Damring Formation During Rotary Kiln Chromite Pre-reduction: Effects of Pulverized Carbonaceous Fuel Selection and Parti
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TRODUCTION
CHROMITE is a mineral with a spinel crystalline structure with the formula [(Mg,Fe2+)(Al,Cr, Fe3+)2O4].[1] Chromite is of great importance since it is the only commercially viable source of new chromium (Cr) units.[2,3] Cr has many applications in the metallurgical, chemical, and refractory fields. The application of importance in this study is the production of ferrochrome (FeCr). FeCr is an alloy used mainly in the production of stainless steel, which is a vital alloy in modern society. According to Rao,[4] approximately 90 pct of all mined chromite is utilized in the production of FeCr.
Y. VAN STADEN, J.P. BEUKES, P.G. VAN ZYL, E.L.J. KLEYNHANS, and J.R. BUNT are with the Chemical Resource Beneficiation, North-West University, Potchefstroom, Private Bag X6001, Potchefstroom, 2520, South Africa. Contact e-mail: [email protected] E. RINGDALEN is with the Sintef, Materials and Chemistry, 7465 Trondheim, Norway. M. TANGSTAD is with the Norweigian University of Science and Technology (NTNU), 7465 Trondheim, Norway. Manuscript submitted November 23, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS B
The single largest cost component in FeCr production is electricity consumption.[5,6] It is therefore important for FeCr producers to apply processes to minimize energy use. Several of these processes have been developed.[7–9] One of these processes, known as Chrome Direct Reduction (CDR), was commercialized in South Africa in the late 1980s and entailed the direct reduction (which is complete or almost complete pre-reduction) of fine chromite ores.[9] However, due to operational difficulties, the process was abandoned fairly quickly. Another process implemented commercially was developed by Showa Denko in the 1970s, i.e., solid-state reduction of chromite (SRC) or otherwise known as pelletized chromite pre-reduction. This process was modified and is being applied by Glencore Alloys at two very large smelters in South Africa (Lydenburg operations and the Lion Ferrochrome smelter).[10] FeCr smelters applying this process have also relatively recently been developed in China, but information regarding these smelters is not yet available in the public peer-reviewed domain. Glencore Alloys refer to their application of pelletized chromite pre-reduction as the Premus process.[10] This process has the lowest energy consumption (specific electricity
consumption (SEC), i.e., MWh/ton FeCr), high Cr recovery, as well as being more environmentally friendly than the conventional process in some respects.[10] In the pelletized chromite pre-reduction process, raw materials (chromite ore, reductants, and clay binder) are dry milled, pelletized, and pre-heated, after which the pellets are fed into a counter current rotary kiln where chromite pre-reduction takes place. These hot, pre-reduced pellets are then fed directly into a closed submerged arc furnace (SAF), with the required fluxes and reductants. Feeding the hot, pre-reduced pellets into the SAF reduces the amount of energy required for smelting.[10,11] The pre-reduction ac
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