CN109983175B

CN109983175B - Apparatus for treatment of process water

Info

Publication number: CN109983175B
Application number: CN201780071918.7A
Authority: CN
Inventors: C.斯特雷姆佩尔; E.古茨穆思; F.阿尔布雷克特; C.亚当斯
Original assignee: Voith Patent GmbH
Current assignee: Voith Patent GmbH
Priority date: 2016-12-22
Filing date: 2017-11-16
Publication date: 2021-03-09
Anticipated expiration: 2037-11-16
Also published as: CN109983175A; WO2018114153A1; DE102016125303A1; EP3559342A1; DE102016125303B4; EP3559342B1

Abstract

The invention relates to a device for treating process water of a machine for producing and/or refining paper, cardboard, tissue or other fibrous material webs, wherein the process water is separated in a separation or filtration device (1) into a plurality of sub-fractions (9, 10) having unequal proportions of fibers. The quality of the process water is improved in that at least two sub-fractions (9, 10) are at least partially introduced into a common cleaning device (2) for at least one predetermined time interval, the fine fraction (12) of the cleaning device (2) is fed into a flotation device (3), and the accept (15) of the flotation device (3) is fed into the machine or into a preceding process for treating the fiber suspension.

Description

Apparatus for treatment of process water

Technical Field

The invention relates to a device for treating process water of a machine for producing and/or refining paper, cardboard, tissue or other fibrous material webs, wherein the process water is separated in a separation or filtration device into a plurality of sub-fractions having unequal proportions of fibers.

The invention also relates to a method for operating said device.

Background

Devices of this type are described, for example, in documents DE 102013105111 a1, DE 69915227T 2, DE 102006034186 a1 and DE 102011005650 a 1.

It is known that paper fiber suspensions, for example for producing a fibrous web, contain not only true paper fibers but also more or less fine amounts of solid matter.

This fine solid matter may be a mineral filler which is normally required for paper making. It is also known as "ash" because mineral fillers are not combustible. However, it can also be fiber fines, which are formed, for example, in the grinding of fibers. Which is also called fines.

The paper fibre suspension is thickened when the consistency of the paper fibre suspension in the stock preparation of the paper machine should be increased for process technical reasons. In this case, not only part of the water but also part of the fine solid matter is transferred to the filtrate, so that the filtrate generally consists of water, fines and filler.

In a typical process flow, the filtrate is used in a position upstream of the dilution of the fibre suspension for process technical reasons. In this way, fine solid matter is not lost, but the fine material and the filler in the filtrate are relatively large. This method of filtrate recirculation, which is inexpensive per se, therefore leads to disturbances in the process. This disturbance also applies to the process water in the machine, which accumulates mainly in the forming section for the sheet formation and in the press section for the dewatering of the fibrous web and is reused in the machine or in the preparation of a preceding stock.

In this case, however, significant accumulations of fine material and fillers can also occur with high old paper contents, which has a negative effect on the strength of the fibrous web.

A possible remedy to avoid this interference consists in removing fines and fillers from the circuit. This can be achieved, for example, in that the existing flotation plant is adjusted so that it removes ash more intensely from the pulp than is later required for the paper itself made of fibres. However, the slurry loss increases and the yield decreases.

Disclosure of Invention

The object of the invention is therefore to reduce the proportion of filler in the fiber web, as required, with the least possible outlay and fiber loss.

According to the invention, the object is achieved in that at least two sub-fractions are at least partially conducted to a common cleaning device for at least one predetermined time interval, and the fine fraction of the cleaning device is fed to a flotation device, the accept of which is fed to the machine, to another machine for producing a fibrous web, or to a preceding process for treating a fibrous suspension.

The apparatus is particularly suitable for treating process water from the forming section of a machine for sheet forming, which is heavily loaded with fibers, fines and fillers. The process water may be at least partially fed to a sorting or filtering device.

The sub-fractions of the separation or filtration plant usually have a higher proportion of fines and fillers than the used old and finished paper.

The sub-fraction with the higher fiber fraction, preferably the sub-stream of the separation or filtration system with the highest fiber fraction, is diluted with the likewise filler-containing, preferably filler-enriched, sub-stream of the separation or filtration system and introduced into the cleaning system.

In the case of this cleaning device, the crude fraction with a high fiber content is recirculated to the machine's pulp circuit or to a preceding process for treating the fiber suspension, while the fine fraction with a high filler content, but a low fiber content, of the cleaning device is passed to the flotation device.

