FR2741638A1 - CONTINUOUS PROCESS AND INSTALLATION FOR PREPARATION OF A CELLULOSE PASTE - Google Patents

Abstract

A method for continuously preparing cellulose pulp, in particular for use in the chemical or paper industry, from a raw material consisting of textile fibres. The method comprises separating the textile fibres from foreign matter, continuously leaching and pre-cutting the textile fibres in a first processing machine (10) to give a pulp, continuing leaching in a first dwell vessel (35), continuously washing and bleaching the pulp in a second processing machine (40) to give a washed and bleached pulp, continuing bleaching in a second dwell vessel (61), diluting the pulp in a first dilution tank (62), and draining and pressing the pulp. An apparatus for carrying out the method is also provided.

Description

 The subject of the present invention is a process and an installation for the continuous preparation of a cellulose pulp intended in particular for the chemical or paper industry from a raw material constituted by textile fibers such as, for example, cotton linters. , flax, hemp or jute.

 For example, the method and the installation according to the present invention allow the continuous preparation of dissolving cellulose pulps or chemical uses intended in particular for the manufacture of viscoses, lacquers, varnishes, sponges, nitrocellulose.

 Generally, cellulose pulp intended in particular for the chemical or paper industry is produced from a lignocellulosic material and, most often wood.

 In addition, the cellulose pulp can also be prepared from a raw material consisting of textile fibers such as, for example, cotton linters which make it possible to obtain products having excellent chemical and mechanical properties.

 These characteristics are required for the production for example of a paper of very high quality.

 The aim of the invention is to propose a method and an installation for preparing a cellulose pulp intended in particular for the chemical or paper industry from a raw material constituted by textile fibers making it possible to continuously manufacture the pulp. cellulose, without breaking the load in the preparation line of said pulp and to significantly reduce the energy consumption, chemical reagents and water usually required to produce such a paste.

The subject of the invention is therefore a process for the continuous preparation of a cellulose pulp intended in particular for the chemical or paper industry from a raw material constituted by textile fibers, characterized in that
the textile fibers are separated from foreign bodies such as agricultural residues, metallic and mineral particles,
densification of the textile fibers is carried out,
- leaching and precutting of the textile fibers is carried out continuously in a first processing machine of the type with two co-rotating screws to obtain a paste having a dryness of between 25 and 40%,
the leaching is continued in a first latency capacity, the retention time of the dough in said first latency capacity being between 30 and 60 min,
washing and bleaching of the dough are continuously carried out in a second co-rotating two screw machine for obtaining a washed and bleached dough having a dryness of between 25 and 40%,
the bleaching is continued in a second latency capacity, the retention time of the dough in said second latency capacity being between 60 and 120 minutes,
the dough is diluted in a first dilution tank to obtain a dough having a concentration of between 1.5 and 3%,
and the dough is dewatered and pressed at the outlet of the first dilution tank to obtain a dough having a dryness of between 30 and 35.

The invention also relates to an installation for continuous preparation of a cellulose pulp intended in particular for the chemical or paper industry from a raw material constituted by textile fibers, characterized in that it comprises
pneumatic means for transporting textile fibers,
means for separating textile fibers and foreign bodies such as agricultural residues, metal and mineral particles,
- a densifier of textile fibers,
means for extracting and filtering dusty air from pneumatic means for transporting textile fibers,
a first co-rotating two-screw type processing machine for continuously leaching and cutting the textile fibers and obtaining a paste having a dryness of between 25 and 40%,
means for transporting the dough at a temperature corresponding to its outlet temperature of said first treatment machine,
a first latency capacity for continuing the leaching of the dough, the retention time of the dough in said first latency capacity being between 30 and 60 minutes,
a second co-rotating screw type processing machine for continuously washing and bleaching the dough and obtaining a washed and bleached dough having a dryness of between 25 and 40%,
means of transporting the bleached and washed pulp,
a second latency capacity for continuing the bleaching of the dough, the retention time of the dough in said second latency capacity being between 60 and 120 min,
a first dough dilution tank equipped with an agitator to obtain a dough having a concentration of between 1.5 and 3W,
- And a screw press to perform a drip and a pressing of the dough and obtain a dough with a dryness of between 30 and 35%.

