Patent Description:
Micro fibrillated cellulose (MFC) comprises very thin cellulose fibers, typically width of which is typically <NUM>-<NUM> and length of which is typically between <NUM>,<NUM>-<NUM>. MFC also typically by definition includes nano fibrillated cellulose. MFC is typically processed of wood based cellulose fibers but it can also be processed of other plant based, non-wood-based sources for example agricultural-based fibers such as straw pulp, bagasse, bamboo and cotton or recycled cotton from recycled textile recycling.

It is known from prior art to refine stock in a refiner to mechanically treat and modify fibers to provide desired properties to the cellulose stock for production of selected fiber web grade with required properties. Mechanical treatment can be improved by chemical and/or enzyme additions. In connection of production of MFC various technologies are used, for example Masuko grinder technology, disk technology, high consistency technology, homogenization technology, micro fluidization technology, extruding technology, disperser technology. Typically, MFC is produced with different types of refiner by recirculating stock from outlet to inlet several times to achieve MFC with desired size and size variation.

In known production systems of MFC one major disadvantage is very high energy per capita consumption, typically over <NUM> MWh/t. Additionally, production capacity of the known systems is very limited and thus, its scaling to industrial use is challenging. Also, investment costs are high, which leads to expensive market price of MFC. In systems, where chemicals and/or enzymes are used in production of MFC, some of the chemicals used may limit usage of MFC to certain end products.

Especially, in MFC production with refining, the applied energy needed is high and major part of that will dissipated to stock and yielding the high stock temperature. Therefore, there exist a strong demand of temperature control of the stock in the MFC production, in particular in connection with refining the MFC stock, to ensure efficient refining results and production at higher capacities. A method for producing nanocellulose is disclosed in <CIT>.

Due to the high applied energy and the multi-recycling of the stock, the process temperatures are at high levels. The high temperature levels of the stock will affect unfavorably in succeeding process stages and may thus limit quality of MFC products. The high temperature levels of the stock may also cause health, safety and environmental (HSE) risks due to the high temperature of equipment surfaces. For example, seals made of rubber can be damaged due to the high temperatures and thus, high temperature stock may escape from the system and cause HSE-risks to operating personnel.

An object of the invention is to create a system and method of producing MFC, in which the disadvantages and problems of prior art are eliminated or at least minimized.

An object of the invention is to create an improved system and method of producing MFC, in which new, alternative ways of producing MFC are provided, especially in view of energy consumption.

A particular, non-binding, object of the invention is to create an effective system and method of producing MFC by mechanical or by mechanochemical production process, in particular using refining by a conical refiner.

In order to achieve the above-mentioned objects, the system of producing MFC according to the invention is mainly characterized by the features of the characterizing clause of the independent system claim and the method of producing MFC according to the invention is in turn mainly characterized by the features of the characterizing clause of the independent method claim. Advantageous embodiments and features are disclosed in the dependent claims.

The disclosed system of producing MFC comprises at least one refiner, wherein the refiner comprises means for refining a stock in at least two refining stages, advantageously at least two refiners for refining the stock in at least two refining stages, and the refiners comprise a number of refining bars, wherein the refining bars have width of <NUM> - <NUM>, preferably <NUM>-<NUM>, more preferably <NUM> -<NUM>, height less than <NUM>, preferably less than <NUM> and groove width of <NUM>-<NUM>, preferably <NUM>-<NUM>, more preferably <NUM>-<NUM>, wherein the system further comprises at least one screen for screening the stock and that each of the screens comprise a screen basket, which screen basket advantageously has holes with diameter of <NUM> - <NUM>, preferably <NUM>-<NUM> or slots with width less than <NUM>, preferably less than <NUM>.

According to an advantageous feature at least two refiners are located in series in the system.

According to an advantageous feature at least two refiners are located parallel in the system.

