A process for steam explosion treatment of non-wood plant material

Abstract

The disclosure relates to a process for steam treatment of non-wood plant material comprising subjecting the plant material to steam treatment and steam explosion in a steam treatment unit (10) comprising a steam treatment section (11) and a pressure relief section (12); characterized in that the process is a dual mode process, in which the steam treatment unit (10)5 is run in two alternating process modes (100a,100b), said process comprising supplying (101) plant material of a first or a second size fraction to a steam treatment unit (10) determining (102) plant material size fraction and selecting (103) a first (100a) or a second (100b) process mode, based on the determined plant material size fraction, subjecting the plant material to steam treatment (104a,104b) at a steam treatment pressure (PST1, PST2) in the steam treatment0 section (11), wherein, during the first process mode (100a), the steam treatment section (11) is operated at a first steam treatment pressure (PST1) and, during the second process mode (100b), the steam treatment section (11) is operated at a second steam treatment pressure (PST2), wherein said second steam treatment pressure (PST2) is higher than said first steam treatment pressure (PST1), followed by discharging (105a,105b) the plant material to a pressure relief5 section (12) operating at a relief pressure (PR) in which is lower than the steam treatment pressure (PST1, PST2), thereby causing steam explosion of the plant material, and forwarding (106a,106b) the treated plant material to storage or further processing. The disclosure pellets manufactured from the material obtained by the process, and use thereof.

Description

[0001] A PROCESS FOR STEAM EXPLOSION TREATMENT OF NON-WOOD PLANT MATERIAL

[0002] Technical field

[0003] The present disclosure relates to a process for steam treatment of non-wood plant material, pellets manufactured from the material obtained by the process, and use thereof.

[0004] Background art

[0005] Steam treatment involving steam explosion of lignocellulose material is a well-known method for defibration of cellulose fibres, asisdescribed, e.g. in W02020 / 005130A1. It isknown to apply steam explosion for defibrating biomass for producing fibres from non-wood plant material for different applications in the paper industry, like packaging papers, tissue and moulded products. In order to obtain valuable defibrated fibre material, the plant material, the material is typically cut to suitable size and screened to retrieve a suitable size fraction to allow processing in the steam treatment equipment. Smaller material fractions are typically considered not useful asraw material for producing fibresand are therefore generally discarded asreject, because they and can have negative impact to final paper, cause drainage disturbance and undesirably increase chemical consumption. The rejected smaller material fraction isoft en burned to produce electricity and / or steam, but this may however be problematic since annual plants generally have a high silica content that can lead to problems in boilers like build-up of e.g. silica scales, which can interfere with heat transfer and cause hot spots. TTiere is thus a need for away of making full use of the non-wood plant raw material without the drawbacks related to burning the small size fraction.

[0006] The present disclosure aims at providing a way to make full use of non-wood plant material used as raw material for fibresfor the paper industry. According to a first aspect of the present disclosure, there is provided a processfor steam treatment of non-wood plant material comprising subjecting the plant material to steam treatment and steam explosion in a steam treatment unit comprising a steam treatment section and a pressure relief section. The process is a dual mode process, in which the steam treatment unit is run in two alternating process modes, the process comprising supplying plant material of a first or a second size fraction to a steam treatment unit, determining plant material size fraction, and selecting a first or asecond process mode based on the determined plant material size fraction, subjecting the plant material to steam treatment at a steam treatment pressure in the steam treatment section, wherein, during the first process mode, the steam treatment section isoperated at a first steam treatment pressure and, during the second process mode, the steam treatment section is operated at asecond steam treatment pressure, wherein the second steam treatment pressure is higher than the first steam treatment pressure, followed by discharging the plant material to a pressure relief section operating at a relief pressure in which is lower than the steam treatment pressure applied in the first and second process mode, respectively, thereby causing steam explosion of the plant material, and forwarding the treated plant material to storage or further processing. Accordingly, the process allows treatment of all size fractions of the plant material, such that the entire plant raw material can be made use of, which is beneficial for economic reasons and sustainability. Preferably, the first steam treatment pressure (Psr1 ) is 3- 15 bar and the second steam treatment pressure is 16-20 bar. TTie relief pressure in said second process mode may preferably be at least 13 bar lower than the st earn treatment pressure, said relief pressure preferably being 2-3 bar. ie process may indude cutting the non-wood plant material prior to steam treatment and separating the cut plant material into a first large size fraction and a second small size fraction. During the first process mode, the plant material supplied to the steam treatment is suitably a first large size fraction plant material, and during said second process mode, the plant material supplied to the steam treatment is suitably a second small size fraction plant material. Preferably, the first large size fraction plant material has a I engt h i n t he range 10-60 mm and t he second smal I si ze tract i on pl ant mat eri al has a I engt h smaller than 10 mm. The retention time in the steam treatment may suitably be 5-30 minutes during the second process mode, preferably 15-30 minutes. If desired, one or more fertilizing compounds may be added to the plant material during the steam treatment in said second process mode, said one or more fertilizing compounds preferably being selected from sodium carbonate or potassium carbonate. The steam treated plant material obtained by said second process mode may preferably be formed into pellets.

