Energy recovery from high temperature slags

Molten slags represent one of the largest untapped energy sources in metal manufacturing operations. The waste heat of slags amounting to ~ 220 TWh/year at temperatures in the range of 1200–1600 °C, presents an opportunity to lower the energy intensity of metal production. Currently, three types of technologies are under development for utilizing the thermal energy of slags; recovery as hot air or steam, conversion to chemical energy as fuel, and thermoelectric power generation. The former route is most developed with its large scale trials demonstrating recovery efficiencies up to 65%. The latter two are emerging as the next generation methods of waste heat recovery. An evaluation of these methods shows that for both thermal and chemical energy recovery routes, a two–step process would yield a high efficiency with minimal technical risk. For thermoelectric power generation, the use of phase change materials appears to solve some of the current challenges including the mismatch between the slag temperature and operating range of thermoelectric materials.The authors wish to thank Ontario Government, Department of Materials Science and Engineering (University of Toronto), and NSERC for financially supporting this study

An in-bath liquidus measurement for molten salts and slags

A technique is being developed to provide a rapid in-bath measurement of the liquidus temperature for salts and metallurgical slags. A copper or nickel cylinder is immersed into a molten bath and a computer based data-logging system is used to record the heating profile of a type K thermocouple centered within the cylinder. The heat transfer is affected initially by the presence of a thin crust on the cylinder surface which freezes from the bath. When the crust melts, the rate of heating shows a subtle increase. Numerical differentiation is used to detect the on-set of this increase so as to provide an indication of the liquidus temperature of the melt. This paper outlines the technique predominantly through measurements of the melting points of pure sodium chloride and sodium nitrate. Factors which may affect the sensitivity of the measurement are discussed also

Basic nickel carbonate: Part I. Microstructure and phase changes during oxidation and reduction processes

A significant industrial problem associated with the production of nickel from basic nickel carbonate has been identified. Fundamental studies of the change of phase, product surface, and internal microstructures taking place during oxidation and reduction processes at temperatures between 110 °C and 900 °C have been carried out. The various elemental reactions and fundamental phenomena that contribute to the change of the physical and chemical characteristics of the samples during the processes taking place in Ni metal production through gas/solid-reduction processes have been identified and thoroughly investigated. The following phenomena affecting the final-product microstructure were identified as follows: (1) chemical changes, i.e., decomposition, reduction reactions, and oxidation reactions; (2) NiO and Ni recrystallization and grain growth; (3) NiO and Ni sintering and densification; and (4) agglomeration of the NiO and Ni particles

Melt Cleanliness Comparison of Chlorine Fluxing and Ar Degassing of Secondary Al-4Cu

The treatment of liquid aluminum prior to casting typically consists of purging gas and/or fluxes through the melt. By the use of several chemicals during these operations, several environmental problems can occur. Therefore, in this study, the melt cleanliness of Al-4Cu secondary alloy was investigated by comparing the use of argon degassing with or without chlorine fluxing. Reduced pressure test was used to assess the melt quality. Highest quality melt was obtained by Ar degassing with preheated graphite lance without the need to use any chemicals