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...

Blast furnace slag granulation at cast house May05

Blast furnace slag granulation at cast house...

Blast furnace slag granulation at cast house Blast Furnaces normally generate 250 to 350 Kg of liquid slag for every ton of hot metal produced. This molten slag is at around 1400 – 1550 deg C temperature.  Till seventies blast furnace (BF) slag was considered a waste product and was being dumped at a convenient place away from the blast furnace.  During early seventies granulation of molten slag with high pressure water started near the slag dumps. The processes of granulation of molten slag were developed during late seventies and early eighties. The processes differ in the method of dewatering of the wet granulated slag. Today granulation of molten BF slag is the well accepted technology and is being used in most of the blast furnaces around the world. In India the credit of commissioning the first cast house slag granulation plant goes to Visakhapatnam Steel Plant when the first blast furnace of the plant was commissioned on 28th march 1990. Major slag granulation processes presently under operation are OCP granulation system, Gipromez designed plants, Rasa system and INBA slag granulations plants of Paul Wurth, modified INBA process or IDE process etc. Concept of slag granulation The process of slag granulation involves pouring the molten slag through a high pressure water spray in a granulation head, located in close proximity to the blast furnace. Granulation process is the controlled quenching of the slag in cold water which does not give time for crystalline growth to take place. Large volume of water is required (10 parts of water to 1 part of molten slag being optimum). During this process of quenching, the molten slag undergoes accelerated cooling under controlled water flow condition and gets converted into glassy sand with 97 % of the solid granulated...