US2078222A - System of fiber liberation - Google Patents

Description

April 27, 1937, c. D. ALTICK ET AL SYSTEM bF FIBER LIBERATION Filed Mafoh 12, 1954 2 Sheets-Sheet l April 1937. c. D. ALTICK ET AL 2,073,222

SYSTEM OF FIBER LIBERATION Filed March 12, 1954. 2 Sheets-Sheet 2 Patented Apr. 27, 1937 TED STATES PATENT OFFICE 2,07d,222 SYSTEM or mun IIBERATION a corporation or time Application March a. 19%, Serial No. 715,150

36 is a iii-mu The present invention relates to a system of preparation of pulp material for paper making and other purposes, and more particularly to a circulatory dlgester apparatus and method of fiber liberation by either sulphite, sulphate, or soda treatment. While, for illustrative purposes, the method and apparatus forming the subject matter hereof is herein described as pertaining tothe treatment of wood chips ior the preparation of cellulose-wood pulp, and the like, it is to be understood that the method and apparatus are not so limited, but are applicable also to the treatment or other fibrous, ligneous and cellulose materials.

Temperature, digester pressure, and concentration of acid in the cooking liquor, are three recognized controlling factors in digesting pulp material. It is equally'important, however, that every portion of the mass shall be treated equally and subjected uniformly to the action of the cooking liquor,

In the usual methods of operation heretofore employed circulation and distribution of the cooking liquor throughout the mass is dependent upon convection currents and gas ebullition, and consequently some portions of the material lying inert within the tank may be under-cooked while other parts are over-cooked and, due to acid losses by evaporation, the cooking liquor varies in strength throughout the cooking operation.

In the present system the digester contents are maintained under a constant hydrostatic head or pressure whereby the liquor is caused to more thoroughly penetrate the terial. The digester is filled full of material and the level of the cooking liquor is raised above that ofthe digester dome so that there is .no space or low pressure area into which gases may rise within the digester. To insure intimate intermirture of the material and cooking liquor during the digesting process, material intermixed with liquor is positively circulated through the digester tank by being withdrawn at one end and reintroduced under pressure at the other end in a more or less continuous cycle of circulation. A portion of the cooking liquor is also circulated through the cooking mass under pressure additionally to such circulation of the intermixtureof material and liqnor by being withdrawn from the digester and reintroduced thereto under pressure and in a, reheated condition either at the bottom or at any suitable elevation whereby the current of liquor and current of intermixture of material and liquor is withdrawn for circulation. The contrary currents meeting within the digester tank cause such disturbance and agitation of the contents that every portion is brought into a zone of active treatment. After withdrawal from the tank the pressure upon the cooking liquor is temporarily reduced and the entrained gases are collected and condensed and the condensate is immediately returned to the liquor to maintain its required strength. Prior to introduction into the dlgester, the material is subjected to a pretreatment in a soak tank where it is saturated with cooking liquor. To insure uniform saturation of the material it is periodically circulated through the soak tank by being withdrawn from one end and reintroduced at the other in quite the same manner that it is later circulated through the digester tank;

The periods of circulation of the intermixture of material and liquor and that of the liquor alone are automatically controlled by suitable power switching means, either on a time basis or by volume control in which case a fluid meter is introduced into the circulatory cycle.

The object of the invention is to improve the apparatus as well as the means and mode of operation of digester cooking systems for pulp making operations whereby such apparatus will not only be cheapened in construction, but will be more emcient in use, uniform in action, economical in operation, automatic, and unlikely to get out of repair.

A further primary object of the invention is to enable the production of pulp of uniform character and quality.

A further and important object of the invention is the more rapid reduction of pulp at a lower cooking temperature and production of pulp of higher quality than now obtainable.

A further object of the invention is to reduce the time required for digestion of the material by providing better preparation of the material before its entry into the digester tank.

A further and important object of the invention is to effect thorough agitation of the material within the digester tank and to enable the cooking liquor to thoroughly and uniformly act upon every portion thereof.

A further object of the invention is to materially increase theyield of pulp for a given digester capacity by reducing the time requirement and by utilizing the entire digester space.

A further object of the invention is to provide an apparatus and method of treatment of fibrous material possessing the advantageous characteristics, features and steps as herein enumerated.

With the above primary and other incidental iii objects in view, as will more fully appear in the specification, the invention consists of the features of construction, the parts and combinations thereof, and the mode of operation, or their equivalents, as hereinafter described and set forth in the claims.

