CA1221205A - Procedure and apparatus for controlling the cellulose bleaching process - Google Patents
Procedure and apparatus for controlling the cellulose bleaching processInfo
- Publication number
- CA1221205A CA1221205A CA000416373A CA416373A CA1221205A CA 1221205 A CA1221205 A CA 1221205A CA 000416373 A CA000416373 A CA 000416373A CA 416373 A CA416373 A CA 416373A CA 1221205 A CA1221205 A CA 1221205A
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- bleaching
- chemicals
- control signal
- pulp
- control
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Abstract
Abstract of Disclosure The invention concerns a procedure and apparatus for controlling the cellulose bleaching process, there being formed on the basis of optical measurement a control signal corresponding to the degree of bleaching of the pulp, and the dispensing of bleaching chemicals to the pulp being controlled by said control signal. The aim is to avoid overdosage and underdosage of the bleaching chemicals. As taught by the invention, from the bleached pulp is determined the residual content of the chemicals employed toward bleaching, on the basis of this determination is formed a correction signal and the control signal is corrected by said correction signal The residual chemicals determination is made possibly from an earlier, or from the same process step in which the control signal is formed, how-ever advantageously from the process step following after the forming of the control signals suitably about 3-10 min., prefer-ably about 5 min. after the optical measurement. The corresponding apparatus for controlling the cellulose bleaching process comprises an optical measuring means (1) for forming a control signal cor-responding to the degree of bleaching of the pulp that is being bleached, a control means (2,3) for controlling the dispersing of bleaching chemicals under control by the control signal with the aid of dispensing means (4,5), and an analyser (6) for determining the residual content of the chemicals used towards bleaching and for forming a corresponding correction signal; this signal having been conducted to correct the control signal. The analyser (6) has been connected to the preceding or the same process step with the optical measuring means (1), advantageously however to the process step following after the optical measuring means.
Description
~l~Z:12~5i Procedure and apparatus for controlling the cellulose bleaching process The present invention concerns a procedure for controlling the cellulose bleaching process wherein the degree of bleaching of the pulp meant to be bleached is optically measured, on the basis of such optical measurement is formed a control signal corresponding to the pulp s degree of bleaching, and the dispensing of bleaching chemicals to the pulp is controlled by the said control signal. The invention further concerns apparatus for controlling the cellulose bleaching process comprising a measuring means for the forming of a control signal corresponding to the degree of bleaching of the pulp that is going to be bleached, and a control means for controlling the dispensing of bleac.hing chemicals under control by said control signal with the aid of dispensing means.
Heretofore, the dispensing of bleaching chemicals in connection with the bleaching process has usually been controlled on the basis of measurements of the bleached pulp s residual chemical contents.
In the residual chemicals measurement is determined, at a given stage in the process, the content of bleaching chemicals thac have failed to react, for instance by an electro-chemical measuring method. In the measuring instrument a signal is generated which is e2uivalent to the concentration of the chemicals, and this signal , ~..
-is conducted so that it controls the dispensing of bleaching chem-icals to the pulp, with the aid of control means, controllers and dispensing means.
Also known in prior art is the optical controlling method defined in the lntroductory part, wherein the pulp's degree of bleachin~ is measured optically and the dispensing of bleaching chemicals to the pulp is controlled with the aid of a signal formed on the basis of said optical measurement, with the ald of measuring, control and dispensing means. It is thus understood that the optical measure-ment is based on determLnation of the result of bleaching made from the pulp that is being bleached, while the residual chemicals measurement is based on determination from the bleached pulp of the chemicals that have failed to react.
In order to be able to implement in a satisfactory way the control of chemicals dispensing in the chlorination step, one must be able to perform the requisite measurements as soon as about 0.5 to 3 min. after the chemical dispensing operations. This implies in practice that not nearly all of the chemlcal has been used up in its reaction with lignin. The reaction rate is also decLsively influenced, individually in each instance, by the reaction temper-ature, viscocity, efficiency of agitation, etc. However, usually these factors are not greatly variable in one plant~ whereby their effect on the result of control is not decisive within one plant.
Therefore, the overwhelmingly most important process variable will be the unc~ntrolled variation in the kappa number of the pulp arriving at the bleaching plant, in such manner that the higher the kappa number of the arriving pulp, the longer is the time required for a given quantity of chemicals to oxidize and dissolve the lignin from the pulp.
