FI129135B

FI129135B - Wash nozzle assembly for atmospheric diffusers in pulp production

Info

Publication number: FI129135B
Application number: FI20185526A
Authority: FI
Inventors: Paavo Tolonen
Original assignee: Andritz Oy
Priority date: 2018-06-08
Filing date: 2018-06-08
Publication date: 2021-08-13
Also published as: WO2019234306A1; EP3802948A1; FI3802948T3; FI20185526A1; EP3802948B1; JP2021527174A; JP7495357B2

Abstract

A wash nozzle assembly for all type of atmospheric diffusers, which nozzle assembly comprises a nozzle which has a wash flow controlling orifice plate or another orifice assembly preferably located at the trailing edge of the nozzle, a orifice locking plate and fixing screws. The wash nozzle assembly is similar for all washing stages in the diffuser. The wash nozzle assembly is direct replacement for all existing nozzles and does not require any modifications for the diffuser.

Description

WASH NOZZLE ASSEMBLY FOR ATMOSPHERIC DIFFUSERS IN PULP PRODUCTION

FIELD OF THE INVENTION The present invention relates to a wash nozzle assembly for atmospheric diffuser washers in the production of chemical cellulose pulp at a pulp mill. The wash nozzle assembly according to the invention may be applied in all types of atmospheric diffusers used for brown stock washing, oxygen delignification and pulp bleaching.

BACKGROUND OF THE INVENTION The following description assumes a two-stage atmospheric brown stock diffuser following a continuous digester. Digester pressure is used to blow the pulp through the blow line into the two-stage diffusion washer. The conical section of the diffuser tank is designed to allow the up flowing stock to be evenly distributed across the diffuser. Inside the diffuser tank are concentric screen rings arranged about a common vertical axis. The lower row of screen rings forms the first washing stage, and the upper row, the second stage. Each washing stage consists of screen rings equally spaced. Between each screen rings there are 1-2 pcs. of wash nozzles which are rotating in order to supply wash water or wash O liguor evenly into pulp between the screen rings. Each screen ring is comprised & of two screen plates spaced approximately 50-60 mm apart. Q 25 The number of rings per row and their height are dependent upon the design = production of the diffuser and stock drainage characteristics. Three, four or six a © arms located between the first and second stages serve to support the screen io assembly and transport extracted filtrate from the screens. 00 > These arms radiate from the diffuser center to the tank's outside wall where they are supported by vertical tie rods which are coupled to hydraulic cylinders. These cylinders give the screen assembly a vertical stroking cycle. The upstroke speed is adjusted to be slightly greater than the up flow rate of the pulp mass.

The diffuser is held at the top of its stroke for some time, and is then down stroked rapidly (approximately one second) in order to clean the screens from fibers.

The extraction flow is shut off and the wash flow reduced during the top delay and down stroke.

As the pulp in a consistency of around ten percent flows upward between the screen rings, clean wash filtrate displaces the dirtier filtrate which is extracted through the screens and arms to a filtrate tank.

First stage extracted liquor is pumped to the cold blow pump or previous stage washer.

Second stage extracted filtrate is returned to the diffuser and is used as first stage wash filtrate.

Heated wash water (decker filtrate, evaporator condensate, etc.) is used to wash in the second stage.

Wash filtrate /water for each stage enters the diffuser through a wide slot in the trailing edge of the wash nozzles.

Both first and second stage wash nozzles rotate with the hollow central shaft in circular paths centered — between the screen rings.

The wash filtrate flow to each of the pulp segments created by the screen rings is controlled by orifice plates in the wash nozzles, and is proportional to the volume of pulp between each ring.

Wash nozzles for the first stage are mounted on a common arm located below the screen rings.

This arm is attached to the central shaft.

The central shaft serves to transport wash filtrate for both the first and second stages.

Second stage wash nozzles are attached to the top scraper assembly above the screen rings.

