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Publication numberUS3884755 A
Publication typeGrant
Publication dateMay 20, 1975
Filing dateJun 18, 1973
Priority dateJun 18, 1973
Also published asCA1001463A, CA1001463A1
Publication numberUS 3884755 A, US 3884755A, US-A-3884755, US3884755 A, US3884755A
InventorsIii Arthur W Frost
Original AssigneeGaf Corp
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Closed cycle paper sheet production
US 3884755 A
Abstract  available in
Images(9)
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Claims  available in
Description  (OCR text may contain errors)

United States Patent 11 1 Frost, III.

[451 May 20, 1975 1 CLOSED CYCLE PAPER SHEET PRODUCTION [75] Inventor: Arthur W. Frost, III., Lansdowne,

[52] US. Cl. 162/190; 162/147; 162/D1G. 9 [51] Int. Cl. D21f l/66 [58] Field of Search 162/189, 190, 158, 182, 162/150, 142, 147, 168, DIG. 9; 210/45, 52, 54

[56] References Cited UNITED STATES PATENTS 3,019,157 1/1962 Reynolds et a1. 162/168 3,130,167 4/1964 Green 210/52 X 3,262,877 7/1966 Le Compte, Jr.... 162/190 X 3,276,998 10/1966 Green 210/52 3,364,101 1/1968 Eek 162/189 X 3,450,680 6/1969 .lursich et al.... 162/168 X 3,576,710 4/1971 Mader et a1. 162/190 X 3,769,116 10/1973 Champeau 162/DIG. 9

FOREIGN PATENTS OR APPLICATIONS 1,275,042 5/1972 United Kingdom l62/DIG. 9 273,650 1970 U.S.S.R 162/147 163,501 1955 Australia 162/168 OTHER PUBLICATIONS Abstract Bul. Institute of Paper Chem., Vol. 41, No. 3 (9-1970), Abstract No. 2261, Dvorak.

Brown, Use of White Water in Manufacture of Groundwood Pulp and Effect on Freeness, Tappi, Tech. Assoc. Papers, Series VI, pp. 91-93.

Primary Examiner-S. Leon Bashore Assistant ExaminerA. DAndrea, Jr.

Attorney, Agent, or FirmWalter C. Kehm; Joshua J. Ward [57] ABSTRACT Construction paper sheets are produced from groundwood stock and other fibrous stocks without undesired sludge accumulation and without undesired discharge of high BOD waste water streams to the environment. The sludge formed upon separation of colloidal material from said waste water streams is coated on the individual strands of wood fiber and, in this form, is recycled to the stock milling zone as a wood stock ingredient of the furnish from which the sheet, e.g., roofing felt, is fabricated. Sludge formation is facilitated by the addition of clay particles to the waste water stream for adsorption of colloidal material therefrom. A flocculent can also be employed to enhance the separation of said clay containing adsorbed material from said waste water stream. The effluent waste stream containing dissolved solids is recycled to said milling zone as make-up water. The sheet fabricated in such closed-cycle operations has properties comparable to those of sheets not having said sludge incorporated therein.

26 Claims, No Drawings CLOSED CYCLE PAPER SHEET PRODUCTION BACKGROUND OF THE INVENTION 1. FIELD OF THE INVENTION This invention relates to the production of paper sheets. More particularly, it relates to closed cycle construction paper sheet production with essentially zero effluent discharge.

2. DESCTIPTION OF THE PRIOR ART In the production of paper sheets, it has been common practice to blend fibrous stocks with water, together usually with other known non-fibrous ingredients, in a milling zone, to produce an aqueous suspension from which a sheet of the desired paper is fabricated. The fibrous and non-fibrous materials blended together in water suspension are generally collectively referred to as the furnish. The nature of the furnish will vary with the kind and grade of paper produced and even with the individual practices of particular mills. For construction paper applications, as for example in the production of roofing felts, groundwood pulp produced by a mechanical pulping process is commonly employed in preference to pulps produced by chemical processes, such as sulfite, soda and sulfate pulps. In such construction paper applications, the groundwood pulp may typically comprise about twothirds of the fibrous stock components of the furnish on a wet weight basis, the remainder of the fibrous stock generally comprising paper stock and rag stock in varying amounts as is well known in the art.

The sheet of paper is fabricated from the aqueous suspension on a paper machine, such as a fourdrinier machine or a cylinder machine, by dewatering the stock and surface finishing the sheet produced. The dewatering is accomplished in a manner that produces a sheet of uniform structure and thickness through the application of natural drainage, induced drainage by partial vacuum, roll pressure and by heat. The water thus removed from the fabrication zone, commonly referred to as vat spill water, will generally contain a variety of dissolved and suspended matter associated therewith. The vat spill is sometimes blended with other refuse waters, producing a so-called dirty white water stream. From this latter stream, particulate objects can be removed by cyclones, screening and the like, and suspended fibers are separated by suitable filters and the like, generally for recycle to the milling zone as paper stock.

The thus-treated dirty white water stream having particulate objects and an appreciable portion of the suspended fiber removed therefrom comprises a so-called clean white water stream. On the order of about 80% by weight of said clean white water stream is conventionally recycled to the wood defibrators in which the groundwood stock is produced and to the hydrapulpers in which mixed paper stock is processed.

The remaining portion of the clean white water stream, i.e., commonly on the order of about by weight thereof, may be passed through disc filters or the like to further reduce the suspended fiber content thereof, the relatively clear filtrate or effluent aqueous stream having colloidal material suspended therein, together with dissolved solids such as lignin derivatives and other residues of the pulping operation employing groundwood stock.

