Emerging trends in improving Blast Furnace (BF) performance of ironmaking – More environment-friendly and cost effective proposition:

Emerging trends in improving Blast Furnace (BF) performance of ironmaking – More environment-friendly and cost effective proposition:

Blast furnace (BF) technology is the central to the crude steel industry and is continually undergoing refinements to improve productivity and reduce operating costs. Continuous improvements in productivity, coke consumption and fuel use within steel works have been driven by competition in world steel market.

The major raw materials generally used in blast furnace technology are high quality of iron ore (lumps, sintered or pallets), coal (ranging from coke to coking coal) as fuel, limestone and dolomite as fluxing materials.

A. At present, the real challenge in ironmaking industry by blast furnace lies to ensure that each process meets the emission limits prescribed by law and for that purpose each process is to examine for (a) use of energy, (b) use of material, (iii) waste generation for the entire life cycle of the project. These factors are believed to be root cause of environmental degradation. Some the processes which can economize on energy, process waste and material inputs are:

(i) High temperature hot blast technology for Blast Furnaces for lower energy consumption.

(ii) Cast House Slag Granulation Technology for utilizing Blast Furnace slag.

(iii) Ceramic welding technology for increasing life and reducing energy loss in coke oven.

(iv) Bell-less top technology for BF for increasing productivity and reducing coke rate.

(v) Continuous casting technology for reducing energy consumption and process waste in steel casting.

(vi) Water treatment technologies for economical water management.

B. As mentioned, coal / coke is an important raw material, which constitutes about 42% of the cost of sales and 58% of the raw material cost of an Integrated Steel Plant. The conventional blast furnace route of iron making needs prime coking coal. In order to reduce the cost of fuel (coke) and to use more of coking or non-coking coal replacing most of coke, many of the emergent technologies have been developed and tried. Many of these coals, extractable through lowcost mining, can be injected directly through the tuyeres of blast furnaces, substituting good quality coke in a very cost-effective manner.

C. In one example, during the implementation of improved method of coal injection to blast furnace, this inferior coal replaces almost same weight of blast furnace grade coke, which is produced from almost one and one-half unit of prime coking coal (at more than double the cost), after carbonization for several hours at substantial processing cost. The coke ovens are very capital intensive and pollute the atmosphere. Thus, coal injection not only reduces the operating cost, but also saves capital expenditure substantially, while maintaining greener and cleaner environment. More important and helpful to the blast furnace (BF) operator is that it facilitates operational stability and optimization by providing endothermic heat to control the combustion. There are two modes of coal injection:

(a) The pulverized coal injection (PCI) and

(b) The granular coal injection (GCI).

Most of the newly constructed blast furnaces generally have installed PCI, a very common technology available everywhere. However, the existing blast furnaces with no injection facilities can go for GCI, which is less energy intensive and more environment friendly. The savings using appropriate variety of low cost non-coking coal would be of the order of about US$ 4 to 6 million per annum per blast furnace of 1 Mtpa capacity.

Experts opine that, for coal injection, GCI is emerging as a more cost effective and energy efficient technology.

D. The advantage of GCI over PCI is given here:

(i) Reduction in coal preparation costs due to low energy consumption (GCI: 20kWh/t, PCI: 32kWh/t);

(ii) Easier to handle in pneumatic conveying systems since granular coal is less sticking to the conveying pipe.

(iii) System availability is more;

(iv) Granular coal’s coarseness delays gas evolution and temperature rise associated with coal combustion in the raceway. Therefore, it is favorable compared to PCI because of less likely generation of high temperature and gas flows at the furnace walls, which results in high heat losses, more refractory wear and poor utilization of reducing gases;

(v) Granular injection system is superior while using low volatile coal to avoid line plugging and other related problems. Thus, the use of granular coal may increase the range of coals available for blast furnace injection.

