US3613564A

US3613564A - Sludge-dewatering apparatus

Info

Publication number: US3613564A
Authority: US
Inventors: Maximilian Adamski; Donald S Schover
Original assignee: General American Transportation Corp
Current assignee: General American Transportation Corp
Priority date: 1969-08-13
Filing date: 1969-08-13
Publication date: 1971-10-19
Anticipated expiration: 1988-10-19

Abstract

An apparatus for removing aqueous liquid from a flowable material, containing aqueous liquid as a continuous phase and suspended solids as a discontinuous phase, to obtain a dewatered product has two endless, driven belts of elongated porous sheets. The belts are supported so that one belt has its path of travel inside that of the other belt and with an upper horizontal run of the outer belt overlying and abutting that of the inner belt moving in the same direction. The sheet of the inner belt is resilient, compressible and made of cellular material capable of absorbing aqueous liquid by a wicking action, whereas the sheet of the outer belt is a fine-mesh sheet with pores providing passage of the liquid through the sheet by a wicking action of the abutting cellular sheet while retaining most of the solids on the outer belt. A feeder for delivering the flowable material onto the outer belt is mounted adjacent the beginning of the dewatering zone where there is the wicking action due to the abutment of the two belts along that zone. A device for removing dewatered product is mounted downstream of that zone. A device to compress the inner belt downstream of the upper horizontal run of that belt includes a pair of opposed rolls. Another compression device may be at the upper horizontal run but downstream of the dewatering zone at which initial wicking occurs.

Description

United States Patent [72] Inventors MaximilianAdamski Wheeling; Donald S. Schover, Highland Park, both of I11.

[21] Appl. No. 849,770

[22] Filed Aug. 13, 1969 [45] Patented Oct. 19, 1971 [73] Assignee General American Transportation Corporation [54] SLUDGE-DEWATERING APPARATUS 15 Claims, 8 Drawing Figs.

Primary ExaminerBilly J. Wilhite Att0rney-Claron N. White ABSTRACT: An apparatus for removing aqueous liquid from a flowable material, containing aqueous liquid as a continuous phase and suspended solids as a discontinuous phase, to obtain a dewatered product has two endless, driven belts olelongated porous sheets. The belts are supported so that one belt has its path of travel inside that of the other belt and with an upper horizontal run of the outer belt overlying and abutting that of the inner belt moving in the same direction. The sheet of the inner belt is resilient, compressible and made of cellular material capable of absorbing aqueous liquid by a wicking action, whereas the sheet of the outer belt is a line-mesh sheet with pores providing passage of the liquid through the sheet by a wicking action of the abutting cellular sheet while retaining most of the solids on the outer belt. A feeder for delivering the flowable material onto the outer belt is mounted adjacent the beginning of the dewatering zone where there is the wicking [56] References Cited action due to the abutment of the two belts along that zone A UNITED STATES PATENTS device for removing dewatered product is mounted 1,778,342 10/1930 Thompson 100/118 X downstream of that zone. A device to compress the inner belt 1,958,279 5/1934 Morgan 100/1 18 X downstream of the upper horizontal run of that belt includes a 2,207,278 7/1940 Albrecht 100/118 UX pair of opposed rolls. Another compression device may be at 2,756,668 7/1956 Seed et al. 100/118 X the upper horizontal run but downstream of the dewatering 3,459,122 8/1969 Pastours et al 100/1 18 zone at which initial wicking occurs.

. 14 UPPEI? FOAM BELT ASH ATE t \l l 1D5ID8104 O/ w Q esa O 53 ,3 2;" B a 3 O o g 45 u; 7

e we 02 47 1 WlCKlNG ZONE oooootfm;

w 3 LIQUIDCOLLECTIDN PAN O Q COMPRESSION Rous e e ee ea a o o o o o 0. 15 4 1 s p grgtgv e 8o BSbBI r 12 o 100$ CONVEYOR m LOWER FOAM BELT";

4 k HEAT ExcHANoEk 95 swws/z LJ'IDT AIR PLENUM To mwstz SCREEN BELT =l EXHAUST PATENTEUdm 19 l97| ne-Mesh Belt 5*" 4am udge Coke/ Air Heat Exchanger f Gases Ara-axi- L SHEET 2 [1F 3 7 2 a m w 9V T Hot Gases PATENTEDOU 19 IBTI SHEET 3 BF 3 SLUDGE-DEWATERING APPARATUS CROSS-REFERENCE TO RELATED APPLICATION This invention related. in subject matter to copending U.S. Pat. application Ser. N0.' 773,204 filed Nov. 4, 1968, by one of us, viz, Donald S. Schover, entitled Sludge Dewatering Apparatus and having with the present application a common assignee. The present invention has advantagesover the' invention in that copending application. For example, there can be longer belt life. The apparatus can be used in an integrated process that can includeflu idized incineration because'of the ability to obtain a relatively thin layer of dewatered material of higher solids content that can be dried substantially before removable from the sheet to which the flowable material is applied. It is not necessary to use a porous cellular material that is stable at elevated temperatures. A scraping action on the surface of that cellular material for removal of the dewatered material is not necessary.

BACKGROUND OF THE INVENTION l. Field of the Invention This invention relates to an apparatus for removing water or other liquid from flowable materials containing such water or liquid as the continuous phase and suspended solids as a discontinuous phase. This invention also relates to the use of novel sheets as the endless belts in the apparatus.

The field of the invention is best illustrated by one use, viz, the use of the apparatus for the dewatering of sludge in which aqueous liquid is removed so that the material remaining has a higher solids content. In this illustrative field the flowable material can be secondary or activated sludge, primary sludge, primary sludge admixed with secondary sludge after a digestion of the mixture, and a digested mixture of primary sludge and sludge cake, which is obtainable by dewatering secondary sludge in accordance with the process, or even degritted sewage. The dewatered product from all of these sludges, except degritted sewage that may be dewatered only to the extent of producing a primary sludge, is a cake that is solid or semisolid and thus lacks the physical characteristics of a liquid which are characteristics of the sludge. This end product can have a solids content that is as highas 95 percent. In that case heating of the dewatered material, while a thin layer on the belt, by drying is utilized. Without'such heating and drying, the product can have a solids content as high as'35 percent. The partial dewatering of activated sludge eliminates the conventional thickening by flotation that is part of-conven tional sludge treatment systems.

2. Description of the Prior Art Although this invention, is useful for removal of liquid from numerous flowable materials, the prior art is illustratively described below by reference to the dewatering of sludges; A detailed description of the prior art of dewateringsludges is presented in said copending application Ser. No. 773,204. The 1 entire disclosure of that copending application, rather than its description of the prior art, is hereby incorporated by reference.

A sludge is the material removed from settling tanks in which settling has been permitted for the settleable solids. Such solids are naturally present in water and waste water or are derived from nonsettleable matter by chemical coagulation and precipitation. Examples of waste waters are domestic sewage and industrial wastes. By treatment of these waste waters by conventional methods a primary sludge, a secondary or activated sludge, and a final aqueous effluent are obtained.

The secondary sludge is obtained by treating the primary aqueous effluent removed from a primary settler in which the primary sludge separates from the degritted sewage. These sludges are mixtures of suspended solids, as a minor percentage of the composition, and water as the major percentage. After a long period of time of settling there can be come separation of solids from the sludge to produce a separated layer of somewhat higher concentration of solids than the sludge from which it has been separated. Of course, the other layer resulting from this separation is a water layer having a lower solids content than the original sludge.

Conventional methods of treatment of sludges for their dewatering include vacuum filtration, centrifugation and gravity dewatering. These conventional processes provide as one end product a material that is a cake or solid rather than a flowable material that is a characteristic of the initial sludge.

Primary sludge contains water and about 2.5 percent to 5 percent by weight of solids. A conventional solids content is about 4 percent. The secondary or activated sludge illustratively contains between 5,000 and 10,000 mg./l. of solids. This is a solids content of 0.5 percent to 1 percent in the secondary sludge. In the prior art processes most of this sludge is recycled to the aeration treatment-in which the primary effluent is aerated and settled to form the secondary sludge and the final effluentLThe rest of this activated sludge is mixed with primary sludge and this mixture is digested, either aerobically or anaerobically, to convert in ingredients. that' are biologically degradable organic materials so that the product does not putrefy to any'objectionable extent, if at all.

For optimum utilization of digestion capability the sludge that is fed to the digester should have a solids content of about 6 percent by weight. The solids content of primary sludge is increased from the conventional4 percent by weight to the desired concentration by the dewatering invention of said copending patent application and by the present invention. When a mixture of primary sludge andsecondary sludge is used for digestion, the secondary sludge reduces the solids content from that conventionalcontent of primary sludge. This is because of the lower solids content of secondary sludge. However, as described in said copending patent appli-, cation, by the dewatering of that invention and by the present invention one can dewater themixture to the desirable solids content that is mentioned above for the feed to be digested. Furthermore, the secondary sludge alone can, be adequately dewatered. The dewatered product when mixed with primary sludge can have the desired solids content for sludge to be fed to the digestion operation.

Prior art processes for treatment of sludge include various concentrating processes, such as gravity thickening, flotation and evaporation, for increasing the solids content of primary sludge prior to its digestion.

Different processes are used to increase the solids content of the digestedv sludge. These different processes include vacuum filtration and centrifugation. Both of these processes can produce products that can be fed to an incinerator that will convert the combustible materials to gas and inorganic materials will remain as ash. The cost disadvantage of vacuum filtration that requires expensive amounts of flocculants to avoid clogging of the filter and the expense of centrifugation requiring a feed containing 10 percent to 12 percent solids, with polymer addition to enhance the dewatering, are known in the prior art. These disadvantages are stated in more detail in said copending patent application.

