EFSOP Holistic Optimization System: how to reduce transformer costs and environmental
impact enhancing safety in EAF melting process.
Davide Masoero, Paolo Clerici - Tenova SpA, Italy
Joe Maiolo - Tenova Goodfellow, Canada
EAF steelmakers today face many challenges in a competitive and rapidly changing global market. For the melting
operation, steelmakers are demanding improved process optimization based on a holistic approach. Factors to be considered
are cost, total energy (electrical plus chemical), productivity, yield, environmental, etc. This paper will outline new
developments at Tenova Goodfellow Inc. (TGI) for a dynamic process control and optimization system for the EAF based
on a holistic approach and the results obtained at Ferriere Nord steel plant in Italy.
INTRODUCTION
Until the 1990’s, electricity was the main source of energy in the melting of steel using electric arc furnaces (EAF’s).
During the last decade, many steelmakers have begun to realize the advantages of supplementing electrical energy in the
EAF with energy from a variety of sources. From our extensive knowledge of the steelmaking and EAF fume control
processes, it became apparent that the ability to measure the off-gas chemistry from an EAF on a continuous basis would
have significant environmental and energy benefits. Although there were many attempts by different corporations to
develop an extractive sampling system during the 1980’s and 1990’s, none of these developments were successful. The
changing environmental priorities and energy issues for EAF steelmakers became the basis for TGI to start a Scientific
Research and Experimental Program to develop an innovative sampling and combustion optimization program. In 2001, the
American Iron and Steel Institute’s (AISI), Steel Industry Technology Roadmap stated that “The successful EAF operations
of the future will be based on real-time measurements of off-gas chemistry to control both the EAF Steelmaking process and
the EAF fume control system”.
The challenge was to develop a robust and reliable sampling system in order to provide continuous measurements of off-gas
composition, which would be used for process control. TGI has developed a proprietary technology called Goodfellow
EFSOP™. It is an off-gas based process control system which measures off-gas from the EAF on a continuous basis and
uses the output in conjunction with a computer model to optimize furnace operations, reduce overall conversion costs and
provide environmental benefits.
DESCRIPTION OF THE EFSOP® SYSTEM AND CLOSED LOOP CONTROL (CLC)
The EFSOP® system measures and analyzes the off gases (CO, CO2, H2, and O2) at the 4th hole in real time for closed loop
control (CLC) process optimization of the EAF. It is a process tool and automatic control system that assists operators and
production personnel to better understand the EAF operation and to reduce overall conversion costs. Figure 1 illustrates the
three main components to the EFSOP® system and how they are integrated into the control of the furnace. The main
components in the EFSOP® system are:
1. Patented EFSOP® probe
2. EFSOP® HMI and SCADA computer
3. EFSOP® Gas Analyzer
Figure 1. Schematic of the EFSOP® system components
The patented water cooled sample probe continuously extracts sample gases from the 4th hole of the furnace as illustrated
above. The water cooled probe, as illustrated below in figure 2, has a purging system designed to purge both the probe and
the filter with pressurized nitrogen. The purging cycle, which occurs when charging, can be customized in terms of the
duration of the probe purge and filter purge as well as the number of cycles. This helps to ensure the probe is cleaned and is
able to sample the furnace gas as quickly as possible after charging. The heated sample line transports the furnace off gas to
the EFSOP® analyzer where the sample is filtered to remove dust and moisture before being analyzed for concentrations of
CO2, CO, O2 and H2.
Figure 2. Installation schematic and components of the EFSOP® probe
The EFSOP® gas analyzer is equipped with a PLC that controls the internal operation the analyzer and provides local
operating information at a panel view interface. The system operational information and off-gas measurements from the
PLC are also provided to the plant to be used for future troubleshooting or off-line analysis. The operating and off-gas data
is passed to the EFSOP® Human- Machine Interface (HMI) and SCADA computer via Ethernet, where it is logged for
future reference. The EFSOP® SCADA system is a software that displays all the analyzer and plant data in real time, logs
data and sends all the new process setpoints back to the plant PLC.
As mentioned, the EFSOP® computer is where all the control logic for CLC is programmed. Based on off gas chemistry
data, the EFSOP® computer sends new burner setpoints back to the PLC. The CLC works around 3 user inputs in addition to
the burner setpoints. They are: 1. Maximum Post Combustion (Max PC) setpoint, 2. Minimum Post Combustion Setpoint
(Min PC) and 3.Default Timer.
