US2948336A - Continuous digester - Google Patents

Description

Aug- 9, 1950 L. G. DURANT ETAL 2,948,336

CONTINUOUS DIGESTER y Filed June e, 1955 s sheets-sheet 1 l1g 9, 1960 l.. G. DURANT ETAL 2,948,336

CONTINUOUS DIGESTER Filed June 6, 1955 5 W EB 3 Sheets-Sheet 2 INVENTORS N G. DURANT 8s 'BY A H E SURINO ATTORNEYS ug- 9, 1960 L. G. DURANT Erm. 2,948,336

CONTINUOUS DIGESTER 3 Sheets-Sheet 5 Filed June 6, 1955 Flc-5 ATTORNEYS" CONTINUOUS .DIGESTER Leonard G. Durant and Alphonse Surino, Pittsfield,

Mass., assignorsto Pandia, Inc., New York, N.Y., a corporation of New York Filed June l6, 1955,'Ser. Ns. 513,456. 1 claim. (cl. 162-236) This invention relates to apparatus and methods for continuously digesting cellulosic materials for'use in the manufacture of pulp and paper. v

The invention has as its primary object to provide continuous digesting apparatus and methods which will make it possible to effect simultaneous cooking vand rnixing of a plurality of raw cellulosic materials to produce a mixed pulp while Ystillproperly controlling the degree or extent of cooking for each different one of the raw starting materials. l' Theinvention has special relation to the production of mixed pulp from a plurality of starting'materials of different characteristics, such for example, as wood chips or other material having relatively long tibers and/or large particles requiring a relatively long cook and a material such as sawdust, shavings, straw or bagasse/ having relatively small or thin particles and/or short fibers which can be adequate digested with a relatively short cook asrcomparedv with the longer bered materials; vIt is an object ofthe present invention to provide continuous apparatus vand methods for simultaneously digesting a plurality of dilerent cellulosic materialsV each requiring a different digestion treatment time by means of which a continuous supply of the material requiring the longer cook is advanced Ialong a predetermined path .through a cooking atmosphere, a continuous supply of thematerial requiring the shorter cook is added to the rst material at an intermediate location along the path, andthe two materials are caused to complete their advancel together along this path with accompanying continuous agitation for elfecting exposure of`all particles therein to vthe digesting atmosphere and thorough mixing of the different base materials together. p

An additional object of the invention is to provide' continuous apparatus for producing substantially uniformly digested and mixed pulp by simultaneously digesting a plurality of dilferent cellulosic materials each requiring a different digestion treatment wherein an elongated conduit is equipped for establishing and maintaining a digesting atmosphere, a iirst feeding unitis constructed and arranged to introduce to the `inlet end of the conduit a continuous supply of the material requiring the maximum digesting treatment, wherein one or more additional feeding units-are located'at positions spaced downstream from the first unit and each operate to intro, duce a continuous supply of a different material requiring a corresponding shorter digesting treatment, and provision is made for agitating the resulting plurality of materials continuously to effect thorough exposure of all particles to the atmosphere and thorough `mixing,

of these initially different materials.

IIt is also an object of the invention to provide continuous digesting apparatus as outlined aboveswherein@ the conduit within which digestion takes place includes a plurality of generally horizontal and vertically spacedy sections joined in succession by ,connections constructed;

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next lower section, and wherein provision is made .at one or more of these gravity delivery connections downstream from the supply end of the uppermost tube section forV continuously introducing a cellulosic lmaterial requiringa shorter digesting treatment than the material supplied to the supply Iend of the uppermost tube in order to elect digestion of the latter material and simultaneous mixing thereof with the partially digested material introduced at the supply end of the uppermost llbr"V Ai Additional objects and advantages of the invention will be apparent from the following description, the

accompanying drawings and the appended claims.

In the drawings: f

Fig. l is la somewhat diagrammatic side elevational view, .showing continuous digesting apparatus in accordance with the inventionA for ,producing mixed pulp from two'different starting materials as outlined above;

Fig. 2 is'a View' looking Ifrom right to left in Fig. 1; Fig'. 3 is a somewhat diagrammatic view in the nature of a perspective illustrating a variation of the system 4shown, in Fig. 1 :wherein the Ysecond feeder unit'is connected between the top two -pairs of reaction tubes; Fig. 4 is an enlarged fragmentary view in axial section showing 4a iiexible joint Ifor use in forming the connection between one of the screw feeders of Fig. 1 and the uppermost tube `10; and

FigfS is a view similarto Fig. 1 illustrating another arrangement of continuous digesting apparatus in accordance with the invention..

