WO2014072576A1

WO2014072576A1 - Method for opening fibres containing cellulose

Info

Publication number: WO2014072576A1
Application number: PCT/FI2013/051042
Authority: WO
Inventors: Ismo Reilama; Kari Kovasin; Esko Turunen
Original assignee: Metsä Fibre Oy
Priority date: 2012-11-07
Filing date: 2013-11-06
Publication date: 2014-05-15
Also published as: FI20126168A

Abstract

Method for opening in a continuous operation fibres containing cellulose. In the method, fiberized raw material with a lignocellulose content is used as the source material, which is in the form of a fibre suspension containing a fibre network. The fibre suspension is transferred in a continuous operation to a pressurized chamber (2, 3, 4, 5), in which the fibre network is dispersed into individual fibres or possibly fibre bunches, by mixing the fibre suspension with a carrier gas. The mixture of carrier gas and fibres or fibre bunches is brought through a rapid pressure drop to a lower pressure, in order to open the fibres. The wall of the fibres to be opened is in a swollen state, the force produced from the effect of the pressure drop on the expanding component in the lumen of the fibres against the fibre wall opens the fibres in an axial direction. The opening of the fibres of the stock promotes the processability of the stock and has an advantageous effect on the properties of the fibres.

Description

Method for Opening Fibres Containing Cellulose

The invention relates to the splitting of vegetable fibres containing cellulose in fibre refining processes. The invention relates specifically to the processing of wood-based fibres. The splitting of vegetable and particularly wood fibres has been known already for a long time. By means of the method, a good yield is obtained from fibrous material and a stock consisting of split fibres has many advantages in the further stages of the fibre-refining process. Most wood fibres and a significant part of vegetable fibres consist of tubular cells, in which there is an elongated cylindrical shell and a hollow space, the lumen, in the middle of it. The wall of such a tubular cell consists of various material layers, which differ between different tree and plant types and species. In the wall, there are small holes, pores, which permit the exchange of liquid and gas between the inner part and the outside of the cellular tube. Normally, the tubular cells remain whole cylindrical structures in present pulp and paper-industry processes. In terms of the further stages of many processes, it would be advantageous to open the cylindrical structures of the tubular fibres. Thus, methods have indeed been developed for splitting the tubular fibres. The methods can be called explosive splitting, because they are based on creating a pressure difference between the lumen of the fibre and the outside of the fibre tube. The first developer of the method is held to be Mason, in the method developed by whom at the end of the 1920s and the start of the 1930s wood chips are first of all heated to a high temperature at art elevated pressure, after which the pressure is rapidly momentarily raised and the chips are feed through a restricted cross-section to atmospheric pressure, when the chip becomes fiberized and the parts of the fibre disintegrate due to the effect of the pressure difference between the lumen and the outside of the fibre. The stock obtained is very suitable for the manufacture of fibreboard and the energy consumption of the method is low. However, the method is not specifically fibre-splitting at a fibre level, instead the result is fibre-based fine particles and part of the chips also remains poorly fiberized.

Steam Explosion pulping, (SEP) has been proposed as an alternative to CMP/CTMP processes, due to its lower energy requirement. In the method, a considerably raised temperature is used and cooking is ended with a rapid drop in pressure. This method too has been primarily developed for disintegrating the structure of the wood matrix, for fiberizing.

Publication WO 2012/080579 discloses a method, in which fibres with a cellulose content are watered and fed to a gas flow at an increased pressure and the gas flow is led to a venturi pipe, in such a way that the pressure drop in the venturi pipe creates a pressure difference between the fibre lumen and the outside, and splits the fibre tube longitudinally. This method has been developed for the intermittent processing of material. The intermittent operation of the method makes its application in large, modern plants complex and also expensive. In addition, the intermittent operation also creates a risk of the fibres caking, which can weaken the splitting of the fibres and increase the number of unsplit fibres.

The present invention is intended to eliminate at least some of the drawbacks of the prior art and create a new solution for the processing of fiberized material.

The invention is based on the idea that fibres containing cellulose are opened by transferring them from a pressurized state to a lower pressure, in such a way that the walls of the fibres of the stock to be processed have swollen in the pressurized state and there is at least one expanding component in the medium in the lumen of the fibres.

