Mid Sweden University

This paper presents a new strategy for steam pressure control during web breaks in the paper machine. The aim was to restart paper production with the same drying properties of the cylinder as before the break. A detailed physical dynamic model of the drying cylinder has been developed. The accuracy of the model has been verified through experiments made at the M-real paper mill in Husum, Sweden. Verifications are made both during normal operation and during web breaks. The dynamic model has been reduced in order to derive simple transfer functions which were used to find the optimal steam pressure trajectory during web breaks. The resulting strategy has been tested on a paper machine with good results and it has been well received at the mill.

In this paper, the problem of calibrating a paper machine dryer section model to measurement data is treated. The model, which is dynamic, nonlinear and of large scale, is implemented in Modelica and Dymola. The purpose of the model is to evaluate, in simulation, new control structures before application to the plant. This approach requires a well calibrated model in order for simulation results to be valid also on the real plant. In this paper, the problem is addressed by parameter optimization. A custom application integrating code generated by Dymola and packages for numerical optimization has been developed. Results are satisfactory, in that the mismatch between the calibrated model response and measured data is small.

A new control strategy for steam pressure control in the drying cylinders during web breaks is presented. The development is performed using a new physical model implemented in Matlab Simulink. The goal of the control strategy is to obtain the same drying properties after the web break as before the break as fast as possible.

Web breaks in the dryer section of a paper machine cause loss of production and quality problems. After a web break, the steam pressure in the cylinders must be reduced to avoid overheating. The goal of this project is to determine optimal steam pressure trajectories during web breaks, so that the production is restarted with the same drying properties of the cylinder as before the break. A detailed physical dynamic model of the drying cylinder has been developed. The model describes the relations between the steam valve position, the steam pressure, the cylinder temperature, and the paper temperature. The model is based on partial differential equations that describe heat conductivity for the cylinder and the paper web, and mass balances of water and dry material in the paper. The accuracy of the model has been verified through experiments made at the M-real paper mill in Husum, Sweden. Verifications are made both during normal operation and during web breaks. The dynamic model has been reduced in order to derive simple transfer functions between the steam pressure and the cylinder temperature, and between a logic signal that is active during web breaks and the cylinder temperature, respectively. The transfer functions obtained were used to find the optimal steam pressure trajectory during web breaks. A new feed-forward strategy for steam pressure control during web breaks is presented. The strategy has been tested on a paper machine with good results. The strategy is built on feed-forward compensation and has been well received at the mill.

A new control strategy for steam pressure control in the drying cylinders during web breaks is presented. The development is performed using a new physical model implemented in Simulink. The goal of the control strategy is that the cylinder temperatures are retained when the production is restarted after the web break.