Observations of the reduction of FeO from slag by graphite, coke and coal char

The reduction of FeO from iron-saturated FeO-CaO-Al2O3-SiO2 slags by graphite, coke and coal char at 1 673 K has been investigated using a sessile drop technique. Metallographic analysis of samples quenched from the reaction temperature, and in situ observations of the reaction interface, reveal significant differences in the slag/carbon contact, and in the morphologies of the product iron and its composition; these differences were found to depend on the carbon type used in the reduction. In particular it has been shown that, in the case of graphite and coke, liquid Fe-C droplets were rapidly formed at the slag/C interface. Reactions of the slag with coal chars, in contrast, result predominantly in the formation of solid iron. These observations indicate that the reaction pathways, and hence reaction kinetics, are dependent on carbon type.

Kinetics of reduction of lead smelting slags with solid carbon

Research techniques and a methodology have been developed that enable the reduction kinetics of molten lead smelting slags with solid carbon to be studied. The rates of reduction of PbO-FeO-Fe2O3-CaO-SiO2 slags with carbon have been measured for a range of slag compositions for PbO concentrations between 3 and 100 weight percent, and temperatures between 1423 and 1573 K. The reduction rates were determined for both graphite and coke. Within the range of process conditions examined, it has been shown that the reaction rates are almost independent of carbon reactivity, SiO2/CaO and SiO2/Fe ratio in the range of compositions investigated and are not influenced by the presence of sulphur in the slag.The apparent first order rate constants for oxygen removal increase with increasing PbO concentration and oxygen activity in the slag. The data indicate that the rate limiting reaction step for the reduction of lead slags with solid carbon is the chemical reaction at the gas/slag interface.

Kinetics of reduction of FeO from slag by graphite and coal chars

The rates of reduction of FeO from iron-saturated FeO-CaO-Al2O3-SiO2 slags by graphite, coke, bituminous coal and anthracitic coal chars at temperatures in the range 1 673-1873 K have been measured using a sessile drop technique. The extents of reaction were determined using EPMA analysis of quenched samples, and on line gas analysis using a quadrupole mass spectrometer. The reaction rates have been shown to be dependent critically on carbon type. For the reaction geometry used in this investigation the reduction rates of graphite and coke are observed to be faster than with coal chars. This unexpected finding is shown to be associated with differences in the dominant chemical and mass transfer mechanisms occurring at the reaction interface. High reaction rates are observed to occur with the formation of liquid Fe-C alloy product and the associated gasification of carbon from the alloy. The rates of reduction by coal chars are determined principally by the chemical reaction at the carbon/gas interface and slag phase mass transfer.

Comparison of blast furnace raceway size with theory

A previously developed one-dimensional mathematical model, to explain raceway hysteresis, is used to predict the raceway diameter in operating blast furnaces and hot models. Raceway size obtained from the open literature under various conditions for various blast furnaces are compared with computed predictions. In addition the predictions are also compared with published outcomes from other hot models. Simulated results on raceway diameter are in very good agreement with published operating blast furnace and hot model data. The effect of various parameters such as tuyere and hearth diameter, coke size and density, void fraction and bed height on raceway diameter has been studied.

Characterization of sugar cane waste biomass derived chars from pressurized gasification

There is interest in the use of sugar cane waste biomass for electricity cogeneration, by integrated gasification combined cycle (IGCC) processes. This paper describes one aspect of an overall investigation into the reactivity of cane wastes under pressurized IGGC conditions, for input into process design. There is currently a gap in understanding the morphological transformations experienced by cane waste biomass undergoing conversion to char during pressurized gasification, which is addressed by this work. Char residuals remaining after pressurized pyrolysis and carbon dioxide gasification were analysed by optical microscope, nitrogen (BET) adsorption analysis, SEM/EDS, TEM/EDS and XPS techniques. The amorphous cane plant silica structures were found to remain physically intact during entrained flow gasification, but chemically altered in the presence of other inorganic species. The resulting crystalline silicates were mesoporous (with surface areas of the order of 20 m(2) g(-1)) and contributed to much of the otherwise limited pore volume present in the residual chars. Coke deposition and intimate blending of the carbonaceous and inorganic species was identified. Progressive sintering of the silicates appeared to trap coke deposits in the pore network. As a result ash residuals showed significant organic contents, even after extensive additional oxidation in air. The implications of the findings are that full conversion of cane trash materials under pressurized IGCC conditions may be significantly hampered by the silica structures inherent in these biomass materials and that further research of the contributing phenomena is recommended.

Hydrogen generation from liquid phase catalytic reforming of sugar solutions using metal-supported catalysts

Most of the hydrogen production processes are designed for large-scale industrial uses and are not suitable for a compact hydrogen device to be used in systems like solid polymer fuel cells. Integrating the reaction step, the gas purification and the heat supply can lead to small-scale hydrogen production systems. The aim of this research is to study the influence of several reaction parameters on hydrogen production using liquid phase reforming of sugar solution over Pt, Pd, and Ni supported on nanostructured supports. It was found that the desired catalytic pathway for H-2 production involves cleavage of C-C, C-H and O-H bonds that adsorb on the catalyst surface. Thus a good catalyst for production of H2 by liquid-phase reforming must facilitate C-C bond cleavage and promote removal of adsorbed CO species by the water-gas shift reaction, but the catalyst must not facilitate C-O bond cleavage and hydrogenation of CO or CO2. Apart from studying various catalysts, a commercial Pt/gamma-alumina catalyst was used to study the effect of temperature at three different temperatures of 458, 473 and 493 K. Some of the spent catalysts were characterised using TGA, SEM and XRD to study coke deposition. The amorphous and organised form of coke was found on the surface of the catalyst. (C) 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.