In the accompanying drawings wherein is illustrated the preferred but obviously not necessarily the only form of embodiment of the invention, Fig. l is an elevation, somewhat diagrammatic, of an apparatus for carrying out the present process of treatment of pulp making material. Fig. 2 is a side elevation of a modification. Fig. 3 is a detail view of a variation of the automatic control means.

Like parts are indicated bysimilar characters of referencethroughout the several views.

Although the present apparatus is primarily intended for the reduction of wood chips for production of paper pulp by the sulphite process, it is to be understood that it is not so limited, but may be employed for soda treatment or for sulphate treatment of not only wood chips but of fibrous material of other character in the preparation of pulp not only for paper making but for other purposes as the manufacture of nitrocellulose, cellulose acetate, pyroxylin, rayon, tannic extract, and other analogous materials. Therefore, the materials herein referred to are for illustrative purposes only and are not mentioned with intent to in any way limit the purpose, application, or result of the invention.

In the drawings, I indicates a storage or soak tank wherein wood chips or other fibrous material is initially stored until thoroughly saturated with water or other liquid. The preferable impregnant is the liquor in which the material is to be later cooked during the digesting process, which may be of either acid or alkaline character.

The storage or soak tank I comprises brick or other vitreous walls 2 enclosed in a thermally insulated jacket 3, and the contents of the tank are heated by heater coils I interiorly thereof or embedded within the vitreous walls 2 and controlled by a thermostatic valve 211.

Surmounting the soak tank I is a condenser 5 by which vapors, arising from the tank I, are condensed and the condensate returned to the tank. Leading from the bottom of the soak tank I is a conduit 6 communicating with a centrifugal pump I, the discharge outlet of which is directed upwardly through the continuation 6a of the conduit 6, which is provided at its top with a lateral discharge outlet 8 communicating with the top of the soak tank I and having therein a cut-ofi valve 9. This forms a closed circuitous path, which includes the soak tank I, through whichthe contents of the tank, consisting of pulp making material intermixed with impregnating liquid, is circulated by operation of the centrifugal pump I. By operating the centrifugal pump from time to time to effect a circulatory motion of the intermixture of pulp making material and impregnating liquor during the process of preparation, the position of individual portions of the; mass within the soak tank is changed and the contents agitated so that every portion of the material is subjected to uniform impregnating action of the liquor. This circulation of material in the preparatory stage not only insures more thorough andhniform saturation, but it also materially reduces the period of time necessary for proper preparation.

Leading from the top of-the circulatory conduit 6a is a second outlet conduit I0, communiconduit II discharges.

eating with the top of the digester tank II and having a cutoff valve I2. After the material has been retained in the soak tank I for sufficient period to become thoroughly saturated and impregnated with the liquor, which condition as before described is facilitated by the circulation of the intermixture of material and impregnating liquid, the valve 9 in the discharge outlet 8 back to the soak tank I is closed and the cutoff valve I2 in the discharge conduit III for prepared material is opened whereupon the material withdrawn from the bottom of the soak tank I is discharged through the conduit Ga and thence through the branch conduit I into the digester tank II. The digester tank II may be of any convenient size and shape, that illustrated being a conventional form of digester having a domed top and conical bottom. At its bottom, the di gester tank II is provided with the usual blowofi or discharge conduit I3, which in the present instance communicates with a centrifugal pump The centrifugal pump I4 discharges upwardly through the continuation I30. of the conduit I3 which, at its upper end, communicates with the supply conduit I0 discharging into the top of the digester tank I I. The circulatory conduit I30 is also provided with a branch I 3b which discharges into the digester tank II at a point opposite the connection of the conduit II). The conduit I0 is provided with a cutofl valve I5 intermediate the circulatory conduit I3a, and the branch conduit I3b is also provided with a cutoff valve I 5a.

The digester tank II, having been filled with prepared material, the valve I2 in the supply conduit I0 is closed and upon operation of the centrifugal pump I4, an intermixture of pulp making material and cooking liquor is withdrawn from the bottom of the digester tank H and discharged upwardly through the circulatory conduits I31; and I3!) by which the intermixture of material and cooking liquor is returned to the top of the digester tank. These return conduits direct the intermixture in intersecting paths within the digester tank II thereby causing violent disturbance and a itation of the contents of the tank whereby every portion thereof will be uniformly subjected to the action of the heated cooking liquor. The conduits I3, I31; and I3b form, with the digester tank II, a closed circulatory system of which the tank II is a part, through which the intermixture of material and cooking liquor may be circulated at will by operation of the pump I I. The digester tank 'II is provided at its top with a screen or baflle I6 for confining the pulp making material while allowing the cooking liquorto pass therebeyond. A cooking liquor conduit I'I leads, in elevated relation, from the top or dome of the digester II, and is provided with an expansion valve or pressure regulator I8 by which the contents of the digester are maintained under predetermined hydrostatic pressure, which pressure falls somewhat in the conduit I 1 beyond the valve or regulator I8.

