FI76843C - Treatment of wood chips. - Google Patents

Description

1 76843

Wood chip handling!

TECHNICAL FIELD The present invention relates to the treatment of wood chips with a chemical-thermomechanical pulp, the so-called CTMP. niistämiseksi.

i

State of the art ί

A chemical-thermomechanical mass, the so-called CTMP, has been started j

10 is increasingly used instead of cellulose in many products

limited raw material resources to improve yields. *

Typically, the chips are treated prior to refining through a series of processing steps that include washing, pre-steaming, pressure impregnation, and preheating. Sodium-based neutral sulfite is usually used as the saturant, but ammonium-based sulfite can also be used. It is also known to carry out the impregnation in two steps, the pre-impregnation being carried out after pre-steaming but before the chips are washed, in this case followed by drying before final impregnation.

Compared to thermomechanical pulps, TMP that has not been chemically modified prior to refining, CTMP has certain improved properties.

Thus, the stick content becomes lower and the long fiber content becomes higher, which manifests itself in higher tensile and tear strength. However, it is desirable to be able to further reduce the stick content and increase the long fiber content.

This is especially true when a high pulp yield is desired, which is suitable for a hydraulic sealing fiberboard 30 or a fluffy pulp. In the latter case, excellent light reflectance is also required, although this is less important for the hydraulic sealing fiber plate. In this case, it is desirable to be able to produce pulps for different purposes in one and the same equipment, and it is also desirable to be able to control the processing so that the pulp acquires the desired combination of properties for each purpose. It is further desired to be able to process the chips 2 76843 evenly, allowing a more homogeneous refined pulp to be obtained after refining.

These and other objects can be achieved to a large extent by more efficient impregnation and chemical treatment of the pulp before refining, which is achieved according to the invention by chipping with pre-evaporation, pre-impregnation with water and / or sulphite solution, washing and drying, but before final impregnation, preheating. and refining is maintained at an intermediate temperature of at least 50 ° C for at least 10 minutes. The pH of the sulfite solution, which is usually sodium sulfite solution, is most preferably between and 11. This treatment will provide a significant increase in long fiber content, which is advantageous for both fluff and fiberboard as well as for all papers requiring high tear strength. At the same time, the stick content decreases, which, like the higher long fiber content, seems to depend on the fact that keeping the pulp hot before final impregnation facilitates the release of the fibers so that they are less susceptible to damage during refining. The pulp also becomes tougher, which is also a desired property of fibreboard pulps. In addition, this treatment also reduces the resin content of the pulp.

The experiments performed have varied the amount of sulfite 25 added during the pre-impregnation and final impregnation steps, and have further investigated the effects of not adding any chemicals to the chips prior to washing. The results of these studies show that the stick content depends on the amount of chemicals added, but that it is less relevant at which stage of the treatment the chemicals are added. In contrast, there appears to be a certain risk of a decrease in light reflectance if the total amount of sulphite is added during the final impregnation step and not during any washing of the chips.

The heat maintenance according to the invention during the actual intermediate step 35 between the washing of the chips and the final impregnation can be performed in different ways. According to a preferred embodiment, the chips are treated with steam in a steam treatment vessel 76843 at atmospheric pressure. Processing can also take place at low overpressure. One possible alternative is to heat the chips during or after washing before passing them to an intermediate reaction vessel where the chips are kept at the temperature in question. Therefore, the container can be insulated if necessary. Combinations of these two methods are also possible. As already mentioned, the temperature in the intermediate reaction vessel is maintained at at least 50 ° C. The temperature may rise to a maximum of 99 ° C at atmospheric pressure, 10 but may rise to about 105 ° C above 0.2 bar. The optimum temperature appears to be between 60 and 85 ° C at atmospheric pressure.

The residence time in the above-mentioned container can also be varied. The optimum time is between 30 and 70 minutes, during which time the sulphite has time to penetrate deep into the chips and react with the wood, at the same time as this softens under the influence of heat.

Other features and advantages of the present invention will become apparent from the following description of the experiments performed.