Although centrifugation can dewater secondary sludge to a solids content of 35 percent the cost is considered prohibitive. The prior art has described a method of converting this high solids product from the centrifuge to a powdery dried substance containing as much as percent to percent solids. The method apparently passes a hot drying gas through a quantity of the sludge of substantial depth. The exit gas carries fine particles of organic material and is quite odorous. That gas requires a heat treatment to oxidize the odorous material.

SUMMARY OF THE INVENTION This invention relates to an apparatus useful for removal of liquid from a flowable material that is a suspension of solids in a liquid, as discontinuous phase and continuous phase, respectively. The use of the invention pertains especially to the dewatering of sludges such as produced in the treatment of domestic sewage and industrial wastes.

In a more specific sense the use of the invention is under conditions to provide a degree of dewatering such that the dewatered product as a cake has sufficiently high solids content that it can be used as a feed material to a fluidized incinerator operation, without requiring the use of auxiliary gas for temperature maintenance and preferably without requiring procedures developed by the prior art for control of the incineration process or control of the manner of feeding the material from the cake. ln such improved aspect of the use of the invention, the use includes utilization of the thermal energy of the combustion gases directly or indirectly, preferably the latter, to provide additional water removal so that the dewatered product can be incinerated satisfactorily without the use of auxiliary fuel. This integral process is made possible because the initial dewatering portion of the treatment of sludge results in the production of a relatively thin layer of cake on a sheet, particularly on an endless belt That layer can be readily subjected to a drying gas at a temperature that is sufficiently elevated for water removal by mere passage of that gas over the layer of the initially dewatered material. At the same time the sheet or belt is of such construction that a substantial amount of water removal can be effectuated from the other side of the layer through the pores of the sheet or belt. In this integral use of the invention, that includes the fluidized incineration and such use of drying gas, a feed product for incineration is obtained without a substantial amount, if any, of contamination of the gas by physically transporting from the drying zone a part of the dried or partially dried material with the exit gas. Such advantage decreases and usually can eliminate the heating of the exit gas to a temperature sufflcient for oxidation of the organic material that would otherwise be carried away with the exit gas along with the moisture removed from the cake, if the prior art process were used.

The apparatus of the invention is an improvement, in several ways, of the apparatus of the invention of said copending patent application. Although the continuous use of the apparatus of that earlier patent application effectuates substantial dewatering of a sludge, the surface of the endless belt made from a compressible, resilient sheet of porous cellular material, that receives the flowable material, is scraped for removal of the cake. In time this scraping changes the belt sufficiently to require replacement. Most materials of such belts cannot be subjected without degradation to a temperature sufficiently elevated for adequate dewatering of the cake by a drying gas passed over the layer of the cake. Some materials, that could be used to provide such sheet with sufflcient resistance to thermal degradation, can add considerably to the cost of the operation in view of the fact that the thickness of the sheet is relatively large, e.g., one-half inch. Furthermore, that surface of the belt would be subjected to mechanical damage during the scraping removal of the dried material somewhat imbedded in the surface portion of that belt. It is apparent that the application of the sludge to be dewatered directly to the surface of such belt requires before reuse a washing of the belt. The application of wash water should be to both sides of the belt to insure maximum removal of any cake that remains in the sheet below that surface.

The apparatus of this invention avoids these disadvantages of the apparatus of the invention of that copending application. The present apparatus places on that surface of the belt of porous cellular material for a portion of its travel, viz, its top run, an endless belt of a sheet having characteristics such that it can be contacted with physical means such as a doctor blade with a substantially lower rate of wear. Thus the useful life of the sheets is much greater than that of the single sheet to which the sludge is applied in the prior apparatus. This belt which is placed over the sheet of porous cellular material is quite thin relative to the belt of porous cellular material. The belt of this thin sheet to which the sludge is applied can be relatively expensive. lts longer life more than compensates for the increased cost of using two endless belts. This substantially thinner belt is a sheet with pores that are sufficiently large for the passage of liquid of the flowable material through the belt but sufficiently small to prevent any substantial transfer of the suspended solids through that belt. As a result, when the belts are separated, the thinness and the porosity of the thinner belt permit the use in the apparatus of other mechanical means that would not be desirable or as effective for the removal of dewatered material from a sheet of porous cellular material. For example, the apparatus can include a pair of rotatable brushes that engage the two major surfaces of the thinner belt.

In the present apparatus there can be a simple water washing of the thinner belt, but ordinarily this is not necessary. Removal of the dewatered material by mechanical action, e.g., the brushes, suffices. Air jets can be directed to either or both major surfaces of the endless belt for removal from the belt of product having a higher solids content. lnstead of the application of mechanical force by a doctor blade or rotatable brushes or of the use of air jets as mentioned above, the thin layer of this product can be readily removed by passing the belt around a roll having a small diameter. This produces sufficient flexing or bending of the endless belt and the product so that the dewatered product as a cake layer breaks up. It can fall from the belt onto a collector.

When the apparatus is to be used for the dewatering of materials, such as activated sludge, to obtain a product of solids content sufficiently high for use as a feed to a digestcr, the apparatus of the present invention can utilize only the one set of belts described above. During their top run the thinner sheet is on and abuts the sheet of porous cellular material. The activated sludge is applied to the top surface of the thinner sheet. As these two sheets move along their top run, water passes through the pores of the thinner sheet by the effect of gravity alone or preferably only when aided by a wicking action produced by the sheet or porous cellular material abutting the bottom surface of the thinner sheet.

Preferably the thinner sheet is made of a material that is nonabsorbing as regards the liquid or at least only slightly absorbing of the liquid. This characteristic avoids retention of liquid that would enhance undesirable adherence of the dc watered product to this sheet. The belt of porous cellular material is preferably water absorbing to enhance the wicking action that draws liquid through the other sheet so that more liquid is removed from the flowable material than can pass, if any, through the thinner sheet when not abutted by the porous cellular sheet. Thus use of a belt of porous cellular material that can absorb the liquid permits, with a porous belt that can by itself pass liquid through it, a faster rate of movement of the belts for a particular degree of removal of liquid from the flowable material being treated.

In the use of the apparatus, described above, in which the one set of two endless belts is present, the removal of liquid from a flowable material is relying on the passage of the liquid through the thinner sheet and removal from that sheet at its pores of the liquid by the sheet of porous cellular material, having a higher degree of removal of liquid from the flowable material. The present apparatus, except for one type of use. includes a second set of such belts. These belts are driven around rolls so that they come together at their bottom run during which the thinner sheet of that set abuts the flowable material already applied to the thinner belt of the first set. The top set of belts at their bottom run are forced downwardly against the flowable material in the other set. This compresses the belt of porous cellular material of the bottom set to remove liquid from that belt. This compression is accomplished in the illustrated apparatus by sets of opposed rolls between which pass the opposed runs of the two sets of belts with the flowable material between the sets. The liquid being forced downwardly through and out the compressed bottom belt of porous cellular material flows by gravity to a collection pan. At the same time, any liquid that has passed upwardly through the pores of the thinner belt on top of the flowable material and has been picked up by the superimposed belt of porous cellular material, flows by the compression of that belt to the top surface of the belt and then moves laterally for ultimate downward flow by gravity. Part of the liquid received in material when the compressive force is released as the assembly of sheets passes from an opposed pair of rolls. The apparatus of this invention includes means to wash the belt of porous cellular material of the first set during the travel from its top run whilejtis still separated from the thinner belt. Likewise the belt of porous cellular material of the second set of belts, when that set is present, is subjected to a liquid washing while it is separated from the thinner belt of that set.

The thinner belt of the first set can be washed with liquid, if desired, after removal of product'of higher solids content and before return of that belt to its top run where the product to be dewatered is added. In most cases the latter washing is unnecessary. ln theuse of the apparatus with the two sets of belts the thinner belt of the upper set may carry with it from its bottom run a small amount of the product. This can be removed by simple water washing before its return to abut the top run of the thinner sheet of the lower set.

v Examples of the sheet of porous material having the characteristics of compressibility and resilience are cellulose sponge and synthetic foams such as polyurethane foam. Although these sheets have substantial thickness, as described above, they do not have fully satisfactory tensile strength for their use alone as a long endless belt. Accordingly, the apparatus of the present invention can include a composite sheet as an endless belt that includes a compressible, resilient sheet of porous cellular material and a backing sheet adhered to the back major surface of the former sheet. The backing sheet has a construction required by the use of the composite sheet in the present invention. It has large openings with the least amount of material of the backing sheet in the path of travel of water later forced out of the sheet of porous cellular material in the use of the composite sheet in the present invention. An endless backing sheet meeting these requirements is a widemesh sheet of extruded polypropylene that has sufficiently large diameter extruded filaments extending longitudinally and transversely to provide adequate strength for use as an endless belt and yet has the desired large openings mentioned above. Such extruded sheet is commercially available. As part of the manufacture of that backing sheet the transverse and longitudinal filaments or strands of extruded material are con-. nected to one another where they intersect.