[0007] According to a second aspect, the present invention relates to pellets manufactured from steam treated non-wood plant material having obtained as a product from the second process mode of the process of the first aspect .

[0008] According to a third aspect the, present invention relates the use of the pellets of the second aspect as livestock bedding material or soil fertilizer.

[0009] The present invention will become apparent from the detailed description given below. The detailed description and specific examples disclose preferred embodiments of the disclosure by way of illustration only. TTiose skilled in the art understand from guidance in the detailed description that changes and modifications may be made within the scope of the disclosure.

[0010] Brief the figure 1 shows a flow scheme of an example of the process according to the present invention; and figure 2 schematically illustrates a system in which the process of daim 1 can be carried out.

[0011] Detailed

[0012] The present invention is directed to treatment of non-wood plant material, fibre crops and agricultural harvest residues, such as annual or perennial plants like wheat straw, hemp, reed, bagasse, dade palm fronds, etc. TTie invention aims at providing away to make full use of the non-wood plant material, i.e. to be able to treat all fractions of the raw material, regardless of size, into valuable products that can be use as they are, or which can be further processed in various applications

[0013] When starting with the full stem of the plant material, the material has to be cut to a suitable size to allow processing in the equipment. In order to obtain valuable fibre material for further processing, the cut plant material is screened to retrieve a large size material fraction having a length suitable for processing into fibresfor the paper industry. ie screened out small size material fraction, which hastraditionallybeendiscarded asreject, comprisesdust, fines and straw lengths too small to be used for making fibresfor the paper industry. The treated small size material fraction can be used in agricultural applications asdescribed in more detail below.

[0014] The non-wood plant material may be provided to the steam treatment site already cut and screened into the two size fractions. However, more likely, it will be received at the site in bales of full stem plant material. In that case, it may be advantageous to add steps of cutting and separating the non-wood plant material into a first large size fraction and a second small size fraction to the process prior to steam treatment to allow efficient handling of the plant material.

[0015] The process of the present disclosure comprises supplying non-wood plant material to a steam treatment unit, and subjecting the plant material to steam treatment and steam explosion in the steam treatment unit, which comprises a steam treatment section and a pressure relief section, as described e.g. in W02020 / 005130A1. ie process is preferably a continuous process. TTie steam treatment section and the pressure relief section may typically be provided as separate pieces of equipment connected to each other. In the steam treatment step the plant material is thermally treated with steam in a pressure vessel and in the steam explosion step the softened hot material is rapidly and violently discharged from the pressure vessel, causing the steam explosion. Steam explosion is normally accomplished with a blow valve. A mixture of softened hot material and steam is blown through the valve whereby pressure is rapidly decreasing and the material is accelerated to high velocity by drag forces. The softened material is defibrated mechanically as steam and condensate in the pores of the material expands and due to impact and friction caused by the high velocity.

