Analysis of the technique for experimental determination of the efficient heat transfer coefficient during drying of iron ore pellets and charge in the dense layer

CIS Iron and Steel Review. 2024. Vol. 27. P. 4–8.

Bobkov V. I., Dli M. I., Orekhov V. A., N. S. Kulyasov

The paper presents the experimental thermogravimetric unit for determination of the efficient heat transfer coefficient during drying and roasting of sintering charge from iron ore lump and pelletized raw material within the temperature ranges and aerodynamic conditions of the operating roasting conveyor machines, during complicated and power-intensive chemical-metallurgical process of iron ore raw material roasting in a moving dense layer with cross feed of the heat-transfer gas. The techniques for experimental determination of the efficient heat transfer coefficient during drying of iron ore pellets and charge in the dense layer are analyzed. It was scientifically substantiated that two periods should be underlined during drying of capillary-porous bodies (e.g. iron ore pellets); these are the periods of permanent and dropping drying rate. It was found out that moisture evaporation from the surface of a wet body during the first drying period occurs in the same way, as from free water surface, and according to the same laws. The temperature of a drying body does not increase practically, because transferred heat is consumed for evaporation until the whole free (capillary) moisture will evaporate. It was established that the second period starts from evaporation of bonded moisture, and drying rate is determined mainly by steam diffusion inside a wet body. Two independent methods were revealed on the base of analysis of the techniques for experimental determination of the efficient heat transfer coefficient. One of these methods is based on enthalpy variation of a drying agent, and another – on weight variation of a wet iron ore sample. It is noted that the experimental thermogravimetric unit, which was designed by the authors, allows to implement both of these methods. The error of variation of the efficient heat transfer coefficient is evaluated.

Keywords: drying, temperature, iron ore raw materials, thermogravimetric unit, heat and mass exchange, roasting conveyor machine, heat-transfer gas, efficient heat transfer coefficient