; Of course, the backing sheet and the sheet of porous cellular material are flexible. Likewise the composite assembly of these two sheets is sufficiently flexible to bend around a drive roll and a number of other rolls mounted'in a manner to provide a top or upper horizontal run with a portion of the balance of the run being a lower horizontal run. The thinner porous sheet is also flexible so that it as an endless belt can pass around a number of rolls, one of which is a drive roll, so

as to provide similar top and bottom runs. Its top run is such that the latter endless belt can rest on the top run of the belt of porous cellular material during the top horizontal run of the latter. The bottom horizontal run of the thinner porous belt is below and spaced from the bottom horizontal run' of the other belt.

Preferably the bottom run of the thinner porous belt passes through a chamber. Drying air or other gas is passed countercurrently through the chamber for additional removal of liquid from the material being treated. The device for discharging the layer of ultimate product, of the precess of removing liquid, is beyond the bottom run of the thinner porous belt, except for the apparatus modified so that the layer of product is removed from that belt in that drying chamber. In the latter case the apparatus can include a conveyor belt having its top run passing through the drying chamber and moving in the same direction as the bottom run of the thinner belt. That conveyor belt has the downstream end of its top run located above a hopper that feeds the material to a screw conveyor. The latter feeds the material to a fluidized incinerator. Thermal energy in the gases from the fluidized incinerator is used for drying the material in the chamber through which the bottom run of the thinner belt passes. The thermal energy can be used either directly by passing the hot combustion product gas into that chamber or indirectly by passing a drying gas in indirect heat exchange with the combustion product gas using a heat exchanger, and the heated drying gas is passed into that chamber. A dry cake layer is formed on the downwardly facing surface of the belt.

Instead of removing the cake material from the thinner belt in the drying chamber, in certain cases it can be removed external of that chamber before the belt passes to the higher elevation for its top run. Such removal can utilize any of the devices mentioned above.

Because the thinner belt may be prone to wrinkle or overlap itself in the transverse direction as it passes over one of the rolls that conveys it in the path of travel mentioned above, the thinner belt can be joined at its longitudinal margins to a pair of elongated narrower sheets of flexible materialjThose sheets usually are not suitable for passage of liquid through them. These sheets may be thin sheets of extruded plastic, e.g., extruded polypropylene. This composite assembly of a thinner sheet,'having the characteristics specified above, and the two narrow sheets secured to it is novel as a sheet or as a belt. This assembly has thicker longitudinal margins. The thicker margin isprovided by a hem at the distal edge of the narrower sheets. A flexible rod of material, such as polypropylene, is in' the hem to complete and insure the thicker margin. Alternatively the pair of narrower sheets that have been extruded as sheets hav ing a single thicker margin can be secured to the thinner porous sheet. i

This composite assembly has the thicker pair of longitudinal margins so thatthey can be moved away from each other by devices of the apparatus in the event that there is some wrinkling or overlapping of the thinner sheet. For maximum water removal of flowable material applied to that thinner sheet, it should be maintained in an unwrinkled condition when overlapping the other sheet of the set. If there is wrinkling of the sheet, the material above the folded portion may not have its liquid pass through the sheet to the same to the same extent, if at all. Of'course, such undesirable result does not impair the effectiveness of the balance or major area of the thinner sheet and the sheet or porous cellular material below such major area. The beaded or thickened longitudinal margins or edges of this composite sheet cooperate with these devices that eliminate wrinkling so as to insure proper tracking of that sheet as an endless belt, but that advantage is of lesser importance because the main reason is the prevention of wrinkling of the thinner sheet. This is because some misalignment of the two sheets of the set will not adversely affect the efficiency of liquid removal and a substantial misalignment of the two sheets at their top run will not prevent the substantial 7 operation of the process with this apparatus.

The novel composite assembly of sheet of'porous cellular material and adhered sheet of large-mesh backing material is preferably modified in a similar manner to provide thickened longitudinal margins that are engaged by devices to insure tracking of that composite sheet as an endless belt. In that case two relatively elongated narrow sheets of extruded polyester will adhere to the longitudinal margins of the backing sheet and their distal ends are either hemmed to provide longitudinal cylindrical channels in which polypropylene flexible rods are also placed or those plastic sheets are extruded with a single thicker margin. The composite assembly with these two sheets mounted on the backing sheet has these thicker margins at the longitudinal edges.

in the foregoing description, the sheet having suitable pores has been referred to as a thinner porous sheet. It is flexible. It can be referred to as a flexible screen cloth that is utilized in form of an endless belt. Such screen cloth can be made by weaving monofilaments of material, such as synthetic organic plastics, e.g., polymers, and various metal wires, e.g., stainless steel and Monel. The plasticcan be a polyester, a nylon Teflon, or other synthetic material having a sufficient tensile strength for use as woven material in the final form of an endless belt. The polyester screen cloth is preferably a monofilament plain weave cloth. When the belt is required by the apparatus to pass through a chamber, as described above, for further liquid removal from the product, the material used for the belt must withstand the high temperature of the drying gas. It can be made of a type of nylon that will withstand such high temperature. A suitable nylon is Nomex.

The use of a set of two belts having different physical characteristics, as described above, has the advantage when dewatering a sludge that the belt on which solids may remain after the partial dewatering of the sludge is resistant to decay by such material. This is the case when the thinner sheet is made of plastic that has either not or a low absorption of water. That is also a desirable property for this endless belt to facilitate cake removal.

The composite assemblies of sheets that constitute endless belts of the present apparatus are also utilized as the two belts of the upper set in the embodiment of the apparatus in which two sets of belts are used.

DESCRIPTION OF THE DRAWINGS The apparatus of the invention and use of that apparatus for the removal of liquid from flowable materials, as defined above, are illustrated by preferred embodiments in the accompanying drawings, in which components that are the same and provide the same function are generally designated by the same numeral and in which:

FIG. 1 is a front elevational view, generally schematic, of a preferred embodiment of the apparatus of the present invention;

FIG. 2 is a fragmentary view ofa second embodiment of the apparatus of the invention showing a modification of the lefthand end and of the bottom portion of the apparatus of FIG. 1, along with the addition of equipment that utilizes and includes fluidized incineration equipment;

FIG. 3 is a fragmentary view of a third embodiment of the apparatus of the present invention showing a modification of part of the apparatus of FIG. 2 by including, as part of the apparatus, a conveyor extending through the drying chamber to insure removal from the thinner porous belt of product that may fall of it during the final drying operation.

FIG. 4 is a perspective fragmentary view of the top run of the bottom set of belts and showing the two belts as they would appear when taken along line 4-4 of FIG. 1, with portions of the two belts cut back different amounts and with one upper composite assembly being turned up to show more clearly the construction of the two belts;

FIG. 5 is a fragmentary top plan view of an initial part of the top run of the endless belt of the composite assembly having the screen cloth, and the initial portion of the top run of the composite assembly as an endless belt of a sheet of porous cellular material and a backing sheet, along with the right-hand portion of the top composite sheet cut away to show the components of the other or lower composite sheet;

FIG. 6 is cross section taken along line 66 of FIG. 5, showing a pair of the devices used to stretch transversely the screen belt after passing around an idler roll to start its top run;

FIG. 7 cross section taken along line 7-7 of FIG. 5; and

FIG. 8 is an enlarged cross section taken along line 8-8 of FIG. 5 and enlarged to show the construction of the pair of the devices used to eliminate any wrinkling that occurs in the thinner sheet as an endless belt.

DETAILED DESCRIPTION Referring to FIG. 1 which shows one of the preferred embodiments of the apparatus of the present invention in its use for the dewatering of sludge as the flowable material, the apparatus is generally indicated at 10. The apparatus 10 includes a lower set of two endless belts, one of which is a foam belt generally indicated at 11 and the other being a screen belt generally indicated indicated at 12. The apparatus 10 has an upper set of two belts. These are a foam belt generally indicated at 13 and a screen belt generally indicated at 14. The

foam belts

11 and 13 have the same construction that is shown in more detail in FIGS. 4, 5, 7 and 8. These belts are shown with legends in FIG. 1 along with legends for other components of the apparatus and with other descriptive legends that simplify understanding of the apparatus. FIGS. 2 through 8 contain similar clarifying legends and in these later figures where the legends appear for belts II and 12, they are referred to as a wicking belt and a fine-mesh belt, respectively. These designations are merely alternative generalized descriptions of the belts.

The belt 11 is passed about or trained around a driving roll 15 and an idler roll 16 that are rotatably mounted by means (not shown) so that their axes are horizontal and parallel to provide an upper path of travel of belt 11 that includes a horizontal run where belt II is supported by a number ofidler rolls 17. The lower portion of travel of belt 11 is over an idler roll 18 and under an idler roll 19, that provide a proper degree of tautness because roll 18 is spring urged in an upward direction by a conventional construction of its mounting by its support. In addition to passing over rolls l8 and [9 that are adjacent to drive roll 15, belt 11 in another part of its lower or bottom run passes over an idler roll 20 that is adjacent to roll 16. The idler roll 20 is positioned to raise the bottom run of belt 11 before it reaches roll 16 so that belt 11 travels horizontally to roll 16. This arrangement is provided to raise the bot tom run of belt 11 from its horizontal position, between roll 19 and roll 20 where belt 11 is washed by a washing device generally indicated at 21. The device 21 is described late in detail.

Sludge to be dewatered is fed to a sludge delivery trough 22 that has a bottom outlet for feeding sludge to a chute 23. The sludge flows out a bottom opening in chute 23 which is positioned so that outflowing sludge is fed to the top upper surface of the horizontal top run of belt 12 at a position where belt I l in its horizontal top run is below belt 12. The rate of flow of sludge from chute 23 is such that the flowable sludge when applied and thereafter, even during the application of a compressive force by a compression device generally indicated at 24, is and remains spaced from the edges of belt 12. This manner of feeding of sludge is provided to prevent a loss of part of the sludge by a flow over the edges of belt 12. If that loss would occur during the compression treatment, the overflowing sludge would flow to a liquid collection pan 25 which receives aqueous liquid that initially passed through belt 12 and into belt 11 from which it is removed by the compression treatment. That loss would increased undesirably the solids content of the liquid received by pan 25.

