US3036949A - Method of preparing pulp for the production of insulating board and the like - Google Patents

Description

May 29, 1962 SUNG H. CHA 3,036,949 METHOD OF PREPARING PULP FOR THE PRODUCTION oF INSULATING BOARD AND THE LIKE Filed Aug. 21, 1959 IIIIIII'IIIIII BY gwwmv ATTORNEY States 3,036,949 Patented May 29, 1962 3 oss 949 METHoD oF PREPAriIN PULP Fon Tim Pao- DIrIrroN oF INSULATING oARn AND THE L This invention relates to the preparation of fibrous pulp, and more particularly, the preparation of pulp suitable especially for the manufacture of fiber insulating board.

In its more specific aspects, the invention relates to and will herein be described with reference to production of such pulp from non-woody cellulosic fiber material such as bagasse. As will be seen, however, the principles of the invention may be adapted also to the treatment of coarse fibrous material produced from wood.

In the preparation of pulp suitable for the manufacture of relatively thick fibrous products, such as insulating board, lfrom sugar-cane bagasse, it has long been the conventional practise to subject the raw bagasse rst to digestion in a chemical pulping liquor, such as an aqueous solution of soda ash, for several hours at temperatures considerably above 212 F., and at corresponding steam pressures. Upon completion of this chemical digestion step, the bagasse is then subjected to grinding, as in a Bauer grinder or grinders, followed by reiining, screening and washing of the pulp and forming a stock of desired consistency for felting the same into relatively thick sheets.

The principal object of the present invention is to provide a method of pulping raw bagasse or other fibrous material by a procedure which avoids the need for high temperature digesting or cooking of the material. Thus, by the present invention, the cost and upkeep of, and the labor required for operating, the digesting equipment are eliminated, as is also the cost of generating the steam required for its operation.

Another object of the invention is to provide a process of the above-described character, wherein raw bagasse or the like, treated according to the invention, is as readily susceptible to grinding and refining by the conventional pulp grinding and refining machines as is bagasse cooked or digested according to the processes now in use.

Still another object of the invention is to provide a process as aforesaid, capable of yielding a fibrous stock having a freeness and othercharacteristics such that it may be formed into relatively thick sheets on standard board-forming machines at substantially the same speeds as in the case of stock prepared from pulp obtained with the conventional cooking or digesting of the raw material.

The adoption and increasing use, in recent years, of mechanical, in place of manual, methods of harvesting sugarcane, has given rise to a number of troublesome problems in the use of the sugar-extracted bagasse as raw material for the production of fibrous pulp. When sugarcane is mechanically harvested, the bagasse delivered from the sugar mills to the pulp mills is unavoidably intermixed with considerable and varying amounts of gritty rock (this being mainly of volcanic origin in the case of sugar mills located in Hawaii), metallic particles, and other abrasive substances. These abrasive materials present in the raw bagasse cause excessive Wear and tear upon the equipment, such as the grinders, refiners, pumps etc., through which the material must pass in order to produce the desired pulp from the bagasse, as well as upon the saws used for trimming board made from the pulp. In terms-of actual experience in the production of board from bagasse obtained from mechanically harvested sugar-cane, it may be stated that the cost of labor and material for repair and replacement of parts of such equipment amounts to from 30 to 35 cents per 1000 square feet of board (1/2 inch basis) more than the cost thereof in the case of bagasse obtained from manually harvested sugar-cane. Aside from this considerable increase in cost of production of the board, the abrasive rock or the like present at or adjacent the bottom surface of board that is made with a paint coating on its other surface, as in the case of so-called decorative tile or acoustical board, causes objectionable scratching of the paint coating when the opposite surfaces of the boards are in moving contact with one another during subsequent handling in manufacture, storage and shipment.

Accordingly, it is still another object of the invention to provide a process of the character above-described, and which will make possible the removal of such rock or other abrasive substance from the bagasse before it is subjected to the grinding and subsequent stages of treatment for the production of pulp therefrom.

