Thermal energy recovery from high-temperature blast furnace slag particles

• Dry granulation for molten blast furnace slag is an attractive alternative to wet granulation.
• The heat transfer characteristic of bench-scale gravity bed waste heat boiler is investigated.
• The relations obtained can be used to calculate heat transfer coefficient within a certain range.

Dry granulation is an attractive alternative to water quenching because of saving energy and reducing water consumption. In many dry granulation technologies, the high-temperature molten slag is atomized to slag particles, and the thermal energy from high-temperature slag particles is recovered by physical and chemical methods. In the present study, a technique for thermal energy recovery from high-temperature slag particles using a gravity bed waste heat boiler was exploited. The heat transfer characteristics of a laboratory-scale gravity bed waste heat boiler were investigated. An increase in Reynolds number (Re) showed no effect on the heat transfer coefficient or recovery efficiency. However, the heat transfer coefficient and recovery efficiency increased with a decrease in particle diameter and an increase in the velocity of descending particles. Compared with those observed with an aligned arrangement of the boiler tubes, the heat transfer coefficient and the recovery efficiency were higher in a staggered arrangement. The semi-empirical relations regarding the heat transfer coefficient between slag particles and boiler tubes were obtained based on experimental data and can be used to calculate the heat transfer coefficient within a certain range.