Other features and advantages of the present invention will become apparent from the following description, made with reference to the accompanying drawings, in which:
FIG. 1 is a schematic view of an installation for continuous preparation of a cellulose pulp, according to the invention,
FIG. 2 is a sectional view in a vertical plane passing through the axis of a screw of the first processing machine,
FIG. 3 is a sectional view along the line 3-3 of FIG. 2
FIG. 4 is a sectional view in a vertical plane passing through the axis of a screw of the second processing machine,
FIG. 5 is a sectional view along line 5-5 of FIG.

 The installation shown schematically in FIG. 1 comprises in series means 1 for opening bales and purification of textile fibers consisting for example of cotton linters, linen, hemp or jute.

 The textile fibers thus purified are conveyed, by a pneumatic conveying system comprising a fan 2, successively through a condenser 3, a weighing system 4, means 5 for separating the textile fibers and metal particles and a densifier 6 of said fibers textiles to ensure a constant density and a controlled and regular flow of these textile fibers to be able to feed the first processing machine 10 downstream of said densifier 6.

 The installation also comprises between the means 5 for separating textile fibers and metal particles and the densifier 6, a second fan 7 for transporting these textile fibers and a fan 8 for extracting dusty air connected to a unit 9 filtration of this air.

 As shown in Figs. 2 and 3, the first processing machine 10 comprises two screws 11 and 12 driven in rotation about their axes by a motor and a reducer, not shown, inside an elongated enclosure forming a sleeve 15 which surrounds them.

 The screws 11 and 12 are provided with helical threads which mesh with each other and the inner wall of the sheath 15 forms two intersecting cylindrical lobes of inner diameter slightly greater than the outer diameter of the threads.

 These threads are nested within each other and the two screws 11 and 12 are driven at the same rotation speed and in the same direction so that the two screws are identical, the threads being simply offset with respect to each other. .

 The screws 11 and 12 advantageously consist of splined shafts 16 and 17 respectively (FIG 3) on which screw sections are stacked.

 The inner bore of these screw sections is provided with grooves corresponding to those of the shaft and the outer portion is provided with helical threads whose pitch differs according to the section considered for the treatment and transport of the material.

 It is thus possible to have a large number of sections to vary the pitch, the depth, the number of nets and the length of each zone.

Thus, the first processing machine 10 comprises continuously, from upstream to downstream in the direction of transport, respectively
a zone A for supplying textile fibers having a dryness of between 92 and 95% and mixing said textile fibers with water injected at the beginning of this zone A,
a compression zone B with effluent recovery at the end of this zone B,
a first zone C of mixing and shearing,
a zone D for conveying and treating with introduction, at the beginning of this zone, of leaching reagents and dilution water,
a second zone E of mixing and shearing,
and a zone F for transporting and discharging the dough.

 In the feeding and mixing zone A, the sleeve 15 is pierced with a feed orifice 10 surmounted by a hopper 19 connected to the outlet of the densifier 6 and a pipe 13 for supplying the recovery water or clear water.

 In this zone, the screws 11 and 12 are provided with threads 20 with a small pitch and reduced section, in order to ensure the transport of the products through this orifice 18 which opens widely over the two screws 11 and 12 and to distribute said produced in fillets 20.

 The textile fibers and the water are immediately conveyed downstream of the processing machine 10 and mixed by rotation and meshing of said screws 11 and 12.

 In zone B, the screws 11 and 12 comprise threads 21 with narrow pitch and thicker section so that the mixture of products will be added compression of these.

 At the end of this zone B, where the compression is maximal, the washing effluents are evacuated by means of filters 15a judiciously placed in the sheath 15.

 The material then passes into the first mixing and shearing zone C.

 For this purpose, the zone C is provided with helical threads 22 whose direction of winding is reversed with respect to that ensuring the transfer of the material in the processing machine 10.

 In these threads 22 are formed openings 23 which extend radially from the core of each screw 11 and 12 to the periphery of the threads and which are furthermore regularly distributed around the axis.

 The screws 11 and 12 are wedged so that two openings 23 come periodically in coincidence in the central meshing zone.

 In this way, it controls the passage of material flow downstream which determines a braking in this area C, and a compression effect upstream.

 Furthermore, it results in a large shear material that homogenizes the mixture, improves the impregnation of textile fibers with water and which is also a first phase of scrolling and cutting textile fibers.

