FI111967B - Process arrangement in a short cycle of a paper machine - Google Patents

Description

111967

The present invention relates to a paper machine short cycle process stage comprising a feed pump, a headbox, means for directing a pulp suspension jet in a closed state from a dewatering, dewatering, dewatering, removal of one additional 10 to drain the tap water from the short circuit which are in fluid communication with the diluent and the outlet.

The invention also relates to a method for controlling the pressure in a short circulator closed loop, wherein the wire section is conducted through a dilution nozzle to a thick stock dilution and excess tap water is discharged from a short circuit through a discharge nozzle which is in fluid communication with one another.

"Closed former" is used herein to mean a two-wire reformer in which a back jet • «20 box lip is fed into a former forming kit in a closed volume '*'; / and also the dewatering of the wire section is performed in a closed manner so that no system !,; there are no free liquid surfaces and no air can ever be mixed with the tap water.

U.S. Patent No. 3,823,062 discloses one such closed former wherein,? the fiber suspension is led from the headbox between the walls of the two-wire forming mold • i ·, - · · so that it does not come into contact with the ambient air.

, The forming part dewateres the fiber suspension through the wire into water-filled »» «dewatering boxes. Of these, the tap water is led to an open tap tank, '! * 30 from which it is further directed to dilute the mass to be introduced into the headbox. When * «I (» '· tap water runs between an open tank, the system cannot utilize the 2 111967 excess pressure remaining in the tap water after the closed headbox and former combination.

Fig. 4 of FI patent application 981327 shows a paper machine short cycle process staging in which the headbox and the wire section are closed and the venting tank is completely missing. The tap water collected from the wire section is fed by a circulating water pump to the first and second dilution steps of the main process line. Part of the vii-slurry is pumped through the sieve into the dilution headbox via a dilution water pump. The process is closed to ambient air since only the overflow of tap water 10, the vortex purification reject and the reject of the second screen are associated with the ambient air. However, the arrangement is complicated and requires a large number of pumps and a large amount of pumping power. Again, the pressure remaining in tap water cannot be fully utilized.

The object of the invention is to make it possible to maintain a higher back pressure in a short circuit of a closed former, which can significantly reduce the energy required for pumping in a short cycle.

In order to achieve these and later objects, the process flow according to the invention is characterized in what is stated in the characterizing part of claim 1. Correspondingly, the method according to the invention is characterized by what is stated in the characterizing part of claim 7.

The stable operation of the ice system requires that the pressure at the inlet side of the feed pump 25 be maintained at a constant speed. In the solution of the invention, 'the short-circuiting surplus water is led by a larger tube to a container positioned at a suitable height above the headbox level and provided; '. * surface level adjustment, which can be, for example, overflow. This ylijuoksusäi- lead to a surplus of water from the reservoir preferably forming part of the end side 30 in dewatering, whereby it tends to be the cleanest aqueous phase forming section.

'': Due to overflow or other level adjustment in the tank, the pressure of 3 111967 from the wire section in the pipeline leading to the mass dilution remains constant. If necessary, the pressure level can be adjusted by means of valves.

There is no need to apply vacuum to the closed former dewatering elements, since the pressure of the pulp suspension fed from the 5 headboxes is sufficient to drain water through the dewatering elements. When there is no direct connection to ambient pressure, tap water overpressure can be effectively utilized in a short cycle, reducing the energy required for pumping. The outlet connection from the short rotation to atmospheric pressure is tracked through the outlet connection and a height-adjustable container located at a level substantially higher than the former level. Alternatively, the height difference may be partially or completely replaced, for example, by a valve or the like.

When a significant amount of air does not enter the tap water cycle, a short circuit 15 does not necessarily require a wire well or a separate venting step. At elevated pressure, the air is more easily dissolved in the circulation water. However, with the thick pulp, air can enter the short circulation, which is easily trapped in the process, which, over time, can become saturated with air. The amount of air in a short circuit can be reduced by passing a small proportion, preferably less than half, of the circulating tap water therein to the vent. Preferably, a portion of the tap water used to adjust the headbox dilution profile is circulated through the vent. In some '* * cases, passive venting of the dilution water may be sufficient to remove dehumidifying water.' J with a wire well type device. In this case, the dilution water may be taken from either the overflow tank or the long-term post-overflow water stream.

25: The solution according to the invention significantly reduces the equipment needed in a short cycle, which is a considerable investment and operating cost; . *, van affordable solution. Also from the point of view of pulp cleaning, the situation is excellent- <* »li» ·. '. because the pulp can be sorted viscous before it enters a short cycle, which allows small currents and low pressure to be used for sorting. Production Efficiency- »» »

* I I

* six gain advantages due to very fast conversion.

* »4 111967

The invention will now be described with reference to Figures 1-3 of the accompanying drawings, however, which are not to be construed as limiting.

Figure 1 schematically shows a short rotation of a paper machine according to the invention.

Fig. 2 schematically illustrates a short cycle including a vortex cleaning step.

10

Fig. 3 schematically shows a short circulation in which part of the tap water is circulated through a deaeration step.

Figure 1 illustrates a short cycle process step for a closed former 15 in which the pulp suspension or tap water is not in contact with the ambient air at any point. Process parts delimited by dashed lines are not necessary in the process circuit according to the invention.

