EP0035679A1 - Process and apparatus for continuous hydrolysis of cellulosic plant materials for obtaining sugars - Google Patents

Abstract

PCT No. PCT/DE81/00036 Sec. 371 Date Oct. 15, 1981 Sec. 102(e) Date Oct. 15, 1981 PCT Filed Feb. 21, 1981 PCT Pub. No. WO81/02428 PCT Pub. Date Sep. 3, 1981.Process and apparatus for the continuous hydrolysis of plant biomass containing cellulose and hemicellulose. Chopped biomass is treated in a first stage in the presence of dilute acid, at temperatures and pressure conditions under which the hemicellulose and, partially, the cellulose are hydrolyzed during a first reaction to pentoses and partially, hexoses, whereupon the reaction mixture pressure is suddenly released and the hydrolysate is separated from the biomass, and in at least a further stage, cellulose in the biomass is hydrolyzed in the presence of dilute mineral acid and under more severe temperature and pressure conditions, to hexoses, whereupon again the reaction mixture pressure is suddenly released and the hydrolysate is separated from the remaining biomass, and in which the neutralized hydrolysate, is further processed for the production of sugars, wherein each hydrolysis stage comprises as reaction chamber, a continuously operating horizontal tube digester containing horizontal conveyor devices, the digester being connected on the entrance side with a conical worm filler with a perforated cone casing for the injection of the biomass and the outlet side is fitted with an outlet device which forms a pressure seal of the exit side of the reaction chamber, and which is connected via a blow pipe with a cyclone-shaped blow tank.

Description

• in einer ersten Stufe unter Anwesenheit von verdünnter Säure Temperatur- und Druckbedingungen unterworfen wird, bei denen im wesentlichen die Hemicellulosen und nur teilweise die Cellulose während einer ersten Reaktionszeit zu Pentosen und teilweise Hexosen hydrolysiert werden, worauf das Reaktionsgemisch einerseits plötzlich entspannt und andererseits das Hydrolysat von der Biosubstanz abgetrennt wird,
• in mindestens einer weiteren Stufe unter Anwesenheit von verdünnter Mineralsäure und unter verschärften Temperatur-und Druckbedingungen Cellulose in der Biosubstanz während einer weiteren Reaktionszeit zu Hexosen hydrolysiert wird, worauf erneut einerseits das Reaktionsgemisch plötzlich entspannt und andererseits das Hydrolysat von der Restbiosubstanz abgetrennt wird,
• und bei dem das neutralisierte Hydrolysat zur Gewinnung der Zucker in geeigneter Weise weiterverarbeitet wird. Die Erfindung betrifft ferner eine Anlage zur Durchführung eines solchen Verfahrens.

The invention relates to a process for the continuous hydrolysis of pentosan-containing hemicelluloses, cellulose and corresponding compounds in plant-based bio-substance to form sugars, in which the bio-substance is comminuted in a suitable manner

• is subjected in a first stage in the presence of dilute acid to temperature and pressure conditions in which essentially the hemicelluloses and only partially the cellulose are hydrolyzed to pentoses and partially hexoses during a first reaction time, whereupon the reaction mixture suddenly relaxes on the one hand and the hydrolyzate of the organic substance is separated,
• in at least one further stage in the presence of dilute mineral acid and under more stringent temperature and pressure conditions, cellulose in the organic substance is hydrolyzed to hexoses during a further reaction time, whereupon the reaction mixture is suddenly expanded again on the one hand and the hydrolyzate is separated off from the residual organic substance on the other hand,
• and in which the neutralized hydrolyzate is processed in a suitable manner to obtain the sugar. The invention further relates to a plant for performing such a method.

The industrial production of sugar from cellulose-containing raw materials, in particular from wood in the form of wood chips, has been carried out for years during the last war, until wood saccharification with the conventional plants became unprofitable due to the more favorable economic conditions after the last war. The recent price increases on the world crude oil market have once again brought considerations into the foreground as to which alternative raw material sources can be used to produce fuels for internal combustion engines. In this context, the saccharification of cellulose-containing, vegetable biosubstance, which has since been abandoned for economic reasons, is again in the focus of interest, since the sugars produced in this way can at least partially be fermented to ethyl alcohol, which can be used as a component in fuels or directly as fuel can.

State of the art

The wood saccharification plants operated during the war worked largely according to the well-known Scholler percolation process, which is described in German patent 640 775. The purely discontinuous Scholler percolation process uses approximately 100 m ³ apparatus. In the liquid cooking phase, the wood is boiled with dilute sulfuric acid at 160/180 ° C for several hours and then the resulting xyloses and glycoses are washed out. The washout takes place according to certain prin Zipien, which have become known under the term "percolysis".

This known method has the disadvantages that, on the one hand, it requires very long cooking times and does not permit the use of voluminous waste materials, such as the remains of annual plants, waste paper and other waste, since the sieves built in for the circulation of the cooking acid in the cooker become clogged and percolysis cannot be carried out do. In addition, the long cooking times required very large cooking volumes, which is why the systems operated in the Federal Republic of Germany at the time had around 30 to 40 percolators with a content of 60 m ³ each, which on the one hand led to considerable capital tied up in the fixed assets and on the other hand an unacceptable energy expenditure for heating up the large ones Volume of liquid required. Not least for these reasons, the plants operated at the time had to be shut down due to inefficiency.

A method developed further on the basis of the Scholler method is described by Eickemeyer in German patent 15 67 335. The further developed process is intended to improve the initial impregnation of the organic substance in discontinuously operated percolators and to reduce the steam consumption for the purpose of saving energy and achieving a higher sugar concentration in the hydrolyzate.

In view of the economic disadvantages of batch hydrolysis processes, continuous processes have also been proposed in the literature. However, it has so far not been possible to put these processes into practice, which is why there is still no continuously operated saccharification plant in operation.

Further, improved hydrolysis processes are also described in US Pat. No. 2,801,939 and in US Pat. No. 3,212,932. The focus of these two patents is on the reaction and other process conditions. In both patents it is mentioned that the methods can also be carried out on a continuous basis, but it is not clear from the patents in detail how this should be carried out with economic means. Only from US Pat. No. 2,801,939 does it appear that the biomass is to be comminuted and mixed with a large excess of liquid in such a way that it becomes pumpable. However, high dilution leads to high energy costs and, more importantly, to a low sugar concentration in the hydrolyzate, the high one. Evaporation energy required.

