METHOD AND DEVICE FOR TREATING AN AQUEOUS WORKING MEDIUM WITH AT LEAST ONE TREATING FLUID

Abstract: A method and device for treating for instance a paper pulp suspension with at least one treatment fluid has a treatment chamber, in which a rotor (1) rotates and carries a number of rigidly interconnected coaxial rotor rings (23) at its periphery, a number of stationary stator rings (25) being coaxially inserted between the rotor rings, so that at least two annular axial treatment slots (27) are formed between the rotor rings and the stator rings. An inlet member (19) for the working medium and an inlet member (21) for the treatment fluid are arranged on one side of said treatment slots and an outlet for the treated working medium on the other side, the working medium with treatment fluid being subjected to a shearing in the slots. The treatment slots are formed in such a way that their radial extensions increase with increasing distance to the rotational axis (A-A) of the rotor so that a substantially homogeneous shearing velocity is achieved in all of the annular treatment slots.

Description: Method and device for treating an aqueous working medium with at least one treating fluid The present invention relates to a method and a device for treating an aqueous working medium, preferably a pulp suspension, in particular a paper pulp suspension, with at least one treating fluid. In this connection, the expression aqueous working medium is intended to mean clean liquids, solutions, suspensions, such as fibre suspensions. In this description the utilisation of the invention for treating pulp suspensions will primarily be described, since the invention has its principal application in this field, but it must be emphasized that it m no way is limited to this technical field. To give the paper pulp the desired properties, such as for instance brightness, the paper pulp is treated with one or more different treating fluids, for instance chlorine gas or oxygen. The pulp is thereby continuously conducted into a treatment device, m which the treatment fluid or fluids are brought into contact with the pulp fibres. To achieve optimal treatment results it is important that the fibres contact the treatment fluid as uniformly as possible, and for that reason fibres should be spread out to the greatest possible extent and the treatment fluid be homogenously distributed m the suspension. In prior so called low intensive devices the concentration of the treatment fluid of the pulp was medium low to low m order to achieve the desired even quality of the fully treated pulp. These low intensive treatment devices have to an ever increasing extent been replaced by high intensive treating devices with a high concentration of the treatment fluid m relation to the previous types. Current devices of this latter type unfortunately suffer from the drawback that the treatment zone, where the working medium undergoes a shearing ;o mix the fibres and there it is subjected to the treatment fluid, does not show a completely homogenous shearing field, which has the consequence that either, 1. a part of the suspension will be incompletely treated, or 2. a part of the suspension will be "overtreated" . The treatment according to point 1 results in a homogenously treated final product, whereas a treatment according to point 2 means that too much treating fluid has to be supplied to the suspension and/or that unnecessarily much energy needs to be supplied to the pulp suspension. Both of these alternatives add to the costs. A treatment device of this type for treating pulp suspensions is disclosed m SE, C, 8001970-6. This device comprises an axial inlet for the pulp suspension, which opens into a mixing chamber, m which a rotor is arranged. The pulp is fed through and is sheared m an annular slot, which is delimited Dy a stator ring and the rotor. The supply fluid is conducted through an axial inlet to the plane end surface of the rotor and thereafter flows radially along this surface up to and into the shearing slot where it is mixed with the suspensior. , whereafter the treated pulp flows out through a tangential outlet arranged after the slot. As shown m figures 7 and 8 of this publication, the shearing area may be divided into several annular shearing slots having the same radial extension formed by several rotor connected rotor rings, which are inserted between interconnected stator rings. Since the present invention to a substantial extent is based on tnis known technique, reference is made to this publication for a more detailed description of the principal construction. However, it should be noted that this known solution suffers from the above stated shortcomings with respect tc mhomogeneous shearing fields. The oD]ect