A method and an apparatus for manufacturing cellulosic slurry for man-made cellulosic fiber production

Abstract

The invention relates to a method for manufacturing cellulosic slurry for man-made cellulosic fiber production having a main process (100), the main process (100) comprising method steps of -providing pulp slurry (101), -dewatering (102) the pulp slurry at least partly to form pulp mass, -opening (108) the pulp mass for producing pulp with loosened cellulosic fibers, -drying (109) the pulp with loosened cellulosic fibers in a flash dryer (11-17) to form fluffy pulp, -mixing (107) the fluffy pulp in a mixer (18; 20) with a cellulose-swelling or dissolving medium to form cellulosic slurry for man-made cellulosic fiber production. The invention relates also to an apparatus (10) for manufacturing cellulosic slurry for man-made cellulosic fiber production.

Description

[0001] A METHOD AND AN APPARATUS FOR MANUFACTURING CELLULOSIC

[0002] SLURRY FOR MAN-MADE CELLULOSIC FIBER PRODUCTION

[0003] Field of invention

[0004] The present invention relates to a method and an apparatus for manufacturing cellulosic slurry for man-made cellulosic fiber production.

[0005] Background of the invention

[0006] Textile fibers are commonly manufactured with three methods: natural, manmade or synthetic fiber production. Man-made cellulosic fibers (hereinafter also MMCFs) are fibers that are manufactured from natural cellulose with semi-chemical methods that involve dissolution of cellulose. As in most MMCF processes cellulose is not dissolved as individual polymer chains but as agglomerates (often called “fringed micelles") also the term “unlimited swelling" is used instead of dissolution to describe the final step of preparing the spinning solution. Also, a method to manufacture MMCF from a suspension of mechanically sufficiently fibrillated cellulose pulp has been developed.

[0007] MMCFs are used widely in textiles, nonwovens, hygiene products, as reinforcement fiber for rubber in tires and in various other applications. MMCFs produced in large scale are viscose, cupro and Lyocell fibers, and many other technologies have been either utilized for production or are being developed. Viscose fibers are manufactured by wet spinning: preparation of alkali cellulose followed by xanthation and dissolution in lye; extrusion of the cellulose xanthate solution into jets, and regeneration of the jets into cellulose fibers in an acidic spin-bath. Cupro is made by complexation of cellulose with copper (II) to give a dope, which is spun into an aqueous bath in a similar manner. Direct-dissolution processes (“Lyocell processes”) employ a direct solvent. Conventional Lyocell is made with a dry-jet wet spinning method, where the cellulose is converted into a solution (“dope") in N-methyl-morpholine oxide monohydrate (NMMO H2O), the solution is extruded to jets, and the jets are coagulated into fibers in water. Essentially the same methods apply to other direct-dissolution processes (non- conventional Lyocell), such as loncell®, HighPerCell®, or other ionic liquid (IL)-based systems, where the IL takes the role of NMM0 H20. The starting material for man-made cellulosic fibers is cellulose pulp, which can be manufactured from wood using the kraft or the sulfite process, or from cotton, where linters are converted into cotton linters pulp.

[0008] Also, bacterial cellulose can be used. The pulp may be delivered in wet or dry form. Wet pulp may refer to pulp slurried in water, typically at 4-10% dry matter content or to a pulp from which free water has been removed by pressing to reach up to c. 40-50% dry matter content. Conventional sheet dried pulp is commonly delivered with 10% moisture content. Usually, this pulp is provided in the “dissolving pulp" grade. However, also other kind of pulps, like, e.g., “paper grade" pulp can be used for the manufacture of MMCFs after suitable wet pre-treatment or by using a modified MMCF process. Additionally, other polymers may be mixed in, as in the blending of kraft lignin into loncell® fibers or when blending proteins with cellulose pulp.

[0009] Excess water is typically introduced to the pulp in processes preceding cellulose dissolution. Some of this water may be removed by pressing, but the pressing is limited to ca. 50%. Excess water prevents dissolution of cellulose. To compensate the introduction of excess water into the dope preparation with wet cellulose, the final water content of recirculated, concentrated solvent (e.g. NMMO) can be lowered in an evaporation plant, which, due to rising boiling point, requires steeply raising the final temperature of the concentrate and generates a higher volume of condensate to be purified.

