US1645754A - Method and apparatus for producing paper pulp - Google Patents

Description

Oct. 18 1997.

- w. HLHQWELL, JR

METHOD AND APPARATUS FOR PRODUCING PAPER PULP Filedsewl gj 55491 if I IAL NVENTOR ATTORNEY(A Patented oi. is, l1921.

iJ- NITEDA STATES Leia-isi "PAT-ENT orifice;

l WALLACE/rr. HOWELL, ne', or wILnsBoIio, Naw Yoax. i

' -lm'rnon AND aranarusron PRoDUorNe PAPEB'PULP.

`Application led September 10, 19%. Serial- No. 134,600.

This invention relates to improved method and apparatus for producing paper pulp by cooking wood and other cellulosic materials with chemical cook-ing liquors.

5 Chemical cooking processes for the production of pulp from Wood and other cellulosic materials entail a largeV consumption of `fuel for heat and.. power; In the processes used hitherto, there `have been very large l0 wastes of heat usually in the formof steam. Thisis particularly true inthe alkaline pulp process such'as-'the soda process and the so- -called sulfate process, but is also 'applicable in a lesser deree to acidprocess such a'sthe various sul te processes.

In the ysoda and sulfate processes, wood or- ,othercellulosic material is cooked byy means of liquors containing caustic' sda in the sodaprocess and a mixture ot' caustic soda, sodium sulfide and small amounts of sodium sulfate and carbonate inthe sulfate process.

' The cooking usually takes place in digesters oflarge size havinga capacity, for example,

of v'about 4% kcords of Wood 1n' the formhof 2 chips.- A large amount of liq'uor containing caustic soda, with or without sodium sulfide,

as thecasemay be, is also introduced into the digester 'and is heated and circulated through the chips by means of steam.

The steam isusually passed through an injector where it picks upliquor frog a liquor chamber inthe bottomof the di ester and introduces the liquor into the top of the digester, at the same time heati' exit. The circulation of liquor, of course, depends on a difference in pressure between thesteam supply and `the'interior of ,the digester :and the' circulation, rapid at first, gradually slows down-as the liquor is heated up and 40 the pressurein the digester approaches that of the steam supply,- when the digester is said to be up to pressure. In order to `continue circulation, itis thennecessa-ry to lower the pressure in the digester which is effected by bleeding steam in to the atmosphere until the pressure-drops sufficiently to cause a resumption of circulation. The heat represented by this steam is lost and as in the ordinary cook, it takes about 2 `hours to bring` the digesterA up to pressure and thereafter, steam must be bled about every minutes for vanother 3 or 4 hours, the

lloss of'steam is high and a further` disadvantage lies in the fact that the circulation is uneven, being fast at first and slowing up Vgradually as the digester comes up to pressure, in m'ost cases practically ceasing, until steamjs bled when circulation aga-in starts i at a fairly rapidrate and again slows down as the digester comes up to pressure. In the ordinaryv process,- therefore, circulation; is

uneven and relativelyI slow l*and considerable amounts of steam'- are wastedby bleeding-- into the atmosphere, f `Atj the completion 'of the", cook, a Valve is 'opened in a large pipe -connected to the lower portion of the digester and steam, pulp and liquor is forced out into the'open tank called a blow pit where the steam escapes into thel atmosp iere and is wasted, entailing -a loss in the soda process of about 2200 pounds of `steam per cord' of wood. or when translated vinto terms of fuel, about 314 pounds of coal; 1

The pulp and liquor is also considerably cooled in the blow pit and is then passed.

'into large tanks provided with perforated 'bottoms' and knownas' wash pans where the liquor is'allowed to drain ofi' into a large liquor reservoir 'or tank and thepulp is successively washed with we'ak'spent liquor and vwith water, the last washing producing the spent liquor to be used in the first washingof the. next batch. The water used .is

` usually cold or at most warm and both 'the spent li uor and concentrated wash liquor produce are considerably cooler than the original liquor present. As 'a result, a large amount of heat is lost by cooling of the liquor and since it is customary to concentrate the liquor and burn itin a rotary furnace in order to recover itsinorganic solid content, additionalsteam is required to heat the liquor up in the evaporator and the `loss in heat therefore constitutes a direct waste.