With the aid of embodiments of the invention, a method is achieved for the continuous opening of vegetable fibres containing cellulose, which comprise a tubular fibre wall, inside which is lumen, in which method a raw material containing fiberized lignocellulose is typically used as the source material, which is in the form of a fibre suspension containing a fibre network, when the fibre suspension is transferred continuously to a pressurized chamber, in which the fibre network of the fibre suspension is dispersed into individual fibres, or possibly fibre bunches by mixing the fibre suspension with a carrier gas, after which the mixture formed by the carrier gas and the fibres or fibre bunches of the dispersed fibre suspension is taken through a rapid pressure drop to a lower pressure, in order to open the fibres.

The wall of the fibres to be opened is in a swollen state, so that the force of the expanding component in the lumen of the fibres against the fibre wall opens the fibres in the axial direction.

According to one embodiment of the invention, the fibre processing process operates continuously. More specifically, the method according to the invention is characterized by what is stated in the characterizing portion of Claim 1.

Considerable advantages are obtained with the aid of the invention. The opening of the fibres of the stock is of great importance to the processability of the stock and the altered fibre prop- erties, and also to the properties of the fibre products to be manufactured from it. Such effects include improved washing, improved mass transfer in bleaching towers, improvement in the reactivity of the mass, improved drying, and a reduction in energy consumption in drying.

With the aid of a continuously operating process it is possible to avoid caking of the stock, so that the stock remains loose and the preconditions for good opening are retained. Other applications and properties of the invention will become apparent from the following detailed description and the related drawings. It should be noted that the drawings are only to illuminate the invention and do not define the scope of protection of the invention, which is referred to in the accompanying Claims.

Figure 1 shows schematically one embodiment of the invention and Figure 2 shows schemati- cally a second embodiment of the invention.

Definitions

The term swelling of a fibre, in connection with the technology presented here particularly of a vegetable fibre, such as a cellulose fibre, refers here to the fact that the distance between the individual fibrils or fibril aggregates of the fibril structure increases. The term "swollen fibre" refers to the fact that the distance between individual fibrils or fibril aggregates of the fibril structure is greater than it is when the fibre is bleached and undried in a neutral water environment.

For example, at the end of sulphate cooking, the fibres are in a swollen state, having been released from the wood-chip matrix. The cooking-liquor alkali in the intermediate space between the fibrils in the fibre wall, the lignin that has reacted in the liquor, and the hemi- celluloses prevent the fibrils and fibril aggregates from coming closer together. The degree of swollenness can be ascertained scientifically by SEM measurement in a transverse image of the fibre. This requires the preparation of a sample, freeze-drying or so-called critical point drying.

The degree of swollenness can be measured indirectly, for example, by measuring the total amount of water contained in the fibre wall by means of the FSP (fibre saturation point) method. The fibre's ability to bind water is measured by measuring the stock's WRV (water retention value). The various standards for determining the aforementioned value differ from each other slightly in how they are performed.

WRV measurement is made by placing the wet stock in a centrifuge tube, in which there is a sinter base. The centrifuge is accelerated to a rotational movement, which is sufficient for the centrifugal force to separate the water around the fibres and in the lumen. This free water exits through the sinter. The centrifuged stock is weighed, dried, and weighed again. The difference between the masses of the stock mass and the dried stock is assumed to correspond to the amount of water in the pores of the fibre wall between the fibrils. The WRV value is the amount of this water in the fibre wall relative to the amount of the dry stock (g water/g fibre). Determining the WRV is usually carried out from a washed mass and it depicts the fibre's ability to swell when suspended in water. How much the fibre has swollen in process conditions has been shown to depend on, amount other things, the predominating pH of the suspension in the fibre wall mass, the total ionic concentra- tion, and the temperature. The ability of the fibre to swell can also be influenced by mechanical processing of the fibre, such as beating, which creates so-called internal fibrillation in the fibre wall, but also fine particles at the same time.

