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Elemental Engineering had been brought in to assist in design and redevelopment of a refinery flowsheet that had been put into care and maintenance due to a lack of feedstock. The plant on reopening anticipated they would need a revised flowsheet to process the new sulphide feedstocks that had higher levels of impurities such as arsenic than the previous feedstock. For efficiency and profitability, the plant required flowsheet changes and a new POX autoclave commissioned for processing of its new sulphide feedstocks.
Elemental Engineering’s role was to investigate and model numerous scenarios of alternative flowsheets, feedstocks at different blends, and operating conditions.
The team modelled these scenarios to find the ideal conditions that would meet the targeted production capacity at maximum recovery, while the plant still operated within the site’s pre-existing physical and environmental constraints at minimal capital cost.
A key focus of the investigation was arsenic removal at the POX via adjustments in the feed blend, as the new concentrates to be processed on site were arsenic-rich when compared with the original feedstocks.
The process involved:
Elemental Engineering utilised process modelling software to accurately design and develop a steady-state plant model to a high degree of detail and complexity. This included modelling mineralogy and complex chemistry at all plant locations, including the POX and solvent extraction, based on available testwork and Elemental Engineering’s experience in battery metal operations.
Activities also included heat balance calculations to understand energy losses and costs, with the potential to investigate a reduction in energy requirements.
All complex plant recycle streams were modelled successfully to fully realise the impacts of different flowsheet decisions and operating conditions.
The steady-state model was also able to calculate the resultant arsenic deportment based on the feed blend and other input conditions to ensure the site and plant met safety and environmental conditions.
All reagents and utility consumptions were calculated accurately to provide an estimate of operating costs.
Elemental Engineering was able to accurately calculate the plant performance under all considered operating conditions and production capacities. This included a large number of flowsheet variations and over 200 different operating scenarios.
Elemental Engineering was also able to recommend certain design decisions to help reduce operating costs, such as the exclusion of low-quality feedstocks that would introduce high levels of impurities.
Drawing on prior experience in battery metal metallurgical operations, Elemental Engineering was able to make numerous recommendations and suggestions to reduce costs, such as in the formation of one intermediate product over another.
The team also made multiple process recommendations for operating within environmental constraints. Recommendations included the inclusion of water softening to reduce calcium in effluent, and alternative bleed locations to reduce sulfphate in effluent.
In particular, the team performed a complete mass and energy balance of the POX autoclave. This included heat generated and lost from reactions, vapour release, quench water, environmental losses, and flash vessels – information required to facilitate the design of the newly required POX autoclave. Elemental Engineering was able to make subsequent recommendations on purchasing equipment based on key operating parameters.
The plant is on track to restart with the confidence their processes are fully optimised for maximum recovery and efficiency.