METHOD AND APPARATUS FOR CONTROL OF DRYING PROCESS TAKING PLACE IN A PULP DRYER

Description

[0001] The invention concerns a method and apparatus for control of the drying process taking place in a pulp dryer.

[0002] Pulp dryers according to the state of the art operate in the following manner. The wet pulp web arriving from the press with a dry matter content of approximately 50 % at this stage is usually fed from above into the pulp dryer, which includes several blowing fan levels. The blowing fan levels are formed by fan boxes mounted adjacent to each other over the whole cross-sectional area of the web and over the pulp dryer length. From the fan levels a drying gas is blown, which is e.g. hot air, steam or any other medium suitable for the purpose, through a nozzle from both sides towards the web.1n such a contact-free drying the web travels back and forth inside the pulp dryer moving from an upper level towards the lower part of the pulp dryer. As the web is leaving the lower part of the pulp dryer, the dry matter content of the web is typically about 90 %.

[0003] Depending on the dryer size there is a section of the web with an approximate length of one kilometre inside the pulp dryer at all times, and the velocity of this web section is between 150 and 250 m/min. Hereby the transit time through the pulp dryer is in a range of 4 - 6 min. During this time the dry matter content of the web increases constantly as the web proceeds in the dryer. According to the state of the art, the drying is typically controlled by one steam valve affecting all blowing fan levels of the entire pulp dryer. The steam valve is regulated according to the moisture information measured in the web after the pulp dryer. Hereby it is very difficult to perform a quick and exact control of the web's final moisture in the different moisture variation situations. A pulp dryer is known, for example, from the FI Patent Publication 102 981.

[0004] The problems in the moisture control taking place in the pulp dryer expose the pulp web to web breaks. Problems are also caused when machine speeds are increased and when the basis weight of the pulp web is increased. In addition, in connection with grade changes the characteristics of the pulp web will change, for example, as the basis weight and the fibre grades of the pulp are changed. Controlling the web moisture becomes more difficult also in these situations. Web breaks usually occur more frequently in the top part of the pulp dryer, where the web is wettest.

[0005] The WO publication 99/18405 presents a method for controlling the process variables of drying gases in a dryer. This method measures and controls the process variables of water vapour evaporating from the web as well as the pressure inside the dryer. These variables are controlled independently of each other. In addition, the method controls the process variables of the steam supplied into the dryer and of the steam leaving the dryer, and both groups of process variables are used to control the drying process. The publication does not mention any utilisation of moisture measurement in the control of drying.

[0006] FI patent 82109 describes a method for improving the quality of the coating of a paper web. The web is coated in a coating station and thereafter dried in three successive drying zones and a cylinder dryer. A first moisture meter is situated between the first and the second drying zone and a second moisture meter is situated between the second and the third drying zone. The first drying zone is adjusted based on the first and the second moisture meter in order to maintain a first set moisture value at the initial end of the second drying zone. The second drying zone is adjusted based on the second moisture meter in order to maintain a second set moisture value at the final end of the second drying zone. The first drying zone can in addition be adjusted based on the moisture measurement of the web leaving the coating station.

[0007] WO publication 02/50370 is prior art under Article 54(3) EPC for the common designated states AT, DE and SE. WO publication 02/50370 is published on 27 June 2002 and claims priority from FI patent application 20002618 filed on 29 November 2000. WO publication 02/50370 discloses a method for drying a pulp web and a drying box used in the method. The drying box is divided into several drying zones and a last separate cooling zone. Each drying zone comprises a steam valve of its own for adjusting the drying temperature in said drying zone. The temperature of the first drying zone can thus be lower than that of one or more subsequent drying zones to prevent water in the incoming web from boiling. A first moisture sensor and a basis weight sensor are provided before the drying box and a second moisture sensor is provided after the drying box. Each drying zone is additionally provided with a temperature sensor and a thermocouple of its own. The basis weight sensor, the first moisture sensor, as well as the first and the second temperature sensor are used to control the first two drying zones. The second moisture sensor, as well as the fourth and the fifth temperature sensor are used to control the two last drying zones. The third temperature sensor is used to control the second, third and forth drying zone.

