CS242478B1 - Method of mechanical treatment of chips for production of lignigated paper fibres - Google Patents

Description

The invention relates to a method of treating chips in the manufacture of lignified paper pulp. '

The current production of lignified fibers is based on grinding of gufatin wood with stone grinding or pulping of wood chips in disc refineries. The refinery process provides pulp with better mechanical properties and is therefore currently the predominant process in the world for the production of lignified pulp for papermaking.

The basic principle of production has several modifications, which differ from each other by the treatment of chips before the actual pulping. The most widespread is the process in which the chips are heated to the plasticization temperature of the lignin in the cell walls before being pulverized in the pressure chamber by direct steam.

In this way, so-called. Thermomechanical pulp (TMV). Another modification is the impregnation of the chips with a solution of some chemicals (sodium sulfite, sodium hydroxide, etc.).

Impregnated chips are pulped directly (chemomechanical pulp - - CMV) or after steaming (chemothermomechanical pulp - CTMV). Pulping of thermally and chemically untreated chips is also possible (refinery wood). Actually, the pulping is usually two-stage, i. j. the processed material passes through two successive refiners.

All of these fiber types have a wide paper application (R. Loask: Pulp and Paper Canada 81 (3) 21 (1980), 82 (3) 23 (1981)).

The process of production of lignified fibers in disc refineries is characterized by simplicity, low investment and operational demands as well as ecological safety. A certain disadvantage, however, is the relatively high specific power consumption required to drive the refiner's grinding discs, which is about 2,000 to 2,200 kWh / t.

In fact, pulping, i. j. only a relatively small portion of the energy input is consumed to break the bonds connecting the individual fiber elements, the remainder is converted to heat and escapes from the refining plants in the form of steam.

By utilizing the resulting steam, the overall energy intensity of the process is relatively reduced (G. E. R. Lamb: Tappi 45/5/364 (1962); G. Tistad, S. Asklund, F. Gosfelt: Svensk Papperstidnig (14) 16 (1981)).

However, direct reduction of specific electricity consumption is preferable to the use of the generated steam.

Splintering of chips is a complex process that can be characterized by several phases. After entering the refiner, the chips are first roughly disintegrated into smaller portions, of which individual fibers are released between the refiner discs as they proceed.

In the last stage of refining, the surface fibrilization of the individual fibers mainly occurs. (J. Polčin: Paper and cellulose 32 (lj 3 (1977))

In order to achieve proper fibrillation, a suitable load of the discs must be used and the necessary rotation speed must be maintained. For perfect fibrilization, the speed of the disks must be high, even though it is not possible to use all the energy supplied to break the bonds connecting the individual fiber elements.

It is an object of the present invention, which reduces the energy consumption of the production of lignified fibers, that the thermally and / or chemically treated chips are pulled at a pressure of 0.3 to 1.5 MPa prior to pulping. The disruption of the compact structure of the chips to be processed is carried out in a cylindrical cone or screw press before. their pulping into refineries.

The first pulping phase, i. j. the coarse chip disintegration is thus not carried out directly in the refiner, the speed of which is determined by the needs of the next stages of the pulping process.

In the first phase, however, such a high velocity is not necessary because it does not yet affect the fibration and is therefore advantageously replaced by a slower operation in which a substantially greater proportion of the energy input is used to disrupt the structure of the material without unnecessary heat loss.

The result of this process is paper pulp with the same properties as TMV, CMV, respectively. CTMV, prepared by current technology, but produced with lower specific electricity consumption.

Example 1

In the production of thermomechanical pulp, the wood chips prepared by the process common in the production of lignified pulp (chopping, sorting, washing) are pre-evaporated to a temperature of 110 ° C.

The chips thus treated are compressed in a cylindrical press with counter-rotating press rolls (preferably, the rolls move at an uneven speed, thereby improving the friction effect) at a pressure of 0.3 MPa. Pressing at the same pressure can also be carried out in a cone or screw press. The integrity-crushed chips are fed into the refiner and pulped through a single or two-stage refining with a specific electricity consumption of 1,400 kWh / t.

After pulping, the material is further processed according to the conventional manufacturing method of TMV. A 400 kWh / t electric energy saving is achieved over the unmodified process, while the mechanical properties of pulp are improved by 10%.

Example 2

In the manufacture of thermomechanical pulp, the wood chips prepared by the process customary for the production of lignified pulp (chopping, sorting, washing) are pre-evaporated to a temperature of 125 ° C.

The chips thus treated are compressed in a cylindrical press with counter-rotating press cylinders (preferably, the cylinders are moved at an uneven speed, thus improving the friction effect) at a pressure of 1.5 MPa. with integrity distortion, they are fed into the refiner and pulled by a single or two-stage refining with a specific electricity consumption of 1,800 kWh / t.

After pulping, the material is further processed according to the conventional manufacturing method of TMV. A 600 kWh / t electric energy saving is achieved over the unmodified process, while the mechanical properties of the fiber are improved by 15%.

Example 3

In the manufacture of CTMV and CMV, wood chips prepared as in Example 1 are impregnated with Na 2 SO 4, NaOH, or other lignin plasticizing agents. In the production of CTMV, the chips thus impregnated are still pre-evaporated to a temperature of 110 ° C.

The chips thus treated are compressed in the same manner as described in Example 1, while their integrity is impaired. The chips are then pulped with a specific electricity consumption of 1,000 kWh / t.

After pulping, the material is further processed according to the conventional method of producing this type of fiber. A 250 kWh / t electric energy saving is achieved over the modified process, while the mechanical properties of the pulp are improved by 10 ° / o.

Example 4

In the production of CTMV and CMV, wood chips prepared as in Example 1 are impregnated with Na 2 SO 4, NaOH, or other lignin plasticizing agents. In the production of CTMV, the chips thus impregnated are still pre-evaporated to a temperature of 125 ° C.

The chips thus treated are compressed in the same manner as described in Example 1, while their integrity is impaired. The chips are then pulped with a specific electricity consumption of 1,500 kWh / t.

After pulping, the material is further processed according to the conventional method of producing this type of fiber. A 500 kWh / t electric energy saving is achieved over the modified process, while the mechanical properties of the fiber are improved by 20%.

Claims (1)

OBJECT OF THE INVENTION The mechanical treatment of the chips or the chemically treated chips prior to the production of lignified papermaking fibers is compressed at a pressure of 0.3 to 1.5 MPa. nin, characterized in that the heat and / or