JP2005089921A - Method for continuously producing pulp by liquid phase continuous digester - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing pulp using a liquid phase continuous digester in which occurrence of tip hanging can be prevented as much as possible in the liquid phase continuous digester for producing kraft pulp. <P>SOLUTION: In a liquid phase continuous digester in which a pulp raw material and a digesting agent are fed from the top of a vessel V and an impregnation zone A, a digesting zone B and a washing zone C are formed from the upper direction in the vessel V and black liquor is extracted from an extraction strainer 4 installed in a middle stage part of the vessel V and a cellulose component is taken out from an outlet device D installed in the bottom of the vessel V, an upper digesting circulation line L<SB>5</SB>for recycling a part of the digesting agent from an upper digesting circulation strainer 1 installed in the boundary part between the impregnation zone A and the digesting zone B to the top of the vessel V is installed and a pulling-out agent line LZ<SB>5</SB>is branched from the upper digesting circulating line and a part of the agent is pulled out as pressure control in the vessel V and a liquid ratio in the digesting zone B and the washing zone C is controlled to prevent occurrence of tip hanging in the continuous digesting oven. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a pulp manufacturing method for pulping a pulp raw material composed of continuously pulverized lignocellulosic material using a liquid phase continuous digester, and more specifically, a chip hanging phenomenon that occurs during continuous cooking of a pulp raw material. The present invention relates to a pulp production method using a liquid phase continuous digester that can be prevented as much as possible.

  In liquid-phase continuous digesters (for example, liquid-phase continuous digesters such as conventional Kamiya-type continuous digesters, MCC-type continuous digesters, and EMCC-type continuous digesters), The raw material chips (chips) and cooking chemicals that are mixed and flowed, during which time the raw material chips are cooked. In this type of continuous digester, the so-called “chip hanging” phenomenon has led to continuous operation. Was interrupted.

  When “chip hanging” occurs, the continuous operation of the continuous digester has to be interrupted to eliminate it, resulting in a great deal of damage.

  FIG. 4 shows a continuous pulp production apparatus using a conventional liquid phase continuous digester. The apparatus example of FIG. 4 will be described briefly. The apparatus is a pressurized liquid phase type pulp continuous that maintains pressure and temperature in a state where the raw material chips and the liquid (the cooking chemical liquid and the cleaning liquid) are always filled in the tower-like vessel V. It is a manufacturing device.

To explain this further, the apparatus supplies a pulp raw material (chip) made of pulverized lignocellulosic material and a cooking chemical liquid in a fixed amount from the top of the tower-like vessel V, and from the upper direction in the vessel V. A permeation zone A for infiltrating the cooking liquid into the pulp raw material (chip), a cooking zone B for dissolving and separating the lignin component in the pulp raw material in the cooking chemical liquid, and a cleaning zone C for cleaning the cellulose component in the pulp raw material. From the extraction strainer 4 provided in the middle part of the vessel V (the boundary between the cooking zone B and the washing zone C) is a black liquor produced by containing the lignin component separated from the pulp raw material in the cooking chemical solution. The cellulose component is extracted and taken out from an outlet device D provided at the bottom of the vessel V. Wash water Cw is supplied from the wash water line L ₉ to the bottom of the vessel V, and the wash water flows upward in the washing zone C with respect to the lowering of the pulp raw material (countercurrent washing), and the lignin separated from the pulp raw material The black liquor containing the components is replaced and washed. The substituted black liquor rises and is extracted from the extraction strainer 4 provided in the middle part of the vessel V.

In the permeation zone A, the permeation action of the cooking chemical liquid into the pulp raw material (chip) is performed. In the cooking zone B, the cooking is heated to the cooking temperature by the heater 7 from the upper cooking circulation strainer 1 to the center of the upper cooking circulation strainer 1 in the vessel V through the upper cooking circulation pump 6, the heater 7 and the top of the vessel V. The chemical solution is refluxed (this reflux line is referred to as “upper cooking circulation line L ₅ ”), and cooking (dissolving and separating the lignin component in the pulp raw material in the cooking chemical solution) is started. Similarly, in the lower cooking circulation line L ₆ , the circulating chemical solution extracted from the lower cooking circulation strainer 2 located below the upper cooking circulation strainer 1 is heated to the cooking temperature by the heater 9, and then the lower cooking circulation pump 8 in the vessel V And the temperature in the upper cooking circulation line L ₅ is uniformly corrected to adjust the cooking reaction in the cooking zone B.

The middle part of the vessel V is the end of the cooking zone B, where an extraction strainer 4 and an upper washing circulation strainer 3 are provided. The cooking chemical liquid (black liquor) containing the lignin component dissolved and separated in the cooking chemical liquid from the pulp raw material (chip) that has fallen after the prescribed cooking reaction residence time in cooking zone B is passed through the upper washing circulation strainer 3 and the middle cooking circulation. After passing through the upper washing circulation pump 10 in the line L _{7 and} the top of the vessel V, it is sent to the extraction strainer 4 in the vessel V and extracted in the black liquor extraction line L ₁₀ . This black liquor extraction stops cooking.

