FIELD OF THE INVENTION The invention relates to processes and apparatuses for deriving information from liquor obtained in the course of a wood digestion reaction. The information can be used to regulate one or more aspects of the wood digestion reaction either automatically or by communicating the information to a human operator that can take the appropriate process control actions. The information can also be used, to regulate processes different from the wood digestion reaction but that depend to at least some extent on the way the wood digestion reaction is being carried out. One example of such other processes is a pulp bleaching process. Another example is a process for burning the liquor from the digester as a source of heat. A further example is a process for fermenting wood sugars in the liquor from the digester to produce alcohol.

BACKGROUND OF THE INVENTION

In the pulp and paper industry, chemical pulping refers to a process of producing pulp using raw wood chips by extracting cellulose fibers from the wood material. Typically, raw wood chips and a solution of active chemicals known as a cooking liquor are combined, at a controlled pressure and temperature, in a vessel known as a digester. A wood digestion reaction occurs in the digester whereby the cellulose fibers, or pulp, are extracted from the wood material by breaking down the lignin which binds the fibers together. Specifically, the active chemicals in the cooking liquor react with the lignin in the wood material such as to break down the lignin and separate the cellulose fibers. The cooking liquor in the digester changes in composition during the wood digestion reaction and contains a varying amount of lignin removed from the wood chips.

When pulp having certain characteristics is desired, the pulp produced by the wood digestion reaction is usually passed to a bleaching section. In the bleaching section, the pulp is subjected to the action of bleaching solutions to modify the cellulose fibers.

In some conventional pulp producing lines, liquor spent during the wood digestion reaction in the digester is recuperated and utilized in various processes. For instance, spent liquor from the digester is often combusted in a combustion device and thus provides a source of heat for the digester or any other equipment of the pulp making line that requires heating. Also, spent liquor from the digester is sometimes recuperated and stored in a fermentation tank where wood sugars in the liquor are allowed to ferment in order to produce alcohol.

In order to produce pulp having a certain yield and certain desired characteristics, it is desirable to obtain real-time information on the pulp being produced. In particular, it is desirable to obtain real-time information on characteristics of the pulp produced during the wood digestion reaction. The information would be useful in regulating one or more aspects of the wood digestion reaction either automatically or by communicating the information to a human operator that could take the appropriate process control actions. However, the pulp in the digester is not readily accessible during the wood digestion reaction. Hence, direct analysis of the pulp in the digester is typically not a suitable option to obtain information on the pulp.

Furthermore, in order to increase the efficiency of the various processes that utilize spent liquor recuperated from the digester, it is desirable to obtain real-time information on the liquor itself. The information would be useful in regulating one or more aspects of these various processes, such as the combustion of the liquor as a source of heat or the fermentation of wood sugars in the liquor to produce alcohol, either automatically or by communicating the information to a human operator that could take the appropriate process control actions.

There is therefore a need in the industry to provide a method and an apparatus for deriving information from liquor obtained in the course of a wood digestion reaction that alleviate at least in part the problems associated with existing methods and apparatuses.

SUMMARY OF THE INVENTION

In accordance with a first broad aspect, the invention provides an apparatus for deriving information from liquor obtained in the course of a wood digestion reaction for producing pulp. The apparatus comprises an electromagnetic radiation source for subjecting the liquor to electromagnetic radiation, the liquor inducing a change in the electromagnetic radiation. The apparatus also comprises a sensor for picking up the electromagnetic radiation with the induced change. The apparatus further comprises a processing unit receiving information from the sensor conveying the induced change and deriving at least in part on a basis of the induced change viscosity and kappa information on the pulp.

In a specific non-limiting example of implementation, the sensor picks up near-infrared radiation in the electromagnetic radiation with the induced change.

In accordance with a second broad aspect, the invention provides a method for deriving information from liquor obtained in the course of a wood digestion reaction for producing pulp. The method comprises subjecting the liquor to electromagnetic radiation, the liquor inducing a change in the electromagnetic radiation. The method also comprises sensing the electromagnetic radiation with the induced change to obtain data conveying the induced change. The method further comprises processing the data conveying the induced change to derive at least in part on a basis of the induced change viscosity and kappa information on the pulp.