of the invention is to provide a method and a device of the above kind defined m the preambles of the corresponding independent claims to treat a working medium by a treatment fluid, which give a treatment zone with a shearing field which allows a substantially homogenous treatment of the working medium at a lower price than hitherto r.as been possible. This cD]ect is achieved by the method and the device according to the invention by the measures defined m the characterizing portion of the independent method claim and by the features defined m the characterizing portion of the independent device claim. In tne following description a couple of embodiments w ll be described in more detail with reference to the accompanying drawings, in which: Figure 1 is a side view, partly sectioned, of a first embodiment of the invention, Figure 2 is a side view, partly sectioned, of a second embodiment of the invention, Figure 3 is a side view, partly sectioned, of a modification of the invention, Figure 4 in a corresponding manner as figure 1-3 shows a further modification of the invention, Figure 5 shows a section on a larger scale of an embodiment of the slot area of the treatment zone. With reference to figure 1, a first embodiment of the device according to the invention comprises a rotor 1, which is fixed on an elongated shaft 3, which is rotatably journalled in a bearing unit 5, not shown in detail. The disc shaped rotor 1 rotates in a cylindrical mixing or treatment chamber formed by a main housing 7, which is covered at the bearing unit side by an end gable 9. The rotor shaft 3 extends through the end gable 9 and is sealed to the latter with traditional sealing means to prevent leakage. A tangential outlet 11 discharges the treated working medium, which in this case is a paper pulp suspension from the treatment chamber. The suspension enters into the treatment chamber 7 from an inlet housing 13, which is connected to the latter and which in the opposite end is sealed with an end plate 15, comprising a central extension 17. A pulp suspen- sion is fed into the inlet housing 13 through an inlet member 19. An inlet member in the form of a pipe connection 21, which opens just ahead of the rotor disc 1, is intended to conduct the treatment fluid for treating the working mediur. to the chamber. At the periphery of the rotor disc 1 a number of con- centrical rings 23 are rigidly connected to the rotor to rotate with the latter as a unit . On the inside 1 of the cylinder wall of the main housing 7 a corresponding coaxial ring arrangement 25 is fixed to a flange 29, which is secured to the cylinder wall. The rotor rings 23 and the stator rings 25 are coaxially interconnected and dimensioned so that several ring shaped shearing slots 27 are formed between them, see also figure 5. As far as is now described the construction corresponds to the device described in the aoove mentioned patent SE, C, 8001970-6, especially figures 7 and 8 with associated text. Thus, the pulp suspension is fed through the inlet member 19 into the inlet housing 13, from where it is conducted to the treatment chamber of the mam housing 7, and is pushed through the ring slots 27 formed by the rotor rings and the stator rings 23 and 25, respectively, m which ring slots 27 the pulp suspension simultaneously is subjected to shearing. The treatment fluid flows through the fluid inlet member 21 towards to the rotor disc and is radially αeflected towards the ring slots 27, m which it affects and 301ns the pulp suspension. After finished treatment m the treatment zone the treated suspension is discharged through the outlet 11. The first embodiment shown 1 figure 1 m many respects differs from prior art. A substantial functional difference is that the inlet member 19 in the inlet housing 13 for the pulp suspension is tangential . This arrangement causes the pulp to rotate already in the inlet housing which increases the dynamic movements of the liquid and is very favourable to the mixing course with the treatment fluid and minimizes the energy required for guiding the suspension into the treatment zone. Furthermore the inlet housing can be assembled m an optional angle to the mam housing 7. This makes possible various assemblage alternatives, which gives a great freedom of choice with respect to installation and pipelining. The inlet member 21, into one opening 31 of which the treatment fluid is supplied to be discharged under pressure through tne opposite opening of the pipe, can be axially ad3ustable to ad3ust the distance to a distribution plate 33 connecteα to the rotor 1 response to the amount and properties of the treatment fluid and the suspension. The treatment fluid hits this distribution plate after having left the inlet member 21 