JP2002523642A - Method and apparatus for pretreating paper pulp - Google Patents

Abstract

The present invention relates to a method and apparatus for pretreating paper pulp. The method and apparatus according to the invention are especially preferably applicable to be used in the paper machine approach system of paper machines producing filler-containing grades. A characterizing feature of the method and apparatus according to the invention is that a propeller pump is used as the gas separation tank (16) feed pump (120).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001] The present invention relates to a method and an apparatus for pretreating paper pulp. The method and the device according to the invention are particularly preferably used for so-called short cycle operations (short c).
It is applicable for use in the ingress system of a paper machine to optimize the irrigation.

[0002] As described in US Pat. No. 4,219,340, for example, almost all conventional entry systems for supplying paper pulp to a paper machine include a white water tank, a supply pump and a different pump. , A centrifugal washing plant with a pump, a gas separation tank with a vacuum generator, a fan pump, a headbox screen, and a paper machine headbox. These components are arranged in connection with the paper machine and arranged to perform the following operations. That is, the so-called white water-diluted filler obtained from the wire section of the paper machine and the fibrous material used for papermaking are separated from the machine chest by white water normally placed at the bottom level of the mill. Dispensed into tank. The fiber suspension is fed by a feed pump located at the bottom level of the press, from a white water tank normally located at the machine level of the press, i.e. at the level of the paper machine, or, as in said patent, a white water tank. Pumped to the first washing step of the centrifugal washing plant above. A centrifugal washing plant usually comprises several stages (typically 4 to 6 stages), each stage usually having its own feed pump. Due to the pressure generated by this feed pump, the fiber suspension received in the first washing stage of the centrifugal washing plant is sent to a gas separation tank, usually located at a level above the machine level. In practice, this transfer means about 10-12 m above the white water tank surface. In the gas separation tank, the fiber suspension is subjected to the action of a vacuum generated by a vacuum device, usually a liquid ring pump, to remove the gas part dissolved in the suspension and the small air bubbles in the suspension. Both rise from the liquid surface in the tank and are discharged from the tank via a vacuum device. The fiber suspension, degassed as completely as possible, flows from the gas separation tank to a fan pump located at the bottom level of the press, by means of a head box screen located at the bottom level of the press ( (Not shown in the U.S. patent) and then into the machine head box at the machine level.

[0003] One problem with prior art paper machine entry systems lies in their huge volume, which is largely comprised of the volume of gas separation tanks and centrifugal washing plants and long and large piping. The volume itself is not a major issue, except for space use and relatively large investment, but the large volume slows down the work and significantly limits the variety change. Waste paper will be generated. When changing varieties, prior to equalizing the relative amounts of all components of the fiber suspension through the ingress system to correspond to the target end product content, all Broken paper is generated from the pulp.

[0004] The problem has already been addressed in Finnish Patent 89728. According to it, different types of white water are collected from a wire section of the paper machine and guided directly to the short cycle of the paper machine, and the conventional white water tank is not used. In the case of said patent, a pump is provided below each white water tray to deliver white water to the appropriate location. The patent publication states that the flow path of the white water is extremely shallow, that is, has a small volume so that the delay is as short as possible. In the solution according to said patent, on the side of the wire section, a small pump vessel and means for pumping are arranged, from which white water is sent to the processing step. The degassing achieved by this device is not efficient and is not sufficient for a smooth operation of the paper machine.

In addition to the problems associated with space utilization and large volumes of liquid, centrifugal washing plants also create other problems. The reason that the conventional position of the centrifugal washing plant in the paper machine entry system is chosen is that the fiber suspension just before entering the paper machine headbox is, for example, particles unsuitable for paper making, called impurities or impure particles, for example, It was described to ensure that it did not contain sand, bark pieces, slivers, too large filler pieces and the like. However, tests performed by us showed that most of the fraction removed by the centrifugal washing plant, especially for paper machines producing varieties containing fillers, that is, the fraction removed from the stream sent to the paper machine headbox As such, it turned out to be suitable for papermaking. One reason is that the cyclone of the centrifugal washing plant is configured to prevent any unsuitable material from passing through the headbox, while the centrifugal washing plant is configured with one material or a small number of It is designed to work optimally only with very similar materials. For example, when applied to materials with very different densities, such as materials containing fibers and mineral-based fillers, centrifugal washing plants may not function optimally for any component. Can be thought of. However, the basic goal of the centrifugal washing plant is to keep the fiber suspension component ratio substantially unchanged during washing and to prevent particles unsuitable for papermaking from flowing into the paper machine headbox. That is. In practice, this same problem is addressed by Finnish Patent No. 933753 and 9
No. 7736, but again, the presence of fractions removed from the centrifugal washing plant is acceptable.