In accordance with a third broad aspect, the invention provides a wood digester comprising a vessel for holding pulp and liquor. The wood digester also comprises an electromagnetic radiation source for subjecting liquor from the vessel to electromagnetic radiation, the liquor inducing a change in the electromagnetic radiation. The wood digester further comprises a sensor for picking up the electromagnetic radiation with the induced change, and a processing unit receiving information from the sensor conveying the induced change and deriving at least in part on a basis of the induced change viscosity and kappa information on the pulp.

In accordance with a fourth broad aspect, the invention provides an apparatus for deriving information from liquor obtained in the course of a wood digestion reaction for producing pulp. The apparatus comprises an electromagnetic radiation source for subjecting the liquor to electromagnetic radiation, the liquor inducing a change in the electromagnetic radiation. The apparatus also comprises a sensor for measuring the electromagnetic radiation with the induced change and outputting data conveying spectra information relating to the electromagnetic radiation with the induced change. The apparatus further comprises a processing unit in communication with the sensor. The processing unit includes a data reduction filter for processing the spectra information to produce filtered spectra information, and an analysis unit for deriving at least in part on a basis of the filtered spectra information at least one characteristic of the pulp.

In a specific non-limiting example of implementation, the at least one characteristic of the pulp is the pulp viscosity. In another specific non-limiting example of implementation, the at least one characteristic of the pulp is the pulp kappa number. In accordance with a fifth broad aspect, the invention provides a method for deriving information from liquor obtained in the course of a wood digestion reaction for producing pulp. The method comprises subjecting the liquor to electromagnetic radiation, the liquor inducing a change in the electromagnetic radiation. The method also comprises sensing the electromagnetic radiation with the induced change and outputting data conveying spectra information relating to the electromagnetic radiation with the induced change. The method further comprises processing the spectra information with a data reduction filter to produce filtered spectra information, and deriving at least in part on a basis of the filtered spectra information at least one characteristic of the pulp.

In accordance with a sixth broad aspect, the invention provides a wood digester comprising a vessel for holding pulp and liquor. The wood digester also comprises an electromagnetic radiation source for subjecting the liquor to electromagnetic radiation, the liquor inducing a change in the electromagnetic radiation. The wood digester further comprises a sensor for measuring the electromagnetic radiation with the induced change and outputting data conveying spectra information relating to the electromagnetic radiation with the induced change. The wood digester also comprises a processing unit in communication with the sensor. The processing unit includes a data reduction filter for processing the spectra information to produce filtered spectra information, and an analysis unit for deriving at least in part on a basis of the filtered spectra information at least one characteristic of the pulp.

In accordance with a seventh broad aspect, the invention provides an apparatus for deriving information from liquor obtained in the course of a wood digestion reaction for producing pulp. The apparatus comprises an electromagnetic radiation source for subjecting the liquor to electromagnetic radiation, the liquor inducing a change in the electromagnetic radiation. The apparatus also comprises a sensor for picking up the electromagnetic radiation with the induced change. The apparatus further comprises a processing unit receiving information from the sensor conveying the induced change and deriving at least in part on a basis of the induced change information on a degree of purity of the pulp.

In accordance with a eighth broad aspect, the invention provides a method for deriving information from liquor obtained in the course of a wood digestion reaction for producing pulp. The method comprises subjecting the liquor to electromagnetic radiation, the liquor inducing a change in the electromagnetic radiation. The method also comprises sensing the electromagnetic radiation with the induced change. The method further comprises deriving at least in part on a basis of the induced change information on a degree of purity of the pulp.

In accordance with a ninth broad aspect, the invention provides an apparatus for bleaching pulp. The apparatus comprises a treatment area for receiving pulp to be bleached. The apparatus also comprises a control unit for regulating an intensity of a pulp bleaching process effected by the apparatus. The control unit is responsive, to a control signal derived from analysis of liquor obtained in the course of a wood digestion reaction for producing pulp.

In accordance with a tenth broad aspect, the invention provides a method for bleaching pulp. The method comprises loading pulp to be bleached in a treatment area. The method also comprises regulating an intensity of a pulp bleaching process in response to a control signal derived from analysis of liquor obtained in the course of a wood digestion reaction for producing pulp.

