US2949395A - Pulp process - Google Patents

Description

1960 R. s. VON HAZMBURG 2,949,395

PULP PROCESS Filed Jan. 12, 1956 wooo CHIPS 'INPREGNATING LIQUOR 1 IMPREGNATOR STORAGE STORAGE STORAGE BIN BIN BIN cooxee COOKER COOKER BL BLOW BLOW PIT PIT PIT C 0 N V E Y 0 R FIBERIZING MlLL INVENTOR.

fima/ig 5 m Way Z27. QM,W%Z 1 hwiz'u @5 PULP PROCESS Romulus S. von Hazmburg, Wilmette, 111. Filed Jan. 12, 1956, Set. No. 558,627

3 Claims. (Cl. 16284) This invention relates to a process of producing pulp and has for an object the provision of a pulp which may be satisfactory for the manufacture of various types of products, such as writing papers, paper liners, corrugated board stock and the like.

In the past, procedures have been proposed for the preparation of semi-chemical pulps which, generally speaking, involve the impregnation of wood chips with a sulfite liquor followed by the steps of cooking and fiberizing the chips to form the desired pulp. However, the procedures that have been suggested, even though many of them have been commercially exploited, have involved processing times of the order of three or four hours or even considerably more. This has resulted in the tying up of rather expensive processing equipment while the chips are undergoing the impregnating and cooking steps prior tofinal fiberizing and pulp formation.

Accordingly, it is a further object of this invention to provide a procedure for the production of a semi-chemical pulp which may be carried out in a comparatively short time.

A further object of this invention is the provision of a process for producing a semi-chemical pulp from wood chips of a large variety of wood species.

A still further object of this invention is the provision of a process which may be readily controlled to produce a uniform pulp product irrespective of the nature of the chips originally introduced into the system.

A still further object of this invention is the provision of a pulping process which involves the use of high pressure cooking equipment but which at the same time involves cooking in increments so that large capacities for the high pressure cookers are not required.

A still further object of this invention is the provision of a pulping process which may be subject at least in certain respects to automatic control, thereby resulting in reduced labor costs.

Further and additional objects of this invention will appear from the following description and the appended c arms.

In accordance with one embodiment of this invention, a process has been provided for preparing a semi-chemical pulp from Wood chips which involves the steps of impregnating the chips with sodium sulfite, steam-cooking the impregnated chips, and thereafter fiberizing the chips while still hot to produce the desired product which ice pregnated chips may be cooked very rapidly in the presence of high pressure steam to produce high yields of a pulp which is very satisfactory for the manufacture of various types of paper products. Thus it has been discovered that wood chips impregnated in the manner above indicated may be cooked rapidly at temperatures higher than heretofore considered feasible in order to produce a semi-refined pulp in yields of between 65% and 80% and of very high quality. This cooking is effected in a period of less than one hour at steam pressures of between 175 and 300 pounds per square inch. Generally speaking, about one hour will be required for temperatures corresponding to the lower pressure range, while times of 15 minutes or even less will be satisfactory for temperatures corresponding to the upper pressure limit.

For a more complete understanding of this invention, reference will here be made to a specific process for carrying it into effect but it will be appreciated that the invention is not to be limited to the details of the procedure given. The accompanying drawing, comprising a flow sheet of one embodiment of the process hereinafter described, will assist in an understanding thereof.

Wood chips are formed in the usual manner from debarked logs of any suitable tree, such as the gum trees, hackberry, sycamore, elm, cottonwood, willow and box elder. The chips usually measure to A; inches in the direction of the grain. The chips that are treated in accordance with the process of this invention are suitably /8 inch chips and may be selected from a large variety of wood species or. any mixtures thereof. After the chips have been screened to remove oversize particles and sawdust, a large mass of them is introduced into a large impregnating vessel which, when filled to capacity, may hold as much as 5 to 6 tons of dry chip material. An impregnating liquor is then prepared comprising an aqueous solution of sodium sulfite which may or may not be treated with an alkaline or acid-reacting material in order to adjust the hydrogen ion concentration thereof for reasons to be hereinafter more fully explained. The concentration of sodium sulfite in the impregnating liquor is such that when the wood chips are thoroughly impregnated with the liquor and then drained dry, the amount of sodium sulfite impregnated into the chips will amount to between 8 and 12 parts of sodium sulfite for every 100 parts of chips on a dry weight basis. With the foregoing in mind, the impregnating liquor may suitably have a concentration of sodium sulfite between about 5 and 15 percent by weight when it is introduced into the impregnating vessel which contains the mass of chips. If the moisture content of the original chip is comparatively high, then increased concentrations of sodium sul- V fite may be necessary in order that the desired amount may be used in the manufacture of various types of papers or other sheet material in accordance with well known procedures. In accordance with this invention it has been discovered that if the impregnated chip prior to cooking contains between about 8 and 12 parts by weight of sodium sulfite for each 100 parts by weight of wood chips on a dry weight basis prior to the cooking step, and if the conditions of impregnation are controlled so that the free water in the chips after the cooking step has a hydrogen ion concentration corresponding to a value between about pH 6' and pH 8, then such imof sodium sulfite will be found in the chip after impregnation.

As indicated above, the hydrogen ion concentration of the impregnating liquor may be adjusted by adding sodium carbonate or sodium bicarbonate. The ratio of sodium sulfite to carbonate in the impregnating liquor may be about 4 to 1 and suitably within the range of'between 3 and 5 to 1. In order that the desired pH conditions of the cooked chip liquor may be obtained (Le. a value between pH 6 and 8), the impregnating liquor may initially have a pH between about 7.5 and 12 which may be arrived at by adjusting with sulfuric acid if desired.

The impregnating liquor is introduced into the impreg- I nating vessel with the wood chips and suitably 4 to 5 parts by drawing a vacuum on the sealed vessel whereafter the contents are heated for a period of one-half to two hours at a steam pressure of 20 to 50 pounds per square inch in order to thoroughly impregnate the chips with the sodium sulfite liquor. Of course it will be apparent that the time for complete impregnation will depend upon a large number of factors, such as temperature, pressure, variety of wood, initial water content of the chips and the like. As above indicated, the improtant feature is to adjust the conditions so that the chips are thoroughly and essentially uniformly impregnated with. the sodium sulfite solution and so that the amount of sodium sulfite actually introduced into the chips amounts to between about 8 and 12 parts of sodium sulfite for each 100 parts of chip material, all on a dry weight basis.

After the impregnation has been completed, the pressure is released on the impregnating vessel and the impregnating liquor is drained away from the chips. This liquor is suitable for use in a subsequent impregnating operation, particularly after make-up sodium sulfite and carbonate is added thereto. The chips thus being drained dry may be charged directly to the cooking operation or may be stored in bins or other containers until such time as it may be convenient to subject them to the cooking step. At this point the chips have a somewhat dry appearance although they still contain a considerable amount of moisture along with the specified percentage of sodium sulfite from the impregnating step.

In accordance with a preferred mode of operation, the drain dried chips are charged to bins or storage hoppers from which they are Withdrawn in increments to smaller high pressure cookers. By operating in this fashion, it is possible to recharge the impregnating vessel with a new batch of chips to be impregnated while the previously impregnated chips are awaiting processing in the chip cookers. The impregnated chips, which may constitute a mass of chips in the amount of five or ten tons, are then introduced in increments into high pressure cooking zones or chambers. These chambers may be vertical cylindrical vessels having a large port for introducing chips into the top and another large port for quickly discharging chips from the bottom. They are constructed in such a manner as to Withstand the pressures that are incident to the cooking operation. In commercial practice about 1000 to 1500 pounds of impregnated chips (on a bone dry basis) are introduced into the cooking chamber and the mass is purged with steam in order to remove the air from the vessel. Thereafter the steam outlet valves are closed and the steam pressure is allowed to build up within the cooker to between about 175 and 300 pounds per square inch and the chips are cooked by the steam until such time as the middle lamellae within the chips have been thoroughly softened. If the chips have been properly impregnated this will require a period of less than about one hour and as little as about 5 or minutes depending upon various factors including the temperature employed, the character and variety of the wood chips, the concentration of sodium sulfite in the impregnated chips, the size of the chips and the like. After the cooking operation has been completed, the steam supply is cut off and the pressure relieved until it has fallen to a value of about 25 pounds per square inch whereafter the valve closing the bottom chip discharge port is opened expelling the chips into a blow pit.

