Why Both Hydrogen and Carbon Are Key for Net-Zero Steelmaking
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49
Why Both Hydrogen and Carbon Are
Key for Net-Zero Steelmaking
The 2021 AIST Howe Memorial Lecture
Carl De Maré
Expert Carbon-Neutral Industry,
Sint-Niklaas, Belgium
carl@carldemare.be
In 2019, four years after the Paris Climate Agreement, Also, within the steel sector, the commitment
the United Nations announced that more than 60 coun- to tackle climate change and CO2 emissions
tries had already committed to become carbon neutral gained momentum. In recent months, the top
by 2050. This included the European Union but not five companies in the sector all committed to carbon-
the three largest CO2 emitters: China, the United neutral steelmaking in 2050 (Table 1).
States and India. In spite of the Paris Agreement, the Steel is a cornerstone of our economy. It is one of
global CO2 emissions continued to grow to a record the most important construction materials that is
high of 36.44 billion tons, 24% higher than in 2005 present in nearly all aspects of our lives. Steel will be
and a 60% increase from 1990 (Fig. 1). crucial to transform to a carbon-neutral economy:
Since the end of 2019, the world has dramatically renewable power generation will require more steel
changed. The coronavirus pandemic quickly spread (Fig. 2), steel for CO2 and hydrogen pipelines will
over the world with an unprecedented impact on be required and the electrification of transport will
our daily lives and economies. Global CO2 emissions boost the demand for electrical steels.
dropped 7% in 2020 to 34 Gtons
and the commitments to tackle cli-
mate change picked up:
» China, the largest CO2 emitter
today, announced in September
2020 its new objectives to peak
CO2 emissions before 2030 and
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to be carbon neutral in 2060.
» The U.S. announced in March
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2021 to become carbon neutral
in 2050 and to reduce its green-
house gases (GHG) in 2030 by
50–52% versus 2005.
» The European Union, tradition-
ally a frontrunner, increased its
commitment in April 2021 to
reach 55% GHG reduction in Fig. 1 Evolution of total CO2 emissions related to use of fossil fuels and cement
2050 versus 1990. production. Land use not included.1
50
Production in 2019
(million tons) Announcement Discussion
ArcelorMittal 97.31 September 2020
GHG Generation Related to Current Iron
Baowu 95.47 January 2021 and Steelmaking Processes — Steelmaking is
Nippon 51.68 December 2020 a mature industry, optimized over the last 150 years.
HBIS 46.56 March 2021 Steel is also the only material that is intrinsically
circular. Recovered steel scrap is representing nearly
POSCO 43.12 December 2020
one-third of the iron resources to make up new steel
Table 1 A nnouncement of Top 5 Steel Producers to Become products. However, in spite of the growing scrap avail-
Carbon Neutral in 2050 ability, it will take until 2050 before primary steelmak-
ing will start to (slowly) come down (Fig. 3).
Primary steelmaking starts with iron ore, which is
It is expected that between now and 2070, steel reduced to iron in a high-temperature gas reaction
demand will further grow to 2.8 billion tons per year with carbon monoxide (CO) and hydrogen (H2).
(Fig. 3). This growth conflicts with the need to reduce The blast furnace–based route (BF/basic oxygen
CO2 emissions. Indeed, steelmaking is energy inten- furnace (BOF)) is dominant, with a market share of
sive and carbon plays a key role. In 2019, 1.875 billion 90%, where mainly carbon (coke and coal) is used
tons of steel was produced, emitting on average 1.85 both for the heating and the chemical reduction but
tons of CO2.3 With a total of 3.45 billion tons of CO2, also for the melting of the iron into hot metal. The
steel is responsible for 8.5% of all GHG emissions and other commercial production is done by so-called
9.5% of the CO2 emissions related to the use of fossil direct reduction in a shaft, where solid iron (direct
fuels. reduced iron (DRI) or sponge iron) is produced by
Going forward, the steel industry needs to assess and using a mixture of reactant gases CO and H2. The
decide which pathways are technologically and eco- sponge iron is melted in an electric arc furnace (EAF)
nomically viable in order to reach carbon neutrality. using electricity. The reduction CO:H2 gas is pro-
duced in that case from natural gas.
In the BF process, typically 70–80% of
the reduction is done by CO and 20–30%
by H2. In the natural gas DRI shaft,
60–70% of the reduction is done by H2,
with the rest by CO reduction, leading to
a lower CO2 generation (Fig. 4).
Comparing the GHG emissions between
BF/BOF and DRI/EAF plants needs to be
done at the system level, including the
co-production of 0.5 MWh per ton crude
steel of power from the syngas generated
during iron reduction and the 200 kg per
ton cement clinker substitute in the BF/
BOF plant. In a DRI/EAF plant, those
byproducts require additional energy to
produce the same amount of power in
Fig. 2 Tons of steel used per MW power generation capacity.2
a separate power and cement kiln. The
analysis of CO2 emission per ton there-
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fore always has to be done referring to the
marginal power production technology
in the system.
In the BF/BOF plant, 40% of the
emissions are due to chemical reduc-
tion, 35% due to the need for high-
temperature heat and 25% is generated
in the power plant with the exported syn-
Fig. 3 Expected evolution of primary (basic oxygen furnace, BOF) and
gas from the reduction process.