' The customary processes are also open to the disadvantage that when the. pulp is 'washed with cool or warm liquor or water'.

much of the lignin which has been loosened and partially dissolvedby the cooking procturn heated ,by y. steam `taken from ,the l .di-v ester and which w`ould otherwise bewasted 1f the Vdigester were blown into a blow pit as in `the' usual process.' I have alsor described `in the above mentioned application the use ofihot water or liquor' .for washing the pulp in order to prevent setting ofthe lignin and tov remove it as thoroughly as possible, at the Sametime preventing lower ing of .temperature'of thespent liquor after the concentrated washliquor is added to 1t.

The lpresent application is in part a continuation of my aforementioned application and includes improvements in the process therein described.

It is an object of the present invention to retain the heat economy of the process of my prior application, above referred to, and at f i invention is in no sense'limitedy to soda and the same time to increase the elliciency and speed of the cooking process itself, Other and `further objects 'and'advantages of my invention will ,be apparent from the followconnection with'soda and sulfate I' cesses inwhich the present invention pre;` supe-A culiar. advantages.' `Many ofthe ad". antages,y

however, are available inl the sullite Aprocsulfate processes'. n 'According to` the present invention, wood or other cellulosic material is cooked with a soda or `sulfate liquor in a 'digester of design similar to that described in my prior application and provided with a liquor chamber and chip chamber separated by a perforated plate, the upper portion of the chip chamber constituting a steam space.

The steam space of the digester is connected ,as shown therein to the steam space of the evaporator through a pipe'provided vwith a suitable control valve and reducing'valve.

Instead, however, of operating the digester' -in the usual manner, thatris to say, introducing steam until the digester comes up to pressure and then bleeding at intervals to maintain circulation, I providefa control to' maintaina permanent minimum pressure differential between the interior of the digester 'and the source of steam supply so that assoon as the pressure in the digester approaches 4that of the steam supply, steam will be continuously bled into the evaporatorv to/maintain the predetermined differential and lcorrespondingly a predetermined speed of circulation. The differential may be brought` about in any ,suitable manner by means of automatic valves, by manual con- 'trol or in anyother desired or .convenient Instead of providing a'vigorous circulation of liquor only when the pressure in the digester .and correspondingly the temperature of the liquor `is relatively low, I provide a continuous, vigorous circulation up to ting oflignin.

the maximum temperature of tlevdi-gester I and by this means, I am enabled to cookl more quickly and more thoroughly andfto produce a pulp of higherquality and freer from,` shives, and .at the same time, I am enabled to reduce the period of cooking v' i' without deleterious effects on the'pulpand Without strengthening the concentration of the liquor whichJ permits Ame to'produce a.A I libre Which-is relatively less attacked than,

inthe ordinary process and yields a pulp and. paper which is stronger, moreuniform and more satisfactory. All these advantages j are obtained Without any further'co'nsump-` tion of fuel or waste of steam since the increased amount of steam bled to providefor vigorous circulation is all utilized'. i The treatment ofthe pulp and liquorgafter the ,cook is complete'dris the same as in myprior application, `that is to say, when the cook is completed, steam is exhausted' to the evaporator and liquor is permitted to drain olf either directly into the evaporator or into a receiving tank in whichit is notpermitted to ,becomel cooled much below its boiling point at atmospheric pressure. lashing is then carried .either by. water or by dilute wash' liquorthfe lhot water or hot liquor being introduced into the upper portionofthe digester. The pulp is `thus maintained at a high temperature preferably 1n the neighborhoodv of 180-212o F., and innowcase below'lllOo F., 'so that there is no serious se't-V i the `concentration is sufficient, the wash liquor and passedlthrough the evaporator.

