WO1999022063A1

WO1999022063A1 - Cooking process for producing cellulose with b-constant based on a mathematical model

Info

Publication number: WO1999022063A1
Application number: PCT/YU1998/000006
Authority: WO
Inventors: Djordje Boskovic
Original assignee: Individual
Current assignee: Individual
Priority date: 1997-10-24
Filing date: 1998-03-16
Publication date: 1999-05-06
Anticipated expiration: 2000-04-24
Also published as: AU6348298A; YU42097A; RS49842B

Abstract

The invention is related to the technological production of cellulose by cooking raw plant material - wood by the variable parameter of amount of chemical reagent in the liquor. The process of cooking is carned out with B-constant based on the mathematical model: 1n L = ln Lo - B (1n Co - 1nC) B-constant. This mathematical model removes the existing problem of defining the exact amounts of active alkalis in the process of cooking, introducing equivalent amount of active alkalis in relation to lignin, as the variable parameter for dosing active alkalis in the course of process. The method can be carried out continuously or in a batch mode. When applied to a batch cooking system, the alkali concentration of the liquor is measural (7), then compared with assigned values in a control unit (9) upon which additional alkali liquor is dosed (10) to the system in order to equalize the measural value to the assigned value.

Description

COOKING PROCESS FOR PRODUCING CELLULOSE WITH B-CONSTANT BASED ON A MATHEMAΗCAL MODEL

In L = In Lo - B ( In Co - InC ) B - constant

DELIGMFICATION OF RAW PLANT MATERIAL - WOOD BY THE

VARIABLE PARAMETER

THE FIELD OF THE TEHNICS TO WHICH THE INVENTION IS RELA TED

The invention relates to the technology of producing cellulose. Delignification of raw plant material - wood by the process of cooking.

TECHNICAL PROBLEM The process of delignification by cooking is done in practice by the five following parameters :

1. Temperature of cooking

2. Duration of cooking

3. Chemical components of liquor for cooking

4. The ratio of solid and liquid phase in the process of cooking 5. The amount of chemical reagent - active alkali added in proportion to absolutely dry wood.

The first three parameters in practice can be realized with desirable accuracy and they are not a problem in performing the process of cooking. The fourth parameter for realizing requires the accurate knowledge of amount of the wood mass as the dampness of the wood mass whose measurement in practice is a problem because it doesn't give asked accuracy.

The fifth parameter is also a problem to be realized. The process of producing cellulose can be roughly presented as separating non - cellulose components of wood in other words raw plant material.

The most important non - cellulose components are:

• Lignin

• Vegetable fats • Resins and waxes

The process is guided in dissolving and separating of lignin as basic component, as separating of vegetable fats, resins and waxes are attained at the same time. Lignin is a macro - molecular organic compound whose formula is only hypothetically given. Chemical reaction of delignification is also unknown, it is in hypothesis, but it is certain that as a chemical product of lignin and chemical reagent of liquor comes to degradation of macro - molecules of lignin and getting of alkali - lignin or lignin sulphurous acid (depending on the applied procedure) which are soluble in water and like those in the farther procedure they leave the system.

The basic problem unknown during the process is how much chemical reagent - liquor should be added for delignification that is how much there are of lignin, vegetable fats, resins and waxes in the process. The fact is uncertain about the absolute amount of dry wood, it was said about this in the passage before, because of different chemical structure of wood, different percentage of amount of lignin and other following materials, whose quantity is also unknown. The amount of lignin, as basic component practically has not been tried to be counted during the process. Taking into consideration that the amount of one component (lignin) in reaction is unknown the amount of other component is defined empirically which is basic problem. In practice it is not possible to dose exactly the chemical reagent - liquor in equivalent proportion with lignin.

Mathematical model gives exact possibility that is equivalent proportion of reagents in the course of the process and it just gives the exact possibility of carrying out the process.

In L = In Lo - B ( In Co - InC )

L - the amount of lignin in non white cellulose at the end of the process of cooking

Lo - the amount of lignin which was present at the beginning of cooking B - the constant of mathematical model

Co - the concentration of the chemical reagent - active alkali at the beginning of the process of cooking

C - the concentration of the chemical reagent - active alkali at the end of the process of cooking

In the logarithmic system the equation represents the straight line and defines completely both components in the process of delignification as their reciprocal relationship.

The constant - B is very complex, chemically regarded it represents equivalent relationship of components in reaction, mathematically regarded constant - B represents the coefficient of direction of the straight line ( tg α ).

