US2302270A - Pulp making process - Google Patents

Description

Nov. 17, 1942. M sKoLNlK PULP MAKING PROCES.

Filed April l2, 1958 4 Sheets-Sheet l m Nm Nh l. Q Mm. QW I Nll Wh. \W r @n i Il n @WP mn wn l M I.- au @Il n mm NIJ Sm. m H SN |16. .l -I

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PULP MAKING PRocEss 4 sheets-shea 2 Filed yApril 12, 1938 INVENTOR Max Skolnik ATTORNEYS Nov. 17, 1942. M vsKoLNlK PULP MAKING PROCESS Filed April 12, 1938 4 Sheets-Sheet 5 im k ,rm ms m wuwm m Nov. 17, 1942. M, SKQLNIK PULP MAKING PROCESS I Filed April 12, 1958 4 Sheets-Sheet 4 SaoA'AsH ATTORN EYSv Patented Nov. 17, l1942 UNITEDv STATES PATENT OFFICE Max Skolnik, Chicago, lll.

'Appucaun April 12, 4193s, seriaiNo. 201,525

sciaims.

This invention relates to the manufacture of pulp from brous, vegetable material, such as cereal straws, grasses, cornstalks, bagasse, and the like.

An object of the invention is to provide an improved method for treating fibrous, vegetable materials, such as straw and the like, in the manufacture of paper pulp therefrom.

Another oject of the invention is to provide an economical method of producing a. high grade i paper pulp from straw and the like, and which method may be carried out easily.

A further object of the invention is to provide a continuous method of making pulp from straw and the like, in which means are provided to regulate the strength of the cooking liquor within predetermined limits.

Another object of the invention is to provide,

an easy and iiexible control of the cooking of the brous, vegetable material by regulating the time of cooking and by regulating the temperature of the cooking liquor, as well as regulating its strength.

AStill another object of the invention is to provide a method and apparatus in which the soluble products obtained from cooking the straw may be recovered and the free alkali content reused in the cooking process.

A further object is to provide a method of cooking brous, vegetable material which may be readily varied for given fibrous, vegetable materials to produce pulps having widely varying characteristics and suitable for many useful applications.

In the drawings is diagrammatically illustrated an embodiment of this invention which is adapted for carrying out the method, and which forms a complete plant for the production of pulp from raw material and the recovery of soda and lignins. The invention is illustrated in connection with straw from wheat or the like and, for convenience, the term straw will be used in the specifcation, but it is to be understood that other types of fibrous, vegetable material, such as grasses, stalks, vines, etc., may be treated according to the method and with thepapparatus disclosed herein.

In the drawings,

Figure 1 is a side elevational view, somewhat diagrammatic, of apparatus in accordance with this invention, and adapted for carrying out the method of this invention.

Fig. 2 is an enlarged sectional view of the cooking tank taken on line 2 2 of Fig. 1.

k Fig. 3 is an end view of one of the cooking basets.

Fig. 4 is a side view of a modiiled form of cooking basket.

Fig. 5 is a side'elevation, largely diagrammatic, of apparatus to reduce the solid material or straw, after it has been cooked, to apulp suitable for paper or the like.l

Fig. 6 is a side elevation, largely diagrammatic, of the recovery apparatus for the-recovery of the free alkali content and lignins from the liquor in which the straw has been cooked. y

Bales I of straw, with their ties cut and removed, are moved along conveyor 2 to a revolving, perforated screen or drum 3 which serves as a chaff screen and permits loose chau and dirt to drop therefrom. The loosened straw coming from the drum is .carried by conveyor l to suitable cutters 5, from which it passes into the opening 6 of a pneumatic conveyor Above the cutters a suitable arrangement of dust collectors 8 may be disposed if, desired, to remove dust as Ithe straw is cut.

'I'he pneumatic conveyor 'l carries the loosened, cut straw to a suitable type of separator for further separating the dust and dirt. Preferably, such a type of separator is a cyclone separator,

as indicated at 9, and is provided with a suitable .the straw before charging it into baskets or containers for cooking. 'Ihe straw may be Wilted with steam or sprayed with hot water, fresh hot cooking liquor, black liquor from the process, or a combination of these. In the drawings vis shown a suitable spray I li, which is preferably supplied with hot cooking liquor.