Referring to the drawings, which illustrate preferred embodiments of the present invention, the system shownl in Figs. 1 and 2 isV similar in'some 'respects to that shown in Beveridge et al. Patent 2,323,194 and the copending applicationl of vFrank B. K. Green Serial No. 420,033, filed :March 31', 1954,V now abandoned, such patent and' application both being assigned to'the assignee of the present application. This'system includes an elongated conduit wherein the digesting of the raw cellulosic material takes place, this conduit being formed in a plurality of vsections comprising multiple generally horizontal tubes' joined in vertically spaced end-to-end relation, four 0f Vthese tubes being shown and identified by the reference characters 10-'13 respectively. Within each of tubes 10-13- is ascrew conveyor 15 yprovided with a `drive indicated generally at 16 for effecting continuous advance' of v'the' cellulosic material in each tube from the supply end of the tubeto its discharge end, and the discharge outlet 17 of each tube 10-1 3 is connected to the inlet v18 of the next lower tube for delivering the cellulosic material by gravity from each tube to the next lower tube. The lowermostt tube 413 similarly discharges by gravity into a discharge unit 20 of a type capable of effectivelyV 'continuously discharging 'the digestedmaterial, preferablygacconipanied byl a defbering action, While maintaining the ,'desiredpressure cooking atmosphere withinl the conduit lll-13. This `discharge Vunitv 20 is shown byE way of illustration as of essentially. that construction disclosed in Kehoe et gal. Patent 2,606,802, issued to the Feeding means are provided for delivering to the inletY end vof the uppermost tube 10 a continuous supply of the raw cellulosic material which requires the maximum cooking treatment. This feeding means is indicated gento deliver material by gravity -fromeach section-1:0 the',I

erally at25 ,andrmay be of any type capable of introducing'anetfectiyely continuous supply of solid material' into .tubelQ without 'substantial loss'. of, gas pressure.

from Lwithinfthe' tube. p It is shown by way of illustra- Patented Aug. 9, 1960 y tion as a pressure feeder of essentially the same construction shown in the above Beveridge et al. patent and incorporates a feed screw for delivering the raw material such as wood chips from a hopper 26 through a short tube section 27 into a T-piece 30 which is in turn constructed to deliver the chips by gravity into the inlet 31 of the tube 10. With this type of pressure feeder,Y

the chips or other raw material are continu'c'lusly` plugged within the tube section 27 as described in the Beveridge et al. patent to prevent substantial lossY of pressure from within the conduit. In addition, the valve 32 is provided for preventing the pressure from yblowing back through the feeder in the event that the feed screw should stall or otherwise fail to maintain the properly pluggedcondition in pipe section 27, the valve 32 being operated by a hydraulic cylinder 33 connected for automatic operation in response to a predetermined drop in the load on the drive motor for the feed screw.

Figs. 1 and 2 show suitable illustrative provision for continuously supplying steam at high pressure and hot liquor to the interior of the tubes -13. A relatively large steam line 40, for example 6 inches in diameter, represents the main steam supply to the conduit, this line 40 being shown as directly connected to the second tube 11 from the top at a position adjacent the discharge end of this tube, thus introducing the steam at approximately the middle of the conduit and being provided with a shutolf valve 41. With this steam supplied at a superatmos'- pheric pressure such, for example as 150 pounds per square inch, this steam supply arrangement Will provide essentially uniform heat conditions throughout the entire conduit. An auxiliary steam system, comprising a line 42 having connections 44 to each tube 10-13, provides for heating up the conduit prior to starting of the digesting operation and while the main steam line is closed, each connection 44 having its own shut off valve 45 for operation after this preliminary heating is completed. This steam supply arrangement is not controlling on the invention and may be varied `as desired for different pulping materials and conditions.

The main supply line for hot liquor is shown at 50, and it is connected by a branch pipe 51 to a header 52 extending a major portion of the full length of the top tube 10. A plurality of branch pipes 53 lead from `the header 52 to corresponding inlet ports 54 located at spaced positions along the top of the tube 10. Each branch pipe 53 is shown as having a shutoff valve 55 to provide for selective control of the delivery of liquor to the interior of the tube 10'.

