CA1057906A - Method for automatic control of the dosageing of two chemicals - Google Patents
Method for automatic control of the dosageing of two chemicalsInfo
- Publication number
- CA1057906A CA1057906A CA229,324A CA229324A CA1057906A CA 1057906 A CA1057906 A CA 1057906A CA 229324 A CA229324 A CA 229324A CA 1057906 A CA1057906 A CA 1057906A
- Authority
- CA
- Canada
- Prior art keywords
- pulp
- chlorine
- stage
- chlorination
- chlorine dioxide
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 238000000034 method Methods 0.000 title claims abstract description 38
- 239000000126 substance Substances 0.000 title description 4
- OSVXSBDYLRYLIG-UHFFFAOYSA-N dioxidochlorine(.) Chemical compound O=Cl=O OSVXSBDYLRYLIG-UHFFFAOYSA-N 0.000 claims abstract description 73
- 238000005660 chlorination reaction Methods 0.000 claims abstract description 47
- ZAMOUSCENKQFHK-UHFFFAOYSA-N Chlorine atom Chemical compound [Cl] ZAMOUSCENKQFHK-UHFFFAOYSA-N 0.000 claims abstract description 45
- 239000000460 chlorine Substances 0.000 claims abstract description 45
- 229910052801 chlorine Inorganic materials 0.000 claims abstract description 45
- 239000004155 Chlorine dioxide Substances 0.000 claims abstract description 37
- 235000019398 chlorine dioxide Nutrition 0.000 claims abstract description 36
- 230000008569 process Effects 0.000 claims abstract description 21
- 239000003513 alkali Substances 0.000 claims abstract description 15
- 238000005406 washing Methods 0.000 claims abstract description 8
- 238000004076 pulp bleaching Methods 0.000 claims abstract description 4
- 238000011005 laboratory method Methods 0.000 claims abstract description 3
- 235000019589 hardness Nutrition 0.000 claims description 12
- 238000004519 manufacturing process Methods 0.000 claims description 6
- 238000004364 calculation method Methods 0.000 claims description 5
- 238000005259 measurement Methods 0.000 description 12
- 238000006243 chemical reaction Methods 0.000 description 5
- 239000013256 coordination polymer Substances 0.000 description 4
- 239000000203 mixture Substances 0.000 description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 3
- 229920002678 cellulose Polymers 0.000 description 2
- 239000001913 cellulose Substances 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 150000002500 ions Chemical class 0.000 description 2
- 230000036632 reaction speed Effects 0.000 description 2
- 241000861718 Chloris <Aves> Species 0.000 description 1
- 108091028140 FREP Proteins 0.000 description 1
- 239000005708 Sodium hypochlorite Substances 0.000 description 1
- 239000002585 base Substances 0.000 description 1
- 238000004061 bleaching Methods 0.000 description 1
- 150000004035 chlorins Chemical class 0.000 description 1
- 230000002844 continuous effect Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000000605 extraction Methods 0.000 description 1
- 238000001914 filtration Methods 0.000 description 1
- 229920005610 lignin Polymers 0.000 description 1
- 238000012423 maintenance Methods 0.000 description 1
- 238000013178 mathematical model Methods 0.000 description 1
- 230000001590 oxidative effect Effects 0.000 description 1
- 238000004886 process control Methods 0.000 description 1
- 238000004088 simulation Methods 0.000 description 1
- SUKJFIGYRHOWBL-UHFFFAOYSA-N sodium hypochlorite Chemical compound [Na+].Cl[O-] SUKJFIGYRHOWBL-UHFFFAOYSA-N 0.000 description 1
- 229960005076 sodium hypochlorite Drugs 0.000 description 1
- 239000002351 wastewater Substances 0.000 description 1
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
- D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
- D21C9/10—Bleaching ; Apparatus therefor
- D21C9/1026—Other features in bleaching processes
- D21C9/1052—Controlling the process
-
- 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
- D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
- D21C9/10—Bleaching ; Apparatus therefor
- D21C9/12—Bleaching ; Apparatus therefor with halogens or halogen-containing compounds
Landscapes
- Life Sciences & Earth Sciences (AREA)
- Engineering & Computer Science (AREA)
- Wood Science & Technology (AREA)
- Paper (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A method for automatic control of the dosageing of chlorine dioxide and chlorine and for controlling the quality of pulp by instrumentation in a continuous pulp bleaching pro-cess. The process involves at least one chlorination step preceded by pretreatment of the pulp with chlorine dioxide.
