WO2022069433A1

WO2022069433A1 - Controlling the treatment of fibrous material

Info

Publication number: WO2022069433A1
Application number: PCT/EP2021/076575
Authority: WO
Inventors: Martin Kemper
Original assignee: Voith Patent Gmbh
Priority date: 2020-09-30
Filing date: 2021-09-28
Publication date: 2022-04-07
Also published as: CN116324083A; EP4222308A1; US20230243097A1; DE102021125006A1

Abstract

The invention relates to a method for controlling a device for treating fibrous material (1), said device comprising a housing (2), in which a first treatment tool (3) and a second treatment tool (4) are arranged, wherein in each case the treatment tools (3,4) are fastened to a base plate (7,8), have a rotationally symmetrical shape, are arranged coaxially to each other, rotate relative to one another about a common axis (5), delimit a treatment nip (6) through which the fibrous material (1) flows, and have in each case a treatment profile (9) which points towards the treatment nip (6), wherein at least one base plate (7,8) of a treatment tool (3,4) is mounted in an axially displaceable manner for compensating the wear of the treatment profiles (9). The control of the device is to be improved in that the distance (s) between the base plates (7,8) of the treatment tools (3,4) of a treatment nip (6) is determined and, for the purpose of controlling the total power (PG), the value of the total power (PG) is adjusted as a function of a change of distance (s) between the base plates (7,8) of the treatment nip (6).

Description

Pulp treatment control

The invention relates to a method for controlling a device for treating fibrous material, the device having a housing in which at least a first treatment tool and a second treatment tool are arranged. The treatment tools are each mounted on a base plate and have a rotationally symmetrical shape and are arranged coaxially with one another and rotate relative to one another about a common axis. The treatment tools delimit a treatment gap through which the fibrous material flows and each have a treatment profile pointing towards the treatment gap, with at least one base plate of a treatment tool being mounted in an axially displaceable manner to compensate for the wear of the treatment profiles. To adjust the total power, the width of the treatment gap is adjusted until the predetermined total power is reached.

Due to the relatively high consistency that the fibrous material has during the treatment, intensive mechanical processing is possible with such devices (refiners, dispersers, deflakers), although the treatment tools that can be moved relative to one another do not touch one another, but rather move past one another at a small distance . Very considerable forces arise here.

Devices of the above kind become e.g. B. used to improve the quality of pulp, TMP or pulp that was obtained from waste paper.

It has long been known to grind cellulose fibers, i.e. fresh cellulose and/or waste paper fibers, in order to be able to achieve the desired properties in the fibrous web produced therefrom, in particular with regard to strength, porosity, formation and surface.

Due to the relatively rapid wear and tear of the refiners used, the grinding surfaces are formed by replaceable grinding sets screwed to the corresponding base plate. In order to achieve the desired fiber properties, in particular the degree of beating, the beating clothing must be optimally adapted to the fibrous material to be treated, also in order to prevent excessive wear of the clothing.

In addition, to increase the efficiency of fiber treatment, an optimal use of the available refining surface is aimed at.

It is known from US 2004/0112 997 A1 as well as DE 2 939 587 A1 and DE 3 602 833 A1 to measure or calculate the no-load power once before commissioning and to use it as a basis for the machine control.

If the height of the treatment profile of the treatment tools decreases as a result of wear, this leads to a reduction in the no-load or pump output. With the overall performance remaining the same, this also leads at the same time to an increase in the specific performance of the device, which is relevant for the desired treatment intensity, and thus to excessive treatment, in particular grinding of the fibers. A constant overall performance is regulated by an axial displacement of the axially displaceable base plate.

If the gap is too small, there is a risk of excessive electrical current consumption and contact between the treatment tools.

It is known from DE 10 2016 207 726 A1 to determine the idle power during operation. For this, however, it is necessary to empty the refiner or to flood it with water and to open and close the treatment gap and to measure the no-load performance. The idle power then measured is then used as a basis for further operation.

