CN1170795A - Improved Batch Preparation of Kraft Pulp - Google Patents

Abstract

The invention discloses an improved batch process for preparing kraft pulp, wherein a portion of green liquor or a derivative thereof is introduced in the impregnation or/and pretreatment stage. The derivative may be mother liquor originating from crystallization of carbonate from green liquor. The procedure facilitates the use of mild conditions in the final cooking stage and short cooking periods and results in higher pulp quality, high production output and good maintenance of the balance of chemicals in the mill.

Description

Improved Batch Preparation of Kraft Pulp

The present invention relates to a method for preparing kraft pulp for treating cellulosic materials with recycled pulping treatment liquor in which lignin is dissolved, uncausticized cooking liquor and causticized white liquor. More precisely, the present invention relates to the use of green liquor or mother liquor crystallized from green liquor carbonate in the early stages of modern displacement kraft batch cooking; and the advantages of the invention in terms of improved kraft pulp quality .

In various kraft pulping processes, cellulosic material such as wood chips is usually treated with an alkaline cooking liquor (known as white liquor) comprising sodium hydroxide and sodium hydrosulfide at high temperature. In these processes, the cooking liquor obtained when the inorganic melt obtained from the recovery furnace is dissolved in water prior to causticizing the carbonates to hydroxides is often referred to as green liquor. Causticized green liquor is usually called white liquor, and cooking waste liquor is usually called black liquor. Typical compositions of green liquor and white liquor are listed in Table 1. Table 1. Typical compositions /1/ of so-called green and white liquors.

    Green Liquor                                                            

g/l g/l

As Na ₂ O NaOH as Na ₂ O 15 95Na ₂ S 37 38Na ₂ CO ₃ 107 261. Clayton, D. et al. In Alkaline Pulping Chemistry in Pulp and Paper Manufacturing, Third Edition, Volume Five, Alkaline pulping (Grace, TM, Malcom, EW, ed., TAPPI, CPPA, 1989. p. 17, 15).

It is worth noting that the concentration of carbonate in green liquor is high and the concentration of hydroxide is low. It is especially important that all reduced sulfur is already in the form of the final available hydrosulfide, HS ^- ion ( _Na2S in water). The carbonate/hydroxide mixture in green liquor will not provide the high pH required by conventional kraft processes and must be converted to so-called "white liquor" by causticizing methods, but this green liquor is a rich Excellent source of hydrosulfide for alkaline buffered carbonates.

Previously, cooking with green liquor was only used in high-yield semi-chemical pulping, where delignification was poor and the pulp still contained most of the lignin, and in green liquor After cooking, the fibers must be released by mechanical refining (Vardheim, S., Green liquor as cooking liquor in the production of semichemical hardwood pulp for corrugation, Paperi ja Puu (1967)). These pulps are not at all suitable for so-called chemical pulps, which cannot be bleached and are used in cardboard manufacture.

From the point of view of cooking chemicals, the industrial kraft pulping process has not changed and developed until today. Although many different chemistries have been proposed to improve various factors such as pulp yield, quality and delignification selectivity, none of the proposals has a practical solution for these purposes because each Both proposals involve complex additional equipment, additional process steps, larger digester capacity or the use of expensive chemicals that are exotic to the pulp mill and cannot be recovered and regenerated. In the early 1970's there was a new trend of increasing environmental pressure on kraft pulp mills in order to drastically reduce the amount of waste water polluting the environment. In order to reduce organic effluents from pulp bleaching, extended kraft cooking is required to obtain much lower residual lignin concentrations in pulp than before. Due to the poor quality of pulp obtained when using conventional cooking methods to obtain low residual lignin concentrations, a modified kraft cooking method had to be developed. Among other things, this development work reveals the role of hydrosulfide ions: i.e. the concentration of hydrosulfide ions must be high in the early stages of cooking, and as the cooking approaches the end, the hydrosulfide is no longer effective. However, the desired effect of hydroxyl ions has been found to be just the opposite (Sjöblom, K., et al., "Extended delignification in kraft cooking by improved selectivity", Paperi ja puu 65:4, 227 (1983); Nordén, S. and Teder, A., "Kraft Process for Modification of Softwood Bleached Grade Pulp", TAPPI Journal 62:7, 49 (1979)). In order to obtain an optimal concentration distribution of hydrosulfide ions and hydroxyl ions, it has been proposed to prepare white liquor with different degrees of sulfidation (Jiang et al., "Improvement of kraft pulping process by controlling the amount of Proceedings of the Seventh International Symposium on Pulp Chemistry, Beijing, China, May 25-28, 1993; Teder, A. and Olm, L., "Extended delignification", Paperi ja Puu 63:4a, 315 (1981)). In another study (Andrews, E.K., "Extended delignification of southern pine using a new theoretical approach within the confines of conventional sulfate and oxygen processes", Department of Wood and Paper Sciences, North Carolina State University PhD dissertation, 1982), attempts have been made to use sulphide-containing liquor as a pretreatment stage prior to conventional kraft cooking with white liquor. It was found that a better pulp viscosity was obtained as predicted by theory. Since these kinds of pretreatments require a separate cooking stage at higher temperatures (up to 7% caustic effective for wood at 135°C), they will take a significant amount of production time per digester and require Improve the method. Predictable production losses and modest advantages have made this technique unfeasible.

