Process of pellet drying on the firing conveyer belt machine has been considered. Phenomenon of 'free moisture' has been discussed. It has been shown that the pellets can absorb the free moisture. This leads to overhumidification of layer surface. Mathematical model of the moisture increase in layer surface has been developed with the use of differential equations. Coefficient of water carry-over in gas flow has been evaluated. Amount of removed free moisture has been determined. It has been noted that decrease in temperature of gas supplied to the drying zone cannot be permissible. Volume of the gas should be increased.