EP3178989A1 - Method and device for treating a press felt - Google Patents

Abstract

In the press section of a machine for producing paper or paperboard, an endless felt (2) successively passes through press rolls (3, 4) for contacting with a paper web (5) to be dewatered, a high-pressure nozzle (12) for recovering an absorbent fabric structure by means of high-pressure water and a drying device (9) before being returned to the press rolls (3, 4). In order to eliminate inorganic residues and to restore the water absorption capacity of the continuous felt (2), the high-pressure water is mixed with carbon dioxide in the liquid or gaseous state before being fed to the continuous felt. The carbon dioxide leads to an acidification of the high-pressure water and thus to a reduction or dissolution of calcareous deposits; Furthermore, the carbon dioxide provides for an increase in volume of the continuous felt and thus contributes significantly to the restoration of water absorbency of the continuous felt.

Description

The invention relates to a method for treating an endless felt used for dewatering a paper web in a process for the production of paper or paperboard, in which the continuous felt is brought into contact with the paper web during one revolution by means of at least one press roll, thereby absorbing water, and then with treated cleaning water supplied through a high-pressure nozzle to restore an absorbent felt structure, dried in a drying device and recycled to the press roller. The invention also relates to a corresponding device.

In paper or board machines numerous circumferential webs are used. For example, in the wire section of a paper machine, filter belts are used, in the press section they are press felts and in the dryer section so-called dryer fabrics.

The press felts used in modern machines for the production of paper or paperboard are circumferential endless felts, which are brought into contact with the paper web to be dried on at least one press roll. The continuous felt absorbs water from the paper web, which is then removed in a drying unit. The drying unit has, for example, suction presses and / or one or more tube suckers in which the water is removed from the continuous felt by means of vacuum. Subsequently, the endless felt is returned to the paper web. Due to the constant compression and absorption of various organic and inorganic impurities, the water absorption capacity of the press felt decreases with time. To counteract this, the press felt is firstly treated with water (also referred to below as "cleaning water") which is applied from a nozzle to the continuous felt at a high pressure of, for example, between 3 bar and 50 bar. This leads to a substantial restoration of an absorbent tissue structure. On the other hand, to eliminate the organic and inorganic impurities, a treatment with cleaning agents, which are added in liquid form from time to time the cleaning water and applied with this on the continuous felt.

Devices in which a circumferential fabric web, in particular a press felt, is cleaned with high-pressure water can be found, for example, in US Pat DE 102 52 812 A1 , of the WO 00/42252 A1 or the EP 1 085 121 B1 ,

In the DE 44 19 540 A1 a device for cleaning a continuous fabric web during operation is described, in which simultaneously at least two different media are applied to the fabric web. As a cleaning medium come in different combinations of compressed air, water, steam or cleaning chemicals, such as caustic soda used. A disadvantage of this article is that this form of cleaning is associated with a significant contamination of the wastewater, with the result of a complicated clarification or disposal.

Also from the DE 20 2004 021 061 U1 is a device for cleaning a circumferential covering of a machine, for example a press felt of a paper machine known. In this article, a cleaning fluid, in particular water, applied under a pressure between 3 bar and 50 bar by means of a cleaning nozzle on the rotating fabric. The cleaning nozzle stands during the treatment in direct contact with the fabric to push the cleaning fluid into the fabric.

Due to the high mechanical load, however, a reduction in volume occurs over time and thus a significant decrease in the water absorption capacity of the press felt. This leads to a correspondingly high energy consumption of a subsequent dryer section to the press section, in which usually about 95% of the total energy required for water removal of a paper machine are spent. In addition, it comes in the fabric of the continuous felt for the storage of inorganic impurities, especially limescale, which is currently usually combated with an environmentally harmful acid treatment.

The object of the invention is therefore to provide a method and a device for cleaning a in the press section of a plant for the production of paper or To disclose continuous felt applied to cardboard, which improves the recovery of the water absorption capacity of the continuous felt and reduces environmental impact.