In the washing zone C, the cellulose component in the pulp raw material that has been cooked is substituted and washed with the washing water Cw supplied from the bottom of the vessel V. This cleaning liquid rises and is sent to the extraction strainer 4 where it is extracted along with the cooking liquid containing the lignin component in the cooking zone B along with the black liquor extraction line L ₁₀ .

The pressure control of the continuous liquid phase digester shown in FIG. 4 is performed by controlling the flow rate of the cleaning water Cw supplied into the vessel V from the bottom of the vessel V in a state where the vessel V is always filled with the liquid (the cooking chemical / cleaning solution). The valve 37 with 63 is adjusted so that the pressure in the vessel V becomes constant. When the pressure in the vessel V exceeds the set value and becomes too high, the supply washing water Cw is reduced and the emergency pressure adjustment with the controller 69 from the emergency extraction line L ₁₃ provided at the bottom of the vessel V as necessary. The valve 46 is adjusted to extract the liquid in the vessel V, and the pressure in the vessel V is adjusted.

  In a tower-shaped vessel type liquid phase continuous digester, a pulp raw material (chip) made of lignocellulosic material and a cooking chemical liquid are mixed and flowed in the tower-shaped vessel, while the raw material chips are cooked. As described above, in this type of continuous digester, the continuous operation may be interrupted due to the so-called “chip hanging” phenomenon.

  “Chip hanging” means that the raw material chips falling in the tower-like vessel have various factors (for example, change in chip moisture content due to differences in chip tree species, change in chip moisture content due to weather fluctuations such as rainfall, etc.) ) Is a phenomenon in which the material chips are concentrated on the inner wall surface side of the vessel to form a lump, and as a result, the lowering of the raw material chips is not smoothly performed.

  Further, the moisture content of the chip always fluctuates finely even when external factors are small, and the liquid ratio in the columnar vessel (ratio of liquid amount L to raw material chip dry amount W = L / W) changes. Affects the cooking reaction.

The fluctuation in the moisture content of the chip results in fluctuations in the volume of pulp raw material (chip) and cooking chemical liquid supplied into the tower vessel, and in a liquid-phase continuous digester, this leads to fluctuations in the pressure in the tower vessel. 4, the supply amount of the pulp cleaning water Cw supplied to the cleaning zone C is adjusted and controlled. Then, the supply amount of change of the wash water Cw undergoes variations in pulp tower-shaped vessel V bottom, extraction of the pulp withdrawn through line L ₁₁ from the bottom of the tower-shaped vessel V varies. The fluctuation of the amount of pulp taken out from the bottom of the tower-like vessel V causes the chip level to be uncontrollable at the top of the tower-like vessel V, which may result in interruption of continuous operation. In FIG. 4, reference numeral 12, 14, 16 pump, heater 13 provided in the lower cooking circulation line L _8, the 18 first flash cyclone, the 19 second flash cyclone, 21～26,28～38 41 to 48 are valves, 61 to 69 are controllers, 71, 73, 76 and 77 are flow sensors, 72 is a pressure sensor, 74 and 75 are liquid level sensors, L ₀ is a top circulation feed line, and L ₁₂ is black liquor. Vacuum evaporator feed lines, S ₁ , S ₅ and S ₆ are flow rate signal lines, S ₂ , S ₃ and S ₄ are pressure signal lines, and S ₇ and S ₈ are liquid level signal lines.

  In addition, the well-known literature which referred the prevention method of the chip | tip hanging in a continuous digester could not be discovered in the range which this inventor investigated. However, as a known document referring to the chip hanging phenomenon in a continuous digester and its detection method, there is the following Patent Document 1.

JP-A-8-247859

  The present invention has been made in an attempt to propose a continuous pulp production method using a liquid-phase continuous digester capable of improving the above-described problem of chip hanging in a conventional liquid-phase continuous digester and performing more stable continuous operation. Thus, the following means are combined.

  The contents of the continuous pulp production method using the liquid phase continuous digester according to the present invention will be described with reference to the apparatus shown in FIGS. 1 to 3. The liquid phase continuous digester shown in FIGS. As with the liquid phase continuous digester shown, this is a pressurized liquid phase continuous pulp production system that maintains the pressure and temperature in a state where the raw material chips and the liquid (the cooking chemical and washing liquid) are always filled in the tower-like vessel V. is there.

In FIGS. 1 to 3, the line LZ ₅ is continuous between *.

  The contents described below are the same as those in the conventional apparatus example described with reference to FIG.

