SE529420C2 - Process for controlling a cooking process based on the levels of easily soluble carbohydrates and lignin in the pulp fibers - Google Patents

Abstract

Special demands are placed on the properties of short-fibred cellulose pulp when this type of pulp is used for the manufacture of paper, and a paper manufacturer primarily desires a pulp with predictable and constant properties. The present invention makes possible the production of such pulp and consists of a method for the production of chemical pulp by the digestion of short-fibred lignocellulose material with the use of a certain ramping profile, a certain maximum temperature, a certain time at this maximum temperature, and certain content of cooking reagents, whereby the pulp in association with the end of the digestion is analysed with respect to at least two properties of the pulp fibres, one of which is constituted by the lignin content of these, and in that also the content of readily soluble carbohydrates in the pulp fibres is determined, which content has an influence on several properties of the pulp and of paper manufactured from the pulp and that control of the specified cooking parameters is based in the first hand, primarily, on the content of readily soluble carbohydrates and in the second hand, secondarily, on the content of lignin, and in this case, preferably, in a manner that is approximate while, however, always taking both contents into consideration.

Description

15 20 25 30 529 420 sulphate pulp from softwood, such as pine and spruce. The completely overshadowing mass property was and is the strength. If you succeed in producing a finished mass, including those with high brightness, with relatively high strength, you are satisfied. How far one goes with the attendance and delignation, ie to which kappa number, varies.

This is due i.a. on the type of sulphate pulp produced, ie what the pulp is to be used for, and on the wood raw material. Furthermore, a balance is made between how much of the wood's original lignin is to be removed during digestion and how much is to be removed in the delignification steps in the bleaching plant. From an environmental point of view, it is preferable to drive the digestion far, because then dissolved lignin (and lignin fragments) in the cooking liquor are easily taken care of, which after evaporation is burned in a recovery boiler. All the time, however, there is the overriding requirement that the strength of the mass be maintained as much as possible.

With regard to the control of sulphate pulp production of hardwood, for example birch, the thinking has simply been adopted when controlling sulphate pulp production of softwood, for example pine. Although the strength of short fi brig sulphate pulp is important for the paper maker, this property is not as dominant as in the case of long fi brig sulphate pulp.

Equally important properties of short-sulphate sulphate pulp are its grindability, porosity, etc. and its chemical properties, for example the content of groups of substances exhibiting charges, etc. As for the strength of paper, there are different ones. Examples are tensile strength and tear strength.

The tensile strength is measured as the tensile index. A related property where the stiffness of the paper also has an effect is measured as the tensile stiffness index. The tear strength is measured as the tear index.

Z-strength shows the paper's resistance to delamination, ie the paper's strength in height.

Furthermore, there is explosive strength, which is measured as explosive index. This describes how the paper withstands a force directed at the paper under it. In some types of paper it can be the tear strength that is important and then the tear index value is of great importance, while in some other types of paper the tensile strength can be of the greatest importance. In a large group of paper types, the strength is of secondary importance, as previously stated, and in these paper types it is the other physical properties and / or the chemical properties that are the most important.

Parameters of great importance to the pulp manufacturer are the boiling yield and the brightness of the pulp after digestion. By boiling yield is meant how much of the original lignocellulosic material remains in the form of pulp after digestion calculated in weight percent. As for the brightness of the pulp, it is partly dependent on the lignin content of the pulp, which is determined as kappa number. The viscosity of the pulp is also that of some interest to the pulp manufacturer and that parameter is likewise partly dependent on the lignin content of the pulp. The main rule is that the viscosity decreases with the kappa number. Under certain conditions, there is a connection between the viscosity of the pulp and the strength of paper produced by the pulp.

Disclosure of the invention Technical problem In the hitherto known control of digestion of short lignocellulosic material, the focus has been on the fact that the pulp after digestion must contain a certain amount of lignin, measured for example as kappa numbers. It has been found that two pulps with the same kappa number, i.e. lignin content, are the digestion in its finished state and when used for the production of paper and give rise to paper with different properties. In each type of paper, one or more properties are of the greatest importance and it is a major problem for the paper maker if pulp delivered at different times gives rise to variations, which can be strong, in this property or these properties of the paper produced.

The solution This problem is solved using the present invention which relates to a process for producing chemical pulp by digestion (boiling) of short lignocellulosic material using a certain run-up product, a certain maximum temperature and a certain time at this temperature and a certain cooking chemical content, whereby the pulp in connection with the finished digestion is analyzed with respect to at least two properties of the pulps, one of which constitutes their lignin content, characterized by the fact that the content of easily soluble carbohydrates in the pulps is also determined, which content has bearing on various properties of the pulp and paper produced from the pulp and that of the above cooking parameters is primarily, primarily, based on the content of easily released carbohydrates and secondarily, secondarily, on the lignin content and then, preferably, in an estimated manner, but always taking into account both contents.

The control method in question is primarily useful for digesting lignocellulosic material under alkaline conditions and especially in the preparation of pulp according to the sulphate method. Central to the invention is that the content of easily released carbohydrates is determined just after digestion. The analysis can take place on the digested chips in the bottom of the digester before it leaves the digester or on the resulting mass or the digester.

