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STEELMAKING AND CASTING
Capacity enhancement at Emirates
Steel through improvement in EAF
performance with hot DRI charge
The two integrated DRI-EAF plants built for Emirates Steel by Danieli in 2009 and 2011 have
consistently outperformed design speciﬁcations. To further increase productivity, plant
number 2 was enhanced in 2013/14 by a combination of plant and process improvements,
while maintaining the basic 150t tap weight and 90:10 hot:cold DRI charge. All key performance
indicators were exceeded, for instance, resulting in a new record of 40 heats/day (247tls/h)
and electric energy consumption of 378kWh/t, with 34Nm3/t oxygen.
Authors: D Patrizio, P Razza and A Pesamosca
Danieli & C. Ofﬁcine Meccaniche and Emirates Steel
T
Item
Tap weight, t
Lower shell diameter, m
Electrode diameter, mm
Pitch circle, mm
wo integrated steel plants (Phase 1 and 2), both
comprising direct reduction plant (DRP), EAF, LF, caster
and rolling mill, were supplied by Danieli to Emirates
Steel, Abu Dhabi, in 2009 and 2011. Both plants produce
steel for rebar and structural applications (including sheet
piles), starting from iron ore as the feed material. They are
based on a DRP (ENERGIRON® technology) that directly
feeds the melt shops by means of a pneumatic transport
(HYTEMP). Both EAFs work by keeping a hot heel of 50t
and are designed for a rated tap size of 150t, producing
1.4Mt/yr. Some EAF key features are reported in
Table 1. The nominal charging practice is 10% cold DRI
and 90% hot DRI, continuously fed from the ﬁfth hole and
coming from the DRI plant through the HYTEMP tower
(see Figures 1 and 2).
The EAF transformer has a rated apparent power of
130 + 20% MVA and allows a selection of 18 tap positions
to obtain the best combination of arc voltage, arc current
and power factor during the various process stages. The
secondary circuit is designed for a maximum current
of 80kA. The main electrical data are summarised in
Table 2.
The performances achieved from EAF Phase 1 have been
described previously [1].
Table 3 and Figure 3 describe the injectors.
A comparison between the EAF design parameters for
plant number 2 and excellent results achieved a few
months after start-up (2011) are summarised in Table 4.
Value
150
7.0
710
1,400
r Table 1 Main geometrical data of EAFs installed
in Phase 1 and 2
Electrical data
EAF transformer rated power
Overload
Frequency
Primary voltage
Secondary voltage range
Secondary voltage at full power
SVC rated power
Series reactor rated reactance
Value
130MVA
20%
50Hz
33kV
1,250-650 V
1,250-1,120 V
170MVAr
1.3ohm
r Table 2 Main electrical data
Although the performance of the two plants has exceeded
expectations, Emirates Steel requested even more
productivity, aiming for 1.68Mt/yr for both plants and
starting from Phase 2.
This was to be achieved by keeping the original heat size
a
r Fig 1 EAF and HYTEMP tower at ESI plant
MILLENNIUM STEEL 2015
NEW PRODUCTIVITY TARGET
45
Module
Oxygen ﬂow
rate Nm3hr
2,200
150
–
Oxygen jet 1-2-3-4-5
Carbon jet 1-2-3
Carbon injector
Material feed
rate kg/min
–
15 – 30
15 – 30
r Table 3 EAF injection system
Parameter
Units
DRI hot/cold
Tap to tap
Power on time
Tapped steel
Productivity
Electrical energy
Oxygen
Charge yield
Electrode consumption
Average power
Charged carbon
Injected carbon
Tap temperature
%
90/10
min
46.0
min
37.0
tls
150
tls/hr
196
kWh/tls
420
Nm3/tls
35.0
%
86.7
kg/tls
1.4
MW
102
kg/tls
0
kg/tls
16
°C
1,630
DRI PLANT
%
91.0
%
94.0
%
2.0
Total Iron
Metallisation
Carbon
Design
target 2011
Results
June 6th 2011
(15 heat
sequence)
92/8
45.4
36.0
153.1
202.3
412
33.2
87.9
1.28
105.2
1.9
10.5
1,643
r Fig 2 Plant sectional view
92.3
95.7
2.18
of 150t and the charge mix at 10:90, cold DRI:hot DRI,
coupled with plant changes as follows:
r Table 4 EAF Phase 2: Results achieved in 2011
` Revamping of DRP and oxygen plants to provide the
additional raw materials.
` Maintaining the high quality of the DRI, but with
MILLENNIUM STEEL 2015
r Fig 3 Layout of oxygen and carbon injectors
46
the possibility to increase carbon content from 2.0 to
2.5%.
