JP3361279B2 - Method for controlling dissolved solids during pulp production - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing kraft pulp.

[0002]

According to the conventional knowledge of cellulose kraft pulp manufacturing technology, soluble organic matter (DOM)-which is mainly composed of dissolved hemicellulose and lignin, is dissolved cellulose, easily extracted. Concentrations of active substances and also other substances extracted from the wood by the cooking process, etc .-- before the active cooking chemicals in the liquor can react with the lignin that remains or is originally present in the wood. It is known that the drug is consumed to interfere with the delignification process and has a detrimental effect on the latter stage of the cooking process. Except for the latter part above, it is believed that the effect of DOM concentration in other parts of the digestion is not significant according to conventional knowledge.

The disturbing effect of DOM on the latter stage of cooking is due to the fact that modern continuous cooking processes, especially New York State,
It is minimized by using the EMCC® digester involved in the manufacture and sale of Kamens, Inc. of Glens Falls. In this case, the liquor (including white liquor) is countercurrently flown at the end of the digestion, so at the end of the "bulk delignification" stage and at all of the so-called "final delignification" stages. This is because the DOM concentration decreases.

[0004]

What has been found according to the present invention is that DOM not only adversely affects cooking at the end of the cooking stage in the first place, but the presence of DOM does not impair any stage of the cooking process, namely It also has an adverse effect on the strength of pulp produced during the early, middle, or late stages of the overall delignification stage.

Although the mechanism by which DOM affects pulp fibers, and thus the adverse effect on pulp strength, has not been clearly elucidated, the mass transfer rate of alkali-extractable organic substances that permeate the cell membrane of fibers is reduced. Is caused by the DOM around the fiber, and that the crystalline region of the fiber has a different extractability compared to the amorphous region (that is, the node portion). There is.

Regardless, what has been made clear by the present invention is that minimizing DOM levels (concentrations) during all stages of cooking significantly increases pulp strength. What has been found according to the present invention is that DOM
When the level of is brought close to zero in all stages of kraft cooking, the tear strength of pulp is greatly increased, that is, it is about 25% (eg, 27%) at 11 km tension as compared with the conventionally produced kraft pulp. Is also increasing. Decreasing the level of DOM to half or a quarter of normal levels will significantly increase pulp strength.

In state-of-the-art kraft cooking cans, the DOM concentration is above 130 grams / liter (g / l) at some points during kraft cooking, and at many points during kraft cooking (eg, Kamiya Corporation). MCC (registered trademark)
10 in the bottom circulation section, trim circulation section, upper section and main extraction section and MC circulation section in continuous digester
It is not uncommon for it to exceed 0 g / l. Even so, the DOM level is maintained at about 30-90 g / l in the wash circulation (following conventional technical wisdom).

In such a conventional situation, the lignin component in the DOM is 60 g / l or more, actually 100 g / l or more, and the hemicellulose component in the DOM is 20 g / l.
It's not uncommon to see more than this. Dissolved hemicellulose is suspected of having a significant effect, but the dissolved hemicellulose component has a greater negative effect on pulp strength than lignin (eg, by adversely affecting the mass transfer of organic matter out of the fiber). It is not yet known whether or not, or vice versa, or whether the effects are synergistic. Minimize DOM concentration at all stages of kraft cooking in order to positively affect the bleachability of the pulp, reduce drug consumption, and, most probably, increase pulp strength. It was first recognized in accordance with the present invention that it should. If the level of DOM is minimized, it may be possible to design a smaller continuous digester with the same throughput, and even if a batch system is used, the benefits of continuous digester can be obtained. It is possible that you can get some.

Many of these beneficial results show that DOM concentrations of 10 at substantially all stages of kraft cooking (ie, early, mid, or late in the overall delignification process).
It can be expected to be maintained by maintaining 0 g / l or less, preferably about 50 g / l or less (the closer the DOM concentration is to zero, the more preferable results are obtained). Lignin component less than 50g / l (preferably about 25g / l
It is especially preferred to maintain the hemicellulose level below 15 g / l (preferably below about 10 g / l).

It has also been found according to the invention that the adverse effect of DOM concentration on pulp strength can be passivated (detoxified), at least to a large extent. According to what has been found according to this aspect of the invention, the black liquor is withdrawn and is disclosed in US Pat. No. 4,929,3.
Pressure heat treatment according to No. 07 (which is incorporated herein by reference), for example at a temperature of about 17
At 0-350 ° C. (preferably 240 ° C.) for about 5-90 minutes (preferably about 30-60 minutes) followed by reintroduction, an increase in tear strength of up to about 15% can be obtained. . The mechanism by which DOM passivation occurs during heat treatment is also not completely understood, but is consistent with the above hypothesis, and the results are factual and dramatic for pulp strength. is there.

According to the present invention, various methods for increasing the strength of kraft pulp while paying attention to the above-mentioned adverse effects of DOM on the pulp strength are provided for both continuous type and batch type systems.

The present invention also provides an apparatus for providing kraft pulp with increased strength and achieving the desired results of the present invention.

Further, according to the present invention, the H factor can also be significantly reduced, eg, the H factor achieving a given number of kappa is reduced by at least about 5%.
Also, the consumption of available alkali can be significantly reduced, eg, by at least about 0.5% (eg, about 4%) on a log basis to achieve a particular Kappa number. Furthermore, improved bleaching properties can be achieved, for example an increase in ISO whiteness of at least one unit at a particular overall sequence copper factor.

According to one aspect of the present invention, there is provided a method of producing kraft pulp by cooking a comminuted cellulosic fibrous material. The method is continuous, at different stages in the kraft cooking of the material from which pulp is to be produced,
(A) extracting a liquor containing substantially sufficient levels of DOM to adversely affect pulp strength, and (b) more effective than the extracted liquor to positively affect pulp strength. A liquid with a substantially low level of DOM,
The step of substituting a part or all of the extracted liquid is included. Step (b) is selected from the group consisting essentially of water, substantially DOM free white liquor, pressure heat treated black liquor, washer filtrate, cold blow filtrate, and mixtures thereof. It is usually done by replacing the withdrawn liquid with a liquid. For example, at a stage of at least one stage during cooking, black liquor is drawn out, and under pressure heat conditions to significantly passivate the adverse effect of DOM (for example, under a pressure higher than normal pressure, 170 to 35).
About 5 to 90 minutes at 0 ° C and at least 2 above the cooking temperature
The black liquor is treated at a temperature higher than 0 ° C).

As used herein and in the claims, the term "effective DOM" means the portion of the DOM that affects pulp strength, H factor, effective alkali consumption, and / or bleachability. . A solution having a low effective DOM concentration is obtained by passivation (except for the effect on bleaching property) or by using a solution having a low DOM concentration from the beginning.

The method of the present invention can be carried out in a continuous upright digester, in which the steps (a) and (b) are carried out in at least two different height positions in the digester. it can. Also typically, the replacement liquid from step (b) is heated to bring it to substantially the same temperature as the withdrawn liquid before introducing the replacement liquid into the material to be cooked and contacting it. There is also step (c). Steps (a) and (b) can be performed at the stages of infiltration, near the beginning of cooking, in the middle of cooking, and at the end of cooking, ie at substantially all stages of the overall delignification process.

According to another aspect of the invention, near the initial stage of kraft cooking, (a) extracting a liquor containing a level of DOM substantially sufficient to adversely affect pulp strength, and ( b) Kraft cooking comprising replacing some or all of the extracted liquor with a liquor having a substantially lower level of available DOM than the extracted liquor to positively affect pulp strength. A method is provided.

According to another aspect of the present invention, in the step of infiltrating the cellulosic fibrous material, (a) extracting a liquor containing a level of DOM substantially sufficient to adversely affect pulp strength, and ( b) Kraft cooking comprising replacing some or all of the extracted liquor with a liquor having a substantially lower level of available DOM than the extracted liquor to positively affect pulp strength. A method is provided.

According to yet another aspect of the present invention, (a)
Extracting black liquor in contact with pulp at a given digestion stage, (b) pressure heat treating the black liquor to a temperature sufficient to significantly passivate the adverse effects of DOM therein on the pulp. And (c) reintroducing the DOM passivated black liquor in the liquor to re-contact with pulp at a given cooking stage.

The present invention also includes the kraft pulp produced by the above method. This kraft pulp differs from the conventionally produced pulp in the following points. That is, compared to kraft pulp produced under the same conditions except that there is no DOM maintenance or removal step of the present invention, a specific tensile (eg, 9
Tear strength as high as 25% at km tension, or 11 km tension) or as high as 15% when using passivated black liquor (eg, at least about 1).
0% greater) tear strength.

The present invention can also be applied to a batch kraft cooking method of cellulose fiber material using a tank containing black liquor and a batch digester containing cellulose fiber material. In such a batch kraft cooking process of the present invention, (a) a step of pressure heat treating the black liquor to a temperature sufficient to passivate the adverse effect of DOM in the black liquor on the pulp, (b) There are two steps: feeding the black liquor to the digester to contact the cellulosic fiber material in the digester. In step (a), the black liquor is treated at a pressure higher than normal pressure at a temperature of about 170 to 350 ° C. for about 5 to 90 minutes (typically at least about 190 ° C. for about 30 to 6).
Heating for 0 minutes and at a temperature of at least about 20 ° C. above the cooking temperature), and step (b) comprises adding black liquor and white liquor to a digester to effect the cooking of the cellulosic fibrous material. It can be done by supplying at the same time.

