What is FASTMET Process of Ironmaking ?

11-Sept-2009
Fastmet – The Process Concept and References  

This is a direct reduction process using a Rotary Hearth Furnace (RHF) which was derived from the work done in USA by Midland Ross and Surface Combustion, in the ‘Heat Fast’ process, treated in 1960s. It is a solid reductant based process in which iron ore concentrate, pulverized coal and a binder are mixed together and pelletized. The resulting green pellets are fed either to a drier or directly to a rotary hearth furnace where the pellets are heated to 1250 - 1400^OC and reduced to metallic iron. Burners and post-combustion the CO evolved provide the heat required to raise the pellets to the reduction temperature.

The first commercial Fastmet plant was commissioned at the Hirohata Works No.1 of Nippon Steel in April, 2000 and Hirohata Works No.2 in February, 2005 with material processing capacities of 190000 tpa each plant. The second plant established was Kobe’s Steel’s Kakogawa Works started from April, 2001 having a material processing capacity of 16000 tpa.  The Fastmet process has allowed the Kakogawa Works to achieve a zero emission rating of steel mill waste. Waste utilization is the principal application of the Fastmet process in Japan.       

FASTMET Process - Flowchart

Advantages of Fastmet

Some of the advantages of Fastmet process as have been reported are summarized as follows:

=> A wide variety of iron ore as well as steel mill wastes including BF dust, BF Sludge, BOF dust, Sinter dust, EAF dust, mill scale, and etc. can be used as the oxide feed.

=> Elimination of waste disposal cost and landfill liability as wastes is changed to a quality source of iron (DRI).

=> Recovery of Zinc contained in wastes (Zn deriving from scrap) which can be sold to zinc producer. Zinc removal: 95% or higher.

=> A wide variety of energy sources can be utilized including natural gas, LPG, coke oven gas, heavy oil, coke breeze and carbon bearing wastes or pulverized non-coking coal.

=> The short reduction time of less than 12 minutes enables easy plant starting and shut-down, and quick adjustment of production rate.

=> Reclamation of carbon is possible. Carbon contained in dusts will be used as reductant. The carbon content of DRI can be adjusted as per the customer’s requirement.

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What is Finmet Process (Technology) of Ironmaking ?

9-Sept-2009
What is Finmet ?

Finmet is a fluidized bed iron ore reduction process developed jointly by Fior de Venezuela and Voest Alpine (VAI) of Austria in 1991 based on the original Fior process operated in Venezuela. Two Finmet plants are currently in operation - one 2 Mtpa plant at Puerto Ordaz, Venezuela and another 2 Mtpa plant at Port Headland, Western Australia operated by BHP (now Bluescope).

Fig: Flow-chart of Finmet Process

Finmet – The Process Concept

The Finmet process uses a train of four fluid bed reactors marked (A) in the adjacent figure 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 550-570^OC 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 780-800^OC and final reduction to 93% metallization is accomplished in this reactor accompanied by carburization of some of the Fe to iron carbide. The hot fine DRI (at 650^OC) is then transported by a sealed system to the briquetting machine (D) 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 40-50^OC 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 (C).          

Finmet: Advantages and Disadvantages

Some of the advantages and disadvantages of Finmet process of iron making are :

=> It can use very large reserves of iron ore fines as feed stock unlike Midrex and HyL, which can use 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.    

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