It will be seen that I retain the advantages of the method of my prior application in that the pulp is washed hot and'lignin is not permitted to set and at the same time a Vhere desired and where Vliquor may be ffiixed with the'original spent rapid and thorough draining of liquor under the slowly diminishing steam ypressure inthe generator is obtained andlittle or no heat contained in the liquor is wasted. lIn addition, my present inventionpossesses the ad vantages of enhanced speed of circulation which is accurately under the control of the operator and which can be varied to suit the particular conditions of individual cooks.

The steam bled from the digester during cooking -passes through a reducing valve into the evaporator which may be of any type, such as, for example, the well known Yaryan evaporator described in my prior' lapplication. The flow ofbled steam is usually not in excess of that required to run the evaporator and is generally a' smaller' quantity. lWhen, however, a digester is blown, the sud-h V'den increase in'steam, even vhen passing through a reducing valve, maybe invexce'ss of that which can be effectively taken care of by the evaporator and this is particularlytrue where the evaporator runs with low pressure steam, for p example, 25 lbs. as

1an f against about -126 lbs., which is common I practice in the digesters. It may, therefore, happen that when a 'digester is'blown, the

evaporator cannot take ca'i'e v of. the large amount of steam given .oisuiliciently rapidly ,and the digester may, therefore, drop in pressure too slowly.v In order to permit the digester toempty ata speed sufficient to reduce its pressure approximately to that of the evaporator within a eriod of time about sufficient to drain'the -pu pI preferably provide for the utilization of the excess steam in heating the yivater which is .to be used for Washing th'e pulp in the digester orfor heating dilute wash liquorwhere this is employedin a tivo-stage wash. This portion of the steam may be taken oft from the main steam line theevapora-tor through a suitable manually controlled valve o r automatic valves may be provided, permitting steam to loiv into the evaporator as long as the pressure thereil remains beloiv a predetermined amount and permits steam flow. into water l orliquor heaters when the evaporator pressure' increases beyond a certain ligure. Any suitable type ofv water or liquor heater may `be used 'such as steam coils in series or parallel, or the steam may be directly injected into the water or Wash liquor. One form of heater is shown in the drawings, but itI should beunderstood that any suitable type of heater may besubstituted therefor.

The drawings illustrate diagrammatically an arrangement of apparatus, partly in section, embodying the features of .the present invention.

The digester 1,is similar in shape and construction to digesters used at present and is shown diagrammatically lWithout insulationin order to simplify the drawing.` Similarly,- allv pipes are shown as uninsulated,

lcont-ains the customary manhole .whereas in practice, of course, a suitable insulation will be provided. The digester is divided by the perforated -bottom 2.into a large chip chamber 3 and a smaller liquor chamber 4. A pipe .5 controlled by gate valve 6 serves for removing the pulp after cookingfand Washing. The digesterI hefad or charging chips andis further provided with a liquorspray pipe 8 and nozzle 9 and-a' steam relief pipe 10 controlled by a valve 11,

the liquorv spray pipe 8 being also provided With suitable shut- oil valves 12 and 13.

The liquor chamber 4`is connected to a steam injector 14 of conventionall design through pipe .15 controlled. by valve 16.

Pipe 1'7 provided with control valve 18 connects the injector 14 to a high pressure steam source, While pipe 19 connects the injector with the liquor spray pipe 8.

Asecond pipe 20 provided ivithia valve 21 leads from the liquor chamber 4 t0. the tanks 22 and 23 through the pipes 25 'and 26 controlled by the valves 28 and 29. A

-wash water tank 24 connected to a source of Water, (not shown), communicates with the bottom ofthe tank 23 through the pipe 31 provided with valves 32 and 33. The T connection 34 between valves 32 and 34 permits .the flow of liquor from tliepipe 31 into the wash liquor pump 30, which, in turn, is conpipe 35 and T 36, flow being controlled b the valve 37.

