METHOD AND PLANT FOR OBTAINING CELLULOSE FIBRES

Abstract

The invention relates to a method for obtaining cellulose fibres from fibrous biomass, in which: the biomass is first subjected to thermo-pressure hydrolysis, preferably with steam explosion, in a thermo-pressure hydrolysis plant, and then separation of the fibrous sludge obtained from the thermo-pressure hydrolysis plant is carried out in at least one separation plant, wherein a press cake of cellulose fibres, preferably with a dry material content of over 20%, preferably of over 25%, and a filtrate of flowable, solids-rich thin sludge are obtained, and wherein the thin sludge is fed to a biogas plant as a fermentation substrate to obtain biogas. The invention also relates to a plant for carrying out this method.

Claims

1. A method for obtaining cellulose fibres from fibrous biomass, comprising: subjecting the biomass to thermo-pressure hydrolysis, preferably with steam explosion, in a thermo-pressure hydrolysis plant, and separating the fibrous sludge obtained from the thermo-pressure hydrolysis plant in at least one separation plant, wherein: a press cake formed of cellulose fibres, preferably having a dry matter content of more than 20%, preferably more than 25%, and a filtrate formed of a flowable, high-solids, thin sludge are obtained, and the thin sludge is fed to a biogas plant as a fermentation substrate in order to obtain biogas.

2. The method according to claim 1, wherein the fibrous sludge obtained after the thermo-pressure hydrolysis is dispersed in a dispersing unit, preferably at a temperature T≥60 C.

3. The method according to claim 1, wherein: the fibrous sludge obtained after the thermo-pressure hydrolysis is adjusted in a subsequent step to a dry matter content of preferably 3% to 20%, particularly preferably 3% to 10%, and the adjustment preferably takes place in a mashing tank, and then the separation of the mashed fibrous sludge takes place in at least one separation plant.

4. The method according to claim 3, wherein, before the separation in the at least one separation plant, first a fibre separation and/or fibre shredding of fibre bundles in the mashed fibrous sludge from the mashing tank takes place in at least one disintegrator, and then a separation of the fibrous sludge takes place in the at least one separation plant.

5. The method according to claim 1, wherein, after the fibrous sludge from the thermo-pressure hydrolysis plant has been separated in at least one first separation plant: the press cake obtained is fed to a mashing tank in order to set a dry matter content of preferably 3% to 20%, particularly preferably 3% to 10%, the mashed fibrous sludge is fed to at least one disintegrator in order to obtain a fibre separation and/or fibre shredding of the fibre bundles contained in the mashed fibrous sludge, and a separation of the fibrous sludge takes place in at least one second separation plant.

6. The method according to claim 4, wherein: the fibre separation and/or fibre shredding in the at least one disintegrator is repeated at least once, preferably multiple times, and the fibrous sludge is routed between the mashing tank and the disintegrator preferably in a cyclic process.

7. The method according to claim 1, wherein the filtrate from the at least one separation plant, which is in the form of a thin sludge, is at least in part fed to the biogas plant as a fermentation substrate.

8. The method according to claim 7, wherein the filtrate from the at least one separation plant, which is in the form of a thin sludge, is collected and is at least in part returned to the process, in particular is fed to the mashing tank and/or is added to the fibrous sludge upstream of the at least one separation plant.

9. The method according to claim 7, wherein: the thin sludge is collected in two sub-fractions, and a first sub-fraction having a lower solids content is returned to the process, while a higher-solids fraction is fed to the biogas plant as a fermentation substrate.

10. The method according to claim 1, wherein the press cake obtained from the at least one separation plant is subjected to a stabilization step, in particular by adding preserving chemicals, and/or to a heat treatment, preferably by supplying process heat.

11. The method according to claim 1, wherein: the press cake obtained from the at least one separation plant is subjected to a further cleaning step in a mixing reactor, and the wash water is separated from the cleaned fibre cake in a further separation plant.

12. The method according to claim 11, wherein the wash water is collected and is preferably fed to the biomass upstream of or in the thermo-pressure hydrolysis plant in order to adjust the water content.

13. The method according to claim 1, wherein the press cake obtained from the at least one separation plant is compacted and then packaged in order to obtain storable, easy-to-handle bales.

