US1816739A - Process for the manufacture of cellulose - Google Patents

Description

July 28, 1931. A. EINIELSEN PROCESS FOR THE MANUFACTURE OF CELLULOSB 2 sheets-sheet 1 Filed lay 14, 1928 Patented July 28, I931 UNITED STATES PATENT OFFICE.

ALBERT ELIAS NIELSEN, OF OSLO, NORWAY PROCESS FOR THE MANUFACTURE OF CELLULOSE Application filed May 14, 1928, Serial No. 277,712, and in Norway November 23,1927.

The present invention has for its object to provide a process for the manufacture of cellulose from wood or other substances by means of indirect steam and by usinga di gesting liquid circulating outside the digester.

Attempts have been made to obtain, by the use of indirect digestion of raw materials' of different kinds, a uniform quality and an increased output, further to reduce the time of digestion, the heat consumption and the quantity of alkali necessary for the production of cellulose. An advantage connected with the indirect digestion consists in this that a recovery of valuable substances con- 16 tained in the waste liquor after the completed digestion is facilitated.

The great drawback of the indirect digestion as hitherto practiced consists in the fact that a larger quantity of black liquor of a 20 lower concentration must be used than is necessary by the use of the direct digestion, whereby the heat consumption is increased and the concentration of the liquor at the charging is reduced. Attempts have been made to reduce the great heat consumption in the sulphite process by using so-called super-leaching and by recovering the condensate from the heating pipes. In the sulphate process the super-leaching could not be uti lized. The condensate would be recovered, just as in case of the sulphite process. The heat recoveryhitherto has not been practically employed, because the. conveyance of the liquor is connected with several difficulties;

In case of direct digestion a condensation of the direct steam takes place during the heating. of the substances under treatment, whereby the digester is filled with liquid before having attained a temperature of 100 degrees centigrade. Thereby a burning of the material in the upper portion of the product is prevented. 1

- In the sulphite process about 25 per cent 5 of the quantity of acid filled into the digester is passed back to the vessel of acid before the material has attained a temperature of 80 degrees centigrade, in order to leave space for the further heating up to the full tem- 9 perature. Furthermore, the material within the digester sinks together and enables the use of a smaller quantity of liquid. This sinking-together of the material. continues until the incrustations of the raw material have been dissolved and distributed in the waste liquor. The sinking-together of the fibrous material is increased the longer time the digestion endures and particularly in case the, digesting liquor be passed in a controlled circulation.

In the sulphate cellulose process by means of direct steam-no liquor is tapped out, because the ioam-formation of the liquor requires a smaller quantity of filled-in liquid. This in turn prevents a burning in the upper portion of the material.

In the indirect process of digestion, however, wherein no condensate occupies the spaces in the material, care must consequently be taken to'have the sulphate digester 7o filled with liquor to a considerably higher level. In sulphite digesters acid is usually pumped in under. pressure in order to pre vent the use of direct steam during the first part of the process and in order to avoid a 'i'". burning of the material.

Experience has shown that up to 30 per cent of the quantity of filled-in acid might be tapped oil' and super lcached without any burning taking place and without a blowingif off of the product meets any difiiculty.

In case the percentage of moisture in the raw materials varies, the liquid contained in the raw material will always vary and so will be true also of the concentration of the dig: gest-ing liquid. This drawback has been avoided partly for sulphate cellulose by regulating the quantity of white and black liquor according to the moisture percentage of the raw material. According to the present invention such v an arrangement is provided that, simultaneously with the dissociation, a concentration of the liquor during successive vaporization thereof takes place, the liquor being passed in circulation and the concentration is increasedaccording as the dissociation progresses, whereby the calorific capacity of the *waste liquor is increased and the consumption of uel is reduced the consumption of raw materials is reduced and the output of product increased.

The invention is illustrated in the annexed drawings, in which Fig. 1 shows a digester combined with a concentrating apparatus partly in side view and partly in vertical section.

