Deposition of carbon from methane on manganese sources

Carbon has been deposited on HCFeMn slag from methane-containing gas with and without CO2, creating C-MnO composites and giving a hydrogen-rich off-gas as a by-product. The maximum deposited amount corresponds to 38 ± 6% of the carbon required for reduction of all manganese in the slag to metallic Mn. This was achieved at 1100 °C with a H2-concentration in the off gas of 76%. Temperature was an important parameter. At 790 °C, no deposited carbon was detected, at temperatures ≥ 1000 °C, deposition increased with temperature. A lower gas-flow leads to more methane decomposition. Experiments with CO2 in the process gas gave less deposited carbon than other experiments. This could be caused by dilution of methane or chemical reactions involving CO2, or a combination. Investigations of fines formation indicate that the deposited carbon sticks well to the HCFeMn-slag, and would not fall off easily during transport and handling. This demonstrates that biogas can potentially be a non-fossil source of carbon in manganese production.publishedVersio

Extent of Ore Prereduction in Pilot-scale Production of High Carbon Ferromanganese

Three pilot-scale experiments have been conducted at SINTEF/NTNU in a 440 kVA AC electric furnace to demonstrate the process operation, energy requirements and CO2 emissions in the production of high carbon ferromanganese alloys. Comilog, UMK and Nchwaning (Assmang) ores blended with other materials, such as sinter and flux, thus achieving different charge mixtures have been utilized in the experiments. In the prereduction zone, higher manganese oxides in the ore are reduced to MnO through solid-gas exothermic reactions and at a temperature around 800oC, the unwanted endothermic Boudouard reaction is also active. As such, the total coke and energy consumption is highly dependent on if the prereduction occurs by CO gas or solid C. The pilot furnace has been excavated after each experiment and the extent of prereduction of the ore has been investigated by collecting samples from specific regions in the prereduction zone. In addition, material, and energy balance calculations for the three pilot experiments have been calculated using HSC Chemistry software. The HSC material and energy balance calculations have shown that the slag/alloy ratios, metal analyses, carbon consumption and the overall energy consumption are mainly affected by the composition of the charge mixtures. The relationship between the specific carbon consumption, the off-gas CO2/(CO2+CO) ratio and energy consumption to produce 1 tonne of HCFeMn alloy is discussed for the three different pilot-scale scenarios