In accordance with an eleventh broad aspect, the invention provides an apparatus for deriving information from liquor obtained in the course of a wood digestion reaction for producing pulp. The apparatus comprises a source for subjecting the liquor to electromagnetic radiation, the liquor inducing a change in the electromagnetic radiation. The apparatus also comprises a sensor for picking up the electromagnetic radiation with the induced change. The apparatus further comprises a processing unit receiving information from the sensor conveying the induced change and deriving at least in part on a basis of the -induced change information on heat energy that can be produced by burning the liquor.

In accordance with a twelfth broad aspect, the invention provides a method for deriving information from liquor obtained in the course of a wood digestion reaction for producing pulp. The method comprises subjecting the liquor to electromagnetic radiation, the liquor inducing a change in the electromagnetic radiation. The method also comprises sensing the electromagnetic radiation with the induced change. The method further comprises processing the induced change and deriving at least in part on a basis of the induced change information on heat energy that can be produced by burning the liquor.

In accordance with a thirteenth broad aspect, the invention provides a combustion device. The combustion device comprises an inlet for receiving fuel to be burned, the fuel including liquor obtained in the course of a wood digestion reaction. The combustion device also comprises a control unit for regulating a' combustion of the fuel at least in part on a basis of the composition of the liquor.

In accordance with a fourteenth broad aspect, the invention provides an apparatus for deriving information from liquor obtained in the course of a wood digestion reaction for producing pulp. The apparatus comprises an electromagnetic radiation source for subjecting the liquor to electromagnetic radiation, the liquor inducing a change in the electromagnetic radiation. The apparatus also comprises a sensor for picking up the electromagnetic radiation with the induced change. The apparatus further comprises a processing unit receiving data from the sensor conveying the induced change and deriving at least in part on a basis of the induced change at least one characteristic of the pulp. The processing unit includes a data validation module for determining whether the data received from the sensor is unreliable as a basis for deriving the at least one characteristic of the pulp. BRIEF DESCRIPTION OF THE DRAWINGS A detailed description of examples of implementation of the present invention is provided hereinbelow with reference to the following drawings, in which:

Figure 1 is a high-level block diagram of the main components of a pulp making line;

Figure 2 is a more detailed block diagram of the process controller in the pulp making line of Figure 1;

Figure 3 is a more detailed block diagram of the processing unit of the process controller in Figure 2;

Figure 4 is a block diagram of an example of a procedure for building the calibration model of the processing unit in Figure 3;

Figure 5 is a block diagram of a first non-limiting example of implementation of the invention where the information delivered by the process controller is delivered to a user interface;

Figure 6 is a block diagram of a second non-limiting example of implementation of the invention where the information delivered by the process controller is delivered to a device for regulating the operation of a wood digester; Figure 7 is a block diagram of a third non-limiting example of implementation of the invention where the information delivered by the process controller is delivered to a device for regulating the combustion of the liquor obtained in the course of a wood digestion reaction;

Figure 8 is a block diagram of a fourth non-limiting example of implementation of the invention where the information delivered by the process controller is delivered to a device for regulating the fermentation of sugars in the liquor obtained in the course of a wood digestion reaction;

Figure 9 is a block diagram of a fifth non-limiting example of implementation of the invention where the information delivered by the process controller is delivered to a device for regulating a pulp bleaching process; and

Figure 10 is a block diagram of the processing unit of the process controller in Figure 2 wherein the processing unit includes a data validation module.

In the drawings, embodiments of the invention are illustrated by way of example. It is to be expressly understood that the description and drawings are only for purposes of illustration and as an aid to understanding, and are not intended to be a definition of the limits of the invention. DETAILED DESCRIPTION

Figure 1 is a high-level block diagram of the main components of a pulp making line. The pulp making line includes a digester 10 that receives wood chips 12 and a solution known as a cooking liquor 13. In a sulfite process, the cooking liquor 13 includes sulfite and, in a sulfate (or kraft) process, the cooking liquor 13 includes sodium hydroxide and sodium sulfide. A wood digestion reaction occurs in the digester 10 as the wood chips 12 and the cooking liquor 13 are combined at a controlled pressure and temperature. The wood digestion reaction extracts the cellulose fibers, or pulp, from the wood material by breaking down the lignin which binds the fibers together. The cooking liquor 13 in the digester 10 changes in composition during the wood digestion reaction and contains a varying amount of lignin removed from the wood chips 12.