[0008] The purpose of the present invention is to bring about a quicker and more exact method than the present ones for controlling and managing the moisture profile of a pulp web in the machine direction.

[0009] It is also a purpose of the present invention to bring about a better moisture control for the pulp web in connection with a change of grades.

[0010] The method according to the invention is mainly characterised by what is defined in claim 1.

[0011] The apparatus according to the invention is characterised by what is defined in claim 8.

[0012] The pulp dryer is divided into two or more sections, each one of which is controlled by its own steam valve. The moisture control of the pulp dryer is improved in such a way that the moisture measurement to be performed in the web section between the press and the pulp dryer and between the drying sections is utilised to regulate the steam valves of the pulp dryer. The information obtained from the measurement points is taken to the control unit of the steam valve controlling the section corresponding to the measurement point of the pulp dryer, which control unit in addition to this preferably uses as control information also the basis weight measurement information and the machine speed information. In this manner the moisture information of the web arriving in the drying section can be used by controlling the steam valve in a derivative manner. The final moisture of the web after the dryer can also be taken into account at the same time.

[0013] Hereby the sections of the dryer divided into two or more parts can be controlled more exactly than before by their own steam valves.

[0014] With the method according to the invention several advantages are achieved compared with state-of-the-art moisture control. Moisture variations after the press can be quickly eliminated by the method according to the invention. In addition, the better moisture management will reduce the occurrence of web breaks. The method according to the invention can be implemented by converting existing control systems, whereby implementation of the invention will not require any significant investment costs.

[0015] By using the method according to the invention the total evaporation of the pulp dryer can be calculated more easily and more exactly and this information can be used in the energy management of the pulp dryer and in trouble diagnostics. At the same time, moisture control during grade change is facilitated thanks to the improved control.

[0016] In the following, the invention will be described in greater detail with reference to the appended figures, wherein:

Figure 1 shows a state-of-the-art control system for a pulp dryer.

Figure 2 shows the moisture profile of the pulp dryer in the machine direction.

Figure 3 shows a block diagram of a control method of a pulp dryer, which does not fall within the scope of the claims.

Figure 4 shows an embodiment of the invention, wherein the pulp dryer is divided into several sections.

Figure 5 shows an embodiment of the invention, which also includes control of the blowing speed of airbome web dryers.

[0017] Figure 1 shows a state-of-the-art control system for a pulp dryer. A Web W arrives from a press P and it is taken through the top part of the pulp dryer 10 into the pulp dryer 10. The pulp dryer 10 includes turning rolls 11 supporting the web W and blowing fan levels for drying the web W. In the pulp dryer 10 the web W travels supported by the turning rolls 11 between the different blowing fan levels. The blowing fan levels include hot air blowing boxes 12, from which hot air is blown through nozzles towards the web from both sides. The web W travels in the dryer 10 through the blowing fan levels step by step from the top downwards and it leaves the dryer 10 through the lower part.

[0018] In the web section between the pulp dryer 10 and the press P, the moisture of the pulp web W is observed by a first moisture sensor S₀, which is mounted to a measuring beam 30₁ or which is separate. The first moisture sensor S₀ may be either a spot measurement sensor or a sensor moving over the cross machine direction of the web back and forth across its width, or any other suitable means measuring the moisture. After the pulp dryer 10 the moisture of the web W is measured by a later moisture sensor S_N, which is located in connection with a measuring beam 30₂, and this moisture information h_N is used in the control unit 21 of a steam valve 20 to control the moisture degree of the pulp web W. The later moisture sensor S_N may also function as a sensor separate from the measuring beam 30₂. Measurement information on the basis weight BW and on the machine velocity v is preferably also brought to the control unit 21.

[0019] Figure 2 shows the moisture profile of the pulp web W in the machine direction inside the pulp dryer, when the moisture content of the pulp web changes in the desired manner. The vertical axis shows the moisture content of the pulp web on an arbitrary scale, while the horizontal axis shows the location of the pulp web inside the pulp dryer. According to the curve shown in the figure, the moisture content of the pulp web is highest at the inlet to the pulp dryer (0 m), and the moisture content drops evenly when travelling towards the final end of the pulp dryer (900 m). The allowed range of variation of the moisture content is also shown by dashed lines in Figure 2, within which range the moisture content may be controlled by the method according to the invention.

