FI71585C - Process for making pulp. - Google Patents

Abstract

1. Process for grinding and washing a cellulosic material for the preparation of a paper pulp by passing the material, reduced in size to chips and impregnated with a reagent for removing lignin in a machine comprising at least two parallel screws driven in rotation inside a casing and provided with helical flights the pitches of which vary so as to determine several successive treatment zones, each zone including a section for conveyance and progressive compression and a braking section constituted by flights of inverted pitch provided with apertures allowing downstream passage of the material, having a size which is adjusted to allow selective advancement in the downstream direction of the material as a function of the degree of grinding achieved upstream of said apertures, characterised by the fact that the grinding and the washing of the chips is carried out simultaneously in the successive treatment zones of the machine, the casing of which is, for this purpose, constituted by an alternating series of filled regions and filtering regions, covering, respectively, the upstream portion and the downstream portion of each section for conveyance, each filled region being extended into the preceding braking section, the material being subjected as it passes from upstream to downstream in the machine whilst passing through each treatment zone, successively to a dilution by carrying out mixing with an actual washing liquid introduced upstream of the treatment zone then, into the flights of the screws to alternation between relaxation phases and phases of increase in pressure and finally to a drainage operation carried out at the same time as the grinding downstream of the section for conveyance and in the braking section, the used liquid being evacuated through the filtering regions of the casing.

Description

1 ^, 1 ANNOUNCEMENT „η • öShP 8 ^ UTLÄGG N1N G SSKRI FT 'IOO 5 (45) t ·· - V t 1 J 01 1007 ^ ^ (51) Kv.lk. * /! Nt.Cl.' D 21 C 9/00 (21) Patent application - Patentansökning 800887 (22) Filing date - Ansökningsdag 21.03.80 (F ·) (23) Starting date - Giltighetsdag 21 .03.80 (41) Made public - Blivit offendig 23-09.80

National Board of Patents and Registration / 44) Date of publication and date of publication. - 10.10.86

Patent and registration authorities V 'Ansökan utlagd och utl.skriften pubiicerad (86) Kv. application - Int. ansökan (32) (33) (31) Privilege claimed - Begärd priority 22.Ο3.79 France-Franconia (FR) PV 7907250 (71) Clextral, 1, Rue du Colonel Rietz, Firminy Cedex, France-France (FR) ( 72) Pierre Berger, Saint-Etienne, Christian de Choudens, Gieres,

Gerard Lombardo, Fontaine, Pierre Monzie, Grenoble,

Robert Angelier, Echirolles, France-France (FR) (7 * 0 Oy Koi ster Ab (5 * 0 Method for making pulp - Förfarande för framställning av pappersmas)

The invention relates to improvements in pulp production processes using finely ground lignocellulosic feedstock and to improved equipment for applying this new process.

It is known that pulp is generally made from ligno-cellulosic raw material and most often from wood. In most of the methods used, the wood is first ground into a groundwood, which is then treated to soften the lignin, after which the pulp is divided into fibers by a mechanical fiberization treatment.

Sometimes the softening of lignin takes place simply by drying the groundwood with steam, in which case the pulp is called hot-milled. However, chemical substances, reagents are commonly used. The importance of the mechanical treatment required to separate the fibers is inverse to the significance of the chemical treatment performed. When the mechanical treatment of the fiberization is relatively important, it is a question of mechanical-chemical or semi-chemical pulps.

The defibering treatment usually takes place in high-speed rotating equipment, the so-called in plate defibrators in 1-fiberizers.

The author of the present invention has developed a new defibering method, which, like the machine used for its application, is described in French Patent Application No. 75-23911 / 31.7.-75.

Such a machine comprises two parallel screws rotating in a frame housing surrounding them. The screws have threads whose pitch varies from the front end to the rear end of the screw and which delimit several successive treatment zones. Each zone then comprises a raw material transfer compartment (as the screws rotate, the raw material moves forward) followed by a braking compartment. The raw material, usually wood chips, passes through an opening in the front end of the frame housing and the screws move it as it rotates to the rear opening. Each braking compartment causes the pulp to progressively compress at the end of the previous transfer compartment and, as the pulp accumulates at a given point, forms a continuous "charge" that separates the two successive zones.

The purpose of the machine described in the above-mentioned patent is to provide a defibering treatment by utilizing the combined compressive and shear effects which arise when the pulp moves in the screws. Each braking compartment then comprises opposite threads which normally raise the mass to the initial end. As a result, a progressive compression of the mass occurs at the end of the transfer compartment to overcome the effect of the braking compartment. On the other hand, the inverted threads have openings through which a certain amount of mass passes forward. In this case, it is also possible to control the pressure rise. According to a significant feature of the patent, the forward displacement of the pulp can be adjusted as desired on the basis of the size of the openings, i.e. a pulp whose degree of defibering is not large enough to be able to go po. through the openings, remains in the most compressed zone where it is efficiently mixed, precisely because it is then in screws rotating in the same direction.

When this function is still associated with the pressure in question, the defibering takes place without, however, significantly shortening the length of the fibers.

3 71585 Thus, by selecting an appropriate orifice size and generally such parameters that affect the mass transfer process in the machine (mechanical structure of the threads, screw diameter, rotational speed, etc.), a different defibering function can be provided in each zone of the machine.

But regardless of the fiberization power used, whenever the lignin softener-1 solvent is used for this purpose, the pulp must be washed after the fiberization treatment so as to remove residues resulting from the reaction of the material used with the wood. In that case, it is precisely a kind of precipitate mixed with wood. However, it must be eliminated so that the pulp contains only fibers suitable for papermaking.

Up to now, the operations involved in the production of pulp have been carried out successively, i.e. the groundwood has first been softened by impregnating it with the chemical in question, followed by defibering and finally washing.

It was only natural that certain special materials were used at that time, but this again required large and expensive equipment, the use of which was economical only in the case of large-scale production.

Instead, the improvements of the present invention provide truly significant savings.

According to the invention, the pulp already impregnated with the chemical in question is washed simultaneously with the defibering operation in at least one treatment zone. The washing liquid is then sprayed at the beginning of the transfer compartment, whereby the pulp can be diluted. The pulp is then dried by filtering part of its liquid phase in openings arranged in the frame housing in front of the braking compartments (2 pcs.) Associated with the treatment zone.

In a preferred embodiment of the invention, the amount of washing liquid to be sprayed in front of the next treatment zone after each drying treatment is adjusted according to the conditions under which the pulp goes po. to the braking zone behind the zone, so that the degree of drying is not more than 50 to 55%, so that the mass can move well to the end of the next braking section.

The invention will now be described in more detail with reference to an embodiment thereof, which is shown by way of example and which is illustrated in the accompanying drawings.

71585

In Fig. 1 there is a longitudinal section of a processing machine according to the invention, Fig. 2 shows a plan view and on an enlarged scale one treatment zone, Fig. 3 is a section along the line III-III in Fig. 2 and Fig. 4 is a section along the line IV-IV in Fig. 2.

Figure 1 (longitudinal section) relates to a processing apparatus of the type described in the above-mentioned French patent application 75-23911.

The apparatus according to the invention comprises a body housing 1 with two cylindrical blocks surrounded by two screws. The screws have overlapping threads (Figure 2). The threads are similar and the screws rotate in the same direction. At one end of the body housing there is an opening 10 for feeding the pulp. As the screws rotate, they pull the pulp all the way to the outlet 11 at the other end.

The screws have a variety of thread pitches that define a series of consecutive zones. In the exemplary structure of the figures, the machine has four successive zones I, II, III and IV, followed by the treated pulp discharge zone V.

Em. according to a structural feature already described in the patent, each treatment zone has a transfer section A (straight thread pitch) by means of which the mass moves forward in the direction of rotation of the screws, e.g. clockwise as shown in Figures 3 and 4. In addition, each treatment zone has a braking compartment B, preferably with inverted threads B, which lift the mass towards the inlet end and thus provide a certain braking function and hence a certain compression at the rear of the compartment A.

