The work focuses on an important scientific problem of modeling thermal processes of thermal technology, which are complicated with non-isothermal chemical reactions during the thermal preparation of raw materials in a dense layer. A mathematical model is presented for heat and mass transfer in a dense layer. The firing phosphate pellets parameters analysis calculated according to the model and performed on a kiln machinery in the scheduled mode was conducted. The features of the course of processes of drying, agglomeration and dissociation of carbonates in the pellets are revealed at their heat treatment. The received results, allow defining the temperature and gas dynamic condition of roasting the pellets for achievement of the required moisture content, necessary extent of dissociation of carbonates and the acceptable durability.