US3587863A - Rotary drum filter - Google Patents

Abstract

IN SUCH A FILTER, AS THE DRUM ROTATES, A LAYER OR SHEET OF PULP MATERIAL COLLECTED FROM THE BATH UPON THE FILTER MEDIA OF THE DRUM, EMERGES AT THE ASCENDING SIDE OF THE DRUM. FEED SUSPENSION OR PULP IS SUPPLIED CONTINUOUSLY TO THE VAT, SO THAT THE SHEET MAY BE DELIVERED CONTINUOUSLY AT THE DESCENDING SIDE OF THE FILTER DRUM, WHILE SEPARATED FILTRATE LIQUID PASSES CONTINUOUSLY FROM THE DRUM. A CAKE-WASHING PHASE AND SUBSEQUENT CAKE-DRYING PHASE MAY BE INTERPOSED BETWEEN THE

POINTS OF CAKE EMERGENCE AND CAKE DISCHARGE, AT THE TOP SIDE OF THE FILTER DRUM.

Description

United States Patent [72] inventor Ferdinand Kristo" Orillia, Ontario, Canada [21] App1.No. 863,669 [22] Filed Sept. 16, 1969 {45) Patented June 28, 1971 [73] Assignee Dorr-Oliver Incorporated Stamford, Conn. Continuation of application Ser. No. 611,077, Jan. 23, 1967, now abandoned.

[54] ROTARY DRUM FILTER 31 Claims, 51 Drawing Figs.

[52] U.S.Cl 210/404 [51) 1nt.C1 B01d33/06 [50] Field otSearch, 210/401, 402, 403, 406, 404, 392; 9/14; 162/363, 364, 366, 369, 370, 371, 372

[56] References Cited UNITED STATES PATENTS 3,409,139 11/1968 Jackson et a1. 210/404 1,509,024 9/1924 Paramor i. 210/402X It; 1i e iiiili Primary ExaminerReuben Friedman Assistant Examiner-T. A. Granger Attorneys-D. Mezzapelle, William J. Fox and Theodore M.

Jablon ABSTRACT: In such a filter, as the drum rotates, a layer or sheet of pulp material collected from the bath upon the filter media of the drum, emerges at the ascending side of the drum. Feed suspension or pulp is supplied continuously to the vat, so that the sheet may be delivered continuously at the descending side of the filter drum, while separated filtrate liquid passes continuously from the drum. A cake-washing phase and subsequent cake-drying phase may be interposed between the points of cake emergence and cake discharge, at the top side of the filter drum.

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ROTARY DRUM FILTER This application is a continuation of Ser. No. 61 1,077, filed Jan. 23, 1967, and now abandoned.

More particularly, the invention relates to rotary drum filters of the type that maybe employed advantageously for the dewatering and washing or rewashing of fibrous pulps, for example bleach pulp from the bleach towers, or the like. In such pulp treatment or washing operations great volumes of liquid or liquor must be handled by such filters also called pulp washers or thickeners which may be required to form sheets or layers of material on the filter media of the drum, having a moisture corresponding to a solids concentration of, say, l2 percent to 14 percent from a dilute feed pulp of perhaps only 0.35 percent to 1.0 percent. A I

In conventional pulp filters a solid cylindrical drum member is mounted for rotation by means of trunnions upon the end walls of the vat. One trunnion is connected to a drive for rotating this drum member. Upon the outside of the drum member there are provided filtrate drainage channels substantially parallel to the drum axis and adjoining one another.

Filter media itself are placed over these drainage channels around the drum. The drainage channels thus covered or closed by the filter media are open at one end of the drum for filtrate discharge. This filtrate discharge end of the drum and the discharge ends of the drainage channels are sealed against the pulp in the vat and where necessary also sealed against the atmosphere, allowing the filtrate liquid to discharge into the atmosphere, or into the vacuum of a barometric leg. Some types of filters therefore employ the so-called deckle strap devices which have a stationary deckle strap element in sealing contact with the periphery of the drum. in other types, a stationary vacuum box is placed sealingly against the very end of the drum, in order that the ends of the drainage channels of the drum may communicate with the vacuum of a barometric leg, aided by the static head of the feed pulp in the vat. The filtration cycle may comprise sheet-forming, and sheet-washing zones, as well as a zone for the continuous discharge of the finished sheet or filter cake.

