FI129925B

FI129925B - Akseptitankin sekoitusjärjestely

Info

Publication number: FI129925B
Application number: FI20215615A
Authority: FI
Inventors: Kimmo Vanhala
Original assignee: Andritz Oy
Priority date: 2021-05-25
Filing date: 2021-05-25
Publication date: 2022-11-15
Also published as: KR20240012431A; MX2023013877A; EP4347948A1; WO2022248765A1; AU2022282597A1; US20240229352A1; FI20215615A1; CN117242222A

Abstract

Keksintö on aseptitankkijärjestely pulpperoidun kuitususpension sekoittamiseksi akseptitankissa ilman että aiheutuu laskeumia tai kertymiä tankin pohjalle. Akseptitankissa on sivuseinät (3,4), joilla on muoto joka koostuu kahdesta vastakkaisesta kaarevasta päädystä (2) ja kahdesta pitkänomaisesta osuudesta (1) kaarevien päätyjen väleissä (2). Akseptitankissa on ainakin kaksi sekoitinta (10), ja ainakin toinen näistä sekoittimista (10) sijaitsee kaarevassa päädyssä (2). Parhaimman suorituskyvyn saamiseksi kahden sekoittimen (10) akselit (11) ovat vaakasuunnassa suunnattu kohti pitkänomaista osuutta (1) ja ainakin yhden sekoittimen (10) akselin (11) keskilinja kohdistuu sivuseinän (3) pisteeseen (P), joka on pitkänomaisen osuuden (1) alkua ainakin 25 % pitkänomaisen osuuden (1) pituutta kauempana. Edullisesti potkurit (12) on sijoitettu ja/tai suunnattu symmetrisesti akseptitankin keskipisteen suhteen. Pitkänomaisen osuuden (1) keskellä on pitkänomainen keskikappale (6), jolla on pyöristetyt päädyt. Akseptitankin pohja on olennaisen tasainen ainakin akseptitankin pitkänomaisella osuudella (1).

Description

AN ACCEPT TANK MIXING ARRANGEMENT

Scope of the invention

The invention is an arrangement for mixing of suspension within an accept tank which has a form of two opposite arched ends and an elongated section between the arched ends. Especially, the invention is aimed for mixing of pulped fiber suspension of cellulosic fibers from recycled material.

Background of the invention

Accept tanks are used in papermaking industry for mixing screened fibers and small particles that are supplied from a drum pulper. The accept tank is placed under a last screen section of the drum pulper. The tank may or may not aim to separate heaviest particles like sand or glass to the bottom of the tank.

Publication CN108330719 discloses an arrangement wherein propulsion of mixers is aligned so that it aims against sidewalls of arched ends of the tank.

Summary of the invention

Least energy consumption is best achieved by sufficiently stable and coherent circular flow within the accept tank. Often separation of the particles is not wanted to happen in the accept tank, as it can be better performed within later phases with

N 25 least fiber loss. Then mixing conditions should keep the particles flowing mixed with

N the liguid and prevent precipitation. A strong coherent and stable flow is desired. 7 Local backflow, swirl and standing water will cause accumulations of particles to

N the bottom of the tank. Accumulations may grow and destabilize flow which will

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& further grow the accumulations. Then the process should be occasionally stopped = 30 for removal of the accumulations. Simulations and practice have revealed that prior = art positions and alignments of propellers of mixers within an accept tank will create excess turbulence, differently flowing areas and even counterflows within the tank.

The object of the invention is to achieve best mixing results with least energy consumption and least precipitation of particles within an accept tank. These and other objects that will be apparent from the following summary and description are achieved by the accept tank arrangement according to the appended claims.

An accept tank for mixing of pulped fiber suspensions has sidewalls which have a form of two opposite arched ends and an elongated section between the arched ends. The tank has an accept outlet and it may have a reject outlet. The accept tank has at least two mixers and at least one of the mixers are located within the arched end. The mixers have propellers at ends of their axles. At least two of the mixers should have an axle which horizontally points to the direction of the elongated section. The axles should point to the same side of the tank when looked from the arched end where the mixer is attached. The center line of at least one axle of a mixer is aimed at a point, which is at the sidewall of the elongated section at least 25% of the length away from the beginning of the elongated section.

Advantageously the length of the tank is 1,5 to 2 times longer than is the width of the tank for best flow conditions. The propellers of the mixers should have a diameter which is from 10% to 20% of the width of the tank for creating suitable sized flow.

Preferably the number of the mixers is two as the number of mixers also raises manufacturing and operation costs. One mixer is not adeguate for the purpose.

Preferably the propellers are positioned and/or aligned symmetric with respect to the centerpoint of the accept tank. In simulations, the feature that the axle is angled

N 25 away from the centerline to point to the sidewall of the elongated section, creates

N most evenly distributed speed of flow within the tank. At least the said axle of the ? mixer which points at the sidewall of the elongated section should point to the other

N side of the tank than the side where the accept outlet is located. For best flowing j properties, the propeller at the end of the at least one axle should be located within = 30 the arched end. The location and position of the accept outlet may affect to the flow, = so that the optimum position and alignment of the propeller at that side may differ from the optimum alignment for the other propeller at other side of the accept tank.

