Drying Kinetics and Process Simulation: From Experiments to Modeling of a Belt Dryer and Heat Recovery Analysis

Drying stands as a significant energy-intensive operation, typically reliant on fossil fuels to heat the drying air. Moreover, the residual energy in the used air, especially the latent heat from evaporated water, often remains largely untapped. Thus, there is a need to analyse the drying process and optimise drying parameters, such as air temperature, to enhance efficiency, and a need to analyse the potential utilisation of the heat contained in the used air. To properly model the dryer, the resistance of the dried material to water diffusion must be taken into account, e.g. by evaluating the drying kinetics of the dried material. This contribution presents an experimental evaluation of drying kinetics using the characteristic drying curve method and a prototype continuous gravimetric device capable of maintaining a uniform temperature, humidity, and velocity profile of the drying air. The kinetics are used in the model of a laboratory belt dryer, which uses empirical equations to calculate the field heat and mass transfer coefficients for the field of air nozzles in the analysed dryer. The model provides key results such as evaporation rate or product temperature along the belt, while key parameters such as air temperature and volume flow can be adjusted and studied. For more complex analyses of the drying process, a so-called toolbox model is used to investigate key heat recovery options and quantify their potential to improve energy efficiency. This toolbox model focuses on the analysis of the equipment before and after the dryer (e.g. heat exchangers, heat pumps). This work was carried out as part of the EDDY – Enhanced Drying, FFG project number 880778, part of the BatWoMan, that received funding from the European Union’s Horizon research and innovation programme under Grant Agreement no. 101069705, and part of the IEA HPT Annex 59 – Heat Pumps for Drying.