The continuous pulp production apparatus using the liquid-phase continuous digester shown in FIGS. 1 to 3 is supplied with a fixed amount of pulp raw material (chip) made of pulverized lignocellulosic material and cooking chemical liquid from the top of the tower-like vessel V. From the upper direction in the vessel V, a permeation zone A in which the cooking chemical liquid penetrates into the pulp raw material (chip), a cooking zone B in which the lignin component in the pulp raw material is dissolved and separated in the cooking chemical liquid, A washing zone C for washing the cellulose component is formed, and black liquor produced by containing the lignin component separated from the pulp raw material in the cooking liquid is extracted from the extraction strainer 4 provided in the middle stage of the vessel V; The cellulose component is extracted from an outlet device D provided at the bottom of the vessel V. Wash water Cw is supplied from the wash water line L ₉ to the bottom of the vessel V, and the wash water flows upward in the washing zone C with respect to the lowering of the pulp raw material (countercurrent washing), and the lignin separated from the pulp raw material The black liquor containing the components is replaced and washed. The substituted black liquor rises and is extracted by the extraction strainer 4 provided in the middle part of the vessel V.

In the permeation zone A, the permeation action of the cooking chemical liquid into the pulp raw material (chip) is performed. In the cooking zone B, the cooking is heated to the cooking temperature by the heater 7 from the upper cooking circulation strainer 1 to the center of the upper cooking circulation strainer 1 in the vessel V through the upper cooking circulation pump 6, the heater 7 and the top of the vessel V. The chemical solution is refluxed (this reflux line is referred to as “upper cooking circulation line L ₅ ”), and cooking (dissolving and separating the lignin component in the pulp raw material in the cooking chemical solution) is started. Similarly, in the lower cooking circulation line L ₆ , the circulating chemical solution extracted from the lower cooking circulation strainer 2 located below the upper cooking circulation strainer 1 is heated to the cooking temperature by the heater 9, and then the lower cooking circulation pump 8 in the vessel V And the temperature in the upper cooking circulation line L ₅ is uniformly corrected to adjust the cooking reaction in the cooking zone B.

The middle part of the vessel V is the end of the cooking zone B, where an extraction strainer 4 and an upper washing circulation strainer 3 are provided. The cooking chemical liquid (black liquor) containing the lignin component dissolved and separated in the cooking chemical liquid from the pulp raw material (chip) that has fallen after the prescribed cooking reaction residence time in cooking zone B is passed through the upper washing circulation strainer 3 and the middle cooking circulation. After passing through the upper washing circulation pump 10 in the line L _{7 and} the top of the vessel V, it is sent to the extraction strainer 4 in the vessel V and extracted in the black liquor extraction line L ₁₀ . This black liquor extraction stops cooking.

In the washing zone C, the cellulose component in the pulp raw material that has been digested is replaced and washed with the washing water Cw supplied from the bottom of the vessel V. This washing liquid rises and is sent to the extraction strainer 4 in the upper washing circulation line L _{7 and is} extracted in the black liquor extraction line L ₁₀ together with the cooking chemical liquid containing the lignin component in the cooking zone B.

Next, a specific configuration of the liquid phase continuous digester shown in FIG. 1 will be described. In the example of the apparatus shown in FIG. 1, a part Z of the circulating fluid from the upper cooking circulation line L ₅ to the upper cooking circulation line L ₅ is used. ₅ branches the extraction chemical line LZ ₅ for extracting a, and to perform pressure control in the vessel V by controlling the amount of the chemical Z ₅ withdrawn withdrawn from the extraction chemical line LZ _5. The extracted chemical solution Z ₅ is sent to the cooking chemical recovery process line.

In the present invention, by controlling the pressure in the extraction chemical Z ₅ of the vessel to control the amount V from extraction chemical line LZ _5, the liquor ratio in cooking zone B and the washing zone C to the top of the column-like vessel V Regardless of fluctuations in the volume of the pulp raw material (chip) to be supplied and the cooking chemical liquid, the occurrence of hanging is prevented by keeping it constant. As the pressure in the vessel V is controlled by the extraction chemical line LZ ₅ in the upper cooking circulation line, the washing water Cw from the washing water line L ₉ A that has been conventionally supplied to the bottom of the tower-like vessel V by pressure control. Can be changed to control at a constant flow rate. If the flow rate of the washing water Cw can be made constant, fluctuations in the pulp concentration at the bottom of the vessel V can be eliminated, and chip level control failure at the top of the vessel V in the conventional apparatus example shown in FIG. The problem can be solved.

The amount of extraction liquid medicine Z ₅ from the upper cooking circulation line L ₅ represents, it is preferable that 5 to 15% of the chemical circulation amount of the upper cooking circulation line L ₅ (less than 5%, the cooking zone B Since the dissolved substance concentration at the top of the slab is high and the chips are decomposed while consuming the cooking chemical, the yield of pulp components may be reduced. On the other hand, if it exceeds 15%, the amount of xylan in the dissolved substance decreases. This leads to a decrease in the yield of the pulp component).

