FI122912B - Apparatus and method for deaerating the pulp - Google Patents

Description

The invention relates to an apparatus and a method for de-aeration of a pulp.

There is always a certain amount of air, 0.25 ... 8.0% by volume, in the stock. When foaming, the air collects impurities that can contaminate the equipment and may migrate to the wire. Air is also detrimental to numerous pumps. The air maintains aerobic growth of 10 mucus, which increases the need for washing and increases the use of washing chemicals. Air binds to the stock when the air / liquid interface is subject to rapid changes, such as in mixing and turbulent flows.

Air is present in the stock in three different forms: free, bound and dissolved. The proportions of these forms depend on the quality, temperature and pH of the pulp. Free air occurs in large bubbles and foam. Much of this shape is spontaneously removed in pipes and tanks, which should be taken into account in the design. However, some are stable foam that does not spontaneously discharge. Free air may become mechanically bound, for example in pumping. The bound air 20 occurs in the form of small bubbles. Removing this type of air is particularly important because the bound air is firmly attached to the non-wetted surfaces of the fibers, binding the fibers to one another, causing formation problems. Dissolved air per se does not affect c / j formation or water drainage on the wire, but it is sought to be removed because it tends to become bound, bubble-like air, e.g., as pressure io 25 drops or temperature changes, oo g.

Chemical removal is mainly used to reduce the amount of free air, and the LO is designed to prevent an excessive increase in the amount of air. Significant passive venting of the air occurs in the wire well (now known as the tap water channel) and the wire section. Not all air can be removed by equipment design and chemicals alone. The only way 2 to achieve almost complete deaeration is by mechanical deaeration using a deaeration tank.

In the vent, the vent is achieved by boiling the fiber suspension under reduced pressure. The fiber suspension is introduced into the container through feed pipes having upper ends above the liquid surface of the container. There is a vacuum in the tank which corresponds to the boiling point of the water in question. temperature. When sprayed vigorously on the roof of the container, the fiber suspension breaks down into falling droplets and forms a downwardly flowing liquid film on the interior surface of the container roof. Boiling occurs in droplets, in the liquid film on the wall of the container and on the surface of the liquid portion. Deeper in the suspension, the water no longer boils. The fiber suspension stays in the tank for an average of 10 seconds and during this time, in addition to free air, part of the air suspended in the fiber suspension is also removed. A typical short-circuit deaeration tank is shown in Figure 1.

15 For pulps containing a high amount of impurities, such as mechanical and recycled fiber pulp, the air content may be much higher than that of a pulp-based paper machine. According to the principle of the venting tank, the change in pressure (vacuum) causes the dissolved air to become free and to escape. The blow contributes to the release of the air bound to the fiber, and the droplet increases the specific surface area (facilitates evacuation and the formation of a bubble). Based on the results of the test shots, the impact has no deaerating effect on the dehumidification of masses with high air content.

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° In this application, the dewatering tank is designed for pulp suspensions with a high air content of 25, so that the pulp is not sprayed into the ceiling of the deaeration tank, but is allowed to discharge below the liquid surface. Pulp Suspension | the sion can be guided below the liquid surface by completely removing the jets and directing the mass flow from the sides of the manifold below the liquid surface.

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Preferably, the manifold space comprises a bulkhead, whereby the mass of the bulkhead above the level of the top surface of the bulkhead is led to an overflow pipe. The pulp manifold extending to the venting tank 3 narrows towards its end and comprises on its side a tube or tubes or flow opening which open towards the bottom of the venting tank.

The apparatus according to the invention and the method for deaerating the pulp are characterized by what is claimed.

The invention will now be described with reference to some preferred embodiments of the invention shown in the figures of the accompanying drawings, which are not, however, to be construed as solely limited thereto.

Figure 1 shows a prior art air vent container in a short rotation of a paper machine in connection with a headbox.

Figure 2 illustrates an air vent container and a solution for evacuating air from a pulp furnace in accordance with the invention.

Figure 3 shows a short rotation of the headbox.

Figure 4 is a graphical comparison between prior art structures and a deaeration container and method according to the invention.

