EP1100605B1 - Thickener - Google Patents

Abstract

Methods and corresponding devices are set forth for the continuous mechanical dewatering of aqueous suspensions or elutriations, particularly of waste-paper suspensions or slurries, between an endless mesh band and an endless compression surface having a closed, smooth surface and running in the direction of operation. The suspension cake to be dewatered is compressed between the mesh band and the compression surface. The requisite pressure is achieved by wrapping the mesh band around the cylindrical compression surface under longitudinal tension, whereby the expelled water is removed from the suspension cake by means of the mesh band. Devices are provided which both increase the operational duration of the dewatering pressure of the existing mesh band on the suspension cake, and at the same time increase the pressure substantially, without obstructing the runoff of the pressed-out water. The method of the invention increases the compression pressure from about 1 bar (heretofore) to a pressure of, e.g., up to 100 bars, and also permits integration into existing dewatering processes in order to increase the solid matter content, without thereby substantially increasing the equipment space or the operational complexity.

Description

The invention relates to a device for continuous mechanical thickening (Dewatering) of water-containing suspensions or sludges with the aid of a first endless Siebgewebebandes and a closed, smooth surface having moving in the running direction, endless pressing surface, wherein the to be drained Suspension cake is compressed between Siebgewebeband and pressing surface and a pressing pressure is created by the Siebgewebeband the cylindrical pressing surface under Longitudinal tension wraps around during the dewatering process.

Such a device is known for example from CH-A-644.414. This device uses only a single mesh belt, which partially surrounds a smooth roller. The advantage lies in the only one-sided rewet of the cake and the simpler Execution with only one band. The disadvantage, however, is that the cake only at this a roller, d. H. drained only once to one side, so that the Final dry content is not optimal. In addition, the cake thickness to be dehydrated is limited, because the water of the roll side the way through the whole cake thickness must take to the mesh. Although this can be done by slower running of the press something be compensated.

A generic device is also shown in EP-B-283,870, in addition a second endless belt acts on the first wire cloth belt. Also DE-A-4,216,968 discloses a generic device, wherein additionally a press pad is present, with adjustable pressure synchronously over a peripheral portion of Press roll runs along. The pressure pad acting at high pressure should rewet of the filter cake can be avoided.

Such devices also serve to integrate into existing dewatering processes for the purpose of increasing the consistency of the solid, without losing the installation space or the operating effort to increase significantly.

Another device known from Bellmer's "Winkelpress" of 1972 carries the suspension cake between two mesh belts; This has the advantage that the cake can be drained to two sides by meandering this sandwich around guide rollers is guided around, so that the discharge of crushed water from the entwined Roll away through the respective outer mesh belt. So can the Diameter of the guide rollers in the course of the bypasses each be reduced, which the pressure increases. But it turns out as a serious disadvantage that in the mesh both sieve fabrics remaining water by adhesion forces, when leaving the nip, flows back into the cake, as the adhesion of the suspension due finer fiber and particle sizes are stronger and thus sucked back.

But it can not be arbitrarily reduced the Leitwalzendurchmesser, since strength and deflection of the guide rollers prevent this.

Another way to increase the pressing forces, lies in the longitudinal tension of the To increase screen cloth belts; here too set strength and deflection of the guide rollers as well as the strength of Siebgewebebänder itself limits for increasing the dry content after the squeeze. In practice, the straining stresses are of the order of magnitude of 10 N / mm, rarely up to 30 N / mm, resulting in a small roll diameter of z. B. 200 mm, a pressure of about 1 bar, rarely 2 bar, results in both ways prevent but not the rewetting by the water in the sieve meshes of both meshes. Optimum performance is therefore not possible: final dry content or throughput stand against each other.

From DE-U-9.203.395 a pressing device with a shoe-pressing unit is known which forms a press nip together with a Gegenwaäze This known device is used for handling a traveling web, i. for smoothing or dewatering a paper web in a papermaking machine.

Fundamental differences from the subject matter of this invention consist in the fact that in the case of paper, the quality of the web to be drained has to be taken into account, d. H. that the incoming Web is very homogeneous, that the pressing takes place with mark insensitive felt, that no crushing of the web may happen, d. H. Moving fibers that are the squeezed out water must not move against the direction of the paper web, since otherwise the paper web is destroyed, and that overall the quality, d. H. the uniformity the dewatered paper web must be guaranteed.

