Dry Granulation of Blast Furnace Slag for Energy Recovery Aug09

Dry Granulation of Blast Furnace Slag for Energy Recovery...

Dry Granulation of Blast Furnace Slag for Energy Recovery  Around 300 kg of liquid slag is produced as byproduct while producing one ton of hot metal in a blast furnace (BF). This slag is at a temperature of around 1500 deg C and has a sensible heat of approximately 400 M Cal per ton. BF slag is rich in CaO, SiO2, Al2O3, and MgO which are similar to the components of Portland cement. When the high temperature liquid BF slag is cooled fast enough then the slag has a large percentage of glassy phase with high cementations activity and hence it can be used as a higher value product, especially for substitution of Portland cement. This is also a good way to reduce CO2 emission because the cement manufacturing also produces large amount of CO2. To obtain glassy phase in BF slag, the liquid BF slag is subjected to water granulation process. Today rapid cooling of liquid slag in a closed water slag granulation plant is state of the art process. The rapid cooling of the liquid BF slag in the water prevents the crystallization of slag and breaks the slag into small particles by thermal stress. The liquid BF slag freezes in an amorphous granulate, called granulated BF slag. The non crystallization rate of the water granulated BF slag can reach to a level of 95 %. By contrast, the glassy phase obtained during crystallization of liquid BF slag by slow cooling in the air is quite limited. However, water granulation of liquid BF slag consumes large volumes of water (1,000 to 1,500 litres of evaporative loss per ton of liquid BF slag processed) and can generate acid mist causing air pollution. Also there is the need of a proper water management on...