According to another aspect of the present invention, there is provided an apparatus for kraft cooking cellulose pulp. This device consists of the following components. That is, an upright continuous digester. At least two withdrawal / extraction screens at different heights of the digester and at different digestion stages. Circulation and extraction lines attached to each screen. Then, a means for supplying a replacement liquid to each circulation line in order to replenish the extracted liquid to the extraction line. Each circulation loop is usually equipped with a heater, and it is possible to attach a separate type permeation tank to the digester. Even in this permeation tank, a liquid with a high DOM concentration should be extracted and replaced with a liquid with a low DOM concentration. (Also in the return line between the top of the permeation tank and the high pressure feeder).

The present invention also provides pulp at least 1 daily.
At a rate of 00 tonnes, comminuted cellulose is obtained by carrying out step (a) of continuously contacting or withdrawing a substantially DOM-free cooking liquor with a cellulosic material until the pulp kraft cooking is completed. It also relates to a commercial method for kraft cooking fibrous materials. In this method, a batch digester, preferably having a capacity of at least 8 (eg, 8-20) tons / day, is used, and prior to step (a), feeding cellulosic fibrous material to the digester (b). ) Is further performed, and after step (a), it is preferable to further perform step (c) of discharging the kraft pulp from the digester.

The present invention also relates to a batch digester system for carrying out this aspect of the invention, wherein each batch digester has a capacity of at least 8 tons per day (ie a commercial scale different from laboratory scale). Scale).

The present invention also provides a number of different types of continuous digester cans, conventional MCC®, to significantly dilute the effective DOM of the cooking liquor during at least one of the early or middle stages of cooking. It relates to modifying and transforming Kamiya digesters or EMCC (R) Kamiya digesters. By arranging the extraction screen and the circulation screen in a specific order, the advantageous result of the present invention is achieved in the existing digester, which is a single tank pressure type, a two tank pressure type. In all conventional continuous digesters, including, simply rearranging the routes of many fluid streams to produce low concentrations of DOM at various locations.
This can be achieved by introducing a diluent and / or a white liquor.

The main object of the present invention is to produce high strength pulp and / or typically to reduce H factor and effective alkali consumption and improve bleachability. This and other objects of the invention will be apparent upon reading the detailed description of the invention and upon review of the appended claims.

[0027]

DETAILED DESCRIPTION OF THE INVENTION FIG. 1 is a system for a two-vessel pressure-type kraft digester, such as the system involved in the sale of Kamier, Inc., Glenfort, NY, modified to carry out an exemplary method of the present invention. Shown system. Of course, any other existing continuous digester system can be modified to practice the present invention. These also include a single-tank pressurized digester, a single-tank vapor-phase digester, and a two-tank vapor-phase digester.

In the exemplary embodiment shown in FIG. 1, a conventional infiltration vessel (IV) 10 is connected to a conventional upright continuous digester 11. The comminuted cellulosic fibrous material entrained with water and cooking liquor is transported from a conventional high pressure feeder through line 12 to the top of permeation tank (IV) 10 and a portion of the liquor is withdrawn from line 13 as is conventional. It is taken out and returned to the high pressure feeder.

According to the present invention, DOM (as used in the specification and claims, is composed of dissolved organic matter, mainly dissolved hemicellulose and lignin,
The liquor is pumped in line 1 to reduce the concentration of dissolved cellulose, extract, and other substances extracted from the wood by the kraft cooking process, etc.).
5 (ie from the top of tank 10) and treated at step 16 to remove or passivate DOM or its selective components. Step 16 includes a sedimentation step (for example, p
By reducing H to 9 or less), absorption step (eg cellulose fiber tower, or activated carbon bed), or filtration (eg ultrafiltration, microfiltration, nanofiltration etc.),
It may include solvent extraction, destruction (eg bombardment with radiation), supercritical extraction, gravity separation, or evaporation (condensation).

Whether the displacement liquid (eg, after step 16) is added to line 13 at pump 14 'in line 17 is permeated cocurrently or countercurrently. Depends on what is done. Substitution liquids added to line 17 in place of the extract liquid treated in step 16 include diluents such as fresh (ie, substantially DOM free) white liquor, water, washer filtrate (eg, , A brown stock wash filtrate), a cold blow filtrate, or a mixture thereof. Line 1
If it is desired to increase the sulfidity of the liquor circulated in 2, 13, black liquor can be added to line 17, but the DOM contained therein is passivated, as described below. Black liquor must be treated as it does.

In any event, the liquor withdrawn at 15 contains a relatively high concentration of DOM, while the effective DOM level of the liquor added at 17 is much lower so that the pulp strength is higher. Will be positively affected.

Also in the permeation tank 10 itself, the DOM is preferably controlled using conventional screens 18, pumps 19, and recirculation conduits 20. To the liquid recirculated to the conduit 20, --diluting liquid--as indicated by line 21--is added to dilute the DOM concentration. Further, the diluting liquid contains white liquor at least to some extent. That is, the liquid reintroduced into the conduit 20 will have a substantially lower effective DOM level than the liquid withdrawn from the screen 18, and will also contain at least some white liquor. Process step 16 '-similar to step 16--is also provided in conduit 20, as shown in phantom in FIG.

From the bottom of the IV tank 10, a slurry of comminuted cellulosic fiber material is sent to the top of the digester 11 via a line 22, and as is known, part of the liquid of the slurry is withdrawn to a line 23. White liquor is added to it at 24, passed through heater 25 (usually an indirect heater) and then reintroduced to the bottom of IV vessel 10 via line 26 and / or 27 of FIG. Conduit 2 as shown at
It is introduced near the beginning of No.2.

In the existing continuous digester, the liquor is usually withdrawn at various heights in the digester, heated, and then reintroduced into the same height as the withdrawal. Liquid is not extracted from the system in
The replacement with the OM concentration reducing liquid is also not performed. In the existing continuous digester, black liquor is extracted in the center of the digester, but the black liquor is not reintroduced, but rather sent to the flash tank,
Then, it is finally sent to a recovery boiler or the like. In sharp contrast to existing continuous digesters, in the continuous digester 11 of the present invention, the liquor is actually extracted at many different stages and heights, and the liquor extracted has a low DOM concentration. Is replaced by. This is done near the beginning of the cook, in the middle of the cook, and near the end of the cook.

By using the digester 11 shown in FIG. 1 and carrying out the process of the invention, the pulp discharged in line 28 is otherwise treated under the same conditions as in the existing continuous digester. It has a higher strength than conventional kraft pulp.

Next to the top of the digester 11,
A first set 30 of withdrawal screens near the beginning of the cooking, a second set 31 of withdrawal screens near the midpoint of the cooking, and a third, fourth set of 32, 32 withdrawal screens near the end of the cooking. And 33 are provided. Screens 30-33 are pumps 3 respectively
4 to 37, and circulation lines 38 to 41, respectively.
, And optionally heaters 42-45 respectively, but these circulation loops themselves are conventional. However, in the present invention, a portion of the withdrawn liquid is withdrawn into lines 46-49, respectively, which, as shown in connection with screen first set 30 of FIG. Through a series of flash tanks 50
Sent to.

The extracted liquor, which has a relatively high DOM concentration, is added with replacement (diluting) liquor to replenish it and lower the DOM level, lines 51-54 respectively. It is as shown in. Line 5
The liquors added to 1-54 have a significantly lower concentration of DOM than the liquors extracted in lines 46-49 and therefore have a positive effect on pulp strength. The liquid added to lines 51-54 can be the same as the diluent described above for line 17. The heaters 42 to 45 are the replacement liquids,
Also, the circulating liquid is heated to a temperature substantially the same as the liquid withdrawn (usually a little higher).

Any number of screens 30 to 33 may be provided on the digester 11.

Before carrying the extracted liquid to a distant place and replacing it with the replacement liquid, the extracted liquid and the replacement liquid can be brought into a heat exchange relationship with each other, which is shown in FIG. It is shown schematically at 56. Furthermore, the extracted liquid is processed to remove or passivate the DOM therein,
It can then be immediately reintroduced as a displacement liquid (along with other diluents added to it if desired). This is indicated schematically in FIG. 1 by reference numeral 57, where the extract in line 48 is treated in step 57 (such as step 16) to remove DOM and then 53. Will be reintroduced to the site. White liquor is also added thereto as shown in FIG. 1, but in fact white liquor is added (in lines 51-54, respectively) at each stage associated with screens 30-33 of FIG.
It can be added.