The hardness of the unbleached pulp, washing losses, and other factors affecting the total demand on active chlorine, or the variation of these factors, are observed, e.g., by means of laboratory methods. The relative share of the chlorine dioxide dosaged in connection with the pretreatment in the total quantity of active chlorine that is dosaged in the pretreatment and in the chlorination stage together is made to follow the hardness of the unbleached pulp, the desired hardness after the chlorina-tion stage or after the alkali stage following after the chlorina-tion stage, and possibly some other process variables. The following takes place in accordance with a mathematical empire function that is being constantly calculated.
A method for automatic control of the dosageing of chlorine dioxide and chlorine and for controlling the quality of pulp by instrumentation in a continuous pulp bleaching pro-cess. The process involves at least one chlorination step preceded by pretreatment of the pulp with chlorine dioxide.
The hardness of the unbleached pulp, washing losses, and other factors affecting the total demand on active chlorine, or the variation of these factors, are observed, e.g., by means of laboratory methods. The relative share of the chlorine dioxide dosaged in connection with the pretreatment in the total quantity of active chlorine that is dosaged in the pretreatment and in the chlorination stage together is made to follow the hardness of the unbleached pulp, the desired hardness after the chlorina-tion stage or after the alkali stage following after the chlorina-tion stage, and possibly some other process variables. The following takes place in accordance with a mathematical empire function that is being constantly calculated.
Description
r~ .
l~s7~a~
The present invention relates to a method for automatic control of the dosageing of chlorine dioxide and chlorine for controlling the quality of pulp by instrumentation in a continu-ous pulp bleaching process, which process involves at least one chlorination step preceded by pretreatment of the pulp with chlorine dioxide and in which process the hardness of the un-bleached pulp (e.g., Kappa number), washing losses, and other factors affecting the total demand on active chlorine, or the variation of these factors, are observed by means of laboratory methods and/or by using continuous analyzers (e.g., Polarox*).
The use of chlorine dioxide for pretreatment of the pulp to be bleached before chlorination is at present known per se.
The use of chlorine dioxide gives, among other things, the follow-ing advantages:
* Polorox is a trademark which refers to the Polarox Analyzer developed by the Finnish Company Rauma-Repola Oy and patented in many countries including Canada. The Polorox Analyzer measures the concentration of oxidizing or reducing chemicals.
The device comprises a measuring cell with four electrodes: two metallic electrodes (measuring and current electrodes~, a refer-ence electrode, and a temperature electrode.
The solution to be measured flows through the measuring cell. Between the measuring electrode and the reference electrode, a constant potential is maintained by feeding a current through the circuit consisting of the measuring and the current electrode.
The current is proportional to the concentration of free chlorine in the solution. In the electronic unit of the device, the electrode current is transformed into a standard signal and a temperature compensation is effected.
~ ., ~ï79~
- the chlorination can be r1m at a higher temperature, - the total quantity of active chlorine to be dosaged (chlorine dioxide and chlorine added together) can be larger without risking the strength of the pulp than when chlorine alone is used, and - the amount of waste-water is lower.
In the methods known at present, the dosageing of chlorine dioxide before chlorination has been performed by usual-ly giving the ratio between the chlorine dioxide flow and the production rate a certain constant value (e.g., l). If necessary, active adjustment has been performed by means of dosageing chlorine, for example by using a redox measurement. Despite the above general advantages, these methods have involved, among other things, the following drawbacks:
. 2 -,, ;
..
1057~Q~
- the quality of the pulp after chlorination has not been uniform, and - on the average, it has been necessary to dosage more of the expensive chlorine dioxide than what would have bePn necessary for the process situation or for the purpose of reaching a certain total chlorination goal - the ratio of the required minimum dosage of chlorine dioxide to the production rate and to the chlorine dosage lwhen a certain total chlorination is aimed at) usually varies from moment to moment when the process situation varies; overlooking of this circumstance has, in a way, implied additional expenses.
