Siemens Reduces Emissions in Steel Mills

2007-Nov-07 |   In cooperation with a Korean steel manufacturer, Siemens has developed a more economical and environmentally friendly method for the hot metal production in a steel mill. The Finex process eliminates the labor- and energy-intensive process steps of sintering and coke-making of the blast furnace route which is the current state of the art technology. The result is an immense reduction in pollutant emissions and increased economic efficiency, reports the research magazine Pictures of the Future. The first large-scale plant is already in operation in South Korea. Others will be built in India and Vietnam. Up until now, sintering and coke-making have been two basic process steps for obtaining hot metal in a blast furnace. During sintering, iron ore fines of some millimeters are partly melted at the surface and form lumpy agglomerates. Direct use of the fines is not possible since they would block the gas channels in the material burden of the furnace. This would consequently result that the iron oxide cannot be reduced to metallic iron by the carbon monoxide reducing gas. During coke-making, the coal is heated in separate oven chamber under airless atmosphere in order to release tars. In case of direct use of coal this coking process would take place in the blast furnace and as a result the tar products would likewise block the gas channels.

With the Korean steel manufacturer Posco, Siemens VAI Metals Technology developed a method that uses ore fines and coal directly. The core technology of Finex is the "fluidized bed reactor system" in which the reducing gas containing carbon monoxide and hydrogen keeps the ore fines in a swirling suspended condition and converts them to metallic sponge iron. In the sub-sequent steps the sponge fines are compacted under hot conditions to lumps in a roller press and they charged to the melter gasifier in order to be melted to hot metal. The heat required for that is generated by direct gasification of the coal with oxygen. The reducing gas produced by this reaction is fed into the fluidized bed reactor system. Finex produces an export gas which is a valuable by-product to operate a power plant. In April 2007, Posco started up the first large-scale plant, which has an annual production capacity of 1.5 million tons. Compared to blast furnaces, emissions such as dust, sulfur oxides and nitrogen oxides were reduced by approximately 90 percent, while the quality of the hot metal is equivalent. At the same time, Finex operating costs are 15 percent less than the conventional processes, and the investment costs for such plants are about 20 percent lower.