In the sulphate process, the WRV is high when the pulp leaves the disgester and then drops as the number of process stages increases, so-called wet ceratinization takes place, the size of the fibre aggregates increases, and the structure of the wall becomes denser. For example, the following development of the WRV (SCAN-C62:00) according to Table 1 was measured on the fibre line in two mills manufacturing softwood sulphate pulp:

Table 1

Mill A, WRV, g/g Mill B, WRV, g/g Digested pulp 1.75 1.73

Oxygen-del igni fed pulp 1.52 1.65

Bleached pulp 1.47 1.56

Dried pulp 0.97 0.97

On the basis of the above, the invention is applied particularly to pulp, which has not been dried before the opening processing (so-called never-dried pulp). In a first embodiment, the WRV value of the fibre being brought to processing is more than 1.5 g/g. According to a se- cond, especially preferred embodiment, the WRV value of the fibre being brought to processing is at least 1.6 g/g, particularly more than 1.6 g/g. The latter range corresponds at the pulp mill to the swelling of the so-called brown pulp (in the washing of the pulp after cooking).

In this connection, the term swelling of the liquor refers to the fact that in the liquor there should either be volatile components (e.g., vaporized water, turpentine, methanol, ethanol) released in the change in pressure state, or dissolved gases (e.g., hydrogen sulphide, methyl- merkaptan, dimethylsulphide, dimethyldisulphide, sulphur dioxide, ammonia, carbon dioxide, oxygen).

Consistency values are given for the fibre suspension - consistency is the weight share of the dry pulp of the weight of the wet pulp, stated as a percentage.

The following depicts, by way of example, two equipment solutions, with the aid of which it is possible to implement the necessary steps of the method according to the invention, operating continuously. As will become apparent from the following, the method is especially preferably implemented in such a way that the pulp being processed does not stop during the pro- cess. This arrangement has the advantage that caking of the pulp can be avoided and the fibre material will remain evenly loose, which is one condition for the good opening of the fibres.

The present invention is intended to create a method and device, with the aid of which the opening of fibres with a cellulose content is possible continuously, already when they are released from the wood matrix. With the aid of the other features and embodiments of the invention, it is intended to create a method and device, with the aid of which the vast majority of the fibres of cellulose pulp can be opened.

According to one embodiment of the invention, the fibres are taken for splitting after sulphate cooking, when they are in a swollen state after cooking.

According to one embodiment of the invention, the fibres are brought to a swollen state by treating them with an alkali substance, for example, with a water solution containing sodium hydroxide.

According to one embodiment of the invention, the stock is transferred to a pressurized state by at least one pulp pump, which can be, for example, a high-consistency pump, a medium- consistency pump, or a low-consistency pump.

According to one embodiment of the invention, the stock in a pressurized state is concentrated by removing the free liquor from between the fibres.

In the arrangement of Figure 1, a vegetable-fibre stock containing cellulose fibre is fed to the system along the line A. Medium-consistency pumps 1 , 1 a are used to transfer the stock. After the pumps 1, 1a, the pressurized part of the apparatus begins, starting with a concentrator 2. In the concentrator, water is removed from the stock along line B. The concentrator 2 is followed by a heater 3, to which steam is fed along line C, and a first expansion stage, in which the stock moves to an expanding cross-section 4. This expanding cross-section 4 can be, for instance, a throttle or a venturi. Next comes a mixing tank 5, a throttle element 6, and a fibre separator 7, in which the fibre material is separated from the carrier gas. The carrier gas is led along line F for possible treatment, such as heat recovery or odoriferous-gas treatment, and the split fibre material is removed through line G for further processing.

