FR2626905A1 - PROCESS FOR DEFIBRING A LIGNOCELLULOSIC MATERIAL - Google Patents

Abstract

The process for mechanical defibration of a lignocellulosic material obtained by a pretreatment of impregnating platelets with a reactive agent promoting the softening of lignin is characterized in that it consists in passing the material through an apparatus 20 of the grinder type with hammers and cylindrical grid. Thanks to this process, a maximum of long fibers is kept in the dough obtained. The process also results in lower energy consumption than in conventional disc refiners.

Description

PROCESS FOR DEFIBRING A LIGNOCELLULOSIC MATERIAL

  The invention relates to a method for defibrating cellulosic material

  which has undergone impregnation pretreatment to soften the

  lignin, with a view to obtaining a pulp and paper.

  The various processes for the manufacture of paper pulp, in particular from wood chips or chips, consist, in the first place, of

  reduce these to the state of fibers.

  To obtain this separation of the fibers, the wood can be broken down purely mechanically by means of grinding wheels. This gives high performance mechanical pulps because we find the

majority of wood constituents.

  This separation can also be achieved by removing the lignin

  ne, which ensures the adhesion of the fibers together, by means of chemical reagents. By subjecting the chips to cooking for a certain time in devices called digesters - with a continuous or discontinuous principle - in the presence of a suitable reagent, lignin and other soluble constituents are completely dissolved in order to preserve only the cellulose whose fibers are perfectly isolated ,. the disintegration of pasta

  Chemicals is obtained by simply blowing.

  Between these two extreme processes are known processes involving both mechanical work and chemical work to varying degrees in combination, where appropriate, with the action of the

  heat that aims to soften lignin binding.

  Thus, before the mechanical treatment of defibration, the

  platelets by the action of a chemical reagent or water vapor at

  high eradication and we obtain so-called mechano-chemical pasta, thermo.

  mechanical or chemo-thermo-mechanical.

  Mechanical treatment is generally provided by refiners

  discs or equivalents which are intended to individualize the fibers.

  Depending on the operating conditions, the disc refiners also allow the release of fibrils which will improve the resistance

mechanical paper obtained.

  The subject of the invention is a process for treating mechanically

  fibrous materials resulting from impregnation pre-treatment, in particular

  by a chemical agent, promoting the softening of lignin.

  The method is characterized by passing the material through a hammer mill and cylindrical grid apparatus. Hammer mills are devices already known per se, but to the knowledge of the plaintiff, they have never been used in

  recommended conditions, that is to say for the defibration of a fat paste.

previously impregnated.

  The mill advantageously replaces disc refiners, for example, usually used in this case, this for two important reasons; By its principle of operation, the fibers subjected to the mechanical treatment are only those which form agglomerates which it is a question of individualizing, whereas the fibers already defeated pass over the surface of the rille san's_ $ ruEbi aucqAvtraiemt

- I -.O

  According to another aspect of the invention, the pretreatment to which the wafers are subjected before their defibration in the hammer mill is carried out inside a twin-screw machine according to the teaching of patent FR 2,418,295. It appears, in fact, that by the short-time impregnation which takes place inside the machine, leading to a softening of interfiber bonds, the optimum conditions are met for a good operation of a hammer apparatus which has

  tendency to open the fibers very quickly and easily enough.

  Other details and advantages of the process will appear in reading

  follows from the description of an embodiment of the invention given to

  As an example and illustrated by the accompanying drawings o:

  FIG. 1 is a partial schematic representation of an installation

  the manufacture of pulp from wood chips; FIG. 2 is a front view, in cross-section, of a grinder with

  hammers capable of being used in the context of the invention.

  FIG. 1 schematically represents a part of an installation of

  A-high yield cardboard pulp production. The arrows in bold lines

indicate material flows.

  It comprises a bi-screw type machine (1) fed with wood chips by a hopper (3) whose capacity is determined to guarantee a satisfactory supply, even in the case of a short interruption.

  of the chain of handling of the machine.

  The recovery of platelets under the hopper is performed by an extractor

  double screw (5) whose rotation speed is slaved to that of the-

  twin-screw machine to ensure proper feeding at all operating speeds. The rotors of the machine are themselves

driven by an engine (7).