According to another invention (Tikka, US 5,183,535), sulfur species found in spent black liquor can impregnate and react with wood chips before finishing cooking with white liquor.

Another trend in the development of the kraft process is to strive for energy efficiency. Therefore, from the early 1960s, continuous cooking equipment began to occupy this field. However, from the early 1980s, the emerging and competitive energy-efficient sulfate batch process using various displacement technologies began to dominate. The displacement kraft batch process is characterized by recovering the hot black liquor at the end of the cooking and reusing its energy in subsequent batches. Good examples of such developments are the methods described in eg US 4,578,149 (Fagerlund) and US 4,764,251 (tman). While these inventions do effectively recover the heat of cooking, the use of cooking chemicals is far from optimal.

Another development of displacement kraft batch cooking involves a combination of energy efficiency and efficient use of residual and fresh cooking chemicals to achieve favorable delignification and high pulp strength. This can be achieved by arranging displacement at the end of the digest so that hot and residual sulfur-rich "raw black liquor" is first recovered in one recovery tank, followed by recovery of solids and lower temperature entrained wash filtrate in another recovery tank. That part of the black liquor is done. The collected black liquor is then reused in reverse order to impregnate and react the chips with the black liquor before final cooking of the next batch of chips with hot white liquor (Hiljanen, Tikka, EP-B520452) . By means of this method, it is possible to carry out kraft cooking with a high amount of hydrosulfide ions and a low concentration of hydroxyl ions, and thus the reaction of sulfur and lignin in the hot black liquor pretreatment section. The required caustic cooking liquor with high hydroxyl ion content, i.e. white liquor, is not added until the final cooking stage where the hydroxyl ions are consumed leaving the white liquor hydrosulfide in the spent black liquor residue to be recycled to In the next batch. To date, the heat and chemicals from batch cooking can be recycled very efficiently by using displacement batch cooking technology.

As far as the overall chemical balance of a modern kraft pulp mill is concerned, a new idea is emerging: the caustic is not purchased externally, but is produced within the chemical system of the pulp mill. This idea will become increasingly important as bleaching methods are being developed that use less chlorine and much more caustic than ever before. When the chlorine/alkali industry is reduced, the cost of caustic increases and the series of problems in the pulp mill to maintain the chemical balance requires a large amount of external sodium input, which must have a complete alkali production for some pulp mills.

The above problems are solved by sending part of the green liquor to the carbonate crystallization process and preparing pure caustic by causticizing the separated carbonate crystals, thereby producing on-site Pure caustic (NaOH) is required. The remaining mother liquor contains residual carbonates, and also any sulfides that were originally present in the green liquor. A new immediate use for this mother liquor has now been found to improve displacement kraft batch cooking by introducing it into the front end of the cooking. It has previously been suggested to causticize the mother liquor separately to produce highly sulfided white liquor, but this again complicates the process at the pulp mill. In a modern plant producing bleached kraft pulp, it is typical that 20% of the total green liquor volume needs to be used for crystallization after the recovery boiler (the remaining 80% is usually causticized to white liquor for cooking). This will produce pure caustic for bleaching equivalent to 25 kg NaOH per ton of dry wood, ie about 60 kg NaOH per metric ton of air-dried pulp, which will normally cover the caustic consumption required in the oxygen bleaching and alkaline extraction stages. The volume of the resulting crystallization mother liquor used for cooking was 0.11 liquor/pulp unit, the liquor contained 16 kg EA(NaOH)/kg wood and 0.23 moles HS/kg wood. Of course, the separation of green liquor and the production of pure caustic vary from case to case.

