CA1308913C - Chlorination control system - Google Patents
Chlorination control systemInfo
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- CA1308913C CA1308913C CA000550378A CA550378A CA1308913C CA 1308913 C CA1308913 C CA 1308913C CA 000550378 A CA000550378 A CA 000550378A CA 550378 A CA550378 A CA 550378A CA 1308913 C CA1308913 C CA 1308913C
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- chlorination
- pulp
- chlorine
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Abstract
CHLORINATION CONTROL SYSTEM
ABSTRACT OF THE DISCLOSURE
A control system and method of controlling the chlorination of pulp includes first and second mixers with chlorine additions to each mixer under the control of a flow controller. Chlorine is added under the control of the flow controller to the pulp in the first mixer to achieve a predetermined chlorination factor in response to a signal from a brightness sensor operating in a region where brightness is linearly responsive to the chlorination factor. The chlorinated pulp stream is fed to a second mixer where chlorine is added in relation (e.g. proportion) to the quantity of chlorine added into the first mixer to achieve a higher predetermined chlorination factor which is in a region where brightness is non-linearly responsive to the chlorination factor.
ABSTRACT OF THE DISCLOSURE
A control system and method of controlling the chlorination of pulp includes first and second mixers with chlorine additions to each mixer under the control of a flow controller. Chlorine is added under the control of the flow controller to the pulp in the first mixer to achieve a predetermined chlorination factor in response to a signal from a brightness sensor operating in a region where brightness is linearly responsive to the chlorination factor. The chlorinated pulp stream is fed to a second mixer where chlorine is added in relation (e.g. proportion) to the quantity of chlorine added into the first mixer to achieve a higher predetermined chlorination factor which is in a region where brightness is non-linearly responsive to the chlorination factor.
Description
~ 3 ~; ~
CELORINATION CONTROL SYSTEM
BACKGROUND AND SUMMARY OF T~ INVENTION
The present invention relates to a control system for the addition of a chemical, for example chlorine, for chemically bleaching pulps and particularly relates to a control system for adding chlorine to pulp in a manner to optimize delignification.
In the production of high-quality pulp, bleaching is used to delignify the pulp. Bleaching is usually carried out in a stepwise sequence using different chemicals and conditions at each stage, with washing between the stages. Chlorination and caustic extraction are usually employed as the first two stages in a pulp bleaching sequence.
Additionally, it has been common practice to apply a small portion of chlorine dioxide in the chlorination stage, displacing an equivalent amount of chlorine.
In a typical chlorination control system, brownstock is provided a first mixer and mixed with chlorine and chlorine dioxide. The bleached or chlorinated pulp stream flows to a second mixer and, subsequently, to a reactor. To control the addition of chlorine and chlorine dioxide to the first mixer, it is customary to employ a brightness sensor in the chlorinated pulp stream downstream of the second mixer. A flow controller responsive to a signal from the brightness sensor controls the chlorine and 13~~i~ 3 chlorine dioxide flow control valves to achieve a certain delignification level. For example, when operating at a .21% chlorination factor, that is, a .21% chlorine per Kappa number, 83% delignification is accomplished across the chlorination extraction.
It has been found desirable, however, to operate at a higher chlorination factor to achieve a higher delignification level. For example, it has been shown that operating at a .24 chlorination factor can achieve 87% delignification. Operations at this higher chlorination factor produce substantial savings in chemical in subsequent pulp processing stages.
However, attempts to operate at higher chlorination factors cause problems in controlling the chlorine addition to the pulp stream necessary to achieve this higher level of delignification. It will be appreciated that the conventional control for the addition of chlorine to a pulp stream is a brightness sensor, usually of the optical type, which senses the brightness of the pulp. In raising the chlorination factor, for example from .21 to .24, it has been found to be difficult to control the required additlonal quantity of chlorine to the pulp due to a lack of sensitivity of the brightness sensor to changes in brightness at those higher levels.
That is, the brightness at such levels ceases to be a well-behaved function of the chlorination factor.
More particularly, the brightness levels out as a function of the chlorination factor at a chlorination factor close to the desired operating chlorination 13(~3~ `
factor of about .24. It will be appreciated that it is important to accurately control the chlorine added to the pulp stream at these relatively high chlorination factors inasmuch as chlorination performance may actually decline when operating at a higher chlorination factor. Additionally, free chlorine gas can and will cause significant problems in the bleaching tower.
According to the present invention, accurate control of the dose of chlorine to achieve higher chlorination factors, for example on the order of .24, is achieved. This is accomplished by providing a first mixer for receiving pulp and a first chlorine addition for forming a pulp/chlorine mixture, a first valve in the chlorine supply conduit being provided to control the flow of chlorine to the first mixer.