Taking into account the factors mentioned, that is the kappa number and the reaction time, it is possible to explain completely why the control based on residue measurement over-doses, and control based on optical measurement under-doses, hard and soft pulps. For ex-ample in the instance of increasing incoming kappa, the slowing 1~3~5 down of ~he reactLon rate causes the resLdual quantlty at the point of measurement to increase. This pheno~enon is even further accen-tuated because owing to the conventional delay of measurement the point of operation still lies on the steep portion of the reaction graph. The consequence is that the control endeavours to attain i~s set-point value by reducing the dose of chemicals, and the result is therefore subchlorination. The opposite phenomenon occurs in the event of diminishing kappa at entrance.
In case the control ls based on optical measurement, the situation is better insofar as the measurement yields direct information as to the chlorination of the pulp. Secondly, owing to the rapid kappa descent the point of operation is not on the steep portion of the graph. Therefore the only remaining factor that has an effect on the control will usually be the variations of reaction rate due to fluctuating incoming kappa. However, as can be deduced from the foregoing, their influence is not equally strong as that in control based on residue measuring. It follows that the over~ and under-chlorinations incurred are also clearly less with equal kappa fluctuations. But it is a fact that fully satisfactory results cannot be achieved by residue measurement any more than by measur-ing the degree of oxidation and by chemicals dispensing carried out on their basis. Overdosage of chemicals implies excessive~consump-tion of chemicals, while underdosage results in insufficient bleaching and thereby in inferior quality.
As set forth in the foregoing, it is a fact that today satisfactory results are not achieved in all and any conditions, owin~ to qual-ity and other reasons, by residual chemicals measurement nor by optical measurement.
The object of the present invention is to eliminate the drawbacks mentioned. It is a particular object of the invention to provide a procedure, and apparatus, for such controlling of the cellulose bleaching process that the bleaching will take place without either under- or overdosage of the bleaching chemicals. It is a further object of the invention to provide a new procedure, and apparatus, .: , ~,..............
~h a~
for such controlling of the bleaching process that control of the bleaching process takes place with more scrupulous obse~vation than before of the kappa number of the pulp that is being bleached.
Regarding the features characteristic of the invention, reference is made to the claims section.
The invention is based on the principle that optically performed measurement of the pulp's degree o~ bleaching is selected to be the basis for control of the chlorinating step in the bleaching pro-cess. It is possible by simultaneously measuring the residual chemicals content, either from the same process step where the determination of degree of bleaching is made, alternatively before the degree of bleaching determination, or preferably e.g. about 5 min. thereafter, to measure continuously also on line the hard-ness of the incoming pulp, i.e., its kappa number. Since measure ment of the optical degree of bleaching is known to cause overdos-age in the case of hard pulps, this implies at the same time a powerful increase of the residual chemicals content at the begin-ning of the reaction step. It is then possible by means of a signal derived from the residual chemicals determination to correct the set-point of the optical measurement consistent with the kappa variations. - -Heretofore there has been no use of the combined optical determi-nation of the puLp's degree of bleaching and of the residual chem-icals measurement in the bleaching in combination to control the bleaching chemicals supply.
Thanks to the present invention, the dispensing of bleaching chem-icals can be effected with substantially higher accuracy than heretofore, taking the kappa variations of the pulp that is being bleached into account. When using the procedure and/or apparatus of the invention, overdosage, and on the other hand underdosage as well, of the chemicals is avoided. Thanks to the invention, the excess consumption of bleaching chemicals is reduced, while on the other hand quality fluctuatLons caused by insufficiently bleached ,' Y
pulp batches are eliminated.
~he invention is described in detail in the following with the aid of embodiment examples, referring to the drawings attached, wherein:
Fig. 1 illustrates the variations in residual chemical level and ;he incomlng kappa, plotted over time, for softwood, Fig. 2 illustrates the variations in residual chemical level and the incoming kappa, plotted over time, for birch wood, .
Fig. 3 illustrates the variations in resid;ual chemical level when the sald measurement has been applied in correction of the set-point value derived from the optical degree of bleaching measure-m?nt in the control of chemicals dispensing, Fig. 4 presents schematically an apparatus according to the invention, Fig. 5 presents schematically another apparatus according to the inventton, and Fig. 6 presents schematically a third apparatus according to the invention.