Another alternative process for process block 57--schematically shown in FIG. 1--is the pressure heat treatment of black liquor. A liquid that may be considered as “black liquor” is extracted from the screen 32, and a part thereof is extracted to the line 48. Pressure heating in step 57 is performed as described in US Pat. No. 4,929,307. This is incorporated herein by reference. Normally, in step 57, the temperature is about 170-350.
℃ (preferably about 190 ℃ or more, for example, about 240 ℃)
During that period, the black liquor is heated at a pressure higher than normal pressure for about 5 to 90 minutes (preferably about 30 to 60 minutes) and at a temperature at least about 20 ° C. higher than the cooking temperature. Do this
Due to the significant passivation of M, the black liquor can be returned as shown in line 53.

The process steps outlined in relation to the final set 33 of the withdraw / extract screen at 58 in FIG. 1 are such as step 16. A step such as 58 may be provided at any height of the digester 11 where extraction is performed instead of adding the diluent, or may be omitted. It is safe to add white liquor to the 58th place, and the DOM-decreased liquor is now in line 54.
Will be returned to.

Whether using the treated extract or the diluent, the present invention provides a total DOM concentration of 100 g / l of the cooking liquor during substantially the entire process of kraft cooking (bulk delignification). Or less, preferably about 50 g / l or less,
Lignin concentration is 50 g / l or less (preferably about 25 g / l
It is preferable to maintain the hemicellulose concentration at 15 g / l or less (preferably about 10 g / l or less). The optimum commercial concentration is not yet known exactly and will vary depending on the species to be cooked.

2 and 3 show the results of actual laboratory tests suitable for the present invention. FIG. 2 shows a set of tear-pull curves for three different Kraft cooks, all prepared from the same wood stock. Tear factor is a measure of intrinsic fiber and pulp strength.

In FIG. 2, curve A is a pulp prepared using a conventional pulp mill liquor sample (from the MCC® commercial full scale pulp process) as the cooking liquor. Curve B is a cooking liquor obtained from the same cooking as that of curve A except that the liquor sample was heated at about 190 ° C. at a pressure above atmospheric for 1 hour before being used for cooking. is there. Curve C was obtained by cooking with synthetic white liquor as the cooking liquor, which was essentially DOM free (ie less than 50 g / l). The digestions for Curve A and Curve B were performed such that the alkali, temperature (about 160 ° C.), and DOM distribution were identical to those from the full-scale pulp process from which the liquor sample was obtained. For curve C, the alkali and temperature distributions were the same as for curves A and B, but DOM was not included.

FIG. 2 clearly shows that at all stages of kraft cooking, the tear strength is increased by about 27% at 11 km tension as a result of contact of the dilute DOM liquor with the chips. DOM using pressure heating of black liquor
Is suitable for curve B of the present invention,
This also results in a considerable increase in strength compared to the standard curve A, in which case the tear strength is about 1 at a tension of 11 km.
It has increased by 5%.

FIG. 3 further illustrates a laboratory test comparing the cooking of the present invention with conventional kraft cooking. The cooking shown by curves D to G was carried out with the same alkali and the same temperature distribution for the same wood stock, but with different concentrations of DOM throughout the cooking process. The DOM concentration for curve D is from the standard MCC (R) kraft cook (mill liquor), the highest and the DOM concentration for curve G is the lowest (essentially DOM free). there were. The DOM concentration for curve E is about 25% lower than the DOM concentration for curve D, while the DOM concentration for curve F is about 5% lower than the DOM concentration for curve D.
It was 0% lower. As can be seen, there is a considerable increase in tear strength inversely proportional to the amount of DOM present at all stages of cooking.

The digestion of the present invention has a pulp strength of at least about 10%, preferably at least about 15% (eg, specific to fully refined pulp) compared to when the DOM is otherwise not treated, except otherwise the conditions are the same. It is preferably carried out in order to achieve an increase in tensile strength, eg tear strength at 9 km or 11 km.

Although the present invention has been described primarily with respect to FIG. 1 with respect to a continuous kraft cook, the principles of the present invention are also applicable to a batch kraft cook.

FIG. 4 illustrates the Beloit RDH ™ batch cooking process or Sand Superbatch ™.
A schematic representation of conventional equipment that can be used to perform the process is shown. The system shown schematically in FIG. 4 comprises a batch digester 60 with a withdrawal screen 61, a chip source 6
2, first, second, third liquid storage device 63, 64, 6 respectively
5, white liquor source 66, filtrate tank 67, blow tank 6
8 and many valve mechanisms (the main valve mechanism is schematically shown at 69) are provided.

In a typical conventional duty cycle for the Beloit RDH ™ process, the chip source 62
The digester 60 is filled with chips and blown with steam as required. Next, warm black liquor is supplied to the digester 60. This warm black liquor typically has a high degree of sulfidity, a low degree of alkalinity and a temperature of about 110-125 ° C. and is supplied from one of the reservoirs (eg 63). Excess warm black liquor is sent to the liquor tank and finally to the evaporator and then to the process of chemical recovery. After the permeation, the warm black liquor in the digester 60 is returned to the reservoir 63, and then the digester 60 is filled with hot black liquor and white liquor. Hot black liquor may come from reservoir 65 and hot white liquor from reservoir 63, but white liquor originally came from source 66. Typically white liquor has a temperature of about 155 ° C and hot black liquor has a temperature of about 15 ° C.
It is 0-165 degreeC. The chips in the digester 60 are then digested for a predetermined period of time at a temperature that achieves the desired H factor, and then the hot liquor is replaced with filtrate and a reservoir 65.
Sent directly to. The filtrate is supplied from the tank 67.
The chips are cold blown from the tank 60 to the blow tank 68 with compressed air or a pump.

In performing a typical RDH ™ process, white liquor is continuously heated with liquor from a hot black liquor reservoir and then stored in hot white liquor reservoir 64. The black liquor flows into the warm weak black liquor reservoir 63, and the warm black liquor passes through the heat exchanger to produce hot water, which is stored in the atmospheric tank.
It is then pumped to the evaporator.

With reference to FIG. 4, the only difference between the present invention and the above process is the heating of the black liquor, which is the reservoir 65.
It can be carried out directly in, so that a significant passivation of the DOM in the black liquor takes place. For example, this is at least 20 ° C. above the cooking temperature of the black liquor, for example up to at least 170 ° C. under pressure above atmospheric pressure for about 5 to 90 minutes, preferably above 190 ° C. (eg 240 ° C.) for about 5 to Achieved by heating for 90 minutes.

FIG. 4 diagrammatically shows that this additional heating takes place at 71. The heat can be provided by any desired heat source. During this pressure heating of the black liquor, exhaust gas rich in organic sulfur compounds is produced and withdrawn as shown at 72. Typically, as is known per se, the DMS (dimethyl sulfide) produced in line 72 is converted to methane and hydrogen sulphide, the methane serving as an auxiliary fuel (eg supplying heat in line 71). Can be used). On the other hand, hydrogen sulfide can also be used to pre-infiltrate the chips at source 62 prior to pulping the chips, can be converted to and removed from elemental sulfur, or can be used for polysulfide formation. It can also be absorbed into white liquor to produce a high sulfidity liquid. The black liquor can be used to effect infiltration during kraft cooking, provided that the heat treatment in the reservoir 65 is up to about 20-40 ° C. above the cooking temperature.

Alternatively, in the case of the present invention, in the embodiment of FIG. 4, the valve mechanism 69 is used in connection with a processing step such as step 16 of FIG. 1 to remove the screen 61 from the screen 61 during batch cooking. It is possible to remove DOM from the cooking liquor that is discharged and circulated to the digester 60.

Referring to FIG. 5, an exemplary commercial (ie, pulp daily volume of at least 8 tonnes, eg, 8 to 20) of the present invention is shown.
A batch digester system 74 for producing tons) is schematically shown. A laboratory scale version of the solid line version of the system 74 as shown in FIG. 5 was used to obtain the curve C seen in FIG. 2, but this method has been used for many years. The system 74 includes a batch digester 75, a top 76 and a bottom 77 attached to it, a tip inlet 78 attached to the top and an outlet 79 attached to the bottom, and a tip tube formed inside during cooking. 80 are included. The screen 81 is provided at a position inside the screen (for example, near the bottom 77), is connected to the extraction line 82 and the pump 83, and the pump is connected to the heater 84. Heater 8
From 4, the heated liquor is cooked via line 85 to the digester 7
5 and is introduced at a height different from that of the screen 81 (eg, near the top 76).

Prior to entering the heater 84, a substantial amount of lignin withdrawn in line 82 (eg, the amount of liquid that makes three revolutions per hour) is extracted in line 86. This liquid containing a relatively high concentration of DOM is replaced at 87 with a liquid that is substantially free of DOM (a liquid that has at least a very low DOM concentration compared to the liquid in line 86). 87
It is also possible for the substantially DOM-free liquor added here to have a varying alkali concentration, if desired, so that a suitable kraft cooking is carried out. When the alkali concentration is changed variously, it is possible to simulate continuous kraft cooking even in the batch type tank 75. By providing the valves 88, 89, the flow of liquid can be stopped or started, or the desired processing can be performed as a proxy or ancillary with the system shown by the dotted line in FIG.

