Steel production - energy efficiency working group
Final report, January 2014
B. de Lamberterie, chair and rapporteur of the ESTEP/EUROFER WG Energy Efficiency
Executive summary
A working group was convened under the auspices of both ESTEP and EUROFER to
investigate the potential still offered by energy efficiency in the Steel sector. It
worked from 2010 until 2013, with 13 participants, under the chairmanship of B. de
Lamberterie, the Secretary General of ESTEP at the time. The rationale was to provide the ESTEP community with precise information on energy consumption in the
steel sector in Europe, accessible levels of improvement and the connection between
energy consumption and CO2 emissions, in order to facilitate the community's interactions with various EU stakeholders related to research and foresight (RFCS, Horizon 2020, SET Plan, ESTEP's working groups, others).
The WG developed a template for collecting energy consumption data relative to
both integrated steel mills (IM) and EAF/scrap based mini-mills (MM) - limited to
the "hot mill"-, in coherence with previous and parallel efforts, for example an ongoing worldsteel survey. Information was collected on a confidential basis from 6
integrated steel mills and 4 EAF steel mills and compared to a reference benchmark
based on the first quartile of the best European mills proposed initially in the group.
This reference was 20 GJ/t of hot rolled product for the IM and 9.5 GJ for the MM.
The level of accessible improvement was defined as the gap between the collected
values and the benchmark. The analysis focused on overall mill data and workshop/
"step of production" data.
On the average, the potential of improvement in energy efficiency is 8%. Some individual plant may have less potential. The group estimated that using all EU steel
mills for the study might raise this figure to 10-12%.
A long appendix proposes a semi-quantitative analysis of potential areas of improvement at each process step, thus pointing out to R&D directions for the coming
years. They include recommendations on energy savings, energy recovery, use of alternative energy sources, incremental or radical process changes and diversifying
input of raw materials. The connection between energy and environmental footprint was also stressed.
1
Steel production - energy efficiency working group
Final report, January 2014
B. de Lamberterie, chair and rapporteur of the ESTEP/EUROFER WG Energy Efficiency
1 Context
The steel sector belongs to the family of Energy Intensive Industries (EII), a concept used by various governments and regional organizations such as the European Union, the US and Japan. In
Europe climate/energy challenges are of utmost importance and one of the headlines for the
2020 Strategy [1] is the “20/20/20” climate/energy target:
- Reduce GHG emissions by at least 20% compared to 1990 levels (The EU is also offering to
increase its emissions reduction to 30% by 2020 if other major economies in the developed
and developing world’s commit to undertake their fair share of a global emissions reduction
effort.);
- Increase the share of Renewable Energy Sources (RES) in our final energy consumption to
20%;
- 20% increase in energy efficiency.
The iron and steel sector plays a key role in Europe’s energy consumption, both through the use
of its products and through its steelmaking processes where our industry is one of the most energy intensive users as ‘process industries’’.
In the energy area, the European Commission has launched in 2008 the SET-Plan, the Strategic
Energy Technology Plan led by the Joint Research Centre (JRC). This plan aims at developing energy technologies, research & innovation in order to improve energy efficiency and renewable
energies. The SET-Plan covers industries producing energy but also the main users of energy
such as the Energy Intensive Industries. ESTEP was invited in 2010 to be part of the SET-Plan as
a process industry [2].
Mid 2010, EUROFER and ESTEP proposed to launch a dedicated process - energy working group
for the European steel industry in order to investigate the potential for further energy efficiency
to produce steel. This temporary group has worked over 3 years - from mid 2010 up to mid
2013- and this report summarizes the main results of the group.
3
2 The missions and activities of the WG – Energy efficiency in steel production
Two main steel production routes will be considered: the BF/BOF route and the scraps/EAF
route. The energy consumption will cover all the types of energy necessary to produce steel: reducing agents, heating fuels, steam and electricity.
The results of this WG should enable ESTEP to:
- Get actively involved in energy related calls within the research European programmes
(RFCS and Horizon 2020)
- Facilitate the steel sector discussions in R&D priorities
- Provide consistent energy indicators to stakeholders (e.g the SET plan, WG1 and WG4 of
ESTEP, climate change and energy committees of EUROFER)
- Demonstrate to stakeholders the interactions between carbon energy (reducing agents and
fuels) and CO2
2.1
Missions
To propose a simple and effcient methodology for quantifying energy use and energy recovery
and if necessary energy data collection. Of course the group would reuse existing methodologies
and results such as those from World Steel Association (Energy use in the steel industry), from
the BREFs (upstream and downstream processes for the steel industry), and from the CO2 emissions ETS scheme. The energies include coal, coke, gas (natural gas and waste gas), fuel oils,
steam and electricity. The study covers all the steps of production
o Coke making
o Sintering
o Ironmaking
o BOF steel making
o EAF steel making
o Secondary metallurgy and continuous casting
o Hot strip mill
o Plate mill
o Bar and Rod mill
o Section mills
o Global energy at plant level
The cold plant and the power plant are out of the scope as well as the steelmaking for stainless steel.
- To analyse the existing results on a representative year of production, i.e. 2010 for the European steel companies, or at least a significant core part.
- To identify the existing and new emerging energy savings technologies for each step of production and for the global optimization of energy management within the plants. The pro4
-
posals for energy savings will come from the best existing practices in Europe, and from an
international benchmarking including America and Asia.
To identify new ideas for Research & Innovation in the field of energy savings for steel production, with the possibility to get European fundings (RFCS, Horizon 2020)
2.2
Participants
The participants were energy experts from European steel companies and steel research centers
(one expert per company or research center).
From European steel companies:
- ArcelorMittal: Bernard Petetin
- Tata Steel: Pepijn Pronk, then Hans Kiesewetter
- TKS: Jurgen Hoffmann, then Hans-Peter Domels
- Tenaris: Alexander Corra
- US Steel Kosice: Ladislas Horvath, then Jaroslav Merc
- Voestalpine : Wolfgang Sparlinek, then Karl Schaumlechner
From steel research centers and associations:
- CRM: Bernard Vanderheyden
- CSM: Pietro Tolve, then Enrico Malfa
- Swerea Mefos: J. Olov Wikstrom and Lawrence Hooey
- Steel institute VDEh: Jean-Theo Ghenda
- BFI: Ralph Sievering and Wolfgang Bender
- Eurofer: David Valenti. Yann de Lassat, independent consultant and expert in energy was also
mandated by Eurofer in this group.
- ESTEP: Bertrand de Lamberterie, chairman of this WG EE and Secretary-General of ESTEP
until June 2013.
2.3
Governance
The working group reported to ESTEP’s Support Group on a regular basis (3 times per year).
This energy working group received the full support from ESTEP’s WG1 (production) and WG4
(environment) whilst EUROFER’s Climate Change, Energy and Research committees were regularly briefed on the state-of-affairs.
2.4
Confidentiality
During the production period of the working group, the energy data and other information were
shared internally only within the members of the WG, remaining confidential externally. A confidentiality agreement was signed by all the members for that purpose. In addition, group members worked in full compliance of competition laws.
This final report doesn’t detail the data collection and the results per plant and companies. Further external communication would need the agreement from EUROFER and ESTEP ad hoc
committees.
5
3 Methodology for energy data collection
Following primary discussions in autumn 2010, it was decided to elaborate a common set of
templates for the energy data collection, taking into account the previous works carried out by
the Worldsteel energy benchmarking study published in 1998 [3] (IISI energy benchmarking)
and the ESEC (European Steel Energy Committee) study in 2001. Yann de Lassat, member of our
group was also strongly involved in the development of the data templates produced by the
ESEC group in 2001. It is also important to mention that over the past ten years, ArcelorMittal,
Tatasteel and voestalpine followed the ESEC data templates for the annual energy data collection
of their plants.
The WG EE worked for 2 years, 2011 and 2012 to improve the energy data templates. This specific study was led by Hans Kiesewetter from Tatasteel and Yann de Lassat. In 2011, Worldsteel
decided to launch a new energy benchmark, worldwide. In order to avoid double work, it was
decided to use the same methodology for these two parallel approaches and especially the data
templates developed by our WG. Eurofer and ESTEP gave their agreement to that.
Main features of the energy data templates
-
-
-
The structure remains similar to templates developed for the ESEC study in 2001: based on a
set of undisputable physical data and the carbon balance for integrated plants (BF/BOF).
Significant improvements for the definition of data, the clarification of boundary conditions.
The contents of physical data were deeply investigated.
Use of standard values for energy conversion factor, whatever the actual situation of each
plant.
Introduction of automatic data check (carbon balance, yield rates, energy balance)
The steps of production are: coke making, sintering, blast furnace iron making, steelmaking
(gathering liquid steel production, secondary metallurgy and casting), hot rolling.
For each step of production the direct energy (the process energy for the step of production) and the total energy (cumulated energy, including the upstream1 part) are calculated.
Clear separation was done at each process between upstream energy and process energy.
The total energy values include the embedded upstream energy (pellets, sinter, coke etc.) using a set of reference values. It is the only way to compare fairly the energy results between
the different plants.