The effluent aqueous stream has a relatively high biological oxygen demand, i.e., BOD, rendering it unacceptable from an environmental viewpoint for discharge to rivers, lakes and tributary streams. Because of the growing awareness and concern relating to water pollution resulting from the discharge of industrual wastes into water streams, various national and state water pollution control laws and regulations are presently in effect or under serious consideration to minimize and control water pollution resulting from the effluent'discharges of the pulp and paper industry and other industrial processing operations.

Efforts to avoid water pollution resulting from the indiscriminate discharge of the effluent aqueous stream referred to above have included the separation of a sludge of colloidal solid wastes from said stream, by clarification and the like, together with various primary, secondary and even tertiary systems of water treatment to acheive 90% or higher removal of contaminants to meet the ever more restrictive BOD reduction standards for permissible effluent aqueous discharge to receiving waters. Such efforts impose, of course, a considerable economic burden upon the overall pulp and paper production operation, however necessary such water pollution controls may be from an environmental viewpoint. Marginal operations may not be able to continue because of the economic infeasibility of meeting operable water pollution control requirements. The economic impact of the highly desirable control standards is further aggravated by the necessity of additional operating expenditures for sludge storage and disposition. In continuous mill operations, the quantities of effluent aqueous waste streams and accumulated sludge thus requiring treatment and/or disposal become such as to result in the expenditure of very considerable sums for pollution control purposes in even the most efficiently run operations.

In an effort to reduce such expenditures, the recycling of accumulated sludge to the milling zone has been proposed in order to reduce the amount of sludge that must be transported to acceptable waste disposal facilities. The incorporation of the sludge as one of the ingredients of the furnish was not generally satisfactory, however, since the presence of the sludge tends to disrupt the orientation of the fibers during the production of the sheet, the properties of the sheet thereby suffering to an unacceptable extent. The presence of said sludge particles between the fibers was likewise found to adversely affect the drainage characteristics of the sheet being fabricated so as to disrupt the operational efficiency of the fabrication operation as well as the quality of the resultant sheet.

In some instances, efforts to recycle the effluent aqueous stream to the milling zone have proved more successful than efforts to recycle accumulated sludge thereto. There has been a tendency, however, to concentrate more upon the improvement of BOD reduction techniques permitting the discharge of all or substantial portions of said effluent aqueous streams to receiving waters as waste water steams of acceptably low BOD content. The reluctance to pursue the recycle of the effluent aqueous stream is, at least in part, motivated by concerns relating to the buildup of dissolved solids in the system and their effect on the properties of the sheet being fabricated and upon the sludge accumulation and disposal operations that must, in any event, be continued in operations of this type.

It is an object of the present invention, therefore, to provide an improved sheet fabrication operation.

It is another object of the invention to provide an improved sheet fabrication having enhanced water pollution control features.

It is another object of the invention to provide a sheet fabrication operation in which the disposition of sludge is facilitated.

It is another object of the invention to provide a sheet fabrication operation in which water pollution and sludge disposal are obviated.

It is another object of the invention to provide a construction paper sheet produced with essentially zero effluent discharge from the overall sheet fabrication operation.

With these and other objects in mind, the invention is hereinafter set forth in detail, the novel features thereof being particularly pointed out in the appended claims.

SUMMARY OF THE INVENTION The sludge of solids separated from the effluent aqueous stream resulting from the fabrication of construction paper sheets from a furnish containing groundwood and other fibrous stocks is coated on the individual strands of groundwood fibers that are to form the groundwood stock component of additional furnish employed in continuous sheet fabrication operations. When recycled to the milling zone in this manner, the sludge does not disrupt the orientation of the fibrous material, with resultant adverse effect upon the properties of the sheet, as when the accumulated sludge is recycled directly to the milling zone. A cationic polyelectrolyte may be employed as a bonding agent to enhance the adherence of the sludge to the groundwood fibers. The effluent aqueous stream having dissolved solids therein that obtains upon removal of the colloidal material therefrom is also recycled to the milling zone as make-up water. The accumulation of dissolved solids therein is readily accommodated as all of the solids beyond the saturation level of said effluent aqueous stream are accumulated in the sludge, resulting in a closed cycle operation with essentially zero effluent discharge. The effluent aqueous stream recycled to the milling zone is at an elevated temperature, thereby minimizing the overall heat requirements of the system. The construction paper sheet obtainded with said closed cycle operation and essentially zero effluent discharge has properties and characteristics comparable to those of said sheets fabricated without said effluent aqueous stream and said sludge recycle.

DETAILED DESCRIPTION OF THE INVENTION The present invention serves to obviate the environmental concern relating to the disposal of liquid and solid waste materials in construction paper sheet production by providing for the recycle of said waste materials to the sheet fabrication operation with essentially zero effluent discharge to waste. Such closed cycle operation is achieved, in the practice of the invention, which producing construction paper sheets of comparable quality to those produced with effluent aqueous steam and sludge recyle. The invention thus represents a highly important advance in the pulp and paper industry, providing a practical and economically attractive process satisfying fully the environmental imperative of overcoming the water pollution and sludge disposal problems associated with conventional sheet fabrication operations.