The equipment operates in such a way that the pumps 1, 1a transfer the stock from line A at a consistency of 8 - 15 % and a pressure of 6... 15 bar. Preferably a single MC pump and two MC pumps connected in series (1 or 1+2) are used as the pumps. With a modern MC pump (medium-consistency pump) the stock is made to behave like a liquid. Medium-consistency stock can be fluidized and then pumped using the centrifugal principle. When the stock is in a strong, rotational movement, it begins to behave like a fluid. The main features of an MC pump are large shear forces and turbulence. Pumps 1 and la are followed by a concentrator, which in this arrangement is a pipe sieve, and concentrates the stock to a consistency of 20 - 30 % by removing the filtrate to line B and the heater 3 heats the stock to a temperature of 80 - 160 °C with a direct-steam nozzle. The first throttle 4 disperses (fluffs) the stock into fibres or bunches of fibres in the first expansion. Next, the dispersed stock is mixed with a carrier gas, which can be steam from line C or compressed air (line E). The purpose of the carrier gas is to ensure continuous movement and turbulence in the stock, so that the fibres and bunches of fibres remain separate from each other. The carrier gas's motion and the pressure in the pressurized chamber discharge the mixture of carrier gas and fibre material through a throttle element 6, in which the fibres open due to the effect of the rapid pressure drop. Finally, the fibre material is separated from the carrier gas. The fibre material is taken for further processing.

The arrangement of Figure 2 differs from the above. In the pressurized section the stock A is first heated by direct steam, after which the stock is concentrated with a screw pump. From the screw pump, the concentrated stock is led to a mechanical shredder, into which carrier gas E is blown through the stock outlet connection of the screw pump. From the shredder, the shredded pulp, carried by the carrier gas, is led to a venturi chamber, into which additional carrier gas and/or steam is fed.

With the aid of the invention, it is sought to control the process conditions and the behaviour of the fibre, in such a way that as many of the fibres as possible are opened. Various factors influencing this are explained in the following.

The invention relates to the conditioning of the fibre in a manner that opens the cylindrical structure of the fibre from one side longitudinally, without creating a significant amount of fines. Here, this is referred to as opening the fibre. Once an individual fibre has been opened, it is possible to significantly affect its behaviour in the various stages of the pulp and paper manufacturing processes. The water in the lumen of the fibre can freely move like the water surrounding the fibre and the surface of the fibre wall on the lumen side has a similar position as the outer surface of the fibre, in terms of the mass transfer between the liquid phase surrounding the fibre and the fibre wall. When the cylindrical structure of the fibre explodes to become 'sheet-like' the fibre wall can swell more freely than before. If most of the fibre of the stock can be opened, this has a great significance also on the properties of the fibre products being manufactured, due to the processability of the pulp and the altered fibre properties. Ef- fects include, among other things, boosted washing, boosted mass transfer in the bleaching towers, improvement of reactivity of the pulp, boosting of drying, and a reduction in the energy consumption of drying. At the present moment, there is no technical device on the market, with which splitting of fibre like that described could satisfactorily be implemented. The tubular fibres characteristic of vegetable material open parallel to their length, i.e. axially, when a sufficient pressure difference is created between the lumen of the fibre and the space surrounding the fibre, by dropping the pressure of the space surrounding the fibre rapidly from an excess pressure to a lower pressure. The pressure in the lumen seeks to equalize to the level of the surrounding pressure through the expansion of the lumen driven by the mate- rial flow taking place through the pore openings (and other possible openings) in the fibre wall and the positive pressure loading the fibre wall. The latter of these loads the fibre wall and makes it open. The fibre splits i.e. opens, if the stress caused by expansion exceeds the breaking limit of the structure of the wall.

The factors influencing the described opening of the fibre can be divided into three main groups, that is

• the fibre should be in a swollen state and filled with liquid,

• the liquid in the lumen of the fibre should be expanding and the expansion should be rapid,

• there should be space in the surroundings of the fibre for the expansion of the fibre. First of all, for splitting to occur reliably, the fibre should be in a swollen state and 'undamaged', i.e. there should be a solution filling in the tubular structure closed at its ends, nor should there be too large tears in it, through which the excess pressure in the lumen can discharge without opening the fibre.

A low fibre-wall Strength naturally assists opening. The strength of the fibre wall is affected by the swollenness of the fibre wall. The more swollen a state the fibre is in, the weaker its wall will be. Swollenness is affected by, for example, sodium in the digested suspension absorbed in the fibre wall and organic compounds, such as lignin and hemicelluloses, that are still in the fibre wall and that have been brought into a suspended form from the fibre wall. The fibre wall is most exposed to damage in an unwashed form immediately after cooking. A high temperature will also increase liability to damage. These phenomena are exploited in various embodiments of the invention.

