US1864619A - Cyclic process of fiber liberation - Google Patents

Description

June 28, 1932. a. A. RICHTER CYCLIC PROCESS OF FIBER LIBERATION Filed Sept. 50, 1925 Patented am as, 1932 UNITE s'rA'ras PATENT OFFICE GEORGE A; arcnrmor 3mm, imw nmsnmn, assrsason r BROWN comm.

or BERLIN, imw means, A ooarona'rrox or Junta orcmc 230cm or'mna mam-nox- Application fled leptember when. Serial in. mm.

, This invention relates to the production of a cellulose pulp suitable for conversion into a paper whic that made from sulphate or kraft pulps so-ca'lled, and has for its. salient object to rovide a cyclic process for such ul prouction through the use of a cookln'g iquor comprising essentiallya mixture of sodium sulp ite, sodium sulphide and caustic soda. Incertam cases, if desired, either of the alkaline constituents, i. e., the caustic soda or the "sodium sulphide, may be omitted from the cooking liquor and the percentages of the other constituents so' adjusted as to yield a pulp substantially equivalent to that result- -mg from a liquor containing all the constltuents. In any event, however, the raw ce11ulosic material, e. g., wood chips, is digested in an alkaline solution of sodium sulphite, the alkalinity being afforded by the sodium hydroxide, the sodium sulphide, or both these alkaline constituents.

In attaining the hereinbefore designated object, this invention provides forthe recovery of the mineral or inorganic content of the spent cooking liquor in the form of chemicals which may be reutilized in the preparation of fresh cooking liquor. A feature incident to the use of a digesting liquor such as herein employed is that I am able to dispense with the use of lime, which, however, must be employed in the sulphate process in the causticizatiomof the soda ash re covered bythe smelting of the concentrated spent digesting liquor.

In the practice of the present invention, the various constituents of the cooking liquor are used in suitable proportion to effect a liberation of fiber, and the cooking or digesting operation is carried out at the desired temperature and under pressure until the cellulose fibers of the wood have been freed or liberated from the encrusting or cementitious material by which they are bound ,together. Thus, for example, I may employ a cooking liquor containing about 1.5% to 4.0% sodium sulphide. andabout 2% to 5% sodium sulphite. In such case, the digestion may be carried on in a closed digester from three to six hours, more or less, and at a hasa strength approximating sodium carbonate.

temperature as h as from; 335 to 345 F., to yield a pulp aving approximately the characteristlcs of kraft pulp, so-called.

The spent black liquor, which is separated from the pulp after the digesting operation and which contains the unspent sodium compounds, together with c'ombustible organic compounds, and spent sodium in the form of various organic sodium compounds, is now treated in a manner to' recover such compoundseconomically in a form for reutilization in the preparation of fresh cooking liquor. In such treatment, the waste liquor is evaporated to the desired degree of concentration, and isthen delivered to a furnace wherein nits combustible organic content is burned and its inorganic or mineral content is smelted in a reducing atmosphere and recovered in a form suitable for the preparation of a fresh cooking liquor, that is, substantially in the form of sodium sulphide and The smelt taken. from the furnace is dissolved in water and is then carbonated, as by bubbling carbon dioxide through the aqueous solution, to cause the liberation of hydrogen sulphide from the sodium sulphide and, accordingly,- the conversion of substantially the entire smelt solution to a solution of sodium carbonate. The sodium carbonate solution is then acidified with sulphur dioxide to cause the liberation of carbon and the production of a solution of sodium sulphite. The carbon dioxide liberated during the acidification of the carbonate liquor is recovered and employed in the carbonation of other smelt liquor, and the hydrogen sulphide liberated during such carbonation of the smelt liquor is recovered and employed in the preparation of the fresh cooking liquor. The hydrogen sulphide liberated during the carbonation of the smelt liq- 'uor is recovered in the form of a sodium salt.

