FI109815B - Device and method for drying cellulose - Google Patents

Description

109815

Apparatus and method for drying cellulose

The present invention relates to an apparatus for drying cellulose comprising at least a wire section into which a cellulose to be dried is introduced from a stern box and a press arrangement comprising at least one press nip through which the wet section of the wire section is arranged to pass.

The invention also relates to a method for increasing the dry matter content of cellulose by a cellulose drying machine comprising at least 10 wire sections and a press section, wherein the dry matter content of the cellulose is increased to at least about 13-20% by dewatering the wire section. by squeezing the web.

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With the exception of paper made entirely from recycled fibers, pulp, i.e. chemical pulp, e.g. reinforcing: to give the web or give it the desired properties. The pulp is typically mixed e.g. mass of the desired amount of material. However, pulp * * »consumes only a fraction of the total amount of paper produced.

»· · \ * Pulp can be obtained through pipelines from the mill's own pulp mill. However, most of the 20 pulps produced are used at paper mills outside the pulp mill * * *. market pulp. In this case, it is natural that: the pulp is desiccated, without the need to transport water between the pulp mill and the · · · ·: ··: paper mill. This pulp drying is accomplished on a pulp drying machine.

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Figure 1 schematically illustrates a major type of prior art wet end for pulp drying machines comprising a wire forming unit 2 in which the pulp feed to the wire 7 is first dewatered, typically with a dry solids content of about 30 to 20%. From the wire section, the web W is guided to a press section comprising e.g.

combi press, in which the web passes through two N2-N3 press nips. As shown in Fig. 1, the wire section may have a separate nipple N1, so-called. a lump breaker whose main purpose is to break down 2 109815 prematurely born and / or too large fiber network interconnections, as the name implies. Such a lumbar press, rolls 3.16, uses standard press rolls. Here, the lumbar press is coupled to the rotation of the top felt of the combi press, which is not necessary. After the Combi press, the web is sufficiently dry (dry matter content greater than about 40%) and thus durable to be fed to a fourth press / stand press, e.g., SymBelt ™ shoe press, rolls 18,19, from which press N4 web is guided for further evaporation drying at a dry matter content of about 50%.

10 However, such a wet end of a pulp drying machine comprises problems. One drawback may be the large number of rolls of the combi press.

• · · v: The Combi press required press rolls, rolls 4, 15, 17, in addition to numerous felt 5.8: V guide rolls and felt restoration equipment. In addition, the combi press has 15 suction rolls in the center roll, which increases the investment cost.

X: 15 v · In addition, the lumbar press in this solution is very sensitive to nip pressure control. If the line pressure is increased too much, the web becomes so-called. for the fuck ts.

* * '.V its fiber-mesh structure is broken and the web can not be guided • · · ·' *.

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Accordingly, it is an object of the invention to provide a pulp drying process which; the above drawbacks are minimized.

In the known solution, a wet wire 7 of the wire section passes through the first nip N1 of the combi press and it is known per se to provide a nip formed by two rolls on the wire section in which the web W is to some extent pressed. However, the overall goals of the process and the interaction of the entire wet end / press section must be considered as a whole, with certain requirements for the pulp web to be dried when it comes from the wire / press section. The main requirements 30 are: the web must be sufficiently dry to withstand transfer to the drying cabinet, and on the other hand the drying must be carried out in such a way that the structure of the pulp used as raw material does not suffer.

3, 109815

The main purpose of a drying machine for drying pulp is to dry the pulp in the most cost-effective manner possible, and it must be remembered that the material to be dried is pulp and not a mixture of different fibers and additives (possibly including only one part of pulp). This involves, among others. the fact that the mechanical dewatering of the pulp should be as efficient as possible, however, so that the pulp fibers themselves will not suffer.

The differences between pulp drying and papermaking are e.g. substantially different basis weights, which in the case of pulp are in the order of 600-1000 g / m2, while paperboard has a maximum basis weight of about 550 g / m2 and paper v · 'has a maximum weight of about 150 g / m2. In addition, pulp drying machines typically have speeds of less than 200 m / min, while paper machine speeds can be in the range of over 1600 m / min. In addition, in a pulp dryer, the temperature of the pulp from the headbox is at least 55 ° C in old machines and typically at about 60 ° C in new machines, while in paper machines the corresponding temperatures are typically below about 45 ° C. . Perhaps one of the most tangible differences is that paper / board is always an end product that is subject to quite different requirements than dried pulp, which is a raw material. The requirements for the dried pulp are mainly related to its handling during drying, the requirements for the treatment of dried pulp, transportation and pulping: at the paper mill. The purpose of a pulp drying machine is not to significantly influence: ··· the properties of the pulp sheet itself. In the manufacture of paper and board, on the other hand, the process is determined by the quality characteristics of the final product, such as smoothness, gloss, opacity, print quality, etc.