At this point the conditions of treatment should have been controlled so that the free water within the cooked chips at this stage of the operation has a hydrogen ion concentration corresponding to a value between about pH 6 and 8. Preferably this value should be between about 6.7 and 7.3 if the best results are to be achieved relative to final pulp yield, color and fiber strength. The pH value at this point in the operation will depend upon many factors, such asthe variety of wood treated, the time and temperature of cooking and the initial pH and the buffering capacity ofthe sodium sulfite impregnating solution that is originally employed to impregnate the chips. Generally speaking, longer cooking periods result in the release of more acids in the wood chips being cooked so that a substantial amount of carbonate buffer may be necessary in the original impregnating solution to prevent the pH value of the cooked chip from falling below the designated pH 6 or pH 6.7. On the other hand, where the cooking is rapid at the higher temperatures the acid released during cooking is considerably less and the alkaline nature of the wood chip material itself may be such as to require the addition of an acid such as sulfuric acid to the impregnating solution in order to insure that the proper pH values will be attained within the chip after the cooking step. As will be appreciated, the various varieties of wood may have different acid-releasing qualities upon cooking and also different acid-releasing qualities may be exhibited depending upon whether the wood is green, is comparatively dry, or may have been stored after cutting for some time prior to forming into chips or impregnation. It will be apparent to one skilled in the art that the acid-releasing qualities can be readily determined experi mentally for any one type of chip or temperature of cook. Thus a small batch of impregnated chips should be experimentally cooked to ascertain whether or not the proper pH conditions are present in the cooked chip and, if not, either the cooking temperature or the buffer capacity of the initial impregnating solution may be adjusted in accordance withthe above principles.

After the chips have been discharged to the blow pit from the cooking chamber, they are then passed while still hot through insulated conveyors to a suitable fiberizing device which is preferably a mill of the disc type. Suitable disc type mills that are useful in this fiberizing operation are the Bauer mils, the Sutherland mills, the Sprount Waldron mills or others which are well known to the industry for fiberizing chip-like material. Preferably such mills are those that operate essentially at atmospheric pressure. In the disc mill an amount of hot water is added to the hot chips being disintegrated in order to form a pulp having a consistency of from about 7 to 15 percent based upon the dry weight of the ultimate pulp. It is preferred that the fiberizing operation be carried out at elevated temperatures, preferably above about F., and that the chips not be allowed to cool below this point after cooking prior to the time that they are subjected to the fiberizing operation. In commercial operations it will be preferable to provide a battery of fiberizing mills which will be operating to accommodate all of the material that is passed through the impregnating and cooking steps.

The fibers formed in the disc mills are then passed through conventional screens from which any oversize material is returned to the mill and where the fibers are then processed into sheets or dewatered into wet laps for pulp storage as will be understood by one skilled in the art.

In accordance with this invention it is important that the cooked chips be passed to the fiberizing step while they are still hot following the cooking step. In order to demonstrate the advantages obtained using the hot refining method, an experiment was carried out in which a quantity of cooked chips was prepared essentially in accordance with the foregoing example. The chips were divided into two batches and one batch was refined while still hot F.) while the other batch was cooled to 70 F. before refining. A Bauer disc mill was used with the same settings in each case and the results are summarized in the following table:

The breaking time in meters is calculated from hand sheets made from the respective pulps. The increased drainage time of sample A indicates a higher degree of refining. Thus the table indicates that best results are achieved when the chips are refined while still hot.

Thus it will be apparent from the foregoing that a semi-chemical process has been disclosed for the preparation of wet pulp which is readily adaptable to existing equipment but which may be carried out much more rapidly than those procedures that have been suggested in the prior art. A high quality product is produced which may be felted into any one of a number of types of papers that have a high strength. The cooking chambers, being comparatively small units, may be readily operated by automatic controls once the cooking times for a particular type of impregnated chip have been established.

While particular embodiments of this invention are suggested above, it will be understood, of course, that the invention is not to be limited thereto, since many modifications may be made, and it is contemplated, therefore, by the appended claims, to cover any such modifications as fall within the true spirit and scope of this invention.

I claim:

1. A process for preparing a semi-chemical pulp which comprises immersing wood chips having lengths predominantly between about and Ms inch in an aqueous buffered sodium sulfite solution having a pH between about 7.5 and 12 for a time suflicient to thorougly impregnate the chips with the sodium sulfite in an amo fit, on a dry weight basis, of between about 8 and 12 parts of sodium sulfite for each 100 parts of chips, thereafter draining the excess sulfite solution from said chips, cooking the chips containing between about 8 and 12 parts of sodium sulfite with steam under a pressure of between about 175 and 300 pounds per square inch at corresponding temperatures for a period of less than one hour butfor a time sufiioient to thoroughly soften the middle lamellae of said chips, and thereafter fiberizing said chips while still hot at a temperature of at least about 150 F. in the presence of added hot water whereby to form the desired pulp, the pH of said sodium sulfite solution prior to chip immersion being adjusted so that the residual water in the cooked chips prior to fiberizing has a pH of between about 6 and 8.