A previously known wash nozzle assembly is disclosed e.g. in document EP0720674 B1 Typical problems with the existing wash nozzles are: N 25 — (i) tendency for clogging by fibers coming from the diffuser tank and entering > backwards into the nozzles.

As the wash filtrate flow velocity through the nozzle is = rather low it cannot keep the fibers away.

Especially the lower wash nozzles (1st N washing stage) are susceptible to clogging.

This is because of gravity as well as z the location of an orifice plate between the nozzle and nozzle arm.

Thus there is © 30 nothing to prevent the pulp from entering to the nozzle if the wash filtrate flow 3 cannot do it.

The clogged nozzles are unable to supply and distribute a sufficient > amount of wash water and the washing efficiency of the diffuser is therefore significantly decreased.

Typically the most susceptible for clogging are the outermost nozzles.

This may be the result of a high velocity of the rotating nozzle which sucks the pulp into the nozzle if the water flow is simultaneously slow. Tendency of clogging of lower nozzles is observed also during short outages when the diffuser tank is not emptied but the wash filtrate feed is closed. (ii) Existing wash nozzles have limited ability to distribute wash liquid due to its construction. (iii) Difficult and time consuming cleaning operation of clogged nozzles which extends diffuser downtime and decreases its availability.

SUMMARY OF THE INVENTION A novel wash nozzle assembly for atmospheric diffusers has been developed so that it prevents pulp fibers from getting from the diffuser tank into the nozzles. This is arranged so that the orifices for adjusting a desired flow of filtrate or water are located right at the point where the wash liquid is released from the nozzle into the pulp, preferably at the trailing edge of the nozzles. The orifice plate / orifice assembly may be located also on another place on the nozzle to release the wash liquid directly into the pulp mass. The nozzle assembly according to the invention is characterized by the characterizing features of the independent claim. The new nozzle type gives significantly more even wash liquid distribution into the pulp as the liquid may be spread on a full height of screen unit and screen area and thus displacement is more efficient. This means an improvement in washing results. O The nozzle is typically vertically elongated and oblong in cross-section. It has a & vertically elongated opening, which is provided with an orifice plate or an orifice e 25 assembly. The opening edges in the nozzle wall are provided with vertical N grooves for disposing and attaching the orifice plate to the nozzle body.

I a a © The nozzle body has a first end and a second end. The first end is provided with a io plate-like extension for the attachment of the nozzle to a nozzle arm in the diffuser © vessel. The first end is open so that wash liquid can be led from the nozzle arm to o N 30 the nozzle interior. The elongated opening with an orifice plate starts at a distance from the first end and extends up to the second end.

The length of the elongated opening depends on the required liquid flow.

The nozzle moves in a direction of the rotation, and so it has a leading edge, a trailing edge, and side edges.

The orifice plate/orifice assembly is preferably located at the trailing edge.

It may be located also at the leading edge, whereby a shielding element is needed in front of leading edge so that the pulp flowing against the nozzle will not prevent the liquid outflow from the nozzle.

The shielding element may be a V-shaped plate.

The orifice plate/orifice assembly may be located at the side edge(s) of the nozzle, whereby a shielding element may also be needed.

The wash nozzle assembly typically comprises a nozzle, an orifice plate with or without a lip type of non-return device.

A pair of the lips releases a wash liquid flow from the orifice into the pulp because wash water or wash filtrate pressure opens the lips.

The pair of lips is closed due to flexibility of the lips immediately once wash flow is stopped and therefore pulp entering into the nozzle is prevented.

The orifice is either a perforated plate with small holes creating a sufficient open area for required flow and also prevents, due to small holes, pulp fibers from entering into the nozzle, or an orifice plate with certain number of holes having a diameter of 5 — 30 millimeters (mm), preferably 8-20 mm, for the flow adjustment and a lip type of non-return for preventing fibers from entering into the nozzle.

The size and number of the holes depend on the open area required for a desired wash liquid flow.

