EP1346103A1 - Procede de cuisson alcaline de materiaux fibreux - Google Patents

Procede de cuisson alcaline de materiaux fibreux

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Publication number
EP1346103A1
EP1346103A1 EP01997586A EP01997586A EP1346103A1 EP 1346103 A1 EP1346103 A1 EP 1346103A1 EP 01997586 A EP01997586 A EP 01997586A EP 01997586 A EP01997586 A EP 01997586A EP 1346103 A1 EP1346103 A1 EP 1346103A1
Authority
EP
European Patent Office
Prior art keywords
cooking
impregnation
liquor
chips
heating
Prior art date
Legal status (The legal status 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 status listed.)
Withdrawn
Application number
EP01997586A
Other languages
German (de)
English (en)
Inventor
Thomas Fant
Mikael Svedman
Lari Lammi
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Valmet Technologies Oy
Original Assignee
Metso Paper Oy
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 Oy filed Critical Metso Paper Oy
Publication of EP1346103A1 publication Critical patent/EP1346103A1/fr
Withdrawn legal-status Critical Current

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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
    • D21C1/00—Pretreatment of the finely-divided materials before digesting
    • D21C1/06—Pretreatment of the finely-divided materials before digesting with alkaline reacting compounds
    • 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
    • D21C3/00—Pulping cellulose-containing materials
    • D21C3/22—Other features of pulping processes
    • D21C3/24—Continuous processes
    • 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
    • D21C3/00—Pulping cellulose-containing materials
    • D21C3/22—Other features of pulping processes
    • D21C3/26—Multistage processes
    • 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