The present invention is applicable in the production of construction paper made from groundwood stock, but is not generally applicable for the production of writing paper and other fine grade papers produced from fibrous stocks prepared by chemical pulping processes. While the invention is thus advantageously suited for the production of various grades of roofing felt, including asphalt saturated paper, it will readily be appreciated by those skilled in the art that a variety of other sheets will fall within the scope of the term construction paper as used herein. Illustrative of such other sheets are so-called deadening felts, stuffing materials, table pads, combination box board and the like. The present invention includes within its scope all such grades of construction paper produced with the waste sludge material incorporated therein as herein provided by the coating thereof on the groundwood stock component of the furnish from which the paper sheets are produced.

As is well known in the art, the groundwood pulp process is mechanical in character, and the use of groundwood stock in the production of construction paper sheets contributes to the existence of a dirty white water stream having a variety of dissolved and suspended matter present therein, including various organic acids, lignin derivatives and the like, as well as suspended fibers, particulate objects and general debris. Upon removal of particulate objects, debris, and an appreciable portion of the suspended fiber content, the resulting aqueous stream, referred to as a clean white water stream, is typically divided into two streams, one comprising generally a major portion of said clean white water stream being commonly recycled to hydrapulpers and defibrators used in the production of additonal quantities of fibrous stock as indicated above, the second stream comprising generally a minor portion of said clean white water stream, e.g., on the order of about 20% thereof by weight, being generally treated for the removal of additional quantities of suspended fibers and colloidal waste materials collected as sludge. In the practice of the present invention, the sludge is recycled with groundwood stock for ultimate incorporation in the sheet being fabricated. The effluent aqueous stream having dissolved solids therein, upon removal of said fibrous material and said sludge, is likewise recycled as make-up water, with the accumulation of soluble solids in excess of the dissolving capacity of said stream and of the dirty and clean white water streams resulting in said excess solids being separated therefrom in the sludge. The fibers separated from said aqueous streams, as indicated above, can likewise be recycled for reuse as a paper stock component'of the furnish of fibrous and non-fibrous materials that are blended together in aqueous suspension to ultimately produce the construction paper sheet of the present invention.

Those skilled in the art will appreciate that the groundwood stock is commonly blended with other fibrous materials, as well as with conventional nonfibrous ingredients, to produce the furnish referred to above. Paper stock, including the recovered fibers originally suspended in the dirty white water stream removed from the sheet fabrication operation, are also commonly blended with said groundwood stock. Rag stock, as is known in-the art, comprises another common fibrous ingredient of the furnish. In the production of roofing felt, for example, about two-thirds by weight of the total fibrous stock, on a wet fiber basis, generally comprises wood stock, i.e., groundwood stock, with about one-third to about 40% by weight typically comprising paper stock, with the balance, typically less than by weight, comprising rag stock. It will be appreciated that the precise proportions of said groundwood stock, said paper stock and said rag stock, are not critical features of the invention and will vary in particular embodiments as a result of varying mill requirements, paper specifications and the like. It should also be noted that, on a dry fiber weight basis, the amount of wood stock employed will be about a half that employed on a wet basis. Those skilled in the art will appreciate that all of the wood stock component of the furnish need not comprise groundwood stock although it will be generally advantageous to thus employ groundwood as the only wood stock in the construction paper applications of the present invention.

In the practice of the invention, it has been desirably determined that all of the accumulated sludge can be recycled without adverse effect upon the properties of the sheet by the coating thereof on the individual strands of groundwood fiber as herein provided. In continuous sheet fabrication operations, therefore, the typical groundwood stock component of the fibrous portion of the furnish will be entirely adequate in amount for the coating thereon of all of the accumulated sludge. No groundwood requirements in excess of those pertaining to conventional operations are thus applicable in the practice of the process of the present invention. On the other hand, it is within the scope of the invention to coat the accumulated sludge on only a portion of the groundwood stock component of the furnish, with the remainder of said groundwood being employed directly in the furnish without being precoated with sludge as herein provided.

As previously indicated, the invention includes within its scope the production of any construction paper sheet the specifications of which do not preclude the presence of the accumulated sludge therein. The typical proportions of fibrous components for roofing felts will not, of course, necessarily apply with respect to other construction paper applications. The relative proportion of wood stock i.e., groundwood, employed is again not a critical feature of the invention, it being understood that a sufficient amount of groundwood stock will be employed so that all of the separated sludge can be coated upon the individual strands of wood fiber, with essentially no excess sludge remaining that necessarily can not be processed with the wood fibers. The invention, in effect, comprises a closed cycle operation with essentially zero effluent discharge in its preferred and entirely feasible operations. Those skilled in the art will appreciate, however, that any portion of the accumulated sludge can be recycled in accordance with the present invention, the remaining portion of the sludge being discarded to waste as in conventional operations. Such limited sludge recycle operations are not preferred, however, since the typical wood fiber component of the furnish is entirely capable of readily accommodating all of the accumulated sludge without adverse effect on the properties-of the sheet, thus obviating the additional expense of sludge storage and disposal.