Paper machine felts, with their fine hair fleece for mark-free homogeneous Pressing worry, are not used in the patent idea. On the one hand, they pollute much easier and on the other hand, the uniform mark-free pressure in the present Invention not required; on the contrary, a marking, d. H. nonuniform Pressing is desirable, because it will exert a certain kneading effect, which is the Better drainage from the cake helps. In addition, it is in the present invention not desirable if the cake forms a stable sheet after thickening. at the patent idea is u. a. by intended differential speed between screen mesh and pressing surface to both sides of the cake and / or by the coarser structure of the additional ones water-permeable belts intended to destroy the railway structure to clear away the water during the squeezing process for easier outflow and to achieve crumbling after thickening.

In addition, in paper and board webs, the suspension does not rest on the same mesh belt brought from a liquid phase to a consistency of about 25%, what is achieved with the invention.

The aim of the invention is to avoid the disadvantages of the techniques used to date, that is, the pressing pressures acting on the suspension cake clearly and for long enough increase with minimal rewetting, in continuous flow operation.

The object is solved by the features of patent claim 1. Based on these Training results in economically interesting solutions:

In the thickening of waste paper suspension, the invention, the washing process, d. H. Separating fines from recyclable fiber material by dewatering a thin-layered low-consistency suspension (<2%) at higher Working speed (> 200 m / min.), Directly attached, with the addition used screen cloth belt with the corresponding belt guide rollers for both steps is used. Also eliminates the transport of the partially dewatered suspension from the scrubber to the thickener.

The thickening of sludges by means of the twin-wire presses, by integration of the invention in the known process (input consistency> 2% at working speed <10 m / min.), To lower water content of the mechanically dewatered cake. This is of high overall economic benefit:
Nowadays, there are high costs for the removal of the thickened sludge and for the then necessary landfill space or the drying or combustion, since 2/3 to 3/4 of the volume consists of water. When reducing the water content, these costs are directly positively affected.
Advantageous embodiments of the patent idea to increase the effectiveness and scope. The application of not very uniformly distributed suspension cake and the avoidance of rewetting when separating finished thickened cake and former sieve fabric is given special attention.

The claims 3 - 6 treat different band constructions, the passage of the allow squeezed out water. It is claimed in claim 7, a band, which does not hold any water in its cavities, and consequently does not hold this water can rewet.

The claims 5 and 8 are concerned with the high Eingesteifigkeit the tape to To unevenness of the cake to bridge or level by pressing, at the same time wallows the cake and thus promotes the drainage of crushed water.

When using a press shoe with hydrostatic or hydrodynamic lubrication, the sliding properties between band and Sliding surface also improved. The inherent rigidity of the band can be transverse to the Machine run be very high, as long as the longitudinal stiffness remains so low that the tape can follow the contours of the rollers and sliding surfaces well.

Claims 12 to 14 show alternatives where the squeezed out water can flow or how this is removed from the press zone, so the squeezing process is not is hampered by a lack of swallowing volume.

Claim 14 discloses that the still unstable filter cake is gradually put under increasing pressure by several tapes are added successively and only as the last stage of the high pressure of a pressure shoe is made.
The claims 15-17 are dedicated to preventing the backflow of free water of the tapes into the cake when separating them from each other after the maximum pressing, because this would worsen the consistency achieved in the cake again. Claim 15 assumes that with rapid complete separation of all water-carrying tapes this water little time remains to be sucked back (application, especially at higher operating speeds).

Claim 16, mainly intended for slow operation, assumes that although the 1st mesh belt on the cake remains a little while longer and can deliver its water to the cake, other water-bearing belts take away their water and do not remoisten.
This is particularly secure if the band lying on the first sieve fabric belt hardly carries water with it. When the strips are placed under the cake, this effect becomes apparent when gravity prevents the backflow to the first wire cloth belt.

If the rewetting by the 1st mesh belt itself is to be kept low, there are two possibilities:
For this purpose, a sieve cloth with a low absorption volume for the pressing water is selected, or this sieve is compressible under the pressing pressure, so that only a small amount of water adheres to it when leaving the pressing zone. Or one removes according to claim 17, the water from the Siebmaschen after leaving the nip before lifting the screen from the suspension cake. This can be done by tangential application of a flat water jet on the screen fabric, the higher jet velocity with their kinetic energy tears the water from the mesh. The same thing can happen by inflating an air jet. These two methods are not very handy, since the departing water must be collected again. It makes more sense, therefore, a pipe sucker, which forms a gap with a longitudinal strip to the screen, through which the suction air flows. Here, the water is torn out of the sieve and immediately removed with the suction air through the pipe sucker. Claims 18 to 22 show variants of how the pressing surface, against which the 1st sieve cloth tape presses the suspension cake, can be designed. Claim 20 shows a shoe roll with progressively narrowing radius of curvature, which is possible without differential speed and friction between roll mantle and Siebgewebeband.

