Granulated Pig Iron (GPI)
From time to time the supply of hotel metal from a blast furnace may exceed the demands of the steel plant, for example due to problems further downstream. In most integrated steel mills, the blast furnace plants are not equipped with pig casters, meaning that the excess hot metal has to be cast into an open air sand pit, a process known as “pooling” or “beaching.” The ensuing dust and fumes constitute an environmental hazard and the resultant pool or beach iron takes a long time to solidify before it can be crushed into usable material.
Granulation of the excess hot metal is a process that deals with these issues and produces a by-product – Granulated Pig Iron (GPI) – that can readily be used internally, for example as BOF coolant, or sold to third parties as feedstock for electric arc furnaces, cupolas and induction furnaces.
Granulated Pig Iron (GPI) can be used, for example, as BOF coolant, or sold to third parties as feedstock for electric arc furnaces, cupolas and induction furnaces.
Composition and Characteristics
GPI has the same chemical analysis as the source hot metal, with no slag contamination and minimal or no oxidation. Typical analysis is 4-4.5 % carbon, 0.5-0.6 % silicon, and 94-95 % iron. Tramp elements (copper, nickel, molybdenum, and tin) are typically at a maximum of 0.05 %. GPI has a deformed spheroidal shape and has a high bulk density of around 4,000 kg/m3. The particle size of GPI is in the range of 5 mm to 25 mm. GPI has a high angle of repose, which allows for effective transport and storage.
Process
The granulation process has four principal steps:
- Control of the flow of hot metal to the granulator
- Granulation by formation of liquid iron droplets, followed by rapid quenching in water
- Discharge of solidified and cooled particles (GPI}
- Dewatering and transport to storage
The diagram above compares the sandpit casting and granulation routes for dealing with excess hot metal, in this case the granulation process is the Granshot® process of IIMA member UHT Uvån Hagfors Teknologi AB.
Benefits of GPI in steelmaking
For further information about GPI and its benefits for EAF steelmaking, see our Fact Sheet:
- Use of Granulated Pig Iron (GPI) in the Electric Arc Furnace (EAF) for steelmaking