The purpose of the present invention is to eliminate the above drawbacks. More precisely, by means of the present invention it is possible to control the dosageing of chlorine dioxide ahead of the chlorination stage, as well as the dosageing of chlorine, and to control ths quality of the pulp after the chlorination stage without the above drawbacks.
The method in accordance with the invention is mainly characterized in L,lat the relative share of the chlorine dioxide dosaged in connection with the pretreatment in the total quaniity of act;ve chlorine that is dosaged in the pre-treatm~nt and in the chlorination stage together is made to follow the hardness of the unbleached pulp, the desired hard-ness after the chlorination stage or after the alkali stage following after the chlorination stage, and possibly the washing losses of the unbleached pulp, the chlorination temperature,and the prcduction rate, which following takes place in accordance with a mathematical empiric function that is being constantly calculated. -~
_ ~ 4 t 1~)579~1~
Below, the invention will be examined by means of a detailed example, wherein reference is made to the attached drawings.
Figure 1 is a diagrammatic view of an industrial process controlled in accordance with the invention.
Figure 2 shows as a block diagram an equipment to be used for controlling the process in accordance with Figure 1. -~
Figurs 3 shows a nomogram that indicates the operations connected with the controlling of the process of Figure 1.
EXAMPLE
The example case is a control method for a pulp bleaching process, which method is directed at the chlorination stage and at the preceding chlorine dioxide treatment. In the process ~Figure 1) a mixture of unbleached pulp and water and chlorine dioxide solution are supplied into a mixer MIX, wherein the ~ -chlorine dioxide starts reacting with the pulp. After the mixer the pulp passes into the pretreatment stage proper DE, in which the reactions between chlorine dioxids and pulp continue. After stags DE, chlorine is dosaged aheaG of stage C, whereupon the pulp comes into the chlorination stage C. As a result of the chlorine dioxide treatment and the chlorination treatment, a considerabl portion of the ligrin contained in the pulp is transformed into a form soluble in water, on one hand, and into a form extractable by alkali. Th~ chlorination stage is usually followed by washing with water and by an alkali stage, in which the extraction of the chlorinated lignin component extractable with alkali, mentioned above, takes place. Normally, the trsatment of the pulp continues further by means of some oxydizer, e.g., sodiumhypochlorite or chlorine dioxide; these steps will, however, not be discussed here.
- - s ~(3579(~
The on-line computer CP (Figure 2) recsives, as measurement signals from the prncess, through an analog-digital converter ADM, a reading Vs indicating ths total flow of pulp, a reading vclO indicating the flow of chlorine dioxide, a reading fCl indicating the flow of chlorine, a reading sC
indicating the thickness of the pulp, and readings ccl and tc indicating the concentration of free chlorine in the pulp and the temperature in the bottom part of the chlorination column C
le.g., Polarox-measurement value). The computer CP is programmed to make use of these values as well as of values that can be set by means of the questioning and control station INFO and that are connected with the process running situation, the mariginal tests concerning measurement results, and with the intermediate aims of the cellulose quality tfor example, the preset Kappa numbEr KIE after the chlorination stage or after the subsequent alkali stage). The comDuter CP is Drogrammed so that it here-upon, by simulation (by predicting by means of mathematical models) gives the control devices Sl to S4 connected with the process, by means of the digital-analog converter DAM and through the converters Ml to M4, set values which are, correspondingly, concerned with the dosageing of chlorine dioxide solution and chlorine and, if necessary, with the chlorination temperature. The final maintenance of the set values is accomplished by said control devices. The set values given remain in force for a period which is (for e~ch 07 them separately) determined by the frequencies of performance of the programs of calculation and putting into effect of the set values. The frequencies of performance of said programs can be selected so that the changes in the process situation are taken into account sufficiently nrecisely and rapidly. The methods of calculation of the set values will be discussed more closely later.
