FR2641803A1 - METHOD FOR DELIVERING PAPER PULP ON THE METALLIC CANVAS OF A PAPER MACHINE - Google Patents

Abstract

Method for delivering pulp onto the wire mesh 11 of a paper machine whereby the pulp is suspended in white water, this suspension then being delivered onto the wire mesh and white water drained from the forming sheet through the web being recycled in the suspension process, characterized in that an enzyme is added to the white water in order to disintegrate constituents such as dissolved hemicellulose or scattered from the dough.

Description

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  The present invention relates to a process for delivering raw pulp or pulp to the wire of a papermachine according to which the paper pulp is suspended in white water, this suspensiLon then being delivered on the wire cloth and the white water drained from the sheet in formation, through the wire mesh

  then being recycled to the suspending process.

  In the papermaking process, an essential step is the sheet-forming process, which is carried out by diluting the thick pulp from the process of making the raw pulp, in order to produce the paper. to obtain a suspension having a low consistency and by pumping this suspension by means of centrifugal purifiers and vents, to bring the suspension to the pulp arrival box of the paper machine and then on a wire mesh, permeable to water, on which is formed a homogeneous sheet during the drainage of water. The sheet thus formed is then treated in subsequent steps

  in order to obtain the finished paper.

  The economic requirements of the papermaking process require maximum retention, which means that fibers transported together with the raw pulp slurry must be retained as effectively as possible in the sheet being formed on the wire mesh. For this purpose, a circulation of the water used in the process is carried out in a closed circuit by recycling the white water drained from the sheet through the wire mesh to the preparation phase. the worked pulp, so that the fibers have, repetitively, the possibility of adhering to the sheet being formed. In addition,. closed water circulation is important to reduce effluents

wastewater.

  However, there is a problem in implementing a closed circuit circulation of water in the papermaking process which results from the fact that a continuously increasing concentration of constituents dissolved or dispersed from the processed work-in-progress of elaboration develops in recycled white water. These constituents interfere with papermaking by impairing retention, preventing the action of the additives, causing accumulations in the papermaking plant, which results in the presence of impurities which are transferred to the paper mill. the paper being

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  -2 - production. A significant part of the dissolved solids in white water consists of carbohydrates, in particular hemicellulose, having a molecular weight of the order of 10 000 ... 100 000. Moreover, the white water contains lignin and extracted constituents which, in view of their lower solubility and higher adsorption capacity, tend to precipitate on the fibers, thus avoiding water enrichment

  white in the same way as carbohydrates.

  Accordingly, the present invention proposes to provide a method for reducing and even eliminating the disadvantages due to the aforementioned problems encountered in the manufacture of paper during a flow of water in a closed circuit. The process according to this invention is essentially characterized in that an enzyme is added to the white water in order to disintegrate constituents such as dissolved or dispersed hemicellulose.

from the raw pasta.

  When the dissolved or dispersed substances in the white water are advantageously disintegrated into very small fragments according to the invention, the drainage of the water from the forming sheet of paper on the wire mesh is improved. Moreover, we have seen that the disintegration of hemicellulose causes the retention of fibers. Without this being able to constitute any limitation of the scope of the invention, an explanation can be given to this phenomenon: it is thought that this effect is due to the fact that hemicellulose, which by its adhesion to the fibers communicates to them characteristics anionic agents, thus causing their mutual rejection, loses its adsorbent capacity during the disintegration, so that the fibers can retain

  their neutral nature, which improves their retention in the forming leaf.

  The prior art as described in the Finnish patent application Y '87 4113 discloses improvements to the drainage of water

  from the forming sheet of using enzymes.

  However, such a known method relates to the addition of enzymes in the high consistency raw dough, so that the effect of the enzymes on the fibers is felt before the resuspension of the thick raw dough to be delivered to the product. wire mesh of the paper machine in the form of a suspension. In contrast, the process according to the present invention relates to the addition of enzymes in the white water system so that these enzymes are used in the white water to effect the disintegration of the dissolved constituents.

  dispersed, including dissolved hemicellulose.

  Among the enzymes which can be used during the implementation of the process according to the invention, mention may in particular be made of hemicellulase, cellulase, esterase and pectinase and their combined mixtures. Cellulase, by

  example a CXC (carboxymethylcellulose) activity of 5000 U / ml or the

  xylosidase having an activity of 2000 nmat / ul is perfectly suitable. The amount of enzymes used can be measured. to 0.01 ... 1 1 / m with respect to the white water using a preferred measuring method in which the pure enzyme is first diluted in a very small amount of water, in which it is then measured in white water. To obtain an operation of the enzyme, the temperature of the water must be of the order of 10 ... 90 C, preferably 40 to 70 C and its pH must be of the order of 3.0. 8.5 from

preferably from 4.0 to 6.0.