bonate liquor. When there is insufiicient hytion of the smelt liquor to effect a conversion of all the make-up caustic soda into sul hidef the cooking liquor'will consist essenti y o a mixture of sodium sul hide, sodium sulbite, and caustic soda.- f desired, the hyrogen sulphide liberatedduring the carf bonation of thesmelt solution may be burned to sulphur dioxide, which may be commingled with other sulphur dioxide used to convert the carbonate solution into a sul hite solution; and the make-up caustlc a may be added, as Such, to tlhe sulphitesolution to roduce a igestin iquor 'con ammg essentially onl sodium sulphite and caustic soda as the p ping chemicals. Thus, the loss of sodium constituent in the cycle is compensated for by the addition of the necessary caustic soda, as previously indicated, and the loss in sul hur constituent is made up durlng the acidification of the carbonate solution by the addition of sulphur dioxide produced by the combustion of sulphur or sulphur-bearmg material. In fact, after the process is in oporation, practically the only chemlcals WhlOh are needed for making up losses are sulphur or sulphur-bearing material and caustic soda.

. The invention may best be understood from the followin more detailed disclosure'thereof, when consixfered in conjunction with the accompanying drawing, which may be termed a flow sheet and in which I have illustrated diagrammatically and conventionally some e instrumentalities employed in the process and have indicated the course of the various solid, liquid and gaseous materials.

Referring to the drawing, at 1, I have shown a digester which is preferably of the type usually employed for alkaline cooking. The digester is first filled with wood chips and the necessar quantity of alkaline liquor, e. g., a cooking l iqpor containing, say, 1.5% to 4% sodium sulp ide and 2% to 5% sodium sulphite, is then pumped into the digester.,

e dlgester is then closed and its contents are gradually heated to, say, 335 to 345 F., whereupon the cooking is continued for a period of time to ensure complete fiber liberation, tests being made in the usual manner from time to time until the cooking or fiber liberation is judged to be com lete.

After the cooking operation as been completed, the contents of the di ester are blown through a blow pipe 3, valve as at 4, into the usual blow pit indicated at 2. It is now necessary to separate the pulp from the spent liquor and to wash the pulp substantially free of such liquor and entrained products of reaction prior to its passage through the usual screens which are employed for removing the so-called screenings therefrom, which consist of knots, shives, particles of brick, cement, etc. For this purpose, the pulp and spent liquor associated therewith are re- 24 washers indicated conventionally at 6. The

washing machine is preferably of the counter-current t e, substantially like that illustrated an described in U. S. Letters Patent -No." 1,421,664, to Brown, Martinson, Moore & Parker, dated July 4, though, if desired, the ordinary rotary vacuum type of washer may be employed. In the washer of the patent referred to, the pulp is carried continuously through tanks in one direction, and the wash water is car ried successively through suchtanks in the opposite dlIGCtIOIL- The wash. water is introduced through a pipe 7 to the pulp delivered at the last washer of the series, from which the washed pul is delivered by a pump 8 througha con uit 9 to the usual screens (not shown The wash water containing substantial y all the, spent liquor originally associated with the pulp is dis- 1 charged from the first pulp washer of the series through a valved conduit 11 into a storage tank 13 which may also serve to receive spent liquor from the pipe 2a communi- "catin with the bottom of the blow pit. It may e desirable to re-employ a portion of the spent black liquor, together with freshly prepared liquor, for the digestion of other raw cellulosic material, in which case spent liquor may be withdrawn through an outlet pipe 12 by a'pump 14 and circulated to the digesters through a pipe 126.

Atv 15, I have illustrated conventionally a IOU series of multiple effect evaporators, the dewhich the spent liquor is delivered at the desired rate, by a pump 140, from the tank 13 through a pipe 16. While I preferably employ multip e effect evaporators, any other tape of evaporator for removing a part of t e aqueous content of the liquor may be used. From the last efiect 15d-of the evaporators, the liquor which has been concentrated to, say, about 16 Baum, and which contains about 25% solids, is passed through a pipe 17 into a storage tank 18, from which it is withdrawn for the combustion of its organic content and the smelting of its inorganic compounds to form the sulphide and carbonate.