[0010] In any MMCF process, reactivity of the pulp fibers with relevant swelling or dissolution medium or, e.g., in the case of the viscose process, with the cellulose derivatization chemical, is a critical factor affecting production efficiency as well as product quality. Practical pulp reactivity is affected by drying and compression of the pulp. In a state-of-the-art solution, the pulp is made into pulp sheets, which are baled. These bales of the pulp sheets are broken down in a pulper. The advantage of this is that feeding the pulp in form of the bales is very fast. Unfortunately, drying and compression has a negative impact on the reactivity. The pulper must compensate this by sufficiently powerful shredding and pulping action and long residence time. However, such equipment requires long batch cycles, large and powerful motors and large and heavy equipment. This also requires a batchwise operated system, and more efficient continuous systems cannot be used.

[0011] Pulp is provided to a MMCF factory either in the form of compressed bales of dry sheets, or directly from a pulp mill in wet form. The Lyocell process uses a well-defined stoichiometry of 1 :1 NMMO / H2O for dissolution of cellulose. This is necessary for dissolution: mixtures with higher or lower water content do not form a solution but a suspension. If the pulp is provided wet, then water entrained in the pulp is excess water that must be removed. There are two strategies to deal with this in industrial practice. The first option, a “wet method”, means that excess water is simply accepted to the process. A wiped-film evaporator (WFE) is used to evaporate the excess water from the slurry to reach target stoichiometry. Alternatively, recovered NMMO may be evaporated to a lower water content (e.g., to <20%) before its re-use in the Lyocell process, so as to compensate the entry of excess water with wet pulp. The inherent drawback of this is that evaporating the excess water from the slurry is thermodynamically less efficient than evaporating from the pulp. The pulp has a porous, fibrillar structure that inherently creates a lot of surface area for evaporation. To achieve the same for the dope, a film of dope must be established by mechanical wiping of the solution against a wall of the evaporator, and even so, it has much less area.

[0012] The second option, a “dry method’, works so that pulp is dried with conventional drying methods, pressed into sheets, and delivered in the form of bales to the MMCF factory. At the factory, the bales are fed into a pulper, where a rotating agitator disintegrates them in - presence of the NMMO- H2O solvent and excess water. At this stage, some excess water (ca. 1 molar equivalent or 13%) is accepted, the composition being near a dihydrate (NMMO 2H2O). This is done because the presence of excess water prevents outright dissolution of the pulp, which would cause viscosity to rise rapidly. Despite this small amount of excess water (ca. 13%), the load on the WFE is still much reduced compared to the “wet method”. Generally, even conventional pulp dryers are equally or more efficient for drying the pulp than using the WFE later in the process to accomplish the same amount of water evaporation. As such, modem installations often use the “dry method’.

[0013] Pulp drying can be done with many methods. Heat transfer mechanisms for drying are convective, contact, and radiative heat transfer. Convective drying can be achieved by forced air circulation, impingement, or entrainment of the fibers in air flow. Contact drying and radiative drying are combined with the convective drying. The main methods used are:

[0014] 1 ) Convective drying: the pulp slurry is formed into a web, which is pressed to remove free water, then dried using the convective drying with air impingement, through-air drying and belt drying (the convective drying), fluidized bed drying, flash drying, rotary drum drying and spray drying.

[0015] 2) Conductive drying (contact drying): the options are heated cylinders, a Yankee dryer (the contact drying combined with impingement), and heated paddle drying.

[0016] 3) Radiative drying: infrared drying, microwave and radio frequency drying.

[0017] Freeze drying, plate drying, and mixed batch drying are not part of this classification, but they are executed by means of the convective drying.

[0018] The focus of this disclosure, flash drying of pulp, is an established method for the pulp drying in the pulp and paper field. In the flash drying, the wet fibers (at moisture of ca. 40-45% typically from a press but can be varied between 30-50%) are entrained in a flow of hot air.

[0019] The high specific surface of the loosened pulp fibers during flash drying enables high evaporation rate of water, which, in turn, keeps fiber temperature low, e.g., at 30°C - 100°C, even when high air temperatures, e.g. 130°C - 150°C are used for drying and the final fiber moisture content at the dryer exit is low, e.g., 8-15%. The fibers are then separated from the airflow using a cyclone.

[0020] Conventional sheet drying is designed for compacting the pulp into sheets during the drying process, primarily to enable efficient storage, handling, and transportation of the dried pulp in the form of compressed bales. The sheet drying, however, compromises the processability of the dry pulp in the MMCF processes, where uniform swelling of the pulp fibers and, finally, dissolution of cellulose microfibrils or molecules is needed, either directly, e.g., in suitable organic solvents or in cold alkali, or after chemical derivatization of cellulose like, e.g., in the viscose or the carbamate process. Given that the conventionally dried pulp sheets are physically hard, they need to be re-pulped in pulpers, which has considerable capital and operating cost. Also, due to the unavoidably un-even drying of the pulp fibers during conventional sheet drying, local over-drying in the pulp sheets occurs, which reduces the reactivity of the pulp fibers with any swelling media, including direct solvents like NMMO, ionic liquids or cold alkali, but also lye (alkali) used in the viscose process for alkali cellulose preparation.