_~ 6 1~579U~
~ elow, the abbreviations and reference numerals appearing in Figures 1 and 2 are explained:
1. Automatic process control equipment CP Central computer AOM Analog-digital converter DAM Digital-analog converter TPR Report printer INFO ~uestioning and control station
l~s7~a~
The present invention relates to a method for automatic control of the dosageing of chlorine dioxide and chlorine for controlling the quality of pulp by instrumentation in a continu-ous pulp bleaching process, which process involves at least one chlorination step preceded by pretreatment of the pulp with chlorine dioxide and in which process the hardness of the un-bleached pulp (e.g., Kappa number), washing losses, and other factors affecting the total demand on active chlorine, or the variation of these factors, are observed by means of laboratory methods and/or by using continuous analyzers (e.g., Polarox*).
The use of chlorine dioxide for pretreatment of the pulp to be bleached before chlorination is at present known per se.
The use of chlorine dioxide gives, among other things, the follow-ing advantages:
* Polorox is a trademark which refers to the Polarox Analyzer developed by the Finnish Company Rauma-Repola Oy and patented in many countries including Canada. The Polorox Analyzer measures the concentration of oxidizing or reducing chemicals.
The device comprises a measuring cell with four electrodes: two metallic electrodes (measuring and current electrodes~, a refer-ence electrode, and a temperature electrode.
The solution to be measured flows through the measuring cell. Between the measuring electrode and the reference electrode, a constant potential is maintained by feeding a current through the circuit consisting of the measuring and the current electrode.
The current is proportional to the concentration of free chlorine in the solution. In the electronic unit of the device, the electrode current is transformed into a standard signal and a temperature compensation is effected.
~ ., ~ï79~
- the chlorination can be r1m at a higher temperature, - the total quantity of active chlorine to be dosaged (chlorine dioxide and chlorine added together) can be larger without risking the strength of the pulp than when chlorine alone is used, and - the amount of waste-water is lower.
In the methods known at present, the dosageing of chlorine dioxide before chlorination has been performed by usual-ly giving the ratio between the chlorine dioxide flow and the production rate a certain constant value (e.g., l). If necessary, active adjustment has been performed by means of dosageing chlorine, for example by using a redox measurement. Despite the above general advantages, these methods have involved, among other things, the following drawbacks:
. 2 -,, ;
..
1057~Q~
- the quality of the pulp after chlorination has not been uniform, and - on the average, it has been necessary to dosage more of the expensive chlorine dioxide than what would have bePn necessary for the process situation or for the purpose of reaching a certain total chlorination goal - the ratio of the required minimum dosage of chlorine dioxide to the production rate and to the chlorine dosage lwhen a certain total chlorination is aimed at) usually varies from moment to moment when the process situation varies; overlooking of this circumstance has, in a way, implied additional expenses.
The purpose of the present invention is to eliminate the above drawbacks. More precisely, by means of the present invention it is possible to control the dosageing of chlorine dioxide ahead of the chlorination stage, as well as the dosageing of chlorine, and to control ths quality of the pulp after the chlorination stage without the above drawbacks.
The method in accordance with the invention is mainly characterized in L,lat the relative share of the chlorine dioxide dosaged in connection with the pretreatment in the total quaniity of act;ve chlorine that is dosaged in the pre-treatm~nt and in the chlorination stage together is made to follow the hardness of the unbleached pulp, the desired hard-ness after the chlorination stage or after the alkali stage following after the chlorination stage, and possibly the washing losses of the unbleached pulp, the chlorination temperature,and the prcduction rate, which following takes place in accordance with a mathematical empiric function that is being constantly calculated. -~
_ ~ 4 t 1~)579~1~
Below, the invention will be examined by means of a detailed example, wherein reference is made to the attached drawings.
Figure 1 is a diagrammatic view of an industrial process controlled in accordance with the invention.
Figure 2 shows as a block diagram an equipment to be used for controlling the process in accordance with Figure 1. -~
Figurs 3 shows a nomogram that indicates the operations connected with the controlling of the process of Figure 1.