Definitions

  • the invention relates to the field of alkaline pulping.
  • alkaline cooking processes and especially kraft cooking are dominant in the production of cellulose or chemical pulp because alkaline cooking provides pulp fibers which are stronger than those from any other commercial pulping process.
  • the lignocellulosic material typically chopped into wood chips, is treated in either batch or continuous digesters.
  • Chip dimensions are of major importance in this context. The longer, wider and especially the thicker the chips are, the longer is the transportation distance to the centers of the chips
  • Pores inside fresh wood chips are also partly filled with liquid and partly with air.
  • the ratio is, among others, determined by the moisture content or dry content of wood.
  • the air should be removed from the chips before they can be fully impregnated by cooking liquor. This is usually done by pre-steaming the chips.
  • Typical heat-up times and at pressure times are 60 to 150 minutes and 60 to 120 minutes, respectively. Typical sum of heat-up and at pressure times is about 150 minutes.
  • Displacement batch pulping processes were developed in the 80's, originally for the sake of energy economy. Following a batch cook, the black liquor was recovered, divided into fractions according to temperature, stored and introduced into a digester charged with fresh lignocellulosic material in order to transfer the heat of the completed cook to a subsequent cook.
  • the total duration of the black liquor impregnation stage in batch displacement processes is typically below 30 min at temperatures below 100 °C. Heating is carried out by displacement with a black liquor having a higher temperature than the impregnation liquor.
  • white liquor is introduced, and a main cooking stage follows. Typically, the total duration of the hot liquor fill stage, temperature adjustment and the cooking stage is in the range 95-120 min.
  • the Kamyr type energy savings are achieved by pre-heating the chips with steam obtained from flashing the hot black liquor.
  • chips are preheated and air is removed from the chips to facilitate later liquor impregnation.
  • the chip impregnation zone typically involves 30-60 min or shorter chip retention at a temperature of 115-130 °C and a high pressure to enhance the pre-impregnation of the chips and the ion transportation into the chips. Since penetration rates increase with increased pressure, impregnation stages operate at pressures that greatly exceed the liquor saturation pressure at the specified temperature, i.e. typically greater than 10 bars operating pressure for impregnation temperatures of 115-130 °C.
  • the chips are heated directly in a vapor phase and/or in several liquor heating circuits to full cooking temperature, and then typically cooked for at least 1.5-2.5 hours in a concurrent cooking zone at temperatures below 165 °C.
  • Practical experience suggests that the process becomes chemical transporta- tion rate limited at cooking times below about 1.5-2.5 hours and temperatures above 165 °C. Therefore, typical cooking temperatures are between 150-165 °C but even cooking temperatures of 140-150 °C can also occur, see for example international patent application WO 98/35091. Thus, a minimum of 1.5-2.5 hours of cooking is required.
  • a countercurrent zone typically referred to as the hi-heat zone
  • a countercurrent zone usually follows for 2-4 hours at temperatures of 130-160 °C.
  • Contemporary continuous cooking as e.g. ITC, EMCC and Lo-solids cooking retains the cooking temperature, typically 150-160°C, all through the countercurrent zone, i.e. enlarging the cooking zone to the counter-current zone.
  • These modern digesters have thus a total cooking zone of about 240-360 minutes.
  • washing filtrate is pumped into the bottom of the vessel.
  • the vessel bottom is also a blow dilution and cooling zone.
  • Discharge temperature is typically 85-90 °C .
  • the continuous processes offer, compared to conventional batch digesters: more space efficiency, less installed power, lower volumes of inlet streams and outlet stream, steady- state operation vs. batch fill and discharge cycles, energy efficiency, lower environmental impact and a first stage of brownstock washing.
  • Impregnation theoretically requires small chips, but modern continuous digesters are based on the principle of maintaining sufficient liquid circulation and a good displacement efficiency. This calls for chip properties that are in conflict with some of the basic requirements for ensuring uniform delignification. Thus, a large chip size must be used, which leads to inferior impregnation and further longer retention times in cooking and expensive technology. Thus, the pulp maker has been trapped by his own technology. It is stated, that the 30-60 min retention time at 115-130°C in impregnation zones of continuous mill digesters could never provide a completely uniform distribution of cooking chemical for all chips (mill chips) before the start of bulk delignification.
  • a pulping process which comprises so-called "cold impregnation" as its main feature.
  • a tempera- ture of about 80-110 °C is specified, the time period being unlimited. However, an optimum of 2-3 hours is suggested. Pressure may be used in order to compress gas bubbles and cause sinking of the chips.
  • the theory behind the cold impregnation stage is, that acid- generating processes within the chips shall be suppressed until the chips are filled with alkali sufficient to neutralize any acid released when reaction commences at higher temperatures, and the impregnation step is defined as resulting in "an alkali concentration sufficient to neutralize all acid produced".
  • the proposed process preferably uses a conventional continuous digester like MCC, EMCC or Lo-solids digester.
  • a conventional continuous digester like MCC, EMCC or Lo-solids digester.
  • the retention times in the cooking stage are in the order of several hours, typically around 2-5 hours.
  • the figures of the application show a residence time in the impregnation stage approximately of the same order as in the cooking stage.
  • the proposed continuous processes have pulp strength advantages, the cooking stage still has a long retention time and low reaction temperature . This requires huge and expensive digesters designed for, from a technical point of view, high pressures and temperatures.
  • an improved, continuous alkaline cooking process according to claim 1 is provided, wherein the raw chip material is preheated and air purged, and impregnated with a liquor at a temperature no higher than the boiling point at atmospheric pressure of the impregnation liquor, at retention times of more than 60 minutes.