A second mixer is also provided for receiving the chlorinated pulp stream from the first mixer and a second chlorine addition. A second valve is also provided in the conduit controlling the flow of the additional chlorine to the second mixer. A sensor is disposed in the chlorinated pulp stream downstream of the first mixer and prior to the second mixer for sensing a characteristic, i.e., brightness, of the chlorinated pulp stream from the first mixer and providing a signal in response thereto. A controller is provided in controlling relation to the first valve and is responsive to the signal to control the first valve to meter a predetermined quantity of the first chlorine addition to the first mixer. The controller is also arranged in controlling relation 13~13 to the second valve to meter an additional quantity of the second chlorine addition into the second mixer in relation (e.g. proportion) to the quantity of chlorine metered into the first mixer.
In this manner, the set point of the controller may be operated to provide a predetermined chlorination factor in the chlorinated pulp stream issuing from the first mixer at a level where the brightness is a well-behaved linear function of the chlorination factor. For example, it is possible to control the addition of chlorine to the first mixer at a chlorination factor of .18. At this chlorination factor, the brightness level is a well-defined linear function, whereby accurate control to that set point may be achieved.
Recognizing that the amount of chlorine added to the first mixer to achieve a particular chlorination factor is in a linear proportion to the total chlorine required to achieve the desired higher chlorination factor, chlorine may be added to the second mixer in proportion to the chlorine added to the first mixer. In short, the dosage of ch~orine to the first mixer is accurately controlled by the brightness sensor in the chlorinated pulp stream issuing from the first mixer to achieve a relatively low chlorination factor, while the remaining chlorine addition is provided the second mixer in a ratio to the chlorine added in the first mixer to achieve the targeted higher chlorination level in the chlorinated pulp stream issuing from the second mixer.
13~ 3 Accordingly, it is a primary object of the present invention to provide a control system for, and a method of, controlling the chlorination of pulp whereby accurate control of the flow of chlorine added to the pulp at relatively high chlorination factors is achieved and in a region where brightness is a non-linear function of the chlorination factor.
These and further objects and advantages of the present invention will become more apparent upon reference to the following specification, appended claims and drawings.
BRIEF DESCRIPTION OF TH~; DRAWING FIGURES
Figure 1 is a schematic representation of a typical chlorination control system of the prior art;
Figure 2 is a graph illustrating brightness as a function of chlorination factor; and Figure 3 is a schematic diagram of a chlorination control system constructed in accordance with the present invention.
DETAILED DESCRIPTION OF 'L~ DRAWING FIGURES
Reference will now be made in detail first to a typical chlorination control system of the prior art and then to a present preferred embodiment of the invention, an example of which is illustrated in Figure 3.
13~3~3 Referring first to Figure 1, there is illustrated a typical chlorination control system of the prior art, generally designated 10, comprised of a first mixer 12 to which brownstock is fed through a conduit 14. Both chlorine and chlorine dioxide, from suitable sources, not shown, are provided mixer 12 via conduits 16 and 18, respectively. Flow control valves 20 and 22 are also provided in each of the conduits 16 and 18, respectively, whereby the flow of chlorine and chlorine dioxide to mixer 12 may be metered. The flow through the valves is under the control of a controller 24 whereby the flow through the valves may be set at a set point dependent upon the desired chlorination factor.
The chlorinated pulp stream flows from mixer 12 through conduit 26 to a second mixer 28 and from there through conduit 30 to a reactor.
To control the chlorination of the pulp stream to a specified chlorination factor, a brightness sensor 32 is customarily disposed in the chlorinated pulp stream downstream of the second mixer 28 and provides an output signal to the controller 24. The output signal from brightness sensor 32 provides a measured value indicative of the brightness of the bleached pulp, and such signal is compared by the controller with a set point to provide an error signal. The controller acts to reduce the error by opening or closing the valves 22 and 24 in order to bring the chlorination factor toward the desired or targeted chlorination factor. The brightness sensor, 13`~J ~3 the controller and flow control valves are well known elements in prior chlorination control systems.
