An experimental and modelling approach to develop a winnowing pilot plant for fine dry coal beneficiation

Abstract

The constant increase in the amount of fine coal being generated through day-to-day mining and processing activities is unavoidable, and thus the technology used to beneficiate fine coal is constantly evolving. Environmental and economic factors such as water shortage, waste management, and processing cost motivate the research in fine coal beneficiation and even more so in dry fine coal beneficiation. One of the more recent developments in dry fine coal beneficiation over the past few years is the use of the winnowing method as a dry beneficiation technique and this method has been proven capable of beneficiating -6 mm coal. The method of winnowing has been successfully implemented in the agricultural and pharmaceutical sectors for many years with several studies showing that the method is a viable option when implemented on the coal sector for dry fine coal beneficiation. Over the past few years several studies have been done on the method, however, there is still very little data available other than lab scale experimental results. Research done on fine coal suggests that winnowing can separate coal particles by size, shape, and density; however, previous studies have shown the system to be size sensitive, and for this reason, a 2-stage separation is needed for the beneficiation of fine coal. The equipment used for the winnowing method has also not been fully developed to suit the needs of the coal mining industry and thus an opportunity exists to design and implement a winnowing machine capable of beneficiating fine coal. This thesis investigates winnowing in general, starting with the method itself and aiming towards designing and ultimately constructing a winnowing plant that can be used to test the method in future studies. The papers presented in this thesis will cover the basics of winnowing but mostly focus on the design of the winnowing equipment which is the aim of this study. Two pieces of equipment were designed with the aid of Computational Fluid Dynamics (CFD) and mathematical models. These prototypes were tested using density tracers and -6 mm coal. The first piece of equipment was a size separation nozzle to aid with the size sensitivity of the method, however initial tests indicated that the nozzle favoured a density separation instead of the intended size separation and further tests are needed to confirmif the nozzle is capable of performing a density separation, or if the nozzle will work as a size separation unit as indicated and by the CFD simulations. The second piece of equipment that was designed was the density separation chamber, capable of separating particles into multiple densities ranging from 1.2 g cm-3 to 2.2 g cm-3. The initial results did indicate that the chamber is size sensitive and that a density separation is possible given the correct size interval. Both units work on negative pressure and initial results show that both machines have the potential to work as a combined 2 stage separation plant. The design of the winnowing plant was successful, and a working pilot plant was constructed. There is still some optimization and testing required to improve the operation of the plant as indicated by the results in the final paper of this thesis, however initial testing looks promising.