Field

The invention relates to a method of processing biomass and an apparatus for processing biomass.

Background

In a digester, which may also be called cooking pulp machine, biomass is cooked with a bio-solvent, which can also be called cooking chemical. The biosolvent typically comprises organic acid and water. The pulp fibers become suspended in the cooking chemical in the process and also organic and inorganic matter are dissolved or broken down in the suspension. The pulp suspension can be divided into liquor phase and solid phase, which becomes pulp that also includes the liquor trapped inside the fibers and other solid cellulose particles. Liquor phase can be at least partly separated from the solid phase by filtrating and/or washing.

Additionally, furfural is formed in the acid condition of heightened temperatures of the digester, furfural and pulp being two of the end products formed from biomass. A person skilled in the art knows that a presence of furfural in a process with organic acid(s) for forming furfural actually impedes further formation of furfural. Furthermore, humins, which are unwanted substances, are also formed in the process, and tend to deteriorate quality of the end product(s) and yield of the end products. Humins are extracted from the process. Also ash, which may affect negatively the end product(s), is separated from the processed biomass. Hence, improvement in yield while simplifying the process and keeping or heightening quality would be welcome in the cooking process of biomass.

Brief description

The present invention seeks to provide improvement in processing biomass.

The invention is defined by the independent claims. Embodiments are defined in the dependent claims. If one or more of the embodiments is considered not to fall under the scope of the independent claims, such an embodiment is or such embodiments are still useful for understanding features of the invention.

List of drawings

Example embodiments of the present invention are described below, by way of example only, with reference to the accompanying drawings, in which

Figure 1 illustrates an example of apparatus for processing biomass;

Figure 2 illustrates an example of separation of substances;

Figure 3 illustrates an example of a digester with separation of solution and pulp;

Figure 4 illustrates an example of separator for acid solvable inorganic substance (s);

Figure 5 illustrates an example of a controller;

Figure 6 illustrates of an example of a flow chart of a processing method for furfural; and

Figure 7 illustrates of an example of a flow chart of a processing method for pulp.

Description of embodiments

The following embodiments are only examples. Although the specification may refer to “an” embodiment in several locations, this does not necessarily mean that each such reference is to the same embodiment(s), or that the feature only applies to a single embodiment.

The articles “a” and “an” give a general sense of entities, structures, components, compositions, operations, functions, connections or the like in this document. Note also that singular terms may include pluralities.

Single features of different embodiments may also be combined to provide other embodiments. Furthermore, words "comprising" and "including" should be understood as not limiting the described embodiments to consist of only those features that have been mentioned and such embodiments may also contain features/structures that have not been specifically mentioned. All combinations of the embodiments are considered possible if their combination does not lead to structural or logical contradiction.

The term “about” means that quantities or any numeric values are not exact and typically need not be exact. The reason may be tolerance, resolution, measurement error, rounding off or the like, or a fact that the feature of the solution in this document only requires that the quantity or numeric value is approximately that large. A certain tolerance is always included in real life quantities and numeric values.

It should be noted that while Figures illustrate various embodiments, they are simplified diagrams that only show some structures and/or functional entities. The connections shown in the Figures may refer to logical or physical connections. It is apparent to a person skilled in the art that the described apparatus may also comprise other functions and structures than those described in Figures and text. It should be appreciated that details of some functions, structures, and the signalling used for measurement and/or controlling are irrelevant to the actual invention. Therefore, they need not be discussed in more detail here.

The term “biomass” refers to cellulose-containing and/or lignocellulose-containing material and may be wood-based or a so-called nonwood biomass, or a combination of these. The biomass may comprise woodchips from e.g. deciduous trees, conifer trees or bamboo, chopped into pieces of a desired size. The term “biomass” may also include materials such as hemicellulose.

The term “hemicellulose” means C5-sugars, C6-sugars, xylose, arabinose, mannose, xylan, arabinan, mannan or the like, for example.

