Solar-thermal beneficiation of iron ore: System-level dynamic simulation and techno-economic optimisation

Abstract

Beneficiation of iron ores is an increasingly important topic, as a result of diminishing reserves of high-grade ores, and the increasing prevalence of mining wetter ores from below the water table. Meanwhile, steelmaking companies globally are committing to decarbonise their processes, so there is increasing interest in fossil-free processes for drying these ores either before or after the other beneficiation steps, which are focussed on the removal of non-ore ‘gangue’. This study presents a novel solar-thermal process for drying iron ores, developed and optimised via a detailed techno-economic analysis. A steady-state physical model of the core process – consisting of a blower, a fluidised bed dryer and a heat exchanger network – is developed in Aspen Plus software. The performance curves extracted from design and off-design simulations of the Aspen model are then incorporated into a dynamic energy-based model in OpenModelica, also incorporating a parabolic trough solar air collector and rock-bed storage. The assumed design-point process thermal input is 50MW˙th at 400°C, and the storage capacity and solar multiple are optimised for minimal levelised cost of drying (LCOD). For the estimated capital and operating costs, the LCOD reaches 14.3USD/t and 12.6USD/t for ores with 9.53% and 5.07% moisture, dropping further to ∼10USD/t at a larger 500MW˙th scale. Estimated benefits in reduced-mass shipping costs and downstream process fuel load are however only ∼2.2USD/t. The future potential of this process would appear to lie in combining solar-thermal beneficiation with magnetic or flotation separation processes, or with low-temperature hydrogen-fired hematite-to-magnetite reduction, which can provide closer to 30USD/t of added value.