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secondary (electric arc furnace, EAF) steelmaking in the 21st In case of a system with natural gas–
century.36 based power, the figures in the DRI/EAF
process are not that different: 33% due to
51
Fig. 4 Major key performance indicators for the two main production pathways to produce iron and steel.
heating, 27% due to reduction
and 40% is related to the power
and cement production (Fig. 5).
The total emissions of the
BF/BOF and the DRI/EAF are
very close to 1,600 kg per ton
crude steel in economies where
natural gas is used for the mar-
ginal power production (is the
case in the next decades for
most of the countries) (Fig. 6).
When the marginal power is
produced with coal (was the
case on the past), the emissions
of the DRI/EAF plant are 25%
higher compared to BF/BOF. Fig. 5 CO2 emissions in blast furnace (BF)/BOF integrated plant and direct reduced iron
When we move to a full zero- (DRI)/EAF plant to co-produce 1 ton steel + 0.5 MWh power + 200 kg cement
clinker in case of natural gas–based power system.
CO2 power generation system
in the future, the DRI/EAF
plant will have 30% lower emis-
sions versus the BF/BOF process.
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The Hydrogen Opportunity for Carbon-
Neutral Steelmaking
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Industrial Experience With Hydrogen Utilization for
Iron Reduction Until Now: The chemical reaction
between iron oxide and the CO and H2-containing
reductant gas is responsible for 40% of the CO2
emissions in the BF/BOF process and 27% in the
DRI shaft process. The basic concept of hydrogen
Fig. 6 CO2 emission in kg per ton steel comparison between
ironmaking is simple: substituting the carbon (or the BF/BOF and DRI/EAF as function of the marginal power
carbon monoxide) in Eq. 1 by hydrogen in Eq. 2 to generation technology.
52
reduce the ore and releasing water vapor instead of produced with 100% renewable power can theoret-
CO2 as byproduct of the reaction. ically reduce the emissions of the DRI shaft process
itself to zero (Table 2). Electrolyzers are also of inter-
Fe2O3 + 6CO = 2Fe + 3CO + 3CO2 + 26.6 kJ est for blast furnaces: the hydrogen can be injected in
the tuyeres to replace coal and the oxygen can be used
(Eq. 1) for oxygen enrichment of the hot blast (Fig. 7).
Fe2O3 + 6H2 = 2Fe + 3H2 + 2H2O – 99.5 kJ The Thermodynamics of Iron Ore Reduction With
Hydrogen: Even when industrial experience with
(Eq. 2) hydrogen to reduce iron ore is limited, the potential
impact on the reduction process of the ore is well
H2 + O2 = H2O + 240 kJ understood. Over the last century, more than 20,000
papers have been published, from which 20% focused
(Eq. 3) on iron ore reduction with CO and 5% specifically
studied the reduction of iron ore with H2.
The need for high temperature is responsible for Thermodynamically, the differences between CO
35% of the CO2 emissions in the BF and 33% in DRI. and hydrogen reduction are explained in the Baur-
Burning hydrogen instead of coal or natural gas for Glassner diagram (Fig. 8). From the point of view
heat is a second opportunity to use hydrogen (Eq. 3). of gas utilization, hydrogen is the best reduction gas
Although this looks easy to do, there is very little with high temperatures (>850°C) as the reduction is
practical experience. The only commercial appli- still ongoing even with >30% H2O in the reduction
cation so far was in Trinidad (Circored) where gas. However, for lower temperatures (650°C), CO gas
DRI was produced with hydrogen from
steam methane reforming in fluidized
bed reactors.4 The DRI production was
not emitting CO2, but the production of
hydrogen was CO2 intensive. The total
need of 84 kg hydrogen per ton steel
resulted in 29% higher emissions versus
the natural gas–based DRI process (Table
2). The higher emissions combined with
technical issues stopped the project and
the hydrogen-based DRI production was
never further industrialized.
In recent years, using hydrogen for
steelmaking has regained attention as
a way to reduce GHG emissions. The
steam methane reformer (SMR) can be
combined with carbon capture and stor-
age (CCS) to produce the so-called blue
hydrogen, or even better the hydrogen
can be produced with water electroly-
sis based on carbon-free power sourc-
es, green hydrogen. Green hydrogen Fig. 7 Integration electrolyzers in steel plants allow for the use of both
hydrogen and oxygen.5
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Hydrogen from Hydrogen from
steam methane reformer SMR + carbon capture Green hydrogen with
DRI fuel Natural gas (SMR)-based DRI and storage (CCS) (89%) renewable power
Fuel per ton DRI 10.5 GJ/ton DRI 84 kg/ton DRI 84 kg/ton DRI 84 kg/ton DRI
CO2 per unit 59 kg/GJ natural gas 9.5 kg/kg hydrogen 1.05 kg/kg H2 0 kg/kg H2
CO2 per ton DRI 620 kg/ton DRI 798 kg/ton DRI 88 kg/ton DRI 0 kg/ton DRI
% vs. natural gas 129% 15% 0%
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Table 2 T
heoretical Consumption of Hydrogen and Related CO2 Emissions in the DRI Shaft Process
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Number of
Search terms papers
Iron (oxide or ore) reduction 20,230
Iron (oxide or ore) reduction CO 3,692
Iron (oxide or ore) reduction H2 109
Iron (oxide or ore) mechanisms 792
Iron (oxide or ore) reduction kinetics 741
Table 3 P
ublications on the Reduction of Iron Oxides From
1900 to 20206
is consumed up to 50% CO2 in the mixture, where Fig. 8 T
he Baur-Glässner diagram for H2 reduction (Fe-O-H2
the hydrogen reduction stops at 25% H2O. From the system – dotted lines) and the CO reduction (Fe-O-C
enthalpy point of view, Eqs. 1 and 2 show that hydro- system – solid lines) as a function of the % H2O and
gen reduction is endothermic (thus is cooling the CO2 in the reduction gas (gas oxidation degree = 0
means 100% H2 or 100% CO).7
burden) while carbon monoxide is exothermic and
helps to keep the burden at temperature.
