US2383684A - Process of continuous alkali treatment of fibrous material - Google Patents

Description

1945- J. c. F. c. RICHTER 2,383,684

PROCESS OF CONTINUOUS ALKALI TREATMENT OF FIBROUS MATERIAL Filed April 29, 1942 a Sheets-Sheet 1 Aug. 28, 1945'- J. c. F. c. RICHTER PROCESS OF CONTINUOUS ALKALI TREATMENT 01f FIBROUS MATERIAL Filed April 29, 1942 s Sheets-Sheet 2 Jnrenzar:

Johan Clzrisfof'/er Fred/'I'A' 6ar/ Rig/afar 5 y Horn 5 I 1945- J. c. F. c. RICHTER 2,383,684

PROCESS OF CONTINUOUS ALKALI TREATMENT OF FIBROUS MATERIAL Filed April 29, 1942 .3 Sheets-Sheet 3 Johan C/znsfof/er Fre ri/r Car/ Ric/Men By 6 M Patented Aug. 28, 1945 I I mocass or CONTINUOUS snxsu manmmor muons MATERIAL Johan Ghristoii'er I'redrik Carl Richter, Oslo, Kamsr.

' Norway,

assignor to Aktiebolaget Karlstad, Sweden, 0. company of Sweden Application April 29, 1942, Serial No. 440,968

In Sweden November 8, 1940 v comm. (01. 92-13) This invention relates to a process of continuous alkali treatment of fibrous material, i. e. material cdnsistingof fibers, such as cellulose fibers produced by digestion of 'ilber-containing raw materials. The fibrous material to be treated may or maynot have been previously subiected to chlorinationfa'nd concentration.

The course of this alkali treatment process is determined, inter alia, "by two' factors, namely the strength of liquor and the temperature used. The higher consistency that the fiber pulp possesses, that is to'say. the less water it contains,

These difilculties and inconveniences are elimiment that a uniform distribution of the alkali in the less quantitiofalkali is obviously required "to obtain a" certain'des'ire'd strength of the liquor, and the l'ess heat is required to attain the required temperature. But in practice the possibility of utilizing a high consistency of the fiber pulp is limited by the necessity otefi'ecting an eificint mixture of the fiber pulp or material and the liquor, jandhlso by the difilculty. oi eflecting eom'eyance of fiber material possessing a high l consistencyfthrough the apparatus used and the V discharg -oi such material from the apparatus ai'ter the treatment has been finished. In view o'f'theseia'ctors a consistency 01' between and lapel-cent of the mixture of fiber material and ilquorhashithertoben regardeda s the highest consistency possiblefin actual-practice. At the said consistency of from"l5"to:" l8 per cent it is p s ible to f'eedthe mixture or pulp into and discharge-tl iesame from the tower'or tank in which the" a ka i treatment is carried-out ut to attain the said consistency it is necessary to overcome certain dimculties. it 'will beobvious that for obtaining the saidfconsi'stencyof 15 to 18 per cent of the mixture of fiber material and liquor,'

the material supplied to the-mixing apparatus must previously" have been concentrated to a higher consistency, for instance 20 to 2 5 per cent. f 'lihis necessitates the use of grooved presses or etherapparatus-suitable for the purpose, which obviously increases the cos't'of the plant as well as of";the operation. 'At'the consistency menudned' dimculti es are also met with inattaining an efilcient'mixture oi the fiber-material and the liquor, sincelforder not to dilute the pulp more than absolutely necessary, the liquor'inust be 'added in a'concentrated state, that is to say, in

the material is effected, and so that the mixture of material and liquor obtains such consistency that it can afterwards be conveyed to a reaction chamber as a fiowing liquid. Before or simultaneously with the introduction'of the mate, rial into the reaction chamber, so large a quantity of liquor is separated from the mixture 'orpulp that the material entering the reaction chamber possesses the desired concentration which is suitable for the reaction to take place in said chamber. The separation oi surplus liquor from the mixture to obtain the desired concentration of the material before the introduction of the sameinto the reaction chamber, may preferably be carried out by pressure, and such pressure may be suitably be utilized also to effect the introduction of the material into the reaction tank and to feed said material into and convey it through said tank.

Accordingto this invention, therefore, the operation is carried out with a surplus quantity of 'thus circulatethrough the system.

