PULP WASHER

Description

[0001] This invention relates to an apparatus for the liquid treatment of cellulose pulp, for example washing and dewatering, The invention, more precisely, refers to an apparatus where the pulp from a head box is allowed to flow out and form a layer on a plane, endless liquid permeable web. The web runs over two end rolls, and treatment liquid is supplied on the upper surface of the pulp layer at the same time as liquid is sucked away from the lower surface of the pulp layer to vacuum vessels beneath the web.

[0002] In such apparatuses the web usually is a wire manufactured of plastic wires. The wire is driven by one end roll and slides over the perforated covers on the underlying vacuum vessels. Owing to the friction between the wire and vessel covers, great forces are required for driving the wire, This gives rise, at the same time, to high tensile stresses in the wire, which thereby is restricted as to its possible length, because the tensile stress increases with the length of the contact surface between wire and vessel covers. When it is desired in an existing mill to increase the capacity, it is therefore necessary in most cases to increase the wire width instead of the wire length. This would imply substantial re-construction of the mill, If a lengthening of the wire would have been possible, this could have been effected by relatively simple measures and at reasonable costs.

[0003] Due to the fact, that the wire is manufactured of interplaited plastic wires, a damage in the form of broken wires renders a very troublesome repair work necessary, which in most cases is so expensive that it is more economic to exchange the entire wire.

[0004] In FI-C-25 895 a pulp washer is disclosed in which washing of the pulp is accomplished with the use of a pair of wire belts between which the pulp layer is provided. A number of tensioning rolls and guide rolls are provided for the wire belts in order to provide the necessary flexibility for the belt to pass about the various rolls.

[0005] Further, in US-A-3 121 660, CH-A-392 239 and FR-C-14 477 603 are disclosed different kinds of papermaking machines where very thin and flexible metal sheets can be used for a fourdrinier- type wire. This type of thin sheets is necessary since in paper-making applications the fourdrinier wire or band is driven at a very high speed and is bent around a number of separate rolls. However, such a band could not satisfactorily be employed in a pulp washing apparatus.

[0006] The present invention has the object to eliminate the aforesaid problems and at the same time to render further advantages possible. According to the invention, the plastic wire referred to above is replaced by a perforated steel web. A steel web having a thickness of between 0.5 and 1.5mm and an open area of between 8 and 25% has a substantially higher tensile strength than a wire. It is, further, relatively simple and inexpensive to repair damages in the web. Since a steel web also has a higher resistance to pressure, the dewatering of the pulp layer according to the invention can be carried out much more effectively. A further advantage is that the open area in the covers of the vacuum vessels can be increased due to the inherent carrying capacity of the steel web.

[0007] The characterizing features of the invention are defined in greater detail in the attached claims.

[0008] The invention is described in the following, with reference to an embodiment thereof and to the accompanying drawings, in which Fig. 1 shows a liquid treatment apparatus according to the invention, and Fig, 2 is a cross-section along II-II in Fig, 1.

[0009] The embodiment shown of the apparatus comprises an endless perforated steel web 1, which runs about a first and a second end roll 2 and, respectively, 3. The rolls are mounted in a stand 4 so that the first roll 2 is movable by means of a stretching device 5, preferably a hydraulic one, for adjusting the web tension. The driving is effected via the second roll 3, and both rolls preferably are coated with a friction-increasing surface layer.

[0010] At the first roll 2 a head box 6 is located for distributing the cellulose pulp in the form of a uniform layer on the web 1, In the head box a rotor 7 is located for deflocculating the pulp. Beneath the web a plurality of vacuum vessels 8 are arranged one after the other in the longitudinal direction of the web. The vessels are provided with perforated covers acting as a support for the web 1.

[0011] Outlets 9 and, respectively, 10 are connected to the vessels 8 for the discharge of liquid and, respectively, gas. Above the web means 11 for the supply of treatment liquid are located. Over the pulp layer a pressure difference is maintained for effecting liquid transport crosswise through the pulp layer. The width of the pulp layer on the web is limited by two endless deckle straps 12, which follow along with the web 1. Also other means for limiting the width, of course, can be imagined. A hood 13 is placed over the web 1.

