WO2001094691A1 - Procede de cuisson par lots - Google Patents

Procede de cuisson par lots Download PDF

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Publication number
WO2001094691A1
WO2001094691A1 PCT/FI2001/000523 FI0100523W WO0194691A1 WO 2001094691 A1 WO2001094691 A1 WO 2001094691A1 FI 0100523 W FI0100523 W FI 0100523W WO 0194691 A1 WO0194691 A1 WO 0194691A1
Authority
WO
WIPO (PCT)
Prior art keywords
digester
liquor
tank
black liquor
hot
Prior art date
Application number
PCT/FI2001/000523
Other languages
English (en)
Inventor
Päivi UUSITALO
Original Assignee
Metso Paper, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Metso Paper, Inc. filed Critical Metso Paper, Inc.
Priority to AU63981/01A priority Critical patent/AU6398101A/en
Publication of WO2001094691A1 publication Critical patent/WO2001094691A1/fr

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Classifications

    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
    • D21C7/00—Digesters
    • D21C7/10—Heating devices

Definitions

  • T e invention relates to batch pulping, More particularly, the invention is related to a s method of designing a batch pulping process in order to save investment costs by using a limited number of tanks in combination with heat exchangers. '
  • the process has been further refined by taking into account the chemical processes at play in different stages of the process, whereby limits are set for the 0 temperature, alkalinity, sulfidity and solids content of the various spent liquors introduced in sequence during the treatment of each chip charge, as disclosed in FI patents 92224 and 93866.
  • the process can also be adapted to suit different sources of raw material by adding more sulfidity early in the process (FI pat. appl. 962260), low pH precleaning (FI pat. appl 974455), or calcium-rich raw material (FI pat. appl. 992132).
  • great flexibility is 5 available to handle situations where the process must be adjusted because of variations in the quality of the lignocellulosic material being used as a starting point.
  • displacement batch cooking is technically complicated and requires a significant amount of equipment in addition to digesters: heating devices, pumps, pipes, valves, o instruments and accumulator tanks.
  • a number of tanks must be pressure vessels in order to store liquors having temperatures clearly above atmospheric boiling point. This tends to lower the attractivity of the process.
  • Pressure vessel codes are strict, and any alterations are connected with time-consuming certifications.
  • the cooking line requires a number of digesters, two pressure tanks for holding black liquor at different temperatures above the atmospheric boiling point (herein called “hot” black liquor) but having different chemical properties, at least one atmospheric tank for holding black liquor at a temperature below its s cooking point (herein called “warm” black liquor), a pressurized white liquor tank, plus tanks for holding wash filtrate and possible other required liquors.
  • Pumps and heat exchangers are provided for transferring energy between streams of liquors to provide the correct temperatures in different stages of the process.
  • warm black liquor is introduced first into the 0 digester, followed by hot black liquor displacing the warm black liquor, and finally white liquor at or near the cooking temperature.
  • Black liquor displaced during these fillmg stages may be collected for further recycling or passed on to the evaporation plant.
  • the resulting black liquor is displaced from the digester by wash filtrate, and may be divided into several fractions depending on its physical and chemical properties. s These fractions may then be used in an appropriate sequence for impregnation and pretreatment of a subsequent chip charge.
  • a method for producing chemical pulp 5 by means of a batch cooking process, wherein a heating device is provided in the piping connecting the pressurized hot liquor tanks with the digester for obtaining the desired temperatures in the liquors entering the digester.
  • a heating device is provided in the piping connecting the pressurized hot liquor tanks with the digester for obtaining the desired temperatures in the liquors entering the digester.
  • the heating device may be included in a circulation loop drawing liquor from a tank and returning it to the same tank. o From such a loop, liquor may be withdrawn after the heat exchanger and conducted to the digester.
  • the heating device according to the present invention is not the heating device found in digester-specific circulation loops according to the prior art.
  • heat exchangers in the digester circulation are eliminated in favor of direct steam injection as described below.
  • the hot black liquor displaced at a temperature above atmospheric boiling temperature is collected into a single hot black liquor accumulation tank.
  • White liquor is s supplied from a hot white liquor tank.
  • indirect steam heating may then be used to bring the entering liquors to temperature; as the hot liquor fill with hot black and white liquor thus brings the digester temperature up to nearly the cooking temperature, direct steam heating can be used in the digester circulation for supplying the additional heat required, instead of digester-specific heat exchangers.