In the non-limiting example of implementation of the pulp making line shown in Figure 1, the pulp 14 that is obtained as a result of the wood digestion reaction is then supplied to a bleaching section 16. The bleaching section 16 has a treatment area that receives the pulp 14 and where the pulp fibers are subjected to the action of bleaching solutions to modify the pulp fibers. For example, in some cases, the bleaching solutions may modify the pulp fibers to render them whiter. The treatment area includes one or more treatment stages depending on a desired degree of modification of the pulp. The bleached pulp 18 is the end product of the pulp making line. The specific example of implementation of the pulp making line shown in Figure 1 further includes a liquor combustion section 17 and a liquor sugar fermentation section 19 each receiving spent liquor 13 from the digester 10. In the liquor combustion section 17, the received liquor 13 is subjected to a steam atomization operation whereby steam is blown into the liquor 13 to break up large molecules therein into finer molecules, thereby changing the consistency of the liquor 13. The resulting liquor 13 is then used as fuel in a combustion device where the liquor 13 is combusted to produce heat or power used in the pulp making line or otherwise. In certain embodiments, other additives are added to the liquor 13 to form the fuel used in the combustion device. In the liquor sugar fermentation section 19, the received liquor 13 is stored in a fermentation tank under controlled conditions to ferment wood sugars in the liquor 13 such as to produce alcohol. Optionally, as shown by the dotted arrow in Figure 1, the liquor 13 passing into the liquor sugar fermentation section 19 can be retrieved and sent to another component of the pulp making line, for example, the liquor combustion section 17 or the digester 10.

The pulp making line also includes a process controller 20 that derives information from liquor 13 obtained in the course of the wood digestion reaction in the digester 10.

Figure 2 is a more detailed block diagram of the process controller 20. The process controller 20 includes a flow-cell 22 through which flows liquor 13 extracted from the digester 10. Any suitable flow path can be used to take a sample of liquor 13 from the digester 10 and pass it to the flow-cell 22. In the example shown in the drawings, the flow path is a re-circulating flow path where liquor 13 is taken out of the digester 10 over an inlet section 23 of the flow path and then returned to the digester 10 from the flow-cell 22 over an outlet section 24 of the flow path. It should be expressly noted that liquor 13 sampled from the digester 10 does not need to be re-circulated back to the digester 10 once it has passed in the flow-cell 22. Embodiments where the sampled liquor 13 is disposed after having passed in the flow-cell 22 or burned, for instance by directing the sampled liquor 13 to the liquor combustion section 17 (Figure 1) , to provide or supplement a source of heat for the wood digestion reaction can be envisaged without departing from the scope of the invention.

The liquor 13 passing in the flow-cell 22 is subjected to electromagnetic (EM) radiation emitted by a source of electromagnetic radiation 26. The liquor 13 in the flow- cell 22 will induce changes in the electromagnetic radiation. Those induced changes reflect the chemical composition of the liquor 13. In a specific example of implementation, the electromagnetic radiation includes near-infrared (NIR) radiation. NIR radiation is characterized by wavelengths from about 700 nm to about 2500 nm. NIR radiation in a range of wavelengths from about 1000 nm to about 2100 nm has been found particularly useful. Thus, the liquor 13 in the flow-cell 22 will induce changes in the NIR radiation. Those induced changes reflect the chemical composition of the liquor 13. The system architecture shown at Figure 2 uses a transmission-type flow-cell 22 where the electromagnetic radiation passes through the liquor 13. In this type of architecture, the changes induced in the electromagnetic radiation are changes due to absorption of some spectral components of the electromagnetic radiation. In a possible variant, the system may be designed such that the flow-cell 22 is a reflectance-type flow-cell where the electromagnetic radiation is reflected by the liquor 13.

The electromagnetic radiation with the induced changes is picked up by a sensor 28. The sensor 28 outputs data 39 conveying the changes induced in the electromagnetic radiation. In a specific and non-limiting example of implementation, the sensor 28 is a spectroscope that outputs spectra information.