The liquid level within the digester II is maintained well above the top of the tank so that there is no space within the digester into which gases and vapors may arise from the cooking liquor. Such vapors and gases, however, pass 'from the digester tank entrained with the liquor through the conduit I'I into a low pressure acid recovery compartment I9 into which the This recovery compartment I 9 extends below the level of the top of the digester and. is so positioned as to contain a quantity of liquor, the fluid level of which is preferably above the outlet of the liquor conduit H which is submerged and fluid sealed thereby. The digester tank ll being maintained entirely full of material and liquor and under pressure, there is little or no gas generation within the digester and consequent ebullition or bubbling, but as the liquor passes the pressure regulator l8 into a zone of lower pressure the hot volatile portions of the liquor expand into gas or vapors which are discharged below the liquid level of the recovery tank l9. This recovery tank i9 is provided with .a battle to prevent violent agitation of the discharged liquor. The vapors and gases arising from the hot liquor at low pressure within the recovery compartment 19 arise into contact with the condenser coil 2| in the top thereof where they are condensed and the condensate returned to the body of liquor in the bottom of the recovery compartment.

From the bottom of the compartment 19 there leads a suction or supply conduit 22 of a power pump 23 by which the liquor is returned to the digester under pressure through the conduit 24 communicating with the bottom of the digester tank Ill.

Surrounding the conduit 23, there is preferably provided a heater unit 25 by which the returned cooking liquor is preheated before its entry into the digester tank. There is also provided in the return conduit 2d a check valve 26. There is thus established a circulatory system in which the digester tank is included and by which the cooking liquor is withdrawn from the top of the digester tank, the volatile gases condensed, and the liquor, restored to its original degree of concentration, is returned under pressure to the bottom of the digester tank in a reheated condition. The cooking liquor in this circulatory system moves in a direction contrary to the circulatory movement of the intermixture of material and cooking liquor through the tank and circulatory conduits [13, 03a and Nb. This contrary movement of the material and the liquor further insures thorough intermixture and uniform reducing action of the liquor upon every portion of the mass of pulp material.

In lieu of reheating the liquor by passing, it

through the heater unit 25, live steam may be introduced through the steam' line fill, into the suction conduit 22, or into the return conduit M,

or, if desired, live steam may be introduced directly into the digester tank H, which in either event intermixes with the liquor to raise its temperature.

As the spent liquor is discharged into'the low pressure recovery compartment iii, the entrained ases arise. as before described. into contact with the condenser coils M in the upper portion and. the condensed liquor and acid falls back into the lower part of the compartment to again enrich the cooking liquor and maintain its original concentration. However, any uncondensed vapors may escape from the recovery compart ment it through the vent line 2%, having therein a cutoff valve 30, through which they are conducted to a condenser or cooler and returned thence to a liquor storage tank 32. The valve 30 of the vapor vent conduit 29 is to be opened and closed as the occasion may require. Within the storage tank 32 the cooking liquor may be preheated by suitable heating coils 33, and any vapors arising therefromare condensed and'returned to the body of liquor by the condenser 34 in the top of the storage tank.

Leading from the bottom of the storage tank 32 is a supply conduit 35 communicating with a centrifugal pump 36, from the outlet of which extends two branch conduits 31 and 38. The conduit 31 is extended to the material storage or soak tank I, with the top of which it communicates to supply impregnating liquor for saturation of the material preparatory to its treatment in the digester. In this supply conduit 31 to the soak tank is located a control valve 39 which, when closed, will divert the supply of liquor to the supply conduit 38 leading to the digester tank I l to which cooking liquor may be supplied under pressure.

Communicating with the supply conduit 38 leading to the digester tank is an equalizer tank wherein an excess of cooking liquor may be accumulated under pressure to maintain the supply tov the digester tank .II when the pump 36 is at rest or is being employed for supplying liquor to the soak tank. At such times the conduit 38 is closed by the valve ll. For illustrative purposes, the equalizer I0 is shown provided with a weighted piston 42 held in elevated position by the liquid pressure of the cooking liquor and which descends by gravity to force the liquor into the digester tomaintain the predetermined hydrostatic pressure.

