Two-stage delignification of lignocellulosic pulp with oxygen

 

(57) Abstract:

The method relates to the oxygen delignification of pulp from lignocellulosic material in an average concentration. Extended delignification is achieved by the fact that the temperature in the first stage support below 90oWith and that the temperature difference between the stages is less than 20C. the Pressure in the first stage is 4-10 bar, and the second stage - 2-5 bar, and the pressure in the first stage is higher than in the second stage. Adding oxygen in the first stage is a large - 5-50 kg/t pulp. Lye is added only in the first stage to achieve high alkalinity in cellulose - 25-50 kg of alkali/t of pulp. The residence time in the first stage is 10-30 minutes, and the second stage - 45-180 minutes This method provides the best pulp output. 3 C.p. f-crystals, 1 Il.

The invention relates to a method for the delignification of lignocellulosic material with oxygen at an average concentration that is 8-16%.

Since the implementation of delignification with oxygen at an average concentration of cellulose little development was devoted to this process. Since then, as the chlorine-free bleaching and closing otborochnyh installations began to be of interest, all b is PA with oxygen. However, extended delignification with oxygen in one or more stages may lead to degraded quality of the pulp. However, the right conditions can lead to certain benefits.

Will be possible to maintain the best pulp output than the long cooking, that is, when cooked to a lower Kappa number.

When multi-stage method, it is possible to distribute the chemicals between stages in order to obtain optimal conditions at each stage. After this can be optimized even more.

The present invention relates to a method extended delignification with oxygen in such a way that achieved a lower Kappa number, without deterioration of the properties of cellulose. By extended delignification in accordance with the invention, the total delignification can reach 50-70% of the lignin content (Kappa number) unbleached pulp. The method is performed at a mean concentration of cellulose, in two successive stages. Features of the invention are apparent from the attached claims.

Hereinafter the invention is described in more detail with reference to the drawing, which schematically polluter is subjected to cooking cellulose with an average concentration that is, 8-16%, is pumped by the first pump 1 from the washing of brown pulp in the oxygen delignification. The first mixer 2 is used for mixing oxygen and alkali to cellulose. Then the pulp is fed to the first reactor 3, which spend the first delignification. From there, cellulose serves, perhaps with the help of the second pump 4 through the second mixer 5 for mixing steam and possibly additional oxygen to the second reactor 6 for the second stage of delignification. After the second reactor 6 pulp served in the purge tank 7 and then on to the next stage of processing.

Thus, the method assumes that the delignification is carried out in two successive stages. In the first mixer 2 is conducted as adding a large quantity of alkali, and adding large quantities of oxygen. This implies downloading 25-50 kg of alkali (NaOH) per 1 ton of pulp, preferably 25-35 kg/T. This is necessary to download the alkali may be partially achieved by ablation of the washing of brown pulp. Thus, the load in the mixer 2 can be reduced in a corresponding degree. Download oxygen will be 25-50 kg/t of pulp, preferably 30-40 kg/so

The temperature of the pulp during the settlement of the stage in the reactor 3 will be carried out at a temperature of cellulose, when she emerges from the washing of brown pulp. The residence time in the reactor 3 will be relatively short - 10-30 minutes, preferably 15-25 minutes

The pressure in the first reactor 3 is 4-10 bar. High pressure together with high alkalinity of the pulp and a large load of oxygen leads to a high rate of delignification. At the same time, the rate of decomposition of cellulose is maintained at a low level due to the relatively low temperature and short residence time.

After the first stage of delignification in the first reactor 3 pulp is served on the second stage of delignification in the second reactor 6. The temperature in the second reactor 6 will be above 90oC, i.e. higher than in the first reactor 3. However, the temperature difference is less than 20oC, preferably 10-15oC. To create the desired increase in temperature in the second mixer 5 serves pairs.

The pressure in the second reactor 6 will be 2-5 bar and lower than in the first reactor 3. The time should be relatively long, 45-180 min, preferably 60 to 120 minutes

The second stage of delignification first of all is a long stage of extraction, where in relation to the first stage of fever and >C achieved a good rate of extraction/leaching.

Due to the fact that the second stage does not produce additional alkali loading even in order to compensate for its consumption in the first stage, the alkalinity of the pulp in the second stage can be maintained relatively low. Through this it is possible to substantially avoid the decomposition of cellulose in spite of the high temperature and long period of stay.

In the second mixer 5 you can add a small amount of oxygen, which can be up to 5 kg/ton of pulp, which may be completed loading of oxygen in the first stage, in order to increase the partial pressure of oxygen.

The residence time in the second stage is determined in connection with temperature in order to achieve optimal results, namely the assumed long delignification without degradation of cellulose. Thus, higher temperatures mean shorter time.

The invention is not limited to the above and may be modified within the scope of the inventive concept.

1. Two-stage method of oxygen delignification of pulp from lignocellulosic m is the atur at the first stage support below 90oC, and the second stage is above 90oC, the temperature difference between stages is less than the 20oC, the pressure in the first stage is 4 to 10 bar, and the second stage - 2 - 5 bar, the pressure in the first stage is higher than in the second stage, the addition of oxygen in the first stage is a high 25 - 50 kg/t of pulp, alkali added only in the first stage to achieve high alkalinity cellulose, 25 to 50 kg of alkali/ton of pulp, and the residence time in the first stage is 10 to 30 minutes, and the second stage 45 to 180 minutes

2. The method according to p. 1, characterized in that the temperature increase between the two oxygen stages is 10 - 15oC.

3. The method according to any of the preceding paragraphs, characterized in that the residence time of pulp in the first stage is 15 - 25 minutes, and the second stage - 60 - 120 minutes

4. The method according to any of the preceding paragraphs, characterized in that the additional oxygen load in 0 - 5 kg/t of pulp in the second stage.

 

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19 cl, 12 tbl, 7 ex

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