FI88415C - PROCESSARRANGEMANG FOER DEN KORTA CIRKULATIONEN I EN PAPPERSMASKIN - Google Patents

Description

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Paper machine short cycle process arrangement Processarrangemang för den korta cirkulationen i en pappersmaskin 5

The invention relates to a process arrangement for producing a paper machine headbox pulp in a short cycle, in which fresh pulp is not mixed into the inlet to the deaeration hopper, and in which the process arrangement uses a composite wire well divided into two compartments or two cooperating shafts.

Tightening environmental protection requirements have led to 15 paper machines using more closed short cycles and raw material recycling. In order to minimize production disruptions, it is also necessary to use an even higher level of wire retention, which leads to an increased use of retention aids.

20 The dynamic response of a short cycle is adversely affected by both the large amounts of wire water used and the low level of wire retention, because the concentration of low retention components in wire water changes significantly more slowly than the concentration of high retention components. Any changes in the retention level cause changes in the raw material distribution of the remaining 25 product. It is therefore necessary to monitor and adjust the retention level of each component separately.

The subject matter of the present invention is contributed by the fact that the paper size; their speeds are constantly increasing, which also places ever-increasing demands on the paper machine's 30 short cycle process, as well as manufacturing *. : in terms of process stability and trouble-free and paper quality management. In addition, the quality of paper is further tightened by printing presses, as their speeds are constantly increasing.

35 *. : Wire wells divided into two compartments are already known per se, for which we refer by way of example to DE-A-2 348 526 (Figure 2).

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After the deaeration tank became part of the short-cycle process, high-speed paper machines producing printing papers had to move from the traditional so-called from a single pump process (Figure 1 attached) to a process running on two main flow pumps (Figure 2). In both process-5 arrangements, the fresh mass is mixed with effluent in the region of the membrane. However, in the previously known two-pump system according to Fig. 2, the machine quality and runnability are disturbed by the machine-weighted basis weight variation of the paper due to pressure pulsations of pumps and screens and fluctuations in pressure and mixing caused by both tank and pipe liquid surfaces. Similar causes are caused by other causes.

The short cycle process of the paper machine is generally arranged so that all the new solids, i.e. the cultures and fillers, are diluted with 15 wire water in the area of the membrane. However, fillers have sometimes also been fed in later stages of the process. In general, all of the fibrous material fed to the headbox of the paper machine has been treated in deaeration and prior or subsequent vortex cleaning. The short-cycle consistency dynamo has thus been quite slow, due to the large volumes of material moving in the short 20 rounds, which are of the order of 200 m3. The above causes e.g. the disadvantage that a large amount of paper is scrapped in a species change situation, because the short cycle process requires quite a long time to stabilize after a species change or other similar change.

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It has previously been proposed (Proceedings of the 24th EUCEPA Conference,

May 8-11, 1990, p. 217-226, Bo Norman: "The Water and Fiber Flow System in the Paper and Board Mill") that in a short cycle only air should be removed from the wire water because the amounts of air in it represent almost all the air entering the short circuit. It is an object of the present invention to further develop this by prof. Norman's idea that it can be used while ensuring stable dilution of fresh pulp and at the same time stable pressure conditions in the headbox feed as well as better process dynamics.

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The general object of the invention is to further develop the previously known short-cycle process arrangements of a paper machine and to provide new, more advantageous solutions for such arrangements.

It is a particular object of the invention to provide a new process arrangement which can eliminate the main problems which cause variations in thickness and pressure in the headbox.

It is a further object of the invention to provide an accelerated short-cycle consistency dynamics so that direct control of the consistency of the headbox mass, measured from within the short-cycle, is practicable if necessary.

In order to achieve the above and later objects, the invention is essentially characterized in that a first compartment or tank of said composite wire well is arranged as an deaeration feed tank and a second compartment or tank as a headbox pulp recovery tank in which fresh feed is arranged.

In the invention, the previously known wire well 20 according to the accompanying Figure 2 is divided into two different tanks or tank compartments, one of which has an overflow flow to the other.

There are two important criteria for this division of a wire well: first; Another reason is that in the process the wire water is treated in the deaerator 25 before the fresh pulp is added and another reason is that the suction pressure of the headbox * feed, the back pressure of the fresh pulp feed and the headbox manifold bypass must be stabilized as well as possible.

