GAS BASED DIRECT REDUCTION IN FLUIDISED BEDS - FINMET PROCESS

The Fluidised Iron Ore Reduction(FIOR) process was developed by Esso Research and Engineering Co., USA for the continuous reduction of iron ore fines by reformed natural gas in a train of fluid bed reactors. Presently there is no FIOR plant operating in the world.

The original FIOR process was substantially improved jointly by Fior de Venezuela and Voest Alpine (VAI) of Austria in 1991 culminating in the development of Finmet Process.

HISTORY

PROCESS

The Finmet process uses a train of four fluid bed reactors with counter-current gas/solids contacting down the reactor train. The feed concentrate (iron ore fines of less than 12 mm size) is charged to the reactor train via a pressurized lock hopper system. The upper lock hopper in this system cycles continuously from ambient to reactor pressure to feed the ore continuously to the reactors maintained at the reactor pressure of 11-13 bars. The feed enters the topmost reactor (R4) where it is pre-heated to 550-570OC by the reducing gas leaving reactor (R3).

Pre-heating, dehydration, decrepitation and reduction of hematite to magnetite take place in reactors R4, R3 and R2. The temperature in R1 is around 780-800OC and final reduction to 93% metallization is accomplished in this reactor accompanied by carburization of some of the Fe to iron carbide.

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The hot fine DRI (at 650OC) is then transported by a sealed system to the briquetting machine to attain a briquette density of around 5 gm/cm3. The product from any Finmet plant is hence, HBI (Hot Briquetted Iron).The gas required for reduction is a mixture of recycled top gas and fresh reformer make-up gas processed in a standard steam reformer from natural gas. The recycled gas (taken from the top gas leaving R4), is first quenched to 40-50OC and scrubbed in a wet scrubber to remove dust and water. The make-up gas required to balance the gas consumed by the reduction reactions is supplied from a conventional steam reformer system . 

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Metallisation and Carbide Formation Reactions

FeO + H2 = Fe + H2OFeO + CO = Fe + CO2

3Fe + 2CO = Fe3C + CO2

3Fe + H2 + CO = Fe3C + H2OFe + CO + H2 = Fe (C free) + H2O3Fe2O3 + 5 H2 + 2CH4 = 2 Fe3C + 9 H2OFe3O4 + 2 H2 + CH4 = Fe3C + 4 H2O

Advantages • Compared to the Midrex and HyL processes, the FINMET technology offers the convenience of using fines, which constitutes a lower-cost input than the pellets or the iron-ore lumps. Midrex and HyL, can use a maximum 5% fines.

• The output from a Finmet plant is HBI with Fe content varying from 91-94%, carbon 1-1.5% (or 3% maximum), metallization 91-93%.

Finmet’s operating pressure is as high as 12 bars to ensure higher degree of metallization. It has been reported that continuous operation at such high pressures has been a major problem in both the Finmet plants.    

Disadvantage

Commercial Finmet Plants

They have been designed with multiple reactor trains, each reactor train having a nominal capacity of 500,000 tpa. The following commercial plants based on the Finmet process have been built :• Orinoco Iron at Puerto Ordaz, Venezuela (1 Mtpa)

• BHP DRI at Port Hedland, Australia ( 2 Mtpa, now closed)

BHP's Finmet Plant in Port Hedland, Australia. 

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