and flows radially along the latter and is spread like a plume along plate 33 up to the treatment zone A great advantage of the proposed solution is that the rotor disc 1 with the rotor rings 23 can be removed as a unit without need for removing pipelinings and other equipment. At the same time also the stator rings 25 are uncovered, so that the treatment zone can be readily cleansed and inspected when necessary. As mentioned previously the known multislot solution suffers from the shortcoming that the shearing fields in the treatment zone are mhomogeneous , resulting the drawbacks stated m the introductory portion of this description. The invention solves this problem by the particular design and dimensioning of the ring slots, whereby reference is now made to figure 5 showing a section on a larger scale of the upper half of the treatment zone. In this drawing the stationary stator rings 25 are square cross-hatched, whereas the rotor rings 23 are only obliquely cross-hatched. The ob3ect of the invention is to provide a mechanical treatment of the pulp suspension which is uniform m all slots the treatment zone. This ob3ect is solved according to the invention by making the shearing velocity invariably the same m all slots, which is exemplified the following with reference to figure 5 by a device having five slots. The rotational axis of the rotor is denoted by A-A, the radial distance from this axis to a rotor ring is denoted by r and the current radial extension of the slot is denoted by s 1 . Other numerals which are utilized tne formula below are v x = velocity at the radius r α m m/sec, ω the angular velocity radius/sec and y the shearing velocity s x m the slot . A condition according to the invention is now that the shearing velocity shall be the same and constant all of the slots, i.e. that Y = v 1 /s = constant all slots, s 1 = r. ω/ le that the radial extension of the slot shall be proportional to the radius of the rotor ring surface wnich limits the current slot. Angular velocity and shearing velocity are operational parameters which are predetermined with respect to the special treatment the suspension is to be sub3ected to. It snould be noted that the ring packages can be readily exchanged for treatment under other operational parameters. In such a case note that the radial extensions of the slots are changed according to the new treatment conditions m accordance with the above formula. Suitable radii and ring thicknesses can be easily calculated from the slot geometry and given operational conditions. By the design according to the invention homogenous and constant shearing fields are obtained all slots in the treatment zone with the required strong relative movements between the various fibres the pulp suspension. Thus, the various slots have increasing radial extensions or widths, the further away from the rotor axis A-A of the device they are. Typically, the radial extension varies between 4 and 20 mm, the number of the ring slots can be from two up to ten. In tne further description of embodiments the same reference numerals have to the greatest possible extent been kept to denote identical or similar elements. In figure 2 an embodiment is shown which in principle is designed m the same manner as the above described embodiment with respect to slot widths, but differs from the first one that it comprises two separate slot treatment zones 27 and 39, Doth of which are composed of coaxially arranged rotor rings 23 and 37, respectively, and stator rings 25 and 35, respectively. In the same manner as previously a tubular treatment fluid inlet member 25 extends to the distribution plate 33 to radially distribute the treatment fluid to the first treatment zone 27. The second slot ring package consisting of stator rings 35 and rotor rings 37 is arranged axially downstream of the first slot ring package at the same level thereof and with the same number of slots. This second zone is provided with a second treatment fluid through a second fluid inlet member 43, which s arranged tne first fluid inlet member 21 and wh cn opens 3ust ahead of a second distribution plate 41, which radially distributes the second treatment fluid to tne second treatment zone 37. The first distribution plate comprises a central passage for the second inlet member 43 and Doth tne first and the second inlet members are individually axially adiustable to optimize the mixing course. The distribution plate 33 also prevents the various treatment fluids from being mixed with one another and for this reason there is only a thin slot of some millimetres or less between the second inlet member 43 and the distribution plate 33, which consequently functions as a dynamic sealing. Just as previously the pulp suspension