  According to the method which is the subject of the invention, the enzyme is firstly added.

  to the short circulation circuit of the rich white water in which the white water is recycled from the formation of the sheet on the wire mesh, to the dilution of the worked pulp delivered. Problems resulting from the presence of dissolved constituents in white water are typically evident in this area. Since it can be supposed that the consistency of the fibers in the rich white water is low, typically of the order of 0.4% at most, the enzyme has the possibility of attacking the dissolved substances in the water. white water, effectively without interfering with the fibers, which satisfies the purpose of the present invention. A suitable location for the addition of the enzymes is in the pit under the wire cloth, in which the white water collected or drained from the forming sheet is entrained to be mixed into the high consistency raw pulp before

to be diluted.

  According to the process which is the subject of the invention it is also possible to carry out the addition of enzymes to the so-called long circulation circuit of depleted white water, in which the white water drained I0 from the forming sheet is recycled for reuse at locations that are located near the starting end of the paper making process. In Aini, for example, a suitable location for effecting enzyme addition is the pit under the wet press which acts as a well for collecting white water drained by aspiration from the forming paper sheet. . Part of the white water collected in the suction box can be removed from the pit under

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  - 4 - the wet press with the short circulation circuit to the pit under the wire mesh, while the rest of this white water is added to the depleted white water of the long circulation circuit described above. A particular advantage of this application is that the white water that enters the pit under the wire mesh has a relatively lower consistency than the white water that enters the pit

under the wire cloth.

  The method according to the present invention is of maximum interest when it is used in paper machines using raw pulp obtained mechanically such as mechanical pulps TMP (thermomechanical pulps) or CTXP (chemical-thermomechanical pulps). This is because the amount of harmful substances dissolved or dispersed in the white water from mechanical pulps is particularly high. Nevertheless, advantageous results are also obtained by carrying out an addition of enzymes, according to the process which is the subject of the invention, in processes for the manufacture of paper.

from chemical pulps.

  In addition, the invention relates to the use of enzymes in the disintegration of dissolved or dispersed organic material from the raw paper pulp in the white water of the paper machine. As indicated above, the preferred enzymes are hemicellulase, cellulase,

  esterase and pectinase and their mixtures combined. -

  Other features and advantages of the present invention

  will emerge from the description given below with reference to the single figure of

  attached drawing which shows schematically the implementation of the method of forming paper sheets according to the invention on which there is shown

  as a whole the short circulation circuit of rich white water.

  As can be seen in the drawing, the thick worked pulp from the preparation of the raw pulp or pulp, with a fiber consistency of approximately 5% is pumped through line 1 to the bottom of the dough. a pit 2 under the wire mesh where it mixes with the white water. The suspension thus obtained is driven via a turbine pump 3 to a centrifugal purifier 4 and the accepted fraction of this suspension continues its journey to a deaeration chamber 5. The fraction rejected by the centrifugal purifier 4 continues its displacement to the centrifugal purification units 6 (only one has been shown in the drawing), the number of such units can in practice be very high in a so-called connection mode

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  --5-- in cascade. The collective fraction accepted from these scrubbers is returned via a pipe 7 to the pit 2 while the fraction released from the last purification unit is removed from the process through a pipe 8. The suspension of The raw pulp purified from the deaeration enclosure 5 is pumped via a feed pump 9 to be delivered to the arrival box of pulp 10 of the paper machine, the rule of this box issuing the dough on an endless wire cloth 11 flowing

  continuously so as to form a homogeneous sheet on this wire mesh.

  A large part of the white water contained in the raw pulp is drained through the wire mesh 11, in the horizontal section of this fabric following the arrival of pulp box 10 and this fraction of white water is collected. along a pipe 12, directly into the pit 2 under the wire mesh. There is provided an upper wire cloth which is disposed after the wire section described above and against a wire mesh 11, the white water drained from this wire cloth 13 also being routed to the pit 2. Boxes of suction 14 are also arranged after the wire section described above and the white water drained from these suction boxes 14 flows along a line 15 to be delivered to a pit 16 under the wet press. Part of the white water collected in this pit is pumped at the same time as the short circulation circuit of the enriched white water, as necessary to complete the white water of the pit 2 in the crude pulp suspension then that the rest of this white water flows along a pipe 17 to the long circuit of

  circulation of depleted white water in the paper machine.

  The essential characteristic of the process which is the subject of the present invention resides in the addition of enzymes in the white water so that the disintegration induced by this addition of enzymes of the substances dissolved and dispersed in the white water causes a drainage of the water. 'water. The material is white from the sheet formed on the wire fabric 11 and improves the retention of fibers in the sheet and, particularly importantly, eliminates the influence of harmful substances on the retention of fibers. According to the invention, the enzyme can be added to the rich white water short circulating circuit described above in which case the recycle line 18 can be connected to the pit 2 under the wire cloth as shown on the drawing. Instead of this provision, or in addition, the pit 16 under the wet press may be provided with a pipe 19 ensuring the supply of enzymes in such a way that the water

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  Enzyme-treated white is available in the flows that occur at the exit of the pit to the short circulation circuit and

  also towards the long circulation circuit of the paper machine.

  The effects of the addition of enzymes on the formation of the paper sheet as well as the characteristics of the paper obtained were determined during

  of experimental tests which are described in the examples mentioned below.