[0012] At the second roll 3 a transfer device 14 for the pulp layer after its completed treatment is located, which for example has the form of a doctor blade. Beneath the same a conveying screw 15 is provided for conveying the pulp to subsequent processing steps. Said second roll 3, also co-operates with means for pressing liquid from the pulp layer. According to the embodiment shown, these means are a liquid-permeable web 16, which is held pressed against the steel web 1. The web 16 runs over two small rolls 17,18 and a stretch roll 19. The second end roll 3 is provided with grooves extending all about the roll to permit liquid to be pressed through the steel web 1. The liquid pressed off is collected in a trough 20 beneath the end roll 3. It is, of course, also possible to use other types of pressing means. The pressing-off implies that a high dry content of the pulp can be obtained. The pulp concentration, for example, can be increased from about 8% to about 30% by this pressing-off. This implies that a greater part than normal of the chemical content of the pulp can be removed already in connection with the liquid treatment. It is possible from a chemical content of 6 - 10% at a conventional fourdrinier wire washing to come down to 1 - 3%. It is thereby possible, for example, to pass the pulp from the treatment plant directly to the bleach plant without further dewatering in special thickeners.

[0013] The steel web used preferably shall have a thickness of 0,5 - 1,5 mm. The diameter of the end rolls must be adapted to the thickness of the web, because the bending stress in the web is directly proportional to the web thickness and reciprocally proportional to the roll diameter. A suitable dimension of the rolls can be about 2 m diameter.

[0014] The hole size must be adapted to the pulp to be treated, but should be in the interval 0,5 - 1,5 mm diameter. It is also imaginable, of course, to form the holes as slits. The open area must under all conditions be between 8 and 25%.

[0015] The length and width of the web are not critical, but can be adapted at option. The desired width can be brought about by welding a number of narrow webs longitudinally to a wider web, because it is not possible to directly manufacture steel webs having widths here in question, for example about 6 m. Steel webs normally are not manufactured in widths exceeding much more than one meter.

Claims

1. An apparatus for liquid treatment of cellulose pulp, comprising a pair of spaced-apart end rolls (2, 3) one of which is a drive roll (3), an endless perforated web (1) arranged about said pair of end rolls (2, 3) so as to provide a substantially horizontally disposed upper portion, said perforated web (1) being adapted to be driven by said end rolls, head box means (6) for supplying cellulose pulp to be treated directly onto said upper portion of said web (1) at the first roll (2), liquid collection means (8) arranged between said pair of end rolls (2, 3) for collecting liquid displaced from said cellulose pulp through said web (1) as said web is driven by said drive roll (3) relative to said liquid collection means, said liquid collection means (8) having a substantially horizontally disposed surface arranged beneath and in direct contact with said upper portion of said web (1), liquid inlet means (11) arranged above said upper portion of said web (1) for supplying a treatment liquid to said cellulose pulp supplied onto said upper portion of said web (1), means for applying a pressure differential across said upper portion of said web to force liquid from said cellulose pulp through said web into said liquid collection means (8) as said web is moved relative to said liquid collection means and removal means (14) for removing treated cellulose pulp from said web (1) after said cellulose pulp has been subjected to said liquid treatment,
characterized in that said web (1) is made of steel having a thickness of between 0.5 and 1.5 mm and being perforated so as to have an open area of between 8% and 25% and that means (16) for pressing-out liquid are arranged so as to cooperate with the steel web (1) at its travel about the second roll (3).

2. The liquid treatment apparatus of Claim 1 wherein said endless steel web (1) is supported by said pair of spaced-apart end rolls (2, 3) and said liquid collection means (8) arranged therebetween; wherein said endless steel web (1) includes a lower portion extending between said end rolls; and wherein said liquid treatment apparatus further includes means (5) for adjusting the spacing between said end rolls to adjust the tension on said endless steel web (1) and maintain said lower portion of said endless steel web substantially horizontally disposed.

3. The liquid treatment apparatus of Claim 2 wherein the length of said horizontally disposed surface of said liquid collection means (8) substantially corresponds to the spacing between said end rolls (2, 3).