So that the fibre can split as described, the fibre should be as a liquid filled 'vessel' in a pressurized state substantially whole at the start. There may not be damage in it, through which pressure could discharge too easily. The swollenness of the fibre wall to a significant extent blocks the natural pore openings and thus also promotes the wished for splitting of the fibre. The swollenness of the fibre wall also rounds fibres that may be flattened into a cylindrical form and ensures their filling with liquid. Bringing the fibre into a swollen state as is known is made more difficult by ceratinization of the fibre, which takes place both on the fibre line and when drying the fibres.

Ways to influence the swelling of the fibre include:

• the location of the opening in the pulp-manufacturing process,

• the use of chemical promoting swelling,

• temperature. One stage that is favourable to the opening of fibre is immediately after the cooking of the stock before the washing of the stock. The use of swelling-promoting chemicals, such as an alkali, increases swelling, as does raising the temperature.

Secondly, the liquid in the lumen should be expandable and the expansion should be rapid.

As is known, a liquid is in practice incompressible. When an attempt is made to open fibres by vaporizing the liquid inside them, a high temperature and a sudden change in pressure is required.

Fibre can in principles be opened, even if the liquid in the lumen is only water.

So that the liquid in the lumen can expand easily in the manner required for opening, it should preferably have either volatile components that are released in a change in pressure state, or a dissolved gas. Black lye is one such liquid and black lye remains in the lumen of the fibres after cooking. The expansion of the liquid can, as is known, be increased by raising the temperature or reducing the pressure.

A change in pressure can be created by, for example, using a venturi tube as a throttle ele- ment, through which the liquid-filled fibre is released from the pressure state. By means of a suitable pressure difference acting over the venture the pressure in the venturi 's throat can momentarily go even to a underpressure when the velocity is at a maximum, which will boost the expansion of the liquid inside the lumen.

Ways of influencing the ability of the liquid in the lumen to expand include: - increasing the partial pressures of the expanding compounds before expansion, the location of opening in the cellulose-manufacturing process, raising the temperature, reducing the minimum pressure level and acceleration of the pressure drop in the expansion, and - increasing the pressure difference and the flow velocity in the throat of the venturi/throttle element.

When operating according to the technology being described, it is possible to exploit at least one of the aforementioned features. It is also possible to combine two or more features.

Of the above, two are the same factors that relate to the swelling of the fibre, i.e. location and temperature. In the case of both, the effects are similar. Pressure differences, partial pressures, and flow velocity can be influenced by equipment design and by adjusting the process.

Thirdly, there should be space surrounding the fibre for the fibre to expand - the aim is a three-phase state.

The medium around the fibre to be opened should be easily compressible: a gas or a combina- tion of gas and liquid, which permits the expansion of an individual fibre. In other words, the inertial forces opposing the movement of the fibre wall should be sufficiently small. The movement of the fibre wall required by the expansion of the lumen is opposed by the inertial forces of the water and other fibres around the individual fibre and in contact with it. For a sufficient and sufficiently rapid expansion to be possible, these inertial forces should be as small as possible. The stock should be dispersed into individual fibres, if the aim is a fibre- specific effect, or into bunches of fibres, which are surrounded by the thinnest possible film of liquid, and between them a compressible gas space. Means of affecting the forces opposing opening are:

- initial consistency, which determines the amount of water on the outer surface of the fibre,

- the amount dispersion energy and dispersion gas, which affects the size of the fibre

bunches, and

- the continuity of the operation of the process, by means of which it is possible to prevent the stock caking into a dense mass that slows splitting.

It has been shown that the opening of high-kappa so-called high-yield pulp in the conditions at the beginning of washing succeeds easily at room temperature. The splitting of the fibre of well washed and centrifuged bleached or unbleached paper pulp did not succeed with corresponding test arrangements in the same conditions.

On the basis of the above, an advantageous stage for the opening of fibre is as soon as possible after cooking, either before washing or in the initial state of washing, when the fibre is well swollen and contains an advantageous medium for splitting, black lye. In the method according to the invention for opening fibres, the wall of the fibre to be processed is in a swollen state when brought to the process, or brought to a swollen state in the process. At the same time, there must be one or more expanding components in the liquid in the lumen of the fibres. This is achieved by taking the fibres for processing at a suitable point in the fibre-refining process, or by treating the fibres with a liquid, which has the necessary properties.