After the straw has been wetted and wilted it is compacted by causing it to pass through a duct of smaller size than the wilting trough. This may be conveniently done by providing a tapered duct I5 adjacent the trough II. This tapered duct I5 may also be provided with a further wilting means, such as the ring pipe I1 and connections I8 to conduct steam into the duct I5 to the straw, and thereby further the wilting and compacting of the straw in this portion of the appa- After the wilted straw has been compacted it passesozrtothedischargebox I9. 'ihisboxis disposed above a cooking basket, to be later described, and is provided at the bottom with a suitable discharge gate, which may take the form of a double clam gate 20. as indicated. 'I'he purpose of the gate is to withhold inthe box the material discharged into it during the time of exchange of an empty basket for a loaded one.

The discharge box I9 is preferably of a size such that it holds somewhat more than the contents of a cooking basket 2i. so that the operation of the wilting and compressing apparatus may be continuous, rather than interrupted after the filling of each basket. Also, the discharge box is preferably made so that it increases in cross sectional dimension in a downward direction. This may be by having two or more of the sides taper outwardly. The purpose of this increase in area from the inlet portion oi the discharge box to the outlet portion thereof is to facilitate descent of the wilted straw material through the box. If desired, however, a suitable ram may be disposed above the discharge box I9 to pack the straw in the cooking basket 2I, which is disposed below the box I9. Such a ram should have a stroke of suiiicient length so that on its return it would come out of the box I9 and not hinder the discharge of wilted straw from the duct I5.

The wilted and compacted straw is discharged from the bottom of the box I9 successively into foraminous or fenestrate containers or baskets, one of which in its loading position is indicated at 2l. There are a plurality of such baskets of the same size. They may be formed of heavy wire mesh or perforated sheet metal suitably reinforced, and fitted with covers which may be readily opened at one or both ends. The baskets 2I aresupported by attached trunnion rollers or wheels 22, adapted to permit easy travel of the baskets along horizontal or inclined tracks, and are further fitted with lugs or projections, so that when progressing along such tracks, in the manner described, there may be a definite space between the faces of each basket and those oi the adjacent baskets.

After a basket 2l is filled with straw from the discharge box it is moved along the track 23 to track 24, where the basket enters a hood or enclosure 25, disposed above the cooking tank 28. The baskets progress along the tracky 24 of the hood until they are received by the cage 21 of a suitable hoist or elevator 28.

The baskets may be of any desired shape, a suitable shape being that shown in the drawings (see Figs. 2 and 4), in which the lbaskets-are shown substantially rectangular in cross section and having substantially rectangular faces. If desired, two opposite sides or faces of the basket may be tapered, or all four of the sides or faces may be tapered, thereby causing the cross sectional area of the basket to increase longitudinally, and thus facilitate discharge of the contents. Side and end views of the basket are shown in Figs. 2 and 3, and it will be noted that reinforcing members, such as channels 29, may be disposed along the sides of the basket substantially at the middle portion thereof to receive the thrust of the ram 30 and to transmit such thrust to other baskets in the course of travel through the cooking tank. Also, these members act as spacers to provide sufficient space between tank to allow adequate circulation of the cooking liquor between thebaskets and through the fo- .raminous faces thereof.

Disposed across the-end portions of the baskets are suitable reinforcing members Il connecting the reinforcing members 2l, and which act as supports for suitable wheels .or rollers 22, which may be mounted on axles 22 supported by plates 33 carried by members 3l. The rollers or wheels 22 may ride on suitable tracks. such as the angle iron tracks 25, carried on the inside of the tank, whereby the baskets are easily propelled through the cooking tank.

In Fig. 4 is shown a modified form of basket. In this form of basket the bottom portion is formed with reentrant V portions 34 which facilitates the penetration of the cooking liquor through the contents of the basket, even though the contents be quite dense and compacted.

'I'he cage of the hoist mechanism is provided with suitable means to engage the trunnions of the basket and hold the basket against displacement relative thereto, so that it may be lowered into the cooking tank.

After a basket of straw has been deposited in the cooking tank by the elevator 28 it may be moved horizontally along the tank by means of a suitable ram 30. Movement of the ram to push the last basket one basket space along the cooking tank moves all the baskets in the cooking tank the same amount. It is, of course, desirable that the pusher or piston rod of the ram enter the tank through a suitable stuiiing box, and it is preferably provided within the tank with a shoe extending laterally across the face of the basket.