2. The process as recited in claim 1 in which the pH of the residual water in the cooked chips prior to fiberizing is between about 6.7 and 7.3.

3. A process for preparing semi-chemical pulp which comprises immersing wood chips of a length predominantly between and /8 inch in an aqueous buffered sodium sulfite solution having a sodium sulfite concentration of about 5 to 15%, said solution having a pH between about 7.5 and 12, for a time sutficient to thoroughly impregnate said chips with said solution, thereafter draining the excess solution from said chips, cooking the chips impregnated with said 5 to 15% sodium sulfite solution with steam under a pressure of between about 175 and 300 pounds per square inch at corresponding temperatures for a period of less than one hour but a for a time sufficient to thoroughly soften the middle lamellae of said chips, and thereafter fiberizing said chips while still hot at a temperature of at least about F., in the presence of added hot water, whereby to form the desired pulp, the pH of said sodium sulfite solution prior to chip immersion being adjusted so that residual water in the cooked chips prior to fiberizing has a pH of between about 6 and 8'.

References Cited in the file of this patent UNITED STATES PATENTS Beveridge June 29, 1943 OTHER REFERENCES UNITED STATES PATENT OFFICE CERTIFICATION OF CORRECTION Patent No. 2,949 395 August 16 1960 Romulus SD von Hazmburg It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

In the grant,, lines l 2 and 3,, for "Romulus S, von Hazmburg of Wilmette, Illinois," read Romulus So von Hazmburg, of Wilmette Illinois assignor to United States Gypsum Company of Chicago Illinois a corporation of Illinois line 12 for Romulus.

SQ von Hazmburg his heirs" read United States Gypsum Company its successors in the heading to the printed specificatiom line 3, for "Romulus So von Hazmburg Wilmette Ills" read rm Romulus S, von Hazmlourg, Wilmette Ill assignor to United States Gypsum Company Chicago Illa a corporation of Illinois column 3, line 9 for "'improtant" read important column 4t line 34, for "mils" read mills line 35 for "Sprount" read Sprout column 6 line 35 list of references cited under "OTHER REFERENCES'Q, for "Hansen" read Hausen Signed and sealed this 18th day of April 1961a (SEAL) Attest:

ERNEST W SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents

Claims (1)

1. A PROCESS FOR PREPARING A SEMI-CHEMICAL PULP WHICH COMPRISES IMMERSING WOOD CHIPS HAVING LENGTHS PREDOMINANTLY BETWEEN ABOUT 3/8 AND 7/8 INCH IN AN AQUEOUS BUFFERED SODIUM SULFITE SOLUTION HAVING A PH BETWEEN ABOUT 7.5 AND 12 FOR A TIME SUFFICIENT TO THOROUGLY IMPREGNATE THE CHIPS WITH THE SODIUM SULFITE IN AN AMOUNT, ON A DRY WEIGHT BASIS, OF BETWEEN ABOUT 8 AND 12 PARTS OF SODIUM SULFITE FOR EACH 100 PARTS OF CHIPS, THEREAFTER DRAINING THE EXCESS SULFITE SOLUTION FROM SAID CHIPS, COOKING THE CHIPS CONTAINING BETWEEN ABOUT 8 TO 12 PARTS OF SODIUM SULFITE WITH STEAM UNDER A PRESSURE OF BETWEEN ABOUT 175 AND 300 POUNDS PER SQUARE INCH AT CORRESPONDING TEMPERATURES FOR A PERIOD OF LESS THAN ONE HOUR BUT FOR A TIME SUFFICIENT TO THOROUGHLY SOFTEN THE MIDDLE LAMELLAE OF SAID CHIPS, AND THEREAFTER FIBERIZING SAID CHIPS WHILE STILL HOT AT A TEMPERATURE OF AT LEAST ABOUT 150* F. IN THE PRESENCE OF ADDED HOT WATER WHEREBY TO FORM THE DESIRED PULP, THE PH OF SAID SODIUM SULFITE SOLUTION PRIOR TO CHIP IMMERSION BEING ADJUSTED SO THAT THE RESIDUAL

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