A blowoff conduit t3, having therein a valve M, leads from the digester it back to the storage tank 32, through which the pressure within the digester tank it may be relieved andthe surplus cooking liquor drained therefrom preparatory to discharging the completely. digested material. Upon completion of the digesting operation, the valves it and We in the circulatory conduits are closed and an outlet valve M in the continuation d5 of the conduit i311 is opened, and by continued operation of the pump M the digested material is withdrawn from the bottom of the digester tank H and discharged thence through the outlet conduit 35 to suitable storage or washing tanks which, per se, iorm no part of the present invention and are not illustrated.

The circulatory systems pertaining to the storage or soak tank and to the digester tank although illustrated as interconnected component parts of a continuous unitary system, are shown in Fig.

1 as capable of simultaneous operation as separate units of such system. However, if the ma- Fig. 2. As is illustrated in Fig. 2, the centrifugal pump la is connected by the conduits 6 and it with both the soak tank and the digester tank and its discharge conduit ta is connected as in Fig. l with both the top of the soak tank and the top of the digester so that by proper manipulation of valves, the partially processed material may be withdrawn from either of the tanks by the pump Ia and returned to the same tank in a continuous circulatory cycle, 'or at will the prepared material may be withdrawn from the bottom of the soak tank l and discharged into the top of the digester tank H for further processing. However, instead of being capable of simultaneous circulation, the material from the respective tanks must be circulated. successively but otherwise the operation and result is the same as before described.

The digester pressure and concentration of the cooking liquor and its temperature being uniformiy maintained, the operation of this system becomes more or less routine and by periodic circulation of the material and the cooking liquor the batch time of preparation is materially reduced. When the time for preparation and proper digesting of a batch of particular material has once been determined, the periodic circulation may be made automatic by providing suitable control means for starting and stopping the driving motors of the respective pumps at predetermined time intervals. Such automatic control may be regulated either by a timing mechanism or by a meter introduced into one or another of the circulatory systems by which the fluid volume of the circulated liquor or material is measured and the period of circulation governed accordingly. Illustrative of such automatic control means, there is shown in Fig. 1 a clock work mechanism 46 including suitable speed reduction means by which there is driven a slowly rotating cam shaft 41 having thereon a series of adjustable cams 48 which, in the present instance, are arranged in pairs, the members of each pair being alternately engageable at predetermined time intervals with an alternating circuit make and break device controlling the electrical circuits 50 to driving motors for the several pumps. As

illustrated in the drawings, there is provided a motor 5| for-each of the pumps 1, l4 and 23, each having its independent energizing circuit 50, in-, cluded in each of which is an oscillatory make and break switch 49. The contact cams d8 are adjustable to different radial positions about the slowly rotating control shaft 47 and may be adjusted thereon to operate the switches 49 in any predetermined sequence. As the shaft d1 rotates, one contact cam of each pairengages the movable switch member 69 to close the switch and energize the corresponding pump motor. After a predetermined period of operation determined by. the relative radial positions of the cams 418 of the corresponding pair of such cam members, the other member of the pair will engage the switch member 49 to oscillate such member in reverse direction and open the circuit to stop the pump -'motor and so terminate the period of circulation of the stock or the liquor as the case may be.

In lieu of employing a clock work mechanism for rotating the cam shaft $9, a fluid meter 52 may be introduced into any one of the several circulation conduits and the slow motion cam shaft 49 may be operatively-connected withsuch meter. In such case the switch operating cams 48 may be adjusted to open-and close the respective switches in the motor circuit 50 when a certain quantity of material has been circulated. For

In operation of the system, the storage or soak tank I is filled with chips or other fibrous material to be treated and animpregnating fluid, preferably the cooking liquor, is introduced into the tank I with the material and this intermixture is periodically circulated by operation of the centrifugal pump 1 until every portion of the material is thoroughly saturated and in a partially softened condition. The valve 9 in the return connection 8 is then closed and the valve l2 in the discharge conduit in is opened, allowing the prepared material to be discharged directly into the digester tank H. jected as is usual to the reducing action of heat and cooking liquor. To facilitate the reduction and minimize the time required therefor, the material is periodically circulated by operation of the pump 14, causing the contents of the tank to be agitated and redistributed so that every portion thereof is uniformly subjected to the reducing action of the cooking liquor and the heat. As further facilitating this distribution of cooking liquor through the mass, the'cooking liquor is drawn off from the digester tank II by being strained from the-material at the top of the tank and the pressure thereon is temporarily relieved to permit volatilization of the gases which are immediately recondensed and returned to again enrich the liquor to its original degree of concentration, and such enriched liquor is returned in preheated condition to the digester.