The perforated plate has a plurality of holes having a diameter of 0,4 - 5 mm, typically 1-2 mm.

N 25 The orifice assembly may further include a non-return device comprising flexible, > impervious members of complementary shapes.

Typically the non-return device is = formed of a pair of lips which are disposed face-to-face in surface contact, so that N there is no through passage between them when the wash liguid is not introduced z into the pulp.

In-flowing liquid will force the lips apart to permit flow between them © 30 from the nozzle through the orifice plate holes to the pulp.

Flow in the opposite 3 direction is prevented by the close surface contact between the lips.

Thus, the > mutually contacting lips prevent fiber flow between them towards the holes and the interior of the nozzle, but the liguid entering the pulp can force the lips apart and flow between them.

The lips are typically made of a thin plate of hardened stainless steel and fixed to the orifice plate with screws or corresponding fastening means. The lips may also be made of plastic or another flexible material. The orifice plate may also have a slot or slots having a size sufficient for a certain 5 wash liquid flow. The wash nozzle may also have an orifice assembly comprising a plurality of non- return valves attached to the orifice plate. The non-return valves may be commercial products or prepared for the new nozzle. The wash nozzle wall has preferably vertical grooves, typically two, for all kind of orifice assemblies and a locking plate and screws for keeping said assembly in place. The new wash nozzle assembly gives higher washing result, because the wash liquid is distributed more evenly into the pulp and the displacement of the dirty liquor is therefore improved. The new wash nozzle assembly significantly reduces the cleaning and replacement time of nozzles in two ways. First, the nozzles are kept long clean as the nozzles cannot be clogged by the pulp from the diffuser tank. Secondly, the orifice plates/orifice assemblies are detachable from the nozzle body and so easy to withdraw out from the nozzles. Thus the possible cleaning of nozzles can be done without detaching the whole heavy nozzles. These are the significant advantages which decrease a needed downtime. The new wash nozzle is similar for all stages of diffuser washers and acts as lower and upper nozzle. It can be used also in a one-stage diffuser. The new wash nozzle assembly can be installed without any changes for all type N of existing nozzle arms by replacing existing nozzles.

N © 25 The nozzles are arranged in an atmospheric diffuser, which typically comprises a Q generally upright vessel having a central vertical shaft; a plurality of annular =E screens which have been mounted concentric with the central vertical shaft; and a © an arm assembly which has been mounted vertically spaced from the screens. N The arm assembly is connected to the central shaft and is rotated by the shaft.

LO ® 30 The vertically elongated nozzles are connected to the arm assembly. The nozzles o N are moved by the shaft in the direction of rotation between the screens, and they introduce wash liguid into the pulp between the screens.

BRIEF DESCRIPTION OF THE DRAWINGS In the following the invention is described in more detail by reference to the accompanying drawings wherein. Fig. 1 illustrates a side view of a two stage atmospheric diffuser with a prior art nozzle assembly, where the new nozzle assembly may be applied. Fig. 2 is a detail perspective view showing a two stage atmospheric diffuser screen and a prior art nozzle assembly, where the new nozzle assembly may be applied. Fig. 3 illustrates a prior art lower wash nozzle embodiment. Fig. 4 illustrates a prior art upper wash nozzle embodiment. Fig. 5 illustrates a prior art orifice plate. Fig. 6 illustrates a known lower wash nozzle assembly installed in a nozzle arm where the orifice plate is located between the nozzles and the nozzle arm. Fig. 7 and 8 illustrate a preferable embodiment of the new wash nozzle with an orifice plate and a lip-type non-return device and grooves for orifice assemblies. Fig. 9 illustrates an embodiment of the new wash nozzles orifice /lip assembly withdrawn partially out. Fig. 10 illustrates a detailed cross-section view of the orifice/ lip assembly of the new wash nozzle and a distribution of the wash liquid through the orifice hole and N lip seal into the pulp.