[0020] Figure 3 a block diagram of a control method of a pulp dryer, wherein the pulp dryer 10' is divided into two sections 10'a, 10'b. From a first moisture sensor S₀ connected to the web section between the press P and the pulp dryer 10', which first moisture sensor is either separate or is mounted to a measuring beam 301, moisture information h₀ is taken to the control unit 21'a of the steam valve 20'a of the first drying section 10'a. The first moisture sensor S₀ is either a spot measurement sensor or a sensor moving over the cross machine direction of the web back and forth across its width or any other moisture measuring means suitable for the purpose. From a later moisture sensor S_N connected after pulp dryer 10' a moisture measurement signal h_N is taken to a web moisture management unit 22'b, which supplies a control signal to the control unit 21'b of the steam valve 20'b of the second section 10'b. The control unit 21'b of the steam valve 20'b of the second section 10'b receives from a steam pressure measurement unit 23 a steam pressure value p_b, which is preferably used in the continuous regulation of the control unit 21'b of the steam valve.

[0021] Information on the basis weight measurement BW and on the machine velocity v is preferably supplied both to the control unit 21'a of the steam valve in the first section and to the moisture management unit 22'b. Measuring of the basis weight BV can be performed either by a basis weight sensor mounted to measuring beam 30₁ or the basis weight information may be supplied in other ways to control unit 21'a.

[0022] The moisture level of the web W is regulated by supplying steam into the drying sections, which steam dries the web W. By moisture measurements of the web W the moisture level of the web W is observed and the quantity of the steam to be supplied is measured by steam pressure measurements in the steam to be supplied. The pressure and/or quantity of the steam is controlled by a steam valve. The setting value of the web's W moisture circle is changed e.g. separately for each grade, and the control of the steam valve is changed continuously as a function of time. The feedforward of moisture information ho from the first moisture sensor So to the control unit 21'a of the steam valve 20'a of the first section 10'a results in a more exact and quicker moisture control for the pulp dryer 10.

[0023] Figure 4 shows an embodiment of the invention, wherein the pulp dryer 10 is divided into more than two drying sections 10₁, 10₂, ..., 10_N. Each drying section may be e.g. one blowing fan level of the pulp dryer 10 including the travelling level of the web W and blowing fan boxes 12 placed on its both sides. Each drying section 10₁, ... 10_N is controlled in a similar manner by steam valves 20₁, ..., 20_N, which for their part are similarly controlled by control units 21₁, ..., 21_N. A first moisture sensor S₀ is located before the pulp dryer 10. In the section between drying section 10₁ and drying section 10₂, for example, in connection with the turning roll, a second moisture sensor S₁ is located. Correspondingly, a moisture sensor S_N-1 is located before the last drying section 10_N, and after the last drying section 10_N, that is, in the web section located at the outlet of the pulp dryer, a moisture sensor S_N is located, which measures the final moisture of the pulp web W after the pulp dryer 10.

[0024] The moisture information h₀ of moisture sensor S₀ is taken to control the unit 21₁, which controls the steam valve 20₁. In addition, information on the web's basis weight and velocity may be taken to the control unit 21₁, and this information may also be used to control the valve 20₁. In this manner feedforward is achieved from the moisture sensor S₀ before the pulp dryer to control the drying section 10₁. A control signal c₁ may also be taken from the control unit 21₁ to one or more control units 21₂, ..., 20_N of the steam valves 20₂, ..., 20_N located later. Hereby the control signal c₁ may be either moisture measurement information or valve control information. In this manner feedforward is achieved from the moisture sensor S₀ before the pulp dryer in order to control one or more drying sections 10₁, ..., 10_N of the pulp dryer 10. The control may take place either based only on the signal arriving from the control unit 21₁ or based only on the signal from the control unit prior to the concerned drying section (e.g. drying section 10₂ would be controlled based only on the control signal of the control unit 21₂) or by using both signals. Each section 10₁, ..., 10_N of the pulp dryer is controlled in a similar manner by a moisture sensor S₁, ..., S_N-1 located before each section. In addition, the last section 10_N of the pulp dryer 10 is controlled in a feedback manner based on the measurement information from the moisture sensor S_N located after the pulp dryer. According to the invention, at least one drying section 10₁, .... 10_N of the pulp dryer is controlled in a feedforward manner and at least one drying section is controlled in a feedback manner. Feedback preferably takes place based on the measurement information of the last section.