Brieiiy, according to the invention, the raw fibrous material, such as bagasse delivered from sugar mills, is subjected to treatment with chemical, such as soda ash, byl

soaking the same for a relatively short period of time in an aqueous solution of the chemical at ambient atmospheric temperature and then, after removing excess water from the soaked material, allowing the material to age in quiescent state while arranged in a relatively deep layer or layers thereof, for a period of time varying from about 40 to about 100 hours. At the conclusion of the ageing period, the treated material may be fed directly and in constant amount to conventional grinders, following which the pulp may be refined in conventional refiners.

Within the broad range of time above indicated for ageing the bagasse, the preferred range will in most cases be from about 50 to about 75 hours.

For the purpose of ageing the material in accordance` with the invention, it may be piled in a warehouse o r other enclosed storage space, to a depth of anywhere from, say, two to twenty feet or more.

By thus ageing the material after it has been substantially completely soaked in the soda ash or other suitable chemical, the necessity for using digesters or similar equipment for high temperature cooking of the raw material, and, consequently, the problems attendent thereon, are eliminated.

It has heretofore been proposed to produce paper making pulp from raw fibrous material, by treatments which do not require the use of digesters or cooking equipment. Such proposals are set forth, for example, in patents to Traquair 1,936,697 and Vazquez 1,876,522. These prior processes contemplate, as in the case of Traquair, the simultaneous mechanical disintegration of the fiber as by passing wood chips through a multi-stage rod-milling treatment together with caustic treating liquor; or, as in the case of Vazquez, the complete submersion of the rawl fibrous material, such as bagasse, in the treating solution and allowing it to remain therein for a period of three to four months. So far as I am aware, none of such prior processes contemplates, or secures the advantages obtainable by, a treatment of the raw material which comprises, essentially, soaking it for a short time in an aqueous solution of the chemical, and then, after draining or oth` erwise effecting removal of excess water therefrom, allowing it to age while arranged in a relatively deep layer or layers for a period of the order of 40 to 100 hours, preferably 50 to 75 hours.

To facilitate a clear understanding of the invention in its broad las well as in its more specific aspects, the accompanying drawing shows a flow diagram illustrating a specific embodiment of the process as applied to the prod-uction of fibrous pulp from a bagasse, for the manufacture of insulating board or the like.

In the practise of the invention according according to the embodiment illustrated and described, shredded bagasse as received from the sugar mill may be fed, as by means of a belt conveyor 11, to be discharged into the top of, and adjacent one end of a treating tank 12 in which it is to be soaked in an aqueous solution of soda ash or other suitable, weakly alkaline chemical. The aqueous solution of the chemical is preferably made up in a separate solution tank 13, from which it may be fed in desired quantities to the treating tank.

The treating solution is made up in the solution tank in a concentration such that the amount of solution required fully to soak and saturate the bagasse delivered to treating tank 12 will provide, in the case of soda ash, an amount in the range of about 3 to 8 pounds, preferably 4 to 5 pounds, for each 1,000 pounds of bagasse, calculated on the weight of the bagasse as received from the sugar mill.

In order to prevent the development and growth of fungus which might otherwise occur during the period of ageing the treated bagasse, as more particularly hereinafter described, a suitable water-soluble fungicide may be incorporated in the treating solution prepared in tank 13. One suitable fungicide which has been employed in the practise of the invention is sodium pentachlorophenate, suoli yas that known by the trade designation Dowicide G, sold by Dow Chemical Company.

The amount of this fungicide incorporated in the treating solution may be such as to provide 0.4 to 0.8 pound thereof for each 1,000 pounds of bagasse, calculated on the basis stated above with reference to the amount of soda ash used.

Desirably, treating tank 12 is provided with suitable agitator or propelling means 14 arranged to thrust the bagasse into the treating solution and, at the same time move it toward the opposi-te end of the tank.

It is an advantage of the invention that suitable mechanism may also be arranged in the treating tank 12 whereby rock, metallic particles and other -abrasive substances intermixed with the raw bagasse may be separated therefrom during the soaking treatment. For this purpose, suitably arranged baffles may be mounted in the tank, to separate the rock etc., which may then be removed by an inclined Slat conveyor 16 discharging onto a slat conveyor 22 extending transversely of the tank at the lower end 17 thereof. The rock etc. may be discharged into a receiving tank 23. By utilizing such separating means within the treating tank, the excessive wear or damage to the working parts of the grinders, refiners and pumps, utilized in preparing fibrous stock from the bagasse, and excessive wear upon the saws utilized for trimming the board produced from the stock may be avoided or greatly minimized. Likewise, by such means, the likelihood of surface scratching of the painted surface or decorative board may be minimized or eliminated.