According to an advantageous feature the refiners comprise a rotor, a stator and wherein the rotor has blade angle in range of +/- <NUM>°, preferably +/- <NUM>° and the stator has blade angel in range of +/-<NUM>°, preferably in range of +/-<NUM>°.

According to an advantageous feature the system comprises a pulper for slushing the stock.

According to an advantageous feature the system comprises a chemical and/or enzyme preparation device connected to a device of the system located before at least one of the refiners.

According to the invention the system comprises a temperature control device for adjusting the temperature of the stock to temperature range of <NUM> - <NUM>.

The temperature control system comprises advantageously as the temperature control device a heat exchanger, for example a tube-type heat exchanger either concurrent or countercurrent heat exchanger or a spiral-type heat exchanger or a tube and shell -type heat exchanger or an absorption pump temperature control device. Tube heat exchangers and spiral heat exchangers are beneficial in view of costs and availability. Preferably at least <NUM> % of the stock flow flowing in the refining loop is configured to also flow in the temperature control system flow, more preferably at least <NUM> % of the stock flow flowing in the refining loop is configured to also flow in the temperature control system flow. By the temperature adjustment and control succeeding process stages are affected favorably and thus quality of MFC products can be improved. Additionally, by the temperature adjustment and control, health, safety and environmental (HSE) risks are eliminated or at least minimized.

According to an advantageous feature the system comprises at least one reject line and the reject line is connected from the screen to the refiner feed, advantageously <NUM>-<NUM> % of the refiner feed flow is flown from the screen.

According to an advantageous feature the system comprises at least one recirculation line back to a refiner feed, advantageously <NUM>-<NUM> % of refiner feed flow is flown from the recirculation line.

According to an advantageous feature the system is configured to be operated as a continuous process.

According to an advantageous feature the system is configured to refine the pulp stock in at least one refining stage in consistency of <NUM> - <NUM>%, and to screen the pulp stock in at least one screening stage in at least one screen in consistency of <NUM>,<NUM>-<NUM> %.

The disclosed method of producing MFC comprises at least two refining stages, in which a pulp stock is refined in at least one refining stage in consistency of <NUM> - <NUM>%, and the method comprises at least one screening stage in at least one screen in consistency of <NUM>,<NUM>-<NUM> %.

According to an advantageous feature the refining of the pulp stock is mechanochemical refining.

According to an advantageous feature the method is operated as a continuous process.

According to an advantageous feature the method comprises a slushing stage in a pulper.

According to an advantageous feature the method comprises a thickening stage for thickening the stock to storage consistency.

According to the invention in the method temperature of the stock is adjusted to temperature range of <NUM> - <NUM>.

According to an advantageous feature in the method at least <NUM> % of the stock flow flowing in the refining loop is also flowing in the temperature control system flow, more preferably at least <NUM> % of the stock flow flowing in the refining loop is also flowing in the temperature control system flow.

Advantageously, the temperature of the stock is adjusted by a temperature control system. A temperature control system may comprise for example a temperature control device. The temperature control system comprises advantageously as the temperature control device a heat exchanger, for example a tube-type heat exchanger either concurrent or countercurrent heat exchanger or a spiral-type heat exchanger or a tube and shell -type heat exchanger or an absorption pump temperature control device. By the temperature adjustment and control succeeding process stages are affected favorably and thus quality of MFC products can be improved. Additionally, by the temperature adjustment and control health, safety and environmental (HSE) risks are eliminated or at least minimized.

According to an advantageous feature in the method in the refining stage the refining bars have width of <NUM> - <NUM>, preferably <NUM>-<NUM>, more preferably <NUM> -<NUM>, height less than <NUM>, preferably less than <NUM> and groove width of <NUM>-<NUM>, preferably <NUM>-<NUM>, more preferably <NUM>-<NUM>, and the screening stage is performed by at least one screen for screening the stock and that each of the screens comprise a screen basket, which screen basket advantageously has holes with diameter of <NUM> - <NUM>, preferably <NUM>-<NUM> or slots with width less than <NUM>, preferably less than <NUM>.