14. The method according to claim 1, wherein: the filtrate from the at least one separation plant, which is in the form of a thin sludge, is separated in a further processing step, in particular in a filtration device, into a high-solids, thickened thick phase and into a low-solids filtrate, and the thick phase is made available to the biogas plant as a fermentation substrate, while the filtrate is returned to the process, in particular as dilution water or mashing water.

15. The method according to claim 1, wherein the fibrous biomass used is plant biomass, in particular energy crops such as maize, Silphium perfoliatum, and/or harvest residues having a sufficient cellulose or lignocellulose content, such as straw and/or green cuttings.

16. The method according to claim 1, wherein the use of the biogas obtained in the biogas plant as an energy source, and/or of the waste heat from the biogas plant, in particular for the thermo-pressure hydrolysis plant.

17. The method according to claim 1, wherein the use of the non-recyclable residues occurring in the biogas plant, in particular containing lignin and/or silicates, as fertilizing and soil improvement agents in agriculture.

18. A plant for carrying out the method a method according to claim 1, for obtaining cellulose fibres from fibrous biomass, the plant comprising: at least one thermo-pressure hydrolysis plant for subjecting the fibres of the biomass firstly to thermo-pressure hydrolysis, preferably with steam explosion, wherein: the thermo-pressure hydrolysis plant is connected via at least one feed line to at least one separation plant, preferably a screw press, into which the fibrous sludge drawn off from the thermo-pressure hydrolysis plant can be fed by means of at least one conveying device, preferably a screw conveyor and/or a thick-matter pump, and the filtrate obtained from the at least one separation plant in the form of a flowable, high-solids, thin sludge can be fed to a biogas plant via at least one further feed line.

19. The plant according to claim 18, further comprising: at least one dispersing unit, which is arranged between the thermo-pressure hydrolysis plant and the at least one separation plant.

20. The plant according to claim 18, further comprising: a mashing tank, which is arranged between the thermo-pressure hydrolysis plant and the at least one separation plant.

21. The plant according to claim 20, wherein: the at least one mashing tank is connected to at least one disintegrator, and the at least one disintegrator is connected to the at least one separation plant preferably via at least one storage tank.

22. The plant according to claim 20, wherein: the at least one mashing tank is arranged downstream of the at least one separation plant, the mashing tank is connected to the at least one disintegrator, and the at least one disintegrator is connected to at least one further separation plant preferably via at least one storage tank.

23. The plant according to claim 18, wherein the filtrate from the at least one separation plant can be collected in at least one collection tank.

24. The plant according to claim 23, wherein the at least one collection tank is connected to the mashing tank via at least one recirculation line and/or to the biogas plant via at least one further feed line.

25. The plant according to claim 18, wherein: the at least one separation plant is connected to at least one further cleaning device for carrying out an additional cleaning step in order to clean the press cake obtained from the at least one separation plant, and the cleaning device is preferably designed as a mixing reactor with at least one further separation plant.

26. The plant according to claim 25, wherein the mixing reactor with the at least one further separation plant is designed as a structural unit, preferably as a washing drum having a compression zone or as a screw conveyor having a pressing and dewatering zone.

27. The plant according to claim 18 further comprising: at least one filtration unit is provided, in which at least one filtrate from the at least one separation plant can be separated into a high-solids, thickened thick phase and into a low-solids filtrate, wherein: the thick phase is made available to the biogas plant as a fermentation substrate, while the filtrate can be returned to the process, in particular as dilution water or mashing water, via at least one recirculation line.

Description

[0051] The invention will be explained in greater detail below on the basis of non-limiting exemplary embodiments together with associated figures, in which:

[0052] FIG. 1A shows a schematic illustration of a first embodiment variant of the plant according to the invention,

[0053] FIG. 1B shows a variant of the plant from FIG. 1A,

[0054] FIG. 1C shows a further variant of the plant from FIG. 1A,

[0055] FIG. 2A shows a schematic illustration of a second embodiment variant of the plant according to the invention,

[0056] FIG. 2B shows a variant of the plant from FIG. 2A,

[0057] FIG. 3A shows a schematic illustration of a third embodiment variant of the plant according to the invention,

[0058] FIG. 3B shows a variant of the plant from FIG. 3A,

[0059] FIG. 4 shows a schematic detail view of one particular embodiment of the second separation plant from FIG. 2,

[0060] FIG. 5 shows a schematic detail view of a post-treatment stage,

[0061] FIG. 6 shows a schematic view of a further post-treatment stage, and

[0062] FIG. 7 shows a schematic illustration of a packaging plant.