In the study, the reference values come from the first quartile data of the European
plants. The data gathered by Yann de Lassat were approved by the group. The tables of reference values are given in annex 1, along with an analysis of what this "1st quartile steel mill"
amounts to in terms of energy consumption.
Upstream has the standard meaning in describing a steel mill: it is the ironmaking and steelmaking parts of the
mill, with all ancillary plants like coke and sinter plants. It does not carry the meaning it has of LCA, which designates burden created before the entry gate of the steel mill, like mines, transport of raw materials, etc.
1
6
-
-
Some corrections values have been added for a better comparison: slag ratio at Blast Furnace,
scrap ratio at BOF and the “scrap” burden at Electrical Arc Furnace (EAF) taking into account
the possible DRI and mill scale charging rate.
Documentation has been added for clarification of definitions and of the way of filling the
templates.
4 Results of energy data collection
The energy templates (see the previous chapter) have been filled by members of the WG coming
from the steel companies.
For the integrated route BF-BOF:
- One plant from ArcelorMittal
- Two plants from Tatasteel
- One plant from TKS
- One plant from US Steel
- One plant from voestalpine.
For the EAF route:
- One plant from ArcelorMittal
- One plant from Tatasteel
- Two plants from Tenaris.
At this stage of communications of the results and for confidentiality reasons, the names of the
plants are not explicitly mentioned and most of the results are presented in percentage compared to the reference values.
BF/BOF route
The overall reference for total energy consumption, coming from the first quartile of European
plants and considering the methodology presented in the previous chapter is 20GJ/ton of hot
rolled product. Two plants are very close to the reference values.
The analysis of the results is composed of:
- Results per plant, with a gap analysis per step of production in order to understand the
bridge from the actual plant result and the reference (baseline in the figures) and a similar
gap analysis at plant level
- Comparison of process energy for each step of production between the plants
- Identification of potential of energy savings based on these types of gap analysis
Examples of gap analysis per step of production for all the sites, integrated plants
7
Fig1: Gap analysis Coke making
Fig2: Gap analysis. Sinter plant
8
Fig3: Gap analysis. Blast Furnaces
Fig 4: Gap analysis. Steelmaking BOF
9
Fig 5: Gap analysis. Hot strip mill
Fig 6: Gap analysis for the whole integrated plants
10
EAF route
The overall reference for energy consumption is around 9,5GJ/t of hot rolled product. One plant
is better than the reference. Compared to the integrated route, similar analysis is presented.
Examples of gap analysis per step of production for the total of the sites, EAF plants
Fig 7: Gap analysis. EAF (all sites)
Fig 8: Gap analysis. Long products mills
11
The last figure (fig 9) shows the potential of energy savings only based on the comparison of the
performances of each step of production for each plant. There is few potential of progress for
the plants close to the reference: BF/BOF 4, BF/BOF 6 and EAF1. These plants, close to the
benchmark are already applying most of the relevant existing technologies and measures for energy efficiency.
MJ/t crude steel
7 000
Coke making
Sintering
Iron Making
BOF Steel Making
EAF Steel Making
Hot strip mill
TSR
Plate mill
Long products
Flares
Power plants
ASU
6 000
5 000
4 000
3 000
2 000
1 000
0
BF/BOF 1
BF/BOF 2
BF/BOF 3
BF/BOF 4
BF/BOF 5
BF/BOF 6
EAF 1
EAF 2
EAF 3
EAF 4
Total
Fig 9: Synthesis of the potential for energy savings for the plants included in this study.
For the other plants included in the study there are significant potentials of progress. On average
for the 10 plants of the study the potential represents around 8% of energy savings. It would be
of course interesting to extend this benchmarking and analysis to all the European plants. As a
similar methodology is used for the new Worldsteel energy benchmark, it would be also interesting to compare the present situation in Europe with a worldwide benchmark. Then the potential
would probably be extended to 10-12%.
It is important to notice that the templates are fully compatible with the draft CEN CO2 performance assessment standard for steel, currently under development. If further actions have to be
carried out for energy efficiency, our WG EE strongly recommends using the present methodology. However, it is important recognizing that energy savings do not translate automatically into
CO2 savings. This is particularly true for BOF steel where the CO2 footprint will depend largely on
the efficient recovery of waste gases (coke oven gas, blast furnace gas and basic oxygen furnace
gas). As regards EAF steel, CO2 performance depends on the CO2 intensity of electricity (either
self-generated or purchased from the grid). Energy savings have therefore a different impact if
they are related to power or fossil fuels consumption.
12
5
Recommendations for further actions for energy savings.
Another mission of this Working Group was to identify the existing and emerging best practices
for energy efficiency as well as proposing new areas for research & development. The work has
been split between the different members of the Group. The purpose was not to duplicate existing studies such as the BREFs [4, 5] or the JRC report on energy efficiency [6]. It is not an exhaustive work and the recommendations include:
- some relevant energy efficient technologies and measures which are applicable and feasible.
- new areas for R&D to be developed within the ad-hoc ESTEP working groups – WG1 and WG4,
and eligible for new EU projects using the existing instruments such as RFCS and Horizon 2020,
including the new PPP SPIRE [7].
The recommendations that follow in the annex 2 are related to:
- Sinter plant
- Blast furnaces
- Steelmaking BOF
- Steelmaking EAF
- Hot Rolling.
Note that the coking plant and the captive power plant are not in the list because of a lack of experts in these two areas.
These recommendations will complete other studies and recent reports from ESTEP [8,9] and
Eurofer [10], especially for the proposals on new areas for R&D in the coming years.
References
[1] European Commission. The EU 2020 Strategy, March 2010
[2] SET-Plan, Technology Map chapter on energy efficiency and CO2 emission reduction in the
Iron and Steel industry, Dec 2010
[3] IISI, International Iron & Steel Institute, Energy benchmark, 1998
[4] EC, JRC, BREF, BAT Reference document for Iron & Steel production, 2013
[5] EC, JRC, BREF, Reference document on the BATs in the ferrous metals processing, 2001
[6] EC, JRC, Prospective scenarios on energy efficiency and CO2 emissions in the EU Iron & Steel
industry, 2012
[7] SPIRE, Sustainable Process Industry through Resource and Energy efficiency, SPIRE
Roadmap, 2013 www.SPIRE2030.EU
[8] ESTEP, A short roadmap addressing the strategy of the steel industry in the fields of sustainability, energy, CO2 and environment. WG4, 2010
[9] ESTEP, Strategic Research agenda, 2nd edition, May 2013
[10]EUROFER, A steel roadmap for a low carbon Europe 2050, July 2013
13
Annex 1
Reference values from the 1st quartile of European plants
14
15
16
17
Comments and analysis on the Energy Efficiency and CO2-Emission of the 1st quartile
European Steel Mills2
This section is based on references values from the 1st quartile of European plants and these data are analyzed here. They have been consolidated in order to show the results in a comprehensive overview on the level of an integrated steel mill. Some additional assumptions were necessary for a calculation of the CO2-emission. These assumptions are listed below:
1.
All mass flows of the essential facilities and the upstream and auxiliary processes have been completely integrated into the
boundaries of the steel mill. The data were consolidated to
1 t of Rolled Steel (RS). This gives the following results for the mass flows of the raw materials,
fuels and intermediate products:
Consolidated mass flows
kg / t RS
341,9
Limestone BF
Coke bought
Anthracite+Graphite
PCI
35,1
154,9
Limestone Si
Limestone Lime
Total CaCO3
188,5
91,9
280,4
Technical Gas
HP Oxygen
LP Oxygen
m 3 / t RS
Light oil
Lime
Sinter
Lump ore
Pellets
99,8
51,5
1.245,9
118,7
160,4
Total ore
1.525,0
Hot metal
948,0
Scrap & alloys
Crude steel
Rolled steel
2.
kg / t RS
Coke prod.
134,8
1.033,5
1.000,0
Nitrogen
Argon
Comp. Air
66,1
32,4
74,5
0,8
101,2
Following the approach of the ISO
14404 some shops have had to be added as facilities of an integrated steel mill. For these
shops the energy input has been calculated as well.
Category 2:
Lime plant:
3.800 MJ/t lime, Natural gas, 40
kWh/t, total: 4.192 MJ/t lime
Pellet plant:
500 MJ/t pellet natural gas, 123
kWh/t pellet, total: 1.702 MJ/t pellet,
Oxygen plant and
Energy for the production of 1 m3
gas: HP O2: 7,0 MJ,
Technical gases
LP O2: 4,9 MJ, N2: 2,0 MJ, Compressed air: 1,1 MJ,
Power station (CHP):
Power is produced with an efficiency of 36,7 %, equivalent to
9,8 MJ/kWh as primary energy factor. Though the conversion
of process gases may have a lower efficiency this factor was used
as a standard. Furthermore it is assumed that the energy of all
remaining process gases and residues like tar and BF-dust
2
This section was authored by Dr.-Ing. Holger Rosemann of BFI, along with the figues and tables attached.
18
-
is completely converted to power. Steam-Boiler efficiency: 90 %,
additional steam is converted to power.