This object is achieved by a method for cleaning fabric webs with the features of patent claim 1 and by a device having the features of patent claim 5.

According to the invention, the cleaning water used to restore an absorbent fabric structure of the continuous felt is thus mixed with carbon dioxide upstream of the high-pressure nozzle in a method of the type and purpose mentioned above. The introduction of carbon dioxide into the cleaning water results in a number of advantages.

On the one hand, the pH value and thus the slowing index of the cleaning water is lowered, thereby suppressing the formation of lime deposits in the continuous felt or on the surface of the endless felt. In a negative Langelier index even existing deposits are brought to resolution. As a result, the use of chemicals to eliminate inorganic deposits can be reduced or even completely eliminated.

On the other hand, at least part of the carbon dioxide dissolves in the cleaning water supplied under pressure to the high-pressure nozzle. The carbon dioxide-added cleaning water is applied from the high pressure nozzle on the continuous felt and penetrates wholly or partly in this, whereby it relaxes to ambient pressure. At this pressure drop, a significant portion of the previously redeemed carbon dioxide from and ensures, if the outgassing occurs within the continuous felt, for an increase in volume of the felt fabric. In this way, the carbon dioxide contributes to restoring the water absorbency of the continuous felt. This not only increases the life of the endless felt, but at the same time sustainably reduced the energy requirement of a dryer section downstream of the press section.

The outgassing carbon dioxide enters the atmosphere or is collected and can be used in a further process, for example in a further process step in paper production. Carbon dioxide is used in papermaking in various processes, for example in the pH adjustment and dewatering of the fiber suspension, in which DE 2006 042 429 A1 described reduction of adhesive residues (stickies) in the fiber suspension or in the synthetic production of calcium carbonate (CaCO ₃ ).

The remaining carbon dioxide in the cleaning water also reduces the Langelier index of waste water and reduces the formation of limescale in the corresponding, the waste water lines leading.

The carbon dioxide is preferably fed into the cleaning water in the liquid or gaseous state. For the supply of carbon dioxide in the liquid state, the cleaning water should have a pressure of at least 5.18 bar, so that the liquid carbon dioxide intimately mix with the cleaning water and thus can easily redeem.

The cleaning water is thus preferably transported under a pressure of more than 5.18 bar to the high-pressure nozzle and applied to the continuous felt. To be able to dissolve more carbon dioxide in the cleaning water, provides an advantageous embodiment of the invention, the cleaning water with a higher pressure, for example, between 15 bar and 50 bar, to lead to the high pressure nozzle.

An essential aspect of the invention is the reduction of inorganic deposits on the surface of the continuous felt or in the interior of the felted fabric. Therefore, a particularly advantageous embodiment of the invention provides that the addition of carbon dioxide is regulated in the cleaning water in response to a determined continuously or at predetermined time intervals chemical or physical parameters. For example, a control to a certain value or range of pH and / or Langelier index of cleaning water. The measurement is carried out by means of a suitable probe, which is arranged for example in the region of the high-pressure nozzle. The setpoint of the corresponding controlled variable depends on the respective requirements.

In a particularly advantageous embodiment, the supply of carbon dioxide is controlled so that the Langelier index of the cleaning water during the treatment of the continuous felt is maintained at a value of LSI ≤ 0. With a value of the Langelier index of LSI = 0, limescale deposits from the cleaning water no longer occur. With a Langelier index of LSI <0 already formed deposits can be reduced. Alternatively or additionally, other parameters may also be determined and included in the metering of the carbon dioxide, such as the volume of the felt at a predetermined distance past the point of application of the cleaning water, the degree of drying of the continuous felt or the energy consumption in the press section drying section.

The object of the invention is also achieved with a device having the features of patent claim 5.