Referring now to Figure 2, there is disclosed a graph of compensated brightness versus chlorination factor which, as indicated above, is the percent chlorine per Kappa number. From a review of Figure 2, it will be appreciated that the brightness of the bleached pulp increases substantially linearly as the chlorination factor increases to a point where the curve substantially flattens out, commencing at about .23 or .24 chlorination factor. The control system illustrated in Figure l, and described above, has been used successfully for bleaching pulp with chlorination factors, for example up to .21. In the region up to and slightly beyond .21 chlorination factor, it will be appreciated that the brightness of the pulp constitutes a linear function of the chlorination factor. Thus, the conventional brightness sensor provides good, accurate response to the brightness of the chlorinated pulp and serves, in conjunction with the controller, to accurately maintain the chlorination factor at the set point, i.e., so long as brightness is a linear function of the chlorination factor.
However, it has been found that it is desirable to operate at a .24 chlorination factor to achieve increased delignification, for example on the order of 87%. However, accurate control over the chlorination of the pulp is difficult to obtain with that chlorination factor inasmuch as brightness is no 13~
longer a linear function of the chlorination factor at such higher chlorination factor. Thus, while the brightness sensor still senses brightness, it cannot discriminate at that brightness level over a wide range of chlorination factors. As stated above, it is particularly important not to over-chlorinate the pulp .
The present invention is directed to a chlorination control system which accurately controls the addition of chlorine to the pulp to achieve the higher chlorination factor. To achieve this, chlorine is added to the pulp to achieve a relatively low chlorination factor in a first chlorination stage. This can be readily achieved through the accurate control afforded by a brightness sensor in the first-stage chlorinated pulp stream because the brightness sensor operates in the linear portion of the curve illustrated in Figure 2. Thus, according to the present invention, chlorine is added in a first stage at a relatively low chlorination factor, which is determined by the set point of a controller. This is achieved by controlling the flow control valve to close the error signal between the set point and the actual chlorination as determined by the brightness sensor in the first-stage pulp/chlorine stage. To achieve the higher chlorination factor, for example on the order of .24, in the range where the brightness of the pulp does not vary sufficiently to indicate the desired chlorination factor, a flow control valve is provided for adding chlorine in a second mixer in a ratio that i8 related to the chlorine added in the first mixer.
The ratio may be proportional, but may also be otherwise related.
To accomplish the foregoing and with reference to Figure 3, there is illustrated a chlorination control system according to the present invention including a first mixer 40 to which brownstock is fed by a conduit 42. Flow conduits 44 and 46 are connected with suitable sources, not shown, of chlorine and chlorine dioxide, respectively, and serve to provide chlorine and chlorine dioxide to mixer 40. Control valves 48 and 50 are provided in the conduits 44 and 46, respectively, to regulate the flow to the mixer. The chlorinated pulp stream is transmitted via a conduit 52 to a second mixer 54.
Additional chlorine and chlorine dioxide are added to the chlorinated pulp stream in the second mixer 54 via conduits 56 and 58, respectively. Flow control valves 60 and 62 are also provided in conduits 56 and 58.
In accordance with the present invention, the flow control valves 48 and 50 in the first stage of chlorination, as well as the flow control valves 60 and 62 in the second stage of chlorination, are under the control of a controller 64. A brightness sensor 66 is disposed in conduit 52 to sense the brightness of the chlorinated pulp stream issuing from mixer 40. The brightness sensor provides a signal indicative of the degree of chlorination to controller 64, which is set by the operator at a predetermined set point to provide a predetermined chlorination of the chlorinated pulp stream 52. As in the prior system disclosed in Figure 1, the controller reduces the error between the detected brightness (chlorination) and the desired brightness (chlorination) determined by the set point of the controller by operating the valves 48 and 50 to open or close to a greater or lesser extent, depending upon the need for greater or lesser quantities of chlorine and chlorine dioxide, respectively.
In accordance with the present invention, the set point of the flow controller 64 is set at a relatively low chlorination factor such that the response of the brightness sensor 66 to the brightness of the chlorinated pulp stream in conduit 52 lies in the linear range of the curve illustrated in Figure 2. Thus, sufficient chlorine and chlorine dioxide are added to the mixer 40 to achieve the set point, for example, .18~ chlorination factor. It will be recalled, however, that it is desirable to operate at a chlorination factor of about .24% in order to achieve high delignification levels. The additional necessary chlorination is achieved by controlling the flow through the flow valves 60 and 62 under control from the controller 64. The valves 60 and 62 are controlled to ratio the additional chlorine and chlorine dioxide to the mixer in proportion to the chlorine and chlorine dioxide added to the first-stage mixer sufficiently to reach the targeted or desired chlorination factor of .24%.
