Patent Application
20230071986
In general, present invention relates to producing of micro fibrillated cellulose (MFC). More especially the present invention relates to a system of producing MFC according to preamble part of the independent system claim and to a method of producing MFC according to preamble part of the independent method claim.
Micro fibrillated cellulose (MFC) comprises very thin cellulose fibers, typically width of which is typically 10-100 nm and length of which is typically between 0.5-10 μm. 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 2 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.
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.
According to the invention the 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 0.5-2.0 mm, preferably 0.8-1.6 mm, more preferably 1.0-1.2 mm, height less than 7 mm, preferably less than 5 mm and groove width of 0.5-3 mm, preferably 0.8-2.2 mm, more preferably 1-2 mm, 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 0.02-0.4 mm, preferably 0.05-0.3 mm or slots with width less than 0.2, preferably less than 0.15 mm.
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 +/−50°, preferably +/−30° and the stator has blade angel in range of +/−30°, preferably in range of +/−10°.
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 40-70° C.
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 50% of the stock flow flowing in the refining loop is configured to also flow in the temperature control system flow, more preferably at least 75% 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 20-40% 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 10-50% 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 3-5%, and to screen the pulp stock in at least one screening stage in at least one screen in consistency of 0.5-5%.
According to the invention the 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 3-5%, and the method comprises at least one screening stage in at least one screen in consistency of 0.5-5%.
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 40-70° C.
According to an advantageous feature in the method at least 50% of the stock flow flowing in the refining loop is also flowing in the temperature control system flow, more preferably at least 75% 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 0.5-2.0 mm, preferably 0.8-1.6 mm, more preferably 1.0-1.2 mm, height less than 7 mm, preferably less than 5 mm and groove width of 0.5-3 mm, preferably 0.8-2.2 mm, more preferably 1-2 mm, 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 0.02-0.4 mm, preferably 0.05-0.3 mm or slots with width less than 0.2, preferably less than 0.15 mm.
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 3-5%. There are at least two refining stages. After the refining the pulp stock is screened in a screen in consistency range of 0.5-5%. 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 1.2 mm, heigh of 5 mm and groove width of 2 mm. Advantageously, the rotor blade angle is 30° and the stator blade angel is 10°. 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 1 mm, heigh of 2 mm and groove width of 1 mm. Advantageously, the rotor blade angle is 30° and the stator blade angel is 10°. 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 4.5%, by which high quality MFC with over 90% fines content (measured by fiber analyzer Fiber Image Analyzer FS5) is produced by very low specific energy consumption of less than 1 MWh/T.
Advantageously, by conducting mid-screening in between at least two refining stages in consistency of 2-5%, high quality MFC with over 90% fines content (measured by fiber analyzer Fiber Image Analyzer FS5) is produced with even lower specific energy consumption of less than 0.5 MWh/T and without the need to use a heat exchanger.
The screen basket advantageously has holes with diameter of 0.02-0.3 mm or slots with less than 0.15 mm 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 1-2%, which provides for even higher quality MFC with over 95% fines content, (measured by fiber analyzer Fiber Image Analyzer FS5) is produced by very low specific energy consumption of less than 1 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 40-70° C. 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 patent application 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 patent application as an open limitation that does not exclude the existence of also unrecited features. The features described hereinafter are mutually freely combinable unless explicitly stated otherwise.
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.
In
In
In
In
In
In
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
In the system 10 of the examples of the
In
In
In
In
In
In
In
In
In
In the description in the foregoing, although some functions have been described with reference to certain features and examples, those functions may be performable by other features and examples whether described or not. Although features have been described with reference to the certain examples, those features may also be present in other examples whether described or not.
Above only some advantageous examples of the invention have been described to which examples the invention is not to be narrowly limited, and many modifications and alterations are possible within the invention.
10 system
11 pulper
12, 12A, 12B dump tower
13 refiner feed tank
14, 14A, 14B refining
15 intermediate tank
16 dilution device
17, 17A, 17B screening
18 thickening device
20 temperature control system
21 chemical and/or enzyme preparation device
22 water treatment device
23 water treatment equipment
25 temperature control device
R, R1, R2 reject flow
RC, RC1, RC2 recirculation
| Number | Date | Country | Kind |
|---|---|---|---|
| 20215931 | Sep 2021 | FI | national |