According to the invention, the extraction and dilution line 86,
Alternatively or in addition to 87, the extracted liquor may be treated for DOM, eg, a high DOM concentration liquid in line 90, treatment step 91--similar to step 16 of FIG. 1--. To the desired level of DOM and its components (eg, DOM <50 g / l, lignin <25 g / l, and hemicellulose <10 g / l.
It is possible to achieve l). In this process, DOM
Alternatively, the selected component is removed and the concentration in the liquid is greatly reduced. Make-up white liquor (not shown) can also be added and the liquor is reheated in heater 92 and then returned to digester 75 via line 93. Lines 90 and 9
Instead of using 3, lines 86 and 87 can be connected to the processor 91, as shown schematically by the dotted lines 95, 96 in FIG.

Other laboratory test data showing the advantageous results that can be achieved according to the present invention are shown in FIGS. In this laboratory test data, a method was used that simulates a continuous digester operation by sequentially circulating heated pulping liquor through a vessel containing a fixed volume of wood chips. The state of different stages of the continuous digester was simulated by changing the time, temperature and chemical agent concentration used for the circulation. In the above simulations, the liquor from the actual factory was used when the corresponding stage of continuous digester was reached in the laboratory digestion.

FIG. 6 shows the required pulping conditions (ie,
The effect of minimizing the DOM of the pulping liquor over time and temperature) has been shown. FIG. 6 compares the relationship between Kappa number and H-factor for laboratory digestion using black liquor from a factory and white liquor containing almost no DOM. The tree species used for digestion shown in FIG. 6 is a typical northwestern coniferous wood mixed with cedar, spruce, pine and hemlock. The H-factor is a standard parameter that characterizes cooking time and temperature as a single variable and is described, for example, in the 1965 edition of Lydholm Pulping Process, page 618.

Line 98 in FIG. 6 shows the relationship between Kappa number and H factor for laboratory digestion using mill liquor (liquor sampled in the mill and then used in the laboratory batch digester). It is a thing. The lower line 99 shows the relationship between the Kappa number and the H factor for a laboratory cook with laboratory-produced white liquor containing little DOM.

Lines 98 and 99 show that for a given kappa number, the H factor is significantly lower when the DOM is low, eg, for the kappa number 30 of FIG. The difference is about 100 units. This means that for the same stock with the same amount of chemicals used, a lower DOM cooking liquor will be less severe than traditional kraft cooking (ie, shorter and lower temperature). ) Is enough. For example, in order to significantly reduce the H factor by extracting a liquid containing a level of DOM that adversely affects the H factor, part or all of the extracted liquid is
By substituting a liquid that has a substantially lower effective DOM level than the extracted liquid, H 2
Steps are preferably performed to reduce the factor by at least about 5%, and steps are taken to maintain the effective DOM concentration below about 50 g / l for most stages of the kraft cooking.

As shown in FIG. 7, the effective alkali consumed (EA) is reduced when using the reduced DOM concentration according to the present invention. EA is a measure of the amount of cooking chemicals, especially NaOH and Na ₂ S. The results obtained in FIG. 7 were obtained using the same stock as in FIG. 6 and the two lines 100 and 101 of the graph were obtained under the same conditions. Line 100 shows the results when the cooking liquor is a conventional mill liquor, while line 101 shows the results when the cooking liquor is white liquor containing almost no DOM. At a kappa number of 30, compared to conventional cooking with a mill,
About 30% less alkali (5% less EA on a log basis) was consumed with the DOM-free solution.

Therefore, a liquid containing a level of DOM that has a detrimental effect on the amount of effective alkali consumed to reach a specific kappa number is extracted, and part or all of the extracted liquid is converted to an effective DOM level. By substituting the liquid with a substantially low amount, the amount of effective alkali consumed for reaching a specific Kappa number can be significantly reduced. For example, the alkali consumption required to reach a certain kappa number is at least about 0.5% (eg,
It can be reduced by about 4% based on logs.

The advantageous results for both H-factor and EA consumption are shown in FIGS. 6 and 7, which show that the extracted relatively high DOM liquor is treated with water, substantially DOM free white liquor. It can be achieved by substituting the black liquor subjected to pressure heat treatment, the filtered liquid, and a mixed liquid thereof.

FIG. 8 is a further graphical representation of how the consumption of available alkali varies as a percentage of mill liquor to white liquor that is substantially free of DOM. Plot curve 101 shows that for the same relative Kappa number, effective alkali consumption decreases as the percentage of mill liquor decreases (ie, as white liquor with little DOM increases). Table 1 below
Shown are the actual laboratory test results used to create the plot curve 101 of FIG.

[0066]

[Table 1]

When the DOM in the pulping liquid is reduced or eliminated, the easiness of bleaching the obtained pulp, that is, the bleaching property is also improved.

FIG. 9 represents actual laboratory test results and shows how the whiteness of bleached Sugi-Spruce-Pine-Tsuga mixed wood pulp increases with increasing bleaching agent usage. . The “full sequence copper factor”, which is a parameter shown on the X axis of the graph of FIG. 9, is the ratio of the equivalent chlorine usage amount to the kappa number of the raw material pulp. That is, this is a somewhat normalized ratio of chlorine usage to the initial lignin content of brownstock pulp. Thus, FIG. 9 shows how pulp brightness responds to the amount of bleaching agent used.

Curves 102, 103, 104 and 105 of FIG. 9 are respectively substantially DOM free white liquor (102), conventional mill liquor (103) and mill cooked pulp (lab with mill liquor). (Not pulp) (104),
And heat treated mill heat treated black liquor (105). These graphical representations clearly show that the best bleaching properties are achieved when substantially DOM-free white liquor is used in the cooking liquor. Therefore,
A liquor containing a substantially sufficient level of DOM to adversely affect the bleaching property of pulp is extracted, and a part or all of this liquor has a significantly higher effective DOM level than the extracted liquor. By displacing with a low liquor, the bleachability of the pulp produced can be significantly improved, for example an ISO brightness of at least one unit can be increased at a certain full sequence copper factor.

In other words, this data shows that
This means that a specific ISO whiteness can be achieved with a small amount of bleaching agent. However, the graph curve 105 indicates that the heat-treated black liquor can improve the delignification property (see FIG. 2), but the residual lignin may not be easily removed. Therefore, it may be undesirable to use the treated black liquor as a diluting solution if good bleaching properties are desired. In this case, rather water, substantially DO
White liquor containing no M and filtered liquor (and of course a mixture thereof) would be more suitable as the diluting liquid. However, the heat-treated liquor can be used for pulp that does not require bleaching, that is, unbleached grade pulp.

As discussed previously, D in the pulping liquor
Reducing OM concentration appears to have the most dramatic effect on pulp strength. This is further supported by the data shown graphically in Figures 10-14B. All of this data is for the same Sugi-Spruce-Pine-Tsuga mixed wood species as discussed above with respect to FIGS. 6-9, which shows that at the same cooking conditions, tear strength and DOM are reduced. It shows that it increases remarkably as it goes. For example, as shown in FIG. 10, the tear strength at 11 km for the laboratory digestion shown here is shown to decrease the amount of mill liquor (thus substantially D
It increases with increasing amount of white liquor without OM) (see line 106). Line 107 in FIG.
Is the mill liquid percentage and 600 CSF (Canadian Standar
d Freeness, freeness) and the tear strength, and FIG. 11 shows the same basic relationship as described above.

Table 2 below shows the tear strength at two tensile strengths for laboratory digestions performed on many cooking liquors, with the tear strength on mill pulp being also shown for comparison. There is. The data from cooking 2 and cooking 3 in Table 2 show that the laboratory cooking with white liquor, which is substantially free of DOM, has a tensile strength of 10 km compared to the laboratory cooking with mill liquor. 20% increase in tearing and 12% tearing at 11 km tension
Is an increase. Laboratory digestions 4, 5, 6 in Table 2 show the results when the DOM-free liquor in a particular part of the digestion was replaced by the corresponding mill liquor. For example, in Cooking 4, the liquid from the bottom circulation (BC) line replaced the liquid produced in the laboratory at the BC stage of the laboratory digestion. Similarly, in cooking 5, the BC cooking mill liquor and the modified cooking (MC) mill liquor were BC and M of laboratory cooking.
The solution was used in stage C, while the DOM-free liquid was used in the other stages. The data in Table 2 show that minimizing DOM is critical at all stages of cooking, not just the latter stages, and that the analysis described above with respect to FIGS. It means to support.

[0073]

[Table 2]

FIGS. 12-14 show the effect of DOM on the strength of bleached pulp. 12A shows the tear strength and tensile strength of unbleached pulp, line 108 represents pulp produced in a laboratory liquid substantially free of DOM, and line 109 is from pressure heat treated black liquor. And line 110 is from a conventional milling fluid. B of FIG.
12 shows the tear vs. tension relationship after bleaching the pulp graphed in FIG. 12A using the laboratory bleaching sequence DEoD (nD). Line 111 is substantially DO
M-free pulp produced from white liquor is bleached pulp, wire 112 is pulp produced in a pressure-milled mill liquor, and wire 113 is pulp bleached from conventional mill liquor. On the other hand, for comparison, line 114 shows the strength of the pulp after being taken from the digester and bleached.
FIG. 12B shows that pulp cooked substantially free of DOM is not only stronger than mill liquor pulp, but this relative strength is maintained after bleaching. The pulp cooked with the heat-treated liquor also retains higher strength after bleaching than the pulp digested with the mill liquor, but the difference in strength after bleaching is only slight.

