SYSTEM AND PROCESS FOR REFINING LIGNOCELLULOSIC BIOMASS MATERIAL

Abstract

A system (1) for refining lignocellulosic biomass material (A) comprising a presteaming bin (2), a dewatering device (3), a preheater (4), a defibrator (9) comprising at least one refining zone (14) wherein steam is generated during refining of said biomass material so that a pressure peak occurs, a blowpipe (19), and a first steam flow path (D) arranged to convey steam from said refining zone to said presteaming bin (2). The system further comprises a second steam flow path (E) arranged to convey steam from said refining zone to said presteaming bin, wherein said first and second steam flow paths are connected to the refining zone on opposite sides of the pressure peakin a biomass material transport direction, and wherein said first and second steam flow paths are separate from said blow pipe. The invention also relates to a process for refining lignocellulosic biomass material.

Claims

1. System for refining lignocellulosic biomass material, said system comprising: a presteaming bin for presteaming said biomass material; a dewatering device for dewatering said presteamed biomass material; a preheater for preheating said dewatered biomass material; a defibrator comprising at least one refining zone wherein said preheated biomass material is refined and wherein steam is generated during the refining of said biomass material so that a pressure peak occurs in the refining zone; a blow pipe for conveying biomass material away from the refining zone; and a first steam flow path arranged to convey steam flowing away from the pressure peak against a biomass material transport direction from said refining zone to said presteaming bin; characterized in that said system comprises: a second steam flow path arranged to convey steam flowing away from the pressure peak in the biomass material transport direction from said refining zone to said presteaming bin; wherein said first and second steam flow paths are connected to the refining zone on opposite sides of the pressure peak in the biomass material transport direction; and wherein said first and second steam flow paths are separate from said blow pipe.

2. System according to claim 1, wherein at least one of said first and second steam flow paths comprises at least a portion of said preheater.

3. System according to claim 1, wherein said first steam flow path comprises at least a portion of a screw feeder arranged to convey said biomass material to said defibrator.

4. System according to claim 1, wherein said dewatering device is a plug screw feeder arranged to convey said biomass material towards said preheater.

5. System according to claim 1, wherein said refining zone is defined by two opposing refining surfaces accommodated within a grinding house, wherein at least one of said refining surfaces is rotatable around an axis of rotation (X) relative the other refining surface.

6. System according to claim 5, wherein said blow pipe is connected to a peripheral portion of said grinding house and said first and second steam flow paths are connected to said refining zone inside of said peripheral portion.

7. Process for refining lignocellulosic biomass material, said process comprising the steps of: presteaming said biomass material in a presteaming bin; dewatering said biomass material in a dewatering device; preheating said biomass material in a preheater; refining said biomass material in a refining zone in a defibrator and generating steam during the refining of said biomass material so that a pressure peak occurs in the refining zone; conveying biomass material away from the refining zone via a blow pipe; and conveying steam flowing away from the pressure peak against a biomass material transport direction from said refining zone to said presteaming bin via a first steam flow path; characterized in that said process comprises the step of: conveying steam flowing away from the pressure peak in the biomass material transport direction from said refining zone to said presteaming bin via a second steam flow path; wherein said first and second steam flow paths are connected to the refining zone on opposite sides of the pressure peak in the biomass material transport direction; and wherein said first and second steam flow paths are separate from said blow pipe.

8. Process according to claim 7, wherein at least one of said first and second steam flow paths comprises at least a portion of said preheater.

9. Process according to claim 7, wherein said first steam flow path comprises at least a portion of a screw feeder arranged to convey biomass material to said defibrator.

10. Process according to claim 7, wherein said refining zone is defined by two opposing refining surfaces accommodated within a grinding house, wherein at least one of said refining surfaces is rotatable around an axis of rotation (X) relative the other refining surface.

11. Process according to claim 10, wherein said blow pipe is connected to a peripheral portion of said grinding house and said first and second steam flow paths are connected to said refining zone inside of said peripheral portion.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0041] These and other aspects of the present invention will now be described in more detail with reference to the appended drawings, wherein some parts have been removed for the sake of clarity, and wherein:

[0042] FIG. 1 is a schematic illustration of a system according to a first embodiment of the invention; and

[0043] FIG. 2 shows a cross section through a portion of the defibrator in FIG. 1.

