WO2007107635A1 - Apparatus and method in removing air from pulp stock - Google Patents

Apparatus and method in removing air from pulp stock Download PDF

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Publication number
WO2007107635A1
WO2007107635A1 PCT/FI2007/050146 FI2007050146W WO2007107635A1 WO 2007107635 A1 WO2007107635 A1 WO 2007107635A1 FI 2007050146 W FI2007050146 W FI 2007050146W WO 2007107635 A1 WO2007107635 A1 WO 2007107635A1
Authority
WO
WIPO (PCT)
Prior art keywords
pulp stock
pulp
space
deaeration tank
stock
Prior art date
Application number
PCT/FI2007/050146
Other languages
French (fr)
Inventor
Leif Piippola
Heli Kellokoski
Original Assignee
Metso Paper, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority to FI20065184 priority Critical
Priority to FI20065184A priority patent/FI122912B/en
Application filed by Metso Paper, Inc. filed Critical Metso Paper, Inc.
Publication of WO2007107635A1 publication Critical patent/WO2007107635A1/en

Links

Classifications

    • DTEXTILES; PAPER
    • D21PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21DTREATMENT OF THE MATERIALS BEFORE PASSING TO THE PAPER-MAKING MACHINE
    • D21D5/00Purification of the pulp suspension by mechanical means; Apparatus therefor
    • D21D5/26De-aeration of paper stock
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D19/00Degasification of liquids
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D19/00Degasification of liquids
    • B01D19/0036Flash degasification
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D19/00Degasification of liquids
    • B01D19/0042Degasification of liquids modifying the liquid flow

Abstract

The invention relates to a deaeration tank (10) for a feed system (200) of pulp stock of a paper machine or equivalent and a method in removing air from pulp stock. Pulp stock (M) is guided to an inlet pipe (11) of the deaeration tank (10) and via it to the inner space of the deaeration tank (10) which space comprises a collecting space (V1) for the pulp stock (M). The pulp stock (M) is first collected so that it forms in the space (V1) a boundary surface (T1) in relation to an upper vacuum space (O1). To the vacuum space (O1) is produced underpressure. From the collecting space (V1) the pulp stock (M), from which air has been removed, is guided to an outlet fitting (15). After having come from the inlet pipe (11) into the deaeration tank (10), the pulp stock (M) is released to the collecting space (V1) of pulp stock (M) below the upper boundary surface (T1) of pulp stock (M), whereby a pipe/pipes (12al 12a2...12an) for the outflow of the pulp stock (M) to the space (V1) opens/open below the boundary surface (T1).