It has been found that the front end of a batch kraft process (i.e. maceration and/or or hot black liquor pretreatment section), improved pulping performance in terms of advantageous cooking section using less white liquor volume than other methods, improved pulp strength and bleaching performance. Since green liquor is always available from pulp mills, it is practical to use green liquor. Where the pure caustic for the oxygen delignification and alkali bleaching stages is produced from carbonates derived from green liquor, it is practical to use mother liquors obtained from the crystallization of green liquor carbonates.

Figure 1 shows a block diagram of a sulfate displacement batch cooking system. The diagram identifies the required sequence of tanks, streams and cooking stages. To illustrate the prior art displacement batch cooking technique, the following description is provided: Kraft batch cooking is initiated by impregnating the chips by filling the digester with chips and filling the digester with black liquor AA from the impregnation black liquor tank 5 . The overflow A2 is preferably sent to the position AB of the black liquor tank 4 in order to remove air and the foremost dilution liquid. After shutting off flow A2, the digester was pressurized and fully soaked. The cooking process is then continued by pumping the hot black liquor B from the hot black liquor tank 1 . The soft cold black liquor A3 replaced by the hot black liquor is sent to the position AB of the black liquor tank 4, and then sent to the evaporation workshop for recovery of cooking chemicals. The cooking process is continued by pumping hot white liquor C from tank 3 into the digester. The liquid D2 replaced by the hot liquid above the boiling point of about normal pressure is sent to the hot black liquor tank 2 . After the filling step described above, the temperature of the digester is close to the final cooking temperature. Final heating is done by using direct or indirect steam heating and recirculation of the digester. After the desired cooking time, when the delignification has proceeded to the desired degree of reaction, it is ready to replace the spent liquor with wash filtrate E. In the final displacement, the first part B1 of the displaced hot black liquor corresponds to the total volume B required in the filling section. The second part D1 of the displaced black liquor is sent to the position D of the hot black liquor tank 2; said D1 is diluted with the washing filtrate but still above its atmospheric boiling point. After the final displacement is complete, the digester contents are drained for additional pulp treatment. The cooking procedure described above can then be repeated.

Hot black liquor tank 2 supplies cooled impregnation black liquor to tank 5 and transfers its heat to white liquor and water by means of heat exchange.

The tank 6 is provided to store the green liquor or its derivatives supplied by the cooking chemical recovery workshop. According to the invention, at least a part of the green liquor or its derivatives X1-X3 is introduced into the impregnation and/or pretreatment section.

According to the present invention, by means of the kraft batch process, an improvement to the kraft pulping process has now been provided, comprising the addition of non-causticized cooking liquor in the "front end" part of the maceration and pretreatment of the displacement kraft batch cooking process (green liquor) or derivatives thereof, and a final delignification stage adding white liquor, the process is advantageous in terms of milder cooking conditions leading to improved pulp quality.

Reference will now be made to the aforementioned drawings.

According to one embodiment of the method of the invention, 0.2-1.0 L of green liquor/kg dry wood of X1 volumes of green liquor ( Corresponding to 0.15-0.7 mol HS ⁻ /kg dry wood) from tank 6 to impregnating warm black liquor AA from tank 5.

According to the second embodiment of the method of the present invention, at first the green liquor (corresponding to 0.15-0.7 mole HS ^- /kg dry wood) of 0.2-1.0L green liquor/kg dry wood X2 volume is directly added from tank 6 To the digester, then add warm black liquor AA for impregnation, and impregnate at a temperature between about 80 and 100° C. and for about 30-60 minutes.

According to the third embodiment of the inventive method, warm black liquor impregnation is carried out as described in the prior art, then, the green liquor (corresponding to 0.15-0.7 mole HS ⁻ /kg dry wood) was added from tank 6 to the thermal black liquor B, and the thermal black liquor treatment was carried out at a temperature between 145 and 165° C. and a time of about 15-30 minutes.

According to the fourth embodiment of the method of the present invention, the mother liquor X1 volume (0.06-0.4L/kg absolute dry wood, equivalent to 0.15-0.7 mole HS ⁻ /kg absolute dry wood) obtained by the crystallization of green liquor is added from tank 6 to Immerse in warm black liquor AA at a temperature between about 90 and 110° C. and for a time of about 30-60 minutes.

