Potential of a thermodynamic liquid fraction based model for dust accretion modeling in a heat recovery boiler for the copper flash smelting process

摘要

Flash smelting is a metallurgical process used in primary copper and nickel production. The off-gas is rich in sulfur dioxide and has a dust load that typically corresponds to 4-10 percent of the solid feed to the flash smelter. The heat in the off-gas is usually recovered in a heat recovery boiler. The dust is oxidized in order to avoid sulfides with a low melting range. Although the dust is oxidized there can still be problems with accretion in the boiler: due to a high SO_2 content oxidized dust will sulfate and may sinter. In the present work, the possibility to use a liquid fraction based model for accretion modeling in the heat recovery boiler in the copper flash smelting process is assessed. The thermodynamic calculation shows that using thermodynamic data for pure phases, no accretion problems are expected. In the literature a eutectic in the system CuO-CuSO_4 has been reported with a first melt appearing around 715 deg C. This can be a possible explanation for deposit build-up. In this work, a preliminary model for the CuO-CuSO_4 system is presented. In addition, a CFD calculation of the heat recovery boiler is undertaken, indicating areas where problematic deposits can be expected in the heat recovery furnace.