In carrying out the invention of the present application, in addition to the upper cooking circulation line L ₅ , the lower cooking steam is returned to the top of the vessel V from the lower cooking circulation strainer 2 provided in the lower direction of the upper cooking circulation strainer 1. the cooking circulation line L ₆ is provided, it is preferable that the addition of cooking liquid medicine W ₆ from the lower portion digester circulation line L _6.

Further, the lower cleaning circulating line L ₈ for recirculating a portion of the cleaning liquid to the bottom of the vessel V from lower cleaning circulation strainer 5 provided below position of the vessel V is provided, cooking chemical W ₈ from said lower wash circulation line L ₈ It is also preferable to add.

At that time, it is added to the cooking liquid medicine W ₆ and lower cleaning circulation line L ₈ the amount of cooking chemical W ₀ to be supplied directly to the top of the vessel V from the top circulation feet line L ₀ is added to the lower cooking circulation line L ₆ it is recommended that 65 to 75% of the total cooking chemical liquid supply amount including a cooking chemical solution W ₈ that.

  That is, if it is less than 65%, the amount of the cooking chemical for neutralizing the acetic acid, formic acid, etc., which are the organic acids in the chip in the permeation zone A is insufficient, and the kappa number of the pulp coming out from the continuous digester becomes high. In order to obtain the target kappa number, it is necessary to increase the cooking temperature in the cooking zone B and the addition amount of the chemical solution, whereby the chips are decomposed and the yield of pulp components and the strength of the pulp are lowered. On the other hand, if it exceeds 75%, a large amount of cooking chemical remains, and the amount of chemical added in the cooking zone B is small, so that the amount of caustic soda necessary for delignification reaction becomes insufficient and there is a possibility of uncooking phenomenon.

Further, the amount of cooking chemical W ₆ added to the lower cooking circulation line L ₆ is determined by the cooking chemical W ₀ supplied directly to the top of the vessel V and the cooking chemical W ₆ added to the lower cooking circulation line L ₆ . it is recommended that 20 to 30% of the total cooking chemical liquid supply amount including a cooking chemical solution W ₈ that is added to the lower cleaning circulating line L _8.

In addition, as in the example of the apparatus shown in FIGS. 1 to 3, the cooking liquid (white liquor) W ₈ is also added to the lower cleaning circulation line L _{8 at} the bottom of the vessel V, and the cleaning that rises in the cleaning zone C is performed. It is preferable to carry out an extended modified cooking method (EMCC method) that suppresses lignin promotion with water and re-adsorption of lignin. In that case, the amount of cooking chemical liquid (white liquor) supplied to the lower washing circulation line L ₈ is preferably 5 to 15% of the total cooking chemical supply amount. The feature of this EMCC method liquid phase continuous digester is that there are three places where the cooking chemical (white liquor) is added. And also in this EMCC method liquid phase continuous digester, a part Z _{5 of the} circulating fluid is extracted from the upper cooking circulation line L ₅ , and the extracted chemical solution Z ₅ is used as a cooking chemical recovery process line (flash cyclones 18, 19). The liquid ratio in the vessel V is controlled by adjusting the amount of the chemical solution to be removed and the chip hanging is prevented from occurring.

  In practicing the present invention, it is recommended that the conifer pulp raw material be cooked in the H factor range of 700-900. That is, when the H factor is less than 700, the amount of cooking chemical added is large, the amount of residual alkali after cooking is also large, and the yield of pulp components decreases. On the other hand, when the H factor exceeds 900, the yield of the pulp component decreases due to thermal decomposition of the chips. For these reasons, it is preferable to digest the pulp raw material in the range of H factor 700 to 900. Moreover, the liquid ratio in the liquid phase continuous digester is from the top to the bottom of the vessel V for the purpose of improving the yield of pulp components by the balance of the heat of the cross section of the continuous digester and the balance (mass balance) of the dispersion of the cooking chemical. It is recommended to control the extraction of the chemical solution so that it becomes smaller toward.

  In carrying out the present invention, the type of raw material chip is not particularly limited, and a hardwood chip or the like can be used in addition to the softwood chip.

Next, the apparatus example of FIGS. 2 and 3 will be described. In the apparatus example of FIG. 1, the extracted chemical liquid line LZ ₅ is branched only from the upper cooking circulation line L ₅ , but in the apparatus example of FIG. The line is branched from both the upper cooking circulation line L ₅ and the lower cooking circulation line L ₆ (L ₆ A), and these are merged to obtain a chemical solution line LZ _{5. In the} example of FIG. 3, the lower cooking circulation is used. The chemical liquid line LZ ₅ is extracted only from the line L ₆ , and otherwise, all of the above description regarding the apparatus example of FIG. 1 is the same as the apparatus example of FIG. 2 and the apparatus of FIG. This is the case.