[0025] Figure 5 shows an embodiment of the present invention wherein the moisture information is used for controlling the blowing speed of the pulp dryer's blowing boxes. In this embodiment the first section 10₁ of the pulp dryer is controlled in the same manner as was described earlier. From the later moisture sensor S_N located after the pulp dryer measurement information h_N is obtained, which is taken to the control unit 12c for the blowing speed of the blowing boxes 12, which control unit controls the blowing speed of the blowing boxes 12. The moisture information h_N obtained from moisture sensor S_N is also taken to the control unit 21_N for the steam valve 20_N, which controls the pulp dryer's steam valve in the manner described above. The embodiment of the invention shown in Figure 5 may also be combined with the control options presented in Figure 4. In Figure 5 the blowing speed control of blowing boxes is shown in connection with one drying section only, but it is possible to implement the control also in more drying sections. Especially the drying sections in the final end of the drying part are preferably controlled.

[0026] It is very difficult to calculate the required target values for the steam pressure of steam valves 20'a; 20'b; 20₁, ..., 20_N when the grade is changed in pulp dryer 10. In consequence of this the steam valves cannot be ramped to control the final moisture content of the web when the grade is changed. It is an advantage of the method according to the invention that the method makes it possible to perform moisture control also during grade changes, whereby the final moisture content can be managed also in such process change situations. During a change of grade it is possible to speed up some adjustments of control settings when required. Different fibre grades act in different ways as regards water removal, whereby each fibre grade demands its own process model and the process amplification is changed according to this model after grade changes. The process models are mathematical models known as such and based on physical principles and on response tests or other experimental methods.

[0027] In the method described above the web moisture is measured before and after the pulp dryer in a manner known as such, wherein the moisture sensor measures the web moisture either as spot measurement or by a traversing measuring device over the entire web width or by some other moisture-measuring method suitable for the purpose. According to the invention, the measured moisture information is utilised in a new manner, wherein the web moisture information measured before the pulp dryer is taken in a feedforward manner to a steam valve performing continuous control of the quantity of steam supplied to the pulp dryer. Alternatively, feedback moisture control can also be used to control the blowing speed of blowing boxes 12. Alternatively, this control may be implemented by feedforwarding the measurement information of the first moisture sensor to the control unit of the blowing boxes.

Claims

1. Method for control of the drying process taking place in a pulp dryer, which pulp dryer comprises several blowing fan levels, from which drying gas is blown on to both sides of the web, and which method comprises measuring the web's moisture information (h₀) on the web section entering the pulp dryer by a first moisture sensor (S₀), measuring the web's moisture information (h_N) on the web section emerging from the pulp dryer by a last moisture sensor (S_N), dividing the pulp dryer (10) into two or more drying sections (10₁,...,10_N), each one of which is controlled by its own steam valve (20₁,..., 20_N), measuring the moisture of the pulp web (W) by a moisture sensor (S₁,..., S_N-1) arranged between each drying section (10₁,...,10_N), and controlling the moisture level of the pulp web (W) separately in each drying section (10₁,...,10_N) by means of a control unit (21₁...21_N) arranged to control the steam valve (20₁,...,20_N) of each drying section (10₁,...,10_N) on the basis of the measurement information of the moisture sensor (S₀,..., S_N-1) located before the drying section.

2. Method according to claim 1, characterised by controlling the moisture level of the pulp web (W) continuously.

3. Method according to claims 1 or 2, characterised by implementing feedback of the pulp dryer's (10) control on the basis of the measurement information of the last section (10_N).

4. Method according to any one of claims 1 - 3, characterised by controlling the pulp web's (W) moisture level by regulating the quantity of steam supplied to the drying section (10₁,...,10_N).

5. Method according to any one of claims 1 - 4, characterised by using the measurement information of the moisture sensor/moisture sensors (S₀,...,S_N) for controlling the blowing speed of blowing boxes (12).

