US2038925A - Method and apparatus for the treatment of fibrous material - Google Patents

Description

April 28, 1936. L DUNBAR 2,038,925

METHOD AND APPARATUS FOR THE TREATMENT OF FIBROUS MATERIAL Filed Nov. 20,1934

' INVENTOR.

J/i w BY I ATTORNE;

Patented Apr. 28, 1936 UNITED STATES METHOD AND APPARATUS FOR THE TREAT- MENT OF FIBROUS MATERIAL Thomas L. Dunbar, Water-town, N. Y., assignor to Chemipulp Process, Incorporated, Watertown, N. Y., a. corporation of New York Application November 20, 1934, Serial No. 753,893

25 Claims.

. quality of the pulp produced, and economies in operation. These improvements are applicable to both acid and alkali pulping processes, as will hereinafterappear.

In the digestion of fibrous material, for example wood chips, for the production therefrom of pulp suitable for use in the manufacture of paper, organic acids formed in the cook have been found to attack the pulp at the end of the cock. It has been the practice to neutralize these acids to some extent by a base in the cooking liquor. base in the cooking liquor is uneconomical, due to the reaction of this base with the active ingredients of the cooking liquor. In accordance with my present invention I remove a part of the acid-forming constituents from the fibrous material before it reaches the digester, with the result that there is less acid formed in the cooking process. 1

It is further important in the digestion of fibrous material that the digestion liquor should penetrate to the center of the chips before reaction starts. Unless this is the case, reaction of the liquor with the outer part of the chips will weaken the liquor, so that that part thereof which eventually penetrates to the center of the chip becomes so weak that this part of the chip is not completely cooked and the fibres are only partially liberated. But when complete penetration is accomplished before reaction starts, the digestion of each individual chip becomes uniform throughout. In my process the chips are rendered more porous by the removal of watersoluble constituents therefrom before the chips come in contact with the digestion liquor. There results a better and quicker'penetration ofthe chip by the cooking liquor, resulting in saving of time, greater yield of pulp and decidedly improved quality thereof.

Furthermore, the chips are in my process brought to a uniform moisture content before being treated with the digestion liquor.

In brief, my invention comprises a'process and apparatus in which fibrous material, for example wood chips, is first treated with water or other suitable solvent liquid at an elevated temperature. After this treatment the fibrous material is conveyed in the novel manner herein- However, the presence of too much water to the tank I.

after described in detail, to a digester, where it is brought to complete fibre liberation by treatment with acid or alkaline liquor. The water in which the fibrous material is pretreated is drained from the fibrous material during the passage from the pretreatment tank to the digester, and some of this water may be re-used in the pretreatment of a subsequent batch of raw material. Further details of my process and apparatus will become apparent as the description proceeds.

In the accompanying drawing:

Fig. 1 is a diagrammatic elevation of apparatus suitable for use in the practice of my invention, certain parts being omitted for greater clearness of illustration, and

Fig. 2 illustrates a modification thereof.

Referring to the drawing, and particularly to Fig. 1, l is a pre-treatment tank which is filled with the fibrous material, for example wood chips, from a storage bin or conveyor (not shown). The tank I is provided with nozzles 2 for the admission of steam thereto. The pipe 3, provided with valve 4, admits a supply of hot The tank I communicates through the valve 5 with the worm conveyor 6 in its casing 1. The worm 6 may conveniently be driven by the motor 8. The pipe 9, with valved branches l0, serves to admit steam into the worm conveyor 6.

The conveyor 6 communicates with the pump II, which in turn communicates with a vertical conduit or leg l2. Steam may be admitted to the leg l2 through the pipe I3 with its valve H.

The top of the leg l2 communicates with the conduit l5, which may be a continuation of the leg l2, and this conduit I5 contains a strainer section l6. Collecting means H are provided in conjunction with the strainer IE, to collect water drained from the chips through the strainer. The strainer section l6 communicates through the valve I9 with the line It, which in turn communicates through the valve l9a with the interior of the digester 20.

The collecting apparatus l'l communicates with a leg or trap 2|, which trap communicates witha tank 22. A valved drain 25 from the leg 2| may go to the sewer or to tank 22. The tank 22 communicates through the pipe 23 and valve 24, with the pro-treatment tank I.

The leg 2| is provided with a vent 26 intothe tank 22, to prevent the leg from becoming gas bound. The tank 22 is also supplied with a vent 21 to the atmosphere.

The collecting apparatus I1 is provided with a.

the valve 33. This line communicates through the eductor 33 with the drop leg 43, which latter communicates through the valve 4| with the interior of the accumulator or storage tank 42. The valved steam line 6| may lead to steamcoils (not shown) within the tank 42 or may admit steam directly to the contents of the tank 42.