In the present invention, as described above, a pulp raw material and a cooking chemical liquid composed of a pulverized lignocellulosic material are supplied from the top of the vessel V whose entire interior is a pressurized liquid phase, and the inside of the vessel V is viewed from above. An infiltration zone A for infiltrating the cooking chemical liquid into the pulp raw material, a cooking zone B for dissolving and separating the lignin component in the pulp raw material in the cooking chemical liquid, and a cleaning zone C for cleaning the cellulose component in the pulp raw material are formed. The black liquor produced by containing the lignin component separated from the pulp raw material in the cooking liquid is extracted from the extraction strainer 4 provided in the middle stage of the vessel V, while the cellulose component is provided in the bottom of the vessel V. In the liquid phase continuous digester adapted to be removed from the outlet device D, at the boundary between the permeation zone A and the digestion zone B Provided with an upper cooking circulation line L ₅ that recirculates part of cooking chemical to the top of the vessel V from only upper cooking circulation strainer 1, the extraction liquid medicine from said upper cooking circulation line L ₅ is branched from the sampling chemical line LZ ₅ A part of the chemical solution Z ₅ is extracted from the circulating fluid of the upper cooking circulation line L ₅ as a pressure control in the vessel V by the line LZ ₅ and sent to the cooking chemical recovery process line. The liquid ratio is controlled, and there is an effect that it is possible to prevent the occurrence of chip hanging in the continuous digester.

  Next, the example of the apparatus shown in FIG. 1 will be described in more detail as a representative example of the liquid phase continuous digester of the present invention, but the explanation part already described about the example of apparatus shown in FIG. In the description of the best mode, this is incorporated as necessary.

In FIG. 1, the symbol L ₀ is a supply line for pulp raw material (chip) and cooking chemical liquid (white liquor) W ₀ , and the pulp raw material and cooking chemical liquid W ₀ are from this line L ₀ to the top of the vessel V (top separator). ) Supplied to T. The vessel V is provided with an upper cooking circulation strainer 1, a lower cooking circulation strainer 2, an extraction strainer 4, an upper washing circulation strainer 3, and a lower washing circulation strainer 5 from the upper side, and generally the top T and the upper cooking circulation of the vessel V. Between the strainer 1 functions as the permeation zone A, generally between the lower cooking circulation strainer 2 and the extraction strainer 4, and between the upper washing circulation strainer 3 and the lower washing circulation strainer 5, functions as the washing zone C. To do.

In the permeation zone A, the permeation action of the cooking chemical into the pulp raw material (chip) is performed. In the cooking zone B, the cooking chemical heated to the cooking temperature by the heater 7 from the upper cooking circulation strainer 1 to the center of the upper cooking circulation strainer 1 in the vessel V through the upper cooking circulation pump 6, the heater 7 and the top of the vessel V. (This reflux line is referred to as “upper cooking circulation line L ₅ ”) and cooking (dissolving and separating the lignin component in the pulp raw material in the cooking chemical) is started. Similarly, in the lower cooking circulation line L ₆ , the circulating chemical solution extracted from the lower cooking circulation strainer 2 located below the upper cooking circulation strainer 1 is heated to the cooking temperature by the heater 9, and then the lower cooking circulation pump 8 in the vessel V And the temperature in the upper cooking circulation line L ₅ is uniformly corrected to adjust the cooking reaction in the cooking zone B.

The middle part of the vessel V is the end of the cooking zone B, where an extraction strainer 4 and an upper washing circulation strainer 3 are provided. After the specified cooking reaction residence time has elapsed in cooking zone B, the pulp raw material (chips) that have fallen fallen from the upper washing circulation strainer 3 to the upper washing circulation pump 10, the vessel containing the lignin component dissolved and separated in the cooking chemical liquid. through the top and V, it is sent to the extraction strainer 4 in the vessel V, extracted with black liquor extraction line L _10. This black liquor extraction stops cooking.

In the washing zone C, the cellulose component in the pulp raw material that has been digested is replaced and washed with the washing water Cw supplied from the bottom of the vessel V. This washing liquid rises, is sent to the extraction strainer 4 in the upper washing circulation line L _{7, and is} extracted in the black liquor extraction line L ₁₀ together with the cooking liquid containing the lignin component in the cooking zone B.

In the embodiment shown in FIG. 1, the upper cooking circulation line L _5, branches the extraction chemical line LZ ₅ for extracting a portion Z ₅ of the circulating liquid of the same upper cooking circulation line L _5, the extraction chemical line LZ ₅ and to perform the pressure control in the vessel V by controlling the amount of the chemical Z ₅ extraction withdrawn from. The extracted chemical solution Z ₅ is sent to the cooking chemical recovery process line (first flash cyclone 18 and second flash cyclone 19).

In the apparatus embodiment shown in FIG. 1, by controlling the pressure in the vessel V by controlling the amount of the chemical Z ₅ withdrawn from extraction chemical line LZ _5, Slender liquid ratio in the washing zone C and cooking zone B Regardless of fluctuations in the volume of pulp raw material (chip) and cooking chemical supplied to the top of the vessel V, the occurrence of hanging is prevented so as to be always constant.