When the'process is carried out with the use of V a circulating quantity of liquor, a portion of said small iiuantities, and it is ofcburse very diflicult to obtain a uniform distribution'of these small quantities in the concentrated mass of material, particularly in view' ofithei'act that the material will easily roll into balls the mixing operation instead of breaking up and becoming dispersed in the liquor.

circulating liquor may be used, according to a further embodiment of the inventioniforthe purpose of'rem'oving by displacement some of the water contained in the fiber material to be treated before such material is supplied to the mixing apparatus, the remaining portion of the circulating liquor being supplied as a diluting liquid to'the mixing apparatus for thepurpose of producing th e desired uniform distribution oi the alkali liquor'in the fiber material and a suitable consistency' of the mixture for enabling it to'be conveyed as a flowing liquid to the'reaction tank. In order to secure the desired concentration of the material suitable for the treatment oi the same in the reaction chamber, the mixture is also in this case relieved of the surplus quantity of liquor before or in connection with the introduction of the material into the reaction chamber. The quantity oi liquor thus removed from the material corresponds substantially to the quantities used for the displacement operation and for the dilution of the material in the mixing apparatus, and is returned as circulating liquor to be re-used for the some purposes.

By utilinng in this manner a portion of the circulating liquor for displacement of some of the water contained in the material supplied to the process, the necessity is avoided of using grooved presses or the like for removing the water, and the problem of supplying the material with the least possible content of water is thus solved in a simple and emcient manner. The liquor used for the displacement operation remains in the fiber material and is conveyed with the latter to the mixing apparatus where is cooperates with the portion of the circulating li uor which is supplied as a diluting liquid to the mixing apparatus, to efiect a uniform and efllcient mixing and impregnation oi the material and to produce a mix. ture of a consistency suitable for an easy conveyance through the apparatus.

For a more complete understanding of the present invention a few constructional forms of appa-.

ratus suitable for performing the present process are illustrated in the accompanying drawings by example and somewhat diagrammatically, i. e. in the form of flow sheets. Fig. 1 illustrates an apparatus in which the material is introduced at the lower end of the reaction chamber. Fig. 2 shows a similar apparatus which includes means tor removal of water by displacement from the fiber material to be treated. Fig. 3 illustrates an apparatus in which the material is introduced at the top of the reaction chamber, and Fig. 4 shows a modified apparatus of the same type. The various apparatus illustrated in the drawings may, for instance, constitute the second step of a bleaching plant in the first step of which the material is chlorinated, after which the material is subjected to treatment with alkali in the second step.

Referring to Fig. 1, the fiber material which thus may be chlorinated, is first supplied to a filter apparatus i having grooved pressure rolls in which it may be thickened to a consistency of, for instance, 20 to 22 per cent, which may be raised to 25 to 28 per cent by aiterwardspassing the stock through a grooved press, not shown in the drawings.

The stock is then passed to the apparatus for the alkali treatment which mainly consists of a mixing apparatus 2 and a reaction tank 3 which are connected to one another by means of a pipe or conduit l. Located above the mixer 2 is a receptacle 5 from which strong alkali liquor is conducted through .a conduit I provided with quantity adjusting means 6 to a conduit 8. which serves for the supply of circulating liquor, and through said conduit 8 to the mixer 2. The quantity of circulating liquor supplied is such that due to the mixing operation in the mixer 2 the pulp obtans a consistency of about 5 to 8 per cent. Due to this considerable dilution the alkali liquor is intimately and uniformly mixed with the fibrous material, and the mixture obtains at'the same time a sufliciently liquid consistency to render it possible to convey the same as a flowing liquid through pipes and bends.

The pipe or conduit 4 leading from the mixer 2 is connected to an angle pipe 9, and between said pipe 8 and the lower or entrance end or opening of the-reaction tank 3 a sieve chamber in is provided from which a discharge pipe i'l provided with a regulating valve I2 leads to a collecting receptacle l3. 'In said sieve chamber l 0 the liquor is separated to the desired extent from the material continuously conveyed downwards' through the pipe 4 to the angle pipe 9. The liquor is pressed out from the material and the continued feeding of the latter through the reaction tank 3 is effected by a press and conveyer worm H or the like which is located within the sieve chamber ill and which is driven from the outside by means 0! any suitable device, which is indicated at i5. By means of the press and conveyer worm H such quantity of liquor is expressed from the material that the latter obtains a consistency oi about 20 to 25 per cent.