In addition to the pulp supply opening 10, a plurality of openings 1, 2, 13, 14 are arranged in the upper part of the frame housing 1 perpendicular to the plane of symmetry, which are located after the respective brake compartments B1, B2 and B3.

In addition, the body housing part 3 has openings 31 in front of each braking compartment B1, B2, B3 and B4, which filter the mass entering the housing due to the rotational movement of the screws. The housing thus consists of closed parts 4 and filter parts 3. Each filter part 3 is placed in front of the braking compartment B and its length corresponds approximately to half of the previous transfer compartment A, the closed part 4 covering the previous braking compartment and extending to the front of the transfer compartment.

5,71585

Since the machine is used for the mechanical defibering treatment of groundwood, the inverted threads forming the braking zones B1, B2, B3 and B4 are provided, as described in the above-mentioned patent application, with openings which facilitate the advance of a certain amount of material in the apparatus.

As shown in Figure 3, the openings 24 are made in inverted threads 23 and extend radially from the center of the screw 21 to the circumference of the thread. The openings 24 are spaced at intervals and the screws are wedged in place so that the two openings are preferably always in a horizontal plane of symmetry running simultaneously through the axis of the screws.

Em. patent application 75-23911 describes a defibering process. The pulp, which is wood chips, enters the machine from the opening 10, and the first of the transfer part AI pulls it forward. When the mass is in zone B1, the inverse thread prevents it from accumulating behind zone A1. Thus, in zone A1, a certain compression up to a certain pressure occurs from the front of the equipment backwards, thus compensating for the braking power as the mass moves to the next zone.

In those zones where the compression of the mass is low, its forward movement takes place mainly parallel to the axes of the screws. But as the mass is compressed, this transfer effect decreases, with friction tending to move the mass around the shafts 21 as it moves from one screw to another.

In the braking zone, the forward movement of the mass in the equipment takes place mainly through the above-mentioned openings, specifically in the central zone, if the openings overlap. For this reason, as stated in the above-mentioned patent application, the braking compartment allows a controlled forward movement of the mass. In this case, the part of the groundwood which is not sufficiently fibrous does not enter the openings depending on their size, but remains in front of them, creating a strong mixing function with a combination of both compression and shear and possibly also fiber rotation, especially when the mass moves. from one screw to another. This operation is then continued until all the sufficiently defibered pulp has moved to the end of the apparatus.

This makes it possible to carry out the progressive defibering of the pulp by that time through successive treatment zones. Each zone then has a progressive transfer and compression section, followed by a braking section with inverted threads and openings, preferably reduced in size from one braking section to another, so that the desired degree of defibering is progressively obtained.

Em. according to the method disclosed in the patent application, it is possible to produce a mechanical pulp, a hot mill or a mechanochemical pulp. The body housing then has nozzles from which lignin removal agents can be transferred to the treatment zones.

However, in this type of machine, it is also possible to process a groundwood which has been subjected to a lignin softening treatment either by means of steam or by the chemical in question. In this case, the pulp must be subjected to a mechanical defibering treatment, the importance of which depends on the chemical treatment previously carried out. This mechanical treatment can advantageously be carried out in a machine of the type described above, since the mechanical properties of the screws and in particular the pitch, the size of the openings and the rotational speed of the screws can be applied to provide the necessary conditions for transferring the pulp to different zones.

Such a defibering machine can be fed with groundwood, which then receives a first lignin removal treatment, and in addition it can be impregnated with the reagent in question in the first treatment zones.

It is known that the reagent and tendons used must be removed by washing the pulp. The main idea of the invention therefore relates to a washing process which is carried out in a machine simultaneously with the defibering process as follows:

The mass fed from the opening 10, which has been cooked, is treated with a lignin remover and its degree of dryness can be e.g. 20%.

As already mentioned, the mass moves to the first transfer compartment A1, and the braking in compartment B1 causes progressive compression in the last screw threads of the transfer compartment.

In the second part of the transfer compartment, the body housing has openings 31 which are so large that the liquid phase and the dissolved residues can pass through them, but the solid phase stops in front of them. In this case, due to the progressive compression, a mass filtration process is created in front of the braking compartment as a function perpendicular to the direction of mass transfer.