The term “bio-cellulosic material” refers to material similar to biomass. The different term for similar kind of material has been used in order to clarify claims because although the biomass and the bio-cellulosic material may be materialistically similar they may come from different sources and they may have different structure. Grass-stemmed plants used as biomass generally refer to non-wood based fibre sources, such as straw, grass, reed, bast fibres, leaf fibres, seed hairs. Straws include for instance cereal straws, such as straws of wheat, barley, oat, rye and rice. Grass refers to esparto, sabai or lemon grass, for instance. Examples of reeds include papyrus, common reed, sugar cane and bamboo. Examples of bast fibre sources include stalks of common flax, stalks of oil flax, kenaf, jute and hemp. Leaf fibre sources include for example abaca and sisal. Seed hair fibre sources include for example cotton and cotton linter fibres. Further, non-woody fibre sources include for instance reed canary grass, timothy, cocksfoot, yellow sweet clover, smooth brome, red fescue, white sweet clover, red clover, goat’s rue and alfalfa.

The term “bio-solvent” refers to a mixture of organic acid and water. The organic acid may include at least one of the following: formic acid and acetic acid. In addition to organic acid and water, the bio-solvent fed to a digester may also include furfural. The bio-solvent can also be considered an organic solvent.

The term “cooking liquor” or “spent cooking liquor” refers to solution including lignin residues, hemicellulose, and inorganic and organic chemicals formed or liberated in the process performed in a digester. The spent cooking liquor is typically the liquid phase that is separated by filtration from output of the digester.

The term “pulp” means a solid phase of material that can be separated by filtration from the output of the digester. Pulp is a fibrous material composed mostly of cellulose.

“Humins” are, according to a person skilled in the art, undesirable byproducts formed in the digester. Humins may be dark, resinous material, and it is a common belief in the field that humins have negative effect on the process and the end produces]. The spent cooking liquor may include humins.

In an example of Fig. 1, a digester 100 of an apparatus for processing biomass receives biomass and bio-solvent including formic acid, acetic acid and water, for example. Percentages of substances in the digester 100 are as follows: formic acid about 0% to about 85 %, acetic acid about 0% to about 85%, furfural about 0.01% to about 10%, water about 0% to about 25%, ash about 0.01% to about 1% and sugars and lignin components about 1% to 5%. Here a combined percentage of formic acid and acetic acid should be at least about 75%. A ratio of bio-solvent and biomass is about 2.5:1 to about 6:1, and the temperature in the digester 100 is in the range about 110°C to about 170° for about 10 minutes to about 120 minutes. Here it should be noted that although a person skilled in the art generally believes that a presence of furfural in the process, also in the beginning of the process, with organic acid(s) for forming furfural impedes further formation of furfural, the result surprisingly turns out to be the opposite.

In an embodiment, the bio-solvent may also include furfural. The digester 100 also receives process control substance, which includes at least one inorganic substance determined as ash or ash components when analyzing the spent cooking liquor, biosolvent and biomass in general. The analysis that gives the ash content of the analyte may be performed according standards ISO 1762 Paper, board and pulps - Determination on residue (ash) on ignition at 525 °C, NREL/TP- 510-48087, for example. The annealing may be performed in a muffle furnace e.g. in temperatures at 525°C or 575°C, for example.

In an embodiment, pressure in the process may be below 20 bar. In an embodiment, pressure in the process may be below 15 bar. In an embodiment, pressure in the process may be below 8 bar. In an embodiment, pressure in the process may be below 6 bar. In an embodiment, pH of the process may be during cooking below 1. In an embodiment, pH of the process may be during cooking below 1.1.

The at least one inorganic substance may be formed from bio-cellulosic material such as the biomass, or it may be formed by other means or acquired separately. The at least one inorganic substance may include ash of biomass. Alternatively, ash of biomass may include the at least one inorganic substance. All in all, the biomass is subjected to both the bio-solvent and the process control substance. In this manner, formation of furfural can be intensified in the digester 100 and/or in the process applied to output of the digester 100. The at least one inorganic substance is mixed in a dissolved form within the digester 100, i.e. the at least one inorganic substance is ionized in the digester 100. In an embodiment, the at least one inorganic substance includes a plurality of inorganic substances.