The data 39 output by the sensor 28 is directed to a processing unit 30 that processes the data to produce process control information 32. The process control information 32 is useful in regulating one or more of the aspects of the wood digestion reaction either automatically or by communicating the process control information 32 to a human operator that can then take the appropriate process control actions. The process control information 32 can also be used to regulate the pulp bleaching process. In addition, the process control information 32 can further be used to regulate a process for burning liquor 13 from the digester 10 as a source of heat, or a process for fermenting wood sugars in the liquor 13 from the digester 10 to produce alcohol. In a non-limiting example of implementation, the process control information 32 includes information indicative of the pulp viscosity and pulp kappa number. Optionally, the process control information 32 may further include information indicative of a degree of purity of the pulp. The process control information 32 may also include information indicative of an amount of heat energy extractable from combustion of the liquor 13, and/or of a sugar content of the liquor 13.

A non-limiting example of implementation of the processing unit 30 is shown in greater detail in Figure 3. The processing unit 30 uses a calibration model 36 for deriving the process control information 32 at least partially on the basis of the data 39 output by the sensor 28. The calibration model 36 includes relationships between data of the type of data 39 output by the sensor 28 and information of the type of the process control information 32 such that, receiving as an input the data 39 output by the sensor 28, the calibration model 36 generates as an output the process control information 32. In a specific example of implementation, the processing unit 30 includes a computing platform that executes software implementing the calibration model 36.

Figure 4 illustrates a non-limiting example of a procedure for building the calibration model 36. In this particular example, the calibration model 36 is built by applying a data reduction filter technique 34 and a multivariate data analysis technique 38 on empirical reference data 37. The empirical reference data 37 relates data of the type output by the sensor 28 to information of the type of the process control information 32 for liquor samples having known characteristics and obtained in the course of production of pulp having known characteristics. In a specific example of implementation, the empirical reference data 37 includes spectra information of liquor samples having known chemical composition parameters and corresponding to pulp having known characteristics. The pulp characteristics can include the pulp kappa number, viscosity, and degree of purity. Also, the known chemical composition parameters of each liquor sample for which spectra information is included in the empirical reference data 37 are indicative of characteristics of that liquor sample, such as an amount of heat energy extractable from that liquor sample and a sugar content of that liquor sample.

In the empirical reference data 37, the correlation between the liquor spectra information and the pulp characteristics is obtained empirically. Similarly, the correlation between the liquor spectra information and the liquor characteristics is also obtained empirically. More specifically, tests are conducted in which pulp is analyzed with known methods to determine its viscosity, kappa number, and degree of purity values. The liquor obtained in the course of the wood digestion reaction which produced the tested pulp is analyzed to obtain spectra information, and that spectra information is associated with the empirically determined pulp viscosity, kappa number, and degree of purity values. The tests are repeated to obtain the desired range of pulp viscosity, kappa number, and degree of purity values and the corresponding liquor spectra information. Similarly, tests are conducted on the liquor itself using known methods to determine an amount of heat energy extractable from the liquor and a sugar content of the liquor (e.g. types of sugar, concentration of each type) , and the spectra information of the liquor is associated with these empirically determined values of liquor characteristics.

The data reduction filter technique 34 processes the empirical reference data 37 by implementing a data reduction filter that removes at least in part systematic variation in the data of the type output by the sensor 28 that is uncorrelated to the information of the type of the process control information 32. Systematic variation in the data of the type output by the sensor 28 that is uncorrelated to the information of the type of the process control information 32 can be caused by, for example, sensor instrumentation drift, temperature variations, etc. More specifically, in the empirical reference data 37, the data of the type output by the sensor 28 includes a number of data elements known as predictors, and the information of the type of the process control information 32 includes a number of information elements known as responses. The data reduction filter technique 34 processes the predictors to derive a data reduction filter that removes at least in part variation in the predictors that is unrelated to the responses. For example, in a particular embodiment, each predictor corresponds to a range or region of wavelengths of electromagnetic radiation and each response corresponds to an information element indicative of one of the pulp kappa number, pulp viscosity, pulp degree of purity, amount of heat energy extractable from the liquor, and sugar content of the liquor. The data reduction filter technique 34 processes the wavelength predictors to derive a data reduction filter that removes at least in part variation in the wavelength predictors that is unrelated to the pulp kappa number, pulp viscosity, pulp degree of purity, amount of heat energy extractable from the liquor, and sugar content of the liquor.

