Industrial Validation of a Multiple Technique Paper Drying Simulator, 1999 Engineering Conferenc Proceedings

Shaun Sidwall, J.-F. Bond and W.J.M. Douglas, Department of Chemical Engineering, Pulp and Paper Research Centre, McGill University, Montreal

An extensive validation of a multiple technique dryer simulator was carried out with papermachines producing grades from 19 g/m 2 tissue paper to 337 g/m 2 containerboard, and dried by several drying processes used both singly and in combination as a multiple technique dryer section. The importance of full microscopic scale modeling of sheet internal conditions is demonstrated. This basis is especially important when considering medium to heavy weight sheets or for high intensity drying techniques with even the thinnest grade because of the large thickness direction gradients for all heat and mass transport variables. For multiple technique drying where the output from one drying element becomes the input for the next, microscopic level modeling is shown to be essential. This pressing-drying simulator is capable of treating 8 basic water removal techniques including normal and extended-nip presses, single/double tier cylinders, and Yankee air impingement cylinders and hoods. The model also allows for the addition and removal of solids and moisture and can therefor be adapted for on-line coating and sizing, commercially important cases of multiple technique processing of the sheet. To demonstrate the accuracy of the simulator, simulations were run using data gathered from papermachines and companies, with the results of uncalibrated machine speed predictions compared to actual speeds. These results for 31 such predictions show that the standard deviation of the difference between actual machine speed and that predicted is 3.4 %, with only a few simulations having a difference greater than 5 %.