In experiments carried out in an industrial plant, the changes of the residual chemicals level was measured with varying kappa number; in these experiments the control of chemicals dispensing W2S based on measuring the optical degree of bleaching. ~oth sensors, i.e., an opttcally operating Cormec' sensor and an electrochemically operating Polarox sensor, had a delay of about
Heretofore, the dispensing of bleaching chemicals in connection with the bleaching process has usually been controlled on the basis of measurements of the bleached pulp s residual chemical contents.
In the residual chemicals measurement is determined, at a given stage in the process, the content of bleaching chemicals thac have failed to react, for instance by an electro-chemical measuring method. In the measuring instrument a signal is generated which is e2uivalent to the concentration of the chemicals, and this signal , ~..
-is conducted so that it controls the dispensing of bleaching chem-icals to the pulp, with the aid of control means, controllers and dispensing means.
Also known in prior art is the optical controlling method defined in the lntroductory part, wherein the pulp's degree of bleachin~ is measured optically and the dispensing of bleaching chemicals to the pulp is controlled with the aid of a signal formed on the basis of said optical measurement, with the ald of measuring, control and dispensing means. It is thus understood that the optical measure-ment is based on determLnation of the result of bleaching made from the pulp that is being bleached, while the residual chemicals measurement is based on determination from the bleached pulp of the chemicals that have failed to react.
In order to be able to implement in a satisfactory way the control of chemicals dispensing in the chlorination step, one must be able to perform the requisite measurements as soon as about 0.5 to 3 min. after the chemical dispensing operations. This implies in practice that not nearly all of the chemlcal has been used up in its reaction with lignin. The reaction rate is also decLsively influenced, individually in each instance, by the reaction temper-ature, viscocity, efficiency of agitation, etc. However, usually these factors are not greatly variable in one plant~ whereby their effect on the result of control is not decisive within one plant.
Therefore, the overwhelmingly most important process variable will be the unc~ntrolled variation in the kappa number of the pulp arriving at the bleaching plant, in such manner that the higher the kappa number of the arriving pulp, the longer is the time required for a given quantity of chemicals to oxidize and dissolve the lignin from the pulp.
Taking into account the factors mentioned, that is the kappa number and the reaction time, it is possible to explain completely why the control based on residue measurement over-doses, and control based on optical measurement under-doses, hard and soft pulps. For ex-ample in the instance of increasing incoming kappa, the slowing 1~3~5 down of ~he reactLon rate causes the resLdual quantlty at the point of measurement to increase. This pheno~enon is even further accen-tuated because owing to the conventional delay of measurement the point of operation still lies on the steep portion of the reaction graph. The consequence is that the control endeavours to attain i~s set-point value by reducing the dose of chemicals, and the result is therefore subchlorination. The opposite phenomenon occurs in the event of diminishing kappa at entrance.
In case the control ls based on optical measurement, the situation is better insofar as the measurement yields direct information as to the chlorination of the pulp. Secondly, owing to the rapid kappa descent the point of operation is not on the steep portion of the graph. Therefore the only remaining factor that has an effect on the control will usually be the variations of reaction rate due to fluctuating incoming kappa. However, as can be deduced from the foregoing, their influence is not equally strong as that in control based on residue measuring. It follows that the over~ and under-chlorinations incurred are also clearly less with equal kappa fluctuations. But it is a fact that fully satisfactory results cannot be achieved by residue measurement any more than by measur-ing the degree of oxidation and by chemicals dispensing carried out on their basis. Overdosage of chemicals implies excessive~consump-tion of chemicals, while underdosage results in insufficient bleaching and thereby in inferior quality.
As set forth in the foregoing, it is a fact that today satisfactory results are not achieved in all and any conditions, owin~ to qual-ity and other reasons, by residual chemicals measurement nor by optical measurement.
The object of the present invention is to eliminate the drawbacks mentioned. It is a particular object of the invention to provide a procedure, and apparatus, for such controlling of the cellulose bleaching process that the bleaching will take place without either under- or overdosage of the bleaching chemicals. It is a further object of the invention to provide a new procedure, and apparatus, .: , ~,..............