The cooking tank 26 is preferably substantially rectangular in cross section and made of any suitable construction, such as steel plate, suitably stiffened. but with the bottom somewhat inclined toward the outlet 31 to facilitate cleaning. Along the sides of the cooking tank are tracks 25 upon which the trunnions of the baskets travel, the baskets being impelled progressively through the tank by the thrust of the ram an.

When a basket reaches the end 32 of the cooking tank it is in position to be raised by a suitable hoist elevator 38, which is similar in construction to the elevator 28 where the baskets are introduced. A ram 40 is also provided in order to propel the elevated basket laterally until the trunnions engage the tracks 4I disposed above the cooking tank.

Upon return of the ram 40 to its withdrawn position another basket may be lifted from the cooking tank by the hoist 39. As the baskets progress along the track 4| above the cooking tank, the cooking liquor drains therefrom into the pan or hopper 42, from which the drainings may be returned directly to the cooking tank by means of the pipe 43.

Adjacent the pan 42 another pan 44 is disposed in the path of the baskets as they progress along the track 4I. Suitable spray or shower pipes 45 disposed above the baskets 22 are arranged to shower on the cooked straw in the baskets a liquid which is preferably weak black liquor obtained by pressure extraction in a successive stage of the process, but which may be weak wash liquor, or even fresh water. By such spraying, more of the entrained cooking liquor and lignins arev removed from the cooked or reduced straw.

It is preferred to employ a weak black liquor for this purpose, as thereby the weak liquor is readily separated from the flbers by subsequent treatment, and the fibers retainl a maximum strengthened and rendered more suitable for economical recovery of the alkalies and lignins contained in the liquor. The pipe 46 from this pan leads to the recovery system.

The sprays may extend over any desired number of baskets, there being a number of stations, however, between the last spray and the end of the track 4l, so that the baskets may drain for a suitable period of time. Upon leaving the track Ill the basket is dumped to discharge the contents thereof onto a suitable conveyor 4l.. Any suitable mechanism for this purpose may be employed to so discharge the contents and to dispose the basket in upright position to roll on the tracks 23, where it may receive another load of straw to be cooked. Diagrammatioally indicated in the drawings is a revolving cage 48 which inverts the basket to discharge the contents on the conveyor al and returns the basket to upright position for reception on the track 23, wherefit may receive straw to be cooked.

The cooking or steeping liquor is preferably a dilute solution of sodium hydroxide. The concentration of the cooking liquor, its temperature, and the time of cooking, depend upon the particular type of straw or iibrous vegetable matter being treated, and also upon the desired amount of` softening or loosening of the bonding material holding the cellulose fibers together.

For a straw such as the straw of wheat, oats or rye, a 1% to 2% solution of sodium hydroxide is very desirable for the cooking liquor. The temperature of the cooking liquor is somewhat dependent upon the concentration of the sodium centration of sodium hydroxide, and with the straws above mentioned, a temperature between 175 F. and the boiling point is satisfactory,

The time that the straw passes through the cookingM tank is also dependent upon the type l of pulp that is being produced and the particular raw material. Where it is not desired to give the straw too drastic a cook, it has been found that when the straw is immersed in the cooking solution for a period of thirty minutes to one hour, with a sodium hydroxide solution of 1% to 2% and a temperature around 200 F., very desirable results are obtained.

By means about to be described it will be seen that the cooking liquor is constantly reheated and revivied, and may be automatically kept to any desired temperature. Also, the time of cooking may be varied by varying the length of time during which the baskets are kept yin the cooking tank, so that the process is readilyradaptable for a large variety of types of Vilbrous vegetable material, and the process and apparatus may be operated to cook such material very efficiently to the desired degree, depending upon the results to be obtained, that is, whether it be desired to disintegrate the material rapidly or to a great degree in the cooking tank, or whether it be desired to cook the material a minimum amount to loosen the encrusting and intercellular constituents of the raw material, sc that they may -be strength and length.

While a rough, coarse and stiff pulp may be obtained in a relatively short cooking time, and with a relatively low strength cooking liquor, and cooking at a relatively low temperature, increasing the causticity of the cooking liquor, increasing the temperature thereof, and .increasing the time of cookng, will materially change vthe characteristics of the pulp, so that it is reduced to a point where it may be bleached to form white paper. Between these ranges pulp may be obtained which is suitable for'egg crates, container board, corrugated board, and many other purposes.