Description of the drawings

In the following description of the experiments performed, reference is made to the accompanying drawings, in which Figure 1 shows a schematic apparatus for producing CTMP using wood chip treatment according to the invention, Figure 2 shows graphite penetration into sulphite before and after treatment according to the invention, Figure 3 shows pulp long fiber fraction as a function of the frequency of treatments and Figure M graphically illustrates the stick content as a function of the degree of grinding of the pulps treated in different ways.

35

Description of the tests performed

The experiments were performed using the apparatus shown schematically in Figure 1. This apparatus comprises a pre-evaporation vessel 1, a screw conveyor 2, a wood chip washing device 3 with sand traps and a dryer 5 leading to a retention and intermediate reaction vessel 6 with a feed screw 7 · This 3 feed screw 7 is connected to a line 8 to break up chips before impregnation, preheating and refining . The return line and the return vessel are denoted by reference numerals 9 and 10, respectively. Usually the apparatus comprises two or more refiners, although only one refiner 11 is shown in Figure 1, to which a preheater 12 and an impregnating device 13 are connected. adapted to be fed to the impregnating device 13 by a Prex screw conveyor lij ("Prex" is the trade name).

The impregnating liquid can be added to the chips on the one hand via line 15 to the feed screw 2 before the chip washing device 3 and on the other hand via line 16 to the impregnating device 13.

In this case, the useful volume of the pre-evaporation vessel 1 was 20 m 2, which requires chips of 15 to / h. The holding vessel 6 was a container known under the trade name "Enso" with a useful volume of 20 m 2 and a bottom with steam inlet means. The need for 15 to / h of chips in the retention vessel was matched to the capacity of the pre-evaporation vessel.

The material to be treated in the experiments was spruce wood chips. The residence time in alkaline cooking vessel 1 was 16 minutes 25 and in holding vessel 6 37 minutes in each experiment.

The impregnating liquid added before washing the chips, i.e. to the screw 2 and the impregnating device 13, was sodium sulfite NagSO 2 with a pH of about 9. Variable amounts of impregnating agent were added at both points. Zero additions were also tested for comparison purposes. The washing was performed with a cold washing liquid in order to achieve the best possible penetration of the impregnation medium in a manner known per se. Excess liquid was removed in the drying screw 5 and recycled. The pressure in the preheater 12 35 varied between 1.0 and 1.8 bar. The temperatures in the pre-evaporation vessel 1 and the retention vessel 6 were varied at about 75-95 ° C. Temperatures, pressures and amounts of chemicals added 76843 5 are shown in Table 1. The left-hand part of the first column, entitled "Test", shows the nominal amount of chemical added to the impregnator 13. The right-hand part of the first column shows the nominal pressure in the preheater 12.

table 1

Experiment Pre-steam- Pre-heating- Sulphite- Pre-impregnation- Final impregnation thymite titration 10 ° c container Tare pH kg S02 / t90 kg S02 / t90