  Orifices (9) are provided along the envelope of the bi-screw machine to allow the injection of a chemical reagent - which in this case is a solution of neutral sulphite of soda - - the interior of the

  different treatment enclosures. Similarly, there are plans

  these (11) for the injection of the quantity of water necessary for the control of

  the dryness of the material in treatment.

  Downstream, the machine opens into an outlet trough (13) whose shape allows the distribution of the flow of material towards the inlet of two

  grinders and hammers (20). A detailed description of these devices is

  given later. The installation example shown in the diagram is

  refers to two grinders in parallel, but this number is not limiting.

  Only one crusher can suffice if necessary.

  The de-grinding operation in the grinders & hammers requires a supply of water in (22) to reduce the siccit4 of. the matter. The raw pulp from the mills falls into a vat (30) where it is agitated and

  taken by a pump (32) to be directed to a battery of class-

  two, in this case (40,42), arranged in series.

  Classification rejects are subject to shredding in a third

  hammer mill (50) of the same type as the previous ones, also fed

  in make-up water in (52) for the control of the dryness of the material which after grinding is recycled to the raw cuvier (30)

through the conduit (56).

  The accepted fart goes out of the classification in (44) towards the aspiration of pulp pumps to undergo various subsequent treatments before being admitted into the stock of fate of the cardboard machine. It is so, so

  in itself, for example by passing through

  cyclones arranged in cascade, then directed on thickeners allowing to adjust its dryness to the value required for its passage

in the carton machine.

  Figure 2 illustrates a model of hammer mills likely to be

  employed in the process according to the invention.

  It comprises two rotors (200) mounted on two horizontal shafts (202) inside a frame (204) open at the same time in its upper part (206) for the admission of the dough to be vibrated and in its part

  lower (208) for the evacuation of the latter after treatment.

  Each rotor consists of parallel discs (210) separated by spacers {a single disc per roter is visible in the figure}. They

  are connected at their periphery by pins (2.14) parallel to the shaft.

  One out of two pins carries a row of hammers (216) parallelepiped-

  radially oriented along their major axis (only one per row is visible in the figure.) The hammers have a certain degree of freedom of rotation about their support axis.In the example shown, each rotor is thus provided with four

rows of hammers.

  On either side of the vertical plane passing through the shaft of each rotor are arranged a central harrow (220) and a side harrow (222) whose teeth are interposed between the planes of rotation of the hammers, and

  extend substantially to the periphery of the discs.

  A grid (230) in the form of a half-cylinder longitudinally covers a

  part of the lower half of each rotor (200)

  the surface swept by the free ends of the hammers. In this way the hammers cooperate with the peripheral grid to break and defiber the material staying in the device. Each grid is pierced with calibrated orifices (holes or slots) so as to allow the passage of the individualized fibers while retaining the maximum. of bows. The fibers that have passed through the grid are drawn towards the outlet opening (208). The calibration of these orifices (holes or slots) is decisive for obtaining the desired result. It is desirable for the diameter of the holes to be between 1 and 5 mm, or in the case of slits with a width between 0.4 and 2 mm.When the shape of the orifices is not cylindrical, these values apply to their more

small transverse dimension.

  Nozzles (240) for injecting water are arranged across

the intake opening (206).

  Tl51es (250) extend the cylindrical grids (230) to confine the rotor-swept enclosure and limit the projections.They are articulated about a longitudinal axis to give access to the rotor

  when we have to maintain it.

  The installation described above makes it possible in particular to obtain high-performance cardboard pulps, of the order of 92%, for example from C

fresh spruce.

  The operation is as follows: The platelets are prepared before their admission in the trêmie (3) they are sieved so that only those who have the

  appropriate dimensions, washed and riddled. of any foreign matter

  manages, They pass from the hopper to the entrance of the twin-screw machine by the extractors. This machine is constituted, according to the teaching of patent FR 2,418,295, two parallel screws whose threads are identical and which are driven in the same direction of rotation inside a sheath.

  The threads consist of successive zones with different pitch.