[0063] FIG. 1A schematically shows a first embodiment variant of the plant 1000 according to the invention. According to the invention, the biomass 10 to be treated, which consists of renewable raw materials or organic residues having a high cellulose fibre content, is introduced into a thermo-pressure hydrolysis plant 100 and subjected to a pressure/temperature pre-treatment, namely a thermo-pressure hydrolysis, preferably with steam explosion. During this, the biomass is pulped, resulting in a fibrous sludge 20 having a dry matter content of 10% to 35%, which is collected in a storage tank 110.

[0064] By means of a conveying device 200A, for example a screw conveyor or thick-matter pump, the fibrous sludge 20 is introduced into a separation plant 300, typically a screw press, and the fibrous sludge 20 is dewatered, resulting in a fibre press cake 30 having a dry matter content of more than 20%, which is ejected into a collection tank 120. This fibrous solid 30 may either be immediately delivered for further processing, for example to a paper mill, or else it may be subjected to further processing (as described below).

[0065] The filtrate 40 from the separation plant 300 is a flowable, high-solids, thin sludge which is collected in an intermediate tank 130 and is subsequently transferred to a biogas plant 2000 as a fermentation substrate by means of a pump device 200B.

[0066] In order to improve the separation effect in the separation plant 300, it is preferably provided that filtrate 40 in the form of thin sludge from the intermediate tank 130 is fed to the fibrous sludge 20 from the storage tank 110 via a recirculation line containing a pump device 200C. As an alternative or in addition to this, fresh water 50 or else a filtrate of the thin sludge that is obtained via a separate separation process (not shown) may be fed to the fibrous sludge 20 via a further feed line. By feeding-in liquid, this helps to flush out fines during the separation. At the same time, if recycled filtrate 40 is used, this concentrates the thin sludge, which is ultimately made available to the biogas plant 2000 as a fermentation substrate.

[0067] FIG. 1B shows a variant of the plant from FIG. 1A, in which the filtrate 40 from the separation plant 300 is additionally concentrated. The reference signs used in FIGS. 1B and 1n the subsequent figures refer to the same elements of the plant as those already used in FIG. 1A.

[0068] In this plant 1000, the thin sludge 40 is channeled from the intermediate storage tank 130 into a filtration unit 800, wherein this filtration unit 800 is designed as a single-stage or multi-stage fine filtration, microfiltration or ultrafiltration plant or combinations thereof. The thickened liquid phase 40B obtained from the filtration unit 800 is fed to the biogas plant 2000 as a fermentation substrate, while the lower-solids filtrate 40A is returned to the intermediate storage tank 130. In this embodiment of the plant 1000, this filtrate can then, if required, be made available again in the process as mashing water, in particular for the fibrous sludge 20 obtained from the thermo-pressure hydrolysis plant 100.

[0069] In the variant of the plant 1000 according to the invention that is shown in FIG. 1C, a dispersing of the fibrous sludge 20 in a dispersing unit 900 takes place prior to the separation step in the separation plant 300. This dispersing step takes place at temperatures ≥60° C. with a high energy input by way of a mixing device arranged in the dispersing unit 900, in order to obtain a more even distribution of the fibres in the fibrous sludge 20. It may also be provided here that liquid, preferably recirculated liquid, is added for the sake of better dispersion. This dispersion further improves the subsequent separation of the fibrous sludge 20 into fibre cake 30 and filtrate 40 in the separation plant 300.

[0070] FIG. 2A shows a further embodiment variant of the plant 1000 according to the invention, wherein in a first step, as already described in FIGS. 1A and 1B, the biomass 10 is pulped in the thermo-pressure hydrolysis plant 100. The fibre cake 30 obtained from the separation plant 300A and already partially cleaned of fines is fed to a mashing tank 400 (also called a “pulper”) via a feed line, optionally by means of a conveying device, such as for example a screw conveyor, conveyor belt or pump. In the mashing tank, this fibre cake 30 is mixed with recirculated filtrate 41 or alternatively with supplied fresh water 50, or mashing water 60, in order to obtain a dry matter content of usually between 3% and 15% which is favourable for the further treatment of the fibre cake 30. A filtrate of the thin sludge (not shown), which is obtained via a separate separation process, may also be fed in as mashing water. Any foreign materials (for example stones) contained in the raw material sink to the bottom of the mashing tank 400 and can easily be discharged through the bottom outlet 401.