The construction of belts 11 and I2 is shown in FIG. 4. It is seen there that each of these belts is made from a composite assembly of elongated sheets joined at the ends of the composite sheetsto form the endless belt. The composite sheet from which belt 11 is made comprises an elongated, compressible, resilient sheet 26 of porous cellular material to which is adhered at its longitudinal margins two elongated, extruded

plastic sheets

27 and 28. In addition, this assembly includes an elongated coarse-mesh extruded plastic sheet 29 that is bonded to

sheets

26, 27 and 28. The sheet 29 is a backing sheet that has wide pores or openings, as described earlier, for the purpose of allowing free flow of water from sheet 26 when it is compressed The sheet 29 provides the necessary strength for belt ll.

At their

distal edges sheets

27 and 28 have

hems

30 and 31 that provide cylindrical channels in which are placed flexible extruded

plastic rods

32 and 33. With this construction belt I I has beads, provided by

hems

30 and 31 and

rods

32 and 33. These marginal beads can be engaged by tracking devices that are disposed along each edge of belt ll at various locations to cooperate for a tracking of belt 11. These pairs of tracking devices are described later in connection with FIG. 8 in which similar pairs of tracking devices engage sheet 12 for the additional and more important function of providing a transverse stretch to remove any wrinkling that has occurred as belt 12 passed around a roll. The composite sheet that is used to. make the endless belt 11 is flexible for passage around the rolls. The plastic used for sheets ,27, 28 and 29, and for

rods

32 and 33 is preferably polypropylene. The sheet 29 is a coarse-mesh screen made by an extrusion operation with the warp strands 34 and the woof strands 34' that are shown in FIGS. 4, 7 and 8. These" strands are'j oined to one another at theirintersections as part of the process of making sheet 29. As

regards sheets

27 and 28, they could be extruded with a thickened part along one edge to provide the equivalent construction produced respectively by hem 30 and rod 32 and by hem 31 and rod 33. l

The sheet'26 is preferably an elongated sheet of fine-pore cellulose sponge. It may be an elongates sheet of material in foam form, such as polyurethane foam, mentioned above, and cellulosic foam. In any event, sheet has open cells so.th at the cells are interconnected but at the sametime these cells are of a size that is sufficiently small in the preferred embodi ment, to prevent downward passage of a substantial amount of suspended solids from the top surface portion of sheet 26 that may be received with water through belt 12 from the sludge during the

top run ofbelts

11 and 12. l

The flexible belt 12 is also made from an elongated composite sheet. That sheet comprises an elongated sheet 35 that has a width substantially that of sheet 26. Adhered to the two longitudinal margins of sheet 35 are extruded

plastic sheets

36 and 36 that like

sheets

27 and 28 have

hams

37 and 38 at belt 12 passes around various rolls to eliminate wrinkling.

The sheet 35 is flexible and has small pores that permit passage of liquid of the sludge for movement to sheet 26. The size of the pores is less than that necessary for transfer of a substantial amount of solids when the sludge is on sheet 35 during its horizontal top run. The preferred material for sheet 35 is a polyester monofilament plain weave cloth that is distributed by Tobler, Ernst and Traber of New York and is manufactured in Switzerland. A number of such screen cloths have been tested satisfactorily with different mesh openings. These screen cloths had mesh openings ranging from 53 microns up to 840 microns. 1n the dewatering of activated sludge it was found that such screencloth with 53-micron mesh openings provided the best degree of dewatering as regards quality of water removed; Apparently this is because the size of the openings provided the best degree of dewatering when the size corresponds generally with the micron size of the activated agglomerates. The 53-micron screen cloth had a 275 mesh count per inch and had a 32 percent open area. The larger the open area, the shorter is the time for the wicking action of the belt 11 to remove a particular percentage of water from the sludge. It is believed that this is because the screen cloth can resist the flow by gravity through the openings for the part of the dewatering action of the present process. The larger mesh-size screen cloth can be used as effectively for the dewatering with a specified water quality if there is an addition of polymers to the sludge so as to provide sufficient coagulation of'solids.

Using the apparatus of the present invention it is not necessary to add polymers to the sludge for the purpose of utilizing a screen cloth of larger mesh openings as belt 12, but such use of polymers can permit the use of the present apparatus of a shorter length or for the same length, as compared with using a screen cloth with 53-micron mesh openings, by operating for increased output by a higher speed of travel of

belts

11 and 12. The addition of polymers to the sludge and the screen cloth of larger mesh openings can produce a higher cake dryness, Le, a cake that has a higher solids content. Also the use of polymers can provide a removal of water of lower solids content. Of the various conventional polymers that are available for such coagulation, the preferred polymer for activated aerobic sludges is Mag nifloc 52l-C, made by American Cyanamid Company.

.Returning to FIG. 1, the lengths of belts 1 1 and 12 are sufflcient to provide a relatively long path of travel of these belts in theircommon horizontal top run from the point ofapplication of the sludge via chute 23 until the belts pass through compression device 24. During this path of travel liquid can pass by gravity from the sludge through the pores or openings of sheet 35 of belt 12 to andinto sheet 26 of belt 11. This flow .into sheet 26 is enhanced by the wicking action that pulls the travel of belts l1 and 12 from chute 23 to device 24, is partially dewateredbefore the sludge and

belts

11 and 12 are sub' jected to compressiveforce. In this partial dewate ring, part of the water of the sludgeis transferred to put water throughout the thickness of sheet 26 of belt 11. The sheet 26 has sufficient thickness, e.g., a thickness of one-half inch, to receive such amount of water during the travel in this zone. Such sheets of fine-pore cellulose sponge are commercially available from a number of manufacture including: E.l. du Pont de Nemours & Co., lnc., Fabrics and Finishes Department, Wilmington, Del.; General Mills, lnc., Chemical Division, Tonawanda, N.Y.; Nylonge Corp., New York, N.Y.; American Sponge and Chamois Co., New York, NY.

The compression device 24 has belts '13 and 14 that are of the same construction as

belts

11 and 12, respectively. The endless belt 13 is driven by a roll 42 about which it is trained. The belt 13 is also trained about an idler roll 43. The bottom run of belt 13 is downwardly inclined from roll 42 and from roll 43. This downward inclination is providedby a set of idler rolls 44 that are above belt 13 in this bottom run and that provide a slightly inclined path of travel for an intermediate portion of the bottom run of belt 13 so that this portion is opposing an intermediate portion of thehorizontal top run of

belts

11 and 12. As belt 13 in its bottom run travels from roll 43 to roll 42 it is in contact with belt 14 so that belt 14 is between belt 13 and a portion ofthe top run of belt 12. As a result, during this slightly inclined path of travel of belt 13 and thus belt 14, there is a decreasing of the space between belts l2 and 14 that are between

belts

11 and 13. This decrease of spacing is in the direction Qf travel of belt 11 toward driving roll 15. The roll 42 drives belt 13 in a direction so that it moves below rolls 44 in the same direction the top run of belt 11.

The compression device 24 has rolls 45 between roll 43 and the set of rolls 44. The

rolls

45 and 46 abut, respectively, sheet 29 of belt 1 3 during the inclined travel of belt 13 downwardly from roll 43 to the inclined bottom run of belt 13 and the inclined travel up to roll 42 from the slightly inclined bottom run of belt 13.

A portion of the top run of belt 13 from roll 42 to roll 43 is diverted by an idler roll 47 and an idler roll 48that engage the inner surface and outer surface, respectively, of belt 13. The .roll 48 is mounted to provide a downward force so that roll 48, in cooperation with roll 47 provide the necessary tautness of belt 13.

The belt 12 is passed around a driving roll 50 and an idler roll 51 that are rotatably mounted with their axes parallel to and outside the axes of rolls l5 and 16 so that belt 12 has a horizontal top run longer than that of belt 11 but belt 12 rests on belt 11 during most ofthe top run of belt 12. Thus belt 12 is also supported by rolls l5 and 16 and rolls 17 with belt 11 separating belt 12 and these rolls. The roll 50 is driven in a manner similar to that described below for the rotation of roll 15.

The belt 14 is passed around a driving roll 52 and an idler roll 53 that have their axes parallel to but above the axes of

rolls

42 and 43 for a top run of belt 14 above and spaced above the entire top run of belt 13. The roll 52 is driven in a manner similar to that described below for the rotation of roll 42.

The driving rolls and 42 are rotated in the following manner. A motor 60 has a shaft 61 on which is fixedly mounted a gear 62 that meshes with a gear 63 fixedly mounted on a shaft 64 mounted for rotating about a fixed axis by a support (not shown). The gear 63 also engages a gear 65 that is fixedly mounted on a shaft 66 that is rotatably mounted on a support (not shown). A pulley 67 is fixedly mounted on shaft 64 and drives a belt 68 that drives a pulley 69 that is fixedly mounted on a shaft 70 on which roll 15 is fixedly mounted. A pulley 71 is fixedly mounted on shaft 66 and drives a belt 72 that drives a pulley 73 that is fixedly mounted on a shaft 74 on which roll 42 is fixedly mounted. Thus, the operation of motor 60 drives rolls 15 and 42 in unison. The dimensions of the gears and pulleys are such that belts 11, l2, l3 and 14 are operated at the same linear speed to avoid an undesirable abrasive action between them.