~h a~
for such controlling of the bleaching process that control of the bleaching process takes place with more scrupulous obse~vation than before of the kappa number of the pulp that is being bleached.
Regarding the features characteristic of the invention, reference is made to the claims section.
The invention is based on the principle that optically performed measurement of the pulp's degree o~ bleaching is selected to be the basis for control of the chlorinating step in the bleaching pro-cess. It is possible by simultaneously measuring the residual chemicals content, either from the same process step where the determination of degree of bleaching is made, alternatively before the degree of bleaching determination, or preferably e.g. about 5 min. thereafter, to measure continuously also on line the hard-ness of the incoming pulp, i.e., its kappa number. Since measure ment of the optical degree of bleaching is known to cause overdos-age in the case of hard pulps, this implies at the same time a powerful increase of the residual chemicals content at the begin-ning of the reaction step. It is then possible by means of a signal derived from the residual chemicals determination to correct the set-point of the optical measurement consistent with the kappa variations. - -Heretofore there has been no use of the combined optical determi-nation of the puLp's degree of bleaching and of the residual chem-icals measurement in the bleaching in combination to control the bleaching chemicals supply.
Thanks to the present invention, the dispensing of bleaching chem-icals can be effected with substantially higher accuracy than heretofore, taking the kappa variations of the pulp that is being bleached into account. When using the procedure and/or apparatus of the invention, overdosage, and on the other hand underdosage as well, of the chemicals is avoided. Thanks to the invention, the excess consumption of bleaching chemicals is reduced, while on the other hand quality fluctuatLons caused by insufficiently bleached ,' Y
pulp batches are eliminated.
~he invention is described in detail in the following with the aid of embodiment examples, referring to the drawings attached, wherein:
Fig. 1 illustrates the variations in residual chemical level and ;he incomlng kappa, plotted over time, for softwood, Fig. 2 illustrates the variations in residual chemical level and the incoming kappa, plotted over time, for birch wood, .
Fig. 3 illustrates the variations in resid;ual chemical level when the sald measurement has been applied in correction of the set-point value derived from the optical degree of bleaching measure-m?nt in the control of chemicals dispensing, Fig. 4 presents schematically an apparatus according to the invention, Fig. 5 presents schematically another apparatus according to the inventton, and Fig. 6 presents schematically a third apparatus according to the invention.
In experiments carried out in an industrial plant, the changes of the residual chemicals level was measured with varying kappa number; in these experiments the control of chemicals dispensing W2S based on measuring the optical degree of bleaching. ~oth sensors, i.e., an opttcally operating Cormec' sensor and an electrochemically operating Polarox sensor, had a delay of about
2 min. from the dispensing of chemicais.
Exa~ples 1 - 3 In the experiments the residual chemicals level of the pulp was ~ .
, .
determined, as a function of tlme, and the incoming kappa similarly as a functlon of time, for softwood and with bleaching chemicals dispensing performed on the basls of degree o~ bleaching measure-ment (Fig. 1), and the same for birch wood (Fig. 2). Furthermore, in the experiments the variation of residual bleaching chemicals level was determined in the case in which the measurement in ques-tion was applied for correction of the chemicals dispensing set-point value formed on the basis of optical degree of bleaching measurement (Flg. 3), the measuring and control arrangements being as Fig. 4 shows. In Fig. 3 the correlation between residual content and incoming kappa is 0.9, in other words, during joint operation of both sensors the residual chemicals measurement correlated exactly with the varLatLon of the kappa number.
In Fig. 4 is depicted an apparatus according to the invention for controlling the bleachLng process. The apparatus comprises a bleachLng reactor 7, to which the pipeline 8 supplies pulp to be bleached. In the pipeline 8 has been mounted an optically operating measuring means 1 for measuring the degree of bleaching of the pulp and for forming a control signal corresponding to the degree of bleaching. The apparatus further includes control means 2 and 3 for controlling the dispensing of the bleaching chemicals C12 and C10 into the pipelLne 8 with the aid of dispensing means 4 and 5. As taught by the invention, an electro-chemLcally operating analyser 6 has been provided to measure the residual chemicals in the pipeline 8 with the same -10 min. delay, i.e., in time between O and 10, preferably about 5-10 min. after the optical measuring means 1. The analyser 6 forms a correction signal for correction of the bleach-ing chemicals dispensing in accordance with the residual co~tent which Lt measured. The correction sLgnal has been conducted to correct the control signal of the measuring means 1 over modulators 9 and 10, to the control means 2 and 3. The apparatus controls the supplying of bleaching chemicals on the basis of measurement of the pulp's optLcal degree of bleachLng, corrected by the residual chemicals measurement.