In order` to control the strength and causticity o f the cooking liquor, and also the temperature, liquor is withdrawn from the tank outlet by pipe 50. from which it is pumped by pump 5I through pipes 52, 53 to the heater 54, supplied with steam through pipe 55. Into the pipe 5D connects pipe 56, having a valve 51 by which fresh caustic liquor may be introduced into the system.

From the heater the hot liquor is transported through pipes 58, 59 to a suitable header pipe 60, which preferably has a plurality of connections through which liquor is distributed to the cooking tank.l 'I'he header pipe may be disposed above the cooking tank and discharged down into it, but it is to be understood that return of the hot liquor may be made into the sides or bottom portions of the cooking tank, if desired. A pipe 58a is connected by a suitable valve to the outlet pipe 58 of the heater, and hot cooking liquor may, if desired, be carried through pipe 58a to pipe ita. Pipe 58a may be connected to pipe Ma for supplying hot cooking liquor for the spray It. Spray I however, may be supplied with steam or other hot liquid for wilting purposes.

Inserted into a tting in the pipe 59 is shown the stem or actuating element of thermostat valve 6| in the steam supply pipe, by means of which the temperature of the cooking liquor may be maintained substantially constant at any desired point.

Also connected to the tank outlet pipe 50 is a pipe 62 with valve 63. 'I'his pipe can be used to drain the cooking liquor from the tank when operation is to be interrupted or stopped, but primarily this pipe may be employed to control the causticity of the cooking liquor, as will be explained.

Due to action of carbon dioxide in the air and in gases given off by the straw or vegetable ilbrous material under action of the cooking liquor, a conversion of caustic soda into sodium carbonate takes place in the cooking tank, which, without withdrawal of a portion of the liquor, may result in so great a conversion of caustic soda as to affect the proper operation of the cooking process. By withdrawal of a portion of the liquor through pipe 62, regulated by valve 63, and replacement of the withdrawn volume by fresh cooking liquor through the pipe 56, the accumu- 'lation of sodium carbonate in the cooking liquor may be held within any desired limit. The withdrawn liquor may be conveyed to the recovery system, wherein it is concentrated, the lignins separated, and the alkaline liquor recausticized.

AV conveyor 10 delivers the straw 'to the hopper of a suitable press 1|, preferably of the screw type to press out the black liquor contained therein, which black liquormay be conveyed by a suitable pipe 12 to the recovery system. In the iirst n press the straw is still substantially in its stalk structure, and by the action of the screw press the material is squeezed and mascerated, causing the extraction of heavy black liquor. In this pressing the stalk formations are distintegrated to a large degree.

From the press 1| the straw pulp is preferably saturated by wash .water through suitable sprays I8 as it is carried along through a suitable conveyor, such as the helical conveyor 18, to a second screw press 15. The water for this purpose may be fresh water, or may be water from the pulp washing apparatus. Preferably, only as much wash water is added to the straw during its passage through the helical conveyor as the pulp will absorb without becoming liquid.

The weak black liquor extracted by the second press may be conveyed to the pipe 16 and sprays 45 to wash the cooked straw while in baskets, as mentioned above. If desired, however, it may be passed directly to the pipe 12, which leads to the black liquor recovery. A pipe 16a, together with valve 16h, is shown for this purpose as an optional connection.

From the second press the materiall is conveyed to a disintegrator in the form of a continuous breaker beater 18, in which water is added to reduce the pulp to a iiuid condition. This beater has the usual perforated backfall 19, which operates as a screening and extraction device to prevent lumps of material passing through'the machine. The roll is adjustable to the bed plate, so that controlled milling of unbroken stalk structures and the like may be effeoted along with the primary purpose of reducing the lumps of pulp delivered from the press to a uniform fluid condition.

From the breaker beater 18 the material goes through a suitable headbox 80 and is fed therefrom to a suitable refining engine, such as a Jordan refiner 8|. While only one reineris indicated in the drawings, it is to be understood that the pulp may be passed, if desired, through a plurality of renners until it has been sufficiently rened. v

The material coming from the rener is sufciently dilute so that it may be readily passed through a suitable screen 82, to which the material is carried by pipe 83. The purpose of the screen is to remove any nodes, weeds or stalks, etc., which have not been previously disintegrated. From the screen the material flows through headbox 84 to a washer 85, wherein the last remaining traces of cooking liquor are eX- tracted. This washermay be one of a variety of forms, a suitable one being a multiple cylinder type washer commonly used in the paper industry, diagrammatically indicated at 85.