  In a first section, the threading is first of all a direct step for the entrainment of the material downstream, then the pitch is inverted for

  curb the material until forming a plug.

  The material passes into a second section and the other through calibrated fengtres, formed in the thread immediately downstream of the plug area, undergoing expansion. The size of the windows is chosen so as not to reduce the length of the windows.

  fibers but a simple fractionation of platelets.

  In the second section the. Thread is again at a direct pitch and then inverted to form a second cap. The machine thus comprises a

  number of successive sections from upstream to downstream.

  Inside each section, the material passes through a series of alternating phases of pressure rise followed by pressure drops which allow impregnation of the material with the desired reagent.

  Indeed, because of the rotation of the screws in the same direction, the progress

  material flow from upstream to downstream, is accompanied by alternation of compressions / releases as it moves from a screw to

the other.

  During each compression phase - which occurs within the threads of a screw preceding the portion o they mesh with the threads of the other screw - the material tends to expel the trapped liquid between the fibers. During the expansion that follows - when it is passed between the threads of the other screw - the liquid comes again

fill in the interfiber spaces.

  The excess liquid released during the compression phases may

  to be eliminated by filters placed at convenient locations.

  ble. This trituration of the material inside each section, but also from one section to another, is thus favorable to its impregnation a

heart by the reactive liquid.

  By an appropriate choice of characteristics of. the machine and its operation: not threads, speed of rotation of the screws, length of the braking zone, caliber of the windows, etc ..., it is possible to raise the pressure & inside the machine up to values high, of the order 100 bars, and obtain an appropriate temperature of the material between 60 and 100 *. In this way, an impregnation is carried out

  heart pads without damaging the fibers.

  Controlled quantities of water are introduced into the different

  sections for the advancement of the subject to occur in

optimal conditions.

  Thus, while the wafers, at their introduction, have a humidity of 35 & 50%, the product produced by the machine comes out with a dryness

  from 25 to 30%. After such treatment, the material is only partially

  defibrée. Under the operating conditions of the example of

  currently shown, the rate is 55%. In order to complete the individualisation of the fibers while keeping them at their maximum length quality, they are mechanically treated by means of the invention. The material is thus conveyed to the mills, where the packets of pretreated fibers are subjected, according to the invention, to mechanical separation treatment in the mill by the action of the mills.

  hammers cooperating with the harrows and the cylindrical grid.

  At the inlet of the mill, the material is watered by means of the nozzles so that at the outlet its dryness is reduced to a value of between 2 and 20%. The adjustment of the dryness allows an adjustment of the relative treatment

  at the blink rate and the BAUER MAC-NETT classification.

  By the action of the hammers sweeping the grid, the fibers not yet

  are easily defeated whereas the already individual fibers

  The production of a pulp with preservation of the length of the fibers is one of the important advantages of the process since it is not subjected to the action. of

  grinder that the piles of fibers to be treated, this is of course an estimate-

  statistics. However, the results show that, overall, the proportion of long fibers resulting from the treatment can in the case

  present be as high as 54%.

  By long fibers is meant the proportion of fibers which are collected

  linked to 28 MESH sieve. This result is to be compared to that of a mechanical grinding wheel pulp for which the proportion of fibers collected at

Mesh screen of 28 MESH is-22 ..

  Another advantage of the use of a hammer mill in these conditions is the significant energy gain achieved compared to defibration performed in conventional refiners which in addition

  of equivalent refining, do not allow the preservation of a proportion

  long fiber content.

  To illustrate the interest of the use of a hammer mill, the same quantity of wood was subjected to four different treatments.

  first treatment A corresponding to that of the invention or the

  were impregnated with sodium neutral sulphite in a twin screw machine and then defibrated in a grinder of the type described above

  grid is pierced with holes 2.5 mm in diameter.

  In a second treatment B, the same raw paste coming out of a pre-treatment

  bi-screw is passed through two series refiners of the type DEF5BRATOR and BAUER 411 to obtain a paste having the same degree

drip.

  In a third treatment C, a dough of chips is passed through the same refiners.

  Finally, in a fourth treatment D, a grinding wheel paste was produced.

