US3873412A

US3873412A - Mechanically refining a mixture of kraft and semichemical pulp

Info

Publication number: US3873412A
Application number: US456455A
Authority: US
Inventors: Michael T Charters; Franklin E Landis
Original assignee: Bauer Brothers Co
Current assignee: Sprout Bauer Inc; Bauer Brothers Co
Priority date: 1974-04-01
Filing date: 1974-04-01
Publication date: 1975-03-25
Anticipated expiration: 1992-03-25
Also published as: FI750031A; SE7500167L; JPS50126901A; CA1051151A; JPS5313001B2

Abstract

Method for producing pulp for use in the manufacture of kraft type products such as linerboard and bag grade paper comprising the steps of steaming small segments of fibrous material, defiberizing the same in a pressurized atmosphere and at an elevated temperature and, while the resultant fiber products are still hot, mixing them with a hot kraft pulp and then refining the mixture so obtained.

Description

1451 Mar. 25, 1975 MECHANICALLY REFINING A MIXTURE 0F KRAFT AND SEMICHEMICAL PULP Inventors: Michael T. Charters; Franklin E. Landis, both of Springfield, Ohio Assignee: The Bauer Bros. Co., Springfield,

Ohio

Filed: Apr. 1, 1974 Appl. No.: 456,455

US. Cl 162/25, 162/26, 162/28, 162/142 lint. Cl D2lb 1/16 Field of Search 162/28, 19, 142, 18, 25, 162/26 References Cited UNITED STATES PATENTS 3/1921 Clapp 162/142 Alsted 162/142 2,660,097 11/1953 Hill i 162/28 X 3,202,569 8/1965 Coggan ct a1 162/142 X 3,811,995 5/1974 Ringley 162/28 x 3,827,934 8/1974 Ringley et al 162/28 Primary ExaminerS. Leon Bashore Assistant Examiner-Arthur L. Corbin [57] ABSTRACT 12 Claims, 5 Drawing Figures PATENTED 3,873, 11 2 SHEET 1 95 g STEAM TO HEAT RECOVERY SYSTEM PULP FROM F OIGESTER PRESSURIZED REFINER WASHEO STOOK TO STORAGE STEAM T0 HEAT nacovem SYSTEM F 2 PULP FROM DIOESTER gREFmERSHscREENsH HERs T0 RECOVERY WASHEO srocx T0 STORAGE MECHANICALLY REFINING A MIXTURE OF KRAFT AND SEMICI-IEMICAL PULP BACKGROUND OF THE INVENTION This invention relates to new and unique means and methods for producing a relatively low cost, high quality pulp for use in making kraft type products such as linerboard and bag grade paper.

The kraft pulp industry has been beset with many problems. A basic and continuing problem is the ever increasing cost of production. However, this problem is overshadowed by the more serious problem that the supply of wood of the quality normally required for the production of kraft pulp is limited. Efforts to heretofore find a satisfactory solution have met with little success.

SUMMARY OF THE INVENTION The present-invention not only provides means and methods for extending the available supply of pulp for kraft type products but also enables a substantial reduction in the cost of producing such a pulp and improves its quality.

Embodiment of the invention provides an arrangement of apparatus enabling a pulping process featuring a mixture of defiberized wood chips, which may be derived from a variety of waste type materials, with a conventional kraft stock. In accordance with a preferred procedure, the wood chips either in a raw or weakly impregnated condition, are steamed, pressure refined in a disc refiner, and, while still hot, mixed with hot kraft pulp and hot black liquor. As a consequence of this mixture, the lignin which coats the disc refined fibers is reacted with the unused chemicals remaining in the black liquor. The composite fiber mixture so obtained can then be conventionally refined and screened and washed either before or after refining.

The equipment and controls of the invention system are so arranged as to minimize the production of steam and the use of chemical liquors. The net result is a most economical and effective procedure for providing a homogeneous pulp mixture eminently suited for use in making high quality kraft type products which have improved strength characteristics.

A primary object of the invention is to provide improvements in apparatus and procedures for producing a quality pulp suited for use in making kraft type products such as linerboard and bag type paper.