To this end, the concentrated spent li nor in the tank 18 is now subjected both to eat and pressure to generate an ex losive efiect therein, substantially as descri ed in U. S. Letters Patent No. 1.326,414 to Moore and Quinn, dated December 30, 1919, and, as a shown, is withdrawn from the tank 18 through a conduit 20 provided with a valve, as at 21, by a pump 22 a circulatory heating system including the pipe 23 and a heater The liquor in passing through the system is heated a temperature above the boiling point by the heater 24, from which it passes through a pipe or series of valved pipes 25, terminating as nozzles 25a extendmg into a furnace indicated as a whole at .26. In the present instance, it is desired that.

the sodium compounds recovered from the furnace should contain sodium sulphide and sodium carbonate. If this recovery takes.

lace in a reducing atmosphere, there is no ifliculty in recovering the desired salts, although, with these salts, there may be a sli ht amount of sodium sulphate, sodium sufiihite, and caustic soda. In other words, the com osition of the smelt is more or less compara le to that of the usual kraft or .sulphate smelt.

The gas leaving the furnace contains some sulphur dioxide resulting from the decompo sition'of the sul hur compounds and also some sublimed so ium' carbonate and sodium sulphide so that provision is made for the recovery of these chemicals. As shown, the gasesemanatingfromthefurnaceareeonduct ed through a stack 28 into the loose end of a 'scrubbin tower, indicated as a whole at 30, filled wit inert interstitial material and in counter-current flow to spent liquor diverted from the (pipe 16 by a pipe 33 entering the upper en of the .tower. The spent liquor dissolves the sulphur dioxide and the sublimed sodium salts of the furnace gases during its downward passage throu h the tower, and collects at the bottom 0 the tower, from which it is withdrawn and returned by a pipe 35 to the tank 13. Any gases which do not dissolve in the spent liquor circulated through the tower are permitted to emerge through a vent 30a.

The smelt produced in the furnace, consisting essentially of sodium sulphide and sodium carbonate, is delivered from spouts 36 to a dissolving tank 37 containing water supplied thereto at seasonable temperatures from a water conduit 39 providedwith a valve indicated at 40. The smelt delivered from the furnace into the dissolving tank yields a hot solution which may contain a certain amount of solid impurities. Such impurities are referably removed from the smelt liquor y filtration before the liquor is carbonated.

The carbonation of the smelt liquor maybe accomplished either by bubbling carbon already indicated, sodium carbonate and sodium' sulphide, wherefore, the carbon dioxide by reaction with the sodium sulphide forms sodium carbonate and generates hydrogen sulphide.

In the present instance, the smelt liquor is withdrawn at the desired rate from the tank 37 for carbonation through a pipe 41b a" pump 42, which forces the liquor throug a lter 43 and thence through a pi 44 to the to of a carbonatin tower, intiigated as a w ole at 45, 'which is packed with inert interstitial material.

In accordance with the present invention I carbonate the smelt liquor with clean and substantially ure carbon dioxide obtained during the acidification of the sodium carbonate solution.

The carbon dioxide is passed into the lower end of the tower 45, and comes into intimate contact with the downwardly flowing smelt liquor. The rates of delive of the smelt liquor and the carbon dioxide into the tower are controlled so that a liquor which is conducted from the top of the .tower 45 through a valved outlet ipe 47, into a gasometer indicated conventionally at 48, from which it is drawn for use either in converting to sodium sul hide the caustic soda liquor employed for ma ing up losses in the cycle, or to be burned in air to sulphur dioxide, which is employed in the acidification of the carbonate liquor.

-The carbonate liquor produced in the tower 45 collects at the bottom thereof, and is withdrawn through an outlet pipe for delivery into a mixing tank 51 for conversion into sulhite. Before conducting the carbonate iquor into the mixing tank, however, it may be desirable to introduce a small quantity of chlorine into the pipe 50, as through a pipe 50a, to oxidize any residual sodium sulphide into sodium sulphite or sodium sul hate.

This avoids reaction of the sodium su phide with sulphur dioxide during acidification and the attendant formation of sodium thiosulphate or the precipitation of sulphur either of which might give rise to objectionable mercaptan odors or the discoloration of the pulp during the digesting process.

