Coal Preparation » Fine Coal
Clay minerals commonly occur in Australian coal deposits and have deleterious effects on coal flotation. Firstly, clay minerals can adsorb on coal particles as slime coatings and reduce coal surface hydrophobicity, resulting in a lower combustible recovery. In addition, clay minerals can be recovered through mechanical entrainment due to their ultrafine particle size and the formation of network structures, which increases the ash content of flotation products. In the previous ACARP project C20024, several methodologies were developed to mitigate the deleterious effect of clay minerals on coal flotation in saline water, and one promising approach for reducing slime coatings was to apply structured non-ionic triblock copolymers as dispersants to remove clay slime coatings. The objective of this ACARP project was to identify the behaviour of the triblock copolymers in plant settings and determine its benefits to plant operations.
Paired t-test design was used for trials in two coal preparation plants. Before each plant trial, the standard deviation of historical data was used to estimate the number of tests required for detecting the required improvement after applying the triblock copolymer. Each plant trial was conducted following the sequential pairs design. Each pair of tests was composed of a normal condition without the addition of reagent and a trial condition with the addition of reagent. The difference between normal condition and trial condition in each pair of tests was calculated and the data collected during the whole plant trial was analyzed by t-tests to generate a conclusion with a given confidence level.
Cost-benefit analysis of applying the triblock copolymer in the two CHPP sites was conducted using discounted cash flow analysis followed by sensitivity analysis. Net Present Value (NPV) was calculated based on the current operating conditions and coal sale prices and the project life of ten years. The calculation showed positive NPV for both sites, AUD 4.8 million in Plant A and AUD 31.3 million in plant B. The NPV is sensitive to the coal price and plant feed throughput.