According to an advantageous aspect in the system and in the method of producing micro fibrillated cellulose (MFC) pulp stock is slushed in a pulper and thereafter optionally the pulp stock is fed to a dump tower. Optionally, the processing of the pulp stock can be enhanced by enzyme addition in the pulper or in the optional dump tower. After this stage the pulp stock is guided to refining cycling of the pulp stock in the refiner in consistency of <NUM>-<NUM> %. There are at least two refining stages. After the refining the pulp stock is screened in a screen in consistency range of <NUM>,<NUM>-<NUM> %. Reject flow from the screening in the screen can be returned to refining in the refiner feed or guided to separate refining stage either thickened or non-thickened. After screening the accept flow is thickened to storage consistency and guided forward to the next unit process. The water of thickening stage can optionally be treated by dissolved air flotation (DAF) or by ultra-filtering or can be used in another process as dilution water or can be guided to wastewater treatment.

This provides that great volumes of MFC can be produced energy efficiently, and thus costs of high degree processed end products of MFC are significantly decreased.

Advantageously, in the refining bars have width of <NUM>, heigh of <NUM> and groove width of <NUM>. Advantageously, the rotor blade angle is <NUM>° and the stator blade angel is <NUM>°. The target is to maximize the cutting length in kilometers per revolutions, the actual number depends on the size and the type of the refiner.

Alternatively advantageously, in the refining bars have width of <NUM>, heigh of <NUM> and groove width of <NUM>. Advantageously, the rotor blade angle is <NUM>° and the stator blade angel is <NUM>°. The target is to maximize the cutting length in kilometers per revolutions, the actual number depends on the size and the type of the refiner.

Advantageously, the refining consistency is at least <NUM> %, by which high quality MFC with over <NUM>% fines content (measured by fiber analyzer Fiber Image Analyzer FS5) is produced by very low specific energy consumption of less than <NUM> MWh/T.

Advantageously, by conducting mid-screening in between at least two refining stages in consistency of <NUM> - <NUM> %, high quality MFC with over <NUM>% fines content (measured by fiber analyzer Fiber Image Analyzer FS5) is produced with even lower specific energy consumption of less than <NUM> MWh/T and without the need to use a heat exchanger.

The screen basket advantageously has holes with diameter of <NUM>,<NUM> - <NUM>,<NUM> or slots with less than <NUM>,<NUM> width, by which it is possible to return reject flow with the longest fiber fraction back to the refining and forward the accept flow with the smallest fibers. Advantageously, the screen basket is a pressure screen basket.

The final screening is advantageously conducted in consistency of <NUM> - <NUM> %, which provides for even higher quality MFC with over <NUM> % fines content, (measured by fiber analyzer Fiber Image Analyzer FS5) is produced by very low specific energy consumption of less than <NUM> MWh/T.

According to the invention in the system and in the method of producing micro fibrillated cellulose (MFC) temperature of the pulp stock is controlled and the temperature of the pulp stock is controlled at either in inlet or outlet side of refining. The temperature can be controlled in the feed or in a discharge tank or in a recycling line or in a separate loop of the process. The temperature can be controlled by a heat exchanger or by using absorption pump temperature control systems. Tank/-s of the system can have a temperature control device for example a blower or a fan or they can have temperature-controlled mantels or there can be coil/-s or other temperature control element/-s inside the tank/s. The temperature control can also be provided in pipes connecting parts of the system.

According to the invention by the temperature control the temperature of pulp stock is adjusted to temperature range <NUM> - <NUM>. Thus, advantageously the temperature control means are provided for cooling of the pulp stock in the system.