[0021] Considering that, in a typical MMCF spinning line of 60,000 t / a capacity operating at continuous 180 t / d production rate, over 20,000,000 individual continuous filaments are created by extruding spinning solution through equally many orifices with approx. 90 pm diameter (while the diameter of poorly swollen pulp fiber may be over 50 pm and the length over 100 times more), and that every day over 30,000,000 dissolved pulp fibers pass through each individual orifice, it’s clear how important it is to avoid appearance of any poorly swollen or only partially dissolved pulp fibers in the spinning solution. Indeed, as a single poorly dissolved pulp fiber can clog an orifice, continuous replacement of partially blocked spinning heads (with 2,000-100,000 orifices in each, depending on the MMCF process in question) with clean ones is a major factor limiting production efficiency of the MMCF spinning lines, thus increasing both operating and investment cost as well as causes disturbances in product quality.

[0022] A solution, currently used in the industry for re-pulping dried pulp, is to feed compacted bales of dried pulp sheets directly into a pulper, which operates batch-wise. Re-pulping progresses in stages. A first stage is rough shredding of the pulp bales by an agitator, or violent turbulence created by it. This, however, does not yet break the dried pulp sheets down sufficiently to enable even swelling of individual pulp fibers. Nevertheless, a second stage is gradual swelling of sturdy cell wall structure of individual pulp fibers, which progresses simultaneously with shredding. Here, slurrying solvent (approximately NMMO 2H2O in the case of NMMO Lyocell process) penetrates into shredded pieces of pulp sheets and inside individual pulp fibers. However, because the agitator disintegrates the bales and the sheets randomly and gradually, the slurry remains nonuniform until through repulping of the entire batch has been achieved. Until that, different sizes of residual agglomerates of unswollen pulp fibers or even dry sheet fragments are present. Because of this, re-pulping of baled sheets of dry pulp is to be done batch-wise. A lengthy delay for swelling must be allowed, usually 20- 30 minutes, to assure proper, even swelling of the cell wall structure of individual pulp fibers. This is inherently inefficient and failure prone.

[0023] Secondly, the pulper itself has a capital cost. These are large pieces of equipment that consume large amounts of electricity, require large and heavy electrical motors, are voluminous and take up large areas of floor space. A design placing less severe requirements on the pulper would be advantageous, as that would allow for the re-pulping to progress faster, which also would mean lower energy consumption.

[0024] Summary of the invention

[0025] The object of the invention is to address the above-mentioned drawbacks of the state-of-the-art processes of manufacturing cellulosic slurry for manmade cellulosic fiber production. Especially, the object of the present invention is to achieve a new method and an apparatus for manufacturing cellulosic slurry for man-made cellulosic fiber production wherein instead of batch-wise process also a continuous process can be applied, allowing dried pulp shredding in manner to form even swelling of the individual pulp fibers without formation of non-uniform slurry with residual agglomerates and / or dry sheet fragments leading to delays in the swelling phase. Furthermore, an object of the present invention is to bring forth a method and an apparatus wherein lighter, less space requiring, and more efficient equipment can be applied in manufacturing of the man-made cellulosic fibers to reduce both capital and operation cost as well as to reduce disturbances in product quality relating to the state-of-the art methods.

[0026] The above-described objects of the present invention are achieved because in the method and the apparatus according to the invention flash drying is applied in pulp preparation before mixing enabling application of continuous process. In simplest form this is achieved by integrated combination of a flash dryer and a mixer, but in some embodiments the solution may also comprise three devices: A flash dryer, a device increasing the bulk density of the dry pulp fibers and a mixer. Nevertheless, the mixer may be either continuously operating mixer or batch-type mixer. More specifically, method for manufacturing cellulosic slurry is characterized by what is described in independent claim 1 , and the apparatus is characterized by what is described in independent claim 9. The dependent claims 2-8 describe advantageous embodiments of the method, and the dependent claims IQ- 15 describe advantageous embodiments of the apparatus.

[0027] An advantage of the invented solution is the avoidance of compressing the pulp and the application of flash drying technology on fluffy pulp flocs, which enables uniform drying, avoidance of local over-drying and fast drying while keeping the pulp temperature moderate or low. As such, the pulp lands into the pulper or mixer in a fluffy state. It does not need to be separately opened. Likewise, it does not need any (inefficient) shredding action inside the pulper. The fluffy pulp is already in a form ready to mix with the slurrying solvent. This is true also after moderate compression of the flash dried pulp.

