HISMELT NEW APPROACH OF IRON MAKING

HIsmelt

HIsmelt, short for high-intensity smelting, is the world's first commercial direct smelting process for making iron straight from the ore.
Fine iron ores and non-coking coals are injected directly into a molten iron bath, contained within a Smelt Reduction Vessel (SRV), to produce high quality molten pig iron. It can be considered both as a potential replacement for the blast furnace and as a new source of low cost iron units for BOF or EAF steelmaking.

HIsmelt technology brings many advantages to the steelmaking industry - such as lower operating costs; lower capital intensity, lower environmental impact, greater raw material and operational flexibility.

HIsmelt process

The core of the HIsmelt technology is the Smelt Reduction Vessel (SRV), which replaces the function of a blast furnace.
Iron ore fines are injected deep into the bath where they are reduced instantly on contact with carbon dissolved in the bath. This reaction produces iron (Fe) and carbon monoxide (CO).
Coal is also injected into the bath, where it is absorbed in the metal to replenish the carbon used in the reduction reaction.
Reaction gas (CO) and coal gasification products are generated from deep within the bath and form a fountain of mostly slag and some metal.
Hot air at 1200°C, which is enriched with oxygen, efficiently combusts the gases generated within the bath - releasing large amounts of energy.
Combustion energy is carried back to the bath via the fountain of slag and metal.
The role of the SRV and a basic flowsheet for a HIsmelt plant are explained in more detail below:


The primary product from the HIsmelt process is hot metal. Liquid iron is tapped continuously through an open forehearth and is free of slag.
Secondary products from the SRV are slag and offgas. Slag is formed from the impurities in the iron ore (gangue) and coal (ash), which are fluxed using lime and dolomite. Slag from the HIsmelt process can be utilised as a raw material in a variety of applications in the construction and agricultural industries. Offgas from the process has energy value and is cleaned, cooled and used as a fuel and for power generation.

Process benefits

The HIsmelt process has the potential to revolutionise the global steel industry - offering benefits to both new and existing steel plants. Not only can the HIsmelt technology offer a more competitive option for greenfield expansions, it can also bring new life to existing steel works by offering a technology that can reduce operating and capital costs and meets the ever-tightening environmental standards.
Compared to conventional iron making technologies, the HIsmelt® process has the potential to deliver:
• Lower operating costs;
• Greater raw material flexibility;
• Lower capital costs;
• Greater operational flexibility;
• Lower environmental impact;

Lower operating costs

Low cost ironmaking is achieved through the elimination of front-end processes such as coke ovens and sinter plants and through the use of cheaper iron ore fines, non-coking coals and the ability to directly use steel plant wastes.

The HIsmelt process delivers value to both the integrated and EAF mill sectors.

Value to integrated mills:
• No need for costly coking coke, lump ore, or pellet feeds.
• Direct use of raw materials without using sinter plants or coke batteries
• Flexible production and raw material options enable the steelmaker to optimise operating costs more easily.
• High quality hot metal - characterised by its very low phosphorus content (which allows the use of high phosphorus ore feeds) and low silicon which leads to a low slag steelmaking practice
• HIsmelt can also easily recycle many streams of carbon or iron units generated by the integrated mill (e.g. Breeze, sludge, BOF slag or mill scale)

Value to EAFs / mini-mills:
Stable supply of high-quality iron results in:
• Reduced exposure to the volatile scrap market.
• Allows the mill access to the flat product market.
• Delivers high value-in-use over other DRI or HBI, especially with hot metal charging.
• Can increase steel production rates by reducing the time to melt scrap.
Greater raw material flexibility
The HIsmelt process directly injects iron ore fines (-6mm) (no sinter, no pellets) and does not require agglomeration. The process also requires non-coking coal (no cokemaking), which is crushed and dried prior to injection into the Smelt Reduction Vessel (SRV). A wide range of coals that are not suitable for the blast furnace can be used.
A variety of feed materials can be used in the HIsmelt process, such as:
Hematite Fine iron ores:
Nominally -6mm sinter fines, however finer material is easily handled.
No blending necessary.
Typically preheated to increase process efficiency, but may be used directly.
Ores containing high levels of phosphorus can be used - process conditions allow for very effective partitioning of phosphorus to the slag.
Magnetite concentrate
By giving value to the reduced nature of this ore, HIsmelt can use this very fine concentrate without the need for pelletising and can produce iron at a lower coal rate than a blast furnace. If the concentrate has a high level of phosphorus, HIsmelt offers a further advantage.
Titano-magnetite ore and Iron Sands:
This type of ore body is very difficult to be used by the blast furnace and other iron making technologies. Its titania content makes it unsuitable for sintering and causes major problems in the slag treatment in the highly reducing zones found in blast furnaces and melter gasifiers. Since HIsmelt evolved from a very different path, it offers a very unique capacity for these abundant, easy to mine and easy to concentrate ores.
Non-coking coals:
Dried and ground to -3mm.
A wide range of coals can be utilised - from semi-anthracites to high volatile steaming coals.
Steel plant wastes:
Fine steel plant wastes and metallic fines - DRI fines, mill-scale, blended reverts and other iron sources.
BOF slag - as a flux and source of iron units.
Coke breeze.
Lower capital costsThe HIsmelt process delivers significantly reduced capital costs when compared to traditional ironmaking technology. This is due to the elimination of coke ovens and sinter and/or pellet plants, a necessary component of blast furnace ironmaking. Plant construction and operation is relatively simple because the HIsmelt technology uses many traditional ironmaking core-plant facilities, such as hot blast stoves, injection systems and power plants.
In addition, due to the raw material flexibility of the HIsmelt technology, large raw material blending yards are unnecessary and therefore significantly reduce the land requirements of a HIsmelt plant.

