summarised in Table 2. The basis of the
comparison is 150 tph (ad) of thickened
flotation concentrate (25 – 30% w/w
solids), with a P
50
of 0.05 mm. The
equipment costs include ancillary items
specific to the dewatering equipment
(vacuum pumps, compressors, air
receivers etc) but excludes structural,
mechanical, civil, piping, electrics and
indirect costs. As such, the equipment
costs are indicative only but provide a
ranking of the technologies against
target moistures.
The ranking indicates that the
screenbowl option has the lowest capital
cost and power requirement; however,
there will be an associated yield loss of
the ultrafine -0.045 mm particles. This
classification can sometimes be
beneficial where the flotation
concentrate contains a significant
proportion of entrained high ash slimes.
The vacuum filter and hyperbaric disc
filter options are both significantly more
expensive than the screenbowl option
(approximately 2 to 5 times the cost
respectively) but these technologies have
the ability to recover all of the -0.045 mm
material. The vacuum filter will achieve
similar moisture to the screenbowl
option, whereas the hyperbaric filter will
achieve a step change in moisture
reduction of about 8% (absolute).
Steam pressure filtration will have an
equipment cost between the vacuum
filter and air only hyperbaric filter
application. This is because the use of
steam will increase the throughput
capacity of the hyperbaric disc filter,
relative to air pressure filtration only
and the additional cost of the boiler
plant and steam cabins etc. will be
offset by the requirement for only one,
rather than two filters. The installed
power will be lower but the extra
operational cost of the boiler fuel is
high. The steam pressure option will
result in a further additional step
change in moisture reduction of about
5% (absolute).
The power costs assume a site bulk
cost of AUS$0.09/kWh, a diversification
factor of 70% and a power factor of
95%. The boiler diesel cost assumes a
steam usage of approximately 80 kg/t
of filter feed and a bulk diesel cost of
AUS$1.15/l.
Closing remarks
Hyperbaric filtration has been
previously tested as an avenue to target
reduced filtercake moistures from coal
froth flotation circuits. High capital
costs to implement pressure filtration
have precluded the take up of the
technology in Australian operating
plants.
Recent QCC study work has
confirmed pressure filtration and/or
pressure filtration with steam addition
could achieve product free moisture
levels in the filtercake as low as 8.5%
depending on the feed particle size
distribution, and process air and steam
consumption rates.
The ability to significantly reduce
flotation product moisture levels using
pressure filtration may provide a path
for thermal coal producers to add
flotation to existing plants to increase
the plant yield without incurring a
penalty with respect to the equivalent
gross as received energy of the product
coal.
Settling ponds cause profit-draining downtime and environmental
headaches. McLanahan Corporation offers a custom engineered
processing solution to help you recover more fines, while saving time
and maximizing production. Where you once had fine-laden slurry,
you now have dry cakes you can market. For a more sustainable
and more profitable operation, call McLanahan at +1 (814) 695 9807.
Filter Press
Filter Press Cake
Dewatering Screen
Thickener
mclanahan.com