Such a washer may consist of any desired number of Vwire-cloth faced cylinders 86. For purposes of illustration a three cylinder washer is shown. In this washer the pulp is puried by addition of fresh water through pipe 81 at the iinalv stage and, for economy of water, as well as with a view to recovery of some of the alkali in the wash water, a countercurrent System of connections is indicated, and the wash water emerging from the washer 85 passes to a waste tank 85a, from which it may be conducted by pump 85h through pipe 85o to the spray 13. An additional connection is shown by which the wash water may, if desired, be merged with the weak black liquor in pipe 16 from the second pressing operation. This connection comprises pipe 85d and valve 85e. From the washer the From the stock chest 88 the pulp may be run ship the pulp to some other plant or manufacturer, the pulp from the stock chest may be run through headbox 89 and then through a wet machine 90. in which the pulp is formed in layers on a drum and removed therefrom as sheets 8| of wet lap for baling and shipment.

In order to carry out the process economically,- a recovery system is provided for the black liquor obtained from the process. The bla/ck liquor to be recovered may come from several stages of the process. The black liquor lwashed from the baskets of cooked straw and the black liquor extracted by the rst pressing operation are usually conducted directly to the recovery system. A portion of the cooking liquor, either from the drainings from the baskets. discharged from the cooking tank, or the black liquor withdrawn from the cooking tank for regulation of the carbonate concentration of the cooking liquor, may go directly to the recovery system. The weak black liquor from the second pressing operation is preferably strengthened by utilizing it for washing the baskets of cooked straw, but. if desired, it may also be sent directly to the recovery system. y

Recorery system Such black liquors from the process are irst passed through a screen iilter |00 of well known type, comprising a revolving wire screen |0| which. removes any residualpulp or coarse iibers that may be therein. From the illter the black liquor goes to the storage tank |02.

In order to economically effect the recovery of the constituents of the black liquor it must be concentrated, preferably in multiple eifect steam evaporators, in order to concentrate the liquor most efiiciently. As illustrated, the liquor goes throughpipe |03 to evaporators |04 and |05 of a multiple eiect system, it being understood that more evaporators may be utilized, if desirable. By using multiple effect evaporators, steam economy results and a supply of distilled water is obtained. which is desirable for the subsequent dialyzing operation.

'Ihe black liquor preferably is directed through the evaporators from the'last eilect toward the first eiect. In the drawings, by way of example. is shown a double effect evaporator. The black liquor flows to the second eiect through pipe |03, thence to the first eiiect through pipe |06, and from the rst eilect is pumped by pump |01 to the storage black liquor tank |08 for receiving concentrated black liquor.

The condensate from the multiple effect evaporatore is pumped through pipe |09 to the condensate tank ||0. From the concentrated black liquor storage tank |08 the liquor is passed to a battery of dialyzing cells |I| which separate the free alkali content from the lignin content by osmotic diffusion through suitable diaphragms, such as vegetable parchment. The free alkali is diused through the diaphragm into the distilled water supplied from the condensate tank ||0. The concentrated black liquor and the water condensate are passed through the dialyzing cells in countercurrent flow, i. e., the freshwater first extracts the alkali from the black liquor weakest in alkali.

'I'he dialyzers are preferably the type in which a series of vegetable parchment diaphragme are disposed between plates and the water and black pulp is preferably delivered to a stock chest 88. liquor pass through a multiplicity of passages separated only by such diaphragme in countercurrent ow, as above mentioned. They may be of the type shown in my copending application Serial No. 6,019, led February 11. 1935.

The water or white liquor emerging from the dialyzer will have received by dialysis substantially all the free alkali content of the black liquor in the form of caustic soda and sodium carbonate. Preferably, the apparatus will be so adlusted and, operated that the water owing through the dialyzers will yield a liquor of about twice the desired strength of the cooking liquor, such, for example, as about 3 or 4% alkali content. The white liquor is conducted through pipe H2 to storage tank H3, from which it may, at periodic intervals, be conducted to any one of a 'series of causticizing tanks H4. In the causticizing tanks lime is added and the mixture agitated and boiled, which results in conversion of the sodium carbonate present in the white liquor into caustic soda and calcium carbonate sludge. The calcium carbonate is allowed to settle and the clear liquor taken oi above the level of the precipitated sludge by pipe H5 to the cooking liquor storage tank H6.