From the bottom of the accumulator or tank 42 the valved line 43 leads to the pump 44, which pump may force liquor from the accumulator 42 through the line 45 and valve 43 into the line H. The leg 32 terminates in a distributor within the liquor storage tank 5|. Liquor from the storage tank 5! may be led through the valved line 52 to the pump 53 and forced by this pump through the line 54, valve 55, check valve 56 and the line 51 to the eductor 39, whence it is carried by the drop leg 40- to the accumulator 42. The pump 53 may also supply liquor to the leg 32 through the valved line 58.

The leg 32 is provided with the gas vent 59 to the storage tank 5i and also with the valved drainilltothetankfl.

In the alternate arrangement shown in Fig. 2,

- a worm conveyor III with its casing H may be provided in the line l8 to force the raw material into the digester 20.

Operation in accordance with my invention may, for example, be as follows:

The pretreatment tank i is filled with the substance to be cooked, for example wood chips, from a storage bin or conveyor. Suitable solvent liquid such as hot water is admitted to the chips in the tank I through the line 3 and valve 4, and liquid may also be admitted from the tank 22 through the line 23 and valve 24. Most of the liquid supplied to the tank I is fresh hot water through the pipe 3; the water in the tank 22 contains solubles which in limited amounts are advantageous in the pretreatment but only a limited amount of this liquid, depending on mill conditions, is returned to the tank I.

Steam is admitted to the tank I through the nozzles 2 and the fibrous material and water therein are brought to approximately the boiling point, C. The length of time of treatnormally made to the blow oil? elbow. At the same ment of the fibrous material in the tank I de-' pends upon the grade of pulp which it is desired to produce and upon the raw material which is being treated and the temperatureof the water. In general the treatment of the fibrous material in the tank i may last from 2 to 5 hours.

After the previous charge in the digester 20 has been cooked and discharged into the blow pit (not shown), the worm conveyor 6 is started, the valve 5 is opened and the pump II is also started. At this time steam is admitted into the worm conveyor through the line 9 and branches l0 ,and also into the vertical leg l2 through the line l3. This steam further treats the chips as they are moved toward the digester, and in addition the steam through the line 9 assists the worm in movingthe chips to the pump i I.

The hot pretreated chips and water are forced by the pump II to the top of the leg I 2, whence they pass through the leg J5 to the strainer section IS. The mixture of raw. material and water passes over the screen I 3 where the water is drained off, this removal of water being assisted by the fact that the strainer and collecting apparatusare under pressure. The water, with dissolved impurities, is forced by this pressure through the leg 21 into the tank 22. The 108 II maintains a pressure on the system so that cooking liquor supplied through the line 45 will not lose its strength, this being particularly necessary when bisulphite acid liquor is used in the cook.. The collecting apparatus ll communicates through the vent 23, line 3li,and valve 3! with the seal leg 32 which again is provided to main- I tain pressure. on the system.

The pressure maintained by the seal legs 2i and 32 notonly maintains the strength of the cooking liquor, but alsoassists the penetration of this liquorinto the raw material being treated. This rapid penetration of the liquor into the material saves time, assists materially in deligniflcation of the fibres and also increases the yield of the pulp. Whereas in the cold acid method of cooking considerable time should be taken to bring the mass in the digester up to a reaction temperature of 110 to C., in order to assure thorough penetration of the individual chips by the cooking liquor, in my preferred process this time is greatly reduced due to the rapidity ofthe penetration, which is assisted by the porous condition of the chips, their uniform moisture content, pressure and the elevated temperature of the liquor.

As previously stated, the chips may, if desired, be forced into the digester by a worm conveyor 10 as shown in Fig. 2.

While the pretreated material is entering the digester '20 through the line l3, cooking liquor from the accumulator or storage tank 42 is supplied thereto by the pump 44 and line 45. When the digester 20 has been filled with chips and either hot or cold acid, the valve i9 is closed and additional cooking liquor is forced into the dl gester by the pump 44 until liquor flows free through the relief valve 33 and the line 31 back to the accumulator, at which time the valve 33 is closed and a pressure is pumped on the digester by the pump 44. This pressure may be anywhere from 40 to 122 pounds gauge, depending upon local plant conditions.

When the proper digester pressure has been attained, the pump 44 is stopped, the valve lBa is closed and steam is admitted at the bottom of the time the valves 33 and 38 are opened and the pump 34 is started, which circulates the digester liquor through the strainer 12 and circulation line 35 into the bottom of the digester through the valve 36. This circulation may be continuous throughout the cooking period or may be intermittent. Its object is to provide more uniform conditions of temperature and liquor concentration throughout the mass undergoing cooking in the digester.

