FI105489B - 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

105489

Method and apparatus for pretreating paper pulp

The present invention relates to a method and apparatus for pretreating paper pulp. Particularly preferably, the method and apparatus according to the invention are suitable for use in a paper machine approach system. to optimize short cycle operation.

Prior art prior art papermaking paper machine approach systems for the papermaking machine. U.S. Pat. No. 4,219,340 consists almost exclusively of the following components. Tailwater tank, vortex purification plant with feed pumps and pumps between the stairs, gas separation tank with vacuum equipment, headbox feed pump, headbox filter, paper machine headbox and sewage collection basins. Said components are located in connection with the paper machine and arranged to operate as follows. The tap water tank, which is usually located at the bottom of the mill, is dosed from the machine tank with papermaking fiber and fillers, which are diluted using the so-called "paper machine" wire. white water. Likewise, with a feed pump located at the bottom of the mill, the fiber suspension 20 is pumped from the tap water tank at the mill's machine plane, to the plane where the paper machine is located or, as in the above patent, to the first cleaning stage of the • t · vortex cleaning plant.

• ....: The vortex cleaning plant usually comprises several (usually 4-6) steps, each typically having its own feed pump.

·: T: 25 The fiber suspension, accepted by the first purification stage of the vortex purification plant, continues to be pressurized by said feed pump to a gas separation vessel, typically positioned above the machine level a · ·. That is, in practice, about 10 -12 meters above the surface of the tap water tank ·: ·. In a gas separation tank, the fiber suspension is subjected to a vacuum created by vacuum devices, which are usually liquid ring pumps, whereby both a portion of the gas dissolved in the suspension and:: small gas bubbles in the suspension rise above the liquid surface of the tank. From the gas separation tank 2,105,489, the deaerated fiber suspension flows to the mill bottom-level headbox feed pump, which also pumps the fiber suspension to the bottom-level headbox screen (not disclosed in the aforementioned U.S. Patent), from which the fiber suspension flows to the machine tray 5.

One problem with the prior art paper machine approach system is its large volume, consisting mainly of the volume of the gas separation tank and vortex treatment plant and the long and large ίο pipelines. Volume itself is not a major problem, not only in terms of space use and a reasonably large investment, but long latency times due to large volumes significantly slow down the conversion and lead to a high rejection rate during the conversion. Specifically, all the amount of pulp that is shipped to the end product is wrecked before the relative amounts of all the ingredients in the fiber suspension have stabilized throughout the approach system to correspond to the content of the desired end product.

This problem has already been addressed in Fl patent 89728, where a paper machine. a. a 20 different parts of the wire are collected and fed directly to the paper machine

• * I

for short circulation without the actual tap water tank. According to this publication • · ·: ·. a pump is placed under each tap water to deliver the tap to a suitable site. The publication describes how tap water gutters are very lax, i.e. small volume so that delays are minimized • · 25. In the solution according to that publication, a small pumping tank and pump-like devices are provided on the side of the wire section, from which the tap water is conveyed to the process. However, this device solution does not allow the airflow to be efficient enough for the paper machine to operate smoothly.

·· · IM »30 In addition to space problems and high fluid volume problems, the vortex cleaning plant can also be seen to bring other problems.

·: ·: Traditionally, the positioning of a vortex purifier in a paper machine approach system is justified by the desire to ensure that just prior to the i 105489 paper machine shoulder box, the fiber suspension is free of papermaking particles such as sand, peel, or as impurity particles. However, in our experiments 5, we have found that, especially on paper machines producing filler species, most of the fraction eliminated by the said vortex purification plant, i.e. removed from the flow to the paper machine, is as such suitable for papermaking. The reason for this is, on the one hand, that cyclones of the vortex purifier are dimensioned so that they do not in any case get unsuitable material into the headbox, and, on the other hand, that vortex purifiers can be designed to work optimally with only one material or some very similar material. Considering, for example, the significantly different densities of the various constituents, such as fibers and mineral based fillers, it is easy to believe that the vortex purifier cannot function optimally for any ingredient, but the starting point for the vortex purifier should be that substantially unchanged in the fiber suspension during the cleaning process and that it does not release any particles unsuitable for papermaking into the papermaking machine,. 20 headboxes. Said problem, though, the reject I I <I 1 t!;! Acknowledging t existence is in fact covered by Fl patents 93753 and:. 97,736.

f i ««

As a preferred solution to the above problem, it is proposed that each of the paper pulp ingredients: fresh fiber suspension, pulp, recycled fiber, fillers, etc., is processed in its own unit before mixing the ingredients. Then you can just select each item

»M

- the type and purification method best suited to the ingredient in question. As a result, · · · · · · · · · · · · · · · · · · ·

HII

30 whirlpools are needed at all. In addition, the cleaning of each ingredient with a tailor-made and tailored device is: · also significantly more efficient and economical in energy and equipment engineering than a prior art vortex cleaning plant.

