阅读说明：本技术 确定纤维素纸浆的幅材的水分含量的方法 (Method for determining the moisture content of a web of cellulose pulp ) 是由 奥拉·拉尔森 于 2019-09-24 设计创作，主要内容包括：本发明涉及一种确定到达纸浆干燥器(1)的纤维素纸浆幅材(3)的水分含量的方法。该方法包括：使用布置在纸浆干燥机(1)上游的水分传感器(19)在预定时间间隔期间在若干时刻测量所述幅材(3)的水分含量；测量所述纸浆干燥机(1)的干燥介质的状态变量；基于所述水分传感器的测量结果,计算在所述预定时间间隔期间由所述幅材(3)的一部分引入到纸浆干燥机(1)中的水分的总值；基于所述测量的状态变量,确定纸浆干燥机(1)内部存在的水分的预测总值；比较所述计算的总值与所述预测总值,以获得其间的偏差；使用所述偏差校准所述水分传感器(19)；以及使用所述经校准的水分传感器(19)测量纤维素纸浆幅材(3)的水分含量。(The invention relates to a method of determining the moisture content of a cellulose pulp web (3) arriving at a pulp dryer (1). The method comprises the following steps: measuring the moisture content of the web (3) at several moments during a predetermined time interval using a moisture sensor (19) arranged upstream of the pulp dryer (1); measuring a state variable of a drying medium of the pulp dryer (1); -calculating a total value of the moisture introduced into the pulp dryer (1) by a portion of the web (3) during the predetermined time interval based on the measurement results of the moisture sensor; -determining a predicted total value of the moisture present inside the pulp dryer (1) based on said measured state variables; comparing said calculated total value with said predicted total value to obtain a deviation therebetween; calibrating the moisture sensor (19) using the deviation; and measuring the moisture content of the cellulose pulp web (3) using the calibrated moisture sensor (19).)

1. A method of determining the moisture content of a cellulose pulp web (3) arriving at a pulp dryer (1), the method comprising:

measuring (S1) the moisture content of the web (3) at several moments during a predetermined time interval using a moisture sensor (19) arranged upstream of the pulp dryer (1);

measuring (S2) a state variable of a drying medium of the pulp dryer (1);

characterized in that it further comprises:

-calculating (S3), based on the measurement results of the moisture sensors, a total value of moisture introduced into the pulp dryer (1) by a portion of the web (3) during the predetermined time interval;

determining (S4) a predicted total value of the moisture present inside the pulp dryer (1) based on said measured state variables;

comparing (S5) the calculated total value with the predicted total value to obtain a deviation therebetween;

calibrating (S6) the moisture sensor (19) using the offset; and

measuring (S7) the moisture content of the cellulose pulp web (3) using the calibrated moisture sensor (19).

2. The method of claim 1, wherein the predicted total value is determined using a mass and/or energy balance calculation.

3. The method according to any of the preceding claims, wherein the step of measuring (S2) a state variable comprises measuring at least an inlet gas condition and an outlet gas condition.

4. The method according to any of the preceding claims, wherein, during said predetermined time interval, said step of measuring (S2) a state variable of a drying medium of the pulp dryer (1) and said step of determining (S4) a predicted total value of moisture present inside the pulp dryer (1) are performed at least once.

5. The method according to any of the preceding claims, wherein said step of measuring (S2) the state variable of the drying medium of the pulp dryer (1) and said step of determining (S4) the predicted total value of the moisture present inside the pulp dryer (1) are performed at several instants during said predetermined time interval.

6. The method according to any one of the preceding claims, wherein said step of calibrating (S6) the moisture sensor (19) is performed several times a day.

Technical Field

The invention relates to a method of determining the moisture content of a cellulosic pulp web arriving at a pulp dryer.

Background

Cellulose pulp is usually dried in a dryer with several horizontal drying decks arranged one above the other. Cellulose pulp having a moisture content of about 50% is fed into the pulp dryer. The web of cellulose pulp is conveyed across the drying deck of the dryer. The dried cellulose pulp having a moisture content of about 10% is discharged at the end of the lowest drying deck.