A problem encountered in such filters is that of maintaining desired optimum vacuum effects while minimizing the required length of the barometric leg. Saving height of the barometric leg means lower building construction cost, as well as lower filtrate pumping cost as in countercurrent bleachwashing operation where several wash filters operate in series, each on its own barometric leg. Thus, spent wash liquor from one filter must be pumped back to height of the preceding filter.

Heretofore, a structural difficulty lay in the fact that in those filters the filtrate discharge outlet could not be located low enough relative to the lowest or 6 oclock position of the drainage channels on the drum. If the location of the filtrate outlet is located higher than the 6 o'clock position, the resulting negative head in the vat will not only reduce the available positive static head of the feed pulp in the vat, but will also detract from the filtration and filtrate drainage capacity of the drum.

Another problem is that of providing simple and effective sealing means between the stationary parts and the filter drum, to seal against the feed pulp in the vat, as well as against the atmosphere. These sealing means should seal evenly and wear evenly along the periphery of the filter drum, and should be readily accessible and serviceable. Frictional power loss incurred in the operation of these sealing means should be minimized. Particularly objectionable is the brake band effect of the conventional deckle strap devices.

Other frictional loss is incurred due to the operation of the so-called bridges in the vacuum box, that is, the partitioning which functionally separates sequential operating zones of the filter-operating cycle from one another to avoid short circuiting between the zones. Heretofore, this sealing effect had to rely upon sliding contact or close-tolerance fitting between the "bridges" and the rotating drum.

Another problem is that of mounting and supporting the vacuum box in cooperative relationship with the filter drum.

Heretofore, the atmospheric pressure exerted upon that box would tend to press the same against the associated end of the filter drum. Moreover, heretofore because of the endwise location of the vacuum box, the design and support of the associated end trunnion of the filter drum and its accessibility have also presented difficulties.

It is among the objects of this invention to overcome the foregoing problems and shortcomings in the construction and operation of the filters, and to provide an improved filter unit of generally simplified economical construction. More particularly, the filter unit should require little if any closetolerance workbetween the vat structure, the vacuum box, and the filter drum, and it should be capable of being readily assembled. Furthermore, this filter unit should have optimum sheet-forming capacity, provide a vacuum with optimum gravity assist from the feed pulp in the vat, should have optimum internal hydraulic and drainage characteristics, and should have deckle strap sealing means of great simplicity that will seal and wear uniformly, are readily accessible, adjustable and replaceable, and are self-compensating for wear and tear. Furthermore, the filter unit should be economically operable with relatively low power consumption by minimizing the aforementioned friction losses and by the use of a relatively short barometric leg.

The foregoing objects are attainable mainly by incorporating the vacuum box into the vat structure itself, in such a manner that the filtrate and wash liquors will flow from the drainage channels of the filter drum directly downwardly into the barometric leg. According to the invention, the vacuum box is in the form of an annular structure herein also termed the peripheral valve or perimeter valve surrounding the drum in direct communication with the drainage channels of the drum. Positive static head of feed pulp in the vat as well as the sheet-forming potential of all the drainage channels on the drum may thus be fully utilized. Simplified and more effective sealing means are provided in the form of a pair of improved self-compensating deckle strap devices associated with respective sides of the annular channel structure, featuring an endless deckle strap element which rotates with the drum, and has lateral sealing contact with the stationary channel structure. Liquid traps or water pockets are provided instead of close tolerance or frictional sealing means or bridges that functionally separate respective phases or zones of the filtration cycle.

7 More particularly, the vacuum box or stationary annular valve structure surrounds the filter drum with substantial clearance, traversing the longitudinal ribs which constitute the drainage channels on the drum. This annular valve structure is partitioned or functionally divided into arcuate sections defining the sequential zones or phases of the filter-operating cycle.

