Search

CA-3114022-C - METHOD OF DETERMINING THE MOISTURE CONTENT OF A WEB OF CELLULOSE PULP

CA3114022CCA 3114022 CCA3114022 CCA 3114022CCA-3114022-C

Abstract

The present invention relates to a method of determining the moisture content of a web (3) of cellulose pulp arriving at a pulp dryer (1). The method comprises measuring, at several instants during a predetermined time interval, the moisture content of said web (3) using a moisture sensor (19) arranged upstream of the pulp dryer (1); measuring state variables of drying medium of said pulp dryer (1); calculating, based on said moisture sensor measurements, a total value of moisture introduced into the pulp dryer (1) by a portion of said web (3) during said predetermined time interval; determining, based on said measured state variables, a predicted total value of moisture present inside the pulp dryer (1); comparing said calculated total value with said predicted total value to obtain a deviation therebetween; calibrating said moisture sensor (19) using said deviation; and measuring the moisture content of a web (3) of cellulose pulp using said calibrated moisture sensor (19).

Inventors

  • Ola Larsson

Assignees

  • ANDRITZ TECHNOLOGY AND ASSET MANAGEMENT GMBH

Dates

Publication Date
20260505
Application Date
20190924
Priority Date
20180925

Claims (6)

  1. 9 CLAIMS 1. Method of determining the moisture content of a web (3) of cellulose pulp arriving at a pulp dryer (1 ), said method comprising: 5 measuring (S1) the moisture content of said web (3) at several instants during a predetermined time interval using a moisture sensor (19) arranged upstream of the pulp dryer (1 ); measuring (S2) state variables of drying medium of said pulp dryer (1 ); characterised by further comprising: 10 calculating (S3}, based on said moisture sensor measurements, a total value of moisture introduced into the pulp dryer (1) by a portion of said web (3) during said predetermined time interval; determining (S4 }, based on said measured state variables, a predicted total value of moisture present inside the pulp dryer (1 ); 15 comparing (S5) said calculated total value with said predicted total value to obtain a deviation therebetween; calibrating (S6) said moisture sensor (19) using said deviation; and measuring (S7) the moisture content of a web (3) of cellulose pulp using said calibrated moisture sensor (19).
  2. 2. A method according to claim 1, wherein said predicted total value is determined using mass- and/or energy balance calculations.
  3. 3. A method according to any one of claims 1 and 2, wherein the step of 25 measuring (S2) state variables comprises measuring at least incoming gas conditions and exhaust gas conditions.
  4. 4. A method according to any one of claims 1 to 3, wherein said step of measuring (S2) state variables of drying medium of the pulp dryer (1) and 30 said step of determining (S4) a predicted total value of moisture present inside the pulp dryer (1) are carried out at least once during said predetermined time interval. Date Re9ue/Date Received 2024-02-23
  5. 5. A method according to any one of claims 1 to 4, wherein said step of measuring (S2) state variables of 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 carried out at several instants during said 5 predetermined time interval.
  6. 6. A method according to any one of claims 1 to 5, wherein said step of calibrating (S6) the moisture sensor (19) is carried out several times a day. Date Re9ue/Date Received 2024-02-23

Description

1 METHOD OF DETERMINING THE MOISTURE CONTENT OF A WEB OF CELLULOSE PULP Technical Field of the Invention The present invention relates to a method of determining the moisture content of a web of cellulose pulp arriving at a pulp dryer. Background Art Cellulose pulp is often dried in a dryer having several superposed horizontal drying decks. Cellulose pulp having about 50% water content is fed into the pulp dryer. A web of cellulose pulp is conveyed across the drying 10 decks of the dryer. Dry cellulose pulp, having about 10% water content, is outputted at the end of the lowest drying deck. An example of a cellulose pulp dryer is illustrated in WO 2012/074462 A1. Hot gas in the form of hot air is blown onto a web of cellulose pulp by means of upper blow boxes and lower blow boxes. The air blown by the blow 15 boxes transfer heat to the web to dry it. In addition, the air blown by the lower blow boxes keeps the web floating above the lower blow boxes. Hot air is supplied to the blow boxes by means of a circulation air system comprising fans and steam radiators heating the drying air. In order to control the drying process different parameters are 20 measured. Such a parameter is the moisture content of the web that is conveyed into the pulp dryer. Typically, the moisture content is measured using a moisture sensor. However, the accuracy of known moisture sensors is considered to be insufficient. Hence, there is a need for a more accurate measuring of the 25 moisture content of a web arriving at a pulp dryer. Summary of the Invention It is an object of the present invention to provide a more accurate method of determining the moisture content of a web of cellulose pulp arriving 30 at a pulp dryer. Date Re9ue/Date Received 2024-02-23 2 According to one aspect of the present disclosure there is provided a method of determining the moisture content of a web of cellulose pulp arriving at a pulp dryer, said method comprising measuring, at several instants during 5 a predetermined time interval, the moisture content of said web using a moisture sensor arranged upstream of the pulp dryer; measuring state variables of drying medium of said pulp dryer; calculating, based on said moisture sensor measurements, a total value of moisture introduced into the pulp dryer by a portion of said web during said predetermined time interval; 10 determining, based on said measured state variables, a predicted total value of moisture present inside the pulp dryer; comparing said calculated total value with said predicted total value to obtain a deviation therebetween; calibrating said moisture sensor using said deviation; and measuring the moisture content of a web of cellulose pulp using said calibrated moisture 15 sensor. A pulp dryer may be seen as a thermodynamic system, which allows the moisture content inside the dryer to be calculated at each instant with high accuracy using energy and/or mass calculations based on measured state variables of drying medium of the pulp dryer. The method of the present 20 disclosure is based on the idea of using the results from such calculations to calibrate a moisture sensor arranged upstream, e.g. at the entry, of a pulp dryer. By calibrating the moisture sensor in this manner a more accurate determination of the moisture content of a pulp web arriving at the dryer is 25 achieved. This provides for a more efficient control of the drying process. Furthermore, it makes it possible to detect deviations occuring upstream of the pulp dryer and to adapt drying conditions in accordance therewith to take them into consideration. Hence, since the moisture content determined by the calibrated sensor is reliable it can be used for different purposes with respect 30 to the overall efficiency of the pulp dryer. For instance, energy consumption and/or pulp quality may be optimized. The method thus allows for quick and reliable detection of deviations and variations in moisture contents. As the calibrated moisture sensor Date Re9ue/Date Received 2024-02-23 3 provides a reliable measurement of the moisture content of pulp web arriving at the pulp dryer, it may be used to optimize the drying efficiency and/or detect deviations upstream of the the pulp dryer at an early stage. In the calculations of the predicted total content of moisture inside the 5 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 10 at which the pulp web is fed into the pulp dryer. Furthermore, a certain time interval may be used during start-up of a drying process whereas a different time interval may be used during normal operation of the pulp dryer. Preferably, said step of measuring state variables comprises measuring at least incoming drying gas conditions and exhaust gas 15 con