The removal of the expressed alkali liquor is effected under control of the regulating valve I! which is regulated by the level of the liquor in the receptacle ill by any suitable means diagrammatically illustrated in the drawings as a float and lever arrangement generally referenced 25. The arrangement is such that the valve l2 decreases the area of flow through the conduit li when the liquor rises in the collecting receptacle l3, and increases said area of flow when the level of liquor in said receptacle falls. A pump l'l conveys the expressed surplus quantity of liquor from the collecting receptacle l3 through a conduit l6, and if desired through a calorisator i8, to the aboveinentioned conduit 8 and back to the mixer 2. Heating of the material may also be effected during the mixing by supplying steam into the mixer 2 through the steam conduit 24. v

In the unit of time a constant quantity of pulp having a constant percentage of dry matter is supplied from the filter apparatus I to the mixer 2. Likewise, the quantity of fresh liquor supplied from the receptacle Ii to the mixing apparatus 2 in the unit of time is constant, and if heating is eflected by supply of direct steam through the steam pipe 26, the quantity oi steam supplied in the unit of time is also constant. By means of the valve 20 in the conduit IS the quantity of circulating liquor supplied by the pump I! through said conduit I5 is adjusted in such manner.that the desired suitable consistency of the pulp in the mixing apparatus 2 is obtained. Since the valve i2 controls the discharge of expressed liquor from the lower end of the tank 3 in such manner that the level of liquor in the receptacle I3 is maintained constant, or in other words, in such manner that the discharged quantity of expressed liquor corresponds exactly to the quantity of liquor conveyed by thepump II, it will be understood that a constant quantity of liquor which is dependent upon the adjustment of the valve 20, will circulate through the system.

As a result hereof the material or pulp charged into the reaction tank 3 by the press and conveyer worm M will also possess a. constant consistency which in this case corresponds to the constant quantities of pulp, fresh liquor, and steam supplied to the mixing apparatus 2.

If liquor is required at some other point in the plant, however, for instance for neutralizing after the pretreatment of the material with chlorine, a portion of the liquor may be withdrawn from the system, for instance at i9. This withdrawal of liquor should be effected continuously,

5 so that a constant quantity of liquor is withdrawn in the unit of time. In this case the quantity of expressed liquor discharged from the lower end oi the reaction tank through the valve I! will correspond to the sum of the circulating quantity of liquor, the quantity of which is adjusted by means of the valve 20. and the quantity of liquor withdrawn at E9. Since these two quantitles of liquor are constant, the pulp charged into the reaction tank 3 willv also in this case .have a constant consistency, which corresponds to the diilerence between the sum of the quantities of pulp, fresh liquor, and steam supplied to the 1221.:a-mm- QQEI8-illl8 2, and the quantity of liquor withdrawn at it.

The liquor circulated by the pump Il may also be allowed first to pass through an evaporation apparatus before it is supplied to the mixing apparatus 2, for in this manner to increase the I liquor concentration of the pulp mixture, whereby the consumption of chemicals is reduced. If the evaporation is carried out in such manner that the quantity of water evaporated from the liquor inthe unit of time is constant, a constant consistency of the pulp charged into the reaction tank Is will also in this casebe maintained, as will be easily understood.

The material charged into the reaction tank has a consistency of about 20 to 25 per cent and moves continuously upwards through the tank, until at the top thereof it is scraped over the rim 22 by a. scraper 20 or the like which may be driven in .any suitable manner, after which the material passes to a washing device 23. If desired, the material may afterwards be subjected to treat- ..ment with hypochlorite, for instance in a third step of the system.

The apparatus illustrated in Fig. 2 is largely arranged in the same manner as that above described in connection with Fig. 1, and like reference numerals are used to designate the same parts. The material to be treated, which also in this case may or may not be previously chlorinated, is first supplied to a suitable apparatus. uch as a filter apparatus M, by means of which a portion of the water contained inthe material may be removed by displacement by means of circulating-liquor which is supplied through the pipes 53. The advantage of such displacement of the water, will easily be understood from the following consideration. With a filter apparatus it is possible to thicken the supplied pulp mixture to such extent-that the pulp leaving the filter contains 12 per cent fiber or dry substance and 88 per cent water. By a displacement operation it is possible from this water content of 88 per cent to force out a quantity of water corresponding to 50 per cent, and to replace this quantity with displacement liquor, so that, not taking into account apparatus M to the apparatus for the alkali treatment, which, as already stated, is arranged in substantially the same manner as that above described with reference to F18. l. The pulp first enters the mixing apparatus 2 to which strong alkali liquor is supplied from the receptacle 5 through the pipe '5 provided with a regulating valve 6, while circulating liquor is supplied to the mixer 2 through the pipe b provided with a valve 23. The supply of circulating liquor through the pipes 88 for the displacement operation on the filter apparatus 3i, and through the pipe 8 to the mixer 3, is adjusted by means of the valves El and it in such manner that due to the mixing in said mixer 2 the pulp obtains a suitable consistency, for instance 5 to 8 per cent, so that the alkali liquor is intimately and uniformly mixed with the fibrous material, and the consistency is suficiently liquid to enable the mixture to be conveyed as a flowing liquid through pipe and conduits. The mixer 2 is connected through the downfiow pipe s with the angle pipe 9 which is connected over the sieve chamber to with the plied to the mixing apparatus, for obtaining which it was hitherto necessary to use grooved presses or other expensive and'power-consuming apparatus.