During the period of digestion, the material within the tank H is maintained under hydrostatic pressure which insures the penetration of the cooking liquor into the pores of the fibrous material. When the treatment of the material is completed, the surplus cooking liquor is drained from the tank through the relief conduit 63 back to the storage tank 32 and the valves l5 and l5a being closed and the discharge valve M beingopen the continued operation of the pump M will discharge the finished products through the outlet conduit il5 to the washing tank or storage compartment. The circulation of the material and the liquor under pressure insures that every portion' of the mass will be thoroughly permeated and uniform treatment will result. The temperature of the cooking batch is uniformly maintained by the frequent reheating of the liquor during its circulation which requires but slight rise in temperature and hence is quite economical. By utilizing the full capacity of the digester at each operation, the quantity of material 1 treated is greatly increased and by circulation the period of treatment is materially decreased. The acid content of the liquor is maintained constant by preventing escPpe or release of gases and by recondensation and return of the acid vapors to the liquor as a part of the continuous cycle of operation. In this way the essential factors of heat, pressure, and acid concentration are uniformly maintained and in addition thereto thorough and uniform reduction action upon every part of the mass of material is insured, thereby resulting in a-rnore rapid reduction of the material at a lower temperature and producing a much higher grade of pulp. The described method and apparatus effect material economy of operation and afford a better quality of products. Less steam than is ordinarily required is used for cooking and the temperature being maintained uniformly at the prescribed cooking temperature, there is less condensation within the digester, and the infiowing liquor being preheated and under pressure, objectionable water hammering is obviated. The maintenance of, uniform temperature is conducive to longer usefulness and less deterioration of the digester and circulatory conduits which are highly susceptible to injury by rapid changes of temperature to which such apparatus has heretofore been subjected. The accurate and automatic control of the concentra- In this digester it is sub- Will tion and enrichment of the preheated liquor and the thorough agitation and intermixture of the liquor and material and periodic redistribution of the portions of the mass 'within thedigester tank incident to its circulation therethrough insures uniformity of successive cooks as well as uniformity of treatment of each particular batch operated upon and more complete digestion of material due to forced penetration of liquor and equalized automatic control of successive batches.

The present system greatly facilitates the recovery of tannic acid from wood chips such as chestnut, oak,-or the like, which may be introduced into the soak tank or storage tank I with an ample quantity of water and brought to a relatively high temperature by circulation of live steam through the coil d. This, together with the agitation due to circulation of the material and impregnating liquid through the conduit 6 and to: back to the tank through the discharge inlet 8, rapidly frees the tannic acid content of the material which may be drawn off from the tank I! in a relatively concentrated solution as a valuable commercialbyproduct, leaving the pulp making material in a much improved condition. Thereafter cooking liquor may be inter mixed with the material in the storage tank before introduction into the digester. For other species of wood chips or other forms of pulp making material, cooking liquor may be introduced into the soak tank in lieu of water with the material supply, thereby insuring a thorough penetration of the cooking liquor into the pores of the chips.

When filling the digester tank It with themtermixture of pulp making material and cooking liquor, or other liquid as may be used, the intermixture will-ordinarily be quite fluid and contain an excess of liquid. it is desirable to fill the digester to the top with material. As the introduction of material continues, the excess liquid is displacedby pulp material and is conducted back to the storage or soak tank i through the overflow pipe lta. ii'he screen it at the top of thedigester it strains out the returning liquid, retaining the pulp material in the digester.

While in the drawings, for illustrative purposes the pumps l and it are shown arranged to withdraw material from the bottoms of the respective tank and return it to the tops thereof, and the pump it is arranged to return to the bottom of the'digester, the liquor withdrawn from the top, it is to be understood that direction of operation of the pumps ylbe reversed and the tanks maintained full, the intermixture of material and liquor may be withdrawn from the top of one or both tanks and returned to the bottoms thereof and that the direction of circulation of the cooking liquor independently of the material might also be reversed. Such changes involving merely reversal of interconnections of the respective pumps without other material change of the apparatus or system are not illustrated.

The continued circulation of the partially digested material through the pump and the friction of the material within the circulatory conduit induces a disintegrating action or beating effect upon the material during the digesting process, which not only hastens the digestion of the material but improves the quality and minimizes necessity for long subsequent beating or defibrating operations.

Not only is the digesting process improved and shortened, but the entire process of pulp making is materially cheapened and shortened and the quality of resulting product is materially raised.