 In addition, these shearing and kneading operations in zone C as well, though to a lesser degree, in zone B, lead to a heating of the material, a large part of mechanical work being converted into thermal energy. .

 Therefore, at the end of its passage in zone C, without external heat input, the material is brought to a temperature that makes it able to undergo the treatment operation in the next zone.

 The conveying and treatment zone D is provided with threads 24 whose pitch and thickness have characteristics close to those of zone B.

 At the beginning of the zone D, the sheath 15 is provided with an opening 25 connected to two pipes respectively 26a and 26b of arrival of the leaching reagents and the dilution water.

 The leaching reagents consist in particular of a solution of caustic soda whose flow corresponds to a value of between 2 and 5% of reactive product relative to the raw material.

 The pipes 26a and 26b are each provided with a dosing pump, respectively 27a and 27b.

 All along the zone D, the textile fibers are brewed and mixed with these reagents to ensure this leaching step.

 The processing machine of the co-rotating two screw type is particularly well suited to perform this operation.

 Indeed, because of the rotation of the screws in the same direction, there is a reversal of the material in the interpenetration zone of the nets which is particularly effective in its mixing, which allows for an intimate mixing reagents and textile fibers that have been in upstream areas impregnated with water.

 In this way, a better use of the reagents is obtained, which results, on the one hand, in a saving thereof, and, on the other hand, in a reduction in the subsequent phases of the washing water and therefore effluents to be treated.

 The conveying and treatment zone D is followed by a second zone E of mixing and shearing which consists, like zone C, of helical threads 30 of winding opposed to that in advance of the material, or counter nets and also having passage windows 31.

 The physical and thermal phenomena, as well as the functions performed in this zone E are similar to those carried out in zone C, ie a high shearing and kneading, as well as a scrolling and cutting of the textile fibers.

 The last zone F has threads 32 whose pitch and thickness are similar to those of zone D.

 The leaching reaction continues during the flow of the material, in this zone F which, moreover, transfers to the outlet orifice 33 constituted by an opening at the downstream end of the sheath 15.

 At the outlet of the first processing machine 10, the dough has a dryness of between 25 and 40%.

 The bleached pulp leaving the first processing machine 10 is poured into transport means 34 consisting of, for example, a screw elevator, which keeps said bleached pulp at a temperature corresponding to its outlet temperature of the first treatment machine 10. .

 This paste is thus transported in a latency capacity which has the essential role of continuing the leaching reaction.

 The retention time of the dough in the latency capacity is between 30 and 60 minutes.

 At the exit of this latency capacity 35, the dough is poured into a second processing machine 40.

 This second processing machine 40 (Figs.

4 and 5) is in its general design similar to the first processing machine 10.

 It comprises at least two screws 41 and 42 driven in rotation about their axes by a motor and a reducer not shown, inside an elongated enclosure forming a sleeve 45 which surrounds them.

 The screws 41 and 42 are provided with helical threads that mesh with each other and the inner wall of the sleeve 45 forms two intersecting cylindrical lobes with an inside diameter slightly greater than the outside diameter of the threads.

 The threads are nested within each other and the two screws 41 and 42 are driven at the same speed of rotation and in the same direction so that these two screws 41 and 42 are identical, the threads being simply offset by compared to others.

This second processing machine 40 comprises continuously, from upstream to downstream in the direction of transport, respectively
a zone G feeding the bleached pulp from the latency capacity 35 and mixing said paste with water injected at the beginning of this zone,
a succession of zones H1, H2, H3 and H4 for compressing, shearing and treating the pulp,
and a zone J for transporting and discharging said paste after treatment.

 In the first zone G, the sleeve 45 is pierced with an introduction orifice 46 surmounted by a hopper 46a for feeding the products.

 For this purpose, the hopper 46a is connected to the output of the latency capacity 35 and to a pipe 43 for supplying recovery water or clear water.

 In this zone G, the screws 41 and 42 are provided with threads 47 with a large pitch and with a reduced cross-section to ensure the transfer of the products introduced through the orifice 46 which opens widely over the two screws 41 and 42 so as to distribute the matter in the nets.

 The pulp and this first fraction of washing water are immediately transported downstream of the processing machine 40 and mixed by the effect of rotation and engagement of the screws 41 and 42.

 Then, the material passes into the first zone H1, shear compressions and pulp processing.