is supplied through tne tangential inlet member 19 of the inlet housing 13 and is thereafter fed to the first treatment zone, the first treatment fluid is being supplied to the pulp 3ust ahead of the inlet the slot treatment zone. From the first treatment zone the pulp flows on towards the second treatment zone, the second treatment fluid being supplied to the pulp 3ust ahead of the inlet of the second slot zone. In th s manner, for example two different fluids can an optimal manner be supplied for treating pulp under the best conditions. Previously one has either been forced to supply two different fluids to one and the same inlet, something which, at least for one of the treatment fluids, does not give optimal treatment conditions, or one has been forced to use a costly series treatment with a first treatment fluid m a first treatment device and a second treatment fluid a second treatment device. Furthermore, it should be noted that one and the same treatment fluid of course can be supplied to both inlets, for instance to obtain a differentiated supply of this fluid. By tne described "twin" arrangement tne suspension car. now be treated m one single device. Although the treatment zones are substantially the same, the same number of slots at the same level, this does not have to be the case but the zones may be located at different levels and have different numcers cf zones order to optimally ad3ust the treatments to the requirements of the treatment fluids and the pulp suspension. Figure 3 shows a modification of the device shown m figure 1. In this case there is a throttling means 45 arranged the inlet housing 13 3ust ahead of the inlet to the mixing chamber of the mam housing 7. The aim of this throttling means is to give the pulp a more turbulent flov. before it enters the treating zone itself. The throttling means 45 also contributes to giving a good initial distribution in the pulp stream. Of course, this modification can also be utilized in the twin embodiment. A further modification, which can be said to constitute something in between the embodiment according to figure 1 and the twin embodiment according to figure 2 can be seen in figure 4. Here one identifies the treatment chamber with one single associated slot treatment zone formed by rotor rings 23 and stator rings 25. In this case there is no similar second slot treatment zone, in spite of the fact that there are two inlet members 21 and 43, respectively, one of which is arranged in the other and opening in front of a distribution plate 41 to the slot treatment zone. On the rotor there is a throttling disc 47 arranged with a passage for the inner inlet pipe 43 in the middle portion. The throttling disc forms a second treatment zone 49 in the mixing chamber upstream of the slot treatment zone with a considerably lower mixing intensity than the latter. Two different treatment fluids with substantially different requirements with respect to treatment can be supplied. Steam may for instance be fed into the inlet member 21 to the throttling disc 47, which is mixed with the pulp in the low intensive zone 49 while a suitable treatment chemical is conducted through the inner inlet member 43 to the slot treatment zone. In all embodiments the ring packages can be disassembled from the bearing unit side.

Claims: CLAIMS 1. A device for treating an aqueous working medium with at least one treatment fluid, comprising a mam housing (7) forming a treatment chamber, a rotatable rotor (1) arranged m said treatment chamber to rotate about aa axis (A-A) , a number of rigidly interconnected coaxially arranged rotor rings (23) carried by the rotor at the periphery of the rotor, a number of stationary stator rings (25) coaxially inserted between the rotor rings, at least two annular axial treatment slots (27) being formed between the rotor rings and the stator rings, inlet members (19 and 21 respectively) for the working medium and the treatment fluid arranged at one side of said treatment slots, and an outlet (11) for the treated working media m the treatment slots (27) arranged on an opposite side of said treatment slots, whereby the working medium is sheared m said treatment slots during operation, characterized in that the radial extension of said annular treatment slots (27) increases with increasing distance to said axis (A-A) of the rotor (1) so that a substantially homogenous shearing velocity is achieved m all of said annular treatment slots. 2. A device according to claim 1, characterized in that the radial extension (s of each annular treatment slot (27) is directly proportional to tne radius (r.) of the confining surface of the rotor ring (23) that defines this annular slot (27) . 