Fig. 1 shows a prior art deaeration tank and solution for removing air from a pulp. As shown in the figure, the pulp is fed through a manifold cp 25 into the spray pipes and sprayed into the ceiling of the venting tank. The pulp stock is maintained 'in the venting space Vi, separated from the overflow space F by the bulkhead E F. From the bottom of the space Vig, the treated degassed pulp is introduced into the headbox of a paper machine or the like. The air is aspirated by a vacuum pump J through space Oi g above the mass interface, i.e. the liquid surface interface Ti. Thus, the state Oi ali o 30 is pressurized in prior art solutions. The mass 4 sprayed onto the top wall of the container drops, whereby in the prior art solution, this droplet mass is degassed in the Oi state.

The application discloses a new method and apparatus 5 for deaerating the solution of Figure 1. Fig. 2 shows a venting vessel 10 according to the invention. The venting vessel 10 comprises an inlet pipe 11 which, at its end, is connected to a tapered manifold 12 which is fitted into the bulk compartment M1 of the pulp M. ... 12an or the flow port is arranged to open in the collector 10 below the interface bordering the vacuum M, i.e. the liquid surface Ti, above the bulkhead M. The inlet pipe 11 is introduced into the venting vessel 10, preferably from the side or bottom of the tank. Thus, the pulp stock M is never sprayed onto the walls of the vacuum chamber Oi of the venting vessel 10, but the stock stock M is smoothly led below the interface Ti and released into the space 15 Vi among the pulp stock M. Preferably, the pipe or pipes 12ai, 12a2 ... 12an or the flow slot are arranged to open toward the lower wall 10b of the venting vessel 10. Preferably the manifold 12 is located completely below the liquid surface Ti, but in some applications it may be located in the vacuum state Oi and the pipe or pipes 12ai. .. through the pulp stock M is conducted below the liquid surface Ti. Generic values are used for pulp pulp-20 le M, such as: - the pulp pulp has a fiber consistency of 0.5 to 2%, - the pulp pulp has a temperature range of 30 to 60 ° C.

In addition, the venting vessel 10 has a vacuum range of 70 to 99 kPa.

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In the venting vessel 10 according to the invention shown in Fig. 2, the vessel comprises an o0 -1 partition 13 over which the overflow Li passes from the space Vi from the pulp M and the overflow to the overflow pipe 14. the removed and substantially g air-free pulp stock is fed to terminal 15 and further to a headbox of a paper machine or the like. In the vacuum state Oi above the interface Ti, the vacuum is drawn by vacuum pump Pi together 16. As shown in Figure 2, from the bypass of the headbox manifold of the papermaking machine 5, the assembly 17 is led to the plenum space Vi so that the assembly 17, such as a tube, opens from the wall or bottom 10b of the venting vessel 10 to the plenum space Vj. As shown in Figure 2, the manifold 12 is arranged to open below the surface Ti of the pulp M 12 from its pipes 5 12a, 12a2 ... 12an leading away from the pulp stock M. Pipes 12ai, 12a2. . . 12an is directed towards the bottom 10b of the venting container 10. It has been found that the above solution removes air from pulp M more efficiently than the jet tube solution shown in Figure 1.

Figure 3 illustrates and schematically illustrates a headlift 100 ly cycle and a pulp barrier feed system 200. Pipes, ducts, or the like are hereinafter referred to as lines or interconnections. The wire well 50 is led by pump P2 along the line or one not along the pulp stock to the vortex purifier 20 and further from the vortex purifier via line 11 to the air purge tank 10. The air outlet 15 15 through the machine screen Q to the headbox 100. From the wire well 50, dilution water is supplied through line e2 and pump P4 through the machine screen C2 and further into dilution water 20 to the headbox 100 to control the basis weight of the web. As a bypass of headbox 100, the pulp stock is guided to line 17 and further to space Vi in the vent chamber 10 among the pulp barrier below the stock barrier interface Ti. Through the liner 16, vacuum is sucked into the internal vacuum space w Oi by the vacuum pump Pi.

Fig. 4 is a graphical representation of the ϊ test values obtained with the structure according to the invention in the deaeration and at different vacuum levels in state Oi.

00 ίο The above-described design of the venting tank 10 at trial scale-30 resulted in greater bubble-like air reduction than the current design.