In conventional construction paper operations and in the present invention, fibrous stocks, including groundwood stock, together with conventional non-fibrous ingredients, are blended together with water in a milling zone to produce an aqueous suspension of said stocks. In this operation, the resulting suspension is heated typically to on the order of about l35-l40F as by the introduction of steam-heated wood stock to the milling zone. The thus-blended stock is thereafter dewatered in a sheet fabrication zone, e.g., a conventional paper making machine such as a fourdrinier machine, in which a sheet of uniform structure and thickness is produced and thereafter surface finished in conventional manner. As previously indicated, dewatering is commonly achieved by a combination of natural drainage, induced drainage, roll pressure and heat. The waste water stream i.e,. that the vat spill water stream, removed from the fabrication zone is at an elevated temperature that will vary with the individual mill practice, but which will range generally from about F to about 150F or more, typically on the order of about -140F. By the recycle of the effluent aqueous stream to the milling zone rather than its treatment and discharge to receiving waters, the process of the invention achieves an appreciable savings in the overall heat requirements of the milling and sheet fabrication operations as noted below. As further in accordance with conventional operations, particulate objects and suspended fiber and other matter are removed from the waste water stream by various commonly available separation devices, such as cyclones, screens, filters, etc., as is well known in the art. The resulting effluent aqueous stream at this point generally known as a clean white water stream, has a very much reduced suspended fiber content, together with dissolved and colloidal material. In conventional mill practice, as indicated above, a major portion of said clean white water stream is commonly passed to hydrapulpers and defibrators employed in the production of additional quantities of fibrous stock. The remaining portion of said stream is commonly passed through disc filters or other suitable devices for removing essentially all of the remaining suspended fibers, the effluent aqueous stream thus resulting comprising an essentially clear filtrate having a minimal suspended fiber content. The suspended fibers removed from the dirty white water stream and form the clean white water stream can, if desired, be recycled to the milling zone as a paper stock component of the furnish. The effluent aqueous stream will, of course, have dissolved and colloidal material present therein, said stream having a relatively high BOD loading. It is this stream that, in conventional operations, is treated so as generally to separate a sludge of colloidal matter therefrom and to reduce its BOD loading, by primary, secondary and even tertiary methods, so as to meet applicable BOD reduction standards and regulations and thus permit the discharge of said treated aqueous stream to rivers and other receiving waters. In accordance with the present invention, on the other hand, said effluent aqueous stream need not be treated for such BOD reduction as it is recycled to the milling zone, as is the accumulated sludge in an essentially zero effluent discharge operation.

In the practice of the invention, colloidal material is separated from the effluent aqueous stream as a sludge of waste solids material, both the sludge and the effluent aqueous stream having dissolved solids therein being recycled to the milling zone. While the colloidal material may be separated from the effluent aqueous stream in any suitable separation or clarification zone,

employing any suitable, commercially available cyclone or other clarification equipment, it has been found generally advantageous to disperse bentonitic clay particles in the effluent aqueous stream having dissolved and colloidal material present therein. The bentonitic clay particles serve to adsorb the colloidal material form the effluent stream, thus facilitating the separation of the colloidal material from the effluent stream. It is further desirable, in those embodiments of the process of the invention in which clay particles are thus employed to adsorb colloidal material, to add a water-dispersible flocculent to the effluent stream subsequent to the dispersing of clay particles therein. The flocculent serves to further enhance the separation of the sludge material from the aqueous stream by flocculating the clay particles having colloidal material adsorbed thereon. In such embodiments, of course, the sludge recycled to the milling zone will comprise said colloidal material adsorbed on the clay particles flocculated by said flocculent, as opposed to the sludge settled or separated from the aqueous stream by other techniques or methods not so employing clay particles and a flocculent.

The bentonitic clay is conveniently employed as an about 1% to about 4%, e.g., about 2%, by weight slurry in fresh water. Illustrative of the commercially available clays that can be employed are KWK Volclay Bentonite, a granular product of American Colloid Company, withan average particle size of between 20 and 70 mesh, U.S. Screen, having a montmorillonite content of at least about 90% by weight, and COAGU- LOlD-20l montmorillonite clay, of Baroid Division N L Industries, lnc., with a screen analysis of about 90% through a 200 mesh screen. While it will be appreciated that the amount of clay particles employed will depend upon a number of factors, such as the particular nature of the colloidal material to be adsorbed, the amount of said material to be adsorbed, the desired clarification rate, and the like, it has been found convenient to employ from about 200 ppm to about 250 ppm by weight based on the total weight of the aqueous stream being treated. It will be understood, however, that dosage levels outside this range may readily be employed in the desired separation of a sludge of waste solids material form the effluent aqueous stream.

As a flocculent or secondary coagulant, any suitable, commercially available cationic flocculent may be employed. Suchflocculents are commonly very high molecular weight materials, such as flocculents having molecular weights of on the order of about 2 t 6 million or more. illustrative examples of suitable, commercially available flocculents that may be employed are Betz Polymer 1260, a cationic, extremely high molecular weight, organic copolymer of acrylamide, and Magnifloc 560-C of American Cyanamid Company, likewise a very high molecular weight cationic polyelectrolyte solid. The flocculent is generally added to the aqueous stream as a slurry in fresh water at a concentration of about 0.05% to about 0.5%, conveniently about 0.1%, by weight. While it will be appreciated that the amount of flocculent employed will also depend upon a number of factors, such as those indicated above with respect to the addition of clay, quantities within the range of from about 7 to about ppm by weight based on the total weight of said effluent aqueous stream being treated may be employed, it being understood that dosage levels outside this range may be employed in partic- As indicated above, varios clarification systems can be employed in the practice of the invention. Thus, a multiple batch tank clarifier may be employed in which the effluent aqueous stream passes into one tak for treatment, and flows to other tanks for sludge settling ,and the like and for ultimate transport back to the milling zone as make-up water. In other embodiments, continuous clarifier units may be employed, as for example so-called upflow clarifiers in which the stream being treated is passed downwardly and upwardly through a clarifier device with appropriate provisions made for the addition of clay particles and subsequently the flocculent material thereto if desired. While the time period desirable between the addition of clay particles and of the flocculent will vary depending upon the overall circumstances of any given application, such time period will generally be at least a few minutes, with a period of from about 2 to about 5 minutes being particularly advantageous in many applications.