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N O Fig. 11 illustrates a cross-section view of the orifice/ lip assembly of the new wash Oo O nozzle.

N E Fig. 12a and 12b illustrate an embodiment of the new wash nozzle with a © 25 perforated orifice plate

LO (O Fig. 13 illustrates an embodiment of the new wash nozzle's perforated orifice S plate withdrawn partially out.

Fig. 14, 15 illustrate an embodiment of the new wash nozzle with a non-return valve orifice plate assembly. Fig. 16 illustrates comparison of wash liquid distribution between the known and new wash nozzle assemblies.

DETAILED DESCRIPTION OF THE DRAWINGS Fig. 1 shows an exemplary atmospheric diffuser in which the present invention may be applied. The diffuser is shown generally by reference numeral 1. The conventional components of the diffuser 1 include a generally upright vessel having a pulp inlet 3 at the bottom thereof and a pulp outlet 4 at the top. Extraction arms 17 (Fig. 2) are mounted within the vessel, extending radially outwardly from a central shaft 9 which defines the central vertical axis of the vessel. The shaft end is connected to a conventional drive 15. Outlets for displaced filtrate from the extraction arms are provided at 7 and 8. The first outlet 7 is for 2" stage filtrate and the second outlet 8 for 1st stage filtrate. A hydraulic cylinder 14, or like mechanism, is provided to effect up and down reciprocation of the extraction arms 17. The reciprocation is at essentially pulp flow velocity in the direction 19 of pulp flow movement, and at a much higher speed opposite to the direction of pulp flow, as is conventional. A back flush tank is illustrated with reference number 18, and a filtrate tank with reference number 16. Mounted on the extraction arms 17 are a plurality of annular screens, such as first and second screens 2 (Figs 1 and 2) extending upwardly and downwardly from the arms 17. Disposed above the screens 2 is an upper arm assembly 10. = The shaft 15, to which the arm assembly 10 is connected, is driven by a motor a 25 connected to the drive end, so that the arm assembly 10 rotates in a first direction O of rotation, shown by arrows 19 in FIG.2. Connected to the arm assembly 10 is a e plurality of treatment fluid introducing nozzles 11 which are vertically elongated, z and are disposed between the screens 2. The nozzles 11 are typically oblong in a © cross-section 22 (see FIG. 3), and at a second end thereof, remote from the arm io 30 assembly 10, have means defining at least one fluid introducing opening 20, 00 typically at the side of the nozzle 11 that trails as the nozzle 11 moves in the a direction of rotation 19.

Washing liquid is supplied to the nozzles 11 from a conduit 5 (FIG. 1) which extends interiorly of the shaft 9, and to the rotating arms 10, the treatment liquid-- typically wash liquid or bleach liquid--flowing through the arm assembly 10 and then to nozzles 11, to be introduced through the openings, as shown by arrows 5’. Where a two stage diffuser being shown in FIGS. 1 and 2 is provided, at least a second conduit 6 is provided for introducing a second washing fluid, that liquid flowing through a conduit within the shaft 9 to the arm assembly 12 to which the nozzles 13 are mounted.

The nozzles 13 for introducing wash liquid 6’ are disposed between the bottom set of annular screens 2 and the arm 12, which arm is located below the lower screens 2. Both first and second stage wash nozzles 11, 13 rotate with the hollow central shaft 9 in circular paths centered between the screen rings.

Heated wash water (filtrate, evaporator condensate, etc.) is typically used to wash in the second stage.

Wash filtrate /water for each stage enters the diffuser through a wide slot 20 in the trailing edge of the wash nozzles 11, 13. The wash filtrate flow to each of the pulp segments created by the screen rings is controlled by orifice plates in the wash nozzles, and is proportional to the volume of pulp between each ring.

Figs. 3-5 show the details of known nozzles.