«Thus, the data reduction filter derived by the data reduction filter technique 34 outputs filtered data 43 in which has been at least partially removed systematic variation in the data of the type output by the sensor 28 that is uncorrelated to the data of the type of the process control information 32. The data reduction filter derived by the data reduction filter technique 34 is included in the calibration model 36 used by the processing unit 30. In a non-limiting example of implementation, the data reduction filter technique 34 is an Orthogonal Signal Correction (OSC) filter technique and thus the data reduction filter is an OSC filter. In other embodiments, the data reduction filter technique 34 is another type of pre-whitening filter technique such as, for example, a First-Derivative, Second-Derivative, or Standard Normal Variate (SNV) technique. Optionally, the data reduction filter technique 34 may also employ wavelet compression to reduce the computation time associated with the filtering operation. Thus, in a particular embodiment, the data reduction filter is an OSC filter with wavelet compression.

The filtered data 43 is then processed by the multivariate data analysis technique 38 that establishes the best possible correlation between predictors and responses in the filtered data 43. In a particular example of implementation, the multivariate data analysis technique 38 is a Partial Least Squares (PLS) technique. Essentially, the multivariate data analysis technique 38 derives relationships that use the predictors in the filtered data 43 to predict the responses in the filtered data 43. In a particular example of implementation, the multivariate data analysis technique 38 derives relationships that use the wavelength predictors to predict the pulp kappa number, pulp viscosity, degree of pulp purity, amount of heat energy extractable from the liquor, and sugar content of the liquor. The relationships derived by the multivariate data analysis technique 38 represent an analysis unit that is included in the calibration model 36 used by the processing unit 30.

While the example procedure for building the calibration model 36 shown in Figure 4 includes using the data reduction filter technique 34, it is to be understood that the data reduction filter technique 34 is purely optional and may be omitted. In an embodiment in which the data reduction filter technique 34 is omitted, the calibration model 36 is built by applying the multivariate analysis technique 38 to the empirical reference data 37 without any pre-filtering of the empirical reference data 37.

With continued reference to Figure 3, the processing unit 30 thus uses the calibration model 36 for deriving the process control information 32 at least partially on the basis of the data 39 output by the sensor 28. Specifically, the processing unit 30 receives the real-time data 39 output by the sensor 28 and submits it to the calibration model 36 which generates the process control information 32. More specifically, the processing unit 30 submits the real-time spectra information of a liquor sample 13 extracted from the digester 10 to the calibration model 36 which generates the process control information 32. The process control information 32 includes information indicative of the pulp kappa number, viscosity, and degree of purity, information indicative of an amount of heat energy extractable from the liquor 13, and information indicative of a sugar content of the liquor 13.

The process control information 32 can be used in various possible applications. Examples of those applications are discussed below.

Figure 5 is a block diagram of a system where the process control information 32 is made available to a human operator through a user interface 40. In one possible form of implementation, the user interface 40 is a display screen and the process control information 32 conveys to the human operator information on the pulp viscosity and the pulp kappa number. On the basis of the pulp viscosity and the pulp kappa number, the human operator can apply his or her experience and judgment to determine when the wood digestion process is to be stopped such as to obtain a good pulp quality and/or yield. The pulp viscosity information is indicative of the degree of degradation of the cellulose while the pulp kappa number is indicative of the lignin content remaining in the pulp. Knowledge of both parameters (i.e., viscosity and kappa number of the pulp) is useful in determining when it is most appropriate to terminate the wood digesting operation. In another possible example of implementation, the process control information 32 conveys to the human operator via the user interface 40 information on a degree of purity of the pulp. The pulp purity information is useful in fine tuning the pulp bleaching operation in the bleaching section 16 (Figure 1) . For example, the bleaching operation for pulp having a relatively lesser degree of purity does not need to be as intensive as for pulp having a greater degree of purity. Again, in this example of implementation, the information on pulp purity is conveyed to the human operator that in turn uses this information to take process control actions, if any. In a non-limiting example of implementation, the degree of purity of the pulp is represented by an S-IO and/or S-18 value.

