In this technology, DRI is produced in a rotary kiln of 3-6 m diameter and ~ 85 m length installed at an incline. The capacity of the kiln depends on metallization degree and usually does not exceed 225,000 – 300,000 t/y. It is operated in counter-current flow with solids moving down the incline in opposite direction to the gases. Iron ore and coal are jointly charged to the kiln from the charge end. As the burden progresses down the slope it is heated up by the gas to a temperature of 1000-1100 °C. A typical retention time of 10-14 hrs, allows for the ore to be reduced to DRI by the CO produced by the carbon content of the burden. The pulverized coal/natural gas/oil burner is installed at the discharge end of the kiln. Metallization varies from 83- 92% and carbon does not exceed 0.5%. Sponge iron is discharged from the kiln at approximately 800 -1000°C. Off gases produced in the kiln contain considerable sensible and chemical heat, the recovery of which represents the biggest opportunity for improving energy efficiency in this process.

The advantages of this process includes low capital requirements, eliminated need for sintering, pelletizing or agglomeration, and ability to use low-grade coals. However, CO₂ and particulate matter emissions of the technology is high and is a major environmental concern.

See also SL/RN process.