CN102421962A - Sizing flow system - Google Patents

Abstract

The invention relates to a device for feeding a fiber suspension (1) to at least one headbox (8) of a paper or board machine, comprising at least one dilution unit (5) in which the fiber suspension (1) is produced by mixing a concentrated fiber suspension (6) with a dilution liquid, wherein the dilution liquid is formed at least in part by white water (2) of the paper or board machine, the white water (2) being pre-degassed in at least one open channel (3) and then fed into the dilution unit (5) by means of a degassing unit (4). The expenditure should be reduced in that the potential energy of the fiber suspension (1) in the channel (3) is not higher than the potential energy of the fiber suspension (1) in the dilution device (5) and the pressure at the outlet of the degassing device (4) is between-0.3 and 1bar or in that the potential energy of the fiber suspension (1) in the channel (3) is higher than the potential energy of the fiber suspension (1) in the dilution device (5).

Description

Sizing flow delivery system

technical field

The invention relates to an apparatus for conveying a fiber suspension to at least one headbox of a paper or board machine with at least one dilution device in which a thick fiber suspension is mixed with a dilution liquid The mixing produces a fibrous suspension, wherein the dilution liquid is formed at least in part from the white water of the paper or board machine, which is pre-deaerated in at least one open channel and then conveyed via the deaeration unit to the dilution unit.

Background technique

This method is used to supply fiber suspensions to paper or board machines. The slurry delivery systems required for this are basically known. The fiber suspension to be conveyed comprises most of the fibers from the thick fiber suspension prepared in the stock preparation plant. Concentrated fiber suspensions typically have a concentration of, for example, between 2.5 and 5%. The consistency is reduced to a value which facilitates the operation of the headbox of the paper machine by mixing in the dilution liquid, especially the white water of the paper machine. Although white water is optimally suited for dilution tasks, it is problematic due to the high gas content, the major part of which is air.

The majority of the gas escapes very quickly, whereas the remaining gas often has to be removed with great effort. Otherwise, the quality of the paper produced would be reduced to an impermissible degree.

A known solution is a large degassing vessel in which a constant negative pressure is maintained by evacuation, which corresponds to the evaporation pressure of the degassed suspension.

Thus, a similar device to that described in the preamble of claim 1 is proposed in DE 10 2004 051 327 .

Contents of the invention

The technical problem addressed by the invention is to reduce the outlay in such installations.

According to the invention, this technical problem is solved in that the potential energy of the fiber suspension in the groove is not higher than the potential energy of the fiber suspension in the dilution device and the pressure at the outlet of the degassing device is between -0.3 and 1 bar Between, or the potential energy of the fiber suspension in the groove is greater than the potential energy of the fiber suspension in the dilution device.

If the potential energy of the fibrous suspension in the trench is higher than that of the fibrous suspension in the dilution device, pumps between the components can be omitted, which significantly reduces the outlay. Here, the potential energy difference substantially determines the flow rate of the fibrous suspension. If the potential energy difference is too great, the excess pressure must be reduced by means of a throttle valve or a degasser, which is disadvantageous in terms of energy.

The difference between the potential energy of the fiber suspension in the trench and the potential energy of the fiber suspension in the dilution device therefore corresponds at most to a height difference of 8 m.

If the potential energy of the fibrous suspension in the channel is not higher than that of the fibrous suspension in the diluting device, the degassing device must be arranged and/or constructed such that a pressure between -0.3 and 1 bar is formed at its outlet. pressure.

Here, there is a height difference between the groove and the degasser, but the pressure increase by the degasser due to its pumping effect is an important influencing factor.

If a pressure of less than -0.3 bar develops at the outlet of the degasser, a small pump should be provided between the degasser and the dilution unit.

Regardless of the embodiment, the pressure at the outlet of the degassing device should advantageously be higher than the pressure at the inlet of the dilution device, so that a pressure difference is used to transport the fiber suspension between these elements. For this purpose it is advantageous if the outlet of the degassing device is arranged above the inlet of the white water flow into the dilution device. In this way, the white water can flow from the degassing device to the dilution device completely without conveying elements.

In any case, however, the pressure at the outlet of the degassing device should be at most 0.5 bar lower than the pressure at the inlet of the dilution device. In this case, a small pump between the degassing unit and the diluting unit can take over the delivery function of the fibrous suspension.

For adaptation to the conditions of the plant, but also for optimization, the flow of the fiber suspension between the trench and the degasser and/or the degasser and the dilution should preferably be variably throttled.

It is also advantageous if the inlet of the degassing device is arranged above the trench.

For the most effective degassing possible, the degassing unit should be connected to a negative pressure source. It is particularly suitable if the degassing device has a rotating rotor, in the interior of which the white water is conveyed, wherein the gas which has accumulated in the center due to centrifugal force is drawn out by the negative pressure source.

The dilution device can be designed as a closed or open container.

After the dilution unit, the fiber suspension should be conveyed as far as possible in a closed system to the headbox by means of a stock pump.

When the degasser is at rest, the liquid level in the degasser drops to that of the dilution device. In order to create the level difference required to deliver white water when the degasser is started, the slurry pump should be started before the degasser is put into operation.

It is particularly advantageous to apply the method in paper machines with screen speeds of 800 to 1600 m/min, since the amount of air contained in the white water is strongly related to the screen speed.

Description of drawings

The present invention will be described in detail in Examples below. A device view is shown in FIG. 1 .

Detailed ways

In this case, the fiber suspension 1 is produced in the usual manner by mixing the thick fiber suspension 6 with a dilution liquid and has accordingly essentially the desired consistency for the operation of the pulp box 8 of the paper or board machine at this location. . It is known that the headbox consistency is in the range of 0.5 to 2%, typically 1%.

The dilution liquid fed into the dilution device 5 comes from the first white water 2 in the example shown, ie the water accumulated in the forming area 10 of the paper or board machine. This water is often referred to as white water I to distinguish it from the second white water II which then accumulates in the paper machine, which contains much less fine material.

It is known that this white water 2 (among others) is mixed with appreciable proportions of air and possibly other gases. White water 2 is collected under the paper machine screen and drained from the side. The open grooves 3 allow most of the contained air to escape here. However, it is often expedient to remove the remaining gas fraction from the white water 2 in a subsequent degasser 4 (as described, for example, in DE 10 2004 051 327 ).

The degassing device 4 is designed as a cylindrical or conical container and is assigned a rotor 13 according to the invention. The fibrous suspension 1 enters the substantially cylindrical interior 14 of the rotor 13 and is set into rapid rotation. The principle is equivalent to a full surface centrifuge. The contained gas moves inwards due to centrifugal force and is sucked out centrally by the vacuum source 7 .

The centrifugal force may be at least 5 times, preferably 10 times, the acceleration of gravity. The negative pressure source 7 does not require a negative pressure corresponding to the vapor pressure of the suspension or in the vicinity thereof. Typical values for the negative pressure here are 0.8 to 0.9 bar.

The inlet 16 of the degassing device 4 can be arranged centrally or eccentrically. The liquid supplied through the inlet is initially strongly accelerated in the circumferential direction, for which acceleration strips can be used, for example. Due to the centrifugal force, the liquid is pressed against the inner wall of the rotor 13 , wherein the gas contained therein, especially air, moves towards the center of the rotor 13 . Usually forms the dividing plane between liquid and gas.

Gas can be extracted via the central degassing line by means of the vacuum source 7 .

In this case, the wall of the rotor 13 is made liquid-permeable in the region of the outlet 15 , for example by providing holes in this region. The outlet 15 is advantageously arranged tangentially in such a way that the swirling flow of the degassed liquid leads to a pressure build-up in the outlet 15 . The holes in the wall of the rotor 13 are so large that they do not lead to separation of the degassed liquid.

The degassing device 4 can also be associated with an outer screen basket (Sortierkorb), by means of which the white water 2 squeezed radially outward can be separated into accept and impurities.

The degassed white water 2 passes through the outlet 15 of the degassing device 4 directly into the dilution device 5 , which is here designed as an open container. Due to the smaller fiber fraction of white water 2 compared to fiber suspension 1, degassing can be easily carried out. However, a precondition for avoiding mass loss is that the thick fiber suspension 6 fed to the dilution device 5 has at most only a small amount of gas content.

A mixing device as described inter alia in DE 10050109 is suitable as dilution device 5 . It is important here that the mixing of the streams is achieved by spraying the concentrated fiber suspension 6 into the white water 2 , wherein the inflow speed of the thick fiber suspension 6 is preferably 3 to 15 times the flow rate of the white water 2 .

Various paper or board machines are known in which the headbox 8 is supplied not only with the already mentioned fiber suspension 1 but additionally with a dilution liquid which, viewed across the width of the headbox 1 Quantitative distribution to each position. Thus, for example, the transverse profile of the fiber layer formed by the headbox 8 can be influenced, in particular optimized.

FIG. 1 shows this possibility, in which white water 2 is not only used as dilution liquid for the concentrated fiber suspension 6 . A part of the white water 2 degassed in the degassing device 4 is introduced via the dilution water pump 20 as dilution liquid into the dosing device 17 of the headbox 8, where the white water is distributed and dosed to the fiber suspension at various points 1 in.

There are often other locations in a paper mill where other dilution liquids degassed by the method described can be used.

When supplying the paper machine, the last sorting stage 18 is usually connected upstream of the headbox 8 in order to prevent impurities from entering the headbox, which interfere with the operation of the headbox 8 or the paper machine.

As mentioned above, this sorting function can also be implemented in the same device in combination with the degassing function.

After leaving the dilution device 5, the fibrous suspension 1 is led via a cleaner 11, a further pump 12 and a sorting stage 18 in a closed system (i.e. a container or tank without openings) to the headstock by means of a stock pump 9 Box 8.