FIG. 13 shows the same cooking / bleaching test results as in FIG. 12, but here only the tearing factor is expressed against Canadian Standard Freeness (CSF). Line 115 is pulp that is substantially free of DOM, line 116 is pulp produced with a pressure-heat treated mill liquor, line 117 is pulp produced with mill liquor, line 11
8 is a bleached pulp produced with a substantially DOM-free liquor, line 119 is a bleached pulp from a pressure-treated mill liquor, and line 120 is a mill liquor. Pulp bleached pulp, wire 121 was taken from a mill decker.

FIG. 14 shows the same digestion / bleaching results as in FIG. 12, but here only the tensile versus freeness is shown. Wire 122 is pulp made from mill liquor, wire 1
Reference numeral 23 is a pulp produced by a pressure-heat-treated mill liquor, line 124 is a pulp produced by a liquid containing substantially no DOM, and line 125 is a bleached pulp of a mill liquor produced pulp. Line 126 is bleached pulp made from a substantially DOM-free liquor, line 127 is at Decker, and line 128 is bleached pulp made from a pressure-treated mill liquor. It is for pulp that has been made. FIG. 14 shows that both the pulp produced by the pressure-heat-treated mill liquid and the pulp produced by the liquid containing substantially no DOM have reduced tensile strength. B shows that upon bleaching, the relative tensile strength of pulp produced with the heat-treated mill liquor is less than that of pulp produced with the DOM-free liquor. Also, as noted above, the heat treated liquor process is believed to be suitable for unbleached pulp.

The above-mentioned laboratory cooking process is carried out by the MC
It was a complete simulation of the pulping sequence of C (R) continuous digester. Each laboratory digestion stage has a corresponding infiltration stage, a co-current digestion stage, a countercurrent MCC® digestion stage, and a countercurrent wash stage. Typical DOM concentrations based on actual liquor analysis are shown in Figure 15 for a laboratory cook using three sources. Line 130 is for mill liquor, line 131 is for 50% mill liquor and 50% lab white liquor that is substantially free of DOM, x
The mark 132 is laboratory white liquor 1 containing substantially no DOM.
It is for 00%.

In FIG. 15, at time = 0, that is, at the beginning of permeation, all laboratory fluids used were DOM free. This was done because there was no reliable method of sampling the liquor at this stage in the cooking at the mill. Therefore, at the end of permeation, the mill solution as well as 50/5
Since the DOM concentration at the time of cooking 0 liquor should be lower than that expected from the above-mentioned set of data, the concentration that is more representative can be obtained by extrapolation and shown in parentheses in FIG. What we are trying to show in FIG. 15 is how each concentration shows a consistent tendency in all stages of cooking, where the concentration gradually increases until reaching the extraction stage, and then countercurrent MCC (registered trademark). And gradually decreases during the washing stage. Of course, even if a liquid source containing substantially no DOM is used, the DOM will be mixed into the liquid as the cooking progresses.

FIG. 16 illustrates an exemplary continuous digester system 133 for making pulp with increased strength utilizing the teachings of the present invention. The system 133 is equipped with a conventional two-vessel Kamiya continuous digester (where MCC® digestion takes place). The permeation tank is not shown in FIG. 16, but the continuous digester 134 is shown. FIG. 16 shows a modification of a conventional MCC® digester can 134 to carry out the low-concentration DOM digestion process of the present invention.

The digester 134 has an inlet 13 at the top thereof.
5, the bottom of which is provided with an outlet 136 for the pulp produced. The crushed cellulose fiber material (ground wood chips) slurry is supplied to the inlet 135 from the permeation tank in the line 137. A portion of the introduced slurry is withdrawn in line 139 at the top screen assembly 138 and the withdrawn liquid is returned to the BC heater and permeation tank.

Below the top screen assembly 138 is an extraction screen assembly 140, which is provided with a line 141, which is the first flash tank 14
2 (typically consisting of a series of multiple flash tanks). Extraction screen assembly 140
Underneath is a cooking screen assembly 143, which is provided with two extending lines, one of which 144 is for extraction (merges into line 141) and the other line 145 is a pump 145 '. Connected to. A valve 146 can be provided between lines 144 and 145 to vary the amount of liquid passing through each line. The liquid in the line 145 passes through the heater 147 and the line 148, and returns to the inside of the digester 134 via the pipe 151 opening near the height of the digestion screen assembly 143. The branch line 149 can also introduce the circulating liquid into the pipe 150 near the height of the extraction screen 140.

Below the digestion screen assembly 143 is a wash screen assembly 152, which has an extraction line 153 leading to a pump 154,
The liquid is sent to line 156 via heater 155 and digester 1 via pipe 157 near the height of screen 152.
The liquid is returned to the inside of 34.

For the system 133, currently, the factory has increased the production rate of digester over the designed rate,
Currently, production is limited by the volume of liquid that can be extracted. This limitation can be successfully circumvented and resolved using the techniques of the present invention, as illustrated in FIG. Since the amount of extract in line 141 is limited, it will be increased in accordance with the invention by also supplying extract from line 144.

For example, the flow rate of the extraction liquid would be about 2 tons of liquid per ton of pulp using the present invention. After all, 1 per ton of pulp extracted in line 144
The ton of liquid is replaced with the diluent (washing liquid) from the liquid source 158. This is achieved in FIG.
A cleaning liquid (for example, filtered water) from 8 is supplied to a pump 159,
By flowing through the valve 160.

Most of the wash liquor (eg, 1.5 tonnes of liquid per ton of pulp) is introduced in line 161 and sent to the bottom of the digester, while the rest (eg, 1 ton of liquid per ton of pulp). The line 162 is entered, and then the line 145 is entered to become a diluent. It is also possible to add substantially DOM free white liquor from source 163 to line 164 and then to line 145 before heater 147 and recycle to digester through pipe 150 and / or 151. it can. Of course, white liquor can also be added to the wash cycle in line 153 (see line 165) to perform the EMCC® digestion. Flow arrow 166 indicates a co-current zone in digester 134. As a result of the modification shown in FIG. 16, the countercurrent in the MCC® digestion zone 167 was cleaner,
A DOM-reduced liquor will be included, resulting in improved pulp strength, which in turn increases digester 134 production rate. The effect of the modification shown in FIG. 16 on DOM concentration was investigated using a computer dynamic model of a continuous cooking digester from Kamiya. The preliminary results of this theoretical study are shown schematically in FIG.

FIG. 17 compares the change in DOM concentration of the conventional MCC® digester with the digester shown in FIG. The results with the conventional MCC® digester are shown by line 168 and the results with the digester of FIG. 16 are shown with 169. As seen in Figure 17,
The DOM concentration in the screen assembly 143 is D
Addition of OM-reduced diluent drastically reduces and also reduces countercurrent DO to the extraction screen assembly 140.
The M concentration is also reduced. In addition, the countercurrent wash, which flows downward, also contains a small amount of DOM. This is because the DOM that accompanies the pulp is small. Graph lines 170, 17
1 and part of the lines 168, 169 show that in the countercurrent cooking zone the DOM always increases in the direction of flow. That is, the countercurrent digests and accumulates DOM as it flows past the downwardly flowing mass of chips.

Thus, FIGS. 16 and 17 show that even a single extraction and dilution has a dramatic impact on the DOM distribution of a continuous digester, thus D
A reduction in OM has a corresponding dramatic effect on the resulting pulp strength.

FIG. 18 shows a technique for performing another mill deformation according to the present invention. Again, a digester 134 is shown, which is part of the two vessel pressure digester. 16 and 1
Many of the components shown in 8 and 8 are the same, so they will be designated by the same reference numerals. Let me explain in detail only the modifications from one to the other.

In the embodiment of FIG. 18, more dramatic DOM reduction will be performed. In this aspect, the screen 1
The screen 40 and the screen 143 are in the reversed positions as compared with the embodiment of FIG. And another screen assembly 173 is also provided between the screen assemblies 138 and 143. The screen assembly 173 is an adjustment screen assembly, and in the present invention, the withdrawal conduit 174 from this assembly causes the flash tank 1 to
Extraction to 42 is performed. In the aspect of FIG. 18, as an example of a specific operation, 2 tons of liquid per ton of pulp are extracted to the line 174, and 4 tons of liquid per ton of pulp are extracted to the line 141. Diluent is added to line 162 and substantially DOM-free white liquor is added to line 162.
4 is added. By doing this, the flow 1 shown in FIG.
76 and 177 occur, so the digester 134 flows in parallel,
It exhibits the characteristics of countercurrent, cocurrent and countercurrent (this can be called alternating flow continuous cooking).

FIG. 19 shows another digester system 1 according to the present invention.
79 is shown. A permeation tank is also shown in this dual tank system, with an inlet 181 at the top and an outlet 182 at the bottom. The liquor withdrawn at 183 is recycled to a conventional high pressure feeder, while white liquor is added at 184. The liquid withdrawn at 185 may be sent to an introduction point located between the first flash tank 186 and the second flash tank 187. Line 182
The slurry from is introduced at 188 to the top of a digester 189 having a "quiet well" structure 190, from which the liquor is withdrawn to 191 and recirculated to permeate tank 180. The liquid is heated in the heater 192 during recirculation.