From this it results that, if we can guide the process of cooking so to provide permanent coefficient of direction of the straight line by variation of one component in reaction - active alkalis we provide equivalent relationship of components in reaction. In this way the variable parameter is obtained by which the process is regulated and the relationship of reagents is defined in it. TECHNICS SITU A TION

Nowadays there is no adequate similar solution. Since it is not possible to determine the amount of lignin as starting component, the other component of delignification reaction is not determined in an exact way . The problem is solved, as it has already been said ,by measurement of the amount of wood mass and wood humidity, in this way the amount of absolutely dry wood is obtained as the chemical reagent - active alkalis are determined in percentage against absolutely dry wood.

Measurement of amount of wood and humidity of wood does not give wanted accuracy, so this has almost been rejected.

In the past and it is probably still present nowadays with little capacity it has been done with known kind of wood. Wood has been assorted by its kind, which reduces problem of determination of amount of chemical reagents - active alkalis because it has been done with known proceeds of wood. Nowadays because of big capacities assortment of wood mass has been left. Besides technical problems, the economic problem is arisen too because assortment is very expensive and it is not profitable.

With today's bigger capacities which consume daily 3000 - 10000 m3 to earn' out assortment to be technically correct and economically acceptable is very hard to perform.

Nowadays in most factories the amount of chemical reagents - active alkalis is determined empirically with experience and laboratory researches have also been doing. The amount of active alkalis is determined in advance without possibility of correction in the course of the process it means there is no variable parameter which will adopt the process and the amount of active alkalis to real need of wood mass in the process.

In these days in practice another mathematical model is used, called as H - factor. It includes the duration of cooking as one of the process parameters.

H = exp. A / R (1 / 373 - 1 / T ) t

A - Energy of activation R - Gas constant

T - Temperature of cooking t - Duration of cooking

The program with H - factor is used to establish experimentally dependence of the curved line between the amount of active alkalis, the H - factor and the degree of delignification Kappa number, the program is only applicable in computer guided process of cooking. The effective alkalis are automatically determined by automatic alkali analyzer led by computer. Based on obtained result and the curved line experimentally determined the computer calculates the H - factor which defines the duration of the process, as variable parameter of the cooking process, whose aim is to realize the assigned degree of delignification - Kappa number.

The delignification reaction is not quantitative reaction but a balance is established so at the end of the process there are both components which have not been taking part in the reaction. The contents of active, that is, effective alkalis at the end of the process is important, because there are parallel processes which are not desirable and which depend on the content of active, that is, effective alkalis. The mentioned system does not give any possibility of control of those parallel processes.

Theoretically viewed ( regarded) H - factor can be also discussed taking into consideration the position of energy activation in equation, for the same other physical conditions of the process, the greater energy activation, the greater H - factor is, this is difficult to understand because H - factor represent the relative speed.

Present ways of cooking do correction of chemical reagents - active alkalis at the end of the process of cooking when the results of cooking have been obtained. So the existing system corrects already arisen error but it does not prevent obtaining an error which is very important difference in comparing the use of variable parameter B - constant, corrections have been done in the course of the process of cooking and so arising of error is prevented.

PRESENTACION OF THE ESSENCE OF INVENTION As the process of delignification is very complex chemical reaction, in order to have chemical reaction under the full control it is necessary to have equivalent amounts of reagents which take part in the process of delignification, lignin and chemical reagent - active alkalis.

Mathematical model of the process of delignification In L = In Lo - B ( In Co - In C ) just gives that possibility of defining equivalent of amount of reagents in the process of cooking, lignin and active alkalis. The coefficient - B mathematically regarded represents the coefficient of the direction of the straight line ( tg α ), the equation in the logarithmic system is the straight line, the chemical coefficient - B represents equivalent relationship of reagents in the process of cooking. With alkali process of obtaining cellulose consumption of alkalis as the fall of concentration of alkalis in solution is very easy to follow by conduct - metric method. In logarithmic system the equation is the straight line and it represents the fall of the active alkali concentration, while the constant - B represents the coefficient of the direction of the line ( tg α ), that is, it represents chemically equivalent relationship of reagents in the process. The problem is brought down to keeping assigned value of the coefficient direction which is not a problem technically and it can be easily done. In this way the dosage of chemical reagent is solved in an exact way in the process of cooking as variable parameter. Defining the amount of active alkalis in the course of the process, the total control of the process is attained, and as full possibility of the reproduction of cellulose of defined quality both by chemically mathematical properties and by the type of cellulose properties which are not strictly defined as chemically mechanical properties.

