WO2012013407A1 - Approach system of a machine for producing a fibrous web - Google Patents

Abstract

The invention relates to a process and an arrangement for producing a fibrous suspension for producing a paper, board, tissue or another fibrous web by mixing at least one high-consistency stream (1) formed by treated fibrous material and filler with at least one low-consistency stream (2) preferably formed by fresh water, white water or the like in a machine for producing the fibrous web, wherein the high-consistency stream (1) is cleaned and, before and after this cleaning operation, is mixed with at least one part-stream of the low-consistency stream (2). In this case, the expenditure is to be reduced by degassing the high-consistency stream (1) for the first time after mixing with a part-stream of the low-consistency stream (2), which follows the cleaning operation.

Description

 CONSTANT PART OF A MACHINE FOR MANUFACTURING A FIBROUS WEB

The invention relates to a process for producing a pulp suspension for producing a paper, board, tissue or other fibrous web by mixing at least one high consistency stream formed from recycled fiber and filler with at least one, preferably fresh, white water or the like , formed low-consistency stream in a machine for producing the fibrous web, wherein the high-consistency stream is cleaned and mixed before and after this cleaning with at least a partial stream of the low-consistency stream.

The invention also relates to an arrangement for producing a pulp suspension for producing a paper, board, tissue or other fibrous web from at least one, made of recycled fiber and filler high-consistency stream and at least one, preferably fresh water, white water or the like. formed low-consistency stream in the constant part of a machine for producing the fibrous web, the high-consistency stream is passed through at least one cleaning device and diluted before and after this cleaning device in at least one mixing device with a partial stream of low consistency stream, in particular for carrying out the method.

In the constant part of paper machines, the previously processed high-consistency accept is diluted with the collected in the paper machine white water, cleaned and degassed before it can be fed to the headbox of the paper machine.

For this purpose, it is known, for example, from WO2004 / 072365 to pass the entire white water through a degassing device before its admixture. It is also known, the cost of cleaning the accept Dilute it by diluting it in two stages and purifying it after the first dilution. In this way, the amount of fluid passed through the cleaning device can be minimized because of the relatively high consistency.

If the white water has not already been degassed before admixing, in the case of the two-stage dilution both degassing of the purified high-consistency stream after the first dilution and degassing of the low-consistency stream for the second dilution are carried out.

Fresh water is used to an ever smaller extent usually only in the paper machine used.

In both versions, the effort is relatively high, especially for the degassing.

The object of the invention is therefore to reduce the effort in the constant part with sufficient ventilation. According to the invention the object has been achieved in that the high-consistency stream is degassed for the first time and in particular once after a mixing following the purification with a partial stream of the low-consistency stream.

In this way, the degassing of the low-consistency stream prior to admixture is eliminated. The load of the cleaning device and the degassing remain relatively low because of the high consistency after the first dilution.

With regard to the arrangement, it is accordingly essential that the high-consistency stream is passed through a degassing device for the first time and in particular once after a mixing device following the cleaning device. The cleaning devices may consist of several stages. It is also possible that only one or more mixing devices are upstream and / or downstream of the cleaning device. In this case, it is deliberately dispensed with a degassing of the supplied after degassing of the high-consistency stream partial flow of the low-consistency stream. This is acceptable, since the vast majority of the headbox supplied amount of fluid is degassed. Even with a headbox with directly supplied dilution water, the degassed portion of the headbox total supplied amount of fluid is about 85 to 90%.

 As the air content after degassing of the high-consistency stream is generally below 0.1% and the air content of the white water around 2%, the maximum air content of less than 0.5% generally required for the headbox can be easily met.

As a result, it is possible to dispense with a second degassing device.

The cleaning devices, such as cleaners or sorters, are often designed for relatively high consistency streams without exploiting their potential. Therefore, the consistency of the high consistency stream should be immediately before cleaning between 1, 5 and 3.5%, preferably more than 2%.

In the mixing devices, it is advantageous in the interest of good mixing, if an injection of the high-consistency stream into the low-consistency stream, wherein the entry velocity of the high-consistency stream should be 3 to 15 times greater than the flow rate of the low-consistency stream.