The digester 189 is also provided with an adjusting screen assembly 194 from which the withdrawal 19
In this case, 5 merges with the circulating liquid in the line 191. A digestion screen assembly 196 is provided below the conditioning screen assembly 194, the liquor is withdrawn in line 197 and enters line 199 via valve 198, with an optional but part of the liquor being separated from valve 198. Follow line 200 to flash tank 186. The liquid in line 199 is a lower concentration DOM liquid, such as
It is diluted with substantially DOM-free white liquor 201 and filtrate 202, then passed through heater 203 and reintroduced into digester 189 by conduit 204 near the height of screen assembly 196.

The extraction screen assembly 206 is provided with a withdrawal line 207, which leads to the flash tank 186. The wash screen assembly 208 is provided with a recirculation line 209, to which white liquor 210 can be added, after which the heater 211 is added.
Through the conduit 212 near the height of the wash screen assembly 208. The wash liquor supplying the filtrate is added at 213, while the pulp produced is withdrawn in line 193.

Note that system 179 has the potential to extract from line 197 to conduit 200 via valve 198. Diluent in the form of filtrate is also added to line 182, preferably at 214, while
Substantially DOM free white liquor is added at 214 '.

FIG. 20 illustrates a single vessel pressure cooker modified in accordance with the teachings of the present invention, which modified cooker also conventionally has two sets of cooking screens. This arrangement increases the possibility of introducing the extraction / dilution at more than one location.

In the system 215 for the single-bath type pressure digester, the chip bin 216, the steam treatment tank 217, the high-pressure transfer device (feeder) 218, and the cellulose fiber material slurry are added to the top 220 of the continuous digester 221. Conventional components of line 219 and tap 222 for manufactured pulp at the bottom of digester 221 are provided. A part of the liquid is withdrawn to the line 223, returned to the high pressure feeder 218, and recirculated. The cooking screen is provided below the line 223, such as the first cooking screen assembly 224 and the second cooking screen assembly 225.

Associated with the first cooking screen assembly 224 is a first cooking screen assembly 224.
First means for recirculating a first portion of the liquor from inside the digester 221 to the interior of the digester 221 that includes line 226, pump 227, and heater 228, and reintroduction conduit 229 at the height of screen assembly 224. Located near. A valve 230 may be provided in front of the heater 228 to allow the extract to enter the line 231, while the diluent, eg white liquor (eg 10% of the total white liquor used),
Immediately before heater 228 is added via conduit 232.

The second means for recirculating some of the extracted liquid and extracting the other is the second digestion screen assembly 2
25. This second system has a conduit 235
, Pump 236, heater 237, valve 238
And a reintroduction conduit 239. A portion of the liquor is made up with diluent in conduit 242, while diluent in the form of white liquor is added to line 241. On the other hand, a part of the liquid is extracted in the line 240. Thus, the DOM concentration is greatly reduced in the cooking zone near the screen assemblies 224,225.

Underneath the second digestion screen assembly 225 is an extraction screen assembly 245, with a conduit 246 extending from it to valve 247. One branch 248 from the valve 247 is the first flash tank 24 of the recovery system.
9 where a second flash tank 250 is usually parked after. A portion of the liquid in line 246 can be recycled to line 251 by turning valve 247.

The digester 221 is further provided with a third screen assembly 253 located below the extraction screen assembly 245, which is equipped with a valve 254 and is branched into a withdrawal conduit 255 and an extraction conduit 256. is doing. That is, liquid can flow from line 246 to line 255 or from line 256 to line 248 depending on the state of valves 247, 254.

Line 255 is connected by pump 257 to heater 260 and return conduit 261 near the height of third screen assembly 253. Diluent is added to line 255 in front of heater 260 to provide white liquor (eg, about 15 of white liquor used for cooking).
%) Is added via line 258 and source 243
Diluate from, eg, wash filtrate, is added via line 259.

The digester 221 is also equipped with a wash screen assembly 263, which has a withdrawal conduit 26.
4 in which line 265 contains white liquor from source 233 (eg, only about 15% of the total white liquor for the process).
It can be added via. The pump 266, the heater 267, and the screen assembly 26
A return conduit 268 for reintroduction near the height of 3 is also provided. The wash filtrate is also provided under the screen assembly 263 with a conduit 26 connected to a source of wash filtrate 243.
Added by 9.

In one exemplary operation of the present invention, the chips are sent by high pressure transfer device 218 and into line 219, but 55% of the white liquor used to treat the pulp is added to line 271. Impregnated into the above chips. 5% of the white liquor is added to high pressure feeder 218 via line 272, 10% (eg 5% each) is added to lines 232 and 241, and 15% to lines 258 and 265 respectively. Is added. Single tank type pressurized continuous digester can assembly 2 of FIG.
With 15, low concentrations of DOM are maintained, but there are many other modes of operation. For example, there are at least three modes of operation, each of which is:

(A) Extract / dilute hand on bottom cooking screen
Expanded Modified Continuous Cooking with Steps In this mode, the digester 221 is operated with conventional extraction in line 246 and expanded modified continuous cooking, with 2 liquors of white liquor.
32, 258, 265. Extraction is line 24
0, the corresponding diluent is added at wash filtrates 243 to 242. The resulting reduced DOM liquor is extracted by the extraction screen assembly 245 and the bottom cooking screen assembly 225 (second screen assembly 2).
25) Flows in countercurrent or cocurrent with Whether the flow is countercurrent or cocurrent is governed by the values of the extraction quantities at 240 and 246.

(B) Extraction / dilution means for modified continuous digestion circulation
Expanded Modified Continuous Cooking with ??? In this mode all the flows just described in connection with (A) are used, but further extraction is done in line 256, valves 247, 254 are controlled and a third screen A portion of the liquor from assembly 253 (modified continuous digestion screen assembly) is directed to line 248. Diluent to replenish this extract is added at 259, resulting in additional countercurrent liquid flow of DOM reducing liquid between screen assemblies 245, 253.

(C) Displacement immersion in the upper digestion screen
Permeation and Extraction-Dilution Method This mode, although used alone, can be used with the conventional modified continuous cooking process or in addition to modes (A) and (B) above. This mode is performed under the control of valve 230, line 23
Upper screen assembly 224 as shown at 1
Includes extraction at (first screen assembly 224) and dilution with white liquor at line 232. Additional dilution is also done from line 259 (not shown in Figure 20). This results in displacement infiltration, which is caused by the amount of liquor entrained in the incoming chips rather than the countercurrent at the entrance to the digester being induced by the extraction. When the amount of the liquid accompanying the chips is small, the diluting liquid is forced to flow back to the inlet 220 in the digester 221 in the pressurized full state, and as a result, the DOM
A countercurrent of the liquid with reduced flow occurs. The system 215 shown in FIG. 20 is not limited to modes AC described above, which incorporates the low DOM principles of the present invention into its flow to produce pulp of increased strength. It is only a few examples of the myriad of modified shapes that can be applied.

Note that the embodiments of FIGS. 16 and 18-20 can all be retrofitted into an existing factory. For precise details on how to use a variety of equipment,
It will depend on the particular factory in which the technology is adopted. All will benefit from the above benefits of reduced DOM, such as increased strength, improved bleaching, reduced consumption of available alkali, and / or reduced H factor. This is different from the configuration of FIG. 19 in FIGS.
Most clearly proved in 5. In FIG. 19, 1
85 is the first extraction, 200 is the second extraction, 207 is the third extraction, 214 is the first dilution, 202 is the second dilution, and 21
3 is considered the third dilution.

FIG. 21 shows a computer simulation comparison of the DOM distribution for a standard EMCC® cook and a similar cook of the present invention using the system of FIG. 19 with an extended co-current cook. Standard EMCC (registered trademark)
In cooking, the extraction is done from a conventional extraction screen, the white liquor is added to the traditional cooking cycle and the wash cycle, the liquor from the top of the digester to the conventional extraction screen is co-current, and the remainder of the digester is The flow against is countercurrent. FIG. 19
According to the extended co-current mode of, the third extraction 207 is the main extraction and co-current cooking occurs all the way to the screen assembly 206. FIG. 21 shows a conventional EMCC® cook at graphical line 275 and a cook with the extended co-current cooking mode at graphical line 276. In the computer model resulting in FIG. 21, the processing ton is 1200 ADMT.
/ D, the distribution of white liquor is 60% in permeation 184, 5% in BC line 214 ′, 15 in MCC® circulation 201.
%, And 30% in wash cycle 210. At 213, 1.5 tonnes of washer filtrate per ton of pulp was added as a countercurrent liquid.

