Research
CO2 Breakthrough in Metal Production Program
Program Leader: Dr Sharif Jahanshahi, CSIRO
Considerable quantities of high grade heat (energy) are lost through water granulation and/or air cooling of molten slags produced in iron and steelmaking processes. Recovery of this energy and its utilisation in the industry will reduce operating cost as well as greenhouse gas emissions. This program aimed to develop and demonstrate breakthrough technologies that could result in deep cuts (10-50 percent) in the greenhouse gas emissions in metal production.
The treatment of molten slags using dry granulation will enable the recovery of waste heat, reduce water consumption and transform the slag into "green" cement, a suitable material for the construction industry. Dry granulation produces a slag suitable as cement substitute; and that the heat released from the slag can be captured by a small volume of air – making the process suitable for high grade heat recovery.
The second area of investigation is the use of renewable biomass as a source of carbon for fuel, reductant and alloying element in metal production. The research aimed to develop specific opportunities for successful use of biomass, in which the biomass is a technically sound and economically viable alternative to the use of fossil carbon and sourced in ways that are ecologically sound and acceptable to the community.
Large amounts of waste biomass are generated each year in rural and regional Australia, in the agricultural, forestry, sewage and waste treatment industries. By utilising these materials in metallurgical processes as a substitute for fossil fuels (such as coal and metallurgical coke), the energy and carbon content and value of the waste materials are recovered. CSRP's focus has been on iron and steel but the application of these technologies to nonferrous metal production is possible.
Achievements
- Engagement of the Australian iron and steel industry, with high level support towards the Australian CO2 breakthrough program and collaboration through the World Steel Association program.
- Successful pilot demonstration of charcoal use as a recarburising agent in steelmaking at OneSteel's Sydney Steel Mill, has encouraged further work on developing an economically viable sourcing route, and improvements in controlling the density and moisture content of the charcoal.
- Assessment of biomass chars as replacement for fossil carbon (coal, coke etc) in bath smelting of iron, carburisation of steels and ilmenite reduction in kilns.
- Pilot scale combustion tests on a range of biochars have demonstrated the superior performance of biochars as an injectant replacement for coal in blast furnaces, potentially covering 30 percent or more of total fuel requirements.
- Successful completion of a pyrolysis trial at the Corrimal coke ovens of the Illawarra Coke Company.
- Charcoal derived from waste biomass produced in Tasmanian forestry and agricultural industries used as a substitute to fossil-based fuels and reductants (such as coal and coke). In particular, substitution occurred in the submerged electric arc furnaces at Bell Bay (TEMCO/BHP Billiton) and in induration (hardening) of iron ore pellets at Port Latta (Australian Bulk Minerals).
- Charcoal produced from biomass residues used as a substitute for coal in the Port Pirie slag fuming operations.
- Development of an advanced Computational Fluid Dynamics tool to model the dry granulation process. The modelling provides insights into the complex process and will play a critical role in planned process scale-up.
- The concept of integrated dry granulation and heat recovery has been successfully demonstrated through the prototype pilot facility. The process has produced fine, glassy slag granules with good cementitious properties suitable for cement.
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Impacts – Dry slag granulation
The dry granulation process produces a high value slag and enables capture/recovery of the waste heat released from slag cooling. A techno-economic evaluation indicated that dry slag granulation has significant advantages over the wet granulation process in terms of both capital and operating cost:
- Heat recovery is viewed to be feasible, with savings estimated to be $1 to $3 per tonne of steel produced.
- Capital cost: According to Siemens VAI (SVAI), their dry granulation plant is 40-60 percent of the cost of an equivalent wet granulation plant. The new CSRP process is likely to be even lower due to a more compact and efficient unit.
- Operating cost: According to SVAI, dry granulation will cost approximately US$2.64 per tonne of slag, compared to wet granulation which is approximately US$6.51 per tonne of slag.
- Potential major benefits: Heat recovery and utilisation could deliver potential savings of US$1.6 to $2.4 per tonne of steel. CO2 Breakthrough in
Metal Production Significant value in using the dry-granulated slag as a low greenhouse gas feedstock for "green" cement.
Other major impacts include:
- An independent assessment of the potential economic impact of dry granulation has confirmed the net present value of the technology to be very large for the Australian steel and cement industries. Given that Australia produces about 1 percent of the world's steel, the full potential of the technology could be very significant in terms of economics and reductions in the environmental impacts of the world steel industry.
- Australia steel companies, OneSteel and BlueScope Steel, have offered strong ongoing support towards planned future work and scale-up through plant trials. Through their participation in a high profile program, they have promoted dry granulation / heat recovery work to a wider audience and potential users and received positive feedback.
- BlueScope Steel and OneSteel produce more than 2 million tonnes of slag each year. Slag discharged at 1,500 degrees Celsius, on cooling to 50 degrees Celsius, releases 1.8 gigajoules per tonne of slag – a large amount of high grade heat/energy potentially available to industry.
- Greenhouse gas benefit from heat recovery: 2 million tonnes of slag producing 4 petajoules of heat per year which is equivalent to about 56,000 households or a reduction of 0.3 million tonnes of carbon dioxide equivalent per year.
- Reduction in fresh water consumption: saving of 1.5 gigalitres per year compared with water granulation.
- Elimination of sulphur emissions to atmosphere.
- Conversion of solid by-product into saleable feedstock for cement production – potential conversion of 200 million tonnes per year (globally) of blast furnace slag into cement.
Impacts – Biomass
- The economics of using biomass as a fuel and reductant depends upon the cost of the charcoal, which is in turn strongly dependent on the cost of the biomass. The mallee-based biomass research has shown that the lowest cost material – the leaf/twig fraction – produced charcoal with attractive properties for metallurgical applications (very high reactivity, high lime content in ash, high phosphorous and alkalis).
- Increased awareness on the part of biomass waste producers (farmers, grain handlers, forestry industries, sewage and waste management industries) and potential customers (metallurgical plant operators) of the benefits of utilising biomass waste in metallurgical processes.
- Through the relationships developed in Tasmania, the waste products from one industry (forestry and agriculture) could become feedstocks for a second industry (metallurgy). This synergistic approach is being pursued elsewhere in Australia, specifically Western Australia and South Australia.
- Carbon dioxide emissions from the blast furnace are minimised by injectants that have a high energy value, low ash and low oxygen content. Many biomass-derived charcoals were shown to be high value injectants, better than any of the coals studied. Their position may be further enhanced upon application of a carbon tax.
Completed Projects
Contact
Dr Sharif Jahanshahi
Minerals Down Under Flagship
CSIRO
p. 03 9545 8621
e. sharif.jahanshahi@csiro.au