Advantageously within the center of the elongated section is an elongated centerpiece, which has a length which is at least 50 % of the length of the elongated center section. Then there would not be standing water and turbulences between the different direction of flows at the centerline of the tank. Preferably, the elongated centerpiece has rounded ends and a width which is less than 30 % of the width of the elongated center section. The tank should have an essentially flat bottom at least within the elongated section of the tank. So, even though it has slanted or concave bottom, variation of depth should be below 5 % of the length of the elongated section. Ouite flat bottom prevents particles accumulating within the area.

Advantageously at least a part of the accept outlet is positioned in flow direction at least partially at the end half of the elongated section and/or within the arched end opposite to the side of the mixer. A reject outlet is preferably located at bottom of at least at one of one the ached ends of the tank. The reject outlet is preferably positioned in flow direction after the accept outlet within the same elongated section or at the next arched end.

List of drawings

The invention will be described in more detail with reference to the appended drawings in which:

Fig. 1 illustrates a top view of an embodiment of an accept tank arrangement and fig. 2 illustrates a side view of the accept tank arrangement. = 25 Detailed description of the invention & 3 Fig. 1 illustrates a top view of an embodiment of an accept tank arrangement and a fig. 2 illustrates a side view of the accept tank arrangement. An accept tank is

E usually placed under a screened end part of a drum pulper, which processes o 30 — wastepaper or other fibrous material. Suspension of pulped fibers and small 8 particles drop through the screen to the accept tank directly or flow down along a

S funnel part 5 surrounding the tank. The accept tank preferably has a substantially flat bottom at least at central elongated section 1 The elongated section 1 has sidewalls 3 which are normally vertical and straight. The sidewall 3 may also be longitudinally curved, preferably outwards in order to create an ovalform of the tank.

At both ends of the tank are arched ends 2 which have vertical arched sidewalls 4.

A straight section may exist between two arched sidewall 4 sections. The arched corner sections ensure that the flow will smoothly circulate in and out of the arched ends 2. The bottom of the accept tank has preferably bevels 7 at all edges for avoiding steady water and precipitation of heaviest particles at the edges. The direction of the circular flow is marked with an arrow in. fig. 1.

Preferably an elongated centerpiece 6 is positioned within the middle of the elongated section 1 for preventing interaction between right and left direction flows.

For best flow properties, both ends of the elongated centerpiece 6 are rounded. The elongated centerpiece should have enough width in order to minimize turbulence at the ends of it, where the circular flow will turn to another side of the tank.

Preferred width of the elongated centerpiece 6 is between 10% to 30% of the width of the tank.

A mixer 10 normally comprises an electric motor, a gearbox, and an axle 11 with a propeller 12 at the end of the axle 11. The propeller 12 typically creates propulsion flow away to the direction of the center line of the axle 11. Any other combinations — thatis illustrated may be used for the implementing the invention as the main effect is based on the initial position and direction of the propulsion flow. For example, a short propellor axle 11 and a 90 degrees gearbox like in outboard engines can be used instead. The propeller 12 may have a fan tube around it for best propulsion performance, but any stable crossflow obstacles should be avoided for avoiding

N 25 accumulation of fibers around them.

N

S Horizontal alignment a of at least one axle 11 of the mixer 10 is such that the

N centerline of the axle i.e. the thrust vector of the mixer is aimed at a point P, which j is at the sidewall of the elongated section 1 at least 25% of the length of the = 30 elongated section 1 away from the beginning of the elongated section 1. More = advantageously, the point P lies within 30 to 60% of the length of the elongated section 1 from the beginning of the elongated section 1. For best flowing properties, the propeller 12 at the end of the at least one axle 11 is located within the arched end 2. In principle, best flow properties are achieved, if the positions and alignments are symmetric with respect to the centerpoint of the tank. The horizontal alignment a of the at least one axle of the mixers is from 15 to 35 degrees and more preferably from 20 to 30 degrees from the longitudinal center line of the accept tank. Because the accept outlet 10 affects a bit to the flow, the propeller 12 at that side of the tank 5 may be positioned and/or aligned differently depending of the position, dimensions and form of the accept outlet 10.

An accept outlet 8 is preferably positioned far away in flow direction from a propeller 12. The accept outlet 8 may be for example a downward curved tube. The accept outlet 8 tube may be profiled to have an optimized streamlined shape for least drag effect to the circular flow. If the tank has a reject outlet 9, it should be placed after the accept outlet 8, where the flow is slowest and most turbulent. Preferably the reject outlet 9 is located at least partially within the curved end 2. Any known design of a reject outlet 9 with conveying means can be used. Some suitable examples of — reject outlets are disclosed in publication CN108330719.