4, 105489

In addition, the vortex cleaning plant poses some additional problems. Due to the large volume of fluid and the complex flow piping, the vortex cleaning plant tends to, if not completely, cause sway 5 to the pulp flow and pulp pressure, at least to maintain and possibly amplify these oscillations. Further, the complex vortex cleaning plant, consisting of several steps (usually 4-6 steps) and containing a large number of relatively small flow pieces, provides a high flow resistance which is compensated by a large amount of electrical power due to the large size centrifugal pumps. Typically, each vortex purification plant cleaning stage has its own feed pump, which means that for a medium-sized paper mill, all short-circuiting pumps in a papermaking machine are of the order of 2 MW.

Another factor affecting pumping power consumption in particular is the placement of short-circuiting components relative to one another at the factory. The first drawback is the positioning of the gas separation tank, which is usually above the machine level. If the gas separation tank could be brought to the machine level by a feed pump, there would be no need to pump the fiber suspension 20 unnecessarily above the machine level. However, this requires that the gas separator tank must be constructed either to operate without overflow because: · · ·: ·. operation of the overflow requires a relatively high free fall, • «· ....: in practice from above the machine level to below the machine level or comprising a pump arranged in connection with the overflow to develop a pressure differential to ensure overload operation. In other words, the height of the gas separator tank m (or more precisely the inlet pressure of the headbox feed pump) could no longer be determined by an overflow in the first alternative, but rather should seek to find a replacement. Since the ultimate purpose of the gas separator tank ·: · is to maintain the level control, as already mentioned above, the inlet pressure of the headbox feed pump is constant, in fact:. it is more advantageous to use a control system which takes into account not only: · · · variations in surface height but also sometimes large variations in the density of the paper pulp. Ultimately, such a change will also result in improved paper quality 105489 and standardization of the manufacturing process. As a result, the result is not only a cheaper solution in terms of pumping energy use, but also a clear positive effect on paper quality and process runtime.

5 Another factor affecting the energy consumption of pumps in a paper machine approach system is the height of the tap water tank. Stripped water tanks, which are so called. The wastewater collected from the paper machine has traditionally been relatively large tanks of almost ten meters in height on the bottom of the paper mill, with varying surface heights. The reason for the difference in surface height 10 is e.g. placement of the tap water tank in connection with the machine.

In the case of so-called. flat wire machine, is a wire water tank, in this case also referred to as a wire mine, located below the wire section, whereby, for structural reasons, its surface height has been relatively low.

Also, the surface height of the wire section or similar off-15 machine silo is not always as high as practically possible. The large size of the tap water tank is justified by the fact that it is considered a good thing and a process stabilizing factor that there is a large buffer tank. This has also resulted in some extra energy consumption, since the first feed pump has had to compensate for the occasionally shallow water level of the tap water tank, as well as extra delays in the process due to the large volume of the tap water tank.

• · I

• · • · ·

This placement of the hot water tank on the bottom of the factory, i.e. below the machine level, is possible in the approach system according to the invention! • · s · '· *: 25 to avoid. The solutions of the invention make it possible to arrange a tap water tank at the machine level, whereby also the gas separation tank feed pump located adjacent to the tap water tank is located at the machine plane.

By solving the above problems, e.g. as described above, the paper machine approach system can be further improved by introducing substantially less electrical power as a feed pump for the gas separation tank: · · A consuming propeller pump with a substantially higher return than the centrifugal pump. In this case, the pulp, either in its entirety or at least its major part, is fed to the gas separation tank by said propeller pump. In practice, a propeller pump is better suited to its function than a centrifugal pump, but previously its use in this application has not been considered because the propeller pump has not met the lifting height requirements of prior art processes. Compared to the above mentioned prior art power requirement of about 2 MW, one propeller pump achieves power consumption of about 200 kW, which means that about 90% of the electrical power can be saved.

The paper machine approach system may be further developed in accordance with a preferred embodiment of the invention by completely excluding the gas separator tank feed pump in question from the approach system. This is made possible, in some suitable circumstances, simply by bringing the gas separator tank down to the machine level, whereby the required differential pressure to transfer the fiber suspension, either completely or at least its major part, from the tap water tank to the gas separator tank is so small that it can be generated If necessary, the system of this embodiment may also be provided with a valve to regulate the flow from the tap water tank to the gas separator tank.

