DRI Kiln Inefficiencies: Where the Coal Goes When It Shouldn't

The Coal Cost Problem in DRI

In a coal-based DRI plant, coal is typically the largest variable cost - representing 30-40% of the total production cost per tonne of DRI. Every percentage point of coal efficiency improvement translates directly to the bottom line.

Three Sources of Inefficiency in Rotary Kiln DRI

Through detailed process audits at multiple DRI plants, ACL has identified three systematic sources of coal waste:

1. Incomplete Reduction in the Kiln

The coal particles at the feed end of the kiln are not yet fully ignited. Cold coal has low reactivity. As a result, the initial reduction zone is inefficient: ore passes through without adequate contact with reactive reducing gases.

2. Volatile Matter Losses

Coal volatile matter represents 20-35% of the energy content of typical DRI-grade coal. In a rotary kiln, volatile matter is released at the feed end and typically escapes without being used for reduction.

3. Unburnt Carbon Carryover

At the discharge end of the kiln, significant quantities of unburnt carbon are present in the DRI product - typically 2-4% elemental carbon. This carbon represents coal that was paid for but did not contribute to reduction.

ACL's Approach

ACL's DRI coal additive is applied at ~1% dosing on input coal. It accelerates volatile matter release and initial coal ignitibility at the feed end, improves carbon reactivity in the reduction zone, and promotes more complete burnout at discharge. The net result is a reduction in coal consumption per tonne of DRI produced.