WO2020226544A1 - Screw assembly for disintegration of lignocellulosic material in a steam explosion process - Google Patents

Screw assembly for disintegration of lignocellulosic material in a steam explosion process Download PDF

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Publication number
WO2020226544A1
WO2020226544A1 PCT/SE2020/050305 SE2020050305W WO2020226544A1 WO 2020226544 A1 WO2020226544 A1 WO 2020226544A1 SE 2020050305 W SE2020050305 W SE 2020050305W WO 2020226544 A1 WO2020226544 A1 WO 2020226544A1
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WO
WIPO (PCT)
Prior art keywords
screw
lignocellulosic material
housing
outlet opening
screw assembly
Prior art date
Application number
PCT/SE2020/050305
Other languages
French (fr)
Inventor
Robert Wahlberg
Original Assignee
Valmet Ab
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Valmet Ab filed Critical Valmet Ab
Publication of WO2020226544A1 publication Critical patent/WO2020226544A1/en

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J19/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
    • B01J19/18—Stationary reactors having moving elements inside
    • B01J19/20—Stationary reactors having moving elements inside in the form of helices, e.g. screw reactors
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
    • B65G—TRANSPORT OR STORAGE DEVICES, e.g. CONVEYORS FOR LOADING OR TIPPING, SHOP CONVEYOR SYSTEMS OR PNEUMATIC TUBE CONVEYORS
    • B65G33/00—Screw or rotary spiral conveyors
    • B65G33/24—Details
    • B65G33/26—Screws
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21B—FIBROUS RAW MATERIALS OR THEIR MECHANICAL TREATMENT
    • D21B1/00—Fibrous raw materials or their mechanical treatment
    • D21B1/04—Fibrous raw materials or their mechanical treatment by dividing raw materials into small particles, e.g. fibres
    • D21B1/12—Fibrous raw materials or their mechanical treatment by dividing raw materials into small particles, e.g. fibres by wet methods, by the use of steam
    • D21B1/30—Defibrating by other means
    • D21B1/36—Explosive disintegration by sudden pressure reduction
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
    • B65G—TRANSPORT OR STORAGE DEVICES, e.g. CONVEYORS FOR LOADING OR TIPPING, SHOP CONVEYOR SYSTEMS OR PNEUMATIC TUBE CONVEYORS
    • B65G33/00—Screw or rotary spiral conveyors
    • B65G33/08—Screw or rotary spiral conveyors for fluent solid materials
    • B65G33/14—Screw or rotary spiral conveyors for fluent solid materials comprising a screw or screws enclosed in a tubular housing
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
    • B65G—TRANSPORT OR STORAGE DEVICES, e.g. CONVEYORS FOR LOADING OR TIPPING, SHOP CONVEYOR SYSTEMS OR PNEUMATIC TUBE CONVEYORS
    • B65G33/00—Screw or rotary spiral conveyors
    • B65G33/08—Screw or rotary spiral conveyors for fluent solid materials
    • B65G33/14—Screw or rotary spiral conveyors for fluent solid materials comprising a screw or screws enclosed in a tubular housing
    • B65G33/18—Screw or rotary spiral conveyors for fluent solid materials comprising a screw or screws enclosed in a tubular housing with multiple screws in parallel arrangements, e.g. concentric
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10L—FUELS NOT OTHERWISE PROVIDED FOR; NATURAL GAS; SYNTHETIC NATURAL GAS OBTAINED BY PROCESSES NOT COVERED BY SUBCLASSES C10G, C10K; LIQUEFIED PETROLEUM GAS; ADDING MATERIALS TO FUELS OR FIRES TO REDUCE SMOKE OR UNDESIRABLE DEPOSITS OR TO FACILITATE SOOT REMOVAL; FIRELIGHTERS
    • C10L5/00—Solid fuels
    • C10L5/02—Solid fuels such as briquettes consisting mainly of carbonaceous materials of mineral or non-mineral origin
    • C10L5/34—Other details of the shaped fuels, e.g. briquettes
    • C10L5/36—Shape
    • C10L5/365—Logs
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10L—FUELS NOT OTHERWISE PROVIDED FOR; NATURAL GAS; SYNTHETIC NATURAL GAS OBTAINED BY PROCESSES NOT COVERED BY SUBCLASSES C10G, C10K; LIQUEFIED PETROLEUM GAS; ADDING MATERIALS TO FUELS OR FIRES TO REDUCE SMOKE OR UNDESIRABLE DEPOSITS OR TO FACILITATE SOOT REMOVAL; FIRELIGHTERS
    • C10L5/00—Solid fuels
    • C10L5/40—Solid fuels essentially based on materials of non-mineral origin
    • C10L5/44—Solid fuels essentially based on materials of non-mineral origin on vegetable substances
    • C10L5/442—Wood or forestry waste
    • C—CHEMISTRY; METALLURGY
    • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12P—FERMENTATION OR ENZYME-USING PROCESSES TO SYNTHESISE A DESIRED CHEMICAL COMPOUND OR COMPOSITION OR TO SEPARATE OPTICAL ISOMERS FROM A RACEMIC MIXTURE
    • C12P2201/00—Pretreatment of cellulosic or lignocellulosic material for subsequent enzymatic treatment or hydrolysis
    • C—CHEMISTRY; METALLURGY
    • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12P—FERMENTATION OR ENZYME-USING PROCESSES TO SYNTHESISE A DESIRED CHEMICAL COMPOUND OR COMPOSITION OR TO SEPARATE OPTICAL ISOMERS FROM A RACEMIC MIXTURE
    • C12P7/00—Preparation of oxygen-containing organic compounds
    • C12P7/02—Preparation of oxygen-containing organic compounds containing a hydroxy group
    • C12P7/04—Preparation of oxygen-containing organic compounds containing a hydroxy group acyclic
    • C12P7/18—Preparation of oxygen-containing organic compounds containing a hydroxy group acyclic polyhydric
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21B—FIBROUS RAW MATERIALS OR THEIR MECHANICAL TREATMENT
    • D21B1/00—Fibrous raw materials or their mechanical treatment
    • D21B1/04—Fibrous raw materials or their mechanical treatment by dividing raw materials into small particles, e.g. fibres
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E50/00—Technologies for the production of fuel of non-fossil origin
    • Y02E50/10—Biofuels, e.g. bio-diesel
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E50/00—Technologies for the production of fuel of non-fossil origin
    • Y02E50/30—Fuel from waste, e.g. synthetic alcohol or diesel

Definitions

  • the present invention relates to a screw assembly for disintegration of lignocellulosic material
  • a screw assembly for disintegration of lignocellulosic material
  • the screw housing has an inlet portion in one area of the screw assembly and an end wall with an outlet opening at the first end so that lignocellulosic material is transported form the inlet portion to the outlet opening.
  • a steam explosion process may be used to disintegrate the material before forming pellets. This is especially the case when producing“black pellets”, i.e. pellets made from a hardwood material. Production of black pellets is described e.g. in WO2013/ 191897, WO2015/ 185751, WO2017/089648 and EP3205707.
  • a lignocellulosic material is treated in a reactor and is combined with hot steam to increase the pressure. It is then subjected to a pressure drop that disintegrates the lignocellulosic material by causing an explosion.
  • a problem associated with screw assemblies used in steam explosion processes is that the screw assembly must be able to feed lignocellulosic material towards an outlet in an even and controlled manner and that the outlet opening must be small in order for the steam explosion to take place as desired. If the material is unevenly fed to the outlet or if the material gathers to form plugs (i.e. dense portions of the slurry comprising the lignocellulosic material and a treatment liquor) the steam explosions may not take place and the intended disintegration of material will not occur. This in turn prevents the formation of pellets from the lignocellulosic material.
  • the object of the present invention is to eliminate or at least to minimize the problems discussed above. This is achieved by a screw assembly according to the appended independent claim.
  • the screw assembly for disintegration of lignocellulosic material in a steam explosion process comprises an elongated screw for transporting lignocellulosic material, the elongated screw comprising a screw core and a screw blade arranged on said core, an elongated screw housing comprising an end wall at a first end, the end wall having an outlet opening for discharging disintegrated lignocellulosic material from the screw assembly such that the lignocellulosic material is disintegrated as it passes through the outlet opening, and the housing further comprising an inlet portion with a material inlet, wherein the screw is arranged in the housing for transporting the lignocellulosic material from the inlet portion to the outlet opening at the first end, the housing being configured to extend around a circumference of the screw, wherein a center of the inlet portion is arranged at a first distance from the first end, the screw blade extending in said inlet portion and further extending a second distance from the center of the
  • the screw core is journalled at the first end and at a second end of the housing, said second end being opposite the first end.
  • the inlet portion is suitably arranged at the second end of the housing. Thereby, the entire length of the screw assembly is used for receiving and transporting the lignocellulosic material.
  • An axial blade is suitably arranged on the screw in a screw portion that is between the first end and an end of the screw blade facing the first end, the axial blade extending in a direction essentially parallel with the screw core and at a distance from said screw core. This blade will be able to rotate with the screw core and scrape the internal wall of the screw housing to prevent a buildup of material along the walls that could hinder the flow towards the outlet opening.
  • the screw assembly also comprises a container configured to receive lignocellulosic material discharged from the outlet opening at a container pressure, wherein the screw is configured to hold lignocellulosic material at a first pressure at the first end of the housing and wherein the container pressure is lower than the first pressure.
  • a container configured to receive lignocellulosic material discharged from the outlet opening at a container pressure
  • the screw is configured to hold lignocellulosic material at a first pressure at the first end of the housing and wherein the container pressure is lower than the first pressure.
  • a steam inlet may be included in the screw assembly for introducing steam into the screw housing.
  • steam will be able to be fed into the screw assembly through the steam inlet and will improve the flow of material in the screw assembly and also serve to improve the steam explosions taking place after the outlet opening.
  • Having a steam inlet instead of supplying steam in the material inlet will have the added benefit of creating a steam flow that will serve to aid the flow of material towards the outlet.