Description

Apparatus and method in removing air from pulp stock
The invention relates to an apparatus and a method in removing air from pulp stock.
There is always naturally air for some amount, 0.25...8.0 vol-%, along with pulp. When producing foam, air gathers impurities which make devices dirty and can be carried onto the wire. Air is also disadvantageous to many pumps. Air maintains aerobic slime growth, whereby the washing need multiplies and the use of washing chemicals increases. Air is bound to pulp when the boundary surface between air and liquid becomes the subject of quick changes, such as e.g. in mixings and turbulent flows.
Air exists in pulp in three different forms: free, bound and dissolved. The portions of these forms are dependent on the quality, temperature and pH of the pulp. Free air exists as large bubbles and foam. A great part of this form exits spontaneously in pipes and tanks, which should be considered in design. However, a part is sta- ble foam which does not exit spontaneously. Free air can develop into bound mechanically e.g. in pumping. Bound air exists as small bubbles. The removal of this air type is especially important as bound air is tightly fastened on the non-damp surfaces of fibres thus binding the fibres to each other, causing formation problems. Dissolved air as such does not affect the formation or the exit of water on the wire, but one tries to remove it, because it has a tendency to change into bound, bubbly air e.g. when pressure decreases or temperature changes.
Generally, the ways of air removal are divided into chemical and mechanical deaeration. By means of chemical deaeration, the amount of free air can be re- duced, and its purpose is to prevent the excessive growth of air volume. Considerable passive deaeration takes place in a wire pit (currently a tail water channel) and on the wire section. AU air cannot be removed solely by device design and chemicals. The only way to achieve almost complete air removal is mechanical deaeration by means of a deaeration tank.
In a deaerator, removing air is provided by boiling fibre suspension in underpressure. The fibre suspension is guided to the tank via feed pipes the upper ends of which are above the liquid surface of the tank. In the tank prevails underpressure which corresponds the boiling point of water in the temperature in question. When spraying forcefully to the tank ceiling, the fibre suspension scatters to dropping beads and forms a down-flowing liquid film on the inner surface of the tank ceiling. Boiling takes place in the beads, in the liquid film on the tank wall and on the surface of the liquid part. Water does not boil anymore deeper in the suspension. The fibre suspension stays in the tank on average for 10 seconds and, during this time, also a part of air bound in the fibre suspension is able to exit alongside with free air. A typical short-circulation deaeration tank is shown in Fig. 1.
In pulps including a lot of impurities, such as mechanical and recycled fibre pulps, air content can grow a lot higher than the one of chemical pulp based paper machine pulp. According to the operational principle of the deaeration tank, a change of pressure (underpressure) provides that dissolved air becomes free and exits. A stroke enhances the freeing of air bound in the fibre and the beading, for its part, increases the specific area (facilitates the exit and the forming of dissolved into bubbles). Based on test run results, the stroke has no intensifying effect in removing air in pulp deaeration with pulps of high air content.
In this application, the deaeration tank is designed for pulp suspensions having high air content so that pulp is not sprayed to the ceiling of the deaeration tank but one lets the pulp to discharge below the liquid surface. The pulp suspension can be guided below the liquid surface by omitting jet pipes totally and by guiding the pulp flow from the sides of a bypass manifold below the liquid surface. An apparatus and a method in removing air from pulp stock according to the invention are characterised by what is presented in the patent claims.
The invention will now be described with reference to some advantageous em- bodiments of the invention shown in the figures of the accompanying drawings, to which the invention is, however, by no means intended to be solely defined.
Fig. 1 shows a deaeration tank according to prior art in a short circulation of a paper machine in connection with a headbox.
Fig. 2 shows a deaeration tank and an arrangement for removing air from pulp stock according to the invention.
Fig. 3 shows the short circulation of the headbox.
Fig. 4 graphically shows a comparison between structures according to prior art and the deaeration tank and method according to the invention.