  • Liquors including fresh cooking liquor are added at an effective alkali concentration in the range from about 0.5 to about 2.2 mol/1 as OH " ions; preferably said concentration is in the range from about 0.5 to about 1.5 mol/1 as OH71; more preferably said concentration is in the range from about 0.75 to about 1.5 mol/1 as OH71.
  • a liquid-to-wood ratio in the range of 3 to 10 m 3 /t odw (m 3 per ton oven dry wood) is to be maintained during the impregnation step; preferably said ratio is in the range of 3 to 6 m 3 /t odw.
  • the impregnated material is subsequently heated to a temperature T2 of at least about 150 °C in a time t 2 after which follows a cooking stage with a retention time t , a maximum temperature T3 of no more than 185 °C, the liquid-to wood ratio being at least 2.5 m 3 /t odw during a substantial part of the heating and cooking step.
  • the total of t 2 and t 3 shall not exceed 65 min.
  • Fresh cooking liquor is added also during the steps following impregnation. After the cooking step, the delignified material is cooled to a temperature where significant cooking reactions no longer occur.
  • a temperature decrease to about 140 °C is sufficient to end the cooking step.
  • the time ti for impregnation is above 120 min, and the temperature TI in the range from 70 °C to the boiling point at atmospheric pressure of the impregnation liquor.
  • the total of t and t is in the range from 10 to 50 min, more preferably in the range from 10 to 40 min.
  • Time t 2 is preferably not more than 30 min.
  • the liquid-to- wood ratio in a substantial part of the heating and cooking steps is preferably at least 3 m 3 /t odw.
  • impregnation takes place at low pressure, for the present purposes defined as up to 5 bar. More preferably, impregnation takes place at about atmospheric pressure.
  • low pressure equipment may be used, which saves investment costs. Use of pressure may be required to ensure sinking of the chips in the liquid phase. If high pressure equipment is installed it can naturally be utilized.
  • the average dry-solid of the material entering the impregnation is preferably over 40 %; More preferably said dry-solid is over 45 %
  • the impregnation time and effective alkali concentration depends mainly on the type of chip. Material hard to impregnate, and consequently requiring longer times, may consist of long and thick chips, or have a large proportion of low-porosity material. The type of equipment and the space available are other factors. As raw material for the process according to the invention, industrial wood chips are used. These commonly have an average length above 10 mm, typically 15-35 mm, and an average thickness above 2 mm, typically 3 - 7 mm.
  • a plant for carrying out the method comprises a digesting system including an impregnation vessel and a digester in fluid communication with the impregnation vessel.
  • the volume N of the impregnation vessel is larger than 1/1, preferably larger than 2/1, more preferably larger than 3/1 of the volume of the digester.
  • the system may comprise a first transfer line between the impregnation vessel and the digester for transporting the impregnated material to the digester; a separator, comprising a withdrawal space, disposed in connection with the first transfer line for separating a transport liquid from the impregnated material; a first return line connected to the separator to conduct the transport liquid from the separator back to the first transfer line; a second return line attached to the first return line and to the impregnation vessel for supply- ing a portion of the transport liquid to an inlet of the impregnation vessel; a supply line connected to a supply space adjacent the level of the material in the impregnation vessel.
  • Figure 1 is a graphic representation of the time-temperature profile of prior art conventional batch cooking
  • Figure 2 is a graphic representation of the time-temperature profile of prior art displacement batch cooking
  • Figure 3 is a graphic representation of the time-temperature profile of prior art continuous cooking of the Kamyr type
  • Figure 4 is a graphic representation of the time-temperature profile of an embodiment of the invention.
  • FIG. 5 is a flowchart showing an embodiment of the invention
  • Figure 6 is a schematic representation of the water balance of a traditional cooking system
  • FIG. 7 is a schematic representation of the water balance of a cooking system in accordance with the present invention.
  • Figure 8 shows the brightness achieved versus consumption of active chlorine in pulps prepared using the conditions set forth in Table 1
  • Figure 9 shows the brightness as a function of viscosity of pulps prepared according to the examples in Table 1
  • Figure 10 shows the active chlorine consumption against bleached yields in the examples according to Table 1, and
  • Figure 11 shows the reject percentage as a function of impregnation time in pulp cooked to two kappa numbers according to the invention.
  • Figures 1 to 4 show the temperature profiles of prior art pulping methods as well as that of the present invention.
  • FIG 1 shows the temperature curve against time in a conventional batch cook
  • region 1 of the curve represents the heat-up phase
  • region 2 illustrates cooking at about the maximum temperature
  • region 3 illustrates the discharge and cooling of the conventional batch digester.
  • region 1 typically, the duration of region 1 is 60 to 150 minutes, and that of region 2 60 to 120 minutes. The sum of region 1 and 2 is typically about 150 minutes.
  • region 5 represents the impregnation phase
  • region 6 the hot liquor fill phase, i.e. hot black liquor treatment and hot white liquor charge
  • region 7 represents the temperature adjustment phase, usually carried out by circulating the digester content and heating
  • region 8 illustrates the cooking phase at cooking temperature.
  • Region 9 represents the displacement with cool wash liquid and region 10 represents the cold discharge.
  • region 5 typically is typically about 30 minutes, but it can be 10 to 40 minutes depending on digester size, at a temperature below 100 °C.
  • Region 6 is typically about 30 minutes (can be 15 to 40 minutes depending on digester size).
  • Regions 7 and 8 are typically 65 to 100 minutes. Thus, regions 6, 7 and 8 together typically represent 95 to 130 minutes.
  • Region 9 is typically 45 minutes (can be 20 minutes to 60 minutes depending on, among other factors, digester size).
  • region 11 represents the impregnation phase
