US20230243097A1

US20230243097A1 - Controlling the treatment of fibrous material

Info

Publication number: US20230243097A1
Application number: US18/127,770
Authority: US
Inventors: Martin Kemper
Original assignee: Voith Patent GmbH
Current assignee: Voith Patent GmbH
Priority date: 2020-09-30
Filing date: 2023-03-29
Publication date: 2023-08-03
Also published as: CN116324083A; EP4222308A1; WO2022069433A1; DE102021125006A1

Abstract

A method for controlling a device for treating a fibrous material includes the steps of: providing that the device includes a housing in which at least a first treatment tool and a second treatment tool are arranged; mounting at least one of the first base plate and the second base plate in an axially movable manner in order to compensate for a wear of the first treatment profile and the second treatment profile; measuring a distance between the first base plate and the second base plate respectively of the first treatment tool and the second treatment tool of a treatment nip during an operation of the device; and selecting a value of a total power depending on the distance between the first base plate and the second base plate of the at least one treatment nip.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of PCT application no. PCT/EP2021/076575, entitled “CONTROLLING THE TREATMENT OF FIBROUS MATERIAL”, filed Sep. 28, 2021, which is incorporated herein by reference. PCT application no. PCT/EP2021/076575 claims priority to German patent application no. DE 10 2020 125 487.3, filed Sep. 30, 2020, which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for controlling a device for the treatment of fibrous material, wherein the device includes a housing, in which at least one first treatment tool and a second treatment tool are arranged. The treatment tools respectively are mounted on a base plate and have a rotationally symmetrical shape and are arranged coaxially to each other, rotating relative to one another about a common axis. The treatment tools delimit a treatment nip through which the fibrous material flows and respectively have a treatment profile which faces toward the treatment nip, wherein at least one base plate of a treatment tool is mounted in an axially movable manner in order to compensate for the wear of the treatment profile.

2. Description of the Related Art

Because of the relatively high consistency of the fibrous material during treatment, intensive mechanical processing with equipment of this type (refiner, disperger, deflaker) is possible, even though the treatment tools which move relative toward one another do not make contact with each other, but rather pass each other at a relatively small distance, whereby considerable forces occur. Devices of the aforementioned type are used, for example, to improve the quality of pulp, TMP or fibrous material obtained from waste paper.
It has been known for a long time to refine pulp fibers, that is virgin pulp and/or waste paper fibers, in order to be able to obtain the desired characteristics in the therefrom produced fibrous web, in particular in regard to strength, porosity, formation and surface.
In the refiners used for this purpose, the refining surfaces are provided by replaceable refiner fillings which – because of the relatively rapid wear – are screwed to the corresponding base plate.
In order to achieve the desired fiber characteristics, in particular the degree of refining, the refiner fillings have to be optimally adapted to the fibers to be treated, also to prevent excessive wear of the fillings.
In addition, optimum use of the available refining surface is strived for in order to increase efficiency of the fiber treatment.
From US 2004/0112 997 A1 as well as DE 2 939 587 A1 and DE 3 602 833 A1 it is known to measure or calculate the no-load power once before start-up and to use it as a basis for the machine control.
If the height of the treatment profile of the treatment tools is reduced due to wear, this leads to a reduction in the no-load power or respectively the pump power. With constant total power, this also leads at the same time to an increase in the specific power of the device that is relevant for the desired treatment intensity and thus to excessive treatment, in particular refining of the fibers. Constant total power is thereby regulated by axial displacement of the axially movable base plate.
In turn, if the nip is too small, there is a risk of excessive electrical current consumption and contact between the treatment tools.
From DE 10 2016 207 726 A1 it is known to determine the no-load power during operation. For this purpose, however, it is necessary to operate the refiner in no-load mode or to flood it with water and to open and close the treatment nip while measuring the no-load power. The thus measured no-load power is then used as a basis for further operation.
What is needed in the art is to make possible a reliable and efficient operation of these devices by the simplest possible ways.

