[1]Patented Oct. 4, 1932 I 1 8 S O t S S 7 UNITED STATES PATENT OFFICE TOHN TRAQUAIR AND FRANCIS G. BAWLING, OF CHILLICOTHr,,, OHIO, ASSIGNORS TO THE MR,,AD RESEARCH ENGINEERING COMPANY, OF DAYTON, OHIO, A CORPORATION OF OHIO PAPER XANUFACTURE ,&pplication illed I)ecember 29,1928. Serial No. 329,082. This iiiventioll relates to the n-ianufacture of papei- alid the like from cellulose containing matei,ials, aiid-pai@ticularly to tlle preparation of pulp to be used in such manufacture. 0 - lie of the principal objects of the invention i@ to provide a method of ti-eating fibrous iiiaterials to produce a siiperio,r pulp product whiell iiiay be formed into paper having 10 strength, color and o4lher characteristics superior to the corresl)ondincr characteristics in paper forl-ned from the saine fibrous materials in other generally knoiin ways previously used. 1. Aiiotlier object of the invention is to provide a method o@f ti-eatin(y hard - deciduous wood, sticli for exaii, to procliice a white iple a@chestnut, Iiigh strenc-ytli suitable for the maiiufacture of higli gr,,ide paper, such as printing paper. Aiiother objoct of the invention is to provide such a inethod in -which material economy in the consuiiaption of chemicals is effe,- ted, aild which admits of recovery as by23 I)rodticts of materials dissolved from the librous material, to thereby cut down the 'Waste of the fibrous iiiaterial which has he-retofore been considered una-voidable. Still ar-loiher object of the invention is to 30 prc. vide ,,.pparatus for carrying out the above liac-tllod. Other objects and advantacres of the invention wi'll be apparent from tKe following description, the accompanying drawings and -ipl,e,-ided claiins. 35 , Iii the drawincrs in whicb like characters of reference desigir@,tte lil,-e parts throughout the several views thereofFi(y. I is a diagrammatic side elevational 40 view of a portion of a preferred embodiment of apparatus constructed for carrying eiit the niethod of this invention; - F; (p - la is a dia,-ramn-iatic side elevational -irieiv of another portion of the apparatus, 45 Fi(rs. I and la when placed end to end disclosin- the complete apparatus; and Fic,r. 2 is a diagrami-natic partial side elevational view of a, somewhat modified form of apparatus. 5o The present invention provides a method pulp product of good color and'iiicomplete digestion with cheirlical under of treating fibrous materials 'of various l@inds, such a@ various types of wood, straw, fibrous grasses and the lili:e, to produce, a finished p,ulp product, of exceptionally Iiiah white color and I hio,,h strenath, with marod economy in the consuinption of chemicals, aiid -%vith yields considerably higlier -than those heretofore obtained in the manufacture of wliite pulp Vith the known afid aenerally used pulping processes. The mef@od Go of this invention is especially adapted for the treatment of hard deciduous or non-resinous broad-leafed wood, such as a chestnut, oalk, gum, and the lil@e, to form a superior wliite or bleached pulp product. In ac- c5 cordance witli the method of this invention, tl-ie fibrous material is first subjected to an s@ch conditions of temperature and pressure and of concentration and character of Cheln- 7o ical as to looseii and soften the bonding materi al holding the fibers in their natural associat ed form, without substin a ' affecting the cellulos'e and while m j y L, a ntainino, the stre nrfth of the fibers. In this c@emical 75 trea tment, the cooking or digestion, which is effective to soften the bonding material bold ing the fibers to(rether is purposely so limit ed in its effects that any considerable defi berin or separatino- of the fibrous - mate- 80 9 2n rial into its ultimate fibers does not result, and there is t resultino, Iiigh strength and 3- ield of the tiltimate pr@duct. The partially dige sted material is then subjected to a multista ge and coordinated chlorination treat- 85 men t to complete the pulping or disintegration thereof, the chlorinaiion treatment bein g carried out in such wise as to prevent injur y to the cellulose fibers, maintain the hi,- Ii'strength of the ultimate product and co wur e a good yield. In accordance with this invention, the fibro us iiiiterial after being cooked and before bein g chlorinated is'extracted with an alkalin e liquor, this eitecting a material &onomy 05 in the consumption of the chlorinatino, agent in the subseqtient chlorination tre"atment wit hout deleteriously a:ffe6tino. the cellulose or appreciably diminishiiig'th'e y@-eld. Better results are secured -where the final stage 100
[2]2 of the d . igestion or cooking is carried out at digester @mtil the required 6harge is'introhigh temperatures itnd pressures, as a subsequent extraction with alkaline liquor then results in a stir further diminished consumption of the chlorinating agent in the followi-nc, chlorination treatment. For purposes o-F illustratiiig'a preferred embodiment of the method, the invention is h ' ereinafter -described in connection with the treat10 ment of wood,-and more partic.ularly of hard deciduous wood such as leached c estnut chips from which tannic acid has been extracted. Referring to the drawin,-s, a conventional 15 chip breaker or hog is indicated at 10 which @erves to subdivide the logs or pieces of wood into chips of suitable size, such as a size @uitable for boiler fuel. If a supply of chips is available, such as leached chestnut chips 20 a chip storage may replace the chip breaker' The chips are fed by a, conveyor 11 into a feeding hopper 12 which discharges into a digester indicated at 13. This may be a conve@ntional digester, such as a stationary, I ro25. tary or tiimbling digester, having a feeding opening 14 closed by a removable c(>ver 15 and a conical discharge end 16 provided with a discharge valve 17. A steam supply pipe 18 is provided, which may,be connected as so shown for a stationary digester, or connected thr6ugh the trunnions in a rotating or tumbling type of digester. Cooking liquor is supplied froma tank 23 through a pipe 24 35 controred by a valve 25. The chips are subjected in the digester 13 to what is termed an "incomplete digest,.on". This is so controlled that the chips retain substantially their. original form, but may thereafter be readily defibered with pro . 