Byproduct-Flares:
2 % flare losses of the process gas
energy (COG,BFG, BOFG),
Category 3:
35 kg/t steam,
3.
Cold Rolling Mill:
500 MJ/t RS Natural Gas, 80 kWh/t,
use of 30 m3/t pressurized air, total: 1.438 MJ/t
For the calculation of the CO2-balance the following standard-CO2intensities and energy conversion factors have been used:
CO2-intensity of power generation: 0,576 kg CO2/kWh (Germany
-
2012)
This is the mix of different types of power stations incl. nuclear and renewable power. This
mix is relevant for the additionally external bought power (indirect CO2).
601/2012:
Fuel data
CO2 intensity
LHV
Fuels
CO gas
in t CO2 / TJ
44,4
in GJ / t
19,7
BF gas
260,0
BOF gas
182,0
9,2
56,1
35,9
Natural gas
3,2
98,0
31,1
Coke
107,0
30,1
Coke breeze
104,1
29,9
Anthracite
98,3
29,3
Light oil
80,0
42,0
Tar
90,0
37,7
107,0
107,0
93,2
kg CO2/kWh
13,7
Coal / PCI
BF dust & sludge
EAF coal
Coking coal
Power
Ext. Power
4.
CO2-intensity factors of fuels acc. to EU-Commission Regulation No.
0,576
31,5
32,2
(Ger 2012)
The reference data were completed in the following issues:
-
The BOF shop and the Hot Rolling Mill normally produce steam by
the use of waste heat.
Therefore the following assumptions were added to the data:
- BOF: generation of 60 kg of steam per t LS with an energy content of 215 MJ/t RS,
use of 20 m3/t RS pressurized air
- HRM: generation of 20 kg of steam per t RS with an energy content of 69 MJ/t RS.
Furthermore it is assumed that the remaining steam is completely produced by waste heat
of the power station and that no additional fuel has to be used for this energy flow.
19
-
The C-balance of the BF and BOF was checked in order to come to a
correct calculation of the CO2-emissions. In order to balance the C-load of the BF-gas and
BOF-gas to the input of carbon by fuels to these shops, a correction of the data of the BFgeneration to
4.952 MJ/t RS and the BOF-generation to 831 MJ/t RS is supposed.
calculation of the CO2-balance:
- Carbon-content of hot metal:
- Carbon-content of steel:
5.
The following additional data have been used for the
4,5 % C
0,15 % C
Key Performance Data
The flow sheet has been completed by key perfor-
mance data of the direct energy use.
HM: is the integration up to LS, but with reference to
1 t HM,
HM+RS+CHP: is the integration about all shops of the integrated plant incl. power plant.
-
The data are presented in the following pages.
20
21
22
Annex 2
Recommendations for energy savings
23
Annex 2
1- Sinter plant Energy Saving and Recovery Opportunities
by B. Vanderheyden, CRM Group, 7/10/2013
STAKES, STATE OF ART AND RECOMMENDATIONS FOR FUTURE R&D
Stakes towards overall iron- & steelmaking route
The total energy consumption (upstream and utilities included) of sinter plants (SP) is nowadays
~ 2.4 – 2.5 GJ/t bell sinter, which represents roughly one tenth of total energy consumption till
Hot Rolled Coil (HRC).
How to increase energy efficiency at the sinter plant
1) Energy savings: Modern sinter plants already operate close to their minimum energy requirements, when looking at the process itself (see background info in appendix for more
details). So, referred to the state-of-art, further process improvements can only bring relatively limited gains, for instance by improved process control tools (soft solutions), or by
implementing special devices like the ones supposed to increase vertical C segregation at
strand feeding (but effectiveness has to be checked case by case, in particular not obvious
when using ever finer ores).
It is nevertheless worth mentioning that some new more “real-time” monitoring tools can
help to compensate for the recent trend of more frequent process drifts (and related increasing gaps towards optimal working points) due to the higher variability of input materials  new on-line measurements like LIBS3, PGNAA4 or XRF5 recently implemented in
some plants for sinter mix basicity control is a first step in the good direction. Such sensor
developments are also needed more generally speaking in the frame of the circular economy (if primary raw materials are to be replaced more and more by secondary raw materials  link with related SPIRE6 topic?)
Laser Induced Breakdown Spectroscopy
Prompt Gamma Neutron Activation Analysis
5 X-Ray Fluorescence
6 Sustainable Process Industry through Resource and Energy Efficiency (European Public-Private Partnership)
3
4
24
The well-known favorable effect of (very) high bed heights on energy efficiency is more
and more challenging in the European context, as the bed permeability has to be ensured
(production capacity constraint) while using ever finer sinter feeds. Therefore, any efficient new technique able to counteract the impact of ore fineness on granulation and resulting bed permeability is welcome regarding as well productivity as energy stakes.
The development of original (staged or selective) sinter mix preparation techniques could
also provide new opportunities for efficient incorporation of any kind of (fine) fluxing
and/or energy-bearing materials (in particular internal or even external residues) into
the more traditional sinter mixture  cross-sectoral symbiosis (topic for RFCS7 and/or
SPIRE?).
Finally, variable speed sintering fans are perhaps also worth looking at, as they allow to
lower the specific electricity consumption while at the same time offering a way to make
SPs more flexible towards variable productivity targets. The pay-back period is nevertheless not always that short in the European context (to be assessed case by case depending
on local situation).
2) Energy recovery: from this viewpoint there is still a potential in Europe, because of the
significant waste heat flows inherent to the sintering process which are mostly not recovered : (i) energy in off-gas (sensible and latent heat /CO), (ii) sinter cake discharged hot
from the sinter strand (most of sensible heat transferred to cooling air, dispersed into the
atmosphere).
Hot air and/or waste gas recycling: the related techniques may be considered to recover
some of the waste energy “internally”, i.e. inside the sintering process itself (150-250
MJ/t), while at the same time reducing the net pollutant emissions, but such techniques
may also have some detrimental effects on productivity and quality depending on local
conditions (pros/cons to be assessed case by case). The optimal lay-out could widely differ depending on local situation (environmental constraints, space limitations, ores used,
sinter/pellets ratio in blast furnace (BF) burden, quality policy…)  there is a need for
optimization tools taking all these aspects into account.
Sinter heat recovery for “external” valorization may occur in steam boilers using (sufficiently) hot air from the sinter cooler (common practice a.o. in Japan, not so much in Europe); or hot water can be produced for heating buildings inside or outside the steel plant
(district heating like in Dunkerque…); in all these cases, energy is recovered without any
impact on the sintering process itself, but the optimal solution is not universal, it will a.o.
depend on local opportunities for industrial symbiosis  R&D need for (intra- & cross7
European Research Fund for Coal and Steel
25
sectoral) energy flows optimization tools (process integration, pinch analysis,…) (topic
for RFCS/SPIRE?).
The economic viability of heat recovery from a sinter cooler would be drastically increased if the same cooling capacity could be obtained with a smaller volume of hotter air
(higher exergy)  new cooling technology to be developed?
3) Alternative energy sources: generally speaking, there could also be some options to use
alternative fuels at the sinter plant, with possibly improved overall energy efficiency (to
be checked more in details) :
- modified ignition (+ post-ignition) hoods fuelled with any kind of alternative fuels
(various process gases, syngas, biogas, pulverised coal, any kind of fine energybearing residues…) (N.B. : overall energetic yield should be increased due to lower socalled “CO-losses”)
- Similarly, overall energetic yield should be higher with so-called (relatively long) postignition hoods, not equipped with burners (like already done industrially in the past),
but instead, fed with hot fumes from a “waste incinerator” or the like (industrial symbiosis) 8 (N.B. : among the side effects : (-) productivity drop; (+) much lower overall
pollutant emissions)
- Remark: similar ideas concerning alternative energy sources could apply to pelletisation (pellet firing) strands or kilns as well
- Alternative solid fuels can also be considered (biomass, wastes), but this was already
extensively studied within the frame of the recently ended RFCS project ACASOS9.
Overall energy savings are not to be expected (replacement ratios ~1).
4) Link with environmental constraints (important aspect in the European context) :
the energy consumption of end-of-pipe gas cleaning systems should not be neglected ; for
instance if de-NOx by SCR10 has to be applied, the related offgas reheating energy may
represent up to ¼ or even 1/3 of the total energy input ! Finding (cheap and) low T° catalysts for SCR would significantly help towards a much more energy-lean deNOx of sintering fumes.
***
This idea was patented in 2003 by CRM and evaluated based on modeling and some preliminary pot tests, in
particular one specific variant in combination with selective waste gas recycling, in view of VERY LOW CO2
SINTERING  overall heat consumption potentially reduced by 10%, solid fuel rate reduction potentially > 50%
9 Alternate carbon sources for sintering of iron ore (ACASOS), Final report published under n° EUR 25151 (2013)
10 Selective Catalytic Reduction
8
26
Annex 2
2- Blast Furnace Energy Saving and Recovery
PL Hooey, Swerea-Mefos
SUMMARY
Blast furnaces already operate close to their minimum energy requirements. Some gains in energy efficiency or direct energy recovery can be made through existing technologies including:
 Top Pressure Recovery Turbines (TRT)
 Improved monitoring and control systems
 Hot stove recuperators.