For example, if .24% chlorination factor is desired and the set point of the controller 64 controlling valves 48 and 50 is set at .18%
chlorination factor, it will be recognized that an additional 33% of the added chlorine and chlorine dioxide is necessary to achieve the targeted .24%
chlorination factor. The controller 64 controls valves 60 and 62 to add that extra increment of chlorine and chlorine dioxide whereby the chlorinated pulp stream issuing from mixer 54 is at the 24%
chlorination factor. Consequently, the desired chlorination factor is achieved accurately by adding chlorine and chlorine dioxide in the first stage at a relatively low chlorination factor controlled by a brightness sensor operating in the region where it is a linear function of the chlorination factor and subsequently related (e.g. proportioning) the flow of chlorine and chlorine dioxide to the chlorinated pulp stream in the second stage in accordance with the chlorine and chlorine dioxide added in the first-stage chlorination. Thus, the desired higher level chlorination factor is accurately achieved.
While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
CELORINATION CONTROL SYSTEM
BACKGROUND AND SUMMARY OF T~ INVENTION
The present invention relates to a control system for the addition of a chemical, for example chlorine, for chemically bleaching pulps and particularly relates to a control system for adding chlorine to pulp in a manner to optimize delignification.
In the production of high-quality pulp, bleaching is used to delignify the pulp. Bleaching is usually carried out in a stepwise sequence using different chemicals and conditions at each stage, with washing between the stages. Chlorination and caustic extraction are usually employed as the first two stages in a pulp bleaching sequence.
Additionally, it has been common practice to apply a small portion of chlorine dioxide in the chlorination stage, displacing an equivalent amount of chlorine.
In a typical chlorination control system, brownstock is provided a first mixer and mixed with chlorine and chlorine dioxide. The bleached or chlorinated pulp stream flows to a second mixer and, subsequently, to a reactor. To control the addition of chlorine and chlorine dioxide to the first mixer, it is customary to employ a brightness sensor in the chlorinated pulp stream downstream of the second mixer. A flow controller responsive to a signal from the brightness sensor controls the chlorine and 13~~i~ 3 chlorine dioxide flow control valves to achieve a certain delignification level. For example, when operating at a .21% chlorination factor, that is, a .21% chlorine per Kappa number, 83% delignification is accomplished across the chlorination extraction.
It has been found desirable, however, to operate at a higher chlorination factor to achieve a higher delignification level. For example, it has been shown that operating at a .24 chlorination factor can achieve 87% delignification. Operations at this higher chlorination factor produce substantial savings in chemical in subsequent pulp processing stages.
However, attempts to operate at higher chlorination factors cause problems in controlling the chlorine addition to the pulp stream necessary to achieve this higher level of delignification. It will be appreciated that the conventional control for the addition of chlorine to a pulp stream is a brightness sensor, usually of the optical type, which senses the brightness of the pulp. In raising the chlorination factor, for example from .21 to .24, it has been found to be difficult to control the required additlonal quantity of chlorine to the pulp due to a lack of sensitivity of the brightness sensor to changes in brightness at those higher levels.
That is, the brightness at such levels ceases to be a well-behaved function of the chlorination factor.
More particularly, the brightness levels out as a function of the chlorination factor at a chlorination factor close to the desired operating chlorination 13(~3~ `
factor of about .24. It will be appreciated that it is important to accurately control the chlorine added to the pulp stream at these relatively high chlorination factors inasmuch as chlorination performance may actually decline when operating at a higher chlorination factor. Additionally, free chlorine gas can and will cause significant problems in the bleaching tower.
According to the present invention, accurate control of the dose of chlorine to achieve higher chlorination factors, for example on the order of .24, is achieved. This is accomplished by providing a first mixer for receiving pulp and a first chlorine addition for forming a pulp/chlorine mixture, a first valve in the chlorine supply conduit being provided to control the flow of chlorine to the first mixer.
A second mixer is also provided for receiving the chlorinated pulp stream from the first mixer and a second chlorine addition. A second valve is also provided in the conduit controlling the flow of the additional chlorine to the second mixer. A sensor is disposed in the chlorinated pulp stream downstream of the first mixer and prior to the second mixer for sensing a characteristic, i.e., brightness, of the chlorinated pulp stream from the first mixer and providing a signal in response thereto. A controller is provided in controlling relation to the first valve and is responsive to the signal to control the first valve to meter a predetermined quantity of the first chlorine addition to the first mixer. The controller is also arranged in controlling relation 13~13 to the second valve to meter an additional quantity of the second chlorine addition into the second mixer in relation (e.g. proportion) to the quantity of chlorine metered into the first mixer.
