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
  • D21C3/00—Pulping cellulose-containing materials
  • D21C3/22—Other features of pulping processes
  • D21C3/228—Automation of the pulping 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
  • D21C7/12—Devices for regulating or controlling
• • 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
  • D21C3/02—Pulping cellulose-containing materials with inorganic bases or alkaline reacting compounds, e.g. sulfate processes

Definitions

• the present invention concerns a method at the production of chemical pulp by the digestion (cooking) of short-fibred lignocellulose material, in particular it concerns a method for controlling the digestion process such that paper manufactured from the pulp consistently demonstrates even quality with respect to one or several properties that are important for different types of paper.
• lignocellulose materials There are many lignocellulose materials and they can be classified as long- fibred and short-fibred materials. It is during the digestion of short- fibred lignocellulose material that the present invention can be used.
• the lignocellulose material that dominates as raw material when producing pulp is wood from trees. Examples of tree types that demonstrate short-fibred wood are deciduous trees, in particular birch, beech, aspen, oak, eucalyptus, etc.
• Parameters of great significance for the pulp producer are the cooking yield and the brightness of the pulp after the digestion.
• cooking yield is used to denote how much of the original lignocellulose material that remains in the form of pulp after the digestion, calculated as a percentage by weight.
• the brightness of the pulp depends partly on the lignin content of the pulp, which is specified by a kappa value.
• the viscosity of the pulp has a certain significance for the pulp producer, and also this parameter depends, similarly, partly on the lignin content of the pulp. The principal rule is that the viscosity decreases with the kappa value. There is, in certain conditions, a correlation between the viscosity of the pulp and the strength of paper that is manufactured from the pulp.
• the measurement methods described above are principally manual, i.e. a sample is removed from the pulp and transferred to a laboratory where the analysis takes place. To the extent to which more automated analysis methods of the type described, possibly in the form of online testing, are available, these are to be preferred from the point of view of time and efficiency.
• the analysis methods described above are examples of wet-chemistry methods.
• R18, S5, SlO and S18 Other methods in addition to those mentioned above are R18, S5, SlO and S18. Other such methods that may be used are colorimetric methods and titration. Other useful methods of analysis are those that fall within the group of chromatographic methods, such as ion chromatography, fluid chromatography, gas chromatography, size-division chromatography, and capillary electrophoresis. Further, flow injection analysis and sequential injection analysis may be used. A further group of analysis methods includes spectroscopic methods such as FTIR, NIR, NMR, Raman, and UV/VIS. One method of analysis that may advantageously be used for online testing is
• the lignin content of the pulp is to be determined. This is to take place either for the digested wood chips at the bottom of the digester or for the pulp after the digester.
• the kappa value is a measure of how large a volume of potassium permanganate (KMnO 4 ) solution, at a concentration of 20 mmol/1, is consumed by 1 g of dry pulp.
• This measurement method has been regulated through the years by international standards such as SCAN-Cl :00, SCAN-Cl :77, ISO 302 1981 and TAPPI T236 cm -85. The most recent standard is ISO 302-2004. All of these standards are fundamentally similar to each other and give very similar results. The measurement is carried out by taking a sample of the pulp and transferring this sample to the laboratory, where it is dried and weighed before being analysed in the manner described above.
• Y ⁇ T2 cl-EA + dl- T ⁇ Tl ⁇ (cl -EA + dl- (c2 ⁇ EA + dXj)
• the constants al, a2, a3, bl, b2, b3, cl, c2, c3, dl, d2 and d3 are determined empirically.
• the measured content of readily soluble carbohydrates for example the R5 value
• the lignin content of the pulp immediately after the cook is measured routinely.
• the numerical values measured do not contribute directly to the control algorithms, and the lignin content of the pulp is, indeed, consciously allowed to vary between different cooks. What is often done from the point of view of control is to study these values and ensure that the kappa value is not allowed to fall outside of certain determined limiting values. It is also possible to control the kappa value to an optimal value by means of what is known as the Kappa-Batch method described in the Swedish patent 367 451 (6795/70).
• the pulp is tailored for a certain paper manufacturer. If this paper manufacturer gives highest priority to a particular property or some particular properties of the paper, the pulp producer can produce with the aid of the invention a pulp with the correct properties.
• the second (and possibly most important) advantage is that the paper manufacturer is sent in a consistent manner a pulp of even quality with respect to the various pulp and paper properties, and this is achieved independently of the fact that the quality of the wood that the pulp producer uses varies and whether various problems (such as failure of monitor equipment and failure of key equipment) arise during the production of pulp.
• knowledge about the condition, i.e. the properties, of the pulp is obtained.