SUMMARY OF THE INVENTION

The present invention relates to a method for controlling a device for the treatment of fibrous material, wherein the device includes a housing, in which at least one first treatment tool and a second treatment tool are arranged. The treatment tools respectively are mounted on a base plate and have a rotationally symmetrical shape and are arranged coaxially to each other, rotating relative to one another about a common axis. The treatment tools delimit a treatment nip through which the fibrous material flows and respectively have a treatment profile which faces toward the treatment nip, wherein at least one base plate of a treatment tool is mounted in an axially movable manner in order to compensate for the wear of the treatment profile. For adjustment of the total power the width of the treatment nip is adjusted until the predetermined total power is achieved.
The present invention provides that the distance between the base plates of the treatment tools of a treatment nip is changed during operation of the device for controlling the total power, and the value of the total power is therein selected depending on the measured distance between the base plates of the treatment nip. The measured distance is understood, in particular, to also represent a change in distance originating from an initial value. On the one hand, the distance can be measured directly in that the distance of, for example, the treatment tools or of the base plates on which the treatment tools are mounted is measured. However, the distance can also be measured indirectly. In one embodiment, for example, the position of the drive for tracking the axially movable plate of the treatment tool can be concluded from the change in distance.
Since the no-load power of the device decreases relatively significantly during the duration of operation of the treatment tools with increasing wear of the profile of the treatment tools, the total power which includes the no-load or pump power and the specific power that is relevant to the strived for treatment intensity must be adjusted accordingly. In this way, an unintended increase in the specific power and thus also of the treatment intensity of the fibers can effectively be countered.
This becomes possible in particular, because the general width of the treatment nip is many times smaller than the profile height of the treatment tools. Thus the width of the treatment nip can be neglected in the control unit. With fiber suspension supplied, the formation of a treatment nip is achieved in operation and a treatment nip width is set until a predetermined total power is achieved. Since the nip width of the treatment nip is negligible compared to the profile height, the variation of the nip width of the treatment nip – whereby the treatment nip width can also be dependent on the throughput – is therefore also negligible compared to the change in position due to the wear of the fillings. From the measured distance/change in distance the profile height or, starting from an initial value, a change in the profile height can thus be determined. In a device having one treatment nip the profile height corresponds to half the distance between the base plates; and in a device having two treatment nips, the profile height, after deduction of the width justified by non-profile components, is a quarter of the determined distance value. It is also possible, starting from an initial distance value, to determine the reduction of the distance by measurement and from this to determine directly the reduction of the profile heights. Depending on the determined profile height and the treatment intensity, the relevant total power is set.
One design variation provides that the wear of each filling rounded to 0.1 mm, optionally rounded to 0.5 mm, is indicated. A displacement sensor or also an incremental encoder can be used as a sensors for determining the position or the change in position.
In order to simplify the control, the value of the total power should be selected solely depending on the measured distance between the base plates of the treatment nip or in connection with the desired refining energy. The measured distance corresponds thereby to the determination of the profile height. Optionally, the ratio of profile height and the therewith associated no-load power is stored in a characteristic diagram. The characteristic diagram can be read in by the operator before start-up or can also have been provided by the manufacturer of the device. This means that it is not necessary to determine the no-load power during operation.
In an optional embodiment it is provided that the rotor in a device having a double nip is mounted in a floating manner. This means that the distance between the treatment tools can be adjusted corresponding to the height of the profiles for both nips by way of an axially movable treatment tool.
A more precise control is possible if the value of the total power is selected by considering additional values such as flow and stock consistency and/or the quality of the fibrous stock suspension.
It is advantageous to adjust the value of the total power at least when a change in distance between the base plates of the treatment nip of at least 1 mm is detected. This corresponds to a reduction of each treatment profile of 0.5 mm at a treatment nip.
However, it is often sufficient if the value of the total power is reselected at predetermined time intervals at a maximum of once a day, optionally at least once a week, depending on the measured change in the distance between the base plates of the treatment nip. Between these time intervals, the distance between the base plates is reduced according to the wear of the treatment profile in order to keep the total power constant at the current value.