In this manner, the set point of the controller may be operated to provide a predetermined chlorination factor in the chlorinated pulp stream issuing from the first mixer at a level where the brightness is a well-behaved linear function of the chlorination factor. For example, it is possible to control the addition of chlorine to the first mixer at a chlorination factor of .18. At this chlorination factor, the brightness level is a well-defined linear function, whereby accurate control to that set point may be achieved.
Recognizing that the amount of chlorine added to the first mixer to achieve a particular chlorination factor is in a linear proportion to the total chlorine required to achieve the desired higher chlorination factor, chlorine may be added to the second mixer in proportion to the chlorine added to the first mixer. In short, the dosage of ch~orine to the first mixer is accurately controlled by the brightness sensor in the chlorinated pulp stream issuing from the first mixer to achieve a relatively low chlorination factor, while the remaining chlorine addition is provided the second mixer in a ratio to the chlorine added in the first mixer to achieve the targeted higher chlorination level in the chlorinated pulp stream issuing from the second mixer.
13~ 3 Accordingly, it is a primary object of the present invention to provide a control system for, and a method of, controlling the chlorination of pulp whereby accurate control of the flow of chlorine added to the pulp at relatively high chlorination factors is achieved and in a region where brightness is a non-linear function of the chlorination factor.
These and further objects and advantages of the present invention will become more apparent upon reference to the following specification, appended claims and drawings.
BRIEF DESCRIPTION OF TH~; DRAWING FIGURES
Figure 1 is a schematic representation of a typical chlorination control system of the prior art;
Figure 2 is a graph illustrating brightness as a function of chlorination factor; and Figure 3 is a schematic diagram of a chlorination control system constructed in accordance with the present invention.
DETAILED DESCRIPTION OF 'L~ DRAWING FIGURES
Reference will now be made in detail first to a typical chlorination control system of the prior art and then to a present preferred embodiment of the invention, an example of which is illustrated in Figure 3.
13~3~3 Referring first to Figure 1, there is illustrated a typical chlorination control system of the prior art, generally designated 10, comprised of a first mixer 12 to which brownstock is fed through a conduit 14. Both chlorine and chlorine dioxide, from suitable sources, not shown, are provided mixer 12 via conduits 16 and 18, respectively. Flow control valves 20 and 22 are also provided in each of the conduits 16 and 18, respectively, whereby the flow of chlorine and chlorine dioxide to mixer 12 may be metered. The flow through the valves is under the control of a controller 24 whereby the flow through the valves may be set at a set point dependent upon the desired chlorination factor.
The chlorinated pulp stream flows from mixer 12 through conduit 26 to a second mixer 28 and from there through conduit 30 to a reactor.
To control the chlorination of the pulp stream to a specified chlorination factor, a brightness sensor 32 is customarily disposed in the chlorinated pulp stream downstream of the second mixer 28 and provides an output signal to the controller 24. The output signal from brightness sensor 32 provides a measured value indicative of the brightness of the bleached pulp, and such signal is compared by the controller with a set point to provide an error signal. The controller acts to reduce the error by opening or closing the valves 22 and 24 in order to bring the chlorination factor toward the desired or targeted chlorination factor. The brightness sensor, 13`~J ~3 the controller and flow control valves are well known elements in prior chlorination control systems.
Referring now to Figure 2, there is disclosed a graph of compensated brightness versus chlorination factor which, as indicated above, is the percent chlorine per Kappa number. From a review of Figure 2, it will be appreciated that the brightness of the bleached pulp increases substantially linearly as the chlorination factor increases to a point where the curve substantially flattens out, commencing at about .23 or .24 chlorination factor. The control system illustrated in Figure l, and described above, has been used successfully for bleaching pulp with chlorination factors, for example up to .21. In the region up to and slightly beyond .21 chlorination factor, it will be appreciated that the brightness of the pulp constitutes a linear function of the chlorination factor. Thus, the conventional brightness sensor provides good, accurate response to the brightness of the chlorinated pulp and serves, in conjunction with the controller, to accurately maintain the chlorination factor at the set point, i.e., so long as brightness is a linear function of the chlorination factor.
However, it has been found that it is desirable to operate at a .24 chlorination factor to achieve increased delignification, for example on the order of 87%. However, accurate control over the chlorination of the pulp is difficult to obtain with that chlorination factor inasmuch as brightness is no 13~
longer a linear function of the chlorination factor at such higher chlorination factor. Thus, while the brightness sensor still senses brightness, it cannot discriminate at that brightness level over a wide range of chlorination factors. As stated above, it is particularly important not to over-chlorinate the pulp .