Savings in upstream processes and efficiency of use of by-products are important in relation to
the BF process. Best available technologies for up/downstream improvements are:
 High levels of coal or other injectants to lower total coke demand.
 Granulation of BF slag for use as replacement of clinker
 More efficient power/heat generation from by-product BF gas, e.g. high pressure steam
cycle, gas turbines, combined heat and power plants.
Heat recovery from BF slag is a promising energy recovery technique that is under development.
1. BF Process
The blast furnace process uses primarily two direct energy sources:
- Coal (in the form of coke and injection coal or alternate injectant, e.g. oil or NG)
o Provides thermal energy and energy for reduction of iron oxides
- Electricity
o Provides power for compressors, fans, conveyers, pumps etc.
The blast furnace exports energy in the following forms:
- Reduced iron oxides, i.e. iron
- Carbon in hot metal
- Thermal energy of molten iron and slag
- Blast furnace gas (chemical energy)
- Electricity (if top pressure recovery turbine is used)
Thermal losses occur from:
- Cooling of the blast furnace, mostly via water cooling
- BF top gas
- Heat losses from hot stoves
The overall BF system is summarized in Figure 1.
27
Fig1
Typical fuel energy and electricity balances are shown in Tables 1 and 2, assuming moderate PCI
rate with a total fuel rate of 500 kg/thm.
Table 1. Example BF fuel consumption11
Fuel Consumption [GJ/thm]
Coke
PCI
Hot stoves COG
Gross Input
Net Export (BFG + C in HM)
Direct fuel consumed
Steam
Net Fuel and steam
11
10.1 (348 kg/thm)
5.1 (152 kg/thm)
0.1
15.3
(5.2)
10.1
0.02 (in blast)
10.1
Hooey, GHGT11, 2012
28
Table 2. Example electricity consumption12
Electricity [MJe/thm)
Main blower*
240
Ancillary
110
TRT export*
(80)
Net Fuel and steam
270
*assumes electrically driven main blower & TRT used with 33% recovery of input electricity to blower
Thus, a breakdown of direct energy consumption is about 97% fossil fuel direct use and 3% electricity (excluding upstream processes). Energy export in the form of top gas, C in hot metal and
electricity (when TRT is applied) represents about 1/3 of input.
2. Energy Losses
Energy losses are primarily from sensible heat from the BF cooling systems, sensible heat of top
gas, heat in slag and hot stoves. These factors are dependent on the furnace size and design (with
smaller furnaces and hot stoves typically having higher losses from cooling and hot stoves due to
higher specific surface areas), as well as the slag rate which is determined by raw material input.
3. Reduction in energy consumption
The total input energy of the BF process has declined dramatically over the past decades and has
reached a plateau, whereby there is only a small potential for further reduction in consumption.
Figure 2 shows schematically the various improvements made since 1950 for German BFs, with
a plateau being reached in the 1980s. This plateau reflects the thermodynamic requirements for
reduction and heating of iron ores, which requires about 9 GJ/thm combined with a CO/CO2 ratio
in the furnace high enough to provide the driving force for iron oxide reduction. The latter effect
results in the production of BF gas which contains about 22% CO and can therefore be used as
fuel, part of which is recycled to the furnace as sensible heat via the hot stoves.
Example estimates only, depends heavily on what is included in the BF system, consistent public statistics are not
available
12
29
Fig2. Reductant consumptions of BFs for Germany13
Some small reductions in net energy consumption can be made, although these cannot be expected to give any dramatic reduction for well-equipped modern furnaces, for example:
- Improved control/expert systems applied to charge distribution and hearth management for stable operation
- Improved maintenance (fewer stops, improved stability)
- Improved cooling systems with lower heat losses (e.g. copper staves)
- Hot stove recuperators
4. Energy recovery
Energy recovery is possible, with potentially gains in net energy use through:
- Heat recovery from hot stoves (e.g. recuperative heat recovery from off-gas, steam
production, PCI coal drying or other secondary uses)
- Application of TRT
- Heat recovery from slag
Of these, the first two are already in use at many locations. Heat recovery from slag, i.e. dry slag
granulation, is being developed. Slag contains about 2 GJ/t slag of sensible heat at 1500 oC. This is
high grade heat, with the possibility to produce high pressure steam. Dry slag granulation has
the reported potential to recover about 60% of this14 which equates to 330 MJ/thm for a furnace
13
14
IPPC BAT ref document, 2012
Norgate, Scanmet IV, 2012
30
with a slag rate of 280 kg/thm. This represents about 2% of the total energy input to the BF and
is a substantial amount considering the scale of production.
Other energy recovery techniques for the lower grade heat from top gas or cooling systems do
not currently appear to be economically viable or efficient enough at the present time, e.g. Organic Rankine Cycle (ORC).
5. Upstream/ Downstream System Changes
System changes, upstream of the BF, such as changes in raw materials, amount of coke required,
and efficient utilization of by-products offer advantages. Four of the most important are:
- High efficiency power plants/CHP
- High levels of injectants (PCI, NG, COG, Oil, plastics etc.)
- Improved iron ore quality
- Slag use in cement
The BF gas exported from the BF is typically used to fire hot stoves, coke batteries and any excess sent to
power plant or CHP. The net efficiency of the system will be largely determined by how efficiently the gas
is used. Gas turbines, modern high pressure steam cycle plants or CHP plants are more efficient than
many of the power plants currently in use at steelworks.
PCI (or other injectants), lowers the amount of coke required in the BF and thereby lowers the amount of
energy required to produce the coke needed. This is both an economic and energy benefit, and is almost
universally practiced. Improved injection systems and control can improve the potential.
Improvements in iron ore quality have been made with improved beneficiation and older lower grade
deposits replaced with high quality ores coming largely from Brazil and Sweden. This has lowered the
slag rates and lowered reducing agents consumptions. The increased use of high grade pellets, particularly as 100% burden, has contributed to low total fuel input. However, iron ores grades have been falling
recently, leading to higher silica and alumina inputs into blast furnace and subsequently higher energy
consumptions at sinter plant and/or at the blast furnace but also higher slag rates. Impact of iron burden
needs to account for upstream agglomeration in sinter and pellet plants, as well as use of lump ore.
It should be noted that granulated blast furnace slag is commonly used to replace a portion of energyintensive clinker. The energy benefit of using granulated blast furnace slag to replace clinker mitigates
the system-wide energy use when increasing slag rate but leads to a higher energy burden on the BF. Approximately 66% of BF slag in the EU is used for cement production, with the majority of the balance for
construction.15 There may be potential to use more BF slag to replace clinker.
5.1 Charging of Metallics
Use of virgin metallics, e.g. DRI or HBI can lower BF fuel consumption and improve productivity
greatly; however the overall energy balance needs further attention because the energy intensive reduction step is made externally in DR-shafts. Some scrap may also be charged, which lowers the energy input requirement, however this competes with EAF and BOF for scrap use.
Replacement of the BF/BOF process with DR/EAF processing is beyond the scope of this document.
15
IPPC BAT reference document, 2012
31
Annex 2
3- Basic Oxygen Furnace(BOF)- Energy savings and recovery
Dipl.-Ing. H.P. Domels, TKSE, Dr.-Ing. H. Rosemann, BFI, Dipl.-Ing B. Stranzinger, BFI,
The Basic Oxygen Furnace (BOF) is a main process of an integrated steel works and it provides
the opportunity for a recovery of energy and improvement of the energy efficiency. In a BOF Oxygen (O2) is injected in to the hot metal in order to remove the Carbon and other minor elements
and to produce steel. The Carbon reacts highly exothermic mainly to Carbon monoxide (CO) and
is removed with the BOF-gas that can be recovered to substitute gaseous fuels in an integrated
steel mill.
In order to balance the heat-input and to cool the process of a BOF additional raw material and
scrap have to be used as coolants. They are added to the hot metal in a range of 5 – 30 % of the
gross metallic charge. The hot metal ratio is then usually adapted to 750 to 950kg / tls depending on the temperature of the heat.
Due to these variable process parameters the heat balance of the BOF-process has a broad range.
It is possible to recover the sensible heat of BOF-gas leaving the BOF with a volume of 80 – 100
m3 STP / tls at a temperature of 1600 – 1800 °C. In a waste-heat boiler the BOF-gas is cooled
down to 250 °C and steam is produced with a heat content equivalent to 0,2 GJ/tls or 60 kg/tls of
steam 16. The CO-rich BOF-gas is recovered as gaseous fuel if closed hood vessels are used and
the combustion of the gas is prevented. Due to environmental and energy-optimizing aspects this
method is used already in more than 70 % of Europe´s steel production 17 and gives the potential
to save up to 0,8 GJ/tls of natural fuels.