• FIG. 1 shows a pulp mill in a very simplified schematic form, in which the control of the cooking process according to the invention will be used.
• Figure 2 shows in a polarity diagram how different pulp and paper properties vary for three pulps, which have been produced according to the prior art.
• Figure 3 shows the relationship between cooking yield as a percentage and the charge of effective alkali as a percentage for various cooks of birch sulphate pulp.
• Figure 4 shows the relationship between the R5 value measured as a percentage and the yield of the cook measured as a percentage in the said cooks of birch sulphate pulp.
• Figure 1 shows a continuous digester 1.
• Lignocellulose material normally wood in the form of chips
• a certain amount of cooking liquor is fed in, such that the desired wood/liquor ratio is achieved.
• the wood chips are digested (cooked) during their passage down through the digester to the extent that the pulp producer desires. The digestion of the wood chips takes place at elevated pressure and elevated temperature. There is often a washing stage at the bottom of the digester in which the digested wood chips are freed from the principal part of the used cooking liquor, i.e. the spent cooking liquor.
• the digested wood chips are fed out from the digester, a severe reduction of pressure down to atmospheric pressure takes place, and this means that the wood chips in their softened and modified form are split into principally free fibres of pulp, i.e. a release of the fibres is achieved and pulp has been formed.
• This pulp is transferred through the line 2 to the remaining part 3 of the pulp mill. Further washing of the pulp is carried out in this part, and, furthermore, screening of the pulp in several stages.
• the pulp is subsequently bleached and the initial bleaching step or steps is or are normally known as the delignification step or steps, since the pulp is freed in this step or these steps from the principal part of the amount of lignin that remains in the pulp after the digestion.
• the information about these properties should be collected from several positions.
• the brightness of the pulp for example, can be determined at one or several positions in the pulp mill 3 and the information is transmitted via the line 11 to the control unit 8.
• Samples can be taken from the final pulp in the line 4 and various properties, including paper properties, can be determined and the information transmitted via the line 12 to the control unit 8.
• samples can be taken from the sheeted pulp at position 5, if it is pulp for sale that is produced, for various analyses, and information about these is transmitted via the line 13 to the control unit 8.
• the final paper can be analysed and information about this transmitted via the line 13 to the control unit 8. It has been specified here that samples of the pulp, and possibly also the paper, are to be picked out and various analyses carried out. It is, of course, possible also to carry out the measurements directly on the pulp as it is fed out by means of what are known as non-destructive testing methods, for example, those of the type mentioned earlier in this document.
• both the ramping profile and the time (t) at the maximum temperature (T) are often pre-determined, since a certain amount of wood chips is fed in at a certain speed at the top of the digester 1. Furthermore, the volume of the digester 1 is predetermined, and this means that also the time that the wood chips are held at the maximum temperature is pre-determined.
• the cooking parameters that are then available to vary, i.e. that can be used for control, are the maximum temperature (T) and the charge of effective alkali (EA). It is appropriate that a computer and software are included in the control unit 8, and that this software is based primarily on the equations that are reproduced elsewhere in this document.
• the software Based on the measured analysis values, and thus principally on the content of readily soluble carbohydrates in the most recently digested wood chips, i.e. in the newly formed pulp, the software provides information not only concerning whether it is necessary to carry out a change, but also about what the change is to consist of.
• the change often consists of a change in the charge of effective alkali (EA), or in the content of effective alkali (EA) during the cooking procedure, or both.
• the time that it takes for the wood chips to pass through the digester is changed, i.e. the time will be shorter. This means that the time at the maximum temperature will be shorter than it was previously.
• the digester In order for the digester to have sufficient time for the desired digestion and delignification, it is generally necessary to increase the maximum temperature, and a further means is available that may be used, namely to increase the charge of effective alkali (EA). The details of how this is to be carried out are made clear by the relationships and equations that are given elsewhere in this document.
• control method according to the invention described above is to be applied, as has been made clear, for continuous cooking. It will not be a problem for one skilled in the art to transfer the instructions to batch-wise cooking.
• Carbohydrates In-house method, KA 10.202
• the wood material in the form of the chips described was cooked in a conventional laboratory circulation digester. Each cooking consisted of a batch of 2 kg chips. Furthermore, industrial white liquor and deionised water were added to give the desired liquor/wood ratio in order to obtain the cooking liquor. The different cooks then followed the ramping profile or temperature profile given below: 20 °C to 120 °C in 5 minutes 120 °C to 145 0 C in 120 minutes 145 °C to 151 °C in 60 minutes. Maintained at 151 0 C for a time that corresponds to a given H factor.