In yet another possible example of implementation, the process control information 32 conveys to the human operator via the user interface 40 information on the amount of heat energy that can be obtained by burning the liquor 13. It is well known in the pulp and paper field that liquor can be burned to provide a source of heat that can be used, for instance, to supply fully or in part the thermal energy necessary to carry out the wood digestion reaction. Knowledge of the amount of heat energy is useful in determining the amount of liquor that is needed to meet the energy needs as well as to fine tune the combustion process. For instance, the information on the amount of heat energy that can be obtained by burning the liquor 13 can assist the human operator in regulating the steam atomization operation occurring in the liquor combustion section 17 (Figure 1) . Alternatively, the information on the amount of heat energy can assist the human operator in regulating the operation of the combustion device in the liquor combustion section (Figure 1), for example, by changing the flow rate of the liquor into the combustion device.

Figure 6 illustrates another example of implementation of the invention, wherein the process control information 32 is used as an input to an automated digester process regulation module 42 that automatically takes decisions on the process control actions to carry out without requiring intervention of a human operator. The digester process regulation module 42 can be in the form on an industrial controller that enforces a digester process control logic on the basis of the individual pulp viscosity and pulp kappa number values or on the basis of a combination of those values. For example, the digester process control logic is designed such that when the pulp viscosity reaches a certain level, the wood digestion reaction is to be stopped. This can be accomplished by decreasing the temperature and/or the pressure in the digester 10 (Figure D •

While Figure 6 suggests that the digester process regulation module 42 is separate from the process controller 20, it can be envisaged to integrate the digester process control logic into the process controller 20 that will then output control signals for implementing corresponding process control actions. For example, as shown in Figure 1, the control signals can be conveyed to the digester 10 via a control line 51. Figure 7 illustrates another example of implementation of the invention, wherein the process control information 32 is used to regulate the liquor combustion process. Specifically, the process control information 32 is used as an input to a liquor combustion regulation module 44 which can also be in the form of an industrial controller that enforces a liquor combustion control logic. The liquor combustion control logic enforces the rate at which liquor is supplied to a • combustion device in order to supply a certain amount of heat, or a certain heat rate, to the digester 10 or to any other equipment that needs to be heated. The liquor combustion control logic uses as a parameter the amount of heat energy that the liquor can provide in order to adjust the rate at which the liquor will be burned on the basis of the energy needs. In a specific example of implementation, the liquor combustion regulation module 44 issues a control signal to regulate the operation of a pump supplying the combustion device in the liquor combustion section 17 (Figure 1) to regulate the rate at which the liquor is being consumed.

In a possible variant, the liquor combustion control logic uses as a parameter the amount of heat energy that the liquor can provide in order to regulate the operation of the combustion device. Specifically, the liquor combustion regulation module 44 issues a control signal to the combustion device in the liquor combustion section 17 (Figure 1) in order to provide this regulation function.

In the example shown in Figure 7, the liquor combustion regulation module 44 is associated with the process controller 20 and controls the combustion of liquor drawn from the digester 10. In a possible variant, liquor from a source other than a wood digester can be used. For example the liquor can be supplied from a storage tank and passed through the process controller 20 whose purpose is then only to derive the parameters necessary for the liquor combustion regulation module 44 to carry out its function.

While Figure 7 suggests that the liquor combustion regulation module 44 is separate from the process controller 20, it can be envisaged to integrate the liquor combustion control logic into the process controller 20 that will then output the control signal to regulate the rate at which the liquor is consumed by the combustion device, regulate the operation of the combustion device, or both. For example, as shown in Figure 1, the control signal can be conveyed to the liquor combustion section 17 via a control line 53.

Figure 8 illustrates yet another example of implementation of the invention, wherein the process control information 32 is used to regulate the process for fermenting wood sugars in the liquor carried out in the liquor sugar fermentation section 19 (Figure 1) . Specifically, the process control information 32 is used as an input to a liquor sugar fermentation process regulation module 48 which can also be in the form of an industrial controller that enforces a liquor sugar fermentation process control logic. The liquor sugar fermentation process control logic regulates the operating conditions of the liquor sugar fermentation section 19 such as to produce alcohol having specified characteristics. The liquor sugar fermentation process control logic uses as a parameter the sugar content of the liquor in order to adjust the operating conditions of the liquor sugar fermentation section 19. Specifically, the operating conditions of the liquor sugar fermentation process can be regulated by varying the pH and/or temperature in the fermentation tank, the residence time of the liquor in the tank, or both. In a particular example of implementation, the liquor sugar fermentation process regulation module 48 issues a control signal that will implement the directives of the liquor sugar fermentation process control logic, such as to act on the pH and/or temperature existing in the fermentation tank or act in a way to regulate the residence time of the liquor in the tank.