40 perly coordiiiated mechanical and chem-cal treatments. This incomplete digestion may'vary coinsiderably, depending upon the fibrous mate.rial bein treated and the ultimate product 45 desired. %s an example of such an incomplete digestion, a so-called "semi-chemical" cook is hereinafter more fully diescribed. This serves to soften the adheri ncrustants n rs such as lignins, holding the fi@ei together 50 7ithout dissolving a large proportion of these !ncrustants and without deleteriously affecting the cellulose, thereby oivinhigh yields. and high strength. Very satisf@ctory results are secured with a cooking liquor comprisii@g r - ,5 an aqueous solution of an alkali metal stil phite containin- a salt of a weakly ionized polybasic acid, @uch as. a mixture of sodium sulphite and sodium bicarbonate. Other alkali metal sulphites, such as potassium sul60 h't , and other salts of wealrly ionized polygials@lice ac;ds, such as alkali m@ial carbonates, tartrates, citrates, borates, oxalates@ and the like, may be used. I The cook is darried out in stages. In prac65 tice, the cover 15 of the digester 13 is rem(ved and chips are fed by the conveyor 11 into the duced. Steam is then introduced for a short period of time by the pipe 18 to heat up the material to facilitate. impregnation. The valie 25 opened and a controlled quan- TO t--'ty of c liquor of controlled concentration is the digester. The tank-23 m-,ty be @osition d at a sufficient height to permit the liquor to feed in by gravity, or a pump may be used. Steam is th@n introduced- into 75 the mixed mass to raise. the temperature to about 125' C. to 150' C. for a peri6d of time, generary -about one hour to two hours, to secure . :)regnation of the liquor throughout 'ml the individual chips. The'valve 25 is then 80 opened, and the unabsorbed liquor within the digester is forced bacli into the tank 23 by means of steam pressure existing within t-he digester. A portion of the liquor is,@etained or absorbed by the chips within the dig@ster. 85 The I;qtior returned to the tank 23 is partially exhausted by reaction during the impregnation staae. Fresh concentrated make-up liquor is supplied from a tank 27 through pipe 28 to the tank 23 to malle up the volume 00 and concentration of the liquor within the tank 23 to provide cooldng liquor for a subsequent charge. The chps with absorbed liquor are then steamed to raise the temperature within the 95 digester above 1600 C. and preferably as high as 180' C. to 2100 C. or higher, and to raiSEf the pressure to about 160 to 200 pounds per @quare inch or higher, for a period of time to secure the desired reaction of the liquor 100 with the Egnins and other bonding material to secure the desired softening of the chips. According to the length of time and temperature of this reaction stage heating treatment the characteristics of the cooked material are' 105 determined, such as whether it can be easily hydrated or not, its bulkiness and the degr@e of hardness or softness of the cook. Satisfactory re@ults are secured with a treating time in this reaction stage of about one to 110 four hours. When the cooking liquor within the digester is maintained approximately neutral stir better results are obtained, the lignins beinr eltectively desolved or softened while the cef- 115 lulose, is substantially uninjurpd. Hi(rhlv satisfactory results ar6 secured when the-p 'H value of the solution is maintained between 5 and 9. During the -coolring, pyroligneous acids are liberated from the wood which tend 121 to render the cooldng liquor acid in character. salt of a weakly as sodium bicarof these acids any alkalinity resulting from hyd f the sodium salts producing caustic so , an excess of carbon dioxide gas is preferably -present during the cooking operation, this forl '=a carbonic acid withm ihe digester and react-
[3]1,880,587 ing -with tlle caustic soda as it forms to pro- niaterialht the completion of the cooking is duce sod-um bicarbohate which is siibstantially neutral in aqueous solution. As the carbonic acid is an extremely weak acid aiid as it is only ionized to a sliglit deoree iii tlle ri cool@in(r liquor, t serves to maintal@'n tile solution st@bstantialiy heiitral, any sli(rht acidity resulti-,ig from tne excess of carbon dioxide being unobjectionable and falling within the I)H l.-mits above mentioned. A pip-- 30 controlled by a valve 31 is provided, thi-ougli wliieh may be introduced carbon dioxi46 gas under pre-qsure to provide an exce,-s of the gas within the digester durin,, both theimpreomation and reaction stages. The control of the neutrality of the cooliing the teniperature and pressure conditions withi,ii tlle digester. If steam alone is injected 23 iiito a digester and other gases or vapors are absent, a definitp, pressure is obtained at any clefinite teiiiperature. By the introduction of carbon dioxide gas, a still Iiigh6r pressure is obta,@ned at any definite temperature than is obtained With steain alone. When a bi25 carbonate containing cookiiig liquor, such as sodiiiiiibicarbonate 7 is iised, a certain amount of decoinposition of the chemical with the f ormation of CO, gas results, so that the presso sure obfaiaed within a digester with such a cooking liquor is due not only to ste'am pressure b-ut also to false pressure of the carbo-.q dioxide gas resulting from the decompositio@-i Of the bicarbonate. By running a series of tests to determine the degree of decomposi36 tion of a sodium bicarbonate solution at hi,-her temperaturbs, a temperature-pressure chart may be plotted which will indicate the pressure which shoulcl be obtained within the digester at any temperature wlien bicarbonate 40 is present' In operation, the actual presslire in the digester may be niaintained sli,-Iitly above this calculated pressure for any given temperature by the infioduction of excess CO, 45' gas through the pipe 30. If the pressure within the d ester falls below the predeteriniiied f(or any giveil temperature, manipulation of the valve 31 toward opening position will restore the