Another object of the invention is to provide a kraft quality pulp product comprising a mixture of conventional kraft fibers and fibers derived from woods not normally accepted or workable as kraft materials.

A further object of the invention is to provide means and methods of making kraft quality pulp which are economical to employ, more efficient and satisfactory in use and adaptable to a wide variety of applications.

Another object of the invention is to provide a workable procedure for employing low cost groundwood type materials in producing a kraft quality pulp.

An additional object of the invention is to provide means and methods for producing a new pulp suitable for use in kraft type products possessing the advantageous features, the inherent meritorious characteristics and the means and mode of use herein described.

With the above and other incidental objects in view as will more fully appear in the specifications, the invention intended to be protected by Letters Patent consists of the features of construction, the parts and combinations thereof, and the mode of operation as hereinafter described or illustrated in the accompanying drawings, or their equivalents.

Referring to the accompanying drawings wherein is shown one but obviously not necessarily the only form of embodiment of the invention,

FIG. 1 is a diagrammatic showing of a preferred installation for practicing a process embodying the concepts of the present invention;

FIG. 2 shows a modification of the installation and procedure illustrated in FIG. 1; and

FIGS. 3-5 diagrammatically illustrate further modifications of the installation and procedure of FIG. 1 which employ basic concepts of the present invention.

Like parts are indicated by similar characters of reference throughout the several views.

The invention system illustrated in FIG. 1 of the accompanying drawings includes, in part and in series relation, a screw press 10, a steaming vessel 12, a disc type refiner 14, a centrifugal separator 16 and a mixing tank 18.

A blow tank 20 is connected to receive hot kraft stock and attendant black liquor from a batch type di gester (not shown) and to discharge such stock to the mixing tank 18 by way of a conduit 22. The latter incorporates a pump 24, the control of which will determine the rate of feed of the hot kraft stock and black liquor to the tank 18.

A pump 26 is incorporated in a conduit 28 which connects at its entrance end to the mixing tank 18. The discharge end of the conduit 28 connects to a disc type refiner 30 which is in a series relation with a screen 32 and a washer 34. There may be one or more series related refiners 30, screens 32 or washers 34. This will depend on the particular application of the invention system.

In the practice of the invention per FIG. 1, raw wood chips, which may be derived from what is normally considered as scrap or waste materials, are first fed into the screw press 10. In the case illustrated, a conventional screw press may be employed but it is preferred that the press 10 be one such as known as an Impressafiner, a product manufactured by The Bauer Bros. Co. of Springfield, Ohio, USA. In the Impressafiner the wood chips are successively compressed and expanded to remove resins and contained liquids and partially defiberized by this procedure. Then, at the discharge end of the press, the pressed chips are subjected to an application of a small amount of liquid conditioning chemical, the nature of which depends on the desired physical characteristics of the end product sought. The conditioning chemical employed may be NaOH, Na- S, NaOI-I Na S, Na Sx (polysulfide), or the like. The fact that the chips readily expand in the presence of liquor after they leave the pressure zone of the press contributes to a most effective pre-treatment of their fiber content.

Free of extracted effluent, the pre-treated chips are then moved through a pressure sealing valve 11 to the steam chamber defined in the vessel 12. The chips are retained in the steam chamber for a period of two to ten minutes during which they are continuously advanced to a discharge station from which they are directed to the inlet of the disc refiner 14. In the preferred embodiment illustrated the refiner 14 will provide a pressurized environment for the partially defiberized and pre-conditioned chips. It is noted that a double revolving disc refiner is preferred, though a sin gle disc refiner will function satisfactorily for some applications of the invention system and process. In passing through the steam chamber in the vessel 12 the chips will be subjected to elevated pressures from to 150 p.s.i.g. and correspondingly to elevated temperatures and at consistencies from to 40 percent. A similar environment will prevail in the refiner 14 as the chips are passed between opposed refiner discs (not shown), one of which revolves relative the other.