While Figure 8 suggests that the liquor sugar fermentation process regulation module 48 is separate from the process controller 20, it can be envisaged to integrate the liquor sugar fermentation process control logic into the process controller 20 that will then output the control signal to regulate the liquor sugar fermentation process. For example, as shown in Figure 1, the control signal can be conveyed to the liquor sugar fermentation section 19 via a control line 55.

Figure 9 illustrates yet another example of implementation of the invention, wherein the process control information 32 is used to regulate the bleach process carried out by the bleaching section 16 (Figure 1) . Specifically, the process control information 32 is used as an input to a bleach process regulation module 46 which can also be in the form of an industrial controller that enforces a bleach process control logic. The bleach process control logic regulates the intensity of the bleach process. The bleach process control logic uses as a parameter the degree of purity of the pulp in order to adjust the intensity of the bleach process. Specifically, the intensity of the bleach process can be regulated by varying the concentration of the bleaching solutions, the residence time of the pulp in the treatment area, or both. In a particular example of implementation, the bleach process regulation module 46 issues a control signal that will implement the directives of the bleach process control logic, such as to act on the bleaching solutions supply in order to adjust the concentration in the treatment area or act in a way to regulate the residence time of the pulp in the treatment area.

While Figure 9 suggests that the bleach process regulation module 46 is separate from the process controller 20, it can be envisaged to integrate the bleach process control logic into the process controller 20 that will then output the control signal to regulate the bleach process. For example, as shown in Figure 1, the control signal can be conveyed to the bleach section 16 via a control line 57.

Figure 10 illustrates a non-limiting example of implementation in which the processing unit 30 also includes a data validation module 61 to determine whether the data 39 output by the sensor 28 is unreliable as a basis for deriving the process control information 32. More specifically, the determination made by the data validation module 61 is made at least partially on a basis of statistical information derived in building the calibration model 36. In a particular example of implementation, the data validation module 61 computes a residual standard deviation of the data 39 output by the sensor 28 and compares that residual standard deviation to a threshold residual standard deviation obtained in building the calibration model 36. If the residual standard deviation of the data 39 output by the sensor 28 is greater than the threshold residual standard deviation, the data validation module 61 determines that the data 39 output by the sensor 28 is unreliable as a basis for deriving the process control information 32. In an embodiment wherein a PLS technique is used to build the calibration model 36, the data validation module 61 computes a distance to model value (DmodX, SPE, etc.) of the data 39 output by the sensor 28 and compares that distance to model value to a threshold distance to model value obtained in building the calibration model 36 to determine whether the data 39 output by the sensor 28 is unreliable as a basis for deriving the process control information 32.

The data validation module 61 can also monitor variation in time of the residual standard deviation of the data 39 output by the sensor 28 to identify patterns or trends in the residual standard deviation. Systematic variation in the residual standard deviation of the data 39 output by the sensor 28 can be an indication of a change in the operating conditions of the pulp production process. Such change may be caused, for instance, by excessive wear or malfunction of process equipment such as the digester 10. Systematic variation in the residual standard deviation of the data 39 output by the sensor 28 can also be an indication of wear or malfunction of the source of electromagnetic radiation 26 or the sensor 28.

The data validation module 61 can convey information to a human operator via the user interface 40 (Figure 5) to allow the human operator to monitor in real-time the reliability of the data 39 output by the sensor 28 as a basis for deriving the process control information 32. For example, when the residual standard deviation of the data 39 output by the sensor 28 is greater than the threshold residual standard deviation, the data validation module 61 indicates to the human operator via the user interface 40 that the data 39 output by the sensor 28 is unreliable as a basis for deriving the process control information 32. The data validation module 61 may also prevent the processing unit 30 from outputting any process control information 32 derived on the basis of the data 39 output by the sensor 28. Furthermore, upon observing a clear pattern in the residual standard deviation of the data 39 output by the sensor 28, the human operator may take any process control actions that he or she deems necessary and may also instigate an investigation of a possible cause of the observed pattern.

Although various embodiments have been illustrated, this was for the purpose of describing, but not limiting, the invention. Various modifications will become apparent to those skilled in the art and are within the scope of the invention, which is defined more particularly by the attached claims.