According to the fifth embodiment of the method of the present invention, at first the mother liquor X2 volume (0.06-0.4L/kg absolute dry wood that is equivalent to 0.15-0.7 mole HS ^- /kg absolute dry wood) obtained by the crystallization of green liquor is directly obtained from tank 6 Add to digester, then add warm black liquor AA for impregnation and impregnate at a temperature between about 80 and 100°C and for about 30-60 minutes.

According to the sixth embodiment of the method of the present invention, warm black liquor impregnation is carried out as described in the prior art, then, the mother liquor X3 volume (0.06-0.4L/kg dry wood that is obtained by green liquor crystallization, is equivalent to 0.15-0.7 mol HS ⁻ /kg dry wood) is added to the hot black liquor from tank 6, and the hot black liquor treatment is carried out at a temperature between 145 and 165° C. and a time of about 15-30 minutes.

If non-causticized cooking liquor is added in the impregnation section of the process, higher temperatures must be used than in the prior art in order to use the chemicals efficiently and avoid too high a residual alkali concentration in the feed to the evaporation plant. The required higher impregnation temperature can be achieved by using recirculation of the digester and direct or indirect steam heating, or by simultaneously feeding a small amount of hot black liquor B from tank 1 to the impregnation black liquor AA.

If non-causticized cooking liquor is added to the hot black liquor, the temperature of the liquor is high enough to provide the desired reaction temperature.

A major advantage of the process of the present invention is that it makes the "front end" of the sulfate displacement batch cooking more efficient. This will improve pulp quality as cooking with white liquor is greatly facilitated at the "back end" of kraft batch cooking, requiring milder back end cooking conditions and can result in pulp strength and easier pulp bleaching Improved pulp quality.

Furthermore, practicing the method of the present invention would be advantageous for at least the following reasons:

Unlike the prior art, no additional cooking steps are required in the cooking program. Since only modifications to the existing cooking steps are required and no major modifications to the equipment are required, there is no need to stop production when implementing the present invention. Due to the improved cooking section, the amount of white liquor required is reduced and the cooking time is shortened resulting in increased throughput.

The amount of non-causticized liquid such as green liquor required is small enough to be handled by a conventional sized evaporation system. The total load on the recovery system does not increase as the use of green liquor increases due to the reduced use of caustic cooking liquor.

In terms of the chemical balance of a modern kraft pulp mill, the use of a mother liquor obtained from green liquor carbonate crystallization would be very advantageous. Causticizing the separated carbonate in situ will produce the pure caustic required in modern kraft pulp bleaching. This will greatly reduce the amount of caustic purchased externally and maintain chemical balance.

The following examples will illustrate the invention and make clear the advantages over the prior art kraft batch displacement cooking process with a black liquor front end.

The following abbreviations are used in the examples: EA effective base = NaOH expressed in NaOH equivalents + 1/2 Na ₂ SAA active base = NaOH expressed in Na ₂ O equivalents + Na ₂ SWBL warm immersion black liquor OWBL overflowed WBLDWBL Displaced WBLHBL Hot black liquor RHBL Displaced HBLWL White liquor, causticized cooking liquor DL Final displacement liquor GL Non-causticized cooking liquor, “green liquor” XGL Mother liquor from carbonate crystallization of GL O Oxygen delignification step D Chlorine dioxide bleaching step E Alkaline extraction step

Results and advantages of the invention are summarized in the table below. Table 2. Summary of the results of the examples. All trials were cooked to a constant kappa number of 20 and residual EA at the end of cooking was 20 gEA/L. Parameter reference example 1 Method example 2 Method example 3 Method example 4 Method example 5 Auxiliary liquid No GL GL GL xGL Charge amount No 0.5 0.5 0.5 0.11 (liquid/wood unit) White liquor charge amount 20.7 16.3 17.1 16.5 17.3 (with EA% based on OD wood) required H-factor 1006 980 1008 1017 978 screening yield (%) 43.6 43.4 43.4 43.9 43.2 viscosity (ml/g) 1052 1041 1081 1088 103590mN/g tensile strength of unbleached pulp Strength, that is, tear index (mNm ² /g) 14.7 16.2 16.2 15.8 16.489% (ISO) Active chlorine consumption multiple (kg active chlorine/ODtxkappa) 4.2 4.2 3.7 3.8 3.7 Brightness upper limit (%ISO) 90.1 90.1 90.5 90.3 90.990mN Strength of bleached pulp per gram of tensile strength, i.e. tear index (mNm ² /g) 14.0 15.0 16.4 15.3 16.4