desired conditions with the digester. Should the actual pressure recorded iii the diaester rise above predeterniined normal fo:rany given temper,ature, the digester is relieved by allowing some of the gas to escape through the pressure relief valve 55 32. A control chart may be provided for the digester, and the control of the cooking con(litions ivithin the diaester effected by proper n,-anipulation of the valves controlling the introduction of steam and carbon dioxide in Go accordance with variations in pressure from the de,-ired predetermined normal as indic.ited on the chart for any particular temperature. The cooked material is discharaed from o,5 the digester 13 into,,a dump tank 35. The 'softened but still maintains to a large degree ent hanis preferd so that 'TO not redded or pulped at this st@-(Ye, but is mainiained inchip form. The niass of softened chips discharged into the dump tank 35 is then washed to remove residual liquor. The washing may 75 be perforiiied by the iiitroductioii:- of wash water through pipe 38 onto the siirf ace of the chips -,@ithin the dump tanlc. These 6hips are supported upon a perforated bottom, wbich may be a latticework as indicated at, 8 0 36, the washing liqLior draining throu-h the, t ! l pipe 37. The dump tank 35 is provided witli n-leads for feeding the softened and drained chips sr, at a controlled rate to a mechanical disintcgrator. As illustrated the botilloill of the diiinp tanl< is provided ,vith aii opening 40 I.ocated adjacent tlle periphery of the tank. This opening is closed by a slidin- valve 41 go t5 durin(y the duji-ipin(Y and washing ol@erations, aiid istthen opened to perinit the feedidg of softened chips at a controred ra'te oiito an endless conveyor 42. Positioned within the dump tank is a leach caster, whieb coinprises 95 a central.vertical shift 45 supported in suita'ble beai-iiicrs ar@d drive-Ti-.throiigh Lrears 46 and 47 froni a drive shaft 48, whicl@'in turn is driven at a controlled aiid variable i-ate, from any stiitable source of power. A tir-'@ ioo ring arn,. 50 is slidably mounted on the shaft 45 for vertical movement thereon and is keyed to the shaf-t so as to rotate therewith. The arm carries a plurali@y of inclined blades oi- fingers 51 which are so inclined as to move jo5 the chips toward the periphery of the tailk upon rotation of the shaft 45 and arm 50. The arm 50 is rotatably supported by a thrust bearing 52 carried by a non-rotatable cross bea m 5"0 which is suspended by cables 54 from iio a windin- druni (not shown) wliieli is aceapted to be r'o'tated iii opposite directions throukh suita ble conveiitional driving liaacli;.nery (not sliow n) at variable speeds to lower or raise the stirring arm 50 in accordance with the 115 level of the chips within the tanl,- 35, so that the arm 50 operates upon the upper surface of the chips. The rate at which the chips are fed to the periphery of the 'Lank is controlled by the rate of rotation of the shaft 45, or by i2o the, rate of lowering of the arm 50, this in tiirn controlling the rate at which the chips are fed througl'l an opening 39 iii tile Idtticewor k 36 and the aligned opening 40 onto the conv eyor 42. 125 The conveyor 42 disclilarges the chips into a recei 'ng hopper 55 feeding into an endv' less bucket elevator 56, which in turn dischar ges onto an endless conveyor 57 feeding into an inlet 58 of a rod mill 60. Any suit- i3o liqiior iiiay be easily acconiplished by noting 1-i ti ce-work and escaping to recovery throu t@ gh
[4]1,880,587 able type of mechanical. diginte-grator can be .used,to. disintegrate th6 softeiled chips at thi.s poiiat. to prepare th.eiia for s@ibseqiient treatmen.t, exaniples of otlier stiitable niecha'nical. disintegrators beilig' cc,ntrifug(LI -.5. type mills such as Bauer iiiills, swiiigliamle,r: mills, edgerunner inills aild the like. Red supply of dilutioii liqiior is admitted conco.mita.ntly with the softeii6d chips throtigh a supply pipe 62. The dilution liqiior is gene'rary controlled to. provide a stocl,- consistency of about 5@lo to 87o within the rod mill. In order to reduce the chlorine consumption of the subsequeiit chloriiiation, the (iigested material is subjected to an extraction ireatment with a caustic liquor, preferably c,,i.ustic soda. ATery satisfactoi@y results are secured witli a ebld dilute NAOH solution of a concentration as low as 114@'o to 17o or even less. This liquor may be maintain6d @at ordinari, i-ooln teinperattire@, or may be heated beljw the boilin- point, the cold extraction proving quite@ satisf actory. The effective.-loss of this extraction treatment has been fciind to vary somewhat with diiterent species of wood. This extraction is preferably carried out duriiig the mechanical disiiite(yratioin. : Thus the dicrested fibrous maleriil aiid the alkaline Equa@ may be added 1,-,)iiconiitaiitly and in proportionate quantities by the conveyor 57 aid the pipe 62 respectively to the rod mill 60 and the extracI tion and the mechanical disintegration a:re' thus carried out vei,y effectively at the same tiiiie. The poundiii- and shredding treatinent in the r(kl mill or other disinte(yrator P,.,ovides an aoitation of the mixednmass )vliieh insur(,s @'effe,-tive penetration of the alkali within the fibrous material wherebv Iiighly satisfactory extraction is secured, while at the same time this treatment in the presence of the alkaline liquor gives super.ior (lisinte(,rration of the fibrous material. 