DEVICE FOR ADMIXING A PROCESSING AGENT TO A PULP SUSPENSION

Abstract: A device for admixing a processing agent to a pulp suspension in a bin, which device is intended to be attached to the bin wall and comprises a conical housing (1) with a rotary shaft (6), on which a propeller (12) with a hub (7) is attached. The propeller is enclosed by a nozzle (11) for accelerating the pulp in the bin. The housing (1) comprises also a dilution chamber (5) for the processing agent and has an aperture (15) to the hub (7). A gap (8) for supply of processing agent to the pulp suspension is defined between the housing (1) and the nozzle (11) in the inlet end of the nozzle (11).

Description: Device for admixing a processing agent to a pulp suspension This invention relates to a device for admixing a processing agent to a pulp suspension in a bin. The agent can consist of liquids and chemicals, substantially in fluid state, for dilution or other treatment. At all kinds of pulp processing, a persistently continuous and proportional admixture of processing agent to the pulp is of decisive importance for obtaining an acceptable result. In known devices the processing agent is admixed in the lower portion of a pulp bin. The mixing device comprises a propeller, which accelerates the pulp to a high rate through a nozzle whereby surrounding pulp is sucked in continuously. The processing agent is added to the pulp before it is sucked into the mixing device. High pulp concentration in the bin, for example 12%, however, implies a problem for achieving continuous admixing. In order to reduce this problem, the bin has been designed so as to have a bottom zone of reduced size. This, however, results in a decrease in processing volume and in a more complicated and more expensive bin design. Such an arrangement also requires more energy, due to an incomplete admixing technique. According to the present invention, the above problem is eliminated in that the processing agent is added and distributed centrally, and the pulp flow is improved. The mixing result is improved, and at the same time the energy consumption is minimized. The characterizing features of the invention are apparent from the attached claims. The invention is described in greater detail in the following, with reference to the accompanying drawing showing an embodiment of the invention. Fief. 1 is a cross-section of a mixing device according to the invention; Fig. 2 is a section according to II-II in Fig. 1; Fig. 3 is an alternative embodiment of the invention. The mixing device in Fig. 1 comprises a.conical housing 1 with a flange 2 to be attached in the lower portion of a bin for the pulp suspension to which the processing agent is to be admixed. The housing 1 comprises a supply chamber 3 with a connection 13, through which the processing agent is introduced. In the housing 1, a rotary shaft 6 is located which is supported in bearings 9 and which via a sealing 4 extends into the bin. The shaft 6 is driven by a motor (not shown) located outside the bin. At the other end of the shaft 6 a propeller 12 is attached and formed with a hug 7. The internal portion of the housing 1 located nearest to the propeller hub 7 consists of an overall dilution chamber 5, which communicates with the supply chamber 3 through a passage 14. The dilution chamber 5 has an annular aperture 15 to the hub 7. Between the housing 1 and the hub 7 a gap 8 is defined which is adjustable by moving the shaft 6 axially. The gap embodies preferably 360° of the circumference. The sealing 4, which substantially is a mechanical one, is located in direct connection to the dilution chamber 5 and, therefore, does not come into contact with the pulp suspension, whereby clogging is prevented. On the conical housing 1 with flange 2 a number of guide bars 10 are attached. The guide bars 10 are substantially radial and constitute a hold for the nozzle 11, which is located about the propeller 12 and comprises a converging inlet and, respectively, outlet portion and a substantially σylindric central portion. The guide bars 10, preferably at least eight in number, extend along the entire length of the nozzle 11 in such a manner, that the outer diameter of the guide bars 10 coincides with the inlet diameter of the nozzle 11. In the cylindric portion of the nozzle 11, the inner diameter of the guide bars 10 is constant. The distance between the blades of the propeller 12 and the guide bars is 10-15 mm. The processing agent is introduced via the chamber 3 to the dilution chamber 5, from which the agent is distributed all about the adjustable gap 8. At its egress from the gap 8, the agent is admixed to the pulp suspension when the suspension by action of the propeller 12 passes the mixing zone outside the gap 8 at a high rate. The flow of the pulp suspension there is substantially greater than that of the processing agent. The admixing takes place by means of the blades of the propeller 12 against the guide bars 10. The guide bars 10 prevent concurrent rotation of the pulp in the inlet to the nozzle 11. The pulp flow, therefore, is substantially laminar all the way to the gap 8. Due to the rotation, the pulp jet leaving the nozzle 11 at a high rate has a greater cast length and at the same time also the through flow increases. This results in a very efficient admixture. In the embodiment according to Fig. 3 a number of holes 16, e.g. 4-8, are made through the hub 7. Further, a second gap 17 is arranged in the hub in front of the blades of the propeller 12. In this embodiment a part of the flow of the processing agent is passing through the holes 16 in the hub 7 and out through the gap 17 for admixing to the pulp suspension after the blades of the propeller 12, counted in the direction of flow. Such an embodiment can be advantageous in some installations. Also, instead of the second gap in the hub there can be arranged a number of holes. The admixture preferably is carried out at a pulp concentration of 1-8% in the mixing zone. The energy input for the mixing work can be limited to 0.5-1.5 kW/m 3 pulp. The rate in the mixing zone can be 1-3 m/sec. The invention is not restricted to the embodiment shown, but can be varied within the scope of the invention idea.