In the liquid phase continuous digester of the embodiment shown in FIG. 1, the amount of the sampling chemical solution Z ₅ is controlled as follows. That is, a control valve 44 whose flow rate is controlled by a pressure signal in the vessel V from the pressure sensor 79 for detecting the pressure inside the vessel V is provided in the middle of the extraction chemical liquid line LZ ₅ , and is detected by the pressure sensor 79. that controls the degree of opening of the control valve 44 in response to pressure fluctuations in the vessel V, so that the pressure in the vessel V is always constant, adjusting the flow rate of the chemical Z ₅ sampling.

As the pressure in the vessel V is controlled by the extraction chemical line LZ ₅ in the upper cooking circulation line, the washing water Cw from the washing water line L ₉ A that has been conventionally supplied to the bottom of the tower-like vessel V by pressure control. Can be changed to control at a constant flow rate. If the flow rate of the washing water Cw can be made constant, fluctuations in the pulp concentration at the bottom of the vessel V can be eliminated, and the problem of chip level control failure at the top of the vessel V in the conventional apparatus example shown in FIG. Can be solved.

In the apparatus embodiment shown in FIG. 1, a method for pressure control, while installing a flow control valve 37 to the wash water upper line L ₉ A supplied from the vessel V bottom, the vessel V in the wash water upper line L ₉ A There is provided an emergency shut-off valve 38 that closes urgently when the pressure in the vessel V becomes abnormally high beyond the operating range of the internal extraction pressure control valve 44. In addition, when the pressure in the vessel V becomes abnormally low beyond the operating range of the extraction pressure control valve 44 in the vessel V, the pressure control valve for urgently replenishing the washing water lower line L ₉ B with the washing water 36 (normally not flowing) is provided. For abnormally high pressure, the emergency pressure control valve 46 is adjusted from the emergency extraction line L ₁₃ provided at the bottom of the vessel V prior to the emergency shutoff valve 38 to extract the liquid in the vessel V. The pressure in the vessel V is adjusted.

The pressure control method in the sampling cooking chemical liquid line LZ ₅ of the upper cooking circulation line L ₅ calculates the extraction flow rate so that the pressure detected by the pressure sensor 79 at the top of the vessel V is constant, and the sampling cooking chemical liquid line LZ ₅ The set value of the flow meter 80 is controlled and the extraction flow rate is adjusted by the flow rate control valve 44 to adjust the pressure in the vessel V. The washing water entering the vessel V and the extraction black liquor from the vessel V extraction strainer 4 and the flow rate of the pulp coming out from the bottom of the vessel V are constant and do not fluctuate. Therefore, the pulp raw material entering from the top of the vessel V (chip containing moisture) if and quantity changes in the cooking chemical (white liquor), the upper cooking amount of the chemical Z ₅ withdrawal of circulation line with changes to the pressure is adjusted, since the upper cooking circulation strainer cooking zone B-washing zone accordingly The liquid ratio between the raw material chip that lowers C and the cooking chemical is always constant. Changes in the liquid ratio due to various factors (for example, changes in chip moisture content due to differences in chip tree species, or changes in chip moisture content due to weather fluctuations such as rainfall, etc.) can be eliminated, and occurrence of hanging can be prevented.

The amount of extraction liquid medicine Z ₅ from the upper cooking circulation line L ₅ represents, it is preferable that 5 to 15% of the chemical circulation amount of the upper cooking circulation line L ₅ (less than 5%, the cooking zone B Since the dissolved substance concentration in the upper part of the chip is high and the chip is decomposed while consuming the cooking chemical, the yield of the pulp component may be reduced. On the other hand, if it exceeds 15%, the amount of xylan in the dissolved substance decreases. This leads to a decrease in the yield of the pulp component).

In the example of the apparatus shown in FIG. 1, in addition to the upper cooking circulation line L ₅ , the lower cooking for recirculating a part of the cooking chemical from the lower cooking circulation strainer 2 provided in the lower direction of the upper cooking circulation strainer 1 to the top of the vessel V. A circulation line L ₆ is provided, and the cooking chemical W ₆ is also added from the lower cooking circulation line L ₆ .

Further, the lower cleaning circulating line L ₈ for recirculating a portion of the cleaning liquid to the bottom of the vessel V from lower cleaning circulation strainer 5 provided below position of the vessel V is provided, cooking chemical W ₈ from said lower wash circulation line L ₈ Is added.

At that time, including cooking chemical W ₈ that is added to the cooking liquid medicine W ₆ and lower cleaning circulation line L ₈ the amount of cooking chemical W ₀ to be supplied directly to the top of the vessel V is added to the lower cooking circulation line L ₆ The total cooking chemical supply amount is 65 to 75%.