DETAILED DESCRIPTION

[0044] FIG. 1 shows a schematic illustration of a system 1 for refining lignocellulosic biomass material according to a first embodiment of the invention.

[0045] Biomass material A, e.g. in the form of wood chips, is fed into a top portion of a presteaming bin 2 by means of a screw feeder (not shown). Fresh steam is injected into the presteaming bin 2 through a steam pipe 5a and recycled steam is injected into the presteaming bin 2 through two steam conduits 7a, 7b connected to a defibrator 9 and a preheater 4, respectively. The injected steam softens the biomass material and raises the temperature of the biomass material to about 90-100° C. The presteamed biomass material is then expelled through a lower portion of the presteaming bin 2 and received in a dewatering device 3. In this embodiment, the dewatering device 3 is a plug screw feeder arranged to convey the biomass material to the preheater 4. The plug screw feeder comprises a narrowing section 3a wherein the biomass material is compressed to form an airtight plug that prevents steam from the preheater 4 from streaming back through the plug screw feeder. Moisture is squeezed out of the biomass material in the dewatering device 3 and water containing impurities, such as VOCs, is conveyed through a conduit 20 to a suitable treatment device (not shown).

[0046] An upper portion of the preheater 4 comprises an inlet arranged to receive biomass material from the dewatering device 3. Steam is injected into the preheater 4 to raise the temperature to about 175-185° C. and the pressure to about 800-1000 kPa. Fresh steam is injected through a steam pipe 5b and recycled steam is injected through a steam conduit 7c. The biomass material is preheated in the preheater 4 and then expelled from a lower portion of the preheater 4 into a first screw feeder 8. A small plug of biomass material may be created in the first screw feeder 8 to maintain the pressure within the preheater 4. The biomass material is then conveyed to a defibrator 9 by means of a second screw feeder 10. In this embodiment, the second screw feeder 10 is a ribbon feeder that permits steam from the defibrator 9 to flow back through a central region of the ribbon feeder. The steam conduit 7c is connected to the second screw feeder 10 and conveys steam from the second screw feeder 10 to the preheater 4.

[0047] Now referring to FIG. 2, is shown a cross section through a portion of the defibrator 9 in FIG. 1.

[0048] The defibrator 9 comprises a grinding house 11 accommodating a stationary stator body 12 and a rotating rotor body 13. The rotor body 13 is rotatable around its axis of rotation X by means of a motor (not shown). The stator body 12 and the rotor body 13 are provided with opposing refining surfaces 15, 16, which between them define a refining zone 14. The biomass material is fed (arrows C) from the second screw feeder 10 into the refining zone 14 where the biomass material is broken down by the refining surfaces 15, 16 when the rotor body 13 is rotated around its axis of rotation X. The refining surfaces 15, 16 are provided with radial grooves (not shown) for this specific purpose. The refined biomass material is forced by the centrifugal force towards an outer periphery of the refining surfaces 15, 16, where the grooves are finer to produce fibers, and from there to a peripheral portion 17 of the grinding house 11. Thereafter, the fibers are conveyed to subsequent processing equipment (not shown), e.g. a dryer, via blow pipe 19 (see FIG. 1) connected to said peripheral portion 17.

[0049] Moisture in the biomass material is converted into steam when the biomass material is broken down into fibers in the refining zone 14. A pressure peak (indicated by axes Y) is generated within the refining zone 14. The position of the pressure peak depends on a plurality of parameters and steam may be injected into the grinding house 11 through steam pipe 5c (see FIG. 1) to adjust the position of the pressure peak. Steam generated within the refining zone 14 flows away from the pressure peak. That is, steam generated inside the pressure peak flows against the biomass material transport direction back through the refining zone 14 and through a center portion of the second screw feeder 10, whereas steam generated outside the pressure peak flows in the biomass material transport direction towards an outer periphery of the refining zone 14. The heavier refined fibers are thrown by the rotor 13 towards the peripheral portion 17 of the grinding house 11 and the blow pipe 19 whereas the lighter steam will accumulate further towards the center of the grinding house 11 and exit through an opening 18 located between the peripheral portion 17 and the axis of rotation X. This steam is then conveyed to the presteaming bin through steam conduit 7a (see FIG. 1).

[0050] The steam injected into the grinding house 11 through steam pipe 5c may, for example, be injected near opening 18.

