Evaporation rate independent state estimation for a spray drying process

The problem of model-based state estimation in absence of a reliable model for the liquid evaporation rate in a spray drying process is addressed. The process is described by a three-state model consisting of the product moisture, air humidity and temperature in the spray drying chamber with measurements of the temperature and air humidity. The state estimation problem is approached within the framework of unknown-input observer design, considering the evaporation rate as unknown time-varying bounded source term. It is shown that using an adequate integral state transformation based on energy and mass conservation mechanisms it is possible to obtain reliable estimates for the product moisture by model-based sensor fusion. The performance of the proposed scheme is evaluated using numerical simulations for a previously validated process model.