The pressure is greatest when the mass reaches the braking compartment B1, which causes the mass to actually dry; the degree of dryness is up to about 50%. The "phase out" of compression of the liquid phase (at the beginning of the braking compartment) rises towards the front end of the equipment in zones of lower compression. The removal takes place via the filterable part 3 of the body housing.

Thus, the degree of pulp dryness entering the transfer compartment A2 is about 50%. On the other hand, if the braking compartment B1 has openings large enough, the pulp is already subjected to the first defibering treatment.

Em. according to the method related to the patent application, the openings of the braking compartment B1 thus only allow a pulp with the desired degree of defibering to pass through. The pulp with an insufficient degree of fiber is then left in front of zone B1, i.e. at the end of zone A1. The compression at this point is even greater so that the pulp dries really efficiently. On the other hand, like po. it is mentioned in the patent application, it is at this point that the main defibering operation takes place, a combination of a pressing and shearing operation, which still involves a certain rotation of the fibers.

This again facilitates the removal of liquid from the pores of the wood and the removal of residues with the washing liquid. Thus, as the pulp dries during the defibering process, the efficiency of the washing operation increases.

However, the drying must not be so effective as to impede the transfer of the pulp to the braking compartment. For this reason, the relevant parameters of the machine, in particular the pitch of the threads and the size of the openings, are adjusted so that a degree of dryness is obtained such that a sufficiently large amount of mass can pass through the machine. In practice, the conditions for the transfer of the mass to the braking compartment are adjusted so that the degree of dryness of the mass at this point does not exceed approx. 40%.

The mass in front of compartment A2 thus has two characteristics. It has already been defibered to a certain degree under the control of the braking section B1 and a considerable amount of liquid has been removed from it, almost half.

The pulp is then treated with a washing liquid, usually clean water, which is fed through the opening 12. This function is facilitated by the mixing effect generated by the screws 8 71585. This gives a homogeneous mixture with a degree of dryness of about 20-25%. It is now compressed again as it moves forward in the transfer compartment A2. As already mentioned, the braking compartment B2 keeps at the end of the compartment A2 a pulp whose degree of defibering is not of the desired size and, on the other hand, makes it possible to dry this part of the pulp. The liquid phase then rises in the zones of lower pressure towards the beginning of the apparatus, from where it exits through the openings 31.

Correspondingly, the pulp entering zone A3 has now received additional fiberization and is dried again so that the degree of dryness becomes about 50%. The pulp is then re-treated with the washing liquid fed from the opening 13.

As a result, a series of washing steps are gradually performed so that a pulp enters the outlet end of the machine, which is both defibered and washed at the same time.

It can now be stated that the method according to the invention uses the same sequence of operations as in the already known washing methods, i.e. filtration always follows after successive dilution operations. However, in the apparatus according to the invention, the dilution and filtration take place under very special conditions. In classical methods, in order to make the fibers well distributed in the washing liquid, the pulp usually has to be treated in a very large amount of liquid. A consequent disadvantage is the increase in water consumption and also in energy consumption when the water is removed in the filtration step following washing.

In contrast, the process according to the invention uses a mass diluted with a much smaller amount of water, because in the part in front of the transfer compartments where the mass is in contact with the washing liquid, the mixing effect of the screws makes the mixture homogeneous without the need for large amounts of water.

However, it has already been suggested in the past that, in order to save water, the washing should be carried out in successive zones of the screw chain press.

The method and machine according to the invention have many considerable advantages over already known methods.

First, as already mentioned, performing the washing at the same time as the defibering increases the efficiency of the washing liquid a lot, so that less liquid is needed. Otherwise, when washing in the previous method 9 71585 takes place in successive zones, the filtered liquid is collected in one zone, from which it is injected back into the previous one. This recirculation is not possible in the method according to the invention, since the filtered liquid is so concentrated that it cannot be used as a washing liquid due to the washing efficiency.

An essential advantage of the invention is that the actual washing equipment is completely eliminated. However, the changes that have to be made to the defibering machine are much less expensive.

