Metso Paper Inc.

Jorma Kari

Hans Sundqvist

Kristian Hamstr&ouml;m

A method and apparatus for controlling the drying process taking place in the dryer section of a paper machine or the like. The total drying efficiency required in the dryer section is first calculated by means of a method known as such, and an optimal drying efficiency distribution is compiled. Using the optimal drying efficiency distribution, the dryer section is divided into two or more imaginary drying segments which differ in their drying action, in at least one of which segments there are at least two dryer units using different forms of energy and/or at least two separately adjustable dryer units using the same form of energy. The total drying efficiency obtained is divided, by means of an optimization method known as such, between the said different drying segments in such a way that a good drying efficiency distribution is achieved in terms of the quality of the web being dried.

Method and apparatus for controlling the drying process in a drying section of a paper machine or the like

A method for controlling the drying process taking place in the dryer section of a paper machine. The dryer section comprises at least one drying cylinder unit and at least one air impingement unit. Optimal evaporation is first compiled in a manner known, for example, on the basis of a recipe or by utilising a machine-direction quality model or quality profile, when the geometry of the dryer section, the process parametersrequired, such as machine speed, paper grade and total evaporation required are known. Limit values are calculated for at least two controlled variables of the dryer section, such as the steam pressure and the temperature of blowing air, making use of drying quality models, such as models representing the adhesion and brightness of paper. After this the dryer section is divided an the basis of the distribution formed by the limit values of the controlled variables into drying segments, so that in two adjacent segments, the limit value of at least one controlled variable is different. The drying process is controlled by adjusting the controlled variables in each drying segment, within the limit values of the controlled variables.

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Mietoinen, Finland

Jorma Kari