Claims: Claims 1. A device for admixing a processing medium to a pulp suspension in a bin, which device is intended to be attached to the bin wall and comprises a conical housing (1) with a rotary shaft (6) , on which a propeller (12) with a hub (7) is attached, which propeller is enclosed by a nozzle (11) for accelerating the pulp in the bin, c h a r a c t e r i z e d in that the housing (1) also comprises a dilution chamber (5) for the processing agent, with an aperture (15) to the hub (7) , and a gap (8) for supply of processing agent to the pulp suspension is defined between the hub (7) and the housing (1) in the inlet end of the nozzle (11) . 2. A device as defined in claim 1, c h a r a c t e r i z e d in that the gap (8) extends all about the entire circumference. 3. A device as defined in claim 1 or 2, c h a r a c t e r i z e d in that a sealing (4) for the shaft (6) through the bin wall is located in direct connection to the dilution chamber (5) without contact with the pulp suspension. 4. A device as defined in any one of the preceding claims, c h a r a c t e r i z e d in that the bars (10) are provided in the nozzle (11) outside the gap (8) and propeller (12) , and the guide bars simultaneously constitute a hold for the nozzle (11) . 5. A device as defined in any one of the preceding claims, c h a r a c t e r i z e d in that the gap (8) is adjustable by axial movement of the shaft (6) . 6. A device as defined in any one of the preceding claims, c h a r a c t e r i z e d in that a number of holes (16) are made through the hub (7) for supply of a part of the flow of the processing agent to the pulp suspension after the blades of the propeller (12) , counted in the direction of flow. AMENDED CLAIMS [received by the International Bureau on 1 November 1993 (01.11.93); original claims 2 and 5 cancelled; claims 1,3,4 and 6 amended renumbered as claims 1-4 other claims unchanged (1 page)] 1. A device for admixing a processing medium to a pulp suspension in a bin, which device is intended to be attached to the bin wall and comprises a conical housing (1) with a rotary shaft (6) , on which a propeller (12) with a hub (7) is attached, the housing (l) comprising a chamber (5) for the processing agent, with an aperture (15) to the hub (7) , c h a r a c t e r i z e d in that a gap (8) for supply of processing agent to the pulp suspension is defined between the hub (7) and the housing (1) in the inlet end of the nozzle (11) , the gap (8) which extends all about the entire circumference being adjustable by axial movement of the shaft (6) , that the propeller is enclosed by a nozzle (11) for accelerating the pulp in the bin and that substantially radial guide bars (10) are provided in the inlet to the nozzle (11) , said guide bars (10) simultaneously constituting a hold for the nozzle (11) . 2. A device as defined in claim 1, c h a r a c t e r i z e d in that a sealing (4) for the shaft (6) through the bin wall is located in direct connection to the chamber (5) without contact with the pulp suspension. 3. A device as defined in any one of the preceding claims, c h a r a c t e r i z e d in that the bars (10) extend along the entire length of the nozzle (11) outside the gap (8) and propeller (12) . 4. A device as defined in any one of the preceding claims, c h a r a c t e r i z e d in that a number of holes (16) are made through the hub (7) for supply of a part of the flow of the processing agent to the pulp suspension after the blades of the propeller (12) , counted in the direction of flow.

Inventors: FORSLUND KJELL, FORSLUND, KJELL
Applicants: FORSLUND KJELL, SUNDS DEFIBRATOR IND AB, SUNDS DEFIBRATOR INDUSTRIES AKTIEBOLAG
Application year: 1993
Main classification: B01F7
IPC codes: B01F7, B01F15, D21B1, D21C9