Under influence of the discs and the pressurized conditions in the refiner 14, maintained by the provision of a valve 13 in a discharge line 15 extending from the refiner to the tangential inlet of the centrifugal separator 16, the chips are converted primarily into individual fibers coated with lignin and small fiber bundles loosely held together by a lignin bond. As the chips are re duced, the resultant fibers and fiber bundles and attendant free liquor are blown past the valve 13 to the inlet of the separator 16. Entering the inlet of the separator 16 together with these fibers is a measured amount of black liquor delivered by way of conduit 17 and through the medium of a pump 19. The suction side of pump 19 connects with a liquor recovery line 21 which connects in turn with the washer or washers 34 at the end of the invention system. The liquor will cause the pulp fibers which enter the separator to assume a dilute slurry form.

For best results, the temperature of the liquor introduced to the separator should be maintained between 140F. and 212F. It is most important for best per formance to keep the temperature of the liquor within the separator close to 212F., to insure an optimal reaction on the fibers by the residual chemicals in the hot black liquor and the maintenance of the fibers at an elevated temperature during and after the conventional cyclone separating procedure in the separator 16.

By keeping the liquor at the noted temperature level heat is retained and the production and escape of steam minimized. Such steam as is produced is directed from the overflow end of the separator to a heat recovery system (not shown).

Accordingly, the fibers produced in the refiner 14 are further chemically treated in the separator 16 by hot black liquor which moves therewithfrom the underflow end of the separator to the mixing tank 18.

As noted previously, the blow tank 20 is connected with a digester containing a batch of conventional kraft pulp. Once the kraft materials in the digester are properly digested, the resultant pulp stock is delivered to the blow tank. The temperature of this stock and that in the mixing tank 18 is controlled by the delivering of metered amounts of hot black liquor. This liquor has its source in the liquor recovery line 21 and is furnished under the influence of pump 19 through

branches

23 and 25 of the conduit 17. As noted in FIG. 1, a branch 27 of conduit 17 can be used to supply black liquor to the refiner 14, if so desired.

As they reach the tank 18, the pressure refined fiber products originating in the refiner 14 will be continuously mixed with the hot kraft pulp. The latter is delivered from the blow tank 20 at a uniform rate so as to achieve a desired proportion of conventional kraft pulp to the disc refined pulp. As will be obvious the mixing takes place in the presence of hot black liquor, the temperature of which, as noted previously, is kept close to 212F. It is significant that the pressure refined pulp will essentially be individual fibers, so that they are continuously exposed to the residual chemical in the hot black liquor and the reaction thereon by the chemical will be continuous throughout the entire process.

The proportion of the disc refined pulp mixed with the conventional hot kraft pulp will preferably becontrolled so that it will be between 5 and 25 percent of the total pulp production. The amounts combined will depend on the required end product strength, bulk, brightness, printability, stiffness, etc. Practice indicates that the most practical pulp produced per the invention will have a disc refined fiber content of 10 to 15 percent. lt appears at this time that if this disc refined fiber content is increased to 25 percent, a new line of kraft type products will be enabled by the present invention. To point out the benefits of the invention as to yield and savings, reference is had to the following illustration of the economics of using a mixture of 10 percent pressure refined pulp fibers and percent kraft type pulp in a 1000 ton per day kraft type linerboard mill.

Assume the following conditions:

Kraft Pulp Yield 55% Pressure Refined Black Liquor Treated Pulp Yield Raw Wood required for 1.000 Tons of 55% Yield Kraft Pulp Raw Wood required for 900 Tons of 5571 Yield Kraft Pulp Raw Wood required for Tons of 9071 Refined Pulp Raw Wood required for 1.000 Tons of Mixed Pulp Wood Savings Per Day using 10% Refined Pulp 1,818 Ton 1.636 Ton l l l Ton 1.747 Ton 71 Ton The resulting savings of 71 ton of wood per day represents a 3.9 percent wood savingsv At a wood cost of $23 per ton, this represents a yearly (350 days) savings of approximately $571,000. Higher percentages of high yield pulp would, of course, increase the saving in wood usage.

The high black liquor temperatures employed per the invention not only improves the conditioning of the pressure refined fibers but they also improve the economics of operating evaporators in a conventionally associated chemical recovery system.