Fig. 2 is a cross-section of the evaporator shown in Fig. 1. i

Fig. 3 shows a battery of three concentrating apparatus connected to each other.

Fig. 4 is a plan view corresponding to Fig. 3.--

Fig. 5 is a diagram showing the combinationof six digesters with threepreheaters.

Fig. 6 is a diagram showing the combination of six digesters with three preheaters and three Vaporizers connected to each other.

Fig. 7 is a diagram showing an arrangement in which each of a battery of six digesters is connected to a preheater and the preheaters on its hand by a common conduit connected to a series of three Vaporizers.

Fig. 8 is a diagram of an arrangement in which each of three pairs of digesters is connected to a preheater, all preheaters being connected to each other by suitable conduits.

Fig. 9 is a diagram of an arrangement in which each. of three pairs of digesters is connected to a series of three preheaters the several series of preheaters being connected to a common conduit.

10 is a sectional View of a part of a high pressure preheater.

Referring to Figs. 14,of the drawin gs, the digester is provided with a device which serves to preheat and vaporize the contents of the succeeding digester. Each device of this kind is hereby preferably connected with its digesters. The exhaust vapour from each device may be used for different purposes, for instance for drying the product, boiling the liquor, central heating, etc., and the condensate may be used asa feed water for steam boilers as washing water for diffusers and the like. fusing of the waste liquor takes place, the liquor is passed into the appertaining device and is subjected to a repeated evaporation, until the desired concentration of the liquor has been obtained, whereupon it is tapped out into the tank for the black liquor.

In the drawings, A, B and C are concen trating devices connected with each other. Each of them may be connected to one or more digesters. By means of a pump of circulation, the bottom portion of the digester is connected with the concentrating device.

'By a fitting 9 on the pipe 12 the concentrating device is connected with the upper portion of the digester. 13 and H designate valves for regulating or closing the said connections. 16 is a heating pipe which is attached at the top portion 17 and at the bottom plate 18. 19 is a casing surrounding the When in the digester a dif-.

condensate chamber 20, and 21 is a draining pipe for the condensate connected with a pipe 22 passing to a condensate pump. 23 is a steam chamber into which the pipe 24 introduces steam and which waste steam is introduced by the inlet pipe 25. 26 is a manhole.

In the bottom portion of the device a plurality of partitions 27 is arranged in star formation, in order to compel the liquor introduced from the digester to take a prolonged path transversely of the heating pipes to the outlet fitting 9 during the concentrating influence of the steam in the pipes. The concentrating device serves simultaneously as a preheater and vaporizer for the liquor according as the latter is brought upon its definite temperature and is further heated during evaporation of the digesting liquor, until the blowing-oil? pressure is obtained. The- Wastevapour of the liquor escapes through the outlet fitting 28 and the pipe 29 arranged in the upper part or" the device and passes into the chamber 30 surrounding the steam chamber, so that a circulation is eliected and acorrcsponding centrifugal movement of the particles of the liquid and a transformation thereof into steam by the heat from the steam chamber 23 is produced. Liquid which might not have been vaporized passing through .the opening 32 into the concentrating device again. The Waste steam from the centrifugal chamber escapes through the pipe and passes through a valve 15 and a fitting 25 into the steam chamber 23 of the next device B.

I'Vhen the digesting liquid is circulating by forced circulation, a circulating pump must be arrange-d for each device. Each pump is connected with its digester through a bottom sieve 7 and a valve 13. The devices A, B and C and possibly a higher number of devices connected through the pipes 31 in series are connected in series with the digesters to be operated. It depends upon the number of digesters and of concentrating devices how the devices are combined. Assuming for instance six digesters and three concentrating devices, each of the latter is connected alternately with two digesters by means of a branch pipe for the circulating operation is used.