Presentation of the invention

The present invention has for its object to technically further develop a method of the type mentioned at the outset, such as can be derived from US Pat. No. 3 212 932 with regard to the chemical-physical process conditions, in such a way that voluminous vegetable waste products are also included Bagasse and straw, for example, and which, in the broadest sense, also include waste paper, can be hydrolytically saccharified economically, with the primary aim being low investment costs, short reaction times and a minimal excess amount of liquid, based on the raw material, on the one hand to obtain a high cellulose yield and on the other hand to obtain a hydrolyzate with the highest possible sugar concentration. The essential object of the invention, however, is to propose a technical process with which process conditions, such as are proposed in US Pat. No. 3,212,932, are practically in operation and from an economic point of view.

This object is achieved according to the invention for a process of the type mentioned at the outset by introducing the biosubstance into the pressurized reaction space by means of a continuously working filling screw which forms a pressure seal and in which air and excess liquid contained in the biosubstance are largely removed , the hydrolysis is carried out in a continuous horizontal tube cooker as a reaction space in the vapor phase and the hydrolyzate is separated from the reaction mixture in several separation stages.

The term continuous horizontal tube cooker is to be understood here to mean cookers such as those used by American Defibrator Inc., New York, NY, USA and by Black-Clawson Co., Pandia Division, Middletown, Ohio, USA of pulp production. Such cookers are described, for example, by W. Herbert in TAPPI, Vol. 45 (1962) No. 7, p.207A-210A and by U. Lowgren in TAPPI, Vol.45 (1962), No.7, p.210A-215A. Such stoves are assumed to be known according to their general structure.

The term “filling screw” is to be understood here to mean a device as it is also known per se in general under the name “screw press”. It is a device with a conical housing which is resistant to high pressure and in which a likewise conical screw with a rotary drive is arranged. The housing is provided at its larger diameter end with a generally radial loading opening and opens at its smaller diameter end into a generally cylindrical, axially extending one Outlet pipe socket. The larger end diameter in the housing entered material is moved back by the screw under high compression and high pressure to the end of smaller diameter, where it is pressed out as a compressed plug of the outlet pipe connection or _P fropfenrohr. The plug tube can be selected such that the plug forms an adequate pressure seal when the material is continuously fed into a pressurized container space. Insofar as the conical housing is provided with through openings, liquid can be squeezed out of the material during the compression.

Screw presses of the type described are also described in the references mentioned in connection with the horizontal tube cooker.

If the term "continuous process" is used here, the word "continuous" should primarily refer to the process sequence within a hydrolysis stage. The at least two-stage hydrolysis process according to the invention can therefore, if necessary, also be carried out with a one-stage system by operating it intermittently as the first stage or subsequent stage. For larger plants, however, the system should be carried out in several stages, as certain ⁱ schaltungstechnische.Vorteile the invention may be realized only with a multi-stage system in accordance.

The use of a continuous tube boiler with _F üllschnecke offers considerable advantages for the technical implementation of a continuous saccharification of biomaterial. The filling screw makes it possible for the pre-comminuted material to be largely free of excess liquid and, more importantly, largely free of air pockets which are disadvantageous affect the chemistry of hydrolysis, to be introduced into the pressurized reaction space in the cooker. In almost all practical process variants, the biosubstance comes into contact with liquid before it enters the reaction space. In process variants with not very short reaction times, the biosubstance is expediently pre-impregnated with the mineral acid-containing digestion liquid before entering the first hydrolyzing stage. For impeccable impregnation, a certain excess of liquid must be used, which can be reduced to the level provided for the hydrolysis again without a further process step by means of the filling screw upstream of the cooker. But even if you want to work with extremely short hydrolysis times, where it is advisable to inject the aqueous mineral acid catalyst solution directly into the cooker, the biosubstance is generally subjected to wet cleaning and possibly preheating beforehand, in contact with liquid comes, the excess of which can then be easily removed in the filling screw of the cooker.

The tube cooker itself offers the possibility of carrying out the hydrolysis with the shortest reaction times and with the least possible excess of liquid in the vapor phase, with considerable immediate energy savings in the cooking and secondary energy savings resulting from the fact that the hydrolyzate is obtained in a relatively high concentration.

The reaction mixture can be discharged from the cooker by means of a known blow valve via a blow line into a cyclone-like blow tank. In this case of carrying out the process, the separation of the hydrolyzate from the reaction mixture is followed by the sudden expansion, namely the blowing out of the reaction mixture mix from the stove. The multistage separation of the hydrolyzate from the reaction mixture is expediently carried out in countercurrent to the hydrolyzate, with separation here being understood to mean practically countercurrent washing with as little hydrolyzate dilution as possible, in which the last separation stage is generally carried out with fresh water for washing out the organic substance and that for further processing Concentrated hydrolyzate to be supplied is discharged from the first separation stage following the cooker alone. Separating screws and / or twin-wire presses are advantageously used as separating or separating devices. In general, a three-stage hydrolyzate separation is sufficient for the process.

In the context of the present application, “separating screws” are to be understood as meaning screw presses which are similar in principle to the filling screws. They are provided with a perforated jacket for the separation of liquids, but, if they are not required to work against a container pressure, do not need to form a pressure-stopper and can also be operated with less compression if required.

In the context of this invention, double wire presses are understood to mean devices as they are manufactured and sold under this name by the machine factory Andritz Actiengesellschaft in Graz, Austria. Embodiments of such twin-wire presses are described by F. Wultsch in "Das Papier" (1968) No. 12, p.908-914.

In principle, the twin-wire press consists of two endless screens that converge in a wedge shape, whereby the dewatering takes place purely mechanically without a vacuum. The substance pumped into the headbox suspension is pre-dewatered in an essentially horizontal wedge zone. In the subsequent inclined pre-press section, the dewatering process is continued by mechanical pressing. Due to the increasing sieve guide, it is possible to arrange water drainage channels in the top sieve behind the individual press points and to drain off the press water escaping into the top sieve before it is taken up again by the fabric. In this way, rewetting is largely avoided.