Provision is also made for applying liquor within the T-piece to the cellulosic material delivered by the feeder 25. A branch line 56 having a shutoff valve 57 leads from the main liquor line 50 to a pair of inlet ports 58 in the top of the T-piece 30. With this arrangement, liquor can be applied to the raw cellulosic material as it is falling in relatively loose condition through the T-piece 30 into the inlet end of the tube 10, or with the valve 57 closed, a preliminary steaming treatment of the chips can be carried out to preheat the chips and to effect substantial elimination of air from the interior thereof before liquor is first applied thereto as they reach the rst of the inle ports 54 whose associated valve 55 is open. j

The system shown in Figs. 1 and 2 is especially designed for the simultaneous digestion and mixing of a first raw material such as Wood chips and a different material requiring less digestion treatment, such as sawdust, shavings, straw, bagasse or the like. A second pressure feeder 65 is located adjacent the opposite end of tube 10 from the feeder 25 and is connected through a T-piece 66 with a second inlet 67 to the tube 10 which is located directly above its discharge outlet 17. The feeder 65 `is provided with a bin 70 for the sawdust or other material having in its lower end a plurality of feed screws 71 for delivering the material into a trough 72 in which there is an additional feed screw 73 which in turn delivers the ma- 4 terial into the upper end of the hopper 75 of the feeder 65. A vertical compression screw 76 may be used to force the sawdust into the main feed screw of the feeder 65, and the pipe section 77 corresponds to the pipe section 27 as already described.

With this general arrangement, the Wood chips or other raw cellulosic material requiring maximum digesting treatment are steamed and thoroughly impregnated with cooking liquor during their advancethrough the tube 10", and when they Areach the end of tube 10, they drop by gravity into the supply end Vof 'the tube 11 for travel in the reverse direction to the tube 12 and so forth. The sawdust or other raw material requiring a relatively mild cook is continuously supplied by the feeder 65 into the discharge end of tube 10, so that `this material is continuously added to the impregnated material from the feeder 25. Since this -newly added material is considerably finer than the initial material, it requires correspondingly less time for impregnation With liquor, and adequate impregnation is obtained by the provision of a liquor supply line 80 similar to the supply line 56 and connecting with a pair of ports 81 in the top of the T-piece 66 so that the sawdust or other material dropping through the T-piece is continuously showered with fresh hot liquor.

It will be apparent that during the free fall of the two materials through the discharge end of tube 10 into the supply end of tube 11, there will be some intermixing of these materials while they are in relatively loose form. Then as the two materials are advanced together through the remaining tubes which constitute the main cooking section of the conduit, the continuous tumbling agitation effective thereon by operation of the several screw con veyors 15 will assure both effective exposure of all particles of both materials to the hot vapor-bearing atmos: phere produced by the steam and liquor, as well as thorough intermixing of both materials. 'Ihere will also be a final intennixing effect resulting from the continuous discharge through the discharge unit 20 so that the final product of the system as delivered into the conduit 22 will be a thoroughly homogeneous mass of digested fibrous material.

l It will be apparent that the proportions of the apparatus, the nature of the digestion media, and the relative times of treatment are closely interrelated and also are subject to wide variations in accordance with the particular materials to be digested, and such factors, including temperatures, pressures and the like, are not controlling on the present inventions. For example, digestion may be carried on in vapor phase, namely where substantially no unabsorbed liquor is present, or with a relatively high liquor to cellulose ratio, or at a desired intermediate condition without departing from the scope of the invention nor is the invention limited tothe use of heat and/ or pressure. It is thought, however, that the invention may be more readily understood by reference to certain detailsY for one illustrative example of the apparatus and method of the invention which relate to the production of neutral sulphite semi-chemical pulp by simultaneous digestion of wood chips supplied by the feeder 25 and sawdust and shavings supplied Iby the feeder 65. The details of this example are given for an installation operating at a rate of tons of wood chips and 140 tons of sawdust and shavings, utilizing four tubes 10-13 arranged as vshown in Fig. 1 with each tube 41 inches in inner diameter and 36 feet in overall length.

In this example, the screw conveyor in the tube 10 is constructed and driven to provide an overall travel time` of 'approximately 14 minutes from one end of the tube tol the other, while the travel time produced bythe screw conveyors in tubes 11-13 is approximately 7 minutes for each tube. Satisfactory results are obtained with liquor' added through selected ports 54 such that the Wood kchips discharged by the feeder 25 are subject to preliminary steaming for an average of 3 minutes followed by` im'- pregnation with liquor, which of course includes some' Y chips at the Vend of this l4minute interval together with additional liquor in the form of a 15 percent solution of NaZSOa at the rate of 58 gallons per minute. l The cookring cycle of mixed material then vcontinues for the remaining 21 minutes required for travel through the successive tubes 11-13, and the total requirements for steam in lthis specic example are approximately 30,000 pounds per hour at 150 pounds per square inch to maintain the temperature within the conduit at approximately 325 F.