In addition, the washing efficiency also depends on the characteristics of the machine in question and the pulp transfer process therein.

As already mentioned, in the machine according to the invention, in which the pulp is transported by two identical threaded screws which are connected to each other and rotate in the same direction, the pulp rotates in the screws in two different ways. In zones with lower compression, the mass is transported mainly as a transfer function parallel to the axis of the screws. In contrast, in zones with higher compression, a larger amount of mass tends to move around the shaft due to friction inside the threads. Therefore, a certain amount of mass is transferred from one screw to another and tends to accumulate in the threaded part in front of the through-zone 25 (Fig. 3). Thus, as soon as the mass begins to compress, a so-called an expanded sector 26 in which the pulp tends to move forward and a compressed sector 27 in which the pulp accumulates in front of the zone 25. The threads are then connected to each other and as the pressure rises, the mass shifts to the adjacent thread of the second screw.

As a result, the zone pressed inside each thread thus alternates between expansion and compression, which in turn is advantageous in terms of washing performance, since the mass accumulating in the pressed compartment 27 squeezes out the liquid rising to the zone 26. Thereafter, as the pulp moves to the expanded zone 26 (adjacent screw), it dilutes to some extent again in the liquid before returning to the compressed zone 270, where the pulp. the process repeats itself.

The significance of zones 27 (compression) and 26 (expansion) varies inversely as the end of the equipment moves as sector 27 grows until they "occupy" the entire thread when it is full of brake section B together. Thus, when the threads are completely full at this point, drying takes place, but when the pulp is in the threads in front of the expanded sectors, the liquid phase rises towards the front, whereby the openings 31 filter it.

All the expanded zones of the same screw are on the same side of the plane passing through the shaft, for example in the above-mentioned figures below the plane of the axes of the screw 26 and above the plane of the axis of the screw 27.

Thus, a certain gap is necessarily created between the circumference of the screw and the body housing, along which the liquid phase can rise from one thread to another towards the zones under lower pressure, i.e. to the beginning of the apparatus. As a result, a certain movement of the liquid phase occurs inside the transfer zone, which facilitates its regeneration.

Initially, the mass from the braking zone (front) merges with the injected fluid. After sem, part of the liquid moves forward with the mass towards the end of the machine with the progressively compressed mass, while the rest of the liquid again fills the expanded zones. In each thread, the alternation of compression and expansion promotes the removal of spent fluid and the absorption of new fluid. As the importance of the compressed portion increases, the "expelled" liquid rises upwardly along the body housing and exits the filter portions 31. Thus, the apparatus continuously filters the spent liquid through the circumference and feeds new liquid within the threads within the apparatus with the Devan mass.

This continuous process of liquid regeneration takes place without the liquid having to be injected at high pressure, since the use of several interconnected screws creates a certain pumping effect, so that the mass is advanced even if the threads are not full, which is not possible with single-screw machines. As a result, the same amount of liquid sprayed achieves a much more efficient washing result by using the above process.

Thus, in the machine according to the invention, the dilution, compression and filtration (25) and drying stages take place both in the longitudinal direction of the apparatus from one washing zone to another and also in the transverse direction from one thread to another in the same zone. This is, by the way, one of the factors influencing the high efficiency of the method.

11 71585

In addition, the arrangement of the openings 31 also contributes to increasing the washing efficiency.

The openings 31 are spaces between the profiles 3 as parallel circumferential sectors and extend approximately transversely to the axis of the screws.

This arrangement, illustrated in plan view 2, is specifically recommended to provide good filtration efficiency. As can be seen from Figure 2, the openings perpendicular to the axis form a small angle with the threads, which are also somewhat inclined. Thus, each "wrapper cavity" always corresponds to one or more openings extending almost over its entire circumference, so that the liquid phase can be removed immediately with a very small load loss on the filter. In addition, due to the displacement associated with the rotation of the threads, a certain wiping function is occasionally created at each opening, so that the mass accumulated in the filter can be fed back into the process at any time. As a result, the filter cannot become clogged.