In a very advantageous embodiment of the process, the hydrolyzate is separated off, at least in the first separation stage, while the pressure in the reaction space is closed, the sudden expansion of the reaction mixture into the blow tank only taking place after this first separation stage. In this case, the first separating device consists of a screw separator which is connected directly to the discharge end of the tube cooker and forms a unit under pressure with the cooker. For this purpose, the screw separator is provided outside of its conical, perforated casing with a pressure-resistant housing arranged at a distance from the casing, through which only the plug tube at the end of the screw casing is passed. The separated liquid collects in the pressure-resistant housing, which can be drawn off via an outlet line under pressure or via a pressure relief valve. The reaction mixture or the mass remaining after the first hydrolyzate separation is blown out of the plug tube of the screw separator into a blow tank via a blow line. Further separation stages for the hydrolyzate separation can then follow the blow tank. In a special embodiment, it may be expedient to blow off the hydrolyzate separated in this screw separator Blow valve into a separate blow tank. If work is to be carried out in the complete countercurrent of the hydrolyzate for the hydrolyzate separation, this must be raised to the corresponding pressure level of the boiler outlet for the first separation stage by means of a pump.

This embodiment of the method or the system provided for carrying out the method has the advantage that a separate blow valve for the solid substance on the cooker, which may has a certain susceptibility to failure, can be dispensed with. The discharge end of the cooker is formed solely by the separating screw and its conical jacket. The metered discharge of the reaction mixture from the cooker takes place by a corresponding rotary movement of the screw. It is not absolutely necessary to squeeze the hydrolyzate in the screw separator, since hydrolyzate separation can already take place due to a pressure drop between the interior of the cooker and the housing surrounding the screw shell. Another advantage of this procedure is that, for example, in a two-stage process, the hydrolyzate separated in the second stage can be kept under such a pressure that either the steam escaping from the hydrolyzate with a certain relaxation can be used to heat the first stage, or the hydrolyzate itself can be used as an acidic disintegrant under pressure for simultaneous heating in the first hydrolyzing stage. The latter option is only available if the hydrolyzates of the individual hydrolyzation stages are not to be sent directly to further processing.

To achieve a minimal use of mineral acid catalyst, it is expedient to proceed as described above and, at least in the case of a two-stage hydrolysis, the hydrolyzate of the second stage, which generally still contains sufficient mineral acids, directly to be used as a digestion liquid for the first hydrolysis stage. In this case, the hydrolyzate would not only be conducted in the hydrolyzate separation stages following each hydrolysis stage, but through the entire system in countercurrent, so that only the hydrolyzate of the first separation stage is fed to the first hydrolysis stage for further processing.

Even if, on the one hand, it brings the advantages mentioned to operate the system according to the invention completely in countercurrent to the hydrolyzate, other considerations can be decisive in doing without such a hydrolyzate system and feeding the hydrolyzate directly to each hydrolyzing stage for further processing.

This is the case in particular in a further advantageous embodiment of the method in which the hydrolyzate is neutralized behind each individual hydrolyzing stage, specifically already in the discharge end of the cooker or in the blow line. The extraordinary advantage of this process variant lies in the fact that the reaction mixture is deprived of its highly corrosive properties and the plant units including the blow tank connected to the blow line, but above all the further separating devices or countercurrent washing devices for the hydrolyzate need not be made from acid-resistant materials . This is important for the practical operation of the system and for the necessary investment costs.

In the event that a further hydrolyzing stage follows the hydrolyzate separation behind a hydrolyzing stage, the filling screw for the boiler of the next stage is expediently used at the same time as the last separation stage for the hydrolyzate separation in the previous stage. This is possible because insofar as Sepa Rierschnecken used for the hydrolyzate separation, these separating screws can be carried out essentially in the same way as the filling screws of the cooker. This results in considerable simplifications in terms of plant technology. Since the filling screw serves to remove excess liquid from the organic substance before it enters the cooker, the filling screw can also be used at the same time to remove residues of the hydrolyzate produced in the previous stage from the mass.

In horizontal tube cookers, as are known from pulp production, a vertical downpipe is generally arranged between the filling screw and the actual cooking tube, in the upper end of which the plug tube opens the filling screw horizontally. This arrangement is therefore chosen in order to arrange a closing device for the mouth, a so-called "blow back damper", opposite the mouth of the filling screw, by means of which the blowout of the cooker can be prevented by the material plug if the pressure closure fails.

In contrast to pulp production, in which the end product is the solid, which should not be damaged in its fiber structure, the hydrolysis does not depend on the solid but on the hydrolyzate as the product, so it is advisable to largely shred the starting material . It has been shown that, under such conditions, a reliable pressure closure can be achieved by grafting the filling screw, so that the filling screw can be opened directly into the cooker tube. This can be important in hydrolysis with a very short reaction time. In order to be able to disintegrate the heavily compacted plug after its immediate entry into the cooker tube for the course of the reaction, it is done partial, for this purpose to provide steam inlets inside the cooker behind the mouth of the filling screw.

If the reaction times in the range from about 1 to 6 minutes are not too short, it is generally expedient to pre-impregnate the biosubstance with the acid-containing digestion liquid before the first hydrolysis step. This can be done, for example, by intensive mixing of the substance with the digestion liquid in excess in a twin-shaft mixer known per se. The excess digestion liquid is then removed again in the filling screw of the cooker. With very short reaction times, it may be necessary to do without the pre-impregnation. In this case, the digestion liquid is injected directly into the cooker in order to achieve defined short reaction times in this way. However, even in the case of this procedure, a two-shaft mixer upstream of the first hydrolyzing stage can be advantageous in order to impregnate the biosubstance with liquid alone, as a result of which the air pockets are reduced, and to preheat it for the cooking process.

The condition of the biosubstance supplied to the first stage is of importance for the feasibility of the claimed process. It may therefore be necessary to subject the biosubstance to dust removal and / or wet cleaning before it is impregnated with the digestion liquid or before preheating. A wet cyclone is preferably used for dust separation and, for example, a device for wet cleaning is used according to the published German patent applications 26 13 510 and 26 20 920. In wet cleaning, an aqueous suspension of the organic substance with about 3-5% consistency is used. The comminution of the organic substance which is generally to be carried out before the cleaning is expediently carried out by means of a shredder, as is known from the mine industry. For a good one V _e rfahrenswirkungsgrad are thereby grain sizes of 0.1 to 3 mm, preferably from 1 mm to sought. 2 The above information about cleaning and shredding essentially relates to vegetable waste products from annual plants, waste paper and the like. Different conditions may be required for processing wood. In any case, the wood must not be present in large chips as in the conventional, discontinuous percolysis processes, but must be in the form of fine chips, sawdust or the like. Multi-stage shredding may be necessary, especially for processing wood.