Fig. 1 shows a deaeration tank and an arrangement for removing air from pulp stock according to prior art. As shown in the figure, pulp is fed via a bypass manifold into jet pipes and sprayed to the ceiling of the deaeration tank. Pulp stock is kept in a space V1 of the deaeration tank divided by a partition wall E from an overflow space F. From the bottom of the space V1, treated pulp stock, from which air has been removed, is guided to the headbox of a paper machine or equivalent. Air is sucked by a vacuum pump via a fitting J from a space O1 above a boundary surface Ti i.e. liquid surface of pulp stock. Thus, the space O1 is un- derpressurised in prior-art arrangements. The pulp sprayed to the upper wall of the tank becomes beaded, whereby air is removed from the beaded pulp in question in the space O1 in the prior-art arrangement. This application describes a novel method and apparatus in air removal in relation to the arrangement of Fig. 1. Fig. 2 shows a deaeration tank 10 according to the invention. The deaeration tank 10 comprises an inlet pipe 11 which joins a bypass manifold 12 narrowing towards its end which manifold is arranged into a collect- ing space Vi of pulp stock M into which space pulp is guided, whereby a pipe or pipes 12ai, 12a2...12an or a flow slot of the bypass manifold of pulp stock M i.e. pulp bypass manifold 12 is/are arranged to open in the collecting space Vi below a boundary surface i.e. liquid surface Ti limited to a vacuum space O1 above the pulp stock M. The inlet pipe 11 is brought inside the deaeration tank 10 advanta- geously from the side or the bottom of the tank. Thus, the pulp stock M is in no stage sprayed to the walls of the vacuum space Oi of the deaeration tank 10, but the pulp stock M is smoothly guided below the boundary surface Ti and released in the space Vi among the pulp stock M. Advantageously, the pipe or pipes 12ai, 12a2...12an or the flow slot is/are arranged to open towards a lower wall 10b of the deaeration tank 10. Advantageously, the bypass manifold 12 is located totally below the liquid surface T1, but in some embodiments it can be located in the vacuum space O1 and via the pipe or pipes 12ai... the pulp stock M is guided below the liquid surface Ti. For the pulp stock M are used general values, such as: - the fibre consistency of pulp stock is 0.5-2%, - the temperature range of pulp stock is 30-60°C.
Furthermore, the range of underpressure in the deaeration tank 10 is 70-99 kPa.
In the deaeration tank 10 according to the invention shown in Fig. 2, the tank comprises a partition wall 13 over which over-run Li from the space V1 from the pulp stock M transfers and further to an overflow pipe i.e. outlet fitting 14. As accept, a flow of pulp stock M, from which pulp stock M air has been removed, is guided from the space V1 and the substantially airless pulp stock is guided to a fitting 15 and further to a headbox 100 of a paper machine or equivalent. Into the vacuum space O1 above the boundary surface T1 is sucked underpressure by a vacuum pump Pi via a fitting 16. As shown in Fig. 2, from the bypass circulation of the bypass manifold of the paper-machine headbox 100 is guided a fitting 17 into connection with the collecting space V1 so that the fitting 17, such as a pipe, opens from the lower wall i.e. bottom 10b of the deaeration tank 10 to the collecting space V1 i.e. below the boundary surface T1. As shown in Fig. 2, the bypass manifold 12 is arranged to open from its pipes 12ai , 12a2...12an out-guiding the pulp stock M below the surface level T1 of pulp stock M. The pipes 12aj, 12a2...12an are directed to open towards the bottom 1 Ob of the deaeration tank 10. It has been found that the above arrangement removes air from the pulp stock M more effectively than the jet pipe arrangement shown in Fig. 1.
Fig. 3 shows illustratively and as a schematic diagram a short circulation of the headbox 100 and a feed system 200 of pulp stock. Pipes, channels or equivalent are called lines or fittings here. From a wire pit 50 is guided by means of a pump P2 along a line or a fitting C1 pulp stock to centrifugal cleaning 20 and further from the centrifugal cleaner via the line 11 as input to the deaeration tank 10. From the deaeration tank 10, pulp stock is guided as over-run of the deaeration tank via the line 14 back to the wire pit 50. The pulp stock M, from which air has been removed, is transferred along the line 15 and by a circulation provided by a pump P3 via a machine screen C1 to the headbox 100. From the wire pit 50 is guided dilution water via a line e2 and by a circulation provided by a pump P4 to a machine screen C2 and further as dilution water to the headbox 100 for adjusting the basis weight of the web for the web width. As a bypass circulation of the headbox 100, pulp stock is guided to the line 17 and further to the space V1 into the deaeration tank 10 among the pulp stock below the boundary surface T1 of pulp stock. Via the line 16 is sucked underpressure to the vacuum space Oi inside the deaeration tank 10 by the vacuum pump P1.
Fig. 4 graphically shows test values provided by a structure in air removal according to the invention and with different underpressure levels in the space O1.
With the above-mentioned construction of the deaeration tank 10, higher reduction of bubbly air was achieved in the mill-dimension test runs compared with the current structure. Fig. 4 shows with line chart fj the removal of air achieved by means of an arrangement according to the invention. Chart f2 is a chart according to prior art in which pulp is sprayed to the vacuum space O1 and to the walls. According to Fig. 4, deaeration is intensified when the pulp stock M is fed below the liquid surface i.e. boundary surface T1 of the deaeration tank 10. Due to the omission of jet pipes, lower underpressure is adequate for air removal, whereby the deaeration tank can be lowered a little, which yields savings in investment and operation costs. Furthermore, the deaeration tank of the arrangement according to the invention is more cost-effective of its manufacturing costs than the arrange- ments of prior art.
A paper machine or equivalent means a paper, board, tissue or pulp-drying machine.