The fibres in a swollen state are mainly in the form of a fibre suspension, i .e. a stock. In the suspension, the fibres are in a liquid medium.

The stock in a swollen state has preferably initially a consistency of 8 - 15 %, or is brought to a consistency of 8 - 15 % by removing liquid from it. Water suspensions are particularly advantageous. Water as such can act as the liquid medium, in which case the question will be of a pure fibre/water stock. Preferably, a water suspension, which contains an alkali or alkaloidally reacting components, is used. The pH value of the medium of such a suspension is at least 10, typically 10 - 14 (or higher than that, always ac- cording to the measurement method used).

The suspension is preferably obtained after the cooking of material with a lignocellulose content, by taking a flow from the digester, which contains fibres in the stock used.

In one embodiment, the fibre suspension used as the initial material comprises an alkali stock used in pulp cooking, for example, black lye, in which there are suspended fibres. The black-lye suspension taken to the processing is then particularly advantageously a suspension, which is not separately treated, for example, chemically or physically before the opening processing.

In one preferred embodiment, the fibre suspension is unwashed.

In a second preferred embodiment, which can be combined with any of the preceding embod- iments, the temperature of the suspension taken to processing is 80 - 160 °C .

For processing, the stock is transferred to a chamber, in which there is a pressure of 8 - 15 bar and in the pressure chamber the stock is dispersed into fibre bunches or individual fibres by mixing with a carrier gas.

In the pressure chamber, the mixture of carrier gas and fibre bunches and/or fibres bunches is kept particularly advantageously in continuous motion and further the mixture of carrier gas and fibre bunches and/or fibres bunches in the pressure chamber is led through a pressure drop to the atmosphere or a chamber close to it, in order to split the fibres with the aid of a rapid reduction in external pressure.

The walls of the fibres containing cellulose are in a swollen state, for example, on account of the alkali and suspended organic substances in the cooking after sulphate cooking, and in the liquid in the lumen of the fibres, there is not only vaporized water but also volatile organic compounds. Therefore it is advantageous to perform splitting as soon as possible after cooking, before further processing. In one preferred embodiment, opening is therefore situated in the process between cooking and washing, both as a process step and in physical location.

The fibre wall can also be brought to a swollen state by adding an alkali to the stock. A suitable added alkali content is in the order of 5 - 15 g NaOH/1 or, if supported by other reasons, for example, an aim to dissolve some of the material, as much as 15 - 150 g NaOH/1.

In one embodiment, determined on the basis of the material to be treated, the alkali dose can be, for example, 5 - 100 kg NaOH/ADt.

The splitting of the fibre wall is also affected by the amount of dissolved organic substance in the fibre wall. It should be, according to one embodiment of the invention, when expressed as a wash loss of the stock, greater than 50 kg COD/ADt.

For the transfer of the stock to the pressurized chamber it is most preferable to use a medium consistency pump, or a combination of several medium consistency pumps. The number of pumps depends on the capacity required and the pressure difference required.

Alternatively, some known shut-off feeder can be used to transfer the stock to the pressurized chamber.

The stock in the pressurized chamber is concentrated to a consistency of 20 - 30 % by removing liquid from. This rise in consistency is performed by a screw pump, by removing liquid from the stock through holes in the wall of the pipe, or in some other known manner. If pipe liquid removal is used, the liquid-removal holes of a diameter of 0.30 mm or less in the wall of the pipe are in a tilted attitude against the flow direction of the stock and their combined transverse surface area is dimensioned in such a way that the velocity of the liquid to be removed in them is less than the velocity of the stock, preferably less than 30 % of the velocity of the stock.