After soaking in the treating solution in tank 12 for a period of two to thirty minutes, desirably two to five minutes, the soaked bagasse may be removed from the tank by means of an inclined slat conveyor 15, passing over a perforated plate to permit liquid to drain away.

It appears from actual practise of the process, that the presence of `a substantially more than about 80% by weight of water in the bagasse at this stage accelerates the rate of hydration of the fibers during the subsequent ageing step, to be hereinafter described. As a result, the fibrous stock produced from the aged material, though not muddy, exhibits lower than a desirable freeness for ready-de-watering of the formed sheets or wet mats by the presses of conventional board-forming machines.

In order to avoid the aforementioned undesirable results of an excess of water during the ageing of the bagasse, the treated bagasse may be discharged from conveyor into mechanism indicated at 18, suitably designed for squeezing excess water out of the bagasse. Preferably, this mechanism should serve to squeeze out sufiicient of the excess to reduce the amount of water which will be present during the ageing step to not substantially more than about by weight of the bagasse.

The treated bagasse, after squeezing out its contained excess water by means of mechanism 18, is then delivered to a suitable place for carrying out the ageing step of the process.

Referring more in detail to the ageing step of the process, this is effected, in accordance with the invention, by permitting the bagasse, after being soaked with the soda ash or other suitable chemical, as described above, to age while maintained in quiescent state in `a relatively deep layer or layers for a period of time which may vary from 40 to 100 hours, preferably about 50 to 75 hours, in an enclosed space, such as in a covered warehouse or in storage bins, indicated at 19. The depth of the layer or layers in which the material is left to age may vary from 2 to 20 feet or more.

During the ageing cycle, there occurs an autogenous increase in the temperature of the bagasse. In actual practise of the process, it has been found that the ternperature reading, taken approximately one foot below the surface of the pile of bagasse at the end of the first 24 hours of the ageing period, was approximately 110 F., compared to an atmospheric temperature of 86 F. At the end of the second 24 hours of the ageing period, the temperature of the bagasse had increased approximately an additional 10 F., reaching approximately 120 F., or a total increase of approximately 34 F., in fortyeight hours. At the end of the third 24 hours of the ageing cycle, however, no further substantial rise in temperature of the bagasse was observed, and the temperature remained substantially constant until the bagasse was ready for use in the succeeding step in the production of pulp therefrom.

The autogenous increase in the temperature of the bagasse during the ageing thereof, as above described, together with the chemical action of the soda ash or other treating chemical employed, effects a sufiicient softening .action upon the -lignin and other substances which bind together the bers or fiber lbundles of the bagasse, to conl dition the latter for ready defibering and refining by con ventional grinders `and refiners, for the formation of fibrous stock suitable for the manufacture of insulating board or the like. This conditioning of the bagasse by the process of the invention, aside from dispensing with the need for high temperature cooking of the raw material, affords the further advantage, in many instances, of higher yields and improved quality of fibrous stock, as compared to those obtained when utilizing high temperature digesting of the raw material.

Moreover, the process of the invention provides other important advantages. lt is known that when bagasse, in the damp condition (containing about 50% moisture) in which it is received from sugar mills, is stored for any substantial period of time, a noticeably obnoxious, very pungent odor of acid fume prevails, evidently as a result of enzyme action and fermentation. Also, the color of the bagasse turns brown, and this coloration is carried over to insulating board or the like produced from pulp made from such bagasse.

Both of the foregoing difficulties, which arise when damp, untreated bagasse is stored, are avoided in the present process wherein the bagasse is aged after being soaked with the aqueous solution of soda ash and Dowicide G. Furthermore, the presence of the latter prevents the development and growth of fungus in the form of mushrooms, as normally occurs when damp, untreated bagasse is stored.

Referring to the above-mentioned time period of ageing the bagasse, it may be pointed out that the greater the ageing time, the greater is the tendency of the resultant fibers to lack the desirable degree of spring-back in the sheet or wet mat produced therefrom, necessary for rapid de-watering of the sheet or mat on the presses of the forming machine.