The BOF-process needs additional external electrical energy for all drives and motors to
transport the material and gases of the process. The total electrical energy input for all motors
and drives of the process varies between 14 to 42 kWh/t (mean value 26 kWh/tls) 1. Furthermore the used high-pressure oxygen (30 bars) has to be produced and this needs additional electrical energy. For an average feed of 52 m3 O2 STP /tls to the BOF and a specific consumption18 to
Energy Use in the Steel Industry, IISI 1998,
Steel´s Contribution to a Low-Carbon Europe 2050. BCG+Steel-Institute VDEh, Mai 2013.
18 Eurofer
16
17
32
produce high-pressure oxygen of 0,71 kWh/m3 STP the indirectly needed electrical energy sums
up to 37 kWh/tls.
Energy saving potential:
Modern BOF-shops have only a little potential for additional energy saving measures. When a gas
recovery system is in operation the aim is to raise the yield of gas and steam up to the technical
limit especially by optimizing the seal ring (see 3.3.1). Another aim is to improve the efficiency of
electric drives by variable speed regulation instead of valves or guide blades.
Energy recovery potential:
In Western Europe al lot of steelmaking plants already have a gas-recovery system due to environmental and energy-optimizing aspects. Including the BOF-gas recovery a steelmaking-shop
has an energy-surplus.
33
1. The BOF-process
The BOF-process was developed for improving the steelmaking process by the use of pure
Oxygen (O2). Fig1 shows the principle flowchart of this process.
Fig1: General process layout of basic oxygen steelmaking indicating the
individual operations and the input and output mass streams 4
The BOF-process is a discontinuous process. In a modern steel works up to 380 tonnes of steel
are produced in only one Converter in a cycle of about 40 minutes duration 19. The carbon content of the hot metal is reduced from 4 – 5 % to the specified level of typically 0,01 – 0,4 % Carbon in the steel product. In this highly exothermal reaction between carbon and oxygen mainly
Carbon monoxide (CO) and Carbon dioxide (CO2) are produced as main components of the BOFgas.
Since the first application in 1952 the BOF-process has been developed further on by optimizing
the way of injecting oxygen and alloy-material as well as additional material for steel upgrading,
such as dephosphoring and desulphuring. Today for the production of 1 t of crude steel about
800 to 950 kg of hot metal are used. Scrap, iron ore and other coolants are added to cool down
the reaction and maintain the temperature of the melting steel at about 1600 – 1700 °C. The
amount of scrap charged depends upon the material price for scrap and the thermal and chemical conditions of the hot metal and varies usually between 150 – 300 kg/tls. Lime, dolomite and
19
Best Available Techniques (BAT) Reference Document for Iron and Steel Production. EU 2013
34
other additives have to be added to the process as well for the reactions with the minor impurities of the hot metal like Silica, Mangenese, Phosphor and Sulphur. Finally the solid product of all
reactions which is the BOF-slag is removed.
Over the years the demands at steel quality and process efficiency have increased, so that a postprocessing of the crude steel has become necessary that is the so called secondary metallurgy.
After steel refinery the liquid steel is casted into intermediate material by ingot casting – or by
continuous casting, which is the more efficient process in relation to energy and material use.
Today more than 90 % of the worldwide steel production is casted by the continuous method 4.
Since the beginning of the nineties last century some new technology has been developed to
combine casting and rolling in form of near shape casting up to thin strip casting with a short finishing rolling process.
35
2. Material and Energy Balance of the BOF-process with Gas Recovery
2.1 Carbon Balance and BOF-Gas Recovery
The BOF-gas produced in a BOF and the potential for its recovery can be estimated on the basis
of a carbon balance of a BOF shown in Fig2. The figure shows general data for the noncombustion method. In this method hoods are installed that prevent the inlet of air to the gas
duct and supress the combustion of the CO-rich BOF-gas. This method is applied in 70 % of Europe´s steel plants1 and it is the best opportunity for both heat and fuel recovery 20.
Fig2: Carbon balance of a BOF with gas recovery system (hot metal rate: 900 kg/tls) 1
Within the BOF 75,6 m3 STP/tls of BOF-gas are produced. A small content of 10 % inleaked air
will be mixed in to the gas and cause 10 % of it to combust. This will raise the volume to 88,5 m 3
STP/ tls and the temperature increases to 1650 to 1800 °C with a sensible heat of about 200 up
to 300 MJ/tls. The sensible heat can be recovered in a waste-heat boiler afterwards in order to
produce steam at medium pressure for process and heating purposes in the steel mill. In the
waste heat boiler, the recovered gas is cooled down to nearly 250°C before entering the dry or
wet gas cleaning facilities.
Fig3 shows the trend of a gas production cycle. At the beginning and at the end of the BOF-gas
recovery cycle a small part of the produced BOF-gas has to be flared because the oxygen content
20
EPA: Available and Emerging Technologies for Reducing Greenhouse Gas Emissions from the Iron and Steel Industry
(Sept. 2012)
36
in the fuel gas is too high. This could cause safety risks (explosions) and quality risks (too low
exergetic heat value). The amount of gas losses to the flare should not exceed 8 -10 % of the gas
produced. Thus 81 m3 STP/tls of BOF-gas can be recovered as a gaseous fuel for other furnaces
within the steel mill with a calorific value of 705 MJ/tls in this case.
Fig3: BOF gas collection in the case of suppressed combustion 4
2.2 Thermal Energy Balance of a BOF
2.2.1 Energy Input to a BOF
The energy input of a BOF is directly influenced by the hot metal ratio, its sensible heat and its
carbon content. Table 1 gives an example and summarizes the main energy input and output data of a BOF. The main input of energy is caused by the sensible heat of the hot metal and the exothermic reactions of Carbon and Silica.
Table 1: Example of an energy balance of a BOF-Converter 21
Energy Input
Sensible heat of hot metal
Sensible heat of scrap and other additives
De-Carburization of C in hot metal
Typical data
(per t Liquid steel)
880 kg/t LS, 1.450 °C,
Scrap-input to converter: 210 kg / t LS
x C =4,6 %
MJ/t LS
Exothermic oxid. reactions, mainly Fe, Si, Mn
1.262
11
1.331
260
Total input
2.863
Comments
(1450°C) = 1.434 kJ/kg
used for cooling
hu,C = 32.763 kJ/kg C
FeO + SiO2 in slag and dust
hhot
metal
Energy output
Lower heat value of converter gas
Sensible heat of liquid steel at 1.650 °C
90 Nm3/t LS, LHV=7-11 MJ / Nm 3
810
after quenching with leakage air
hFe (1.900 K) = 1.372 kJ/kg
115 kg/ t LS
Sensible heat in slag at 1.650 °C
hSlag (1.650 °C) = 2,3 MJ/kg slag
1.372
265
Sensible heat of converter gas at 1700 °C
Sensible heat of dust losses
90 Nm3/ t LS, cp=1,6 kJ/Nm 3*K
mDust = 20 kg / t LS
242
20
hFeO (1.370 °C) = 1.056 kJ/kg
madditiv es = 15 kg / t LS
75
∆HR =5.000 kJ/kg (estimation)
80
estimation
Reduction of sinter, ore, alloys
Heat loss of walls and cooling water
Total output
21
2.863
Calculated with typical thermo-chemical data and additional estimations
37
In the practical operation of a BOF it is necessary to adjust the energy input by hot metal to the
actual pig iron temperature of each heat. The energy input can be corrected by reducing the hot
metal ratio and adding more scrap or ore to the BOF if the pig iron temperature of the heat is
higher than expected. This relationship is shown in Fig 4. This figure illustrates typical hot metal
and scrap ratios versus the temperature of the pig iron. It can be seen for example that a difference of 100 °C in the pig iron temperature (1400 °C instead of 1300 °C) may be adjusted by a reduction of the hot metal ratio from 870 to 830 kg and adding 250 kg instead of 210 kg of scrap
per ton of steel as coolant.
Fig 4: Input of pig iron and scrap versus the pig iron temperature 1
2.3 Energy output of a BOF
An example of an energy balance with input and output energy flows of a BOF is shown in Table
1.
If a gas recovery with hoods is installed at the converter of the BOF-process the energy output
takes place together with the following material flows:







BOF-gas as by-product, a) to gasholder, b) to flare
Steam produced in the waste-heat boiler
Waste gas (de-dusted)
Dust
Hot liquid steel products
BOF slag
Cooling water
38
Energy can be recovered by the use of BOF-gas as gaseous fuel for other shops or by the use of
steam for other processes. The energy losses by dust, slags and cooling water cannot be recovered.
2.3.1 BOF-gas
As shown in Fig2 and chapter 2.1 the BOF-gas can be recovered by nearly 90 %. This will give the
potential to use the BOF-gas as a gaseous fuel with a potential of 705 MJ/tls in this case. Only a
small part of the BOF-gas (7,5 m3 STP/tls) is lost and has to be sent to the flares with an energy
content of 65 MJ/t ls.
2.3.2 Steam
In a waste-heat boiler 60 kg/tls of steam can be produced out of the sensible heat of the BOF-gas.
This gives the potential to recover up to 200 MJ/tls.