  • the outlet opening has a diameter that may be less than 50 % of the diameter of the end wall, preferably less than 30 % and more preferably less than 20 %.
  • the outlet opening is eccentrically arranged on a lower part of the end wall.
  • the screw core may be journalled in the center of the end wall without interfering with the outlet opening, and by providing the outlet opening on the lower part of the end wall the material will more easily be fed through the outlet opening.
  • a scraper may suitably be arranged on the screw core at the first end, the scraper being configured to rotate with the screw core and to scrape the outlet opening on the end wall. Thereby, the outlet opening will be kept clean and plugging of material will be prevented.
  • the scraper By arranging the scraper on the screw core, a suitable rotation will be achieved without requiring additional components in the screw assembly.
  • the screw blade may suitably be a ribbon flight. Also, the screw blade may extend throughout the inlet portion, so that material fed into any part of the inlet portion will be transported by the screw in an efficient way.
  • Fig. 1 discloses a planar view of the screw assembly according to a preferred embodiment of the present invention, the screw assembly being shown from the side without an external wall of the housing in order to clearly show the screw inside the housing;
  • Fig. 2 discloses a planar view of the screw assembly from the side
  • Fig. 3 discloses a cross-sectional view of the screw assembly according to a second embodiment of the invention
  • Fig. 4 discloses a planar view of the screw assembly from the side with a container for receiving material from the screw assembly.
  • the present invention is used within the field of pulping when a pulp is produced from a raw material in the form of a lignocellulosic material.
  • lignocellulosic material is used herein to mean materials containing lignin, cellulose and hemicellulose.
  • One example of such materials is wood, others include other agricultural or forestry wastes.
  • the lignocellulosic material is commonly divided into small pieces, chips or fragments before the pulping process is initiated.
  • Figs. 1-2 disclose a preferred embodiment of a screw assembly 10 having an elongated screw housing 1 that extends around an elongated screw 2 configured to transport lignocellulosic material in a direction towards a first end 1 1 of the screw housing 1.
  • the screw 2 comprises a screw core 21 that is journalled at the first end 1 1 and at an opposing second end 12 of the screw housing 1 so that the screw core 21 is able to rotate.
  • a screw blade 22 is mounted on the screw core 21 and serves to rotate with the screw core 21 for transporting material towards the first end 1 1, i.e. to the left in Fig. 1-2.
  • a marker A shows a center of the inlet portion 15 having a material inlet 14 into which lignocellulosic material is introduced, preferably by a second screw assembly that feeds lignocellulosic material at high pressure into the screw assembly 10 according to the present invention.
  • Steam is also added and is transported together with the lignocellulosic material towards the first end 1 1, either by introduction into the material inlet 14 or by introduction into a steam inlet 16 that is shown in Fig. 2 in the vicinity of the material inlet 14 but that may be located at any suitable part of the screw housing 1.
  • the screw housing 1 preferably fits around the screw so that an inner shape of the screw housing 1 matches an outer shape of the screw 2.
  • the screw blade 22 may suitably be a ribbon flight. This is a highly suitable and efficient type of screw blade that allows for a continuous and even feeding of material towards the outlet opening 13.
  • a distance the center A of the inlet portion 15 to an end wall 17 at the first end 1 1 is a first distance d 1 and this is the distance that any material fed into the inlet portion 15 will travel to reach the first end 1 1.
  • the screw blade 22 of the screw 2 extends a second distance d2 from the center A of the inlet portion in a direction towards the first end 1 1.
  • the first distance d 1 is larger than the second distance d2 so that a space 18 is formed inside the screw housing 1 where lignocellulosic material can flow without being contacted by a screw blade 22 of the screw 2.
  • lignocellulosic material and steam are transported by being pushed by lignocellulosic material that is closer to the material inlet 14.
  • an outlet opening 13 is provided to feed lignocellulosic material from the screw assembly 10 out into an adjacent container 3 (see Fig. 4).
