Slag is a by-product generated during manufacturing of pig iron and steel. It is produced by action of various fluxes upon gangue materials within their on ore during the process of pig iron manufacturing in blast furnace and steel manufacturing in steel melting shop.Primarily, the slag consists of calcium, magnesium, manganese and aluminum silicates in various combinations.The cooling process of slag is responsible mainly for generating different types of slags required for various end-use consumers. Although the chemical composition of the slag may remain unchanged, physical properties vary widely with the changing process of cooling.
slag granulation process
Wet granulation of blast furnace slag has been practised for many years. Various systems are in use and all are based on the quenching of molten slag with water. The original process was the OCP granulation system (gravel layer filtering plant) – the starting point for further development of the granulation process and plant design. Improvements have become a must since the environmental demands imposed by local authorities in various countries become ever more stringent.
The aim of wet granulation is the fast quenching of molten slag. During the quenching process the molten slag converts into glassy sand with 97% of the particles less than 3mm, and an average slag sand particle size of less than 1mm. The impact point of the slag stream and the granulation water depends on the slag flow, its temperature and the slope and shape of the hot runner. The heat exchange between molten slag and granulation water has to take place very quickly. The granulation water jets break up the slag stream into molten slag lamellae which decompose initially into filaments and then into droplets. The best heat transfer occurs when the contact surface between the molten slag and the water is at maximum, ie, when slag has been converted into droplets and fully enclosed with water. The solidification time depends on the size of the slag droplets, the temperature difference between the molten slag and the granulation water, and the contact environment between the slag and the water. Depending on the granulation water temperature around the slag droplet, different heat transfer mechanisms take place.