  • region 12 represents heating
  • region 13 represents a cooking phase, which can occur in both concurrent and countercurrent modes.
  • Region 14 represents displacement and cooling of the cooked material before discharge from the digester.
  • Region 11 is typically 30 to 60 minutes or shorter at a temperature of 115-130°C.
  • Regions 12 and 13 are over 90 minutes, typically 240 to 360 minutes.
  • FIG. 4 shows the advantageous temperature profile of the present invention.
  • Region 20 represents the impregnation phase, which as can be seen is substantially extended relative to processes presently in use.
  • Region 21 represents the heating-up phase.
  • Region 22 represents the short reaction time and region 23 the cooling of the cooked material.
  • Curve 24 illustrates schematically an optional cooling and washing method. Between regions 20 and 21, feeding of the pre-impregnated material to the cooking reactor takes place.
  • FIG. 5 is a flowchart of a process according to the invention.
  • Lignocellulosic material 30 in the form of industrial wood chips enters a pre-steaming phase 31.
  • Steam 36 is supplied to heat the chip flow and purge air therefrom, and gases 37 are removed from phase 31, preferably to a closed system.
  • the chips are heated to a temperature of 80- 120 °C, preferably 95-110 °C.
  • the retention time at the above temperature should preferably be 5 - 40 min.
  • Pre-steamed material 38 enters the impregnation stage 32.
  • the transfer method and equipment in point 38 between phase 31 and 32 depends on the counter- pressure in stage 32.
  • the residence time of the stage 32 is at least 60 minutes. It can be significantly longer, depending on the available size of equipment.
  • impregnation times of more than about 24 h may be used for example when combining the impregnation stage with chip storage between the chipping unit and the cooking plant.
  • the impregnation time rarely exceeds 120 hours in the same equipment.
  • the impregnation equipment may be a down-flow vertical vessel or a horizontal conveyer type vessel with at least one inflow and at least one outflow point for the material, known to the person skilled in the art.
  • Installed continuous digester vessels can be used e.g. when upgrading an existing plant.
  • the impregnation device can be considered to be of the chip silo vessel type.
  • Several vessels can be used in series or in parallel.
  • the impregnation vessels are preferably dimensioned for a low pressure, i.e. pressure in the area from about 0 to 5 bar; more preferably, the vessels are dimensioned for pressure in the range from atmospheric to about 1 bar.
  • High-pressure equipment over 5 bar design pressure
  • Fresh alkali 39 is added to the stage. The amount may be, for example, 30 per cent or more of the total fresh alkali to be added calculated as total titrable alkali (TTA) per charged unit of wood, but additional fresh alkali is invariably added in the cooking stage.
  • Spent liquor 46 is added as needed, recycled from e.g. a subsequent liquor- separation stage.
  • the effective alkali concentration of the added liquors is 0.5-2.2 mol OH " /I; preferably 0.5-1.5 mol OH71.
  • the fresh alkali 39 and spent liquor 46 can be added together at one addition point, or in sequences during the impregnation.
  • Spent liquor can be added first, and then fresh alkali is added and some spent liquor withdrawn.
  • Fresh alkali can also be added first and then spent liquor.
  • Parts of spent liquor and fresh alkali can also be added first, and then fresh alkali is added together with some withdrawal of spent liquor.
  • the fresh alkali used can be both caustisized liquor, normally referred to as white liquor, and uncaustisized liquor, normally referred to as green liquor, or also derivates of the above mentioned liquors, e.g. a mother liquor from crystallization of sodium carbonate from green liquor.
  • Impregnated material 40 leaves the impregnation reactor via a transfer system 41, which may be one of various combinations of discharge systems in the outlet part of the impregnation vessel and feeding technology known to the person skilled in the art.
  • the system is supplied with liquor 45 as required e.g. for dilution.
  • Transfer systems to be used are pumps, chamber feeders (e.g. of the high-pressure (HP) feeder type), screws, scrapers and injectors etc., and combinations thereof, known to the person skilled in the art.
  • the stream may enter a device 43 for liquid removal, which device may be a screen or a liquor separator of a known type.
  • the free liquor 48 not absorbed by the chips is essentially removed, or the amount of liquor surrounding the chips is adjusted to a predefined value, after which the chips 44 enter the cooking stage 33.
  • the remaining required amount of fresh cooking liquor 47 is added to the cooking stage 33 together with spent liquor 60 in order to e.g. adjust the alkalinity and liquor-to-wood ratio in cooking stage 33.
  • the liquor- to-wood ratio is at least 2.5 mVtons odw. In practice, the liquor-to-wood is always below 100 m 3 /tons odw.
  • the temperature of the liquor may require adjustment to hold the preferable temperature between 70 °C and atmospheric boiling point.
  • the digester used must be able of heating the chips to the cooking threshold temperature T2, preferably within about 30 minutes. This can be accomplished by direct steaming and/or by pre-heating the added liquors. In practice the heating time t 2 is always above about 1 minute. After the threshold temperature T2 is reached, exothermic reactions and possible additional heating raise the temperature to a maximum temperature T3. The total time of heating and cooking at maximum temperature must not exceed 65 min.
  • the cooking zone can be a vertical or horizontal reactor with at least one input and one output of material.
  • a vertical re- actor can be fed from either top or bottom, i.e. down-flow or up-flow reactor or a combination of down-flow and up-flow reactor.
  • a horizontal reactor can be equipped with a conveyor device, as a chain conveyor or a screw.
  • the cooking zone can also be a reactor inclined at a certain angle, e.g. 45°.
  • the cooking reactor can be equipped with liquor and steam addition points and with withdrawal points for both gas and liquors. These addition and withdrawal points can be several.
  • the effective alkali concentration of the cooking liquor can be 0.05- 0.7 mol OH71, preferably in the range OJ-0.5 mol OH71.
  • the cooked material 53 exits the cooking stage and enters a washing and cooling phase 34, in which cooler liquor is introduced to essentially end the cooking reactions, leach out dissolved material inside the cooked chips, and wash the cooked material.