  That is, if it is less than 65%, the amount of the cooking chemical for neutralizing the acetic acid, formic acid, etc., which are the organic acids in the chip in the permeation zone A is insufficient, and the kappa number of the pulp coming out from the continuous digester becomes high. In order to obtain the target kappa number, it is necessary to increase the cooking temperature in the cooking zone B and the addition amount of the chemical solution, whereby the chips are decomposed and the yield of pulp components and the strength of the pulp are lowered. On the other hand, if it exceeds 75%, a large amount of cooking chemical remains, and the amount of chemical added in the cooking zone B is small, so that the amount of caustic soda necessary for delignification reaction becomes insufficient and there is a possibility of uncooking phenomenon.

Further, the amount of cooking chemical W ₆ added to the lower cooking circulation line L ₆ is determined by the cooking chemical W ₀ supplied directly to the top of the vessel V and the cooking chemical W ₆ added to the lower cooking circulation line L ₆ . are as 20 to 30% of the total cooking chemical liquid supply amount including a cooking chemical solution W ₈ that is added to the lower cleaning circulating line L _8.

In the example of the apparatus shown in FIG. 1, cooking chemical liquid (white liquor) W ₈ is also added to the lower washing circulation line L _{8 at} the bottom of the vessel V, and delignification with washing water rising in the washing zone C is performed. And an extended modified cooking method (EMCC method) that suppresses re-adsorption of lignin. In that case, the amount of cooking chemical liquid (white liquor) supplied to the lower washing circulation line L ₈ is preferably 5 to 15% of the total cooking chemical supply amount. The feature of this EMCC method liquid phase continuous digester is that there are three places where the cooking chemical (white liquor) is added. And also in this EMCC method liquid phase continuous digester, a part Z _{5 of the} circulating fluid is extracted from the upper cooking circulation line L ₅ and the extracted chemical solution Z ₅ is sent to the cooking chemical recovery process line (flash cyclone) 18. By adjusting the amount of the extracted chemical solution, the liquid ratio in the vessel V is controlled to prevent the occurrence of chip hanging.

  In the example of the apparatus shown in FIG. 1, the conifer pulp raw material is digested in the range of H factor 700 to 900. That is, when the H factor is less than 700, the amount of cooking chemical added is large, the amount of residual alkali after cooking is also large, and the yield of pulp components decreases. On the other hand, when the H factor exceeds 900, the yield of the pulp component decreases due to thermal decomposition of the chips. For these reasons, it is preferable to digest the pulp raw material in the range of H factor 700 to 900. Moreover, the liquid ratio in the liquid phase continuous digester is from the top to the bottom of the vessel V for the purpose of improving the yield of pulp components by the balance of the heat of the cross section of the continuous digester and the balance (mass balance) of the dispersion of the cooking chemical. It is recommended to control the extraction of the chemical solution so that it becomes smaller toward.

  Further, in the apparatus example of FIG. 1, the kind of raw material chip is not particularly limited, but a softwood chip is used as the raw material chip.

2 and 3 will be described. As described above, in the example of FIG. 1, the extracted chemical liquid line LZ ₅ is branched only from the upper cooking circulation line L ₅ . In the apparatus example of FIG. 3, the extracted chemical liquid line is branched from both the upper cooking circulation line L ₅ and the lower cooking circulation line L ₆ (L ₆ A), and they are merged to obtain the extracted chemical liquid line LZ ₅ . In the example, the chemical liquid line LZ ₅ is branched only from the lower cooking circulation line L ₆ , and otherwise, all of the above description describing the apparatus example of FIG. 1 is the apparatus of FIG. This applies to the example and the device example of FIG.

1 to 3, reference numerals 12, 14, 16 are pumps, 13 are heaters, 21-26, 28-35, 41-43, 45, 47, 48 are valves, 61-69, 81-85 are controllers. , 71, 73, 76, to 78 are flow sensors, 72 is a pressure sensor, 74 and 75 are liquid level sensors, L ₁₂ is a black liquor vacuum evaporator feed line, S ₁ and S ₅ are flow signal lines, S ₂ and S _4, S ₁₀ is a pressure signal line, S _7, S ₈ indicates a liquid level signal line.

It is a system diagram of a liquid phase continuous digester according to an embodiment of the present invention. It is a system diagram of a liquid phase continuous digester according to another embodiment of the present invention. It is a system diagram of a liquid phase continuous digester according to still another embodiment of the present invention. It is a system diagram of a liquid phase continuous digester having a conventional structure.

