Borate Ore Calcination: 2D Kiln and Lump Profile

Kiln

Peak gas temperature 650 C

Residence time 40 min

Lump size 20 mm

Burner position 0.75

Discharge product

Dehydration

-

Loss on ignition

-

B2O3 grade

-

Decrepitated fines

-

Energy to product

-

Hottest lump

-

Colemanite loses 5 H2O (21.7 wt%) near 400 C: da/dt = A exp(-Ea/RT)(1-a), Ea 160 kJ/mol, endothermic. Radial conduction + convection/radiation heats each lump; fast steam release (rate x size) cracks it into fines (decrepitation). B2O3 = 50.8/(1 - 0.217 a).