As can be seen from FIG. 21, although the concentration of DOM is reduced in the cooking zone at the beginning,
The concentration is higher in the countercurrent stage. Therefore, there is little improvement in DOM concentration with this form of extended co-current cooking (276). Although the computer model is somewhat limited, FIG. 21 shows that the DOM concentration can be varied throughout the cooking period. Figure 2
No. 2 shows the theoretical effect of adding the white liquor at 201 and the low-concentration DOM liquid at 202. In FIG. 22, 1.0 ton of liquid per ton of pulp cleaning device filtrate is added at 202 along with 0.6 ton / ton pulp (t / tp) of white liquor. The corresponding liquid stream 1.6 t / tp is extracted at 200. As can be seen in graph line 277, the resulting DOM concentration drops dramatically between screens 196, 206, as compared to graph line 276 in FIG.

FIG. 23 shows the effect of varying the distribution of washer filtrate added for dilution at 202 and 213. In this case, the total amount (1.5 + 1.0 = 2.5t / tp) of the washing device filtrate is added separately at 213 and 202. Graph line 27
8 added 1/3 of the diluted solution at 202, line 27
9 shows the simulation with 1/2 added at 202 and line 280 with 2/3 added at 202 (the rest in each case at 213). Thus, it is clear that the distribution of DOM changes significantly as the flow of diluent changes, with more diluent added to the digestion zone resulting in less DOM there (although it increases in the wash zone). ).

FIG. 24 shows the theoretical effect of varying the amount of extraction at 200. The line 281 of the graph is DO when the extraction amount at 200 is 1.35 t / tp.
For predicting the M distribution, the line 282 is obtained when the extraction amount at 200 is 1.85 t / tp, and the line 283.
Indicates the case where the extraction amount at 200 is 2.6 t / tp. In each case, a total of 2.5 t / tp of diluent was divided evenly between 202 and 213, with a further 0.6
t / tp white liquor is added at 201. Figure 24
Clearly shows that the theoretical DOM concentration in the digestion zone is 2
It means that the amount of extraction at 00 increases as it increases and remains essentially unchanged throughout the countercurrent zone. Therefore, this extraction amount can be changed to allow the extraction-screen pressure drop without significantly changing the DOM distribution.

FIG. 25 shows the effect of extracting from 185 (top of permeation tank 180) to create a zone of countercurrent permeation while employing enhanced co-current digestion with dilution. In this case, the reference co-current permeation bath data is the same as that shown in FIG. Extract flow 185
Is 1.1 t / tp and the extracted liquor is replaced by white liquor at 184 rather than by the washer filtrate. In the model before FIGS. 21 to 24, 60% of white liquor
At 184, 5% was added at 214 ', but in Figure 25 they were reversed. That is, 5%
At 184 and 60% at 214 '.

Line 284 of the graph shows the results for the co-current permeation tank flow, while line 285 shows the results for the countercurrent (60% white liquor at 214 '). Thus, this proves that the theoretical DOM concentration decreases both in tank 180 and in the digestion zone, which is equivalent to in the countercurrent digestion zone. Therefore, the low concentration of DOM is
This is made possible by extraction in tank 180 in addition to extraction / dilution operations in digester 189.

It is therefore apparent that according to the invention, the strength of kraft pulp is removed, minimized (for example by dilution) or passivated DOM in any part of the kraft cooking. Improve
And / or methods and apparatus for improving other pulp or process parameters. Since the present invention is shown and described herein in what is presently considered to be the most practical and preferred embodiments, many partial modifications will occur to those skilled in the art within the scope of the invention. Will be clear to. Therefore, the scope of the appended claims should be construed broadly to include all equivalent structures, methods, and products.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an exemplary embodiment of a continuous kraft digester of the present invention that performs the exemplary method of the present invention.

FIG. 2 is a graphical representation of the strength of pulp produced in accordance with the present invention and is compared to kraft pulp produced under the same conditions except that the present invention is not used.

FIG. 3 is a graphical representation of the strength of pulp produced in accordance with the present invention and is compared to kraft pulp produced under the same conditions except that the present invention is not used.

FIG. 4 is a schematic diagram of an exemplary apparatus for practicing the improved batch kraft cooking method of the present invention.

FIG. 5 is a schematic side view of another embodiment of an exemplary batch digester of a digester of the present invention.

FIG. 6 is a graphical representation of the H-factor of pulp produced according to the present invention, for comparison with kraft pulp produced under the same conditions except that the present invention is not used.

FIG. 7 is a graphical representation of the effective alkali consumption when producing pulp according to the present invention, for comparison with pulp produced under the same conditions except that the present invention is not used.

FIG. 8 is a graphical representation of effective alkali consumption vs. mill cooking liquor% for comparison with DOM-free liquor.

FIG. 9 is a graphical representation comparing the whiteness response of pulps made in accordance with the present invention, compared to kraft pulp made under the same conditions except without the present invention.

FIG. 10 is a further graphical representation of the strength aspect of pulp produced in accordance with the present invention.

FIG. 11 is a further graphical representation of the strength surface of pulp produced in accordance with the present invention.

FIG. 12 is a further graphical representation of the strength surface of pulp produced in accordance with the present invention. A comparison is made with kraft pulp produced under the same conditions except that the present invention is not used.

FIG. 13 is a further graphical representation of the strength surface of pulp produced in accordance with the present invention.

FIG. 14 is a further graphical representation of the strength surface of pulp produced in accordance with the present invention.

FIG. 15 is a graphical representation of DOM concentration based on actual liquor analysis for laboratory cooking with different liquor sources at various stages during cooking.

FIG. 16 is a schematic diagram of an exemplary digester for a two-bath pressure cooker system for practicing the present invention.

FIG. 17 DO in conventional MCC® digester
A graphical representation of theoretical studies comparing M concentrations,
It is to be compared with the digester of FIG.

FIG. 18 is a schematic diagram of another exemplary digester of the present invention.

FIG. 19 is a schematic diagram of another exemplary digester of the present invention.

FIG. 20 is a schematic diagram of another exemplary digester of the present invention.

FIG. 21 is a graphical representation of a theoretical study of varying dilution and extraction parameters using the digester of FIG.

22 is a graphical representation of a theoretical study of varying dilution and extraction parameters using the digester of FIG.

23 is a graphical representation of a theoretical study of varying dilution and extraction parameters using the digester of FIG.

FIG. 24 is a graphical representation of a theoretical study of varying dilution and extraction parameters using the digester of FIG.

FIG. 25 is a graphical representation of a theoretical study of varying dilution and extraction parameters using the digester of FIG.

[Explanation of symbols]

10 Infiltration tank 11 Conventional independent continuous digester 14 pumps 14 'pump 15 lines 16 steps 18 Conventional screen 19 pumps 25 heater 30 screen first set 31 screen second set 32 Extraction screen third set 33 Extraction screen 4th set 34 pumps 35 pumps 36 pumps 37 pumps 42 heater 43 heater 44 heater 45 heater 50 flash tanks 57 steps 60 batch cooking digester 61 Extraction screen 62 chip source 63 First reservoir 64 Second reservoir 65 Third reservoir 66 White liquor source 67 Filtrate tank 68 Blow tank 69 valve mechanism 74 batch digester system 75 batch digesters 76 Top 77 Bottom 78 Tip entrance 79 exit 80 tip tube 81 screen 82 Extraction line 83 pumps 84 heater 91 processing steps 101 Plot curve 133 Exemplary continuous digester system 134 Continuous digester 135 entrance 136 exit 138 Top Screen Assembly 140 Extraction Screen Assembly 142 First flash tank 143 Cooking Screen Assembly 145 'pump 146 valve 147 heater 152 Wash Screen Assembly 153 Extraction line 154 pump 155 heater 158 liquid source 163 Liquid source 166 flow arrow 167 cooking zone 173 screen assembly 179 digester system 180 Penetration tank 181 entrance 182 exit 183 Conventional high pressure feeder 186 First Flash Tank 187 Second Flash Tank 189 cooking can 192 heater 194 Adjustment Screen Assembly 196 Cooking Screen Assembly 201 White liquor 202 filtrate 203 heater 206 Extraction Screen Assembly 208 Cleaning Screen Assembly 210 white liquor 211 heater 212 conduit 215 Single tank pressure digester system 216 Chip Bin 217 steam treatment tank 218 High-pressure transfer device (feeder) 220 top 221 Continuous digester 222 Pulp outlet 224 First Cooking Screen Assembly 225 Second Cooking Screen Assembly 227 pump 228 heater 229 Reintroduction conduit 233 Liquid source 236 pump 237 heater 239 Reintroduction conduit 243 liquid source 245 Extraction Screen Assembly 248 branch The first flash tank of the 249 recovery system 250 second flash tank 253 Third Screen Assembly 257 pump 260 heater 263 Cleaning Screen Assembly 264 Extraction conduit 266 pump 267 heater 268 Return conduit 269 conduit

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Richard Olaxo 22, Oakwood Drive, Queensbury, New York, USA 12804 (72) Inventor, Joseph Earl Phillips, United States, 12804 Van Court, Queensbury, NY 4804 (72) Inventor Rolf Seeliham, United States, 30077 No. 30 Mansell Court, Roswell, Georgia (72) Inventor Jean T. Richardsen United States, 12801 Ridge Center, Glens Falls, NY (no street number) Within Earlstrom Machinery Incorporated (72 ) Inventor Earl Fred Chasse USA, 128 04 No. 6 Gentry Lane, Queensbury, New York (56) Reference JP-A-4-300378 (JP, A) JP-A-5-195464 (JP, A) JP-A-8-511583 (JP, A) JP Table Sho 63-502674 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) D21C 3/00-7/14