The filtrate liquid passing through the filter media flows along the longitudinal horizontal drainage channels into an annular collecting space or peripheral open zone or channel on the filter drum, that is a zone not covered by the filter media, but surrounded by the aforementioned peripheral valve structure, and which delivers filtrate liquid directly downwardly into and through a barometric leg. A deckle strap device is provided at each side of the annular channel structure for maintaining the operating vacuum by sealing that structure with respect to the rotating drum.

The peripheral valve structure is horizontally split into a lower arcuate portion structurally integrated into the vat, and a complementary upper arcuate portion or archlike member detachably but rigidly and tightly secured to the lower arcuate portion. Thus, when assembling the filter unit, one need only place the filter drum into its trunnion bearings on the end walls of the vat so as to have the lower part of the annular collecting channel of the filter drum register with the arcuate channel portion of the vat, then place the separate complementary arcuate valve member over the filter drum to cover and register with the remaining part of the collecting channel of the filter drum, and then rigidly and tightly securing that member to the vat. The two deckle strap devices may then be readily applied by threading them into place around the drum at the respective sides of the annular valve structure, for sealing the vacuum system against the feed pulp in the vat, as well as against the atmosphere. The required operating vacuum is thus maintainable in respective operating zones of the filtration cycle as defined by the compartmentation provided in the annular valve structure. Nonfrictional hydraulic seals are provided within the annular valve structure for functionally separating or bridging" the operating zones from one another.

Specific features are found in the construction and internal compartmentation of the annular valve structure, defining the filter-operating cycle, and also in the arrangement of nonfrictional water seals in the annular channel structure, functionally separating the zones or phases of the filtration cycle.

Still other features are found in various structural and functional aspects of thedeckle strap devices, involving low-friction characteristics and the ability to automatically and evenly compensate for wear and tear.

The peripheral or perimeter valve construction of this invention may be 'disposed midway between the ends of the drum, so that the filtrate liquid in the drainage channel may reach the annular collecting zone rapidly from both ends of a long filter drum before discharging in stream-flow fashion directly downward through the surrounding channel structure into the barometric leg.

Other features and advantages will hereinafter appear.

FIG. I is a longitudinal vertical sectional view of one embodiment of the filter unit, showing the peripheral valve structure surrounding the filter drum midway between the ends of the filter unit, and sealed by a pair of deckle strap devices, with the drum shaft sealingly penetrating the end walls of the vat.

FIG. la is a detail sectional view taken on line Ia-Ia in FIG.

FIG. 2 is a vertical transverse sectional view of the filter unit taken on line 2-2 in FIG. 1, showing the partitioning or bridging" within the filter box, which define the operating zones of the filtration cycle.

FIGS. 2a through FIG. 2h are detail sections of the peripheral valve structure taken respectively on lines 2a-2a through 2h-2h.

FIG. 3 is a greatly enlarged detail view taken from FIG. 1, showing a cross section of the top part of the peripheral valve structure and of the deckle strap devices.

FIG. 3a is a further enlarged detail cross-sectional view of one of the deckle strap devices of FIG. 3, illustrating the feature of uniform wear and tear.

FIG. 3b is an enlarged fragmentary longitudinal sectional view of one form of the deckle strap.

FIG. 30 is a detail cross-sectional view of another form of the deckle strap device.

FIG. 3d is a sectional view taken on line 3d-3d in FIG. 30.

FIG. 4 is a longitudinal vertical sectional view of another embodiment of the filter unit showing the vacuum box sur rounding one end of the filter unit.

FIG. 5 is a vertical transverse sectional view taken on line 5-5 in FIG. 4, showing one end of the filter drum peripherally sealed by one of the deckle strap devices.

FIG. 6 is a greatly enlarged detail view taken from FIG. 4, showing the vacuum box with the deckle strap devices.

FIG. 7 is a transverse sectional view of the vat structure of FIG. 1 separated from the filter drum, showing the lower part of the peripheral valve integrated in the vat, and the upper complementary part in the form ofa detachable arch member connected to the vat.