An example of a cellulose pulp dryer is shown in WO 2012/074462 a 1. Hot gases in the form of hot air are blown onto the web of cellulose pulp by means of an upper blow box and a lower blow box. The air blown by the blow boxes transfers heat to the web to dry it. Additionally, the air blown by the lower blow box keeps the web floating above the lower blow box. Hot air is supplied to the blow box by a circulating air system comprising a fan and a steam radiator for heating the drying air.

In order to control the drying process, different parameters were measured. Such a parameter is the moisture content of the web conveyed into the pulp dryer. Typically, moisture sensors are used to measure moisture content.

However, the accuracy of the known moisture sensors is considered to be insufficient. Therefore, there is a need for more accurate measurement of the moisture content of the web reaching the pulp dryer.

Disclosure of Invention

It is an object of the invention to provide a more accurate method of determining the moisture content of a cellulosic pulp web arriving at a pulp dryer.

This and other objects that will be apparent from the following summary and description are achieved by a method according to the appended claims.

According to one aspect of the present disclosure, there is provided a method of determining the moisture content of a cellulosic pulp web arriving at a pulp dryer, the method comprising: measuring the moisture content of the web at several moments during a predetermined time interval using a moisture sensor arranged upstream of the pulp dryer; measuring a state variable of a drying medium of the pulp dryer; calculating a total value of moisture introduced into the pulp dryer by a portion of the web during the predetermined time interval based on the moisture sensor measurements; determining a predicted total value of moisture present inside the pulp dryer based on the measured state variables; comparing said calculated total value with said predicted total value to obtain a deviation therebetween; calibrating the moisture sensor using the offset; and measuring the moisture content of the cellulose pulp web using the calibrated moisture sensor.

The pulp dryer can be seen as a thermodynamic system which allows calculating the moisture content inside the dryer at each moment with high accuracy using energy and/or mass calculations based on measured state variables of the drying medium of the pulp dryer. The method of the present disclosure is based on the following idea: the results from such calculations are used to calibrate a moisture sensor arranged upstream (e.g. at the inlet) of the pulp dryer.

By calibrating the moisture sensor in this way, a more accurate determination of the moisture content of the pulp web arriving at the dryer is achieved. This provides for a more efficient control of the drying process. Furthermore, it makes it possible to detect deviations occurring upstream of the pulp dryer and to adjust the drying conditions accordingly taking them into account. Thus, since the moisture content determined by the calibrated sensor is reliable, it can be used for different purposes with respect to the overall efficiency of the pulp dryer. For example, energy consumption and/or pulp quality may be optimized.

Thus, the method allows for rapid and reliable detection of deviations and changes in moisture content. Since the calibrated moisture sensor provides a reliable measurement of the moisture content of the pulp web arriving at the pulp dryer, it can be used to optimize the drying efficiency and/or to detect deviations upstream of the pulp dryer at an early stage.

In calculating the predicted total moisture content inside the pulp dryer, state variables such as drying medium pressure, drying medium temperature, drying medium flow, steam pressure, steam temperature, steam flow, pulp web temperature, pulp web flow and moisture content of the dried pulp web may be used.

The predetermined time interval may vary and depends on the speed at which the pulp web is fed into the pulp dryer. Furthermore, a certain time interval may be used during the start-up of the drying process, whereas a different time interval may be used during normal operation of the pulp dryer.

Preferably, the step of measuring the state variable comprises measuring at least an inlet gas condition and an outlet gas condition.

During said predetermined time interval, said step of measuring a state variable of the drying medium of the pulp dryer and said step of determining a predicted total value of the moisture present inside the pulp dryer may be performed at least once.

Preferably, said step of measuring a state variable of the drying medium of the pulp dryer and said step of determining a predicted total value of the moisture present inside the pulp dryer are performed at several moments during said predetermined time interval.