[0071] The mashing tank 400 is emptied by means of a further centrifugal pump 200D, which is preferably especially suitable for fibrous media, and the fibre cake 31, to which water has been fed, is routed to a fibre disintegrator 500 (for example a “refiner” or “de-flaker”). In this device 500, the filter cake is exposed to high shear forces by device internals in the form of rotating and static elements.

[0072] By means of a de-flaker or refiner, the fibres that are still in the form of bundles are separated, without significantly shortening the fibres themselves. This fibre processing procedure in the form of fibre singulation is also a method step that is necessary in papermaking, this step usually being carried out in the paper mill itself.

[0073] As an alternative or in addition to this, the use of a device for the purpose of fibre shortening, in particular a refiner, may also be provided, depending on the biomass 10 used and the desired end product.

[0074] Depending on the raw material used, it may be necessary to carry out the fibre singulation and/or fibre shortening in multiple stages. To this end, in the plant 1000 shown in FIG. 2A, the fibrous material 32 obtained in the disintegrator 500 is returned to the mashing tank 400, thereby enabling the fibrous material 32 to pass through multiple times. Fibrous sludge 31 that has not yet been processed may also be fed to the mashing tank 400, as well as, if required, fresh water 50, mashing water 60 and/or recirculated filtrate 41, and added to the fibres 32 that have already been processed in the disintegrator 500. The singulated fibre material is thus optionally fed to the pulper 400 and then to the disintegrator 500 multiple times in a cyclic process. This results in fibres that are better able to be used, and bothersome fines are also separated from the fibres in addition. This thus also increases the fibre purity in the end product. As soon as the fibres are of the quality that is to be achieved in this step, they are fed to a storage tank 140. Alternatively, it may also be provided that the fibres are fed directly to a second separation step, without intermediate storage in the storage tank 140.

[0075] In the plant 1000 shown in FIG. 2A, this second separation stage is provided by a further mechanical separation plant 300B, typically a screw press. In this variant of the invention, the fibrous material 32 obtained from the disintegrator 500 is introduced into this second separation plant 300B from the storage tank 140 by means of a conveying device 200E, and the fibres 32 are dewatered to a dry matter content of at least 25%, preferably more than 40%. Water 50 may optionally be introduced into the pressing process in a targeted manner via a feed line. A washing of the press cake 30 optionally additionally takes place, in particular also in the form of a zoned dewatering process. In this way, relatively large quantities of filtrate 41 in the form of thin sludge are again obtained, which are collected in a storage tank 130B.

[0076] The filtrate 41 may optionally be reintroduced from the storage tank 130B into the mashing tank 400 via the recirculation line. A feed line for feeding the filtrate 41 into the biogas plant 2000 is also provided.

[0077] The plant 1000 shown in FIG. 2B comprises all the plant elements of the plant 1000 from FIG. 2A, with two filtration units 800A, 800B being provided in addition, which respectively process the thin sludge fractions 40, 41 from the two separation plants 300A, 300B. The resulting low-solids filtrates 40A, 41A are returned to the process, preferably added to the fibrous sludge 20 from the thermo-pressure hydrolysis plant 100 and/or added to the mashing tank 400 as mashing water. The high-solids fractions 40B, 41B from the filtration units 800 are again made available to the biogas plant 2000 as a fermentation substrate.

[0078] In a further space-saving variant of the plant 1000 according to the invention, as shown in FIG. 3A, again only a single-stage separation process is provided by means of the separation plant 300 which, in contrast to the plant 1000 described in FIGS. 2A and 2B, is arranged downstream of the disintegrator 500, while a separation stage upstream of the pulper 400 has been omitted. In this embodiment of the plant 1000 according to the invention, therefore, after the thermo-pressure hydrolysis of the biomass 10 in the thermo-pressure hydrolysis plant 100, the fibre bundles are immediately singulated in the disintegrator 300 after setting the required (lower) dry matter content in the pulper 400, without further pre-treatment steps.

[0079] For this purpose, in a further embodiment of this plant shown in FIG. 3B, at least one filtration unit 800 may again be provided, in which the thin sludge 40 from the separation unit 300 is thickened before being fed to the biogas plant 2000 as a fermentation substrate 40B, while the filtrate 40A is returned to the intermediate storage tank 130.