FIG. 8 is a sectional view taken on line 8-8 in FIG. 7, looking downward upon the vacuum box portion of the vat structure.

FIG. 9 is a sectional view taken on line 9-9 in FIG. 7, looking upward upon the bottom side of the arch member of the vacuum box.

FIG. 10 is an outside view upon the cake discharge side of the filter unit of FIG. 1.

FIG. 11 is an end view taken on line 11-11 of the filter unit of FIG. I0.

FIG. 12 is a side view, at reduced scale, of the filter drum per se, taken from the filter unit of FIG. 10, with some of the filter media removed.

FIG. 13 is a cross-sectional view taken on line 13-13 of the filter drum of FIG. 12.

FIG. 14 is an outside view upon the cake discharge side of the filter unit of FIG. 4.

FIG. 15 is an end view taken on line 15-15 ofFIG.14.

FIG. 16 is a side view, at reduced scale, of the filter drum per se taken from the filter unit of FIG. 14, with the filter media omitted.

FIG. 17 is a cross-sectional view taken on line 17-17 of the filter drum of FIG. 16.

FIG. 18 is a reduced semicliagrammatic cross-sectional view of a filter unit similar to FIG. 2 complete with gravity and barometric discharge legs.

FIG. 19 is a longitudinal vertical sectional view of a modified form of the drum filter shown in FIG. 1, featuring a recessed annular filtrate-collecting channel midway between the ends ofthe filter drum.

FIG. 20 is a cross-sectional view on line 20-20 in FIG. 19, showing the zones of a filtration cycle in connection with the peripheral valve structure, along with respective filtrate discharge legs.

FIG. 20a is a detail sectional view taken on line 20a-20a in FIG. 20.

FIG. 21 shows the peripheral valve structure of FIG. 20, separate from the filter drum.

FIG. 22 is a horizontal sectional view on line 22-22 in FIG. 21, looking downward upon the valve portion of the vat.

FIG. 23 is a horizontal sectional view on line 23-23 in FIG. 21 looking upward upon the complementary arcuate valve member.

FIG. 24 is a longitudinal vertical sectional view of a modified form of the drum filter shown in FIG. 4, featuring a recessed annular filtrate-collecting zone at the end of the filter drum.

FIG. 25 is a vertical transverse sectional view on line 25-25 in FIG. 24, showing a deckle strap anchored laterally upon the peripheral valve construction.

FIG. 25a is an enlarged detail view taken from FIG. 25, showing the anchoring of both ends of the deckle strap.

FIG. 25b is a further enlarged and further detailed end view of the anchoring of one end of the deckle strap, taken on line 25b-25 in FIG. 25a.

FIG. 25c is a sectional view of the anchoring of FIG. 25b, taken on line 25c-25c in FIG. 25b.

FIG. 25d is an enlarged detail view of the cross section of the peripheral valve, taken from FIG. 24, including the cross section of a novel tubular deckle strap anchored as in FIG. 250.

FIG. 25a is the cross section of another kind of tubular deckle strap which may be anchored as in FIG. 25a.

FIG. 25f is the cross section of still another deckle strap having circular cross-sectional configuration, which may be anchored as in FIG. 25a.

FIG. 26 is an enlarged detail view taken from FIG. 19, of the deckle strap devices at each side of the peripheral valve construction.

FIG. 27 is an enlarged detail view taken from FIG. 24, of the deckle strap devices at each side of the peripheral valve construction.

FIG. 28 is a side view upon the cake discharge side of the drum filter of FIG. 19, with parts of the vat wall broken away to show the recessed annular filtrate-collecting channel.

I FIG. 29 is an end view on line 29-29 of the drum filter of FIG. 28.

FIG. 30 is a side view upon the cake discharge side of the drum filter of FIG. 24, with parts of the vat wall broken away to show the recessed annular filtrate-collecting channel.

FIG. 31 is an end view on line 31-31 of the drum filter of FIG. 30.

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