Assuming there are for instance 6 digesters connected to a circulatingconduit. from the bottom of the digester, 3 concentrating devices A, B and C may be arranged, each havinga circulating pump, or they may be arranged for natural circulations. The digesting liquor is passed from a'digester through the sieve 7, the valve 13 and the circulating pump into the concentrator, further in zigzag to the outlet fitting 9 through the circulating pipe 12 and through the valve 14 into the upper portiongof the digester. In the digester'the liquor Will pass uniformly through the material and further again through the sieve 7 to the pump so as to arrive into the concentrating device.

During this digestion the waste steam from each of the devices A, B and G is regulated by the valves 15, the vaporization being regulated according as each charge is heated to the desired temperature, consideration being taken to the material sinking together within the digester. During the starting of this series of digesting two digesters must always be ready charged, before the first digester has attained its highest temperature, i. e. about one hour after the starting of the first digester, when this has attained a temperature of 100 Centigrade. About 20 minutes after the starting or earlier the valve 15 of the device 5 is opened and the circulating pump of this device enters into operation in the same manner as in the device A. The Wastesteam from A new passes through the pipes 28, 29 into the centrifugal device 30, passes through the waste' steam pipe 31 and a valve into the heating .space 23, further through the heating pipes 33, where it is condensed. The condensate contains, in additionto water, also organic substances which at lower pressure are not condensed, but may be transformed for the most part into other chemical compounds.

If for instance a maximum temperature of 170 be used and if a removal of gas be effected down to 146 centigrade (3.5 kg.), the temperature in the second digester will not be higher than 130 when the first digester has been gassed down. The exceeding heat of the second digester is passed in the manner described above into the device C, which in this case, has attained a temperature of 76. The first digester can now be blown off. The direct steam is then passed into the device B, andthe second digester is brought upon full temperature, and simultaneously the third digester is brought by the device C upon the previous temperature of the second digester, and so on.

Before the third digester has attained its boiling point, a new digester must be cut in. The device A thus receiveswaste steam from the device C, and so on.

in longitudinal direction in accordance with extensions and contractions taking place owing to varying temperatures.

The upper and lower head of the device is connected to the casing'by means of bolts. When the bank of pipes has to be replaced, the flanges of the condensate casing are disconnected and the bolts in the upper portion of the device are removed, whereupon this upper portion with the bankof pipes is accessible and may be lifted out from the casing. In the manner described above the digestion takes place in a definite succession, each charge being heated'by the preceeding one. The consumption of live steam is thereby maintained practically constant, when the system has once been brought into operation. For instance, if 2600 kg. water of the liquor is vaporized for each 1000 kg. of the material, a reduction of 23% of consumed direct steam, further a triple heat return and a black liquor of 8 Be. higher concentration are obtained as compared with. the previous values. Owing to the vaporization of the digesting liquor taking place in the manner described above during the digestion, the active alkali is concentrated in the same proportion as it By this mode of operationa varying water 4 content inthe final material will be without any inconvenience, because the evaporation is regulated correspondingly. By the present system the further advantage 1s ob-' tained that the raw material may belused without previousstoring.

The large heat quantity lost during the blowing-off of the digester, will be reduced in the same proportionas the evaporation ofthe liquor takes place. The increase of the calorific capacity of the liquor results firstly in avoiding a later evaporation and secondly.

in utilization of the heat quantity obtained from the dry substance of .the black liquor in.

the melting furnace by insertinga steam boiler of a sufficiently great capacity to utiuor obtained by this system constitutes a great progress towards the aim of each cellulose technician: to become independent of the supply of fuel by utilizing the combustible substances of the incrustations of the raw material.

The present invention may also be carried out by means of devices in actual use.