45 It is found that wlien the cooking in the reaction stage is carried to temperatures in excess of 160' C., then the extracti(in- step eilects still further reduction in clilorine C'6n.,3iiiiiption in the subsequent chlorination. r,o Verv satisfactory results are,secured Nvhere the lemperature in the reaction stage of the 'k' coo Ig is ra'sed as h h as 180' C. to 2100 C., or even hileher, an@a pressure of 160 to 200 pounds p4, -@square inch or hiaher is mai,.qg5 tained. Where substantial neutrality of the cooldng liquor is maintained, these hi.gh temperatures and pressures do not injuriously affect the cellulose and high strength and Iiigh yield of the resulting product is neverGo theless secured. Reaction of ineutral sodium s-ulphite liquor with the lignins.and other mcrustants is apparontly most effective at temperatures in excess of 1600 C-. , While it has not been delcmitely ascertained, it is be06 lieved that the lignins are in the main not dissolved out l@y this high temperature cook, but are converted into oth6r compounds which are soluble in dilute NAOH so,that they are readily extracted. Other compounds mily be converted into a stable form To such that they do not take up as much chlo. rine to'forin highly substituted chlorination prodilets diiring the subsequ6,nt clilorination. The net result is that a pulp of high yield aiid high strength is obtained -%vith a mate- T5 rially decreased chlorine consumption. Very satisfactory results are sec-ured with an economy in the. operation in this rea@tion sta-e where the temperature is maintained abo-ut 1601 C., or not materially above, for 80 several hours, and the temperature is then raised to a high point of 1800 C. to 2100 C. - or even higher for a short time, such as about half an hoiir. The rod mill 60 comprises an outer rotary 85 shell 63 which cbntains thereila a plurality of lose parallelly arranged rods extending substaiitially tllrou-liout the lenlyth of the shell. The contracted ends 58 and 6iof the shell are siipported in suitable bearinos (not shown) 90 and the body of the shell is p@rovidecl with an aiinular gear 65 which is driven through geariii(r froiii a suitable power shaft (not S own). The softened chips are simultaneously fed into the inlet 58 with'dilution 95 liqtiid from pipe 62, and the stock feeds from the iiilet 58 to the discharge 61 as the casino63 is r6tated to thereby give a thorou " gh poundino,, rubbing and shredding treatment to the fflrous material which serves to're- 100 duce the softened chips and to hydrate the fibei-s without objectionable cutt'ing of the fibers, to thereby directly ex'Pose the small es partiel or hara fiber bundles or shives to 'f-,icilitate the subsequent chlorination. In 105 disintegrating mills of this character provided with loose or swinging iml)actina elements, the unreduced bundles or lum@s of fibrous material receive substantially the entire action of the movable elements, such as 110 the@ rods, while the porti6ns that are sufficiently reduced are protected by the lumps against further reduction and cu'tt,@ng action. The rod mill has a certain definite capacity and the fibrous material feeds in until the 115 mill is properly flued, or until the treated stock begins t-o overflow from the discharge end 64. The dischar-c from the mill then proceeds in accordanew with the rate at which fresh niaterial is fed into the mill, the time of 120 treatment within the rod mill being thereby controlled by the rate of feed. The material 'discharged throuoh the end 64 of the rod mill feeds into a stc@k chest 68 provided with suitable agitating mechanism, 126 such as driven- shaft 69 having agitating blades, 70. At this pbint additional dilution liquid, such as white water@ is added throucrh a pipe 71 tG reduce the consistency of the stock within the. chest 68 to a point such that 230
[5]1,880,687 6rough con it can be readily. PUMT,,,ed duits, a consistency range o about 3@'o to 5@'o giv,ng satisfactory results. Stock is withdrawn f rom the'ehest 68 through pipe 72 by a suitable pump such'as a centrifugal pump 73, which feeds it through a pipe 74 to the central compartmenf 75 of a conventit)nal head box 76. As sbown, the box 76 is divided by . parti10 tions 77 and 78 into outer compartments 79 and 80 and central compartment 75. The comp I artment 79 is connected by pipe 81 with the stock chest 68, whereby the excess of stock pumped to the head box and dverflowiii(-r the 15 partition 77 is returned to the stock chest 68. The compartment 80 is conrilected by pipe 82 to a conventional mixing box 83. The partition 78 is provided with an adjustable Lyaie or weir 84. which serves to pr6vide for-the 20 feeding of a coiitrolled amount of stock. to D g box has a pluthemixingbox83. Themi-Ki rality of staggered baffles 85 to citect a tborough mixing of ihe stock and additional dil-iition'liquor introduced by a pipe 86, this serv25 ing to further redilice the consistenev of the stock to a point most effective for sereeniny and filtering, such as 6bout 1% to 2@'o. The gtock discharges from the mixing box 83 through pipe 87 into a conventional coarse 30 screen, illustrated as a rotary screen 90. This compnses an outer confining casing 91 within which is rotatably mounted a spaced cylindrical screen 92. The stoc'k feeds frem, the .pipe 87 into the interior of the rotary scireen, 35. ihe mesbes of which are sufficiently large to permi' the material which has been sufficiently defibered and the dilution liqtior to iyass therethrough into the outer confining casin(,, 91 from wliere it discharges througli pipe 93. 40 The larner undefibered particles, Itimps and knots which do not pass through the screen are discharged at the end onto a suit,,ible coneted, for the -purinto the inlet 58 45 the tailings are r fur-ther reduction. The screened material discharges from the pipe 93 into a continuous filter mechanism 95 r)O which serves to wash and thielren the treated material. This filter mechanism may be a conventional rotary vaci-iiim filter such as an Oliver filter. This comprises a cyli-ndrical rotary screen 96 divided into compartments 55 of definite suction areas. The screen dips into the stock confined within a. tank 97 into which the stock from the pipe 93 discharges. Suction within the compartments ofthe screen eaLises the fibrous m,,Lterial to aectimulate on 60 t@ie surface of the screen as the water passes therethrou(rh into t,he siietion coinpartments. As the screen rotates carrying the filtered fibrous mat above the liquia level in the taiik, a. supply of wash water is directed upon the 65 mat from supply pipes 98. This serves to remove )oking liquor any remammg cc from the material. As the filter continues to rotate the mat which has thus been washed and, thi@Vened arrives at an area which is not subject to suction, and at this point a flexible To sertiper member 99 scrapes the material from the filter into a chute 100 whi6h discharges into a stock chest 102 similar to the stoelc chest 68. The chest 102 has itn agitator 103 and a pipe 104 for the introduction of dilu- 75 tion liquor. A,pump 105 serves to withdra* the stock through a pipe 106 and to @force it through. pipe 107 to a conventional head box 10 8 similar in con--truction to the head box 76 . The overflow pumped to t.he head box so 10 8 is returned by p,ipe 109 to the stock chest 10 2, and a controlled quantity, of the stock pa sses by pipe 110 tG the chlorination appiratus where the disintegration of the fibrous m aterial into pulp is completed. 