In the flotation plant, the fines and fillers and stickies are separated without substantial fiber loss and are subsequently discarded or even reused.

If necessary, chemical agents or other process water of the machine or of a preceding process for treating the fiber suspension can also be additionally introduced into the cleaning installation in order to dilute the substream with the high fiber fraction. For this purpose, for example, white water of a paper machine is also suitable.

The sorting or filtering device is advantageously designed as a disk filter. Disc filters have been known for a long time and are used for separating liquids from suspensions.

Depending on the content of fibres, fillers and fines of the suspension, the substreams of the disc filters are referred to as fibre filtrate (also known as fangstaff), turbid filtrate, clear filtrate and ultra-clear filtrate.

For separating the packing, a pressure-reducing flotation device is particularly suitable as a flotation device.

In pressure-reducing flotation, the process water is saturated with air at overpressure and is subsequently introduced into the flotation cell. After depressurization, excess air foams out in the form of fine bubbles. The bubbles combine the fines and the packing and bring them to the surface of the flotation cell where they can be skimmed off.

Machines for producing fiber suspensions also typically have a press section for dewatering the fiber web. The process water originating from the press section contains felts in addition to fibres, fines and fillers, in view of the contact with the press felts which are jointly guided there through the press nip.

In general, the process water from the press section is at least partly led directly to the cleaning plant or the flotation plant.

Particularly advantageous for separating the felts, however, is that the process water of the press section is also guided beforehand through other sorting devices, for example fine sorting devices or sieve arcs.

In continuous operation, the aggregation of fine materials and fillers can be effectively eliminated.

However, it is also possible to introduce the sub-fractions of the classifying or filtering device into the cleaning device only within a defined time range in order to reduce the average filler content of the process water reused in the machine.

It is also possible to control the amount of filler content in the fibrous web by the amount of subfractions introduced into the cleaning device.

Drawings

The present invention will be described in more detail with reference to the following examples. In the drawing, fig. 1 shows a plant concept for wastewater treatment.

Detailed Description

As is known per se, fibre suspensions are produced in that the paper material is continuously treated in the dissolving section with water in the form of old paper by mechanical means and, if necessary, chemical means, so that a pumpable fibre suspension is formed. The subsequent first cleaning can, for example, be provided with a pressure classifier and a hydrocyclone in order to separate out coarse impurities as early as possible.

The cleaned fibre suspension is immediately and continuously thickened upstream, preferably by means of a filter device, for example a sieve press, a disc filter or a screw press.

After thickening, the fibers have a significantly higher concentration (e.g., 15 to 30%) and a slurry treatment is initiated in which one or more process steps requiring the higher concentration are carried out. This can be, for example, a dispersion with or without a decolorizing agent, for which auxiliary measures or adjuvants in the form of energy and/or chemical agents are provided. After the high consistency treatment, the slurry is re-diluted.

The fibre suspension produced is finally provided in the form of a base material for processing in a paper or board machine.

The paper or board machine is shown here only schematically. A portion of the white water deposited here can be used for pulp preparation as dilution water, for example to provide part of the water for the dissolving section, or even for additional dilution at other locations.

In order to avoid the return of the ash fraction originating from the paper machine into the stock preparation by means of this dilution water, later white water, for example white water or press water, with a lower ash fraction can be used for this purpose.

The proportion of fines and fillers in the process water is generally so high that ash removal is necessary.

According to the figures, the waste water 16 of the forming section 7 of the machine is at least partially fed to the sorting or filtering device 1 in the form of a disc filter for this purpose, in which the sheet forming is completed. Another part of the process water 16 of the forming section can be fed into the white water tank 5.

In a disc filter, the waste water is then divided into a plurality of

sub-fractions

9, 10, which are usually referred to as fibre filtrate, turbid filtrate, clear filtrate or ultra-clear filtrate.

The division of the sub-fraction 9 with a high fiber fraction (which corresponds to the fiber filtrate) and the sub-fraction 10 with a low fiber fraction is also shown in the drawing.

Both

sub-fractions

9, 10 also contain a very large amount of fines and fillers, i.e. ash. In order to reduce the ash content, at least a part of the sub-fraction 9 with a high fiber content, a further sub-fraction 10 with a low fiber content and, if appropriate, process water from the white water sump 5 are therefore fed into the cleaning device 2.