 The first zone H1 comprises a first zone element H11 for compression and washing and a second zone element H12 for braking and shearing.

 In the zone element H11, the screws 41 and 42 comprise threads 48 with a smaller pitch and a thicker section than the threads 47 of the zone G.

 In this way, to the mixture of products will be added a compression of the dough. Therefore, all along the zone element H11, the dough is stirred and mixed with the wash water introduced into the feed hopper 46a to remove the residual reagents and products from the action. reagents on the dough.

 At the end of the zone element H11, where the compression is maximum, the washing effluents are discharged by means of filters 53 suitably placed in the sleeve 45.

 The zone element H12 is provided with threads 49 whose winding direction is reversed with respect to that ensuring the transfer of the dough into the processing machine 40.

 In these threads 49 are formed openings 50 which extend radially from the core of each screw 41 and 42 to the periphery of the threads and are furthermore regularly distributed around the axis.

The screws 41 and 42 are wedged so that two openings 50 come into coincidence periodically in the central meshing zone.
In this way, it controls the passage of the pulp flow downstream, which determines a braking in this zone element H12 and a compression effect upstream.

 Moreover, it follows a large shearing of the dough and a homogenization thereof.

After the first zone H1, the paste passes into a second zone H2 of compression, shear and treatment identical to said first zone H1 and which comprises, on the one hand, a first compression zone element H21 and, on the other hand, a second zone element
H22 shear.

 The first zone element H21 is identical to the first zone element H11 and comprises threads 48 with a narrow pitch and the second zone element H22 is identical to the second zone element H11 and comprises threads 49 whose winding direction is inverted relative to that ensuring the transfer of the dough in the processing machine 40.

 In these threads 49 are formed openings 50 which extend radially from the core of each screw 41 and 42 to the periphery of the threads.

 At the beginning of the first zone element H21, the sleeve 45 is connected to a pipe 52 for supplying washing water.

 Therefore, all along the first zone element H21, the pulp is stirred and mixed with the dilution water to remove residual reagents and products from the action of the reactants on the pulp.

 At the end of this first zone element H22, where the compression is maximum, the washing effluents are evacuated by means of filters 53 judiciously placed in the sleeve 45.

 The third compression, shear and treatment zone H3 is identical to the first two zones H1 and H2 respectively and comprises, on the one hand, a first compression zone element H31 and, on the other hand, a second element H32 of shear.

 In the first zone element H31, the screws 41 and 42 comprise threads 48 with a narrow pitch and in the second zone element H32, the screws 41 and 42 are provided with threads 49 whose winding direction is reversed with respect to that ensuring the transfer of the material in the processing machine 40.

 In these threads 49 are formed openings 50 which extend radially from the core of each screw 41 and 42 to the periphery of the threads.

 At the beginning of the first zone element H31, the sleeve 45 is also connected to a pipe 52 for supplying dilution water. As a result, all along the zone element H31 the dough is brewed and mixed with the dilution water to remove residual reagents and products from the reactants on the dough.

 At the outlet of the first zone element H31, where the compression is maximum, the washing effluents are discharged by means of filters 53 suitably placed in the sleeve 45.

 The fourth compression, shear, and processing zone H4 comprises, on the one hand, a first compression zone element H41 and, on the other hand, a second shear zone element H42.

 In the first zone element H41 identical to the first zone elements H11, H21 and H31, the screws 41 and 42 comprise threads 48 with a narrow pitch. The second zone element H42 is identical to the second zone elements H12, H22 and H32 and has threads 49 whose winding direction is reversed with respect to that ensuring the transfer of the paste in the processing machine 40.

 In these threads 49 are formed openings 50 which extend radially from the core of each screw 41 and 42 to the periphery of the threads.

 At the beginning of the first zone element H41 of the zone H4, the sleeve 45 is connected to a pipe 54 which is itself connected to three pipes 55a, 55b and 55c respectively (FIG.1) for the simultaneous supply of dilution water , a solution of caustic soda whose flow corresponds to a value between 0.5 and 2k of reactive product relative to the raw material and a solution of hydrogen peroxide whose flow corresponds to a value between 2 and 6% of active product relative to the raw material.

 Therefore, throughout the zone H4, the dough is brewed and mixed with these bleaching reagents to ensure this essential step in the manufacture of cellulose pulp.