Figure 3. Description of EFSOP® closed loop control logic
In addition to the implementation of closed-loop-control of the chemical package, algorithms can be implemented to operate
the 4th hole damper control, which further helped improve the furnace efficiency and reduce operating costs. The control of
the 4th-hole damper in response to off-gas composition as determined with EFSOP is based on the calculated percentage of
nitrogen in the off-gas. Nitrogen is determined as the balance concentration in the off-gas (N2% = 100% - O2% - CO% CO2% - H2%). Nitrogen does not participle in the combustion reaction and can lead to the generation of NOx if passed
under the arc of the electrode. Also, the continuous drafting of air through the furnace robs the furnace of heat and slows the
melting process.
The dynamic control helps increasing post combustion in the furnace; thereby improving the efficiency of heating and scrap
melting, decreases overall conversion costs; and reduces the heat load on the fume system.
Water detection
An additional features of the EFSOP ® system is capability to determine abnormal water quantity inside the furnace through
EAF off-gas measurements: the Water Detection Technology. The methodology first characterises the normal level of water
during EAF operations arising from electrode water spray, moisture contained in the scrap and as a by-product from
combustion reactions. This normal safe level is compared to the actual level of water encountered during the heat to trigger
an alert condition. Abnormal water events in the EAF can be created by water panel leaks, seasonal changes resulting in
heavy rain or snow contained in the scrap charge and changes in scrap that contain higher than normal levels of oils or
organic material (turnings, tyre wire, etc). The benefits for detecting abnormal water can minimise the risk of furnace and
fume system explosions that can lead to equipment damage, injury and possible loss of life. The water detection technology
employs a statistical method and so there exists a trade-off between the confidence level of abnormal water detection and
false alarms. For instance, if the confidence limits for water-detection are set to 100%, the system will alert at all probable
water events but with an unacceptable number of false alarms. At a lower confidence limit, the number of false alarms
decreases but at the risk of missing probably water events. Tuning requires that the confidence limits are set such that the
maximum number of water events are indicated at an acceptable level of false alarms. The technology uses the
concentration of hydrogen and the ratio of hydrogen to carbon monoxide measured in the off-gas as an indication of the
level water in the furnace. Water participates in oxidation reactions in the EAF, such as the conversion of carbon monoxide
to carbon dioxide and that of iron to iron oxide. These oxidation reactions produce hydrogen resulting in an increase in
hydrogen concentration. The oxidation of carbon monoxide by water is indicated by an increase in the ratio of hydrogen to
carbon monoxide. The ratio of hydrogen to carbon monoxide will vary throughout the melting and refining periods of any
one heat and from one heat to another. The pattern of this variability is similar over a given time period of heats using the
same burner practice and scrap mix. Using statistical off-gas data of historic heats, a general fingerprint of the H2 and
H2/CO ratio is made for each burner practice broken down by charge and refining periods. The fingerprint profiles of H2
concentration and H2/CO ratio determined at Valsabbia are plotted on an energy consumption basis (kWh/charge,
MWh/charge tonne, melting % etc), as shown in Fig 1. The practice is characterised by segmenting the H2 and H2/CO ratio
into defined timing ‘bins’ (kWh/charge, MWh/charge tonne, etc).
Fig 2 provides an example of alert threshold bins for detecting abnormal levels of hydrogen. More information and details
on fingerprinting of the water detection alerting metrics can be found in technical paper 5. The alert thresholds are generated
based on the statistics from the fingerprint of historic heats. A dynamic model based on a moving window of historic heats
continuously updates the alert thresholds on a heat by heat basis to account for changes in the process, scrap mix and
seasonal variations. In addition, the water detection technology provides tiered alerting levels to indicate the probability of
an actual abnormal water event. The tiered alerting provides three levels of alerts (low, medium, high) based on the duration
of the heat or charge in an alert condition (cumulative alerting of both H2 and H2/CO metrics).
Fig 1 Example of H2/CO fingerprint for single charge
Fig 2 Example of H2 alert threshold bins for single charge
OPTIMIZATION AND RESULTS
Tenova Goodfellow’s EFSOP ® system was commissioned at Ferriere Nord S.p.A., (UD) Italy in January 2009 to further
optimize the already efficient 125 ton EAF. Ferriere Nord produces and commercializes different types of steel and steel
products mainly used in the construction of buildings and infrastructures in the mechanical sector. All the steel produced is
of HD (high ductility) and designed for use in concrete steel structures installed in seismic areas. Table I provides
equipment details of the 125 ton EAF furnace.
Table I. Electric arc furnace details at Ferriere Nord
Knowledge of the furnace off-gasses is valuable to understand the operation and determine opportunities for improvement. The
EFSOP® system was first used to collect off-gas measurements of numerous heats in order to characterize the operation and to
determine areas for improvements. Figure 4 shows typical heat chemistry at Ferriere Nord with areas targeted during the
optimization of the furnace operation. It is important to note that the plant operated charges with and without pig iron. The analysis
and optimization strategies and savings were achieved for both practices.
