JP3378228B2 - Countercurrent multistage washing method for pulp - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pulp countercurrent multi-stage washing method in which both a non-bleaching washing line for pulp and a bleaching line having one to multiple washing stages before and after a bleaching stage such as an oxygen stage are installed in parallel. Regarding

[0002]

2. Description of the Related Art FIG. 2 shows a flow chart of a conventional pulp multi-stage washing / bleaching process in which both a non-bleaching washing line for pulp and a bleaching line for oxygen stage are installed in parallel. In FIG. 2, the pulp from the cooking / coarse selection step is stored in a pulp tank P0, washed with the filtrate from the post-stage washing machine W2 in the first-stage washing machine W1, and the filtrate obtained by washing the pulp with the washing machine W1 is the filtrate tank. Housed in F1. Part of the filtrate from the filtrate tank F1 is refluxed into the pulp tank P0 and the pulp slurry from the pulp tank P0 to adjust the pulp concentration supplied to the washing machine. The filtrate from the filtrate tank F1 is sent to the previous step and gradually taken out while being concentrated. Then, dissolved organic solids such as lignin are used as fuel for the boiler, and dissolved inorganic solids such as sodium are recovered and reused.

The pulp slurry washed by the first-stage washing machine W1 is collected in a pulp tank P1 and
From the second stage washer W2 to the second stage washer W3, W
Pulp tank P2 washed with filtrate from 3'as above
Be recovered to. One of the pulps collected in the pulp tank P2 is branched and fed to an unbleached line which is not bleached and the other is a bleached line which is bleached.

That is, the pulp sent to the unbleached line is washed from the pulp tank P2 by the washing machine W3 'in the final washing stage without passing through the bleaching step, and is recovered as unbleached pulp in the pulp tank P3' and out of the system. Taken out. In addition,
The washing water supplied to the washing machine W3 'of the final washing stage is clean water such as warm water, and the washing filtrate is collected in the filtrate tank F3' and is returned to the filtrate from the filtrate tank F3 of the third washing machine W3. And is used as cleaning water for the second-stage cleaning machine W2 in the preceding stage.

The pulp slurry sent from the pulp tank P2 to the bleaching line is sent to the third stage washing machine W3. It is washed with the filtrate from the post-stage washing machine W4 in the washing machine W3, heated to a predetermined temperature via the steam mixer SM, and fed to the pulp tank P3.

The pulp slurry from the pulp tank P3 is charged with a bleaching chemical by a chemical mixer CM, and a bleaching tower BT is obtained.
Sent to and bleached. The bleached pulp is sent to the pulp tank P4, and the fourth stage washer W4 in the latter stage is used.
Then, the washing filtrate is sequentially collected in the fifth-stage washing machine W5, the washing filtrate is collected in the filtrate tanks F4 and F5, and the pulp slurry is collected in the pulp tanks P5 and P6, respectively.

In the illustrated example, since the fifth washing machine W5 is the final washing stage, clean water such as warm water is supplied to the washing machine, and the bleached pulp washed with the washing water is supplied from the pulp tank P6 to the system. Taken out. In the figure, PS indicates a pulp slurry transfer pump, and PW indicates a washing filtrate transfer pump.

In the conventional washing and bleaching process, the washing water in the third washing stage of the pulp slurry diverged from the pulp tank P2 to the bleaching line is the filtrate from the fourth washing machine which washed the bleached pulp. Is used. However, this filtrate contains dissolved solids such as bleaching chemicals added to the pulp slurry at the bleaching stage.

Therefore, the second-stage washer W2, which is the front stage, is used.
In order to wash the pulp washed with relatively clean wash water from the filtrate tank F3 'with a filtrate having a high solid content concentration, the third stage washing machine W3 before the bleaching stage uses the solid content from the pulp. On the contrary, the solid content in the pulp is increased without being washed and sent to the next step, while the solid content in the recovered filtrate is decreased conversely. At the tier, the cleaning function was not fulfilled.

[0010]

DISCLOSURE OF THE INVENTION The present invention provides a pulp that has been washed in the washing stage by exhibiting the washing function in the washing stage before the bleaching treatment of the pulp divergently fed to the bleaching line of the oxygen stage or the like. The purpose of the present invention is to collect dissolved solids in the filtrate without increasing the amount of solids attached and to improve the bleaching property in the bleaching stage and reduce the amount of chemicals added.