  • the lignocellulosic material in the screw assembly 10 is held at a first pressure and an inside of the container 3 is held at a second pressure that is significantly lower than the first pressure.
  • the pressure difference may be upheld by the outlet opening 13 being small, preferably having a diameter that less than 50 % of a diameter of the end wall 17, preferably less than 30 % and more preferably less than 20 %.
  • the outlet opening may in the preferred embodiment have a diameter of about 80 mm.
  • the first pressure is achieved by the lignocellulosic material being fed into the screw assembly 10 at a high pressure, by the addition of pressurized steam to the screw assembly 10 and by the screw blade 22 being configured to transport the lignocellulosic material towards the outlet opening 13.
  • the screw blade 22 suitably extends throughout the inlet portion 15 so that material fed into any part of the material inlet 14 is received by the screw and fed towards the first end 1 1. In some embodiments, the screw blade 22 further extends all the way to the second end 12 of the housing 1. This prevents material from flowing towards the second end 12 and being stuck there, since any material fed into the screw at the inlet portion 15 will be subjected to the rotating screw blade 22 and transported towards the first end 1 1.
  • a scraper 23 may advantageously be mounted on the screw core 21 to rotate with the screw 2 and scrape the end wall 17 or at least a portion of the end wall 17 where the outlet opening 13 is located. This enables a continuous cleaning of the outlet opening 13 to prevent it from being blocked by the lignocellulosic material and ensures a smooth operation of the discharge of material from the screw assembly 10.
  • the housing 1 is dimensioned to fit around the screw 2 and in the preferred embodiment has an essentially cylindrical inner space in which the screw 2 is arranged.
  • the screw 2 in turn is configured to transport lignocellulosic material from the material inlet 14 in the inlet portion 15 to the outlet opening 13 where the material is discharged from the screw assembly 10.
  • the inlet portion 15 is arranged at the second end 12 of the housing 1.
  • Fig. 4 shows the screw assembly 10 of Fig. 2 with the container 3 connected thereto.
  • the container 3 is arranged to receive the lignocellulosic material that is discharged through the outlet opening 13 and to hold the material at the second pressure as described above.
  • the lignocellulosic material may be transported from the container 3 to further process steps such as the formation of pellets.
  • Fig. 3 discloses a second embodiment of the invention that differs from the preferred embodiment described above mainly in the presence of an axial blade 24 that is arranged on the screw 2 and extends in an axial direction at a distance from the screw core 21.
  • the axial blade 24 is arranged in a direction essentially parallel with the screw core 21 at an outer circumference of the screw 2 and joins an end of the screw blade 22 at the second distance d2 from the inlet portion 15 with the scraper 23 at the first end 1 1, i.e. at the first distance d l from the inlet portion 15.
  • the axial blade 24 serves to rotate with the screw core 2 1 and to scrape an inner wall of the housing 1 in the space 18 between the end of the screw blade 22 and the first end 1 1 to prevent material from adhering to the wall of the housing 1.
  • the outlet opening 13 may in both embodiments described above be arranged eccentrically on the end wall 17 and is advantageously located on a lower part of the end wall 17. This has the benefits that the screw core 21 can be journalled on a center of the end wall 17 without disturbing the outlet opening 13 and that the lignocellulosic material will be aided by gravity in reaching the outlet opening 13.
  • the screw assembly 10 may serve as a reactor for treating the lignocellulosic material.
  • a treatment liquor is added and the dimensions of the screw assembly 10 as well as a rotary speed of the screw 2 are adapted to ensure that the lignocellulosic material is held inside the screw assembly 10 for a suitable treatment time before being discharged though the outlet opening 13.
  • steam may also be added to control the pressure inside the screw assembly 10.
  • the treatment liquor may itself be steam.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Mechanical Engineering (AREA)
  • Organic Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Wood Science & Technology (AREA)
  • Disintegrating Or Milling (AREA)
  • Mixers Of The Rotary Stirring Type (AREA)
  • Screw Conveyors (AREA)