The present invention is directed to a chlorination control system which accurately controls the addition of chlorine to the pulp to achieve the higher chlorination factor. To achieve this, chlorine is added to the pulp to achieve a relatively low chlorination factor in a first chlorination stage. This can be readily achieved through the accurate control afforded by a brightness sensor in the first-stage chlorinated pulp stream because the brightness sensor operates in the linear portion of the curve illustrated in Figure 2. Thus, according to the present invention, chlorine is added in a first stage at a relatively low chlorination factor, which is determined by the set point of a controller. This is achieved by controlling the flow control valve to close the error signal between the set point and the actual chlorination as determined by the brightness sensor in the first-stage pulp/chlorine stage. To achieve the higher chlorination factor, for example on the order of .24, in the range where the brightness of the pulp does not vary sufficiently to indicate the desired chlorination factor, a flow control valve is provided for adding chlorine in a second mixer in a ratio that i8 related to the chlorine added in the first mixer.
The ratio may be proportional, but may also be otherwise related.
To accomplish the foregoing and with reference to Figure 3, there is illustrated a chlorination control system according to the present invention including a first mixer 40 to which brownstock is fed by a conduit 42. Flow conduits 44 and 46 are connected with suitable sources, not shown, of chlorine and chlorine dioxide, respectively, and serve to provide chlorine and chlorine dioxide to mixer 40. Control valves 48 and 50 are provided in the conduits 44 and 46, respectively, to regulate the flow to the mixer. The chlorinated pulp stream is transmitted via a conduit 52 to a second mixer 54.
Additional chlorine and chlorine dioxide are added to the chlorinated pulp stream in the second mixer 54 via conduits 56 and 58, respectively. Flow control valves 60 and 62 are also provided in conduits 56 and 58.
In accordance with the present invention, the flow control valves 48 and 50 in the first stage of chlorination, as well as the flow control valves 60 and 62 in the second stage of chlorination, are under the control of a controller 64. A brightness sensor 66 is disposed in conduit 52 to sense the brightness of the chlorinated pulp stream issuing from mixer 40. The brightness sensor provides a signal indicative of the degree of chlorination to controller 64, which is set by the operator at a predetermined set point to provide a predetermined chlorination of the chlorinated pulp stream 52. As in the prior system disclosed in Figure 1, the controller reduces the error between the detected brightness (chlorination) and the desired brightness (chlorination) determined by the set point of the controller by operating the valves 48 and 50 to open or close to a greater or lesser extent, depending upon the need for greater or lesser quantities of chlorine and chlorine dioxide, respectively.
In accordance with the present invention, the set point of the flow controller 64 is set at a relatively low chlorination factor such that the response of the brightness sensor 66 to the brightness of the chlorinated pulp stream in conduit 52 lies in the linear range of the curve illustrated in Figure 2. Thus, sufficient chlorine and chlorine dioxide are added to the mixer 40 to achieve the set point, for example, .18~ chlorination factor. It will be recalled, however, that it is desirable to operate at a chlorination factor of about .24% in order to achieve high delignification levels. The additional necessary chlorination is achieved by controlling the flow through the flow valves 60 and 62 under control from the controller 64. The valves 60 and 62 are controlled to ratio the additional chlorine and chlorine dioxide to the mixer in proportion to the chlorine and chlorine dioxide added to the first-stage mixer sufficiently to reach the targeted or desired chlorination factor of .24%.
For example, if .24% chlorination factor is desired and the set point of the controller 64 controlling valves 48 and 50 is set at .18%
chlorination factor, it will be recognized that an additional 33% of the added chlorine and chlorine dioxide is necessary to achieve the targeted .24%
chlorination factor. The controller 64 controls valves 60 and 62 to add that extra increment of chlorine and chlorine dioxide whereby the chlorinated pulp stream issuing from mixer 54 is at the 24%
chlorination factor. Consequently, the desired chlorination factor is achieved accurately by adding chlorine and chlorine dioxide in the first stage at a relatively low chlorination factor controlled by a brightness sensor operating in the region where it is a linear function of the chlorination factor and subsequently related (e.g. proportioning) the flow of chlorine and chlorine dioxide to the chlorinated pulp stream in the second stage in accordance with the chlorine and chlorine dioxide added in the first-stage chlorination. Thus, the desired higher level chlorination factor is accurately achieved.