Because temperature substantially affects the behaviour of the fibre in the manner described above, the temperature of the stock in the pressurized chamber is set to be about 80 - 160 °C. If necessary, the stock mass can be heated in the pressured chamber or in connection with the feed to the pressurized chamber to a temperature of 80 - 160 °C. The heating of the stock can be performed by mixing steam with it, which is at least partly allowed to condense. Heating and liquid removal can be combined by dividing the liquid- removal holes into groups, of which at least some operate according to a controlled sequence as alternating steam-feed routes, which will ensure than the holes remain open. The stock can be dispersed to form individual fibres or bunches of fibres with a mechanical shredder and then mixed with the carrier-gas flow. Mechanical shredding can take place before or after feeding to the pressurized chamber. However, the stock is preferably dispersed into individual fibres or bunches of fibres by guiding the carrier gas and the stock to a throttle element, in which the turbulence created divides the stock in fibres and bunches of fibres. The mixture of fibres, fibre bunches, and carrier gas is kept in continuous movement in the pressurized chamber by leading it in a single pass through the mixing chamber to fibre splitting. The mixture of fibres, fibre bunches, and carrier gas can also be kept in continuous movement by circulating it in a so-called circulating bed. The essential feature in this is that the fibres are in continuous movement, so that they cannot adhere to each other. The mixture of fibres, fibre bunches, and carrier gas in the pressurized chamber is led through a fixed or adjustable-throat throttle element to an atmospheric or nearly atmospheric chamber, in order to expand the liquid in the fibre lumen and to split the fibre. It can, of course, be envisaged that the throttle element is followed by a chamber, the pressure in which is reduced below the ambient pressure. The throttle element is preferably a venturi, because it is simple in structure and effective for this purpose. The carrier gas is preferably water vapour, compressed air, or a mixture of these, but other gases too or gas mixtures can also be considered. According to one embodiment, at least part of the carrier gas is water vapour that expands in the pressure reduction taking place in the throttle element.

List of reference numbers:

A line

1, la; 11, 1 1a pump

2; 12 concentrator

B line

3; 13 heater

C steam line

4; 14 expanding cross- section 5; 15 mixing tank 6; 16 throttle element 7; 17 fibre separator

F circulation line

G outlet line

List of references:

Dl : WO2012/080579

Claims

1. Method for the continuous operation opening of vegetable fibres containing cellulose, which comprise a tubular fibre wall, inside which is lumen, characterized in that

- a raw material with a lignocellulose content, which is in the form of a fibre suspension contained in a fibre network, is used as the source material,

- the fibre suspension is transferred to a pressurized chamber (2, 3, 4, 5) in a continuous operation,

- the fibre network of the fibre suspension is dispersed in the chamber (2, 3, 4, 5) into individual fibres or possibly fibre bunches by mixing the fibre suspension with a carrier gas, and

- the mixture formed by the carrier gas and the fibres and/or fibre bunches of the dispersed fibre suspension is transferred through a rapid pressure drop to a lower pressure to open the fibres, so that

- the wall of the fibres to be opened is in a swollen state, and so that as a result of the pressure drop the force produced by the expensing component in the lumen of the fibres against the fibre wall opens the fibres in an axial direction.

2. Method according to Claim 1, characterized in that fibres, which are in a swollen state, are transferred to the pressurized chamber.

3. Method according to Claim 1 or 2, characterized in that the fibres in a swollen state are taken from an alkali pulp cooking.

4. Method according to any of the above Claims, characterized in that the fibre suspension to be used as the source material comprises used cooking liquor from alkali pulp cooking, especially black lye, which contains suspended fibres.

5. Method according to any of the above Claims, characterized in that

- the fibre suspension to be used as a source material is taken after cooking, preferably immediately after cooking, and comprises, for example, a black-lye suspension,

- the fibre suspension to be used as a source material is not separately processed prior to transfer to the pressurized chamber (2, 3, 4, 5), and/or

- the fibre suspension to be used as a source material is used at essentially the cooking temperature, for example, 80 - 180 °C.

6. Method according to any of the above Claims, characterized in that the fibres are not dried prior to the opening processing.

7. Method according to any of the above Claim, characterized in that the WRV value of the fibre to be fed to the pressurized chamber is greater than 1.5 g g, particularly the WRV value of the fibre is at least 1.6 g/g, most suitably greater than 1.6 g/g.

