SE426854B - Process for the preparation of sulphate pulp from a lignocellulose-containing material - Google Patents

Abstract

Process for the preparation of sulphate pulp from a lignocellulose-containing material. The yield of the pulp can be raised here because of the very short time of contact between the material and the cooking liquor in the temperature range of 80-140 degrees C. The impregnation is essentially carried out at a temperature outside these limits and at a value below the cooking temperature. <IMAGE>

Description

7s12o47-4 .2 10 15 20 25 30 35 then meets the cooking liquid in the sulphate boil, it has become possible to design a new high-temperature impregnation step, which both clearly differs from the actual boiling and contains the required temperature level to give maximum yield effect. For more difficult-to-boil wood, a short initial pre-treatment can take place in cooking liquid at temperatures well below 80 ° C. An important part of the elimination of this process is that the yield gain is to be achieved without significant deterioration of the paper properties, in contrast to what has been the case in the more drastic yield effects in connection with, for example, polysulfide boiling. What is important in that case is not theoretically investigated and we have only been able to find an empirical way to achieve this goal. This current process seems to preserve the positive properties of the sulphate pulp in a somewhat unexpected way. An important part of the design of this step has been to adapt the time and temperature for the impregnation step and to instruct principles for how to avoid mechanical damage to the material in the event of transfer to the cooking step in a continuous cooking apparatus.

The temperature in the new impregnation step can be so high that a limit is exceeded as the fibrous material in the current environment becomes hypersensitive to mechanical processing.

Another important issue for certain applications of the process is to adapt the cooking step, so that the chain length of the carbohydrates in the pulp is not reduced beyond what is normal in sulphate cooking. So-called bush shaking according to a previous design has shown a greater carbohydrate breakdown (a carbohydrate breakdown, which, however, is not visible on the yield). This is especially important for pulp to bleaching, the chain length dies after bleaching often becomes critically short.

Quite unexpectedly, it has been found that a combination of a slightly prolonged high-temperature impregnation and a slightly reduced boiling temperature is very favorable in this respect.

The features of the invention appear from the claims.

The invention will be described in more detail in the following in connection with the figure, which shows a plant for continuous sulphate boiling according to the invention. From a chip container 1, the chips are transferred via a locking device 2 to a basing vessel 3 "for basing. The chips are discharged from this vessel via a dry pressure lock 4, so-called high-pressure layer, directly into a pressure impregnation vessel 5. There, the chips meet boiling liquid which has previously been preheated in a heat exchanger 6 and introduced through a hinge 10 15 20 25 30 35 7812047- The temperature of the cooking liquid is 150-190 ° C, preferably 160-180 ° C, preferably about 170 ° C. This gives a mixing temperature of 140 ° C, preferably 14 ° C, 16 ° C, about 150 ° C. possibly a certain fine adjustment of the temperature can be done with direct steam. The chips are treated in the impregnation vessel 5 without further heating. A certain temperature rise can still occur due to heat of reaction. The residence time of the chips in contact with the cooking liquid within the temperature range 80-140 ° C should be very short, shorter than 20 minutes, preferably shorter than 3 minutes and preferably shorter than 1-2 minutes. The chips are fed through the impregnation bin 5 with scrapers or screws, which do not give any critical mechanical processing. After the impregnation basket, chips and cooking liquid are allowed to fall freely in a precipice 8 down into a circulation line 9 through which the chips are fed up to the top of a digester 11 by means of a pump 10. If desired, a pressure lock can be laid between the impregnation kiln 5 and the precipitate 8.

The plunge is designed with some release and opens directly into the circulation line 9 so that the chips can be moved from the impregnation vessel 5 to the line without additional mechanical devices. The heating of cooking liquid and chips for the final cooking can either take place indirectly in the circulation line 9 or directly with steam in the top of the boiler 11. The boiling temperature should, if pulp is produced for bleaching or the like, die decomposition of the carbohydrate chain length (usually met with so-called pulp viscosity) must be kept below k ° nff ° 11, selected to 150-175 ° c, preferably 15s-16s ° c, probably 16o ° c. The result of the invention applied in continuous cooking is illustrated by the following examples. 9 _ Softwood chips were fed to a basing pan, where the basing was carried out at 1.3 bar (overpressure). The chips were further fed into a pressure impregnation vessel via a pressure lock and immediately after this. With the aid of the directly long residence times in the impregnation, the boiling point was brought to 17 ° C. the temperature was fine-tuned to 150 ° C. the ring grain at 150 ° C was 30 minutes. The chips were then fed to the top of a downstream boiler and the temperature was raised to 160 ° C with the help of direct steam. The residence time at 160 ° C was 2% hour. An alkali batch of 210 kg VA (NUOH) per tonne of wood and a wood: liquid ratio of 1: 3.0 gave a pulp with a kappa number of 35. According to laboratory tests, the total pulp was obtained. to the same kappatal. 7812047-4 - 4. the yield thereby 49.6% compared with 48.1% with conventional heating- The result is reported in table 1. With the new procedure, about 3% more l mass was obtained from the same amount of wood compared to conventional technology. ger.