Claims (29)

(57) [Claims] 1. A top, a bottom, an inlet for comminuted cellulosic fibrous material provided at the top, an outlet for cooked pulp provided at the bottom, a top screen assembly, an extraction provided below the top screen assembly. A process for producing kraft pulp using a continuous digester equipped with a screen and a cooking screen assembly provided below the extraction screen assembly, a) introducing a slurry of cellulosic material to be cooked into an inlet, b) A small amount of liquor is drawn from the cellulosic slurry in the top screen assembly, c) extracting black liquor from the extraction screen, d) extracting liquor from the cooking screen, which is divided into at least a first portion and a second portion, and e) Send the first part to the collection, f) increment the liquid containing dissolved organic matter in low concentration to the second part, And a) recycling the incremented second portion into the interior of the digester at the approximate location of the cooking screen assembly. 2. Step (f) is performed by at least partially adding white liquor containing a low concentration of dissolved organics to the incremented second portion. Method. 3. Step (d) is performed such that about 2 tons of liquid is withdrawn per ton of pulp to make the first and second portions substantially equal, and step (f) comprises A cleaning liquid containing a low concentration of about 1 ton of dissolved organics per ton, together with a small amount of white liquor containing a low concentration of dissolved organics, is added to the second portion. 2. The method described in 2. 4. A process according to claim 3, characterized in that the cooking is carried out in a digester and steps (a) to (g) are carried out at the stage of infiltration or near the beginning of the cooking . 5. A process for the continuous production of chemical cellulose pulp digester, a) dissolved organics into the slurry liquid screen assembly of comminuted cellulosic fibrous material containing a first concentration, and scan <br / > Run through the clean assembly, b) withdrawing a portion of the liquid containing dissolved organics in a first concentration from the slurry at the screen assembly, and c) removing the first portion of the liquid withdrawn in step (b). Sent for recovery or for processing outside the digester, d) a second portion of the liquor withdrawn in step (b) is recycled back to the digester in the approximate position of the screen assembly in a recirculation loop. Circulation, e) introducing cooking liquor into the recirculation loop, f) well below the first concentration of dissolved organic matter, pulp strength,
A diluent having a second concentration of dissolved organic matter that beneficially affects the available alkali, H-factor, or bleaching consumed is introduced into the recycle loop, and g) well below the first concentration of dissolved organic matter and pulp strength. ,
Process for continuous production of chemical cellulose pulp comprising the steps of introducing into a digester a liquor of a recycle loop having a third concentration of dissolved organic matter which advantageously influences the available alkali, H-factor, or bleaching consumed. . 6. A process according to claim 5, characterized in that an additional step of heating the liquid in the recirculation loop before returning it to the digester is carried out between steps (f) and (g). 7. The method according to claim 5, wherein step (f) is carried out by introducing a washing device filtrate or water or a combination thereof. 8. The method according to claim 7, wherein steps (e) and (f) are performed by reintroducing an amount substantially the same as the amount of the liquid removed when performing step (c). the method of. 9. The method of claim 7 wherein the liquid flow is co-current with the comminuted cellulosic fibrous material at the screen assembly. 10. The method of claim 7 wherein the liquid flow is countercurrent to the comminuted cellulosic fibrous material at the screen assembly. 11. The method of claim 5 wherein the liquid flow is co-current with the comminuted cellulosic fibrous material at the screen assembly. 12. The method of claim 5, wherein the liquid flow is countercurrent to the comminuted cellulosic fibrous material at the screen assembly. 13. The method according to claim 5, wherein steps (a) to (g) are carried out constantly with a dissolved organic matter concentration of less than 100 g / l. 14. A method of continuously producing a click Rafutoparupu in the digester, a) the comminuted cellulosic fibrous material slurry of, the screen assembly, and flow through the screen assembly, b) liquid part of Withdrawing from the slurry at the screen assembly, c) sending a first portion of the liquor withdrawn in step (b) for recovery or treatment outside the digester, and d) withdrawing in step (b). A second portion of the liquor circulated in a recirculation loop back to the digester at the approximate location of the screen assembly for recirculation, e) introducing the cooking liquor into the recirculation loop, f) water, washer filtrate, Or a craft comprising the steps of introducing into the recirculation loop a diluent comprising a combination of water and washer filtrate, and g) returning the recirculation loop liquor to the digester. Help continuous manufacturing method. 15. A process according to claim 14 , characterized in that an additional step of heating the liquid in the recirculation loop before returning it to the digester is carried out between steps (f) and (g). Flow 16. liquid The method of claim 15, wherein it is a comminuted cellulosic fibrous material and co-current at the screen assembly. 17. A method according to claim 15 wherein the liquid flow is countercurrent to the comminuted cellulosic fibrous material at the screen assembly. 18. A process for the continuous production of chemical cellulose pulp with a first screen assembly and a second screen assembly disposed at a interval to each other in the digester, a) dissolved organics first the slurry of comminuted cellulosic fibrous material containing a concentration to the first screen assembly, and
Flow Te passes through the first screen assembly, b) dissolving the organics extracted liquid containing a first concentration of the slurry at the first screen assembly, the withdrawn liquid outside or for digester recovery feed for processing, after c) steps (a) and of (b), the slurries in the direction of the second screen assembly, flow through the second screen assembly, d) at the second screen assembly Slurry liquid is withdrawn and in a recirculation loop back to the digester at the approximate location of the second screen assembly for recirculation, e) introduction of the cooking liquor into the recirculation loop, f) well below the first concentration of dissolved organics. , Pulp strength,
A diluent having a second concentration of dissolved organic matter that beneficially affects the consumed available alkali, H-factor, or bleaching degree is introduced into the recycle loop, and g) well below the first concentration of dissolved organic matter and pulp strength. ,
Process for continuous production of chemical cellulose pulp comprising the steps of introducing into a digester a liquor of a recycle loop having a third concentration of dissolved organic matter which advantageously influences the available alkali, H-factor, or bleaching consumed. . 19. A process according to claim 18 , characterized in that an additional step of heating the liquor of the recirculation loop before returning it to the digester is carried out between steps (f) and (g). 20. The liquor flows co-currently into the comminuted cellulosic fibrous material between the first and second screen assemblies and countercurrently with the cellulosic material immediately before and after the screen assembly. The method according to claim 18 , wherein 21. The method of claim 18 , further comprising the step of heating and recirculating the liquid withdrawn in step (b) at a general location of the first screen assembly section. 22. The method according to claim 18 , wherein step (f) is carried out by introducing a washing device filtrate or water or a combination thereof. 23. Steps (e) and (f) are approximately the same as the amount of liquor sent for recovery during step (b) or for other processing outside the digester. 23. The method of claim 22 , wherein is performed by reintroducing. 24. Steps (e) and (f) are approximately the same as the amount of liquor sent for recovery during step (b) or for other processing outside the digester. 19. The method according to claim 18 , characterized in that 25. The method according to claim 18 , characterized in that the cooking is carried out in a digester and steps (a) to (g) are carried out before or at the beginning of the cooking. 26. The method according to claim 18 , wherein steps (a) to (g) are always carried out at a dissolved organic matter concentration of less than 100 g / l. 27. A digester having a top and a bottom, wherein an inlet for digested comminuted cellulosic fibrous material is provided at the top of the digester, and a digested pulp is provided at the bottom. An outlet of the digester, a top screen assembly for withdrawing liquor from the top of the digester and an extraction screen provided below the top screen assembly, a digestion screen assembly provided between the extraction screen assembly and the bottom of the digester, digestion Means for withdrawing a first portion of the liquor passing through the screen assembly, sending it to recovery, leaving the second portion of the liquor passing through the digestion screen assembly, adding a liquid with a low dissolved organic matter concentration to said second portion, Means for obtaining an incremented second portion, and digesting the incremented second portion at a general location of the digestion screen assembly Continuous digester with means to recirculate into the can. 28. A continuous digester having a top and a bottom, the inlet for the digested cellulosic material provided at the top, the outlet for the digested pulp provided at the bottom, the top. A screen assembly, a trim circulation screen provided under the top screen assembly, a first screen assembly provided under the trim circulation screen assembly and having a first withdrawal conduit, provided under the first screen assembly A second screen assembly comprising a second withdrawal conduit connected to the flash tank and operated, means for adding a liquid with a low dissolved organic matter concentration to said first withdrawal conduit, and an added liquid with a low dissolved organic matter concentration. Together, the liquid in the first withdrawal conduit is removed from the digester at the approximate location of the first screen assembly. Continuous digester equipped with means for recycling to the section. 29. The first withdrawal conduit is selectively connected to the second withdrawal conduit so that part of the liquid in the first withdrawal conduit is a liquid with a low dissolved organic matter concentration into the first withdrawal conduit. JP, further comprising means to be able to send to the flash tank in front of said means for adding
29. The continuous digester for cooking according to claim 28 .