° C

0 / 0-1.0 98 95 1.0 9.0 0 0 0 / 10-1.0 96 91 1.0 9.1 0 10.1 15 0 / 20-1.0 98 89 1.0 8.8 0 20.2 0 / 30-1.0 98 1.0 0 30.3 0 / 0-1.8 81 91 1.8 9.2 0 0 0 / 10-1.8 91 78 1.8 8.9 0 10.2 0 / 20-1.8. 98 77 1.8 9.0 0 20.4 0 / 30-1.8 97 76 1.8 8.8 0 29.1 5 / 0-1.0 93 86 1.0 9.0 4.9 0 20 · 5 / 10-1.0 68 90 1.0 9.1 4.9 9.9 5 / 20-1.0 79 91 1.0 9.0 4.9 19.8 5 / 30-1.0 82 89 1.0 7.3 5.0 29.8 5 / 10-1.3 95 36 1.27 8.1 2.45 5.5 5 / 20-1.3 94 93 1.31 8.2 2.60 10.2 5 / 30-1.3 98 32 1.23 7.1 2.6 16.7 25 5/0 -1.8 92 88 1.8 8.7 5.2 0 5 / 10-1.8 95 90 1.8 9.7 5.0 10.0 5 / 20-1.8 95 87 1.8 9.5 5.1 20.6 5 / 30-1.8 97 94 1.8 7.3 5.1 30.9 15 / 0-1.0 87 89 1.0 7.0 12.0 0 15 / 5-1.0 90 85 1.0 9.0 12.0 5.2 15 / 15-1.0 66 84 1.0 7.7 12.0 15.5 30 15 / 0-1.3 94 86 1.3 9.2 12.0 0 15 / 5-1.3 93 93 1.3 9.5 11.6 5.1 15/15 -1.3 79 87 1.3 7.8 11.6 15.0 15 / 0-1.8 78 88 1.8 9.0 11.6 0 15 / 5-1.8 85 95 1.8 9.1 11.6 5.1 15 / 15-1.8 83 81 1.8 9.0 11.6 15.0 35 6 76843

It was found that the treatment in the holding vessel significantly improved the penetration of chemicals into the wood that had been added before the chips were washed. This can be seen in Table 2 below and is also illustrated in the graphical representation in Figure 2.

Table

Sulfur content in small and large chips before and after the holding vessel. Addition of sulphite, 10 corresponding to 1.2 kg S0 £ before washing the chips.

Dry matter- Total S content% g S / kg

Chips_large_chips ^ Before the holding container 38.0 0.9

After the detention vessel 37.0 1.2

Hakkeen_gienet_lastut

Before the holding container 3 ^. ^ 1.5 20 After the holding container 35 * 3 1.7

It is evident that the efficient penetration of chemicals into the wood in combination with the retention time and temperature promoted the softening of the chips and its chemical modification. This was also manifested as an increased long fiber fraction and a reduced stick and resin content after refining, as can be seen from the following Table 3 and the graphs in Figures 3 and 4. Fig. M also clearly shows that the addition of kerni-30 cabbage must take place in two steps, so to speak, both before washing the chips and in the impregnating device, in order to achieve the lowest possible stick content, while Fig. 3 shows that water penetration into the wood together with heat treatment -35 in vessel 6 improves the long fiber fraction. The addition of sulfite in the preheating step, on the other hand, reduces the light reflectance. Graphs 3 and M also show that the best values are obtained when the total amount of chemical added is 25-35 kg SCg / to chip, but very good values can already be achieved with the addition of 10-20 kg SOg / to.

5 However, the tests performed do not clearly show the way in which the chemicals should be distributed between the pre-impregnation and the final impregnation device 13 carried out before the chip washing device 3. The following Table 3 compares some characteristic values of the screened CTMP for the production of a fibreboard treated according to the invention and according to a known treatment comprising pre-impregnation before washing but without a heat treatment period in a holding vessel 6. According to the invention, treatment in a holding vessel is carried out at atmospheric pressure.

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Claims (6)

76843 A process for producing a chemical-thermomechanical pulp from wood chips, which process comprises pre-steaming, pre-impregnating with wood and / or sulphite solution, washing, drying, final impregnation, preheating and refining, characterized in that after pre-steaming, pre-impregnation and pre-impregnation washing -saturation, preheating and refining are maintained at a temperature of at least 50 ° C for at least 10 minutes. Process according to Claim 1, characterized in that the chips are pre-impregnated with a sulphite solution, preferably sodium sulphite solution, at a pH between 4 and 11. A method according to claim 1 or 2, characterized in that the chips are kept at said temperature by steam treatment. Method according to any one of claims 1 to 3, characterized in that the chips are kept at said temperature by heating it during or after washing and then keeping it hot. Method according to any one of claims 1 to 4, characterized in that the chips are kept at said temperature for 30 to 70 minutes. Method according to one of Claims 1 to 5, characterized in that the chips are kept at a temperature of 50 to 105 ° C and preferably at a temperature of 60 to 90 ° C.