When controlling or regulating the device, the no-load power, which relates to the throughput of fibrous material per unit of time and which, in refiners, is for example usually between 40 and 250, in particular between 40 and 150 kWh per ton of dry weight, should also be taken into account if possible.
After an intervention in the device, i.e. by replacing only part of the fillings, a distance value measured during opening and/or closing of the treatment nip can be used once as a new starting value of a no-load power for establishing a reference to a stored characteristic diagram. In the subsequent control of the total power, in addition to the distance value, further links with other parameter values can be used to control the total power and thus also the specific power of the device.
Provisions can moreover be made to measure the no-load power each time before the refiner is shut down. Furthermore it can be provided additionally or alternatively that a determination of the no-load power is only made after a predetermined minimum operating time. This prevents the no-load power from being determined every time the device is stopped, several times a day. A no-load determination every 1 to 2 weeks is completely sufficient due to the stored characteristic diagrams and a corresponding tracking of the total power. This reliably prevents an undesirably high refining power.
It has hitherto been customary to determine the no-load power of the device at start up and to store it for the control system or to use a predefined value for this purpose.
With increasing operating time of the respective treatment tools and thus also increasing wear of the latter, in particular of their profiles, the current no load power of the device decreases. As a result, the total power consumption would have to be reduced accordingly.
However, since the no-load power is regarded as constant in previous control systems, the total power consumed may be 20% or more too high for the desired treatment intensity.
In order to be able to store a start value for the controller in the memory after replacement of at least one treatment tool, it can be advantageous to have the no-load power measured and entered by the service personnel or to have the no-load power measured by the controller itself, in particular when closing the treatment nip.
Irrespective of this, the value of the total power for controlling the device should be selected in such a way that the specific power of the device relevant for the desired treatment intensity, which results from the difference between the total power and the no-load power, is constant over the operating period. In this way, constant treatment intensity can be ensured. The specific power is considered constant if the specific power deviates by less than 5% from its arithmetic average value.
If the redetermination of the value of the total power is not carried out continuously but at certain time intervals, the length of these time intervals must be selected in such a way that possible changes due to wear of the processing profile are tolerable with regard to the then increasing specific power. A change of less than 5% of the last assumed no-load power and/or a position change of less than 1 mm per nip is considered tolerable.
When determining the value of the total power subject to the distance between the base plates of the treatment nip, it is advantageous to refer to values stored in a memory of the control system, in particular to a characteristic diagram. The stored values or the characteristic diagram were specified by the manufacturer of the device or determined in advance by the operator of the device during tests.
The values stored in the memory are based on knowledge or experience regarding the no-load power with the corresponding distance between the two base plates of the treatment nip and related to this, also on the degree of wear of the treatment profiles. Taking into account the desired treatment intensity of the fibers and thereby the specific power, this results in the specified value for the total power of the controller as a sum.
In the interest of a simple design of the device, one treatment tool should rotate and the other should not, with at least one treatment tool being mounted so as to be axially movable.
In special designs, the treatment tool and base plate can also be made in one piece.
It is also possible for the housing to have several, in particular two parallel treatment nips arranged next to one another, optionally each with one treatment tool rotating on a shaft, and one non-rotating treatment tool. As a rule, the two treatment tools respectively adjacent to the other treatment nip are mounted on a common base plate, wherein this common base plate and at least one of the treatment tools not mounted on this base plate are mounted in an axially movable manner.
The application of the method according to the present invention is especially advantageous in a refiner, in particular an LC (low-consistency) refiner, wherein the consistency of the pulp is between 2 and 6, optionally between 3.5 and 4.5% of the dry weight.
Fibrous material can in particular also be TMP, high-yield cellulose, MDF (medium-density fireboard) fibrous material, wood chips or similar substances.
The present invention is explained in more detail below with reference to an exemplary design example.