The system and the method are suitable for processing different types of pulp stocks for example wood based cellulose fibers, for example pine or eucalyptus, but in can also be processed of other plant based, non-wood-based sources for example agricultural-based fibers such as straw pulp, bagasse, bamboo, cotton or recycled cotton from recycled textile recycling. The system and the method are suitable for processing recycled pulp stocks, for example DIP and OCC, and bio-based pulp stocks and recycled textile stocks.

The exemplifying embodiments of the invention presented in this description are not to be interpreted to pose limitations to the applicability of the appended claims. The verb "to comprise" and its derivatives are used in this description as an open limitation that does not exclude the existence of also unrecited features.

In the following the invention is explained in detail with reference to the accompanying drawing to which the invention is not to be narrowly limited.

During the course of the following description like numbers and signs will be used to identify like elements according to the different views which illustrate the invention and its advantageous examples. In the figure some repetitive reference signs have been omitted for clarity reasons.

In <FIG> is shown schematically an example of a system <NUM> and the method of producing micro fibrillated cellulose (MFC). The pulp stock is slushed in a pulper <NUM> in consistency of <NUM>-<NUM> % and thereafter optionally the pulp stock is fed to a first dump tower 12A. Optionally, the processing of the pulp stock can be enhanced by enzyme addition from a chemical and/or enzyme preparation device <NUM> in the pulper <NUM> or in the optional first dump tower 12A. By this energy savings can be enhanced using the enzyme as catalysator for the processing. After this stage the pulp stock is guided directly or via an optional refiner feed tank <NUM> to refining of the pulp stock in the refiner <NUM> in consistency of <NUM>-<NUM> %. There is at least two refining stages. In case the optional refiner feed tank <NUM> is used there can be recirculation RC from the refiner <NUM> back to the refiner feed tank <NUM>. After the refining in the refiner <NUM> the pulp stock is guided directly or via an optional intermediate tank <NUM> and/or optional dilution <NUM> to a screen <NUM>. The pulp stock is screened in the screen <NUM> in consistency of <NUM>-<NUM> % or in consistency of <NUM>-<NUM> %. Reject flow R from the screening in the screen <NUM> can be returned to refining in the refiner <NUM> via the optional refiner feed tank <NUM> or guided directly to the refiner <NUM> or guided to separate refining stage. After screening the accept flow forwards is guided to an optional thickening stage in a thickening device <NUM> or directly to a second dump tower 12B. The reject flow can also be returned to the reining after the thickening. After refining the accept flow is optionally thickened to storage consistency and thereafter guided to the second dump tower 12B. The water of thickening stage can be treated by a water treatment device <NUM> with water treatment equipment <NUM>, for example by a dissolved air flotation (DAF) or by ultra-filtering.

In the system <NUM> of the examples of the <FIG> the refining comprises two refining stages, first refining stage 14A and second refining stage 14B, which are in series, <FIG> or parallel, <FIG>. In both examples the pulp stock is slushed in a pulper <NUM> in consistency of <NUM>-<NUM> % and thereafter the pulp stock is fed to a dump tower <NUM>. After this stage the pulp stock is guided directly or via an optional refiner feed tank <NUM> to refining stages 14A, 14B of the pulp stock in consistency of <NUM>-<NUM> %. In the example of <FIG>, in which the refining stages 14A, 14B are in series, there is a recirculation line RC from the second refining stage 14B its feed. In the example of <FIG>, in which the refining stages 14A, 14B are in parallel, there is a first recirculation line RC1 from the first refining stage 14B its feed or to the optional refiner feed tank <NUM>. There is also a second recirculation line RC2 from the second refining stage 14B to its feed. After the refining in the refiner <NUM> the pulp stock is guided forwards as explained in connection with the example of <FIG>.