  • a washing and cooling phase 34 in which cooler liquor is introduced to essentially end the cooking reactions, leach out dissolved material inside the cooked chips, and wash the cooked material.
  • Any suitable combination of displacement, liquor withdrawal, dewatering and dilution may be used. Technically, this may be accomplished using a liquor displacement and withdrawal zone in the cooking reactor, dilution of the cooked material, dewatering and displacement stages oc- curring outside the cooking reactor in a subsequent vessel, or pulp washing equipment known to persons skilled in the art.
  • the washing stage is supplied with a substantially aqueous liquid, which can be e.g. water, condensate or suitable diluted process liquor.
  • Spent liquor 52 from the washing stage may be re-circulated 60 to the digester, preferably through a heating device (not shown) and possibly mixed with an additional liquor which may be a liquor from the impregnation stage, e.g. from point 55.
  • Spent liquor 56 and 57 from the cooking and washing stages, respectively, is removed from the process.
  • the heat of the combined liquor 62 is recovered either separately of at least one the liquors representing liquor 62, i.e. liquors 56, 57 and 58, or of the combined liquor 62.
  • the recovery of heat can take place by flashing or heat exchange in one or several stage.
  • the recovered heat can be used to heat the material 30 in the pre-steaming stage 31, and/or the recovered heat can be used to heat the fresh alkali 47 or the spent liquors 60, 52 or 59, to heat other process liquids, e.g. in evaporation, or to heat water.
  • the liquor balance of the process may further include circulation of liquor 48 and 49 from the separation device and from any phase of the impregnation stage, respectively, to the beginning of the impregnation stage.
  • Liquor 55 from the impregnation stage may also be conducted to the chemicals recovery through line 58.
  • the washed material 61 proceeds to further treatment stages as e.g. delignification, bleaching, refining, screening etc. depending on the purpose of the final product.
  • Figure 6 shows a typical water balance of a prior art process, compared with the water balance of a process according to the present invention in Figure 7. It can be seen, that the method according to the invention does not affect the water balance of the plant, but the difference in relation to conventional cooking is clear. A substantial part of the white liq- uor is added to a pre-treatment stage to completely impregnate the chips prior to cooking. In addition, some residual liquor after the pre-treatment is re-circulated to the liquors introduced in the impregnation to dilute the EA of added liquors and thereby avoid too strong liquors being applied on the wood chips, which may lower the quality of the pulp.
  • Table 1 shows the results of, on the one hand, comparative laboratory cooking experiments (1-4) using various typical conditions for prior art continuous and batch cooking, and on the other hand experiments (5-11) using conditions according to the present invention.
  • Example 3 Production of eucalyptus pulp according to prior-art process disclosed in U.S. Pat 3,664,918 (vapor phase pulping of water saturated lignocellulosic materials) and example 1 of U.S. 3,664,918.
  • the industrial eucalyptus chips (5.5 kg oven dry weight) were first submerged in water overnight at 2 bar overpressure and room temperature. The excess water was separated. The water saturation resulted in chips of 44.6 % dry solids.
  • the water-submerged chips were metered into a chip basked positioned in a 32-liter jacketed displacement digester with liquor circulation.
  • the chips were impregnated with white liquor (EA charge of 33.7 % NaOH calculated on wood, EA 122 g NaOH/1 and sulfidity 30 %) at a liquor-to-wood ratio of 4 m 3 per ton of dry wood at 90 °C, 60 minutes and atmospheric pressure.
  • Example 4 show laboratory simulation data of a process simulated according to prior-art displacement batch cooking of industrial Eucalyptus.
  • eucalyptus chips (oven dry basis) were metered into a chip basket positioned in a 26-liter jacketed displacement digester with liquor circulation. The same chip raw material as shown in Example 3 were used. The chips were pre-steamed for 10 minutes at 100 °C. Then impregnation liquor fill was conducted with an impregnation liquor containing 0.29 mol OH71 of EA. After 30 minutes impregnation, hot black liquor treatment occurred for 20 minutes with a HBL containing 0.205 mol OH71 of EA and a temperature of 148 °C.
  • Example 5 The experiment was carried out as disclosed in Example 5, but the impregnation time was 60 min and the cooking conditions were adjusted to give about the same kappa number as in Example 5.
  • Example 6 The experiment was carried out as disclosed in Example 6, but the cooking conditions were adjusted to give a higher cooking kappa number.
  • Example 7 The experiment was carried out as disclosed in Example 7, but the impregnation time was adjusted to 180 minutes and the cooking conditions were adjusted to give slightly higher kappa number than in Example 7.
  • Example 8 The experiment was carried out as disclosed in Example 8, but the impregnation time was adjusted to 3 days and the cooking conditions were adjusted to give slightly higher kappa number compared to Example 8.
  • Example 6 The experiment was carried out as disclosed in Example 6, but the impregnation pressure was adjusted to 10 bar and the cooking conditions were adjusted to give slightly higher kappa number compared to Example 6.
  • Example 8 The experiment was carried out as disclosed in Example 8, but the impregnation pressure was adjusted to 10 bar and the cooking conditions were adjusted to give slightly lower kappa number compared to Example 8.
  • Table 1 shows the cooking characteristics, unbleached pulp results and the subsequent oxygen delignification, ECF bleaching and PFI beating results. All oxygen delignifica- tions, ECF bleachings, PFI beatings and tests were performed in the laboratory.
  • the reject level depends on the impregnation time and kappa number target (see figure 10 showing reject levels of pulps at kappa numbers 20 and 25 and impregnation times of 0-3 days using a retention time of 25 minutes in heating and cooking)
  • the reject level is independent on impregnation pressure in the range 0.5 bar to 10 bar for pre-steamed chips implementing that low-pressure impregnation equipment can be used in impregnation
  • Example 7 used more