The other great advantage attained by applying B - constant is that the process is not any more delicate to the use of different kinds of wood, which in the situation of the deficit of cellulose wood is also very important. The mentioned advantages have great economic effect which is attained though:

1. The constancy of produced quality of cellulose practically worse quality is turned off.

2. Price reduction of the cost of produced cellulose, through reduction of cost by better use of wood amount, savings on chemical for bleaching. 3. Better and greater capacity usage

4. Possibility of an easy introduction of ISSO standards, the process is now completely defined.

In the picture 1 and 2 the simplified schematic review of the batch cooking system and continual cooking system are given. In practice there are more technical solutions for both processes of cooking, which do not have any essential influence on the application of the invention, B - constant method.

In the picture 1 the schematic review of the batch cooking system is given with applied B - constant in guiding the process. Conduct - metric measurement ( position - 7 on the scheme ) constantly measures the fall of alkalis concentration in the system, the measured values are conveyed to the control program unit ( position - 9 ), which compares real values according to assigned values and gives an impulse - the command to the automatic valve ( position - 10 ) for liquor dosage, so the measured value can be equalized to the assigned value and in that way B - constant is realized.

In the picture 2 the solution with continual cooking process is given, the problem is solved by permanent conduct - metric measurements of concentration of active alkalis in liquor at three positions. At the very beginning of the process ( position - 5 on the scheme ) and in the course of the process ( position - 6,7 ) in this way three values are attained - the points which in logarithmic system should lie on the same assigned line defined by ( tg α ), more exactly B - constant. Every deviation from the assigned value is corrected by dosage of fresh liquor through automatic valves ( position - 5', 6',7' ) so that the concentration values of active alkalis equalize with the assigned values and in that way the process is guided by B - constant. DETAIL DESCRIPTION OF THE INVENTION

The process of delignification represents a complex chemical reaction between lignin, following materials of cellulose in raw plant material and chemical reagents by which delignification is performed. In order to perform the process of delignification with sufficient accuracy it is necessary to have equivalent amounts of the reagents, on the contrary if there are not any equivalent amount of reagents it comes to deviation in the delignification process which represents the basic problem. The unknown amount of one component in the process becomes the problem in defining of determined equivalent amount of the other component and so this problem is solved by the mathematical model B - constant, introducing the variable parameter of the amount of chemical reagent - active alkalis. The mathematical model is represented by the equation.

ln L = ln Lo - B ( ln Co - In C )

The equation fully defines both components as their equivalent relationship with B - constant. Mathematically regarded the equation is the straight line in the logarithmic system where the constant - B is the coefficient of the direction of the straight line that is tg α. Changes in concentration of active alkalis can be analyzed by conduct - metric method and tg α of found straight line can be defined. Introducing the variable parameter of amount of active alkalis and prescribing a dose in the course of the process, tg α is corrected at the assigned value of B - constant so described in this way the problem is solved because the equivalent relationship is realized and so the process has also been defined itself.

In the pictures 1. and 2. the schematic review of cooking is given where the way of application is represented, the given technical solution is simple it can be easily applied to different installations ( equipment, plan, factory ) which are used for cellulose production. As the concentration of active alkalis is easier kept on by bringing of active alkalis in the system, in other words the regulation is adjusted from less values to greater ones, which is given in schematic reviews of the process. The regulation from higher values to lower ones is possible in principle but it is more complicated in performing.

DESCRIPTION OF THE PICTURES

Picture 1. The schematic review of the batch cooking system 1. Batch digester

2. Filling of digester

3. Circulation system

4. Circulation pump

5. The valve for digester blowing 6. Steam heater of liquor

7. Conduct - metric determination of the concentration of liquor

8. White liquor pump

9. Control - program system 10. Valve for automatic dosage of liquor

Picture 2. The schematic review of continual digester

1. System for digester filling 2. Continual digester

3. System of digester blowing

4. Heaters of liquor

5. First point of regulation of alkali concentration in the system

6. Second point of regulation of alkali concentration in the system 7. Third point of regulation of alkali concentration in the system

8. Control program system

Claims

PΛ TENT CLΛIMS

1. The method of cooking cellulose with B - constant based on the mathematical model In L = In Lo - B ( In Co - InC ) B - constant delignification of raw plant material - wood, marked like this, by introducing the variable parameter of amount of chemical reagent - liquor in the course of the very process.

2. The variable parameter according to request 1, marked like this, which defines the equivalent relation of lignin and liquor during the process.