The potential energy of the fibrous suspension 1 in the trench 3 is higher than the potential energy of the fibrous suspension 1 in the dilution device 5 . As a result, pumps for conveying the white water 2 in this area can be omitted, which significantly reduces costs. However, the energy difference must also not be too large, since excess energy would otherwise be eliminated by adjustable throttle elements 21 , 22 in the form of valves.

In order to ensure that the fibrous suspension 1 can also be conveyed between the degasser 4 and the dilution device 5 without an additional pump, the pressure at the outlet 15 of the degasser 4 is equal to the pressure at the inlet 19 of the dilution device 5 above. Furthermore, the outlet 15 of the degassing device 4 is arranged above the inlet 19 of the white water 2 into the dilution device 5 .

In the stationary state, the liquid level 2 in the degasser 4 drops to the level in the dilution device 5 , so that the level difference described for the delivery of white water 2 must be recreated before the degasser 4 is put into operation.

The liquid level difference can be achieved by lowering the liquid level in the dilution unit 5 with the slurry pump 9 to the desired extent before the degassing unit 4 is operated.

Claims (16)

1. one kind is used for the equipment that conveying fiber turbid liquid (1) arrives at least one head box (8) of paper machine or board machine; This equipment has at least one air mix facilities (5); In air mix facilities,, dense fiber suspension (6) produces fiber suspension through being mixed with diluent liquid; Wherein, Diluent liquid is at least partly formed by the plain boiled water (2) of paper machine or board machine; Said plain boiled water (2) also then is transported in the air mix facilities (5) through degasser (4) by the preparatory degassing in the groove (3) of at least one opening, it is characterized in that, the potential energy of the fiber suspension (1) in the said groove (3) is not higher than the pressure in exit of potential energy and said degasser (4) of the fiber suspension (1) in the said air mix facilities (5) between-0.3 to 1bar.

2. one kind is used for the equipment that conveying fiber turbid liquid (1) arrives at least one head box (8) of paper machine or board machine; This equipment has at least one air mix facilities (5); In air mix facilities,, dense fiber suspension (6) produces fiber suspension (1) through being mixed with diluent liquid; Wherein, diluent liquid is at least partly formed by the plain boiled water (2) of paper machine or board machine, and said plain boiled water (2) is outgased in advance in the groove (3) of at least one opening and also then is transported in the air mix facilities (5) through degasser (4); It is characterized in that the potential energy of the fiber suspension (1) in the said groove (3) is higher than the potential energy of the fiber suspension (1) in the said air mix facilities (5).

3. equipment as claimed in claim 2 is characterized in that, the potential energy of the fiber suspension (1) in the said groove (3) and the potential energy of the fiber suspension in the said air mix facilities (5) are equivalent to the difference in height of 8m at most.

4. as the described equipment of one of aforementioned each claim, it is characterized in that the pressure in the exit of said degasser (4) is higher than the pressure that the inlet (19) of said degasser (5) is located.

5. like the described equipment of one of claim 1 to 3; It is characterized in that; The low at most 0.5bar of the pressure that the inlet (19) of the said air mix facilities of pressure ratio (5) that the outlet (15) of said degasser (4) is located is located, and between degasser (4) and air mix facilities (5), be furnished with pump.

6. like one of aforementioned each claim described equipment, it is characterized in that the said fiber suspension stream (1) between said groove (3) and the said degasser (4) is preferably changeably by throttling.

7. like one of aforementioned each claim described equipment, it is characterized in that the fiber suspension stream (1) between said degasser (4) and the said air mix facilities (5) is preferably changeably by throttling.

8. like one of aforementioned each claim described equipment, it is characterized in that the inlet (16) of said degasser (4) is arranged in said groove (3) top.

9. like one of aforementioned each claim described equipment, it is characterized in that the outlet (15) of said degasser (4) is arranged in inlet (19) top that said plain boiled water (2) gets into said air mix facilities (5).

10. like one of aforementioned each claim described equipment, it is characterized in that said degasser (4) is connected with negative pressure source (7).

11. equipment as claimed in claim 10 is characterized in that, said degasser (4) has rotor rotated (13), and said plain boiled water (2) is guided in the inner chamber of rotor, wherein, is taken away by negative pressure source (7) because centrifugal force collects in middle gas.

12., it is characterized in that the container that said air mix facilities (5) is designed to seal like one of aforementioned each claim described equipment.

13., it is characterized in that said air mix facilities (5) is designed to the container of opening like the described equipment of one of claim 1 to 11.

14., it is characterized in that said fiber suspension (1) is guided through mashing pump (9) at air mix facilities (5) afterwards like one of aforementioned each claim described equipment.

15. equipment as claimed in claim 14 is characterized in that, said mashing pump (9) makes fiber suspension (1) in closed system, be directed to head box (8).

16. one kind is used to move the method like claim 14 or 15 described equipment, it is characterized in that, before said degasser (4) puts into operation, starts mashing pump (9).

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