There are a very large number of ways to determine the mass content of easily released carbohydrates.

One way is to contact a certain amount of pulp with a low concentration sodium hydroxide solution, for example somewhere in the range 1-10% NaOH. A suitable concentration is 5%. The RS value of the pulp can be analyzed and this can be done according to the method SCAN-C2: 61. By RS value is meant the percentage of the pulp that does not dissolve in a sodium hydroxide solution with a concentration of 5%, ie the percentage of the pulp that is resistant to this solution, which is usually called lye. In the case of birch sulphate pulp, the R5 value in% is usually in the range 70-85. There is a connection between a mass's different R-values in% and therefore the individual pulp maker is free to choose his own R-value, for example R3 or R7 instead of, for example, RS. However, one should decide on one and the same R-value when analyzing the mass or each cooker when using a certain control connection, i.e. formula for controlling the cooker. The measurement methods described above are primarily manual, ie a sample is taken from the mass and the sample is transferred to the laboratory where the analysis takes place. To the extent that there are more automated analysis methods of the type described, possibly in the form of line testing, these are preferable from a time and efficiency point of view.

The analysis methods described above are examples of wet chemical methods. In addition to the above methods, there are R18, S5, S10 and S18. Other such methods that can be used are colometric determination and titration. Other useful methods of analysis are those which fall into the group of chromatographic methods, such as ion chromatography, liquid chromatography, gas chromatography, size chromatography and capillary electrophoresis.

Furthermore, there are fate injection methods, such as “ow injection analysis” and “sequential injection analysis”. Another analysis group are spectroscopic methods, such as FTIR, NIR, NMR, Raman and UVN IS.

An analysis method that can be used to advantage for line testing is NIR (Near InfraRed) - spectroscopy. This is done so that the mass is irradiated with electromagnetic waves with wavelengths within the NIR range. Some wavelengths are absorbed by the easily released carbohydrates present in the mass and then you can measure either the absorption or the transmission and you can say that you get a fingerprint, which is caused by just the easily released carbohydrates. This is an indirect measurement method because you have to calibrate the impression footprint against a value of easily released carbohydrates, for example the R5 value, which is known to be correct. A large number of experiments have been carried out, which show an even and stable relationship between measured values obtained according to this measuring method and the RS value. As stated earlier, a line test assay is preferred. The lignin content, preferably expressed as kappa number, of the pulp must also be determined. This should be done either on the trapped wood fl ice at the bottom of the boiler or on the mass after the boiler. The kappa number is a measure of the volume of potassium permanganate (KMnO4) solution, with a concentration of 20 mmol / l, consumed by one gram of dry mass. This measurement method has been regulated over the years by international standards such as SCAN-Cl: O0, SCAN-C1: 77, ISO 302 1981 and TAPPI T236 cm -85. The latest standard is ISO 302-2004. All these standards are fundamentally similar and give very similar results. The measurement is made by taking a sample of the mass and passing this sample to the laboratory where it is dried and weighed before it is analyzed in the manner described above.

There are also line test methods that indirectly measure the kappa number. These are based on NlR spectroscopy. An example of such a measurement system is ABB AB's "Smart Pulp Platform". Another kappa number meter based on NIR spectroscopy is BTG AB's KNA-5200.

As stated earlier, the paper tasters are not fully satisfied with those, for example birch sulphate pulps, which are digested according to styr fi losofm, that the lignin content of the just cooked pulp should be kept constant. Within the pulp factory, there is no objection to such a control fi loso fi, since the bleaching of the pulp is facilitated if one has a substantially constant kappa number of the pulp that enters the bleaching plant. The one who suffers is the paper-maker, since the pulp digested according to the approximate governing philosophy fi varies in terms of one or fl your essential properties for the paper-maker. This relationship has led to a new thinking that there may be some reinforced object and / or property of the newly digested mass (other than the lignin content) that the control should be focused on and based on.

It has surprisingly been found that this object consists of a calculated cooking yield = Y (from the English "Yield"). This is primarily due to the fact that the amount of easily released carbohydrates in the mass after cooking, which can be relatively easily analyzed, has been shown to be in a certain relation to Y. The reason why a calculated cooking yield was used as a basis or dominant for the control is that it is not possible to determine this parameter or property in an efficient and reliable manner directly in the cookery or pulp mill. On the basis of a large number of laboratory cooks, a formula has been developed to calculate Y and it reads: Y = 76.25 - 0.56 - EA - 0.064 -T - 0.0002 - t- 0.006 H, where EA = the rate of effective alkali in%, T = the maximum temperature in ° C, t == the time at maximum temperature in minutes and the H = H factor, according to a de fi nition reproduced elsewhere in this shift. From the above it is understood that the constants in the formula have been produced empirically. In order to be able to control the cooking, the calculated cooking yield must be linked to one or more of the cooking parameters, for example the maximum temperature T and the batch of effective alkali EA.

Below are a number of formulas that will be used in the execution of the control.