At the termination of the desired ageing, the bagasse may be conveyed by suitable constant-feed mechanism, indicated at 24, to Bauer or other conventional form of grinders 25 for defibering the treated bagasse. From the grinders, the pulp is fed to a decker 26 discharging into a stock chest 27, from which it is delivered to a Clain or similar rener 28 discharging into a stock chest 29. From the latter, the stock is passed through a Jordan rener 30 and delivered to the board-forming machine 31, such as an Oliver or Fourdrinier. After being formed into sheets, the latter are dried in drying ovens 32.

In actual practise, brous stock produced from the bagasse, in accordance with the invention exhibited substantially the same board-forming characteristics as those of stock made from the bagasse when cooked by the conventional process, and the iinished board produced from the pulp prepared in accordance herewith possessed substantially the same physical properties and quality standards as those of the board produced from the cooked bagasse.

In the practise of the invention, provision may be made for blending the stock prepared from the bagasse treated and aged as above described, with desired amounts of stock prepared from raw and unaged bagasse, in instances where the former is too slow as indicated by a freeness tester or is too soft and pliable to exhibit proper springback for normal de-watering in the presses of the boardforming machine. To that end, as indicated by dotted lines in the accompanying drawing, portions of bagasse delivered by conveyor `11 may be diverted therefrom as by means of a drop-gate to a stock-pile 33, from which desired quantities may be blended in the feeding device 24 with treated and aged bagasse.

What I claim is:

1. The method of forming fibrous stock for the production of ber insulating board from bagasse, which comprises soaking the bagasse at ambient atmospheric temperature for a period of about two to thirty minutes in an aqueous solution containing an alkaline treating chemical in a concentration such that the amount of said solution required to fully saturate the bagasse will provide the equivalent of about 3 to 8 pounds of soda ash per 1000 pounds of bagasse, reducing the aqueous content of the thus soaked bagasse to an amount not substantially in excess of by weight of the bagasse, arranging the thus treated bagasse in a relatively deep layer and permitting the same to age, while thus arranged, for a period of about 40 to 101) hours, during which period the temperature of the bagasse does not exceed approximately F., feeding the thus aged bagasse directly from said layer to grinders for debering the same to a pulp, and

refining the ground pulp to form a brous stock suitable for the production of ber insulating board on a conventional board-forming machine.

2. The method of claim 1, and wherein said solution also contains a fungicidal agent in an amount suicient to prevent the development and growth of fungus during said ageing period.

3. The method ofrclaim 1, and wherein extraneous rock or other abrasive substance mixed with said bagasse is mechanically separated from the latter during said soaking step.

4. The method of claim 1, wherein said agedV material is blended with bagasse which has not undergone said soaking and ageing treatment.

References Cited in the le of this patent UNITED STATES PATENTS 126,293 Harang Apr. 30, 1872 1,627,103 Mason May 3, 1927 1,739,645 Munroe Dec. 17, 1929 1,818,897 Kumagawa Aug. 11, 1931 2,899,350 Birdseye Aug. 11, 1959

Claims (1)

1. THE METHOD OF FORMING FIBROUS STOCK FOR THE PRODUCTION OF FIBER INSULATING BOARD FROM BAGASSE, WHICH COMPRISES SOAKING THE BAGASSE AT AMBIENT ATMOSPHERIC TEMPERATURE FOR A PERIOD OF ABOUT TWO TO THIRTY MINUTES IN AN AQUEOUS SOLUTION CONTAINING AN ALKALINE TREATING CHEMICAL IN A CONCENTRATION SUCH THAT THE AMOUNT OF SAID SOLUTION REQUIRED TO FULLY SATURATE THE BAGASSE WILL PROVIDE THE EQUIVALENT OF ABOUT 3 TO 8 POUNDS OF SODA ASH PER 1000 POUNDS OF BAGASSE, REDUCING THE AQUEOUS CONTENT OF THE THUS SOAKED BAGASSE TO AN AMOUNT NOT SUBSTANTIALLY IN EXCESS OF 80% BY WEIGHT OF THE BAGASSE, ARRANGING THE THUS TREATED BAGASSE IN A RELATIVELY DEEP LAYER AND PER-

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