Modelling of paper drying: a comprehensive computational model used by the industry

In paper industry, drying simulation programs can be used in order to calculate new drying arch or to optimize paper quality through better moisture profile or adequate non-contact dryer location. Few years ago, LERMAB and SOLARONICS IRT developed a drying model to address those needs. A simplified set of equations, deduced from realistic physical assumptions, was used as first step. This set allowed us to finalize an easy-to-use computer tool, developed in VBA (Visual Basic Application) and running with all graphical facilities provided by Excel. This tool has been used on actual industrial plants for several applications and a large range of process data to size innovative solutions. In most cases, the simplified assumption proved to be relevant. Nevertheless, in some specific cases, some discrepancies happened between simulated results and data measured on site. This paper describes a new model that has been developed to take into account the moisture distribution across paper thickness and its internal gaseous pressure. Because this second set of equations is dramatically more demanding in numerical strategy, the initial computational solution had to be revisited. However, it was very important for the SOLARONICS IRT company and its staff to keep the same graphical facilities. A solution has been found in which a very efficient computational heart is written in Fortran with up-to-date numerical strategies and compiled as a dynamically linked library used by the former VBA software. By this way, the improvement of the physical description of paper drying is just invisible for final users: neither the interface, nor the computational time changed, but the results are more relevant