The effluent aqueous stream having dissolved solids therein, but having colloidal material removed therefrom, is returned to the milling zone as make-up water at a pH on the acid side, typically on the order of from about 4 to about 5.5, e.g., about 4.2-4.5, in the absence of the addition of a suitable pH modifier to the system. The pH of aqueous stream has significance primarily as a measure of the ph of the overall system. That is, when said effluent stream is at an acidic pH, the continuous overall system will likewise be at agenerally equivalent pH, including the waste water stream removed from the fabrictation zone, the sludge separated therefrom, the aqueous suspension in the milling zone, and, of course, the sheet being fabricated. The sheet applications other than roofing felt and similar applications, in which the sheet is subsequently to be contacted with hot, fluid organic materials, the fabrication of such an acid sheet is generally satisfactory from a product viewpoint.

In roofing felt production, the fabrication of an acid sheet appears satisfactory insofar as the apparent properties of the construction paper sheet leaving the fabrication zone are concerned. Thus, the paper has good absorption characteristics, good strength and good flexibility and other desirable characteristics. Upon contact with hot asphalt in the saturators in which the sheet is saturated therewith in the production of a finished roofing felt product, the solubilizing properites of the hot asphalt are found to so weaken or otherwise alter the roofing felt sheet that said sheet has a tendency to readily tear to the extent that satisfactory passage through the saturators can not be effectively maintained. In such applications, therefore, the system is maintained under generally neutral conditions, the pH of the overall system being conveniently reflected by pH of the effluent aqueous stream recycled to the milling zone as indicated above. The pH of the system is commonly and advantageously controlled by the addition of caustic to the system, although other less desirable materials, such as lime, can also be employed for the desired pH control. While the pH of the effluent aqueous stream is a convenient measure of the pH of the system, the caustic or other pH control modifier need not be added to the effluent aqueous stream itself, but may be added at any other convenient point in a particular effluent system as will readily be appreciated by those skilled in the art. It will also be appreciated that the pH of the system can be monitored at any other convenient point, as by monitoring the pH of the vat fibers entering the fabrication zone. In roofing felt and other applications in which the fabricated sheet is contacted by hot organic material, such as asphalt, having solubilizing properties with respect to constituents of the sheet, the pH of the system, as reflected by the pH of the effluent aqueous stream, is generally maintained within the range of from about 5.4 to about 6.5, preferably at from about 5.8 to about 6.2, more preferably at about 5.9 to about 6.0. At lower pH values, the acid sheet will, as indicated, lack the requisite strength for acceptable passage through the necessary asphalt saturation zone in the production of roofing felts. At higher pH values, as on the order of about 8.5, the sheet will be found to become brittle and generally unsatisfactory. Before reaching this undesired point, however, the system will be subjected to highly disadvantageous foaming under alkaline conditions such as a pH of on the order of about 7.5 or less. For this reason, pH modification to avoid the production of an acid sheet advantageously is accomplished in a manner as to avoid the difficulties thus associated with alkaline conditions to the degree referred to above.

The effluent aqueous stream, having dissolved wood sugars, cresols, lignins and organic acids therein, but a substantial portion of the colloidal material removed therefrom as sludge, is recycled to the milling zone as make-up water in a relatively warm condition. The overall heat requirements of the sheet fabrication operation are thereby reduced and minimized in the practice of the invention vis-a-vis conventional operations in which fresh water must be preheated from ambient conditions to the desired temperature conditions under which the aqueous suspension is prepared and the sheet is fabricated. The recycle aqueous stream of the invention will have a temperature of from about 100F to about 140F, commonly on the order of about 120F to about 125F. As compared with the necessity for heating fresh water from about 60F up to the operable temperature conditions for sheet fabrication, e.g., about l35-l40F, the use of the relatively warm recycle effluent stream as herein provided results in an additional highly desirable feature of the present invention, not only from a technical and economic viewpoint but from an environmental aspect as well. Thus, localized energy shortages, and the prospects of curtailed operating schedules as a result thereof, have occasioned genuine concern in various pulp and paper facilities. The present invention not only makes a major contribution in the field of pollution control, therefore, but likewise enables the desired sheet fabrication operations to be carried out with significantly reduced heat requirements and consequent demands for fuel.

In conventional operations, the sludge of colloidal material separated from the effluent aqueous stream, typically at a consistency of about 12l8% solids by weight, must be stored, transported and dischargedto appropriate waste collection areas, all of which entails a very considerable peripheral expense in the overall sheet fabrication Operations. Recycling said sludge to the milling zone for incorporation in the aqueous suspension of fibrous and non-fibrous materials treated in the production of the sheet, as indicated above, disrupts the orientation of the fibers, resulting in poor fiber formation and a lumpy, non-uniform sheet having inadequate strength and drainage characteristics, and

otherwise disrupts conventional operations and the quality of the products obtained. In the present invention, however, the sludge is neither discarded to waste nor utilized in such a disruptive and unsatisfactory manner. Rather the sludge is mixed with groundwood stock or other wood fiber prepared in conventional defibrators so as to coat the sludge onto the individual strands of fiber. The wood fibers thus coated with the accumulated sludge are passed to the milling zone as a wood stock component of the aqueous suspension produced therein, paper stock and rag stock being blended therein in accordance with the desired specifications pertaining to any particular grade and type of construction paper sheet. When recycled in this fashion, the sludge does not interfere with the customary interlocking and orientation of the fibers and does not have any appreciable adverse effect on the uniformity and properties of the resulting sheet. The sludge thus incorporated in the sheet likewise does not interfere with the.

customary drainage characteristics of the sheet or otherwise disrupt conventional sheet fabrication operations. The resulting sheet produced in a closed cycle operation under essentially zero effluent discharge conditions, therefore, has properties comparable to those of conventional sheets produced without the recycle and incorporation of said sludge therein.

As previously indicated, the wood stock component of the furnish from which construction grade paper sheets are fabricated will generally comprise groundwood stock, typically blended with paper stock and/or rag stock. The wood stock component will generally constitute at least on the order of about one-third of the fibrous content of the furnish on a dry fiber weight basis and, of course, correspondingly higher as the paper stock and rag stock components may be reduced from the typical amounts recited above in particular applications of the invention. In all such construction paper applications, the wood fiber content of the furnish will be sufficient in quantity to provide adequate fibers for the coating of recovered sludge thereon for recycle in continuous sheet fabrication operations at essentially zero effluent discharge. It is also within the scope of the invention to mix the accumulated sludge with only a portion of the wood fiber content of the furnish, the remainder of said wood fiber being passed directly to the milling zone without precoating by said sludge.

To the extent that any of the sludge coated on the strands of wood fiber become dislodged and thereby present in fabricated sheet as loose particles, it will be appreciated that the presence of such loose sludge particles in the fabricated sheet could tend to diminish somewhat the extent of the advantages of the sheet of the invention over sheets produced by the incorporation of the sludge therein as loose particles. To minimize any such tendency, therefore, a polyelectrolyte material is incorporated in the blend of wood fiber and sludge, in preferred embodiments of the invention, to enhance the adherence of the sludge on the individual strands of fiber. The polyelectrolyte, which serves in effect to bond the sludge to the fibers so as to minimize the amount of said sludge dislodged therefrom upon subsequent recycle to the milling zone and the sheet fabrication zone, may conveniently be the same high molecular weight, cationic polyelectolyte materials disclosed above for use in the flocculation of clay particles having colloidal material adsorbed thereon. The polyelectrolytes will ordinarily be employed as a slurry in fresh water as also noted above.

It will be appreciated that the amount of said polyelectrolyte material employed for bonding the sludge to the individual strands of wood fiber will depend upon a variety of factors in any given application, e.g., the nature of the wood fiber and sludge, the relative amounts thereof, the particular high molecular weight, cationic polyelectrolyte or other said polyelectrolyte bonding agent employed and the like. In general, however, the polyelectrolyte will commonly be employed in an amount within the range of from about to about 50% by weight of that employed for flocculation pur' poses, typically on the order of about to about e.g., 25% by weight thereof. Thus, the polyelectolyte bonding agent, such as the cationic polyacrylamide bonding agents referred to above, will ordinarily be employed in concentrations of on the order of 0.5 to about 100 ppm, i.e., parts per million parts of said sludge-fiber slurry by weight, preferably about 1 to about 75 ppm, although it will be appreciated that amounts outside said ranges may be employed within the scope of the novel process of the invention.

Groundwood fibers having a somewhat gray appearance due to the presence of sludge on the individual strands thereof, due to the blending of sludge and fiber so as to coat, bond or otherwise adhere said recycle sludge to the fibers, may be blended in the milling zone with other components of the furnish and employed in the fabrication zone without adverse effect on the formation of the sheet or its properties and characteristics.

In this regard, the sludge-coated fibers perform as conventional non-sludge-coated groundwood fiber performs, resulting in uniform, non-lumpy sheets, having good drainage characteristics and suitable strength, said sheets being readily employed in roofing felt applications without the tearing and breaking of the sheet upon application of hot asphalt as encountered heretofore in efforts to recycle sludge directly to the milling zone for incorporation in the fabricated sheet.

In particular illustrative embodiments of the invention, groundwood fibers, such as pine and oak, are employed together with paper stock and rag stock in roofing felt production, with about one-third of the fibrous content of the furnish comprising groundwood fiber on a dry fiber weight basis. The dirty white water separated from the fabricated sheet at about l40F has particulate objects and suspended fibers removed therefrom, the resulting effluent aqueous stream being divided so that about 80% by weight thereof passes to the hydrapulpers employed in the production of said groundwood fiber. Upon having additional suspended fiber material removed therefrom, the remaining portion of the effluent aqueous stream, i.e., about 20% of the clean white water stream, comprises a high BOD stream, e.g., about 2,000 BOD, at a temperature of about 1l5-l20F. In conventional, non-closed operations, the stream is likewise at a high BOD level, usually about 2,000 BOD. The subject stream is contacted with a 2% by weight clay slurry in fresh water, said clay comprising KWK Volclay bentonite clay employed in an amount of about 200 ppm based on the weight of said aqueous stream being treated. After about 2-3 minutes, the resulting clay slurry having adsorbed colloidal material associated therewith is contacted with a very high molecular weight polyacrylamide cationic flocculent, i.e., Magnifloc 560-C flocculent, in an amount of about 7- /2 ppm based on the dry weight of said clay particles, thus facilitating the separation of the clayadsorbed colloidal material from the effluent aqueous stream as waste sludge material. The effluent aqueous stream having its colloidal material content thus significantly reduced is recycled to the milling zone at a pH of about 6.0. The recycle stream, having approximately 2.2% dissolved solids therein, is at a temperature of about F, minimizing the heat requirements to bring the contents of the milling zone up to the desired temperature range, the sheet being fabricated at about -140F. The sludge separated from the effluent aqueous stream at about 120F at a consistency of about 12% by weight in aqueous slurry is blended with the groundwood fiber portion of the furnish so as to coat the individual fiber strands with the sludge. Using about 25% by weight of the amount employed above for flocculation purposes, the indicated high molecular weight polyacrylamide, cationic flocculent is blended with the aqueous slurry of groundwood fiber with sludge coated thereon in order to enhance the bonding of the sludge to the individual fiber strands. The sludge thus adhering to the fibers comprises essentially all of the waste sludge, so that together with the indicated recycle of the effluent aqueous stream, the overall sheet fabrication operation is carried on on a closed-cycled basis with essentially zero effluent discharge to waste.

The sludge, as thus bonded to the groundwood fiber, is recycled to the milling zone wherein said groundwood fiber, paper stock and rag stock, together with conventional non-fibrous ingredients, are blended and passed to the fabrication zone. Therein, the sheet having said sludge incorporated therein not as loose particles, but essentially adhering to the groundwood fiber strands, is produced as a uniform, non-lumpy sheet. The sludge in this form does not interfere with the customery orientation of the fibers to produce an acceptable sheet. As the system likewise was maintained at a pH of about 6 by the addition of caustic thereto, the sheet thus-containing said waste sludge is suitable for roofing felt application and is found to readily pass through conventional saturators without breaking upon exposure to hot asphalt. The resulting roofing felt, therefore, is comparable in quality with conventional roofing felt produced without recycle of said effluent aqueous stream and of said accumulated waste sludge.

It will be readily appreciated that various other conventional ingredients may be incorporated in the overall system herein described to overcome or obviate particular operating difficulties or effects encountered in such operations. Thus, a water soluble foam suppressant, such as Betz Foam-Trol C, a nonionic antifoam product designed for use in paper production may be employed in conventional amounts. Likewise, any suitable, commercially available corrosion-inhibiting agent can be incorporated in the system in conventional amounts as required. A typical agent employed for this purpose is Betz Petromeen WS-54, a semipolar, water-soluble, organic filming agent. As the sludge materials handled comprise biological waste material, it is also generally desirable to employ a conventional slime-control agent, such as conventionally available chlorophenols such as Betz RX-l7, in the system in conventionally recommended dosages. As with the other known agents employed for their customary purpose, such slime-control additives can be employed at any convenient point in the overall system as described herein. It will be appreciated, in this regard, that slime formation can occur anywhere in the system and is not a problem peculiar to a closed-cycle mill.

The dissolved solids present in the recyled effluent aqueous stream comprise a variety of wood sugars, cresols, lignins and organic acids. In the continuous operations of the present invention, such solids in excess of the saturation level of the aqueous streams involved in the overall operation are present as suspended material that is removed from the effluent aqueous stream as sludge for incorporation in the sheet in accordance with the essentially zero effluent discharge of the present invention. The sheet fabrication operation of the invention, in which comparable sheet quality is combined with total utilization of Waste materials, represents a major contribution to the environmental aspects of constuction paper fabrication. This contribution, most significantly, is made in a technically and economically feasible manner highly suited for commercial application. As extensive investigation has determined that the novel sheet produced with sludge incorporated therein, as herein provided, has acceptable properties and can successfully be employed in roofing felt and like applications, it can be seen that, contraty to all expectations, essentially zero effluent discharge operations are, in fact, feasible, with the immense environmental advantages accruing to such operations.

Therefore, I claim:

1. An improved process for the production of constuction paper sheets comprising:

a. blending fibrous stocks including groundwood stock having dissolved solids therein, together with water, in a milling zone to produce an aqueous suspension of said stocks;

b. dewatering said suspension in a sheet fabrication zone as to fabricate said paper sheets;

c. removing particulate objects and suspended fiber from the waste water stream removed from said fabrication zone, thereby producing an effluent aqueous stream having dissolved and colloidal material present therein, said stream having a relatively high BOD loading;

d. separating said colloidal material from the effluent aqueous stream as a sludge of waste solids material;

e. blending said sludge and groundwood stock so as to coat individual strands of the wood fibers with said sludge;

f. recycling essentially all of said effluent aqueous stream having dissolved solids therein to said milling zone as make-up water for blending with additional quantities of said fibrous stocks; and

g. recycling said sludge coated on the fibers of said groundwood stock to the milling zone, the sludgecoated wood fibers serving as said wood stock components of the aqueous suspension produced in the milling zone, essentially all of said sludge separated from the effluent aqueous stream thus being recycled to said milling zone,

whereby said sheet is produced essentially without discharge of high BOD aqueous effluent to waste and without undesired sludge accumulation, the disruption of the orientation of the fibers of the resulting sheet, with accompanying adverse effect on the properties and quality of the sheet, occasioned by the incorporation of loose sludge particles in the aqueous suspension being substantially obviated by the indicated coating of said sludge on the individual strands of wood fiber prior to incorporation into said aqueous suspension, the properties of the resulting sheet thus being comparable to those of said sheet produced without the recycle and incorporation of said sludge therein.