6. Method according to any one of claims 1 - 5, characterised by bringing the information from measurement of the basis weight (BW) and of the machine velocity (v) to the control unit (21₁,...,21_N) of the steam valve (20₁,...,20_N).

7. Method according to any one of claims 1 - 6, characterised by controlling the operation of the press (P) on the basis of measurement information (h₀) given by the first moisture sensor (S₀) located before the pulp dryer (10).

8. Apparatus for control of the drying process taking place in a pulp dryer, in which apparatus the pulp dryer comprises several blowing fan levels, from which the blowing of drying gas is arranged on both sides of the web and wherein a first moisture sensor (S₁) is arranged for the web section entering the pulp dryer and a last moisture sensor (S_N) is arranged for the web section emerging from the pulp dryer, and wherein the pulp web's moisture level existing in the pulp dryer is controlled by a steam valve/steam valves, and wherein the pulp dryer (10) is divided into two or more drying sections (10₁,...,10_N), each one of which is controlled by its own steam valve (20₁, ..., 20_N), a moisture sensor (S₁,..,S_N-1) is arranged in between each drying section (10₁,...,10_N), and a separate control of the pulp web's (W) moisture level is arranged for each drying section (10₁,...,10_N) by means of a control unit (21₁,...,21_N) arranged to control the steam valve (20₁, ..., 20_N) of each drying section (10₁,...10_N) on the basis of the measurement information of the moisture sensor (S₀,...,S_N-1) located before the drying section.

9. Apparatus according to claim 8, characterised in that the moisture control of each drying section (10₁,...10_N) in the pulp dryer is continuous.

10. Apparatus according to claim 8 or 9, characterised in that the control for the steam valve (20₁) of the pulp dryer's (10) first drying section (10₁) is accomplished on the basis of the measurement information (h₀) given by the first moisture sensor (S₀).

Ansprüche

1. Verfahren zum Steuern des in einem Pulpetrockner stattfindenden Trocknungsprozesses, wobei der Pulpetrockner mehrere Gebläselüfterstufen aufweist, von denen Trocknungsgas zu beiden Seiten der Bahn hin geblasen wird, und wobei das Verfahren die folgenden Schritte aufweist:

Messen der Feuchtigkeitsinformation (h₀) der Bahn an dem Bahnabschnitt, der in den Pulpetrockner eintritt, durch einen ersten Feuchtigkeitssensor (S₀),

Messen der Feuchtigkeitsinformation (h_N) der Bahn an dem aus dem Pulpetrockner herauskommenden Bahnabschnitt durch einen letzten Feuchtigkeitssensor (S_N),

Teilen des Pulpetrockners (10) in zwei oder mehr Trocknungsabschnitte (10₁, ..., 10_N), von denen jeder durch sein eigenes Dampfventil (20₁, ..., 20_N) gesteuert ist,

Messen der Feuchtigkeit der Pulpebahn (W) durch einen Feuchtigkeitssensor (S₁, ..., S_N-1), der zwischen jedem Trocknungsabschnitt (10₁, ..., 10_N) angeordnet ist, und

Steuern der Feuchtigkeitshöhe der Pulpebahn (W) separat in jedem Trocknungsabschnitt (10₁, ..., 10_N) durch eine Steuereinheit (21₁, ..., 21_N), die eingerichtet ist, um das Dampfventil (20₁, ..., 20_N) jedes Trocknungsabschnitts (10₁, ..., 10_N) auf Grundlage der Messinformation des Feuchtigkeitssensors (S₀, ..., S_N-1), der vor dem Trocknungsabschnitt liegt, zu steuern.

2. Verfahren gemäß Anspruch 1, gekennzeichnet durch Steuern der Feuchtigkeitshöhe der Pulpebahn (W) in kontinuierlicher Weise.

3. Verfahren gemäß einem der Ansprüche 1 oder 2, gekennzeichnet durch Ausführen einer Rückführung der Steuerung des Pulpetrockners (10) auf der Grundlage der Messinformation des letzten Abschnitts (10_N).

4. Verfahren gemäß einem der Ansprüche 1 bis 3, gekennzeichnet durch Steuern der Feuchtigkeitshöhe der Pulpebahn (W) durch Regulieren der Menge an Dampf, die zu einem Trocknungsabschnitt (10₁, ..., 10_N) geliefert wird.