The object of the invention is to enable safe and efficient operation of these devices with the simplest possible means. According to the invention, the object is achieved in that the distance between the base plates of the treatment tools of a treatment gap is changed during operation of the device for controlling the total power, and the value of the total power is selected as a function of the measured distance between the base plates of the treatment gap. The measured distance is also understood to mean, in particular, a change in distance starting from an initial value. On the one hand, the distance can be measured directly by measuring the distance, for example, between the treatment tools or the base plates on which the treatment tools are attached. However, the distance can also be measured indirectly. For example, in one embodiment, the position of the drive for tracking the axially displaceable base plate of the treatment tool can be inferred from the change in distance.

Since the no-load power of the device decreases relatively significantly during the operating time of the treatment tools with increasing wear of the profile of the treatment tools, the total power, which is made up of the no-load or pump power and the specific power relevant to the desired treatment intensity, must be adjusted accordingly. In this way, an unwanted increase in the specific power and thus also the intensity of the treatment of the fibers can be effectively and easily counteracted.

This is also possible in particular because the usual width of the treatment gap is many times smaller than the profile height of the treatment tools and so the width of the treatment gap can be neglected in the control. When the fiber suspension is supplied, a treatment gap is formed during operation and a treatment gap width is set until a predetermined overall output is reached. Since the gap width of the treatment gap is negligible compared to the profile height, the variation in the gap width of the treatment gap is thus also the treatment gap width also dependent on the throughput can be negligible compared to the change in position due to wear of the clothing. The profile height can thus be determined from the measured distance/distance change, or a change in the profile height based on an initial value. In a device with one treatment gap, the profile height corresponds to half the distance between the base plates and in a device with two treatment gaps, the profile height after deducting the width of the distances caused by non-profile components is a quarter of the determined distance value. Starting from an initial distance value, the reduction in the distance can also be determined by measurement and the reduction in the profile heights can be determined directly from this. Depending on the specific profile height and the desired treatment intensity, the corresponding overall performance is set.

In one embodiment variant, it is provided that the wear of each set should be indicated rounded to 0.1 mm, preferably rounded to 0.5 mm. A displacement sensor or an incremental encoder can be used as sensors for determining the position or the change in position.

In order to simplify the control, the value of the total power should be chosen solely as a function of the measured distance between the base plates of the treatment gap or in connection with the desired grinding energy. The measured distance corresponds to the determination of the profile height. The relationships between the profile height and the idle power associated with it are preferably stored in a characteristic map. This characteristic map can be read in by the operator before it is put into operation or it can also be made available by the manufacturer of the device. This means that it is not necessary to determine the no-load power during operation.

In a preferred embodiment, it is provided that the rotor is mounted in a floating manner in a device with a double gap. This allows an adjustment of the distance between the treatment tools corresponding to the Height of the profiles for both gaps is carried out by an axially displaceable treatment tool.

A more precise control is possible if the value of the total output is selected taking into account other values such as flow and consistency and/or the quality of the pulp suspension.

Advantageously, the value of the total power should be adjusted at least when a change in the distance between the base plates of the treatment gap of at least 1 mm is detected. This corresponds to a reduction of each treatment profile of 0.5 mm at a treatment gap.

However, it is often sufficient if the value of the total power is reselected at predetermined time intervals at most once a day, preferably at least once a week, depending on the measured change in the distance between the base plates of the treatment gap. 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 output 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 is usually between 40 and 250, in particular between 40 and 150, kWh per ton of dry weight in refiners, should also be included if possible.