85 A controlled supply of chlorinating @g@nt su ch as chlorine water or chlorine gas is intro duced into the stream of fibrous material by pipe 111 egntrolled by valve 112. The sto ck may be made down to low consistency in 90 , th e stock chest 102, or the chlorine water may be quite dilute to additionally lower the consis tency of the stock such t.hat objectionable te mperature rise of the diluted mass in th6 iiii tial chlorinatipn is avoided. In dilute con- 95 sis tency, the waier in which the fibers are su spended apparently serves as a heat-absorbin g mediuul, serving to prevent an objectionab le temperature rise of the mass due to the chlorination, and alsc, serving to dilute hydro- iOO chloric acid formed in the reaction, this additionally diminishing objectionable results. Very sa-@isf actory results have, been secured with consistencies below 5@'o. Such low consistencies provide a fluid mass that may be 1(! readily flowed or pumped through cond-aits or t reatino, chambers. The fibrou's mass and c hlorirrating agent pass together into a mixer 1 13 which comprises a length of pipe having i spiral baffle 114 th6rein to create turbulence 1 10 i n the flowing stoelc stream to mix the chlor inating aoent with the mass. The mixed P-iass th(@n @iasses into the chlorinating tank or c hamber 115 which is constructed of acidp roof n-iaterial such as tile or the like an(I is 1 15 d ivided into a plurality of connected chamb ers, represented in the drawing by two c hambers 116 and 117 divided by a central p artition 118 termi,.iating short of the bot,- t om of the tank. The mixed mass and chlorin12 0 a ting agent flow downwardty through the s pace 116 and beneath the lower end of the p artition 118, and up through the space 117 to t he o-verflow pipe 120. The tank 115 is constructed of a capacity to 125 a ccommodate sufficient material to provide t he desired reaction time as the stock flows f rom the inlet to the outlet. In this manner, a continuous chlorination is effected as the mass fl(yws along. The amount of chlorinat1 .0
[6]1,880,587 ing agent is continuously colitrolled by -the valve 112, preferably in an am6u-fit insufficient. for complete chlorination. As a result,themorereadilychlorihatedmaterialfir@t reacts with the chlorinating agent in a compa:ratively short time as the mass flows alono,. The amount of chlorinating agent, however, is preferably' @ontroHe4 to be as niuch as will be readily taken up by the fibers in this 10 short treating period, while insurmg substantially complete reaction. This initial reaction is rapid, and it has been ascertained that the.reaction 6f about 859'o of the chlorine required for complete chlorination of a given 15 fibrous mass goes to substantial eompletion in about 15 to 20 minutes. Generally the acl@. dition of about 657o to 957o of the'ehlorine needed for complete chlorination in this first stage with a treating time of about half an 20 hour Lives very satisfactory results. Vari'ous reagents may be used for this first stage, such as chlorine, sodium hypochlorite, bromine and the like, which for purposes of des;cription are herein termed "chlorinatingi) 25 a ents. Chlorine i@ preferred due to the ease Of control, effectiveness and rapidity of reaction, and lesser cost of the chemical. However, the use of ordinary bleach liquor or other calcium compounds at this point is n ot so so satisfactory, due to the formation of insoluble calcium compounds in the pulp which are not readily washed out in subsequent washing treatments. At this stage, the chlorine may be added in a roughly controlled amount sufficient to effect this initial chlorination, and this is usually done by addin 9 chlorine water of a strength and in an amount to dilute the stock to the desired low consisten suw and to preferably provide an amount in40 cient for complete chlorination within the limits above mentioned. The addition of chlorine is in practice controlled accordinor to ..the characteristics of the particular type of fibrous material or, stoel- being treated, as re45 gards chlorine consumption, rate of reaction, and the like, and this may be determined for each particular fibrous material by tests. The overfl'ow outlet 120 from the chlorination chamber 115 discharges into a conven50 tiongl type of washing apparatus,. shown diagi-ammaticaRy,,a8 a worm-type drum washer. This comp@ises an. acid-proof perforated rotary drum or scre6n 123 having an interior ribbon conveyor or spiral 124 and spr ay 55 pipes 125 for spraying wash water upon the s.tock. The stock feeds into the interior of one end of the rotary drum and is carried continuously through by the spiral cofiveyor as it is washed by the sprays and discharges 60 from the other end. A part of the water in the stock drains through the perforated drum into a receiving tank 126 having a discharoe pipe 127, so that the stock generally,discharges from the washer at a'consistency of 65 about 107'o to 127o. The shoit time of treatment in-the chlorination chamber coupl6d witli the fact that the free Acid foriiied in the reaction is waslied out iminediately after chlorir@ation further serves to prevent injury to the fibers. An additional spray pipe 128 70 i8 prefer@bly provided to direct an alk aline liquor upon the chlorinated material upon the screen to neutralize any acid or free chlorine remaining i-n the fibrous mass, thereby avoiding the necessity for further acicl-proof 76 apparatus, @s well 9@@ assisting iia dissolving out reaction products 6 . f the chlorination. If desired, an alkaene steeping may be criven at this point, this being a,diantageou@'in the case of fibrous stock which is less defibered. 