During the cook, the relief valve 33 and the customary side relief valve (not shown) are operated in the usual manner to withdraw the necessary liquors, gases and vapors from the digester to the eductor 39 and accumulator 42. The eductor 39 is similar to that shown and described in Patent No. 1,888,632, issued November 22, 1932 to me and A. D. Merrill. This eductor is supplied with partiallyprepared acid fromthe storage tank aosaoes- .by the. pump 53 and lines SI and 51. The

contacting of this relatively cold liquor with the a cooler so that the liquor entering the tank 42 will be cooled and thus there will be less tendency for gams to escape therefrom. Or the tank 42 may be designed to withstand low pressures, being for example a reinforced concrete tank provided with an acid-proof lining in the case of'the acid cooking process. If the tank -is soT-='designed to withstand. low pressures, the cooler in the line 31 need not be of such large capacity' as if the'tank 42 is at ptmospheric pressure.

In the case of the alkaline pulping process, the

seal legs 2| and 32 may still be used to obtain pressure on the line I 8 and thus to secure the advantage of proper penetration :of the-raw material by the cooking liquor. In the alkaline-process,

the tank 42 may be provided with heating coils or. steam may be admitted directly thereto to bring the temperature of the cooking liquor up to at least the temperature of theraw material enter j ing the. digester.

I prefer to have the temperature of the liquor entering the digester high'erthan that of the chips and I have found that thetemperature of the liquor in the tankvoi abeiii'niilator 42 can be maintained as high as 130 C..without premature initiation of cooking of the chips, since theaddition of cooking liquor at 130 C. to the raw material at 100 C. will result in a temperature of the mass at which thorough penetration is obtained before reaction temperatures are actually reached.

The legs or traps 2i and 32 are of a proper height to meet different pressure conditions due to variations in liquor concentration required by difierent mills. This is particularly so in the case of the acid cooking process since the concentration of th'e liquor is proportional to the temperature and pressure.

The vent 26 into the tank 22 prevents the seal leg 2| from becoming gas bound and this vent 26 conserves heat units contained in the hot gases or air from the leg 2|. Similarly, the vent 59 to the storage tank 5i prevents the leg 32 from becoming gas bound.

The leg'2l may be drained through the drain elbow 25 whenever necessary. The liquor so removed may be led to the sewer or may be pumped into the tank 22. The leg 32 is similarly provided with a drain 60. The distributor 50 at the bottom of the tank 5| ensures propendistribution of any liquor forced into this tank through the leg 32.

My invention not only makes possible improved yield and quality of pulp but also results in economies in operation as compared with methods heretofore employed in the treatment of fibrous material.

Having thus described by invention, I claim:

I. In apparatus of the character described, a digester, a pretreatment tank, a conduit for fibrous material connecting the pretreatment tank with the digester, aworm conveyor interposed in said conduit, and means for injecting steam into said pretreatment tank and into said conduit.

2. In apparatus of the character described, a digester, a pretreatment tank for fibrous material, and a vertical conduit for fibrous material connecting withthe-pretreatment tank and with the digester, said conduit provided with a worm conveyor for forcing therethrough a fluent mixture I of fibrous material and treating liquid from the pretreatment tank against the head rial in said vertical conduit.

3. In apparatus of the character described, a

of the matedigester, a pretreatment tank "provided with means for supplying liquid thereto, a conduit'for fibrous material connecting the pretreatment tank with the digester, said conduit having interposed therein a worm conveyor, and means for injecting pretreatment steam into said conduit between the tank and the digester.

4. In apparatus of the character described, a digester, a container for fibrous material, a worm conveyor connecting with the container for flbrous material, a pump connecting with the worm conveyor, and a conduit connecting said worm and said pump with the digester. Y

5. Apparatus as described in claim 4, including means for injecting steam into the worm.

conveyor and into the conduit;

- 6. In apparatus of the character described, a digester, a pretreatment tank, a conduit con necting the pretreatment tank with the digester and having interposed therein means for separating liquid from fibrous material, and a trap" for collecting liquid so separated and passingthe' same to the pretreatment tank while maintaining fluid pressure on the separating means.

7. In apparatus of the character described, a digester, a pretreatment tank, a conduit connecting the pretreatment tank with the digester, said conduit provided with a strainer and with means for collecting liquid separated by the strainer, and means for maintaining pressure within the conduit and collecting means while -withdrawing liquid therefrom.

8. In apparatus of. the character described, a digester, a pretreatment tank, a conduit connecting the pretreatment tank with the digester, a trap communicating with said conduit and adapted to permit the escape of gas therefrom while maintaining pressure therein, and a second trap communicating with said conduit and adapted to permit the escape of liquid therefrom.