' The invention may also be carried out in the manner that a preheating of the liquor by means of direct steam takes place simultaneously with indirect vaporization. In this manncris obtained that the quantity of the liquor in the product ordinarily present in case of direct digestion is maintained during the blowing oif. Thereby a concentrated liq uor is obtained and simultaneously also a greatereconomy as to heat is obtained, because the device the the quantity of liquid which has become diluted by the condensate of the direct steam is again concentrated by the evaporation. In the sulphite process this arrangement of the digesting process results in this that a removal of liquor during the development of the pressure in the material is prevented, because this portion of the liquid or acid is evaporated and waste vapour of sulphurous acid is recovered.

A combination of the reheating and vaporization systems may ta e place in different manner. I

In the sulphite cellulose process the heat of vaporization of the waste vapour is utilized indirectly for heating purpose in the next charge, because the condensate of the waste vapour and the sulphurous acid contained in the waste vapour is pressed into a collecting tank, from which the condensate is again removed by means of a pump or a con densing pot. The sulphurous acld may be used either for enriching the gas before the" charging or it may be passed into a digester which is under a lower pressure, or the gas may also be compressed to a higher pressure in order to be used for the same digester, in which the blowing-off and the vaporization has taken place. In this way gas is supplied to the digester and the acid container which contains sulphurous acid (about 100 per cent) and from which the condensate has already been removed. \Vhen gas is removed from a digester in operation, the latter is simultaneously heated indirectly or by direct supply of steam.

It is well known that the pressure in the digester in case of direct digestion and circulation of the acid will under ordinary circumstances appear only when the charge has attained a temperature of 110l.20 centi-- and the circulation of the digesting will be the more strong by means of lower is the difierence in temgrade, liquid digesting acid in proportion to perature and the lower is the, pressure of the digester as compared with the temperature of the charge, because thereby the gases are superheated at a smaller degree.

In case of direct digestion, however, a pressure of 5 kg. per square centimeter will prevail already when the charge has a temperature of about 80, whereupon removal of liquor and gases must take place, if it is desired to reheat thecharge. Thereby the quantity of digesting acid to be used in the charge is reduced with about 25 per cent. This quantity of removed acid must again be cooled, before it is passed back into the tank, from which follows a great loss in heat and a reduction in the acid-quantity of the di ester-contents.

In case of indirect digestion with vaporization, the charge is supplied with practically the same quantity of acid, though usually a somewhat less concentrated acid would be sufficient.

As a stronger acid richer in gas will always assist in the dissociation of the incrustations of the wood and the bleaching, it is obviously of the greatest importance for the time of digestion and for the quality of the product, that the digesting acid is maintained at the highest possible concentration during the digestion and further that it is present in a sufiicient quantity to enable a reduction of the temperature of digestion,

because thereby a higher quality of material is obtained.

The vaporization of the sulphite liquor therefore has to take place only, when the charge has attained the digester pressure viz at temperatures of 110-120". In case a digesting liquid is used containing about 3,53% S0 (2.6% thereof being in a free state and 0,9% combined), the total quantity of SO in direct digestion with preheater at 110 'will be reduced to 1,9% S0 The maximum temperature for the sill-- phite process varies from 120140 or more.

The reduction of the SO -contents of the the total quantity of acid will take place only, when the vaporization of the digesting liquid takes place. But as in' direct digestion no removal of digesting acid takes place, an excess of free SO in the digesting acid is obtained. and at the same time the digesting liquid is concentrated corresponding to the reduction in the quantity of liquid in the digester. As the vaporization only takes place later on, the dilution of the digesting acid in the digester will not result in any prolongation of the time of digestion. nor in any decrease in the bleaching capacity of the mass. The acid rich in gas and absorbed in the charge will be expelled at a reduction in pressure. This diffusion of the gaseous acid ir the material results generally spoken into ation of the dissociation when the contents within the a more rapid digestion and into a quantity of material which is easier bleachable.