In the practice of the present invention, I preferably employ the equivalent of a substantially pure sulphur dioxide for the acidification of the carbon ate liquor. This may be had by treating such liquor with a solution of sulphurous acid produced, for example, by dissolving in water the products of combustion of the hydrogen sulphide liberated in the carbonating tower. Since practically no inert or insoluble gas accompanies a sulphurous acid solution, the carbon dioxide liberated from the carbonate liquor during acidification is practically undiluted by inert gas, and can consequently serve as the gas to be employed in, the carbonating tower for the liberation of substantially pure hydrogen sulphide.

sodium sulphite without the carbonatingtower.

The sulphurous acid solution is delivered through a valved conduit 52 into the mixing tank 51 in amount sufiicient to efiect' a complete conversion of the sodium carbonate to however, introducing an excess which would dilute the carbon dioxide liberated thereby and rising to the top of the tank, from which it is delivered through the conduit 100 into the lower end of It is thus seen that the carbon dioxide liberated during the acidification dioxide of' the sodium carbonate liquor is employed for the carbonation of the smelt liquor, and is again liberated as carbon dioxide during the acidificatlon of the resultingr carbonate solution.

he sulphurous acid solution emplo ed foracidifying the carbonate solution can e prepared by dissolving in water sulphur d1ox1de obtained from any suitable source, as through the combustion of the recovered hydrogen sulphide or sulphur-bearing material. Any suitable method of forming a sul hurous a c1d solution may be employed, as y bubbling the sul hur dioxide through water (refrlgerated, i desired, so as to secure a maximum concentration of S0 or by passing it into counter-current contact with such water through one or more towers arranged 1 n series. As shown on the drawing, sulphur 1s fed in molten state from the tank 55 into a rotary sulphur burner 56, wherein the sulphur is burned in the presence of atmospheric air, and wherefrom t e products of combustion of the sulphur are conducted into a combustion chamber or stack 58, wherein the conversion of all sulphur vapor to sulphur dioxide is completed to form a as comprising about 16% sulphur dioxide. he gas passes into a coolin and scrubbing tower indicated conventionalIy as a whole at 59, wherein the gases are more or less cooled and purified. The cooled gas istaken through a conduit 61 by a blower 62 and forced through a conduit 63 into the lower end of a tower indicated as a whole at 64, which is filled with a mass of inert interstitial material. The tower is supplied at its u per end with water from a valved pipe 65, the water absorbing the SO, gas passed in counter flow thereto.

In case the hydrogen sulphide is burned and recovered as sulphur dioxide, the hydrogen sulphide stored in the gasometer 48 is taken therefrom at the desired pressure and velocity through a gas pipe or pipes 67, provided-with regulatmg valves as at 67a, and terminating with nozzles or jets 68, which extend into a gas furnace indicated as a whole at 70. The hydrogen sulphide gas issuing from the nozzles is burned in the presence of air to form sulphur dioxide and water, the amount of air introduced into the furnace being accurately regulated to ensure complete combustion without the presence of unnecessary diluting air. The products of combustion(,) after cooling, contain about 10% to 11% S and may be commingled and em loyed together with the cooled and more or ess puri ed sulphur burner ases in the preparation of a sulphurous acid solution.

0 this end, the combustionproducts of the hydrogen sulphide in the gas furnace 70 may pass therefrom through a conduit 71, and thence through a suitable cooler, for examplei 61 and mixed with the sulphur burner gas.

By properly regulating the flow of gas from the sulphur dioxide sources and the rate of flow of water delivered-into the tower 64, a

2% sulphurous acid solution is obtainable at the bottom of the tower. This solution can be taken from the tower through an outlet pipe into a storage tank 76, from which it is drawn by a pump 77 and delivered through the pipe 52 into the mixing tank 51 in regulated amount. Any gases not absorbed by the sulphurous acid solution in the tower 64 are allowed to escape through a vent 176 at the top of the tower.

