Direct reduced iron

Direct reduced iron (DRI) is iron produced from iron-ore pellets by reducing the ore in the solid state, using natural gas, hydrogen or coal as the reducing agent. DRI feeds electric arc furnaces and is the leading candidate for low-carbon iron-making, particularly with hydrogen as the reducer.

DRI dust-handling issues

DRI processes generate fine iron-bearing dust at multiple points:

• DRI plant baghouse hoppers
• DRI cooler dust extraction
• HBI (hot-briquetted iron) hot screening dust
• Storage-silo discharge points

The dust is fine, dense, and prone to bridging under self-weight in tall silos. Sonic horns on DRI dust hoppers prevent the discharge interruptions that would otherwise force operator intervention.

Process routes

Gas-based DRI uses a shaft furnace where iron-ore pellets descend against a rising stream of reducing gas rich in hydrogen and carbon monoxide. Coal-based rotary kiln routes use solid carbon and high temperature to reduce ore. The product can be discharged hot, cooled, or compacted into hot-briquetted iron to reduce reoxidation and improve handling.

DRI has high metallic iron content but can be reactive, especially when freshly produced and porous. Storage and transport must control moisture, oxygen exposure and heat build-up. HBI is less reactive because briquetting reduces surface area and closes pores.

Dust and solids-handling issues

DRI plants generate iron oxide, metallic iron, carbon and lime-bearing dust from screening, transfer points, coolers, reformers, baghouses and briquetting. The dust can be dense, abrasive and cohesive. Some fractions may be combustible or prone to self-heating depending on metallic iron content and moisture.

Hopper and silo problems include ratholing, arching, feeder flooding, dust collector pluggage and abrasion at bends or rotary valves. Because DRI plants often run continuously, a blocked dust hopper can quickly become a production or housekeeping issue.

Acoustic-cleaning context

Sonic horns are relevant to DRI dust hoppers, transfer chutes, baghouse compartments and storage vessels where fine iron-bearing dust bridges. They do not affect the reduction chemistry or metallisation directly. Their value is keeping dust-control and by-product handling systems available so the ironmaking process does not slow for preventable solids-flow interruptions.

Field checks

DRI plants are watched through metallisation, carbon content, reformer or reducing-gas quality, shaft pressure drop, bustle gas distribution, product temperature and fines generation. The product can reoxidise if handled hot or exposed to moisture, so storage and conveying arrangements are part of the safety case as well as the process design. Dust collection around screens, conveyors and briquetting equipment is important because iron-rich fines can be reactive.

Maintenance checks cover seals, burden distribution, gas heaters, scrubbers, baghouses, bins and discharge equipment. Bridging, rat-holing and dust build-up are common where hot porous solids cool and absorb moisture. Acoustic cleaning is relevant in dry dust collectors, bins, transfer chutes and gas-cleaning ducts where iron oxide dust builds into restrictions. It is not normally applied inside the reduction shaft, where temperature, reducing atmosphere and process containment control the available cleaning methods.

Related terms

• Electric arc furnace (EAF)
• Hopper
• Bridging