[0006] One preferred solution to the above problem is to separate each component of the paper pulp, ie fresh fiber suspension, pulp broke, recycled fibers, fillers, etc., in separate sections before mixing these components. It is said to be processed. In that case, when applying each, the optimal cleaning method and cleaning apparatus can be selected for each component. As a result, only the clean fraction is introduced into the short circulation headbox of the paper machine, and no centrifugal washing plant is required. In addition to this, the cleaning of each component by the cleaning device sized and adapted for this particular purpose is different from the prior art centrifugal cleaning plant in terms of energy consumption and the selection of a suitable device for cleaning. It is much more efficient and economical in comparison.

There are also some additional problems created by centrifugal washing plants. Centrifugal washing plants tend to at least maintain and possibly augment the generated fluctuations, due to the large volume of liquids and complex piping, without directly generating fluctuations in the paper pulp stream and pulp pressure. In addition, complex centrifugal washing plants with several stages (usually 4 to 6 stages) and a large number of relatively small flow path units generate large flow resistances and require several steps to overcome this resistance. Since a large centrifugal pump is used, a very large amount of power is consumed. Usually a separate feed pump is used for each washing stage of the centrifugal washing plant, in which case the total power requirement of all short circulation pumps of the paper machine in an average size paper machine is about 2 megawatts ( MW).

[0008] Another factor affecting power consumption, particularly by operating the pump, is the arrangement of the short circulation components of the papermaking machine. The first disadvantage is the location of the gas separation tank, which is usually located at a level above the machine level. If the gas separation tank can be arranged at the machine level, it is not necessary to feed the fiber suspension higher than the machine level with the feed pump. A prerequisite for such an arrangement is to configure the gas separation tank to function without an overflow, because the overflow must function for a relatively large free fall, actually This is because a free fall from a position higher than the machine level to a position lower than the machine level is required. Yet another prerequisite is that the gas separation tank be configured to include a pump connected to the overflow to provide a pressure differential that ensures the function of the overflow. In other words, the surface level of the gas separation tank (more precisely, the inlet pressure of the fan pump)
Can not be determined by the overflow when applying the first option,
We have to find an alternative. Since the basic goal of adjusting the surface level of the gas separation tank is to keep the inlet pressure of the fan pump constant, as described above, in practice, in addition to the fluctuations in the surface level, sometimes significant paper pulp It is more economical to use a regulating system taking into account density variations. As a result, this type of variation is accompanied by an improvement in paper quality and stabilization of the manufacturing process. Thus, as a result, this solution is more economical in terms of energy consumption when operating the pump, while at the same time having a positive effect on the paper quality and the progress of the process.

[0009] Another factor affecting the energy consumption of the pump operation in the paper machine entry system is the height of the white water tank. White water tanks, or so-called tanks for collecting so-called white water from a paper machine, are conventionally relatively large containers, which have a height of approximately 10 meters and are located at the bottom level of the papermaking machine, the surface level of these tanks. Fluctuated significantly.
One contributor to surface level variation is, for example, the location of the white water tank relative to the paper machine. In the case of so-called fourdrinier paper machines, the white water tank, also called the wire pit,
Located below the section, the surface level of the white water tank was also relatively low for structural reasons. On the other hand, wire sections, etc. (so-called outside silos)
Also, the surface level of the white water tank located next to is not always at the height that can actually be reached. The large dimensions of white water tanks have been justified because the presence of large buffer tanks has been regarded as a positive factor in stabilizing the process. This also increased energy consumption and caused extra processing delays due to the large volume of the white water tank, since sometimes low white water tank surface levels had to be compensated by the feed pump.