 The co-rotating two screw type processing machine is particularly well suited to perform this operation.

 Indeed, because of the rotation of the screws in the same direction, there is a reversal of the material in the interpenetration zone nets which is particularly effective in its mixing which allows for an intimate mixture of the dough and reagents.

 Thus, a better action of the reagents is obtained, which results, on the one hand, in an economy thereof, and on the other hand, in a reduction in the subsequent phases of the wash water and therefore effluents to be treated.

 The last zone J of the second processing machine 40 is a zone for transporting and discharging the dough in a conveyor 60 constituted for example by a screw elevator (FIG.

 At the outlet of the second processing machine 40, the dough has a dryness of between 25 and 40%.

 As shown in FIG. 1, the conveyor 60 transports the paste in a second latency capacity 61.

 This second latency capacity 61 has the essential role of continuing the whitening reaction and the retention time of this paste in said second latency capacity 60 is between 60 and 120 minutes.

 Then, the paste is poured into a dilution tank 62 equipped with a stirrer 63.

 This dilution tank 62 is supplied by a line 64 of recylated water necessary for the dilution of the dough, whose concentration at the outlet of said dilution tank 62 is between 1 and 3%.

 The thus-diluted dough is transferred by a pump 65 to a screw press 66 which drains and presses the dough to obtain a dough with a dryness of between 30 and 35.

 The effluents from the screw press 66 are recovered by a pipe 67 in a vat 68 from which a portion can be recycled in the processing machines 10 and 40.

 According to one variant, the dough drained and pressed out of the screw press 66 is transferred to a second dilution tank 69 equipped with a stirrer 70 and which is supplied with recycled water via a pipe 71 for the dilution of the dough whose concentration is included, at the outlet of said second dilution tank 69, between 3 and 5%.

 According to yet another variant, the pulp is then pumped by means of a transfer pump 72 towards a tank 73 said storage comprising an agitator 74 for ensuring the suspension suspension of the fibers.

As an indication, the physical and papermaking properties of the paste obtained with the process and the installation according to the invention from a cotton linter quality originating from Central Asia are the following: - Physical Properties
- Whiteness: 85% ISO
- average fiber length between 1.5 and 6mm
- Impurity rate. less than 3,5mm2 / m2
- Alfa cellulose content: greater than or equal to 98%
- Variable degree of polymerization between 650 and 3000
depending on the treatment conditions.

- Panet Properties

<tb><SEP> Index <SEP> Weight <SEP> Resistance <SEP> Porosity <SEP> Resistance
<tb> refining <SEP> gr / m2 <SEP> to <SEP> the <SEP> trac- <SEP> CHEF- <SEP> to <SEP> the <SEP> tear
<tb><SEP> OSR <SEP> tion <SEP>: <SEP> daN <SEP> FIELD <SEP> rure <SEP>: <SEP> mN
<tb><SEP> SU
<tb><SEP> 33 <SEP> 70 <SEP> 6.5 <SEP> 315 <SEP> 679
<tb><SEP> 60 <SEP> 70 <SEP> 7.5 <SEP> 24 <SEP> 850
<Tb>
The analyzes were carried out from pasta previously refined using a device of the "Pile Valley" type11.

 By the method according to the invention, the continuous preparation time of a cellulose pulp is between 2 and 3 hours whereas in traditional processes, the time required for this preparation was greater than 10 hours.

 The process according to the invention requires a volume of water equal to 30 cubic meters of water per ton of pulp, whereas the traditional method requires a consumption of 100 to 150 cubic meters of water per ton of pulp.

 Thus, the process according to the invention allows a significant reduction of the effluents to be treated and also significantly reduces the floor area of the installation of the installation.

 The process according to the invention also generates energy savings of 20 to 50% and chemical reagents. It makes it possible to obtain pasta having constant physical and mechanical properties.