Abstract

The present invention relates to a screw assembly comprising an elongated screw for transporting lignocellulosic material, the elongated screw comprising a screw core and a screw blade arranged on said core, and an elongated screw housing comprising an end wall at a first end, the end wall having an outlet opening, and the housing further comprising an inlet portion with a material inlet, wherein the screw is arranged in the housing for transporting the lignocellulosic material from the inlet portion to the outlet opening at the first end, the housing being configured to fit around a circumference of the screw, wherein a center of the inlet portion is arranged at a first distance from the first end, the screw blade extending in said inlet portion and further extending a second distance from the center of the inlet portion towards the first end, said second distance being smaller than the first distance.

Description

SCREW ASSEMBLY FOR DISINTEGRATION OF LIGNOCELLULOSIC MATERIAL IN A
STEAM EXPLOSION PROCESS
TECHNICAL FIELD
The present invention relates to a screw assembly for disintegration of lignocellulosic material comprising an elongated screw and a screw housing in which the screw is arranged for transporting lignocellulosic material from the inlet portion to the outlet opening at a first end. The screw housing has an inlet portion in one area of the screw assembly and an end wall with an outlet opening at the first end so that lignocellulosic material is transported form the inlet portion to the outlet opening.
BACKGROUND
During production of pelletized biomass fuel from a lignocellulosic material, a steam explosion process may be used to disintegrate the material before forming pellets. This is especially the case when producing“black pellets”, i.e. pellets made from a hardwood material. Production of black pellets is described e.g. in WO2013/ 191897, WO2015/ 185751, WO2017/089648 and EP3205707.
In a steam explosion process, a lignocellulosic material is treated in a reactor and is combined with hot steam to increase the pressure. It is then subjected to a pressure drop that disintegrates the lignocellulosic material by causing an explosion.
A problem associated with screw assemblies used in steam explosion processes is that the screw assembly must be able to feed lignocellulosic material towards an outlet in an even and controlled manner and that the outlet opening must be small in order for the steam explosion to take place as desired. If the material is unevenly fed to the outlet or if the material gathers to form plugs (i.e. dense portions of the slurry comprising the lignocellulosic material and a treatment liquor) the steam explosions may not take place and the intended disintegration of material will not occur. This in turn prevents the formation of pellets from the lignocellulosic material.
Prior art screw assemblies are not able to ensure the even and continuous flow of material to the outlet opening and also cannot ensure that the outlet opening is prevented from being blocked by material plugs. There is therefore a need for improvements within this area.
SUMMARY
The object of the present invention is to eliminate or at least to minimize the problems discussed above. This is achieved by a screw assembly according to the appended independent claim.
According to the invention, the screw assembly for disintegration of lignocellulosic material in a steam explosion process comprises an elongated screw for transporting lignocellulosic material, the elongated screw comprising a screw core and a screw blade arranged on said core, an elongated screw housing comprising an end wall at a first end, the end wall having an outlet opening for discharging disintegrated lignocellulosic material from the screw assembly such that the lignocellulosic material is disintegrated as it passes through the outlet opening, and the housing further comprising an inlet portion with a material inlet, wherein the screw is arranged in the housing for transporting the lignocellulosic material from the inlet portion to the outlet opening at the first end, the housing being configured to extend around a circumference of the screw, wherein a center of the inlet portion is arranged at a first distance from the first end, the screw blade extending in said inlet portion and further extending a second distance from the center of the inlet portion towards the first end, said second distance being smaller than the first distance.
This has the advantage that there will be a space near the first end where the lignocellulosic material will be able to follow the flow towards the outlet opening without being hindered by the screw blade. The flow is thereby rendered more even and the risk of plugging at the outlet is decreased. Suitably, the screw core is journalled at the first end and at a second end of the housing, said second end being opposite the first end. Thereby, a stable and robust screw assembly is achieved, and since the screw core will extend all the way to the first end it will be possible to add other components to the screw core there that may rotate with the screw core.
The inlet portion is suitably arranged at the second end of the housing. Thereby, the entire length of the screw assembly is used for receiving and transporting the lignocellulosic material.
An axial blade is suitably arranged on the screw in a screw portion that is between the first end and an end of the screw blade facing the first end, the axial blade extending in a direction essentially parallel with the screw core and at a distance from said screw core. This blade will be able to rotate with the screw core and scrape the internal wall of the screw housing to prevent a buildup of material along the walls that could hinder the flow towards the outlet opening.