  • the total number of required heat exchangers decreases.
  • Figure 1 shows a prior art displacement batch cooking system with two pressurized hot 75 black liquor tanks, with the tank farm and a schematic of the digester filling sequence during one batch;
  • Figure 2 shows another prior art displacement batch cooking system using one pressurized hot black liquor tank only but without the characterizing features of the present invention
  • Figure 3 shows a displacement batch cooking system according to the present invention
  • Figure 4 shows another embodiment of the present invention, having a piping design different from the system of Figure 3;
  • Figure 5 shows an embodiment of the present invention which provides for handling of calcium-rich raw material
  • FIG 6 shows an embodiment of the present invention, in which no impregnation step is 25. used, but instead pre-steaming of the chips is included.
  • FIG. 1 shows a displacement batch cooking system according to the prior art. The required tanks are shown at the top, while the sequence of steps carried out in the digester during one batch is diagrammatically shown at the bottom, with the corresponding liquor flows indicated.
  • the digester is filled with impregnation black liquor A from atmospheric tank 5.
  • the impregnation black liquor is displaced by hot black liquor B from tank 1 and is transferred to receiving tank 4 and further to the evaporation and recovery facilities.
  • the hot black liquor is in turn displaced by white liquor C from pressurized tank 3 and a smaller amount of hot black liquor B from pressurized tank 1.
  • the displaced liquor from the impregnation liquor and hot black liquor treatment, Al and A2, below about atmospheric boiling point is conducted to black liquor tank 4.
  • the displaced liquor above about atmospheric boiling point B2 is conducted to hot black liquor tank 2.
  • the digester temperature is brought to the desired cooking temperature by direct steam heating, i.e. steam is injected into the digester circulation loop.
  • the resulting black liquor is displaced using wash filtrate E from tank 6 into tanks 1 and 2 as fractions Bl and Dl respectively, depending on the quality of the liquor leaving the digester.
  • the displacement with wash liquor brings the temperature of the digester content below about the boiling point at atmospheric pressure.
  • the cooked raw material is discharged from the digester.
  • the liquor displacements typically occur from bottom to top of the digester.
  • hot black liquor is conveyed to tank 5 to generate new impregnation black liquor, its heat content being partly transferred to white liquor or to a water stream through heat exchangers.
  • Tank 5 is provided with soap separation.
  • Tanks 1 and 3 are further provided with circulation loops and heat exchangers for adjusting temperatures.
  • FIG. 2 shows another, less sophisticated system according to the prior art.
  • the digester is filled with impregnation liquor AA from tank 5.
  • Hot black liquor B from tank 2 displaces the impregnation liquor A2 and the displaced liquor AB is led to receiving tank 5 and further to the evaporation and recovery facilities.
  • White liquor and a small amount of hot black liquor displaces the hot black liquor.
  • the displaced liquor above about atmospheric boiling point is conducted to hot black liquor tank 2.
  • the heat content of the liquors charged to the digester is not sufficient to bring the digester contents close to cooking temperature prior to the cooking step, but a circulation loop with heat exchangers is used in the digester to supply the required additional heat.
  • the resulting black liquor is displaced with wash liquor E to a single pressurized black liquor tank 2, which step brings the temperature of the digester contents to below the boiling point at atmospheric pressure.
  • the temperature within tank 2 in figure 2 is approximately the weighed average temperature of tank 1 and tank 2 in figure 1.
  • the temperature of the hot black liquor conducted to the digester is therefore lower in the process shown in figure 2, compared to the process shown in figure 1.
  • FIG. 3 shows a system according to the present invention.
  • tank 1 has been eUminated and displaced hot black liquors B frorr different stages all enter the same pressure tank, tank 2.
  • this tank is equipped as shown with a heating circuit comprising a steam operated heat exchanger, and piping to draw off heated black liquor from the circuit to the digester.
  • a heating circuit comprising a steam operated heat exchanger, and piping to draw off heated black liquor from the circuit to the digester.
  • the temperature of hot black liquor to be charged to the reactor is adjusted in said heat exchanger, and any additional heating in the digester after filling can be carried out with direct steam injection.
  • heat adjustment takes place in the transfer line, less heating capacity is required for heating the digester contents in the digester itself.
  • the number of digesters being larger than the number of tank sets as shown in the figure, a corresponding amount of heat exchange equipment can be eliminated in the initial investment.