Area 1 shows high CO and H2 off-gas levels in the melting phase of each charge that were targeted with CLC of the burners in
order to increase post combustion efficiency. CLC was initially implemented on two (2) burners, which were chosen based on
their positions in the furnace, height, and considerations from the plant. The key concerns were excess refractory wear and high
water cooled panel temperatures in specified areas of the furnace; the so called hot-spots. The two burners were chosen because
their height in the furnace relative to other burners was ideal for post combustion and did not pose concerns for the safe operation
of the furnace.
CLC of the two burners was implemented with setpoints that decreased the amount of methane and increased the amount of
oxygen in certain steps of heats where higher chemical energy was measured in the off-gas. This allowed for more efficient
combustion of CO and H2, which resulted in a net increase of chemical energy within the furnace even with less methane usage.
The higher net chemical energy obtained from increased post combustion efficiency helped to reduce electrical energy, carbon
consumption and power on time (POT). This methodology was then applied to the supersonic oxygen lances that were also used
during melting as post combustion burners. Overall the methane consumptions were decreased by 16% for the plant’s pig iron
practice and 13.6% for the practice without pig iron.
Figure 4. Typical heat chemistry at Ferriere Nord before EFSOP ® optimization
A common element in Area 2 was the increase of O2 in the off-gas measurements as the liquid level in the furnace increases near
the end of the melting phase and at the start of lancing. By applying CLC setpoints to one of the supersonic lances, the transition
between melting and the lancing phase was much smoother with less wasted injected O 2. In this manner, heats with a higher
chemical energy would use the lance oxygen as in the original profile. However, for heats with slightly less carbon available, less
lance oxygen would be used. This small change contributed to the overall oxygen savings achieved. The reduced lance oxygen
also allowed more carbon to remain in the bath until refining and thus helped to reduce carbon consumption.
Finally, the third main area targeted was during refining (Area 3), which typically showed an increase of oxygen in the off-gas at
the end of refining indicating oxidizing conditions. By reviewing numerous heats along with their respective slag analysis results,
the high oxygen at the end of refining was linked to high FeO values. To reduce this, CLC was implemented to one of the
supersonic lances in the last step of the refining phase where minimum and maximum setpoints were used either to continue or to
disable the use of the one lance. For heats with high CO or reducing conditions in the refining phase, the operation of the lance
would be maintained for decarburization as needed. Whereas heats with high O2 indicating oxidized conditions would discontinue
the use of the one lance to reduce oxidation of the steel. This change contributed to reducing oxygen consumption but more
importantly aided the overall improvement of the yield. The reduced lancing in refining for oxidized heats also helped to reduce
injected carbon consumption while maintaining a good foamy slag.
Another interesting effect of the above changes in subsequent months was an improvement in the overall control of FeO. The
measured FeO values fell within a tighter distribution with fewer extreme outlier points. The overall improvements to the chemical
profile and being able to correlate the heat chemistry to slag analysis data allowed the operators to take the slag samples at the
most opportune moment to prevent over-oxidizing and superheating the bath.
Figure 5 shows typical heat chemistry following the implementation of the optimization strategies. Note the reduced levels of CO
and H2 during melting, elimination of O2 during the transition phase between melting and refining and higher generation of CO
during refining indicating better decarburization from lancing.
Figure 5. Typical heat chemistry (heat 7194) at Ferriere Nord after EFSOP® optimization
One final consideration is the use of the EFSOP® system as a tool to understand the furnace operation. Throughout the
optimization phase, changes in the process such as scrap or equipment issue affected the operation of the furnace. One such
example was a period where some heats had higher than normal fume system temperatures; something that was not common but
could clearly be seen in the chemistry by the higher peaks in CO. The cause was quickly determined to be the malfunction of a
carbon injector. At startup, the flow of carbon would be extremely high for a short amount of time but would quickly return to the
set value. The large amount of carbon would burn causing peaks of CO and high fume system temperatures. By having the off gas
chemistry, the exact cause of the problem was quickly determined.
The overall savings achieved with the EFSOP® system for both practices are shown in Table II. Significant savings were achieved
in all performance parameters including electrical, methane, oxygen, charge carbon, injected carbon, yield and productivity.
Table II. Overall savings achieved at Ferriere Nord with the EFSOP ® system
ENVIRONMENTAL BENEFITS
With regards to environmental concerns, Tenova is nowadays focusing their technologies in order to meet customer demand.
EFSOP®, thanks to the melting efficiency increasing, helps steelmakers in facing more and more restrictive laws.
