EOF: The Reliable Choice For Indian "Start-Up" Steel Plants
EOF: The Reliable Choice For Indian "Start-Up" Steel Plants
EOF: The Reliable Choice For Indian "Start-Up" Steel Plants
Henrique C. Pfeifer
Mini Tech, Brasil
Email : pfeifer@minitec.eng.br
Abstract
The steel industry in India has gone through a big change in the past two decades. The
coming years are bringing newer challenges and opportunities. Rich mineral ores are
depleting and scrap availability are increasing. New challenges and opportunities demand
a careful selection of capacities, process routes and technologies. In such scenario the
Energy Optimizing Furnace (EOF) is emerging as a reliable choice for steel makers.
Developed in Brazil, the EOF technology has grown and is now striving to occupy its
position in the iron and steel world, contesting with the established processes of Electric
Arc Furnace (EAF) and the oxygen converter (BOF or LD). Notwithstanding its 25 years
of successful operation at the GERDAU Divinopolis plant in Brazil, delivering more than
42 heats per day and about 600.000 t/y liquid steel and the three efficient units operating
in India, the EOF is still little known. This paper endeavors to present the technology with
its latest achievements and developments.
Actually, with the three units operating in India since the turn of the century, the EOF
experienced a strong evolution and became a reference also in terms of quality steels
used for die-forging, seamless pipes, cold heading, roller bearings etc, approved by the
strictest clients regarding quality control. One of the most remarkable aspects in this
regard is the ultralow phos content (< 0.01 %) which may be reached consistently, without
impairing the high productivity of the furnace - above 36 heats per day, on 330 working
days per year. In time of decreasing quality of iron ores and increasing phos content in
hot metal, this is an important technology. Slag-free tapping is an additional feature
warranting high quality production. Today´s EOF presents itself as a dynamic furnace,
with a high level of automation, and combining two usually antagonistic factors: high
productivity, essential in any modern iron and steel process; and extraordinary quality, a
must in the production of quality steels.
Energy optimization, which bestows the name to the process (“Energy Optimizing
Furnace”) allows the EOF to operate with up to 40 % solid charge, pre-heated in the
process, in addition to 60 % hot metal. This feature outfits the EOF with extraordinary
flexibility regarding charge composiiton. Combined with carbon injection devices, the
proportion of DRI in the charge may rise to 25 % and even more - impossible for the
BOF and only achievable in the EAF, at a high cost of electric energy. The ongoing
evolution of the process, in view of the engineering solutions, warrant growing operational
availability and ease of maintenance.
In the past two decades, the steel industry in India has seen vast changes in Technology,
Size, Productivity levels, Energy consumption, etc. With the changing raw material
scenario and demands, the steel producers adopted new process routes, new
technologies and energy efficient equipments, seizing the opportunities and accepting the
challenges.
The coming years are bringing newer challenges and opportunities in steel industries.
The huge expansion of Chinese steelmaking capacity has brought about a worldwide
excess steel supply. India, however, is today the only country where new steel plants are
needed, especially mini steel plants for long products, to serve local markets. The coming
years are bringing new challenges and opportunities.
The harmful effects of global warming and climate change, depleting rich mineral
resources, power shortage and it’s increasing cost, stagnation in GDP growth, are having
a big impact on the steel plants. Most of the DRI units and mini steel melt shops have
faced closures eventhough the coal prices and scrap prices have dropped drastically.
Some high capacity units are also running at lower production levels due to accumulated
stocks and high costs.
The scrap availability has improved and prices have plunged. This will continue as China
and India will be generating more scrap in the coming years as they are adopting newer
technologies for their basic infrastructure. High quality steel is no more a costly affair and
low quality steel is high on cost. This is a delight to the quality steel producers.
These new challenges and opportunities call for careful selection of capacities, process
routes, technologies and equipment which ensure producing very good quality steel at
low costs, low energy consumption and low project costs. In such scenario, the Energy
Optimizing Furnace is emerging as the reliable choice for steel makers.
The EOF
Developed about 35 years ago, the Energy Optimizing Furnace or EOF was conceived to
utilize the sensible heat of small and medium sized steel converters in an effective way. It
is a combined blowing basic oxygen steel making process where a mix of hot metal,
scrap and DRI forms the charge. Oxygen is blown through two numbers of submerged
tuyeres and one or two numbers of supersonic lances. Post-combustion of the emerging
gases above the steel bath is done using four numbers of atmospheric injectors and by
air leaking in through the door, thus supplying a part of the heat to the metallic bath and
rest for scrap preheating for the subsequent heat. The tap-hole and tilting mechanism is
designed for efficient slag-free tapping.