Fig. 3 shows diagrammatically `another arrangement of apparatus in accordance with the invention in which provision is made for causing the cellulosic material introduced at the inlet end ofthe conduit to advance for impregnation and initial cooking through a pair of tubes 100 and 101 before the second'cellulosic material is added thereto for joint advance 'and cooking in the tubes 102 and 103. The feeder 25 corresponds'to the feeder 25 in Fig. 1 and is similarly connected to the inlet 105 of the uppermost tube 100 by the T-pi'ece 30. It will be understood that the necessary connections for steam and liquor can be provided in essentially the sameV manner as shown 'in' Figs.Y 1 and'2 but are omitted from the diagrammatic showing of Fig. v3 for simplicityof illustration.. l

The feeder 65 in'Fig. 3 'corresponds to feeder-65 in Figs. land 2, and 'it is arranged to deliver a continuous supply ofcellulosic material into the inlet 108 of ltube 1.02, which is connected to the outlet l109 of tube 101 by a spacer pipe 110. The T-piece 111 into which feeder 65 delivers 'sawdust' or other cellulosic material is accordingly connected Ias shown to deliver this material downwardly at an angle into the pipe 110, and this action may be aided by a continuous ow of liquor into the top of T-piece 111 by way of the supply pipe 112. This system is therefore comparable to that described in connection with Figs. l and 2, and it will also be apparent that additional feeders may be provided for supplying other raw materials to the conduit if desired, as by employing a third feeder in the system of Fig. l in the manner shown in Fig. 3.

Fig. 4 shows a flexible joint which may be employed between a feeder and the adjacent digesting tube in an installation embodying multiple feeders similar to that in Figs. 1 and 2 wherein thev feeders connected with the same tube are rigidly mounted as indicated by the floor 115 and wherein the structural materials and the temperatures employed in operation are such as to cause appreci-able thermal elongation of the tube.- For example, the tube inlet 67 and the pipe section 77 correspond to the similarly numbered parts in Fig. 1, but the T-piece 120--121 is constructed to provide for movement of tube inlet 67 with respect to pipe section 77 in response to thermal elongation and contraction of the tube 10. This T-piece includes a main horizontal portion 120 and a depending arm portion 121 having a ange 122 at its outer end by which it is connected to the inlet 67. An additional horizontal section of tubing 123 forms a sleeve which extends slidably through the section 120 and is formed with a cutout 124 coinciding withmthe inner end of the arm portion 121.

The sleeve 123 telescopes. over a replaceable wear sleeve 130 which forms an extension of the pipe section 77, and the ange 131 at this end of sleeve 123 is secured to a mating flange 132 on pipe 77 by nuts 133 on elongated bolts 135, .the sleeve 130 also having a flange 136 thereon which is clamped between the flanges 131 and 132. 'I'he other end of sleeve 123 is closed by a plate 140 which forms the mounting for the operating cylinder 33 for the blow-back valve 32, the stem 141 for valve 32 extending slidably through a suitable pressure seal 142 carried by plate`140. n Y y y The portion of the T-piece is provided with a slidable sealed mounting onthe sleeve 123." Each end of sleeve 123 has an annular recess which receives a packing ring 150, and a gland 151 of angular section cooperates with each of these sealing rings. The desired compression of the sealing rings is obtained by bolts 152 directly connecting the glands 151 with flanges 153 and 154 respectively on opposite ends of tubing 123. The composite T-piece 120-121 is therefore able -to slide on sleeve 123 as required by thermal elongation of tube 1,0, and at the same time, the pressure within the T-piece is balanced between the two sealing rings 150. The extent of movement of part 120 on sleeve 123 may be controlled by stop nuts 155 on bolts 135, the latter extending slidably through the ange 154and also serving to maintain the arm pontion 121 in angularly aligned relation with the opening 124.

Fig. 5 shows diagrammatically afurther'arrangement ofv apparatus in accordance with the invention in which the several cooking tubes are constructed essentially as shown in the above-Beveridge `et al. patent, the tubes being arranged in pairs and'having the main inlet and outlet of each pair of tubes located at'the centers thereof so that the cellulosic material travels in both directions in each tube. The feeder 25 in Fig. 5 corresponds tofthe feeder 25 in the other views, and it delivers a continuous supply of the material requiring maximum digestion treatment'into the inlet'1-60 at the center of the uppermost tube 161. At each end of tube 161 is an outlet 162 connecting with. an inlet 163 to the next tube 164, and the screw conveyor 165 inv tube 161 has its flights reversed at the center Vof the tube so as to cause the cellulosic material to travel in both directions from the inlet to the outlets 162. A similar screw conveyor in tube 164 conveys the cellulosic material back toward the center of tube 164 from which its outlet 166 connects with the inlet 167 of the next lower tube 168.