In addition, the cross-section of the profiles is trapezoidal, with its large base then facing inwards and the inner surface being cylindrical and concave. As a result, the precipitate particles that accumulate in the opening are immediately wiped off or completely removed. In any case, they cannot block the opening, because the partitions of the profiles are at a certain distance from each other and thus facilitate emptying.

Thus, in combination with the above-mentioned features, the method according to the invention and the machine specifically developed for its application are able to perform a very efficient and fast washing.

It is therefore very advantageous that mechanical defibering and washing can be performed simultaneously in the machine. The effectiveness of these functions depends on the conditions under which the mass enters the braking compartments, which - as already mentioned - are specifically controlled by selecting the pitch and depth of threads, the number of threads in each zone, the size of the openings and the screw speed. In each braking compartment, the greatest possible drying is preferably used, which, however, is limited to a degree of dryness that allows the mass to move well from one zone to another.

12 71 585

The conditions under which progressive compression and drying take place do not depend solely on the size of the openings. Therefore, the compression can be increased in a known manner and further accelerated by reducing the threads at the end of the transfer zone. It is thus possible to control the washing process separately from the defibering process by using different parameters of the machine in question. Thus, the machine can in a way adapt to the quality of the pulp. If the pulp has been cooked for only a short time, in order to obtain a qualitatively good mechanochemical pulp, considerable mechanical defibering and a relatively low power pe must be performed. Conversely, if the groundwood has been cooked for a long time, the washing must be very vigorous so that the liquid and residue used can be removed from the pulp. The mechanical work required is then quite minimal.

Thus, the method described above and the machine used to apply it have many advantages in total.

First, washing is faster and more efficient. It also applies to more compacted pulp and water consumption is reduced, as is the liquid waste used.

Washing efficiency is usually measured as the ratio of the difference between the amount of liquid entering the equipment and the amount of liquid removed to the equipment relative to the amount of liquid fed. In the machine according to the invention, this ratio is about 60%, sometimes even 80%.

On the other hand, the transition from one washing station to another takes place as a continuous operation. In addition, the machine is smaller in size than similar conventional machines.

Although only a unit with four drying compartments is described here as an example - which is otherwise usually sufficient - it is clear that the number of washing stations can be varied depending on the situation.

Furthermore, the invention is not limited to the details of the structure described above, but several modifications can be made and other similar devices can be used so as to achieve the desired result.

Thus, with the machine according to the invention, if desired, a countercurrent washing can be carried out very easily by recovering the filtered liquid for recirculation po. in the zone above the zone. However, such recycling is not necessary as in previous installations, as a much smaller amount of washing liquid is now used and the filtered liquids are now in a much more concentrated form.

Claims (3)

A method for peeling and washing a cellulose-containing material for making pulp by conducting a material reduced to chips and impregnated with a delignifying reagent by a machine consisting of at least two parallel screws which are rotated inside a casing and which are provided with spiral threads, the pitch of which is alternated to obtain several successive treatment zones, each of which comprises a transport section and a section for progressive compression as well as a braking section which consists of threads with opposite pitch and provided with openings lowered with the material flow, dimensions are selected so that the openings allow selective advancement of the material in the flow direction depending on the punch line that the material obtained countercurrent the openings, characterized in that punching and washing of the chips are performed simultaneously in the successive processing zone of the machine, for the purpose of several alternatively filled parts and filtering parts, which in each case cover the part upstream and downstream respectively in each transport section and each filled part continues into the preceding braking zone, so that the material as it flows from upstream to downstream through each successive treatment zone, diluted by adding a suitable washing liquid which is fed into the upstream treatment zone, that the material inside the threads is subjected to a pressure reduction phase and a compression phase and dewatering, which is carried out simultaneously with the upstream transport zone and in the braking zone, the liquid is removed from the filtration portions of the cap. 2. A method according to claim 1, characterized in that the amount of detergent sprayed after the dewatering in the upstream zone is controlled according to the conditions under which the material flows in the downstream braking zone, so that the effluent carried out is limited to a degree of drying sufficient downstream in the subsequent braking zone. Method according to claim 1, characterized in that in each look-up zone,