In the access system according to the invention, placing a white water tank at the bottom level of the press,
That is, it is possible to avoid disposing the white water tank below the machine level.
The solution according to the invention makes it possible to arrange the white water tank at the machine level, whereby the feed pump of the gas separation tank arranged next to the white water tank is also arranged at the machine level. If the above problem is solved, for example, by the method described above, by adopting a propeller pump having much less power requirement and a much better capacity / water pressure ratio as a supply pump for the gas separation tank as compared with a centrifugal pump. Thus, it is possible to further improve the entry system of the paper machine. In practice, propeller pumps are more purposeful than centrifugal pumps, but have not been used before because they do not meet the hydraulic requirements of prior art processes. About 2M of the prior art device
As a result of employing one propeller pump compared to the required power of W, power consumption is about 2
00 kW, in other words about 90% of the required power is saved.

Further, a paper machine entry system can be developed according to a preferred embodiment of the present invention without using any feed pump for the gas separation tank in the entry system. This is easily possible by lowering the gas separation tank to the machine level under some suitable conditions. As a result, the pressure difference required for transporting the fiber suspension from the white water tank to the gas separation tank is completely unnecessary, or at least for the most part, a vacuum device, i.e. one or more vacuum pumps of the gas separation tank Is small enough to be able to be generated. The arrangement according to this embodiment may include a valve for controlling the flow from the white water tank to the gas separation tank, if necessary.

Some of the advantages of using the method according to the invention are as follows. • Finer sorting (sieving) reduces overall rejects in papermaking.・ The short circulation operation of the paper machine becomes more stable.・ The flow resistance in short circulation of the paper machine is smaller.・ Short circulation space of paper machine is saved.・ The energy required for pump operation is reduced.・ The degree of delay is reduced.・ It is possible to change varieties quickly.・ The process is cleaner and the growth of microorganisms is eliminated.・ Simple structure saves investment. The features of the method and the device according to the invention are as set forth in the claims.

In the following, the method and the device according to the present invention will be described in more detail with reference to the accompanying drawings. The prior art ingress system shown in FIG. 1 comprises a white water tank 10, a supply pump 12, a centrifugal washing plant 14 (some stages are omitted), a gas separation tank 16 having a vacuum device 17, and a fan pump. 18, a headbox screen 20, a paper machine headbox 22, and a white water catchment (not shown). These components are located in relation to the paper machine and are configured to operate as follows. The fibrous material used for papermaking, including any or all of fresh pulp, secondary pulp, broke, and filler diluted with so-called white water, mainly obtained from the wire section of the paper machine, are stored in the white water tank 10. be introduced. White water is collected in the white water tank, and the white water tank 10 is usually located at the bottom level of the press in a conventional arrangement for producing paper pulp. By means of a feed pump 12 also arranged at the bottom level of the press, the paper pulp is transferred from the white water tank 10 to a centrifugal washing plant 14 normally arranged at the machine level K of the press (placement level of the paper machine 24). Pumped. The centrifugal washing plant 14 usually includes 4 to 6 stages. The stock received by the first stage of the centrifugal washing plant 14 is further placed under the pressure generated by the feed pump 12 (and also due to the vacuum action of the gas separation tank) at a level T above the machine level. To the gas separation tank 16. The gas separation tank 16 typically includes an overflow to maintain a constant stock surface level in the tank. The stock discharged from the tank flows from the overflow to below the machine level and into the white water tank 10 located at the bottom level of the press. From the gas separation tank 16, virtually gas-free paper pulp, that is, pulp degassed as completely as possible by a vacuum device, flows into a fan pump 18 arranged at the bottom level of the press. The fan pump 18 also sends the paper pulp to a headbox screen 20, also located at the bottom of the press. From here the pulp rises to machine level K,
It is introduced into the head box 22 of the paper machine 24.