EXAMPLE
The example case is a control method for a pulp bleaching process, which method is directed at the chlorination stage and at the preceding chlorine dioxide treatment. In the process ~Figure 1) a mixture of unbleached pulp and water and chlorine dioxide solution are supplied into a mixer MIX, wherein the ~ -chlorine dioxide starts reacting with the pulp. After the mixer the pulp passes into the pretreatment stage proper DE, in which the reactions between chlorine dioxids and pulp continue. After stags DE, chlorine is dosaged aheaG of stage C, whereupon the pulp comes into the chlorination stage C. As a result of the chlorine dioxide treatment and the chlorination treatment, a considerabl portion of the ligrin contained in the pulp is transformed into a form soluble in water, on one hand, and into a form extractable by alkali. Th~ chlorination stage is usually followed by washing with water and by an alkali stage, in which the extraction of the chlorinated lignin component extractable with alkali, mentioned above, takes place. Normally, the trsatment of the pulp continues further by means of some oxydizer, e.g., sodiumhypochlorite or chlorine dioxide; these steps will, however, not be discussed here.
- - s ~(3579(~
The on-line computer CP (Figure 2) recsives, as measurement signals from the prncess, through an analog-digital converter ADM, a reading Vs indicating ths total flow of pulp, a reading vclO indicating the flow of chlorine dioxide, a reading fCl indicating the flow of chlorine, a reading sC
indicating the thickness of the pulp, and readings ccl and tc indicating the concentration of free chlorine in the pulp and the temperature in the bottom part of the chlorination column C
le.g., Polarox-measurement value). The computer CP is programmed to make use of these values as well as of values that can be set by means of the questioning and control station INFO and that are connected with the process running situation, the mariginal tests concerning measurement results, and with the intermediate aims of the cellulose quality tfor example, the preset Kappa numbEr KIE after the chlorination stage or after the subsequent alkali stage). The comDuter CP is Drogrammed so that it here-upon, by simulation (by predicting by means of mathematical models) gives the control devices Sl to S4 connected with the process, by means of the digital-analog converter DAM and through the converters Ml to M4, set values which are, correspondingly, concerned with the dosageing of chlorine dioxide solution and chlorine and, if necessary, with the chlorination temperature. The final maintenance of the set values is accomplished by said control devices. The set values given remain in force for a period which is (for e~ch 07 them separately) determined by the frequencies of performance of the programs of calculation and putting into effect of the set values. The frequencies of performance of said programs can be selected so that the changes in the process situation are taken into account sufficiently nrecisely and rapidly. The methods of calculation of the set values will be discussed more closely later.
_~ 6 1~579U~
~ elow, the abbreviations and reference numerals appearing in Figures 1 and 2 are explained:
1. Automatic process control equipment CP Central computer AOM Analog-digital converter DAM Digital-analog converter TPR Report printer INFO ~uestioning and control station
2. Process instruments 2.1 Analog measurements VS Measurement indicating the total flow of pulp tm3/h) vclO Measursment indicating the flow of chlorine dioxide solution (m3/h) fcl2 Measurement indicating the flow of chlorine (kg/h~
sC Measurement indicating the thickness of the pulp (per cent) ccl2 Measurement indicating the concentration of freP
chlorine in the pulp in the bottom part of the chlori:~'ion column te.g., Polarox) (per cent of the range of O to 400 mg/l) tC Measurement of the temperature of the pulp in Ihe bottom part nf the chlorination column (C) 2,2 Converters Ml, M2, M3, M4 Flow-pressure converters M6, M7, M8, M9 Prsssure-flow converters 2.3 Set values given by the comput~r, and the corresponding analog control devices (in parentheses) VclO (Sl) Flow of chlorine dioxide solution (m3/h) ~_ ~ 7 ~s7glo6 Fcl (S2) Flow of chlorine (kg/h) TC ~S3) Temperature of puln (C) SC ~S4~ Thickness of pulp tper cent)
sC Measurement indicating the thickness of the pulp (per cent) ccl2 Measurement indicating the concentration of freP
chlorine in the pulp in the bottom part of the chlori:~'ion column te.g., Polarox) (per cent of the range of O to 400 mg/l) tC Measurement of the temperature of the pulp in Ihe bottom part nf the chlorination column (C) 2,2 Converters Ml, M2, M3, M4 Flow-pressure converters M6, M7, M8, M9 Prsssure-flow converters 2.3 Set values given by the comput~r, and the corresponding analog control devices (in parentheses) VclO (Sl) Flow of chlorine dioxide solution (m3/h) ~_ ~ 7 ~s7glo6 Fcl (S2) Flow of chlorine (kg/h) TC ~S3) Temperature of puln (C) SC ~S4~ Thickness of pulp tper cent)
3. Tanks and reaction columns MIX Chlorins dioxide mixsr DE Pretreatment stage C Chlorination column The demand on active chlorine of the cellulose entering the bleaching process, in the chlorination per unit of mass, depends on the hardness ~Kappa number) of the pulp and on the desired chlorination effect, i.e., the desired Kappa number after the chlorination stage or the subsequent alkali stage. The washing losses accompanying the pulp also affect the total demand on chlorine. Moreover, successful chlorination requi^es correct reaction conditions, temperature and thickness, which in part affect the efficiency of chlorination and the quantity of active chlorine required per mass unit of pulp to be chlorinated. The demand on active chlorine per mass unit of the pulp to be bleachsd, presented in Figure 3, is calculatEd out ;~
of an empiric function ~1) which is based on observation of the reaction speed and reaction condit;.ns and, thereby also on nbservation of the hardn~ss of the pulp to be bleached at the beginning of the chlorination stage.
