A supplementary study to the definitive feasibility study (undertaken to compile the results of the blending study and yield optimisation study) confirmed that the economic benefits of processing the coal to a finer state outweighed the additional capital and operating costs that would be incurred.
In a comprehensive large-scale coke test conducted by a testing provider, Washpool coal was blended (1:2 ratio) with a lower ash semi-hard coking coal (from the Rangal coal measures) to successfully produce a blended hard coking coal with ash content of approximately 10%.
The testwork demonstrated that the coking properties of Washpool coal significantly improved the coke strength of coal it was blended with.
The blend coal generated higher coke strength (CSR) than would be expected based on mass weighted averages of the blend’s individual components.
Other parameters, such as proximate analysis, ash analysis and calorific value, showed a good correlation between the expected weighted averages and the actual blend test result, according to the supplementary study.
Aquila commissioned MinAxis to report on the marketability of a blended product.
“Based on this analysis, the company is confident that Washpool coal can be successfully blended with complementary Queensland coking coals to produce internationally saleable products,” it said.
“The DFS assumed an average coking coal yield of approximately 36.5% for a target product ash of 15%.
“It was noted that the majority of product coal would be recovered from the finer fractions of plant feed and a washed product size of 88% passing 6mm was anticipated.”
In 2012, a desktop report indicated higher product yields could be achievable through liberation at substantially finer sizes than previously investigated, in line with other operations in Mozambique, South Africa and India.
DRA Pacific was subsequently commissioned to determine the effects of increased crushing and grinding on product yield.
A drilling program was undertaken to compile in excess of 500kg of sample for testing.
Coal plies from three large diameter cores were combined to provide a bulk sample as an approximation of the resource average.
The bulk sample underwent a testing procedure specifically designed to establish the potential to increase coking coal recovery via the liberation of additional product from the middlings coal, which reported to rejects in the DFS plant design.
The testwork investigated the recovery of additional product through four different configurations.
Product yield increases were measured in all four options considered, with the magnitude increasing as crushing size reduced.
Capital and operating cost estimates were then derived for the implementation and continual operation of the processing infrastructure under each option.
This included estimates for the coal handling and preparation plant, coal handling facilities, a briquetting facility (to manage the additional fines created in the washing process) and train load-out.
On the basis of the above analysis, recovery of additional product from the coarse (50mm by 6mm) middlings by crushing to finer sizes was recommended, resulting in an additional 4.1% overall yield compared to what could be expected without the additional crushing.
