FI101721B - Method and apparatus for continuous cooking and washing of pulp in a continuous digester - Google Patents

Description

101 '/ 2 "ι

Method and apparatus for continuous cooking and washing of pulp in a continuous digester

The present invention relates to a continuous, so-called continuous, so-called pulping process for use in the wood processing industry. Improvement of Kamyr soup. In particular, the invention relates to the improvement of the washing efficiency of the washing zone used in connection with said cooker.

10 In a continuous process according to traditional technology, i.e. the so-called The Kamyr cooker has a so-called Hi-Heat washing zone, where the mass cooked at the top of the digester is washed at the bottom of the digester with hot water, usually well over 100 degrees, due to the overpressure in the digester. The basic operating principles of the mentioned Kamyr-15 cooker are shown in e.g. U.S. Pat. No. 4,668,340 and EP-A-0 476 230. Wash water, usually from the wash filtrate from the scrubber following cooking, is introduced into the bottom of the digester, where part of the filtrate is used to dilute the cooked mass and another 20 of the filtrate flows countercurrently to the digester. to screens for separating liquid and liquid-dissolved matter from the mass. The pulp is washed in the Hi-Heat section at the bottom of the digester, where the pulp flows downwards and the washing water upwards-25 upstream. The screen-separated wash liquor is heated in the wash liquor circuit so that the temperature of the upstream liquid is 120 to 170 degrees, depending on the process options. At the bottom of the cooker is an outlet device, also known as a floor scraper. The pulp is discharged from the digester at the bottom of the tower with the aid of said bottom scraper] through a butt valve.

Thus, in Hi-Heat washing, the washing liquid is brought to the bottom of the digester, of which part of the washing liquid in the first cool washing step flows upwards to the above-mentioned screens, while a part remains to dilute the cooked mass. With sieves, the washing liquid in which, for example, e.g. organic substances, 101721 2 \ <are separated from the pulp and returned to the pulp through the heat exchanger to the Hi-Heat washing zone. In other words, the same liquid is circulated in the digester first in the colder and then heated.

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On the other hand, in the TAPPI publication "A Mathematical Model of Fractional Pulp Washing and Applications in a Bleach Plant",

Tervola, Henricson, Gullichsen; Tappi Pulping Conference,

Atlanta, November 1993, Book 1, ss. 151 - 154 deals with 10 ns. fractional washing with bleach. In one figure of said publication, a diffuser (either pressurized or atmospheric) is shown, the sieve zone of which is divided into two parts so as to obtain two filtrate streams.

The first filtrate stream at the beginning of the wash is dirtier, i.e. 15 contains more organic matter and cooking liquor, and the second, later, cleaner. Another of the images in the article presents the so-called DD ™ scrubber, in which two filtrate streams with different properties are obtained in the same way.

In experiments with the above-mentioned scrubbers, it has been found that the efficiency of wash-20 is improved by the use of fractional washing by 10-25, on average about 20%.

Washing efficiency generally refers to the ability of the washing step to separate impurities from the pulp. Improving washing efficiency provides a variety of benefits. For example, improving the washing efficiency of a kettle can, at best, result in one whole scrubber being saved in the washing step. Further, the improvement in washing efficiency results in the use of smaller amounts of water in the washing, resulting in less volatile liquids in the after-treatment. The chemical consumption of bleaching is also reduced because there are fewer chemical-consuming impurities among the pulp. Furthermore, with the amount of contaminants and the consumption of chemicals being lower, less waste is released from the process into water bodies.

At no point in the past, however, has the use of fractional washing been proposed. Kamyr digester.

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It is characteristic of an embodiment of the method according to the present invention that at least two washing liquids of different purity are introduced into the washing zone of the continuous digester.

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The device according to the present invention is characterized in that the bottom part of the digester and the washing zone are provided with at least two separate devices for feeding two washing liquids of different purity to the digester.

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The good results obtained in the experiments with the invention described above are based on the fact that the washing with a dirty organic filtrate from the scrubber takes place at the top of the digester washing zone, with most of the washing liquid and fibers dissolved in the fibers flowing countercurrently to the digester. .