  • Impregnation black liquor is generated by conveying hot black liquor from tank 2 to the atmospheric impregnation liquor tank 5 via a heat exchanger, whereby the liquor transfers part of its heat to white liquor entering white liquor tank 3.
  • the displaced liquor in the impregnation and hot fill stages below about atmospheric boiling point is conducted to black liquor tank 4 and above about atmospheric boiling point is conducted to hot black liquor tank 2.
  • Figure 4 shows a system corresponding to that shown in Figure 3, but with piping interconnecting the heating circuits of the hot black liquor tank and of the white liquor tank.
  • This embodiment provides great flexibility, since only two heat exchangers are required in, for example, a batch digester system with multiple lines used, typically in plants at higher pulp production levels. For example, a set-up of eight digesters is typically dived into two lines, i.e. four digesters per line. Each line in a displacement batch digester system comprises a number of digesters, e.g. typically three to five digesters, served by line-specific pumps and pipes connecting the digesters and the tanks, but all digesters in the plant (all lines) are served by the same set of tanks.
  • the embodiment shown in figure 4 therefore provides further simplification in comparison to a system as shown in figure 3.
  • a batch system according to figure 3 with two lines two heat exchanger circuits of the hot black liquor tank and one heat exchanger circuit of the white liquor tank 3 would be required.
  • a batch system according to figure 4 with two lines only two heat exchanger circuits woulr* be r quirecs for both the hot black and white liquor tanks 2 and 3, thus, a saving of one heat exchanger in comparison to figure 3.
  • the embodiment requires a lower number of pumps in a multiple line digester system.
  • the heating circuits of the hot black liquor tank and of the white liquor tank can be used to heat the content of the tanks 2 and 3, especially when the circuit B and/or C connected to the digesters is not in use in the batch sequence. This flexibility is especially important for heating of the white liquor in tank 3 and for steam leveling in the system.
  • the process of figure 4 can also be used in a batch digester system with a single line.
  • Figure 5 shows a batch cooking system according to the present invention, in which provisions are made for handling raw material rich in calcium.
  • the first portion of black liquor displaced from the digester during a batch, following the impregnation stage may contain a large amount of calcium bound to dissolved organic material.
  • this organic material is broken down at high temperatures during later stages of the process, calcium is released and may cause severe scaling if allowed to precipitate as carbonate on heat exchange surfaces in the black liquor evaporation plant of the cooking chemicals recovery system. For this reason, it may be advantageous to use such calcium-rich liquors for final displacement of the cooking liquor after a batch.
  • the calcium is thereby released in the liquor due to the high temperature, but will not encounter any heat exchange surfaces and no scaling occurs.
  • hot black liquor tank and white liquor tank is identical to that of Figure 4.
  • No impregnation liquor tank is provided, but the first liquor introduced during the batch may originate from the countercurrent wash process.
  • the liquor displaced during the next liquor introduction is rich in calcium, and is stored in an atmospheric tank until it is reintroduced after the cook to displace the spent cooking liquor, which is at cooking temperature. Breakdown of organic material and calcium release then takes place where it cannot cause scaling.
  • tanks 4 and 6 of Figure 5 may be combined into one.
  • FIG. 6 shows a further embodiment of the present invention, wherein the impregnation stage is replaced with a steaming stage.
  • a process may be used for treating the raw material with steam for packing and removing gases in the digester whereby measures for removal of so-called non-process compounds are taken during the steaming step (FI appl 982411).
  • An atmospheric impregnation black liquor tank is not required, but the temperature of the black and white liquor fed to the digester is regulated using indirect heat exchange according to the present invention, as described above.
  • tank 2 is designed to enable uniform physical and chemical properties of the liquor conducted from the tank to the next stage.
  • the tank is designed to dampen the swings in liquor properties of the inlet to the tank.
  • Such internal tank arrangements are for example described in FI 992802.
  • the inlet to the tank can be separated from the outlet to avoid "channelling" through the tank.
  • the inlet and outlet can be separated by internal separator elements, interconnected internal chambers separating the inlet and outlet of the tank, long enough distance between tank inlet and tank outlet, mixing arrangement in the tank, and proper size of the tank.
  • the alkali content of the hot black liquor conducted from tank 2 in the various embodiments of the invention may be adjusted with white liquor to a pre-set constant value before introduction to the next stage.