The advantages achieved by the method according to the invention include e.g. the following: - any reduction in the papermaking reject due to more precise sorting, · · · · · 25 - more stable operation of the paper machine short cycle, reduced flow resistance of the paper machine short cycle, - space saving in paper machine short cycle, - pumping energy savings, * - shorter delays »30 - fast species change, - cleaner process, no microbial growth, •« · - simple structure - low cost investment.

7 105489

Characteristic features of the method and apparatus of the invention will be apparent from the appended claims.

In the following, the method and apparatus of the invention will be described in more detail with reference to the accompanying drawings, of which Figure 1 illustrates a prior art solution of US Patent 4,219,340, Figure 2 illustrates a preferred embodiment of the invention, and Figure 3 illustrates a preferred embodiment of the invention.

The prior art paper machine approach system shown in Figs. shown). Said components are disposed in connection with the paper machine 24 and arranged to operate as follows. The tap water tank 10, where the tap water is collected and which is usually located in the prior art systems at the mill floor level, is fed from the "9 9 9 9" machine tank to the papermaking fiber which may consist of · · ·: ·. of fresh pulp, secondary pulp and / or debris and fillers which are diluted with paper, mainly from the wire, in a so-called "pulp".

• · _______________ tap water to form a pulp. Likewise, with the feed bottom 12 at the mill bottom level, the pulp is pumped from the tap water tank 10 to a vortex cleaning plant 14, usually at mill level K (the plane where the paper machine 24 sits), which typically comprises 4-6 steps. The paper mass accepted by the first ··· steps of the vortex purification plant continues to continue with the pressure generated by said feed pump 12 (· with the help of the vacuum in the gas separator) * \ m. " a gas separation vessel 16 located at ·: · level T above the machine level. The gas separation vessel 16 typically includes an overflow at which the paper pulp surface level in the container is kept constant. The pulp discharged from the overflow tank 105489 flows down below the machine level to the mill bottom level tank 10. the accepted pulp flows to machine tray K into the headbox 22 of the paper machine 24.

Fig. 2 shows a solution of a preferred embodiment of the invention in combination with a prior art traditional tap water tank 10. In the figure embodiment, three pipelines 40, 42 and 44 are connected to the tap water tank 10, each of which introduces a different fiber mass into the tap water tank.

Each tube of lines 40-44 is connected to its own vortex purifier arrangement 46, 48 and 50, respectively. It should be noted, however, that vortex cleaning is by no means the only sorting option, but that new types of pressure separators, preferably equipped with slit drums, are well suited for finishing sorting of various pulp fractions. It should further be noted that it is also possible to combine all of the above mentioned pipelines, whereby different types of pulp are mixed together before the tap water tank, for example in a special mixing tank from which. . 20 paper pulp is exported to a so-called buffer container. machine tank. Of course, * V,: * such mixing requires proper dosing, which is not described here in greater detail as it is considered to be within the ordinary skill in the art. In this embodiment of the invention, · · each of its vortex cleaner arrangements 46-50 is thought to handle its own • · 25 pulp type, for example such that arrangement 46 deals with paper pulp rejection pulp, arrangement 48 recycled pulp, and arrangement 50 fresh pulp. In the figure, for each vortex cleaner arrangement, a pump is also drawn to feed the different masses through the cleaner (s) to the tap water tank 10. However, these pumps may also be located much further away from the cleaner (s) in the process. Even different processing equipment can be located between the pump and the cleaner (s). With this arrangement, each type of pulp can be handled as optimally as possible, that is, each of the 9 105489 purifiers can be selected and each purifier can be run according to the optimum sorting of that particular pulp type. Following the purifiers shown in the figure, the process may include various intermediate tanks, pumps, or other equipment required for the treatment of each pulp fraction. In addition, the embodiment of Figure 5 shows a filler handling system including a mixing / dispersion tank 56, a filler slurry feed pump 58 and a filler sorting vortex cleaner arrangement 54, and a removed from the filler stream and either completely removed from the system or, for example, returned to the dispersion stage. Thus, this solution prevents the rejection of larger filler particles that are much thinner than the paper thickness, which would be normal with a prior art vortex cleaner plant. The propeller pump 120 is a propeller pump of sufficient lift height when the vortex cleaning plant is not developing a flow resistance between the pump 120 and the gas separation tank 16. And, as mentioned above, the feed pump may in some cases be replaced by a vacuum apparatus for the gas separation tank 20, which generates a differential pressure for transferring the pulp.