Hydrogen Injection in Existing BF and DRI Plants: consumption of 34.5 million tons/year. When all the
The preceding text explains why injection H2 in the hydrogen is green, a significant CO2 reduction of 400
existing BF or DRI process is possible without major million tons/year is possible.
adaptations up to a certain threshold. Modern blast
furnaces are equipped with gas and coal injection The Constraints to Move to Full Hydrogen
systems at the tuyeres and have experience with inject- Steelmaking: A logical next step could be to move
ing hydrogen-rich coke gas. Injection of pre-heated to the full hydrogen way by replacing all the natural
natural gas to 320°C is possible up to 140 kg/ton hot gas in the DRI shaft process. In Europe, the HYBRIT
metal.8 Modeling the injection of pre-heated hydro- consortium aims to demonstrate the full supply chain
gen shows that until 27.5 kg hydrogen injection per from power to hydrogen, including storage, iron ore
ton hot metal through the tuyeres is possible without pelletizing, reduction and steelmaking.37 Recently
major changes in the thermal balance of the blast also in Sweden, a second project was announced —
furnace.5 With an average scrap ratio in the BOF, this GreenH2Steel — to move quickly to a commercial
results in approximately 25 kg of hydrogen consump- phase.38 ArcelorMittal also announced a collaboration
tion per ton of steel and when the hydrogen is green,
CO2 is reduced with 300 kg/ton steel
(approximately 20%).
In the existing DRI shafts (both 25 kg/t H2 injection Blue hydrogen Green hydrogen
MIDREX and HYL based), up to 30% Steel production (billion tons) 1.38 1.38
of the natural gas can be replaced
H2 demand (million tons) 34.5 34.5
by hydrogen without major adapta-
tions. This results in 22.5 kg/ton DRI Greenhouse gas reduction (million tons) 358 402
or approximately 25 kg hydrogen Power Consumption (TWh) 1,725
consumption per ton of steel and Power Consumption (EJ) 6.2
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enables a CO2 reduction of 200 kg/
Full hydrogen steelmaking Blue hydrogen Green hydrogen
ton steel.
Steel production (billion tons) 1.38 1.38
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Based on the current experiences,
it can be concluded at both for the H2 demand (million tons) 115.9 115.9
existing BF/BOF plants as well as Greenhouse gas reduction (million tons) 358 402
for the DRI gas shaft plants, at least
Power Consumption (TWh) 5,796
25 kg/ton steel of hydrogen displace
coal and natural gas. For the 1.38 Power Consumption (EJ) 20.9
billion tons of steel produced in Table 4 Demand for Hydrogen, CCS, Renewable Power in Case of 25 kg H2
2018 with hot metal and gas-based Injection and in Case of Full Hydrogen Steelmaking Simulated for Steel
DRI, this would lead to a hydrogen Production in 2018
54
together with MIDREX to build a 100,000-ton DRI scenarios (Fig. 9). The Net Zero by 2050 scenario
pilot plant that can run on 100% hydrogen.9 of the International Energy Agency (IEA)11 shows
However, a number of constraints need to be con- a potential power production from wind and solar
sidered when moving to full hydrogen steelmaking: of 110 EJ (Fig. 9). Full green hydrogen steelmaking
would thus consume 20% of all solar and wind energy
1. Green Hydrogen Supply Challenge for the Full worldwide. In that case it would not be available for
Hydrogen Pathway: The potential consumption of other sectors and applications.
34.5 million tons of hydrogen in existing BF and DRI The IEA’s Net Zero by 2050 scenario itself projects
plants is comparable to the global refining industry approximately 35 million tons of hydrogen consump-
(38.2 million tons) or global ammonia production tion in the iron and steel sector (Fig. 10). This figure
(31.5 million tons).10 It is 45% of the current annual matches the 25 kg/ton hydrogen injection possible
hydrogen consumption and all this hydrogen produc- without adapting the BF and DRI plants. Hydrogen
tion must be blue or green. In the case of green hydro- supply in 2050 will still be limited and insufficient to
gen, 402 million tons of CO2 would be avoided, but it justify a complete rebuild of the steelmaking assets for
creates an annual demand of 1,725 TWh or 6.2 EJ per the full hydrogen pathway.
year of renewable power (Table 4).