[0016] The process of the present is a dual mode process where both the large size material fraction and the small size material fraction can be treated to obtain valuable products, and there will thus be no need to discard or burn the small size fraction. Tie screened out small size plant material fraction can amount to up to ca 30 %of the total raw material weight, and it is advantageous to be able to convert also that fraction into a useful product. TTie dual mode process means that the steam treatment unit is run in two different alternating process modes, depending on which raw material fraction is to be treated at a certain point in time, such that the same steam treatment equipment can be used for both process modes. This providesaway of recovering and treating all raw material fractions without requiring large investment in additional steam treatment equipment. The two process modes may typically alternate as necessary, based on the demand for treatment of the plant material fractions. ie two different process modes will be described in more detail below. If desired, the plant material may be subjected to previous treatment steps known in the art prior to steam treatment.

[0017] Prior to the steam treatment, the two fractionsof raw plant material are suitably stored in storage containers. Duringthe running of each process mode, the plant material is preferably continuously conveyed, for example with screws, to the steam treatment section. The plant material i s typical ly forwarded to the pressure relief section by adischarge screw and is suitably released through a blow-valve.

[0018] The plant material is subjected to st earn treatment at apre-determined steam treatment pressure in the steam treatment section of the steam treatment unit according to the first or second process mode. In the second process mode, the steam treatment section is operated at a second steam treatment pressure, which is higher than the first steam treatment pressure at which the steam treatment section is operated in the first process mode. TTie plant material is then discharged to a pressure relief section, where the pressure is lower than the steam treatment pressure, thereby causing steam explosion of the plant material. The treated plant material is then forwarded to storage or further processing, suitably by means of a three-way valve allowing steam separation.

[0019] The process includes determining plant material size fraction and selecting the first or the second process mode, based on the determined plant material size fraction, "fi is can be made manually, e.g. by an operator monitoring the process and the process equipment and selecting the relevant process mode, or in the alternative, the steps of determining plant material size fraction and selecting the first or the second process mode can be made automatically by means of sensors obtaining information about the relevant plant material fraction and comparing with set values, and a control unit processing this information and activating the steam treatment unit parameters according to a relevant process mode. TTiere could also be a combination of automatic and manual input in determining plant material size fraction and selecting process mode, "fhe selection and running time of each process mode may be based on the amount of each raw material fraction available or on product demand.

[0020] The first process mode isadapted to treat plant material of a first large size fraction, i.e. having a length suitable for processing into fibres for the paper industry. TTie first large size fraction suitably comprises plant material having a length in the range 10-60 mm. Material over 60 mm length will generally be recut. The treatment according to the first process mode corresponds essentially to previously known steam treatment and steam explosion methods as described e.g. in W02020 / 005130A1. The st earn treatment pressure applied in the first process mode is pref er ably 3-15 bar wit h a suitable retent ion ti me, e.g. 1 -20 mi nutes, to enable efficient defibration by the subsequent steam explosion, in which the steam treated material is released to a lower pressure, such as 1-3 bar. TTie resulting fibre material can then be use in various paper industry applications.

[0021] The second process mode is adapted to treat plant material of a second small size fraction, i.e. material being too small for making valuable fibres for the paper industry. The second small size fraction plant material has a length smaller than 10 mm, thus typically comprising dust, fines and material having a length in the range 0.2-9 mm, often with a major part smaller than 4 mm. TTie steam treatment pressure applied in the second process mode is preferably is 16-20 bar, i.e. higher than for the first mode steam treatment. The steam treatment pressure applied in the second process mode may more preferably be 17-20 bar, and most preferably 18-20 bar. TTie retention time in the steam treatment in the second process mode ispreferably 5-30 minutes, more preferably 15-30 minutes, to allow the material to soften sufficiently. Tie material isthen released to a relief pressure of 2-3 bar for steam explosion. Tie large pressure drop, preferably at least at least 13 bar, in the steam explosion disint egratesthe small size fraction material even further, preferably into a size range of 0.2-2 mm. Tie steam explosion of the second process also mode causes the morphological structure of the plant material to open up, thus allowing increased access for enzymes and soil bacteria in a later decomposition situation.