5. Verfahren gemäß einem der Ansprüche 1 bis 4, gekennzeichnet durch Anwenden der Messinformation des Feuchtigkeitssensors / der Feuchtigkeitssensoren (S₀, ..., S_N) zum Steuern der Gebläsegeschwindigkeit von Gebläsekästen (12).

6. Verfahren gemäß einem der Ansprüche 1 bis 5, gekennzeichnet durch Bringen der Information der Messung des Basisgewichts (BW) und der Maschinengeschwindigkeit (v) zu der Steuereinheit (21₁, ..., 21_N) des Dampfventils (20; 20'a; 20'b; (20₁, ..., 20_N).

7. Verfahren gemäß einem der Ansprüche 1 bis 6, gekennzeichnet durch Steuern des Betriebs der Presse (P) auf der Grundlage der Messinformation (h₀), die durch den ersten Feuchtigkeitssensor (S₀) geliefert wird, der vor dem Pulpetrockner (10) angeordnet ist.

8. Gerät zum Steuern des in einem Pulpetrockner stattfindenden Trocknungsprozesses, wobei in dem Gerät der Pulpetrockner mehrere Gebläselüfterstufen aufweist, von denen der Gebläsestrom aus Trocknungsgas an beiden Seiten der Bahn eingerichtet ist, und wobei ein erster Feuchtigkeitssensor (S₁) für den Bahnabschnitt angeordnet ist, der in den Pulpetrockner eintritt, und ein letzter Feuchtigkeitssensor (S_N) für den Bahnabschnitt angeordnet ist, der aus dem Pulpetrockner herauskommt und wobei die Feuchtigkeitshöhe der Pulpebahn, die in dem Pulpetrockner vorhanden ist, durch ein Dampfventil / durch Dampfventile gesteuert wird, und wobei der Pulpetrockner (10) in zwei oder mehr Trocknungsabschnitte (10₁, ..., 10_N) geteilt ist, von denen jeder durch sein eigenes Dampfventil (20₁, ..., 20_N) gesteuert ist, ein Feuchtigkeitssensor (S₁, ..., S_N-1) zwischen jedem Trocknungsabschnitt (10₁, ..., 10_N) angeordnet ist, und eine separate Steuerung der Feuchtigkeitshöhe der Pulpebahn (W) für jeden Trocknungsabschnitt (10₁, ..., 10_N) mit Hilfe einer Steuereinheit (21₁, ..., 21_N) zum Steuern des Dampfventils (20₁, ..., 20_N) jedes Trocknungsabschnitts (10₁, ..., 10_N) auf der Grundlage der Messinformation des Feuchtigkeitssensors (S₀, ..., S_N-1), der vor dem Trocknungsabschnitt liegt, eingerichtet ist.

9. Gerät gemäß Anspruch 8, dadurch gekennzeichnet, dass die Feuchtigkeitssteuerung jedes Trocknungsabschnitts (10₁, ..., 10_N) in dem Pulpetrockner kontinuierlich ist.

10. Gerät gemäß Anspruch 8 oder 9, dadurch gekennzeichnet, dass die Steuerung für das Dampfventil (20₁) von dem ersten Trocknungsabschnitt (10₁) des Pulpetrockners (10) auf der Grundlage der Messinformation (h₀) verwirklicht wird, die durch den ersten Feuchtigkeitssensor (S₀) geliefert wird.

Revendications

1. Procédé de commande du processus de séchage qui intervient dans un séchoir de pulpe, lequel séchoir de pulpe comprend plusieurs niveaux de ventilateurs soufflants, à partir desquels le gaz asséchant est soufflé sur les deux côtés de la bande et lequel procédé comprenant le mesurage des informations relatives à l'humidité de la bande (h₀) sur la section de bande entrant dans le séchoir de pulpe au moyen d'un premier capteur d'humidité (S₀), le mesurage des informations relatives à l'humidité de la bande (h_N) sur la section de bande sortante au moyen d'un dernier capteur d'humidité (S_N), la division du séchoir de pulpe (10) en deux sections de séchage ou plus (10₁, ..., 10_N) chacune étant contrôlée par sa propre soupape d'admission de vapeur (20₁, ..., 20_N), le mesurage de l'humidité de la bande de pulpe (W) par un capteur d'humidité (S₀), ..., S_N-1) situé entre chaque section de séchage (10₁, ..., 10_N), le contrôle du niveau d'humidité de la bande de pulpe (W) séparément dans chaque section de séchage (10₁, ..., 10_N), au moyen d'une unité de contrôle (21₁, ..., 21_N) disposée pour contrôler la soupape d'admission de vapeur (20₁, ..., 20_N) de chaque section de séchage (10₁, ..., 10_N) sur la base des informations de mesure du capteur d'humidité (S₀, ..., S_N-1) situé en amont de la section de séchage.