FIG. 2 shows a solution according to a preferred embodiment of the present invention connected to a prior art conventional white water tank 10. In the solution of this figure, three lines 40, 42
, 44 are connected to the white water tank 10 and each pipe feeds different paper pulp to the white water tank. Each of the conduits 40 to 44 is connected to its own centrifugal washing facility 46, 48, 50. However, it must be said that centrifugal washing is by no means the only possible type of sorting. This is because a new type of pressure screen, preferably equipped with slot drums, is very suitable for the final sorting of a plurality of different pulp fractions. Furthermore, it must be noted that all the said lines can also be connected together, so that different types of pulp can be transferred to a white water tank, for example in a special mixing tank. The stock can be mixed together and the stock taken therefrom into a so-called machine chest which is used as a buffer tank. Of course, this type of mixing requires suitable dosing, which will be known to those skilled in the art and will not be described in further detail here. In this embodiment of the invention, it is contemplated that each of the centrifugal washing facilities 46-50 will process a respective type of pulp. For example, facility 46 processes pulp broke from a paper machine broke machine, facility 48 processes recycled fiber pulp, and facility 50 processes fresh fiber pulp. The drawing further shows a pump connected to each centrifugal washing facility. With each pump, different pulp is introduced into the white water tank 10 via one or more washing facilities. The pump, however, may be located significantly further from the cleaning equipment in this step. Various processing devices can be arranged between the pump and the cleaning equipment. With this configuration, various types of pulp can be processed as optimally as possible. In other words, each washing facility is selected and operated accordingly to optimally sort the type of pulp. After the illustrated washing facility, the process may include various intermediate tanks, pumps, and other equipment needed to process each pulp fraction. Further, the illustrated embodiment includes a filler processing facility including a mixing / dispersion tank 56, a filler slurry supply pump 58, and a centrifugal washing facility 54 for sorting fillers.
A pipe 52 for supplying the selected filler between the white water tank 10 and the supply pump 120;
And With this arrangement, only the oversized filler pieces are actually removed from the filler stream and completely removed from the ingress system or returned, for example, to the dispersion stage. Thus, this solution prevents rejecting filler pieces that are clearly thinner than paper but rather large. This rejection of the filler pieces will be normal in conventional centrifugal washing plants. A propeller pump is adopted as the feed pump 120. The propeller pump has a sufficient water pressure at least when, for example, a centrifugal washing plant that creates a flow resistance between the pump 120 and the gas separation tank 16 does not exist. appear. As already mentioned, in some cases the feed pump can be replaced by a vacuum device in the gas separation tank, which generates the pressure difference required for feeding the paper pulp.

FIG. 3 shows a solution according to a second preferred embodiment of the present invention. This solution is based on a new kind of white water tank 100, which is located virtually at the machine level of the press.
(The main part of the white water tank is above the machine level surface and the water level is clearly above the machine level surface). The fiber fraction is fed into the white water tank via lines 40 to 44, and the surface level of the white water tank is level S100. In the figure, a dashed line shows a conventional white water tank 10 having a surface level S10 and a supply pump 12, located at the bottom level of the press. In some cases, especially when the wire pit is below the wire section of the paper machine, the height difference between the surface levels S100 and S10 is several meters, and this difference in height is less than in prior art configurations. Directly accounted for, the extra consumption of pump operating energy. In addition, large white water tanks are delayed during processing. In the case of the solution shown, the difference in height between the surface level of the white water tank 100 and the surface level of the gas separation tank 16 is less than 9 meters, preferably less than 6 meters, and in particular 2 to 4 meters is suitable. . As a result, the required water pressure of the pump 120 is low enough to use the propeller pump.

It should be noted that while the invention has been described with reference to a paper machine short cycle without a centrifugal washing plant, this is one particular embodiment of the method of the invention. It is just that. In other words, the method and the device according to the invention are also applicable in the case of short circulation where the centrifugal washing plant is located in a conventional position. In the case of such an embodiment, some of the advantages that would be achieved in the case of an embodiment that is entirely consistent with the invention are lost. Nevertheless, by employing a propeller pump according to the present invention, the obvious advantage that its use is always justified will be obtained in all applications.

As will be appreciated from the above, a new method of pretreating paper pulp fed to a paper machine has been developed. This approach eliminates many of the shortcomings and shortcomings of the prior art and solves the problems that have prevented the use of prior art access systems. However, it should be noted that each new feature described in the different embodiments is independently applicable and applicable without necessarily being related to what has been presented above. It is in.

[Brief description of the drawings]

1 shows a prior art solution mainly according to US Pat. No. 4,219,340.

FIG. 2 shows a solution according to a first preferred embodiment of the present invention.

FIG. 3 shows a solution according to a second preferred embodiment of the present invention.