.When'the pulp has been concentrated in this .manner relatively to the quantity or water remaining in the same, it is conveyed from the filter inlet end of the reaction tank 3. In the sieve chamberit liquor is expressed from the material to the desired extent by means or the rotatable press or conveyor worm M which is driven by suitable means indicated at iii.

The worm it also serves to feed the material continuously upward in the tank 3 until at the top oi the latter the scraper 2i scrapes the material over the rim 22 after which the material is conveyed to the Washing device 23. By means of the worm the material is pressed to a consistency of about 20 to 25 per cent. The expressed liquor is conveyed from the sieve chamber iii to the tank is through the pipe il which is provided. with the regulating valve i2 which is controlled by-the level of liquor in the tank l3 by the float and lever arrangement 25 in such manner that the flow through the valve is decreased when the level rises in the tank is and is increasedwhen the level in the tank falls. The liquor. d} discharged in the tank i3 is conveyed by the pump ll through a conduit i5, and if desired, through a. calorizator l8, to the abovementioned pipe 8 and through the regulating valve 51 to the pipes 56 to be used again for dilution in the mixer 2 and for. isplacement on the filter l. Also in this case a steam conduit 24: is provided for effecting heating of the material, if desired, by introducing steam intothe mixer 2.

Also in this case the filter 8! shall operate in such manner that in the unit of time it delivers a constant quantity of pulp having a constant content of fiber or drymatter. Likewise, the quantity of fresh liquor supplied from the recep tacle 5 to the mixer 2 in the unit of time is constant, and if heating is effected by means ct steam supplied through the pipe 24, the quantity of steam supplied in the unit of time shall also be constant. By means of the valves 5'! and 20 the quantity of circulating liquor supplied by the pump I! through the conduit I6 is adjusted in such manner that the desired displacement is obtained on the filter I and the desired sutiable consistency of the pulp is obtained in the mixer 2.

Since the valve, l2 controls the discharge of expressed liquor from the lower end of the reaction tank 3 in such manner that the level of liquor in the tank [3 is maintained constant, and consequently, the quantity of expressed liquor discharged to the tank corresponds exactly to the quantity of liquor conveyed by the pump ll, it will be understood that a constant quantity of liquor will circulate through the system, and that this quantity is dependent upon the adjustment of the valves 51 and 20. Accordingly, the material red into the reaction tank 3 by the press and conveyer worm M will also possess a constant consistency which in this case corresponds to the sum of the constant quantities or dry matter and waterwith the exception of the displacement liquor-contained in the pulp supplied to the mixer 2 and the constant quantities of fresh liquor and steam. If it is desired that the pulp material charged into the tank I! shall have a consistency higher than that which corresponds to the sum oi. the said constant quantities, a quantity of liquor constant in the unit time may 'be withdrawn, for instance through the branch pipe I! on the conduit ii, in which case the pulp charged into the reaction tank I obtains a constant consistency which corresponds to the dimerence between the abovementioned constant quanabove the reaction tank 61.

The material which has been subjected to pressure in the press and conveyer device l0, it, falls from the outlet I9 of said device into the reaction tank 63, which in this case consists of a tower in which the material gradually sinks downward and from the lower end of which it is discharged by the aid of a stirrer 8|. Also in this case the discharge of the expressed liquor from the sieve chamber ill through the discharge pipe II is controlled by the valve in said pipe which in its turn is controlled by the level of the liquor in the tank I 3 through the device 25, so that in this manner a constant quantity of liquor always circulates through the system, and consequently, the material delivered to the tower 8! always has a constant consistency.

