INVESTIGATION OF SOLID BIO PELLET FUELS AS SUBSTITUTION IN REFINERY COAL SYSTEMS

The use of bio pellet derivatives as a coal replacement for alumina refinery boilers offers an opportunity for practical decarbonisation in the short to medium term, supporting a transition to longer term renewable steam generation. This work compares the fuel characteristics of three commercially available bio pellets to bituminous coal (currently used in the Yarwun alumina refinery). The influence of processes including biomass torrefaction (300°C), steam explosion (180°C) and pyrolysis (550°C) on characteristics including proximate / ultimate analysis, calorific value, grindability are compared. Torrefied and steam exploded pellets offer up to 75% of coal’s calorific value, while that of biochar (through pyrolysis) is higher (than coal, aligned with a fixed carbon increase). Additionally, practical grindability concerns associated with the inherent anisotropic / fibrous character of biomass derivatives are explored.
Following these laboratory studies a series of trials and techno-economic assessments is planned at Rio Tinto’s Gladstone based refineries, to understand the practical aspects of substituting these fuels to achieve the lowest cost system solution, balancing safety, operating fuel costs, maintenance, boiler performance and capital modification requirements. A high-level review of trial considerations and results are outlined.
Rio Tinto is investigating the safe and cost-effective use of bio pellets as a potential to provide a real decarbonisation solution for the alumina industry whilst supporting the development of a sustainable local biomass industry.