In the drawings is shown an assembly of three causticizing tanks, so that the boiling operation,

the settling operation, and the Washing of the .l

sludge, may be carried on in rotation inthe three tanks.

After boiling the white liquor with a predetermined amount of lime and allowing the calcium carbonate sludge to settle, it is preferable to make an extraction of the alkali liquor from the sludge by adding a weak liquor obtained from a subse.-

quent washing, agitating the sludge and the added liquor, and permitting the sludge again to settle. Such claried weak liquor is then added to the ilrst liquor to form the cooking liquor, and, if the white liquor coming from the dialyzer is of about double the strength desired for cooking, di-

-- lutionwith the clarified weak liquor just de-A scribed renders the liquor of substantially the proper strength for cooking additional fibrous material.

Itis usually economical to make a second extraction of alkali from the sludge, and, if it be desired to do this, fresh water is added and the mixture agitated and allowed to settle. This second weak liquor may be used in the previously described second extraction of lignins and solid material from the cooked brous material.

A collecting box lll for collecting the water from the condenser i i8 is provided, and such water may be supplied to the causticizng tanks. To this end a pump IIS and pipe |20 are shown. The supplying of the warm water from the condenser to the tanks is economical, since by its use the consumption of steam in causticizing is lessened. Also, this Water may contain a slight amount -of alkali which has been entrained in the .vapor passingv from the last effect of the evaporator to the condenser, and, by utilizing thecon- |26 and pipe |25, where the liquid lignins may be put in barrels |26 for shipment. A portion or all of the liquid lignins may, if desired, be passed to the film evaporator, which comprises a tank |21 7s and heated drum |28, from whichthe dried lm may be removed and passed to a suitable conveyor |29 for taking the dried material to a suit-v able place for storage or shipment. `The lignins produced by thisprocess have commercial utility. They may be used as binders in various compositions, or certain of the constituent parts may be segregated for use in various arts and industries.

It will be seen that according to the method and apparatus disclosed in this application, which is a continuation-impart of my application Serial No. 6,019, iiled February l1, 1935, for 'Pulp production process and apparatus, a simple and ilexible control of the cooking of straw and the like is readily obtained. By withdrawing cooking liquor from the outlet portion of the tank, either continuously or intermittently, reheating, and returning a portion of the liquor to the tank, the temperature of the cooking liquor may be maintained substantially constant, the causticity and sodium carbonate concentration may be readily maintained within predetermined desirable limits, and, of course, the time of cooking is entirely within the control of the operator as the unit containers of straw may be passed through the cooking tank at any desired speed.

By cooking at temperatures below the boiling point, stronger liber is obtained than when cooking under pressure at high temperatures, and, also, disintegration of the nodes and other matter deleterious to the quality of the pulp is minimized. The maintenance of the strength of the caustic alkali substantially constant, or within ingly, the chemical action may beeffected at temperatures lower than could be used in systems employing quantities of chemical andraw material proportioned to achieve practically a complete exhaustion of the alkali at the completion of the cook, as, for example, in batch cooking in pressure digesters.

The time of cooking is reduced and the efficiency of the cooking is increased by utilizing the countercurrent iiow principle, that is, in adding fresh cooking liquor at the end of the tank where the cooking of the straw is substantially completed.

It may also be noted that masceration and mechanical action on .the straw is avoided during cooking and subsequent draining of the cooking liquor from the straw in the containers, so that a much higher recovery of cooking liquor by drainage results, as the liquor willl drain more readily from the unbroken stalks than it will from a quantity of mascerated liber. Also, the preliminary Washing of the straw is provided for in my apparatus-prior to the mechanical action on the straw, which further facilitates the high recovery of cooking liquor.

By making provision for thoroughly wetting, wilting and compacting the straw before charging it into the cooking containers the capacity of the containers is greatly increased and the productive capacity of thecooking tank is increased.

The provision of means for successively squeezing, wetting, and again squeezing the cooked straw previous to the nal washing aids the extraction of the cooking liquor not previously removed from the straw. The liquor obtained by the iirst squeezing operation may pass directly to the black liquor recovery system, and preferably the liquor obtained from the second squeezing may be utilized, as indicated above, to extract further cooking liquor from the straw while it is still in the cooking container, and then may be sent through the recovery system. Y

The provision of means for separation of the ligneous soaps from the free alkali content of the black liquor permits recovery of both the caustic soda and sodium carbonate which may be present in the liquor, and the solution may be recausticized with lime for repeated use in the process of cooking straw. The lignins, after extraction by dialysis of the free alkali content from the black liquor, may be saved and used industrially for many purposes. This saving of the lignins is a distinct advantage of the process, in that it has been customary to incinerate or calcine the black liquors to recover the sodium content, and this method involved a total loss of the ligneous material.