Thus, by reason of the invention, the problem of a limited supply of the raw materials normally required for producing kraft pulp is considerably diminished, if not eliminated. Moreover the cost of producing a pulp capable of use for kraft type products has become significantly reduced. Add to this the high quality of this newly conceived homogeneous pulp mixture and the net result is a substantial advantage to and advance in the pulping art and installations therefor.

FIG. 2 of the drawings shows an installation which is identical to that shown in and described with reference to FIG. 1 except that the screw press 10 and the pre impregnation procedure effected therein is eliminated. Here the raw chips will be first steamed and the rest of the procedure will be as previously described. The system will be completely adquate for preparing pulp for use in kraft type products. This is due to the fact the chemical reaction enabled by use and application of hot black liquor as described is highly effective to control the physical characteristics of the desired end product.

FIG. 3 shows a modification of the system of FIG. 1 wherein the screw press and mixing tank 18 are both eliminated. In this sytem the centrifugal or cyclone separator 16 is so placed that its underflow end discharges the disc refined materials in the form of fibers chemically treated by hot black liquor, as previously described, directly to the blow tank 20.

In this embodiment of the invention the rate of feed of hot kraft pulp from the kraft digester to the blow tank will be maintained at a uniform level. As the disc refined chemically treated fibers flow into the hot kraft pulp, an automatic mixture will inherently take place. A continuous cooking effect results as the residual chemicals in the black liquor in the blow tank react on the intermixed fibers. In this case the black liquor should be kept at a temperature in the range from about I40F. to 250F.

The embodiment of FIG. 3 is not preferred since the control factors are not as well defined as in the other described embodiments of the invention. However, the resultant pulp will be well suited for lesser quality kraft type products and advantages of the basic concept of the invention are still retained.

It is noted that where the kraft pulp is produced in a system which discharges the cooked pulp at atmospheric pressure, the conventional blow tank 20 would not be required for steam separation. In such case the kraft pulp could be discharged, in a metered flow, directly to the tank 18.

The system of FIG. 4 of the drawings differs from that of FIG. 2 only in that the hot kraft stock is not combined with the disc refined stock in the tank 18 but in the course of a merging flow in the conduit 28. In this case conduit 22 is eliminated and replaced by a conduit 32 which directs the hot kraft stock from the blow tank 20 to the discharge conduit 28 at a point immediately following a pump 26. The latter is incorporated in the conduit 28 to induce a pressured flow of stock from the tank l8 to the following disc refiner 30. Thus, as disc refined stock, diluted by hot black liquor in the tank [8, is drawn from the mixing tank and moved with the hot liquor, under pressure, to the refiner 30, the hot kraft stock is discharged into the body thereof by way of the conduit 32 and so mixed in the course of a continuous flow. In the course of the movement of this mixture to and through the disc refiner 30, the liquor content, still hot, continues to react on the disc refined fibers. The process and equipment employed in the system of FIG. 4 is otherwise as previously described.

The installation of FIG. 5 ofthe drawings differs from that of FIG. 4 in that the cyclone separator 16 and the mixing tank 18 have been eliminated and replaced by a dilution tank 40. In this embodiment of the invention the delivery line 17, which carries hot black liquor, is provided with two branches 42 and 44 which connect the line with the tank 40. The branches 42 and 44 embody

control valves

41 and 43 and are connected to respectively discharge into the upper and lower ends of the tank 40.

With a system so modified as shown in FIG. 5, the fiber stock created in the refiner 14, as previously described, is discharged directly to the tank 40 wherein pressure is carefully controlled. In this instance black liquor of a proper temperature must be introduced to the case of the refiner 14, in the course of the disc refining procedure, in an amount sufficient to cause condensation of most of the steam which may occur during the refining operation. This will obviate the need for a separator 16 in following relation to the disc refiner. In the tank 40 which constitutes a dilution tank, the disc refined fibers are embodied in a body of hot black liquor to which liquor may be added, as required, below the level of the liquid in the tank, by way of the branches 42 and 44. With this arrangement there is a controlled consistency of the material in the tank 40 and the heat lost as steam is reduced to a minimum. Utilizing the pump 27, the dilute slurry form of the disc refined fibers which have been reacted with hot liquor in the dilution tank is channeled to the conduit 28 to be flowed therethrough under pressure. A control valve 29 is incorporated in the conduit 28 in a following relation to the pump 27. In the embodiment of FIG. 5 the blow tank 20 is connected to the conduit 28 by way of a conduit 45 in which is incorporated the pump 24 followed by a control valve 46. The discharge end of the conduit 45 connects into the conduit 28 immediately following the valve 29. It may thus be seen that in this embodiment of the invention there is a metered control of the disc refined stock as well as a metered control of the hot kraft stockuThe respective disc refined stock and hot kraft stock may thus be caused to merge in a continuing flow in the conduit 28 following the valve 29 and in proportions which may be precisely arranged. The so merged portions of the respective stocks will be thoroughly intermixed in the course of flow and there will be a continuing reaction of the hot black liquor forming part of the flow on the disc refined fibers which is continued as the fibers and the hot kraft stock are intermixed in a further refining procedure in a disc re-.