As mentioned earlier belt 11 has a bottom run with an intermediate portion that has a horizontal path of travel. This portion of the run is below a plane tangential to the bottom of

rolls

15 and 16. The purpose of roll to raise belt 11 up to this plane before belt 11 reaches roll 16 has also been mentioned. This bottom horizontal path of travel of belt 11 is at a horizontal plane that is tangential to the bottom of roll 19 and to a rinse idler roll 80 that the inner surface of belt 11 passes over before belt 11 passes over roll 20. The roll 80 and an intermediate rinse idler roll 81 that also contacts the backing sheet 29 of belt 11 in this horizontal path are part of washing device 21. The other surface of belt 11 is abutted by a similar pair of

rolls

82 and 83 that are also rotatably mounted. The

rolls

82 and 83 are belt rolls 80 and 81, respectively. Thus belt 11, in its bottom horizontal path of travel, passes between

rolls

81 and 83 and after a distance passes between

rolls

80 and 82. In each case belt 11 is compressed to squeeze excess water that remains after two washing operations that are provided as described below.

Before belt 11 passes between

rolls

81 and 83, it passes between an upper spray pipe 84 and a lower spray pipe 85 that furnish sprays of water across and on both sides of belt 11. The spray of water from pipe 85 removes any sludge cake on the outer surface portion of sheet 26 of belt 11.

The water from pipe 84 backwashers aqueous liquid in belt 11 that was part of the aqueous liquid removed from the sludge during the compression of the latter between

rolls

17 and 44 in the dewatering process. Much of the water from pipe 85 and material washed by it from the surface portion of belt 11 falls into pan 87 that is below rolls 80 through 83 and piped 84 and 85, as well as

water spray pipes

89 and 90, that are above and below, respectively, belt 11. The pipe 89 is between

rolls

80 and 81 while pipe 90 is between roll 82 and roll 83.

The water added to belt 11 from

pipes

84 and 85 is removed when belt 11 is squeezed by passing between rolls, 81 and 83. Thus the addition of spray water from

pipes

84 and 85 and the removal of water from belt 11 by

rolls

81 and 83 provides for a substantial removal from belt 11 of some of aqueous liquid removed from the sludge. The further washing of belt 11 is accomplished by the sprays of wash water from

pipes

89 and 90 and the subsequent passage of belt 11 between

rolls

80 and 82. The

pipes

84 and 85 and

pipes

89 and 90 have openings along their length to provide sprays of wash liquid toward and across the width of belt 11. Liquid is removed from pan 87 by an unnumbered outlet (not shown).

It is preferred that water be used for the feed to

pipes

84, 85, 89 and 90; however, there can be used an aqueous liquid of low solids content, such as the final effluent that is removed from a final settler from which activated sludge is removed also, as described earlier and in said copending application.

The belt 12 has a bottom or lower run that is substantially below its top run. This bottom run is made possible by belt 12 being trained around a roll 91 and a roll 92 that have their axes parallel to each other and in a horizontal plane. After belt 12 passes over roll 50, it passes downwardly in an inclined manner, then over rolls 91 and 92 in that order and finally upwardly in an inclined manner to roll 51. The

rolls

91 and 92 are rotatably mounted in theenlarged entrance and exit ends, respectively, of an elongated drying chamber 93. A blower 94 is connected at its inlet to a pipe 95 for receiving drying gas, such as hot air. The outlet of blower 94 is connected to the outlet end of drying chamber 93 in which is located a heat exhanger 96. The heating chamber 93 has slots in its upper wall in the enlarged ends for the downward and upward inclined passage of belt 12 into and out of, respectively, chamber 93. The heat exhanger 96 can be of the tube-and-tank type with the drying gas passing through the tubes (not shown) and the hot gas for heating the drying gas passing into and out of the tank of heat exchanger 96 by pipe (not shown). With this arrangement the hot drying gas passes countercurrently to the direction of movement of belt 12 in its bottom run through chamber 93.

The belt 12 during its inclined upper movement from chamber 93 to roll 51 has the thin layer of dewatered and further dried cake product on its outer or downwardly facing surface. During this inclined movement, belt 12 passes a cake removal device generally indicated at 97 that comprises a pair of rotatable cylindrical brushes 98 and 99 that contact the outer and inner surfaces of belt 12. The cake is removed from the outer surface of belt 12 by brush 98. Brush 99 assists in that removal by its bristles engaging the inner surface of belt 12 and thus the pores or openings of belt 12. The cake that is thus removed falls by gravity to a conveyor generally indicated at 100 by which the cake is removed either for incineration or other treatment or for disposal.

The compression device 24 has associated with it a washing device generally indicated at 101 that has rolls 102 and 103 that support belt 14 in its top horizontal path of travel. The device 101 has

idler rolls

104 and 105 that are above rolls 102 and 103. The belt 14 passes between rolls 102 and 104 where it is compressed again. Prior to the first passage belt 14 is washed by spray water from spray pipe 106 that is above belt 14 and from below by spray pipe 107. After compression of belt 14 by passage between rolls 102 and 104, belt 14 is further washed with liquid from above by spray pipe 108 and from below by spray pipe 109. Excess liquid is removed then by passage of belt 14 between

rolls

103 and 105. The wash collection pan 110 and removed from it by an unnumbered numbered outlet.

During the use of apparatus 24 belt 14 may pick up dcwatered sludge on belt 12 to a slight extent. if this happens, it is desirable to wash belt 14 before its return for the application of compression by passing along with belt 13 below rolls 44. Accordingly apparatus 10 of the first embodiment includes a water spray pipe 111 and a water spray pipe 112 that are positioned above and below the top run of belt 14. Water is sprayed downwardly from pipe 111 and upwardly from pipe 112.

Referring to FIG. 2, apparatus 10 of the second embodiment is constructed in the same manner as described above for the first embodiment shown in H0. 1, except as described below. The belt 12 in its upwardly inclined movement from its lower run to roll 51 has cake on its outer or downwardly facing surface removed by a cake breaker generally indicated at 113 which comprises a small-diameter roll 114 and a roll 115. The

rolls

114 and 115 are rotatably mounted and are placed so that belt 12 passes out a slot in the exit end wall of modified drying chamber 93 and then has a substantial reverse in its direction by passing around roll 114. The its direction is reversed somewhat by passing around roll 115 to start the upwardly inclined travel of belt 12 to roll 51. in this case the axes of

rolls

114 and 115 are parallel and generally in a vertical plane. The roll 115 is above roll 114. Thus belt 12 after its passage out of chamber 93 passes around roll 114 that con tacts the inner surface of belt 12 and then passes around roll 115 that contacts the outer surface of belt 12. This processes a flexing or substantial bending of belt 12 while passing around roll 114 so that the thin layer of cake on belt 12 is broken up. Particles of cake fall by gravity on to a belt conveyor generally indicated at 116 that has a belt 117 trained around a driving roll 118 and an idler roll 119 having their axes in a generally horizontal plane. The cake particles or pieces fall on belt 117 and are moved along its top run. As belt 117 passes around roll ll8 these cake particles fall by gravity into a hopper 119 that feeds a screw conveyor generally indicated at 120. The exit end of screw conveyor 120 is connected to a downwardly inclined feed pipe 121 through which the cake particles fall into a fluidized incinerator generally indicated at 122.

In view of the foregoing description of some of the additional components of apparatus 10 of FIG. 2, it is seen that the exit end of drying chamber 93 is modified by eliminating the enlarged exit end portion. The heat exchanger 96 of the apparatus of FIG. 2 is absent. The roll 115 takes the place of roll 92 of the firstfembodiment of the apparatus to provide with roll 51 an upwardly inclined path of travel of belt 12. Also the exit of belt 12 from chamber 93 is through a slot in the end wall rather than-the top wall of the'first embodiment. In view of that end wall exit of belt 12, blower 94 is mounted so thatits outlet end is adjacent, rather than at, the end wall and actually the air is introduced at an angle through the bottom wall of chamber 93.

The fluidized incinerator 122 can be of any of the designs of the prior art. The incinerator shown in FIG. 2 has a construction that does not utilize a manner of introduction of material to be incinerated such that the material isabove the dense phase of the fluidized system, although such type of incinerator or the use of controls of other prior art incinerating devices of the fluidized type, may be utilized.

As seen in the bottom portion of FIG. 2, incinerator 122 has a chamber 123 in which are located granules of sand or other material that is inert under the conditions used'for the incineration of the cake. The granules of sand or the like are above a plate 124 that separates chamber 123 into a large upper chamber and a small lower chamber. The plate 124 has vertical passages 125 through which the gas is passed at a flow rate sufficient to put the bed of granules into a turbulent state that provides a dense lower phase. Air is forced into-the lower part of chamber 123 by a blower 126.connected at its outlet to a pipe 127 that has its other end communicating with-that lower part of chamber 123. This air passes upwardly through vertical openings 125 of plate 124 and has sufficient velocity to fluidize the granules of sand or the like. Air exits from incinerator 122 by passing out the top wall .of chamber 123 to which is connected a pipe 128.