──────────────────────────────────────────────────続 き Continuation of front page (81) Designated country EP (AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE, IT, LU, MC, NL, PT, SE ), OA (BF, BJ, CF, CG, CI, CM, GA, GN, GW, ML, MR, NE, SN, TD, TG), AP (GH, GM, KE, LS, MW, SD, SL, SZ, UG, ZW), EA (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM), AE, AL, AM, AT, AU, AZ, BA, BB, BG, BR , BY, CA, CH, CN, CU, CZ, DE, DK, EE, ES, FI, GB, GD, GE, GH, GM, HR, HU, ID, IL, IN, IS , JP, KE, KG, KP, KR, KZ, LC, LK, LR, LS, LT, LU, LV, MD, MG, MK, MN, MW, MX, NO, NZ, PL, PT, RO, RU, SD, SE, SG, SI, SK, SL, TJ, TM, TR, TT, UA, UG, US, UZ, VN, YU, ZA, ZW

Claims (18)

[Claims] 1. All or at least a major part of the paper pulp is sent to a gas separation tank (16) by a gas separation tank feed pump (12, 120);
From there, a fan pump (18) is used to further feed the paper machine head box (22)
A method for pretreating paper pulp, wherein the paper pulp is sent to a gas separation tank (16) by a propeller pump (12). 2. Prior to being sent to a gas separation tank (16), at least the filler fraction and the fiber fraction of the fractions forming the paper pulp are treated separately in a sieving stage for each, The method according to claim 1, wherein impurities are removed from the fractions, and then the two fractions are mixed to form a paper pulp. 3. A different type of fiber pulp (eg, V) contained in paper pulp.
F, DIP, BR) are separately treated in a sieving stage for each of them, according to claim 1, characterized in that: 4. The method for pretreating paper pulp according to claim 2, wherein centrifugal washing is used in the sieving step. 5. The method for pretreating paper pulp according to claim 2, wherein a pressure screen is used in the sieving step. 6. The paper pulp is fed directly from a white water tank (10) to a gas separation tank (16) by a propeller pump (12) without special washing. 2. The method for pretreating paper pulp according to item 1. 7. The paper pulp according to claim 1, wherein the paper pulp is sent from a white water tank (100) arranged essentially at the machine level to a gas separation tank (16). Preprocessing method. 8. A paper pulp pretreatment apparatus having at least a gas separation tank supply pump (12), a gas separation tank (16), a fan pump (18), and a paper machine head box (22). The gas separation tank (16) supply pump is a propeller pump (120), wherein the paper pulp is sent by the propeller pump from the white water tank (10) or similar components to the gas separation tank (16). Paper pulp pretreatment equipment. 9. A filler slurry sieving device (54) and a fiber pulp sieving device (46, 4) before the gas separation tank feed pump (120) in the processing sequence.
The device according to claim 8, characterized in that it has both of (8, 50). 10. The apparatus according to claim 9, wherein the filler slurry sieving apparatus includes a centrifugal washing facility (54). 11. The fiber pulp sieving apparatus is a centrifugal washing facility (46, 48).
Device according to claim 9, characterized in that it comprises: 12. The apparatus according to claim 9, wherein said fiber pulp sieving apparatus comprises a pressure screen. 13. The fiber pulp sieving apparatus according to claim 9, further comprising a separate sieve (46, 48, 50) dedicated to each type of fiber pulp. An apparatus according to any one of the preceding claims. 14. The fiber pulp sieve (46, 48, 50) is arranged in the processing sequence before a white water tank (10) or similar component,
14. Apparatus as claimed in any one of claims 11 to 13, wherein the white water tank or similar component is located in front of the gas separation tank feed pump. 15. The gas separation tank (16) provided with a device for regulating the inlet pressure of a fan pump (18) without overflow.
An apparatus as described in. 16. The apparatus according to claim 8, wherein the white water tank (100) and the feed pump (120) are arranged essentially at the machine level (K). 17. The white water tank (100) and the gas separation tank (16).
2. The difference between the height of the surface level and the height is less than 9 meters.
6. The apparatus according to 6. 18. The white water tank (100) and the gas separation tank (16).
Is preferably less than 6 meters, more preferably less than 2 meters.
17. The device according to claim 16, wherein the distance is between -4 meters.