FI107055B - Process for streamlining an alkaline cellulose production process - Google Patents

Description

107055

METHOD FOR EFFICIENT ALKALINE PULP MAKING PROCESS

The present invention relates to a process for enhancing the alkaline pulp making process wherein waste liquors from cooking and washing liquids from pulping are recycled in or between the cooking compartment, washing compartment.

In the alkaline chemical pulping process, lignosel-10 lulose-containing material, such as wood chips, is treated in a cooking solution with the active chemicals being mainly sodium sulfide and sodium hydroxide or sodium hydroxide alone. After cooking, the liquor used is separated from the pulp, which is subjected to further processing such as washing, sorting and bleaching. Of the spent liquor, the so-called. in turn, the chemicals are recovered to make a new cooking solution.

In the cooking wood resin fats and resin acids are saponified • 2.4 into sodium soaps, crude. Conventionally, the black liquor is separated from the soap before passing the liquor to evaporation and • '' to form green liquor and further white liquor.

The soup rises to a lighter surface than the lye, where it can be decanted off. Stripping is important because it is a highly foam-forming substance and thus causes many problems in the process. However, some of the desiccant is dissolved:. black liquor and thus does not settle on the surface of the liquor.

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Not only during the cooking process, the soap is transferred from the pulp to its lye, also during * 30 pulp washing. Soap differs in solubility from other solids and therefore does not wash as easily as other solids. During filter washing, the soap is removed at a later stage than any other dry substance. Dehydrating soap also makes it difficult to clean the pulp filter.

As is known, chemical pulp can be produced by alkaline delignification in both batch and continuous 35, 107055 2 cookers. Rather than passing the black liquor to the digester for recovery, hot black liquor can be used to treat the wood chips prior to the actual cooking step to improve the process. In continuous cooking, the hot black liquor can be recycled to the wood chips during the impregnation step, as disclosed, for example, in EP 527 294. The hot pressurized black liquor can also be expanded to produce steam and increase the dry solids content of the black liquor. In batch cooking, black liquor can be stored at various temperatures in lye containers, called "lye batteries", for use in the processing of chips.

Recycling black liquor offers many benefits. The heat economy of the process improves. When soup occurs in the presence of sulfur, 15 black liquors add sulfur compounds to the cellulosic material which have a very beneficial effect in impregnation steps by reducing the kappa number of the pulp. The recycling of black liquor also presents problems, since the soap contained in the black liquor is enriched in the process unless it is effectively removed from the "20 solutions which are recyclable. 1 '" Previously, due consideration has not been given to the effective removal of the desalt in the processes described in EP 520 452. 2 <5 with three tanks for black liquor. After replacement by washing filtrate, black liquor is initially introduced: · · is fed to the first hot liquor battery at substantially cooking temperature and pressure and dry matter content achieved by cooking. The second black liquor battery is supplied with black liquor * 30 pe, the temperature of which corresponds to the boiling point of the liquor at atmospheric pressure. · The black liquor content of the second battery is lower than the black liquor contained in the first battery, washing liquid, which also has a higher salt content of 35. According to this publication, the second black liquor is used to heat the white liquor to the digester, then it is fed to a tank where 3,107055 pe of this black liquor is used to absorb a new batch of chips. The chips are then also impregnated with hot black liquor from the first tank.

However, it has now been found that the above-described measures for desertification are not sufficient. If the soap is not removed efficiently from reusable solutions such as black liquor and washing liquids, the soap will become rich in the kitchen, where it will dissolve in further processing. As mass 10 is further removed from the digester to the butt tank and for washing, the strongly dripping mildew causes problems in the butt tank and washer filters, thereby causing production disruption and deterioration of the pulp quality.

The object of the present invention is to eliminate the above-mentioned problems and to provide a method by which the batch concentration of recyclable solutions in the batch, both batch and continuous, can be adjusted to a desired level where the batch does not interfere with cooking or washing.