The hydrolysis of the hemicelluloses in the first hydrolysis stage is advantageously carried out at temperatures in the range from about 135 to 190 ^° C. and corresponding pressure during a reaction time of preferably about 0.05 to 5 minutes. Depending on requirements, the response times can also be extended up to 20 minutes. For the hydrolysis of the cellulose in the second or a further stage, work is preferably carried out at temperatures in the range from 210 to 250 ° C. and corresponding pressures. The response time can be of the same order of magnitude as for the first stage. The lowest possible liquid-to-solid ratio should be aimed for, which should be in the range of 3: 1 to 1.5: 1, but preferably in the range of 2: 1. The use of a filling screw with a perforated screw housing offers the particular advantage that even after impregnation of the organic substance in a twin-shaft mixer, excess digestion liquid can be squeezed out again immediately before the mass enters the cooker, without the need for an additional process step. It should again be emphasized that an essential point of the claimed method is that it is used A filling screw is able to remove almost 100% of the air, which is extremely harmful to the hydrolysis, from the shredded organic substance before it enters the cooker.

As known per se, mineral acids, preferably sulfuric or hydrochloric acid, are used as acids for the hydrolysis according to the claimed process in dilute form. Since the acid which merely serves as a catalyst has to be removed from the hydrolyzate again, the aim is to use as little mineral acid as possible. This is favored by the relatively high hydrolysis temperatures claimed, since under these conditions the organic acids contained in the biosubstance already start to act hydrolytically, so that it is sometimes possible to work autohydrolytically. If the hydrolyzate is passed completely countercurrently through all stages without intermediate neutralization, mineral acid generally only has to be added in the last stage anyway.

Even if the special process conditions aim to keep the use of foreign chemicals as low as possible, it is still important for the economic viability of the process to recover the auxiliary materials used, particularly in the case of intermediate neutralization. The removal of the acids from the hydrolyzate is generally carried out with the neutra. lization by precipitation of certain salts of the acids. In a preferred development of the claimed process, the salts precipitated from the hydrolyzate are subjected to a two-stage combustion together with the remaining biosubstance leaving the hydrolysis process, which essentially consists only of lignin, in which reducing, i.e. reducing, is carried out with excess CO and oxidizing in the second combustion stage in order to recover the mineral acid anhydride and the neutralizing agent.

If, as is customary, dilute sulfuric acid is used as the mineral acid, the acid from the hydrolyzate is generally precipitated with lime to form calcium silicate. When the lime is burned together with the biomass, the latter serving as an energy source, calcium sulfide, for example, is formed in the reducing combustion stage, which is converted into calcium oxide in the second, oxidizing combustion stage. Sulfur dioxide is recovered from the flue gases and processed again to sulfuric acid.

For easier chemical recovery, it may be advantageous to work directly with sulfur dioxide as a catalyst in the hydrolysis.

The invention also relates to a system suitable for carrying out the method. The above description of the features essential to the method of the invention is also largely applicable to the associated system.

The horizontal tube cookers can each consist of one or more tubes, depending on the required throughput and reaction time. In the case of a plurality of horizontal cooker tubes, these are generally arranged one below the other and are each connected at their discharge end to the input end of the next tube by a short downpipe. Each tube generally contains a screw conveyor as a means of transportation for the reaction mixture.

The process according to the invention and associated systems are explained in more detail below with reference to the attached process diagrams.

Brief description of the drawings

• Fig. 1 ein Verfahrensschema einer ersten Ausführungsform des erfindungsgemäßen Verfahrens;
• Fig. 2 ein Verfahrensschema der ersten Hydrolysierstufe einer Verfahrensvariante;
• Fig. 3 ein Verfahrensschema einer weiteren Variante;
• Fig. 4 eine spezielle Anordnung des Schneckenfüllers im Verhältnis zum Horizontalröhrenkocher.

Show it:

• 1 shows a process diagram of a first embodiment of the method according to the invention;
• 2 shows a process diagram of the first hydrolysis stage of a process variant;
• 3 shows a process diagram of a further variant;
• Fig. 4 shows a special arrangement of the screw filler in relation to the horizontal tube cooker.

Description of the best modes for carrying out the invention

According to the process diagram of FIG. 1, the comminuted and pre-cleaned organic substance at 1 reaches a double-shaft mixer 3 of a known type by means of a conveyor belt 2, which is preferably provided with an automatic weighing device (not shown), in which the organic substance is pre-impregnated with acidic digestion liquid, which is supplied via a line 5 provided with an automatic control valve 4. The digestion liquid is expediently metered as a function of the biological substance weighed in per unit of time via the conveyor belt. Blown steam from the process for heating the bio-substance is additionally fed into the twin-shaft mixer via a line 6.

In the double-shaft mixer 3, which is preferably used as an impregnator, the liquid is intensively mixed with the organic substance by the two rotating screws of the mixer, the liquid penetrating the moist raw material in order to prepare it for the rapid vapor phase digestion. From the discharge opening of the twin-shaft mixer, the impregnated organic substance falls by gravity through a chute 7 into the feed opening of the screw filler 8, which is part of the cooker. In the screw filler 8, the bio-substance is pressed into the cone shell surrounding the screw by the filling screw rotatably mounted in the screw filler, whereby a dense plug is formed which forms the pressure-side closure of the interior of the cooker. Through the perforated conical screw housing through excess liquid is squeezed from the _B iosubstanz which is recycled via a line 9 into the Imprägnierkreislauf. In the screw filler 8, most of the air contained in the organic substance is also removed and the filling screw transports the material with a low moisture content into the cooker, which saves cooking steam and facilitates hydrolysis in the steam phase.

The organic substance falls from the outlet opening of the screw filler 8 through a chamber designed as a chute 10, which opens into the horizontal cooker tube of the cooker 11. The inside of the cooker 11 is provided with a screw conveyor (not shown in FIG. 1), the speed of which can be changed in order to be able to influence the residence time of the organic substance in the cooker. In the schematic representation of FIG. 1, the cooker 11 is also only shown with one cooker tube, but depending on the throughput and dwell time, it can also be designed as a two-tube cooker or as a cooker with several cooker tubes.