From the above description it will be apparent that there is thus provided a device of the character described possessing the particular features of advantage before 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 the preferred form of several modes of putting the invention into efiect, and the invention is therefore claimed in any of its forms or modifications within the legitimate and valid scope of the appended claims.

Having thus described our invention, we claim:

1. In an apparatus for treatment of pulp making material, a soak tank for preparation of material, a digester tank for the reduction of the prepared material, a circulatory conduit for an intermixture of material and liquid leading from one end of the soak tank and discharging into the opposite end thereof, a second discharge connection from said circulatory conduit to the digester tank, a circulatory conduit for an intermixture of material and cooking liquor leading from one end of the digester tank and discharging into the opposite end thereof, and a circulatory conduit for cooking liquor leading from one end of the digester tank and discharging into the opposite end thereof in reverse relation to the direction of circulation of the intermixture of material and liquor, and means for effecting circulation of material and liquor through the respective conduits.

2. In an apparatus for treatment of pulp making material, a digester tank, a conduit for an intermixture of material and cooking liquor leading from one end of the digester tank and discharging into the opposite end thereof and formingaclosed circulatory cycle including the digester through which material intermixed with cooking liquor is circulated, a separate conduit for cooking liquor leading from one end of the digester tank and discharging into the opposite end thereof and forming a closed circulatory cycle including the digester through which cooking liquor is circulated apart from the material and means for inducing circulatory flow of material and liquor in the respective conduits.

3. In an apparatus for treatment of pulp making material, a tank operative at substantially atmospheric pressure, a conduit for an intermixture of material and liquor leading from one end'of the tank and discharging into the opposite end thereof and forming a closed circulatory cycle including the tank through which material intermixed with liquor is circulated, a heater coil within the tank, a condenser for vapors arising from the tank connected therewith to return passages for material and for cooking liquor being in common wherein the cooking liquor is intermixed with the material, and means for inducing circulatory motion of the material and the cooking liquorin the respective circuitous passages.

5. In an apparatus for treatment of pulp making material, a digester tank, a circulatory conduit for an intermixture of material and cooking liquor leading therefrom and a mum-discharge connection of said conduit with the digester tank directing streams of material and liquor in intersecting paths within the digester tank to effect thorough agitation of the contents thereof, and means for inducing a circulatory flow of material and liquor through the conduit from and thence back to the digester tank.

6. In an apparatus for treatment of pulp making material, a digester tank, a conduit for an intermixture of material and cooking liquor leading therefrom, multi-discharge outlets from said conduit, one of which communicates with the digester tank for return thereto of unfinished product, and another of which leads away therefrom '7. In an apparatus for treatment of pulp mak-' ing material, a digester tank and a soak tank in which material is prepared for admission to the digester tank, a conduit for pulp making material and a liquid in which the material is intermixed leading from the soak tank, multi-discharge outlets from said conduit, one of which communicates with the soak tank for the return thereto of incompletely prepared material and another of which communicates with the digester tank for supplying thereto prepared material, control means for directing the flow of material through the respective discharge outlets and means for inducing a flow of the intermixture of material and soakingliquid through the conduit.

8. In an apparatus for treatment of pulp making material, a treatment tank to receive an intermixture of material and treatment liquid, a circulatory conduit leading therefrom andreturning thereto and forming therewith a closed cycle circulatory system in which the tank is included through which the intermixture of material and liquid is circulated, means for inducing circulatory movement of the intermixture of material and liquid therethrough, and automatic control means for periodically initiating and arresting such circulatory motion.

9. In an apparatus for reduction of pulp making material, a tank, a normally open vent from the top of the tank to atmosphere, a conduit for an intermixture of pulp making material and a liquid extending exteriorly of the tank from the bottom to the top thereof, and forming a closed cycle circulatory system including the tank through which the intermixture of pulp making material and the liquid is circulated and a condenser associated with said normally open vent for condensation of vapors arising from the circulated material and from which the condensate is returned to the tank for maintenance of the liquid content of the material substantially constant, and a pump for inducing a circulatory flow of such intermixture therethrough.,

10. In an apparatus for preparation of pulp making material, a soak tank in which the matecooking operation, a conduit for an intermixture of pulp making material and soaking liquid extending exteriorly of the tank from the bottom I and returning to the top of the soak tank and forming a closed cycle circulatory system in which the tank is included through which the intermixture of material and soaking liquid is circulated, means for maintaining the liquid contents of the material substantially constant by automatically returning thereto vaporized portions arising therefrom and means for inducing a circulatory flow of the intermixture therethrough.