When all the hydrogen sulphide available from carbonation of the smelt liquor is burned to sulphur dioxide, the finished cooking liquor will be made up from the sodium sulphite solution in the mixing tank 51 and the caustic soda used for makin up sodium losses occurring in the cycle. .lhe sodium sulphite solution will in such case be conducted from the mixing valved pipe 177 to the stora e tank 78, and the coo 'ng liquor be finis ed by adding thereto sodium constituent in the form of caustic soda solution taken from a storage tank 80 through the valved pipe 81'. The finished cooking liquor may then be withdrawn from the tank 78 by a pump 90 and tank through a able to provide a cooking liquor containing sodium sulphite and sodium sulphide or one containing sodium sulphite, sodium sulphide. and caustic soda. In such case, in place of burning the hydrogen sulphide to sulphur dioxide, the hydrogen sulphide is used in convertin the caustic soda solution employed for ma 'ng up losses in the oycleinto sodium sulphide, as by bubbling the hydrogen sulphide thereinto, or by passing. the caustic soda solution through one or more towers arranged in series in countercurrent contact with the h drogen sulphide. As shown, the caustic soda solution is fed from a storage tank 83 into the upper end of an absorption tower, indicated generally at 85, and containing a mass of inert interstitial material. The lower end of the tower may be supplied with available from the carbonatin just the quantities and relative 1 amen dium sulphate mayalso be'preeent, dependhydrogen sulphide from a conduit anomglaniiitingwith the conluit 47. d'fhzggmtifi a quor :11 passing ownwar y the tower under neutralization by the 4 hydrogen sulphi e, resulting in a solution of sodium sulphide, which collectsat the bottom of the tower and which may be conducted therefrom through a valved outlet pi 88 to the tank 78, from which it may be wit drawn m for use in the di esters. It is evident that cient hydrogen sulphide tower to convert all the caustic soda to so um sulphide, the liquor leaving the tower 85' will consist if there is ins of a mixture of sodium sulphide and caustic soda, so that the finished or prepared cookin liquor in the tank 78 for digesting the W0 chips will consist essentially of sodium sulphite, sodium sulphide, and some caustic 2e soda. Any inert gases accumulating at the top of the tower may leave through the vent 85a.

By the control of the various instrumentalities employed in the process, one may adroportions of sodiumsulphite,sodiumsulphi e,andcaustic soda in the finished cooking liquor. The

v higher the percentage of sodium sulphite or caustic soda, the closer ,the final ulp approaches kraft pulp in character. asmuch as there is a certain limiting amount of caustic soda which may be used to replace losses in the cycle, if the proportion of caustic soda in the cooln'ng liquor is to be increased beond this amount, it should be accom lished y the causticization of a portion of t e carbonate liquor with lime. The preferred procedure, however, is one wherein all the canstic soda is converted into sodium sulphide by hydrogen sulphide, the remaining sodium present in the form of sodium sulphite. uch a liquor has .a less drastic effect on cellulosic material than when a portion of the make-up sodium con- 3 stituent remains therein as caustic soda, and

thus yields a stronger pulp which more closely approaches kraft pulps.

'It is evident that in the practice ofthe procass herein described, it is possible, though not ordinarily desirable, to recover a part of-the hydrogen sulphide coming from the carbonating tower in the formof sulphur dioxide,

and-the remainder in the form of sodium sul phide, so that one may simultaneously prac-' tise both forms of sulphur recovery. The'sulphur of the hydrogen sulphide is in any event recovered as a sodium-sulphur salt, to wit, either sodium sulphite or sodium sulphide,

and thus is re-employed in the digesting op.-

eration. The cooking liquor is thus formed of a soluble sodium sulphur salt, e. g., sodium sulphite, and rendered alkaline by caustic soda, or sodium sulphide, or both, as hereinbefore pointed out. A slight amount of sou 11 conditions of'reco vh rtIclaimis: 'very 1 1. A process which com rises cookin raw cellulosic material in an a aline solution of sodium sulphite; separating the pulp from ganic content and burning the combustible "content ofsuch spent liquor; recovering the 'mor nicsmeltedcompounds;and as the pr nets of combustion from such sm ting operation in contactv with like spent liquor for the recovery of the soluble content of such products of combustion.

2. 'A'process which com rises cooking raw celluloslc material in an a aline solution of 7.0 the spent cooking liquo'r;.smel ting the inor- I sodium sulphite; separating the pulp fromthe tion of the smelt; and recovering the sulphur of the hydrogen sulphide liberated in such carbonation in the form of sodium sulphide.