[0011]

[Means for Solving the Problems] In a countercurrent multistage washing / bleaching process of pulp in which both a bleaching line for pulp and a bleaching line for oxygen stage and the like are installed in parallel, a washing filtrate from the final washing stage of the unbleaching line Is combined with the washing stage before branching into the bleaching line and the non-bleaching line, and the washing stage before the bleaching stage of the bleaching line is mixed with the washing filtrate supplied from the subsequent washing stage.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a flow chart of a multi-stage countercurrent washing / bleaching process in which both a pulp unbleaching line and an oxygen stage bleaching line according to the present invention are arranged in parallel. The same parts as those in the flowchart of the conventional unbleaching line and bleaching line of pulp in FIG.

According to the present invention, in a pulp washing line in which both a bleaching line for pulp and a bleaching line for an oxygen stage or the like are provided in parallel, the washing filtrate from the final washing stage of the unbleached pulp line is bleached with the bleaching line. It is characterized in that the washing stage before branching into the line and the washing stage before the bleaching stage of the bleaching line are mixed and mixed with the washing filtrate supplied from the subsequent washing stage.

In order to avoid duplication of explanation, only the points in FIG. 1 different from the above-mentioned prior art of FIG. 2 will be explained. The first-stage washing machine W1, the second-stage washing machine W2, and the final-stage washing machine W3 ′ that form the unbleached line
The washing filtrate having a low content of dissolved solids recovered from the 3'to the filtrate tank F3 'is passed to the fourth stage washing machine W4 of the bleaching line.
Is mixed and mixed into the washing filtrate fed from the filtrate tank F4 of the above to the third stage washing machine W3 of the preceding stage, and further, the washing mixture thus mixed and mixed is adjusted in dilution coefficient via the flow rate control valve V. The mixed amount is mixed and mixed with the washing filtrate fed from the filtrate tank F3 of the third-stage washing machine W3 to the second-stage washing machine W2 of the preceding stage.

With the above construction, in the bleaching line, the content of dissolved solids recovered in the filtrate tank F3 'in the washing filtrate fed from the filtrate tank F4 to the preceding third-stage washing machine W3 By mixing and mixing a small amount of the washing filtrate, the concentration of dissolved solids in the washing filtrate fed to the third-stage washing machine W3 decreases, and the washing action is performed without impairing the washing function in the third washing stage. The illustrated washing machine is a known drum type washing machine, but not limited to the drum type, any type of washing machine such as a press type or a substitution type is used. Further, the number of stages of the washing machine shown in the drawing may be an arbitrary number of stages depending on the application for each process.

[0016]

According to the present invention, the washing filtrate from the final washing stage of the non-bleaching line is fed to the washer of the pulp bleaching treatment before the bleaching treatment of the pulp. By confluent mixing in, it is possible to exert the cleaning function in the washing machine before the bleaching treatment of the pulp, without increasing the dissolved solids associated with the pulp washed in the conventional washing stage, The effect of improving the recovery efficiency of the dissolved solids in the filtrate taken out of the system, improving the bleaching property in the bleaching stage, and reducing the amount of chemicals added.

[Brief description of drawings]

FIG. 1 is a flowchart of a countercurrent multi-stage washing / bleaching process of pulp according to the present invention.

FIG. 2 is a flowchart of a conventionally known pulp countercurrent multistage washing / bleaching process.

[Explanation of symbols]

BT Bleach Tower CM chemical mixer F1-5 filtrate tank P1 ~ 6 pulp tank PS Pulp slurry transport pump PW filtrate transport pump SM steam mixer W1-5 washing machine

Claims (2)

(57) [Claims] 1. A washing filtrate from a washing stage of a non-bleaching line in a countercurrent multistage washing / bleaching process of a pulp in which both a non-bleaching line of pulp and a bleaching line such as an oxygen stage are installed in parallel.
A countercurrent type of pulp characterized in that the washing stage before branching into the bleaching line and the non-bleaching line and the washing stage before the bleaching stage of the bleaching line are combined and mixed with the washing filtrate supplied from the respective washing stages after the washing stage. Multi-stage cleaning method. 2. A washing filtrate from a washing stage of an unbleached line,
The washing filtrate of the bleaching stage front washing machine of the bleaching line is mixed and mixed with the washing filtrate from the bleaching stage rear washing machine, and the combined washing mixture is passed through a flow control valve V to a bleaching line and a non-bleaching line. 2. The countercurrent multistage washing method for pulp according to claim 1, wherein the washing filtrate from the latter washing stage fed to the washing stage before branching is combined and mixed.