In the cleaning device 2, a high concentration of fines and fillers in its fine fraction 12 can also be achieved due to the low slurry concentration.

The crude fraction 11 of the cleaning installation 2 contains a high fiber fraction and a relatively low fraction of fines and fillers and can therefore be used without problems in the stock preparation or in the customary parts of the machine. Thus, a return flow of the crude fraction 11 of the cleaning device 2 to the stock chest 6, if necessary via the buffer chest 18, is effected.

As the cleaning device 2, a known inclined screen, a curved screen, a drum thickener, or the like is applied.

The fine fraction 12 of the cleaning device 2, which is rich in fines and fillers, is here fed, for example, together with chemical reagents 14 for the preparation of the stock and process water 13 originating from the press section 8 of the paper machine into the flotation device 3, which is in the form of a vacuum flotation device.

The reject 17 of the flotation plant 3 is disposed of or reused in the machine or another machine for producing a fibrous web, in contrast to the accept 15 of the flotation plant 3 being conducted as dilution water to the paper machine or to a preceding stock treatment, here the white water basin 5.

In addition to the fines and the filler, a fine slime can also be deposited in the filter residue 17 by the flotation device 3.

The press section 8 serves for dewatering the fibrous web, which is guided for this purpose together with a press felt through one or more roll nips. The process water 13 of the press section 8 therefore also has a significant proportion of felts which are removed by means of the classifying device 4 before being conducted to the flotation device 3 and/or the cleaning device 2.

The plant unit with the cleaning device 2 and the flotation device 3 can be operated continuously for the purpose of removing ash from the process. However, in order to increase the strength of the fiber web, the device unit can be switched on in particular only when the weight per unit area of the fiber web is low.

It is also possible to vary the amount of fines and fillers that are removed from the process by the proportion of the

sub-fractions

9, 10 of the classifying or filtering device 1 that are introduced into the cleaning device 2.

The more ash is removed, the lower the proportion of final fine material and filler in the fibrous web, so that this can be controlled and regulated by the installation unit.

Claims

1. An apparatus for treating process water of a machine for producing and/or refining paper, cardboard or other fibrous material webs, wherein the process water is divided in a sorting or filtering apparatus (1) into a plurality of sub-fractions (9, 10) with unequal fractions of fibers, characterized in that at least two sub-fractions (9, 10) are conducted at least partially in at least one predetermined time interval into a common cleaning apparatus (2), the fine fraction (12) of the cleaning apparatus (2) is fed into a flotation apparatus (3), the accept (15) of the flotation apparatus (3) is fed into the machine, into another machine for producing fibrous material webs or into a preceding process for treating fibrous material suspensions.

2. The apparatus according to claim 1, characterized in that the crude fraction (11) of the cleaning apparatus (2) is recirculated to the pulp circulation of the machine or to a preceding process for treating the fibre suspension.

3. The apparatus according to claim 1 or 2, characterized in that the machine or other process water of a preceding process for treating the fibre suspension is fed into the washing apparatus (2).

4. The apparatus according to claim 1 or 2, characterized in that the sub-fraction (9) of the sorting or filtering apparatus (1) with the highest fiber fraction is conducted into the cleaning apparatus (2).

5. The plant as claimed in claim 1 or 2, characterized in that the flotation plant (3) is designed as a vacuum flotation plant.

6. The device according to claim 1 or 2, characterized in that the sorting or filtering device (1) is configured as a disc filter.

7. The apparatus according to claim 1 or 2, characterized in that the machine has a forming section (7) for sheet forming and that the process water (16) of the forming section is at least partly led into the sorting or filtering apparatus (1).

8. The apparatus according to claim 1 or 2, characterized in that the machine has a press section (8) for dewatering the fibrous web, and the process water (13) of the press section is at least partly conducted into the cleaning apparatus (2) and/or the flotation apparatus (3).

9. The apparatus according to claim 8, characterized in that the process water (13) of the press section (8) is conducted through a further sorting apparatus (4) before the cleaning apparatus (2) or the flotation apparatus (3).

10. An apparatus according to claim 1 or 2, characterized in that the paper web is a tissue web.

11. A method for operating an apparatus according to one of the preceding claims, characterized in that the sub-fractions (9, 10) of the sorting or filtering apparatus (1) are introduced into the cleaning apparatus (2) only within a defined time frame in order to reduce the average filler content of the process water reused in the machine.