To achieve these objects, the present invention relates to a process for enhancing the alkaline pulp making process, wherein the removal of desiccant is enhanced by adjusting the Na + content of the desiccant so as to dissolve the desiccant in the desiccant. .25 extinguishes and stands out, and the invention is characterized, ···. the fact that the soy-containing substance is black liquor and / or pulp from the wood chips boiling • · liquor cycle and / or • 1 «* .1.1. · washing washings which are treated to adjust their Na - • · · * · 1 1 concentration and 30 of said liquids are dewatered before being recycled in the boiler •, · - 1 ... · to, in and between the washing compartment.

- The solubility of lava depends on the sodium content. It is regulated ·! it is possible to influence the balance of solid / dissolved 35 marshes. As the sodium concentration rises, the solubility of the filtrate decreases and the salt can be desalted out of solution. Suovan soluble /; 1 may depend on the concentration of sodium ions 107055 as shown in Figure 1. By adjusting the amount of sodium in the solution so that it is within the low solubility of the salt, the salt is saline out of the solution. Figure 1 shows the amount of dissolved neutral substances in the strainer. Neutral agents do not directly dissolve in the wash liquid, but are soluble in the micelles formed by the solute, whereby their amount in the solution is directly proportional to the amount of solute in the solution, such as the wash liquid. In the case illustrated in Figure 1, the salt is separated from the solution when the Na content is preferably greater than 12 g / l.

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Depending on the cooking method, there are several cycles of solution in the preparation of the pulp that require attention to the salt content. For example, in the wash compartment, the sodium content of the wash filtrates is higher at the beginning of the wash compartment than at the end 15.

As previously described in batch cooking, it is now common to treat wood chips with black liquor prior to cooking the chips in white liquor. The reasons for this are the benefits of black liquor treatment, e.g. better energy economy. Of course, this requires the process to operate optimally. By removing the salt from the solutions containing it, this objective can be facilitated. In batch cooking, the salinity of black liquor depends on where the black liquor from the digester is replaced. As previously described, the black liquor is drained · ***. from the kettle to at least two tanks during displacement.

• · ·:. ·. The salinity content of black liquor rises when the • • ·. ·; ·. the sludge is discharged from the digester. The salt content of the • ♦ «stock coming to the washing department can be 80-100 ... 30 kg / tm under Scandinavian conditions. By controlling the salt content of the washing filtrate that is already being introduced to the displacement, the amount of salt entering the digester ♦ · ··· * is reduced because the black liquor containing the washing filtrate is used: V; typically by absorbing the next batch. Further, prior to this absorption, it is preferable to remove 35 soils from this black liquor. Also, the black liquor removed at the beginning of the displacement may be lowered if necessary. All these * · measures can reduce the amount of desiccation that comes with the pulp in the butt tank and 5 107055 still in the wash compartment.

In continuous cooking, the black liquor is recycled to pre-treat, slurry and absorb the chips. The black liquor is removed from the digester and, if necessary, fed to expansion vessels before re-use. By adjusting the salt content of the black liquor to the chips pre-treatment after the expansion tanks, any problems caused by leaching can be avoided.

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There are many sources of sodium ion available at the pulp mill which can be used to carry out the process of the invention. Sodium can be added as various sodium compounds that are otherwise used in the factory, such as sodium sulfide, -15 hydroxide or sulfate. The mill has a solution mainly containing NaOH, e.g. pulp mill chemical cycle from caustic soda. Very preferably, the required sodium may be added as a white liquor containing sodium hydroxide and sodium sulfide for use in cooking. Green liquor containing sodium kar-20 bonate and sodium sulfide may also be used.

: The soap removal should take place at a point in the solution circulation where J 25 after the addition of sodium can be provided with a sufficient delay time for the solution (tank (s)). out to allow salting out and leaching to separate.

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The sodium ion and salt content of the solution cycles should be monitored • · · * just before the process points where high salt content of 30 is found to cause production disruption. Applying the process of the present invention to these points · · · - can eliminate the disadvantages.

««. ···. The present invention will be explained in more detail with reference to the accompanying Figure 2, which shows an embodiment V 'for carrying out the invention in batch cooking.