It is a well known .fact' that it is of the greatest importance that the pressure in the digester during the gas-0E of the charge be most possibly maintained, so that a largest possible quantity of sO -gas is forced out. Consequently the removal of gas may advantageously be efi'ected at a simultaneous vaporization, the pressure being unchanged at the beginning as well as later on. During the removal of gases" the vaporization will have the effect that the pressure will be maintained as long as possible and that on the other hand, owing to the large heating surface, the largest possible quantity of gas is forced ofl. V

When transferring the digesting acid from one digester into the next one in the sulphite process experience has shown thatif a portion of the quantity of liquid in the digester be tapped off and a space filled with gas has been formed in the digestera rapid altertakes place. During the further progress of the process a remarkable bleaching of the contents in the digester will be observed. Consequently, it is very important that a space filled with gas is present, digester has sunk" together. In this manner just the evaporation of the liquid above the contents during the digesting process will assist in the dissociation, and at the same time the vaporization heat of the waste vapour will be utilized indirectly, and the free SO -gas will be passed in circulation.

The condensate of the waste vapour may advantageously be used to effect the difl'usion of the waste liquor from the finished product because the diffusion of the waste liquor takes place most advantageously in a manner similar to that occurring in the sulphate cellulose factories. This takes place in the manner that diluted waste liquor from a previous charge is firstly introduced into the digester, and then the condensate of the waste vapour is introduced in steps. Thereby a higher output of the waste liquor and a highest possible concentration and also a productmost waste liquor are ob-.

possibly freed from tained.

As is known, about 9 cubic meters of liquid per 1000 kg. of product is used, and the water contents of the wood varies from 20-60%. In the direct and indirect process the average quantity of waste liquor is calculated to be 5 cubic meters per 1000 kg. of product. If a similar diffusion system as that indicated be used, considerable. advantages will be obtained as regards output of waste liquor which may. be used for different purposes: Sulphite spirit as a motor fuel, sulphite carbon, tannic acid, ink, as an additional product in the briquetting of coal and so on.

The economical advantageobtaining the scale ofl', namely,

the. manner that steel.

By the most vaporization-devices the liquor to be evaporated is introduced in the inner partof heating pipes, so that a very high velocity of the liquid along the heating surface and consequently a highest'possible vaporization per unit of area of the heating surface is obtained.

Now, the digesting liquor in the sulphite and sulphate process contains incrusting salts which are produced at the ordinary preheating and vaporization and are settled in the interior of the heating pipes, so as to produce difiiculties in'the cleaning of same. If, however, the liquor is'passed outside and the heating steam inside the pipes, the conditions will be altered. In the sulphate and soda cellulose process in this event no incrustations will occur, because the same cannot be produced on the heating pipes, if the liquor is not tapped off at each charge. The waste liquor which settles on the heating pipes at each charge, will namely dry and and at the next charge it will again be introduced by means of the circulating pump into the digester, wherein it will be dissolved again.

In the sulphite process, however, a layer.

of nearly 3 mm. of calcium-monosulphit'e will settle already after one charge. by reason of the strong heat transmission from steam to the liquor, and by this layer the heat transmission will be considerably reduced. In order to remove this drawback, a strong heat transmission must be avoided. This is obtained in the present case by causing the condensate together with the steam to take a pulsating movement, whereby the, heat transmission in the heating pipes is reduced.

As regards the special arrangements to be taken into consideration, should be mentioned:

For digesting sulphate or soda cellulose v The vaporization devices are connected in series and the liquor is concentrated by pass ing from one device into the next one. The

liquor is introduced into the interior of the the following heating pipes, whereas the steam is outside same. This arrangement may be modified in the liquor is passed'outside and the steam inside the pipes. sure or high pressure devices may be used;

In case of low pressure devices the same may be arranged as indicated in Figs. 5, 6, 7 8 or 9. According to Fig. 1 the liquor in the Low presdigester is heated by hot steam, and durin the digesting process waste liquor isconducte ofi, according as the contents within the digester sinks, and is then again pumped into the digester. In Fig. 5 and the following figures of the drawings a desi ates the digesters, b the preheaters and a ti: Vaporizers. In Fig. 7 the waste liquor is vaporized only when the charge has attained its highest temperature, whereas the blowing-ofi may take place with the least possible waste liquor in the mass. The vaporizing devices in this case are provided with liquor circulating from one device to the otherone in a pipe bank, the steam having an under-pressure.