• · · · · · · · · · · · · · · ·

Figure 3 illustrates a solution according to another preferred embodiment of the invention. Namely, this is a new type of substantially · · (most of the tap water tank is above the machine surface and the water surface is · 25 well above the machine surface) 1 paper machine vessel 100 located at the machine plane, where fiber fractions are introduced through pipelines 40-44 Sk »The dashed line illustrates a prior art groundwater tank 10 with a surface of ··· Sio and a feed pump 12. In some cases, the height difference between the surfaces S10 and S10« «« «30 is more than a meter, especially in the case of a wire well. : ·! Under the wire section of the paper machine, whereby the height difference can be directly calculated I II -.:; As an additional consumption of pumping energy in the prior art system, and a large size tap water tank causes its own 10 105489 process delay. the difference dh between the pitch and the height of the gas separator tank 16 is less than 9 meters, preferably less than 6 meters, suitably 2-4 meters, so that the lift height requirement of pump 120 is so small that full propulsion pump operation is possible.

As noted above, it has been possible to develop a new type of pre-treatment process for pulp fed to a paper machine, which removes many of the weaknesses and drawbacks of the prior art and solves problems that have hindered the use of prior art approach systems. However, it should be noted that the individual novelties presented in the various embodiments are applicable individually and by no means in the context in which they are presented.

«

• I I «I

• f «I ·

• f I

i «a • • ·» ·

• · I

«• · • · · · ·

I I I

I I

Fl fl fl fl fl fl t t t t t t t t fl fl t

«M

MM

• «· f« • · • · 1 I · · «« <· ·

Claims (18)

A method of pre-treating pulp, wherein the method of the pulp either in its entirety or at least the bulk of the pulp 5 is fed with the gas separator (12, 120) of the gas separator (16) and thereafter to the inlet of the papermachine (22). ), characterized in that the pulp is fed into the gas separation vessel (16) with a propeller pump (12). 10 2. A method for pre-treating pulp as claimed in claim 1, characterized in that prior to loading into the gas scavenger container (16), at least the filler fraction and the fiber fraction of the fractions constituting the pulp are treated separately in their own screening step to remove the contaminants, to achieve pulp. 3. A method for pre-treating pulp according to claim 1, characterized in that the different fiber pulp qualities (e.g. VF, DIP, 20 BR) contained in the pulp is treated separately in its own screening step. I r Method for pre-treating pulp according to claim 2 or 3, characterized in that swirl cleaning is used in the screening steps. Method for pre-treating pulp according to claim 2 or 3, characterized in that a pressure screen is used in the screening steps. Method for pre-treating pulp according to claim 1, characterized in that the pulp is fed into the gas separation tank (16) with a propeller pump (12) directly from the wirewater funnel (10) without any particular purification. 15 105489 Process for pre-treating pulp according to claim 1, characterized in that the pulp is introduced into the gas separation container (16) from the wirewater funnel (100) which is substantially at machine level. Apparatus for pre-treating pulp, which comprises at least the gas separator (12), a gas separator (16), the inlet drawer (18) and the paper machine inlet carriage (22), a gas separator (16), the gas separator (16) ), with which the pulp is fed from the wirewater funnel (10) or correspondingly into the gas separation container (16). Devices according to Claim 8, characterized in that in the arrangement of the devices, the inlet pump (120) of the gas separating container includes both devices (54) for screening of filler sludge and devices (46, 48, 50) for sieving fiber pulp. Devices according to claim 9, characterized in that the devices for screening of filler sludge include a vortex cleaning arrangement (54). 20 Devices according to Claim 9, characterized in that the devices for sieving fiber pulp include a vortex cleaning arrangement (46, 48, 50). Devices according to Claim 9, characterized in that in the devices 25 for sieving fiber pulp there is a pressure strainer. Devices according to Claim 9, 11 or 12, characterized in that, in the fiber pulp screening devices, there is a separate screening device (46, 48, 50) for each individual fiber pulp quality. Devices according to Claim 11, 12 or 13, characterized in that the devices (46, 48, 50) for sieving fiber pulp are in process order 105489 before the wire funnel (10) or the like, which for its part is in front of the gas separator container feed pump. Devices according to Claim 8, characterized in that the gas washing tank (16) is provided with devices for controlling the inlet pressure of the inlet carriage pump (18) without overflow. Devices according to claim 8, characterized in that the wire funnel (100) and the feed pump (120) are substantially at machine level (K). ίο Devices according to claim 16, characterized in that the level difference between the wire funnel (100) and the gas separation tank (16) is at most 9 meters. Devices according to claim 16, characterized in that the level difference 15 between the wire funnel (100) and the gas separating container (16) is preferably below 6 meters, preferably 2-4 meters. 20 <r (f »« I <f I K · 'I c {«*' l