The annual worldwide production of iron and steel in foundries adds up to approximately 100 Mt. With an energy consumption of around 1 MWh/t of iron or steel produced, the total worldwide energy need is about 100 TW per year. Some of these foundries are located in regions with high solar radiation and are therefore very well positioned to applicate a cost-effective solar particle system.
Induction furnaces are widely used in foundries to melt metals like iron and aluminum with electricity. Compared to coke fired cupolas they have the advantage of lower emissions, of operational simplicity and flexibility. Some alloys like ductile iron even require electric heating to avoid contamination with sulfur. Commercially available systems use fossil fuels to preheat the educts, like scrap or pig-iron to about 600°C. This saves about 30 percent of electricity and raises the melting capacity of the furnace correspondingly. But such preheating systems are not yet widely used in induction furnaces. However, in electric arc furnaces for steel recycling charge preheating is an established process.
In regions where fossil fuels are expensive and with sufficient solar radiaton, foundries can use solar energy instead to preheat the material. A commercially available hot air generator and a pre-heating system can be applied to integrate solar heat from ceramic particles into the system (see scheme below).
A batch pre-heating system conventionally used for electric arc furnaces as shown below is chosen for the foundry application. The inlet temperature to the preheat system is set to 750°C to avoid oxidation of small pieces of scrap. Typical average heat efficiency coefficients in batch pre-heating systems are 0.6-0.7 .
An average efficiency of 0.6 leads to an average air outlet temperature of 300°C at 750°C inlet temperature. Since no oxygen is needed to burn fuel, the air loop can be built as closed cycle, where the air is recirculated in the system. Thus, no exhaust losses reduce the system efficiency.
For the case study, a foundry in Sao Paulo State, Brazil, with a production capacity of 70,000 t/a was analyzed. The foundry operates a induction furnace with an electric capacity of 12 MW and could incorporate a baseload preheat system with a capacity of 4 MWth. The site has an annual direct normal solar radiation of 2,175 kWh/m²a. To supply the preheat power a solar system with five identical particle tower modules with a peak capacity of 2.5 MWth each and a 15-hours storage was assumed. Using current cost estimates, an attractive payback time of four years is achieved, mainly caused by the high value of electricity savings.
 Lars Amsbeck, Reiner Buck, Tobias Prosin, Particle Tower Technology Applied to Metallurgic Plants and Peak-Time Boosting of Steam Power Plants. SolarPACES 2015, Oct. 13 – 16, 2015, Capetown, South Africa.