80 A discharge 130 from the worm washer feeds to a further thickening device where the stoelc is deweitered- to a consistency of substantially, 157o or higlier, preferably 207o to 307o, to render it readily permeable to gas. 85 A contini-ious centrifugal thickener functions vety satisfactorily for this purpose, and such a macliine is diagrammatically illustrated herein. This comprises an inner distributing rotor 131 having a spiral flange 132, the 00 rotor being keyed to a shaft 133 driven by a motor 134, and a second rotor or perforated filterl screen 135 carried by a sleeve 136 Illy m rotat -- tounted upon shaft 133, and also driven from motor 134 throu-ah gearing (not 95 shown) at a speed which is preferably se-htly less than the speed of the rotor 131. T@e outer screen is surrounded by a stationary anriular casing or trough 138. The. discharge 130 continuously feeds the stock into the !co space between the innef rotor 131 and the out7 er perforated filteriiag screen 135, where it is carried through the machirie by the spiral fla-nge 132 while being subjected to such centrifugal force as to, cause a portion of the 105 retained water in the mass to pd-s through the filterin@ screen 135 into the trough 138, from where the filtrate is removed by a pipe 139. Other well known types, of continuous thickeners may be used for this purpose, 110 such as rotary vacuum filters or cylindrical thickeners with pressure rolls to regulate the water content of the stock. The dewatered stoc'k dis6harged froin the centrifugal machine is fed by a chiite 140 to 115 EL supply trou h 141 from where it is scooped by an endless fiieliet elevator 142 and fed into a chlorination tower 143 constructed of acid and chlorine proof material, where the second stage of the chlorination is e-ffected. 120 After th@ initial chlorination, it is found that the fibers ]may be subjected to a strong or drastic chlorinating treatment with chlorine gas or bromine at high density or consistency without obje6tionable results. In this.stage 125 of more drastic action, in which a higb chlorine concentration is effective in the fibroi,,s mass, the chlorine gas reacts with the more resistant ligneous matter with consequent resolution of the shives or other, undefibered ma- l@'i
[7]1,880,587 terial, this pel;mitting the successful resolution of liard wood into satisfactory pulp. At t@e same tim6 the strength of the ribers is maintained and other high quality charac5 tt-risties are seciij:ed. Durinc., sucli reaction, the ligneoiis and otlier material in the sliives is apparently changed by the action of the io line solutions, or which are of such character as to color and other characteristics as to be I.;;ubsequently unobjectionable and ineffective to lower the qiiality of the resultiiig pulp. As shown diagr@ramatically hetein, the ele15 vator 142 discharges into a hopper 145 which f'eeds into a screiv conveyor 146 havin- an opening 147 6n the lower side@ tliereof opl;@ositd the opeii upper end of the tower 143. Stock feeds through the opening 147 into the upper 2o eiid of the tower 143 as needed t6 maintain the tower f ull of stock, the surplus stock handl6d by the screw conveyor 146 being dis,cliarg@d at the end 148 and returned to the source of supply. The tower 143 is provided 25 with an inlet 150 for the introduction of a controlled supply of chlorine o-as and controlled outlets 151 and 152 for the di@scharge of gas. The gas discharging from the tower which contains some free. chlorine is preferably 30 passed to recovery apparatus (not shown), such as a water absorption system, wliere chlorine water is formed which may be iised in the first stage of the chlorination. Water or other slushing liquid is introduced adja35@ cent the base of the tower at 154 to dilute and slush out the Dulp throligh the water sealed discharge 155 fornied betiveeii t'lle low,-r end 156 of the sliell of the tower and a base 157, the stock passing into an annular trough'158. 4o The stock passes from the tipper end to the lower end of,the tower by gravity in -,iccardance -with the rate at whick it is slushed out at the bottom, thereby providing a continlious trtvel of dew,,itered stocli: through a con46 trollecl and maintained atmosphere of chlotine ga wliieh thoroughly permeates the mass fibers and effects intimate co' ntact therewith. Generallv a treatiiig eriod of 15 to 30 miniites in this second sta e is satisfactorv, 5o althougli ,t lon(yer period ii@ay be used. The chlorinated sto-k slished out at the. b,-,se of the to-wer 143 is discharged, with the aid of additional sliisliinop liquid int-roduced into the troticrh 158 by i @ipe 16.0, throucrh a 55 pipe 161 ipto a solvent tank 162. Here it is mixed with a colitrolled quantity of alkali continuo-Lisly supplied from a pipe 163 havina control valve 164 for the purpose of dissolving out re,,iction products of the chlorination. 60 The allzaline liquor washed otit of the extracted fibroiis materiil prior to clilorination by the Oliver filter 95 is quite satisfactory for thi-s purpose, and stich Lquor lilay be slipplied directly to the pipe 163. The tanlc 162 65 is coiistructed to effect a continuous aiid uniform treatment of the fibrous material to secure a -thorough mixing of the materiil with the solvent alkali. For this purpose the tank is provided.with a plurality of staggered bafflos 166 which provide. a circuitous path for the flow of material from the inlet 167 to the discharge 168 connected to the suction side agitating meelianism such as a driven ghqft 170 liaving a plurality of rotary stirring arms .75. 