A liquor evaporator 27 of the Well known Yaiyan type takes liquor Afrom the tank V22v 'nected lto the liquor spray pipe 8 through the vthrough the pipe 38 by means of the pump 39. The steam space of the .evaporator is connected tovthe steam relief pipe 10 through .the pipes 40 and 41 and Ts 42 and 43, the

pipe 41 being provided with' the shut-oli valve 44 and the automatic reducing valve 45.bet\veen the Ts 42 and 43. This. pipe ex# tends beyond the T 42 and connects with the pipes 46 and 47, leading into the heater- 48 of tank 23 and the heater 49 of tank 24, respectively. An automatic valve 50 is also provided 'in the pipe 41 between the T 42 and the pipe 46 and a shut-oil valve 51 is incorporated in the samepipe beyond the connection with the pipe, 46. A by-pass pipe 52 protanks 22, 23 and 24 are shown diagrammatically and Without insulation, but it should be understood that in practice, the tanks, and

loo

particularly tank 22, together with the pipes 20 and 38 are heavily insulated'to reduce the loss of heat by radiation to a minimum.

In operation, the digester is charged with chips and liquor in the usual manner. The valves 6, 21 and 37 are closed and the valves 12, 13, 16 and 18 are opened. The valve 11 is automatically retained in a closed position by the diaphragm 58, which is controlledby the differential in pressure existing in the pipe. 1.9 and in the digester, the valve being set to openonly when the differential drops.

below a certain predetermined minimum, for example, 5 lbs., when the steam pressure in pipe 13 is about 120.

Steam rushes through the injector 14. picking up liquor owing through the -pipe .l 15 and sprays this liquor through the nozzle 9l onto the chips, the liquor flowing down through the chips and perforated bottom 2.

back to the li uor chamber 4. The steam not only causes t e liquor to circulate, but also gradually heats it up, thus gradually raising l the steam pressure in the chip chamber of fby closing the valve 60.

'the digester. When 'the pressure'within the digester reaches a lcertain gure, which may, 'forexample, bey 5 lbs. less" than the steam ressure, vthevalve 1l 'is opened and steam is lil'ed out through it.` This steam is permitted to -ow through pipe 41 byopening the valveV 44 and is prevented from es caping, tothe atmosphere through the pipef59- Steamis more or less continuouslybled through the valve 11 as long as the digester continues to cook and a continuous vigorous circulation of liquor is thereby insured which results in a very even quired After the cook is over, the steam valve V18 is closed'and 'the valve 11, of course, autocook and considerably reduces the time rematically opens, rapidly discharging steam through theL valves 21 an closed, the liquor thereby draining into tank 23 under the gravity head augmented-by the steam pressure in the digester. which is (pipe 41. At the same t1me,the

'I .lowered gradually through the valve 11 and pipe 41.

After the steam in the digester has dropped to the4 pressure 4existing inthe evaporator, rabout 25 lbs., valves 32 and 37 are opened and the pum is started, forcing dilute wash liquor rom the tank 23 through the pipe 35, T 36 and spray nozzle 9 into the digester. The' hotA liquor flowing through jthe. chips washes out some of the cooking liquor adhering to the chips and removes much of the softened and partially emulsiliquor.

tied lignin, the temperature, of course, being maintained at a high point, due to the fact that the liquor introduced is close to the boiling point. The wash liquor,l after passing through the chips and being enriched by the cooking liquor adhering to the chips,

flows through the pipe 20 into the tank 22v where it is mixed with the original spent After the washing witlrdilute liquor is complete, valves 28 and 31 are closed and valves 29 and'33' are opened, hot water from the tank 24 being circulated by means ofthe pump lthrough the pipe 35, connection 36 and nozzle 9 into the digestercompleting the washing of the pulp therein, the dilute wash liquor flowing through the pipes 20 and 26 into the tank 23. After the wash is comvplete, valves 2L 29,` 33and 37 are closed,

valve 6 is opened and valves '13 and 18 may also be opened, the pulp being blown out through the pipe 5 by steam pressure. 'After the pulp is blown out. valve 18 is closed and any steam condensed can be drained voff through the pipe 20 by opening thevalvesf 21 and 29. The digester is then ready for a second cook and the cycle described above is repeated.

