The evaluation of sintering as a potential cause of duct blockages for a submerged arc furnace applied in silicomanganese production

Abstract

A study was undertaken to evaluate sintering as a potential cause of duct blockage for a submerged arc furnace applied in silicomanganese production. Within the broader aim of the study, four research questions were of principal interest. The research questions were as follows:  Is there a potential for dust to sinter in the off-gas duct?  If so, what mechanism of sintering is applicable, under the given conditions?  Does the firing temperature have an effect on sinter formation and the compressive strength of the dust, given a fixed PSD?  Does PSD have an effect on sinter formation and the compressive strength of the dust, given a fixed firing temperature? In order to address the aforementioned research questions, several plant-based, laboratory-based, and desktop-based activities were undertaken. The activities were divided into five chronological stages as follows:  Stage 1: Smelter based activities –entailed the collection of dust samples from the three streams in the baghouse and the measurement of the furnace duct temperatures. From this exercise, a total of 505 kg of dust across the three streams was collected. The duct temperature was found to vary between 600‒1300°C.  Stage 2: Laboratory dust samples preparations–entailed sample preparation, and PSD and chemical characterisation of each dust stream.  Stage 3: Laboratory pellet-pressing and firing tests –entailed the pressing of pellets at a pressure of 5 MPa pressure, followed by oven drying, and then firing in a muffle furnace at 600‒1300°C (the measured duct temperature) in an air atmosphere. For each temperature and dust stream, forty one pellets were fired.  Stage 4: Fired dust examination: the fired pellets were examined for sintering using observations of their: physical appearance, compressive strength, bulk chemistry, bulk phase chemical composition.  Stage 5: Chemical thermodynamic evaluation: thermodynamic calculations were performed using FactSageTM, to determine the amount of liquid formed from bulk mixtures, as well phases that were observed to have sintered together. Following the testwork, the following research outcomes were found:  There was sound evidence of sintering in the off-gas duct of the smelter in question.  Both solid-and liquid-state sintering were observed. The former was more localised‒ observed only in some areas in the sample‒and most prominent at firing temperatures of 600‒900°C. The latter was observed between 600‒1100°C; it was prevalent at 1100°C‒ where long networks of sintered materials were observed.  The firing temperature was found to have an effect on sinter formation and the compressive strength.  The PSD was also found to have an effect on sinter formation and the compressive strength of the formed sinters