As shown in Fig. 3 the lower nozzle 13 is elongated, and oblong in cross-section 22 (Fig. 3). The nozzle has a first end 13a and a second end 13b.

As shown by arrows 5’, the wash liquid flows through the first end into the nozzle and is discharged from the nozzle through a slot 24 located at distances from the first end and the second end.

Fig. 4 shows the upper nozzle 11, which is also elongated and oblong in cross-section, and it has a first end and a second end.

The wash liquid flows through the first end into the nozzle and is discharged through a slot 23 which is N located at the second end, as shown by arrows 6’. The nozzles are attached to > the nozzle arms so that there is an orifice plate 25 between the nozzle and the ? arm.

As shown in Fig. 5, the orifice plate 25 has holes 26 the cross-sectional area N of which is predetermined in relation to the desired liquid flow passing through the E 30 nozzle.

This way the liquid flow is adjusted.

Fig. 6 illustrates how the lower nozzle © 13 is attached to the arm 12. The orifice plate 25 is located between the nozzle 13 E and the arm 12 to which arm the nozzle will be attached.

The wash liquid 6” flows = from the arm 13 through the orifice plate holes to the nozzle 13. The first end of N the nozzle is provided with a plate-like extension 21 for the attachment (Figs. 3, 4 and 6). The upper nozzle 11 is connected to the arm 10 in the corresponding way.

A problem with the known wash nozzles is their tendency to become clogged by fibers coming from the diffuser tank and entering backwards into the nozzles. This can be avoided by using a nozzle according to the present invention shown in Figs. 7-16, which illustrate a lower nozzle of the two stage diffuser, but an upper nozzle may have the same configuration. The nozzle 27 is elongated and oblong in cross-section. It has a vertically elongated opening 38, which is provided with an orifice plate 28 having a plurality of holes for introducing wash liquid into the pulp. The diameter of the holes is 5-35 millimeters (mm), preferably 8-20 mm. The size and number of the holes depend on the open area required for a desired wash liquid flow. The orifice assembly further includes a non-return device 30 comprising flexible, impervious members of complementary shapes. Typically the non-return device is formed of a pair of lips which are disposed face-to-face in surface contact, so that there is no through passage between them when the wash liquid is not introduced into the pulp. In-flowing liquid will force the lips 35 — (Fig. 10 and 11) apart to permit flow between them from the nozzle through the orifice plate holes to the pulp. Flow in the opposite direction is prevented by the close surface contact between the lips. Thus, the mutually contacting lips prevent fiber flow between them towards the holes and the interior of the nozzle, but the liquid entering the pulp can force the lips apart and flow between them. The opening edges in the nozzle wall are provided with vertical grooves 34 for disposing and attaching the orifice plate 28 to the nozzle body 27 (Fig. 8). The lips 30 are attached to the orifice plate with screws 29 or corresponding fastening means. The orifice plate assembly is locked into place by means of a locking plate 31 and locking screws 32. The nozzle body 27 has a first end 27a and a second end 27b. The first end is N provided with a plate-like extension for the attachment of the nozzle to the nozzle > arm, such as the arm 12 in Fig. 1. The first end is open for leading wash liguid ? from the nozzle arm to the nozzle interior. The elongated opening 38 with the N orifice plate 28 starts at a distance from the first end 27a and extends up to the E 30 second end 27b. The length of the elongated opening may be shorter depending © on the required liquid flow.

LO o Fig. 9 shows the orifice plate/lip assembly when it is withdrawn partially out. The N orifice plate with or without lips may simply be removed from the nozzle if there is any need for cleaning or replacing them with new ones.

