Method and apparatus for removing impurities from paper pulp in pulpers

Abstract: The pulping space, whereto the paper pulp to be purified is conducted, is provided with e.g. a rotor unit and a connecting screenplate. According to the method, the pulping space (2) enclosed by a solid jacket (1,3,4) is divided into a primary and a secondary space (5,12) by means of a partition wall construction (13). Both the primary and the secondary space (5,12) are provided with separate rotor units (6,15) and perforated screenplates (8,16) in connection with said rotor units (5,16). The paper pulp to be purified is conducted into the primary space (5) and a connection between the primary and secondary spaces (5,12) is arranged within the partition wall construction (13).

Description: The invention relates to a method for removing impurities from paper pulp in pulpers where the pulping space into which the paper pulp to be purified is conducted is provided with a rotor unit or the like and a screenplate connecting therewith. Prior art methods and apparatuses are described for instance in publications FI-74496 (equivalent to GB-A-2 128 498), DE-3 639 200 and EP-279 022. The methods and apparatuses presented in these publications contain a separate wash space which connects with the pulping space and is relatively small in volume compared to that of the pulping space. For instance, the apparatus according to FI-74496 or GB-A-2 128 498 is operated and constructed as set forth in the preambles of claims 1 and 4 respectively. Therefore, the methods and apparatuses presented need separate attachments to be connected to the actual pulping space. Handling of the rejected portion is particularly difficult. Application of the methods requires a substantial amount of wash water. The capacity of said methods is low and some of them involve batch operation. The object of this invention is to provide a method by which it is possible to remove impurities from paper pulp - especially the light impurities - in the most efficient way and without interfering with the pulping process, while keeping fiber losses low, so that the extraction efficiency of the impurities remains high. In order to attain these objects, the invention provides a method of removing impurities from paper pulp in pulpers comprising : dividing the pulping space, whereto the paper pulp to be purified is conducted, into a primary and a secondary space; providing both the primary and the secondary spaces with a separate rotor unit or the like, a separate perforated screenplate or the like cooperating with said rotor unit, a separate accepted material outlet and a separate rejected material outlet; introducing the paper pulp to be purified into the primary space; and arranging a connection between the primary and secondary spaces, characterized in that it further comprises enclosing the pulping space with a solid jacket having a lower portion and vertical side portions such that the division between said primary and secondary spaces is effected by means of a vertically-extending partition wall construction, and in that said connection between the primary and secondary spaces is provided within the partition wall construction. The benefits attainable by the method according to the invention are: the method can be applied in connection with either a completely new pulper construction or one already in operation, the method in the latter case having no adverse effect on the pulping time; the method can be implemented on a high capacity pulper and whose volume can be dimensioned according to the needs of purification; the pulper implementing the method can be designed to be configured so that it efficiently prevents the large heavy impurities from entering the screenplate in the secondary space, and efficiently collects the light impurities; by using the pulper implementing the method the bale submerging efficiency is increased; pulping efficiency is increased since two rotor units are provided in the pulping space whereby the power consumption per unit mass of paper pulp to be screened is decreased relative to known solutions; the pulper applying the method can be easily configured and designed so that the outgoing accepted pulp portions can be jointly conducted forward to the following processing stage, so obviating the need for recycling (which decreases the capacity); since the total area of the screening surfaces or the like can be made large, it is possible to use a smaller hole size and thereby achieve a purer paper pulp to be conducted forward for the next processing stage; expensive and large automatic valves are not needed in the method, making the process control cheaper and simpler; removal of the accepted pulp portions from the secondary space can be effected either periodically or continuously e.g. by means of a screw conveyor; in the method, the outlet consistency of the rejected portion removed from the secondary space can exceed 20% so that the subsequent processing of the rejected portion or removal from the pulping process (for instance for use in ballasting or in combustion) can be achieved e.g. by means of belt conveyors. In this respect, it is possible to wash the rejected portion at the screw conveyor, allowing complete collection of fibers using small amounts of water. Also, the accepted portion filtered in the screw conveyor can be conducted to the main pump and forward along the process line; application of the method does not disturb the automation of the rotor unit functioning as the actual pulper in the primary space and does not produce any major consistency variations for the main pump; application of the method, and in particular the design, allows conduction of a major part of the paper pulp through the secondary space, if necessary; when the method is applied, impurities will be conducted into the secondary space, thus making it unnecessary to stop the rotor unit for cleaning the screenplate in the primary space, which functions as the actual pulping space. Other beneficial characteristics according to the method of the invention are set forth in the ensuing sub-claims. The invention also relates to an apparatus for application of the method, as defined in claim 4. The invention is explained in more detail in the following description referring to the embodiment of the enclosed drawings in which: figures 1 and 2 show a vertical cross-section of a pulper applying the method according to the invention; figure 3 shows the pulper of figures 1 and 2 in a horizontal cross-section, seen from above. The application of figures 1-3 comprises a pulping space 2 enclosed by a solid jacket 1. As seen particularly in figure 3, the jacket 1 of the pulping space 2 is essentially circular in its horizontal cross-section. Furthermore, the vertically disposed cylindrical jacket 1 contains an upper end portion 3 on the one hand and on the other hand a lower end portion 4, which essentially restricts the pulping space 2 in the horizontal direction. The paper pulp to be purified is introduced into the pulping space 2 from the side of the upper end portion 3 (not shown) into the primary space 5 accommodating a horizontally rotating rotor unit 6 in connection with the lower end portion 4. The rotor unit 6 has a vertical drive shaft 7, that is parallel to the center line VK of the jacket and is arranged to rotate around said center line VK, passing through the lower end portion 4. Under the rotor unit 6 there is provided a perforated horizontal screenplate 8 through which there is a connection from the primary space 5 into the accepted material outlet chamber 9 below the rotor unit 6 and the screenplate 8, the outlet chamber 9 having an accepted material outlet connection 10. Furthermore, in connection with the lower end portion 4 there is provided an essentially annular groove 11a surrounding the rotor unit having at its lowest portion the rejected material outlet connection 11. The pulping space 2 is also provided with a secondary space 12 by means of a vertical partition wall construction 13 dividing the pulping space 2. The secondary space 12 accomodates a corresponding rotor unit 15 arranged to rotate in a vertical plane round a horizontal shaft 14. In the proximity of the rotor unit 15, the jacket 1 has a perforated vertical screenplate 16 through which there is provided a connection from the secondary space 12 via the rotor unit 15 into the outlet chamber 17 for the accepted portion of the secondary space 12, the outlet chamber 17 having an accepted material outlet connection 18. There is also a rejected material outlet connection 19 in the lower part of the secondary space 12. There is also provided a screw conveyor 20 or the like mounted in contact with the outlet connection 19 of the secondary space 12 for removing the rejected portion from the secondary space. As can be noted in figures 1-3, the primary space 5 is larger in volume than the secondary space 12, this being due to the disposition of the partition wall construction 13. In the horizontal cross-section, the partition wall construction divides the upper cross-section of pulping space 2 (fig. 3) into two segments, the larger one constituting the primary space 5 and the smaller one the secondary space 12. The partition wall construction 13 can be a plate structure attached by its vertical sides to the inner walls of the pulping space 2. The plate structure can be partly or wholly perforated whereby there will be flow of the paper pulp to be purified through the perforations from the primary space 5 into the secondary space 12. Furthermore, the upper part of the partition wall construction 13 in proximity to the surface of the paper pulp may have a directing flow channel 21 extending essentially horizontally and downwards to the secondary space as illustrated particularly in figure 1. This channel is particularly intended to conduct the lighter impurities into the secondary space 12. The flow channel 21 is formed by means of two plates: a plate 13b disposed on the upper edge of the vertical plate 13a of the lower part 13f of the partition wall construction 13 and directed obliquely downwards from said upper edge towards the secondary space 12, and the lower guide plate 13c of the upper part 13e of the partition wall structure 13, disposed over said plate 13b and being situated at a distance therefrom. The lower guide plate 13c, which is essentially parallel with the plate 13b in the vertical cross-section (figure 1), is joined within its horizontal edge facing the primary space 5 to the plate 13d, being directed obliquely upwards away from the primary space 5. Plate 13d thus forms the upper part 13e of the partition wall structure 13 together with plate 13c. The upper edge of the partition wall construction 13 therefore is located below the inner surface of the upper end portion 3 at a distance therefrom. As can be noted particularly in figures 1 and 3, the inner surfaces of the jacket 1 in the pulping space 2 are equipped with essentially vertical flow guide vanes 22 (four of them at a specific distance). The embodiment of the apparatus shown in figures 1-3 functions in the following way: paper pulp is supplied e.g. in bales into the primary space 5 where the bales are broken down and simultaneously mixed with water, which is supplied into the primary space 5 (not shown). In the primary space 5, a rotary motion created by the rotor unit 6 and the accepted portion moves via the blades of the rotor unit 6 from the screenplate 8 through the perforation into the accepted material outlet chamber 9, and therefrom to the outlet connection 10 which is connected to e.g. a pulp vat whereto the pulp is pumped by means of a pump attached to a pipe in the outlet connection 10. The rejected portion drains away through the outlet connection 11 of the primary space 5 and is treated after the outlet connection by means of high pressure water in order to return any usable fibers in the rejected portion into recycling. The paper pulp going into the secondary space 12 through the partition wall construction 13 is driven into rotary motion by the influence of the rotor unit 15 in the secondary space and, via the blades of the rotor unit 15, the accepted portion goes through the perforation of the screenplate 16 into the accepted material outlet chamber 17 and further into a pipe connected to the accepted material outlet connection 18 wherefrom it is further conducted using said pump into a pulp vat. In the processing of the rejected portion, which has been removed from the bottom of the secondary space by means of a screw conveyor or corresponding, high pressure water is used for separating any usable fibers still in the rejected portion.