An apparatus for treating an endless felt used for dewatering a paper web, in particular in a machine for producing paper or paperboard, has an at least one press roll for contacting with the paper web to be dewatered and endless felt clamped over at least one deflecting roll, a high-pressure nozzle connected to a water supply line Loading the continuous felt with cleaning water and a drying device for drying the continuous felt and is inventively characterized in that in the water supply, upstream of the high-pressure nozzle, a fluidly connected to a source of liquid or gaseous carbon dioxide feed line for carbon dioxide opens.

About the with a source of carbon dioxide, such as a tank or a compressed gas cylinder bundle, flow-connected supply carbon dioxide in the liquid or gaseous state is fed into the cleaning water. The carbon dioxide dissolves at least partially in the cleaning water and is sprayed together with this from the high pressure nozzle onto the continuous felt, wherein a portion of the cleaning water penetrates into the fabric of the continuous felt. In the case of the pressure drop occurring at the outlet from the high-pressure nozzle, a portion of the carbon dioxide that has been dissolved in the gas exhausts and leads within the fabric of the endless felt an increase in volume, which has a particularly positive effect on the restoration of absorbency of the felt.

Incidentally, the high-pressure nozzle can be pivotally mounted and / or arranged on a traverse device running transversely to the running direction of the continuous felt and moved by means of a control. Several high-pressure nozzles can also be used, which are connected to the water supply line. Furthermore, it is conceivable to equip the high-pressure nozzle with a plurality of nozzle heads which extend transversely to the continuous felt and thus uniformly apply cleaning water to the entire width of the endless felt. Appropriately, a suction device is also provided, by means of which the outgassing and emerging from the continuous felt gaseous carbon dioxide can be at least largely absorbed. The collected carbon dioxide can be advantageously used, for example, in various processes, in particular in different sub-processes of paper production.

A particularly advantageous embodiment of the invention provides that the feed line for carbon dioxide is equipped with a check valve. This prevents water from flowing into the carbon dioxide feed line during a controlled supply of carbon dioxide into the cleaning water. A suitable for this purpose check valve, for example, in the EP 1 867 902 B1 or the EP 2 179 782 B1 described, which is incorporated herein by reference.

In order to enable a feed of the usually stored at a pressure between 15 bar and 22 bar carbon dioxide even at higher pressures in the water supply, for example, 25 bar to 30 bar or more, the supply line for carbon dioxide is suitably equipped with a compressor. As an alternative or in addition to a compressor, in an advantageous embodiment of the invention, a Venturi nozzle is provided at the mouth of the feed line for carbon dioxide into the water feed line, by means of which the carbon dioxide is sucked into the water feed line due to the water flowing through the water feed line.

An advantageous embodiment of the invention provides that the water supply line is equipped with a measuring probe, which is preferably arranged in the region of the high-pressure nozzle, and the feed line for carbon dioxide is equipped with a control valve, wherein the measuring probe and control valve are in data communication with a control unit. With this arrangement, the carbon dioxide input can be controlled by a parameter measured in the cleaning water, for example the pH.

Reference to the drawings, an embodiment of the invention will be explained in more detail.

The only drawing ( Fig .1 ) schematically shows the section of a press section of a paper machine with a device according to the invention for cleaning an endless felt used for pressing.

In the illustrated press section 1 of a paper machine is an all-round continuous felt (press felt) 2 on two press rollers 3, 4 in contact with a paper web 5. About several pulleys 6 of the endless felt 2 - in the direction of arrow 7 - to the beginning of the press section, ie returned to the press rolls 3, 4. The endless felt 2 successively passes through a cleaning device 8 and a drying device 9.

The cleaning device 8 comprises a high-pressure nozzle 12 connected to a water supply line 11. Fresh water or purified process water is introduced under high pressure through the water supply line 11 and discharged at the high-pressure nozzle 12 in the direction of the endless felt 2. The high-pressure nozzle 12 includes, for example, a single nozzle head or a plurality of nozzle heads, which are mounted, for example, pivotable and act in this way the entire width of the endless felt 2 with high pressure water. It is also possible, one or more high-pressure nozzles 12 on a - not shown here - across the endless felt 2 extending traverse fixed or slidable to achieve in this way uniform loading of the endless felt 2 with high pressure water, or multiple high-pressure nozzles 12 - Viewing direction of the felt - to arrange one after the other.