The invention can be used both to extract a higher yield at an otherwise relatively normal sulphate boiling effort and to boil slightly longer in connection with, for example, bleaching without the yield level deteriorating.

The invention can also be applied to discontinuous cooking.

This is illustrated in the following example. - The boiler was filled with softwood chips using steam filling and the chips were based to approximately 100 ° C. Free condensate was drained off.

- To 180-190 ° C preheated cooking liquid was pressed over to the chip-filled cooker within about 10 minutes. The mixing temperature then became 150-160 ° C. The boiler was allowed to stand and impregnate at this temperature for 1 hour, after which the temperature was raised to -170 ° C in 30 minutes. The residence time at 170 ° C was chosen for 1 hour. With an alkali charge of 210 kg VA (NaOH) per tonne of wood and a wood: liquid ratio of 1: 3.5, the cutting number was then about 35. According to performed laboratory tests, the total the mass yield §8,8Z compared to 48,12 if the heating of the boiler had been done in a conventional way with cooking to the same kappa number.- This is a slightly smaller effect than for the continuous embodiment where required temperature levels can be contained with greater precision (easier to heat quickly).> The following example shows a process according to the invention in which the impregnation is mainly carried out at a temperature below 80 ° C.

Softwood chips were fed to an impregnation vessel, where the impregnation with sulphate cooking liquid took place at 30 ° C and at a pressure of 10 bar (overpressure) for 30 minutes. The chips were then fed on to a cooking vessel at the same time as the temperature was momentarily raised by means of direct steam to 160 ° C. The residence time at 160 ° C was 2 hours 50 minutes. With an alkali charge of 210 kg WO (NaOH) ptv and a wood: liquid ratio of 1: 3.0, a pulp with a kappa number of 35 was obtained. The pulp yield was 49.4% compared to 48.1%. with conventional heating technology and cooking to the same kappa number. 7812047-4 m? má ñm E »3 E? ¶. ššm »mi 33 .im. m2. E ¶ _ mN 73. än .XS mm .rrmcowpcwëox mmß. @. M _.m. ONF. .Nm mv. ._ = fl m = M == «~ Qi. mä: .Hm 0: .. mm ... a ä? . m5 _ i? mm 19.3 uuïcm mE \ m ¥ @ ¥ \ ~ Ez mx \ 2 = m ¥ \ E2 ¥: WE mmm _ xmEz. xmu fi xmuí 6.5 vf subject pwpfmcmm |> wm | m = mLQm | mmLo »Fda | -z po». vmnw wmfwm mL «=> o ~ @ w» @@@ ø @: ao ^ ~ mm ~ s pw> v m = «= F ~ E> m- ~>. R Wm ~> n »= Pmpmqqmx mwmuoga om fl ounwsnm. .m cømcwccwwmm: vuwano mcfwrxox mwauøncwvcovfsocom E.

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Claims (4)

7812047-4% s _ P a t e n t k r a v Sweetening for the production of sulphate pulp from lignocellulosic material, comprising impregnation of the material with boiling liquid following boiling, characterized in that the impregnation is carried out mainly at a temperature lower than the boiling temperature and which is outside the temperature range 80-140 ° C, that the residence time of the material in contact with the cooking liquid within the temperature range: so _ 14o ° approx .; nyekef km a v e knrtere an 20 minutes, lumen- gen shorter than 3 minutes, preferably shorter ön 1-2 minutes, and a kekningen takes place at 1so_17s ° .c. ' Sweet according to claim 1, characterized in that the impregnation is carried out on a main scale at a temperature lower than 0 ° C. e 'i Set according to claim 1, the impregnation is mainly carried out at a temperature higher than 14 ° C. '' Sweet according to claim 3, characterized in that the material before the impregnation is based to a temperature of approximately 100 ° C and that the cooking liquid is then added to the material so that the temperature is rapidly raised to over 140 ° C for impregnation of the material.