The formulas and the method of using the formulas depend on whether there is a change in production during cooking or whether a certain operating mode is maintained. The batches of effective alkali (EA) indicated in the formulas can in practical application be supplemented with the content of effective alkali (EA) in the cooking liquid during the cooking.

In the first case, the following formulas apply to the respective temperature ranges (it has been found necessary to adapt the formulas to two maximum temperature ranges, such as 150-160 ° C and 160-170 ° C, respectively): YTKRTZLIn-Rs _ Tn _ Rs-brjes-bzj ' "a1 Tz-Ti ai az Yïmqsmbz-Rs _ T-Tz _ Rs-bzjzs-bs) _ _ a2 T3-T2 a2 a3 Ved fl ice's perceived EA-rate at the exchange Y is described by: Hmmm: Y-d1_ r-ri _ Y -akr-azj _ _ cl T2-Tl cl c2 EAWRÜ: Y-a2_ T-Tz _ Y-azjf-ds) '"c2 T3-T2 c2 c3 When changing the operating mode at the current EA batch, the new cooking yield is determined by: 20 ~ 529 420 T-T1 Yri sTsTz- * Cl 'EAHU - T2_T1 - (c1 -EA + di - (cz -EA + dz)) T-T2 YT25T5T3 = C2' EA + d2- T3_T2 - (cz-EA + az- (c3-EA + <13)) To return to the original boiling yield, the batch of effective alkali = EA is changed according to EAWRTZ: Y-d1_ Tn _ Y-dij-dz) "" cl TZ-Tl cl c2 EAWRÜ: Y -dz_ T ~ Tz _ Y-dkr-ds) '' cz Tz-Tz cz cs Constant theme al, a2, a3, bl, b2, b3, cl, c2, c3, dl, d2 and d3 are determined empirically.

In the second case, the following formulas apply to the respective temperature range.

Initially, a setpoint is used here with regard to the content of easily released carbohydrates, R5, in the pulp, and at this setpoint the boiling yield is determined by: Y = bl-Rs _ T-Ti _ [Rs-b1_1es-bz) "Jm a1 Tz-Ti al az Y _bz-Rs T-rz Rs-bz Its-ba) <<_ '' _ ”J” az Ts-Tz az as and where the EA theorem is described by: Y-dl T-Tl Y-d2 Y-dZ EÅr1sTsTz = - ~) cl T2-Tl cl c2 _ _ _ -da EAMTSTFY dz_r Tz (Y d1_Y J c2 T 3 - T2 c2 c3 When measured RS value shows that the boiling yield has changed from Y1 to Y2, the batch is compensated by effective alkali, EA, by calculation by means of the immediately above equation according to AEA = EAY; - EAY; way.

As can be seen from the above, measured content of easily released carbohydrates, for example the R5 value, has a direct connection to the control of the cooker. The lignin content of the pulp, preferably represented as kappa numbers, just after cooking is also routinely meshed. Measured numerical values are not directly included in the control algorithms and the line content in the mass is of course allowed to vary between different cooks and what is usually done from the control synpurilct is to study these values and ensure that the kappa number must not fall outside certain given values. It is also possible to control the kappa number to optimal value by means of the so-called The Kappa-Batch method described in the Swedish patent 367 451 (6795/70).

Advantages There are two major advantages to the control procedure according to the invention.

One is to tailor the pulp to a specific paper maker. If this paper maker prioritises a certain property or some properties of his paper, then the pulp maker can, with the help of the invention, produce a pulp with the right properties.

The second (and perhaps most important) is that papermakers are persistently sent a pulp of consistent quality in terms of different pulp and paper properties, regardless of whether the quality of the wood used by the pulp maker varies and whether different problems (such as failing meters and failing key apparatus) in mass production occurs. By frequently measuring the content of the digested material, ie the mass, of easily released carbohydrates, you get to know the condition of the mass, ie the properties.

The invention also provides an opportunity for the pulp maker to optimize important circumstances for him. For example, there is an opportunity to optimize the pulp yield when producing pulp with certain paper properties. A higher yield gives more pulp and since the payment for the pulp takes place per tonne of pulp, a larger amount of pulp means a higher income.

Figure description Figure 1 shows a pulp mill in a very simplified schematic form, in which the boiling control method according to the invention is used. Figure 15 shows in a polar diagram how different pulp and paper properties vary in three pulps, which are produced according to the prior art.

Figure 3 shows the relationship between the boiling yield in% and the batch of effective alkali in% in different birch sulphate pulps.

Figure 4 shows the relationship between the RS value in% and the cooking yield in% in said birch sulphate pulp.

Best Mode for Embodiment In the following, with reference to Figure 1, a dry embodiment of the method according to the invention is described and, finally, two embodiments are given.