` Increase hot DRI maximum feeding capacity to
6.5 t/min
` Reduce the power-on time from 37 to 32 minutes via
use of increased chemical energy input
` Reduce power-off time from 9 to 6 minutes by increasing
the taphole (EBT) diameter from 180 to 200mm
and by using a gunning robot, to allow signiﬁcant
improvement in refractory repair operations.
` Engineer the EAF slag to improve foaming consistency
and increase the life of shell refractory, monitored with
a 3D laser scan
` Increase the size of the oxygen jets to 2,500Nm3/h
in order to sustain the higher DRI feed rate and also
to decrease electrical energy consumption by higher
chemical energy input.
As a consequence the new nominal productivity target
increased from 196 to 236.8tls/hr.
STEELMAKING AND CASTING
PHASE 2 RESULTS
After the modiﬁcations, the Energiron plant was in
operation at an average rate higher than the design, of
more than 250t/h.
The EAF melting practice was based on the continuous
feeding of cold and hot DRI during the heat, reaching
a maximum feed rate of 5.8t/min. The new revamp
targets were deﬁned as reported in Table 5: the goal for
productivity was 236.8tls/hr.
During the ﬁrst weeks of operation after DRP and oxygen
plant revamp, some tuning was necessary to deﬁne the
optimum DRI characteristics. Eventually the best results
were achieved and are reported in Table 5 where it can
be appreciated how the initial targets of the project were
reached with a different DRI composition:
With the aim of maximising yield, it was decided to
change the chemistry of the DRI by lowering the carbon
content from 2.5 to 2% and increasing the metallisation
from 94 to 95.7%. At the same time, tuning of process
parameters allowed maintenance of DRI temperature at
510°C at EAF inlet.
The lower oxygen input (-6Nm3/tls compared to the
new design value) would result in a potential loss of
useful energy in the range of 18-21kWh/tls, but the
improved DRI metallisation gives a beneﬁt of 24kWh/tls.
Considering the lower tapping temperature, the change
of strategy did not modify the electrical consumption, but
improved the yield.
The productivity exceeded the initial revamp target of
236.8tls/h reaching 247.3tls/h on 12 April 2014, when
40 heats were tapped (power-off 4.8 min and average
power 111MW).
Figure 4 shows target and the best daily performances
before and after the revamp. Even before the enhancement,
the original target productivity had already been exceeded,
and a record of 36 heats/day was obtained in 2013,
based on an average power of 107.6MW and 5.8 minutes
power-off. Both indicators exceed the original nominal
values, and the application of higher power input was a
result of ﬁne process tuning with special attention to the
control of slag chemistry, while the reduced power-off was
made possible by operational excellence and utilisation of
gunning robot for refractory monitoring and repair.
The productivity record after the capacity upgrade was
achieved by several factors. The increased capacity of
oxygen injection system allowed higher chemical energy
Parameter
Units
New design
Targets
DRI hot/cold
Tap to tap
Power on time
Tapped steel
Productivity
Electrical energy
Oxygen
Charge yield
Electrode consumption
Average power
Charged carbon
Injected carbon
Slag builders
Tap temperature
%
min
min
tls
tls/h
kWh/tls
Nm3/tls
%
kg/tls
MW
kg/tls
kg/tls
kg/tls
°C
DRI PLANT
%
%
%
90/10
38.0
32.0
150
236.8
380
41
86.1
1.3
106.9
Total iron
Metallisation
Carbon
94
2.5
Results: 14 April
2014 (21heat
sequence)
90/10
36.7
31.4
151.1
247
378
34.1
87.0
1.05
109.1
6.2
10.0
36.2
1,617
92.4
95.7
2.01
r Table 5 EAF Phase 2: capacity enhancement targets and results
r Fig 4 Best daily performances, EAF 2
utilisation and the higher decarburisation rate needed to
match the higher DRI input. The optimisation of melting
resulted in an average active power of 111MW (+4.1
MW higher than design target). Power-off was further
decreased to 4.8 minutes, thus improving previous record
and demonstrating the great effort and professionalism
of ESI personnel that made it possible to achieve the
performance guarantee tests after only two months from
completion of revamping.
Figure 5 shows the power-off frequency distribution
showing the repeatability of EAF operation and the
improvements achieved.
a
MILLENNIUM STEEL 2015
The modiﬁcations for Phase 2 started in December 2013
and were completed in March 2014, culminating in a
successful performance test. In April 2014, only one month
after commissioning completion, more than 181,500t high
quality DRI had been produced, strongly contributing to
the extraordinary records achieved at the EAF plant.
47
ELECTRICAL POWER PROFILE
The electrical proﬁle is one of the key factors that allowed
the plant to reach the above-mentioned results. Figure
6 shows a typical melting proﬁle recorded during the
capacity enhancement. The key characteristics can be
summarised as follows:
` Aggressive power ramp up: the maximum power is
applied in less than 20 seconds.