[0022] The resulting material obtained by treating the second small size fraction according to the second process mode has been found to be excellent for use in agricultural applications, for exampl e as beddi ng mat eri al i n I i vest ock housi ngs and / or as soi I f ert i I izers. If desi red, t he second process mode may include adding one or more fertilizing compounds to the plant material during the steam treatment, in order to further improve the use of the treated material as soil fertiliser. ie fertilizing compounds may preferably be selected from sodium carbonate or potassium carbonate. Further, if desired, pelletizing can be included in the treatment process after steam explosion, or pelletizing can be performed separately.

[0023] The present invention further relatesto pel lets manufactured from steam treated nonwood plant material having obtained as a product from the second process mode of the process of the above process, and to the use of the pellets of as livestock bedding material or soil fertilizer. The pellets of the present invention can provide a valuable alternative to common livestock bedding materials, such as straw or compressed wood fibres. The material obtained by the second process mode will be slightly hydrophobicdue to lignin exposed due to the st earn explosion. Pellets formed from that material will thus be slightly hydrophobic. TTiereby, they don’t disintegrate as easily as compressed untreated wood fibres, produce lessdust than straw bedding and require less storage space, but have nonetheless capacity to absorb manure when used as livestock bedding material.

[0024] The used pellet bedding material, holding absorbed manure, can be distributed to fields and used as soil fertilizer. ie pellets of the invention can also be used directly as fertiliser if desired, especially if fertilizing compounds were added during the steam treatment process. Due to their slight hydrophobicity, the pelletsdeteriorate slowly and thus release the fertilizer slowly. TTie release of fertilizer and disintegration and decomposition of the pellet material by enzymes and soil bacteria is enhanced due to the changed and more open morphological structure caused by the steam explosion in the second process mode treatment. If desired, separate equipment can be arranged for the above described second process mode, such that the two process modes can be run in parallel, or steam treatment according to the second process mode could even be run a different site. fig. 1 schematically ill ust rates the step of the process for steam treatment of non-wood plant material comprising subjectingthe plant material to steam treatment and steam explosion in a steam treatment unit is a dual mode process. TTie steam treatment unit is run in two alternating process modes 100a, 100b, the process comprises the steps of supplying 101 plant material of a first or a second size fraction to a steam treatment unit, determining 102 plant material size fraction and selecting 103 a first 100a or a second 100b process mode, based on the determined plant material size fraction, subjecting the plant material to steam treatment 104a, 104b at a st earn treatment pressure Psr1 , Psr2 in the steam treatment section, wherein, during the first process mode 100a, the steam treatment section is operated at a first steam treatment pressure Psr1 , and, during the second process mode 100b, the steam treatment section is operated at a second steam treatment pressure Psr2, wherein the second steam treatment pressure Psr2 is higher than the first steam treatment pressure Psr1 , followed by discharging 105a, 105b the plant material to a pressure relief section operating at a relief pressure PR in which is lower than the steam treatment pressure Psr1 , Psr2, thereby causing steam explosion of the plant material, and forwarding 106a, 106b the treated plant material to storage or further processing. If desired, the process may include cutting 107 the non-wood plant material prior to steam treatment and separating 108 the cut plant material into a first large size fraction and a second small size fraction. figure 2 illustrates an example of a system for carrying out the process of the present disclosure. The system comprises a raw material storage container 3 for large size fraction plant material and a raw material storage container 4 for small size fraction plant material. A steam treatment unit 10 is provided, comprising a high-pressure steam treatment section 11 , operating at a steam treatment pressure Psr1 , Rsr2, and a pressure relief section 12 operating at a relief section pressure PR, which is lower than the steam treatment pressure Psr1 , Psr2, thereby causing steam explosion of the plant material. 9eam 7, and optionally fertilizer compounds 8, are supplied to the steam treatment section 11. The pressure relief section 12 suitably includes a blow-valve 9. Conveyors 5a, 5b are provided for supplying plant material from the storage containers 3, 4 to the steam treatment unit 10. A control unit 13 coupled to the steam treatment unit 10, can be configured to obtain or receive information related to the plant material size fraction to be treated and to select the first or second process mode for the steam treatment unit 10 based on the received information. Adosing system 6a, 6b can also be controlled by the control unit. Sbnsors(not shown) can be provided as necessary to provide the control unit with information necessary for selecting the relevant process mode. If desired, a cutter 1 and a plant material fraction separator 2 can be arranged ahead of the raw material storage containers 3,4. After the steam explosion, the treated plant material is forwarded to storage 14a, 14b or further processing 15a, 15b. The further processing of the treated second small size plant material fraction from the second processispreferably pelletizing in apelletizer 14a.