According to Fig. 9 three vaporizing devices are used for two digesters. If a high pressure preheater is used as combined preeating and vaporizing devices, the liquor must circulate outside the heating pipes. The digesting liquid forthe heating purpose is taken out in the middle of the heating surface through an outlet fitting arranged for this purpose. In vertical Vaporizers special tops are arranged for removing direct steam and waste vapour.

' Such a high pressure preheater is shown in Fig. 10. In this figure 41 is a, tubular heating chamber, into which steam and condensate is passed through the interior of the pipes, whereas the waste liquor circulates outside the pipes. 42 is the inlet for the liquor from digester, 43 the outlet for the liquor to the next digester, 44 the vapour out- 'let, 45 the head piece which is divided into two chambers. The lower one is the top chamber for the heating chamber 41 and is provided with inlets 46, 47 for direct steam and waste vapour respectively from the preceding concentrators. The upper' chamber is through the pipe 48 connected with the heating chamber and through the opening 49 with a separator having an outlet 51 for waste vapour separated out.

The number of the series-connected devices depends upon the size of the present devices and of the digester. The outlet pipe for the condensate is outside the device ent into S-shape, in order to efiect a pulsation in the heating pipes.

' As combined geheating or vaporizing devices they may arranged in another manner according to Figs. 8 and 9.

In these arrangement the waste liquor is preferably concentrated at 45 at 130 centigrade without being crystallized. This is connected with the advantage that rotating furnaces in the soda house ma be avoid ed, because the waste liquor at t 's concentration is crystallized at atmospheric pressure. The dry substance from the devices may thereby be passed direct into melting furnaces. from which the esca ing gases may be passed direct to steam ilers. this manner not only heat economy but also removal of bad smelling gases are obtained. The waste liquor is concentrated in the vadifl'users at the highest possible concentration and temperature.

For digestingeulphite celhtlose The vaporizing devices are connected in series and the liquor is concentrated during its passage from device to device. The liquor passes in the interior, of the heating pipes,

whereas the steam circulates outside same.

Vacuum devices and Vaporizers for low or high pressure may-be used for evaporation of the sulphite waste liquor. In this case incrustations in the waste liquor must be taken into consideration and generally spoken the arrangement should be made according to the rules set forth for the sulphate process. The preheating and the vaporization are certainly somewhat reduced, but on the other hand the device will show a higher efiiciency, if the pipes are maintained free from incrustations, so that practically any cleaning of the pipes may be avoided.

I claim:

1. A process of digesting cellulose from wood and other materials by indirect steam under circulation of the digesting liquid outside the digester, characterized y this that simultaneously with the dissociation a concentration of the liquor is eflected by a gradporizing devices after having passed )the ual vaporizing of the same in the circulating device, the waste vapour from each concentrating apparatus being used for heating the digesters which are connected in series, the first concentratin device being connected to the digester in w iich the temperature is the highest one and the last digester being connected to the digester in which the temperature is the lowest one.

2. A rocess accordin acterize by this, that t e digestin liquid is reduced to the same extent as the pu p sinks together within the digester and simultaneously with the decrease of the active agents.

3. A process according to claim 1, characterized b this, that the vaporization heat to claim 1, charprocess andis used in the concentrators and the digesters under a lower temperature and under a lower pressure. i 4. A rocess according to claim 1, characterize by this, that the condensate of fresh steam is returned directly into the boiler whereas the condensate of the exhaust steam is utilized for diffusion of the waste liquor the condensate being forced with a higher temperature than the waste liquor into the digester as the waste li uor ifiuses from the product whereupon t e waste li nor isagain concentrated in order to be urther utilized.