Calibration of the moisture sensor may be performed periodically in order to control the operation of the pulp dryer over time in an efficient manner during an operation cycle. For example, calibration of the moisture sensor may be performed several times a day.

These and other aspects of the invention will be apparent from and elucidated with reference to the claims and embodiments described hereinafter.

Drawings

The invention will now be described in more detail with reference to the accompanying drawings, in which:

fig. 1 is a schematic view and shows a dryer for drying cellulose pulp.

Fig. 2 illustrates steps of a method according to an embodiment of the disclosure.

Detailed Description

Fig. 1 shows in a schematic way a cellulose pulp dryer 1 for drying cellulose pulp according to the airborne web principle, in which cellulose pulp is dried by means of hot air while travelling along a horizontal drying section of the pulp dryer 1. Thus, the dryer 1 utilizes heated air for drying and supporting the pulp web. Typically, the dryer 1 will comprise 4 to 40 drying decks. A large dryer may even include more than 50 drying decks.

The wet pulp web 3 enters the dryer 1 at a known speed via an inlet 5 arranged in the first side wall 7 of the pulp dryer casing 9. In the pulp dryer of fig. 1, the inlet 5 is arranged in an upper portion of the side wall 7, but in an alternative dryer the inlet may be arranged in a lower portion of the first side wall 7. The web 3 is advanced horizontally to the right in the dryer 1 until the web 3 reaches a turning roll (not shown). The web 3 is diverted around a turning roll and then travels horizontally to the left until the web 3 reaches a subsequent turning roll, where the web 3 is again turned. In this way, the web 3 is fed from the inlet 5 through the casing 9 and travels from the top to the bottom of the dryer 1 in a zigzag (zig zag) manner at a set speed. The dried web 11 leaves the dryer 1 via an outlet 13 arranged in a second side wall 15 of the pulp dryer housing 9. In the pulp dryer of fig. 1, the outlet 13 is arranged in a lower portion of the second side wall 15, but in an alternative embodiment the outlet 13 may be arranged in an upper portion of the second side wall 15.

In each drying deck of the dryer 1 a blow box (not shown) is arranged for drying the web. As schematically illustrated by arrow a in fig. 1, heated air is supplied to the blow box of the dryer 1 through an air inlet. The drying air can be heated, for example, by directing it through a set of boilers heated with steam. For this purpose, steam for heating the drying air is fed into the pulp dryer 1, as schematically illustrated by arrow B in fig. 1.

The exhaust air is removed from the pulp dryer 1 through an air outlet, as schematically illustrated by arrow C in fig. 1, and the steam condensate is removed from the pulp dryer 1, as schematically illustrated by arrow D in fig. 1.

Typically, the drying process uses air at a temperature of 80 ℃ to 250 ℃. Cellulose paper entering dryer 1The pulp web 3 typically has a dry solids content of 40-60% by weight and the cellulose pulp web 3 leaving the dryer 1 has a dry solids content of typically 85-95% by weight. The cellulose pulp web 11 leaving the dryer 1 typically has a moisture content of 800g/m when measured as 0.11 kg water/kg dry matter²To 1500g/m²And a thickness of 0.8mm to 3 mm.

At the pulp web inlet 5, a moisture measuring unit 17 is arranged, which is capable of measuring the dry solids content of the pulp web 3 fed into the pulp dryer 1. The moisture measuring unit 17 comprises a moisture sensor 19, for example in the form of an IR moisture sensor or a sensor using another measuring principle. The moisture sensor may be a stationary sensor or a traverse sensor arranged to move across the travelling direction of the pulp web 3.

At the web outlet 13, a web condition monitoring unit 21 comprising a second moisture sensor 23 is arranged to measure the moisture content of the dried web 11. The web condition monitoring unit 17 is also capable of measuring the temperature and flow of the dried pulp web 11.

During operation of the pulp dryer 1 several state variables are measured in a conventional manner. As schematically illustrated by the dashed lines in fig. 1, the control unit 25 is arranged to receive information from several measurement units. Typically, during operation of the pulp dryer 1, inlet air conditions, exhaust air conditions, inlet steam conditions, outlet steam/condensate conditions and pulp outlet conditions are measured periodically and sent to the control unit 25.