2. Procédé selon la revendication 1, caractérisé en ce que le niveau d'humidité de la bande de pulpe (W) est contrôlé en continu.

3. Procédé selon l'une quelconque des revendications 1 ou 2, caractérisé en ce que la rétroaction du contrôle du séchoir de pulpe (10) est mise en oeuvre sur la base des informations de mesure de la dernière section (10_N).

4. Procédé selon l'une quelconque des revendications 1 à 3, caractérisé en ce que le niveau d'humidité de la bande de pulpe (W) est contrôlé par régulation de la quantité de vapeur fournie à la section de séchage (10₁, ..., 10_N).

5. Procédé selon l'une quelconque des revendications 1 à 4, caractérisé en ce que les informations de mesure du capteur d'humidité/des capteurs d'humidité (S₀, ..., S_N) sont utilisées pour contrôler la vitesse de soufflage des compartiments de soufflage (12).

6. Procédé selon l'une quelconque des revendications 1 à 5, caractérisé en ce que les informations résultant de la mesure du grammage (BW) et de la vitesse de la machine (v) sont fournies à l'unité de commande (21_1, ..., 21_N) de la soupape d'admission de vapeur (20₁, ..., 20_N).

7. Procédé selon l'une quelconque des revendications 1 à 6, caractérisé en ce que le fonctionnement de la presse (P) est contrôlé sur la base des informations de mesure (h₀) fournies par le premier capteur d'humidité (S₀) situé en amont du séchoir de pulpe (10).

8. Appareil de commande du processus de séchage qui intervient dans un séchoir de pulpe, appareil dans lequel le séchoir de pulpe comprend plusieurs niveaux de ventilateurs soufflants à partir desquels le soufflage du gaz asséchant est assuré des deux côtés de la bande et dans lequel un premier capteur d'humidité (S₁) est disposé pour la section de bande entrant dans le séchoir à pulpe et un dernier capteur d'humidité (S_N) est disposé pour la section de bande qui sort du séchoir de pulpe et dans lequel le niveau d'humidité de la bande de pulpe existant dans le séchoir de pulpe est contrôlé au moyen d'une soupape d'admission de vapeur/de soupapes d'admission de vapeur, et dans lequel le séchoir de pulpe (10) est divisé en deux sections de séchage ou plus (10₁, ...., 10_N), chacune étant contrôlée par sa propre soupape d'admission de vapeur (20_1, ..., 20_N), un capteur d'humidité (S₁, ..., S_N-1) est disposé entre chacune des sections de séchage (10₁, ...., 10_N), et un contrôle séparé du niveau d'humidité de la bande de pulpe (W) est assuré pour chaque section de séchage (10₁, ...., 10_N), au moyen d'une unité de contrôle (21₁, ..., 21_N) disposée pour contrôler la soupape d'admission de vapeur (20₁, ..., 20_N) de chaque section de séchage (10₁, ..., 10_N) sur la base des informations de mesure du capteur d'humidité (S₀, ..., S_N-1) situé en amont de la section de séchage.

9. Appareil selon la revendication 8, caractérisé en ce que le contrôle de l'humidité de chaque section de séchage (10₁, ...., 10_N) dans le séchoir de pulpe est continu.

10. Appareil selon la revendication 8 ou 9, caractérisé en ce que le contrôle de la soupape d'admission de vapeur (20₁) de la première section de séchage (10₁) du séchoir de pulpe (10) est réalisé sur la base des informations de mesure (h₀) données par le premier capteur d'humidité (S₀).

Drawing