KIBIPLE 1

  A hemicellulase enzyme having an activity of 2000 U / ml was added to a sample of 1200 ml of rich white water from the short circulation circuit of the paper machine and a sample of 1200 ml of water. impoverished white of the long circulation circuit. The enzyme was measured in such a way as to obtain doses of 0 μM (reference test), 3 μl and 30 μl per liter of white water. The pH of the water was approximately 5.0 and its temperature was 50 ° C. and in each sample the enzyme was allowed to act for three hours with intermittent mixing. After reaction of the enzyme, a volume of 300 ml of untreated thermomechanical raw paste (paste T] P) was mixed with each sample of white water and the suspensions thus obtained were immediately subjected to dewatering measures ( according to the Scandinavian standard method 'Scan X 4:65', used to measure drainage), which characterize the drainage of water from the raw p-te. to the Neimo process as specified in KCL Circular No 18,

  1983). The results are shown in Table 1 below.

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TABLE 1

  Circulating water Dosing of the enzyme Draining Concentration anion (41/1) (ml) (mekv / 1) White water 0 49 0.418 impoverished

3 55 0.037

57 0.032

White water 0 40 0.133 rich

3 40 0.070

49 0

  The thermomechanical pulp mixed with the rich white water samples from the short circulation circuit was shaped into sheets meeting the Scandinavian standard Scan X 45:76, that is to say having a basis weight of 100 g / m =. Tests were performed on the sheets thus obtained in accordance with the Scandinavian standard Scan X 8:76. The results are recorded in

Table 2 below.

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TABLE 2

  Dosage Weight Porosity Resistance Elongation Enzyme Factor from tear to tear sheet tear (pl / l) (g / m2) (s / 100 ml) (<m / g) (%) (Nm / Ikg)

0 99.1 287 36.3 2.31 6.16

0.3 101.0 345 37.4 2.33 5.54

3 102.9 306 36.7 2.18 5.78

  The results in Table 1 show that the enzyme treatment of the rich white water and the depleted white water, respectively in the short circulation circuit and in the long circulation circuit, causes an increase in the dewatering rate, which which indicates improved water drainage and a significant reduction in anton concentration, which provides an indication of improved fiber retention and savings in the use of additives to improve retention. In addition, Table 2 shows that enzyme treatment does not impair the properties of

  Paper strength obtained from the raw dough samples.

EXEPLE 2

  A hemicellulase enzyme according to Example 1 was added in concentrations of 0.13 and 3.11 / 1 to a sample of 1800 ml of rich white water from the short circulation circuit. The pH of the water was substantially 5.0 and its temperature of 50 C and in each sample the enzyme was allowed to act.

  for three hours intermittently mixing.

  After the reaction of the enzyme, a volume of 300 ml untreated thermomechanical pulp was mixed with each white water sample and the suspensions thus obtained were immediately subjected to fiber retention measurements (using the device). says DDJ). The results are shown in Table 3 below.

TABLE 3

  Retention enzyme assay (pl / 1) (X)

0 84.3

3 88.6

85.9

  The results obtained highlight the improvements made by

enzyme treatment.

  It remains understood that the present invention is not limited to the examples of ease and implementation described and mentioned above but

  that it encompasses all variants.

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REVE DICATIONS

  A method for delivering pulp and paper to the wire mesh (11) of a paper machine wherein the pulp is suspended in white water, which slurry is then delivered to the wire mesh and the white water drained from the forming sheet through the web being recycled in the slurrying process, characterized by adding an enzyme to the white water to disintegrate the constituents

  such as hemicellulose dissolved or dispersed from the pulp.

  2. Method according to claim 1, characterized in that the enzyme is added to the short circuit of the paper machine according to which the white water is reduced from the forming step of the sheet to the suspending process.

dough.

  3. Method according to claim 2, characterized in that the enzyme is added to the white water in a well <2) under the wire cloth in which one

  Collect the drained white water from the forming leaf.

  4. Method according to claim 1, characterized in that the enzyme is added to the long circulation circuit of the paper machine in a pit (16) under the wet press in which the white water drained by

  suction from the leaf in formation.

  5. Method according to any one of the preceding claims,

  characterized in that the enzyme is added to the white water having a consistency

  maximum fibers of the order of 0.4%.

  6. Method according to any one of the preceding claims,

  characterized in that the enzyme is added in a proportion of 0.01 to 1

liter / m3 of white water.

  7. Method according to any one of the preceding claims,

  characterized in that the enzyme is hemicellulase, cellulase, esterase,

  pectinase or a combined mixture of these enzymes.

  8. Process according to any one of the preceding claims,

  characterized in that the pulp used is a mechanical pulp such as

  in particular a thermomechanical paste or a chemo-thermomechanical paste.

  9. Application of an enzyme to disintegrate dissolved or dispersed organic material from the pulp into the white water of a paper machine; 10. Application of a hemicellulase, a cellulase, an esterase, a pectinase or a combined mixture of these enzymes according to claim 9 for effecting the disintegration of dissolved or dispersed organic materials.

  from the pulp into the white water of the paper machine.