finer or refiners 30.

Of course, as in each described embodiment of the invention, this last described disc refining is followed by screening and washing of a suitable and conven tional nature. The resultant stock mixture, as washed, is directed to storage and/or immediately forwarded for further use while the hot black liquor remaining after washing is recovered and transmitted from the. washers by way of a line 21 into which is connected the hot liquor delivery line 17.

In this last described embodiment of the invention it may be necessary to bleed some steam from the top of the tank 40 in order to control the pressure in this tank and within the case of the disc refiner 14. The mechanics of this are believed quite obvious and need not be specifically described.

From the foregoing it will be clear that the invention provides a simple but unique process of extending conventional kraft stock which results in a high quality pulp usable for a great variety of kraft type products. Not only are economies inherent in the system and answers to problems which have been prevalent in the art as described, but the invention appears to have developed the possibility ofnew products which are basically kraft type products.

Various installations have been suggested to embody the invention concept and illustrated in generally descending order of preference. The differences in the installations as here proposed are with a practical recognition of the fact that differences in available equipment or the nature of the end product desired may make it more reasonable or suitable that one installation may be preferred in preference to others.

From the above description it will be apparent that there is thus provided a device of the character debefore enumerated as desirable, but which obviously is susceptible of modification in its form, proportions, detail construction and arrangement of parts without departing from the principle involved or sacrificing any of its advantages.

While in order to comply with the statute the invention has been described in language more or less specific as to structural features, it is to be understood that the invention is not limited to the specific features shown, but that the means and construction herein disclosed comprise but one ofseveral modes of putting the invention into effect and the invention is therefore claimed in any of its forms or modifications within the legitimate and valid scope of the appended claims.

We claim:

1. A process of producing a pulp suited for use in the manufacture of kraft type products, for example linerboard and bag grade paper, comprising the steps of steaming small segments of fibrous material, defiberizing the same and elevating the temperature thereof and while the defiberized materials are still at elevated temperature mixing them with a hot kraft pulp and me chanically refining the mixture so obtained.

2. A process of producing pulp as in claim 1 characterized by elevating the temperature of said defiberized material by subjecting the same to a hot black liquor having a temperature in the range of 140F. to 250F. prior to mixing thereof with said hot kraft stock.

3. A process of producing pulp as in claim 2 characterized by applying said hot black liquor at a temperature in the neighborhood of 212F.

4. A process of producing pulp as in claim 2 wherein the step of defiberizing said segments is carried out by a disc refining said steamed segments.

5. A process of producing pulp as in claim 4 wherein said disc refining step is carried out in a pressurized environment.

6. A process of producing pulp as in claim 1 wherein, immediately following the defiberizing of said steamed segments, the said defiberized material is introduced to a vessel with hot black liquor and in said vessel subjected with said liquor to a centrifugal separation action, in the course of which the fibers of said defiberized material are subjected to the chemical content of said liquor and caused to achieve and maintain an elevated temperature and then discharge and in a continuing movement thereof combine with the hot kraft stock to produce said mixture which is then further refined.

7. A process of producing pulp as in claim 6 wherein the said segments of fibrous material, following defiberizing thereof, are discharged to a blow tank which commonly receives said hot kraft stock and the mixture so produced is subjected to an application of hot black liquor at a temperature in the range of F. to 250F. to maintain the temperature of said defiberized material and react thereon in the course of flow therewith to refiner means wherein the mixture so obtained is subjected to a further refining procedure and the resultant stock forwarded for screening and washing.

