The Hernic Ferrochrome Project
Bateman Titaco Limited has engineered, supplied and constructed one
of the most sophisticated charge-chrome producing plants in the world
for Hernic Ferrochrome(Pty) Ltd. the state-of-the-art technology together
with the benefits of large-scale production have enabled Hernic to improve
its competition have advantage by improving the stability of its furnace
operation, increasing chrome recovery and saving energy.
The project is part of Hernic’s long-term business strategy. As
a result of this expansion it will be able to maintain its position
as the third largest producer of ferrochrome in South Africa and be
a global player with one of the lowest production costs for charge-chrome
in the world.
The project involved installing a new submerged arc furnace, preheating
and sintering plants, ball ills, conveyors and overhead cranes. Rated
at 54MVA,the furnace which is the largest ferrochrome smelter in Southern
Africa, constituted about half the total cost of the expansion project.
Bateman Titaco also installed the first two furnaces at Hernic, two
37 MVA fine smelting units, which were supplied in 1994. The process
technology for the new furnace combines
Outokumpu’s ore sintering and furnace charge pre-heating processes.
Bateman Titaco designed the large closed-type submerged ore smelter
in close collaboration with Hernic and Outokumpu.
SMELTING
The furnace is fed with sintered pellets comprising finely ground ore
sintered with coke and fixed with other raw materials. The resulting
pellets are then heated to a temperature of 700 °C. The preheating reduces
the energy consumption during ferrochrome production by between 20 %
and 30% compared to conventional plants.
Sintered pellets also significantly increase chrome recovery and reduce
electrode consumption.
The pellets contain finely ground chromite with a high specific surface
which increases the reduction rate and avoids non-uniform reduction.
The rapid smelting, improved furnace stability, ease of operation and
high chromium yield mean that pre-treatment costs are quickly recovered.
The absence of moisture and other volatiles in the smelting furnace
together with better gas permeability of the burden (from the use of
pellets instead of fines) reduce eruptions and hence furnace downtime.
Bateman Titaco designed and constructed the 54 MVA furnace including
all of its infrastructure. A vital technology component in the furnace
is the Bateman Titaco electrode holder, designed specifically for closed
submerged-arc furnaces using Söderberg paste. The electrically actuated
lipping device provides a fail-safe means of holding the electrode in
position even if the electric power fails. The contact shoes through
which electricity flows into the electrode can be lifted above the furnace
cover and a section of the heat shield removed, greatly facilitating
and speeding up maintenance. The level of protection afforded the furnace
components enables it to operate continuously at 900°C and higher.
The process gas from the closed smelting furnace is cleaned using two
wet scrubber units, rendering it suitable as a heating fuel by burning
by-product carbon monoxide. Some of this gas is used in the sintering
process and for pre-heating the smelter feed. The remaining gas is used
or general heating or drying purposes or is flared if not used
Pelletising and sintering The new plant installed at Hernic feeds both
the new 54 MVA furnace as well as the existing two 37 MVA units and
has been designed to improve the availability, performance and production
volumes.
The ore and coke are ground to 90% minus 200 mesh, graded, filtered
to remove excess water, mixed with bentonite and pelletised in a drum.
Green pellets between 10 and 5 mm are fed into a steel-belt sintering
furnace at temperatures up to 1350°C and passthrough drying, preheating,
firing and cooling zones. The pre-treated pellets containing iron in
its more easily reducible
Further details are available from Jurgens van Tonder, General Manager,
AC Furnaces, on +27-11-899-2363 or
Email acfurnaces@batemanengineering.com
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