cycle 117. In the next cycle, the following discharge cycle and thus the duration for a reject discharge is extended. Due to the inertia of screening device 50, immediate intervention in an already started throughput cycle 117 is not yet possible with the currently available screening devices 50. However, if drive power 162 of rotor 58 drops below a predetermined limit value, an alarm is issued.

[0087] System (1) can be provided with a pulper (20) and at least one screening device (50, 250) and a control unit (100) to carry out the method according to the present invention, wherein control valve (65) is arranged in the infeed of rinsing water to screening device (50, 250), wherein control valve (65) is optionally a control valve (65) which can be actuated at least depending on a detected power consumption (162) of rotor drive (59, 259).

[0088] FIG. 5 shows examples of temporal progressions. The inflow of fibrous suspension 112 and the outflow of accepted stock 114, power consumption 162 of the drive of rotor 58 and the inflow of rinsing water 152 are shown in relation to each other and over time. From the temporal progression of the inflow of rinsing water, a reduced inflow 158 of rinsing water can be seen. In discharge cycle 137 the maximum inflow of rinsing water is supplied. Cycles such as throughput cycle 117, post-dissolving cycle 119, rinse cycle 127 and discharge cycle 137 are entered.

[0089] This process makes it possible to dynamically adapt the yield of fibers and the volume of purified suspension to the quality of the supplied suspension. The duration of rinse cycle 127 and the volume of rinsing water added can be dynamically adjusted.

Component Reference Listing

TABLE-US-00001 1 System for producing a fibrous suspension 10 Water supply 11 Conveyor 13 Wastepaper bales 15 Infeed dilution water 17 Infeed accepted stock from screening device 19 Infeed accepted stock from post-screening device 20 Pulper 21 Accepted stock discharge, pulper 23 Contaminant discharge, pulper 25 Rotor, pulper 27 Drive, pulper 29 Screen, pulper 30 Storage tank 31 Outlet, contaminant storage tank 33 Outlet, suspension, storage tank 40 pump 45 Pump drive 50 Screening device 51 Housing 52 Infeed-screening device 53 Switching valve suspension supply 56 Switching valve contaminant discharge 57 Screen (screening device) 58 Rotor (screening device) 59 Drivescreening device 60 Pump for rinsing water 61 Water supply 65 Control valve 66 Contaminant discharge 67 Accepted stock discharge 68 Large storage tankaccepted stock screening device 69 Switching valve, accepted stock discharge, screening device 70 Post screening device 71 Infeed, post-screening 73 Accepted stock discharge 75 Dilution water supply 76 Contaminant discharge 100 Control unit 110 Throughput cyclecontrol 112 Inflow, suspension 114 Outflow, accepted stock 117 Throughput cycle 119 Post-dissolving cycle 120 Rinse cyclecontrol 127 Rinse cycle, wash cycle 130 Control unit, discharge cycle control 137 Discharge cycle, reject cycle 140 Pump control unit (fibrous suspension) 150 Control unit, rinsing water supply (flow and volume) 151 2.sup.nd screening device 152 Infeed rinsing water 154 Rinsing water inflow, maximum 158 Reduced rinsing water volume 160 Control unit, rotor drive 162 Power consumption, rotor drive 250 2nd screening device 251 Housing, 2.sup.nd screening device 252 Infeed, 2.sup.nd screening device 259 Drive, 2.sup.nd screening device 261 Rinsing water infeed 266 Contaminant discharge 267 Accepted stock discharge

[0090] While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.