(vi) There is a significant economic advantage to using granular coal over pulverized coal, since not only is less grinding equipment required resulting in capital savings, but operating costs are also reduced as approximately 60% less grinding energy is required for granular coal. Capital including infrastructure costs for GCI are lower than those for PCI. (PCI ~ US$ 43,000 whereas GCI ~ US$ 37,500 per daily ton of injected coal).

Environment-friendly COREX®, FINEX® and MIDREX® Ironmaking processes – Essential in today’s changing scenario – A discussion:

Environment-friendly COREX®, FINEX® and MIDREX® Ironmaking processes – Essential in today’s changing scenario – A discussion:

A. Global demand for iron and steel is constantly growing, while at the same time prices for raw materials, energy, and transport continue to increase. At the same time, the requirements of iron making processes are to go compatible with the present ecology and environmental criteria of the region. In this dynamic environment completely new strategies are required for both iron making plant builders and operators. New ironmaking processes have been extensively explored with a view to saving resources and energy, as well as reducing environmental pollution.

Therefore, certain criteria processes should follow, such as:

(a) Full range of cutting-edge solutions in the iron and steelmaking sector,

(b) Increased environmental protection and optimized processes for economical production,

(c) Processes with extended raw material flexibility to encounter increasing raw material availability and cost.

The present scenario of iron and steel sector is very much challenging. Consolidation of the iron and steel branches manifested itself in a significant increase of mergers and takeovers. Nevertheless, the global iron and steel industry continues to expect strong growth. According to the latest analysis, demand for steel will grow by up to 25% by the year 2015, mainly due to rapid economic development in the highly populated Asian countries. In addition to transport and logistics, above all, raw materials and energy are the global driving forces behind the market’s dynamics. Energy costs will also continue to increase.

Growing environmental consciousness also contributes to market dynamics by prompting construction of plants that meet increasingly stringent environmental standards. However, existing plants that produce hot metal must continue to optimize their consumption parameters in the future to achieve increased quality with constant or even lowered operation costs. This is the only way they will be able to strengthen their market performance over the long term. Exact analyses required to keep an overview of this complex market. These include analyses of raw material and energy, feasibility studies and examinations of environmental performance. Today a plant for hot metal and/or DRI production is much more than just a plant. It is part of the entire value added chain in iron and steel production.

B. Today, direct smelting is a much sought-after prize. The traditional blast furnace route for ironmaking is coming under increasing pressure - environmental and economic. Many have tried to develop direct smelting technologies, but the challenge appears to be particularly difficult, certainly more so than one might expect. Out of many processes following three are considered to be most environment-friendly technology for ironmaking: (a) COREX® technology, (b) FINEX® technology, (c) MIDREX® technology.

(a) COREX® technology – It is an industrially and commercially proven direct smelting reduction process that allows for cost-efficient and environmentally compatible production of hot metal directly from iron ore and non-coking coal. This is the only alternative to the conventional blast furnace route consisting of sinter plant, coke oven and blast furnace. It distinguishes itself from the blast furnace route by: (i) Direct use of non-coking coal as reducing agent and energy source and (ii) Iron ore can be directly and feasibly charged to the process in form of lump ore, pellets and sinter.

In this technology, iron ore (lump ore, pellets, sinter or a mixture thereof) are charged into a reduction shaft where they are reduced to direct reduced iron (DRI) by a reduction gas moving in counter flow. Discharge screws convey the DRI from the reduction shaft into the melter gasifier, where final reduction and melting takes place in addition to all other metallurgical reactions. Hot metal and slag tapping are done as in conventional blast furnace practice. Coal is directly charged into the melter gasifier. Coal combustion by oxygen injected into the melter gasifier results in the generation of a highly efficient reduction gas. This gas exits the melter, is cooled and is then blown into the reduction shaft, reducing the iron ores in counter flow to DRI, as described above. The gas leaving the reduction shaft is cooled and cleaned and is suitable for a wide range of applications (e.g., power generation, DRI production or use in reheating furnaces).