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Abstract

L'invention concerne un procédé alcalin de production continue de pâte à papier à partir de copeaux de bois. Selon ce procédé, les copeaux préchauffés sont soumis à une étape d'imprégnation prolongée pendant au moins 60 mn, de préférence, pendant plus longtemps, à une température n'excédant pas le point de lessivage de la liqueur d'imprégnation, dans des conditions atmosphériques. Ces copeaux sont ensuite soumis à un chauffage et une cuisson rapide de moins de 65 mn, et de préférence, encore moins, avant d'être refroidis à une température inférieure à la température de réaction. On ajoute de l'alcali frais pendant l'imprégnation et le chauffage/la cuisson.
EP01997586A 2000-11-24 2001-11-21 Procede de cuisson alcaline de materiaux fibreux Withdrawn EP1346103A1 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
FI20002587 2000-11-24
FI20002587A FI20002587A (fi) 2000-11-24 2000-11-24 Alkalinen keittomenetelmä kuitumateriaalille
PCT/FI2001/001009 WO2002042550A1 (fr) 2000-11-24 2001-11-21 Procede de cuisson alcaline de materiaux fibreux

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EP1346103A1 true EP1346103A1 (fr) 2003-09-24

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EP01997586A Withdrawn EP1346103A1 (fr) 2000-11-24 2001-11-21 Procede de cuisson alcaline de materiaux fibreux

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US (1) US20040089430A1 (fr)
EP (1) EP1346103A1 (fr)
AU (1) AU2002223714A1 (fr)
FI (1) FI20002587A (fr)
WO (1) WO2002042550A1 (fr)

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SE518538C2 (sv) * 2001-12-14 2002-10-22 Kvaerner Pulping Tech Förbehandling av flis med färsk vitlut före behandling med svartlut
FI20105799A0 (fi) * 2010-07-13 2010-07-13 Olli Joutsimo Parantunut kemiallisen massan valmistusprosessi

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FI20002587A0 (fi) 2000-11-24
US20040089430A1 (en) 2004-05-13
AU2002223714A1 (en) 2002-06-03
WO2002042550A1 (fr) 2002-05-30
FI20002587A (fi) 2002-05-25

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