Liquor from the tank 22, which has not 28 are opened and valve29 is f. l. l l

I 5 l" v been'coled to a substallntialjfdegre, iis continuously circulated bymeansof- -hefy 'pump 39 through the pipe 38' into the "rst `reflect `of the'ev'aporator and thisfow' of liquo'rlvvill,y

usually take place contin'uousl as in pr'ao- ,70-

tice a purality of digesters will be connected to a single set of water iquor' tanks and a .single evaporator, altho'ilig for simplicity, only a'single digesterfis illustrated in the drawing. Whenope'rating with a plurality 75 of digesters, for example 5 or 6, in the case of a mill of ordinary size, the digesters are cooked' and blown in rotation'sovthat one ,of

the digesters is always `bein blown or the pulp being washed therein, t us insuring a cooking and the after passing' through-the reducing valve 45 9 and being reduced in pressure from approximately 120 lbs., to about 25 lbs., it serves to heat the first eifect ofthe evaporator. `When however, the supplyxof steam is in excess of the heating requirements of the evaporator,

the pressure in the-pipe 40 gradually rises until it exceeds the pressure at which the valve 50 opens. Ordinarily, this openingl pressure is adjusted so that the valve 50 will open when the pressure materially exceeds 10 25 lbs., for example, the valve 50 ma advantageously open at 30 lbs.,ythe particular steam pressure ein dependent on the operating conditions o any iven installation.

When valve 50 opens, te exhaust steam 105 passes on through the pipe V41 and into the heaters 48 and 49, serving to heat up water in the tank 24V and dilute liquor in the tank 23. The flow through the heaters may be in series or in'parallel or a combinationA of 110 Y series and parallel as will be readily appar-` ent from a consideration ofthe pipe and valve connections. For most purposes, a. parallel circulation is advantageous as the heating demands of the . tanks 23 and 24 are n? not necessarily uniform 'and when a parallel flow is used by closing' thevalve-55 and opening valves 51 and 53,' the .proportion of steam flowing throught-he different heaters can be adjusted to suit varyin needs. v' i l lVhen 'a digester is first lown and the valves 21 and 28 are openedf-the liquor from the chip' chambers rushes into tank 22, Where the pressure is reduced .from about lbs., to 25 lbs. Since the liquor usually is' ap- 125 proxiniately at the boiling point under 120 lbs. pressure, a considerable evolution of 'steam will'take place in tank 22 and. this" steam passes of through the .pipe 56 controlled by the valve 5'( wliichmay be a 130 into the pipe 41 is that 86 manual valve, but is preferably a` check valve' as illustrated. Not only does the steam thus formed result in a removal of ,water from the liquor and reduce accordingly the amount of water which must be evaporated in the evaporator, but thisv steam is permitted to flow through pipe 41 and performs the additional function of adding its heat to thesteam used invheating the'first effect of the evaporator. Adouble saving is thereby obtained since an amount of watercorrespon'd'- -ing to twice the Weight of steam evolved in 'and if this first step is carried out with a high temperature, the water wash can be carried out at a somewhat lower temperature. Of course, the dilute wash liquor'will be Ysomewhat cooler, but this isnot a serious objectionas the waste steam from the digest- Yao er. is used to heat the spent liquor. Preferably, however,I heat both the water and the spent liquor and carry out the washing at a uniformly `high temperature.

-It should be understood that the tank 22 lis not of the same design as is the liquor receiving tanks of the ordinaryv pulp niill, On the contrary, the tank 22 is preferably kept as small as possible and is thoroughly insulated, thereby conserving the maximum amount of heat in the liquor.I

I have illustrated a process in which the pulp is washed in two stages and I have found that this process', which'follows'the ordinary practice of two-stage wash, is very satisfactory and constitutes thel preferred embodiment of my invention. It willbe un-A derstood, however, that it is perfectly practicable to wash in a single step with hot water where this may bev desirable for certain purposes. The Wash lliquor produced, however, becomes progressively. more diluteand if all of the liquor is to be evaporated, the amount of water which must he removed is very considerably increased. For this reason, the two-stage wash, first with dilute liquor and Athen with water, is generally economically more advantageous, although, of course, my invention is not limited to such a sequence.

