SL/RN process

The SL/RN process, developed in the early 1960s by Metso in collaboration with three US companies, laid the foundation for numerous rotary kiln plants. SL/RN and the new SL/RN Xtra processes remain the dominant technology for the direct reduction of lump ore or pellets using coal.

Benefits

The process principles are the basis for numerous rotary kiln plants and still represent the dominant technology for the direct reduction of lump ore or pellets using coal.

Operates with the widest range of iron-bearing materials, such as pellets, lump ore, beach sand, ilmenite and also iron ore fines with SL/RN-Xtra.
Works with an extensive range of reductants, such as sub-bituminous coals and lignites, bituminous coals, and in special cases also anthracite and coke breeze
Improves thermal efficiency with waste heat recovery systems in combination with export power generation
Meets environmental standards for emissions control
Can increase capacity with multiple line installations and an optimized material flow

In the standard SL/RN process, iron ore, coal, and dolomite or limestone as desulfurizing agent are charged into a rotary kiln and heated up by a countercurrent gas flow. Heat is generated by the controlled combustion of volatiles from the coal and surplus CO from the charge. The reduction of iron oxides in the solid state is achieved at temperatures between 920°C and 1100°C.

As an answer to decreasing ore grades, availability of lump ore and ever-increasing amount of fine ores and concentrates, Metso has developed a variant of the process, the SL/RN-Xtra direct reduction process, which allows customers to produce direct reduced iron (DRI) for steelmaking directly from concentrates in a single plant, combining pelletizing and direct reduction.

Reduction and coal gasification reactions take place simultaneously within the charge, creating surplus CO leaving the charge. The produced DRI and the residual non-magnetic fraction are magnetically separated after cooling. The waste gas passes through a waste heat boiler to recover heat for steam and subsequent power generation.

Iron ore fines resulting from the concentration process are frequently available at high levels of quality (high iron and low gangue contents) and are therefore most suitable for high-quality DRI production.

Both standard SL/RN and SL/RN-Xtra plants use the following main equipment:

Raw material handling facilities
Rotary kiln
Rotary cooler
After burning chamber (ABC)
Waste heat boiler
Electrostatic precipitator
Product separation and handling facilities

SL/RN-Xtra also includes:

Pelletizing facilities
Pre-hardening grate

Metso has comprehensive research and development capabilities with laboratories and pilot plants for testing customers' raw materials. These tests form the basis for determining the layout and achievable capacity of a plant. Our standard rotary kiln (4.8 x 80 m) is capable of producing up to 160,000 tons DRI per annum depending on the raw material. In the SL/RN-Xtra version, this figure goes up to 200,000 t/a.

Typical consumption figures per ton of DRI produced from lump ore or pellets are: