Vol.4, No.1, 2019 01 PBM·Wet Pressing Models Wet Pressing Models to Reduce Energy Consumption in Papermaking Abstract: Improved wet pressing reduces the need for drying and consequently energy needed in papermaking. Accordingly, it is desirable to optimize wet pressing, but the process is very complex with many interacting variables. It is therefore desirable to employ a mathematical model that accounts for the major variables to estimate the effects of changes in equipment and operating variables. This paper descibes such a model called the Decreasing Permeability Model (DPM). Mill and pilot plant applications over a wide range of basis weights for paper and paper board are described. Keywords: wet pressing; Decreasing Permeability Model (DPM); papermaking; water removal; rewet; mathemeitical model J. David McDonald 1, * , Richard J. Kerekes 2 , Joe R. Zhao 3 1. JDMcD Consulting Inc., Vaudreuil-Dorion, Quebec, J7V 0G1, Canada 2. Pulp and Paper Centre, the University of British Columbia, Vancouver, BC V6T 1Z4, Canada 3. Tri-Y Environmental Research Institute, Vancouver, BC V5M 3H9, Canada Received: 17 October 2018; accepted: 21 November 2018. * Corresponding author: J. David McDonald, PhD; research interests: papermaking, mechanical pulping, and bio- materials; E-mail: mcdonald.jdavid@ gmail.com 1 Introduction Improved wet pressing is a major means of energy conservation by reducing the need for drying in paper and paper board production. In non-integrated mills, steam for drying must be generated by combustion of gas, oil, coal or biomass. Kraft and TMP mills often have excess steam, but even low-pressure steam can now be used in condensing turbines to produce electricity rather than to dry paper. Thus, removing more water mechanically in the pressing process reduces energy consumption and may liberate steam that could be converted into high-value energy. There are other potential benefts as well, such as improved runnability and higher machine speeds which result in greater production rates. Given these benefts, there is a strong desire to optimize press sections. The objective of this study is to describe a model of wet pressing that enables this. 2 Overview Pressing is a very complex process affected by many variables: