Vacuum dipping cooking pulping process

Experimental research on vacuum impregnation cooking pulping process DU Duo ZHANG An-long2, DONG Ji-xian2, WANG Mei2 (1. Chengdu Banknote Printing Corporation, Chengdu 611130, China; 2. Shaanxi University of Science and Technology, Xianyang 712081, Shaanxi Province) It can be seen that the temperature rise In the high process, no matter the drug absorbed by the material shows an upward trend.

Vacuum degree In the impregnation process, the pressure difference is used to accelerate the impregnation of the cooking material with the fiber material. Under the condition of different impregnation vacuum degree (other parameters unchanged), the impregnation of the fiber raw material under a certain degree of vacuum for each impregnation process, after the impregnation of the fiber raw material, the quality of the absorption liquid of the fiber material and the percentage of the absorption liquid as shown.

As the degree of vacuum rises, the amount of liquid absorbed by the material and the percentage of absorbed liquid gradually increase.

The time is at different dipping times (other parameters are unchanged).

It can be seen that as the immersion time is prolonged, the amount of liquid absorbed by the fiber raw material and the percentage of the liquid to be absorbed gradually increase, but after a period of time, when the change is not collapsed, the time can be (min) to vacuum impregnation. The influence of the three factors of influence degree, temperature, and time on the two quality indicators of the impregnation results is BCA (primary one), that is, the primary and secondary relationships of each factor in the vacuum impregnation process are: temperature, time, and vacuum degree.

From the range analysis, the optimal combination of factors can be determined as: liquid absorption AiBsC3 Percent liquid absorption A3 In the above process, due to the effect of delignification during the vacuum impregnation pretreatment, the effect is less In the subsequent cooking process, the lignin can be quickly and completely removed. The cooking liquid that absorbs more raw materials is a necessary condition for the delignification reaction. In the case of a certain amount of cooking liquid, the percentage of the absorption liquid directly indicates the amount of cooking liquid that enters the cell cavity.

It is known from this that the diffusion rate increases as the degree of vacuum increases. It can be judged that the ratio of infiltrating the retort material into the fiber material at a large degree of vacuum under a relatively large degree of vacuum is increased. Therefore, A3 should be selected as the optimum process conditions for the vacuum degree; and for the selection of the factor B, it seems that the two quality indicators are consistent, that is, the higher immersion temperature should be selected, so the choice of 氏 as the optimum process condition; From the perspective of the pretreatment time of factor C, it can be seen that as the time goes by, the slope of the curve becomes smaller and smaller, that is, the influence of time on the impregnation effect becomes smaller and smaller, and the impregnation is performed for 45 min and the vacuum impregnation cooking process is obtained. Good process conditions, this.

Table 3 Comparison of impregnation results between optimal vacuum impregnation and conventional impregnation processes Immersion vacuum degree time temperature Solution liquid absorption Absorption of one-hundred square vacuum As can be seen from Table 3, the degree of delignification is not much different under vacuum-like conditions. The reaction type and reaction degree of the lignin and some carbohydrates in the raw materials and the cooking liquor are basically the same.

In addition, with the vacuum dip cooking method, the maximum cooking temperature is reduced by 10C compared with the conventional sulphate method, and the holding time is shortened by 30 minutes. Under the action of the vacuum mechanism, the boiling point of the cooking solution will be reduced to an appropriate degree so that the temperature is lowered. Under boiling cooking liquid boiling occurs. In the vacuum impregnation process, the cooking liquid penetrates into the raw material of the sputum fiber faster, and due to the effect of vacuum, the air and the non-condensable gas in the cooking system can be eliminated, the heat transfer effect is increased, the heating time is shortened, and the saving is increased. After impregnating the material in the state, the absorption amount of the liquid is 35% higher than that in the normal state, and the percentage of the absorption cooking liquid is increased by 88%, and more cooking liquid enters the cell wall and intercellular space of the material. In the layer, a series of delignification reactions will occur in advance under the action of the cooking liquor. Although the reaction rate is slow and the lignin removed is only a small part, the lignin will soften and the fibers will be easy to isolate and disperse, creating the necessary conditions for the subsequent delignification process and improving the quality of the slurry.

After vacuum impregnation, the raw materials for the vacuum impregnation cooking pulping process were continuously heated to carry out cooking experiments. For the vacuum impregnation cooking process, the primary and secondary factors of each influencing factor are A, D, B, C, and E. That is, the primary and secondary order of the influencing factors is: alkali amount, maximum temperature, vulcanization degree, heating time, holding time .

Under the premise of fully considering each quality index and production cost, according to the principle of majority tendency, the optimum process conditions for vacuum impregnation cooking can be determined as: A4B2C3D2E2. That is, the alkali amount is 24.%, the degree of sulfuration is 20°%, and the heating time is 120 minutes. , The maximum temperature is 155*C, and the holding time is 90min. The confirmatory test results are the yield of fine slurry 42.08°%, the slag slag rate 0.94°%, Pulp hardness Table 5 Comparison of two kinds of cooking processes and results The conventional cooking vacuum impregnation Alkali for cooking (as NaOHf, %) Vulcanization degree (%) Heating time (min) Maximum temperature CC) Holding time (min) Liquid ratio Slurry yield (%) Screening rate (%) Pulp hardness (KMnO4 value) Residual alkali (as NaOH) (%) Black liquor volume (mL) Number average length (mm) Weight average length (mm) Double weight average length (mm) Whiteness (%) Freeness (*SR) Tensile index ( N*m/g) Tear index (mN*m2/g) Flexibility (secondary) thermal energy, reducing production costs. The cooking liquor reacts with lignin and some carbohydrates earlier, and when the delignification reaction starts, the rate of reaction is proportional to the concentration of the reactants, so the reaction rate can be accelerated and reached in a relatively short period of time. The purpose of removing lignin. With the same degree of lignin removal, the holding time at the highest temperature can be shortened.

It can also be seen from Table 5 that under vacuum, the volume of black liquor at the end of cooking is about 20% less than that of the conventional cooking method black liquor, and its CODQ concentration is relatively increased by about 20%. During vacuuming Part of the water vapor is eliminated, so that the black liquor is concentrated, its volume is reduced, and the CODcr concentration is increased. Partial heating steam can be saved in the process of alkali recovery evaporation, reducing costs.

It can be seen from Table 5 that the average fiber length of the pulp obtained by the vacuum impregnation cooking is longer than the average fiber length of the pulp obtained by the conventional cooking method. This is mainly due to the fact that during the vacuum impregnation cooking process, due to the relatively short reaction time of the raw material of the fiber material and the cooking liquid at a higher temperature, the fiber is less affected by the cooking liquid, and the peeling reaction during the process of delignification and The degree of alkaline hydrolysis is lower, ie less degradation and higher degree of pulp polymerization.

5 Conclusion The vacuum impregnation cooking process has obvious influence on cooking results; vacuum vacuum impregnation is the best process conditions: vacuum degree 0.06MPa, impregnation temperature 60*C, impregnation time 45min; optimum vacuum impregnation cooking process conditions: use alkali amount 24° %, vulcanization degree 20°%, warm-up time * C, adopt vacuum dip cooking method when keeping warm, can lower 10*C than regular kraft method in the highest cooking temperature, and shorten the holding time under the highest temperature 30min. Under the action of the vacuum mechanism, the black liquor is concentrated at the end of cooking, the concentration of COD is increased by approximately 20%, which reduces the discharge of waste liquor and reduces the cost of alkali recovery; in addition, the average fiber length of the pulp obtained by vacuum dipping and cooking It is long, and the strength of the pulp is slightly higher than that of the pulp obtained by the conventional method. *

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