Explanation of symbols

1 is an upper cooking circulation strainer, 2 is a lower cooking circulation strainer, 3 is an upper washing circulation strainer, 4 is an extraction strainer, 5 is a lower washing circulation strainer, 6, 8, 10, 12, 14, and 16 are pumps, 7 and 9 , 13 is a heater, 18, 19 are first and second flash cyclones, 21-26, 28-38, 41-48 are valves, 61-69, 81-85 are controllers, 71, 73, 76, 77, 78. , 80 is a flow sensor, 72 and 79 are pressure sensors, 74 and 75 are liquid level sensors, A is an infiltration zone, B is a digestion zone, C is a wash zone, Cw is wash water, D is an outlet device, and L ₀ is top circulating feed line, L ₅ is an upper cooking circulation line, L ₆ is lower cooking circulation line, L ₇ is an upper wash circulation line, L ₈ is lower cleaning circulation line, L ₉ is washing water Supply lines, L ₉ A cleaning water top line, L ₉ B washing water lower lines, L ₁₀ is black liquor extraction lines, L ₁₁ cellulose extraction line, L ₁₂ is black liquor vacuum evaporator feed line, LZ ₅ is withdrawn Chemical liquid lines, S ₁ , S ₅ and S ₆ are flow signal lines, S ₂ , S ₃ , S ₄ and S ₁₀ are pressure signal lines, S ₇ and S ₈ are liquid level signal lines, T is a top separator, and V is Vessel, W ₀ , W ₆ , W ₈ are cooking chemicals (white liquor), Z ₅ is sampling chemicals

Claims (8)

The pulp raw material and cooking chemical liquid made of pulverized lignocellulosic material are supplied from the top of the vessel V having the entire interior as a pressurized liquid phase, and the cooking chemical liquid penetrates into the pulp raw material from above in the vessel V. A permeation zone A, a cooking zone B for dissolving and separating the lignin component in the pulp raw material in the cooking chemical solution, and a cleaning zone C for washing the cellulose component in the pulp raw material are formed, and the pulp raw material in the cooking chemical solution The black liquor produced containing the lignin component separated from the water is extracted from the extraction strainer 4 provided at the middle stage of the vessel V, while the cellulose component is taken out from the outlet device D provided at the bottom of the vessel V. In a continuous liquid phase digester, the upper cooking circulation stray provided at the boundary between the permeation zone A and the cooking zone B Provided with an upper cooking circulation line L ₅ that recirculates part of cooking chemical to the top of the vessel V from -1, by the extraction chemical line LZ ₅ and the upper cooking circulation line L ₅ branches the extraction chemical line LZ ₅ A part of the chemical solution Z ₅ is extracted from the circulating fluid of the upper cooking circulation line L ₅ as pressure control in the vessel V and sent to the cooking chemical recovery process line, thereby controlling the liquid ratio in the cooking zone B and cleaning zone C. And a continuous pulp production method using a liquid-phase continuous digester, wherein the occurrence of chip hanging in the continuous digester is prevented. Claim 1, wherein the liquid phase continuous digester, wherein the chemical solution amount extraction from the upper cooking circulation line L ₅ by the extraction chemical line LZ ₅ is 5-15% of the chemical circulation of the upper cooking circulation line L ₅ Continuous pulp production method using a kettle. In addition to the upper cooking circulation line L ₅ , there is provided a lower cooking circulation line L ₆ for returning a part of the cooking chemical from the lower cooking circulation strainer 2 provided in the lower direction of the upper cooking circulation strainer 1 to the top of the vessel V, The continuous pulp production method using a liquid phase continuous digester according to claim 1 or 2, wherein the cooking chemical liquid W ₆ is also added from the lower cooking circulation line L ₆ . A lower cleaning circulation line L ₈ for returning a part of the cleaning liquid from the lower cleaning circulation strainer 5 provided in the lower direction of the vessel V to the bottom of the vessel V is provided, and the cooking chemical W ₈ is also added from the lower cleaning circulation line L _8. A method for continuously producing pulp using a liquid phase continuous digester according to claim 1, 2 or 3. All digestion the amount of cooking chemical W ₀ to be supplied directly to the top of the vessel V is including cooking chemical W ₈ that is added to the cooking liquid medicine W ₆ and lower cleaning circulation line L ₈ is added to the lower cooking circulation line L ₆ The continuous pulp production method using a liquid-phase continuous digester according to claim 4, wherein the amount is 65 to 75% of the chemical supply amount. The amount of cooking liquid medicine W ₆ being added to the lower cooking circulation line L ₆ is a cooking chemical solution W ₀ to be supplied directly to the top of the vessel V, cooking chemical W ₆ and lower cleaning to be added to the lower cooking circulation line L ₆ pulp continuous process by liquid phase digester according to claim 4, wherein the including cooking chemical W ₈ being added to the circulation line L ₈ 20 to 30% of the total cooking chemical supply.   The liquid according to any one of claims 1 to 6, wherein the extraction of the chemical liquid is controlled so that the liquid ratio in the liquid phase continuous digester decreases from the top to the bottom of the vessel V. A continuous pulp production method using a phase continuous digester.   A pulp raw material is a coniferous chip, The pulp continuous manufacturing method by the liquid phase continuous digester of any one of Claim 1 thru | or 7 characterized by the above-mentioned.

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