4. The apparatus of Claim 2 wherein said liquid collection means (8) comprises a plurality of vessels (8) arranged between said pair of end rolls (2, 3), said vessels (8) each being arranged transversely of the longitudinal direction of movement of said endless web (1) and said vessels (8) collectively extending one after the other in said longitudinal direction of movement of said web, each of said vessels being provided with perforated covers in contact said upper portion of said web (1).

Ansprüche

1. Vorrichtung zur flüssigen Behandlung celluloser Pülpe, bestehend aus einem endlosen perforierten Band (1), das um ein Paar Abstand voneinander aufweisende Rollen (2, 3), von denen eine eine angetriebene Rolle (3) ist, läuft, wodurch es einen im wesentlichen horizontal verlaufenden Oberteil aufweist, wobei das Band (1) dazu vorgesehen ist, von den Endrollen bewegt zu werden, mit einer Kopfaufgabevorrichtung (6) um Cellulosepülpe bei der ersten Rolle (2) zur direkten Behandlung auf dem oberen Teil des Bandes (1) aufzubringen, mit Flüssigkeitssammeleinrichtungen (8), die zwischen dem Paar Endrollen (2, 3) vorgesehen sind, um die Flüssigkeit zu sammeln, die aus der Cellulosepülpe durch das Band (1) durchtritt, wenn das Band durch die Antriebsrolle (3) relativ zu den Flüssigkeitssammeleinrichtungen bewegt wird, diese Flüssigkeitssammeleinrichtungen (8) haben eine im wesentlichen horizontal verlaufende Oberfläche, die unterhalb und im direkten Kontakt mit dem Oberteil des Bandes (1) angeordnet sind, mit Flüssigkeitsaufbringvorrichtungen (11), die oberhalb des Oberteils des Bandes angeordnet sind, um der dem Oberteil des Bandes zugeführten Cellulosepülpe Behandlungsflüssigkeit zuzuführen, mit Mitteln, um einen über den Oberteil des Bandes unterschiedlichen Druck aufbringen zu können, um Flüssigkeit aus der Cellulosepülpe durch das Band in die Flüssigkeitssammelvorrichtungen (8) zu pressen, wenn das Band relativ zu den Flüssigkeitssammelvorrichtungen bewegt wird und mit Abnahmemitteln (14), um die behandelte Cellulosepülpe vom Band (1) abzunehmen, nachdem die Cellulosepülpe der Flüssigbehandlung unterworfen worden ist,
dadurch gekennzeichnet, daß das Band (1) aus Stahl besteht und eine Dicke zwischen 0,5 und 1,5 mm aufweist und so perforiert ist, daß seine - offene Fläche zwischen 8% und 25% liegt, und daß die Mittel (16) zum Auspressen der Flüssigkeit so angeordnet sind, daß sie mit dem Stahlband (1) während seines Umlaufes um die zweite Rolle (3) zusammenwirken.

2. Vorrichtung nach Anspruch 1, wobei das endlose Stahlband (1) von dem Paar Abstand voneinander aufweisender Endrollen (2, 3) gestützt wird und die Flüssigkeitssammelvorrichtungen (8) dazwischen angeordnet sind; wobei das endlose Stahlband (1) einen unteren Teil aufweist, der sich zwischen den Endrollen erstreckt; und wobei die Vorrichtung zur flüssigen Behandlung weiters Mittel (5) aufweist, um den Abstand zwischen den Endrollen verändern zu können, um die Spannung des endlosen Stahlbandes (1) regeln zu können und den unteren Teil des endlosen Stahlbandes im wesentlichen horizontal zu halten.

3. Vorrichtung nach Anspruch 2, wobei die Länge der horizontal angeordneten Oberfläche der Flüssigkeitssammeleinrichtungen (8) im wesentlichen dem Abstand zwischen den Endrollen (2, 3) entspricht.

4. Vorrichtung nach Anspruch 2, wobei die Flüssigkeitssammeleinrichtungen (8) eine Mehrzahl von Behältern (8) umfassen, die zwischen dem Paar von Endrollen (2, 3) angeordnet sind, wobei die Behälter (8) einzeln quer zur Längsrichtung der Bewegung des endlosen Gewebes (1) angeordnet sind und die Behälter (8) hintereinander in der Längsrichtung der Bewegung des Bandes sich erstrecken, wobei jeder der Behälter mit perforierten Abdeckungen versehen ist, die im Kontakt mit dem Oberteil des Bandes (1) stehen.