In particular, emission of dioxins is a growing concern in scrap-based Electric Arc Furnace (EAF) steelmaking. For a given
the scrap charge, same amount of precursors to PCCDs/Fs (dioxins and furans) will be released regardless the EAF
technology being used. The amount of PCCDs/Fs generated and to be treated in the downstream off-gas cleaning system
depends on the process performed. Among all EAF technologies available today, Consteel® offers the most favorable
conditions for the minimization of these emissions, thus allowing the compliance with the increasingly restrictive
environmental regulations at the lowest possible cost.
At present times, Consteel® is the only proven technology that achieves a truly continuous scrap feeding to the EAF. The
favorable conditions for PCCDs/Fs abatement offered by Consteel® can be appreciated by the comparison of the data
reported in Table 1, which are referred to four plants operating in Europe: two Consteel® and two conventional bucketcharged EAFs, with similar scrap charges.
The next generation of Consteel® furnaces will further improve the benefits of this technology10.
Charge system
Quenching Tower
PAC Injection
Plant 1
Consteel®
YES
NO
0
0
0.15
Plant 2
Consteel®
YES
YES
25
25
0.005
Plant 3
Bucket-charged
YES
NO
0
0
0.4
YES/NO
YES/NO
mg/m3
kg/h
PCDD/F Emissions
g Teq/ Nm3
* Uses a forced heat exchanger
Table 1 - PCDD/F emissions data for some European plants.
Plant 4
Bucket-charged
YES*
YES
50
35
0.09
SUMMARY
A holistic approach to EAF Steelmaking represents a significant opportunity to improve steel quality, productivity, lower
conversion costs, improve environmental performance, and improved safety. In closing, I am reminded of the philosophy of
Sir William Thompson, Lord Kelvin (1824-1907): "When you can measure what you are speaking about, and express it in
numbers, you know something about it; but when you cannot measure it, your knowledge of it is meagre and
unsatisfactory."
The installation and implementation of the Tenova Goodfellow EFSOP ® system at Ferriere Nord was a great success and a
great addition to the steel plant’s technology. The integration of the EFSOP ® system with the current level 2 was
straightforward and allowed the plant to build upon their current technology. The reliability of the EFSOP ® system has been
high and easy to maintain. More importantly, it has helped increase the efficiency of the furnace and has proven to be a
valuable tool for analyzing furnace operation and changes. EFSOP® has achieved significant savings in methane, electrical,
oxygen, charged and injected carbon, yield and productivity. As can be seen in Table II above, over a 9 month period, the
overall conversion costs have been decreased by approximately 3.8% in the practice using pig iron and 4.4% for the
standard practice without pig iron.
REFERENCES
1. M.I. Khan, E.J. Evenson, “Results of Goodfellow EFSOP® at Birmingham Steel Corp., Seattle, WA, USA,” ISS Tech
2003, Iron & Steel Society, Indianapolis, IN, April 2003.
2. J. Maiolo, E.J. Evenson, O.I. Negru, “Goodfellow EFSOP® Successes at TAMSA, Veracruz”, AISTech 2004 Conference,
Nashville, TN, September 2004
3. J. Kelleher, M.I. Khan, “Yield and Productivity Savings Using Goodfellow EFSOP® at MacSteel Arkansas”, AISTech
2006 Conference, Cleveland, OH, May 2006
4. D. Vensel, M.I. Khan, “EAF Performance Improvement at Nucor Steel Auburn using Goodfellow EFSOP®”, AISTech
2006Conference, Cleveland, OH, May 2006
5. K.Nikkanen, M.I.Khan, J. Gavina, “Furnace Water Leak Detection and Reduced Conversion Costs Efforts at Aceria
Compacta de Bizkaia, Spain using the Goodfellow EFSOP® System”, AISTech 2007 Conference, May 2007
6. H.D. Goodfellow "EAF Fume Control Technology - A Historical Perspective and Future Trends" Gerrard Heffernan
Symposium, Toronto, On, Aug 26-29, 2001
7. H.D. Goodfellow "Process Optimization of EAF Steelmaking Using Goodfellow EFSOP™ Technology" SEAISI
Seminar, Gyeongiu, Korea, November 2003
8. J.G. Bekker, I.K. Craig and P.C. Pistorius, "Model Predictive of an electric arc furnace off-gas process" Control
Engineering Practice 8, September 10, 1999
9 N Boin, M I Khan, M Missio, ‘Optimization results at Ferriere Nord using EFSOP Technology’, AISTech 2010
Conference, May 2010
10 C. Giavani, “Dioxins Emissions in Electric Arc Furnace Steelmaking and the Advantages of Consteel ® Technology,
2011