For the above reasons, the overflow of deaeration is led in a biscuit / ·· 30 line to a wire water tank from which there is no hydraulic connection to the supply and dilution of fresh pulp, whichever occurs in the overflow pipe. the unstable surface is disturbed in prior art solutions. Thanks to the process arrangement of the invention, the stern feed pump obtains a constant suction pressure because the pressure level of the air combustion tank or:; 35 vacuum fluctuations cannot be caused up to the pump because there is a free open surface in between that is stabilized by the overflow flow.

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The process arrangement of the invention improves the consistency dynamics of the process so that an even sharper response is obtained to changes in the fresh pulp feed used in active consistency control and in connection with the change in basis weight and / or machine speed of the paper. The benefit of the arrangement 5 of the invention is emphasized when the control of the consistency of the machine masses (approx. 3% consistency) is made even more reliable than at present, whereby the consistency of the headbox mass can be kept very precisely constant.

In the practice of the invention, the by-pass flow of the headbox manifold can, as in prior art solutions, be led to either a deaeration tank or a dilution tank corresponding to a wire well.

The most preferred embodiment of the process arrangement according to the invention is a circuit in which vortex cleaning does not take place in a short cycle. The rationale is that vortex cleaners, mainly for sand removal, and similar equipment for removing heavy contaminants should be placed at an earlier stage in the process. Such are e.g. grinding, TMP plant, recycled pulp plant, etc. In this case, a separate separation of sand is not required in a short cycle, in which, while sand 20 and other heavy impurities are removed, expensive fillers are also removed. If in any process the vortex cleaning has to be placed in a short cycle, its most preferred location is indicated by dashed lines in Figure 3 (reference numeral 24).

. ' In the following, the prior art of the invention and some preferred application examples of the invention will be described in detail with reference to some short-cycle process arrangements shown in the figures of the accompanying drawing.

Figure 1 schematically shows a previously known short cycle process arrangement used on slow paper machines.

Figure 2 shows a currently known short circuit process arrangement in general use, provided with deaeration 35, which is the closest starting point of the present invention.

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Figure 3 schematically shows the main principle of the process arrangement according to the invention.

Figure 4 shows a schematic central vertical section of a tank solution used in the process arrangement according to the invention.

Figure 5 shows another container solution of the invention in a manner similar to Figure 4.

10 The following describes the prior art to which the background of the invention is understood with reference to Figures 1 and 2.

Figure 1 shows a so-called short cycle of a paper machine according to the prior art. a single-pump process commonly used in older slow 15 paper machines. According to Fig. 1, the headbox 10 feeds a pulp suspension jet J through its lip opening 11 to a forming wire 13 passing over the breast roll 14. Inside the loop of the wire 13 there are water collecting devices 15 which conduct the water leaving through the wire 13 as a flow F! to the wire well 16. The mixing area 16a of the wire well 16 is fed with a fresh mass-20 flow FB, the consistency of which is generally of the order of 3%. In the wire well 16, the freshener is diluted to a headbox consistency of the order of 1%. The dilution takes place as the flow Fx from the wire water and with the mass bypass Fout from the headbox manifold 12. A suction side of the mixing and feed pump 17 is added to the mixing area 16a of the wire well 16. 25 From the pressure side of the pump 17, the diluted to headbox consistency is controlled; the mass flow Fs to the vortex cleaner 18 and the bridge further to the machine screen 19, from the output side of which the inlet mass Fin of the headbox is fed to its manifold 12. The flows Fx, - F5, Fln form the so-called a short circuit from which water exits as a flow F2 through the overflow of the wire well 16: / ·· 30 16a.

: Figure 2 shows a prior art short cycle process arrangement * used on faster paper machines, in which the. the deaeration tank 20. The upper side of the free mass surface Sa:. ** i 35 of the wire well 16 is connected by a joint 16c to the outside air pressure. As shown in Figure 2, the short circuit has two main flow pumps 17a and 17b.

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The first pump 17a supplies the mass flow Fs diluted to the headbox consistency through the vortex cleaners 18 to the deaeration tank 20. The deaeration tank has a pre-pressurized air space 20a above the free surface S0 of the pulp. The height of the surface of the pulp is determined by the overflow 21, 5 of the tank 20, over which the mass flow F8, from which the air has been removed, flows. This flow Fe is directed to the mixing zone 16b of the wire film 16. In addition, a return flow F * from vortex cleaners and a fresh mass flow Fm are introduced into said mixing zone 16b.