F
~11 tot fl ~VCl02' CCl02' fC12' tot' sC tc~ CCl2' ~E) A
wherein ;
FC n the new required total flow of chlorine tot ~kg of active C12tt) 10579(~ :
A = productior. rate ~t/h) fl ~ the function concerned VCl02 ~ volumetric flow of chlorine dioxide solution Cm /h3 cclO = concentration of chlorine dioxide solution ~g/l) fcl2 = chlorine flow ~kg/h) VS ' total flow of pulp ~m3/h) 8C = thickness of pulp (per cent) tC = temperature in the bottom part of chlorination column (C) ccl2 ~ concentration of free chlorine in the bottom part of the chlorination column (mg~l) KIE ' the desired Kappa number after the alkali stage following the chlorination stage.
Among the variables of the above function, vclO is by -the delay between the dosageing of chlorine dioxide and the -measurement of the free chlorine concentration older and fC
i5 by the delay between the dosageing of chlorine and the measurement of the concentration of free chlorine older than the other variables. The total chlorine demand of the pUlP to be bleached can also be followed by determining the hardness of the pulp in the laboratory; a drawback is, however, the long delay involved in the determination. In Figure 3 the brok~n line provided with arrow marking shows the proceeding ~T the calculation operations starting from the total demand on chlorine determined above. On the basis of the prevailing production rate, the required total flow of chlorine Fc i5 obtained. The distribution of the total flow of chlorine between chlorine dioxide and chlorine is hereupon determined from the function (2), which takes into account the desired .. ... ~;
.' ' ~'- ',' ':- ' , ' ' : ~ ' 9 10579~ :
Kappa number after the alkali stage following the chlorination stage (Figure 3).
(21 1 2 = f2 tFC ' KIE) = d Fcl2 c wherein FC10 = the new set value of the chlorine dioxide flow (kg/h) Fcl2 = the new set value of the chlorine flow tkg/h) f2 ~ the funct.ion concerned FC = the required total flow of chlorine (kg of active tot C12 per ton) KIE = desired Kappa after the alkali stage d/c = ratio of the above chemical flows. .~-The final set values of the chemical flows are determined,~
possibly by filtering, on the basis of the ratio calculated above.
C102 cld CtOt ccl02 and FCl = d FC
whersin Vc~O ~ the new set value of the volumetric flow of the chlorine dio,:ide solution (m3/h) CC ~ = concentration of tlle chlorine dioxide solution (g/l) and the rest of the variables are the same as those indicated in connection with equation (2).
Thus, the new set values of chlorine dioxide and chlorine dosage as well as their ratio depend on the desired Kaopa and, through the variable FC ~ also on the total chlorine demand tot on the pulp to be bleached (hardness, washing losses, etc.), on the production rate, and on the reaction conditions.
10579U~ .
By means of the method in accordance with the invention, the quality of pulp can be controlled by giving the desired Kappa KIE after the alkali stage different values, whereby, -correspondingly, the factual Kappa number of the pulp after the alkali stage is also developed to the desired level.