The foregoing indicates that the conditions in the pulp drying machine and the papermaking machine are substantially different, so that the solutions implemented in the papermaking machine are not normally suitable as such for the pulp machine environment.

To achieve the above objects, the apparatus for drying cellulose of the invention comprises at least a wire section into which the drying cellulose is led from a headbox and a press arrangement comprising at least one press nip through which the wet screen of the flat wire section is arranged is arranged to pass through at least one nip of the long nip press, and that the long nip press has means for effecting dewatering in two directions.

The method of the invention for increasing the dry cellulose content of a cellulose dryer comprising at least a wire portion and a press portion, wherein the dry matter content of the cellulose is increased by dewatering the wire portion to at least about 15-20%, followed by further increased by compression of the cellulose web is characterized in that the dry content of the cellulose * * is increased after dewatering of the wire section by passing the cellulose web together with at least the wire section wire through a press member which raises the dry content of the cellulose web to about 40%; whereupon the cellulose web is passed from the wire section to the next step of raising the dry matter content.

The wire section of the pulp drying machine according to the invention, comprising at least 20 wire loops below which the pulp can be led for pulp dewatering, is characterized in that the bottom wire; the loop is adapted to pass through a longitudinal nip roll formed on the outside of the wire loop and a long nip press formed by an inner roll roll: ··· together with a felt adapted to pass around the long nip roll in which the dewatering of the pulp web is arranged in substantially two directions.

According to a preferred embodiment of the invention, the method of increasing the dry cellulose content of a cellulose dryer by a method of increasing the dry cellulose content by desiccation of a wire section arranged preferably at least partially in two directions, at least about 15-20% increasing the dry solids content of the cellulose after dewatering the wire section 5 109815 by passing the cellulose web with the wire section fabric and the overlay felt through a first long nip press to remove water from the cellulose web in two directions, through yet another long nip press between the felts, removing water from the cellulosic web in two directions, where in another long nip press the cellulosic web Preferably, the solids content of the invention is increased to more than about 55%. The invention will now be described in more detail with reference to the accompanying drawings, in which: * V is a diagram illustrating a prior art press arrangement, v. Fig. 3 shows another preferred embodiment of a press arrangement according to the invention, and Fig. 4 shows a third embodiment of the invention.

The pulp drying machine according to Fig. 1, schematically illustrated, comprises a head box 1 for feeding pulp to a flat wire of a flat wire section 2, which wires 7 25 through a folding roll 3 and a pull roll 4 at the end of the wire section and several guide rolls. The flat wire section 2 typically includes e.g. foil strips, foil suction boxes and suction boxes not shown in the figure for dewatering the pulp carried on a flat wire so that the dry matter content of the pulp web is about 13-20% after the flat wire portion. After the flat wire section 30, the web W is led to the first press nip N1 of the combi press, which is a so-called. a lumbar clamp, described in greater detail above, formed by rolls 3 and 16, and thence to nipples N2 and N3 having a central roll for suction rolls 15 and counter rolls e.g. smooth rolls 4 and 17 respectively. Rolls 15 and 16 6 109815 through the upper blanket 5 and through the roller 17 and the lower blanket 8 through the guide rollers, the web W from the nip N3 of the combi press is led to the nip formed by the rolls 18 and 19 through which the upper blanket 6 and the lower blanket 9 respectively. lead to evaporation drying. The dry solids content of the web after nip N4 is typically about 50% and the maximum dry solids content in current machines is about 53%.

In a preferred embodiment of the invention according to Fig. 2, the combi press formed by the two nips N2-N3 of Fig. 10 is replaced by: ": a long nip press comprising a long nip roll 10 outside the wire 7 and a * inner wire roll 4 between which a long nip PN1 is formed. The length of the long nip according to the invention is so selected that the retention time of the pulp web is preferably greater than 40 ms, most preferably greater than 50 ms. It can be roughly stated that the retention time of the solution according to the invention is about five times the is typically very thick, so that the long compression action time of the invention is particularly advantageous, particularly at the dry solids content of the invention, i.e., the stage where the fibrous web of the cellulose web is already sufficiently bonded, but still containing a large amount of water. n provides the dry solids content of the cellulose web W; about 20% of the value after the flat wire section with one nipple ·: ··! greater than about 40%, which corresponds to the dry cell content of the pulp web after the combi-press of Figure 1, after two separate nips N2-25 N3. The long nip PN1 pulp web is pulled into an auxiliary nip press formed by rolls 11 and 12, the lower roll 11 being preferably a long nip roll, the web W passing between two successive long nip PN1 and PN2 before being fed to the drying apparatus 14. The dry solids content of the web after the second long nip PN2 is greater than about 50%, preferably greater than about 55%, and most preferably greater than about 30 to 60%.