3. A rocess which comprises concentrating and urning the combustible content and smelting the inorganic content of spent liquor result from the di stion of raw cellulosic materia in analka e solution of sodium sulphite in a manner to produce sodium sulphide and sodium carbonate; recovering the smelted inorganic compounds in water; carbonating the smelt solution; recovering the sulphur of the hydrogen sulphide liberated in such carbonation in the form of a sodium salt; acidifyin thecarbonate solution with a solution 0 s phurous acid; and recoveri and utilizingthe carbon dioxide liberated in such acidification in the carbonation of other smelt liquor.

4. A rocess which comprises concentrating and urning the combustible content and smelting the inorganic content of spent liquor resulting from the di estion of raw cellulosic material in an a aline solution of 5.- A rocess which comprises concentratting an burning the combustible content and smelting the inorganic content of spent liquor resulting from the digestion of raw cellulosic material in an alkaline solution of sodium sul phite in a manner to produce sodium sulphide and sodium carbonate; recovering the smelted inorganic compounds in water; carbonating the smelt solution with substantially ure carbon dioxide and controlling such car onation .to produce substanti'allypure produce a substantial y pure carbon,dioxide;

and recovering and utihzing such carbon dioxide in the carbonation of other smelt liquor.

6. A process which comprises concentrating and burning the combustible content and I smelting the inorganic content of spent liquor resulting from the digestion of raw cellulosic material in an alkaline liquor containin sodiumsulphite in a manner to produce so ium sulphide and sodium carbonate; recovering the smelted inorganic compounds in water; carbonating the smelt solution with substantially pure carbon dioxide and controlling such carbonation to produce substantially pure hydrogen sulphide; recovering such hydrogen sulphide; acidifying the carbonated solution with substantially pure sulphur dioxide to convert the sodium carbonate to so.- dium sulphite and controllin such'acidification to produce a substantia ly pure carbon dioxide; utilizing such carbon dioxide in the carbonation of other smelt solution; treatihg .a solution of caustic soda employed for making up losses in the rocess with said recovered hydrogen sulphide or conversion into sodium sulphide; mixing said treated solution with said sodium sulphite solution; and employing the mixed solution for the digestion of other raw cellulosic material.

A process which comprises digfsting raw cellulos1c material in an alkaline 'quor containing sodium sulphite; concentrating and burning the combustible content and smeltin the inorganic content of spent liquor resu ting from such digestion in a manner to roduce sodium sulphide and sodium caronate; recovering the inorganic smelted compounds in water; carbonating the smelt solution with carbon dioxide and controlling such carbonation to produce substantially pure hydrogen sulphide and to efiect a conversion of substantially all the sodium sulphide to sodium carbonate; recovering the sulphur of such hydrogen sulphide in the form of a sodium salt; acidifying the sodium carbonate solution with a solution of sulphur dioxide and controlling such acidification to produce a substantially pure carbon dioxide and a sodium sulphite solution; and utilizing the carbon dioxide obtained in such acidifi-' cation for the carbonation of other smelt solution. o

8. A process which comprises digesting raw cellulosic material in an alkaline cookering the smelted inorganic compounds in water; carbonatin the smelt solution with carbon dioxide; acidifyin the carbonate solution with sulphur dioxi e to produce a solution of sodium sulphide; recovering the hydrogen sulphite-liberated in such acidification in the orm of a sodium salt; and addmg sodium constituent-to said liquor in the form of caustic soda for making up losses in the cycle.

9. A rocess which comprises cooking raw celluloslc material in an alkaline solution of sod um sulphite and sodium sulphide; se aratlng the pulp from the spent cooking iq-' uor; smelting the inorganic content and burning the combustible content of such s nt liquor 1n a reducing atmosphere to pro i ice sodium sulphide; and recovering the inorganic smelted compounds for reuse in the cookin of other cellulosicmaterial.

10. process which com rises cooking raw cellulosic material in an all aline cooking liquor containing sodium-sulphur compounds; separating the pulp from the spent cookin liquor; burning the combustible content and smelting the inorganic content of such spent liquor in a reducing atmosphere to form sodium sulphide; recovering the sodium sulphide in water; carbonatin the sodium sulphide solution to sodium car onate; and aciddioxi e.

In testimony whereof I have aflixed my signature.

GEORGE A. RICHTER.

ifyin the carbonate solution with sulphur

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