171 . The @apacity of the tank 162 is such that the treated material is allowed to remain ab out half. an hour tliereinl this g ' suffi'vin cie nt time for soluble reaction produgets Of the ch'orination to be dissolved. Any suitable 80. alk ali'may be used for this purpose, dilute col d soluiions of caustic socia, sodium carbo nate or sodium @ulphite giving very satisfac tory results. The puiiap 169 feeds the diluted stock 85 tlir otigh a pipe 175 to a contiiiuous filter'mechani sm indicated generally at 176 which may be a conventional rotary vac-Lium filter , such as an Oli*er filter, similar in construction to the filter 95. The dissolved reaction products 90 of the chorination and the excess alkaline lic ,iior are washed out of the stock by wash wat er from spray pipes 177, and the filtered ,tnd thickened material is removed from the stirf ace of the filter by a scraper 178 into a 95 chut e 179 which discharges into the first tank 180 of a bleaclier which is preferably of the coiit inuotis type. The alkaline liqtior and was h water arawn by suction into. the iiiterior of the rotary screen 176 are discharged thro ugh a central pipe 182, and a portion of this ilkaline liquor may be supplied to the stip ply pipe 128 of the worm washer. A.ny suitable construction of continuous 105 bl eacher may be iised. As sho-wn, three conn ected tanl@s 180, 183 and 184, ea@h having a r otary shaft 185 provided with st"rring arms 1 86, are pron,ided. The tanks are arraii.,-ed at s uccessively lower elevations a'nd the bottom 1 10 of a precedinz t-ank is connected to the upper e nd of a siicceeding tank bi, a pipe conneeti oti 187. Eacli connection - i87 has its hicrht@ e st I)oint located below the level of the stock in the I)receding tadk, whereby a head is ef1 15 fe ctivetasectireaflawtlirotighthep-'pe. The c auacity of the tanks is such as to ;nstire uffici e'nt tiiiie for the completion oi th,,'sfinal bl eaching action during the t;.me.the material fl oivs through the bleaching t-,iii]@s.. A con1 20 tr olled qtiantity of sil-itabl3 bleachin- a(Yent st ich as bleach liquor, sod-@UM hypoelilorl;te or c hlorine water, is continuotisly added by a pi re 188 I'laving a control v,,ili,e 189. Due to th e effective chlorination treatment vv@hich 1 25 s erves to furtlier disiiite-rate a-@ld complete th e piilpin(r of the fibroiis material, the quantit y of b r ed u@ed, a e o n the d s uffi@ient 130 chlorine gas into coinpound which inay of a pump 169. The first compartment of the thereafter be ieadily washed out with alka.@ tanl- 162 is. preferably provided with suitable
[8]1,88q,587 to pr,Dduce a p@lp haviiag a high white color. The bleached pulp stock continuously discharged from the last tank 184 througn pipe 190 is forced by a. pump 191 to a rotai-y vac6'uum filter indicated generally at 192, similar in construction -to the filter 176, where the pulp is washed and thicl@ened. The bleached pulp is then discharged through chute 193 into a stock chest 194 where it is stored for 10 further treatment or for use. The mechanical disintegration and the extraction'may be carried out as separate steps if desired. As illustrated in Fi(r. 2, the conveyor 57' discharges cooked fibrous liaaterial 15 concomitant@y wfi-h dilution liquor from pipe 62' into the rod raih 60'. The more or less disi.ntegrated fibrous material discharged from 't-he rod mill -'Ls introduced into a hopper 200 of an @xtfact,@on tank 201 constructed 20 similarly to the solvent tank 162. A pipe 202 having a control . valve 203 is provided to admit controlled'quantities of alkaline liquor intb the extraction tank along with the fibrous material. The tank 201 is provided 25 with staggered baffles 204 and an a@itator' 205 for the first con-ipartment. The cons:istency of the stock is made down to less than 5@'o at this point, and a pump 73' feeds the extracted stock thr-ough a pipe 74' to a con30 ventional head box in the manner in which the stock is fed from the stock chest 68 in Fi(r. 1. Or if desii.-ed, alkaline liquor may be introduced into the rod miR 60' by the pipe 62' to secure extraction and mechanical dis86 inteoration in the presence of alkali, and the extr-action then co:mpleted in the tank 201, further alkaline Equor or dilution liquor being introduced by the pipe 202. . The construction.of the apparatus and the operation 40 is otherwise the same as that of Fig. 1. In order to conserve as by-products of this pulpino, treatment the ligneous and otlier incrustant material dissolved out of the fibrous material thereby effectina a further economy 45 in the process, this organic raatorial is preferably separated from the solvent liquor. Where a mild sul)stantially iaeutral cook is used as iia the incomplete digestion above described, these organic materials are not con50 verted into objectionable reaction products which are subsequently difficult to handle -as is the case in the conventional practice where a drastic cook@ing treatment with strong cooli:ing liquo@ is used, but these materials'may be 55 readily separated from the cooking liquor and from the extraction or solvent liquor. Th,Lis the cooking liquor drained from the cool@ed material t hrough the pipe 37 may be treated to recover ligneous by-products 60 therefrom. The combined extraco'lion and alkali solvent Equor removed from the fibrous niaterial by the filter 176 mav be also treated to recover these organic materials as bypro@uct The spent cook-in(y liquor aiid the combine@ extraction and alka-li solvent Equor are preferably separately treated, this progressive extraction of the recovered organic material being advanta-eous in that higher quality by-products are generally secured from the extract@@bn and solvent liquor than 70 from the cooking liquor. Thi@ . orgailic material readily aamits of separation into two fractions, 6ne of which appears to be phenolic @m char'acter and is precipitated by sol75 uble carbonates from aia alkaline sblutioni and anbther fraction which is preci@itated by acids. The cooking andehlorination treatments as carried out in accordance with ihis invention'- are so control,led. or limited in their 80 offects upon the cerulose content. of the fibrous material, that even the'less resi4ant beta and gamma celluloses are substantially uninjured, and only small amounts are lost by solution in contradistinction to the con- 85 ventioiaal pulping methods heretoforia used. The alpha cellulose content is not materiany hydrolyzed or converted into oxyccldulose. The result is that a novel and superior white pulp product having unusually advantageous 90 characteristics with a high yield is obtained. In aetual tests using chestilut and gum, this pulp roduct has been found