When the granules are in fluidized condition a valve 129 in a pipe 130 is opened to pass part of the air to a burner 131 that provides hot combustion gases to the lower part of chamber 123. The burner is fed fluid fuel from a storage tank 132 that is connected by a pipe 133 and a valve 134 to pipe 130 adjacent burner 131. With

valves

129 and 134 open and the liquid fuel being burned in the lower part of chamber 123, hot combustion product gases pass through the fluidized granules in the upper part of chamber 123 to heat those granules to a temperature sufficiently elevated for proper incineration of cake when it is introduced to chamber 123 by pipe 121. To provide an odorless exit gas from the incinerator 122 the exit gas should be at a temperature of at least 1,200 F., preferably a temperature of at least l,350 F., as is well known in the prior art.

When introduction of cake is started, the incineration of the cake by the air can maintain combustion without the presence of combustion of fuel through the use of burner 131. This is true when the conditions of use of the dewatering apparatus provides a cake of high solids content as mentioned earlier. Thus from the start of the introductioncontinuously'of cake by pipe 121 the burning of fuel is ceased by'the closing of

valves

129 and 134.

The combustion product gas from this incineration of cake passes from chamber 123 by pipe 128 through a pipe 135 connected to a tank 137 and then out an exit pipe 138 to be exhausted into the atmosphere. The pipe 128 above its connection with pipe 135 is connected to a valve 139 that-has its outlet connected' to pipe 95 that is connected to the inlet of I blower 94. The pipe is also mnected by a pipe 140 and a valve 141 to a tube 142 that passes through tank 137. Thus tank 137 and tube 142 constitute a heat exchanger. When valve 136 is open and valve 139 is closed valve 141 is open for the introduction of air through pipe 142 to pipe 95 and then to blower 94. Air thus introduced through blower 94 is heated by passing through pipe 142. The hot air passes ultimately into chamber 93 for countercurrent flow relative to belt 12 for the drying of cake to produce a cake of high solidscontent. This is a utilization of the apparatus for an incineration that provides a combustion product that has its thermal energy utilized indirectly to provide this further drying of cake from the sludge.

To utilize directly the thermal energy of the hot combustion gases by the apparatus described above, valves 136 and 141 are closed and valve 139 is opened. In this case the heat exchanger having tank 137 and pipe 142 is not utilized. The combustion product gases are fed to drying chamber 93 for the drying operation. Part may be exhausted to the atmosphere rather than passing to chamber 93.

FIG. 3 shows a modification of. pait of the overall apparatus shown in FIG. 2 and described above. In this third embodiment of the apparatus of the present invention heat drying has is fed by pipe 95 and blower 94 to chamber 93. The exit end wall ofchamber 93 has a second slot through which passes the top run ofa conveyor belt 143 that passes around an idler roll (not shown) and a driving roll 144 to provide a top run of belt 143 that moves from right to left, as viewed in FIG. 3, through chamber 93. Of course, in this case there is a slot in the entrance end wall of chamber 93 and the idler roll is to the right of the slot. Obviously the right hand end of chamber 93 could be-modified to provide the idler roll in chamber 93 with entrance of belt 143 through the bottom wall adjacent that end, if desired.

Because of the location of the top run of belt 143 through the bottom portion of drying chamber 93, blower 94 is mounted so that its outlet moves gas into chamber 93 at an angle above belt 143 and even preferably above belt 12.

This embodiment of the apparatus of the present invention permits the use of conditions within the drying chamber 93 such that the thin layer of cake may break up into particles.

-When this happens they will fall on belt 143 and be carried to a position where belt 143 passes around roll 144 from which they will fall by gravity into hopper 119 (not shown in FIG. 3). From hopper 119 they can be fed to a fluidized incineration system such as shown in FIG. 2 as a part of an overall system.

When desired, most of the dried cake can be carried out of chamber 93 on belt 12 and be removed from belt 12 by passing around rolls 114 and 1.15 of cake breaker device 113. In this case, particles of cake fall on to the top run of belt 143 and are carried for ultimate falling by gravity to hopper 119.

As seen in FIG. 5, the apparatus of the present invention includes pairs of antiwrinkling devices generally indicated at that engage sheet 12. The apparatus also includes pairs of tracking devices generally indicated at 151 that engage sheet 11. The construction of devices 150 and devices 151 is the same. This construction is shown in greater detail in FIG. 8 for one of the pairs of antiwrinkling devices 150. Pairs of devices 150 are located at various positions around a path of travel of sheet 12 and serve to-remove transverse wrinkling of sheet 35 of belt 12. Also pairs of tracking devices 151 are placed placed at various positions around the path of travel of belt 11. Further pairs of

devices

150 and 151 are located in the paths of travel of

belt

14 and 13, respectively, of compression device 24.

' As seen in FIG. 8, device 150 includes a top guide bar 152 and a bottom guide bar 153 that are generally straight in their central portions but at their end portions are curved toward the centerline of travel of belt 12. One pair of guide bars 152 and 153 is located so that sheet 36passes between them. The hem 38 with plastic rod 40 in it is on the side so bars 152 and 153 is located so that sheet 36 passes between them. The hem 38 with plastic rod 40 in it is on the side of

bars

152 and 153 opposite belt 12 when belt 12 is properly positioned. The

other device 150 of the pair has corresponding guide bars 152 and 153 of the opposing device 150 of the pair.

The

bars

152 and 153 are between the upper and lower arms of a U-shaped plate 154 with bar 152 secured to the upper arm and bar 153 secured to the bottom arm. These arms of U-shaped plate 154 are prevented from spreading apart by a bolt 155 and a nut 156 on it and extending through both arms. The web or base of U-shaped plate 154 has a hole through which extends a rod 157. This end of rod 157 is welded to plate 154. This rod 157 is slideably mounted on another U-shaped plate 158 having vertical arms and a horizontal web that is parallel to the arms of U-shaped plate 154. A spring 159 is mounted on rod 157 between the vertical arms of U-shaped plate 158 so that one end of spring 159 abuts the vertical arm closer to plate 154 and the other end of spring 159 is prevented from moving to the right (as shown in FIG. 8) by a stop ring 160 adjustably secured on rod 157. The plate 158 is mounted on a fixed support 161.

In the event that there has been some wrinkling of sheet as

belt

12 or 14 passes around one of the rolls in its path of

travel hems

37 and 38 are brought closer together but there will be a limit to the extent of such wrinkling by the presence of a number of pairs of devices 150 along the path of travel as mentioned above. The hem 38 and rod 40 in it are maintained in a straight line of travel except for longitudinal portions moved toward the centerline of belt 12. The latter movement will be corrected as the leading edge of the thus-produced arcuate line of that portion of the length of the hem reaches and abuts the curved leading end portions of

rods

152 and 153. The same return to rectilinear movement of hem 37 and rod 39 will be insured by the other device 150 of the pair.

1n the event that there is a shifting of a portion of

belt

12 or 14 from the desired travel of the center plane of

belt

12 or 14, one of such pair of devices 150 will return the adjacent hem and rod when it later abuts the curved leading end of

rods

152 and 153. Of course the other device 150 of that pair does not provide any straightening effect during that realignment because the hem and plastic rod adjacent to it are farther away from

rods

152 and 153 and are merely brought to contact those rods when

rods

152 and 153 of the other device 150 causes the corrective movement. Of course, devices 151 are located at a different elevation than devices 150 so that their guide bars corresponding to guide

bars

152 and 153 of device 150 have between them

sheets

27 or 28 of

belt

11 or 13.

In view of the foregoing description of the invention it is apparent that sheet 35 is preferably a screen cloth and when sludge is to be dewatered the screen cloth is preferably a polyester monofilament plain weave cloth having a mesh size between about 50 microns and about 1,000 microns and at least 25 percent open area. When the sludge is activated sludge or the latter comprises at least 10 percent by volume of the sludge, it is preferred that such weave cloth have a mesh size of 53 microns microns and an open area of 32 percent.

From the foregoing description of the invention it is also apparent that the apparatus comprises a set of endless belts, one belt containing an elongated sheet of porous cellular material having the characteristics stated above and the other belt containing a different elongated porous sheet having the characteristics also stated above. The apparatus further includes means to support the first belt at various positions to provide an upper portion of that belt that has the outer surface of said elongated sheet in a horizontal plane and means to move that belt through a path of travel including a horizontal top run in which said outer surface is at said horizontal plane.

The apparatus also includes means to support the second belt at various positions to provide an upper portion of that belt that has the inner surface of said elongated different porous sheet at said horizontal plane to abut said elongated sheet of said first belt at its top run and to extend beyond both ends of said top run of said first belt; and means to move said second belt through a path of travel including a horizontal run in which said inner surface abuts said other surface for a common part of their top runs and said belts are separated from each other for a portion of the rest of their cyclic parts of travel.

There are also means to compress said sheet of porous cellular material during the cyclic path of travel of the first belt and the compression means may be while the belts abut or at a zone where they are spaced apart in their cyclic paths of travel, and means to remove material from the outer surface of said different porous sheet of the second belt, said removal means being preferably located so as to provide such removal at a zone where the belts are spaced apart.

Preferably, except for a relatively small removal of liquid, a second set of such belts are present to provide means to compress said porous cellular sheet of the first belt of the first set when overlaid by the different sheet of the other belt of that set. The second set of belts are supported and are moved to provide a common bottom run with their two sheets, defined above, abutting each other with their two sheets, defined above, abutting each other and the different sheet of that set abutting said different sheet of the first set at a zone constituting a part of the top run of the first set of belts. The belts of the second set are spaced apart at another part of their cyclic paths of travel.

Of course, the apparatus includes means to apply such flowable material to the upper surface of said different porous sheet ofthe second belt of the first set of belts.