[0028] Coming straight from the flash drying, the pulp will have higher accessibility than pulp dried in a conventional sheet dryer. The high uniformity of the flash drying process enables setting the endpoint of drying precisely, therefore the humidity of the pulp can be more uniform than with a potentially unevenly drying pulp sheet. The apparatus will be inherently simpler. The simple flash dryer-small mixer combination will take up much less floor space than a conventional solution, comprising a dryer, a baler and a large pulper. With significantly fewer moving parts, its maintenance will be less costly.

[0029] An advantage in terms of capital cost is that the pulper or the mixer can be much smaller in size and in motor specification, because it does not need to be powered enough to shred dry pulp sheets, which have undergone wet densification and loss of reactivity in the conventional pulp dryer. Accordingly, its electricity consumption will be reduced as well, thereby reducing also operating costs.

[0030] Repulping fluffy, reactive pulp, as when the pulp is fed directly from the cyclone, requires less energy. The pulping time is shorter, and the equipment can be more compact and more efficient. This avoids the risk in conventional batch pulping of conventionally dried pulp, that clumps remain due to incomplete pulping.

[0031] Comparing this to evaporating the same amount of water in the wiped-film evaporator of the Lyocell (or other direct dissolution MMCF) process itself, the flash drying is thermodynamically more efficient. This advantage is shared with using the conventional baled pulp. The difference is that such a system is not integrated, and needs a separate shredder / pulper, requiring significantly more equipment.

[0032] The method and the apparatus of the invention is also well applicable with processes where there is a pretreatment step for the pulp before feeding. Such pretreatment requires hydrating the pulp on site. Installing another sheet dryer on the same site is an unlikely and expensive solution. Of course, the present solution should not be considered useful only when it is applied in connection with any pretreatment process. This is because application of the method and apparatus according to the present invention is not limited in using or not using such pretreatment. It is simply a case where it is particularly advantageous vs. a conventional solution. In the following some aspects of the method and the apparatus according to the invention are briefly described:

[0033] According to a first aspect of the method, the pulp slurry is provided from a fiberline of a pulp mill.

[0034] According to a second aspect of the method the pulp is chemically or physically pretreated as a slurry prior to dewatering.

[0035] According to a third aspect of the method the method comprises an auxiliary process comprising feeding of external pulp to the main process.

[0036] According to a fourth aspect of the method the external pulp being fed into the main process is taken from at least one bale of external pulp.

[0037] According to a fifth aspect of the method the external pulp is shredded before feeding to the main process.

[0038] According to a sixth aspect of the method the external pulp is pulped, dewatered, and fed to the main process upstream of the opening phase of the main process.

[0039] According to a seventh aspect of the method the main process comprises compacting of the fluffy pulp after flash drying to increase density of the fluffy pulp.

[0040] According to a first aspect of the apparatus the dewatering arrangement comprises a twin-wire press, a screw press, a belt press or other press for dewatering a wet pulp.

[0041] According to a second aspect of the apparatus the flash dryer comprises a cyclone being directly connected to a mixer.

[0042] According to a third aspect of the apparatus the apparatus comprises feeding device to feed fluffy pulp into the mixer.

[0043] According to a fourth aspect of the apparatus the apparatus comprises a compacting device for increasing density of the fluffy pulp to be fed into the mixer. According to a fifth aspect of the apparatus the mixer is a pulper.

[0044] According to a sixth aspect of the apparatus the mixer is a screw mixer or a paddle mixer.

[0045] Brief description of the drawings

[0046] In the following, the invention will be described in more detail with reference to the appended drawings in which:

[0047] Fig. 1 shows a flow chart describing a method for manufacturing cellulosic slurry for man-made cellulosic fiber production according to prior art,

[0048] Fig. 2 shows a flow chart describing a first embodiment of a method for manufacturing cellulosic slurry for man-made cellulosic fiber production according to the invention,

[0049] Fig. 3 shows a flow chart describing a second embodiment of a method for manufacturing cellulosic slurry for man-made cellulosic fiber production according to the invention,

[0050] Fig. 4 shows a flow chart describing a third embodiment of the method for manufacturing cellulosic slurry for man-made cellulosic fiber production according to the invention,

[0051] Fig. 5 shows a flow chart describing a fourth embodiment of the method for manufacturing cellulosic slurry for man-made cellulosic fiber production according to the invention,

[0052] Fig. 6 shows a flow chart describing a fifth embodiment of the method for manufacturing cellulosic slurry for man-made cellulosic fiber production according to the invention,

[0053] Fig. 7 shows a principle drawing of a first embodiment of the apparatus for manufacturing cellulosic slurry for man-made cellulosic fiber production according to the invention, Fig. 8 shows a principle drawing of a second embodiment of the apparatus for manufacturing cellulosic slurry for man-made cellulosic fiber production according to the invention, and

[0054] Fig. 9 shows a principle drawing of a third embodiment of the apparatus for manufacturing cellulosic slurry for man-made cellulosic fiber production according to the invention.