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A cooker 10 for soup is charged with wood chips and white-fudge from a container 40 through lines 41 and 42. At the end of the cooking, which occurs at an elevated temperature, about 155-180 ° C, the black liquor formed in the cooking is removed from the digester by freezing it with a washing filtrate from pulp washing.

The first hot black liquor leaving is passed through line 21 of the hot liquor accumulator 20. The temperature of the hot liquor battery is almost the same as the cooking temperature.

At a certain point, the temperature of the black liquor removed from the displacement digester decreases because the temperature of the displacement solution is less than 100 ° C. This lower temperature black liquor is fed to the second alkaline battery 30 via line 31. After displacement, the pulp is discharged to the butt tank 50 along lines 11 through 15.

The black liquors in the liquor accumulators 20 and 30 can be used to pre-treat the chips of the next batch. The black liquor in the lower temperature lye battery 30 contains soap from the washing filtrate 20 and the pulp, which must be removed as much as possible before the lye is discharged to heat the next batch of chips in the digester. To this end, in accordance with the invention, the lye is led from the battery 30 through line 32 to the tank 33. The sodium content of the lye is then measured and, if necessary, adjusted by addition of 25 sodium-containing solutions through line 34 such that · * '*. the salt is salted from the solution. The reservoir 33 is sized to provide a sufficiently long delay to desalt the soluble * ♦ i · · · filtrate contained in the liquor and to separate the filtrate ♦ · · lighter on the surface of the liquor. Known sludge separators can be used to remove the soap from the surface of the solution. Soap is removed along line 35 · · ··· *, depending on the mill, for tall oil production or evaporation: V: mill and incineration. Substantially undesirable black liquor is • passed through line 36 to digester 10 to heat and absorb 35 chips.

The heating and impregnating black liquor is displaced from the digester by hot 107055 club with black liquor from the battery 20 and removed from the digester along line 22 to the reservoir 33 to separate the filtrate and further to the black liquor evaporator through line 36.

Before being introduced into the digester, the hot black liquor from the battery 20 may also be treated to remove desiccant in a similar manner to the cooler black liquor from the battery 30. The hot black liquor flowing in line 23 may first heat the white liquor 41 in the heat exchanger 42. 24 through. Reservoir 25 undergoes salt desalting and separation from solution. The soap exits through line 26 and hot, low-flow black liquor is pumped in line 27, 42 to the digester to displace the cooler black liquor.

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After the supply of hot black liquor, white liquor from the container 40 is introduced into the digester together with the hot black liquor to carry out the cooking step.

After cooking, the pulp is introduced into the butt tank 50, the storage tank 51, and any graft separation 52 to the washing filters 53, which are preferably the scrubbers described in, for example, U.S. Patents 4,919,158, 5,116,423, 5,139,671 and 5,120,398.

25 Washers may transfer a large amount of soap to the wash. «**. susuodokseen. When such washing filtrate is recycled to the digester:. ♦ ♦ # *, ·; · [the problems caused by the mass and the high volume of the foaming agent in the butt tank. The desiccant enrichment can be prevented here ... 30 processes in the same way as in the lye cycle between the black liquor batteries and • · _ * ♦♦ · *. To this end, the sodium concentration of the washing filtrate is measured and adjusted in line 54 as necessary by adding sodium-containing solution from line 55. The soap is desalted from the wash filtrate in tank 56 and the separated soap 35 is removed through line 57. A controlled filtrate amount of washing · · · * · '* is passed to the displacement lye in digester 10 via line 42.

8 107055

The pulp washed with the filters 53 is further passed to a screening plant 60 and to the filters 61, which are preferably filters which are further described e.g. in U.S. Patent 5,227,058. The pulp is further passed through line 62 for bleaching. Filters 61 5 are supplied with washing liquid bleach water along line 63.