The arrangement depicted Ln FLg. 4 is based on so-called cascade control. The chemicals control means, that is the flow control circuits 2,3, receive their external set-polnt from a modulator based on the optical measure~ent 1, that is from a whiteness con-trol circuit 10. This, in its turn, receives an external set-point value dependent on the residue measurement 6 and affecting the overall control. This has in practice been implemented e.g. by carrying the residue measurement signal from the analyser 6 to a pure P controller, that is to the modulator 9, of which the output is directed to become the set-point for the whiteness control circuit. It is possible to change this relationship, according to the situation, by altering the proportional band width of the P
controller 9.
The embodiment depicted in Fig. 5 is largely equivalent to that of Fig. 4. In Fig. 5, the signals derived from the optical measurement 1 and from the residue measurement 6 have been conducted over mod-ulators 9,10 to a proportion relay 13 to constitute a so-called control signal, which has been carried to be the set-point value for the flow controller 2. It is possible in the proportion relay 13 to take into account in such manner as is desired, the influence of the residue measurement on the optical measurement.
The apparatus depicted in Fig. 6 is based on compensation, or cal-culation. The fundamental idea is then that the signal ~rom the optical measurement 1 is corrected by calculation with the aid of the residue measurement 6, for instance according to the formula:
CONTROL VARIABLE = K x OPTICAL + (l-K) x ~ESID~E
This corresponds in practice to the situation in which the set-point of the optical control circuit is altered with the aid of the residue measurement. The calculation is performed e.g. with a cal-culator unit 9,10 known in itself in the art. It is obviously pos-sible in the calculator unit to establish programmed controllers according to analog control and to implement the control on the sa~e basis.
In Fig. 6, the optical measurement 1 and the resldue measurement 6 are made in the same process step, i.e., with the same delay after addition of the chemicals from pipeline 11 into pipeline 8.
Example 4 . .
In a plant run, dispensing oi chemicals was carried out by a pro-cedure according to the invention, with the arrangement shown in Fig. 4. The optical measurement was made with so-called "Cormec"
equipment, optically, and the residue measurement was made with a so-called "Polarox" apparatus, electro-chemically. In this meas-urement the kappa number oi the incoming pulp 8 and the intermedi-ate kappa were determined. The reEerence method employed was opti-cal bleaching chemicals control with the "Cormec" apparatus; it has previously been found in practice that control based on residue measurement alone yields a result inferior to that obtained with optical ~easurement.
Table 1 RESULTS OF CORMEC CONTROL
Mean Max. Min. Standard Deviation Incoming kappa36.9 46 28 3.20 Intermediate kappa 6.4 7.9 5.1 0.50 RESULTS OF CORMEC + POLAROX CONTROL
Mean Max. Min. Standard Deviation Incoming kappa33.6 44 28 3.27 Intermediate kappa 5.6 7!9 4.5 0.31 ,~ g , `.
In the embodiment examples presented above, the residual chem cals determination was made from the same process step as the forming of the control signal, or alternatively from the process step follow-ing after the forming of the control signal. If-desired, ho~ever, the residual chemicals determination may e~ually be made from the process step preceding the forming of the control signalJ i.e., before the optical measurement. This is particularly to be conte~-plated when the process involves Long delay periods. Thus, when the optiral delay is for instance on the order of 10 min., the residual content of chemicals may be determined, in time, e.g. 0-1 min. or even several minutes, such as 1-10 min., before the optical meas-urement.
The invention is not confined to the examples that have been pre-sented: its applications may vary within the scope of the claims following below. Then, the procedure in question, and the appara-tus, is appropriate for controlling the dispensing of any chemic21 whatsoever in connection with bleaching. Furthermore, the procedure and the apparatus may be used in connection with any kind of meth-ods of determination, and apparatus, for determining degree of bleaching and residual chemicals.