2.3.3 Waste gas and dust
The typical waste gas after first heat recovery has a temperature of about 250°C and it is
quenched with water or additional steam for conditioning the gas when it is cleaned in a dry gas
cleaning facility. The gas leaves the cleaning system with about 60 °C and is cooled down in a final cooler for transporting with blowers to the gas holder. The dust is separated and recycled if
possible.
2.3.4 Hot liquid steel products
The hot liquid steel is transported by ladles to the secondary metallurgy and then to the casting
shop. Heat losses during transport have to be avoided and compensated. In order to keep the
necessary temperature of the liquid steel before casting it is necessary to heat up the ladles with
burners again. This needs an additional use of gas and other fuels for the ladle heating.
2.3.5 Slags (from different process steps: desulfurizing, BOF, secondary metallurgy, CC)
From different process steps the slags are retained in different amounts and different temperatures. Slags are used as by-products in different applications like road building or as fertilizer.
Up till now there is no technology available that enables a recovery of the sensible heat of the
slags.
39
2.4
Use and Recovery of Primary Energy (PE) in a BOF-shop (direct and indirect PE)
The predominant energy flows in a BOF-shop are given by the input of hot metal to the BOF shop
and the produced liquid steel. It is possible to recover the energy partly by the production of
BOF-gas and steam. But an additional input of electrical and thermal energy is necessary for the
following energy users that are part of an integrated steelworks:



Electrical energy to produce high pressure oxygen (15 bar)
Electrical energy to be used for all motors and drives of the BOF-shop
Thermal energy to heat up ladles and other equipment of the shop before casting
The primary energy used for the production of additives like lime or alloys is not considered in
this balance. In order to calculate the total balance of primary energy (directly or indirectly
used) operating results of several industrial plants have been analysed 1 and an EcoTech - plant
has been defined 22 that represents proven technology of the process. The following figures are
based on a mean hot metal ratio of 900 kg/tls and the use of 170 kg scrap+others / t ladle steel.
22
EcoTech = Proven energy saving and technology, Source of data: IISI Study Energy use in the steel industry 1998, page 78
40
Table 2: Balance of the Primary Energy used in an EcoTech BOF+CC-plant 1
BOF Plant
Specific consumption
Conversion factors
Primary
Energy MJ
/ t ls
9,2 kJ / kWh
259
Primary Energy Input
Oxygen (15 bars)
52
m3 STP / t
ls
0,54
Electricity
Other fuels
26 kWh / t ls
kWh/m3 O2
STP
9,2 kJ / kWh
172 MJ / t ls
239
172
Total input [A]
670
Recovered energy
m3 STP/t
ls
BOF Gas
86
Steam
60 kg/ t ls
8,7 MJ/m3 STP
-
744
3,1 MJ/kg
-
186
-
930
-
260
Total recovered [B]
Net Input (BOF-plant) [A+B]
CC plant
Primary Energy Input
Electricity
7,7 kwh / t ls
Others
30 MJ / t ls
Total input [C]
Net Input (BOF plant + CC
plant) [A+B+C]
9,2 kJ / kWh
71
30
101
-
159
The table shows that the BOF- and CC- shop together produce an excess of primary energy of
159 MJ/tls in this case. The primary energy used for electricity is incorporated in this balance.
41
3. Measures to save Energy
3.1 Measures related to thermal energy savings
3.1.1 Programmed and efficient ladle heating 5
The ladle of the BOF vessel is heated with gas burners. The heat losses can be reduced by installing temperature controls, hoods, an efficient ladle management, recuperative burners and
oxy-fuel burners 4. The amount of heat stored in the ladles has to be used efficiently by a controlled scheduling of ladle heating.
3.1.2 Improvement of process monitoring/control 5
Examples of an improved process monitoring include automated gas analysing systems, sensoring systems and systems to determine the steel/slag composition simultaneously. The data may
be used for process models that enable a precise process control. By this the cycle time of the
BOF process and the amount of additives and oxygen can be controlled and limited in an efficient
way.
3.1.3 Energy monitoring and management systems
The efficient use of energy is not only related to technical issues. Main improvements can be
made by the involvement of all people in the plant. Improvement for an efficient plan plans need
the support of different departments in a company and need a clear communication on all levels.
Energy monitoring and management systems help to implement a continuous improvement of
the energy efficiency.
3.1.4 Efficient Tundish heating
Tundishes are heated to reduce the heat loss of the molten steel and to avoid negative quality
influences. New developed electrical induction methods will possibly improve the efficiency
compared to gas burners.
3.2 Measures related to electrical energy savings
3.2.1 Gas cleaning system
As mentioned above there are two types of gas cleaning systems: Wet or dry cleaning. In relation
to the dry gas cleaning system the power demand of the wet cleaning system is about 2-8
kWh/tls higher. The reason is that the BOF-gas is sucked through a venturi scrubber for intensive cleaning with water with a pressure loss of about 150 mbar. Additional there is a lot of
42
sludge handling and pumping necessary, so that a dry gas cleaning system is more energy saving.
Variable speed control (VSC) can be a chance for energy saving in the process, where pumps and
vans are working continuously on different loads.
3.2.2. Switch-off and soft-start systems for cooling water pumps during CC-downtime
Since many years special electronic devices are available for energy saving at pumps and fans,
which help to manage a shutdown with automatical switch-off system and soft-starting the motor again, when the production is ready to start again.
3.2.3. VSC for exhausting fans in the primary and secondary dedusting system
In both systems very big fans are transporting big amounts of gas. The BOF-process is a batchtype, so that the fans in the meantime between process running and material handling can come
to idle modes. Depending on the layout of the secondary dedusting system there can be phases of
intensive use of the system beneath the main steelmaking process, e.g. when hot metal is reladled or charged to the converter. Power saving by this measure can be up to 10 kWh/t ls.
3.2.4. VSC for exhausting fans in the steam exhauster in the continuous casting line
In the continuous casting lines the casting is cooled by a lot of water sprayed on and part of this
is evaporated. The steam has to be taken out of the plant and this is done by motor driven steam
exhausters. VSC can reduce the power input at about 0.2 kWh/tls.
3.2.5 VSC for transport rollers for casted material
After cutting the strand the material is transported on rollers. Some of them are only used for
short times and so the can also be switched off or set on slow speed for saving energy.
3.2.6 Power regeneration by crane drives
In new times modern electronic devices are able to recover power when cranes are lowering the
load. In these moments the motors can work as generators and can feed the power to the grid.
The epuipment is available but still quite expensive.
43
3.3
Measures related to by-product energy
3.3.1 Increasing the yield of the by-product gas recovery
The yield of a BOF-gas recovery can be increased by optimizing the following process steps:
 The blowing has to take place in an efficient way with low oxygen consumption and a low
formation of Carbon dioxide in the gas phase.
 The seal ring has to be optimized in order to minimize the quantity of leakage air.
 The start and the end of the blowing period have to be optimized in a way that the losses
of BOF-gas to the flare are minimized.
These measures will increase the calorific value and reduce the CO2- and N2-content of the BOFgas and have a potential of up to 0,1 GJ/tls.
3.3.2 Increasing the yield out of the steam recovery
New cooling stacks have been developed for the off-gas system of a BOF converter. These systems will get a better nozzle spray system23. The transfer of waste heat to the steam during cooling of the BOF-gas shall be improved with this new system.
New modelling methods24 aim at precise online-models in order to calculate the mass- and energy- balance for the steam production and to forecast the heat generation by steam. The leakage
air has to be controlled in a better way so that the operation scheme of the off-gas and its temperature can be optimized. The energy recovery as steam or as recovered fuel-gas can be partly
adjusted with modern control systems.
23
24
Siemens AG: Siemens to modernize offgas cooling in Eisenhüttenstadt for ArcelorMittal, Siemens-News, Aug. 2013.
Born, C. et al.: Potential and difficulties of heat recovery in steel plants. MPT international 2/2013, p. 50 – 60.
44
Annex 2
4- Electric Arc Furnace (EAF) – New R&D areas for energy savings
Enrico Malfa- CSM
Background
The scrap based steelmaking route involves many different types of energy inputs. The
main source is still electrical energy (60%),
but in many furnaces a significant part of the
process energy input comes from various
types of chemical energy (mainly the C and H
content in fossil fuels like natural gas, coal, oil
and in the pig iron or DRI/HBI but also by oxidation of metals and metallurgical dusts) or
sensible energy (mainly by charging of preheating scrap or hot pig iron or DRI/HBI).
These energy sources are utilized in different
ways and strongly affect the efficiency of the
applied energy, material and energy flow
sheets in the EAF. Figure 1 reports a tipical
energy balance of a top charge EAF.
Some attend are also on-going to use C substitute in EAF both using biomass (char coal and
sysngas – RFCS GREENEAF) than by-products
(plastics, car fluff, rubber, etc) .
Fig 1 – EAF Sankey diagram[1]
Efforts have been done during the years to optimize the energy use of the different energy
sources in the EAF (figure 2).
Fig 2 –EAF improvements during years 1965-2010
45
However options for further improvements are possible. The relevant actions do not require
revolutionary breakthrough process but rather the simultaneous contribution of suitable advanced technologies and an intelligent management of the process integrating a number of important key technologies already available.
