Experimental study of infrared-convective drying of hydrous ferrous sulphate

This study describes the combined drying (convective and infrared) of hydrous ferrous sulphate. The objective is to reduce the free water fraction in order to obtain a loss of 20% of the initial mass. The drying kinetics was investigated for three thin layers of product (0.5, 1, and 2 mm) placed in a rectangular crucible. During the experiment, the upper face of the samples is subjected to infrared irradiation and air flow. Results show that IR irradiation makes it possible to reduce the drying time in an important way and that it is necessary to modulate the infrared irradiation with the thickness. The high amount of IR irradiation applied to the product can generate gradients of moisture in the product. So, the formation of a crust on the surface of the material can be observed and the temperature of the material becomes higher than the melting temperature (64 °C). This crust limits the migration of water towards the surface. It is then necessary to apply appropriate control to the infrared emitters.