Finex is an innovative ironmaking process developed by Posco and Siemens VAI for the production of hot-metal based on the direct use of iron ore fines and non-coking coal.
The production of hot metal is simplified because the sintering and coking steps, necessary in the blast-furnace route, are eliminated.
Fine iron ore is charged into a series of fluidized-bed reactors together with fluxes such as limestone or dolomite. The iron-ore fines pass in a downward direction through four reactors where they are heated and reduced to direct-reduced iron (DRI) by means of a reduction gas derived from the gasification of the coal that flows in the counter-current direction to the ore.
After exiting the final reactor, the DRI fines are hot-compacted to HCI (hot-compacted iron), transferred to a charging bin positioned above the melter gasifier and then charged by gravity into the melter gasifier where smelting takes place. The tapped product, liquid hot metal, is equivalent in quality to the hot metal produced in a blast furnace or Corex plant.
Briquetted coal fines and/or lump coal are charged into the dome of the melter-gasifier, while pulverized coal is injected into the vessel together with oxygen. The coal is gasified and a reducing gas is generated which is comprised mainly of CO and H2. After exiting the top of the melter gasifier, this gas is ducted to the fluidized-bed reactor system to reduce the iron ore fines. A portion of the consumed reducing gas which exits from the top of the fluidized-bed reactor train is recycled back into the system after CO2 removal in order to achieve a higher gas-utilization rate. The heat generated from the gasification of the coal with oxygen also serves as the energy source for the melting of the HCI to hot metal as well as for the formation of liquid slag. Both hot metal and slag are tapped exactly as in standard blast furnace procedure.
The excess gas from the Finex Process is a valuable by-product which can be used for a variety of industrial applications such as for heating purposes within a steel works, power generation or for additional DRI/HBI (hot-briquetted iron) production.
The unique characteristics of the Finex process and its ability to use low-cost raw materials means that both capital investment and production costs are much lower than in the blast furnace route. A 1.5-million-ton-per-year Finex plant can produce hot metal more cost effectively than a modern three-million-ton-per-year blast furnace. When oxygen and power plants are included in the comparison, the capital and operating costs of a Finex plant will be approximately 20% and 15% lower, respectively, than in the blast furnace route.
The environmentally friendly nature of the Finex process ensures that it will be even more attractive in the future. SOx, NOx and dust emissions are significantly lower in the Finex Process compared to blast furnace route. This is due to the elimination of the coke oven and sinter plants – both major sources of emissions. The sulfur contained mostly in the coal reacts with limestone to form CaS, which is bound in the slag. Therefore, there is almost no opportunity for SOx to escape to the environment. NOx emissions hardly occur in the Finex Process because the metallurgical reactions take place in a reducing atmosphere, unlike the oxidizing atmosphere inherent in the sinter plant, coking plant and hot-stoves of the blast-furnace route. Dust emissions are low as well, due to the integrated and closed nature of the Finex Process. It has also been verified that no dioxins are generated in Finex operations.
Simplified Flow Sheet of the Finex Process
The further development and optimization of Finex technology by Posco and Siemens VAI continues with the goal to further improve the feasibility of the process and its overall competitiveness. The Finex Process is thus an outstanding example of a highly successful cooperation between a plant operator and plant builder, which allows hot metal to be produced in a highly cost-effective and environmentally friendly manner.