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Abstract

L'invention concerne un procédé de cuisson par lots pour la production de pulpe, selon lequel le nombre de réservoirs nécessaires pour stocker la liqueur noire à différentes températures est réduit, grâce à l'utilisation de l'échange de chaleur dans la voie du flux entre le réservoir et le digesteur, indépendamment des dispositifs de chauffage du digesteur. On peut ainsi introduire la liqueur noire à une température voulue dans le digesteur à tous les niveaux du processus, les besoins en chauffage dans les circuits du digesteur étant réduits et les échangeurs de chaleur pouvant être supprimés.
PCT/FI2001/000523 2000-06-06 2001-06-01 Procede de cuisson par lots WO2001094691A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU63981/01A AU6398101A (en) 2000-06-06 2001-06-01 Method for batch cooking

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FI20001351 2000-06-06
FI20001351A FI20001351A0 (fi) 2000-06-06 2000-06-06 Eräkeittomenetelmä

Publications (1)

Publication Number Publication Date
WO2001094691A1 true WO2001094691A1 (fr) 2001-12-13

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PCT/FI2001/000523 WO2001094691A1 (fr) 2000-06-06 2001-06-01 Procede de cuisson par lots

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AU (1) AU6398101A (fr)
FI (1) FI20001351A0 (fr)
WO (1) WO2001094691A1 (fr)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN1297708C (zh) * 2003-08-26 2007-01-31 山东泉林纸业有限责任公司 一种用球内洗涤分级蒸煮工艺生产的浓黑液、黑液
CN1318690C (zh) * 2003-08-26 2007-05-30 山东泉林纸业有限责任公司 一种球内洗涤分级蒸煮工艺
CN102154874A (zh) * 2011-04-29 2011-08-17 白福安 一种置换蒸煮制浆方法

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
SE174655C1 (fr) *
WO1995023891A1 (fr) * 1994-03-04 1995-09-08 Beloit Technologies, Inc. Incidence de la temperature et de la charge en alcalis sur la brillance de la pate a papier

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
SE174655C1 (fr) *
WO1995023891A1 (fr) * 1994-03-04 1995-09-08 Beloit Technologies, Inc. Incidence de la temperature et de la charge en alcalis sur la brillance de la pate a papier

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN1297708C (zh) * 2003-08-26 2007-01-31 山东泉林纸业有限责任公司 一种用球内洗涤分级蒸煮工艺生产的浓黑液、黑液
CN1318690C (zh) * 2003-08-26 2007-05-30 山东泉林纸业有限责任公司 一种球内洗涤分级蒸煮工艺
CN102154874A (zh) * 2011-04-29 2011-08-17 白福安 一种置换蒸煮制浆方法
CN102154874B (zh) * 2011-04-29 2012-11-21 白福安 一种置换蒸煮制浆方法

Also Published As

Publication number Publication date
FI20001351A0 (fi) 2000-06-06
AU6398101A (en) 2001-12-17

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