The apparatus for processing biomass also comprises a filter 102, which separates solution from the biomass processed in the digester 100, and separates solution and pulp to separate outputs. Solution refers to a liquid or flowing portion of the material that is inside the digester 100 and pulp refers to a solid portion of the material that is inside the digester 100. Solution may include particles of solid material and it may be considered suspension the medium of which is liquid.

Additionally or alternatively, the digester 100 may include a filter and circulation arrangement, which corresponds to the filter 102, separates solution from pulp of the biomass processed in the digester 100, and separates pulp for output. The filter and the circulation arrangement may comprise a diffuser washer, for example. These kinds of filters 102 and filter and circulation arrangements, per se, are known by a person skilled in the art, although not utilized in the manner described in this document.

The apparatus for processing biomass also comprises a filter 102, which separates solution from the biomass processed in the digester 100, and separates solution and pulp to separate outputs.

The filter 102 may comprise a plurality of process phases. Fig. 2 illustrates a little bit more detailed form the filter 102. First, the separation of solid material i.e. raw pulp and liquid phase may be performed in a separator 200, which may carry out any suitable solid /liquid separation based on sieve, centrifuge, screw press, drum washer, belt washer or the like, for example. The solid material (raw pulp) comprises cellulosic fibers with a residue of spent cooking liquor. The separated liquid phase includes bio-solvent, furfural, carbo-hydrates (sugars) such as C5-carbo-hydrate products, an example of which is xylose, hemicellulose, lignin and other compounds formed in reactions in the digester 100.

The separation of furfural from the liquid phase may be performed by evaporating and distilling the spent cooking liquor and then separating acetic acid, formic acid, furfural and water from other substances in the liquid phase. The separation may be carried out by distillation using the furfural formed in the process as a distilling aid in the distillation. The formation of furfural is not explained more because a person skilled in the art is familiar with the filter 102, per se.

An advantage of adding process control substance, which includes the at least one inorganic substance, is increase of furfural yield. Additionally, it is possible to recycle a process product of bio-cellulosic material inside a factory or from one factory to another factory instead of wasting and discarding it.

Additionally or alternatively, pulp can be produced from the biomass processed in the digester 100 by fractionating biomass into pulp and monomeric sugars, which are then converted into furfural. Finally, furfural is separated from spent cooking liquor in distillation process. Furfural and pulp are output separately. It has been found that the addition of the control substance, which includes the at least one inorganic substance, which may be formed from bio- cellulosic material, causes the process to produce pulp and other end products of a similar quality as with pure bio-solvent without the control substance. In this manner, bio-solvent does not need to be as pure as expected in the prior art, which facilitates the process conditions and apparatuses needed in the process. Namely, purification of the spent cooking liquor is not needed at least in the extent it is believed by a person skilled in the art and done in the prior art. Another advantage of adding process control substance, which includes the at least one inorganic substance, is a possibility of closed reuse or recycling a process product of bio- cellulosic material instead of wasting and discarding it which is environmentally important. Still another advantage is energy conservation which is due to reduced cooking chemical purification which also results in cost savings. Cost savings may also come from the possibility that no separate catalyst is required, although it may be used but preferably in reduced amounts, for intensifying the conversion of sugars to furfural.

In an embodiment, the process control substance may be fed to the digester 100 in order to dissolve and/or mix the process control substance with the bio-solvent. In an embodiment, the process control substance may be mixed with the bio-solvent prior to the feed to the digester 100. In an embodiment, the process control substance may include the at least one inorganic substance, which may be based on biomass.

In an embodiment, the process control substance may be formed by burning biomass material and dissolving the at least one inorganic substance that is a nonvolatile residue into the bio-solvent. The residue may be based on the burnt biomass material. A part of the at least one inorganic substance may come from humins.

In an embodiment an example of which is illustrated in Fig. 4, the process control substance may include acid solvable inorganic substances separated from the burnt biomass material or spent cooking liquor output from the digester 100 by a separator 300. The separator 300 may be based on what a person skilled in the art is familiar with such as adsorption, ion exchange and solvent extraction, membrane technologies, capacitive deionization or any combination of these, for example. A part of the acid solvable inorganic substances may come from humins. It should be noted, however, that the separator 300 is not necessary and the burnt biomass material including the acid solvable inorganic substances and/or the spent cooking liquor output from the digester 100 can be fed to the digester 100 without the separation.