Greater operational flexibility
The highly responsive nature of the HIsmelt process means that it converts iron ore, coal and flux to metal, slag and energy almost instantaneously. These process capabilities allow for raw material feed rates to be changed very efficiently without affecting product quality. This operating flexibility maximises productivity, as it is easy to maintain a steady-state operating window. Unlike blast furnaces, the HIsmelt process can be started, stopped or idled with ease.

Lower environmental impact
Through the combination of high process efficiency and the elimination of coke and sinter making, the HIsmelt process meets the highest environmental standards in ironmaking. In general, a HIsmelt plant will have lower than industry best practice emissions of CO2, SO2 and NOx. Furthermore, dioxin, furan, tar and phenol creation is avoided and steel plant wastes can be recycled in an efficient manner. More recently in collaboration with ULCOS/Tata Steel, the HIsarna flow sheet has been developed which offers an opportunity to reduce the emission of greenhouse gas significantly.

End products

The main product of the HIsmelt process is hot metal, which can be used as direct charge to steelmaking processes or cast into pig iron. Slag is produced as a by-product.
The hot metal product is continuously tapped from the Smelt Reduction Vessel (SRV) via a foreheath. As slag is batch tapped through a slag notch (similar to mini blast furnaces) the hot metal is slag free.

If required, the hot metal can be treated in a hot metal desulphurisation plant to remove sulphur. The slag can be used as a valuable raw material in a variety of applications.

Comparison of hot metal quality produced by HIsmelt and blast furnace

Typical analysis	Blast furnace	HIsmelt
Carbon	4.5%	4.4 +/- 0.15%
Silicon	0.5 +/- 0.3%	<0 .01="" nbsp="" td="">
Manganese	0.4 +/- 0.2%	<0 .02="" td="">
Phosphorus	0.09 +/- 0.02% *	0.02 +/- 0.01% **
Sulphur	0.04 +/- 0.02%	0.1 +- 0.05% #
Temperature	1430 - 1500°C	1420°C

*Whilst using high phosphorus ore; # After hot metal desulphurisation Slag by-product
Slag is produced in the smelting process due to the reaction between the flux, the gangue in the ore and the ash in the coal.
Slag can be granulated or directed into pits for further processing. It can then be used as a raw material for a variety of purposes such as cement manufacture, road base and soil conditioning.

If titano-magnetite ore is used, the slag becomes a valuable co-product if its content in titania is rich enough (typically above 50 per cent) to be considered as pigment feed stock.

Operating plants

The first commercial HIsmelt plant was located in Kwinana, Western Australia with a design rate of 100 tonnes per hour of pig iron (800,000 tonnes per annum), and was owned by a Joint Venture comprising Rio Tinto (60 per cent), Nucor Corporation (25 per cent), Mitsubishi Corporation (10 per cent) and Shougang Corporation (5 per cent).  The construction of the HIsmelt Kwinana plant commenced in January 2003, and was hot commissioned in April 2005. The plant operated until December 2008 at production rates of more than 80 tonnes per hour when the global financial crisis forced the closure of the Kwinana operation.
To further develop the HIsmelt technology, Rio Tinto has signed a Development Agreement with a Chinese steelmaker.  This agreement involves the relocation of some Kwinana HIsmelt plant equipment from Australia to a new HIsmelt facility to be built in China. The new plant is expected to be commissioned in 2014. 
The partnership seeks to finalise the development of the HIsmelt technology and to work together to further improve the technology to higher levels of environmental and economic performance.