Moving to full hydrogen increases the demand 2. Technological Challenges for Full Hydrogen
to 115.9 million tons or three times the current Pathway Related to the Ironmaking Assets: Moving
demand for the global refining industry. 20.9 EJ of to full hydrogen steelmaking is for sure not possible
renewable power would be required, which needs to with the blast furnace process. Metallurgical coal
be put into the perspective of long-term zero-carbon plays a key role in creating the permeability for reduc-
tion gas and to create a high-temperature
melting zone. The current assets would
need to be rebuilt by gas-based DRI assets,
which need to be redesigned, as in the
current processes CO is playing a key
role. In-depth research on the impact of
H2/CO ratio in a DRI shaft was done in
the ULCOS project. Experimental results
show an important impact on the metalli-
zation of the DRI with increasing H2/CO
ration (Fig. 11). The lower metallization
is due to the thermal gradient caused
by the endothermic hydrogen reduction
(lower temperature at the center) com-
bined with slower reduction kinetics at
lower temperature. To keep the current
Fig. 9 The global total final energy consumption by fuel in the net-zero
scenario of the International Energy Agency (IEA) (hydrogen-based metallization degree, the productivity
includes hydrogen, ammonia and synthetic fuels). 11 of the shaft needs to come down. New
designs will be required to overcome
these problems for full H2 reduction.
In the cooling zone, natural gas is
injected, which results in a minimum
1.5% up to 4% carbon in the DRI. Cooling
by nitrogen will require a new concept
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for the evacuation zone. The tightness
between the cooling zone and reactor
will be crucial in order to avoid nitrogen
buildup in the reactor.
To avoid sticking and powdering in the
shaft, the selection of raw material will be
more strict, putting pressure on the sup-
ply of pellets (Fig. 12). Interesting, there-
fore, is the announcement by Primetals
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Fig. 10 Hydrogen and hydrogen derived fuels in the Net Zero by 2050 Technologies, which is restarting the
scenario of IEA.11 R&D for a hydrogen-based reduction
55
Fig. 11 M
etallization degree of DRI as function of the
temperature and H/CO ratio as tested in the ULCOS
research program.12
plant with fines and with fluidized bed reactors to
overcome those problems.14
3. Technological Challenges for Full Fig. 12 Challenges with sticking and powdering in full
Hydrogen Pathway Related to the hydrogen DRI shaft will put pressure on raw material
Steelmaking Assets: Moving to hydrogen- supply.13
based ironmaking will have a major impact on steel-
making assets. The average heat size of EAF today
is relatively small as the EAF is feeding casters for
long products or casting–strip rolling plants (Fig. 13). will lead to a high FeO content in the slag and thus
When steelmakers want to keep the high productivity important yield losses. For that reason, steelmakers
of secondary metallurgy and continuous slab casting, are moving to 4% carbon in the DRI. When starting
heat sizes above 300 tons with tap-to-tap times below from zero-carbon DRI, the existing EAF design will
40 minutes are required. This is a challenge for both require a significant amount of carbon and oxygen
the electrical transformer as well as for the EAF equip- injection to create a protective atmosphere, a foaming
ment itself as a specific power consumption above 600 slag and keeping the Fe losses under control. In the
kWh/ton steel is expected. HYBRIT project, bio-carbon would be injected in the
For high-quality-grade steel, nitrogen pickup from bath for that purpose. However, the yield of the car-
the air during the process will be needed. The lower bon injection in EAF can be problematic.
metallization and zero carbon content of the DRI
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(a) (b)
Fig. 13 Average heat size for current EAF plants (a) and specific power consumption as function of the charge (b).15
56
voestalpine is
announcing the
development of
hydrogen plasma
melting reduction
to overcome the
a forement ioned
problems.39 A hydro-
gen plasma would
be used to directly
move to steel in a
type of electric arc
reduction/melting
furnace. However,
this development is
still at low technolo- ensitivity of Hydrogen cost in 2030 in the IEA Net Zero 2050 scenario.11 Renewable power
Fig. 14 S
cost US$40/MWh, full load hours at best locations.
gy readiness level.
Interesting is the
announcement from thyssenkrupp Steel Europe to
develop an electrical hot metal production unit.16
The idea is to melt the DRI from a shaft furnace in
an adapted submerged-arc furnace where carbon is
added to reach a 4% carbon alloyed hot metal. This
hot metal can go to the existing BOF plants and slab
casters. As 4% carbon is required in the “liquid DRI,”
this innovation fits well with the approach to inject 25
kg hydrogen in DRI shaft, but is less suited for a full
hydrogen pathway.
4. Economical Challenges for the Full Hydrogen
Pathway: Probably the largest challenge is economic,
Fig. 15 Energy density of gaseous and liquid fuels.17
which can be expressed in the CO2 abatement cost.
CO2 abatement cost is the break-even price needed to
make green hydrogen-based process break even with
the current processes.
The production of hydrogen from water electrol- 44% of the hydrogen would be consumed. In this case,
ysis requires 50–55 kWh/kg hydrogen. The power the total hydrogen cost for the steelmaker increases
consumption is responsible for approximately 80% to US$4.32/kg but this is still lower versus the on-site
of the hydrogen cost. The IEA predicts a 2030 hydro- hydrogen cost of US$5/kg as projected by IEA. The
gen cost of US$3/kg in the case of off-side hydrogen CO2 abatement cost in case of 25 kg hydrogen injec-
generation with low-cost renewable power from wind tion per ton of steel in the existing blast furnace is
and solar PV, while US$5/kg is expected for on-site US$342 where US$474 is found for the DRI case
grid-connected hydrogen generation (Fig. 14). (Table 5).