In <FIG> is shown example of the system <NUM> with two refining stages 14A, 14B with an intermediate screening stage 17A. The pulp stock is slushed in a pulper <NUM> in consistency of <NUM>-<NUM> % and thereafter optionally the pulp stock is fed to a first dump tower 12A. Optionally, the processing of the pulp stock can be enhanced by enzyme addition from a chemical and/or enzyme preparation <NUM> in the pulper <NUM> or in the optional first dump tower 12A. After this stage the pulp stock is guided directly or via an optional refiner feed tank <NUM> to refining stages 14A, 14B of the pulp stock in consistency of <NUM>-<NUM> %. In the example there is a recirculation line RC from the first refining stage 14A its feed or to the optional refiner feed tank <NUM>. After the refining in the first refining stage 14A the pulp stock is guided to the intermediate screening stage in an intermediate screen 17A. The pulp stock is screened in the intermediate screen 17A in consistency of <NUM>-<NUM> % or in consistency of <NUM>-<NUM> %. Reject flow R from the intermediate screening in the intermediate screen 17A can be returned to first refining stage 14A. After the intermediate screening stage 17A the accept flow forwards is guided to a second refining stage 14B. After the second refining stage 14B the pulp stock is guided directly or via an optional dilution <NUM> and/or via an optional screening stage 17B in an optional second screen 17B. The pulp stock is screened in the optional second screen 17B in consistency of <NUM>-<NUM> % or in consistency of <NUM>-<NUM> %. Reject flow R from the optional second screening 17B can be returned to the second refining stage 14B. After the second screening stage 17B the accept flow forwards is guided to an optional thickening stage in a thickening device <NUM> or directly to a second dump tower 12B. After refining the accept flow is optionally thickened to storage consistency and thereafter guided to the second dump tower 12B. The water of thickening stage can be treated by a water treatment device <NUM> with water treatment equipment <NUM>, for example by a dissolved air flotation (DAF) or by ultra-filtering.

In <FIG> is shown example of the system <NUM> with screening <NUM>. The pulp stock is slushed in a pulper <NUM> in consistency of <NUM>-<NUM> % and thereafter optionally the pulp stock is fed to a first dump tower 12A. Optionally, the processing of the pulp stock can be enhanced by enzyme addition from a chemical and/or enzyme preparation <NUM> in the pulper <NUM> or in the optional first dump tower 12A. After this stage the pulp stock is guided directly or via an optional refiner feed tank <NUM> to refining <NUM> of the pulp stock in consistency of <NUM>-<NUM> %. In the example there is a recirculation line RC from the refining <NUM> to the optional refiner feed tank <NUM> or to the dump tower 12A. After the refining in the refining <NUM> the pulp stock is guided to a tank <NUM> and thereafter to a dilution stage <NUM> and then guided in consistency of <NUM>-<NUM> % to the screening stage in a screen <NUM>. Reject flow R from the screening in the screen <NUM> can be returned to the optional refiner feed tank <NUM> or to the refining stage <NUM>. After the screening stage <NUM> the accept flow forwards is guided to a thickening stage in a thickening device <NUM> and thereafter to the second dump tower 12B. The water of thickening stage can be treated by a water treatment device <NUM> with water treatment equipment <NUM>, for example by a dissolved air flotation (DAF) or by ultra-filtering.

In <FIG> is shown an example of a temperature control system <NUM> of a system and a method of producing micro fibrillated cellulose (MFC). In the example of the <FIG> the pulp stock is fed from a feed tank <NUM> to refining <NUM> and thereafter to a tank <NUM>, for example a discharge tank. The temperature of the pulp stock is controlled by a temperature control device <NUM> located in a recirculation line RC from outlet of the refining <NUM> to the feed tank <NUM>. The temperature control device <NUM> can be for example a heat exchanger or an absorption pump temperature control system. By the temperature control the temperature of pulp stock is adjusted to temperature range <NUM> - <NUM>. Thus, typically the temperature control device <NUM> cools of the pulp stock in the system.

In <FIG> is shown schematically advantageous examples of temperature controls systems <NUM> of a system <NUM> of producing micro fibrillated cellulose. Preferably at least <NUM> % of the stock flow flowing in the refining loop is configured to also flow in the temperature control system flow, more preferably at least <NUM> % of the stock flow flowing in the refining loop is configured to also flow in the temperature control system flow.