Claims (26)

 Process for the continuous preparation of a cellulose pulp intended, in particular for the chemical or paper industry, from a raw material constituted by textile fibers, characterized in that  the textile fibers are separated from foreign bodies such as agricultural residues, metallic and mineral particles,  densification of the textile fibers is carried out,  - Leaching is carried out continuously, and a pre-cutting of the textile fibers in a first processing machine (10) with two corotative screws (11, 12) to obtain a paste having a dryness of between 25 and 40% ,  the leaching is continued in a first latency capacity (35), the retention time of the dough in said first latency capacity (35) being between 30 and 60 min,  continuous washing and bleaching of the dough is carried out in a second co-rotating twin-screw processing machine (40) (41) for obtaining a washed and bleached dough having a dryness between 25 and 40%,  the bleaching is continued in a second latency capacity (61), the retention time of the dough in said second latency capacity (61) being between 60 and 120 minutes,  the dough is diluted in a first dilution tank (62) to obtain a dough having a concentration of between 1.5 and 3%;  - And the dough is dewatered and pressed at the outlet of said first dilution tank (62) to obtain a paste having a dryness of between 30 and 35W.  2. Method according to claim 1, characterized in that, after dewatering and pressing of the dough at the outlet of the first dilution tank (62), the dough is again diluted in a second dilution tank for obtaining a paste in a second dilution tank for obtaining a paste having a concentration of between 3 and 5%.  3. Method according to claim 2, characterized in that, after the second dilution of the dough, the dough is stored in a vat equipped with stirring means.  4. Method according to claim 1, characterized in that the first processing machine (10) comprises continuously, from upstream to downstream in the direction of transfer, respectively  a phase A for feeding the textile fibers and mixing said textile fibers with water injected at the beginning of this phase,  a compression phase B,  a first phase C of mixing and shearing,  a phase D of conveying and treatment with introduction, at the beginning of this phase, of leaching reagents and dilution water, the leaching reagents consisting in particular of a solution of caustic soda whose flow corresponds to a value between 2 and 5% of reactive product relative to the raw material,  a second phase E of mixing and shearing,  and a final phase F for transporting and discharging the pulp in the first latency capacity (35).  5. Method according to claim 4, charac terized in that the water injected at the beginning of the supply phase A of the first processing machine (10) is constituted by the recovery water coming from the dewatering and the pressing the dough and with clear water.  6. Process according to claim 4, characterized in that at the end of the compression phase B, the effluents are recovered.  7. Method according to claims 1 and 4, characterized in that between the output of the first processing machine (10) and the first latency capacity (35), the dough is maintained at a temperature corresponding to its outlet temperature of said first processing machine (10).  8. Method according to claim 1, characterized in that the second processing machine (40) comprises continuously, from upstream to downstream in the direction of transfer, respectively  a phase G feeding the bleached pulp from the first latency capacity (35) and mixing said dough with water injected at the beginning of this phase,  a succession of phases H1, H2, H3 and H4 of compression, shearing and treatment of the dough,  and a final phase J for transporting and discharging the pulp in the second latency capacity (61).  9. Method according to claim 8, characterized in that the water injected at the beginning of the supply phase G of the second processing machine (40) is constituted by the recovery water from the dewatering and pressing dough and clear water.  10. A method according to claim 8, charac terized in that the first phase H1 compression, shearing and treatment comprises, on the one hand, a compression phase H11 with evacuation, at the end of this phase, effluents and , on the other hand, a phase H12 shear.  11. The method of claim 8, characterized in that the second phase H2 compression, shearing and treatment comprises, firstly, a compression phase H21 with introduction at the beginning of this phase, dilution water and with evacuation, at the end of this phase, effluents and, secondly, a H22 shear phase.  12. Method according to claim 8, characterized in that the third phase H3 compression, shearing and treatment comprises, firstly, a compression phase H31 with introduction at the beginning of this phase, dilution water and with evacuation at the end of this phase of the effluents and, on the other hand, a H32 shear phase.  13. Method according to claim 8, characterized in that the fourth phase H4 compression, shearing and treatment comprises, firstly, a compression phase H41 with simultaneous introduction at the beginning of this phase of dilution water, a solution of caustic soda whose flow corresponds to a value of between 0.5 and 2% of reactive product relative to the raw material and a solution of hydrogen peroxide whose flow rate corresponds to a value between 2 and 6% of active product relative to the raw material and, secondly, a shear phase H42.  14. Process according to claim 1, characterized in that white water is injected into each dilution tank (62, 69).  