[0080] FIG. 4A shows, in a detail view of a further embodiment of the plant 1000 according to the invention, a variant of the separation stage comprising the separation plant 300, in which the filtrate 40 is collected not in a single storage tank 130, but rather in sub-streams 40C, 40D. In this case, a first sub-stream 40C from at least one first area of the separator 300, which has a higher solids content, is routed to a first storage tank 130C via one outlet line, while a second sub-stream 40D from at least one second dewatering zone of the separator 300, which contains a high proportion of the pressing water stream and thus has a lower solids content, is fed to a second storage tank 130D via a second outlet line.

[0081] Preferably, the high-solids filtrate 40C collected in the first storage tank 130C is fed to the biogas plant 2000, while the low-solids filtrate 40D from the second storage tank 130D is fed back via the recirculation line to the pulper 400 for the mashing process. It will be understood that this variant can be used for any separation unit in the plant 1000 according to the invention.

[0082] In this connection, it is additionally pointed out that the at least one separation plant 300 may have more than just two different dewatering zones, depending on the way in which it is built and designed. The important thing in this variant of the plant 1000 according to the invention is that at least two sub-streams of filtrate 40C, 40D having a different solids content are collected from the at least one separation plant 300 separately from each other and put to further use.

[0083] In one variant of this plant 1000, as shown in FIG. 4B, a filtration unit 800 may be provided, which further concentrates the higher-solids fraction 40C from the separation plant 300. The high-solids fraction 40E from the filtration plant 800 is in this case fed to the biogas plant 2000, while the lower-solids filtrate 40F from the filtration unit 800 is routed into the intermediate storage tank 130D and, if required, is routed jointly with the sub-fraction 40C from the separation plant 300 into the process as process water, for example for mashing purposes.

[0084] In the further variant of the plant 1000 according to the invention that is shown in a detail view in FIG. 5, a further treatment stage comprising a mixing reactor 600 is provided downstream of a separation plant 300C. In this mixing reactor 600, the fibrous material 30 obtained from the separation plant 300C is mixed with wash water 50 that is fed in via a feed line. The contaminated wash water 50A from the mixing reactor 600 is separated from the cleaned fibrous material 33 in a further separation plant 300D, and the end product 30 is fed to the collection tank 120.

[0085] In an alternative embodiment, it is provided that the mixing reactor 600 and the separation plant 300D are designed as a structural unit, for example in the form of a washing drum having a compression zone, or integrated in a screw conveyor having a pressing and dewatering zone.

[0086] The filtrate 50A thus produced is collected in a storage tank 130E and, if required, is fed to the thermo-pressure hydrolysis plant 100 and/or to the mashing tank 400 by means of a pump device 200F, for example as mashing water, in order to adjust the raw material located therein to a suitable water content.

[0087] Of course, this additional treatment stage can additionally or alternatively be used in any of the aforementioned plant variants shown in FIGS. 1A to 4B in combination with the respective separation plants 300, 300A, 300B.

[0088] FIG. 6 shows an optional post-treatment of the pulp produced in the method according to the invention. For this, the pulp 30 obtained from the separation plant 300 is stabilized in a post-treatment reactor 700 by means of conditioning chemicals 70 and process heat 80. Of course, it may also be provided that the post-treatment takes place only by means of conditioning chemicals, or exclusively by a heat treatment. In addition or as an alternative, the pulp may additionally be dried in a suitable device, in particular in the post-treatment reactor 700, wherein it is particularly preferably provided that this heat treatment takes place using process heat 80 from the biogas plant 2000 and/or from the thermo-pressure hydrolysis plant 100. This use of waste heat also has a positive effect on the energy balance of the method according to the invention.

[0089] The condensates and/or effluent occurring in the post-treatment may be returned to the post-treatment and/or may also be used as process water.

[0090] FIG. 7 schematically shows an optional compacting and packaging of the pulp 30 produced in the method according to the invention. For this, the pulp 30 obtained from the at least one separation plant 300 (with or without post-treatment) is compacted in a high-pressure press 910 to form cuboid or cylindrical bales, and the bales thus produced are wrapped with a film or another suitable fabric in a packaging plant 920 in order in this way to obtain storable, easy-to-handle bales, which can then be safely stored and transported in the form of bale stacks 930.

[0091] The method according to the invention using the associated plants may in principle be operated as a continuous system or as a cyclic system. Mixed operation is also conceivable, in which, for example, the separation plants are operated continuously, while the mashing and/or disintegrating steps take place intermittently.