The claims 21 and 22 have a modified principle to the content in that the pressing surface in the press zone assumes a concave shape (shoe roll) and presses against a round roller.
Although the basic principle of this invention is not necessarily bound to a basic spatial position of the components, it is in the execution of claims 21 and 22 of great use when the round counter-roller is arranged below the nip. Thus, the flow of the Preßwassers is the easiest. Especially at the low operating speed when dewatering of sludge this is entspr. Claim 22 advantageous. So squish water can also run counter to the direction of rotation.
The removal of the bands after pressing is to be aimed at with decreasing slope, so that no white water can run back to the cake.

Fig. 1

zeigt die Darstellung einer Entwässerungseinrichtung unter Verwendung mehrerer Bänder und einer Walze als Preßfläche;

Fig. 2

zeigt die Verwendung eines undurchlässigen Bandes mit Anpreßschuh;

Fig. 3

zeigt die Verwendung mehrerer Bänder und eines undurchlässigen Bandes mit Anpreßschuh bei einer erfindungsgemässen Ausführung;

Fig. 4

zeigt Fig. 3, allerdings mit Verbleib des 1. Siebgewebebandes am Suspensionskuchen auch nach der verstärkten Pressung bei einer erfindungsgemässen Ausführung;

Fig. 5

zeigt die Darstellung einer Entwässerungseinrichtung für langsame Entwässerungsgeschwindigkeit und dicken Suspensionskuchen mit Ablauf von Quetschwasser auch gegen die Laufrichtung;

Fig. 6

zeigt die progressive Entwässerung durch ein oder mehrere Bänder unter Anwendung eines sich verkleinernden Krümmungsradiusses der glatten Preßfläche;

Fig. 7

zeigt die Pressung an einem perforierten Walzenrohr;

Fig. 8

zeigt ähnlich Fig. 7 die Pressung an einer Walze mit Umfangsrillung;

The inventive concept will be explained in more detail below with reference to simplified and schematically illustrated embodiments with reference to the drawings. Only the figures 3 and 4 show embodiments according to claim 1. The other figures serve to explain the dependent claims.

Fig. 1

shows the representation of a dewatering device using a plurality of belts and a roller as a pressing surface;

Fig. 2

shows the use of an impermeable belt with pressure shoe;

Fig. 3

shows the use of multiple bands and an impermeable belt with pressure shoe in an inventive embodiment;

Fig. 4

3, but with the whereabouts of the first Siebgewebebandes on the suspension cake even after the increased pressure in an inventive embodiment;

Fig. 5

shows the representation of a dewatering device for slow dewatering rate and thick suspension cake with expiration of crushed water also against the direction of travel;

Fig. 6

Figure 3 shows progressive drainage through one or more belts using a decreasing radius of curvature of the smooth pressing surface;

Fig. 7

shows the pressure on a perforated roller tube;

Fig. 8

similar to Figure 7 shows the pressure on a roll with Umfangsrillung.

In Fig. 1, a dewatering device is shown in which the fiber suspension (12) with a distributor device (16) between a roller as a pressing surface (7) and a Siebgewebeband (1) is injected. Under the pressure of the Siebgewebebandes (1) and the centrifugal force, the suspension (12) is subjected to a first dewatering, whereby also fines of the suspension are intended washed out. The corresponding press water (14) is less and less with increasing thickening. By a second looping permeable belt (2) of the pressing pressure is increased, so that further pressing water (14) is squeezed out. Now, a third band (3), in this case an impermeable band, is also applied to the preceding bands by means of longitudinal tension and the pressing pressure is increased once more. It is now left open whether the now squeezed amount of water in the cavities of the first two bands (1, 2) can still be recorded or whether for a swallow volume, z. B. grooves or blind holes on the outside of the third band (3) are present. At the end of the three-stage pressing all three bands (1, 2, 3) leave the pressing surface (7) together and separate only on the band guide roller (11). Thereafter, all three bands are freed from water in a manner not shown and cleaned. The thickened suspension cake (13) adheres to the pressing surface (7) and is removed by a scraper (15). The two bands (2, 3) have been added to the known device to reduce the water content of the suspension cake (13).
The device shown runs at speeds above 200 m / min.

In Fig. 2, the same dewatering device is shown as in Fig. 1, but instead with two further bands, here with an additional impermeable band (4), which is pressed by means of a sliding surface (5) of a pressure shoe (6). This Band (4) has volume of swallowing on the surface and therefore hurls that in it absorbed water (14) after Venassen the nip from. Both bands are simultaneously routed away from the suspension cake to rewet to minimize.