After an intervention in the device, eg by replacing only a part of the clothing, a distance value measured when opening and/or closing the treatment gap can be used once as a new output value for no-load power for establishing a reference to an interleaved characteristic map. In the subsequent control of the overall performance, in addition to the distance value, further links with other parameter values can be used to control the overall performance and thus also the specific performance of the device. Provision can furthermore be made for the no-load power to be measured each time before the refiner is shut down. Furthermore, it can additionally or alternatively be provided that a determination of the no-load power is determined only after a predetermined minimum operating time. This prevents the no-load power being determined every time the device is stopped several times a day. An idle determination every 1 to 2 weeks is completely sufficient due to the stored maps and a corresponding tracking of the overall performance. As a result, an undesirably high grinding capacity can be reliably prevented.

It has hitherto been customary to determine the no-load power of the device when it is put into operation and to store it for the control or to use a predetermined value for this purpose.

With increasing operating time of the respective treatment tools and thus also increasing wear of the same, in particular their profile, 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 with previous controls/regulations, it can happen that the total power consumed for the desired treatment intensity is set too high by values of 20% and more.

In order to be able to store a starting value for the controller in the memory after changing at least one treatment tool, it can be advantageous for service personnel to measure and enter the no-load power, or to have the no-load power measured by the controller itself, especially when the treatment gap is closed.

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 to the desired treatment intensity, which results from the difference between the total power and the no-load power, is constant over the operating period. This ensures a constant treatment intensity will. The specific power is regarded as constant if the specific power deviates by less than 5% from its arithmetic mean.

If the value of the total power is not redetermined continuously but at specific 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 with regard to the then increasing specific power are tolerable. A change of less than 5% of the last assumed idle power and/or a change in position of less than 1 mm per gap is considered to be tolerable.

When determining the value of the total power as a function of the distance between the base plates of the treatment gap, values stored in a memory of the controller, in particular a characteristic map, should advantageously be used. The stored values or the map were specified by the manufacturer of the device or determined in advance by the operator of the device in tests.

These values stored in the memory are based on knowledge or experience regarding the no-load power at the corresponding distance between the two base plates of the treatment gap and, related to this, also the degree of wear of the treatment profiles. Taking into account the desired intensity of treatment of the fibers and thus the specific power, the specified value for the total power of the controller is the sum.

In the interests of a simple construction of the device, one treatment tool should rotate and the other should not, with at least one treatment tool being mounted so that it can be displaced axially.

In the case of 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 gaps arranged next to one another, each with a treatment tool rotating on a shaft and a non-rotating treatment tool. As a rule, the two treatment tools adjacent to the other treatment gap are attached to a common base plate, this common base plate and at least one of the treatment tools not attached to this base plate being mounted so as to be axially displaceable.

It is particularly advantageous to use the method according to the invention in a refiner, in particular an LC (low-consistency) refiner, the consistency of the pulp being between 2 and 6, preferably between 3.5 and 4.5% of the dry weight.

The fibrous material can in particular also be TMP, high-yield cellulose, MDF fibrous material, wood chips or similar substances.

The invention will be explained in more detail below using an exemplary embodiment.

In the attached drawing shows:

Figure 1: a schematic cross section through a refiner and

Figure 2: the change in no-load power PL and the adjustment of the total power PG over time t and over the distance s between the base plates 7.8.

According to Figure 1, the paper pulp 1 is pressed directly into the central, i.e. radially inner area of the refiner clothing, which is formed by the two treatment tools 3,4.

While one treatment tool 3 is fixed and thus designed as a stator, the other treatment tool 4 is rotatably mounted in the housing 2 of the refiner. The treatment tools 3.4 each have a rotationally symmetrical shape, with the two annular grinding surfaces being arranged parallel to one another. The treatment gap 6 between the grinding surfaces is adjusted via an axial displacement in order to achieve a predetermined overall performance. The treatment intensity of the paper pulp 1 flowing into the gap, also referred to as fiber suspension, is determined by the gap width of the treatment gap 6 . The axial extent of this gap width of the treatment gap 6 is negligible in comparison with the height of the treatment profiles 9 of the treatment tools 3 , 4 .