The boiler 11 is heated by a line 12 with a plurality of terminals boiler with steam, which will be, as further unte be explained in the present embodiment is obtained by expanding the _H held under pressure ydrolysats the second hydrolysis stage. At the end of the cooker, the reaction mixture falls into one Discharge device, which in the exemplary embodiment consists of a screw separator 13 which is similar in construction to the screw filler 8. At the entrance of the screw separator 13, the reaction mixture is fed via a line 14 hydrolyzate from the second hydrolyzate separation stage operated in countercurrent. The hydrolyzate separated by the cone jacket of the screw separator 13, which is the total hydrolyzate from the two hydrolysis stages shown in the circuit of the exemplary embodiment, leaves the hydrolysis plant here and is fed to the intended further processing. The narrowed mouthpiece of the screw separator 13 is connected via a blue line 15 to a cyclone-like blow tank 16, into which the blow line 15 is inserted tangentially at the upper end. An emergency valve 17 is also provided in the blow line 15 immediately behind the mouthpiece of the screw separator 13. The amount of discharge from the cooker is determined by the speed of rotation of the screw. The hydrolyzate is separated by the pressure drop between the interior of the cooker 11 or the screw separator 13 and the exterior surrounding the cone housing. An additional pressing action by the screw can be advantageous, but is not absolutely necessary.

The residual substance remaining in the screw separator 13 after separation of the total hydrolyzate is blown out via the blow line 15 into the blow tank 16, in which a pressure release takes place, through which steam is released from the remaining reaction mixture. The blow tank 16 is essentially closed and is kept under a slight excess pressure in order to catch the released steam and to feed it back into the process. As already mentioned, part of this blow steam is fed to the twin-shaft mixer 3 via the line 6. Remaining blow steam passes through line 17 to other recycling points in the process.

Connected in series to the lower discharge end of the blow tank 16 are two further screw separators 18 and 19, which are operated in the liquid countercurrent for the most complete and dilution-limited washing out of the hydrolyzate from the bio substance. The screw separator 19 also serves as a screw filler for the digester of the following stage and thus represents the connection point between the first and second hydrolyzing stage.

In accordance with the countercurrent washing principle, the liquid squeezed out in each screw separator is in each case returned to the previous hydrolyzate separation stage. Thus, the liquid squeezed out in the screw separator 19 returns via a line 20 to the blow tank 16 and thus in front of the screw separator 18, and the liquid separated therein via the already mentioned line 14 into the discharge end of the cooker 11 in front of the screw separator 13 directly connected to it Since this requires the liquid to be fed into the pressure chamber of the cooker, a pressure booster pump 21 is provided in line 14 in order to raise the washing hydrolyzate to the corresponding pressure level.

After the residual hydrolyzate of the first hydrolyzation stage has been largely removed from the remaining biosubstance in the worm separator 19 working as the third hydrolyzate separation stage, the biosubstance, after it has passed the mouthpiece of the worm filler 19 forming the worm filler for the second hydrolysis stage, is metered in via a line 22 mineral acid , preferably dilute sulfuric acid, added as a catalyst for the hydrolysis. By relaxing the material behind the snail mouthpiece, the acid is readily absorbed by it. The impregnated residual organic substance passes from the screw filler 19 a chute 22 in the tube cooker 23 of the second hydrolysis stage, which is of the same type as the cooker 11 of the first hydrolysis stage, but the specific data of which can be adapted to the requirements of the second stage and therefore need not exactly match the cooker of the first stage. In the exemplary embodiment, the cooker 23 of the second hydrolysis stage, which is generally operated under higher pressure than the first stage, is heated with live steam via a line 24.

The aggregates following the cooker 23 of the second hydrolysis stage essentially correspond to those of the first hydrolysis stage. The cooker 23 is connected at its discharge end to a screw separator 25 which is connected to a blow tank 28 via a blow line 27 provided with an additional blow valve 26. This is followed by two further screw separators 29 and 30.

The residual bio-substance emerging from the mouthpiece of the last screw separator 30 and consisting largely of lignin leaves the process here and is expediently used for energy generation by combustion in a boiler system. Between the screw separators 29 and 30, the residual organic substance is added via a line 31 washing water, which is preferably heated and can be process water obtained elsewhere in the overall system. The last washing hydrolyzate separated in the screw separator 30 is returned via a line 32 into the blow tank 28 and thus before the screw separator 29 forming the second hydrolyzate separation stage. The liquid separated in this passes through a line 33 upstream of the screw separator 25, which is under boiler pressure, which is why a pressure booster pump 34 is also provided in this line 33. The pressurized hydrolyzate of the second hydrolyzing stage, which is separated in the screw separator 25 connected to the cooker 23, is led via a line 35 back into the first hydrolysis stage and first to a flash tank 36 from which the steam released by flashing, as already mentioned above, via line 12 as Heating steam is introduced into the first stage cooker 11. The relaxed hydrolyzate of the second stage passes from the expansion vessel 36 via line "4 for pre-impregnation of the fresh organic substance into the twin-shaft mixer 3 of the first hydrolysis stage.

As can be seen from the overall process diagram of FIG. 1, live steam is only used to heat the second stage cooker. The first stage cooker is heated with the flash steam from the second stage hydrolyzate. The hydrolyzate is passed through the entire system in counterflow and enriched. Washing water is added only before the last separation stage after the second hydrolysis stage. The three-stage hydrolyzate separation behind the second cooker is operated in countercurrent, and the hydrolyzate separated in the first separation stage behind the second cooker, namely in the screw separator 25, is completely added to the biosubstance before the first hydrolyzing stage and enriched with the hydrolyzate of this stage within the first hydrolyzing stage , a countercurrent washout also taking place behind the first stage digester, so that the concentrated total hydrolyzate of both hydrolysis stages can be removed from the first hydrolyzate separation stage behind the first digester. Since the mineral acid-containing hydrolyzate of the second hydrolysis stage is used as the digestion liquid in the first hydrolysis stage, mineral acid need not be added again here. Fresh mineral acid is added alone before the boiler of the second hydrolysis stage. On the additional representation known per se Means for controlling and regulating the process flow were intentionally omitted in the process diagram of FIG. 1.

2 shows a variant of the process according to the invention in the form of a simplified process scheme, but only the first hydrolysis stage is shown here, to which one or two further similar hydrolysis stages can follow.

The process variant of FIG. 2 differs from the process diagram of FIG. 1 in that the screw discharge end of the cooker 11 is not connected to the discharge end of the cooker 11, but only a vessel 40 is provided, which is connected via the blow line 15 with the blow tank 16 is connected. In this embodiment, the discharge from the cooker 11 is regulated solely by the blow valve 17. To compensate for the missing screw separator at the cooker outlet, a three-stage hydrolyzate separation by means of screw separators 18, 41 and 42 is provided behind the blow tank 16 in the variant of FIG. 2, none of these separation stages being under pressure.