9. In apparatus of the character described, a

, digester, a container for fibrous material, a conduit connecting the said container with the digester, a strainer interposed in said conduit, collecting means for liquid separated by the strainer, said collecting means communicating through a trap with a storage tank for-said liquid, and a gas vent from the trap to said storage tank.

10.'In apparatus of the character-described, a digester, a pretreatment tank, a conduit for fibrous material connecting the pretreatment tank with the digester, a storage receptacle for digestion liquor, and means for passing digestion liquor from said. storage receptacle into said conduit between the pretreatment tank and the digester. '11. In apparatus of the character described,

a digester, a pretreatment tank, a conduit conand a trap communicating with said conduit and adapted to maintain pressure therein while permitting the escape of gas therefrom. I

13. In apparatus of the character described, a digester, a pretreatment tank, a conduit connecting the pretreatment 'tank with the digester, a storage receptacle for liquor, a trap communicating with the conduit and terminating in a liquor distributor within said storage receptacle, and a gas vent from said trap to said storage receptacle.

14. In apparatus of the character described, a digester, a pretreatment tank, a conduit connecting the pretreatment tank with the digester, a trap communicating with said conduit, a storage receptacle for liquor, and means for supplying liquor from said storage receptacle to said trap.

15. The process of treating fibrous material which comprises initially removing acid-forming constituents of the material and increasing the porosity thereof by immersing the material in water and injecting steam into the resulting mass, removing the fibrous material from the initial treatment chamber and injecting additional steam thereinto while passing the material to a digester and thereafter digesting the material to complete fibre liberation in acid liquor.

16. The process of treating fibrous material which comprises removing acid-forming constituents of the material by treatment of the material with heated water, straining water from the material while maintaining the same under fluid pressure and thereafter cooking the material to complete fibre liberation in a single type of digestion liquor.

17. The treatment of fibrous material which comprises removing water-soluble constituents therefrom by treating the material with heated water, then conveying the material so treated to a digester and injecting steam into the material during its passage from the water treatment to the digester, and thereafter cooking the material under heat and pressure to liberate the fibres thereof.

18. The treatment of fibrous material which comprises initially removing acid-forming constituents of the material and increasing theporosity thereof by treatment of the material in alheated solvent liquid, said treatment including forcing said material in the presence of the solvent liquid and of steam vertically through a conduit against the head of the mixture, and subsequently cooking the material to complete fibre liberation in acid liquor under heat and pressure.

19. The process of treating fibrous material which comprises increasing the porosity of the material and removing acid-forming constituents thereof by treating the same with water to liberate said constituents, treating the material with steam while conveying it to a strainer, and thereafter straining the material to remove water and liberated acid-forming constituents, and

finally cooking the material under heat and pressure to liberate fibres thereof.

20. The treatment of fibrous material which comprises initially increasing the porosity of the material and removing acid-forming constituents therefrom by treating the material with water containing limited amounts of acid forming constituents extracted from a previous batch of similar material, and thereafter digesting the material to complete fibre liberation.

21. The process of treating fibrous material which comprises removing acid-forming constituents therefrom by pretreatment of a first batch of such material with heated water, draining from the material said water with contained acid-forming constituents, cooking the pretreated material to liberate the fibres thereof, and pretreating a subsequent batch of fibrous material with water and contained constituents drained from said first batch of material.

22. In the treatment of fibrous material, pretreating such material in heated liquid to liberate acid-forming constituents therefrom, passing the pretreated material to a strainer and straining therefrom the pretreatment liquid containing acid-forming constituents, thereafter introducing digestion liquor into the fibrous material, and maintaining the fibrous material under gaseous pressure during the said straining and during the introduction of said digestion liquor.

23. In a process for the treatment of fibrous material, subjecting fibrous material to pretreatment to liberate acid-forming constituents therefrom, adding digestion liquor to the pretreated fibrous material, and thereafter introducing the mingled fibrous material and digestion liquor into a digestion chamber.

24. In a process of the character described, subjecting fibrous material to pretreatment in heated liquid to liberate acid-forming constituents of said material and to increase the porosity thereof, straining from the fibrous material pre-- treatment liquid with contained acid-forming constituents and returning said liquid to the pretreatment of a subsequent batch of fibrous material, adding heated digestion liquor to the fibrous material, then passing the fibrous material and digestion liquor to a digestion chamber and therein cooking the said material in the said liquor to liberate the fibres of the material.

25. In the treatment of fibrous material, subjecting fibrous material to pretreatment to liberate acid-forming constituents therefrom and increase the porosity thereof, said pretreatment involving heating the material to a temperaturein the neighborhood of C., adding digestion liquor heated to a temperature above C. to the porous pretreated fibrous material while said material is at a temperature in the neighborhood of 100 C., then raising the temperature of the resulting mixture above 110 C. to initiate reaction of the liquor with constituents of the fibrous material.

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