Add Additionally there can be heating means for further removal by evaporation of liquid from the material, on the second belt of the first set, as a layer while that belt is separated from the first belt of that set. ln the integrated apparatus that includes fluidized incineration it has means to use the thermal energy of the combustion product gas to heat that layer of material.

In the use of the invention there is placed on the top surface of a compressible, resilient sheet of porous cellular material a different porous sheet having a pore size as described above. The flowable material is added to the top surface of the different porous sheet and maintained on it for a sufficient period of time for liquid to pass through the pores and to enter into the sheet of porous cellular material. The two sheets are separated. Liquid is removed from the sheet of porous cellular material by compressing that sheet before or after the separa tion of the sheets. Material of higher solids content is removed from the different sheet.

In view of the foregoing description of the apparatus of the present invention, many modifications will be obvious to one of ordinary skill in this art. The description has been presented solely for the purpose of illustration and not by way of limitation of the invention because the later is limited only by the claims that follow.

We claim:

1. An apparatus for removing aqueous liquid having a lower content of solids, if any, form a flowable material, containing aqueous liquid as a continuous phase and suspended solids as a discontinuous phase, to produce a material having a higher solids content, which comprises:

a first endless belt including an elongated, compressible and resilient sheet of a porous cellular material capable of absorbing said aqueous liquid by a wicking action:

means to support said belt at various positions to provide a portion of the belt as an upper horizontal run at which the outer surface of said elongated sheet is at a horizontal plane and to provide another portion of the belt as a lower run;

means to move said endless belt through a path of travel including said upper horizontal run at which said outer surface of said elongated sheet is at said horizontal plane;

a second endless belt including an elongated different porous sheet, said different porous sheet being a finemesh sheet with pores extending through the sheet and of a size within a predetermined range for passage of said aqueous liquid of the continuous phase of said flowable material through said pores from the outer surface to the inner surface of said different sheet, by a wicking action of said cellular sheet wlieii it is in abutment with said inner surface of said different sheet, and for retention at the same time on said outer surface of said different porous sheet of a major portion of the suspended solids of said flowable material to obtain at least a partial removal of said aqueous liquid from said flowable material;

means to support said second endless belt at various positions to provide a portion of the belt as an upper run at which the outer surface of said different porous sheet faces upwardly, including a horizontal part, containing an elongated, partial dewatering zone, where said second belt along at least a part of its said horizontal run overlies said first belt so that the inner surface of said different porous sheet is in abutment with the outer surface of said elongated sheet of porous cellular material for said wicking action at said dewatering zone and to provide another portion of said second belt as a lower run means to move said second belt through a path of travel including said portion as said upper run and said another portion as said lower run, said moving means moving said second belt so that its said upper run is in the same direction as said upper run of said first belt;

means mounted above said upper run of said second belt to deliver said flowable material to said upwardly facing outer surface of said different porous sheet at a location adjacent the beginning of said dewatering zone;

means mounted downstream of said dewatering zone to remove product of lower liquid content and thus product product of higher solids content from the outer surface of said different porous sheet of said second endless belt and means downstream of said upper horizontal run of said first belt to compress said sheet of porous cellular material by opposed forces acting on the outer and inner surfaces of said cellulose sheet 2. The apparatus of claim 1 wherein:

said elongated sheet of porous cellulose material is a sheet of fine-pore cellulose sponge;

said elongated different porous sheet is at most only slightly absorbingof said liquid; and

said second belt has its said upper run extending beyond the downstream end of said upper run of said first belt.

3. The apparatus of claim 2 wherein:

said different sheet is a plastic sheet substantially thinner than said sheet of porous cellular material and has a mesh size between about 50 microns and about 1,000microns and with at least percent open area.

4. The apparatus of claim 3 wherein:

said different sheet is a screen cloth and said second belt has its upper run extending also beyond the beginning of said upper run of said first belt.

5. The apparatus of claim 4 wherein:

said different sheet is a polyester monofilament plain weave cloth 6. The apparatus of claim 1 wherein:

said first endless belt is a composite assembly that includes,

along with said sheet of porous cellular material, an elongated sheet of course-mesh, as at least a part of a backing sheet, and adhered to the inner surface of said sheet of porous cellular material to provide a composite sheet having sufficient strength against breaking under tension to constitute an endless belt.

11 The apparatus of claim 6 wherein:

said backing sheet is of greater width than said sheet of porous cellular material and has thickened marginal edges as longitudinal beads; an

said apparatus further including pairs of devices engaging said beads, said pairs being located at various positions in the path of travel of said first endless belt to insure proper tracking of said first endless belt in its path of travel.

8. The apparatus of claim 1 wherein:

said different porous sheet of the second belt is capable of transverse wrinkling;

said second belt is mad fffil a second composite sheet including said different porous sheet and a pair of elongated plastic sheets secured to the two marginal portions of said different porous sheet and having at their distal margins a construction to provide two thickened edges as longitudinal beads for the marginal edges of the second belt; and

said apparatus further including pairs of devices engaging said beads of said second composite sheet as a belt during its path of travel to provide forces at the margins in a direction away from the centerline of the belt at that location so as to eliminate any transverse wrinkling of said different sheet.

9. The apparatus of claim 1 and further including:

means to provide a downward pressure against said first and second belts at a part of their said upper runs beyond the downstream end of said dewatering zone with sufficient pressure to provide a compression of said first belt;

means mounted below said belts at their said upper runs and below said pressure means to collect liquid removed from said first belt by its compression; and

means mounted below said belts at their said upper runs and below said pressure means to resist downward movement of said first belt so as to effectuate said compression by said pressure means but constructed to permit downward flow by gravity of liquid from the compressed first belt to said liquid collection means.

10. The apparatus of claim 9 wherein:

said cellular sheet is a sheet of finepore cellulose sponge having a thickness such that it is incapable of transferring aqueous liquid through it in a reasonable time when the amount of said flowable material is less than the amount that would overflow aid cellular sheet of said first belt, and when the only force that would be applied to that sheet containing that amount of flowablc aqueous material would be the force of gravity.

11. The apparatus of claim 9 wherein said means to compress said first belt at a part of its said upper run comprises:

a third endless belt including an elongated, compressible and resilient sheet of a porous cellular material;

means to support said third belt at various positions to provide a lowermost portion of the belt that has its outer surface facing said first and second belts at said part of their said upper runs beyond the downstream end of said dewatering zone;

means to move said third belt through a path of travel including a bottom run at said lower most portion, said moving means moving the third belt so that its bottom run is in the same direction as said upper runs of said first and second belts;

a fourth endless belt having the physical characteristics of said second endless belt;

means to support said fourth endless belt so that it has at its lowermost portion an outer surface parallel to and facing the outer surface of said second belt at said part of that belts upper horizontal run beyond the downstream end of said dewatering zone and at the same time has its inner surface facing the outer surface of said third belt at its said lowermost portion;

means to move said fourth belt on a path of travel including a bottom run at said lowermost portion said moving means moving said fourth belt so that its bottom run is in the same direction as the bottom run of said third belt, said four belts being positioned so that said different sheet of porous material of said second belt at its upper run is in alignment with and above above said sheet of cellular material of said first belt at its upper run and in alignment above these beyond the downstream end of said dewatering zone are said different sheet of said fourth belt and said sheet of porous cellular material of said third belt.

R2. The apparatus of claim 11 wherein said compression means and downward-resisting means include;

upper runs and said top rolls being above above said third and fourth belts at their said lowermost portion of run, said bottom rolls being said means resisting downward movement of said first belt and said top rolls being said compression means.

13. An apparatus for removing aqueous liquid having a lower content of solids, if any, from a flowable material, containing aqueous liquid as a continuous phase and suspended solids as a discontinuous phase, to produce a material having a higher solids content, which comprises:

a first endless belt including an elongated, compressible and resilient sheet of fine-pore cellulose sponge;

means to support said belt at various positions to provide an upper portion of the belt that has the outer surface of the upper portion of said elongated sheet in a horizontal plane and to provide a bottom portion of the belt;

means to move said endless belt through a path of travel including a horizontal top run in which said outer surface of said elongated sheet is at said horizontal plane;

a second endless belt including an elongated different porous sheet, said different sheet being a polyester monofilament plain weave cloth having a mesh size between about 50 microns and about 1,000 microns and at least 25 percent open area;

means to support said second endless belt at various positions to provide an upper portion of the belt with a horizontal disposition so that the inside surface of said different porous sheet is at a horizontal plane with said inside surface abutting and extending beyond both ends of the horizontal top run of said elongated sheet of porous cellular material and to provide a lower portion that is below and spaced from said bottom run of said first endless belt;

means to move said second belt through a path of travel ineluding said upper portion as a top run and said lower portion as a bottom run, said moving means moving said second belt so that its top run is in the same direction as said top run of said first belt;

means mounted above the top run of said second belt to deliver flowable material to said top run of said different porous sheet;

means to remove product of lower liquid content and thus product of higher solids content from the outer surface of said different porous sheet of said second endless belt downstream in the path of travel of the portion to which the flowable material is delivered; and

means to compress said sheet of porous cellular material downstream in the path of travel of the portion to which the flowable material is delivered to said different porous sheet.

14. The apparatus of claim 13 wherein:

said first endless belt is a composite assembly that includes, along with said sheet of porous cellular material, a sheet of coarse-mesh, as at least part ofa backing sheet, and adhered to the inside surface of said sheet of porous cellular material to provide a composite sheet having sufficient strength against breaking under tension to constitute an endless belt.