11. In an apparatus. for the reduction of pulp making material, a digester tank, a circulatory conduit for an intermixture of pulp making material and cooking liquor leading therefrom and returning thereto and a circulatory conduit for cooking liquor apart from the pulp making material leading therefrom and returning thereto, the discharge outlets of the respective circulatory conduits into the digester tank being arranged to direct streams of material and cooking liquor in intersecting paths within the tank to insure thorough intermixture thereof, and means for inducing circulatory motion of the material and the cooking liquor through the respective conduits. 12. In an apparatus for treatment of pulp making material, a circulatory system for circulation of an intermixture of material in process of preparation and soaking liquid, a circulatory system for an intermixture of material, in process of reduction, and cooking liquor, a circulatory system for cooking liquor apart from the material, means for inducing circulatory flow in the respective systems,-and automatic means for initiating and arresting the flow of material and liquids in the respective systems in predetermined sequence.

13. In an apparatus for treatment of pulp making material, a circulatory system for circulation of an intermixture of material in process of preparation and a soaking liquid, means for inducing circulatory flow through such system,.

and automatic means for periodically initiating and arresting the circulation through such system.

14. In a systemof reduction of pulp making material, a tank to receive pulp making material intermixed with a liquid, a conduit leading from the tank, alternative discharge branches of said conduit, one of which discharges back into the tank to afford a closed circulatory circuit for incompietely treated material and another of which branches affords a discharge outlet for completely treated material, means for inducing the flow of material from the tank through said conduit and one of said branches, and selective means for said branches.

15. In an apparatus of the character described, a soak tank for pulp making material, a thermal insulating jacket therefor, a supply conduit for impregnating liquid, and heater means for raising the temperature of the material and impregnating liquid during preparation 'of the material for subsequent digesting operation.

.16. In an apparatus of the character described, a digester tank, a conduit through which material is withdrawn from the digester tank, a plurality of discharge inlets through which material may be simultaneously discharged into different portions of the digester tank and circulating means for returning to the digester tank through said plurality of inlets the material withdrawn from the tank through said withdrawal conduit intermixture of material and treatment liquid" to thereby establish a circulation of material wherein the material will be agitated and mixed within the digester tank.

17. In an apparatus making material, a tank for receiving the material to be treated, a circulatory conduit for an intermixture of material and treatment liquid leading therefrom and returning thereto, means for inducing a circulatory motion of the intermixture of material and treatment liquid through the conduit and the tank, and means for automatically controlling the circulatory period.

18. In an apparatus for treatment of pulp making material, a tank for receiving the material to be treated, a circulatory conduit for an leading therefrom and returning thereto, means for inducing a circulatory motion of the intermixture of material and treatment liquid through till the conduit and the tank, including a motor.

driven pump and an electric motor therefor, an

energizing electric circuit for the motor, a make and break switch therein, and means for automatically opening and closing such switch.

19. In an apparatus for treatment of pulp making material, a tank for receiving the material to be treated, a circulatory conduit for an intermixture of material and treatment liquid leaddng therefrom and returning thereto, means for inducing a circulatory motion of the intermixtureoi material and treatment liquid through the conduit and the tank, including a motor driven pump and an electric motor therefor, an

energizing electrical circuit for the motor, a make and break switch in said circuit, a flow meter in said circulatory conduit, and'switch' operating means controlled thereby for automatically controlling the circulatory period.

20. In a system of the character described, a digester tank for pulp making material, a storage tank for a supply mixture of pulp making material and an impregnatingliquid, a supply conduit leading from the storage tank to the digester tank for transferring the intermixture of material and impregnating liquid from such storage tank to the digester tank, and a return conduit from the digester tank to the storage tank for return oi surplus liquid displaced from the digester tank by the introduction of additional material. I

21. The herein described method of treatment oi pulp making material including soaking the material in an impregnating liquid, heating the material and liquid independently of the circulation thereof, circulating an intermixture or the material and impregnating liquid during the soaking operation andthen subjecting the soaked material to a subsequent digesting operation.

22. The herein described method of treatment of pulp making material including saturating the material with cooking liquor prior to a digesting operation, flowing an intermixture of material and cooking liquor through a circuitous path of travel during the saturation operation, maintaining the strength of the cook liquor substantially for treatment of pulp' the supply thereof and returning such withdrawn portions thereto through a circuitous path of travel under hydrostatic pressure during the digesting operation.

