Blast furnace related technologies for the production of iron are still by far the most common however pressures on environmental resources are driving the introduction of new technologies which do not require blast furnaces to produce.
Demands on primary resource, energy consumption, production costs and environmental impact in the iron and steel industry link closely to the ironmaking process, process equipment and technology itself. At present, the blast furnace ironmaking is still the dominant process in ironmaking.
Despite the apparent environmental advantages of the new ironmaking technologies, the blast furnace is still predicted to be the single largest process for ironmaking from iron ore until 2050. However, the proportion of blast furnace (BF) – basic oxygen furnace (BOF) steelmaking could drop to 40 % in 2050 from the current level of 60 % as the blast furnace ironmaking proportion falls from around 95 % to 60 % of the total iron ore processed.
Non blast furnace ironmaking technology process is currently a supplementary system, and there is certain room for development in the future. To reduce the coke rate and to reduce carbon dioxide emissions as the main goal, it needs to reform the existing blast furnace ironmaking process, explore a new technology to radically reduce emissions of CO2 and form a green metallurgy within a new energy complex process.
In order to achieve an efficient operation from an energy, economic and environmental point of view, competitive alternative ironmaking technologies have been extensively investigated since the 1960’s, which can be classified into two main types. According to the final product of the processes (sponge iron and hot metal), these processes can be grouped as direct reduction DR processes and smelting reduction SR processes. According to the type of fuel used, these processes can also be grouped as gas-based and coal-based processes.
Table 1.2 illustrates the important characteristics and current status of some selected alternative ironmaking processes. More than the direct reduction process, with solid iron as end product, the SR process can be regarded as a direct competitor of the conventional blast furnace as the product is liquid pig iron or (in some cases) liquid steel. The smelting reduction process has several advantages compared to the conventional blast furnace process as mentioned below, which may lead to the adoption of smelting reduction as the main process for hot metal production in the future.
- Smaller units, allowing a more flexible production;
- Fewer restrictions as to the raw materials used;
- Use of coal as fuel avoiding operation of a coke oven plant;
- Not always a need for an ore agglomeration step avoiding operation of pellet and sinter plants;
- Lower capital costs.
It is also recognized that any alternative ironmaking processes ultimately are strongly dependent on local conditions such as availability and the cost of natural gas, power and coal, as well as on product requirements. The economics, possibilities and limitations are still largely unknown. Several smelting reduction processes are under further development.
The process variants differ in the number of reactors, operating temperature, the ore feed (pellet, lump ore or fines). The variant processes that are relatively well developed are: COREX, DIOS, HIsmelt, CCF, Romelt and HIsarna. The most promising direct reduction processes in the worldwide include Hyl III, Midrex, Circored, Circofer, FASTMET and Finmet. Midrex and Hyl III are the only truly established gas based direct reduction processes. The increasing price of the natural gas hampered the development of the gas based direct reduction process.
On the other hand, both of them are fed with pellet and lump ore, which results in a high operating cost compared to fines-based processes. However, the sharp drop in gas prices due to the Marcellus shale development has led to resurgence in interest in gas based DRI production. COREX is the first commercially operating alternative to the blast furnace for hot metal production, and HIsmelt is the world’s first commercial smelting process for making iron straight from the ore. In addition, HIsmelt is the only hot air based direct smelting process, enabling to recycle a significant proportion of off-gas as fuel for air preheating.
Table 1.2: Characteristics of selected alternative ironmaking processes
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2. Y.Qu: Experimental Study of the Melting and Reduction Behaviour of Ore Used in the HIsarna Process, PhD thesis, Northeastern University, Shenyang, China, 2013, ISBN: 978-90-6562-330-0.