Also in the constructional i'orm illustrated in Fig. 4 a plurality of the parts previously described are used, and they are designated by the same reierence numerals. This constructional form differs from that described in connection with Fig. 3 in that the pulp mixture discharged from the mixer 2 flows through the pipe l to a thickener or uptaking machine 90 in which the liquor is removed and expressed from the fibrous material to the required extent, after which the material may be allowed to pass through a shredder 9i and ised material. In this case it is desired to obtain a concentration of about 30 per cent dry matter by means 01 the press device ll or the uptaking machine 80. Consequently, it is desirable in this case to carry out the displacement operation on the filter Ii as far as possible, so as not to introduce an unnecessary quantity of water into th process.

The constructional forms above described and illustrated in the drawings are only to be regarded as examples, and it will be understood that they may be modified in several ways as regards their details without departing from the principle of the invention. In Figs. 1 and 2, for instance, the reaction tank may be located horizontally and may have a horizontal press and conveyerworm. In such case the material may be allowed to flow from the mixer straight down to the worm which expresses the excess liquor and-feeds the pulp in the horizontal direction through the tank. At the other end of the tank the alkali-treated material may be allowed to drop over the edge of the tank without the aid of a mechanical discharge device, or it may be flushed over the edge. At the discharge end of the tank the material assumes in this case an angle of repose or about 45 degrees, and for this reason the tank should be made very narrow, that is, with a small diameter and a 'great length. I I claim:

1. The process of continuous alkali treatment of fibrous material, which consists in removing water from the fibrous material by displacement then falls into the tower 63. Also in this case the discharge conduit i I for the expressed liquor from the uptaking machine 90 to the tank I3 is provided with a control valve I! which is controlled by the level of liquor in said tank through the fioat and lever arrangement 25 in such manner that the function and the operation become the same as those above described.

For the purpose of mercerizing cellulose, for instance for the manufacture of artificial silk, an apparatus arranged in accordance with the principles above explained, may be used, with the sole modification that in such case the mixing apparatus 2 is combined with a reaction zone in which the material is subjected to alkali treatment during a few minutes, and that the tower will correspond to the ripening apparatus for the mowerof water therein with alkali liquor, intimately mixing the fibrous material in a suitable mixing apparatus with a quantity of alkali liquor sufiicient to effect treatment 01 said material and with an additional surplus quantity of alkali liquor sufilcient to produce uniform distribution of the alkali in said material and a mixture of material and alkali liquor having a consistency such that said mixture is capable of being conveyed as a flowing liquid, causing such mixture of fiber material and liquor to flow to a reaction chamber, removing from said mixture preparatory to introducing it into said reaction chamber a quantity of alkali liquor substantially equal to the total quantity of alkali liquor used for displacement of water from the material and as surplus liquor mixed with the material in the mixing apparatus and such that due to its removal the material obtains a concentration suitable for the reaction, introducing said material into the reaction chamber, subjecting said material in said reaction chamber to treatment with the alkali liquor remaining in the material, employing a portion of such quantity of alkali liquor removed from the material preparatory to its introduction into the reaction chamber for removing water by displacement from a fresh quantity of fibrous material, and returning the remaining portion of such removed quantity of alkali liquor to the mixing apparatus and using such portion as surplus mixing liquor for a fresh quantity of fibrous material.

2. The process of continuous alkali treatment of fibrous material, which consists in removing water from the fibrous material by displacement of water therein with alkali liquor, intimately mixing the fibrous material in a mixing apparatus with a quantity of alkali liquor suflicient to efi'ect treatment of said material and with an additional surplus quantity of alkali liquor sumcient to produce uniform distribution of the alkali in said material while providing amixture of material and alkali liquor having aconsi's'tency such that the mixture is capable of being conveyed as a flowing liquid, causing the mixture of fiber material and liquor to flow continuously to a reaction chamber, continuously subjecting said mixture to pressure so as to separate from. the mixture a quantity of alkali liquor substantially equal to the total quantity of alkali liquor used for displacement oi. water from the material and as surplus liquor mixed with the material in the mixing apparatus thereby reducing the concentration of the mixture to a concentration suitable for the reaction, said pressure serving also to continuously introduce the material into and convey the same through, the reaction chamber, subjecting said material in said reaction chamber to treatment with the alkali liquor remaining in the material, employing a portion of the alkali liquor pressed out from the material for continuously removing water by displacement irom iresh quantities of fibrous material, and continuously recycling the remaining portion of such pressed out alkali liquor, to the mixing apparatus and using such portion as surplus mixing liquor for fresh quantities of fibrous material.

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