An essential feature of the process diagram shown in FIG. 2 is that a line 43 is led into the blow line 15, via which a neutralizing agent, preferably milk of lime, can be injected directly into the blow line. The mouth of the line 43 into the blow line 15, which consists of suitable injection devices, is preferably located close behind the blow valve in the practical embodiment, in order to achieve an effective mixing between the reaction mixture and neutralizing agent, which is practically one, by the turbulence prevailing in the blow line abrupt neutralization of the reaction mixture should lead.

The decisive advantage of this procedure is that the blow tank 16 and all subsequent units of this stage, in particular the screw separators 18, 41 and 42, do not have to be made of acid-resistant material. For the same reason, this variant also dispenses with the advantageous arrangement of a screw separator directly at the outlet of the cooker 11.

Provided that the second (not shown) hydrolyzing stage is operated in a corresponding manner, however, it is not possible to return the neutralized hydrolyzate from the second stage as a digestion liquid to the first stage, since the acid contained in it, necessary as a catalyst, passes through neutralization has been removed. Accordingly, fresh acid is already supplied to the first hydrolysis stage via a line 44 as a catalyst. It is introduced into the twin-shaft mixer 3 and into the screw filler 8.

If a first hydrolyzate separation stage working under pressure is faulty behind the boiler of the second hydrolysis stage (not shown), there is not enough hydrolyzate under pressure from which the entire heating steam for the boiler of the first stage could be obtained by expansion. Therefore, in this embodiment, the cooker 11 of the first stage is at least partially heated with live steam via a line 45. However, there is the possibility of withdrawing part of the hydrolyzate from the second cooker immediately after the pressure has been closed, from a vessel corresponding to the vessel 40 behind the first cooker 11 without an actual separating device, and of recovering some of the steam by relaxing this hydrolyzate portion. the, as shown in the embodiment of FIG. 2, via a line 46 as a partial heating steam can be fed to the lower stage cooker 11 of the first stage. This measure makes it possible, at least in part, to take on certain advantages of the circuit according to FIG. 1 in the method sequence according to FIG. 2.

1, the hydrolyzate is passed completely countercurrently through the entire system, in the intermediate neutralization according to FIG. 2 it is only possible to combine the neutralized hydrolysates of the individual stages as such in order to subject them to further processing . Apart from the complete countercurrent flow of the hydrolyzate, the process features of both embodiments can also be combined. It is thus possible to provide a separating device operating under the pressure of the cooker at the outlet of each cooker, even in a process according to FIG. Such a measure can also be limited to the second hydrolyzing stage alone, since it is then at least possible to utilize the entire hydrolyzate obtained under pressure in the second stage of the production of cooking steam for the first stage. The disadvantage compared to the embodiment according to FIG. 2 is then that at least the separating device which is arranged in front of the blow tank and is under pressure must be made of acid-resistant material, since the neutralization only takes place in the blow line behind this separation stage. On the other hand, according to the procedure of FIG. 1, it is also possible to neutralize the reaction mixture in the blow line 15 of the first hydrolysis stage, but to dispense with a corresponding measure in the second hydrolysis stage. This means that at least the screw separators 18 and 19 can be made from cheaper material.

With a hydrolysis plant according to the process diagram of FIG. 2 in two stages, from a ton of dry mixed organic matter, consisting of one third wood, residual and waste materials, _Ge straw and straw waste paper about 500 kg of sugar, as a mixture Pentoses and hexoses are made. The amount of catalyst required is about 0.3%, based on the raw material used.

The reaction time in the first hydrolysis stage is approximately 2 1/2 minutes at 180 ° C. and the reaction time in the second hydrolysis stage is approximately 4 1/2 minutes at approximately 235 ° C. The remaining cellulignin after the second stage is about 25 to 28% of the starting substance and is sufficient to obtain the required process heat as a vapor by combustion at a pressure of about 28 to 30 bar. _-

In Fig. 3, the essential parts of a variant of a hydrolysis stage are shown schematically, which can serve as the first hydrolysis stage, for example. For reasons of clarity, auxiliary devices and the representation of the instrumentation of the process sequence which is generally familiar to the person skilled in the art are also omitted here.

In FIG. 3, only the discharge end of the horizontal tube cooker 11 is shown on the left, in the interior of which the screw conveyor 80 causing the material transport in the reaction space is indicated. At the end of the cooker, the reaction mixture reaches a screw separator 13 by free fall, as in the embodiment according to FIG. For this purpose, the perforated screw casing 81 is surrounded by a pressure-tight housing 82, through which only the plug tube 83 of the screw separator is passed. From the plug tube 83 leads, as in the embodiment according to FIG. 1, a blow line 15 secured by an emergency valve 17 into the blow tank 16 for the biomass. The housing 82 of the screw separator 13 is provided with a discharge connection 84 for discharging the hydrolyzate that accumulates between the cone shell 81 and the housing 82. Since this hydrolyzate space is also under pressure, a blow valve 85 is connected to the connector 84, behind which the hydrolyzate is expanded and blown through a second blow line 86 into a hydrolyzate blow tank 87. From here, the hydrolyzate runs by gravity into a hydrolyzate collecting container 88, from where it is fed for further processing by means of a pump 89. As will become apparent from the following description, the hydrolyzate separated in the screw separator 13 is the concentrated and already neutralized hydrolyzate of the last separation stage.

The vapor generated in the blow tanks 16 and 87 is expediently fed to a heat recovery device 90 in which, for example, the fresh water for the last washing out of the biomass can be preheated up to 60 ° in the last hydrolyzate separation stage, for example.

The biomass is drawn off at the lower end of the blow tank 16 by means of a screw conveyor 91 and fed via a stock feed device 92 to a twin-wire press 93 for further hydrolyzate separation. The twin-wire press 93 has an endlessly rotating lower sieve 94 and an endlessly rotating upper sieve 95, which form an increasingly narrowing gap region 97 between a row of horizontal roller pairs 96, in which the biomass introduced between the sieves passes through both sieves under the pressure of the roller pairs 96 liquid is separated, which is collected in a first collecting pan 98. The lower sieve 94 has one of Rollers 99 carried leading section for feeding in the biomass, above which a driven leveling roller 100 is additionally arranged in order to pre-compress and equalize the biomass lying on the bottom wire 94 before entering the gap area 97. At the end of the first liquid separation section with the roller pairs 96, the screens 94 and 95 enclosing the biomass between them are guided around a washing shoe 101, with which preheated fresh water or other washing water is expediently introduced into the biomass for washing out the last hydrolyzate. Behind the washing shoe 101, the two sieves pass through three press roller pairs 102 in an inclined section. Before the second and third press roller pairs 102, washing water is again applied to the sieves from above by means of distributor pipes 103. The liquid separated from the biomass by the press roller pairs 102 is collected in a second collecting trough 104. The water squeezed out in the press roller pairs 102 through the top sieve 95 can be gripped and led into the collecting trough 104 without any risk of rewetting the biomass in front of each of them, due to the rising sieve guide through collecting channels (not shown) arranged in front of each upper press roller, as seen in the conveying direction Press inlet exists. The biomass leaving the press section is moved by gravity into a screw conveyor 105, with which it is fed for further use.