Figure 1 shows a continuous boiler 1.Lignoce1lulose material, usually. wood in the form of chips, is fed at a certain speed to the top of the digester 1. To this is also fed a certain amount of cooking liquid so that the desired wood / liquid ratio arises. Furthermore, the concentration of the cooking liquid is controlled so that the desired amount of, for example, effective alkali = EA is obtained. During its way down through the digester, the wood ice is digested (boiled) to the extent desired by the pulp maker. The digestion of wood ice takes place under elevated pressure and elevated temperature. At the bottom of the boiler there is also a washing step where the digested wood ice is freed from the main part of the used cooking liquid, ie the cooking liquor. As the digested wood ice is discharged from the boiler, a sharp drop in pressure takes place down to atmospheric pressure and this means that the wood ice in softened and altered form is split up into mainly free masses, ie a build-up takes place and mass has formed. This pulp is conveyed via the line 2 to the remaining part of the pulp factory 3. In this further washing of the pulp is performed and further it is filtered in your steps. Thereafter, the pulp is bleached and the initial bleaching step or bleaching steps are usually called deligriation steps, since the pulp in this or these steps is freed from the majority of the amount of lignin remaining in the pulp after digestion. This is usually followed by further bleaching steps where the brightness of the pulp is substantially increased and the pulp is further freed from chromophoric groups.

Additional purification steps can follow this before the pulp is passed via line 4 to either a pulp pick-up machine for converting the pulp to a waste pulp or a paper machine 5. Central to the invention is to determine the content of easily release carbohydrates in the arising mass. As a measure of the content of easily released carbohydrates, the R5 value in% can be chosen as stated earlier. It is preferred to determine by means of NlR spectroscopy the RS value (as previously described) of the mass somewhere along the line 2, for example in position 6. Specifically, it can be done that a defined washed sample of the mass is measured with the electromagnetic waves within the NIR the area. In some boilers it is possible to take samples of in the bottom of the cooker significantly enclosed wood ice. By passing this sample out of the boiler, you get a fi ber release so that mass is formed, which process is similar to the above-described fi ber fi loading process. The measuring signal or value is fed via the line 7 to a control unit 8.

Correspondingly, the content of lignin in the digested wood, i.e. the pulp, is measured in position 9 and via the line 10 the measurement signal or value is transmitted to the control unit 8. As stated earlier, there is existing commercial equipment that can be used.

Such measurement is routinely performed in many cookeries today.

In the process for controlling the cooker according to the invention, it is common for the lignin content of the digested wood ice, i.e. the pulp, to be allowed to vary with time and if one looks at batch boiling (not shown here) from cooker to cooker. In particular, the delignifying bleaching must be adapted to the fact that the lignin content of the constituent mass in the form of kappa varies from time to time during continuous cooking and from boil to boil during batch cooking. There are different control systems also related to this and the variations in lignin content of the pulp are routinely handled by the bleacher. This means that the mass leaving the manufacturing process has the predetermined brightness, for example.

In order to check that the pulp in different positions and especially the finished pulp has the properties that both the pulp maker and the paper maker expect, information about these should be obtained from your positions. For example, the brightness of the pulp can be determined in one or more positions in the pulp mill 3 and the information is sent via line 11 to the control unit 8. Samples can be taken on the finished pulp in line 4 and various properties including paper properties can be determined and the information sent via line 12 to the control unit 8. Furthermore, samples can be taken of the sheet pulp in position S if the pulp is produced for various analyzes and information about this is sent via line 13 to the control unit 8. If the pulp is transported in slurry form to a paper machine 5, finished paper can be analyzed and information about this sent at 10 20 25 30 529 420 ll the line 13 to the control unit 8. Here it is stated that one must take samples of the pulp and possibly the paper and perform various analyzes. Of course, it is also possible to make measurements directly on the flowing mass and the paper by means of so-called non-material-destroying analysis methods, for example of the type mentioned earlier in this document.

In the case of continuous production of cellulose pulp and then in terms of digestion or boiling, both the boiling point and the time (t) at the maximum temperature (T) are given, as the wood ice is fed in a certain amount at a certain speed at the top of the digester 1. Furthermore, the volume in the digester is 1 given and this means that the time the wood ice is at maximum temperature is given. The cooking paranites you then have to vary, ie control with, are the maximum temperature (T) and the batch of effective alkali (EA). The control unit 8 suitably includes a computer and computer program and this computer program is based primarily on the formulas, which are reproduced in another place in this document. Based on measured analysis values and then primarily the newly digested wood ice, ie the newly formed mass, content of easily released carbohydrates, the computer program provides information about, partly if it is necessary to make a change and if so, where the change should last. O fl a the change consists in changing the batch of effective alkali (EA) and / or the content of effective alkali (EA) during the cooking process.

If you are to change the production of pulp at a certain time, for example increase production, then the time it takes for the wood ice to pass through the boiler changes, ie it becomes shorter. This means that the time at maximum temperature will be shorter than before. In order for the boiler to have the desired digestion and delignification, you must usually increase the maximum temperature and you have another means to take and that is to increase the batch of effective alkali (EA). How this is to be done in detail is stated in the links and formulas that are reproduced elsewhere in this publication.

The above control procedure according to the invention applies as shown for continuous cooking. For those skilled in the art, it is no problem to transfer the instructions to batch cooking.

Example 1 In a laboratory, three experiments were made with digestion (boiling) of birch wood according to the sulphate method. The attempts were to control the attendance according to conventional 20. 529 420 12 technology, i.e. so that one and the same kappa number was achieved in the pulps despite variation in certain cooking parameters.

