Method for producing a fibrous material

Abstract

A method for producing a fibrous material from lignocellulose from wood, preferably in the form of wood chips. The lignocellulose material is impregnated with a mixture of sodium sulfite and sodium bisulfite and subsequently undergoes a comminution process in a refiner. Additional chemicals from a mixture of sodium sulfite and sodium bisulfite are directly introduced into the refiner, allowing optimal conditions to be set for both additive flows of chemicals such that the process can be operated in an energetically advantageous manner and corrosion and scale formation in the refiner and subsequent aggregates can be prevented as much as possible.

Claims

1. A method for producing pulp from a lignocellulose material made from wood in a manner that avoids or reduces corrosion and coating in a refiner, where the lignocellulose material is impregnated with chemicals from a mixture of sodium sulfite and sodium bisulfite in a reactor and subsequently grinded in the refiner, comprising: feeding chemicals to the reactor during impregnation of the lignocellulose material; and feeding chemicals directly to the refiner, wherein the chemicals comprise a mixture of sodium sulfite and sodium bisulfite, the chemicals fed to the reactor during impregnation have a pH within a range of 6.0-7.5, and the chemicals fed to the refiner have a pH within a range of 4.0-5.5 and that is sufficient to avoid or reduce corrosion and coating in the refiner.

2. The method according to claim 1, wherein the chemicals fed to the refiner have a pH within the range of 4.2-4.5.

3. The method according to claim 2, wherein chemicals fed to the reactor during impregnation have a pH within the range of 6.5-7.0.

4. The method according to claim 1, wherein chemicals fed to the reactor during impregnation have a pH within the range of 6.5-7.0.

5. The method according to claim 1, wherein the lignocellulose material is in the form of wood chips.

6. The method according to claim 1, wherein the chemicals fed to the reactor during impregnation and the chemicals fed to the refiner combine to 100%, characterized in that 60-80% of said 100% are added to the reactor during impregnation.

7. The method according to claim 6, characterized in that impregnation takes place at a temperature within a range of 80-170° C.

8. The method according to claim 7, characterized in that impregnation takes place at a temperature within the range of 120-140° C.

9. The method according to claim 1, characterized in that impregnation takes place at a temperature within a range of 80-170° C.

10. The method according to claim 9, characterized in that impregnation takes place at a temperature within a range of 120-140° C.

11. The method according to claim 1, characterized in that the total quantity of chemicals added amounts to 1-20 kg of chemicals per ton of wood.

12. The method according to claim 1, characterized in that the total quantity of chemicals added amounts to 10-15 kg of chemicals per ton of wood.

13. A method of producing pulp from a lignocellulose material made from wood, where the lignocellulose material is impregnated with chemicals from a mixture of sodium sulfite and sodium bisulfite in a reactor and subsequently grinded in a refiner, comprising: feeding a wood material to a reactor for impregnation and adding chemicals comprising sodium sulfite and sodium bisulfite having a pH adjusted to reduce or prevent corrosion and coating in the refiner and within a range of 6.0-7.5 to the reactor during impregnation to yield impregnated wood material; transferring the impregnated wood material from the reactor to a refiner and adding chemicals comprising sodium sulfite and sodium bisulfite having a pH adjusted to reduce or prevent corrosion and coating in the refiner and within a range of 4.0-5.5 directly to the refiner, wherein impregnation in the reactor occurs at a temperature within a range of 80-170° C.

14. The method according to claim 13, wherein the chemicals fed to the refiner have a pH within the range of 4.2-4.5.

15. The method according to claim 13, wherein chemicals fed to the reactor during impregnation have a pH within the range of 6.5-7.0.

16. A method of producing pulp from a lignocellulose material made from wood in a manner that avoids or prevents corrosion and coating in refiner plates of a refiner, where the lignocellulose material is impregnated with chemicals from a mixture of sodium sulfite and sodium bisulfite in a reactor and subsequently grinded in a refiner, comprising: providing chemicals comprising a mixture of sodium sulfite and sodium bisulfite; feeding a wood material to a reactor for impregnation and adding 60-80% of the chemicals at a pH within a range of 6.0-7.5 to the reactor during impregnation to yield impregnated wood material; and transferring the impregnated wood material from the reactor to the refiner and adding the rest of the chemicals at a pH within a range of 4.0-5.5 directly to the refiner at a grinding zone, wherein the impregnation in the reactor occurs at a temperature within a range of 80-170° C., wherein the chemicals added during impregnation amount to 60-80% of the chemicals used in the reactor and the refiner, and wherein the chemicals added to the refiner amount to 20-40% of the chemicals used in the reactor and the refiner.

17. The method according to claim 16, wherein the chemicals fed to the refiner have a pH within the range of 4.2-4.5.

18. The method according to claim 16, wherein chemicals fed to the reactor during impregnation have a pH within the range of 6.5-7.0.

19. The method according to claim 1, wherein the ranges of pH are sufficient to prevent or avoid deposits and coating of calcium sulfite on refiner plates of the refiner and any gaseous sulfer dioxide formed in a refiner zone of the refiner is condensed with steam.

20. The method according to claim 13, wherein the ranges of pH are sufficient to prevent or avoid deposits and coating of calcium sulfite on refiner plates of the refiner and any gaseous sulfer dioxide formed in a refiner zone of the refiner is condensed with steam.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The invention will now be described in examples and referring to drawings, where the figure contains a flow chart of a pre-treatment plant with impregnation and subsequent grinding in the refiner.

(2) The FIGURE shows an example of a plant arrangement according to the invention.

DETAILED DESCRIPTION

(3) Wood chips, which can be pre-treated if necessary, are taken from a storage bin 1 and fed to a reactor 2 for impregnation. A chemical is added through a pipe 3 at the beginning of this reactor. This chemical is a mixture of sodium sulphite and sodium bisulphite. The chemical added here has a pH of approximately 6.5-7.5 and amounts to some 60-80% of the total chemicals added. It has been shown that 60-80% of the reaction is already complete after a short time, often only a few seconds of reaction time, at a pH of 6.5-7.0. As a basic principle, the pH can be between 6.0 and 7.5. The impregnated chips are fed on a conveyor 4, for example a screw conveyor, to a refiner 5 for grinding. At the same time, the remaining quantity of chemicals, amounting to approximately 20-40% and again being a mixture of sodium sulphite and sodium bisulphite, is fed through a pipe 6. Besides the chemicals being added directly in the grinding zone of the refiner 5, chemicals can also be fed into the grinding zone together with the dilution water through holes in the stator refiner plates. Here, too, it is a mixture of sodium sulphite and sodium bisulphite, preferably with a pH of 4.0-4.5. As a basic principle, the pH here can be between 4.0 and 5.5. This results in a pH in the refining zone that prevents deposits and coating on the refiner plates, especially calcium sulphite coating. If gaseous SO.sub.2 forms in the refining zone, this would be carried off with the recycled steam 7 and then absorbed or neutralized by lignocellulose material with a higher pH. The steam 7 can be fed to a plug screw feeder after the storage bin 1 in order to heat the chips. Additional steam is normally fed to a heat recovery plant. As addition of the chemicals, particularly the bisulphite, is split up, the pH can be adjusted optimally to the given needs. In this way, a low pH in the grinding process can keep the specific energy consumption down while securing the strength and optical properties of the pulp and at the same time avoiding corrosion and coating in the refiner and subsequent apparatus.

(4) The invention is not limited to the examples as described. In fact, it can be applied both to hardwood and softwood.