Suitably, the screw assembly also comprises a container configured to receive lignocellulosic material discharged from the outlet opening at a container pressure, wherein the screw is configured to hold lignocellulosic material at a first pressure at the first end of the housing and wherein the container pressure is lower than the first pressure. Thereby, the pressure drop needed for the steam explosions will be created when the lignocellulosic material is fed out of the outlet opening and enters the container.
A steam inlet may be included in the screw assembly for introducing steam into the screw housing. Thereby, steam will be able to be fed into the screw assembly through the steam inlet and will improve the flow of material in the screw assembly and also serve to improve the steam explosions taking place after the outlet opening. Having a steam inlet instead of supplying steam in the material inlet will have the added benefit of creating a steam flow that will serve to aid the flow of material towards the outlet. The outlet opening has a diameter that may be less than 50 % of the diameter of the end wall, preferably less than 30 % and more preferably less than 20 %. Thereby, steam explosions are more easily generated and the pressure inside the screw assembly is more easily maintained.
Suitably, the outlet opening is eccentrically arranged on a lower part of the end wall. Thereby, the screw core may be journalled in the center of the end wall without interfering with the outlet opening, and by providing the outlet opening on the lower part of the end wall the material will more easily be fed through the outlet opening.
A scraper may suitably be arranged on the screw core at the first end, the scraper being configured to rotate with the screw core and to scrape the outlet opening on the end wall. Thereby, the outlet opening will be kept clean and plugging of material will be prevented. By arranging the scraper on the screw core, a suitable rotation will be achieved without requiring additional components in the screw assembly.
The screw blade may suitably be a ribbon flight. Also, the screw blade may extend throughout the inlet portion, so that material fed into any part of the inlet portion will be transported by the screw in an efficient way.
Many additional benefits and advantages of the present invention will be readily understood by the skilled person in view of the detailed description below. DRAWINGS
The invention will now be described in more detail with reference to the appended drawings, wherein:
Fig. 1 discloses a planar view of the screw assembly according to a preferred embodiment of the present invention, the screw assembly being shown from the side without an external wall of the housing in order to clearly show the screw inside the housing;
Fig. 2 discloses a planar view of the screw assembly from the side;
Fig. 3 discloses a cross-sectional view of the screw assembly according to a second embodiment of the invention; and Fig. 4 discloses a planar view of the screw assembly from the side with a container for receiving material from the screw assembly.
DETAILED DESCRIPTION
The present invention is used within the field of pulping when a pulp is produced from a raw material in the form of a lignocellulosic material. The term lignocellulosic material is used herein to mean materials containing lignin, cellulose and hemicellulose. One example of such materials is wood, others include other agricultural or forestry wastes. The lignocellulosic material is commonly divided into small pieces, chips or fragments before the pulping process is initiated.
Figs. 1-2 disclose a preferred embodiment of a screw assembly 10 having an elongated screw housing 1 that extends around an elongated screw 2 configured to transport lignocellulosic material in a direction towards a first end 1 1 of the screw housing 1. The screw 2 comprises a screw core 21 that is journalled at the first end 1 1 and at an opposing second end 12 of the screw housing 1 so that the screw core 21 is able to rotate. A screw blade 22 is mounted on the screw core 21 and serves to rotate with the screw core 21 for transporting material towards the first end 1 1, i.e. to the left in Fig. 1-2. A marker A shows a center of the inlet portion 15 having a material inlet 14 into which lignocellulosic material is introduced, preferably by a second screw assembly that feeds lignocellulosic material at high pressure into the screw assembly 10 according to the present invention. Steam is also added and is transported together with the lignocellulosic material towards the first end 1 1, either by introduction into the material inlet 14 or by introduction into a steam inlet 16 that is shown in Fig. 2 in the vicinity of the material inlet 14 but that may be located at any suitable part of the screw housing 1. The screw housing 1 preferably fits around the screw so that an inner shape of the screw housing 1 matches an outer shape of the screw 2.