In an embodiment, the process control substance may include at least one compound that provides the bio-solvent in the digester 100 with acid solvable inorganic metal ions. Ions may include, without restricting to these aluminum, cobalt, chromium, copper, iron, manganese, nickel, zinc, magnesium, chloride, phosphate, sulphate and nitrate. That is, the ions may all be metal ions or a part of them may be metal ions. On the other hand, the ions may also be or include non- metal ions.

Metal ions and cooking chemical removed from pulp in the washing process may be collected and reused by feeding either of both of them back to the digester 100.

In an embodiment an example of which is illustrated in Fig. 2, the process control substance may include washing filtrate formed by filtrating output from the digester 100 in the filter 102. A part of the washing filtrate may include acid dissolvable components of the at least one inorganic substance.

In an embodiment an example of which is illustrated in Fig. 1, spent cooking liquor formed as a result of the filtration of the output from the digester 100 may be fed back to the digester 100. The spent cooking liquor may include acid dissolvable components of the at least one inorganic substance.

In an embodiment an example which is illustrated in Fig. 1, the process control substance may include furfural. Against the knowledge of a person skilled in the art, it was noticed that furfural input to the digester 100 does not lower the yield of furfural. The input of additional furfural has no negative effect on quality of pulp.

In an embodiment an example which is illustrated in Fig. 1, the process control substance may include hemisugars, which may increase yield of furfural without decreasing quality of pulp. In an embodiment, the process control substance may include both furfural and hemisugars.

In an embodiment an example of which is illustrated in Fig. 1, the apparatus for processing biomass may comprise a controller 104, which may control the addition of the process control substance to the digester 100. The apparatus for processing biomass may comprise at least one sensor 108, which measures the output of furfural from the process. The controller 104 may also receive information on the biomass fed to the digester 100. The information may include amount or flow of biomass fed to the digester 100, a type of biomass or types of biomasses. The type of biomass refer to virgin biomass, non-virgin biomass, recycled biomass material, kind of trees used to make biomass, kind of plants to make biomass, for example.

The apparatus for processing biomass may comprise at least one actuator 106, 110, which receive control signals from the controller 104. Then the at least one actuator 106, 110 may adjust the feed of the process control substance to the digester 100 in response to yield of furfural in order to adjust or set the yield of furfural at a desired level or at a desired range. The feed of the at least one inorganic substance as such or at least one inorganic substance determined as ash, the spent cooking liquor, furfural and hemisugars may be separately controlled and adjusted. In an embodiment, the controller 104 may control feed of different types of biomass to the digester 100 in order to control the yield of furfural and/or quality of pulp. For example, in a certain situation the controller 104 may increase feed on non-virgin biomass to the digester 100.

In an embodiment, the at least one actuator 106, 110 may adjust the feed of the at least one inorganic substance as such or at least one inorganic substance determined as ash and the spent cooking liquor to the digester 100 separately according to the signals from the controller 104. In this manner, it can be selected which substance is fed and how much. In certain situations, it may be useful to feed a certain amount of the at least one inorganic substance as such or at least one inorganic substance determined as ash and a certain amount of the spent cooking liquor together. In a similar manner, feed of all the at least one inorganic substance as such or at least one inorganic substance determined as ash, spent cooking liquor, furfural and hemisugars may be weighted in a desired manner.

In an embodiment, the apparatus for processing biomass may comprise at least one inorganic substance sensor 112, which measures directly or indirectly a percentage of the at least one inorganic substance and/or one or more ash components in the spent cooking liquor. The controller 104 may then adjust the input to the digester 100 in response to the measured percentage of the at least one inorganic substance and/or one or more ash components.