In the case of off-side hydrogen generation, addi- Those levels are significantly above the project-
tional costs for transport of hydrogen to the steel ed CO2 prices for 2050 (Table 6). Moving to full
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plant and temporary storage are required to deal with hydrogen steelmaking will only further increase this
fluctuations in the variable renewable power produc- number as additional capital costs will be required
tion. Hydrogen is known for its low energy density per to rebuild the existing assets. As three times more
liter, which explains why more energy is required for hydrogen would be required, it is likely that hydrogen
the compression or the liquefaction for transport and will need to be transported over longer distances and
storage compared to other energy carriers (Fig. 15). become more expensive.
According to Bossel, approximately 10% of the
hydrogen is consumed per 1,000 km pipeline and 40%
of the hydrogen energy is consumed to liquefy and Electrification of High-Temperature Heat
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store the hydrogen. When we assume 2,000 km trans- With Zero-Carbon Power — Hydrogen will play
port on average and storage of 60% of the hydrogen, an important role in carbon-neutral steelmaking as
57
Per ton steel 25kg injection in BF 25kg injection in DRI
Off-side H2 generation from renewables (US$/kg) US$3.00 US$3.00
H2 consumption for transport, temporary storage 44% 44%
Total cost of Hydrogen (US$/kg) US$4.32 US$4.32
Green H2 cost (US$/ton steel) US$113 US$113
Savings in coal and gas cost (US$/ton steel) US$10 US$20
CO2 abatement (kg/ton steel) 300 195
CO2 abatement cost (US$/ton CO2) US$342 US$474
Table 5 CO2 Abatement Cost of 25 kg/ton Steel Hydrogen Injection in Existing BF and DRI Plants
USD (2019) per metric ton of CO2 2025 2030 2040 2050
Advanced economies 75 130 205 250
Selected emerging market and developing economies 45 90 160 200
Other emerging market and developing economies 3 15 35 55
Table 6 C
O2 Price Evolution in the Net-Zero-Carbon Scenario According to IEA (Selected Emerging Markets Include China, Russia,
Brazil and South Africa)11
injected gas in existing BF and DRI plants. However, superheat the hot blast of the blast furnace. Plasma
banning carbon and moving to full hydrogen is is an ionized state of gas containing free charge car-
extremely challenging in relation to supply, econom- riers and therefore is electrically conductive. In the
ics and process technology. To reach carbon neutrali- thermal plasma, temperatures of 1,000 K and above
ty, steelmakers need to combine in a smart way the use are reached, which results in very fast and efficient
of hydrogen, zero-carbon power and carbon. thermal conversion without any catalyst. Plasma torch-
The need for high-temperature heat is responsi- es up to 2.4 MW are commercially available to replace
ble for 35%, resp. 33% of the CO2 emissions in the fossil fuel burners and have electrical efficiencies
current BF, resp. DRI plants (Fig. 4). Technology above 85%.19 In the course of the ULCOS project,
exists to directly electrify the generation of high- the integration of 2 MW torches into the tuyeres of a
temperature heat instead of indirectly working with large blast furnace was studied (Fig. 16). Power con-
green hydrogen. As the conversion of power to hydro- sumption is approximately 250 kWh/ton hot metal
gen and hydrogen to heat has a yield of below 50%, (or 0.9 GJ), which is significantly below the current
it is smarter and cheaper to directly use power for consumption in the hot stoves and 220 kg/ton hot
heating. metal CO2 emission is avoided by not burning blast
furnace gas.
Plasma Torch Applications to Generate High- Once the plasma torches are integrated in the
Temperature Heat: An attractive technology for tuyeres, superheating of the hot blast can be consid-
steelmakers is for plasma torches to heat up and to ered as there is no constraint anymore due to the
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(a) (b)
Fig. 16 Plasma torches integrated in the tuyeres of a blast furnace to heat up the hot blast.20
58
CH4 + CO2 = 2CO + 2H2 – 247 kJ
(Eq. 5)
CH4 + H2O = CO + 3H2 – 208 kJ
(Eq. 6)
In dry CO2 reforming, CO2 is used instead of steam
to produce a syngas from methane. The reaction is
also endothermic and the energy penalty compared
to the steam methane reforming is limited (approx-
Fig. 17 R
eduction of fuel rate and CO2 in the blast furnace imately 20%). Thanks to the high temperature gen-
when superheating the hot blast with plasma torches.21 erated in a plasma (>1,000 K), the dry reforming
reaction is fast and complete without any catalyst. The
plasma system is flexible to follow a fluctuating sup-
ply of renewable power. The high temperature of the
refractory of the hot blast main. Fig. 17 shows the syngas in the plasma makes it compatible with direct
impact on the CO2 generated in the blast furnace injection in the DRI shaft.
when the hot air is superheated up to 1,800°C. The For a DRI plant, approximately 1 MWh per ton DRI
coke rate is reduced to the minimum theoretical will be required for the reforming and heating of the
amount needed for iron carburization and burden reductant gas without changing the DRI shaft process
support. The flame temperature and top gas tempera-
ture are kept constant. Significantly higher pulver-
ized coal injection (PCI) and productivity of the BF
are possible without further oxygen consumption. For
a typical medium-sized 6,000-tons-per-day BF, 28 MW
of power is consumed, which is less than 1 MW per
tuyere. This potentially reduces the CO2 generation
by 270 kg/ton.