Since degassing does not necessarily have to take place immediately after the cleaning, it is advantageous for degassing the largest possible portion of the pulp suspension if the high-consistency stream is degassed after the last cleaning following mixing with a partial flow of the low-consistency stream. This means for the arrangement that the high-consistency stream is passed through a degassing device after the last mixing device following the cleaning device. To ensure a high efficiency of degassing, however, it is advantageous if the consistency of the high-consistency stream immediately before degassing is between 1 and 1, 5%.

In order to minimize the effort for degassing, the low-consistency stream should therefore not be degassed or passed through any degassing device.

This also applies to headboxes in which, as described in EP1645684, streams of different consistency are mixed to control the basis weight cross-section of the fibrous web to be produced.

 In this case, a partial flow of the low-consistency stream without degassing but preferably via a cleaning unit to the headbox of the machine.

Because of the fluctuations in the incoming and outgoing fluid is mainly diverted from the degassing an overflow with degassed pulp suspension, which is mixed with advantage only after cleaning the high-consistency stream this. With regard to the arrangement, this means that the overflow stream of the degassing device is passed to a mixing device following the cleaning device of the high-consistency stream. This additionally relieves the cleaning device.

In order to avoid disturbances in the headbox and thus in the production of the fibrous web, the high-consistency stream after the last mixing device should preferably be guided via a cleaning unit to the headbox. This cleaning unit can also act degassing depending on the design. For the widest possible use of the fibers and fillers, it is advantageous if the reject of at least one usually arranged immediately before the headbox cleaning unit of high-consistency or low-consistency stream is passed to another cleaning unit, the Accept is preferably performed to degasification.

The invention will be explained in more detail with reference to an exemplary embodiment. In the accompanying drawing, the figure shows a schematic representation of the constant part of a paper machine.

In the constant part of the paper machine, the high-consistency stream 1 is prepared in a manner known per se from fibrous materials and fillers in accordance with the specifications of the papermaker, i. combined in predetermined mixing ratios in a mixing chest and mixed.

Thereafter, the high consistency stream 1 has a consistency of 3-4% and an air content in the range of about 3%.

In the constant part, the high-consistency stream 1 is subsequently diluted several times, in this case specifically in two mixing devices 3, 4, with a partial stream of the low-consistency stream 2. In addition, a cleaning and a one-time degassing of the high-consistency stream 1 before it reaches the headbox 10 of the paper machine.

 From the headbox 10, the finished pulp suspension for sheet formation is placed on or between the former screens of the following former via one or more nozzles.

In the former and subsequent units of the machine, the white water is collected and returned as a low consistency stream 2 in the constant part of the machine, so that as little fiber and fillers are lost and little fresh water is needed. To minimize the effort, the entire white water used for dilution in the mixing devices 3,4 and directly at the headbox 10 is not degassed. After the first mixing device 3 for dilution of the high-consistency stream 1, this has a consistency of less than 3.5%, which allows the cleaning in a following cleaning device 5 in the form of a centrifugal separator. The relatively high consistency reduces due to the low throughput investment costs for the cleaning device 5, but is not so high that the efficiency of the cleaning device 5 is too much affected.

Following the purification, a further dilution of the high-consistency stream 1 takes place in a following mixing device 4, which reduces the consistency to 1 to 1, 5%.

Only then is the high-consistency stream 1 fed to a degassing device 6 in which the fluid is brought under reduced pressure to the boiling point and thus degassed. To compensate for throughput fluctuations, the degassing device 6 includes an overflow, the overflow stream is returned to the immediately preceding mixing device 4 and the high-consistency stream 1 is mixed. Thus, this at least partially degassed overflow current is not again performed by the cleaning device 4 contrary to the prior art, which relieves them.

After the degassing device 6, the high-consistency stream 1 is passed to the headbox 10 for safety via an additional cleaning unit 7 in the form of a vertical sight with a built-in screen basket (pressure sorter). If, as indicated in the figure, a partial flow of white water is fed directly to the headbox 10, this is done via a cleaning unit 9 also in the form of a vertical seal with built-in screen basket (pressure sorter). With the help of the white water so the basis weight cross profile can be influenced at the headbox 10 in a known manner.