In <FIG> is shown an example of a temperature control system <NUM> of a system and a method of producing micro fibrillated cellulose (MFC). In the example of the <FIG> the pulp stock is fed from a feed tank <NUM> to a temperature control device <NUM> and therefrom to refining <NUM> and thereafter to a tank <NUM>, for example a discharge tank. There is also a recirculation line RC from outlet of the refining <NUM> to the feed tank <NUM>. The temperature control system <NUM> comprises at least one temperature control device <NUM>, which is advantageously a heat exchanger, for example a tube-type heat exchanger either concurrent or countercurrent heat exchanger or a spiral-type heat exchanger or a tube and shell -type heat exchanger or an absorption pump temperature control device.

In <FIG> is shown an example of a temperature control system <NUM> of a system and a method of producing micro fibrillated cellulose (MFC). In the example of the <FIG> the pulp stock is fed from a feed tank <NUM> to refining <NUM> and therefrom to a temperature control device <NUM> and thereafter to a tank <NUM>, for example a discharge tank. There is also a recirculation line RC from outlet of the temperature control device <NUM> to the feed tank <NUM>. The temperature control system <NUM> comprises at least one temperature control device <NUM>, which is advantageously a heat exchanger, for example a tube-type heat exchanger either concurrent or countercurrent heat exchanger or a spiral-type heat exchanger or a tube and shell -type heat exchanger or an absorption pump temperature control device.

In <FIG> is shown an example of a temperature control system <NUM> of a system and a method of producing micro fibrillated cellulose (MFC). In the example of the <FIG> the pulp stock is fed from a feed tank <NUM> to refining <NUM> and thereafter to a tank <NUM>, for example a discharge tank. The feed tank <NUM> is connected to a temperature control device <NUM>. There is also a recirculation line RC from outlet of the refiner <NUM> to the feed tank <NUM>. The temperature control system <NUM> comprises at least one temperature control device <NUM>, which is advantageously a heat exchanger, for example a tube-type heat exchanger either concurrent or countercurrent heat exchanger or a spiral-type heat exchanger or a tube and shell -type heat exchanger or an absorption pump temperature control device.

In <FIG> is shown an example of a temperature control system <NUM> of a system and a method of producing micro fibrillated cellulose (MFC). In the example of the <FIG> the pulp stock is fed from a feed tank <NUM> to refining <NUM> and thereafter to a tank <NUM>, for example a discharge tank. The feed tank <NUM> is provided with a temperature control device <NUM>. There is also a recirculation line RC from outlet of the refiner <NUM> to the feed tank <NUM>. The temperature of the feed tank <NUM> can be controlled using as the temperature control device <NUM> for example a blower or a fan or temperature-controlled mantel of the feed tank <NUM> or there can be coil/-s or other temperature control element/-s inside the feed tank <NUM>.

Claim 1:
System of producing MFC (micro fibrillated cellulose), which system (<NUM>) comprises at least one refiner (<NUM>, 14A, 14B), which refiner comprises means for refining a stock in at least two refining stages, advantageously at least two refiners (<NUM>, 14A, 14B) for refining the stock in at least two refining stages, and the refiners comprise a number of refining bars,
which refining bars have width of <NUM> - <NUM>, height less than <NUM>, and groove width <NUM>-<NUM>,
which system (<NUM>) further comprises at least one screen (<NUM>, 17A, 17B) for screening the stock and each of the screens comprise a screen basket, which screen basket advantageously has holes with diameter of <NUM> - <NUM>, or slots with width less than <NUM>,
wherein the system (<NUM>) comprises a temperature control device (<NUM>) for adjusting the temperature of the stock to temperature range of <NUM> - <NUM> and that the temperature of the stock is configured to be controlled at either in inlet or outlet side of the refiner.