3. A device according to claim 1 or 2 , characterized in that an inlet nousmg (13) with a cylindrical inlet chamber is connected to the mam housing (7) and is provided with a tangential inlet (19) to the inlet chamoer for the working medium, wnereby the working medium forms a swirl m the inlet chamber cefore it enters the treatment chamber of the inlet housing. 4. A device according to one of claims 1-3, characterized in that the treatment fluid is supplied through a central treatment fluid inlet memoer (21) opening at a distance from a distribution means (33) connected with the rotor (1), said distribution means being arranged to distribute the incoming treatment fluid radially towards the annular treatment slots (27) . 5. A device according to claim 4, characterized in that the distribution means is a substantially annular disc (33) . 6. A device according to claims 4 or 5 , characterized in tnat the opening of the treatment fluid mlet member (21) is axially ad3ustable relative to the distribution means (33) . 7. A device according to one of claims 1-6, characterized in that a throttling means (45) for the working medium is arranged oetween the working medium mlet member (19) and tne treatment chamber to give the working medium a turbulent flow before it enters the treatment chamber. 8. A device according to one of claims 1-7, characterized in that a treatment zone (35, 37, 39; 49) for further treating the working medium with a second treatment fluid is arranged m the flow path of the working medium m the treatment chamber. 9. A device according to claim 8, further comprising a central treatment fluid mlet member (21) for the supply of the first treatment fluid, characterized by a second fluid mlet member (43) for supplying the second treatment fluid, one treatment fluid mlet member being arranged m the other. 10. A device according to claim 9, characterized in that Doth treatment fluid inlets members (21, 43) are axially ad3ustable independently of each other. 11. A device according to one of claims 8-10, characterized in that tne rotor (1) is provided with a first and a second distribution means (33, 41) for the first and the second treatment fluid, respectively. 12. A device according to claim 11, characterized in that the distribution means is constituted by two annular plates (33, 41) spaced apart and lying perpendicular to the axis (A-A) . 13. A device according to one of claims 8-12, characterized in that the second treatment zone is formed by a radial throttling disc (47) connected to the rotor (1) , the second treatment zone being formed to provide a lower mechanical working intensity than the first zone. 14. A device according to one of claims 8-12, characterized in that the second treatment zone is formed by second coaxial rotor rings (37) , m which second stator rings (35) are coaxially inserted to form second treatment slots (39) . 15. A device according to claim 14, characterized in that the second treatment slots like the first treatment slots have radial extensions that increases with increasing distance from the axis (A-A) of the rotor. 16. A device according to claims 15, characterized in that the treatment zones are formed to provide different shearing velocities . 17. A device according to one of claims 1-16, characterized in that tne elements of the device can be disassembled from the bearing unit side. 18. A metnod of treating an aqueous working medium with a treatment fluid m a device according to any of the preceding claims, tne working medium being conducted from an mlet housing (13) to a treatment chamber of a mam housing (7) with a treatment zone, m which coaxially arranged rotor rings (23 are rigidly connected to a rotor (1) having a rotational axis (A-A) and stator rings (25) are coaxially inserted oet een the rotor rings, so that at least two annular treatment slots (27) are formed, the working medium being suoiected to shearing m said slots when flowing through tne latter and a treatment fluid oemg supplied through treatment fluid mlet members (21 upstream of the treatment zone, characterized by designing the slots (27) so that the the radial extensions of the slots increase with increasing distance from the axis (A-A) of the rotor (1) . 19. A method according to claim 18, characterized by designing each slot (27) so that the radial extension thereof is proportional to the distance from the rotor ring (23) of the slot to the axis (A-A) of the rotor (1) .

Inventors: DANIELSSON MAGNUS, FORSLUND KJELL, KRISTROEM KLAS, DANIELSSON, MAGNUS, FORSLUND, KJELL, KRISTROEM, KLAS
Applicants: DANIELSSON MAGNUS, FORSLUND KJELL, KRISTROEM KLAS, SUNDS DEFIBRATOR IND AB, DANIELSSON, MAGNUS, FORSLUND, KJELL, KRISTROEM, KLAS, SUNDS DEFIBRATOR INDUSTRIES AB
Application year: 1998
Main classification: B01F7
IPC codes: B01F7, D21C9