.
Exa~ples 1 - 3 In the experiments the residual chemicals level of the pulp was ~ .
, .
determined, as a function of tlme, and the incoming kappa similarly as a functlon of time, for softwood and with bleaching chemicals dispensing performed on the basls of degree o~ bleaching measure-ment (Fig. 1), and the same for birch wood (Fig. 2). Furthermore, in the experiments the variation of residual bleaching chemicals level was determined in the case in which the measurement in ques-tion was applied for correction of the chemicals dispensing set-point value formed on the basis of optical degree of bleaching measurement (Flg. 3), the measuring and control arrangements being as Fig. 4 shows. In Fig. 3 the correlation between residual content and incoming kappa is 0.9, in other words, during joint operation of both sensors the residual chemicals measurement correlated exactly with the varLatLon of the kappa number.
In Fig. 4 is depicted an apparatus according to the invention for controlling the bleachLng process. The apparatus comprises a bleachLng reactor 7, to which the pipeline 8 supplies pulp to be bleached. In the pipeline 8 has been mounted an optically operating measuring means 1 for measuring the degree of bleaching of the pulp and for forming a control signal corresponding to the degree of bleaching. The apparatus further includes control means 2 and 3 for controlling the dispensing of the bleaching chemicals C12 and C10 into the pipelLne 8 with the aid of dispensing means 4 and 5. As taught by the invention, an electro-chemLcally operating analyser 6 has been provided to measure the residual chemicals in the pipeline 8 with the same -10 min. delay, i.e., in time between O and 10, preferably about 5-10 min. after the optical measuring means 1. The analyser 6 forms a correction signal for correction of the bleach-ing chemicals dispensing in accordance with the residual co~tent which Lt measured. The correction sLgnal has been conducted to correct the control signal of the measuring means 1 over modulators 9 and 10, to the control means 2 and 3. The apparatus controls the supplying of bleaching chemicals on the basis of measurement of the pulp's optLcal degree of bleachLng, corrected by the residual chemicals measurement.
The arrangement depicted Ln FLg. 4 is based on so-called cascade control. The chemicals control means, that is the flow control circuits 2,3, receive their external set-polnt from a modulator based on the optical measure~ent 1, that is from a whiteness con-trol circuit 10. This, in its turn, receives an external set-point value dependent on the residue measurement 6 and affecting the overall control. This has in practice been implemented e.g. by carrying the residue measurement signal from the analyser 6 to a pure P controller, that is to the modulator 9, of which the output is directed to become the set-point for the whiteness control circuit. It is possible to change this relationship, according to the situation, by altering the proportional band width of the P
controller 9.
The embodiment depicted in Fig. 5 is largely equivalent to that of Fig. 4. In Fig. 5, the signals derived from the optical measurement 1 and from the residue measurement 6 have been conducted over mod-ulators 9,10 to a proportion relay 13 to constitute a so-called control signal, which has been carried to be the set-point value for the flow controller 2. It is possible in the proportion relay 13 to take into account in such manner as is desired, the influence of the residue measurement on the optical measurement.
The apparatus depicted in Fig. 6 is based on compensation, or cal-culation. The fundamental idea is then that the signal ~rom the optical measurement 1 is corrected by calculation with the aid of the residue measurement 6, for instance according to the formula:
CONTROL VARIABLE = K x OPTICAL + (l-K) x ~ESID~E
This corresponds in practice to the situation in which the set-point of the optical control circuit is altered with the aid of the residue measurement. The calculation is performed e.g. with a cal-culator unit 9,10 known in itself in the art. It is obviously pos-sible in the calculator unit to establish programmed controllers according to analog control and to implement the control on the sa~e basis.
In Fig. 6, the optical measurement 1 and the resldue measurement 6 are made in the same process step, i.e., with the same delay after addition of the chemicals from pipeline 11 into pipeline 8.
Example 4 . .
In a plant run, dispensing oi chemicals was carried out by a pro-cedure according to the invention, with the arrangement shown in Fig. 4. The optical measurement was made with so-called "Cormec"
equipment, optically, and the residue measurement was made with a so-called "Polarox" apparatus, electro-chemically. In this meas-urement the kappa number oi the incoming pulp 8 and the intermedi-ate kappa were determined. The reEerence method employed was opti-cal bleaching chemicals control with the "Cormec" apparatus; it has previously been found in practice that control based on residue measurement alone yields a result inferior to that obtained with optical ~easurement.