The computer system sends electrical signals corresponding~
to calculated new set values Vcl02 and FCl2 dioxide flow and chlorine flow through the converters Ml and M2 to the analog control devices Sl and S2, which adjust the system in view of said set values.
In the example case, set values are also calculated separately for the chlorination temperature ~Tc) and chlorination thickness (Sc). The bases of calculation of these will not be discussed here any further; the goal is a sufficiently high reaction speed and efficient use of chlorine dioxide and chlorine. The computer system sends electrical signals corresponding to said set values through the converters M3 and M4 to the analog control devices S3 and S4, which adjust the system in view of said set values.
~''
of an empiric function ~1) which is based on observation of the reaction speed and reaction condit;.ns and, thereby also on nbservation of the hardn~ss of the pulp to be bleached at the beginning of the chlorination stage.
F
~11 tot fl ~VCl02' CCl02' fC12' tot' sC tc~ CCl2' ~E) A
wherein ;
FC n the new required total flow of chlorine tot ~kg of active C12tt) 10579(~ :
A = productior. rate ~t/h) fl ~ the function concerned VCl02 ~ volumetric flow of chlorine dioxide solution Cm /h3 cclO = concentration of chlorine dioxide solution ~g/l) fcl2 = chlorine flow ~kg/h) VS ' total flow of pulp ~m3/h) 8C = thickness of pulp (per cent) tC = temperature in the bottom part of chlorination column (C) ccl2 ~ concentration of free chlorine in the bottom part of the chlorination column (mg~l) KIE ' the desired Kappa number after the alkali stage following the chlorination stage.
Among the variables of the above function, vclO is by -the delay between the dosageing of chlorine dioxide and the -measurement of the free chlorine concentration older and fC
i5 by the delay between the dosageing of chlorine and the measurement of the concentration of free chlorine older than the other variables. The total chlorine demand of the pUlP to be bleached can also be followed by determining the hardness of the pulp in the laboratory; a drawback is, however, the long delay involved in the determination. In Figure 3 the brok~n line provided with arrow marking shows the proceeding ~T the calculation operations starting from the total demand on chlorine determined above. On the basis of the prevailing production rate, the required total flow of chlorine Fc i5 obtained. The distribution of the total flow of chlorine between chlorine dioxide and chlorine is hereupon determined from the function (2), which takes into account the desired .. ... ~;
.' ' ~'- ',' ':- ' , ' ' : ~ ' 9 10579~ :
Kappa number after the alkali stage following the chlorination stage (Figure 3).
(21 1 2 = f2 tFC ' KIE) = d Fcl2 c wherein FC10 = the new set value of the chlorine dioxide flow (kg/h) Fcl2 = the new set value of the chlorine flow tkg/h) f2 ~ the funct.ion concerned FC = the required total flow of chlorine (kg of active tot C12 per ton) KIE = desired Kappa after the alkali stage d/c = ratio of the above chemical flows. .~-The final set values of the chemical flows are determined,~
possibly by filtering, on the basis of the ratio calculated above.
C102 cld CtOt ccl02 and FCl = d FC
whersin Vc~O ~ the new set value of the volumetric flow of the chlorine dio,:ide solution (m3/h) CC ~ = concentration of tlle chlorine dioxide solution (g/l) and the rest of the variables are the same as those indicated in connection with equation (2).
Thus, the new set values of chlorine dioxide and chlorine dosage as well as their ratio depend on the desired Kaopa and, through the variable FC ~ also on the total chlorine demand tot on the pulp to be bleached (hardness, washing losses, etc.), on the production rate, and on the reaction conditions.
10579U~ .
By means of the method in accordance with the invention, the quality of pulp can be controlled by giving the desired Kappa KIE after the alkali stage different values, whereby, -correspondingly, the factual Kappa number of the pulp after the alkali stage is also developed to the desired level.
The computer system sends electrical signals corresponding~
to calculated new set values Vcl02 and FCl2 dioxide flow and chlorine flow through the converters Ml and M2 to the analog control devices Sl and S2, which adjust the system in view of said set values.
In the example case, set values are also calculated separately for the chlorination temperature ~Tc) and chlorination thickness (Sc). The bases of calculation of these will not be discussed here any further; the goal is a sufficiently high reaction speed and efficient use of chlorine dioxide and chlorine. The computer system sends electrical signals corresponding to said set values through the converters M3 and M4 to the analog control devices S3 and S4, which adjust the system in view of said set values.