[0025] The person skilled in the art realizes that the present disclosure is not limited to the preferred embodiments described above. TTie person skilled in the art further realizes that modificationsand variations are possible within the scope of the appended claims.

Claims

CLAIMS1. A processfor steam treatment of non-wood plant material comprising subjecting the plant material to steam treatment and steam explosion in a steam treatment unit (10) comprising a steam treatment section (11 ) and a pressure relief section (12); characterized in that the process is a dual mode process, in which the steam treatment unit (10) is run in two alternating process modes (100a, 100b), said process comprising supplying (101 ) plant material of a first or a second size fraction to a steam treatment unit (10) determining (102) plant material size fraction and selecting (103) a first (100a) or a second (100b) process mode, based on the determined plant material size fraction, subjecting the plant material to steam treatment (104a, 104b) at a steam treatment pressure (Psr1 , Psr2) in the steam treatment section (11 ), wherein, during the first process mode (100a), the steam treatment section (1 1 ) is operated at a first steam treatment pressure (Psr1 ) and, during the second process mode (100b), the steam treatment section (11 ) is operated at a second steam treatment pressure (Psr2), wherein said second steam treatment pressure (Psr2) is higher than said first steam treatment pressure (Psr1 ), followed by discharging (105a, 105b) the plant material to a pressure relief section (12) operating at a relief pressure (Fh) in which is lower than the steam treatment pressure (Psr1 , Psr2) applied in the first and second process mode, respectively, thereby causing steam explosion of the plant material, and forwarding (106a, 106b) the treated plant material to storage or further processing.

2. The process of claim 1 , wherein said first steam treatment pressure (Psr1 ) is 3-15 bar and said second steam treatment pressure (Psr2) is 16-20 bar.

3. The process of any one of d ai ms 1 or 2, wherei n t he process i ncl udes cut t i ng ( 107) t he non-wood plant material prior to steam treatment and separating (108) the cut plant material into afirst large size fraction and a second small size fraction.

4. The process of any one of claims 1-3, wherein, during the first process mode (100a), the plant material supplied to the steam treatment is a first large size fraction plant material, and during said second process mode (100b), the plant material supplied to the steam treatment isa second small size fraction plant material.

5. TTie process of daim 4, wherein the first large size fraction plant material hasalength in the range 10-60 mm, and the second small size fraction plant material has a length smaller than 10 mm.

6. Tie process of claim any one of claims 1-5, wherein the retention time in the steam treatment is5-30 minutesduring the second process mode (100b), preferably 15-30 minutes.

7. The process of any one of daims 1-6, wherein one or more fertilizing compounds are added to the plant material during the steam treatment in said second process mode (100b), said one or more fertilizing compounds preferably being selected from sodium carbonate or potassium carbonate.

8. TTie process of any one of claims 1-7, wherein the steam treated plant material obtained by said second process mode (100b) isformed into pel lets.

9. The process of any one of claims 1-8, wherein the relief pressure (Ffa) in said second process mode (100b) is at least 13 bar lower than the steam treatment pressure (Psr2), said relief pressure (PR) preferably being 2-3 bar.

10. Pellets manufactured from steam treated non-wood plant material obtained from the second process mode of the process of any one of claims 1 -9.11 . TTie pelletsof claim 10, wherein said steam treated non-wood plant material issmall size fraction plant material having a length smaller than 10 mm, wherein the second steam treatment pressure (Psr2) of the second process mode was 16-20 bar, and the relief pressure (Fh) in said second process mode (100b) was at least 13 bar lower than the steam treatment pressure (Psr2).

12. Use of the pelletsof claim 10 or 11 , as livestock bedding material or soil fertilizer.

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