  The features of BAUER MAC NET are mentioned below for

each pasta.

!!!! t! = ,! T B! ! t D

! I! !. I

I% T14 t 31,6)! 25.3) I 9.8) t 8.7)

! I (54.4 (49.1) (35.3 (22.8%)

  I T28! 22.8) 23.8) 1 25.5) t 14.1) T! t! I - t J% T48 1 16.3 t 18.7 A 21, 3 21t, 4! J 5! !! t

% T200! 9.9 12.0 16.9! 28.3!

  J 2 !. 1 t S Q% finxes 16.9 1 20.1 1 26.5 27.5 t T 1 t t S% Bands! 10.2! 14,7 t 8,6 t 8,9 1! = =! =! t! It is found that the treatment recommended by the invention produces a pulp whose proportion of long fibers collected by the T28 sieve is 54.4%, ie more than 10% higher than that obtained in conventional refiners with a lower proportion of fines. 20%, this for

  equivalent degrees of dewatering.

  If we return to the description of the treatment of matter in

  the installation illustrated in Figure 1, the raw pulp from the mill whose dryness. fell for example & 2%, has only one, blink rate of the order of 15%. The dough is collected in a

  cuvier with the rejections of classification o it undergoes a continuous stirring.

  At the exit of the vat, the paste is pumped to the battery of files that will eliminate the bends. Thus the pulp accepted by the classification contains only about 0.6% of logs and can be submitted to

  conventional operations of purification and thickening before deli-

to the machine stock.

  Grading rejects are subjected to grinding in a milling machine.

  50 similar to the first two (20)}, a make-up (32) reduced

  the dryness of the pulp that has returned to the vat (30).

  The process which has just been described has the advantage of producing a high yielding pulp whose fiber length is maximally conserved with a decreased energy expenditure. It is obvious that the hammer mills can be fed by other raw pastes than those resulting from pre-treatment with the twin-screw machine as long as this paste has an impregnation. at heart sufficient for exploitation

optimal in-the grinders.

  Finally, the installation may include a combination of conventional refiners

  hammers and crushers if necessary.

Claims (11)

RVENDICATIONS   1. Process for mechanical defibration of a lignocellulosic material obtained by a platelet impregnation pretreatment by a   reagent for the softening of lignin,   rised in that it consists in passing the matter. through a   Apparatus (20) of the hammer mill and cylindrical grid type.   2. Method according to claim 1, characterized in that the defibration is carried out in a humid medium, the dryness of the material at the outlet of   the apparatus being between 2 and 20%.   3. Method according to claim 2, characterized in that the water is injected (22) at the inlet hopper of the material to   inside the hammer mill.   4. Method according to one of the preceding claims, characterized in   what the holes of the grid are holes of diameter included between 1 and 5 mmi.   5. Method according to one of claims 1 to 3, characterized in that   the orifices of the grid are slots of width between 0.4 and 2 mm.   6. Method according to one of the preceding claims, characterized in   the pretreatment of the material is carried out in a bi-screw type machine (1) in which the chips are subjected to a succession of alternations compression / release with injection   one or more solutions of at least one chemical agent.   7. Method according to the preceding claim, characterized in that the.   material is fed during pre-treatment at a temperature   between 60 and 100- by the action of compressive forces and- friction.   8. Method according to one of the preceding claims, characterized in   what said lignocellulosic material is classified, then the classification discharges are processed in a hammer mill type apparatus. 9. Process for preparing a pasta dough from wood chips consisting of pre-treating said wood chips in a twin screw machine (1) where they are subjected to a succession of   compression / release with injection of one or more   at least one chemical agent.and then defibering the material from the machine by a mechanical means, characterized in that after the material has been subjected to a grading operation, and in that the grading rejects are subjected to to a defibration in   a hammer mill type apparatus (50).   10. A method according to claim 9, characterized in that the moisture of the grading waste subjected to defibration is controlled by water injection into the hammer mill so that at the output of said mill the dryness of the machine is between 2 and%. 11. The method of claim 10, characterized in that after passing through the hammer mill the material is recycled ein upstream classification apparatus (40,42). 3O