By the process of dialysis for separation of the free alkali content from the ligneous matter in the black liquor, such caustic soda as exists as such in the black liquor is not rst converted into sodium carbonate prior to recausticizing, as is the case in the recovery process in which the black liquor is incinerated or calcined. Thus, less lime-is required for recausticizing the sodium carbonate and economies are effected in recovering the caustic soda for reuse in cooking.

Furthermore, it is to be understood that the particular forms of apparatus shown and described, and the particular procedure set forth, are presented for purposes of explanation and illustration, and that various modications of said apparatus and procedure can be made without departing from my invention, as defined in the appended claims.

What I claim is:

l. In the preparation ofpulp from straw, the method of continuously cutting, wilting and compacting the straw, loading the compacted straw into successive foraminouscontainers, substantially submerging said containers in -a mild, hot sodium hydroxide liquor and passing them through the cooking liquor at a predetermined rate at substantiallyatmospheric pressure and at a temperature below the boiling point of such liquor, withdrawing the container from the cooking liquor, and returning the cooking liquor that drains from said containers to the cooking liquor tank.

2. In the preparation of paper forming stock from straw, the method which comprises submerging the straw in unit containers in a mild alkaline cooking liquor at a temperature below the boiling point and at substantially atmospheric pressure, and controlling the cooking by maintaining the causticity of the cooking liquor and regulating the concentration of the sodium carbonate within the cooking liquor within predetermined limits.

3. In the preparation of paper forming stock from straw, the method which comprises submerging the straw in unit containers inv a mild alkaline cooking liquor at a temperature below the boiling point and at substantially atmospheric pressure, and controlling the cooking by maintaining the proportions oi sodium hydroxide and carbonatos within the desired limits in the cooking liquor.

4. In the preparation of paper forming stock from straw, the method which comprises submerging the straw in unit containers in a mild alkaline cooking liquor at a temperature below the boiling point and at substantially atmospheric pressure, and controlling the cooking by regulating the causticity of the cooking liquor and maintaining the lignin concentration within predetermined limits.

5. In combination, a cooking tank adapted to contain a hot, alkaline cooking liquor, means for introducing and submerging in the cooking liquor foraminous unit containers loaded with wet, compacted straw, means for passing the containers through the cooking liquor at a predetermined rate, a drainage runway ior'the containers, means for withdrawing the unit containers from the cooking liquor and placing them on said runway, means for delivering the liquor drained from said containers into the tank, and means for maintaining the temperature and causticity of the cooking liquor substantially constant.

6. In combination, a cooking tank adapted to contain a hot, alkaline cooking liquor, means for introducing and submerging in the cooking liquor foraminous unit containers loaded with wet, compacted straw, means for passing the containers through the liquor and causing countercurrent relative movement of the containers and liquor, a drainage runway for the containers, means for withdrawing the unit containers fromthe cooking liquor and placing them on said runway, means for delivering the liquor drained from said containers into the tank, and means for maintaining the temperature and causticity of the cooking liquor substantially constant.

'7. In the preparation of pulp from straw, the steps which comprise submerging the straw in a hot, dilute, alkaline liquor, withdrawing portions of the liquor from time to time as it becomes charged with organic material extracted from the straw, concentrating the withdrawn liquor in steani heated evaporators and conserving the steam condensate obtained from the evaporation, causing a countercurrent flow o! the concentrated black liquor and warm condensate in alternate dialytic cells separated by vegetable parchment membranes, whereby the uncombined alkali content of the black liquor is recovered for cooking additional straw and a ligneous product is conserved.

. 8. In the preparation of pulp from straw and the like, the method which comprises introducing unit carriers containing'wilted, cut straw into a bath of mild, hot, alkaline cooking liquor of a strength below 5% at substantially atmospheric pressure for a predetermined time, removing the units of cooked straw from the bath and permitting the cooking liquor to drain from the cooked straw into the cooking bath, removing the straw from the containers, extracting the remaining black liquor in the straw and mascerating the straw, and subjecting the straw to a mechanical debering treatment to reduce it to pulp.

MAX SKOLNIK.

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