The drying device 9 comprises, in particular, a vacuum drying unit, for example one or more tube suckers.

Upstream to the high-pressure nozzle 12 opens into the water supply line 11 at an outlet point 14 a connected to a source of liquid carbon dioxide, not shown here, a pressure line 15 a. As a source of carbon dioxide, for example, a gas cylinder bundle or a stationary tank into consideration, in which the carbon dioxide is stored at a pressure of usually 15 bar to 22 bar. At higher operating pressures of the cleaning water, therefore, a compressor 13 is provided, by means of which the pressure of the carbon dioxide in the pressure line 15 is adapted to the higher operating pressure of the cleaning water in the water supply line 11. Instead of a compressor 13, a venturi nozzle (not shown here) may be used for this purpose, by means of which the carbon dioxide from the pressure line 15 is sucked into the water supply line 11. In the area of the discharge point 14, a check valve 16 is provided in the pressure line 15, which is intended to prevent the ingress of water from the water supply line 11 into the pressure line 15. Furthermore, a controllable control valve 17 is arranged in the pressure line 15. The control valve 17 and a measuring probe 18 arranged in the region of the high-pressure nozzle 12 are in data connection with a control unit 19.

During operation of the press section 1, the paper web 5 and endless felt 2 run in the same direction through the press rolls 3, 4. The paper web 5 is pressed tightly against the endless felt 2 by the press rolls 3, 4, the continuous felt 2 receiving water from the paper web 5. The loaded continuous felt 2 is then treated with water (hereinafter referred to as "high-pressure water") for producing an absorbent fabric structure at the high-pressure nozzle 12, which is applied to the continuous felt at a pressure of, for example, between 15 bar and 30 bar and partially into the fabric structure of the endless felt 2 penetrates. Subsequently, in the drying device 9, a substantial part of the water absorbed by the endless felt 2 is removed by suction and removed via a discharge line 21. Finally, the endless felt 2 is returned via deflection rollers 6 to the press rollers 3, 4.

During operation, the continuous felt 2 is contaminated with organic and inorganic contaminants, which settle in the fabric of the endless felt 2. At the same time, the tissue of the continuous felt 2 becomes denser over time, with the result that the water absorption capacity of the endless felt 2 decreases.

To counteract both, the high-pressure water in the water supply line 11 is mixed with liquid carbon dioxide from the pressure line 15. The liquid carbon dioxide mixes downstream of the mouth 14 intimately with the high pressure water and is at least partially in solution. The high-pressure water is acidified by this; pH value and Langer index go back. The high-pressure water mixed with carbon dioxide is applied to the surface of the high-pressure nozzle 12 and introduced into the fabric of the endless felt 2. The pressure drop to ambient pressure occurring at the exit from the high-pressure nozzle 12 leads to a partial outgassing of the carbon dioxide dissolved in the high-pressure water. As a result, there is an increase in volume in the felt fabric, which favors the water absorbency.

The control of the 19 and the control valve 17, the supply of carbon dioxide in response to a detected at the measuring probe 18 physical or chemical parameters of the high-pressure water, such as the pH, regulated. For example, the carbon dioxide entry is chosen so that the Langelier index is negative ("CO ₂ overdose"), or it is trying as constant as possible a pH in the acidic range, for example, between pH = 5 and pH = 6, 5 in the cleaning water in the high pressure nozzle 12 to achieve. As a result, the formation of limescale is avoided, and already existing lime deposits dissolve. Furthermore, it is conceivable that a supply of carbon dioxide via the pressure line 15 takes place only at predetermined time intervals. The check valve 16 prevents that during a phase in which no carbon dioxide is supplied via the pressure line 15, high-pressure water from the water supply line 11 penetrates into the pressure line 15. With the aid of the compressor 13, the pressure of the supplied carbon dioxide is optionally adapted to the pressure of the high-pressure water in the water supply line 11.