Table 1 RESULTS OF CORMEC CONTROL
Mean Max. Min. Standard Deviation Incoming kappa36.9 46 28 3.20 Intermediate kappa 6.4 7.9 5.1 0.50 RESULTS OF CORMEC + POLAROX CONTROL
Mean Max. Min. Standard Deviation Incoming kappa33.6 44 28 3.27 Intermediate kappa 5.6 7!9 4.5 0.31 ,~ g , `.
In the embodiment examples presented above, the residual chem cals determination was made from the same process step as the forming of the control signal, or alternatively from the process step follow-ing after the forming of the control signal. If-desired, ho~ever, the residual chemicals determination may e~ually be made from the process step preceding the forming of the control signalJ i.e., before the optical measurement. This is particularly to be conte~-plated when the process involves Long delay periods. Thus, when the optiral delay is for instance on the order of 10 min., the residual content of chemicals may be determined, in time, e.g. 0-1 min. or even several minutes, such as 1-10 min., before the optical meas-urement.
The invention is not confined to the examples that have been pre-sented: its applications may vary within the scope of the claims following below. Then, the procedure in question, and the appara-tus, is appropriate for controlling the dispensing of any chemic21 whatsoever in connection with bleaching. Furthermore, the procedure and the apparatus may be used in connection with any kind of meth-ods of determination, and apparatus, for determining degree of bleaching and residual chemicals.
.
Claims (10)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. Procedure for controlling the cellulose bleaching process, the degree of bleaching of the pulp to be bleached being measured optically, on the basis of the optical measurement being formed a control signal corresponding to the pulp's degree of bleaching, and the dispensing of bleaching chemicals being controlled with the aid of said control signal, characterized in that from the pulp to be bleached is determined the residual content of the chemicals employed to the purpose of bleaching, on the basis of this determination a correction signal is formed, and the control signal is corrected by said correction signal.
2. Procedure according to claim 1, characterized in that the residual chemicals determination is made from the same process step as the forming of the control signal.
3. Procedure according to claim 1, characterized in that the residual. chemicals determination is made from the process step following after the forming of the control signal after the optical measurement.
4. Procedure according to any one of claims 1-3, characterized in that the bleaching is carried out by chlorination and that in the residual chemicals determination is determined the residual content of the chlorination chemicals.
5. Procedure according to any one of claims 1-3, characterized in that the optical measurement is carried out in the process step 0.5 to 3 min. after the chemicals dispensing.
6. Apparatus for controlling the cellulose bleaching process, comprising an optical measuring means for forming a control signal corresponding to the degree of bleaching of the pulp and a control. means for controlling the dispensing of bleaching chemicals under control by the control signal with the aid of dispensing means, characterized in that the apparatus comprises an analyser for determining the residual content of the chemicals used towards bleaching and for forming a corresponding correcting signal, this correction signal having been conducted to correct the control signal.
7. Apparatus according to claim 6, characterized in that the analyser has been connected to the same process step with the measuring means.
8. Apparatus according to claim 6, characterized in that the analyser has been connected to the process step after the optical measuring means.
9. Apparatus according to any one of claims 6-8, characterized in that the optical measuring means has been disposed in the process step after the dispensing means.
10. procedure according to claim 1, characterized in that the residual chemicals determination is made from the process step preceding the forming of the control signals before the optical measurement.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000416373A CA1221205A (en) | 1982-11-25 | 1982-11-25 | Procedure and apparatus for controlling the cellulose bleaching process |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000416373A CA1221205A (en) | 1982-11-25 | 1982-11-25 | Procedure and apparatus for controlling the cellulose bleaching process |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1221205A true CA1221205A (en) | 1987-05-05 |
Family
ID=4124025
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000416373A Expired CA1221205A (en) | 1982-11-25 | 1982-11-25 | Procedure and apparatus for controlling the cellulose bleaching process |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1221205A (en) |
-
1982
- 1982-11-25 CA CA000416373A patent/CA1221205A/en not_active Expired
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