[0055] Detailed description of some preferred embodiments

[0056] Figure 1 shows a flow chart of method according to prior art that is so called “dry method”. In that method there is a main process 100’ wherein in a first phase cellulosic slurry is taken from a fiberline of a pulp mill in phase 10T. Thereafter the pulp slurry is at first dewatered with a press in phase102’ to form continuous cellulosic mass web. The following stages comprise sheet forming 103’ wherein the continuous pulp mass web is cut into sheets, sheet drying 104’ wherein the sheets are dried in a sheet dryer, baling 105’ wherein the sheets are baled, and storing 106’ wherein the bales are stored. The final stage is a slurry mixing phase 107’ which most commonly is accomplished in known processes by a pulper that works batch-wise. To form cellulosic slurry with more than one pulp grade, the production includes an auxiliary process 200’ wherein external bales are brought to the mill from an external pulp provider and stored with the bales of the main process, wherefrom the external pulp bales are fed to the mixing phase 107’ to blend them with the pulp of the main process 100’.

[0057] Figures 2-6 show flow charts of some embodiments of the method according to the invention. However, the method should not be limited in these examples. For instance, many combinations of them may be possible. Each of these example embodiments of the method comprise main process 100 and auxiliary process 200. The purpose of auxiliary process 200 is to ensure continuous production during the maintenance breaks as well as to enable mixing of different pulp grades to have suitable properties of the slurry for production of different types of MMCFs. A first embodiment of the method according to the invention is shown in figure 2. It differs from the closest prior art method of the figure 1 in that in the main process 100, the pulp mass is not cut into pulp sheets after dewatering phase 102 but kept in a form of continuous pulp mass also in the subsequent process phases.

[0058] Consequently, in the first embodiment of the method according to the invention shown in figure 2 the main process 100 comprises method steps of

[0059] -providing pulp slurry 101

[0060] -dewatering 102 the pulp slurry at least partly to form pulp mass,

[0061] -opening 108 the pulp mass for producing pulp with loosened cellulosic fibers,

[0062] -drying 109 the pulp with loosened cellulosic fibers in a flash dryer to form fluffy pulp,

[0063] -mixing 107 the fluffy pulp in a mixer to form slurry for man-made cellulosic fiber production.

[0064] By the term fluffy pulp (or fluffed pulp) herein is meant pulp in a form with at least partly disintegrated fibers that practically means that pulp may be e.g., in form of flocs having reduced density and increased moisture absorption properties compared to wet pulp mass after dewatering. The bulk density may be 100 kg / m3 or less, preferably 50 kg / m3 or less, most preferably 30 kg / m3 or less after drying in the flash dryer.

[0065] Mixing is herein meant process phase wherein fluffy pulp is mixed with a cellulose-swelling or dissolving medium to form (cellulosic) slurry for manmade cellulosic fiber production. The mixer may be, for instance a pulper, a screw mixer or a paddle mixer being able to operate in continuous or batch- wise manner. The screw mixer is most typically horizontally positioned device in which a screw moves the pulp while it is mixed and thereby screw mixer suits well for continuous process. The paddle mixers can be continuous or batch-wise. Continuously working paddle mixers have corresponding working principle as the screw mixer, but mixing in it is accomplished by paddle-shaped agitators positioned in a screwing orientation in a horizontally oriented mixing chamber. However, the screw mixer or the paddle mixer applied in this patent application should not be limited to the version being in horizontal orientation, but their position can be designed e.g., according to position and orientation of the respective devices being applied in previous and / or subsequent process phases.

[0066] In the embodiment of the method according to figure 2 the method may have an auxiliary process 200 comprising feeding of external pulp bales to the main process 100. The external pulp bales to be fed into the main process 100 are preferably dry bales 201 brought to cellulosic slurry production site by an external pulp supplier and being stored in phase 202 in suitable location proximity of the main process 100. In the embodiment of method according to figure 2 the pulp bales are shredded 203 before feeding into the main process 100. As shown in figure 2 the shredded pulp may be fed to main process prior to mixing 107 by blending the shredded pulp with the fluffy pulp of the main process 100.