Birch logs were taken out on a wood farm in a pulp mill and transported to the laboratory. The stock was barked by hand and chopped into ice in a plunge-fed ice chop.

The obtained ice was characterized with respect to geometry, density and chemical composition. Analysis methods used are given in Table 1 and analysis results in Table 2.

Table 1 Dry content = SCAN-CM 39:94 Dry raw density = SCAN-CM 43:95 Bulk density = SCAN-CM 46:92 Carbohydrates = Own method, KA 10.202 Acetonexuaia = scAN-CM 49:93 Metals = SCAN-CM 38: 96 Lignin = CCA 5, slightly modified Fiber length = KCL 225: 89 Table 2 Xylose, g / kg = 169 Mannose, g / kg = 11.3 Galactose, g / kg = 10.1 Arabinos, g / kg = 3.1 Glucose, g / kg = 313 Fiber length, mm = 1.04 Dry matter content,% = 64.1 Bulk density, kg / ms = 170 Dry bulk density, kg / ms f ub = 500 Lignin content,% = 20.6 Acetonextrald,% = 1.62 Iron, mg / kg = 49.7 Calcium, mg / kg = 639 Copper, mg / kg = 1.6 10 15 20 25 30 i 529 420 13 Magnesium, mg / kg = 177 Manganese, mg / kg = l 10 The wood material in the form of the described ice was boiled in a conventional laboratory circulation boiler. In each boil, 2 kg of ice was charged. Furthermore, industrial white liquor and deionized water were added to the desired liquid / wood ratio to obtain boiling liquid.

The different cooks then followed the following boiling or temperature profile. 20 ° C to 120 ° C for 5 minutes 120 ° C to 145 ° C for 120 minutes 145 ° C to 151 ° C for 60 minutes.

At 15 ° C for a time corresponding to a certain H-factor. 8144250) t 3 The following H-factor was used = I e i 273 + T 0 Other conditions for each experiment (boil) are shown below.

Boil 1 Alkali charge = 25% effective alkali (EA), ie NaOH + 1/2 NagS, calculated on the wood.

Liquid / wood content = 3.5 l / kg H-factor = 270 Boil 2 Alkali rate = 20% EA Liquid / wood ratio = 3.5 l / kg H-factor = 350 Boil 3 Alkali rate = 17% EA Liquid / wood content = 3.5 l / kg H-factor = 500 At the end of the digestion (cooking), the cooking liquid was sampled to check the residual alkali content.

After washing the mass with deionized water in the boiler, the mass was filtered.

The screened mass was analyzed using the analysis methods given in Table 3 below. 529 420 14 Table 3 Coating number = SCAN-C 1:00 Viscosity = SCAN-CM 15:88 Lightness = SCAN-P 3:93 Total yield = Own standard Shrimp content = Own standard Residual alkali = SCAN-N 33:94 Carbohydrates = KA 10.202 Ground speed = EN 25264-211994 Ground degree = ISO 5267-11999 Surface weight = ISO 536: 1995 E-module, tensile strength, tensile stiffness = SCAN-P 67:93 Tear strength = EN 21974: 1994 Burst strength = SCAN -P 24:99 Z-strength = ISO 8791-4 529 420 15 The analysis results for each mass are shown in Table 4 below.

Table 4 Boiling Property l 2 3 Kappata] 16.0 16-3 Viscosity, ml / gl 193 1264 1386 Brightness,% ISO 44.0 41.3 38-1 Restaman, g / l 17.9 8-0 23 Yield, left, 50.5 52.3 54.2 Lignin yield , yield - 0.15 - Coat 48.1 49.8 51.6 Reject,% 0.02 0.03 0.04 Hemicellulose,% 26.4 28.2 23-6 Tensile index, Nm / g, mean value at 83.8 97.5 105.3 milling revolutions 1000, 2000, 3000 Tensile stiffness index, MNm / kg mean value 9.7 10.3 1 1.0 at grinding speed 1000, 2000, 3000 Grinding degree, ° SR, average value at grinding speed 20.7 22.3 24.0 1000, 2000, 3000 Tear index, mNmz / g, average value at 7.8 7-2 7-0 tensile index 70, 80, 90 Explosion index, lcPa m2 / g , average value at 4.8 5.4 6.2 grinding revolutions 1000, 2000, 3000 Z-strength, kPa, average value at grinding revolutions 651 731 753 1000, 2000, 3000 Some of these measured property values of each mass have been entered in the polar diagram shown in Figure 2. The diagram shows nine axes and each axis has property values as follows: 14 = Kappatal, 12-20 15. Boiling yield, 50-55 1 6 = Tensile index, 80-1 10 17 = Tensile stiffness index, 9-1 1 18 = Malgrad, 20-25 19 = Tear index, 6-8 10 15 20 25 _30 ~ 52.9 420 16 20 = Explosion index, 4-7 21 = Z-strength, 600-800 22 = Brightness, 35-45 As for the numerical values given eñer the property, the lower value for the center of the diagram (origin), ie where the axis begins, and the higher value for the end of the shaft. As an example, axis 15 can be studied, which represents the cooking yield in%. A yield of 50% applies to the origin and the end or end of the shaft corresponds to a yield of 55%.