2. The process of claim 1 in which a water-dispersible bonding agent is blended with said sludge and groundwood stock so as to bond said sludge to the individual wood fiber strands, thereby minimizing undesired dislodging of said sludge from the wood fiber during the formation of said aqueous suspension and the fabrication of said sheet.

3. The process of claim 2 in which said bonding agent comprises a high molecular weight cationic polyelectrolyte.

4. The process of claim 2 in which said pH of the effluent aqueous stream is from about 5.4 to about 6.5.

5. The process of claim 2 and including dispersing bentonitic clay particles in said effluent aqueous stream having dissolved and colloidal material present therein, said clay serving to adsorb the colloidal material from the effluent stream, facilitating said separation of colloidal material from the effluent stream.

6. The process of claim 5 and including contacting said effluent stream, subsequent to said dispersing of clay particles therein for the adsorption of colloidal material, with a water-dispersible flocculent, thereby flocculating said clay particles having colloidal material adsorbed thereon, and thus further facilitating said separation of colloidal material from said effluent aqueous stream.

7. The process of claim 5 in which the pH of said effluent aqueous stream is from about 5.8 to about 6.2.

8. The process of claim 1 in which said waste water removed from said fabrication zone is relatively hot, said effluent aqueous stream recycled to said milling zone as make-up water having a temperature of from about F to about 140F, thereby reducing the overall heat requirements of the sheet production operation.

9. The process of claim 8 in which said recycled effluent water is at a temperature of from about F to about F.

10. The process of claim 8 in which the pH of said effluent aqueous stream is from about 5.8 to about 6.2.

11. The process of claim 10 and including dispersing bentonitic clay particles in said effluent aqueous stream having dissolved and colloidal material present therein.

12. The process of claim 11 and including contacting said effluent stream, subsequent to said dispersing of clay particles therein for adsorption of colloidal material, with a water-dispersible flocculent, thereby flocculating said clay particles having colloidal material adsorbed thereon, and thus further facilitating said separation of colloidal material from said effluent aqueous stream.

13. The process of claim 4 in which said sheet produced comprises a sheet of roofing felt.

14. The process of claim 13 in which the pH of said effluent aqueous stream is from about 5.8 to about 6.2.

15. The process of claim 14 in which the pH of said stream is from about 5.9 to about 6.0.

16. The process of claim 13 in which said bonding agent comprises a high molecular weight cationic polyelectrolyte.

17. The process of claim 13 and including dispersing bentonitic clay particles in said effluent aqueous stream having dissolved and colloidal material present therein,

said clay serving to adsorb the colloidal material from the effluent stream, facilitating said separation of colloidal material from said effluent stream.

18. The process of claim 17 and including contacting said effluent stream, subsequent to said dispersing of clay particles therein for the adsorption of colloidal material, with a water-dispersible flocculent, thereby flocculating said clay particles having colloidal material adsorbed therein and thus further facilitating said separation of colloidal material from the effluent aqueous stream.

19. The process of claim 18 in which said waste water removed from the fabrication zone is relatively hot, said effluent aqueous stream recycled to said milling zone as make-up water having a temperature of from about 100F to about 140F, thereby reducing the overall heat requirements of the sheet production operation.

20. The process of claim 13 in which said roofing felt comprises a blend of said wood stock, paper stock, and rag stock.

21. The process of claim 20 and including recycling fiber removed from the waste water stream to said milling zone as paper stock.

22. The process of claim 20 in which the pH of said effluent aqueous stream is from about 5.9 to about 6.0.

23. The process of claim 5 in which the bonding agent is an organic copolymer of acrylamide.

24. The process of claim 6 in which the bonding agent is an organic copolymer of acrylamide and the flocculant is the same or a different organic copolymer of acrylamide.

25. The process of claim 23 in which the bonding agent is blended with sludge and groundwood stock in amounts between about 0.5 and about 100 ppm based on total weight of said sludge and groundwood stock.

26. The process of claim 24 in which the flocculant is contacted with said effluent stream in amounts between about 7 and about 20 ppm based on the total weight of said effluent stream.

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Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US4889594 *Dec 3, 1987Dec 26, 1989Mo Och Domsjo AktiebolagMethod for manufacturing filler-containing paper
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Classifications
U.S. Classification162/190, 162/DIG.900, 162/147
International ClassificationD21F1/66
Cooperative ClassificationD21F1/66, Y10S162/09
European ClassificationD21F1/66
Legal Events
DateCodeEventDescription
Aug 13, 1992ASAssignment
Owner name: GAF BUILDING MATERIALS CORPORATION
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Effective date: 19920804
Owner name: GAF CHEMICALS CORPORATION
Owner name: SUTTON LABORATORIES, INC.
Dec 3, 1990ASAssignment
Owner name: CHASE MANHATTAN BANK, THE, (NATIONAL ASSOCIATION)
Free format text: SECURITY INTEREST;ASSIGNOR:GAF BUILDING MATERIALS CORPORATION, A CORP. OF DE;REEL/FRAME:005648/0038
Effective date: 19900917
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Owner name: CHASE MANHATTAN BANK (NATIONAL ASSOC.) THE
Effective date: 19890329
Owner name: EDGECLIFF INC.
Jun 14, 1989ASAssignment
Owner name: CHASE MANHATTAN BANK (NATIONAL ASSOC.) THE
Free format text: SECURITY INTEREST;ASSIGNOR:EDGECLIFF INC.;REEL/FRAME:005146/0242
Owner name: CHASE MANHATTAN BANK, THE NATIONAL ASSOCIATION
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Effective date: 19890329