In the following, the method and the device according to the invention will be explained in more detail with reference to the accompanying figures, of which Figure 1 shows a so-called The lower part of the Kamyr digester, Fig. 2 shows the fractional washing already mentioned in the above-mentioned Pin article 25 in connection with the diffuser, Fig. 3 shows the corresponding fractional washing so-called In connection with a DD washer, Figure 4 shows a so-called DD washer according to a preferred embodiment of the invention. The bottom of the Kamyr cooker, 30 in Figure 5 is shown in more detail in the continuous section shown in Figure 4. connection of a digester and a fractionating scrubber, Figures 6 and 7 show two alternative embodiments for introducing washing liquid into the lower part of a continuous digester.

Figure 1 shows a continuation of the conventional technique, i.e. the so-called Kam-cooker Hi-Heat wash zone. In Fig. 1, the washing water is introduced to the bottom of the digester 10 along the line 12 along 101721 4. At the bottom there is an outlet device 14, which with the second so-called is a bottom scraper. The pulp is discharged from the digester at the bottom of the tower 10 through a butt valve 16. The pulp is washed in the Hi-Heat section 18 of the digester 10, where the pulp flows downstream 5 and the washing water upstream. The wash liquid is heated in the wash cycle 20 so that the temperature of the upstream liquid is 120 to 170 degrees depending on the process options.

Figure 2 schematically shows a diffuser 30 (either pressurized or atmospheric) into which the washable pulp is fed from the joint 32 and the washed pulp is removed from the joint 34. The sieve zone of the diffuser 30 is divided into two parts so that two filtrate streams 36 and 38 are obtained. -15 stream 36 at the beginning of the wash is dirtier, more organic, and another 38, later, cleaner.

Figure 3 shows a drum-type so-called DD ™ scrubber 40, to which the washable mass is fed from the joint 42 and the washed mass 20 is removed from the joint 44. In a manner corresponding to the diffuser, two filtrate streams 46 and 48 of different purity are obtained.

The solution according to a preferred embodiment of the invention according to Fig. 4 shows the bottom part of the continuous digester 10 already known from Fig. 1, into which the first washing liquid F1 is introduced from line 52. According to the invention, the so-called A second wash liquid F2 from line 54 is introduced into the Hi-Heat wash zone by feeding it to the wash liquid circuit 56. The wash liquid circuit 56 30 consists of () arranged inside the wall of the digester.

from the screening devices 58, the circulating pump 60, the heat exchanger 62 and the heated washing liquid return / supply devices 64. The screening devices 58 separate a liquid from the pulp into which both solids and cooking liquor have separated from the pulp.

In the solution according to the invention, both the liquid separated from the pulp and the washing liquid entering the washing liquid circuit 56 line 54 are heated in a heat exchanger 62. Said washing liquid, F2, is preferably taken at such a point in the process that it is dirtier, i.e. more organic. It is contacted in the Hi-Heat zone with a completely unwashed mass. Correspondingly, the washing liquid F1 that comes into contact with the pulp in the bottom section of the cleaner cooker is cleaner, te. taken from a point in the process that contains less organic matter.

Figure 5 shows the bottom part of a continuous digester 10, already known from the previous figures, from which the pulp is removed with the aid of a bottom scraper 14 to a butt line 66 leading to a scrubber 40 described as a drum scrubber, preferably a so-called drum scrubber. As a DD ™ scrubber, although a diffuser (cf. Fig. 3) or some other washing device capable of fractionation can be used quite well. In the embodiment of the figure, the washing liquid introduced into the scrubber 40 along the line 68 is divided into two fractions F1 and F2 in the pipelines 70 and 72 in the embodiment of the figure. However, the washing liquid can already be introduced to the scrubber in several levels. The cleaner fraction F1 is piped along line 70 to the bottom of the continuous digester 10. The amount of fraction F1 is preferably 4-14 mV pellets, more preferably 4-10 mV pellets and most preferably 6-10 mV pellets. The cleaner washing liquid is fed from at least one of the following points: the nozzles on the bottom of the digester, the nozzles on the wall of the bottom of the digester and the nozzles on the arms of the rotating, hollow bottom scraper. In other words, the washing liquid F1 is fed essentially to the bottom of the digester.