The different cooks have been given the following symbols: -ê - = cook -I- = cook2 -Å ~ = cook3 The difference between the different cooks in terms of cooking parameters is the cooking chemical content, ie the alkali batch in the form of effective alkali, and the time at maximum temperature , here regulated and reproduced as H-factor. It is clear to a person skilled in the art that if one lowers the cooking chemical content, one must increase the time for cooking and then usually at the maximum temperature to obtain the same delignification of the wood, i.e. to achieve a certain and constant kappa number. As can be seen from the polar diagonal rune (see axis 14), all three cooks have resulted in a mass with the same kappa number. This year is also the only trait that shows similarity.

As for all the other properties, the difference between the different masses is very noticeable. The diagram shows in an illustrative way that in the production of sulphate pulp from birch wood and where the control of the coke is based on sustainably achieving a certain kappa number, it is not possible to och produce and deliver a pulp with properties prioritized by the paper maker, ie on a certain level and worst of all, that pulp with the priority property can not be guaranteed from delivery to delivery. This applies to all papermakers, regardless of whether they receive the pulp in dried (and arcade or fl ing) form or in non-dried form, as a slurry, from a nearby pulp mill.

Example 2 In a laboratory, a very large number of experiments were made with digestion (boiling) of birch wood according to the sulphate method. The purpose of the experiments was partly to develop a control model suitable for digestion of short-lived lignocellulosic material based on measuring the content of easily release carbohydrates in the resulting mass and partly to see if the control model gave the intended result.

Birch logs were taken out on a wood farm in a pulp mill and transported to the laboratory. The stock was barked by hand and chopped into ice in a plunge-fed ice chop.

The obtained ice was characterized with respect to geometry, density and chemical composition. The analysis methods used are shown in Table 1 in Example 1.

The analysis results are shown in Table 5 below.

Table 5 Glucose, g / kg = 320 Xylos, g / kg = 173 Mannos, g / kg = 12.0 Galactose, g / kg = ll.l Arabinos, g / kg = 2.8 Dry content,% = 63.1 Trouser density, kg / mß = 172 'Dry rot density, kg / m3 ub = 498 The wood material in the form of the described ice was boiled in a conventional laboratory circulation boiler. I vaij e kok satsades 2 kg fl is. Further, industrial white liquor and deionized water were added to the desired liquid / wood ratio to obtain boiling liquid.

The different cooks then followed the following boiling or temperature profile. 20 ° C to 80 ° C for 5 minutes 80 ° C to maximum temperature for 60 minutes Maximum temperature according to table 6. 3s, z-142so) In Föijanae H-faiaof was used = I el 21s + T o Other conditions for each boil are shown in table 6. After boiling, the mass in the boiler was washed with deionized water. The pulp was then screened to be finally analyzed by a number of the analysis methods listed in Table 3 of Example 1.

Table 6 below shows the promised other conditions and raw data from in twenty-five boils with regard to different pulp properties. 3529 420 18 Table 6 Boil Alkali- Max- Time H- Total Lignin- Shrimp Coat- Whisk. ISO- R5 rate temp at factor yield given number brightness _ *% ° C 11:11:11; %: ïbyte% ml / g% ISO% ITIIII 4 17 160 120 429 53.8 52.5 0.60 16.6 1340 39.3 76.3 5 19 160 120 429 52.8 51.7 0.10 14 , 4 1198 42.9 76, 7 6 21 160 120 429 51.8 50.6 0.11 14.9 1126 42.1 78.2. 7 23 160 100 363 51.7 50.6 0.10 14.7 1064 42.6 78, 7 8 25 160 100 363 50.7 49.7 0.07 13.1 1026 43.3 80, 1 9 27 160 80 297 49.4 48.4 0.12 13.4 995 45.0 81.5 10 29 160 80 297 48.3 47.4 0.23 12.7 939 44.7 83, 4 11 17 150 220 350 54.9 53.4 0.91 18.5 1431 37.7 74.6 12 19 150 220 350 53.9 52.6 0.05 16.4 1309 40.3 75, 6 13 21 150 220 350 53 , 2 51.6 0.03 16.4 1256 42.1 76.5 14 23 150 200 320 50.4 49.3 0.01 14.9 1206 42.8 78.2 15 25 _ 150 200 320 51, 1 50.0 0.01 14.2 1143 43.5 79.2 16 27 15 0 160 290 49.4 48.3 0.05 14.5 1 127 44.2 80.7 17 29 150 160 290 49, 2 48.2 0.06 13.4 1068 44.9 82.6 18 17 170 80 627 52.1 50.6 1.10 17.5 1291 37.8 76.1 19 19 170 80 627 50.8 49 , 7 0.15 I 14.6 1098 41.5 77.3 20 21 170 80 627 50.0 48.9 0.15 14.5 1027 40.8 78.5 21 23 170 60 488 49.1 48, 0 0.50 15.2 900 41.7 79.5 22 25 170 60 488 48.0 47.0 0.25 13.9 886 42.6 81, 5 23 27 170 40 349 47.6 46.7 0 .38 13.0 892 43.7 82.5 24 29 170 40 349 45.9 45.1 0.57 12.3 791 44.6 84.3 25 18 150 220 350 54.5 53.0 0.24 17.8 1384 39.3 77.0 26 18 160 120 429 53.1 51.8 0.14 16.9 1291 39.4 74.8 27 22 160 100 363 51.2 50.0 0.05 15.2 1 108 42.2 78.1 28 22 170 60 488 49.8 48.7 0.12 14.5 1019 41.9 78.8 * Lignin fi ítt yield = Total yield (1 - 0.15 - kappa / 100) 10 15 20 25 t 529 420 19 At study from what is stated in the table it appears that the selected levels in batch of effective alkali (in the table and fi gures 3 and 4 indicated as alkali batch), maximum temperature and time at maximum temperature gave large variations in mass properties. Boil yield, for example, varied between 46 and 55%, ie a difference of nine percentage points. Boil yield decreases with increasing batch of effective alkali, increased temperature and increased time. There is a marked reduction in yield as the maximum temperature is raised from 160 to 170 ° C. The difference in yield between the masses cooked at 150 ° C and 160 ° C, respectively, is not as great. It is likely that the cellulose in the pulp is attacked to a greater extent at high boiling temperatures.