The filters 61 are coupled upstream with the filters 53. Also, the washing filtrate of the filters 61 may be treated prior to being passed to the filters 53 to separate the filter. The wash filtrate is passed through a line 64 where its sodium-10 content is determined and, if necessary, added to the tank 66. The sodium filtrate solution is removed (68) and the wash filtrate is pumped to the pulp washing filters 53.

The present invention can be used to control the salt content of the pulp mill's cooking and washing section solution circuits so that the soap is effectively separated at suitable locations, thereby avoiding the difficulties of too high amounts of salt in various process equipment such as butt and wash filters.

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Claims (8)

9 107055 1. A process for enhancing the alkaline pulping process, wherein desalting is effected by adjusting the Na + content of the salt-containing substance so that the salt dissolved therein is salted out and separated from it, characterized in that the black liquor from the wood chips boiling into the digester or washing filtrates from pulp washing, which are treated to adjust their Na + content and from which the liquids are removed before being recycled in and between the cooking compartment, washing compartment. Process according to Claim 1, characterized in that the Na + content is adjusted by the addition of a sodium-containing solution, followed by a sufficient delay to allow desalting and separation from the solution. Process according to Claim 2, characterized in that the sodium-containing solution is a sodium hydroxide solution. I i <4 The process according to claim 2, characterized in that the sodium-containing solution is white liquor. 20: 5. The method of claim 2, wherein the sodium-containing solution is; is green liquor. • 5. Förfarande enligt patentkravet 2, kännetecknat av att den sodium halalt lösningen v .: 30 utgörs av grönlut. 11 107055 6. Förfarande enligt nägot av föregäende patentkrav, kännetecknat av att chemisk mass framställs genom att använda satsvis kokning, colors svartiuten som skall använda för flisimpregnering behandlas. 5 7. Förfarande enligt nägot av föregäende patentkrav 1-5, kännetecknat av att chemisk mass framställs genom att använda satsvis kokning, colors det frän tvättning av massan erhällna tvättfiltratet som skall använ som somängängningslut behandlas. Method according to one of the preceding claims, characterized in that the pulp is produced by a batch cooking process, which is used for the absorption of chips. .'j, black liquor is being processed. • 4 · • · «» «· · Method according to one of the preceding claims 1 to 5, characterized in that the pulp is produced by a batch cooking process, whereby the pulp washing is treated as a washing filtrate used as a digestion liquid. 10 107055 Process according to one of Claims 1 to 5, characterized in that the pulp is produced continuously, whereby the black liquor removed from the digester is treated, which, after treatment, is recycled to the absorption of the chips or to the beginning of the cooking step. 5 io 1. Förfarande för effektivering av alkaiisk framställningsprocess för chemisk mass, vid flashing förfarande sapavskiljningen effektiveras genomic att justera Na + -halten i enpinnehandland substantant, att den i substansen från får på avskalt. av svartlut som erhälls frän kokning av träflis account kokarens lutcirkulation / -er, och / eller tvättfiltrat som 15 erhälls frän tvättning av massan, livelihood behandlas för justering av deras Na + -halt och frän livelihood littlcr llc llc. oh däremellan. : '2. Förfarande enligt patentkravet 1, kännetecknat av att Na + -halten justeras genome 20 att tildet sodium salt lösning, varefter en tillräckligt län fördröjning arrangeras for att möjliggöra utsaltning och avskiljning av patan frän. ; 1: ·. 3. Förfarande enligt patentkravet 2, kännetecknat av att den sodium halalt lösningen «utgörs av en sodium hydroxydlösning. 25 * · • · ·; ***. 4. Förfarande enligt patentkravet 2, kännetecknat av att den sodium halalt lösningen • · · \ utgörs av vitlut. • · · • · · 1 1 · • · 8. Förfarande enligt vorte av föregäende patentkrav 1-5, kännetecknat av att chemisk 10 mass framställs kontinuerligt, colors den frän kokaren avlägsnade svartiuten behandlas och efter behandlingen ätercirkuleras account början av flisimpregnerings- eller kokn. • • • • • • • • • • • • • • • • • • • • • • • •••• I * ·