The plant has three series-connected, countercurrent hydrolyzate washing stages, of which the first one is formed by the screw separator 13 and the other two are located in the twin-wire press 93 when viewed in the direction of conveyance of the biomass. The individual hydrolyzate washout cycles are as follows:

In front of and between the pairs of press rolls 102, fresh water, preferably preheated by means of process waste heat, is introduced from a fresh water line 106 from a supply line 106 for the last hydrolyzate washout into the biomass. The wash water collected in this last hydrolyzate separation stage in the collecting trough 104 is fed by means of a pump 107 via a line 108 by feeding into the blow tank 16 before the second hydrolyzate separation stage, which is formed by the horizontal dewatering section of the screens 94 and 95 flanked by the roller pairs 96 . The weak hydrolyzate collected at this stage in the collecting trough 98 is introduced by means of a pressure booster pump 109 via a line 110 into the discharge end of the cooker 11 in front of the screw separator 13. The final hydrolyzate of the highest concentration level is then drawn off in the screw separator 13 and passed on for further processing via the blow tank 87 and the storage container 88.

A special feature of the embodiment shown in FIG. 3 is that a neutralizing agent addition device 111 is provided, with which neutralizing agent can be introduced directly into the weak hydrolyzate conveyed through line 110 and thus reaches the discharge end of the cooker 11 in order to obtain the reaction mixture obtained there neutralize even before entering the screw separator 13 in order to take away its highly corrosive properties. This measure makes it possible to carry out the neutralization without using further dilution water before the first hydrolyzate separation stage in the cooker. This practically combines the advantages according to the embodiments of FIGS. 1 and 2. The neutralizing agent adding device 111 is provided with a bypass line 112. Also indicated in FIG. 3 is a catalyst or acid treatment device 113, from which catalyst is under pressure by means of one or more inlets guide socket 114 can be introduced into the cooker 11 at a suitable point.

The circles shown in FIG. 3 and containing an M symbolize the drive motors for the various units.

As already mentioned above, the type of introduction of the biomass into the horizontal tube cooker 11 can be important. FIG. 4 shows a spatially-objective arrangement of the screw filler 8 in relation to the horizontal tube cooker 11, as provided for the plant embodiment according to FIG. 3, but is not shown in the process diagram. In known cookers, such as those used for the production of cellulose, for the reasons described above, the profpen tube of the screw filler opens into a vertical downpipe 10, as is shown in the embodiments of FIGS. 1 and 2. It has now been found that, under the conditions for the hydrolysis of comminuted organic matter, it is also possible for the screw filler 8 with its plug tube 115 (FIG. 4) to open directly into the cooker tube of the cooker 11. Here, an arrangement is particularly expedient in which the axis of the screw filler 8 runs horizontally, but at right angles to the horizontal axis of the cooker 11, and in which the plug tube opens approximately tangentially into the upper region of the cooker tube, as shown in FIG. 4 emerges. 4, an intermediate silo 116 is indicated above the loading end of the screw filler 8, from which the biomass can be fed into the screw filler 8 by means of a screw conveyor 117 or directly by means of an upstream mixer.

For the direct connection of the screw filler 8 to the cooker tube 11 shown in FIG. 4, special conditions for the dimensioning of the screw are shown and the formation of the plug tube is necessary in order to prevent the cooker from occasionally being blown back by the screw filler 8 with a high degree of certainty. It has been shown that these conditions can be achieved in particular if there is a volumetric compression ratio of at least 1: 4 within the screw filler between the screw inlet and the plug tube and the ratio of length to diameter of the plug tube is at least 2: 1. The screw should then be dimensioned overall so that a density of the biomass in the plug tube of at least 350 kg / m ^{3 is} generated with the intended material loading. Under these conditions, it is possible to work safely with a direct connection between the screw filler and the cooker, this direct connection being preferred for short reaction times and a fast reaction sequence.

In order to sufficiently disintegrate the plug of relatively high density that enters the cooker for the subsequent reaction process, it is expedient to arrange the steam supply that is required for the cooking process in such a way that the steam entry is provided immediately behind the entry point of the compressed biomass and in this way the plug that disintegration can take place through the steam.

Claims (28)