Figures 3 and 4 show that if connections for different driving modes - in this case the maximum temperature - are produced, the yield can be measured indirectly by analyzing the mass content of easily soluble carbohydrates, for example R5.

This relationship and this insight form the basis for the control strategy shown for, for example, sulphate pulp adjustment according to the invention.

Via PLS (“Particle Last Square”) - calculations on the results ån robbery reported above twenty-five boils, a model for each answer or response - yield, kappa number, viscosity and R5 - fi- has been obtained. Linear models are obtained and can be exemplified by the formula for calculating the cooking yield, given on page 6 of this document.

Table 7 below shows stock models, which are based on PLC treatment of the laboratory cooks made.

Table 7 Control variables Constants Yield% Del. ml / g Kappatal R5% 76.25 2509.001 27.46 62.661 Batch of EA,% 21 -0.556 -30.72 -0.395 0.579l Maximum temperature, ° C 160 -0.064 -4.689 -0.023 0.026l Time at max.temp . min 120 -0,0002 0.789 0.003 -0.007 H-factor 429 51.6 1161 15.6 77.9 The physical properties of the masses, such as tensile index, tear index, degree of grinding, etc., at different yields have been approximated by linear regression on physical properties obtained at different yield in the experiments reported in Example 1.

Finally, three further experiments were made in the form of cookers 29, 30 and 31. In these experiments, soft chips were used as in Example 1 and furthermore the same heating and temperature profile was used as in this example.

The cooking was done in laboratory cookers according to the batch method, but continuous cooking on a full scale was simulated in the following way. In a first operating mode 29 which simulates a certain production of pulp in a continuous digester, the cooking parameters were as follows; batch of effective alkali = 21%, maximum temperature = 160 ° C, time at maximum temperature = 120 minutes and H-factor = 429. In the second operating mode it is simulated that the mass production is increased to a certain higher level. This means that the wood ice flows down through the boiler at a higher speed than before, which also leads to the time at maximum temperature being reduced and in this case to 100 min. The person skilled in the art then knows that to get. approximately the same degree of digestion of the treated wood fl ice leaving the digester as before, the maximum temperature must be raised. In this case, the maximum temperature was raised to 165 ° C, which meant that the H-factor was raised to 532. The batch of effective alkali was intact, i.e. 21%. In the third three-way mode, one strives to return to the same pulp and paper properties as the pulp according to the original position, i.e. boil 29, exhibits. In this situation, the control method according to the invention comes into use. The time at the maximum temperature is given and can not be changed and it is, as in cooking, one hundred (100) minutes. Using the measured RS value and from this calculated boiling yield, the previously described control relationship (see the formulas for the higher maximum temperature range, ie 160-170 ° C) showed that the maximum temperature = 165 ° C and the H-factor = 532 could be kept intact from mode two, ie boil 30, and that the batch of effective alkali would be reduced to 19%.

Table 8 below shows measured pulp and paper properties. i 529 420 21 Table 8 Boil 29 30 31 Yield,% 51.6 50.6 51.8 Kappatal 15.6 15.3 16.1 Viscosity, ml / gl 161 ll 10 1172 Brightness,% ISO 42.4 44, 0 42.0 RS,% 77.9 78.1 77.0 Tensile index, Nm / g 92.2 83.8 93.7 Tensile stiffness index, MNm / kg 10.1 9.7 10.1 Malgrad, ° SR 21, 7 20.9 21.9 Rivinaex, mN m ”7.4 7.8 7.4 burst index, KPa mZ / g 5.2 4.8 5.2 Z-strength, KPa 700 651 709 If one studies the paper properties of the masses produced in cooker 29, 30 and 31 it is found that all these properties with respect to cooks 29 and 31 are almost identical, while these properties with respect to cooker 30 differ markedly.