` The pipe 59 and valve 60 are shown yas leading away from'- 'the steam circuit and mayeither lead directly to-the atmosphere,

acting-in the nature of an emergency valve i to reduce an excessive pressure,` for example `in the case of ,temporarystoppage in the pipe 4l, or the pipe 59 may vbe connected to other apparatus in the pulp mill which requires exhaust steam for heating purposes. Thus,

for example, acertain amount of steam may be led through the pipe 59 into drying rolls where theI pulp produced is made into rolls 'for shipment or where a pa er mill is combined with the pulpmill. ther apparatus requirin'gsteam heatfmay also be connected to the pipe 59, such as-for example, liquor heaters and the like. In'a similar manner, any steam passing out through the pipe 54? A may be 4utilized for further heating. In fact, excess steam may be tapped off froml v any portion of the exhaust steam circuit shown and utilized for'heating or for any other purpose. ,It should be noted that 'in the drawing th arrangement of steam pipes is shown purely y'diagra'mmatically and in no sense indicates the structural placement. Thus, for example, thel steam pipe 4l passes to a lower 'level than theheaters in tanks 23 and 24 in order to bviatea lconfusion of piping. `In

practice, of (course, the piping will usually,V be 'arranged so 'that there is a steady slope in o'rder' to provide for proper drainage of vcondensate -or, if. a steam pipe 'I passesas shown diagrammatically in the drawin suitable condensate'rtraps must be provide In general, ,it should be understood that in an actual installation, the arrangement of piping and. other accessories will be dictated 'by the same conditions as in an ordinary in,-

stallation and the present drawing is intended -merely to schematically" indicatethe steam circuits, without in'any sense limiting the apparatus placement or'structural' de slgn. t

Coil heaters are shown in tanks 23 and 24 and for many purposes, these heaters are very satisfactory. However, the liquor and water intanks 23 and 24 may be heated by direct injection of steam or by a combination of direct injection-and indirect heating by nlea-ns of steam coils, steam jackets or the 1 re. may also be used, for example, indirect heating in tank 23 and steam injection in tank 24. This system has the advantage that the 'hot condensate in tank 24' is added to the volume of hot water therein. -It, however, possesses the disadvantage that excessive steam flow may cause flooding of the tank. These reand the resent invention is not limited to any particular neating. design or arrangement.

A combination of these two methods;

, It is usually unnecessary to heat the liquor in tank 22,- but insome cases, particularly where a large number "of digesters are usedinvention `will 'be clear to those skilled, in`

` the art and are included within the scope of the invention.

` The lcharges of wood steam pressure and the likemay be substantially the saine in my improved process as in the ordinaiyprocesses which are at resent practiced in .producing soda and sulfate pulp. 'The more rapid circulation which is possible b means vof the present invention, however, requently permits a shorter cooking time ora reduction in liquor concentration or amountor both, the savings varying, of course, with the quality of pulp :desired and it is an advantage of the resent invention that pulp of a given Iqua ity can be produced from any given grade of wood with a minimum of cooking time and liquor strength. The particular balance of these factors will be determined by the pulp quality desired and by the value oi time saved in cooking. It is -an advantage of the present invention that it is adaptable to mills of the most varied design and canbe fitted in with advantage in plants having operating conditions of the most 'varied kind.