` Very stable active power throughout the heat. The
r Fig 5 Power-off frequency distribution (October 2011, April 2014)
MILLENNIUM STEEL 2015
r Fig 6 Typical electrical melting profile post enhancement
48
r Fig 7 Specific power applied in DRI-based EAF
average active power applied is 111.5MW, with a
maximum power of 114.3MW. The stability exceeded
the original expectations achieving a ratio Pavg/Pmax
= 97.5% and a relative standard deviation of 1.1%.
` The maximum power input is practically utilised for
the total duration of the power-on time. The working
point corresponds to an active power of 114.3MW,
secondary current of 76.3kA, and arc voltage of 470V.
The resulting refactory wear index (RWI) is in the range
of 230-235kWV/cm2 and it can be considered the
average RWI.
Good management of the hot heel and the ability to
foam the slag in the early stages of the process enables
maximum power to be applied.
The stability of the active power was helped by controlling
the DRI feed rate via level 2: the average feed rate
being 5.7t/min, with an average speciﬁc feed rate of
52kg min/MW.
Among other AC EAFs that operate with DRI, the case of
ESI represents the plant with the highest value of speciﬁc
power, deﬁned as active power /(tap weight * bath
surface) and expressed in kW/(t*m2).
Data from three other Danieli installations are as
follows:
Plant A 100% Hot DRI
Plant B 20% scrap + 80% Cold DRI
Plant C 35% scrap + 65% Cold DRI
These are shown in Figure 7 where it can be seen that
ESI has the highest value of speciﬁc power, (22.8kW/t/
m2), and the smallest difference between the maximum
value and the average value along the heat (0.5kW/t/
m2), indicating the high level of optimisation of the
process.
If now we relate the productivity reached, 24.3tls/h,
with the utilised power, 111.5MW, the phase 2 EAF has
reached the remarkable value of 2.21tls/h/MW. Despite
melting hot DRI, the speciﬁc productivity is comparable
with some of the most efﬁcient scrap based EAFs. In
Figure 8, the speciﬁc productivity of Emirates Steel EAF
is compared to the values obtained in other furnaces
supplied by Danieli.
STEELMAKING AND CASTING
In a DRI-based process, ﬂat bath conditions with variable
slag level throughout the heat result in severe stress on
the whole lining. For this reason it is necessary to check
internals quite frequently and act promptly to avoid
local wear leading to bricks collapsing and, in the worst
case, a furnace breakout. In particular, major wear is
observed for the slag door area, and hot spots in front
of electrode 1 (on the left of slag door) and phase 2
(transformer side). The utilisation of the gunning robot
signiﬁcantly improves repair operations as it reduces
personnel exposure, increasing operational safety, and
allows for fast and precise detection of damaged areas,
which in turn results in decreased power-off time and also
in lower consumption of gunning material. The possibility
of performing a complete laser scan of internal surfaces
with 3D visualisation of actual refractory status (residual
thickness) is a further tool to monitor the results of the
repair operations.
Due to 100% ﬂat bath operation, the control of slag
chemistry is a key factor in allowing high power input and
avoiding excessive refractory wear. The electrical power
proﬁle adopted is very aggressive and, in order to sustain
this, adequate foaming is needed from the very beginning
of power-on. During the ﬁrst stages of DRI feeding good
foaming is observed even without oxygen injection. Apart
from slag basicity, this can be explained considering that
the initial slag is more oxidised compared to the average
slag produced during the melt. Also, the very short poweroff time between end of tapping and start of power-on
minimises bath cooling. These factors allow fast kinetics of
reaction between iron oxide and DRI carbon. It is therefore
possible to reach maximum power quickly due to complete
arc coverage.
The presence of stable foaming slag during the heat
is ensured by continuous feeding of slag builders at a
feed rate of 80-100kg/min, with a total consumption of
18kg/t lime and 18kg/t dololime. In Figure 9, the slag
isothermal solubility diagram at 1,600°C is reported,
considering the average slag composition of samples
taken towards the end of the heat. The IB2 and IB3
basicity indexes are 2.46 and 1.9 respectively (37% CaO,
15% SiO2, 4.5% Al2O3). IB2 is CaO/ SiO2 and IB3 is
CaO/( SiO2 + Al2O3).
In theory, optimal foaming should be achieved by
reaching saturation in MgO-FeO or 2CaO-SiO2, due to
increased slag viscosity. In practice, a major role is played
by the high CO generation rate (average 660Nm3/
m2hr) allowing good foaming even if slag does not reach
saturation point.
In principle, some improvement could be made to
maximise iron recovery, but it should be considered that
the fast process with intensive oxygen blowing makes it
EAF campaign No.