BRIEF DESCRIPTION OF THE DRAWINGS

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 at least one embodiment of the invention taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a schematic cross section through a refiner; and

FIG. 2 is the change in no-load power P_L and the adjustment of the total power PG over time t and over the distance s between base plates 7,8.

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

According to FIG. 1 , fibrous material 1 is pressed directly into the central, that is the radially inner, region of the refiner fillings, which is formed by the two treatment tools 3,4.
While one treatment tool 3 is fixed and is thus designed as a stator, the other treatment tool 4 is rotatably mounted in housing 2 of the refiner.
Treatment tools 3,4 each have a rotationally symmetrical shape, whereby the two circular refining surfaces are arranged parallel to one another. Treatment nip 6 between the refining surfaces is adapted via an axial movement in order to achieve a predetermined total power. The treatment intensity of fibrous material 1 – also referred to as fibrous suspension –flowing into the nip is established by the nip width of treatment nip 6. The axial extent of said nip width of treatment nip 6 is negligible in comparison with the height of treatment profiles 9 of treatment tools 3, 4.
Rotating refining surface 9 is herein moved in the direction of rotation by a shaft rotatably mounted in housing 2. This shaft is driven by a drive, also provided in housing 2. In the illustrated example, fibrous suspension 1 passes via an inlet through the center into treatment nip 6 between the refining surfaces of both treatment tools 3,4.
Fibrous suspension 1 passes the interacting refining surfaces in a radially outward direction and exits the adjoining annular space through an outlet.
Both refining surfaces are formed respectively by several refining plates, each of which extends over a peripheral segment of the corresponding refining surface. Arranged side-by-side in peripheral direction, the refining plates provide a continuous refining surface.
The refining plates and thereby also the refining surfaces have a treatment profile 9, facing toward treatment nip 6, wherein said profile is generally formed by a multitude of essentially radially progressing refining bars and grooves between them.
The already known ways with which non-rotating treatment tool 3 is axially moved is not shown. The extent of this axial movement is measured by a displacement sensor. Rotating treatment tool 4 does not change its axial position.
It can also be measured by way of an incremental encoder on the drive for setting the axial position of the non-rotating but axially movable treatment tool 3 (not shown).
Furthermore, treatment tools 3,4 are attached to corresponding base plates 7,8.
In contrast to the example shown here, treatment nip 6 can progress not only perpendicular, but also – as in the case with cone-refiners – inclined toward axis of rotation 5. In addition, housing 2 can also include several, in particular two treatment nips 6.
FIG. 2 illustrates the change in the real no-load power P_L of the refiner over distance S, which decreases with increasing operating time t and thereby also with increasing wear of treatment profile 9 of treatment tools 3,4.
The total power P_G, which is supplied to the treatment device consists of the no-load power P_L and the specific power P_S responsible for the treatment intensity, that is the refining power of fibrous material 1.
The total power is set to a predetermined value that corresponds to the desired treatment intensity at a known no-load power. In order to avoid that the specific power Ps becomes significantly higher over the service life of treatment tools 3, 4 than would be required for the desired treatment intensity of fibrous material 1, the assumed no-load power P_L is adapted accordingly depending on measured distance s between base plates 7, 8 and/or the distance between treatment tools 3,4 by accessing the stored values or the stored characteristics diagram.
By changing the distance s between base plates 7,8 of treatment tools 3,4 of treatment nip 6 during operation, the total power P_G consumed by the device can be controlled easily and efficiently. It is essential to the present invention that the value of the total power P_G is selected depending on distance s between base plates 7,8 of treatment nip 6.
The value of total power P_G is herein optionally chosen so that the specific power Ps of the device, which is relevant for the desired treatment intensity, is as constant as possible over the operating time.
When selecting the value of total power P depending on distance s between base plates 7,8 of treatment nip 6, values stored in the memory of the controller are accessed which are specified by the manufacturer of the device or were determined by the operator of the device during tests.
The value of total power P specified for the control of the device can be continuously adapted to distance s between base plates 7,8 of treatment nip 6, as shown in FIG. 2 as a dashed line.
Alternatively, according to the solid line for total power P_G in FIG. 2 , it is also possible to readjust the value of total power P_G to distance s between base plates 7,8 of treatment nip 6 at certain time intervals. Alternatively it may also be provided that the total power is adapted depending on change s. The adaptation is based on the no-load power assigned to distance s. The specified value of total power P_G remains constant between the respective adjustments. The slight increase in specific power P_S that has occurred in the meantime can be tolerated.
The no-load power P_L relevant for the control of the treatment device is updated via the measured distance.
A no-load power P_L is verified when fibrous material 1 is present during opening and/or closing of treatment nip 6 at normal operating parameters, such as pressure, flow rate and stock consistency. This verification can be scheduled every 1-2 weeks, up to once daily.
For this purpose, the no-load power P_L of the treatment device is measured when the treatment nip is opened and/or closed, and it is checked whether the assumed value of the no-load power P_L is consistent with the measured value. As a result, a malfunction in the distance measurement can also be reliably detected if the measured value of the no-load power deviates clearly from the value stored for the respective distance.
Also, on start-up of the treatment device or when treatment tools 3, 4 or their fillings are replaced, the no-load power P_L is measured when treatment nip 6 is closed and is stored in the memory as a starting value for the controller.
The knowledge of the at least approximately real no-load power P_L not only has an influence on the specific power and the corresponding total power to be regulated, but if a specified, minimum no-load power P_L is not reached a correspondingly high level of wear on treatment tools 3, 4 can be concluded, making replacement of the latter necessary. Provision can also be made for informing the user if a predetermined distance value is not met, so that the user can plan and prepare for an imminently needed replacement of the refining fillings.
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.