Whatis claimed as new' is: 1

1. The method of cooking cellulosic mate rial which comprises subjecting the material to-A the action of a chemical liquor in a digester, circulating the liquor by means of steam, and continuously maintaining' such circulation by bleeding steam from the digester, said steam being utilized to heat the iirst eiect of an evaporator and passing the liquor after completing the cook. through gester, circulating tlie liquor said evaporator. 1 4

2. The method of ooking collulosicmaterial which comprises :subjecting the material to the action of a chemical li uor in a diy means of steam, continuously maintaining such circulation by bleeding steam from the digester,

said steam being utilized to heat the first effect of an evaporator, and passing said liquor without considerable cooling'into said evaporator.V @j v 3. The method of producing pulp which comprises cooking cellulosic material in ai digester 'with a chemical liquor, circulating saidliquor by means of steam, maintaining .a continuous circulation -by-bleeding steam from the digesteriiit the irst effect of an evaporator, rcontinuing the bleeding until the cook is completed, blowing steam from chips and liquor,

the d'igester intolthe evaporator, removing A the `liquor from the'cookedI material, and

liquor through the evaporator.

4 The method according to claim V3in which the pulp is washed in the digestierat i a` temperature suiiciently elevated to prevent setting of lignin to a substantial extent. 5. The method according -to claim 3V in' .which the pulp is washed in the digester first with dilute wash liquor and thenvwith water at a temperature'sutliciently high to prevent substantial setting of lignin, the concen- .withoiit lsubstantial cooling passingA said tiated wash liquor produced from the first stage beingmixed with the spent liquor drained from the chips and passed through the evaporator,

6. The method according to claim 3 in which the pulp is washed in the digester first with dilutewash liquor and then with water at a temperature sufficiently elevated to prevent lsubstantial settin of lignin and causing the steam bled an gester in excess oithe evaporator.. require? ments to pass in heat exchanging relation with the dilute wash liquor and with the Wash water whereby they are heated upto an elevated tem erature.

7. The metho according to claim 3 in which the spent cooking liquor after removal from the digester is permitted to expand to .a lower pressure without substantial coo'ling wherebysteam is evolved, and passing said steam through the steam portion ofthe evaporator. l

8. Apparatus for cooking cellulosic material comprising in combination a digester, a 4perforated partition in said diester separating it into a chip chamber'andl chamber, a source of steam under high pressure, means for introducing said steam into the chip chamber, means for causing said blown from the di-n liquor steam to inject liquor from the liquonchamber into the chi-p chamber, a steam bleeder pipe connected to the upper portion of the `chip chamber, a valve, said bleeder pipe connecting to the steam space of the evaporator, and means for continuously bleeding steam into the evaporator whenever the pressure differential between the steam source and the digester drops below a predetermined minimum.

9. An apparatus according to claim 8 in which means is provided for drawing oif liquor from the liquor chamber ofthe digester andintroducing. it without substan-JA tial cooling' intc'the evaporator.

10. Apparatus according to claimS v'in'- With a. reducing valve.

vIl. Apparat-us, according to Aclaim 8' in which a steam .bleeding pipe is provided which means are provided for introducing.

washing tluid into the chip chamber.

1 2. Apparatus for cooking cellulosie ma- I terial comprising in combination a ist;

provided with a perforated partition dividing it intoA a, chip chamber and a liquor chamber, a vsource of high pressure'steam connection from said steam source through an injector into the upper portion of the chip chamber, means for causing liquor to flow from the liquor chamber into the in jector, an evaporator, a 4steam bleeding connection between the chip chamber and the evaporator, means for electing continuous bleeding Wheneverthe pressure differential between the steam source and the digester interior falls below a predetermined minimum, means for blowingsteam into said evaporator, means for introducing Washing iiuid into the chip chamber, means for withdrawing liquor frorn the liquor chamber and introducing it into the evaporator 'without substantialcooling, pipe connections between the steam space of the evaporator and wash liquor heaters, and means for causing steam bled or blown to pass through said heaters whenever the steam supply is in excess of the requirements for beating the evaporator. `13. Apparatus according to claim 12 in which la reducing valve is provided in the steam bleeding pipe between the digester and. the evaporator, and an automatic valve is provided inthe connection between the evaporator and the wash water heaters, said valve being opened by a steam pressure in excess of that required for operation of the evaporator.

Signed at l/Villsboro, N. Y., this 6th day of September, 1926.

WALLACE H. HOWELL, JR.

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