Claims: Method of removing impurities from paper pulp in pulpers comprising : dividing the pulping space, whereto the paper pulp to be purified is conducted, into a primary and a secondary space (5, 12); providing both the primary and the secondary spaces with a separate rotor unit (6, 15) or the like, a separate perforated screenplate (8, 16) or the like cooperating with said rotor unit (6, 15), a separate accepted material outlet (10, 18) and a separate rejected material outlet (11, 19); introducing the paper pulp to be purified into the primary space (5); and arranging a connection between the primary and secondary spaces (5, 12), characterized in that it further comprises enclosing the pulping space (2) with a solid jacket (1, 3, 4) having a lower portion (4) and vertical side portions such that the division between said primary and secondary spaces is effected by means of a vertically-extending partition wall construction (13), and in that said connection between the primary and secondary spaces is provided within the partition wall construction (13). Method according to claim 1, characterized in that, in the primary space (5), the rotor unit (6) or the like, the screenplate (8) or the like, a drainage channel (11a) and said outlet (11) for the rejected portion are disposed at the lower end portion (4) of the jacket (1), said lower end portion restricting the pulping space (2) in the horizontal direction, and in that in the secondary space (12) the rotor unit (15) and the screenplate (16) are disposed on the vertical side portion of the jacket (1) and the rejected material outlet (19) is disposed at the lower end portion of the secondary space (12). Method according to claims 1 and 2, characterized in that the connection between the primary and secondary spaces (5, 12) within the vertically-extending partition wall construction (13) is accomplished by making the partition wall (13), or at least a portion of its area, penetrable by paper pulp by means of perforations and/or providing the upper portion of the partition wall construction (13) with means allowing flow from the primary space (5) to the secondary space (12) so that as the surface level of the paper pulp exceeds the height of the partition wall construction (13) there will be flow of paper pulp from the primary space (5) into the secondary space (12). Apparatus for removing impurities from paper pulp, said apparatus comprising : a pulping space (2), whereto the paper pulp to be purified is conducted, which is divided into a primary and a secondary space (5, 12); respective rotor units (6, 15), screenplates (8, 16) or the like, cooperating with said rotor units (6, 15), accepted material outlets (10, 18) and rejected material outlets (11, 19) provided for each of the primary and the secondary spaces; means for introducing the paper pulp to be purified into the primary space (5); and connection means for providing connection between the primary and secondary spaces (5, 12); characterized in that said pulping space (2) is enclosed by a solid jacket (1, 3, 4), having a lower portion (4) and vertical side portions, and is divided into primary and secondary spaces (5, 12) by means of a vertically-extending partition wall construction (13) and in that said connection means are provided within the partition wall construction (13). Apparatus according to claim 4, characterized in that the partition wall construction (13), or at least part of its area, is made penetrable by paper pulp especially, by means of perforations. Apparatus according to claim 4, characterized in that the upper portion of the partition wall construction (13) is provided with a flow connection from the primary space (5) into the secondary space (12). Apparatus according to claim 6, characterized in that the flow connection in the partition wall construction (12) is accomplished by means of a horizontal flow channel (21) or the like, whereby the vertically-extending partition wall construction (13) is divided into two parts (13e, 13f), said flow channel (21) being disposed between them. Apparatus according to claim 4, characterized in that the partition wall (13), viewed along the horizontal cross-section of the jacket (1), is arranged to divide the pulping space (2), into two segments forming said primary and secondary spaces (5, 12), said pulping space being essentially circular in said cross-section. Apparatus according to claim 8, characterized in that the partition wall construction (13) divides the pulping space (2) so that the primary space (5) is larger than the secondary space (12).

Inventors: VUORINEN TIMO, VUORINEN, TIMO
Applicants: VALMET PAPER MACHINERY INC, VALMET PAPER MACHINERY INC.
Application year: 1990
Main classification: D21B1
IPC codes: D21B1