Abstract:
Coal mining is a thriving industry and 53% of the coal mined in South
Africa is used for electricity generation. Mechanization has made coal
mining more efficient, but fines generation has subsequently increased. Up
to 6% of the run of mine material can report to the -200 μm fraction.
Common problems associated with fines handling include dust formation,
storage problems, and high moisture levels. A method to turn this material
into a saleable product instead of stockpiling it can add value to a
company.
Briquetting is a pressure agglomeration method where loose material is
compacted into a dense mass (FEECO International, 2014). The briquettes
must be able to withstand rigorous handling and transport operations
without disintegrating. This study aims to investigate the optimum binder
and moisture conditions required to produce a mechanically strong
briquette using two different binders – a PVA powder (binder A) and a
starch powder (binder B).
It was found that for binder A the optimum moisture level was 12% to
14%. At this moisture level the greatest compression strength gains were
observed, and low amounts of fines produced in impact and abrasion tests.
The minimum amount of binder added while still obtaining a strong
briquette was 0.5% binder A. For binder B the optimum moisture level was
also 12% and the minimum amount of Binder B to be added was found to
be 1%. Briquettes that were dried outside reached their peak strength after
about four days, whereas the briquettes that dried inside took about 20
days to reach their strength plateau. Hardly any degradation took place on
the surface of the binder A film after exposure of 300 hours of artificial
weathering. Thermogravimetric analysis confirmed that neither binder A
nor binder B will add to the ash content of the coal fines, as both binders
totally decompose above 530°C.
Binder B yielded stronger briquettes after 15 days and also generated
less fines. It is therefore superior to binder A and would be recommended
for further use.