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Claims

VAATIMUKSET

1. Akseptitankkijärjestely — pulpperoidun — kuitususpension — sekoittamiseksi akseptitankissa, jossa akseptitankissa on sivuseinät (3,4), joilla on muoto joka koostuu kahdesta vastakkaisesta kaarevasta päädystä (2) ja kahdesta pitkänomaisesta osuudesta (1) kaarevien päätyjen väleissä (2) ja akseptitankissa on ainakin kaksi sekoitinta (10), ja ainakin toinen näistä sekoittimista (10) sijaitsee kaarevassa päädyssä (2) ja sekoittimilla (10) on potkurit (12) akseleidensa (11) päässä ja nämä sekoittimien (10) akselit (11) on suunnattu samalle puolelle — akseptitankkia katsottuna kaarevasta päädystä (2), jonne kyseinen sekoitin (10) on kiinitetty ja tankilla on akseptipoisto (8), tunnettu siitä, että ainakin kahden sekoittimen (10) akselit (11) ovat vaakasuunnassa suunnattu kohti pitkänomaista osuutta (1) ja ainakin yhden sekoittimen (10) akselin (11) keskilinja kohdistuu sivuseinän (3) pisteeseen (P), joka on pitkänomaisen osuuden (1) alkua ainakin 25 % pitkänomaisen osuuden (1) pituutta kauempana.

2. Vaatimuksen 1 mukainen akseptitankkijärjestely, jossa mainittu ainakin yksi sekoittimen (10) akseli (11) on toisella puolella pituussuuntaista akseptitankin keskilinjaa kuin akseptipoisto (8) ja tämän akselin (11) päässä oleva potkuri (12) — sijaitsee kaarevassa päädyssä (2).

3. Vaatimuksen 1 tai 2 mukainen akseptitankkijärjestely, jossa sekoittimien (10) lukumäärä on kaksi. N 25

4 Jonkin aiemman vaatimuksen mukainen akseptitankkijärjestely, jossa potkurit 5 (12) on sijoitettu ja/tai suunnattu symmetrisesti akseptitankin keskipisteen suhteen. 2

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5. Jonkin aiemman vaatimuksen mukainen akseptitankkijarjestely, jossa j pitkänomaisen osuuden (1) keskellä on pitkänomainen keskikappale (6), jolla on = 30 — pituus, joka on vähintään 50 % pitkänomaisen osuuden (1) pituudesta. N

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6. Vaatimuksen 5 mukainen akseptitankkijarjestely, jossa pitkänomaisella keskikappaleella (6) on pyöristetyt päädyt ja leveys, joka on vähemmän kuin 30 % pitkänomaisen osuuden (1) leveydestä.

7. Jonkin aiemman vaatimuksen mukainen akseptitankkijarjestely, jossa akseptitankin pohja on tasainen ainakin akseptitankin pitkänomaisella osuudella (1) ja/tai pitkänomaisen osuuden (1) syvyyden vaihtely on alle 5 % pitkänomaisen osuuden (1) pituudesta.

8. Jonkin aiemman vaatimuksen mukainen akseptitankkijärjestely, jossa rejektinpoisto (9) on sijoitettu ainakin osittain ainakin toisen akseptitankin kaarevan päädyn (2) pohjalle.

9. Jonkin aiemman vaatimuksen mukainen akseptitankkijärjestely, jossa ainakin osa akseptipoistosta (8) on sijoitettu pitkänomaisen osuuden (1) puolikkaan loppuosalle, jonne sekoitin (10) suuntautuu ja tai kaarevaan päätyyn (2) vastapäätä sekoitinta (10).

10. Jonkin aiemman vaatimuksen mukainen akseptitankkijarjestely, jossa rejektinpoisto (9) on sijoitettu virtaussuunnassa akseptipoiston (8) jälkeen samaan within pitkänomaiseen osuuteen (1) ja/tai seuraavaan kaarevaan päätyyn (2).

11. Jonkin aiemman vaatimuksen mukainen akseptitankkijärjestely, jossa ainakin yhden sekoittimen (10) akseli (11) on suunnattu vaakasuunnassa 15 - 35 astetta sivuun akseptitankin pituussuuntaisesta keskilinjasta.

12. Jonkin aiemman vaatimuksen mukainen akseptitankkijärjestely, jossa ainakin N 25 — yhden sekoittimen (10) akseli (11) on suunnattu vaakasuunnassa 20 - 30 astetta 5 sivuun akseptitankin pituussuuntaisesta keskilinjasta. <Q O ©

13. Jonkin aiemman vaatimuksen mukainen akseptitankkijarjestely, jossa j akseptitankin pituus on 1,5 - 2 kertaa pidempi kuin akseptitankin leveys. 2 30 O =

14. Jonkin aiemman vaatimuksen mukainen akseptitankkijarjestely, jossa N sekoittimen (10) potkurilla (12) on halkaisija, joka on 10% - 20% akseptitankin leveydestä.