The rotating grinding surface 9 is here moved in the direction of rotation by a shaft rotatably mounted in the housing 2 . This shaft is driven by a drive that is also present in the housing 2 . In the example shown, the fiber suspension 1 to be ground passes via an inlet through the center into the treatment gap 6 between the grinding surfaces of the two treatment tools 3,4.

The fiber suspension 1 passes the interacting beating surfaces radially outwards and leaves the adjoining annular space through an outlet.

Both grinding surfaces are each formed by a plurality of grinding plates, each of which extends over a peripheral segment of the corresponding grinding surface. Arranged side by side in the circumferential direction, the grinding plates form a continuous grinding surface.

The refining plates and thus also the refining surfaces have a treatment profile 9 directed towards the treatment gap 6, which is generally formed by a multiplicity of essentially radially running grinding bars and grooves in between.

The means known per se, with which the non-rotating treatment tool 3 is displaced axially, are not shown. The extent of this axial displacement is measured by a displacement sensor 10. The rotating treatment tool 4 does not change its axial position. It can also be measured by means of an incremental encoder on the drive for setting the axial position of the non-rotating but axially displaceable treatment tool 3 (not shown).

Furthermore, the treatment tools 3.4 are attached to corresponding base plates 7.8.

In contrast to the example shown here, the treatment gap 6 can run not only perpendicular but also inclined to the axis of rotation 5, as in the case of cone refiners. In addition, the housing 2 can also include several, in particular two, treatment gaps 6 .

FIG. 2 illustrates the change in the real no-load power PL of the refiner over the distance S, which decreases with increasing operating time t and thus also with increasing wear of the treatment profile 9 of the treatment tools 3, 4.

The total power PG, which is supplied to the treatment device, is made up of the no-load power PL and the specific power Ps responsible for the treatment intensity of the fibrous material 1, i.e. the beating power.

The total power is set to a predetermined value that corresponds to the desired treatment intensity with a known idle power. In order to avoid that the specific power P _s over the service life of the treatment tools 3, 4 becomes significantly higher than would be necessary for the desired treatment intensity of the fibrous material 1, the assumed no-load power PL depends on the measured distance s between the base plates 7 , 8 or the distance between the treatment tools 3, 4 is adjusted accordingly with recourse to the stored values or the stored characteristics map. By changing the distance s between the base plates 7.8 of the treatment tools 3.4 of the treatment gap 6 during operation, the total power PG consumed by the device can be controlled easily and efficiently. It is essential to the invention that the value of the total power PG is selected as a function of the distance s between the base plates 7 , 8 of the treatment gap 6 .

In this case, the value of the total power PG is preferably chosen such 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 the total power PG as a function of the distance s between the base plates 7, 8 of the treatment gap 6, values stored in a memory of the controller are used, which are specified by the manufacturer of the device or determined by the operator of the device in tests.

The value of the total power PG specified for the control of the device can be continuously adapted to the distance s between the base plates 7, 8 of the treatment gap 6, as shown in FIG. 2 as a dashed line.

Alternatively, according to the solid line for the total power PG in FIG. 2, it is also possible to readjust the value of the total power PG to the distance s between the base plates 7.8 of the treatment gap 6 at specific time intervals. Alternatively, it can also be provided that the total power is adjusted as a function of the change s. The adaptation is based on the no-load power assigned to the distance s.

The specified value of the total power PG remains constant between the respective adjustments. The slight increase in the specific power Ps that has occurred in the meantime can be tolerated. The value of the no-load power PL relevant for the control of the treatment device is updated via the measured distance.

A no-load power PL is verified when fibrous material 1 is present during an opening and/or closing of the treatment gap 6 with normal operating parameters such as pressure, flow rate and consistency. This verification can be scheduled every 1-2 weeks up to once a day.

For this purpose, the no-load power PL of the treatment device is measured when the treatment gap is opened and/or closed, and it is checked whether the assumed value of the no-load power PL matches 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 significantly from the value stored for the respective distance.