While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
Claims (21)
1. A control system for bleaching pulp comprising:
a first mixer for mixing pulp and a first chemical and forming a first pulp stream;
a first valve for controlling the flow of chemical to said first mixer;
a second mixer for mixing said first pulp stream and a second chemical;
a second valve for controlling the flow of the second chemical to said second mixer;
a sensor for sensing a characteristic of the first pulp stream and providing a signal in response thereto;
a controller arranged in controlling relation to said first flow control valve and responsive to said signal to control said first flow control valve to meter a quantity of the first chemical to said first mixer; and means for controlling said second flow control valve to meter a quantity of the second chemical into said second mixer related to the quantity of the the first chemical metered into said first mixer.
a first mixer for mixing pulp and a first chemical and forming a first pulp stream;
a first valve for controlling the flow of chemical to said first mixer;
a second mixer for mixing said first pulp stream and a second chemical;
a second valve for controlling the flow of the second chemical to said second mixer;
a sensor for sensing a characteristic of the first pulp stream and providing a signal in response thereto;
a controller arranged in controlling relation to said first flow control valve and responsive to said signal to control said first flow control valve to meter a quantity of the first chemical to said first mixer; and means for controlling said second flow control valve to meter a quantity of the second chemical into said second mixer related to the quantity of the the first chemical metered into said first mixer.
2. A control system according to Claim 1 wherein said first and second chemicals are both chlorine.
3. A control system according to Claim 2 including means for flowing chlorine dioxide to said first mixer.
4. A control system according to Claim 2 including means for flowing chlorine dioxide to said second mixer.
5. A control system according to Claim 2 including means for flowing chlorine dioxide to both said first and second mixers.
6. A control system according to Claim 2 including means for flowing chlorine dioxide to said first mixer, a third valve for controlling the flow of chlorine dioxide to said first mixer;
means for flowing chlorine dioxide to said second mixer, a fourth valve for controlling the flow of chlorine dioxide to said second mixer;
said controller being arranged in controlling relation to said third valve and responsive to said signal to control said first and third valves to meter quantities of chlorine and chlorine dioxide, respectively, to said first mixer; and means for controlling said second and fourth valves to meter quantities of chlorine and chlorine dioxide, respectively, into said second mixer in proportion to the quantities of chlorine and chlorine dioxide metered into the first mixer.
means for flowing chlorine dioxide to said second mixer, a fourth valve for controlling the flow of chlorine dioxide to said second mixer;
said controller being arranged in controlling relation to said third valve and responsive to said signal to control said first and third valves to meter quantities of chlorine and chlorine dioxide, respectively, to said first mixer; and means for controlling said second and fourth valves to meter quantities of chlorine and chlorine dioxide, respectively, into said second mixer in proportion to the quantities of chlorine and chlorine dioxide metered into the first mixer.
7. A method of controlling the chlorination of pulp comprising the steps of:
feeding pulp to a first mixer;
flowing chlorine to said first mixer;
mixing the pulp and chlorine in the first mixer and forming a chlorinated pulp stream;
feeding the chlorinated pulp stream from the first mixer to a second mixer;
flowing chlorine to said second mixer;
sensing the brightness of the chlorinated pulp stream from said first mixer and providing a signal in response thereto;
controlling the flow of chlorine to said first mixer in response to said signal to meter a quantity of chlorine to said first mixer to obtain a chlorination level less than a predetermined chlorination level; and controlling the flow of chlorine to said second mixer related to the quantity of chlorine metered to said first mixer to provide pulp issuing from said second mixer with said predetermined chlorination level.
feeding pulp to a first mixer;
flowing chlorine to said first mixer;
mixing the pulp and chlorine in the first mixer and forming a chlorinated pulp stream;
feeding the chlorinated pulp stream from the first mixer to a second mixer;
flowing chlorine to said second mixer;
sensing the brightness of the chlorinated pulp stream from said first mixer and providing a signal in response thereto;
controlling the flow of chlorine to said first mixer in response to said signal to meter a quantity of chlorine to said first mixer to obtain a chlorination level less than a predetermined chlorination level; and controlling the flow of chlorine to said second mixer related to the quantity of chlorine metered to said first mixer to provide pulp issuing from said second mixer with said predetermined chlorination level.
8. A method according to Claim 7 including flowing chlorine dioxide to said first mixer, mixing the pulp, chlorine and chlorine dioxide in the first mixer to form the chlorinated pulp stream, flowing chlorine dioxide to said second mixer, controlling the flow of chlorine dioxide to said first mixer in response to said signal to meter a quantity of chlorine dioxide to said first mixer to obtain a chlorination level less than a predetermined chlorination level and controlling the flow of chlorine dioxide to said second mixer in proportion to the quantity of chlorine dioxide metered to said first mixer to provide pulp issuing from said second mixer with said predetermined chlorination level.