The submerged injected oxygen reacts with the carbon of the bath, generating CO
bubbles which promote intense bath agitation, beneficial for reaction kinetics and
temperature homogenization. Once the bubbles leave the bath CO is burnt with the
oxygen from the atmospheric injectors. The projections of liquid metal caused by the
eruption of the CO bubbles promote an extraordinary increase in bath surface, increasing
the exposure to oxygen from the supersonic lances and capturing part of the heat
generated by after-burning, which is drawn to the bath. The combination of these factors
explains the extremely fast decarburizing and temperature rise of the bath, resulting in
blowing times similar to that of the BOF. The possibility of tilting of the furnace, allowing
continuous extraction of slag through the slag door as well as tapping at the very moment
of finishing decarburizing, as well as the instantaneous release of scrap from the scrap
preheater, allow tap-to-tap times of less than 30 minutes - an impossibility for the BOF.
Another edge on the BOF is the flexibility of the EOF to operate with up to 40 % scrap in
the charge or 15 % DRI. These proportions may be even higher if Carbon injection
system is provided.
A further important aspect is the very low investment demanded by the EOF, as
compared to the LD converter, while the conversion cost is comparable to LD
steelmaking. Actually, the possibility of charging a higher amount of DRI to the EOF
reduces its production cost in comparison to the BOF. The investment cost of EOF is
lower than that of EAF, considering the high cost of electrical installations.
Hence EOF is the most suitable equipment for converting the liquid hot metal, scrap and
DRI to steel, especially for heat sizes of 30 t to 80 t, or annual capacities of 0.3 to
0.8 Mt/yr.
Furnace shell
4
Furnace bottom
Bottom car 5
Opening to GCP
Openings for scrap pre-heater by-pass
6
7
Recent Performance Data
Table 1 presents the main operating figures of the EOFs in operation, in Brazil and in
India. Figures are averages for the year 2013.
Heats per shift: 16 heats tapped in a shift at Hospet Steels Ltd, Karnataka, India.
Heats per day: 42 heats tapped in a day at Hospet Steels Ltd, Karnataka, India.
48 heats tapped in a day at GERDAU Divinopolis, Brazil
Heats per year: 13.338 heats tapped in a year (2005) at GERDAU Divinópolis, Brazil.
Heats per campaign: 1.314, at GERDAU Divinopolis (Campaign Nr. 199 - July
2008) a result of the improvement in tuyere design.
Electrical Energy: 22 units per Ton
Phosphorous levels: 0.01 %
Design Improvements
Economical Considerations
Table 2 presents the Operating Cost Index, in %, of the EOF (GERDAU Divinopolis), BOF
(GERDAU Barão de Cocais) and the best performing EAF of the GERDAU Group in
Brazil (excluding raw materials).
Remarks
It may be observed that during the period covered by this survey, total operating cost
(including maintenance) of the BOF was 8 % higher than that of the EOF, while the
cost of EAFs was much higher - of course compensated by the lower raw material
(scrap) cost.
The Divinopolis EOF is a 43,5 t unit (originally 35 t), while the Barão de Cocais BOF
is a 35 t unit (originally 28 t). Both operate with hot metal from charcoal blast furnaces,
while the BOF charges on average 16 % scrap, the EOF averages 36 % scrap.
Conclusions
EOF is proving itself to be the most suitable option for production capacities up to 0.8
mtpa for converting hot metal and varying proportions of scrap and DRI. The quality and
productivity levels have been appreciable and are still being enhanced by desing
improvemtns. Operation and maintenance is much easier than in case of Converter or
EAF.
Today the EOF is a proven technology, competing with the classical steel melting
processe, with the advantage of producing the most critical quality steels as a routine.
Low investment cost (capex) and low operating cost (opex), combined with great flexibility
regarding charge mix and low demand of electric energy render the EOF most attractive
for any new steel meltshop. This is especially true in areas where electric energy is
scarce and expensive, and unavilability of scrap. These conditions previal in India
now-a-days.
An integrated Mini Steel Plant bsed on mini blast furnaces and an EOF, supported by
ladle furnace and continuous casting machine, presents the following advantages:
Though the number of installations are still few, the coming years will see many
installations coming up with new improvements making it an even better option.