Techno-economic impact of advanced coal beneficiation using models for predicting liberation functions
Date
2014-09-03
Authors
Bergh, Jacobus Petrus
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
This thesis evaluates the entire coal value chain in order to understand the economic
and environmental impacts of the various beneficiation pathways, including modern
coal processing techniques required to produce different specifications of local and
export quality thermal coal products. Three South African coals, one from the
Witbank coalfield No 4 seam, a second from the Waterberg Upper Ecca group and,
to a lesser extent for comparative purposes, a third from the Free State
(Vereeniging) coalfield were evaluated. The ultimate objective was to determine
whether it would be advantageous from the techno-economic and environmental
viewpoint, to produce low grade thermal coal for export from any of these coalfields.
Against this background, this thesis serves to explain the extended value chain in the
production of export coal with a view to technically and economically evaluating the
advantages and disadvantages of low grade export versus domestic coal production.
Detailed experimental work was undertaken on samples from the Witbank No 4
seam and Waterberg Upper Ecca coals. Apart from conventional analyses, detailed
petrographic and mineral liberation analyses (using QEMSCAN and XRD) were
performed on a series of washability density fractions for each coal. Trace element
analysis (for the environmental studies) was also undertaken using ICP-MS on the
same washability fractions. These data were combined in the thesis (i) to produce
liberation models for the macerals and the minerals using M-curves, and (ii) to
determine the association of sulphur and trace elements with the macerals and
minerals using Principal Component Analysis.
The thesis applied coal process modelling to a wide range of coal preparation
options in order to produce various thermal coal products from the three South
African coals under investigation. The impacts of the different beneficiation process
options on the rejection of specific ash-forming minerals were evaluated at various
separation densities. Costing of the various processing options was conducted.
This was combined with the projected income expected from each thermal coal
product. The economic analysis was subsequently evaluated in conjunction with the
power required to produce each product as well as the carbon footprint and emission
rates of carbon and sulphur dioxide for each processing option. The multifaceted
outcome then produces a series of results from which conclusions can be drawn as
to what product is best produced from which coal field technically and feasibly.
Key words: Coal preparation, beneficiation, process modelling, mineralogy,
liberation analysis, trace elements, coal petrography, energy utilisation, technoeconomic
modelling, low grade thermal coal export, carbon footprint