THE APPLICATION OF A MODEL FOR TWO PHASE FLOW THROUGH A COMPRESSIBLE POROUS MEDIA TO THE WETPRESSING OF PAPER

The purpose of this study was to apply a model for two phase flow through a compressible porous media to the dewatering of paper sheets in a transversal flow press nip. This process took place in several stages. The first step was to develop equations describing the dynamic compression, permeability, and capillary pressure behavior of the paper sheets. These relationships were then input to the model and computer simulations were done to compare with dewatering studies on the dynamic compression tester. The model was found to work very well under these circumstances. Next pilot trials were conducted at Beloit on a pilot press and compared to the laboratory studies conducted at the University of Maine on the dynamic compression tester. There was a substantial difference in water removal in these two studies which seemed to be caused by nonuniform application of pressure to the paper sheet by the felt. A nip efficiency factor to be applied to press impulse was developed to account for this difference. Using the nip efficiency factor, the model was able to predict dewatering on both the pilot press and mill press section. With this knowledge, the model was used in a variation of parameters study to better understand the general dewatering behavior of paper sheets and in an optimization study of the mill trial press section.