The reject of the two cleaning units 7, 9 in front of the headbox 10 is recirculated to increase the yield in a further purification unit 8 and its accept in the degassing device 6.

To create the required pressures, the high-consistency stream 1 is passed before the cleaning device 5, before the degassing device 6 and before the last cleaning unit 7 via a respective material pump 1 1, 12,13.

By using only one degassing device 6, the number of required pumps is reduced by at least one.

The amount of low-consistency stream 2 (white water) fed via the cleaning unit 9 to the headbox 10 directly via a low-consistency pump 14 usually comprises 10 to 15% of the total quantity of fluid supplied to the headbox 10.

Since the white water usually has an air content of about 2% and the air content of 85% to 90% constituting high consistency stream 1 is less than 0.1%, can easily without degassing of the white water total air content of less than 0.5% Headbox 10 can be ensured.

Furthermore, there is an efficient use of the cleaning device 5, since this happens with a relatively high substance content and the overflow stream of the degassing device 6 is added to the high-consistency stream 1 only after the cleaning device 5.

Claims

claims 1 . A process for producing a pulp suspension for producing a paper, board, tissue or another fibrous web by mixing at least one high consistency flow (1) formed by treated fibrous and filler with at least one, preferably fresh, white water or the like. in a machine for producing the fibrous web, wherein the high consistency stream (1) is cleaned and mixed with at least one substream of the low consistency stream (2) before and after this cleaning, characterized in that the high consistency stream (1) first after a , the degassing cleaning is degassed with a partial flow of the low-consistency stream (2). 2. The method according to claim 1, characterized in that the high-consistency stream (1) is degassed after the last, the cleaning following mixing with a partial flow of the low-consistency stream (2). 3. The method according to claim 1 or 2, characterized in that the Low consistency flow (2) is not degassed. 4. The method according to any one of the preceding claims, characterized in that a partial flow of the low consistency stream (2) to the headbox (10) of the machine is performed. 5. The method according to any one of the preceding claims, characterized in that a resulting in the degassing overflow stream only after the cleaning of the high consistency stream (1) is admixed thereto. 6. The method according to any one of the preceding claims, characterized in that the consistency of the high consistency stream (1) immediately before cleaning between 1, 5 and 3.5%, preferably more than 2%. 7. The method according to any one of the preceding claims, characterized in that the consistency of the high consistency stream (1) immediately before degassing between 1 and 1, 5%. 8. Arrangement for producing a pulp suspension for producing a paper, board, tissue or another fibrous web from at least one, made of recycled fiber and filler high consistency stream (1) and at least one, preferably fresh water, white water or similar. formed low Konstistenzstrom (2) in the constant part of a machine for producing the fibrous web, the high consistency current (1) passed through at least one cleaning device (5) and before and after this cleaning device (5) in at least one mixing device (3,4) with a substream of the low-consistency stream (2) is diluted, in particular for carrying out the method according to one of the preceding claims, characterized in that the high consistency stream (1) for the first time after a, the cleaning device (5) following mixing device (4) by a degassing device (6 ) to be led. 9. Arrangement according to claim 8, characterized in that the high consistency current (1) after the last, the cleaning device (5) following Mixing device (4) through a degassing device (6) is guided. 10. Arrangement according to claim 8 or 9, characterized in that the Low consistency stream (2) is passed through no degassing. 1 1. Arrangement according to one of claims 8 to 10, characterized in that a partial flow of the low-consistency stream (2) is preferably guided via a cleaning unit (9) to the headbox (10) of the machine. 12.Anordnung according to any one of claims 8 to 1 1, characterized in that an overflow stream of the degassing device (6) to one of Cleaning device (5) of the high consistency stream (1) following mixing device (4) is passed. 13. Anorndung according to any one of claims 8 to 12, characterized in that the high-consistency stream (1) after the last mixing device (4) preferably via a cleaning unit (7) to the headbox (10) is guided. 14. Arrangement according to one of claims 1 1 to 13, characterized in that the reject of at least one cleaning unit (7,9) is passed to a further cleaning unit (8), the Accept is preferably performed to the degassing device (6).