The screw blade 22 may suitably be a ribbon flight. This is a highly suitable and efficient type of screw blade that allows for a continuous and even feeding of material towards the outlet opening 13. A distance the center A of the inlet portion 15 to an end wall 17 at the first end 1 1 is a first distance d 1 and this is the distance that any material fed into the inlet portion 15 will travel to reach the first end 1 1. The screw blade 22 of the screw 2 extends a second distance d2 from the center A of the inlet portion in a direction towards the first end 1 1. The first distance d 1 is larger than the second distance d2 so that a space 18 is formed inside the screw housing 1 where lignocellulosic material can flow without being contacted by a screw blade 22 of the screw 2. In the space 18 lignocellulosic material and steam are transported by being pushed by lignocellulosic material that is closer to the material inlet 14. In the end wall 17 at the first end 1 1, an outlet opening 13 is provided to feed lignocellulosic material from the screw assembly 10 out into an adjacent container 3 (see Fig. 4). The lignocellulosic material in the screw assembly 10 is held at a first pressure and an inside of the container 3 is held at a second pressure that is significantly lower than the first pressure. The pressure difference may be upheld by the outlet opening 13 being small, preferably having a diameter that less than 50 % of a diameter of the end wall 17, preferably less than 30 % and more preferably less than 20 %. For an end wall having a diameter of about 500 mm, the outlet opening may in the preferred embodiment have a diameter of about 80 mm. Thus, the pressure inside the screw assembly 10 is maintained, and for the material being discharged through the outlet opening 13 the pressure drop will result in a steam explosion that disintegrates the material into smaller pieces.
The first pressure is achieved by the lignocellulosic material being fed into the screw assembly 10 at a high pressure, by the addition of pressurized steam to the screw assembly 10 and by the screw blade 22 being configured to transport the lignocellulosic material towards the outlet opening 13.
The screw blade 22 suitably extends throughout the inlet portion 15 so that material fed into any part of the material inlet 14 is received by the screw and fed towards the first end 1 1. In some embodiments, the screw blade 22 further extends all the way to the second end 12 of the housing 1. This prevents material from flowing towards the second end 12 and being stuck there, since any material fed into the screw at the inlet portion 15 will be subjected to the rotating screw blade 22 and transported towards the first end 1 1.
A scraper 23 may advantageously be mounted on the screw core 21 to rotate with the screw 2 and scrape the end wall 17 or at least a portion of the end wall 17 where the outlet opening 13 is located. This enables a continuous cleaning of the outlet opening 13 to prevent it from being blocked by the lignocellulosic material and ensures a smooth operation of the discharge of material from the screw assembly 10. The housing 1 is dimensioned to fit around the screw 2 and in the preferred embodiment has an essentially cylindrical inner space in which the screw 2 is arranged. The screw 2 in turn is configured to transport lignocellulosic material from the material inlet 14 in the inlet portion 15 to the outlet opening 13 where the material is discharged from the screw assembly 10. The inlet portion 15 is arranged at the second end 12 of the housing 1.
Fig. 4 shows the screw assembly 10 of Fig. 2 with the container 3 connected thereto. The container 3 is arranged to receive the lignocellulosic material that is discharged through the outlet opening 13 and to hold the material at the second pressure as described above. The lignocellulosic material may be transported from the container 3 to further process steps such as the formation of pellets.
Fig. 3 discloses a second embodiment of the invention that differs from the preferred embodiment described above mainly in the presence of an axial blade 24 that is arranged on the screw 2 and extends in an axial direction at a distance from the screw core 21. In the second embodiment, the axial blade 24 is arranged in a direction essentially parallel with the screw core 21 at an outer circumference of the screw 2 and joins an end of the screw blade 22 at the second distance d2 from the inlet portion 15 with the scraper 23 at the first end 1 1, i.e. at the first distance d l from the inlet portion 15. The axial blade 24 serves to rotate with the screw core 2 1 and to scrape an inner wall of the housing 1 in the space 18 between the end of the screw blade 22 and the first end 1 1 to prevent material from adhering to the wall of the housing 1.
The outlet opening 13 may in both embodiments described above be arranged eccentrically on the end wall 17 and is advantageously located on a lower part of the end wall 17. This has the benefits that the screw core 21 can be journalled on a center of the end wall 17 without disturbing the outlet opening 13 and that the lignocellulosic material will be aided by gravity in reaching the outlet opening 13.
In some embodiments, the screw assembly 10 may serve as a reactor for treating the lignocellulosic material. In such embodiments, a treatment liquor is added and the dimensions of the screw assembly 10 as well as a rotary speed of the screw 2 are adapted to ensure that the lignocellulosic material is held inside the screw assembly 10 for a suitable treatment time before being discharged though the outlet opening 13. In such embodiments, steam may also be added to control the pressure inside the screw assembly 10. The treatment liquor may itself be steam.
It is to be noted that features from the various embodiments described herein may freely be combined, unless it is explicitly stated that such a combination would be unsuitable.