15. Plant for continuous preparation of a cellulose pulp intended, in particular for the chemical or paper industry, from a raw material consisting of textile fibers, characterized in that it comprises  pneumatic means (2, 7) for transporting textile fibers,  means (5) for separating textile fibers and foreign bodies such as agricultural residues, metal and mineral particles,  a densifier (6) for textile fibers,  means (8, 9) for extracting and filtering the dusty air from the pneumatic means (2.7) for conveying the textile fibers,  - a first co-rotating screw type processing machine (10) (11, 12) for continuously leaching and precutting the textile fibers and obtaining a pulp having a dryness of between 25 and 40%,  means (34) for transporting the dough at a temperature corresponding to its outlet temperature of said first processing machine (10),  a first latency capacity (35) for continuing the leaching of the dough, the retention time of the dough in said first latency capacity (35) being between 30 and 60 minutes,  a second co-rotating screw type processing machine (41, 42) for continuously washing and bleaching the pulp and obtaining a washed and bleached pulp having a dryness of between 25 and 40%,  means (60) for transporting the washed and bleached pulp,  a second latency capacity (61) for continuing the bleaching of the dough, the retention time of the dough in said second latency capacity (61) being between 60 and 120 minutes,  - a first dilution tank (62) of the pulp, provided with a stirrer (63) to obtain a paste having a concentration of between 1.5 and 3%,  and a screw press (66) for draining and pressing the dough and obtaining a dough having a dryness of between 30 and 35%.  16. Installation according to claim 15, characterized in that it comprises, downstream of the screw press, a second dough dilution tank equipped with a stirrer to obtain a paste having a concentration of between 3 and 5% .  17. Installation according to claim 16, characterized in that it comprises, downstream of the second dough dilution tank, a dough storage tank provided with a stirrer.  18. Installation according to claim 15, characterized in that the first processing machine (10) comprises continuously, from upstream to downstream in the direction of transport, respectively  a zone A for supplying textile fibers and for mixing said textile fibers with water injected at the beginning of this zone,  a compression zone B with effluent recovery at the end of this zone,  a first zone C of mixing and shearing,  a zone D for conveying and treatment with introduction at the beginning of this zone, leaching reagents and dilution water, the leaching reagents consisting in particular of a solution of caustic soda whose flow corresponds to a value between between 2 and 5% of reactive product relative to the raw material,  a second zone E of mixing and shearing,  and a zone F for transporting and discharging the pulp in the first latency capacity (35).  19. Installation according to claim 18, characterized in that the water injected at the beginning of the supply zone A of the first treatment machine (10) is constituted by the recovery water coming from the screw press ( 66) and by clear water.  20. Installation according to claim 15, characterized in that the second processing machine (40) comprises continuously, from upstream to downstream in the direction of transfer, respectively  a zone G feeding the bleached pulp from the first latency capacity (35) and mixing said dough with water injected at the beginning of this zone,  a succession of zones H1, H2, H3 and H4 for compressing, shearing and treating the pulp,  and a zone J for transporting and discharging the pulp in the second latency capacity (61).  21. Installation according to claim 20, characterized in that the water injected at the beginning of the feed zone G of the second treatment machine (40) is constituted by the recovery water coming from the screw press (66). ) or by clear water.  22. Installation according to claim 20, characterized in that the first zone of shearing and processing compression H1 comprises a first compression zone element H11 with evacuation at the end of this effluent zone and a second zone element H12 of shear.  23. Installation according to claim 20, characterized in that the second zone H2 compression, shearing and treatment comprises, firstly, a first compression zone element H21 with introduction, at the beginning of this first element H21, dilution water and with evacuation, at the end of this first element H21, effluents and, secondly, a second shear zone element H22.  24. Installation according to claim 20, characterized in that the third compression, shearing and treatment zone H3 comprises, on the one hand, a first compression zone element H31 with introduction, at the beginning of this first element H31, dilution water and with evacuation, at the end of this first element H31, effluents and, secondly, a second shear zone element H32.  25. Installation according to claim 20, characterized in that the fourth compression, shearing and processing zone H4 comprises, on the one hand, a first compression zone element H41 with simultaneous introduction, at the beginning of this first element. H41, dilution water, a solution of caustic soda whose flow corresponds to a value between 0.5 and 2% of reactive product relative to the raw material and a solution of hydrogen peroxide of which the flow rate corresponds to a value between 2 and 6% of active product relative to the raw material, and, secondly, a second shear zone element H42.  26. Installation according to claim 15, characterized in that each dilution tank (62, 69) is provided with means (64, 71) for injecting white water.