Benefits of this process -

(i) Substantially reduced specific investment costs and operation costs compared with conventional blast furnace route,

(ii) Outstanding overall environmental compatibility, as less carbon dioxide is produced;

(iii) Use of COREX export gas for a wide range of applications,

(iv) Use of a wide variety of iron ores and coals,

(v) Elimination of coking plants,

(vi) Hot-metal quality suitable for all steel applications.

COREX process of iron making is in operation at (i) Mittal Steel South Africa, Saldanha Steel Works, South Africa; (ii) Jindal South West Steel, Toranagallu Works, India; (iii) Posco, Pohang Works, Korea; (iv) Baosteel, China (v) Essar steel, India etc.

(b) FINEX® technology – It is an optimized fine-ore reduction process for the direct utilization of the world's vast resources of low-cost iron ore fines for the production of iron. The FINEX® smelting-reduction process based on the direct use of non-coking coal and fine ore is perhaps the most exciting iron making technology on the market today. This is a process with great potential with regard to productivity and the low cost production of hot metal.

In this process fine iron ore is preheated and reduced to fine direct reduced iron (DRI) in a three or four stage fluidized bed reactor system. The upper reactor stage serves primarily as a preheating stage. In the succeeding stages the iron ore is progressively reduced to fine DRI. The fine DRI will be compacted and then charged in the form of hot compacted iron (HCI) into the melter gasifier. The charged HCI is subsequently reduced to metallic iron and melted. The heat needed for the metallurgical reduction work and the melting is supplied by coal gasification with oxygen. The reduction gas, also produced by the coal gasification, is passed through the fluidized bed reactors. The generated FINEX export gas is a highly valuable product and can be further used for DRI/HBI production, electric energy generation or heating purposes.

Benefits of this process -

(i) Favorable economics in comparison to the blast furnace route,

(ii) Environmental benefits due to savings in resources and energy, as well as lower emissions,

(iii) Direct utilization of non-coking coal,

(iv) High valuable export gas for a wide range of applications in metallurgical processes and energy production,

(v) Production of hot metal with similar quality to the blast furnace,

(vi) Reduction of process steps.

FINEX process of iron making is in development / trial-operation stage at Posco, Pohang Works, Korea.

(c) MIDREX® technology – This is a natural gas based shaft furnace process that converts iron oxides in the form of pellets or lump ore into direct reduced iron (DRI).

Benefits of this process -

(i) Fastest start-up, (ii) Simple operation, (iii) Low pressure shaft furnace etc.

MIDREX process of iron making is in operation at Saudi Iron and Steel Company Ltd. (HADEED), Al-Jubail, Saudi Arabia.

C. Discussion: Now the fact is, blast furnace steelmakers, as a group, are only too aware that they are under considerable pressure. Environmental issues with coke ovens and sinter plants continue to plague them, and periodic blast furnace re-lines (in some cases costing a significant proportion of what a new direct smelting plant might cost) continually force re-examination of alternatives. For most, margins are already thin and capital investments needed to address individual environmental issues are not sufficiently attractive. The temptation is to hold off until a decision on the next significant reline falls due, or coke ovens have to be replaced, then assess whether or not a new 'clean' solution, such as direct smelting is more cost-effective.

What benefits would a steelmaker in this situation hope to achieve from direct smelting? In my opinion, the wish-list might be: (i) Ability to use iron ore fines directly, without the need to sinter or pelletise. This will make environmental issues currently associated with sinter plants disappear. (ii) Ability to use coal directly, with no coking or other thermal pre-treatment. Environmental concerns related to coke ovens will vanish as a result. (iii) Ability to use iron ore with higher phosphorus levels, leading to increased iron ore reserves. (iv) Coal consumption rates better than or comparable to those of the blast furnace, leading to similar (or lower) carbon dioxide emissions. (v) Single-train capacities which can sensibly replace a blast furnace, in the range 1.5-4.0 Mt/a. (vi) Ability to recycle iron-bearing wastes.

Therefore, the challenge to the direct smelting technology provider is to tackle most of the above problems faced by steel makers and make the process more compatible with greener environment standards with better economy.