Iron Nuggets are produced by ITmk3 process, which is also known as ‘Iron making Technologies mark 3’. The process is based on coal reduction technology and developed by Kobe Steel.
The laboratory testing of the process was carried out during 1996 to 1998. During 1999 to 2000, a pilot plant of capacity 3,000 TPD was constructed and operated at Kakogawa Works of Kobe Steel, Japan. During 2002-2004, a Pilot Demonstration Plant (PDP) of 25,000 MT per year was constructed and operated at Minnesota, USA.
The PDP had a 14 meter diameter RHF (Rotary Hearth Furnace), all the required material handling & off gas treatment systems. Four campaigns were run from 2002 to 2004 and their total run time was 230 days, with the longest campaign of being 81 days. Overall plant availability was 93-94% and 9,561 MT of high quality Nuggets were produced. On June 12, 2003 about 19 MT of Nuggets were shipped to Steel Dynamics’ Butler, Indiana, mini-mill and melted the next day to produce Steel Coils. Overall, the plant operation was considered very successful.
The construction of first commercial plant, with capacity of 0.5 MnT per year started at Hoyt Lakes Minnesota in 2007 and the operation of the plant started in January 2010. The estimated capital cost of this ITmk3 Plant was around USD 260 millions and with an estimated 100 permanent jobs for operation and another 200 jobs for support services.
The Iron Nuggets process directly produces solid, high density, highly metalized Iron Nuggets from dry green balls of iron ore fines, Pulverized Coal, Fluxes & Binders. The pulverized coal is reductant, which is added to the system to supply carbon required for the reduction & carburization. Binder (Bentonite) in conjunction with the finely ground Iron ore particles serves to improve properties of green balls in wet and dried conditions. The flux is Limestone, which fluidizes the slag and also prevents excessive of iron loss in the slag. Iron Nuggets are produced using a direct reduction process. The reduction process is carried out in a Rotary Hearth Furnace, using coal as the reductant and energy source. The direct reduction of iron by this process is more energy efficient & more environmentally friendly than traditional iron making processes.
Main Features of Iron Nuggets Production
1. Utilization of low grade Iron ore Fines which is minutely grinded & beneficiated, in order to produce high grade Iron ore concentrate. This concentrate is converted into green pellets.
2. Non coking coal is used as a reductant.
3. These pellets are charged into a Rotary Hearth Furnace (RHF), heated to 1350 Deg C, reduced, melted and separated into metal & slag.
4. The molten iron solidifies into Nuggets in the furnace, discharged after cooling and separated from the slag.
5. In this process, the reduction reaction takes place in 10 minutes unlike 8 hours in Blast Furnace and 6 hours by the gas based DR (Direct Reduction) process.
6. The process is simple and uses conventional equipment. Further, small retention time also facilitates start up and stopping of the plant. Iron ore Fines and pulverized coal are agglomerated into composite pellets.