When the treatment device is started up or when the treatment tools 3, 4 or their sets are changed, the no-load power PL is measured when the treatment gap 6 is closed and stored in the memory as a starting value for the controller.

The knowledge of the at least approximately real no-load power PL not only has an influence on the specific power and the corresponding total power to be adjusted, but if a specified, minimum no-load power PL is not reached, a correspondingly high level of wear on the treatment tools 3.4 can be concluded, which makes change necessary. Provision can also be made for informing the user if the distance falls below a predetermined value, so that the user can plan and prepare for an soon-to-be-needed replacement of the grinding sets.

Claims

patent claims

1 . Method for controlling a device for treating fibrous material (1), the device having a housing (2) in which at least a first treatment tool (3) and a second treatment tool (4) are arranged, the treatment tools (3, 4) each are attached to a base plate (7, 8), have a rotationally symmetrical shape, are arranged coaxially to one another, rotate relative to one another about a common axis (5), delimit at least one treatment gap (6) through which the fibrous material (1) flows and each have a have a treatment profile (9) pointing towards the treatment gap (6), at least one base plate (7, 8) of a treatment tool (3, 4) being mounted in an axially displaceable manner to compensate for wear on the treatment profiles (9), characterized in that the distance between the base plates (7.8) of the treatment tools (3.4) of a treatment gap (6) is measured during operation of the device and the value of the total power (PG) depending on the distance (s) between the base plates (7.8) of the treatment gap (6) is selected.

2. The method according to claim 1, characterized in that the value of the total power (PG) is selected solely as a function of the distance (s) between the base plates (7.8) of the treatment gap (6).

3. The method according to claim 1, characterized in that the value of the total power (PG) is selected in conjunction with other values depending on the distance (s) between the base plates (7, 8) of the treatment gap (6).

4. Method according to one of the preceding claims, characterized in that the value of the total power (PG) is adjusted at least when the distance between the base plates (7, 8) of the treatment gap (6) changes by at least 1 mm. Method according to one of claims 1 to 3, characterized in that the value of the total power (PG) at predetermined time intervals, at least every 1 to 2 weeks depending on the distance (s) between the base plates (7, 8) of the treatment gap (6) is adjusted. Method according to one of the preceding claims, characterized in that after changing at least one treatment tool (3,4), the no-load power (PL) is measured, preferably when the treatment gap (6) is closed, and stored in a memory as an initial value for the controller. Method according to one of the preceding claims, characterized in that for a target treatment intensity, a relevant specific power (Ps) of the device, which results from the difference between the total power (PG) and the no-load power (PL), is kept constant over the operating period and a changing no-load power is taken into account. Method according to one of the preceding claims, characterized in that when determining the value of the total power (PG) as a function of the distance (s) between the base plates (7, 8) of the treatment gap (6), values stored in a memory of the controller , in particular map, is used. Application of the method according to one of the preceding claims in a refiner, in particular an LC refiner. . Device for treating fibrous material, the device having a housing (2) in which at least a first treatment tool (3) and a second treatment tool (4) are arranged, the treatment tools (3, 4) each on a base plate (7, 8 ) are fixed, have a rotationally symmetrical shape, are arranged coaxially to one another, rotate relative to one another about a common axis (5), at least one of the fibrous material (1) - 15 - limit the treatment gap (6) through which flow occurs and each have a treatment profile (9) pointing towards the treatment gap (6), with at least one base plate (7, 8) of a treatment tool (3, 4) axially to compensate for the wear of the treatment profiles (9). displaceably mounted, characterized in that a sensor is provided for determining the position of the axially displaceable treatment tool and a characteristic map is stored in a memory, the characteristic map containing a dependency of an idle power as a function of a change in the distance between the treatment tools (3, 4). . Device according to Claim 10, characterized in that the device comprises a wear indicator for the treatment tools (3, 4), a signal being triggered when the distance falls below a predetermined value or a predetermined change in distance.