Claims

What is claimed is:

1. A method for controlling a device for treating a fibrous material, the method comprising the steps of:

providing that the device includes a housing in which at least a first treatment tool and a second treatment tool are arranged, the first treatment tool and the second treatment tool:

being mounted on a first base plate and a second base plate respectively;

having a rotationally symmetrical shape;

being arranged coaxially relative to each other in that the first treatment tool and the second treatment tool rotate relative to one another about a common axis;

delimiting at least one treatment nip through which the fibrous material flows; and

having respectively a first treatment profile and a second treatment profile facing toward the at least one treatment nip;

mounting at least one of the first base plate and the second base plate respectively of at least one of the first treatment tool and the second treatment tool in an axially movable manner in order to compensate for a wear of the first treatment profile and the second treatment profile;

measuring a distance between the first base plate and the second base plate respectively of the first treatment tool and the second treatment tool of the at least one treatment nip during an operation of the device; and

selecting a value of a total power depending on the distance between the first base plate and the second base plate of the at least one treatment nip.

2. The method according to claim 1, wherein the value of the total power is selected depending solely on the distance between the first base plate and the second base plate of the at least one treatment nip.

3. The method according to claim 1, wherein the value of the total power is selected in conjunction with a plurality of additional values, depending on the distance between the first base plate and the second base plate of the at least one treatment nip.

4. The method according to claim 1, wherein the value of the total power is adjusted at least when a change in the distance between the first base plate and the second base plate of the at least one treatment nip of at least 1 mm is detected.

5. The method according to claim 1, wherein the value of the total power is adjusted at a plurality of predetermined time intervals, which is at least every 1 to 2 weeks, depending on the distance between the first base plate and the second base plate of the at least one treatment nip.

6. The method according to claim 1, wherein, after replacing at least one of the first treatment tool and the second treatment tool, a no-load power is measured and is stored in a memory as a starting value for a control system.

7. The method according to claim 6, wherein, for a desired treatment intensity, a relevant specific power of the device, which results from a difference between the total power and the no-load power, is kept constant over an operating period, taking into account a changing no-load power.

8. The method according to claim 1, wherein, after replacing at least one of the first treatment tool and the second treatment tool, a no-load power is measured – when the at least one treatment nip is closed – and is stored in a memory as a starting value for a control system.

9. The method according to claim 1, wherein, in determining the value of the total power depending on the distance between the first base plate and the second base plate of the at least one treatment nip, a plurality of values are accessed.

10. The method according to claim 9, wherein the plurality of values are a plurality of characteristic diagrams stored in a memory of a controller.

11. The method according to claim 1, wherein the method is used in a refiner.

12. The method according to claim 11, wherein the refiner is an LC refiner.

13. A device for treating a fibrous material, the device comprising:

a first base plate;

a second base plate;

a first treatment tool;

a second treatment tool;

a housing in which at least the first treatment tool and the second treatment tool are arranged, the first treatment tool and the second treatment tool:

being mounted on a first base plate and a second base plate respectively;

having a rotationally symmetrical shape;

being arranged coaxially relative to each other;

rotating relative to one another about a common axi;

delimiting at least one treatment nip through which the fibrous material flows; and having respectively a first treatment profile and a second treatment profile facing toward the at least one treatment nip, at least one of the first base plate and the second base plate respectively of at least one of the first treatment tool and the second treatment tool being mounted in an axially movable manner in order to compensate for a wear of the first treatment profile and the second treatment profile;

a sensor configured for determining a position of an axially movable one of at least one of the first treatment tool and the second treatment tool; and

a memory, in which a characteristic diagram is stored, the characteristic diagram containing a dependency of a no-load power depending on a change in a distance between the first treatment tool and the second treatment tool.

14. The device according to claim 13, wherein the device includes a wear indicator configured for treating the first treatment tool and the second treatment tool, wherein the device is configured for triggering a signal when a value associated with the signal falls below a predetermined distance value or a predetermined distance change.