Fig. 4 shows the exhaust air 6 obtained by the arrangement fi in accordance with the invention. The graph ΐι is a state of the art graph where the mass is sprayed into a vacuum space Oi and to the walls. As shown in Figure 4, the deaeration is enhanced when the pulp stock M is fed below the liquid surface, i.e. the interface Ti, of the deaeration tank 10. Thanks to the removal of the jets, the lower air pressure is sufficient to remove the air, allowing a lower lowering of the air vent and saving on investment and operating costs. Furthermore, the deaeration tank of the solution according to the invention is cheaper in manufacturing than the solutions of the prior art.

By papermaking machine or the like is meant paper, board tissue paper or 10 pulp drying machines.

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Claims (5)

7 An air vent container (10) to a paper machine or similar pulp feed system (200), wherein the pulp stack (M) is introduced into an inlet 5 (11) of the vent container (10) and through the interior of the vent container (10) ), to which the pulp stock (M) is first collected so as to form, in space (Vi), its vacuum (Oi) above the interface (Ti) above the interface (Ti), and from which the bulk stock (Vi) contains air pulp (M) removed, is led to an outlet (15), characterized in that 10 pulp (M) entering the exhaust pipe (11) from the inlet pipe (11) is released to the accumulation space (V) of the pulp (M) below the upper surface (Ti) of the pulp (M) the pipes (12ai, 12a2 ... 12an) open / open below the interface (Ti) for the outflow of the pulp barrier (M) to the space (Vj), and that the size matrix (Vi) comprises a partition wall (13), Ti), when over-filling the bulkhead (13), the upper surface level mass (M) is led to the overflow pipe (14). The deaeration tank (10) according to claim 1, characterized in that the pipe (s) (12ai, 12a2 ... 12an) of the mass distribution log (12) opens at its end below the interface (Ti) of the pulp shield (Mi), whereby the pulp is not sprayed (Oh). A venting container according to claim 1 or 2, characterized in that the pulp manifold (12) extending to the venting container (10) narrows towards its end and the cc 25 comprises on its side a pipe (s) (12ai, 12a2 ... 12an) or a flow opening. which 'open towards the bottom (10b) of the venting vessel (10). CC CL A venting container (10) for feeding a papermaking machine or similar pulp slurry (200), wherein the pulp slurry (M) is introduced into the inlet pipe 30 (11) of the venting tank (10) and therewith into the interior of the venting tank (10). (Vi), to which the pulp stock (M) is first collected so as to form a space (Vi) relative to the vacuum (Oi) above the interface (Ti), to which vacuum (Oi) the vacuum is generated and from which the bulk (Vi) ), which has been deaerated, is led to an outlet (15), characterized in that the pulp block (M) from the inlet pipe (11) to the venting tank (10) is discharged by its accumulation mass (Vi) below the interface (Ti) whereby the pipe (s) (12ai, 12a2 ... 12an) for the outflow of pulp barrier (M) into space (Vi) opens / opens below the interface (Ti), and that the pulp manifold (12) extending to the deaeration tank (10) ätyään from its side and includes a tube or tubes (element 12al, 12a2 ... 12aN) or a flow orifice, which is / are open towards the bottom 10 of the deaeration tank (10), (10b). A method of deaerating the pulp in a paper machine or similar headbox (100) feeding system (200), wherein the feeding system (200) delivers the pulp (M) to the deaerating tank (10) through an inlet (11) and suctioning the vacuum an internal space (Oi) above the bulkhead collector (V)) above the interface (Ti) and wherein the deflated stock (M) is discharged from the collector space (Vj) to a paper machine or similar headbox (100), characterized in that the pulp stock (M) is vented to the bleed tank (10), below the interface (Ti) of the pulp stock (M) bordering the vacuum chamber (M), and that the pulp stock (M) 11) through the mass distribution gate (12) which opens into the accumulation space (Vi) of the pulp barrier (M) ° below the upper interface (Ti), whereby the mass manifold (12) has a mass pipe 0 25 ki / pipes (12ai, 12a2 ... 12an) or a flow port for the outflow of the pulp shield (M) to 00> state (Vi) from the pulp shield (M) 12) open (s) below the interface (Ti) ε and preferably such that the flow from the manifold (12) g of the pulp barrier (M) is directed towards the wall (10b) below the space (Vi), in CO 1 30 9