Development of a green reductant for high-temperature smelting

Abstract

Coal is a significant energy source worldwide, supplying 25% of global energy needs. In the smelting industry, coal is used as a reductant, typically in the form of anthracite or coke produced from bituminous coal. Coal releases CO2 when burned and emits high levels of methane during mining. Despite coal being an exceptional energy source, the growing concern over global warming necessitates the exploration of greener alternatives to fossil fuels.

The study initially commenced with three biomass samples: pine sawdust, maize stover, and sugarcane bagasse. In addition to determining the most suitable biomass type for the development of a green reductant for high-temperature smelting, the biomass charring temperature was simultaneously investigated. Maize stover and sugarcane bagasse were subsequently excluded from the study due to the high ash content and low compressive strength of the pellets produced. Pine sawdust was selected for pyrolysis at 850 °C due to the high compressive strength and fixed carbon content of the resulting material. Following this initial pre-screening step, briquettes were produced using polyvinyl alcohol (PVA) and molasses (MOL) as binders, with 5%, 10%, and 15% addition.

The briquettes were cured in a temperature-controlled room for 0, 1, 3, 5, 7, and 10 days before undergoing compressive strength, drop shatter, and water resistance tests, which demonstrated improved quality due to curing. Additional tests such as abrasion resistance, proximate analysis, ultimate analysis, calorific value, X-ray fluorescence, and measurements of bulk, particle, and true density were performed on the cured briquettes and two imported anthracite materials (high volatile (HA) and low volatile (LA)) sourced from an industrial smelting company. The briquettes displayed similar chemical properties to HA and LA, with approximately 85% fixed carbon and 5% ash content, differing mainly in mineral composition. Mechanically, the briquettes outperformed HA and LA, with a compressive strength of 19 MPa for the 15% MOL addition, though performing poorly in water. The briquettes' bulk density was half that of HA and LA, potentially causing logistical issues. MOL briquettes were chosen for thermal tests due to their superior performance compared to PVA-bound briquettes.

During thermal shock tests, MOL briquettes performed exceedingly well, outperforming both HA and LA. However, the CO2 reactivity of MOL was 100 times greater than HA and LA, potentially problematic for use in a smelter, as it would possibly react before entering the slag bath. Nonetheless, MOL displayed reducing capabilities comparable to anthracites HA and LA. Taken together, these findings suggest that MOL outperforms HA and LA in many areas but is hindered by low bulk density, extremely poor water resistance, and high CO2 reactivity. Further testing is required to understand the impact of reactivity, but MOL may still be suitable if stored correctly.