In Fig. 3 are also the same device as in Fig. 1 and 2. But the thickening is achieved by a combination of FIGS. 1 and 2, d. H. one second transmissive (2) and third impermeable band (4) are provided but the third band (4) is pressed by a sliding surface (5). This third Band (4) has no volume in this case, which is why no pressing water is thrown off this. The three bands (1, 2, 4) will turn simultaneously led away from the cake (13), but each in a different direction.

FIG. 4 corresponds essentially to FIG. 3, but with the following differences: the third band (4) has again swallow volume and hurls water (14). In addition, the 1st Siebgewebeband is not simultaneously led away from the cake like the other two bands (2, 4), but still remains under longitudinal tension at the cake. During this stretch, the tissue is having a one-sided with Dry suction of the distance from the sieve positioned vacuum cleaner (17).

Fig. 5 shows a sludge dewatering apparatus running very slowly (less than 10 m / min.), Which itself is provided with two screen belts (1, 2) and a number of belt guide rollers (11) for alternately passing the sludge after each one Dehydrate side.
Here, advantageously, the device is then immediately integrated using one of the two Siebgewebebänder (1). In addition, a smooth roller as a pressing surface (7), which is partially wrapped by the existing mesh belt (1). The second tape will not be used anymore because only one tape is needed. As a pressing device now serves a third impermeable belt (4) and a pressure shoe (6) with sliding surface (5), wherein the band (4) has circumferential grooves.

This makes it possible, each accumulating Preßwassermenge (14) in or against Derive the direction. Residual water in the belt (1) is also no longer running Cake back, as the tape (1) is led away falling. The at the pressing surface (7) Adhesive cake (13) is removed from the scraper (15).

FIG. 6 illustrates a combination of FIGS. 1 and 5:
Similar to FIG. 5, the cake and the first fabric belt wrap around the pressing surface (7), which itself does not consist of a round roller, but of a smooth, impermeable belt (4) guided by a pressure shoe (6) with sliding surface (5) becomes. As a special feature, this sliding surface is provided in the running direction with a progressively narrowing contour (R1 - R4), whereby the pressing pressure on the suspension cake steadily increases.
Shown are dashed lines further bands (2, 3), which may be added in accordance with Fig. 1 in order to increase the pressing pressure even further.

Fig. 7 also relates to the device of Fig. 5 and leaves there shown leadership of the 1st Siebgewebebandes. Only the two "rollers" (4, 7) reversed, whereby the impermeable belt with pressure shoe for smooth Pressing surface is (as Fig. 6), but with a concave sliding surface (5), to the here provided roll tube (8) to correspond as counter surface. The pressed water can flow radially through the holes introduced in the roller tube (8).

In Fig. 8, in contrast to Fig. 7, the roller tube (8) by a solid roller with circumferential grooves (9) replaced. So the water can tangentially as in Fig. 5 proceed in both directions.

This roller is also called solid roller with blind holes on the surface conceivable (10).

Also here is another band shown in dashed lines, if the tape printing before the shoe press (6) should already be increased.

Claims (21)