Plasma Torches for Methane Cracking and Dry Fig. 18 P
lasma heating and reforming of hot syngas for
Reforming of CO2 : Another way to electrify is to use injection in the BF or in the DRI shaft.20
plasma to replace the reformer/heater in the DRI
shaft. Today plasma torches are commercially used
for methane cracking.
CH4 = C + 2H2 – 74.5 kJ
(Eq. 4)
Methane cracking or pyrolysis is the chemical split-
ting of hydrocarbons into hydrogen and solid carbon
(Eq. 4). The gaseous hydrogen and solid carbon are
produced (no CO or CO2 is produced as no oxygen
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is entering the system). The most prominent example
is Monolith Materials, which is operating a 16-MW
plasma to produce carbon black with hydrogen as
a byproduct. Steelmakers can use the hydrogen for
injection in BF or DRI and the solid carbon to dis-
place coal for cokemaking and PCI.
Using plasma torch for dry methane reforming has
been developed in the course of ULCOS (Eq. 5). Dry
reforming is comparable to the traditional and well-
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known steam methane reforming (Eq. 6). Fig. 19 IGAR Blast Furnace concept with shaft injection at
950°C.959
plasma technology is mainly used today
in the waste sector to clean gases from
waste gasifiers. Municipal waste is gas-
ified in fluidized bed reactors of 160
MW or more. After cleaning the gas for
chlorine, it can be used to reform CO2
in the plasma torch and produce a sta-
ble CO:H2 syngas for injection.
Using Waste Streams for Biocoal
Injection in BF and EAF: Direct plastic
injection in the tuyeres of a blast fur-
nace or the use of charcoal in the EAF
Fig. 20 Process scheme and yield for torrefaction process of wood. are other examples of waste sources
used as alternative reductants. In Brazil,
several smaller BFs are even running
on 100% charcoal produced from euca-
itself. It avoids the generation of 220 kg CO2 due to lyptus. The low mechanical resistance
the current combustion of DRI top gas (Fig. 18). and limited supply of fresh wood do not allow for
By a moderate adaptation of the existing BF, shaft the replacement of coke in large blast furnaces, but
injection of reformed gas is possible at 950°C (Fig. 19). this is not the case for the coal injection. Indeed the
ArcelorMittal is developing this hybrid BF-DRI process carbon sourced into state-of-the-art blast furnaces
in the IGAR project in Dunkerque.9 Approximately accounts for nearly 50% of the injected grinded coal.
100 kg of cokes and coal input can be replaced by hot Waste wood can be an excellent substitute for coal
syngas shaft injection without major changes in the injection after a torrefaction treatment of the wood.
operating point of the blast furnace. Torrefaction occurs when biomass is heated at 250–
300°C in the absence of oxygen, where charcoal is
produced by a slow pyrolysis process at temperatures
Alternative Carbon Reductants as a Third of 400°C or more. Thanks to the lower temperature,
Step the yield is significantly better compared to charcoal
(Fig. 20).
Gasification of Waste to Replace Natural Gas: The Research has shown that torrefied wood, with dif-
use of plasma reforming for DRI and BFI is compatible ferent ash content and different temperature treat-
with using waste hydrocarbons instead of natural gas. ments, combusts faster than fossil coal (Fig. 21). The
Plasma reforming is done at very high temperature reason is the greater specific surface of biocoal thanks
without catalyst. An advantage is that no purification to the cellular structure of the wood.
of the methane or CO2 is required. For this reason,
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I IRON & STEEL TECHNOLOGY I AIST.ORG
Fig. 22 T
orrefaction of waste wood in a rotating drum as
developed by TorrCoal.40
Fig. 21 C
ombustion rate of different types of biocoal and
pulverized coal injection coal during injection in the BF.2760
A demonstrated technology for large-scale torre-
faction of waste wood is the external heated rotating CCU Technology to Close the Carbon Circle
drum as is commercialized by Torrcoal (Fig. 22). In and Create Value — The consequence of the
the TORERO project, ArcelorMittal is building a first described electrification is an increase of the amount
torrefaction plant for 100,000 tons of biocoal injection of available steel waste gas, which will be more and
in the BF which will start in 2022.9 more produced from waste carbon but which eventu-
ally still is converted into CO2 as long as the exported
Supply Constraint for Waste Wood and Waste waste gas is burned in a power plant. It does not make
Plastic: As is the case for green hydrogen, the injec- sense to first electrify the heat supply instead but as a
tion of biocoal and use of plastic waste will rather consequence export the surplus waste gas to a power
be constraint by the supply and not due to technical plant to generate power.