Claims

1. Screw assembly (10) for disintegration of lignocellulosic material in a steam explosion process, the screw assembly (10) comprising
an elongated screw (2) for transporting lignocellulosic material, the elongated screw (2) comprising a screw core (21) and a screw blade (22) arranged on said core, an elongated screw housing (1) comprising an end wall (17) at a first end (11), the end wall (17) having an outlet opening for discharging disintegrated lignocellulosic material (13) from the screw assembly (10) such that the lignocellulosic material is disintegrated as it passes through the outlet opening, and the housing (1) further comprising an inlet portion (15) with a material inlet (14), wherein the screw (2) is arranged in the housing (1) for transporting the lignocellulosic material from the inlet portion (15) to the outlet opening (13) at the first end (11), the housing (1) being configured to extend around a circumference of the screw (2),
wherein a center (A) of the inlet portion (15) is arranged at a first distance (dl) from the first end, the screw blade (22) extending in said inlet portion (15) and further extending a second distance (d2) from the center (A) of the inlet portion (15) towards the first end (11), said second distance (d2) being smaller than the first distance (dl).
2. Screw assembly (10) according to claim 1, wherein the screw core (21) is journalled at the first end (11) and at a second end (12) of the housing (1), said second end (12) being opposite the first end (11).
3. Screw assembly ( 10) according to claim 2, wherein the inlet portion ( 15) is arranged at the second end of the housing ( 1).
4. Screw assembly ( 10) according to any previous claim, further comprising a scraper (23) arranged on the screw core (21) at the first end ( 1 1), the scraper (23) being configured to rotate with the screw core (21) and to scrape the outlet opening ( 13) on the end wall ( 17).
5. Screw assembly ( 10) according to any previous claim, further comprising an axial blade (24) arranged on the screw in a screw portion that is between the first end ( 1 1) and an end of the screw blade (22) facing the first end ( 1 1), the axial blade (24) extending in a direction essentially parallel with the screw core (21) and at a distance from said screw core (21).
6. Screw assembly ( 10) according to any previous claim, further comprising a container (3) configured to receive lignocellulosic material discharged from the outlet opening ( 13), wherein the screw assembly ( 10) is configured to hold lignocellulosic material at a first pressure at the first end ( 1 1) of the housing ( 1) and the container (3) holds lignocellulosic material at a second pressure, and wherein the second pressure is lower than the first pressure.
7. Screw assembly ( 10) according to any previous claim, further comprising a steam inlet ( 16) for introducing steam into the screw housing ( 1).
8. Screw assembly ( 10) according to any previous claim, wherein the outlet opening ( 13) has a diameter that is less than 50 % of the diameter of the end wall, preferably less than 30 % and more preferably less than 20 %.
9. Screw assembly ( 10) according to any previous claim, wherein the outlet opening ( 13) is eccentrically arranged on a lower part of the end wall ( 1 1).
10. Screw assembly ( 10) according to any previous claim, wherein the screw blade (22) is a ribbon flight.
1 1. Screw assembly ( 10) according to any previous claim, wherein the screw blade (22) extends throughout said inlet portion ( 15).
PCT/SE2020/050305 2019-05-06 2020-03-24 Screw assembly for disintegration of lignocellulosic material in a steam explosion process WO2020226544A1 (en)

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Citations (4)

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Publication number Priority date Publication date Assignee Title
US4274786A (en) * 1978-02-10 1981-06-23 Mo Och Domsjo Aktiebolag Process and apparatus for continuously conveying particulate compressible fibrous material from a zone at a first gas pressure to a zone at a second gas pressure
CN101463570A (en) * 2009-01-12 2009-06-24 广州华新科实业有限公司 Screw rod injection type plant fibre steam blasting device and method
JP2013006164A (en) * 2011-06-27 2013-01-10 Kobelco Eco-Solutions Co Ltd Wet type methane fermentation treatment method for organic waste
WO2017089648A1 (en) * 2015-11-26 2017-06-01 Valmet Technologies Oy Biomass based fuel configured to reduce a chemical and/or mechanical effect of flue gas on heat transfer surfaces and a method for making the same

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4274786A (en) * 1978-02-10 1981-06-23 Mo Och Domsjo Aktiebolag Process and apparatus for continuously conveying particulate compressible fibrous material from a zone at a first gas pressure to a zone at a second gas pressure
CN101463570A (en) * 2009-01-12 2009-06-24 广州华新科实业有限公司 Screw rod injection type plant fibre steam blasting device and method
JP2013006164A (en) * 2011-06-27 2013-01-10 Kobelco Eco-Solutions Co Ltd Wet type methane fermentation treatment method for organic waste
WO2017089648A1 (en) * 2015-11-26 2017-06-01 Valmet Technologies Oy Biomass based fuel configured to reduce a chemical and/or mechanical effect of flue gas on heat transfer surfaces and a method for making the same

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