Based on the results in Table X, the present invention provides the following surprising benefits over similar prior art cooking methods: Using a small amount of uncausticized cooking liquor,

A 20% reduction in causticizing caustic cooking liquor or white liquor volume while maintaining unchanged pulp yield, viscosity and required H-factor, i.e. cooking time,

10% increase in strength of unbleached pulp,

10% reduction in bleach chemical consumption,

The maximum brightness increase that can be achieved by the brightness upper limit,

And the strength advantage of the pulp remains unchanged after bleaching. Example 1 Production of normal "reference" pine kraft pulp by using displacement kraft batch technology

3.5 kg of pine (scot pine) chips (on a dry basis) were metered into a chip basket set in a 20 liter jacketed displacement batch digester which was forced to circulate. The digester lid was closed and the chips were steamed at 100°C for 10 minutes at atmospheric pressure. The impregnation black liquor (WBL, 80-90°C, 8gEA/l) was pumped over 20 minutes with some overflow (OWBL), followed by 20 minutes of impregnation at 80°C and 5 bar pressure. After impregnation, before adding hot black liquor (HBL, 165°C, 20gEA/l) to the bottom of the digester and displacing dipping waste black liquor (DWBL) from the top of the digester is a hot black liquor pretreatment section. After a 20-minute hot black liquor section, hot white liquor (105 g EA(NaOH)/l; degree of sulfidation 40%) was introduced into the bottom of the digester and a corresponding volume of hot spent black liquor was displaced from the top of the digester ( RHBL). The temperature was raised from 155°C to a cooking temperature of 170°C after 25 minutes of cyclic heating. After the cooking time required to achieve the target H-factor, the wash buffer solution DL (0.02 molar _{Na2CO3 /} l + 0.05 molar _Na2S /l) was introduced into the bottom of the digester, displacing it from the top of the digester. The final replacement begins with hot waste black liquor. The part of the hot black liquor (HBL1) from the first replacement compensates the impregnation liquor required for the next cooking by 171. The liquid part of the second displacement (BL2) compensates 131 for cooling down and the hot black liquor required for the next impregnation. After the final exchange, the pulp is dissociated, washed with deionized water, screened and analyzed. This cooking step was repeated three times by recycling the displacement fluid to the next cooking. By these means, a balance of the cooking process is achieved and the cooking itself begins to repeat itself in line with industrial batch cooking systems. In all cooking trials, the cooking conditions were adjusted so that the final kappa number was 20 and the residual EA at the end of the cooking stage was 20 g EA/l. In Table E1.1 below the liquid feed and output (volume, liter) and the conditions of the corresponding cooking section are listed. Unbleached pulp is analyzed for overall yield, screening yield, kappa number, viscosity, brightness and pulp strength by beating and testing. In addition, the unbleached pulp was bleached with the OD-Eop-DED bleaching procedure. Determine the bleaching chemicals required for a given pulp brightness and determine pulp strength by beating and testing. The bleaching process conditions are listed in Table E1.2. Cooking characteristics and results are listed in Table E1.3. Table E1.1. The amount of liquid added and output in Example 1 and the corresponding cooking section conditions (volume, liter) The liquid process section of the added liquid output WBL 30.7 OWBL 12 Warm black liquor immersion at 80 ° C for 40 minutes HBL 13.3 DWBL 13.5 Hot black liquor pretreatment 155℃, 20 minutes HWL, according to hot white liquor filling charge about 7+3.5HBL RHBL about 10DL 30 HBL 17 Final replacement

BL2 13 Table E1.2. Bleaching Process Conditions in All Examples Section 0 D0 Eop D1 E D2 Time (minutes) 90 30 120 180 90 240 Temperature (°C) 105 60 70 75 60 75 Concentration (%) 10 10 12 12 12 12 Pressure (bar) 6(O ₂ ) Atmospheric pressure 2(O ₂ ) Atmospheric pressure Atmospheric pressure Atmospheric pressure NaOH(%) 1.1-1.2 --- 0.6×D0 --- 0.5 ---

