Waste heat utilization from a submerged arc furnace producing ferrosilicon

This paper addresses some of the technical aspects related to waste heat recovery from ferrosilicon production in a Submerged Arc Furnace. More than half of the energy supplied to the furnace in the form of electricity and black raw materials is lost to the environment as heat. Possibilities for utilizing waste heat at Elkems plant Grundartangi in Iceland were studied, with emphasis on electricity production. Other utilization possibilities considered are district heating and steam generation. Elkem Iceland currently produces two categories of products, ferrosilicon and microsilica, but there is a potential for the third product by utilizing the waste heat. An energy and exergy analysis on a 47 MW furnace producing FeSi75 is preformed based on measurements and data from Elkem Iceland. The production of ferrosilicon involves large exergy destruction, estimated to be 46.5 MW, and the exergetic efficiency of the furnace is about 30%. The energy analysis shows that much of the energy used in the production of ferrosilicon at Grundartangi goes out to the environment as waste heat. Only 35.6 MW of the 98 MW of the energy supplied to the process are retrieved as chemical energy in the product. Comparison of ORC and steam Rankine cycle configurations were performed, given certain design constraints on the investment, and the best configuration gave maximum net power of about 10 MW and 8 MW, respectively. If the waste heat is used in district heating it could supply about 11800 m3/day of water at 80°C to a nearby municipality.