9. A method according to Claim 7 wherein the predetermined chlorination level corresponds to a chlorination factor which lies in a region where brightness is a non-linear function of the chlorination factor.
10. A method according to Claim 7 wherein the chlorination level less than the predetermined chlorination level corresponds to a chlorination factor which lies in a region where brightness is a linear function of the chlorination factor.
11. A method according to Claim 7 wherein the flow of chlorine to the second mixer is proportional to the quantity of chlorine metered to the first mixer.
12. A method according to Claim 8 wherein the predetermined chlorination level corresponds to a chlorination factor which lies in a region where brightness is a non-linear function of the chlorination factor less than the predetermined chlorination factor.
13. A method of controlling the chlorination of pulp comprising the steps of providing a pulp stream;
providing a first flow of chlorine into the pulp stream to establish a first chlorinated pulp flow stream;
establishing a desired predetermined chlorination factor for the pulp;
adjusting the flow of chlorine to the pulp stream to obtain a chlorination factor for said first chlorinated pulp flow stream less than the predetermined chlorination factor;
providing a second flow of chlorine into the first chlorinated pulp stream at a location therealong downstream from the establishment of the first chlorinated pulp flow stream; and adjusting the second flow of chlorine into the first chlorinated pulp flow stream in relation to the first mentioned flow of chlorine into the pulp stream to obtain said predetermined chlorination factor.
providing a first flow of chlorine into the pulp stream to establish a first chlorinated pulp flow stream;
establishing a desired predetermined chlorination factor for the pulp;
adjusting the flow of chlorine to the pulp stream to obtain a chlorination factor for said first chlorinated pulp flow stream less than the predetermined chlorination factor;
providing a second flow of chlorine into the first chlorinated pulp stream at a location therealong downstream from the establishment of the first chlorinated pulp flow stream; and adjusting the second flow of chlorine into the first chlorinated pulp flow stream in relation to the first mentioned flow of chlorine into the pulp stream to obtain said predetermined chlorination factor.
14. A method according to Claim 13 wherein the chlorination factor for the first pulp flow stream lies in a region where brightness is a linear function of the chlorination factor.
15. A method according to Claim 13 wherein the predetermined chlorination factor lies in a region where brightness is a non-linear function of the chlorination factor.
16. A method according to Claim 15 wherein the chlorination factor for the first pulp flow stream lies in a region where brightness is a linear function of the chlorination factor.
17. A method according to Claim 13 including providing a first flow of chlorine dioxide into the pulp stream to establish the first chlorinated pulp flow stream, adjusting the flow of chlorine dioxide to the pulp stream to obtain said chlorinated pulp flow stream less than the predetermined first chlorination factor, providing a second flow of chlorine dioxide into the first chlorinated pulp stream at a location downstream of the first chlorinated pulp flow stream, and adjusting the
18 second flow of chlorine dioxide into the chlorinated first pulp stream in proportion to the first mentioned flow of chlorine dioxide into the pulp stream to obtain said predetermined chlorination factor.
18. A method according to Claim 17 wherein the chlorination factor for the first pulp flow stream lies in a region where brightness is a linear function of the chlorination factor.
18. A method according to Claim 17 wherein the chlorination factor for the first pulp flow stream lies in a region where brightness is a linear function of the chlorination factor.
19. A method according to Claim 17 wherein the predetermined chlorination factor lies in a region where brightness is a non-linear function of the chlorination factor.
20. A method according to Claim 19 wherein the chlorination factor for the first pulp flow stream lies in a region where brightness is a linear function of the chlorination factor.
21. A method according to Claim 13 wherein the flow of chlorine to the second mixer is in proportion to the quantity of chlorine metered to the first mixer.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US4273587A | 1987-04-27 | 1987-04-27 | |
| US042,735 | 1987-04-27 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1308913C true CA1308913C (en) | 1992-10-20 |
Family
ID=21923480
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000550378A Expired - Lifetime CA1308913C (en) | 1987-04-27 | 1987-10-27 | Chlorination control system |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1308913C (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6153300A (en) | 1994-04-18 | 2000-11-28 | Ahlstrom Machinery, Inc. | Bleaching cellulose pulp having cleanliness which varies significantly over time using at least two different bleaching stages and bleaching chemicals |
-
1987
- 1987-10-27 CA CA000550378A patent/CA1308913C/en not_active Expired - Lifetime
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6153300A (en) | 1994-04-18 | 2000-11-28 | Ahlstrom Machinery, Inc. | Bleaching cellulose pulp having cleanliness which varies significantly over time using at least two different bleaching stages and bleaching chemicals |
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