Active Chlorine MgSO ₄ (%) 0.5 --- --- --- ---ClO ₂ , Active Chlorine (%) --- 0.2 --- Changed --- Changed H ₂ O ₂ ( %) --- --- 0.3 --- --- --- Final pH 11 2 --- 3.5-4 --- 3.5-4 Kappa Number Reduction (%) 40-45 Table E1.3. Implementation Results of Example 1 Cooking uncausticized cooking liquor charge in liquid/wood unit 0 in TA, i.e. total alkali (NaOH) 0 white liquor charge (EA, %(NaOH)) 20.7H-factor 1006 cal Primary value 20 Cooking residue (gEA(NaOH)/l) 20 Screening yield (%) 43.6SCAN viscosity (ml/g) 1052ISO brightness (%) 34.0 Tear index when the tensile index is 90Nm/g (mNm ² /g) 18.3 Bleaching 89% (ISO) brightness active chlorine consumption multiples (kg active chlorine / (ODtonxkappa)) 4.2 brightness upper limit (% ISO) 90.1 ISO89% brightness SCAN viscosity (ml/g) 765 tensile index is Tear Index at 90 Nm/g ( ^mNm2 /g) 14 Example 2 This test was carried out as described in Example 1, except that 0.5 liquor/wood unit of uncausticized cooking liquor was used as follows:

After steaming the chips, a new liquor procedure for impregnation was introduced: first, 18.71 WBL (90°C) was added, then 0.5 liquor/wood unit (1.751) of uncausticized cooking liquor GL (90°C) and 3.51 HBL (168°C). In order to increase the impregnation temperature up to 100° C., a hot black liquor is used here. Table E2.1 lists the liquid volumes and conditions. First 20 minutes are spent filling the liquid, followed by 40 minutes of impregnation at 100° C. and 5 bar with digester circulation. Due to the reduced amount of WBL (18.71), WBL only contained RHBL and BL2, the second part of the fluid that was finally displaced. For Reference Example 1, the improved results are listed in Table E2.2. Table E2.1. The amount of addition and output of liquid in Example 2 and the corresponding cooking section conditions (volume, liter) Liquid added Liquid output Process section WBL 18.7 Warm black liquor immersion GL 1.75 90/100°C, 60 minutes HBL 3.5 OWBL 5.25HBL 13.3 DWBL 13.5 Hot black liquor pretreatment 155℃, 20 minutes HWL, according to hot white liquor filling charge about 7+3.5HBL RHBL replacement about 10DL 30 1 7 final HBL

BL2 13 Table E2.2. The result of embodiment 2 cooking uncausticized cooking liquor charging amount is calculated in liquid/wood unit 0.5 in % TA, i.e. total alkali (NaOH) 9 white liquor charging amount (EA, %( NaOH)) 16.3 H-factor 980 kappa number 20 cooking residue (gEA(NaOH)/l) 20 screening yield (%) 43.4 SCAN viscosity (ml/g) 1041 ISO brightness (%) 33.9 tensile index 90Nm/ Tear index at g (mNm ² /g) 16.2 Active chlorine consumption multiple (kg active chlorine/(ODtonxkappa)) when bleaching 89% (IS0) brightness 4.2 Brightness upper limit (%ISO) SCAN viscosity at 90.1ISO89% brightness ( ml/g) 763 Tear Index at Tensile Index 90 Nm/g ( ^mNm2 /g) 15 Example 3 The test was performed as described in Example 1 except that 0.5 liquid/wood was used as described below Unit ratio of non-causticized cooking liquor:

After steaming the chips, a new liquid procedure for impregnation is introduced: 0.5 liquid/wood units (1.751) of uncausticized cooking liquor GL (90°C) is first introduced into the digester for 10 minutes before the introduction of the WBL. Bottom, then, 231WBL was added over 20 minutes, followed by a 30-minute soak at 90°C and 5 bar while the digester was circulating. Table E3.1 lists the liquid volumes and conditions. Here instead of using a WBL+GL mixture, the GL is first brought into contact with the steam-treated wood chips and impregnated in a less dilute environment. For Reference Example 1, the improved results are listed in Table E3.2. Table E3.1. The amount of addition and output of liquid in Example 3 and the corresponding cooking section conditions (volume, liter) Liquid added Liquid output Process section GL 1.75WBL 23 OWBL 6 Warm black liquor immersion at 90°C for 60 minutes HBL 13.5 DWBL 13.5 Hot black liquor pretreatment 155°C, 20 minutes HWL according to Hot white liquor filling charge about 7+3.5HBL RHBL about 10DL 30 HBL1 17 Final replacement