The embodiment of Fig. 3 differs from the embodiment of Fig. 2 in that the wire section wire 7 is arranged to rotate through the folding roller 3 and the pulling roller 4 in a similar manner to the prior art solution of Fig. 1, wherein the first long nip PN1 is formed Furthermore, the upper felt loops 5 and 6 shown in the solution of Fig. 2 are connected in Fig. 3 into a single felt loop 13 which rotates the first longitudinal nip 5 via the long nip roll 10 and the second long nip back roll 12 as well as the required guide rolls.

In the solution according to the invention shown in Fig. 4, the cellulosic pulp is led from the headbox 1 to the tapered 10 formed by two wire loops in the wire section 2, in which the dry matter content of the cellulose web is increased substantially immediately in two directions. The region-v formed by two wires is preferably provided with a so-called. a lumbar clamp N1 ', followed by a planar box arrangement downstream. The pulp web is then passed, supported by the lower wire, in accordance with the invention, together with at least the wet section wire of the wire section, through a long nip press PN1. The cellulose web is then moved forward at the wire support v through a second long nip press PN2 through a second long nip press between the felts to remove water from the cellulose web in two directions, raising the dry matter content of the cellulose web to about 55%.

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The solution of Figure 4 provides e.g. reduced machine length; essentially, allowing for, for example, machine rebuilds to increase the size of the evaporative drying cabinet, allowing the production of the entire line to be increased.

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In the embodiment of Figures 2 to 4, separate heating devices may be provided in the direction of web travel before the long nip presses, and preferably before the second long nip press, to further increase the dry solids content of the cellulose web. These heaters can heat either directly against the pulp web or against the blanket facing the pulp web. In addition, dewatering devices located above the wire section may be added to the embodiments of Figures 2 and 3, if necessary, to enhance the increase in dry matter content of the cellulose web.

Claims (13)

Device for drying cellulose, said device consisting of at least one wire portion (2), to which cellulose to be dried is measured from the inlet carriage (1) or equivalent, and a pressing system formed by said at least one press nip through which said wire portion The weft wire is arranged to run, and wherein the weft wire (7) of the wire portion is arranged to run through at least one roll nip (PN1) to a long nip press, characterized in that said long nip press exhibits a long nip roller (10) outside the wire and a support roll. (3; 4) inside the wire and that the longitudinal roll support roll (3, 4) is a pierced casing roll to effect water separation in two directions from the cellulose web. 2. Device according to claim 1, characterized in that the system therein comprises at least one additional nip press, wherein the water separation is arranged to take place in two directions. 3. Device according to claim 2, characterized in that the additional nip press (11,12) is also a long nip press. 20 .... 4. Apparatus according to claim 2, characterized in that the longitudinal press of the longitudinal press of the longitudinal press of the longitudinal press is arranged in the end portion of the wire portion ... the pull roller (4) or deflection roller (3). * · Device according to any one of claims 1-4, characterized in that the support roll (3,4) of the longitudinal press is cut thereon. Device according to any one of claims 2-5, characterized in that:. between the longitudinal nip press of the wire section and the additional press, heating means are provided to increase the dry matter content of the cellulose web (W). 12 109815 Device according to any one of claims 1-6, characterized in that the wire portion comprises a tapered gap formed by at least two wire links, in which the dry matter content of the cellulose web is increased in substantially two directions. 8. A method for increasing the dry matter content of the cellulose, which drying device comprises at least one wire portion and a pressing portion, in which the dry matter content of the cellulose is increased with water separation in the wire portion to at least about 13-20%, whereafter the dry matter content of the cellulose web is further increased, that the dry matter content of the cellulose web is increased after the water separation of the wire part by passing the cellulose web with at least the wire part of the wire through a pressing member, in which the dry matter content of the cellulose web is raised to a value of over about 40%, whereupon the cellulose web is led from the next wire part dry content. Method according to claim 8, characterized in that a longitudinal press is used in the method as pressing means. . . 20 tl »» 10. A method according to claim 8 or 9, characterized in that, in the process, a second pressing means is used to increase the dry matter content to a value of about 50%, preferably to more than about 55%, more preferably tili. ·. ·. a value above about 60%. • 25 • · · 11. A method according to claim 10, characterized in that a longitudinal press is used in the method as the second pressing means. • · • 12. A process according to claim 9 or 11, characterized in that cellulose. The retention time of the web in the longitudinal nip press is preferably over 40 ms, preferably over 50 ms. • * * • · * tl * 13 109815 13. A method according to claim 8 or 10, characterized in that the dry matter content of the cellulose is increased after the water separation of the wire part by conducting the cellulose web with the hydrogen part of the wire part and the overlying felt to a first longitudinal press separating water from the cellulose web in two directions. the longitudinal press of the cellulose web's dry matter content is raised to a value of over about 40%, after which the cellulose web is still passed through a second longitudinal press between blankets, water being separated from the cellulose web in two directions, in which the second longitudinal press of the cellulose web's dry matter is raised to a value of about 50 %. • · IMI • · «· <·« · · · · · * · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · •> II> · • • * I • I i »