For example, state variables such as inlet drying air pressure, inlet drying air temperature, inlet drying air flow, outlet air pressure, outlet air temperature and outlet air flow may be measured and used to calculate a predicted amount of moisture inside the pulp dryer 1. Furthermore, state variables such as the entering steam pressure, entering steam temperature, entering steam flow, exiting steam/condensate pressure, exiting steam/condensate temperature and exiting steam/condensate flow can be measured and used to calculate a predicted amount of moisture inside the pulp dryer 1.

Furthermore, state variables in the form of temperature, flow and moisture content of the dried web can be measured and used to calculate a predicted amount of moisture inside the pulp dryer 1.

With reference to fig. 1 and 2, a method of determining the moisture content of a cellulose pulp web 3 arriving at a pulp dryer 1 will now be described.

In a first measurement step S1, the moisture content of the cellulose pulp web 3 arriving at the pulp dryer 1 is measured using the moisture sensor 19 of the moisture measurement unit 17. The moisture content of the web 3 is measured at several moments during a predetermined time interval. The measurement result performed by the moisture sensor 19 is sent to the control unit 25.

In a second measurement step S2, the state variables are measured. Typically, state variables, such as inlet drying air conditions and outlet air conditions, are measured periodically during operation of the pulp dryer 1. Furthermore, the state variable of the steam heating the drying air and the state variable of the dried web 11 leaving the pulp dryer 1 are measured periodically.

In a calculation step S3, a total value of moisture introduced into the pulp dryer 1 by a portion of the web 3 during a predetermined time interval is calculated by the control unit 25 on the basis of the moisture content measurements performed by the moisture sensor 19 in step S1 and the actual web speed. The calculated total value is thus established in this step.

In the determination step S4, a predicted total value of moisture present inside the pulp dryer is determined. Based on the measurement performed in the second measurement step S2, a predicted total value is determined using mass and/or energy balance calculations. The predicted total value is determined at least one time during a predetermined time interval. The pulp dryer 1 is thus regarded as a thermodynamic system which allows the total amount of moisture present inside the dryer 1 at each moment in time to be determined with high accuracy on the basis of the measurement results of the state variables.

Thus, the temperature, pressure and flow of the drying medium (i.e. in this case heated air) fed in and discharged can be measured and used to calculate the total amount of moisture present inside the pulp dryer by mass and/or energy balance calculations.

Alternatively, when determining the predicted total value of the moisture present inside the pulp dryer, measured conditions of the steam heating the drying medium (such as steam pressure, steam temperature and steam flow) and/or measured conditions of the dried pulp web 11 measured by the web condition monitoring unit 21 (such as temperature, pressure and moisture content) may be used, which may further improve the accuracy of the determination.

After performing the above-mentioned steps S1-S4, in a comparison step S5, the calculated total value of the moisture present inside the pulp dryer 1 is compared with the predicted total value of the moisture present inside the pulp dryer 1 to obtain a deviation therebetween.

Then, in the calibration step S6, the moisture sensor 19 of the moisture measurement unit 17 is calibrated using the deviation between the calculated total value of moisture and the predicted total value of moisture.

Finally, in a third measurement step S7, the moisture content of the web 3 reaching the pulp dryer 1 is measured using the calibrated moisture sensor 19.

The moisture sensor 19 may be calibrated periodically (e.g., several times a day) in this manner. The measurement for calibrating the moisture sensor 19 is performed before such a calibration operation.

The person skilled in the art realizes that the present invention by no means is limited to the embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims.

With reference to fig. 1, it has been described that the method according to the present disclosure can be used for determining the moisture content of a cellulose pulp web arriving at a pulp dryer, which dries cellulose pulp according to the airborne web principle. However, it should be appreciated that the method may be used for determining the moisture content of a cellulosic pulp web arriving at other types of pulp dryers, e.g. pulp dryers comprising steam heated cylinders.