BL2 13 Table E3.2. The result of embodiment 3 cooking uncausticized cooking liquor charging amount is calculated in liquid/wood unit 0.5 in % TA, i.e. total alkali (NaOH) 9 white liquor charging amount (EA, %( NaOH)) 17.1 H-factor 1008 kappa number 20 cooking residue (gEA(NaOH)/l) 20 screening yield (%) 43.4 SCAN viscosity (ml/g) 1081 ISO brightness (%) 34.0 tensile index 90Nm/ Tear index at g (mNm ² /g) 16.2 Active chlorine consumption multiple (kg active chlorine/(ODtonxkappa)) when bleaching 89% (ISO) brightness 3.7 Brightness upper limit (%ISO) SCAN viscosity at 90.5ISO89% brightness ( ml/g) 813 Tear Index ( ^mNm2 /g) at a Tensile Index of 90 Nm/g 16.4 Example 4 The test was carried out as described in Example 1 except that 0.5 liquid/wood was used as described below Units of non-causticized cooking liquor:

The impregnation portion of the process was performed as described in Example 1, except that the volume of the WBL was 241. Together with the thermal black liquor, 0.5 liquor/wood unit (1.751) of GL, ie non-causticized cooking liquor, was introduced into the thermal black liquor pretreatment. In all other respects the method was carried out as in Example 1. Table E4.1. lists the liquid volumes and conditions. For Reference Example 1, the improved results are listed in Table E4.2. Table E4.1. The amount of addition and output of liquid in Example 4 and the corresponding cooking section conditions (volume, liter) Liquid added Liquid output Process section WBL 24 OWBL 5 Warm black liquor immersion at 80°C for 40 minutes HBL 13.3 DWBL 15.5 Hot black liquor pretreatment 155℃, 20 minutes GL 1.75HWL, according to hot white liquor filling charge about 7+3.5HBL RHBL about 10DL 30 HBL1 17 Final replacement

BL2 13 Table E4.2. The result of embodiment 4 cooking uncausticized cooking liquor charging amount is calculated in liquid/wood unit 0.5 in % TA, i.e. total alkali (NaOH) 9 white liquor charging amount (EA, %( NaOH)) 16.5 H-factor 1017 kappa number 20 cooking residue (gEA(NaOH)/l) 20 screening yield (%) 43.9 SCAN viscosity (ml/g) 1088 ISO brightness (%) 33.5 tensile index 90Nm/ Tear index at g (mNm ² /g) 15.8 Active chlorine consumption multiple (kg active chlorine/(ODtonxkappa)) when bleaching 89% (ISO) brightness 3.8 Brightness upper limit (%ISO) SCAN viscosity at 90.3ISO89% brightness ( ml/g) 786 Tear Index (mNm ² /g) at a Tensile Index of 90 Nm/g 15.3 Example 5 The test was carried out as described in Example 1, except that carbon from GL was used as described below Non-causticized mother liquor obtained by salt crystallization:

After steaming the chips, a new liquid procedure for impregnation is introduced: 0.11 liquid/wood units of non-causticised mother liquor xGL (0.391, 90°C) is first introduced into the bottom of the digester for 10 minutes before the introduction of the WBL , then 231WBL was added over 20 minutes followed by a 30 minute soak at 90°C and 5 bar while the digester was circulating. Table E5.1 lists the liquid volumes and conditions. For Reference Example 1, the improved results are listed in Table E5.2. Table E5.1. The addition and output of liquid in Example 5 and the corresponding cooking section conditions (volume, liter) Added liquid Output liquid Process section xGL 0.39WBL 23 OWBL 5 Warm black liquor immersion at 90°C for 60 minutes HBL 13.5 DWBL 13.5 Hot black liquor pretreatment 155℃, 20 minutes HWL, according to hot white liquor filling charge about 7+3.5HBL RHBL about 10DL 30 HBL1 17 Final replacement

BL2 13 Table E5.2. The result of embodiment 5 cooking uncausticized GL crystallization mother liquor charging amount is calculated in liquid/wood unit 0.11 in %TA, i.e. total alkali (NaOH) meter 2.9 white liquor charging amount (EA, % (NaOH)) 17.3 H-Factor 978 Kappa Number 20 Cooking Residue (gEA(NaOH)/l) 20 Screening Yield (%) 43.2 SCAN Viscosity (ml/g) 1035 ISO Brightness (%) 31.4 Tensile Index 90Nm Tear index at /g (mNm ² /g) 16.6 Active chlorine consumption multiple (kg active chlorine/(ODtonxkappa)) when bleaching 89% (ISO) brightness 3.7 Brightness upper limit (%ISO) SCAN viscosity at 90.9ISO89% brightness (ml/g) 773 tear index when the tensile index is 90Nm/g (mNm ² /g) 16.4

