Induration & cooling
Compare the complete process route, fuel system and operating case.
What happens here
Induration dries and hardens green pellets through thermal treatment, followed by cooling. Straight-grate and grate-kiln are established process arrangements; evaluate the complete project basis rather than the technology name alone.
Equipment in this stage
Induration systems, burners, fans and coolers.
Inputs to define
Ore and product basis; fuel and utility scope; heat-recovery interfaces; emissions controls; acceptance conditions.
A useful review question
Keep supplier predictions separate from demonstrated reference results. Ask what operating envelope applies to a guarantee.
Continue to the practical guide ↗Why the same furnace setting can produce a different pellet
Magnetite oxidation releases heat during induration. Pot-furnace research demonstrates that oxygen availability and position within the bed influence temperature development and pellet properties. The implication for analysis is that a furnace setpoint alone does not represent the thermal history of every pellet. Feed mineralogy, bed structure, gas conditions and time must be considered together.
Pellet-size research also shows that the surface and core do not necessarily transform at the same time. A change in the size distribution entering the furnace can therefore alter product behaviour even when external operating settings remain unchanged.
Separate three possible origins of weak product
| Potential origin | Useful evidence | Next comparison |
|---|---|---|
| Weak or damaged green feed | Green strength and fines before the furnace | Balling discharge versus final feed point. |
| Uneven treatment within the bed | Spatial samples, gas data and bed loading | Edges versus centre and upper versus lower locations where authorised sampling permits. |
| Damage after cooling | Quality at cooler discharge and downstream transfers | Matched size fractions before and after handling. |
A plant-average compression value can conceal a weak subpopulation. Preserve individual test results or the agreed distribution summary, sample count and size classes. Trend the proportion below an agreed limit alongside the average, using the same sampling method.
Qualify an operating envelope, not a single favourable test
A robust acceptance programme includes representative feed variability, product requirements, stable operation and calibrated measurements. Establish whether fuel, fan electricity, saleable tonnes and emissions share the same time boundary. Startups, shutdowns and recycle can materially change a monthly figure. A short performance test and an annual operating budget answer different questions.
Technical references
ISIJ International — oxygen level, oxidation and magnetite pellet-bed induration (2021) ↗
ISIJ International — influence of pellet size on quality and microstructure (2008) ↗
ISIJ International — optimisation of firing temperature for hematite pellets (2013) ↗
References support the underlying principles. Diagnostic sequences, worked examples and procurement questions are original engineering analysis; they are not plant operating instructions or verified supplier performance results.
Qualify the thermal route with representative ore
Preheated strength has particular importance before grate-to-kiln transfer. In a straight-grate arrangement, differences through the stationary bed also need attention. Mineralogy, oxidation, size distribution and local gas conditions affect the thermal response; neither a route name nor a furnace setpoint is a complete specification.