The present trend is to reduce the electrical consumption of the process by increasing:
− the use of chemical energy,
− the heat exchange between scrap and the process off‐gas.
Continuous or semi-continuous charge furnace are traditionally seen as the best configuration to
achieve these results since they naturally favor the heating of the scrap charge by means of the
process off‐gas. Table 1 shows reference values from literature of commercial available technologies.
Technology
Type
Charge
Conventional
top cahrge
Bucket
EAF
Consteel
Consteel
Continuous
Quantum
Shaft
3-4 batches
COSS
Shaft
3-4 batches
EPC
Shaft
3-4 batches
EcoArc
Shaft
Semicontinuos
Consteel
Consteel
Continuous
Evolution
EE
O2
CH4
kWh/tLS Nm3/tLS Nm3/tLs
C
kg/tLs
~ 380
~ 38
~8
~ 15
~ 350
~ 280
~ 300
~ 300
~ 280
~ 30
~ 30
~ 30
~ 38
~ 35
~0
~4
~2
~3
~2
~ 20
~ 30
~ 20
~ 20
~ 35
~ 310
~ 30
~8
~ 20
Table 1 - Map of Technologies
In addition to that it must be considered that in the EAF process a large amount of energy
is lost in cooling the
furnace
structures.
Usually the furnace
shell and fume ducts
are water-cooled to
cope with the very
high
temperatures
(about 1700°C) and in
many cases the energy
transferred to the
cooling water is simply lost into the environment. The energy
losses from the flue
Fig.3 - Scheme of 2-stage heat recovery for an EAF [2]
gases represent about
20-25% of the total
46
input of energy considering the energy balance in figure 1, while shell losses the 10-15%. Direct
recovery and use of a relevant part of this energy in the EAF process can be pursued by scrap
preheating (up to 800°C) and continuous (i.e Consteel) or semi-continuous (i.e Coss, ecoarc, etc.)
charging. As an alternative the energy lost from EAF process in the off-gas can be recovered by
evaporation cooling technology producing saturated steam which can be used as the energy
transfer media for following processes. The steam can be used directly in the secondary metallurgy when available (VD or VOD) or for the generation of electric power, compressed air or
most simplified for operating a heat exchanger, which is providing heat for processes, buildings
or warm water. Some industrial example already exists in which the heat is recovered in the EAF
duct up to 500-600°C off-gas temperature (figure 2). On going projects target to enlarge the temperature range up to 250-200°C adding traditional waste heat boiler or innovative heat exchanger with cooling rate comparable to the quacking tower (~300°C/s). Basic research is also started
to study the feasibility of … application at very low temperature heat recovery.
The objective is to develop new technological concepts aimed at more efficient and more
flexible process for steel production by EAF route through the optimization of direct and alternative input of energy in EAF with evident benefits in terms of production costs, productivity
and environmental impact.
In the future, the EAF route in Europe will
also move in the direction of using a number
of Alternative Iron Sources (AIS) besides
scrap, in order to obtain higher quality steel
production and/or due to scrap shortage.
The most common AIS are Direct Reduced
Iron (DRI) and Pig Iron. DRI is produced in
solid state by reduction of iron ore with natural gas and is available in two forms:
Sponge iron and Hot Briquetted Iron (HBI).
Pig iron is solid pieces of hot metal from
blast furnaces or any other iron smelting reduction process. These processes will be
leaner in energy and raw materials (yield,
Fig. 4– Saving in EE due to hot charge of DRI [3]
especially), but will also provide a template
for substantially reduce global energy consumption and CO2 emission respect to integral cycle. For example, the concept of DRI plant or
iron smelter located inside the EAF plant results the ideal condition to feed AIS hot to EAF. Figure 3 shows the relevant recovery of the additional energy required to melt DRI in comparison
with 100% scrap using hot charging. Example are available outside Europe.
Use of scale, that contain a relevant percentage of Fe oxide (~95%), as partial substitution of
scrap is also demonstrated in some plants. Realistic value of the scrap substitution rate to have a
good compromise between the increased cost due to additional energy required for oxide reduction and the savings due to scrap substitution are in the range 2-4%.
Ways and means - Research areas
47
To reach these objectives, interdisciplinary teams should work to develop new technological
concepts integrating a number of important key technologies already available:
 highly reliable and well proven new real time measurement system of global variable (such
as off-gas measurement at 4th hole (composition, flow rate, temperature) and local ones
(such as continuous measurement of liquid bath temperature or scrap detection in front of
burners);
 advanced control systems that integrate available local and global measurement system
(HW sensor) with mathematical models able to give the information that presently are impossible to obtain (SW sensors)
 lances for injecting oxygen and carbon and burners to optimise the chemical to manage in
real time both the melting and refining phase with particular regard to the post combustion
optimization and yield improvement;
 new generation of electrodes to improve electrical arc stability such as hollow electrode
 process chain integration (scrap yard + EAF + secondary steelmaking + CC)
Specific efforts must be devoted to design improve or find alternative way to recovery, storage
and use the lost energy and solid residuals. Different ambitious R&D objectives are aimed at:
 develop a new generation of EAF panels that limit the shall losses to couple in particular
with the new generation of continuous scrap preheating and charging operating in the flat
bath condition;
 reduce the cost and at the same time increase the efficiency and reliability of the very high
flux heat exchanger working at high temperature, high dust concentration and corrosive environment;
 develop thermal storage systems to improve the energy efficiency of batch processes by
compensation of the mismatch between available waste heat and energy demand;
 find a general solution to recovery the heat at medium-low temperature (<500°C) avoiding
the risk of dioxin formation due to DeNovo syntheses;
 set-up software solutions to achieve a better integration between different source of recovered energy and optimization of energy re-use.
 develop dynamic approaches for electricity demand monitoring and timely reactions to grid
situation to avoid non flexible equipment disconnection and financial fines when deviating
from energy contingent. develop processes with proper scale to be integrated with EAF
route and assuring competitive ROI for residual recovery and valorisation (i.e. slag, EAF
dust)
In general but in particular for the heat recovery from off-gas the technology is not the challenge.
The true challenges are the use of recovered energy and the optimum size of the heat recovery
equipment. In fact despite all complaints about high energy prices the main challenge for heat
recovery is reaching a sensible amortization [4].
Having that in mind key actions for the next years are:
 R&D&I centers: new idea
 Efforts to improve the incremental progress and generate new technologies & breakthrough
 Methodologies, tools and indicators for sustainability assessment of energy and resource efficient solutions in the steel industry
 Associations: common industrial vision
48








Promote cross-sectorial collaborative initiatives (different industries)
Give the technologists a target: industry’s roadmap to 20xx ?
Industry: work to reduce cost impacts
Take the risk to prove and optimise new systems at pilot/demo scale
Look at possible synergy both inside the plant and with nearby plants
Governments: support to innovation
Introduce financial support mechanism for early deployment of new technologies to drive
private financing of projects
Incentivize cross-sectorial collaborative initiatives
Reference
[1] A-P Hollands et al., “Concepts for energy recovery in mini-mills”, METEC InSteel Conference,
Düsseldorf, 27 June – 1 July 2011
[2] H. Schliephake, “Heat Recovery for the EAF of Georgsmarienhütte, Germany”, AISTech 2010
Proceeding, Volume I
[3] P. Durante, T. Scarnati, “ Advances in Energy Consumption and Environmental Impact Improvements using High Carbon DRI in an EAF Shop, EAF Perspective on Automation, Material, Energy & Environment, Milan, Italy, 29-20 March 2012
[4] C. Born, R. Granderath, The Challenge of Heat Recovery in Integrated Steel Plants, AISTech
2011
Annex2
49
5- Hot Rolling Mills – Energy savings opportunities
Bertrand de Lamberterie, Wolfgang Bender, June 2013
Introduction
This paper presents energy efficient measures to be implemented in the hot rolling mills. They
could be used for most of the hot rolling processes: hot strip mills, heavy-plate mills and longproducts rolling mills. The document is splitted in 2 parts, reheating furnaces and hot rolling,
and some general measures. The implementation of the energy efficient measures would correspond to the benchmark situation as proposed in the template of Fig.
type of equipments
unit
Conventional Hot strip
Mill
Thin slab casting Hot
strip Mill
Heavy Plate Mill
Reheating furnace
electricity
benchmark EU average Maxi benchmark E. average maxi
kwh/
GJ/t
GJ/t
GJ/t
kwh/t
kwh/t
t
1,1
1,5
2
70
95
140
0,6
2
0,8
2,5
1
3,5
60
60
70
80
90
120
95
131
240
67
57
106
101
188
150
69
88
101
Wire rod mill
1,2
1,5
2,3
Bar Mill (merchant &
rebar)
0,7
1,6
2,8
Structural Mill
1,3
2,2
3,1
Near net shape structural Mill
1,3
2,1
2,3
Fig1: Energy consumption in hot rolling (European references)
Considering the very good level already achieved by the benchmark values, the additional potential of progress by new actions of R&D is really very limited, and probably not on new technologies, but more on the overall process optimization of the hot rolling plants ( reheating furnace
control, mill pacing, optimization of the temperature patterns for reheating & rolling, scheduling
optimization, overall reliability).