This shows that with the control method according to the invention it is possible to return to producing a pulp with the desired pulp and paper properties in an array-rich manner after drilling changes and also unplanned drilling disturbances. This can be ironed with the pulps which in the production with respect to the digestion have been controlled in accordance with prior art and whose pulp and paper properties are reproduced in the polar diagram rune in Figure 2.

As can be seen, for example, the paper properties of these pulps vary in a very uncontrollable manner.

Claims (9)

10 15 20 25 30 529 420 22 PATENT REQUIREMENTS A process for producing chemical pulp by digestion (boiling) of short lignocellulosic material using a certain boiling point, a certain maximum temperature and a certain time at this temperature and a certain cooking chemical content, the pulp in connection with the finished digestion being analyzed for at least two properties of pulps, one of which constitutes their lignin content, is characterized by the fact that the content of easily released carbohydrates in the pulps is also determined, which content is based on various properties of the pulp and paper produced from the pulp and that control of the above cooking parameters in the first place, primarily, based on the content of easily released carbohydrates and in the second place, secondarily, on the lignin content and then, preferably, in an estimated manner, but always taking into account both levels. 2. A method according to claim 1, characterized in that the digestion takes place under alkaline conditions. 3. A method according to claims 1 and 2, characterized in that the digestion takes place according to the sulphate method, i.e. so that sulphate pulp is prepared. 4. A process according to claims 1-3, characterized in that the content of readily soluble carbohydrates in the broth is determined by immersing the brems in a sodium hydroxide solution with a concentration of 140% NaOH, preferably 5%. 5. A method according to claims 1-3, characterized in that the content of readily soluble carbohydrates in the bulk brim is indirectly controlled by NIR (Near IrifraRötO spectroscopy). 6. A method according to claims 1-3, characterized in that the lignin content of the pulp bromine is determined as kappa number in an indirect manner by means of NIR (Near InfraRötÛ spectroscopy. 529 420 A23 7. A method according to claim 1, characterized in that the cooking yield (Y), which is related to the measured amount of easily released carbohydrates, is selected as dominant for controlling the cooking together with the cooking parameters; maximum temperature (T) in ° C, time (t) at maximum temperature in minutes, H-factor and cooked cooking chemicals in the form of effective alkali (EA) in weight percent (%), and content of effective alkali (EA) during cooking. Method according to claims 1 and 7, characterized in that the control of the boiler is based on a constant maintenance of the calculated boiler yield Y and in the event of a production disturbance change takes place as follows, the boiler yield for the current mode is determined on the basis of the mass content of easily triggerable carbohydrates in the form of analysis of RS according to (for the respective temperature range D: YT1 STST2 = bi-Rs _ T-Tl (Rs-bijes-bzj al T2-T1 al a2 bz-Rs T-Tz (Rs-az les-ba) Yrzsrsrs = '- az': P3 -Tz az as and where the wood's experienced EA rate at the exchange Y is described by EATISTSTZ: Y-d1_ T-Ti cl TZ-Tl Y-dky-dz] cl c2 EAMTSTB: Y-dz_ T- Tz _ (Y-dkY-ds) c2 T3-T2 c2 c3 and when changing the dri fi mode at the current EA set, the new cooking yield is described by: Ynsmfci-I-: A fi ii - å "7; r11- (c1-BA + <11 -_ (cz-EA + az) T-Tl y¶25T5T3 = C2 'EA + d2 - Tz-Tl - (c2-EA + d2- (c3 -EA + d3) and to return to the original cooking yield change the batch of effective alkali EA according to y_ _ _ ._ EATISTSTZ: d1_T Tr (Y d1_Y az) cl T2-Tl cl c2 529 420 24 Y-dz _ T-Tz _ Y-d1_ Y-ds) c2 T3 - T2 c2 c3 and where the constants a1, a2, a3, bl, b2, b3, cl, c2, c3, dl, d2 and d3 determined empirically. EÅrz srsrz = 9. A method according to claims 1 and 7, characterized in that the control of the cooker is based on a constant maintenance of the calculated cooking yield Y and when maintaining a specific driving mode takes place as follows, initially a setpoint is used with respect to the content of easily released carbohydrates, R5, and at this setpoint the boiling yield is determined by (for the respective temperature range) Y = b1-Rs _ T-Ti (Rs-bljes-bz) TI J-Tz al T2-T1 al a2 Ynqm: bz-Rs _ T-Tz (Rs-bjes-bs) '"az Ta-Tz az as and where the EA theorem is described by: EATKRÜ: Y-d1_ T-Ti _ Y-dkr-dz) _' cl Tz-n cr az EAWRB: Y-d2_ T-Tz _ Y-dij / -dsj _ _ c2 T3-T2 c2 c3 and when measured RS value shows that the boiling yield has changed fi than Y1 to Y2, the batch of effective alkali, EA, is compensated by calculation by means of the nearest the above equation according to A EA = EAY; - EAY; and where the constants a1, a2, a3, bl, b2, b3, cl, c2, c3, dl, d2, d3 are determined empirically.