5. A rocess according to claim 1, characterize by this, that the concentrating dev by means of'walls vice is connected alternately-with several the upper edge-of the outlet as long as the shutting valve is closed.

7. A process accordin to claim 1, characterized by this, that t e formatlon of incrustations is prevented by a pulsating motion of the fluid before blowing out.

8. A process according to claim 1, characterized by this, that the waste vapour 1s given a circulating motion and thefluid vaporized in a centrifugal head surrounded by a steam chamber.

9. A process according to clalm 1, characterized by this, that the liquor in the heating chamber of the device is given a c1rcu lating motion transversal to the heatlngplpes placed in the device 1n the form of a star.

10. A process according to claim 1, characterized by this, that the active liquor is concentrated by passing a series of apparatus the liquor passing outside heating pipes the vapour circulating inside.

11. A process according to claim 1, characterized by this, that the active liquor is cona vaporizing device,

centrated by passing a series of apparatus the liquor passing outside heating pipes and the vapour circulating inside, and further characterized by this, that the waste liquor is conoentrated to such an extent that the liquor is crystallized at atmospheric pressure thenecessary addition of sulphate of sodium taking place before the strongly concentrated waste liquor is brought into the atmosphere and the evaporationbeing caused by means of the caloric heat of the dry substance and by burning the latter in melting furnaces the said heat being utilized for steam boilers and any addition of steam being avoided by means of a wet pressing during the production of a product containing 50% of moisture and the concentration of the waste liquor to dryness being simultaneously obtained without any further addition of fuel thanthat contained in the waste liquor. I

12. A process according to claim 1, characterized by this,-that the active liquor is pre; heated and vaporized by passing first through a preheater and afterwards through whereupon it is returned to the digester, the liquor in the'vaporizing device passing outside heating pipes and the vapourcirculating inside.

13. A process according to claim 1, characterized by this, that the active liquor is concentrated by passing a series of apparatus, the liquor'passing outside heating pipes and the vapour circulating inside, the activ'ity of the concentrating apparatus being controlled w to claim 1, charthe vapour circulating inside,

by admitting waste vapour and fresh steam into separate distributing chambers.

14. Aprocess according to claim 1, characterized by this, that the active liquor is concentrated by passing a series of apparatus,

the liquor passing outside heating pipes and the vapour circulating inside, the liquor being vaporized to the densa-te of direct steam which is passed into the digester increases the quantity of the said liquor.

same extent as the con- 15. A process according to claim 1, charac- V terized by this, that the active liquor is concentrated by passing a series of apparatus, the liquor passing outside heating pipes and a pulsating motion of the condensate during the removal from the vaporizing and preheating devices being caused by means of S-shaped pipes placed in a vertical plane.

. 16. A terized by this, centrated by passing a-' series of the liquor passing outside heating the vapour circulating inside, and further characterized by this that, whendigesting sulphite cellulose,'the SO v gas contained in process according to claim 1, characthat the active liquor is con-.

apparatus,

pipes and s the waste vapour is first freed from the condensate during a simultaneous condensation of the waste vapour 1n preheating, respectively vaporizing devices, and passed into a starting tank, whereupon the condensate is separated, the S0 gas being removed and added to'the digesting acid for the purpose of enriching the same.

17. A process according to claim 1, charaoterized by this, that the active liquor is concentrated by passing a series of apparatus the liquor passing outside heating pipes and the vapour circulating inside, and further characterized by this that, when digesting sulphate'cellulose, the badly smelling gases are first freed from the condensate during a simultaneous condensation of the waste vapour in preheating, respectively vaporizing devices, and passed into a starting tank, where upon the condensate is separated, the waste gases being passed to filters in order that organic constituents may be removed and the rest of the condensate be utilized for heating purposes. I

In witness whereof I afiix my signature. ALBERT ELIAS NIELSEN.

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