Total heats
Hot repair (kg/tls)
Cold repair (kg/tls)
67
660
1.04
0.47
1.00
0.43
0.30
3.24
Gunning
Fettling
Slag door
Brick
Ramming
Total refractory
consumption (kg/tls)
68
617
1.01
0.52
1.11
0.45
0.26
3.36
69
722
1.13
0.69
0.21
0.50
0.28
2.81
70
601
1.19
1.00
0.37
0.54
0.33
3.44
r Table 6 Refractory consumption
MgO source
DRI
Dololime
Refractory
kg/tls
3.4
5.4
3.1
%
29
45
26
r Table 7 Estimated origin of MgO in slag
Location
Settling chamber
Cyclone
Bag ﬁlter
Total
April
2.7
2.9
4.9
10.5
May
3.4
3.0
5.4
11.8
June
3.3
3.3
4.7
11.2
July
3.8
3.9
6.7
14.3
r Table 8 Dust generation in 2014, kg/t
r Fig 8 Specific productivity in Danieli-supplied EAFs
more difﬁcult to obtain equilibrium conditions inside the
furnace. Since slag chemistry is not far from the MgO
saturation curve, the driving force for MgO-based brick
dissolution into the slag is somewhat reduced. The relevant
results of refractory consumption and bottom shell life are
reported in Table 6 for some consecutive campaigns in
2014.
Considering that slag generated is around 165kg/t with
7.2% MgO, the total quantity of MgO in slag is 11.9kg/t
with the MgO sources as shown in Table 7.
The result is quite consistent with the total amount of
a
MILLENNIUM STEEL 2015
SLAG PRACTICE AND REFRACTORY LIFE
49
STEELMAKING AND CASTING
r Fig 9 Isothermal slag solubility diagram
r Fig 10 Refractory scan at the end of campaign
MILLENNIUM STEEL 2015
refractory material employed for hot and cold repairs.
Figure 10 is a refractory scan at the end of campaign
68 (617 heats). Apart from the slag door area, which is
particularly subject to erosion due to continuous slag
ﬂow, the refractory wear is quite uniform in all zones,
residual wall thickness being more than 250mm.
Even if the refractory consumption achieved can be
considered as a benchmark for 100% DRI use, there is
some margin of improvement if we consider that slag is
not saturated in MgO. It also has to be considered that,
in view of overall process optimisation, increasing the
amount of slag would have a negative effect material
yield, and higher dololime addition would result in higher
energy, consumption mainly because of the quality of
material (ignition losses).
The iron content in the slag represents the main factor
affecting material yield; for instance, dust losses are very
low, as shown in Table 8.
50
2014. The target was to increase nominal plant productivity
from the original design value of 196tls/h to 237tls/h by
a combination of:
` Revamping of DRP and oxygen plants to provide the
additional raw materials.
` Increasing hot DRI max feeding capacity to 6.5t/min
` Reducing the tap to tap time from 46 to 38 minutes
` Reducing power-off time from 9 to 6 minutes
` Engineering the EAF slag to improve foaming
consistency and increase the life of shell refractory,
monitored with a 3D laser scan
` Increasing oxygen injection to sustain the higher
DRI feed rate and also to decrease electrical energy
consumption by higher chemical energy input
` Use of a gunning robot for the detection and repair of
lining wear.
Following rapid revamping and rapid commissioning,
all key performance indicators have been exceeded, for
example, average power 111MW, (97% of maximum
power), a new productivity record of 40 heats/
day (247tls/h), and electric energy consumption of
378kWh/t, with 34Nm3/tls oxygen.
The minimisation of refractory consumption in a DRIbased process also depends on the strategy adopted to
control furnace lining and to perform the necessary repairs
when and where needed. In this regard, the utilisation of
the gunning robot signiﬁcantly improved the detection of
the areas subject to the erosion, allowing prompt repair
and extending the life of refractory lining. A major role is
then played by the process stability and repeatability, with
extremely reduced power-off and very short melting time
during which the arc is always well covered.
FUTURE
Further actions are planned, including on-line slag
composition monitoring to help maximise EAF yield,
improve efﬁciency of operations during power-off,
including utilisation of automatic electrode jointer,
electrode equalisation platform and EBT automatic sand
feeding. Emirates Steel is conﬁdent that new performance
records will be achieved in 2015. MS
REFERENCES
[1] D Patrizio and P Razza, ‘Operating results with hot
DRI charge at ESI (Emirates Steel Industries)’, in Steel &
Metallurgy, September 2010.
CONCLUSIONS
D Patrizio and A Pesamosca are with Danieli & C.
Ofﬁcine Meccaniche, Buttrio, Italy.
P Razza is with Emirates Steel Abu Dhabi, UAE.
At Emirates Steel’s integrated EAF plant number 2, a
capacity enhancement was completed at the beginning of
CONTACT: [email protected]