30 The dirtier fraction F2, which contains more substances dissolved in the cooking, is in turn fed along the line 72 into the Hi-Heat washing liquid circuit 56 of the digester 10. The amount of the fraction F2 is of the order of 1-6 mV per ton of pulp, preferably 2-4 m3 / ton of pulp. As already described above, the washing liquid circuit 56 consists of digester strainers 58, a circulation pump 60, a heat exchanger 62 and feeders 64. According to one embodiment, the washing liquid F2 is fed between the circulation pump 60 and the heat exchanger 62. However, it is essential that the filtrate F2 can either be introduced into the connecting pipes outside the digester connecting the components of the washing liquid cycle or led directly into the pulp inside the digester. The heated washing liquid of the heat exchanger 5a 62 is led through the supply devices 64 downwards in the washing part of the digester 10, presumably still into the pulp flowing in the form of chips. According to one embodiment, the heated washing liquid is fed into the pulp to a level slightly higher than the screens of the washing cycle.

10 Some of the heated washing liquid rises upwards in the digester 10 with the heating cycle, heating the pulp. A portion of the liquid fed to the wash cycle is removed from the pulp through screens 58. Throughout the journey, from the digester 10 to the scrubber 40, dry matter, especially organic matter, is released from the fibers of the pulp for two different reasons. When the chip form of the pulp breaks, the organic dry matter separates into the aqueous phase. Organic matter is also released from the fibers by diffusion and extraction. The extraction can be facilitated by keeping the buffer line 66 hot, preferably between 80 and 2070 degrees, most preferably between 80 and 150 degrees. If the scrubber used is not pressurized, the appropriate temperature is naturally lower, i.e. in the order of 80 to 95 degrees. In this case, during the washing cycle 56, the bottom of the digester and the butt line 66, the organic matter dissolves and this substance is largely returned to the digester 10 via the line 72.

Fractionation of the washing liquid improves the washing efficiency for two different reasons: the dirtier liquid is returned to the previous point 30 process, and the organic matter dissolves between the digester and the scrubber and is returned to the dirtier wash water and returned to the digester, assuming that the countercurrent wash liquid stream drifts to the top of the digester and from there on to recover chemicals.

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Figure 6 shows a way according to a preferred embodiment of the invention for introducing the washing liquid into the digester 10 in the bottom part. In the embodiment of the figure, the cleaner washing liquid F1 is introduced to the bottom level of the digester 10 via the pipeline 70 and the dirtier washing liquid F2 through the shaft 78 of the bottom scraper 14 to the nozzle shaft 80 and further to the nozzle arms 82 or the like. As the nozzle (s) 82 or nozzle arms rotate, the wash liquid is evenly distributed throughout the mass over the entire cross-sectional area of the digester 10.

Figure 7 shows a way according to another preferred embodiment of the invention for introducing the washing liquid into the digester 10 in the bottom part. The washing liquid F1 is introduced as in Fig. 6, but the dirty liquid F2 is introduced along the pipe 84 passing through the shaft 78 of the bottom scraper 14 into the center of the digester. As it absorbs through the pulp bed toward the sieves of the scrubber 58, the scrubbing liquid is evenly distributed in the diameter direction of the digester 10.

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As can be seen from the above, the fractional washing previously described in connection with water bleaches in a scientific article has also been able to be applied to pulp cooking with promising results. It should be noted, however, that only a few preferred embodiments of the invention have been described above, which are not intended to limit the invention in any way from what is set forth in the appended claims. It is also worth noting that, although it has been shown above that the buffer line leads directly from the digester to the scrubber, a mass thief tank, an extraction tank or a pumping tank, for example, can be placed in the buffer line 30 as required. On the other hand, it should be remembered that although it has been described above that the washing liquids fed to the digester come from the next scrubber in the process, it is clear that the washing liquids can be introduced into the digester from somewhere else or even outside the process.