The deaeration tank 20 of Figure 2 is known per se in structure and operation, and reference is made to FI patent 70945 (Clark & Vicario Corporation) as one example. A mass flow F? Is derived from the lower part of the deaeration tank 20. on the suction side of the second pulp pump 17b. The pressure side of this pump 17b is connected via a machine screen 19 to the manifold 12 of the headbox 10 15 for supplying its inlet mass flow Fln. The bypass flow Fout of the manifold 12 of the headbox 10 is returned to the lower part of the deaeration tank 20.

An embodiment of the present new invention will now be described with reference to Figure 3, using, mutatis mutandis, the same reference numerals and representations as above in connection with the description of the prior art of Figures 1 and 2. According to Figure 3, a new type of compound wire well 30 is used, which is divided into two compartments 31 and 32. Alternatively, the new wire well is formed of two different containers connected to each other. The first compartment 31 of the wire film 30 acts as a supply tank for the deaeration tank 20, and the supply flow Fe to the deaeration tank 20 is taken from the first compartment 31 by a pump 17d. The overflow Fe of the deaeration tank 20 is returned to the compartment. The compartment 31 is provided with an overflow 33 through which an overflow flow F2 passes, which keeps the surface Sx of the tank 30 at a certain constant level.

As shown in Figure 3, the second compartment 32 of the composite wire well 30 acts as a dilution tank for the head blade. A fresh pulp flow Fn is fed to the supply connection 32a of the compartment 32. In addition, a bypass flow Fout is introduced into the compartment 32 35, which can also be introduced into the deaeration tank 20 (dashed line). A mass F9, from which the air has been deaerated, is introduced into the central region of the compartment 32 from the deaeration tank 20. The second compartment 32 sekoitusyhde 32a is connected to the second stock pump 17c to the suction side and for supplying it via 17c of the pressure side is connected to the machine screen perdlaatikon 10 of the manifold 12 to the input side of the mass inflow FLN headbox 10. The second pump 5 17c of the discharge tube may also be accompanied if necessary pyörrepuhdis- carbonate 24.

According to Figure 3, the fresh mass flow Fm is not fed at all through the air extraction, because an insignificant amount of air enters the process with the fresh mass. The fresh pulp feed area of the second compartment 32 of the wire well 30, which is at 32a, is calmed and stabilized. The stabilization of the supply of fresh pulp is contributed to by the standardized surface height S1 of the second compartment 32 (which is provided by the overflow flow F10 from the second tank compartment 32 to the first tank compartment 15 31 at the overflow 32b.

As described above, a short cycle process arrangement has been provided in which the effect of flow and pressure disturbances on the mass jet J can be minimized. In addition, a more stable pulp-20 system and even faster response times for the controls are provided, because e.g. the flow control of the fresh mass flow Fm has an even shorter delay on the pulp jet J, because the fresh mass flow Fm is not passed through the deaeration tank. 1

Figure 4 shows a preferred wire well * used in the invention. 30, which according to the invention is divided into two compartments 31 and 32.

The compartments 31 and 32 are preferably of circular cross-section in a horizontal section. The second compartment 32 is formed by a vertical tube connected upwards to the protruding part 31b of the first compartment 31 into which the wire water flow Fj is introduced. The upper end 32b of the pipe compartment 32 forms an overflow which is slightly higher than the flow 31c over the first compartment 31, · through which the overflow flow Fz passes from the first compartment 31.

. A pulp flow Fg is introduced into the second compartment 32 by means of a pipe 36. from the lower part of the tank. The lower end 36a of the tube 36 is located substantially below the upper end 32b of the compartment 32. A flow FgS is discharged from the pipe 36, which is directed to the feed connection 32a below, to which 8 88415 fresh pulp flow FB is introduced. The diluted headbox flow F5 described above originates from connection 32a. The flow Fe of the overflow 21 of the air tank 20 is introduced into the lower part of the first compartment 31 by a pipe 37. Otherwise, the structure and operation of the composite wire well 30 shown in Fig. 4 is as described above in connection with Fig. 5.