Fig. 10 shows a top view of the orifice plate/lips assembly at the trailing edge of the nozzle. The orifice plate has been disposed in the grooves in the wall of the nozzle body 27. Wash liquid flows through the hole 28 of the orifice plate and further from between the two mutually opposite lips 35, as shown with arrows 33. — This way the wash liquid is introduced evenly along the length of the nozzle to the pulp, as illustrated in Fig. 7. Fig. 11 shows an embodiment, in which the orifice assembly 28, 35 is located at the leading edge of the nozzle 27. The nozzle is provided with a shielding element, which is a V-shaped plate 40. It is attached to the nozzle so that there is a gap between the plate and the nozzle. Wash liquid flows from the nozzle and through the gap into the pulp, as shown with arrows 33’. The shielding element is needed in front of leading edge so that the pulp flowing against the nozzle will not prevent the outflow of the liquid from the nozzle. Figs 12a and 12 b show another embodiment of the new nozzle. The orifice plate is a perforated plate 36. The holes of the plate are smaller than those in the embodiment of Figs. 7-11 so that their diameter is 0,4 - 5 mm, typically 1-2 mm creating a sufficient open area for a required flow. Such small holes prevent pulp fibers from entering into the nozzle. Figs. 14 and 15 show still another embodiment of the new nozzle 27. The orifice plate is provided with a plurality of non-return valves 37 which allow a wash liquid to flow in only one direction. This way any clogging caused by pulp fibers may be prevented. Fig. 16 illustrates a wash liquid distribution to diffuser screens 2 by using the prior art nozzle 13 and the new nozzle 27. The new nozzle distributes wash liquid 33 N 25 — more evenly along the screen height 39 and the screen area, whereas the known > nozzle is able to distribute wash liquid only to a smaller area. The new nozzle type = gives significantly more even wash liguid distribution into the pulp and thus N displacement washing of pulp is more efficient. This improves washing results. j

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Claims

CLAIMS:

1. A wash liquid introduction nozzle assembly for an atmospheric diffuser, said assembly comprising an elongated vertical nozzle (27) characterized in that the nozzle wall has an elongated opening (38) which is provided with an orifice plate (28) or an orifice assembly comprising an orifice plate for delivering liquid from the nozzle (27).

2. A wash nozzle assembly according to claim 1, characterized in that the orifice plate (28) has an open area for introducing a predetermined flow of the washing liquid from the nozzle into pulp in the diffuser vessel.

3. A wash nozzle assembly according to claim 1 or 2, characterized in that the nozzle has grooves (34) in the nozzle wall for fixing the orifice plate/ orifice assembly.

4. A wash nozzle assembly according to claim 1, 2 or 3, characterized in that the orifice assembly comprises an orifice plate with a plurality of holes having a diameter of 5 - 35 mm, preferably 8 — 20 mm and a lip type (35) of non- return device (30).

5. A wash nozzle assembly according to claim 1, 2 or 3, characterized in that the orifice assembly comprises an orifice plate with a slot or slots having a sufficient size for required wash flow and lip type of non-return device (30).

6. A wash nozzle assembly according to claim 1, 2 or 3, characterized in that the orifice plate is formed of a perforated plate (36) with a plurality of holes having a diameter of 0,4 - 5 mm, typically 1-2 mm.

=

7. A wash nozzle assembly according to claim 1, 2 or 3, characterized N in that the orifice assembly comprises an orifice plate with a plurality of non-return © 25 valves (37).

N

8. A wash nozzle assembly according to any of claims 1-7,

I = characterized in that the nozzle has a leading edge, a trailing edge, and side O edges, and the orifice plate/orifice assembly is located at the trailing edge of the

LO O nozzle.

O N 30

9. A wash nozzle assembly according to any of claims 1-7, characterized in that the nozzle has a leading edge, a trailing edge, and side edges, and the orifice plate/orifice assembly is located at the leading edge of the nozzle.

10. A wash nozzle assembly according to any of claims 1-7, characterized in that the nozzle has a leading edge, a trailing edge, and side edges, and the orifice plate/orifice assembly is located at a side edge of the nozzle.

11. A wash nozzle assembly according to any of preceding claims, characterized in that the nozzle is a nozzle for any washing stage of the atmospheric diffuser.

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