[0051] Now referring to FIGS. 1 and 2, steam is conveyed from the refining zone 14 in the defibrator 9 to the presteaming bin 2 through a first steam flow path D and a second steam flow path E.

[0052] In this embodiment, the first steam flow path D comprises a portion of the second screw feeder 10, the steam conduit 7c, a portion of the preheater 4 and the steam conduit 7b. That is, steam is conveyed from the refining zone 14 in the defibrator 14 via the second screw feeder 10 and the steam conduit 7c to the preheater 4, where the recycled steam is used to preheat the biomass material at optimal pressure, thus reducing the amount of fresh steam that must be added to the preheater 4 through steam pipe 5b. Thereafter, steam is conveyed via steam conduit 7b to the presteaming bin 2, where the recycled steam is used to soften and preheat the biomass material, thus reducing the amount of fresh steam that must be added to the presteaming bin 2 through steam pipe 5a.

[0053] In this embodiment, the second steam flow path E comprises a portion of the grinding house 11, the opening 18 and steam conduit 7a. That is, steam is conveyed from the refining zone 14 in the defibrator via the grinding house 11, the opening 18 and the steam conduit 7a to the presteaming bin 4, where the recycled steam is used to soften and preheat the biomass material, thus reducing the amount of fresh steam that must be added to the presteaming bin 2 through steam pipe 5a.

[0054] The blow pipe 19 is provided with a blow valve 24 that is used to regulate the steam flow through the blow pipe. Usually, about 60-80% of the steam in the defibrator 9 is conveyed through the blow pipe 19 to convey the biomass material to subsequent processing equipment. Steam conduits 7a-c are provided with valves 21, 22, 23 configured for regulation of the steam flows through the first and second steam flow paths D, E. These valves are used to ensure that the optimal temperature and pressure is maintained in the presteaming bin 2, the preheater 4 and the defibrator 9. Advantageously, a control unit (not shown) is configured to regulate the valves in the system 1 based on data received from temperature and pressure sensors (not shown) configured to determine the temperature and/or pressure in the presteaming bin 2, the preheater 4 and the defibrator 9.

[0055] In alternative embodiments, the first and second steam flow paths D, E may be arranged differently and may comprise any number of suitable elements or portions thereof.

[0056] For example, the first and/or second steam flow paths D, E may comprise a portion of steam pipe 5a.

[0057] For example, in an alternative embodiment, steam conduit 7c may be used to convey steam directly from the second screw feeder 10 to the presteaming bin 2, thus bypassing the preheater 4 and steam conduit 7b, so that the first steam flow path comprises a portion of the second screw feeder 10 and steam conduit 7c only.

[0058] Also, in an alternative embodiment, steam conduit 7a may be used to convey steam from the refining zone 14 in the defibrator 9 to the preheater 4, so that the second steam flow path comprises a portion of the grinding house 11, the opening 18, steam conduit 7a, the preheater 4 and steam conduit 7b.

[0059] In yet another embodiment, both the first and second steam flow paths may be used to convey steam from the refining zone 14 in the defibrator 9 to the preheater 4, thus further reducing the amount of fresh steam that must be added to the preheater 4.

[0060] As mentioned above, steam that is conveyed from the defibrator 9 to the presteaming bin 2 contains impurities, such as VOCs. These impurities will be removed from the biomass material when water containing said impurities is squeezed out of the biomass material in the dewatering device 3. Thus, the system according to the invention ensures that the amount of impurities that is released into the atmosphere is minimized.

[0061] Some of the steam generated in the defibrator 9 is used to propel the biomass material through blow pipe 19. This steam may be separated from the biomass material in a separator (not shown) and conveyed back to the presteaming bin 2, thus further reducing the amount of impurities that is released into the atmosphere.

[0062] The description above and the appended drawings are to be considered as non-limiting examples of the invention. The person skilled in the art realizes that several changes and modifications may be made within the scope of the invention. For example, one or more of the steam pipes for fresh steam may be superfluous, and may be removed, if the amount of recycled steam is sufficient for presteaming and/or preheating the biomass material. As mentioned, the first and second steam flow paths may comprise any number of suitable elements or portions thereof. Also, it is possible to add additional steam flow paths for conveying steam from the refining zone in the defibrator to the presteaming bin. Finally, one or more steam flow paths may merge at some point between the refining zone and the presteaming bin and form a joint steam flow path portion, i.e. said joint steam flow path portion becomes a part of both steam flow paths.