The evaluation of ultra fine coal treatment options at the Western Coal Complex
Date
2012-09-25
Authors
Van Schalkwyk, Vicky
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Abstract
The aim of this research project was to test the response of ultra fine coal sourced at
Klipspruit Colliery to froth flotation and the response of the froth flotation products
to dewatering using two different types of filter presses, namely the Tecnicas
Hidraulicas (TH) and the Ishigakhi presses. During test work, some difficulty was
experienced with coarse material feeding the froth flotation pilot plant. This led to
pilot plant modifications. Further process complexities necessitated laboratory scale
flotation test work on the Klipspruit coal to be carried out.
The results for both the laboratory scale and pilot plant test work for froth flotation
indicated that froth flotation as applied to the Klipspruit fines was not economically
feasible because neither the required quality of the product (calorific value of 27.80
MJ/kg) nor the product yield of 50% could be achieved when subjected to a primary
and secondary stage of froth flotation. The coarse material, which fed the pilot plant
and the Ishigakhi filter press, gave low moisture values (12.3%) not typical of ultra
fine coal moisture values. However when fed with very fine particle size
distributions, prior test work with the Ishigakhi showed that moisture values below
20% could be achieved. The moisture values obtained for very fine particles using
the TH filter press on product thickener underflow material sourced at Goedehoop
colliery reached values below 20%. Thus both of the two dewatering options, i.e. the
Ishigakhi filter press equipment or TH filter press equipment for the ultra fine coal
dewatering, can be utilized. Since the filter rate is the determining factor specifying
filter press size, it was determined that a larger TH filter area is required in
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comparison with the Ishigakhi press. Based upon the pilot and laboratory scale test
work undertaken and the assessment of the results, it appears that both dewatering
options could be successfully employed on a technical basis for the dewatering of
coal flotation products, tailings and the arising raw ultra fine fraction.
Froth flotation for Klipspruit ultra fine coal was deemed unfeasible for both pilot
plant and laboratory scale tests conducted. For this reason a capital expenditure for
the construction of a froth flotation plant at the Western Coal Complex Phola plant
was not considered feasible since Klipspruit coal forms part of the feed that will
feed the Phola plant.
In conclusion, following dewatering using either the TH filter press or the Ishigakhi
filter press, it was established that both froth flotation concentrate and
unbeneficiated ultra fines gave acceptable total moisture results (below 20%). These
dewatered raw ultra fines may therefore be blended into inland product as thermal
coal to be utilised by Eskom for power generation. Based upon this premise, it is
estimated that profits of 76.5 million Rand could be generated by blending
Klipspruit ultra fine coal into thermal coal production at the new Phola plant.
Description
M.Sc. (Eng.), Faculty of Engineering and the Built Environment, University of the Witwatersrand, 2012
Keywords
froth flotation, dewatering, laboratory scale flotation, froth flotation pilot plant modifications, filter rate