• Alkali charge 25% effective alkali (EA), i.e. NaOH + !Z 2 Na 2 S 5 calculated on the basis of the wood
• Kappa value SCAN-C 1:00
• Carbohydrates KA 10.202
• the lower value corresponds to the centre of the diagram (the origin), i.e. where the axis starts, while the higher value corresponds to the end of the axis.
• the axis 15 can be studied as an example, giving the cook yield as a percentage. A yield of 50% is valid for the origin, while the termination, or end, of the axis corresponds to a yield of 55%.
• the parameters that differ between the various cooks with respect to the cooking parameters are the levels of cooking chemicals, i.e. the alkali charge in the form of effective alkali, and the time at the maximum temperature, here regulated by, and reproduced as, H factor. It will be clear to one skilled in the art that if the level of cooking chemicals is reduced, the time for the cook must be increased, and in that case, normally the time at the maximum temperature, in order to achieve the same delignification of the wood, " i.e. in order to achieve a given, constant, value of kappa. As the polar diagram makes clear (see Axis 14), all three cooks have resulted in a pulp with the same kappa value. This is the only property that demonstrates equality.
• the diagram shows in an illustrative manner that it is not possible to produce and deliver a pulp with properties that are given a high priority by the paper manufacturer, i.e. properties of a pre-determined value during the production of sulphate pulp from birch wood when the control of the cooking is based on consistently obtaining a certain kappa value, and worst of all that it is not possible to guarantee pulp with the properties given priority from one delivery to another.
• properties of a pre-determined value during the production of sulphate pulp from birch wood when the control of the cooking is based on consistently obtaining a certain kappa value, and worst of all that it is not possible to guarantee pulp with the properties given priority from one delivery to another.
• This is the case for all paper manufacturers, independently of whether the manufacturer receives pulp in a dried form (and sheeted or flaked), or in a non- dry form, as a slurry, from a closely lying pulp mill.
• Birch logs were extracted from a lumber yard at a pulp mill and transported to the laboratory. The logs were debarked by hand and chopped to chips in a chute-fed chip mill. The obtained chips were characterised with respect to geometry, density and chemical composition. The analysis methods used is clear from Table 1 in Example 1. The analysis results are presented in Table 5 below.
• the wood material in the form of the chips described was cooked in a conventional laboratory circulation digester. Each cook consisted of a batch of 2 kg chips.
• the cooking yield for example, varied between 46 and 55%, i.e. a difference of 9 percentage points.
• the cooking yield decreases with increased charge of effective alkali, increased temperature and increased time. There is a marked reduction in yield when the temperature is raised from 160 to 170 °C.
• the difference in yield between the pulps cooked at 150 °C and 160 0 C is not as large. It is probable that the cellulose in the pulp is degraded to a higher degree at high cooking temperatures.
• a model for the relevant reply, or response - yield, kappa value, viscosity and R5 - has been developed using PLS ("Particle Least Square") calculations on the results of the 25 cooks.
• the models obtained are linear models and they can be exemplified by the equation for calculating the yield, given on Page 6 of this document.
• Table 7 shows control models that are based on the PLS treatment of the laboratory cooks carried out.
• the physical properties, such as tensile index, tear index, beatability, etc., of the pulps at different yields have been approximated using linear regression for the physical properties obtained at different yields in the experiments that are presented in Example 1.
• the second operating condition 30 it is simulated that the production of pulp is increased to a certain higher level. This means that the wood chips flow down through the digester at a higher speed than previously, which leads to the time at the maximum temperature also being reduced, in this case to 100 minutes.
• the maximum temperature must be raised in order to obtain approximately the same degree of digestion of the treated wood chips that leave the digester as previously.
• the maximum temperature was raised in this case to 165 °C, which meant that the H factor was raised to 532.
• the charge of effective alkali was the same as previously, i.e. 21%.
• it is attempted to return to the same pulp and paper properties as those demonstrated by the pulp according to the original condition, i.e. cook 29. It is in this condition that the control method according to the invention will be used.
• the time at the maximum temperature is pre-determined and cannot be changed, and it is, as it was in cook 30, one hundred (100) minutes.

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• 2005
  • 2005-12-23 SE SE0502899A patent/SE529420C2/sv not_active IP Right Cessation
• 2006
  • 2006-12-21 CA CA002632124A patent/CA2632124A1/en not_active Abandoned
  • 2006-12-21 DE DE602006020182T patent/DE602006020182D1/de active Active
  • 2006-12-21 PT PT06835895T patent/PT1969176E/pt unknown
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  • 2006-12-21 WO PCT/SE2006/001486 patent/WO2007073312A1/en not_active Ceased
  • 2006-12-21 EP EP06835895A patent/EP1969176B1/de not_active Not-in-force
  • 2006-12-21 ES ES06835895T patent/ES2359163T3/es active Active
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