Fig gives an impression of the energy balance of a typical reheating furnace. In this case the efficiency factor is about 50 %.
50
Fig2: Energy balance of a reheating furnace (BFI measurements)
1. Reheating furnaces
Fumes heat recovery
Modern reheating furnaces are equipped with efficient heat recovery systems. This is fully necessary for the energy efficiency of the furnace. The most current technology is end- of- pipe recuperator, preheating the combustion air from the outgoing exhaust gas. Monitoring systems
and preventive maintenance have to be used in order to check on a regular basis the exchangers’
efficiency Still some R&D developments to be done on advanced monitoring.
Regenerative burners
Recuperative burners and moreover regenerative burners have been developed over the past 30
years for substantial reduction of energy consumption. Reference work at European level evaluation of performance of different technologies both in terms of NOx emission and energy efficiency are NOXREF, Smartfire and CO2RED. Regenerative burners can reach an overall efficiency
of 85% and then reduce the overall fuel consumption by 10 up to 20% compared to conventional
furnaces. Regenerative burners can be added in an existing reheating furnace, in replacement of
existing burners. It is easy to implant this technology for the side burners of the bottom heating
zones of continuous slab reheating furnaces (hot strip mill and plate mills). Roof burners have
been installed successfully at batch furnaces. Regenerative burners are available as high velocity
burners and recently as flat flame burners, generally the reducing of fuel consumption at batch
furnaces is around 30 % and higher than at continuous furnaces, 10 % to 20 %. Both compared
to furnaces with conventional recuperative heat recovery.
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Figure 3 Flat flame burner with regenerator
Fuel preheating
Although combustion air preheating is widely used in current burner systems, the fuel is seldom
preheated. Especially in case of LHV( Low Heating Value) gas such as BF-gas, the preheating increases the flame temperature and enables the substitution of HHV (High Heating Value) gas
such as Natural Gas, COG and BOF gas. A R&D project in the frame of RFCS is on-going (
HELNOX-BFG). The use of process gases lowers consumption of natural gas. Due to small flow
paths in burners the cleaning of process gas is an important requirement.
Oxygen enrichment
The use of Oxygen enrichment of the combustion air helps to lower the waste heat by lowering
the mass flow of waste gases. However a higher combustion temperature may be reached with
negative impact on NOx emissions. This measure must be checked in respect to the burner technologies (e.g. low NOx flameless burners have been developed also in case of oxy-burner) and
local costs of oxygen.
Hot charging
The principle of hot charging is to avoid the cooling of the semi- products coming from the continuous casting, where the semi charging temperature remains over 300°C. Depending of the
configuration of the plant we can achieve batch hot charging (with intermediate hot inventory)
reaching average charging temperature between 300 and 600°C or direct hot charging (the
52
schedule of the hot rolling mill is the same than the schedule of the casters) reaching average
temperature between 500 and 800°C. The effect of hot charging on reheating consumption will
depend on the average charging temperature and the % of hot charging. We consider a minimum
of 30% of hot charging for a significant effect. The actual savings will be plant dependent. An estimation is that 1% of hot charging at 550° brings around 0.005 GJ/t of the overall consumption.
Heat recovery evaporative beam cooling
Waste heat can be recovered from the walking beam furnaces both from the hot strip mill and
plate mills. The cooling water is used to produce low-pressure steam, reducing also thermal
losses of the cooled beams. Fuel savings are around 0.05GJ/t. This technology was widely developed in the seventies and eighties. Not so used today due to higher operating and maintenance
costs.
Waste heat to electric power
Even by using modern heat recovery technologies reheating furnaces have a natewathy waste
heat flow at a temperature level from 200°C up to 600°C. This can be used for producing electricity with technologies as ORC, steam motor or thermoelectric generator. This measure is technical possible to install at nearly every furnace, the aim of the future is to reduce the investment
costs.
Combustion control and Variable Speed Drive on air fans
Modern reheating furnaces are equipped with Oxygen sensors in the furnaces in order to optimize the fuel-air ratios, with a closed loop on O2 measurement. Implementing a VSD on a combustion fan allows a better control of the fuel-air ratio, whatever the load of the furnace, as well
as reduction of electricity consumption. We can estimate the savings GJ/t at 5% as conservative
value and up to 10%. In addition combustion control reduces the quantity of scale produced in
the furnace by around 10% so 0.1% of the total yield.
Reheating furnace process control
All the modern Reheating Furnaces have computer control in order to achieve the proper heating temperature for semi products prior to rolling. It is always relevant to avoid over heating, in
respect of the metallurgy requirements and the rolling forces and torques limitations. The best
results of process control are obtain with a good schedule of the rolling mill ( to get some homogeneity of discharged temperatures according the schedule) and an accurate mill pacing model (
prediction of the reheating time depending on the products to be rolled ). As a result it is considered that an optimized RF process control brings energy savings between 3 and 10%.
Furnace construction
The structure of the furnace has a great impact of the energy efficiency as well. Longer preheating zones with optimized heat transfer conditions lower the necessary fuel demand. The wall
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heat losses can be minimized by the use of modern insulation materials, e.g. microporous insulation.
Process planning
The optimised scheduling of production leads to efficiency and throughput optimisation due to
better arrangement of heating campaigns and planning of stoppages, avoiding unnecessary
changes in tracking temperature.
Maintenance
An often forgotten issue in respect of energy efficiency of reheating furnace is the condition of furnace
encasement as well as measure and control devices. In this case energy savings up to 10% are reachable at some furnaces
2 Rolling mill
2.1 Measures related to the temperature of the product
The control of the temperature of the product during the rolling sequences has an effect both on
the thermal consumption at reheating furnaces and the electricity consumption.
Mill pacing
It is key to predict in the best way the time necessary for the different rolling steps (Roughing,
intermediate, finishing, post-finishing) and then to optimize the reheating temperature.
Induction bar heater
Bar heaters exist both for hot strip mill and bar mills. The purpose is to reheat the product – at
standard process speed- in the range of 40 °up to 80°C. The bar heaters allow to reduce the reheating temperature and to reduce the electricity consumption of rolling motors.
Insulating cover-panels
Movable cover-panels are located on the bar table, between the roughing and the finishing mills.
Cover-panels are suitable when rolling thin gages (lower than 3mm). Along the bar length cover
panels reduce heat losses by around 25-30°, and then reduce the reheating temperature by 3545°.
Near Net Shape Casting
The purpose is to cast metal to a shape closer to the onea required for the finished products.
NNSC integrates the casting and the hot rolling into one process step, fully continuous.
It is the thin slab casting for the hot strip mill, with a slab thickness between 35 to 10mm offering both significant thermal and electricity savings as shown in the figure 1.
It is the near shape cast bloom and billet for the beam rolling (structural mill) in figure1.
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2.2 Measures related to electricity savings
Variable Speed Control for descaling pumps
High pressure water descaling devices are necessary for hot rolling. High pressure are used before the rolling at rougher, both in the case of long and flat products (pressure between 80 and
140 bars). High pressure descaler is also necessary before the finishing of hot strip mill. Variable
speed control (in this case Variable Voltage Variable Frequency) offers a better use of the pumps
with a more steady pressure at the headers and reduction of electricity consumption.
Variable Speed Control for cooling water pumps
Using a similar system (VVVF) for cooling pumps- range of pressure between 4 up to 18 bars-,
the variable speed allows a better adjustment of water-flow and pressure depending on the demand of cooling (mill rolls, roller-tables, product cooling).
Depending on the mill configuration, the optimization of water cooling and descaling provide
electricity savings estimated at 5 up to 15kWh/ton.
Energy Efficient Drives
High- Efficiency Alternating Current (HE-AC) motors of rolling stands can save 1 up to 5 percent
of the electricity consumption. HE-AC drives can be use in place of conventional AC drives for the
roughing mills (at constant rolling speed). For the finishing mills of hot rolling, the trend is also
to replace the conventional DC motors (Direct Current) by High –Efficiency Variable Speed Alternating Current, AC motors. The Gate Communicated Turn-Off inverters are typically used to
drive steel rolling with a wide range of speeds and torques.
Engines and transport systems
All material handling systems need to be reviewed for potential of efficiency improvements. This
covers for instance pusher engines, walking beam systems and roller trains which may substantially gain in efficiency by the help of frequency converters. Also the hydraulic systems used for
material movement may offer room for improvements.
Global energy optimization
We may recommend having a global energy optimization system for the supervision of electricity consumption. For example for the cooling and descaling systems the number of pumps, and
the water flows are depending of the product mix to be rolled as well as the level of production
to be achieved (productivity in t/h and then mill pacing ). On top of that in case of scheduled
stoppages (like work rolls changing) or unpredictable stoppages (for some minutes or up to
some hours) a suitable strategy to reduce electricity losses may reduce the average monthly
electricity consumption up to minus 10%.
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