Revendications

1. Dispositif pour le traitement liquide de pâte de cellulose qui comprend une paire de rouleaux d'extrémités espacés l'un de l'autre (2, 3), l'un de ces rouleaux étant un rouleau moteur (3), une bande perforée sans fin (1) disposée autour de ladite paire de rouleaux d'extrémité (2, 3), de manière à obtenir une partie supérieure disposée sensiblement horizontalement, ladite bande perforée (1) étant conçue de manière à être entraînée par lesdits rouleaux d'extrémité, un système de caisse d'arrivée de pâte (6) pour délivrer de la pâte de cellulose devant être traitée directement sur ladite partie supérieure de ladite bande (1), sur le premier rouleau (2), des moyens (8) pour recueillir le liquide disposés entre ladite paire de rouleaux d'extrémité (2, 3) pour recueillir le liquide extrait de ladite pâte de cellulose au travers de ladite bande (1) lorsque cette dernière est entraînée par ledit rouleau moteur (3) par rapport auxdits moyens de recueil de liquide, lesdits moyens de recueil de liquide (8) comportant une surface sensiblement horizontale disposée en dessous de ladite partie supérieure de la bande (1) et en contact direct avec cette partie, des moyens d'admission de liquide (11) disposés au-dessus de ladite partie supérieure de la bande (1) pour délivrer un liquide de traitement à ladite pâte de cellulose amenée sur ladite partie supérieure de la bande (1 ), des moyens pour appliquer un différentiel de pression sur ladite partie supérieure de la bande afin d'obliger le liquide extrait de cette pâte de cellulose à passer au travers de ladite bande dans les moyens de recueil de liquide (8) lorsque ladite bande se déplace par rapport à ces moyens de recueil de liquide et, des moyens d'enlèvement (14) pour enlever de ladite bande (1), la pâte de cellulose traitée après que ladite pâte de cellulose ait été soumise audit traitement liquide, caractérisé en ce que ladite bande (1) est réalisée en acier présentant une épaisseur comprise entre 0,5 et 1,5 mm et elle est perforée de manière à présenter une aire ouverte de 8 à 25% et en ce qu'on prévoit des moyens (16) pour expulser le liquide qui sont disposés de manière à coopérer avec la bande d'acier (1) lors de son déplacement autour du second rouleau (3).

2. Dispositif pour le traitement liquide selon la revendication 1 dans lequel la bande sans fin en acier (1) est supportée par ladite paire de rouleaux d'extrémité espacés l'un de l'autre (2, 3), lesdits moyens de recueil du liquide (8) étant disposés entre ces rouleaux dans lequel ladite bande d'acier sans fin (1) comporte une partie inférieure s'étendant entre lesdits rouleaux d'extrémité et ce dispositif pour le traitement liquide comprend en outre des moyens (5) pour régler l'espacement entre lesdits rouleaux d'extrémité afin de régler la tension sur ladite bande d'acier sans fin (1) et de maintenir ladite partie inférieure de cette bande d'acier sans fin selon une disposition sensiblement horizontale.

3. Dispositif pour le traitement liquide selon la revendication 2 dans lequel la longueur de ladite surface horizontale des moyens de recueil de liquide (8) correspond sensiblement à l'espacement entre lesdits rouleaux d'extrémité (2, 3).

4. Dispositif selon la revendication 2 dans lequel les moyens de recueil (8) sont constitués par une pluralité de récipients (8) disposés entre ladite paire de rouleaux d'extrémité (2, 3), chacun desdits récipients (8) étant disposé transversal- ment à la direction longitudinale du déplacement de ladite bande sans fin (1) et lesdits récipients (8) s'étendant collectivement l'un après l'autre dans ladite direction longitudinale du déplacement de ladite bande, chaque récipient étant muni de couvercles perforés au contact de ladite partie supérieure de ladite bande (1).

Drawing