1. An apparatus for continuous mechanical thickening (dewatering) aqueous suspensions or slurries with the aid of a first endless wire belt (1) and an endless press surface (7) comprising a dense, smooth surface, moving in the machine direction, the suspension cake to be dewatered being compressed between wire belt and press surface (7), and compression resulting from the wire belt wrapping the cylindrical press surface (7) in being subjected to longitudinal tension during dewatering, characterized in that at least one water-permeable or water-receiving, second, endless belt (2, 3) acts on said first wire belt (1), and a water-impermeable third endless belt (4) is pressed against said other belts (1, 2, 3) with the aid of at least one sliding surface (5) formed on a press shoe (6) to conform with said counter-acting press surface (7).
2. The apparatus as set forth in claim 1, characterized in that the sum of the longitudinal tensions of all additional belts (2, 3) corresponds to at least the longitudinal tension of said first wire belt (1).
3. The apparatus as set forth in claim 2, characterized in that at least one additional belt (2) is made of a wire.
4. The apparatus as set forth in claim 1, characterized in that at least one additional belt (2) is made of of machine direction (MD) threads and cross machine direction (CD) threads joined unwovenly stacked with adhesion or without firm adhesion.
5. The apparatus as set forth in claim 3 or 4, characterized in that at least one of said additional endless belts (2) is made of MD and CD threads, said CD threads having a higher flexural rigidity than said MD threads so that said belt in its structure is less flexible in the cross machine direction.
6. The apparatus as set forth in claim 1, characterized in that at least one of said additional endless belts (2) is foraminous permitting white water passage.
7. The apparatus as set forth in claim 1, characterized in that displacement is provided in the form of blind holes or grooves in the outer surface of said impermeable belt (3).
8. The apparatus as set forth in any of the claims 5 to 7, characterized in that at least one of said additional belts (2, 3) is sufficiently rigid, at least in the cross machine direction, to bridge surface irregularities of said suspension cake (13).
9. The apparatus as set forth in claim 1, characterized in that the dewatering pressure on said suspension cake (13) is at least ten times the dewatering pressure (compression) attained by said wire belt (1) itself over a sufficiently long period of time, the water drain (14) being assured by said first wire belt (1).
10. The apparatus as set forth in claim 1, characterized in that the direction of the contact pressure exerted on said press shoe (6) is oriented symmetrically or non-symmetrically in accordance with the expansion of said press shoe (6) in the machine direction so that said contact pressure in the machine direction is either substantially consistent or increasing.
11. The apparatus as set forth in claim 1, characterized in that said water-impermeable endless belt (4) is shaped only in said press zone by at least one press shoe (6) to conform with the contour of said counteracting press surface (7), is guided by circulating side shields in the remainder of its orbit substantially circular cylindrically, sealing its edges, said press shoe (6) being supported by a carrier clasping said circulating belt whilst being sealed from said side shields and non-rotatively mounted in the frame structure.
12. The apparatus as set forth in claim 1, characterized in that exclusively said at least one additional, endless belt (2) receives and removes the water (14) flowing off said first wire belt (1).
13. The apparatus as set forth in claim 1, characterized in that both said at least one endless belt (2) and said water-impermeable, endless belt (3, 4) receives and drains the water (14) flowing off from said first wire belt (1) by means of the plurality of blind holes or circumferential grooves provided in its outer surface.
14. The apparatus as set forth in claim 1, characterized in that at least one additional, endless belt (2) is pressed under longitudinal tension from without on said first wire belt (1) after a pre-dewatering phase and that after an effective duration of at least said second belt (2, 3) a water-impermeable endless belt (4) is pressed on said already pressing belts (1, 2, 3) also with the effect of a sliding surface (5), resulting in compression on said suspension cake (13) being increased incrementally.
15. The apparatus as set forth in claim 1, characterized in that after leaving the zone of maximum compression said first wire belt (1) is still not retracted from said suspension cake (13), its longitudinal tension thus still exerting dewatering pressure, and that air (17) or water can be applied at a velocity substantially different to the speed of said belt, resulting in water (14) being jetted from said wire mesh.
16. The apparatus as set forth in claim 1, characterized in that said press surface (7) is formed by a round tubular roll supported on its inside to withstand, among other things, the dewatering forces by either stiffeners or by supporting members on a stationary mount.
17. The apparatus as set forth in claim 1, characterized in that said smooth, endless press surface (7) moving in the machine direction is formed by a water-impermeable endless belt (4) running within the belt loop (4) over at least one suitable sliding surface (5) supporting said belt against the dewatering pressure at least in the region of said thickening process.
18. The apparatus as set forth in claim 17, characterized in that said sliding surface (5) features in the machine direction a contour differing from said circular cylindrical shape consistent in width comprising more particularly a convex curve (R1 - R3) tapered in the machine direction of said belt during compression.
19. The apparatus as set forth in claim 17, characterized in that said dense, smooth press surface (7) is formed by a water-impermeable endless belt (4) which is pressed with the aid of at least one suitable concave sliding surface (5) (press shoe (6)) against a round tubular roll (8) provided with a plurality of radially perforations so that said suspension cake (13) is squeezed between said water-impermeable belt (4) and said wire belt (1) whilst said wire belt (1) is supported by said foraminous tubular roll (8) which permits draining said white water (14) radially.
20. The apparatus as set forth in claim 17, characterized in that said dense, smooth press surface (7) is formed by a water-impermeable endless belt (4) which is pressed with the aid of at least one suitable concave sliding surface (5) (press shoe (6)) against a circular cylindrical roll (9, 10) provided with a plurality of blind holes or circumferential grooves so that said suspension cake (13) is squeezed between said water-impermeable belt (4) and said wire belt (1) whilst said wire belt (1) is supported by said roll (9, 10) which receives said white water (14) in said blind holes or grooves.
21. The apparatus as set forth in any of the preceding claims, characterized in that the compressive pressure on said suspension cake (13) amounts to at least 10 bar, more particularly at least 20 or 30 or 40 or 50 bar over a length of approximately 100 mm in the machine direction.

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