Claims

Claims
1. A deaeration tank (10) to a feed system (200) of pulp stock of a paper machine or equivalent, in which pulp stock (M) is guided to an inlet pipe (11)
'5 of the deaeration tank (10) and via it to an inner space of the deaeration tank (10) which space comprises a collecting space (V1) for the pulp stock (M) into which collecting space the pulp stock (M) is first collected so that it forms in the space (V1) a boundary surface (T1) in relation to an upper vacuum space (O1) into which vacuum space (Oj) underpressure is pro- 0 duced and from which collecting space (V1) the pulp stock (M), from which air has been removed, is guided to an outlet fitting (15), characterised in that, after the pulp stock (M) has come from the inlet pipe (11) to the deaeration tank (10), it is released in the collecting space (V1) of pulp stock (M) below the upper boundary surface (T1) of pulp stock (M), 5 whereby a pipe/pipes (12al5 12a2...12an) for the outflow of pulp stock (M) into the space (V1) opens/open below the boundary surface (T1).
2. A deaeration tank (10) according to claim 1, characterised in that the pipe/pipes (12al5 12a2...12an) of a pulp bypass manifold (12) open from 0 their end below the boundary surface (T1) of pulp stock (M1), whereby pulp is not sprayed into the vacuum space (O1).
3. A deaeration tank according to any one of preceding claims, characterised in that the collecting space (V1) comprises a partition wall (13), 5 whereby when the surface (T1) of the pulp stock (M) exceeds the level of the upper surface of the partition wall (13), the pulp (M) is guided to an overflow pipe (14).
4. A deaeration tank according to any one of preceding claims, character- ised in that the pulp bypass manifold (12) extending to the deaeration tank
(10) narrows towards its end and comprises at its side a pipe or pipes (12ai, 12a2...12an) or a flow slot which opens/open towards a bottom (10b) of the deaeration tank (10).
5. A method in removing air from pulp stock in a feed system (200) of a headbox (100) of a paper machine or equivalent, in which feed system
(200) pulp stock (M) is guided to a deaeration tank (10) via an inlet pipe (11) and in which system underpressure is sucked to a space (O1) inside the deaeration tank (10) above an upper boundary surface (Ti) of a collecting space (V1) of pulp stock and in which system from the collecting space (V1) the pulp stock (M), from which air has been removed, is guided further to the headbox (100) of the paper machine or equivalent, characterised in that, in the method, when guiding the pulp stock (M) to the deaeration tank (10), it is released to the collecting space (V1) of pulp stock (M) inside the deaeration tank (10) below the boundary surface (T1) of pulp stock (M) limited to the vacuum space (Oi).
6. A method according to claim 5, characterised in that, in the method, the pulp stock (M) is guided via the pipe (11) to a pulp bypass manifold (12) which opens to the collecting space (Vi) of pulp stock (M) below the up- per boundary surface (T1) of pulp stock (M), whereby a pulp pipe/pipes
(12als 12a2...12an) or a flow slot of the pulp bypass manifold (12) for the outflow of pulp stock (M) to the space (Vi) from the bypass manifold (12) of pulp stock (M) opens/open below the boundary surface (T1) and advantageously so that the flow from the bypass manifold (12) of pulp stock (M) is directed towards a lower wall (10b) of the space (V1).
PCT/FI2007/050146 2006-03-20 2007-03-19 Apparatus and method in removing air from pulp stock WO2007107635A1 (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
FI20065184 2006-03-20
FI20065184A FI122912B (en) 2006-03-20 2006-03-20 Apparatus and method for deaerating the pulp

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
DE112007000609T DE112007000609T5 (en) 2006-03-20 2007-03-19 Apparatus and method for removing air from pulp

Publications (1)

Publication Number Publication Date
WO2007107635A1 true WO2007107635A1 (en) 2007-09-27

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PCT/FI2007/050146 WO2007107635A1 (en) 2006-03-20 2007-03-19 Apparatus and method in removing air from pulp stock

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DE (1) DE112007000609T5 (en)
FI (1) FI122912B (en)
WO (1) WO2007107635A1 (en)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2012056108A1 (en) * 2010-10-26 2012-05-03 Aikawa Fiber Technologies Oy Deaeration of stock in a pulp drying machine
US11015292B2 (en) * 2016-09-01 2021-05-25 Essity Hygiene And Health Aktiebolag Process and apparatus for wetlaying nonwovens

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102008056505A1 (en) * 2008-11-08 2010-05-12 Voith Patent Gmbh Arrangement for production of finished fibrous material suspension for manufacturing paper-, cardboard-, tissue- or another fibrous material web, has high-consistency flow containing fiber or filler material and low-consistency flow

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS63305905A (en) * 1987-06-08 1988-12-13 Shinichi Sugano Deaerator
US4997464A (en) * 1990-03-23 1991-03-05 Kopf Henry B Deaeration apparatus
WO1997015717A1 (en) * 1995-10-24 1997-05-01 Ahlstrom Machinery Oy Deaeration vessel
WO2002026346A1 (en) * 2000-09-29 2002-04-04 Tetra Laval Holdings & Finance Sa A method and an apparatus for continuously deaerating a liquid

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS63305905A (en) * 1987-06-08 1988-12-13 Shinichi Sugano Deaerator
US4997464A (en) * 1990-03-23 1991-03-05 Kopf Henry B Deaeration apparatus
WO1997015717A1 (en) * 1995-10-24 1997-05-01 Ahlstrom Machinery Oy Deaeration vessel
WO2002026346A1 (en) * 2000-09-29 2002-04-04 Tetra Laval Holdings & Finance Sa A method and an apparatus for continuously deaerating a liquid

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2012056108A1 (en) * 2010-10-26 2012-05-03 Aikawa Fiber Technologies Oy Deaeration of stock in a pulp drying machine
US11015292B2 (en) * 2016-09-01 2021-05-25 Essity Hygiene And Health Aktiebolag Process and apparatus for wetlaying nonwovens

Also Published As

Publication number Publication date
FI20065184A0 (en) 2006-03-20
DE112007000609T5 (en) 2009-01-22
FI122912B (en) 2012-08-31
FI20065184A (en) 2007-09-21

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