The thick mass M to be supplied to the paper machine is introduced, possibly through a sorting step, ·, · 20 20, into the tap water flowing into dilution port 17 into the inlet side of the feed pump V. 10. The mass dilution is carried out by tube dilution without a separate * · wire well. The feed pump 10 pumps the diluted pulp suspension F1 into the auxiliary box I. From the headbox 11, a pulp suspension jet J is conducted between the lip 12: Between 15.16 the jet of pulp suspension will not come into contact with the surrounding air at all. In the following two-wire zone forming defect »•,>, the pulp suspension is dewatered by dewatering boxes 15 and 16 on both sides of the web, sealed against wires t · i · 13,14. Each of the water boxes, ·, 30, den and 15 boxes are divided into compartments which are in the direction of travel of the web! »» «» · Filled with water. The dewatering connections of the compartments can be equipped with regulating valves * I i »5 111967 to regulate the dewatering pressure. The dewatering boxes 15,16 do not require negative pressure since the wires are pressed against the web, whereby the water in the overpressure state is discharged through the wires 13, 14 to the dewatering boxes 15,16.

A portion of the tap water recovered through the dewatering boxes 13,14 is returned through the diluent nozzle 17 to the feed pump 10 and along the way a thick mass flow M is introduced into this tap water flow Fo. The dilution line 17 and the outlet line 18 are in direct flow communication with each other, with substantially the same pressure. To keep this pressure constant, regardless of any pressure fluctuations that may occur during dewatering, the outlet conduit 18 is connected to a reservoir 19 positioned at a suitable height above the wire section and provided with overflow or other level control. From the tank 19, the tap water flow Fout is further led to a long circulation of the paper machine. The pressure present in the dilution port 17 is then directly dependent on the location of the tank 19 and its level, which are kept constant. Further, the controllability of pressure can be improved by tracking the outlet 18 with a control valve 22 for restricting the flow of wire water in the outlet 18.

20: The arrangement of the invention makes it possible to keep the pressure constant • · '.'; on the suction side of the feed pump 10, which is an important factor in achieving uniform dilution of the mass and feed to the headbox. The process arrangement according to the invention can also reduce the amount of equipment needed in a short cycle. Minimum · ·: * "25 any short circuit requires, in addition to the closed former, only one feed pump 10, a conduit for conducting a mass flow Fi from feed pump 10 k '·· to headbox 11, and dilution and discharge lines 17 and 18 for recirculating and draining In a short cycle, the energy required for pumping I can be reduced due to the higher back pressure and a simpler process.The thick pulp M brought to the paper machine can be sorted 6111967 undiluted before being fed into a short cycle.

Fig. 2 shows an alternative solution in which the diluted pulp is purified by vortex purifiers 23 prior to the feed pump 10. When the tap water flow Fo from the dewatering elements 15.16 23.

The examples in Figures 1 and 2 do not include any venting tank or other open tank where air can escape from the tap water. Over time and under certain conditions, there may be a risk of short-term accumulation of air, whereby it may be necessary to circulate some of the water through the vent. The solution of Figure 3 includes a deaeration tank 25 into which a portion of the tap water from dewatering elements 15, 16, 15 is conducted along a pipeline 24. The amount of water that can be recirculated through the deaeration is not more than 50% of the amount of circulating water in short circuits. From the bleed tank 25, tap water is led through pump 26 to headbox 11 for use as a dilution water for adjusting the transverse profile of the headbox.

20:. j In this context, "paper machine" means paperboard or tissue paper; and pulp drying machines.

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Claims (9)

111967 A paper machine short cycle processor comprising a feed pump (10), a headbox (11), means (12) for conducting a pulp suspension jet (J) from a headbox (11) in a closed state to a two forming wire (13,14) (13,14) dewatering elements (15,16) disposed against the diluent assembly (17) to direct the water from the dewatering elements (15,16) to the pulp dilution and to drain the excess tap water from the drain (18) from the short circuit which the diluent (17) and 18) are in fluid communication with one another, characterized in that means (19,22) are provided in the outlet connection (18) to maintain a constant pressure in the dilution connection (17). Process processor according to Claim 1, characterized in that the means (19) for maintaining a constant pressure in the dilution port (17) comprise a tank (19) with an overflow 15 or a surface control to which the outlet (18) is connected. Process processor according to Claim 2, characterized in that the tank (19) is disposed at a level *: substantially above the dewatering elements (15,16). 20 Processor inspection according to one of Claims 1 to 3, characterized in that a pressure loss generating device (22), such as a valve, is provided on the outlet connection (18). 5. A processor test as claimed in any one of claims 1 to 4, characterized in that the headbox (11) is a dilution headbox and the dilution water used therein is: taken from a short circuit through a deaeration device (25). I Processor according to one of Claims 1 to 5, characterized in that:.,. · The dewatering elements (15,16) are divided into compartments, each of which is provided with a vent · · ·: 30 bricks (21) for controlling the dewatering pressure in that compartment. »· 111967 A method for controlling pressure in a short circuit of a closed former, comprising the step of directing tap water from a wire section through a dilution port (17) to a dilute pulp (M), and excess tap water from a short circuit through a discharge port (18) 5 in connection with each other, characterized in that the excess tap water is discharged from the short circuit via an overflow or other level control container (19) and / or other pressure-conditioning device (22). A method according to claim 7, characterized in that the tap water to be drained from the short coil is taken from the purest tap water fractions of the wire section. »» 9 111967