8. Method according to any of the above Claims, characterized in that the walls of the fibres are brought to a swollen state in sulphate cooking, after which the fibres are in a swollen state on account of the alkali and dissolved organic substances in the cooking, and in the liquid in the lumen of the fibres there is not only vaporized water but also volatile organic compounds.

9. Method according to any of the above Claims, characterized in that stock in a swollen state is used, the consistency of which is 8 - 15 %.

10. Method according to any of the above Claims, characterized in that the pressure in the pressurized chamber (2, 3, 4, 5) is 8 - 15 bar.

11. Method according to any of the above Claims, characterized in that the mixture of a car- rier gas and fibres bunches and/or fibre bunches is kept in continuous movement in the pressurized chamber (2, 3, 4, 5).

12. Method according to any of the above Claims, characterized in that the amount of dissolved organic substance in the fibre wall of the fibres in a swollen state, expressed as a wash loss of the stock, is greater than 50 kg COD/ADt.

13. Method according to any of the above Claims, characterized in that the fibre wall is in a swollen state on account of an alkali added to the stock.

14. Method according to Claim 13, characterized in that, on account of the effect of the added alkali, the alkali content of the fibre suspension is 15 - 150 g NaOH/1.

15. Method according to any of the above Claims, characterized in that at least one medium consistency pump is used to transfer the stock to the pressurized chamber.

16. Method according to any of Claims 1 - 14, characterized in that some shut-off feeder is used to transfer the stock to the pressurized chamber.

17. Method according to any of the above Claims, characterized in that the stock in a pressurized chamber is concentrated to a consistency of 15 - 30 % by removing liquid from it.

18. Method according to any of the above Claims, characterized in that the temperature of the stock in the pressurized chamber is 80 - 150°C.

19. Method according to Claim 18, characterized in that the stock is heated to a preselected temperature, when the heating is preferably performed by mixing steam, at least part of which condenses, with the stock.

20. Method according to any of the above Claims, characterized in that the mixture of fibres, fibre bunches, and carrier gas is kept continuously in motion in the pressurized chamber (2, 3, 4, 5) by leading it in a single run through a mixing chamber (5) to the fibre splitting (6).

21. Method according to any of Claims 1 - 19, characterized in that the mixture of fibres, fibre bunches, and carrier gas is kept continuously in motion in the pressurized chamber by circulating the mixture in a circulating bed.

22. Method according to any of the above Claims, characterized in that the carrier gas is water vapour, compressed air, or a mixture of these.

23. Method according to any of the above Claims, characterized in that at least part of the carrier gas is water vapour that expands in the pressure drop taking place in the throttle element.

24. Method according to any of the above Claims, characterized in that a venturi is used as the throttle element.

25. Method according to any of the above Claims, characterized in that the consistency of the suspension in the pressurized chamber is brought to a value of 8 - 15 % by removing liquid from the suspension.

26. Method according to Claim 25, characterized in that the raising of the consistency taking place in the pressurized chamber (2, 3, 4, 5) is performed with a screw pump.

27. Method according to Claim 25, characterized in that the raising of the consistency taking place in the pressurized chamber (2, 3, 4, 5) is performed by removing liquid from the stock through holes or gaps in the wall of the pipe.

28. Method according to Claim 27, characterized in that the liquid-removal holes of a diame- ter of 0.30 mm or less in the wall of the pipe are arranged in a tilted attitude against the flow direction of the stock, and their combined cross-sectional surface area is dimensioned in such a way that the velocity of the exiting water in them is less than the velocity of the stock, preferably less than 30 % of the velocity of the stock.

29. Method according to Claim 27 or 28, characterized in that the liquid-removal holes are divided into groups, of which at least some according to a controlled sequence alternating as steam-feed routes, by which it is ensured that the holes remain open.

30. Method according to any of the above Claims, characterized in that the stock is dispersed into individual fibres or fibre bunches with a mechanical shredder and mixed with the carrier- gas flow.

31. Method according to any of the above Claims, characterized in that the mixture of fibres, fibre bunches, and carrier gas in the pressurized chamber is led through a fixed or adjustable- throat throttle element to an atmospheric or nearly atmospheric chamber, in order to expand the liquid in the fibre lumen and to split the fibre.