24. The herein described method of treatment of pulp making material including saturating the material in cooking liquor, circulating an'intermixture of material and cooking liquor through a circuitous path of travel, by withdrawing successive portions thereof from the supply portion and progressively returning the withdrawn material thereto during the saturation period, maintaining the strength of the cooking liquor substantially constant during circulation, subjecting the saturated material to a digesting operation and continuing the circulation of the material and cooking liquor by withdrawing successive portions thereof from the supply portion and progressively returning the withdrawn portions thereto under hydrostatic pressure during the digesting period.

25. The herein described method of treating pulp making material including subjecting the material to a digesting operation under hydrostatic pressure, progressively withdrawing suc- I cessive'portions of material from the supply portion thereof being digested, subjecting the withdrawn portions to disintegrating. action and progressively returning the partially disintegrated portions. to the supply portion for further digestion while maintaining such material under hydrostatic pressure.

26. In an apparatus for treatment of pulp making material, a tank for containing pulp making material and an impregnating liquid, means for circulating an intermixture of the pulp making material and impregnating liquid, heater means for raising the temperature of the material and impregnating liquid during preparation of the material independently of the circulation thereof, and a condenser connected with the tank for returning thereto condensation of vapors arising from the impregnating liquid. I

2'7. In an apparatus of the character described, a digester tank to contain an intermixture of materialand treatment liquid, a circulatory conduitthe treatment liquid may be circulated separately from the material, and means for inducing such independent liquid circulation.

28. In an apparatus for the treatment of pulp making material, a tank to contain an intermixture of pulp making material and treatment liquid, a circulatory system through which both pulp making material and treatment liquid may be progressively withdrawn from the tank and returned thereto, means for inducing circulation thereof, and means for heating the treatment liquid independently of the pulp'making material.

29. In an apparatus for treatment of pulp making material, a tank to contain pulp making material andtreatment liquid, a conduit leading from one end of the tank and discharging intothe other end thereof for circulation of treatment liquid, a pressure operated valve restraining the outflow of liquid from the tank and a pump for returning the withdrawn liquid thereto whereby the tank will be maintained completely filled with material and liquid under hydrostatic pressure.

30. In an apparatus for preparation of pulp material, a tank to contain an intermixture of pulp making material and treatment liquid, 9. storage reservoir for a supplemental supply of treatment liquid, a passage leading from the storage reservoir to the tank, a pump for supplying liquid from the reservoir to the tank through said passage, a return passage from the tank to the reservoir, and a condenser for vapors associated with said reservoir.

31. In an apparatus for preparation of pulp material, a tank to contain an intermixture of pulp making material and treatment liquid, a storage reservoir for a supplemental supply of treatment liquid, conduits connecting the sup- .ply reservoir and tank into a circuitous system,

material and impregnating liquid during prepa ration of the material, means for circulating the pulp making material and liquid independently of the operation of the heating means, and a condenser connected with the tank for returning thereto condensation of vapors arising therefrom. 33. The herein described method of treatment of pulp making material including subjecting the material to a digesting operation including cooking the material-in a cooking liquor, withdrawing portions of the intermixture of the material and cooking liquor from the supply thereof, and returning such withdrawn portions thereto through a circuitouspath of travel, and simultaneously withdrawing a portion of the cooking liquor independently of the material from the supply of intermixture of material and liquor and returning the withdrawn liquor thereto through a different circuitous path.

34. The herein described method of treatment of pulp making material including subjecting the material to a digesting operation including cooking the material in a cooking liquor, withdrawing portions of the intermixture of the material and cooking liquor from the supply thereof and returning such withdrawn portions thereto through a circuitous path of travel, and simultaneously withdrawing a portion of the cooking liquor independently of the material from the supply of intermixture of material and liquor and returning the withdrawn liquor thereto through a circuitous path in a direction opposite to the general direction of circulation of the withdrawn portion of the mixture of cooking liquor and material.

35. The herein described method of treatment of pulp making material including subjecting the material to a digestion operation by cooking the material in a cooking liquor, withdrawing a portion of the intermixture of material and cooking liquor from the bottom of a digester and returning it to the top thereof and simultaneously withdrawing a portion of the cooking liquor independently of the material from the top of the digester and returning it to the bottom thereof during the digesting operation.

36. The herein described method of treatment of pulp making material including subjecting the material to a digesting operation including cooking the material in'a cooking liquor, withdrawing portions of the intermixture of the material and cooking liquor from the supply thereof and returning such withdrawn portions thereto through a circuitous path of travel, and simultaneously maintaining the intermixture of cooking liquor and material under hydrostatic pressure during circulation.

CHARLES D. ALTICK. LLOYD D. SMILEY. EDWARD T. TURNER.

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