[0067] In embodiments of the method shown in the figures 3-6 the pulp is pretreated in a phase 110. Figures 3-6 show each different embodiments of the method wherein pretreatment 110 is applied. However, in some other embodiments of a method according to the invention (such as in the embodiment shown in figure 2) cellulose slurry for MMCF production can be manufactured also without pretreatment.

[0068] In the embodiment of the method according to the figure 3 pulp slurry provided in phase 101 e.g., from a fiberline of a pulp mill is at first dewatered in phase 102. Thereafter the pulp sheets are formed in phase 103 from pulp mass, the pulp sheets are dried in phase 104, baled in phase 105 and stored in phase 106 before their pretreatment in phase 110. After pretreatment 110 the pretreated pulp sheets are dewatered in phase 111. Dewatering 111 as well as the dewatering 102 may be preferably accomplished by a suitable press such as a twin-wire press, a screw press, a belt press or other suitable press.

[0069] Embodiments of the method according to the figures 4 and 5 differ from that of figure 3 is that the pulp sheets are not formed from pulp mass dewatered in the phase 102 at all whereas the pretreatment 110 is carried out for continuous pulp mass. The pulp mass is thereafter dewatered in phase 111 and opened in phase 108. Next, the fluffy pulp formed in opening 108 is flash dried in phase 109 and mixed in phase 107 to form slurry, as in case of embodiments shown in figures 2 and 3.

[0070] The main process 100 of the embodiment of the method according to figure 6 differs from those of figures 4 and 5 in that the main process 100 comprises dry pressing in phase 112 wherein the fluffy pulp is pressed after the flash drying 109 to increase density of the fluffy pulp to be mixed.

[0071] In the external process 200 of the method according to the embodiment of figure 2 the external bales 201 are stored in phase 202 in suitable storage from where the pulp of bales can be fed (blended) to the pulp being processed in the main process 100. In case of the embodiment of the method according to figure 2 the external pulp bales are shredded in phase 203 before feeding them to the main process 100. After shredding 203 the pulp is in form of flocs which assists its blending with the fluffy pulp of the main process 100. In case of embodiments of figures 2-4 the shredded pulp bales are fed directly into the mixing 107. In general, feeding pulp bales to the main process 100 is meant herein that pulp sheets or pulp slabs stored to a bale are at first dismantled from the bale and then the separate sheets or slabs are fed into the main process. In some cases, feeding may mean that bales are fed as whole (i.e., without dismantling) or in part (i.e., by division of larger entities than single sheets or slabs) to the main process 100.

[0072] In case of embodiment of the method according to figure 4 the external bales 201 may be fed to the main process 100 correspondingly as in the embodiment of the method according to figure 2. However, in the embodiment of the method according to figure 3 external bales 201 may be alternatively or in addition blended to pulp bales of main process 100 stored in the storage of phase 106 before pretreatment 110.

[0073] In case of embodiments of the method according to figures 5 and 6 the external process 200 comprises method steps of providing external pulp bales in phase 201 , storing the external bales in phase 202 and pulping the external bales in phase 204, before feeding into the main process 100. Feeding is in these embodiments accomplished, for instance, by blending the pulp slurry of pulped external pulp bales to the pretreated pulp mass of the main process 100 to be dewatered in dewatering at phase 111.

[0074] In embodiments of the method according to the figures 2-6 the main process 100 and the auxiliary process 200 may be located on a pulp mill site, providing the benefits of mill integration. In such case the pulp slurry may be provided 101 from a fiberline of an integrated pulp mill to which the necessary apparatuses (e.g., one of those shown in the figures 7-9) have been arranged for respective processing. Advantage of such an integrated arrangement is that separate transportation phases and any risk of production breaks due to interruptions in logistics chain can be avoided. Alternatively, both the main process 100 and the auxiliary process 200 may be arranged independently. In such case the pulp to be processed can be supplied from any pulp mill, for instance, in the form of bales that are repulped before feeding to the main process 100, or so that pulp will be transported to the processing site as a slurry or mass form from any external pulp mill, and stored into a storage tank at the process site, from where it can be pumped to the main process 100. Advantage of such non-integrated arrangements are that they allow to use multiple different pulp grades non- simultaneously or simultaneously. The external bales are preferably brought to the processing site in form of bales from one or more pulp bale providers so that several different pulp grades can be used to form suitable properties for the produced cellulosic slurry according to its intended use. Figures 7-9 show some examples of combined flash dryers and mixers of the apparatuses that can be applied in the method according to the invention.