Claims (10)

1. one kind prepares the discontinuous method of sulfate pulp by the cellulosic material that contains lignin, and this method comprises the steps:

The not causticization cooking liquor of certain volume is added in the container of cellulose-containing material;

Fill described container with waste cooking liquid;

Cooking liquor and this cellulosic material of waste cooking liquid impregnation mixture with the not causticization of gained;

Hot cooking waste liquor with another volume is replaced the liquid that is used to flood, and with the hot cooking waste liquor of described another volume this cellulosic material is carried out preliminary treatment;

Hot cooking liquor displacement with causticization is used for pretreated liquid, and the delignification degree of this cellulosic material boiling extremely being wished with the hot cooking liquor of described causticization;

The liquid that is used for boiling with the wash filtrate displacement, collect the hot cooking waste liquor of first volume, this waste liquid amount be equivalent to the pretreatment of fiber cellulosic material and in other filled section of next batch of material the required cumulative volume of the dispensable interpolation of arbitrariness, and be collected in the displacement liquid that is cooled in next batch of material and is used for second volume of impregnation of fibers cellulosic material.

2. method as claimed in claim 1, wherein, the boiling liquid measure of the not causticization of being added is the 0.2-1.01/kg ovendriedwood.

3. method as claimed in claim 1, wherein, the cooking liquor of the employed not causticization not resulting mother liquor of carbonate crystallization of causticization cooking liquor of serving as reasons, and its addition is the 0.06-0.41/kg ovendriedwood.

4. one kind prepares the discontinuous method of sulfate pulp by the cellulosic material that contains lignin, and this method comprises the steps:

Fill the container of cellulose-containing material with the waste cooking liquid that is added with a certain amount of not causticization cooking liquor;

This cellulosic material of liquid infiltration with gained;

Hot cooking waste liquor with another volume is replaced the liquid that is used to flood, and with described liquid this cellulosic material is carried out preliminary treatment;

Hot cooking liquor displacement with causticization is used for pretreated liquid, and the delignification degree of this cellulosic material boiling extremely being wished with the hot cooking liquor of described causticization;

The liquid that is used for boiling with the wash filtrate displacement, collect the hot cooking waste liquor of first volume, this waste liquid amount be equivalent to the pretreatment of fiber cellulosic material and in other filled section of next batch of material the required cumulative volume of the dispensable interpolation of arbitrariness, and be collected in the displacement liquid that is cooled in next batch of material and is used for second volume of impregnation of fibers cellulosic material.

5. method as claimed in claim 4, wherein, the boiling liquid measure of the not causticization of being added is the 0.2-1.01/kg ovendriedwood.

6. method as claimed in claim 4, wherein, the cooking liquor of the employed not causticization not resulting mother liquor of carbonate crystallization of causticization cooking liquor of serving as reasons, and its addition is the 0.06-0.41/kg ovendriedwood.

7. one kind prepares the discontinuous method of sulfate pulp by the cellulosic material that contains lignin, and this method comprises the steps:

Fill the container of cellulose-containing material with waste cooking liquid;

Flood this cellulosic material with described waste cooking liquid;

The described waste cooking liquid that is used to flood with the hot cooking waste liquor displacement of another volume of the not causticization cooking liquor that is added with certain volume, and this cellulosic material is carried out preliminary treatment with the mixture of causticization cooking liquor and cooking waste liquor not;

Hot cooking liquor displacement with causticization is used for pretreated liquid, and the delignification degree of this cellulosic material boiling extremely being wished with the hot cooking liquor of described causticization;

The liquid that is used for boiling with the wash filtrate displacement, collect the hot cooking waste liquor of first volume, this waste liquid amount be equivalent to the pretreatment of fiber cellulosic material and in other filled section of next batch of material the required cumulative volume of the dispensable interpolation of arbitrariness, and be collected in the displacement liquid that is cooled in next batch of material and is used for second volume of impregnation of fibers cellulosic material.

8. method as claimed in claim 7, wherein, the boiling liquid measure of the not causticization of being added is the 0.2-1.01/kg ovendriedwood.

9. method as claimed in claim 7, wherein, the cooking liquor of the employed not causticization not resulting mother liquor of carbonate crystallization of causticization cooking liquor of serving as reasons, and its addition is the 0.06-0.41/kg ovendriedwood.

10. method as claimed in claim 7 wherein, is also introduced a part of green liquor or derivatives thereof according to claim 1 or claim 4.

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