8. A process of producing pulp as in claim 6 wherein following the centrifugal separating action said definerized material at an elevated temperature is introduced to a vessel wherein the hot kraft stock is also introduced and mixed therewith in the presence of hot black liquor prior to refining the resultant mixture.

9. A process of producing pulp as in claim 6 wherein following the centrifugal separating action said defiberized material at elevated temperature is introduced to a vessel wherein additional hot black liquor is added to maintain it at an elevated temperature and have the chemical content react thereon and then the resultant mixture is flowed to a further refiner means and in the course of its flow the hot kraft stock is introduced thereto to merge and mix therewith in movement to said further refiner means wherein the resulting mixture is subjected to refining as a composite to result in an intermingled pulp product.

10. A process of producing pulp according to claim 1 wherein prior to being steamed said segments are pressed and subjected upon release from the pressing action to an application of chemicals such as NaOH, Na s, NaOH-l-Na- S or Na Sx (polysulfide),

11. A process for producing pulp as in claim 1 wherein said segments are steamed for a period up to ten minutes at pressures of 10 to psig and at consistencies from 15 to 40 percent before defiberizing and the defiberizing is effected under conditions of elevated pressure.

12. A process of producing pulp as in claim 11 char acterized by mixing the defiberized segments with hot kraft pulp in hot black liquor at a temperature of [40F. to 250F.

PATENT NO. 3,873,412

DATED -larcil 25 3.9 75

lNVENTORtS) Michael Charters; Frairk lin Lanrliirs It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Cole 4 line 43, "iza'aproves is corrected to read improve Col, 7, line 35, delete "a".

C01. 7, line 42 a is inserted following "with" Col 8, line 15, "definer" is corrected to read defiber and fifth of August 1975 [SEAL] A nest:

RUTH C. MASON Arresting Officer

Claims

1. A PROCESS OF PRODUCING A PULP SUITED FOR USE IN THE MANUFACTURE OF KRAFT TYPE PRODUCTS, FOR EXAMPLE LINERBOARD AND BAG GRADE PAPER, COMPRISING THE STEPS OF STEAMING SMALL SEGMENTS OF FIBEROUS MATERIAL, DEFIBERIZING THE SAME AND ELEVATING THE TEMPERATURE THEREOF AND WHILE THE DEFIBERIZED MATERIALS ARE STILL AT ELEVATED TEMPERATURE MIXING THEM WITH A HOT KRAFT AND MECHANICALLY REFINING THE MIXTURE SO OBTAINED.

2. A process of producing pulp as in claim 1 characterized by elevating the temperature of said defiberized material by subjecting the same to a hot black liquor having a temperature in the range of 140*F. to 250*F. prior to mixing thereof with said hot kraft stock.

3. A process of producing pulp as in claim 2 characterized by applying said hot black liquor at a temperature in the neighborhood of 212*F.

7. A process of producing pulp as in claim 6 wherein the said segments of fibrous material, following defiberizing thereof, are discharged to a blow tank which commonly receives said hot kraft stock and the mixture so produced is subjected to an application of hot black liquor at a temperature in the range of 140*F. to 250*F. to maintain the temperature of said defiberized material and react thereon in the course of flow therewith to refiner means wherein the mixture so obtained is subjected to a further refining procedure and the resultant stock forwarded for screening and washing.

10. A process of producing pulp according to claim 1 wherein prior to being steamed said segments are pressed and subjected upon release from the pressing action to an application of chemicals such as NaOH, Na2S, NaOH+ Na2S or Na2Sx (polysulfide).

11. A process for producing pulp as in claim 1 wherein said segments are steamed for a period up to ten minutes at pressures of 10 to 150 p.s.i.g. and at consistencies from 15 to 40 percent before defiberizing and the defiberizing is effected under conditions of elevated pressure.

12. A process of producing pulp as in claim 11 characterized by mixing the defiberized segments with hot kraft pulp in hot black liquor at a temperature of 140*F. to 250*F.