limitations to adapt the existing DRI and BF plants. Fig. 23 illustrates the impact of electrification of
In Europe, approximately 100 kg wood waste per the external heater/reformer as is used in the Midrex
capita of 52.9 million tons is generated by end-of-life DRI Shaft. There are no changes for the inputs and
products from which 25–30% come from the demoli- outputs of the DRI process itself. However, where
tion and construction market. Only 15% of this waste today with the thermal heater/reformer approximate-
is recycled.28 By closing the coal-fired power plants, ly 4 GJ of syngas is incinerated to supply the heat, this
waste wood becomes more and more available for is replaced by 1 MWh power supply to the plasma
other purposes. reactor and thus creating 4 GJ of syngas which needs
In 2018, 367 million tons of plastics were produced. to be exported. Another example is the electrification
Approximately 9% of end-of-life plastics are recy- of the hot blast of the BF: approximately 1.5 GJ per
cled and 12% are incinerated. The remaining 80% ton hot metal of steel waste gas will be replaced by
(approximately 280 million tons per year) is polluting 0.25 MWh of power.
the environment. One-third of plastics are produced The steel sector is probably the largest producer of
in China, and 15% are produced in Europe (55 mil- syngas. Globally, the steel sector generates approxi-
lion tons). mately 7,000 terajoules of syngas. This is comparable
Substitution of 50 kg of PCI with waste wood and 3 to the total natural gas consumption of Germany and
GJ of gas with plastic waste gasification at European Italy, the two largest economies in Europe.
steel plants results in a demand of approximately 10 Syngas is produced on purpose in the chemical
million tons waste wood and 11 million tons of plastics sector as the first step to produce CO and H2 for the
(approximately 20% of supply for both waste streams). production of hydrocarbons. As the steel waste gas is
Such a scale of waste recycling is feasible both from already available as CO and H2, little or no cracking
technology as from supply point of view, and will and reforming need to be done in order to use it
create significant value for society and reduce CO2 as feedstock for chemicals. Carbon capture and use
emissions by 350 kg/ton crude steel. (CCU) technologies are bringing new options to con-
vert waste gas into products and
avoid the incineration of gas in a
power plant.
In 2015, thyssenkrupp Steel
Europe launched a large pro-
gram, Carbon2Chem, to convert
syngas into chemicals.23 Tata
Steel and ArcelorMittal are study-
ing the same approach in the
Steel2Chemicals project.24 The
I IRON & STEEL TECHNOLOGY I AIST.ORG
major challenge, however, is to
clean the steel waste gas up to
levels at which catalysts are not
poisoned. On top the CO:H2
ratio needs to be shifted to the
right amount with the water gas
shift reaction which is consuming
energy.
A promising approach is the
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Fig. 23 T
raditional process scheme (left) and scheme after electrification (right) of gas fermentation technology as
DRI/EAF plant. developed by Lanzatech. In con-
trast to the traditional catalytic61
(a) (b)
Fig. 24 Gasfermentation of carbon-containing waste gas into microbes.
chemistry, a fermentation by microbes is used to con-
vert CO and hydrogen into products. The fermenta-
tion can be compared with the fermentation of sugar
from corn or sugarcane into ethanol by yeast. In the
gas fermentation, the gas is pressurized and injected
into water tanks with microbes. The microbes are
directly consuming CO and H2 to produce ethanol
(C2H5OH) which is continuously distillated out of the
broth (Fig. 24).
The main advantage is the compatibility and flex-
ibility of the gas fermentation with DRI and BF gas:
Fig. 25 C
onstruction of the Steelanol plant at ArcelorMittal
» The microbe is driven by CO and H2. In case
Gent.26
there is a lack of H2, the microbe will itself
perform the water shift reaction by picking up
hydrogen from the water.
» The microbe is adapted to the typical DRI and steel. Further processing of the ethanol into 120 kg
BF atmosphere. Very little or no cleaning is ethylene per ton steel is straightforward with existing
necessary. technology. Applying this to the European market as
» The gases do not need to be pure. The pres- a business case, the steel sector can supply 12 million
ence of CO2 and nitrogen will not impact the tons of ethylene to the chemical sector, avoiding 24
fermentation process as such and does not need million tons of CO2. This is approximately 50% of the
to be removed. current ethylene market of Europe. Fig. 26 illustrates
» The energy conservation of the bio-based sys- a number of potential markets for Ethanol in 2030,
tem is very high: approximately 70% of the which is 25 times larger compared to the current
energy is converted into alcohol, while the application to blend ethanol in the gasoline.
other 30% is converted into biomass. This bio- By combining the recycling of waste wood and plas-
mass can be fermented into biogas or can also tics into the DRI and BF process with the conversion
be used as animal feed. of the steel waste gas into ethanol and chemicals, the
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» By changing the microbes, different chemicals steel sector is an enabler of the circular economy by
can be made and other markets can be reached. converting waste into products at large scale.
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The Lanzatech technology was first used at com-
mercial scale at Shougang steel where the plant Waste Heat Enables Low-Cost Carbon
started in 2018. Currently a large investment with Capture and Export (CCE) of CO2 — The
ArcelorMittal is close to commissioning and will start remaining CO2 emissions (approximately 200 kg/ton)
up in 2022 (Fig. 25). are mainly from biological origin or from carbon in
When applied at full scale and using all the steel the plastic waste. Capturing this CO2 for transport
waste gas, a yield of 200 kg of alcohol per ton of steel and storage (CCS) is straightforward and can result
is possible, avoiding 400 kg/ton CO2 per ton of crude62
Fig. 26 Potential demand for ethanol (in billion liters) in the EU market is 25 times larger compared to the blending into gasoline.25
even in negative CO2 emissions: the so-called BECCS plant is under construction at ArcelorMittal in the
(bio-energy with CCS). course of the 3D-CCUS project (Fig. 26).