15. The apparatus of claim 14 wherein:

said backing sheet is of greater width than said sheet of porous cellular material and has thickened marginal edges as longitudinal beads; and

said apparatus further including pairs of devices engaging said beads and being located at various positions in the path of travel of said first endless belt to insure proper tracking of said first endless belt in its path of travel.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 ,613.554 Dated October 19 1971 Invent fls) Maximilian Adamski, et al It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 4, change "related" to is related line 72, change "come" to some Column 2, line 19, cancel "in". Column 4, line 33, change "or" to of Column 5, line 65, change "precess" to process Column 6, line 41, cancel "to the same" (first occurrence) 3 line 44, change "or" to of Column 7, line 15, change "not" to no line 45, change "of" to off line 63, before "cross" insert is a Column 8, line 33, change "late" to later 3 line 51, change "increased" to increase Column 9, line 17, change "elongates" to elongated line 31, change "hams" to hems line 60, change the part" to that part Column 10, line 48, after "same direction" insert as Column 11, line 30, change "belt" to below line 42, change "backwashers" to backwashesline 48, change "piped" to pipes Column 12, line 12, change "pipe" to pipes lines 42-44, change "The wash collection pan 110 and removed from it by an unnumbered numbered outlet." to read The wash water and water removed by squeezing is collected in a wash collection pan 110 and removed from it by an unnumbered outlet. line 64, change "The" to Then line 71, change "processes" to produces Column 14, line 22, change "hot drying has" to hot drying gas line 61, delete "placed" after "are" to avoid a repitition; line 71, through column 15, line 2, change "The hem 38 with plastic .....of the pair." to read The hem 38 with plastic rod 40 in it is on the side of

bars

152 and 153 opposite belt 12 when belt 12 is properly positioned. The other device 150 of the pair has corresponding guide bars 152 and 153 that have between them sheets 36 and their turned ends are turned toward guide bars 152 and 153 of the opposing device 150 of the pair. Column 15, line 54, delete "microns" (second occurrence) 3 line 74, change "other" RM PO-IOSO (10-69) USCOMM-DC 60376-F'69 Q U 5 GOVERNMENT PRINTING OFFICE I969 0-386-334.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No- 3,613,564 Dated October 19, 1971 Inventor(s) Maximilian Adamski, et a1 2 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

to outer Column 16, line 17, delete entire line that reads "above, .....defined" line 26, cancel "Add" 3 line 49, change "later" to latter line 53, change "form" to from Column 17, line 30, cancel "product" before "of higher solids"

lines

35 and 37, change "cellulose" to cellular line 65, change the number of the claim from "1" to 7 Column 18, line 33, change "aid" to said line 66, cancel "above" (second occurrence). Column 19, line 1, cancel "above" (second occurrence) Signed and sealed this 10th day of October 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents W PC4050 USCOMM-DC ooanmoo Q U GOVERNMINY PRINTING OFHCE lili 0-4601.

Claims

2. The apparatus of claim 1 wherein: said elongated sheet of porous cellulose material is a sheet of fine-pore cellulose sponge; said elongated different porous sheet is at most only slightly absorbing of said liquid; and said second belt has its said upper run extending beyond the downstream end of said upper run of said first belt.
3. The apparatus of claim 2 wherein: said different sheet is a plastic sheet substantially thinner than said sheet of porous cellular material and has a mesh size between about 50 microns and about 1,000microns and with at least 25percent open area.
4. The apparatus of claim 3 wherein: said different sheet is a screen cloth and said second belt has its upper run extending also beyond the beginning of said upper run of said first belt.
5. The apparatus of claim 4 wherein: said different sheet is a polyester monofilament plain weave cloth
6. The apparatus of claim 1 wherein: said first endless belt is a composite assembly that includes, along with said sheet of porous cellular material, an elongated sheet of course-mesh, as at least a part of a backing sheet, and adhered to the inner surface of said sheet of porous cellular material to provide a composite sheet having sufficient strength against breaking under tension to constitute an endless belt. 1 The apparatus of claim 6 wherein: said backing sheet is of greater width than said sheet of porous cellular material and has thickened marginal edges as longitudinal beads; and said apparatus further including pairs of devices engaging said beads, said pairs being located at various positions in the path of travel of said first endless belt to insure proper tracking of said first endless belt in its path of travel.
8. The apparatus of claim 1 wherein: said different porous sheet of the second belt is capable of transverse wrinkling; said second belt is made from a second composite sheet including said different porous sheet and a pair of elongated plastic sheets secured to the two marginal portions of said different porous sheet and having at their distal margins a construction to provide two thickened edges as longitudinal beads for the marginal edges of the second belt; and said apparatus further including pairs of devices engaging said beads of said second composite sheet as a belt during its path of travel to provide forces at the margins in a direction away from the centerline of the belt at that location so as to eliminate any transverse wrinkling of said different sheet.
9. The apparatus of claim 1 and further including: means to provide a downward pressure against said first and second belts at a part of their said upper runs beyond the downstream end of said dewatering zone with sufficient pressure to provide a compression of said first belt; means mounted below said belts at their said upper runs and below said pressure means to collect liquid removed from said first belt by its compression; and means mounted below said belts at their said upper runs and below said pressure means to resist downward movement of said first belt so as to effectuate said compression by said pressure means but constructed to permit downward flow by gravity of liquid from the compressed first belt to said liquid collection means.
10. The apparatus of claim 9 wherein: said cellular sheet is a sheet of fine-pore cellulose sponge having a thickness such that it is incapable of transferring aqueous liquid through it in a reasonable time when the amount of said flowable material is less than the amount that would overflow aid cellular sheet of said first belt, and when the only force that would be applied to that sheet containing that amount of flowable aqueous material would be the force of gravity.
11. The apparatus of claim 9 wherein said means to compress said first belt at a part of its said upper run comprises: a third endless belt including an elongated, compressible and resilient sheet of a porous cellular material; means to support said third belt at various positions to provide a lowermost portion of the belt that has its outer surface facing said first and second belts at said part of their said upper runs beyond the downstream end of said dewatering zone; means to move said third belt through a path of travel including a bottom run at said lower most portion, said moving means moving the third belt so that its bottom run is in the same direction as said upper runs of said first and second belts; a fourth endless belt having the physical characteristics of said second endless belt; means to support said fourth endless belt so that it has at its lowermost portion an outer surface parallel to and facing the outer surface of said second belt at said part of that belt''s upper horizontal run beyond the downstream end of said dewatering zone and at the same time has its inner surface facing the outer surface of said third belt at its said lowermost portion; means to move said fourth belt on a path of travel including a bottom run at said lowermost portion said moving means moving said fourth belt so that its bottom run is in the same direction as the bottom run of said third belt, said four belts being positioned so that said different sheet of porous material of said second belt at its upper run is in alignment with and above above said sheet of cellular material of said first belt at its upper run and in alignment above these beyond the downstream end of said dewatering zone are said different sheet of said fourth belt and said sheet of porous cellular material of said third belt.
12. The apparatus of claim 11 wherein said compression means and downward-resisting means include; pairs of top and bottom rolls with said bottom rolls being below and supporting said first and second belts at their upper runs and said top rolls being above above said third and fourth belts at their said lowermost portion of run, said bottom rolls being said means resisting downward movement of said first belt and said top rolls being said compression means.
13. An apparatus for removing aqueous liquid having a lower content of solids, if any, from a flowable material, containing aqueous liquid as a continuous phase and suspended solids as a discontinuous phase, to produce a material having a higher solids content, which comprises: a first endless belt including an elongated, compressible and resilient sheet of fine-pore cellulose sponge; means to support said belt at various positions to provide an upper portion of the belt that has the outer surface of the upper portion of said elongated sheet in a horizontal plane and to provide a bottom portion of the belt; means to move said eNdless belt through a path of travel including a horizontal top run in which said outer surface of said elongated sheet is at said horizontal plane; a second endless belt including an elongated different porous sheet, said different sheet being a polyester monofilament plain weave cloth having a mesh size between about 50 microns and about 1,000 microns and at least 25 percent open area; means to support said second endless belt at various positions to provide an upper portion of the belt with a horizontal disposition so that the inside surface of said different porous sheet is at a horizontal plane with said inside surface abutting and extending beyond both ends of the horizontal top run of said elongated sheet of porous cellular material and to provide a lower portion that is below and spaced from said bottom run of said first endless belt; means to move said second belt through a path of travel including said upper portion as a top run and said lower portion as a bottom run, said moving means moving said second belt so that its top run is in the same direction as said top run of said first belt; means mounted above the top run of said second belt to deliver flowable material to said top run of said different porous sheet; means to remove product of lower liquid content and thus product of higher solids content from the outer surface of said different porous sheet of said second endless belt downstream in the path of travel of the portion to which the flowable material is delivered; and means to compress said sheet of porous cellular material downstream in the path of travel of the portion to which the flowable material is delivered to said different porous sheet.
14. The apparatus of claim 13 wherein: said first endless belt is a composite assembly that includes, along with said sheet of porous cellular material, a sheet of coarse-mesh, as at least part of a backing sheet, and adhered to the inside surface of said sheet of porous cellular material to provide a composite sheet having sufficient strength against breaking under tension to constitute an endless belt.
15. The apparatus of claim 14 wherein: said backing sheet is of greater width than said sheet of porous cellular material and has thickened marginal edges as longitudinal beads; and said apparatus further including pairs of devices engaging said beads and being located at various positions in the path of travel of said first endless belt to insure proper tracking of said first endless belt in its path of travel.