In the context of the invention, by the way, further cleaning chemicals can be added to the high-pressure water at the same time or with a time delay for supplying the carbon dioxide, in particular alkali-containing cleaning agents for controlling organic deposits in the fabric of the endless felt 2.

By using the invention, the water absorption capacity of the endless felt 2 is improved, whereby the energy requirement of a subsequent to the press section 1 dryer section (not shown here), in which the water content of the paper web 5 is further reduced by means of heated rollers, is significantly reduced. Furthermore, the usual in the art for controlling inorganic deposits introduction of mineral acids in the high-pressure water is unnecessary. The supply of carbon dioxide improves felt fabric regeneration and life, thereby reducing or even eliminating stoppages due to replacement of the continuous felt.

LIST OF REFERENCE NUMBERS

• 1 press section
• 2 endless felt
• 3 press roll
• 4 press roll
• 5 paper web
• 6 pulley
• 7 arrow
• 8 cleaning device
• 9 drying device
• 10 -
• 11 water supply
• 12 high pressure nozzle
• 13 compressor
• 14 estuarine site
• 15 pressure line
• 16 check valve
• 17 control valve
• 18 measuring probe
• 19 control unit
• 20 -
• 21 derivative

Claims (9)

Method for treating an endless felt used for dewatering a paper web in a process for producing paper or cardboard, in which the continuous felt (2) is brought into contact with the paper web (5) during one revolution by means of at least one press roll (3, 4), thereby receiving water, and then treated with a high-pressure nozzle (12) supplied cleaning water to restore an absorbent felt structure, dried in a drying device (9) and returned to the press roll (3, 4),
characterized,
in that the cleaning water used to restore an absorbent fabric structure of the continuous felt (2) is mixed with carbon dioxide upstream of the high-pressure nozzle (12). A method according to claim 1, characterized in that the carbon dioxide is fed in the liquid or gaseous state in the cleaning water. A method according to claim 1 or 2, characterized in that the cleaning water is applied under a pressure between 5.18 bar and 50 bar, preferably between 15 bar and 50 bar on the continuous felt (2). Method according to one of the preceding claims, characterized in that the supply of carbon dioxide into the cleaning water according to a predetermined program depending on a continuously or at predetermined intervals determined value of a physical or chemical parameter, such as pH or Langelier index of cleaning water , is regulated. Apparatus for treating a continuous felt used for dewatering a paper web of a machine for the production of paper or cardboard, comprising an endless felt (2) which is connected via at least one press roll (3, 4) to the dewatering paper web (5) and via at least one deflection roller (6) is braced, with a high-pressure nozzle (12) connected to a water supply line (11) for impinging the endless felt (2) with cleaning water and with a drying device (9) for drying the continuous felt (2),
characterized,
that in the water supply line (11) upstream of the high-pressure nozzle (12) opens with a source of liquid or gaseous carbon dioxide flow-connected supply line (15) for carbon dioxide. Apparatus according to claim 5, characterized in that the feed line (15) for carbon dioxide is equipped with a check valve (16). Apparatus according to claim 5 or 6, characterized in that the supply line (15) is equipped for carbon dioxide for the purpose of pressure equalization with a compressor. Device according to one of claims 5 to 7, characterized
characterized in that the supply line (15) opens for carbon dioxide at a Venturi nozzle in the water supply line (11). Device according to one of claims 5 to 8, characterized in that the water supply line (11) with a measuring probe (18) and the supply line (15) for carbon dioxide with a control valve (17) is equipped, wherein the measuring probe (18) and the control valve (17) with a control unit (19), for the purpose of controlling the carbon dioxide entry into the cleaning water, are in data communication.

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