[0075] In general, the apparatus for manufacturing slurry for man-made cellulose fiber comprises at least:

[0076] -a feeding arrangement configured to dewater pulp slurry at least partly to form pulp mass,

[0077] -an opener arranged to form pulp with loosened cellulosic fibers from the pulp mass,

[0078] -a flash dryer arranged to dry the pulp with loosened cellulosic fibers to form fluffy pulp,

[0079] -mixer arranged to mix fluffy pulp to form cellulosic slurry for man-made cellulose fiber production.

[0080] The feeding arrangement typically comprises a press that may be for instance a twin-wire press, a screw press, a belt press or other press for dewatering a wet pulp slurry. The opener is a device that loosens the pulp fibers so that pulp fibers of the mass formed in the pressing 102 phase is loosened. Thus, the opener can be e.g., such a machine arranged to apply mechanical and / or air separation techniques for creating loosened pulp fibers.

[0081] Examples of the flash dryers having a combined mixer are shown in the figures 7-9. It should be bear in mind that these are only preferred examples and this part of the apparatus according to the invention may be realized also in manner that differs from these exemplary embodiments.

[0082] In the solutions shown in the figures 7-9 the flash dryer 11 -17 comprises, an air inlet 11 , a pulp inlet 12, an air-blower 13, a drying chamber 14, an intermediate channel 15, a cyclone 16 and an air-outlet 17. The air-inlet 11 is a conduit that extends from the blower 13 at the air blower’s 13 vacuum side. The air-inlet 11 may comprise an air heater to heat the incoming air, or an air heater may be arranged separately before the air-inlet 11. The air heater may be e.g. an electric heater or a heating system utilizing heat provided by flue gas of an existing furnace at an integrated pulp mill or an additional furnace provided for this purpose. It may be also connected to the air-outlet 17 so that air being used for drying can be circulated. In such cases some kind of a heat exchanger or condenser may be arranged to the connecting channel between the air-inlet 11 and the air-outlet 17 to remove moisture from the air before returning it to the air-inlet 11 . The pulp inlet 12 has, in these embodiments, a cone-shaped or correspondingly shaped feeding part which aids in feeding the loosened pulp fibers into the entering airflow at the vacuum side of the air blower 13. The air-blower 13 is e.g., a fan corresponding device that is able to cause enough high airflow so that loosened pulp fibers being fed into the flash dryer 11 -17 through the pulp inlet 12 are entrained with the airflow flowing through drying chamber 14 to the cyclone 16. In the drying chamber 14 that is typically a vertical columnlike chamber, the hot air flow causes moisture content of the loosened pulp fibers reduces, and fluffy pulp is formed. In cyclone 16, the air is separated from the dry fibers so that the fluffy pulp drops downwards into the mixer 18 (or in figures 8 and 9 mixer 20) and air is exhausted through air outlet 17. Furthermore, in embodiments shown in the figures 7-9 or in some other embodiments the flash dryer may include a buffer silo. The buffer silo allows the fibers to settle and homogenize, ensuring consistent moisture and temperature before further processing. This prevents fluctuations that could affect downstream operations like compacting or mixing.

[0083] In the solutions shown in the figures 7-9 a mixer 18 is combined with the flash drier 11 -17 such that fluffy pulp coming from the cyclone 16 will fall due to its gravity from the cyclone 16 into the mixer 18. For this reason, in each of these embodiments the mixer is positioned under the lower end of cyclone 16 so that connection between the upper end of the mixer 18 and the lower end of the cyclone 16 is as unrestrained as possible.

[0084] In figure 7 the mixer is a pulper which has feed device 19 to feed the fluffy pulp into the mixer 18. The advantage of such feeding device 19 is that the amount of fluffy pulp that arrives at the mixer 18 can be more easily controlled in real time. Especially, if mixer 18 is working in batch-wise, it would be advantageous to have possibility to enable controllable interruptions and accelerated periods of the feed from cyclone 16 to the mixer 18. The feeding device 19 will also ensure that fluffy pulp flows smoothly and that any blockings between the cyclone 16 and the mixer 18 are much more improbable. Thus, the feeding device 19 assists the mixer 18 regardless of whether it operates either continuously or in batch-wise.