The travel path of the cellulosic material in tube 168 is essentially the same as in tube 161. The outlets 162 of tube 168 connect with the inlets 163 at opposite ends of the fourth tube 170, and the centrally located outlet 171 of tube 170 is shown as connecting with a discharge unit 20 corresponding to the similarly numbered parts in Figs. 1 and 2. The necessary connections for steam and liquor maybe provided as desired for the system of Fig. 5 in essentially the same manner as shown in Figs. l and 2 but are omitted from the diagrammatic showing of Fig. 5 for simplicity of illustration.

Fig. 5 also shows the uppermost tube 161 as provided with an additional inlet 175 located directly above one of its outlets 162 and connected to receive a continuous supply of cellulosic material requiring a lesser digestion treatment from an additional feeder identified generally as 180. This feeder may be of the same characteristics as vthe feeder 65 as already described, and it incorporates similar hoppers and conveyors 70-76. Instead of discharging into a screw type feeder as in Fig. l, however, the compression screw 76 is shown as feeding the cellulosic material into the inlet 175 by way of a rotary valve indicated genenally at 181 of a conventional type incorporating a rotor having pockets therein (not shown) arranged to receive material in succession from the conveyor screw 76 and then to dump this material intoV the inlet 175 while at the same time sealing against substantial loss of pressure from within the series of cooking tubes.

It is believed that the operation of this system as shown in Fig. 5 will be readily understood from the foregoing description in conjunction with the other views in the drawing. It will also be apparent that additional feeders can readily be added to the system of Fig. 5 or connected at other points, for example at the opposite end of tube 161 or at the connection between the outlet 7 166 and inlet 167 in essentially the same manner as described inconnection with Fig. 3. Selection of suitable variations of this system will be dictated primarily by the particular materials to be digested and the respective times 0f vdigestion treatment applicable thereto.

While the methods and forms of apparatus herein described constitute preferred embodiments of the invention, it is to be understood that ythe invention is not limited to these precise methods and forms of apparatus, and that changes may be made therein without departing from the scope of the invention which is defined in the appended claim.

What is claimed is:

Continuous -apparatus for simultaneously digesting a plurality of diierent cellulosic materials each requiring a diterent digestion treatment time to produce a pulp composed of said dilerent materials in substantially uniformly mixed digested condition, comprising an elongated conduit tube having an inlet and an outlet, means for establishing and maintaining in said tube a hot vaporbearing atmosphere, feeding means for continuously introducing to said inlet of said tube a quantity of a first cellulosic material requiring maximum digesting treatment, additional feeding means located downstream of said tube from said rst named feeding means for continuously introducing into said tube a quantity of a Vdifferent cellulosic material requiring a shorter digesting treatment than said first cellulosic materialfmeans mounting said feeding means in rigid relation with each other, means connecting one of said feeding means with said tube, a sleeve connected `with the other said feeding means to receive the discharge therefrom and having an opening in the side thereof, a T-member slidably mounted on said -sleevc with the projecting arm portion thereof angu- 8 i larly aligned with said opening, means connecting said arm portion to said tube, means forming a movable seal between said T-member and said sleeve on both slides of said opening Kto seal said members together while pro-r viding for movement of said T-member With'said tube and vvith respect to said sleeve in response to thermal expansion and contraction of said tube, and means in sfaid tube for effecting continuous advance of all of said cellulosic material ytherein to said outlet thereof while continuously agitating said material to expose all particles of said material to said atmosphere and to mixv said different cellulosic material with said iirst cellulosic material while conveying said materials Vthrough said atmosphere to said outlet.

`References Cited in the le of this v'patent UNITED STATES PATENTS 71,783 Pettebone Dec..3, 18.67 253,655 Allen Feb. 14, 1882 1,034,974 Burkheiser Aug. 6, 1912 1,525,050 Savery Feb.- 3, 1925 1,604,253 Barnhart Oct. 26, 19.26 1,954,012 Lemberger et al n Apr. 10, 19,34 2,286,942 T-uten June 16, 1942 2,323,194 Beveridge et al. June 29, 1943 2,334,663 Whitney .'Nov. 16, 1943 2,364,133 De La Roza Dec. 5, 1944 2,410,964 De La ROza Nov. 12, 1946 2,425,024 Beveridge et al. Aug. 5, 1947 2,616,802 Khoe et al Nov. 4, 1,952 2,673,690 Segl Mar. 3.0, 1954 2,757,115 Heritage July 31, 1956 2,862,813 Birdseye Dec. 2, 1958 2,862,814

Birdseye a Dec. 2, 1958

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