to contain a p cellulose conte in excess of 20@'o of beta and gamma ce'll, Of 05 . ulose and less than 8070 alpha cellulose. The averate strength is more thall 507o hi,-her than that of paper formed from conventional soda pulp from the same species of wood, often being twice as strono,, and is superior to that of paper 100 formed from strong sulphite pulp. The bleached product is of the highest color rade' The pulp is characterized by high g I fe till and clay carrying qualities, and it may @e loaded to contain as much as 40@'o of 05 filler without dusting. Pa,per formed from the product is free of the objectionable fuzziness, which is a characteristic- of paper formed from soda p'ulp. The combination of high strength, good color and exceptional '10 clay. carrying qiialities makes the prodtict highly satisfactory for use in priintin- paper, such as book paper. The pulp i@'free, that is water draiiis rapidly through a niat underloing formation on a forming wire, 115 and is easily hydrated, which mal-es the piilp especially suitable for other tvpes of hiahgrade paper, such as bond@s ai@4 -writino', tp-aper, parchnient, glassine, waxing, a.nd the like. The yield of unbleached pulp gener- 120 ally averages between 75,yo to 80@'o on the dry weight of the -wood, while the yield of bleached pulp generally averages over 609'o on the dry weio-,ht of t he wood. This is an 125 average increased yield of over 307o as compared to the soda process, and is materially hioher than average, yiel-ds obtained by the sul-phite and kraft processes. The following is a typical example of a. . pulping treatment carried out in accordance
[9]with this invention. To a charge of arouiid 'The chlorinated stock is washed axid give'n an 14,000 @ounds of leached. chestnut chips (dry alkaline treatment with cold dilute caustic basis), a cookinf liquor, consisting of about sW&, and then after beink thickened to about 18(0 pounds o sodium sulphite and 700 20'Yo to30@'o consiste is fed to the chlorT)ounds of sodium bicarboristo (both calen- inating tower 143. geyre . it is. subjected to 70 faied,as sodiuni carbonate) in su:fficient water. the second stage chlorination by pa@ sing to provide a concentration of about 8% to 127'o sodimn sull)hite aiid 3,yo t6 59'o sodium bicarbonate, is added to the digester. The 10 wood is preferably steamed for about hal-f an hour before the cooking liquor is added. The charge i@ then brouglit up to approxi!nately 1251 C. with steam, tliecooking bemg continued at around this temperature for 15 approximately two hours. The control of the neutrality of the cooking liquor is effected by the introduction of carbon dioxide gas through the pipe 30, or the relief of excess pressure througn the pipe 32. The valve 20 25 is then opened and the liquor in the digester is blown back into the receiving t"k -23 where fresh liquor is added from tank 27 to bring it up to strength and volume - for the treatmbnt of a subsequent charge. 25 The chips impregnated with the liquor are then steamed until the temperature is brought up to about 185' C. or higher, an excess of carbon dioxide gas being maintained. This second stage of the cooking is generary 30 carried on from one to four hours. The cooked chips are then dii@aped into the dump tank 35 and washed, the plug valve for the Qutlet being closed. The plug valve is then opened and the shaft 45 gnd the leach caster 36 driven to feed the softened chips at a controlled rate to the rod miR 60. With a miU havi-ng a shell approximately twelve :Feet long and six feet iia diameter and containing about. 40,000 pounds of rods, a rate of :feed40 ing of the chips diluted to a consistency of 5 % to 8 'yo to give a controlled output o:f about thirteen tons to eighteen tons of rod mffled stock in twenty-four hours is quite satisfactory. The dilution in the rod miU is 45 preferably effected with a cold dilute NAOH solution of a concentration of approximately one-half per cent. The disintegrated material is then diluted, screened to remove -undesirable lumps and knots, ffitered, and then i5O furtherdilutedforthefi@sti3tiV@chlorination. Chlorine water containing approximately 80@'o to 90% of the chlorine required for colnplete chlorination of the pulp is used. The chlorine is added to the stock in the form of 55 solution in water containing approxumtely .2@'o to .4,yo chlorine or is aaded directly as chlorine gas. In the former case the fibrous material is inade down to a consistency of about 4@'o to 6,yo, the addition of the chl6rine 60 water brino-iiag the consistency to about lyo to 4@' . ID. the latter case the consi@Uncy of the material is made down initiary to about 2Tc or even less. The rate of flow the chlorination chamber 115 is c 05 ' a treating time of about half ho-ar. glvpthrough a maintained layer of chlorine gas for about 15 to 30 minutes. Both staoes of the chlorination are carried on'at ordiniiy rooxq temperatures. . The chlorinated stock is 75 then introduced into the'alkali solvent tank 162 with asuffici6nt qtiantity of cold .17o NAOR solution to render the mass distinctly alkaline and is a-itated aifd st6eped therein for about half a@'hour. After, washing and 80 makiiag down to about 5 @lo consistency, the . inateri al is introduced into the bleachei with a quantity of hypo6hlorite liquor sufficient to bring the consistency to about 47o to 57o andto provide about 1,7o chloriiae on the dry 85 weigh t of the pulp. The flow of stock throug h the bleacher is corttrored to pri)vide a treating time of about one hour or more. A preliminary high density bleach may be given, if desired, before the siock is dililted. 90 The bleached pulp is then washed and thickened and dropped to a stock chest where it is ready for use in the manufacture of hilhomde paper' ' While the methods herein described, and 9 5 the forms of apparatus for carrying these metho ds into effect, constitute preferred embodim ents of the iii.venti6n, it is to be understood that the invention is not limited to these precis e methods and forms of apparatus and 100 that changes may be made in either without dep arting from the scope of the invention which is defined in the appended claims. What is