~''
Claims (7)
1. A method for automatic control of the dosageing of chlorine dioxide and chlorine and for controlling the quality of pulp by instrumentation in a continuous pulp bleaching pro-cess, which process involves at least one chlorination step preceded by pretreatment of the pulp with chlorine dioxide and in which process the hardness of the unbleached pulp and washing losses, are observed by means of laboratory methods and/or by using continuous analyzers wherein the relative share of the chlorine dioxide dosaged in connection with the pretreatment in the total quantity of active chlorine that is dosaged in the pretreatment and in the chlorination stage together is made to follow the hardness of the unbleached pulp and the desired hard-ness after the chlorination stage, which following takes place in accordance with a mathematical empiric function that is being constantly calculated.
2. A method as claimed in Claim 1, wherein said following takes place after the alkali stage following upon the chlorina-tion stage.
3. A method as claimed in Claim 1, wherein said share of chlorine dioxide is further made to follow the washing losses of the unbleached pulp.
4. A method as claimed in Claim 1, wherein said share of chlorine dioxide is further made to follow the chlorination temp-erature.
5. A method as claimed in Claim 1, wherein said share of chlorine dioxide is further made to follow the production rate.
6. A method as claimed in Claim 1, wherein for the calcu-lation of the mathematical empiric function a digital computer connected on-line to the process is used.
7. A method as claimed in Claim 1, wherein by changing, as a parameter, the desired hardness after the chlorination stage or after the alkali stage following the chlorination stage, which hardness is a variable in the mathematical empiric function, the hardness of the pulp after the chlorination stage or after the alkali stage following the chlorination stage is controlled.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FI741828A FI50745C (en) | 1974-06-14 | 1974-06-14 | Procedure for automatic control of the dosage of two chemicals. |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1057906A true CA1057906A (en) | 1979-07-10 |
Family
ID=8506257
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA229,324A Expired CA1057906A (en) | 1974-06-14 | 1975-06-13 | Method for automatic control of the dosageing of two chemicals |
Country Status (3)
| Country | Link |
|---|---|
| CA (1) | CA1057906A (en) |
| FI (1) | FI50745C (en) |
| SE (1) | SE7506844L (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1998023810A1 (en) * | 1996-11-26 | 1998-06-04 | Sunds Defibrator Industries Ab | Method for controlling oxygen delignification of pulp |
| US6153050A (en) * | 1998-03-24 | 2000-11-28 | Noranda Forest Inc. | Method and system for controlling the addition of bleaching reagents to obtain a substantially constant percentage of pulp delignification across the first bleaching/delignifying stage |
-
1974
- 1974-06-14 FI FI741828A patent/FI50745C/en active
-
1975
- 1975-06-13 SE SE7506844A patent/SE7506844L/en unknown
- 1975-06-13 CA CA229,324A patent/CA1057906A/en not_active Expired
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1998023810A1 (en) * | 1996-11-26 | 1998-06-04 | Sunds Defibrator Industries Ab | Method for controlling oxygen delignification of pulp |
| AU723369B2 (en) * | 1996-11-26 | 2000-08-24 | Valmet Fibertech Ab | Method for controlling oxygen delignification of pulp |
| US6238517B1 (en) | 1996-11-26 | 2001-05-29 | Valmet Fibertech Aktiebolag | Method for controlling oxygen delignification of pulp |
| CN1103833C (en) * | 1996-11-26 | 2003-03-26 | 瑞典商顺智公司 | Method for controlling oxygen delignification of pulp |
| US6153050A (en) * | 1998-03-24 | 2000-11-28 | Noranda Forest Inc. | Method and system for controlling the addition of bleaching reagents to obtain a substantially constant percentage of pulp delignification across the first bleaching/delignifying stage |
Also Published As
| Publication number | Publication date |
|---|---|
| FI182874A (en) | 1975-12-15 |
| SE7506844L (en) | 1975-12-15 |
| FI50745B (en) | 1976-03-01 |
| FI50745C (en) | 1976-06-10 |
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