1. A process for the continuous hydrolysis of pentosan-containing hemicelluloses, cellulose and corresponding compounds in plant-based organic substance to form sugars, in which the appropriately pre-comminuted organic substance is subjected to temperature and pressure conditions in a first stage in the presence of dilute acid, in which essentially the hemicelluloses and only partially hydrolyze the cellulose to pentoses and partially hexoses during a first reaction time, whereupon the reaction mixture is suddenly expanded on the one hand and the hydrolyzate is separated from the biosubstance on the other hand, in at least one further stage in the presence of dilute mineral acid and under more stringent temperature and pressure conditions Cellulose in the bio-substance is hydrolyzed to hexoses during a further reaction time, whereupon the reaction mixture is suddenly expanded again on the one hand and the hydrolyzate is separated from the residual bio-substance on the other hand , and in which the neutralized hydrolyzate is processed in a suitable manner to obtain the sugar. becomes, characterized in that the infiltration of the biomaterial in the pressurized reaction _- space by means of a pressure seal forming charging screw (8,19) is made to be substantially removed in the contained in the biomaterial air and excess fluid, hydrolysis in a continuous horizontal tube boiler ( 11, 23) as a reaction space in the vapor phase and the hydrolyzate is separated from the reaction mixture in several separation stages (for example 13, 18, 19). 2. The method according to claim 1, characterized in that the biomass in the filling screw (8) compressed in a volume ratio of at least 1: 4 and the plug produced in the outlet end of the filling screw (8) brought to a plug density of at least 350 kg / m ³ and is pressed through a plug tube (115) with a length-to-diameter ratio of at least 2: 1, and - that the plug is disintegrated after exiting the plug tube (115) by applying steam to the reaction sequence in the cooker (11). 3. The method according to claim 1, characterized in that the multi-stage hydrolyzate separation is carried out only after the sudden relaxation of the reaction mixture. 4. The method according to claim 1, characterized in that a hydrolyzate is separated in at least a first separation stage (13, 25) under the pressure closure of the reaction chamber (11, 23) and the sudden relaxation only after this (these) separation stage (s) (13 , 25) is made. 5. The method according to claim 4, characterized in that the hydrolyzate separated off under pressure is suddenly expanded separately from the solids. 6. The method according to claim 4, characterized in that a separating screw (13, 25) is used as the separating device for the first separation stage, which is directly connected to the outlet end of the cooker (11, 23), and that the sudden relaxation the remaining reaction mixture from the plug tube of the separating screw (13, 25). 7. The method according to claim 4, characterized in that the sudden expansion is followed by further separation stages (18, 19; 29, 30) in which separating screws and / or twin-wire presses (93) are used as separating devices. 8. The method according to claim 7, characterized in that two or more separation stages are carried out by means of a twin-wire press (93). 9. The method according to claim 1, characterized in that the hydrolyzate is separated after each hydrolysis step in countercurrent of the hydrolyzate by adding fresh water before the last separation step in general and adding the liquid separated in a separation step before the previous separation step, the hydrolyzate in In the event of sudden relaxation between the separation stages for the separation stage (s), the pressure is raised to the correspondingly higher level before the relaxation. 10. The method according to claim 1, characterized in that except in the last hydrolysing step in each hydrolyzing step hydrolyzate from the next hydrolysing step is used as an acidic digestion liquid and only the hydrolyzate separated off in the first separation step after the first hydrolyzing step is fed to further processing. 11. The method according to claim 1, characterized in that the hydrolyzate is fed to each hydrolyzing stage directly for further processing. 12. The method according to claim 11, characterized in that the neutralization of the hydrolyzate takes place before or during the sudden relaxation of the respective reaction mixture by the neutralizing agent, preferably lime milk, is introduced into the discharge end of the horizontal tube cooker (11) or into the blow line (15) leading into the relaxation space. 13. The method according to claim 4, characterized in that the neutralization of the hydrolyzate before the first, under pressure separation stage (13) by introducing the neutralizing agent into the discharge end of the horizontal tube cooker (11). 14. The method according to claim 1, characterized in that the reaction mixture is kept under a certain excess pressure even after the sudden relaxation in the relaxation room in order to be able to use the steam released during relaxation. 15. The method according to any one of claims 1 to 14, characterized in that the pre-comminuted 'biosubstance is pre-impregnated with the acidic, aqueous digestion liquid before introduction into the filling screw of the first hydrolysis stage. 16. The method according to any one of claims 1 to 14, characterized in that the acidic, aqueous digestion liquid is injected directly into the reaction chamber under pressure. 17. The method according to any one of claims 1 to 14, characterized in that the organic substance is crushed to grain sizes of about 0.1-3 mm, preferably 1-2 mm. 18. The method according to one of claims 1 to 14, in which in the further processing of the hydrolyzate the neutralized mineral acid in the form of a salt of this acid is separated from the hydrolyzate, characterized in that the in the last stage of Process-occurring residual largely consisting of lignin organic substance together with the salt is subjected to a two-stage combustion, in which reducing in the first combustion stage and oxidizing in the second combustion stage to the mineral acid anhydride and the neutralizing _. recovery agent. 19. Plant for the continuous hydrolysis of pentosan-containing hemicelluloses, cellulose and corresponding compounds in plant-based organic substance to form sugars, in which the suitably pre-comminuted organic substance is subjected to temperature and pressure conditions in a first stage in the presence of dilute acid, in which essentially the hemicelluloses and only partially hydrolyze the cellulose to pentoses and partially hexoses during a first reaction time, whereupon the reaction mixture is suddenly expanded on the one hand and the hydrolyzate is separated from the biosubstance on the other hand, in at least one further stage in the presence of dilute mineral acid and under more stringent temperature and pressure conditions Cellulose in the biosubstance is hydrolyzed to hexoses during a rather longer reaction time, whereupon the reaction mixture is suddenly expanded again on the one hand and the hydrolyzate is separated from the residual biosubstance on the other hand, and in which the neutralized hydrolyzate is processed in a suitable manner to obtain the sugars, characterized in that each hydrolysis stage as a reaction chamber is operated continuously and inside with. Has horizontal conveying organs provided horizontal tube cooker (11, 23) which on the input side with a screw filler (8, 19) with a conical screw and perforated cone jacket for Introducing the biosubstance into the reaction chamber, and the discharge end of which is provided with a discharge device which forms the outlet-side pressure seal of the reaction chamber and which is connected via a blow line (15, 27) to a cyclone-like blow tank (16, 28). 20. Plant according to claim 19, characterized in that the first separating device for separating the hydrolyzate in a hydrolyzing stage is connected directly to the discharge end of the tube cooker (11, 23) and together with the cooker is under pressure and at the same time forms the discharge device forming screw separator (13 , 25), whose perforated conical casing (66) is surrounded by a pressure-tight housing (71). 21. Plant according to claim 20, characterized in that behind the on the pressurized screw separator (13, 25) connected blow tank (16, 28) further separating devices in the form of screw separators (18, 19; 29, 30) and / or twin-wire presses (93) are connected. 22. Plant according to claim 21, characterized in that the screw separators are of essentially the same type as the screw filler. 23. Plant according to claim 22, characterized in that in the case of a further hydrolyzing stage the screw filler (19, 42) for the following tube cooker (23) serves simultaneously as the last separating device of the previous stage. 24. Plant according to claim 21, characterized in that the further separating devices consist of at least one twin-wire press (93) with two Press sections (96; 102) is provided with separate hydrolyzate collecting devices (98; 104) for carrying out a two-stage hydrolyzate separation. 25. Plant according to claim 24, characterized in that a feed device (101) for fresh water or hydrolysate-containing wash water is provided between the two press sections (96; 102). 26. Plant according to claim 19, characterized in that the plug tube (115) of the screw filler (8) opens directly into the cooker tube (11). 27. Plant according to claim 26, characterized in that steam supply devices are provided directly behind the outlet end of the plug tube ( ₁₁₅ ) in the interior of the cooker. 28. Plant according to claim 26 or 27, characterized in that the ratio of length to diameter of the plug tube (115) is at least 2: 1 and the volumetric compression ratio of the screw from the screw inlet to the plug tube is at least 1: 4.

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