Fig. 5 illustrates an example of the controller 104. The controller 104 may comprise one or more processors 400, and one or more memories 402 including computer program code. The one or more memories 402 and the computer program code may be configured to, with the one or more processors 400, cause the apparatus for processing biomass at least to feed the process control substance to the digester 100 in response to yield of furfural in order to adjust or set the yield of furfural at a desired level or at a desired range. The controller 104 may also comprise a user interphase 404 through which a user may input information to the one or more memory 402. Instead of automatic control, the user may input information on the yield of furfural, type of biomass, amount of the process control substance to be added, type of the process control substance. The type of the process control substance may be the at least one inorganic substance as such or at least one inorganic substance determined as ash or spent cooking liquor, for example.

Examine now an example of embodiments with the help of Fig. 1 and Fig. 2. Biomass is fed to the digester 100 with bio-solvent that may be mixed with spent cooking liquor. The biomass, the bio-solvent and the spent cooking liquor are allowed to react in heightened temperature for a suitable period. During the cooking period lignin and hemicellulose is dissolved from the biomass because of the bio-solvent, and a portion of C5-sugars convert to furfural. After cooking the dissolved components and furfural are separated from pulp with the filter 102. The separation may be performed mechanically or using a pulp washing apparatus 202. The separated and washed pulp may continue to further processing. The liquid phase filtrate separated from pulp is the spent cooking liquor, which includes biosolvent and dissolved components from the biomass, such as lignin, sugar and the at least one inorganic substance, which may include ash components or components determined as ash. A portion of the spent cooking liquor may be directed to recovery of chemicals such that amounts of substances of removed from and input to the process correspond to each other.

Table 1. Characteristic percentages related with an example process. In Table 1, kappa number is about 17 to about 19, and pentosans content is about 13 w-% to about 14 w-%, where w-% means weight percent. All percentages are weight percentages in Table 1.

In an embodiment, percentage of at least one inorganic substance determined as ash in the digester may be about 0.05% to about 1 %. In an embodiment, percentage of ash in the digester may be about 0.1% to about 0.5 %. The controller 104 or the user may estimate the percentage of ash based on the input of the biomass and/or types of biomass. In an embodiment, the percentage of ash can be measured using the ash sensor 112 from the spent cooking liquor and the controller 103 may adjust the input to the digester 100 accordingly.

Figure 6 is a flow chart of the processing method. In step 600, the biomass is subjected, in a digester 100, to bio-solvent and process control substance, which includes at least one inorganic substance determined as ash formed from bio-cellulosic material for intensifying formation of furfural in conditions, where percentages are as follows: formic acid 0% to 85 %, acetic acid 0% to 85%, furfural 0.01% to 10%, water 0% to 25%, ash 0.01% to 1% and sugars and lignin components 1% to 5%, a combined percentage of formic acid and acetic acid being at least 75%; and ratio of bio-solvent and biomass is 2.5:1 to 6:1, and the temperature in the digester 100 being in the range 110°C to 170° for 10 minutes to 120 minutes. In step 602, furfural is produced from the biomass processed in the digester 100, and furfural and pulp are separated to separate outputs.

Figure 7 is a flow chart of the processing method. In step 700, the biomass is subjected, in a digester 100, to bio-solvent and process control substance, which includes at least one inorganic substance determined as, which may be formed from bio-cellulosic material for closed reuse of material. In step 702, pulp is formed from the biomass processed in the digester 100, and furfural and pulp are separated to separate outputs.

Strict environmental regulations and focus on cost efficiency can be met by following teachings of this document. The methods shown in Figs 6 and 7 may be controlled using a logic circuit solution or computer program. The computer program may be placed on a computer program distribution means for the distribution thereof. The computer program distribution means is readable by a data processing device, and it encodes the computer program commands, carries out the control.

The computer program may be distributed using a distribution medium which may be any medium readable by the controller. The medium may be a program storage medium, a memory, a software distribution package, or a compressed software package. In some cases, the distribution may be performed using at least one of the following: a near field communication signal, a short distance signal, and a telecommunications signal.

It will be obvious to a person skilled in the art that, as technology advances, the inventive concept can be implemented in various ways. The invention and its embodiments are not limited to the example embodiments described above but may vary within the scope of the claims.