Direct Reduction of Iron Ores with Methane, Methanol and Methane/Steam Gas, and Catalytic Effect of Nickel and Cobalt Supported on Ores

Abstract

In order to develop the one step direct reduction process of iron ores and contribute to the save energy of iron manufacturing industry, the fundamental investigations on the reducing gas (CH4, CH3OH, CH4-H2O mixture) and the effects of catalyst (Ni, Co) added and Al2O3 contained. etc. were carried out.The iron ores employed were three kinds of hematites and two kinds of magnetites. Furthermore, Fe2O3, Fe2O3-Al2O3 to clearify the effect of impurities in natural ores, and NiO, Co3O4 to clearify the catalytic effects of Ni and Co added were employed. These metal oxides were prepared by the precipitation from the nitrates with NH3 aq.The reduction experiments were carried out by using a thermobalance and a packed bed reactor under atmospheric pressure and at 300-950°C. The average diameters of the granular samples were 0.25 mm for the thermobalance and 0.50 mm for the packed bed reactor. On the other hand, the gases formed were determined by gaschromatograph, and the chemical changes before and after reaction of solid samples were analyzed by X-ray diffraction. Inlet gas concentrations were 3-50%, CH4-0-6%H2O-N2, 4%CH3OH-N2, 4%CO-8%H2-N2, 12%H2-N, and 12%CO-N2, and the total gas flow rate was 650 Ncm3/min toward ca. 350 mg as iron component.The main results and informations were as follows:(1) In the reduction of ores with CH4, the Al2O3 component in or ecatalyzed the decomposition of CH4 to H2 and carbon under the state of wiistite (Fe1-xO). The reduction rate was promoted above ca. 850°C. However, the catalytic activity of a small amount (1-2%) of Ni or Co was sufficient to promote the reduction with the fairly reasonable rate at ca. 700°C. Also, a small of sulfur added was very effective to restrain the carbon deposit, but poisoned the activity of catalyst.(2) In the reduction of ores with CH3OH above 800°C, CH3OH decomposed rapidly to H2 and CO, and these gases reduced the ores to Fe without any side reactions. Also, Ni was effective to promote the reduction.(3) In generally, the reduction rate of magnetite was much lower than that of hematite with any reducing gas, but the reactivity of magnetite ores was increased by oxidation to hematite with air prior to the reduction.(4) In the reduction of ores with CH4-H2O mixure, Ni acted as a reforming catalyst to H2 and CO (mainly H2), and the selection of the operation conditions such as the ratio of CH4/H2O, the reaction temperature and space velocity was very important.