As shown in Figure 5, the compartments 31 and 32 of the composite wire well 30 are coaxially nested. The horizontal sections of the walls of the compartments 31 and 32 are preferably circular as well as the tubes 36 and 37. The part 10 to 31 is annular and bounded on the outside by a cylindrical jacket, below the tank bottom 31d through which the compartment 32 tube passes, inside the second compartment 32 and above 34. The cylindrical jacket of the first compartment 31, the cylindrical jacket of the second container compartment 2 and the jacket of the tube 36 are preferably coaxial so that their central axes 15 coincide with the vertical central axis KK of the container 30. The composite wire well 30 of Figure 5 is particularly compact and bulky in construction, while the container of Figure 4 is likely to be simpler to implement. Otherwise, the structure and operation of the composite wire well 30 shown in Figure 5 and its connection to the other short cycle process 20 is as shown above in connection with Figures 3 and 4.

· '; The following claims set forth within the scope of the inventive idea defined by the various details of the invention may vary and differ from those set forth above by way of example only.

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Claims (10)

1. Process arrangement for producing a mass for the inlet side of a paper machine 1 for a short circulation, in which in the feed it is preferable not to mix fresh air (Fn) in the feed (20) and in which process arrangement one uses a combination virus well (30). , which is divided into two compartments (31,32) or into two cooperating containers, characterized in that the first compartment (31) or the container of the combination wire well (30) is arranged in the form of a supply container for the venting and the second compartment. (32) or the container in the form of a dilution container for the inlet leather mass, in which the fresh mass (Fm) is arranged to be measured. Process arrangement according to claim 1, characterized in that in one compartment (32) of the combination virus well (30) there is an open standardized surface (Sx) for standardizing the suction pressure of the feed pump (17c) for the pulp and the counterpressure of the fresh mass feed ( Fm) in relation to the outdoor air. Process arrangement according to claim 1 or 2, characterized in that the return currents with pulsating pressure level or Current, such as the overcurrent current (Fe) of the venting container (20) and / or the wirewater stream (Fx) are introduced into the first compartment (31) or the combination of the combination well. (30). 25 Process arrangement according to any one of claims 1,2 or 3, characterized in that the return currents coming from the inlet carriage (10) as well as the passage circulation (Fout) of the distribution bar (12) and the overcurrent of the inlet carriage (10) are led to the dilution container 32 ) of the combination virus well (30) and / or into the accepted stream of the vent. Process arrangement according to any one of claims 1,2 or 3, characterized in that the return currents (Fout) which come V-; From the inlet carriage (10) is led into the process venting container (10). 12 88415 Processing arrangement according to any one of claims 1-5, characterized in that there is an overcurrent (F10) from the scavenger container compartment (32) of the combustion fluid well (30) to the feed container compartment (31) of the vent. 5 Process arrangement according to any one of claims 1-6, characterized in that there is an overcurrent (F2) from the supply container compartment (31) for venting of the combination wire well (30) out of the short circulation. 10 Process arrangement according to any one of claims 1-7, characterized in that the dispensing container compartment (32) of the combination wire well (30) and the feeding container compartment (31) for the vent are compartments separated by a partition in a container, in which compartments are located. an overcurrent (F10) from the dilution container compartment (32) to the feed container compartment (31) (Figure 5) or to the wirewater channel (31b). Process arrangement according to claim 8, characterized in that the dispensing container compartment (32) of the combination wire well (30) is located within the feeding container compartment (31), that said container compartments (31,32) are coaxial to the middle of the feed. the feed container compartment (32) inserted a feed tube (36) from the vent container (20), that the feed container compartment (32) proceeds by mediating an angular portion, thereby forming a feed connection (32a) to which the feed tube (stream) of fresh pulp, said outer annular feed container compartment (31) comprises a bottom portion (31d) through which the inner dispensing compartment compartment (32) is passed, the outer feed container compartment (31) includes a cover portion (34), under which there is a feed connection. (31b) and an overflow (31c) for wire water, and that the upper end of the inner dilution container the divider (32) forms an overflow (32b) to the outer vent container compartment (31) for the vent. 35 13 8841 5 Process arrangements according to any one of claims 1-7, characterized in that the container compartments of the combination virus (30) are separate containers in such a way that they have a connection to each other via the overflow stream (F10). means that the overcurrent of the dispensing container compartment (32) flows directly to the dispensing container compartment (31) for the air compartment or via the wirewater channel to the dispensing container compartment.