Ferrometals' Furnace 4 upgraded
to 60 MVA
BATEMAN has completed an upgrade of Ferrometals' Furnace 4 (F4) in Witbank,
RSA, for Newsam Pty Ltd (a joint venture between Samancor and Poschrome)
to increase the furnace's production capacity from 100 000 t/yr of ferrochrome
to 125 000 t/yr.
The project site work was undertaken during a shutdown
of the plant from 30 June to 4 September 2003 and was finished four
days ahead of schedule.
The upgrade and rebuild of F4 follows a similar upgrade
of Furnace 5 at the same site during 2002 and involved the existing
48 MVA furnace being upgraded to a 60 MVA closed submerged arc furnace.
The nominal operating power is expected to be about 48-50 MW, with capability
to operate at a maximum of 52-55 MW.
The shutdown started with the demolition of the furnace
(roof, shell and feed chutes) and removal of the furnace burden. Civil
work on the furnace supports started when the area had been cleared
and upgrade work commenced on the raw materials handling system at the
same time.
The two closed furnaces at Ferrometals' site in Witbank,
F4 and F5, share a common feed system. The raw materials are fed to
the furnaces' respective proportioning bunkers via a fines screen and
flopper gate system onto a series of conveyors. The raw material handling
system was upgraded by rearranging existing feeders and installing new
vibrating feeders to increase feed capacity by 25 %.
After proportioning, an incline conveyor raises the
material to the Outokumpu pre-heater. The feed mixture is heated by
furnace off-gas, mainly carbon monoxide (CO), before being choke fed
into the furnace via nine refractory lined chutes, which were also replaced
during the shutdown.
The feed material is then smelted in the furnace,
the main reaction being the reduction of chromite, during which CO is
generated. The furnace off-gas is removed by extractor fans and passes
through wet scrubbers for cleaning and cooling. The pre-heater consumes
the CO gas for pre-heating and the remainder of the gas is available
in the network or it can be flared. In order to control the furnace
pressure, two new CO fans were installed to cope with the increased
volumes of CO being generated in the furnace. Knock-out separators were
installed after the furnace venturi scrubbers to remove remaining solid
particles and moisture in the gas stream.
The furnace was replaced by a BATEMAN-designed furnace
and roof. The shell diameter was increased from 13 m to 13,7 m, incorporating
a UCAR / BATEMAN Chill KoteTM lining. This lining consists of conductive
refractory on the cold face and insulating refractory on the hot face
in the metal and slag zone. This effectively increased the crucible
diameter by more than 2 m.
Three 21 MVA transformers replaced the three 16 MVA
transformers. The increased furnace power input also necessitated an
increase of the electrode pitch circle diameter (PCD).
The Chill KoteTM / freeze layer on the hot face of
the refractory relies on adequate and continuous cooling to ensure that
the hot face temperature stays below the solidus temperature of the
metal and slag. A furnace refractory lining monitoring system was developed
by Bateman and installed to monitor refractory wear and Chill KoteTM
/ freeze thickness. Shell film cooling water is collected in a tank
from where it is redistributed to the header and tundish of the furnace
shell. A side-stream filter unit removes solids in the water.
Roof cooling is accomplished by a closed-circuit cooling-water
system and dedicated cooling towers.
A single, main taphole was provided together with
an emergency taphole above the main taphole at an angle from the centre
line, to be used for upset conditions.
Commissioning was a continuous process, signing off systems as they
were completed by the construction teams. Start-up was accomplished
with no significant mechanical, electrical or instrumentation malfunctions.
For further information contact Jurgens van Tonder,
General Manager, AC Furnaces, on +27-11-899-2363 or email acfurnaces@batemanengineering.com.
VIEW
PDF
