Techno-Economic Feasibility of a Peroxidation Process to Enhance Prereduction of Chromite

"Ferrochrome (FeCr) is vital for the production of stainless and high-alloy ferritic steels, since it is the only source of new Cr units. FeCr production is an energy-intensive process. The pelletized chromite prereduction process is most likely the FeCr production process with the lowest specific electricity consumption (SEC), i.e. MWh/t, currently in operation. However, due to increases in costs, efficiency, and environmental pressures, FeCr producers are attempting to lower their overall energy consumption even further. Recently, it was proven that pre-oxidation of chromite ore prior to pelletization and prereduction significantly decreases both the SEC and lumpy carbonaceous reductants required for smelting. This paper presents the first attempt at conceptualizing the technoeconomic feasibility of integrating chromite pre-oxidation into the prereduction process. Financial modelling yielded a net present value (NPV) at a 10% discount rate of approximately R900 million and an internal rate of return (IRR) of approximatelyy 30.5% after tax, suggesting that the implementation of pre-oxidation prior to pellet prereduction may be financially viable. Sensitivity analysis indicated that the parameter with the greatest influence on project NPV and IRR is the level of prereduction. This indicates that the relationship between maintaining the optimum pre-oxidation temperature and the degree of prereduction is critical for maximium process efficiency. IntroductionStainless steel is a crucial alloy in modern society. Virgin chromium (Cr) units used in the manufacturing of stainless steel are obtained from ferrochrome (FeCr) – a relatively crude alloy consisting predominantly of Cr and iron (Fe) (Murthy, Tripathy, and Kumar, 2011; Beukes, van Zyl, and Ras, 2012). FeCr is produced mainly by the carbothermic reduction of chromite ore in submerged arc furnaces (SAFs) and direct current arc furnaces (DCFs) (Neizel et al., 2013; Beukes, Dawson, and van Zyl, 2010; Dwarapudi et al., 2013). The energy required to heat, smelt, and reduce the chromite ore to the metallized state is supplied by electricity (Pan, 2013). FeCr production is an energy-intensive process, with a specific electricity consumption (SEC) varying from 2.4 MWh/t to more than 4.0 MWh/t FeCr produced, depending on the process applied (Pan, 2013; Neizel et al., 2013). Daavittila, Honkaniemi, and Jokinen (2004) stated that the typical operational costs of FeCr smelters can be divided into four categories, i.e. chromite ore (30%), carbonaceous reductant (20%), electricity (30%), and other production costs (20%). This makes electricity consumption the joint largest factor that influences operational costs in FeCr production."