Claims (18)

A method for continuous boiling and washing of pulp in a continuous boiler, in which process in the pulp flowing down into the digester, washing liquid is mixed in the boiler's so-called. wash zone, said washing liquid is diverted from the digester, it is heated and fed back to the digester, characterized in that in the wash zone is introduced to be used as a wash liquor, at least two to its degrees of purity, different filtrates for the detergent following the digester to effect the washing in the digester . 2. A process according to claim 1, characterized in that of the washing liquids, the one containing the most organic substance is first mixed in the pulp. at the top of the boiler. Method according to Claim 1, characterized in that in the boiler's so-called. washing liquid circulation is added to that of the washing liquids containing the most organic matter. 20 Method according to claim 1, characterized in that the purest of the washing liquids, ie. the one containing the least organic matter is added to the pulp substantially at the bottom of the boiler. 25 5. A process according to claim 3, characterized in that said washing liquid is added in an amount of 1-6 m3 / ton of pulp, most preferably 2-4 m3 / ton of pulp. 30 6. A process according to claim 4, characterized in that, at the bottom of the boiler, washing liquid is added in an amount of 4 - 14 m 3 / t cellulose pulp. Process according to Claim 4, characterized in that, in the bottom of the digester, washing liquid is added in an amount of 4 - 10 m 3 / ton cellulose pulp. 101721 8. A process according to claim 4, characterized in that, in the bottom of the boiler, washing liquid is added in an amount of 6-10 m3 / ton cellulose pulp. 5 9. A process according to claim 1, characterized in that the cooked mass is measured into the washer (30, 40), from which two different degrees of purity are introduced into the digester, of which filtrate the filtrate F2 containing more organic matter is introduced into the digester. (10) washing liquid circulation (56) and the filtrate F1 containing less organic matter are substantially directed to the bottom of the boiler (10). Process according to claim 2 or 9, characterized in that the more organic substance containing the filtrate is heated to a temperature of 120-170 ° C before being mixed into the pulp. 11. A process according to claim 9, characterized in that the pulp is introduced into the washer (30, 40) at a temperature of 80 - 170 ° C, most preferably 80 - 150 ° C. Devices for continuous boiling and washing of pulp in a continuous boiler, which boiler consists of a boiler (10), a washing zone disposed therein with wash liquid circulation (56), which includes devices (58) for draining liquid from the boiler (10). ), liquid circulation devices (6 p), liquid heating devices (62) and liquid feeding / feeding devices (64), and a bottom cutter (14) provided for removing pulp from the boiler (10), characterized in that the bottom part and the washing zone of the digester (10) are provided with at least two separate devices for feeding two tiles of different degrees of purity into the digester (10). 35 Devices according to claim 12, characterized in, said inlet devices are two in number, of which the first one is connected substantially to the bottom of the boiler (10) and the second to the washing liquid circulation either purely physically or at least functionally. Devices according to claim 12, characterized in that the digester (10) is connected to a digester through a blow line (66) to a fractional washer (30, 40) which is for its part connected to at least two filtrate lines (70, 72). 10 Devices according to claim 14, characterized in that the filtrate line (70) is connected substantially to the bottom of the boiler (10) to direct the cleaner, less organic substance containing the filtrate to the boiler (10) for use as a washing liquid. Devices according to claim 14, characterized in that the filtrate line (72) is connected to the washing liquid circulation (56) of the boiler (10) to direct the more organic substance containing the filtrate to the boiler (10) for use as a washing liquid. Devices according to claim 14, characterized in that the filtrate line (72) is connected either through the shaft (78) of the bottom shaver (14) to a nozzle shaft (80) with nozzle arm and nozzle (82) or to a pipe (84), through which the wash liquid is measured into the pulp, or to some of the wash liquid circulation connection (56) outside the digester (10), which tube connects the wash liquid circulation components (56). Devices according to claim 12, characterized in that the fractional washer is a drum washer, atmospheric diffuser or pressure diffuser. 35