[0085] In the figures 8 and 9 the mixer is a screw mixer 20. In the embodiment shown in the figure 8 the fluffy pulp is arranged to fall through the opening at the lower end of the cyclone into the screw mixer 20 only by its gravity. In the embodiment of figure 9 there is further a compacting device 21 before the mixer 20. The compacting device 21 may be formed of e.g., (as shown in the figure 9) a pair of rollers being arranged to abut each other such that fluffy pulp flowing from the lower end of the cyclone 16 is compressed so that its density will be increased before it arrives at the screw mixer 20. In some embodiments the compacting device 21 may be combined with a feeding device and in some other embodiments there may be separate feeding device in addition to the compacting device.

[0086] The method and apparatus according to the present invention applies analogously to related and allied methods, such as ionic liquid-based spinning (loncell®, with a bicyclic amidinium / guanidium acetate), alkalibased spinning (e.g., Biocelsol® with alkaline sodium zincate), or superphosphoric acid spinning (e.g., Bocell®), or derivatizations such as dissolution in NMMO monohydrate combined with carbamation, all of which require precise control of feed water stoichiometry. Similarly, the solution applies analogously to other processes where a cellulose dope is made, as in casting of films or other extrudates such as shaped fibers or surface coatings, e.g. impregnating a surface with the dope (cellulose solution) to make it less porous.

[0087] Within the scope of the present invention many modifications and combinations of the method and apparatus departing the embodiments described above are possible. The solution may, for instance, include additional method steps e.g., to further improve quality of the final product and / or efficiency of the process. For instance, in some embodiments of the apparatus it may comprise a capturing device, such as a filter, to capture pulp fibers escaped by air being exhausted out from the flash dryer through the air outlet.

[0088] Consequently, the method and apparatus according to the invention is not limited to the embodiments described above but can vary within the scope of the appended claims.

Claims

Claims1 . A method for manufacturing cellulosic slurry for man-made cellulosic fiber production having a main process (100), the main process (100) comprising method steps of-providing pulp slurry (101 ),-dewatering (102) the pulp slurry at least partly to form pulp mass,-opening (108) the pulp mass for producing pulp with loosened cellulosic fibers-drying (109) the pulp with loosened cellulosic fibers in a flash dryer (11 -17) to form fluffy pulp-mixing (107) the fluffy pulp in a mixer (18; 20) with a cellulose-swelling or dissolving medium to form cellulosic slurry for man-made cellulosic fiber production.

2. The method according to claim 1 wherein the pulp slurry is provided (101 ) from a fiberline of a pulp mill.

3. The method according to claim 1 or 2, wherein the pulp is chemically or physically pretreated (110) as slurry prior to dewatering (111 ).

4. The method according to any of preceding claims, wherein the method comprises an auxiliary process (200) comprising feeding of external pulp to the main process (100).

5. The method according to claim 4 wherein the external pulp being fed into the main process (100) is taken from at least one bale of external pulp (201 ).

6. The method according to claim 4 or 5 wherein the external pulp is shredded (202) before feeding to the main process (100).

7. The method according to claim 4 or 5 wherein the external pulp is pulped (204), dewatered (111 ) and fed to the main process (100) upstream of the opening phase (108) of the main process (100).

8. The method according to any of preceding claims, wherein the main process (100) comprises compacting (112) of the fluffy pulp after flash drying (109) to increase density of the fluffy pulp.

9. An apparatus (10) for manufacturing cellulosic slurry for man-made cellulose fiber production, the apparatus (10) comprising- a feeding arrangement configured dewater pulp slurry at least partly to form pulp mass,-an opener arranged to form pulp with loosened cellulosic fibers from the pulp mass,-a flash dryer (11 -17) arranged to dry the pulp with loosened cellulosic fibers to form fluffy pulp,-a mixer (18, 20) arranged to mix fluffy pulp with a cellulose-swelling or dissolving medium to form slurry for man-made cellulosic fiber production.

10. The apparatus (10) according claim 9 wherein the feeding arrangement comprises a twin-wire press, a screw press, a belt press or other press for dewatering a wet pulp.11 . The apparatus (10) according claim 9 or 10 wherein the flash dryer (11 - 17) comprises a cyclone (16) being directly connected to the mixer (18, 20).

12. The apparatus (10) according to any of claims 9-11 wherein the apparatus (10) comprises a feeding device (19) to feed fluffy pulp into the mixer (18, 20).

13. The apparatus (10) according to any of claims 9-12 wherein the apparatus (10) comprises a compacting device (21 ) for increasing density of the fluffy pulp to be fed into the mixer (18, 20).

14. The apparatus (10) according to any of claims 9-13 wherein the mixer (18, 20) is a pulper (18).

15. The apparatus (10) according to any of claims 9-13 wherein the mixer (18, 20) is a screw mixer (20) or a paddle mixer.

Images