In-situ capture of CO2 in the BF and DRI plant can Opex cost for capture and liquefaction of CO2 with
be done at a low cost by using waste heat from the waste heat will be in the range of US$10–20/ton CO2.
steelmaking process. Novel approaches with amine Liquid CO2 can be shipped over long distances with
washing allows for the capture of 99% of the CO2 with the same technology that is used for liquefied natural
approximately 2.3 GJ/ton CO2 of low-pressure steam, gas (LNG). Shipping costs on the base of 1 million
which is recovered at the steel plant.31 A first pilot tons of CO2 per year over 1,000 km distance are in the
range of US$10–15/ton33 depending on the size of the
ships, resulting in overall cost for carbon capture and
export (CCE) below US$50/ton CO2.
In a net-zero world, industrial regions with high
concentrations of chemical and steel plants will
need to import renewable power over long distances.
Fig. 27 shows the long-term gap between potential of
renewable energy generation versus renewable energy
needs for West Europe. Northern France, Belgium,
Netherlands and west Germany up to northern Italy
are lacking up to 1,000 TWh in total.
New specializations will be created in the global
net-zero economy. Renewable power generated in
regions with abundant sun need to be converted to a
I IRON & STEEL TECHNOLOGY I AIST.ORG
liquid energy carrier to transport the cheap energy to
the industrial regions.
Fig. 28 shows the result of a study where the import
of renewable energy from four regions to Zeebrugge
(Belgium) was studied with liquid hydrogen, liquid
methane (LNG) and methanol as carriers. Methanol
offers the most attractive case but requires CO2 to
convert the hydrogen from PV into methanol. This
opens new opportunities to use CO2 : as stockfeed to
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Fig. 27 CO2 capture unit under construction at the blast make methanol with low-cost renewables.
furnace of ArcelorMittal Dunkerque.3163
Conclusions
The Smart Carbon Pathway — In this paper, five
key enabling technologies to move to carbon neutral-
ity have been reviewed in detail with a focus on the
constraints to scale up each solution. All five technolo-
gies can be integrated with the BF/BOF plants as with
the DRI/EAF plants with only minor adaptations to
the existing processes. The fossil inputs (coal and nat-
ural gas) are replaced by renewable power, cellulosic
waste and recycled polymers. CCU and CCE allows to
convert the carbon-containing steel waste gas into eth-
anol and methanol. Biogenic CO2 can be combined
with CCS to realize even negative emissions (BECCS
as a sixth key enabling technology).
As a result, the initial CO2 emissions of 1,600 kg for
BF plants and 1,100 kg for DRI plants in the future
net-zero-power world, is stepwise reduced to zero
(Fig. 29).
» The renewable power allows to electrify the
high-temperature heat generation.
» Renewable power is converted into 25 kg green
Fig. 28 B
alance of renewable power potential versus demand
(including hydrogen) per region in EU.34
hydrogen for injection in BF and DRI plants.
» The cellulosic biowaste is converted into biocoal
for the BF and the EAF.
» The recycled polymers are gasified in order to
With a CO2 captured and exported at a cost below reform with CO2 into a syngas.
US$50/ton, the cost of green methanol is even below » The waste gas of the DRI and BF plant is con-
the current fossil methanol cost. This illustrates verted into high-value molecules with biological
again the issue with hydrogen: it requires less energy gasfermentation.
to convert hydrogen in methanol and transport the » The remaining fossil CO2 is captured, liquefied
methanol compared to liquefy and transporting the and exported at low cost and imported again as
hydrogen itself. The methanol can be supplied to the green methanol produced with low-cost photo-
chemical sector or can be reformed back to syngas voltaic power.
and used in DRI or BF shaft injection.35
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I IRON & STEEL TECHNOLOGY I AIST.ORG
Fig. 29 A
verage levelized cost of hydrogen (H2), methane (CH4 ) and methanol (CH3OH) in Zeebrugge (B), produced in Chile, Oman,
Australia, Morocco from renewables (as function of cost of CO2: EUR160/ton, EUR80/ton and EUR40/ton).3464
» The biological CO2 from cellulosic biomass and the hydrogen narrative, which are competing
waste can also be captured for BECCS (negative with each other (point A and B in Fig. 30).
carbon emissions). The CCS narrative was at the base of the ULCOS
project in 2005 in Europe. It states that carbon is a
The key enabling technologies (KETs) as integrated mandatory resource, and that steelmaking always will
in Fig. 29 have a number of elements in common. produce a lot of CO2. Large-scale CCS integration is
enabling to move to carbon neutrality at the lowest
» All technologies exist at commercial scale or cost. It allows to continue to current infrastructure
are currently in demonstration. and keep the jobs. In this way, CCS is promoted as a
» All technologies can be stepwise integrated contributor to the “Just Transition.”41
with both BF and DRI plants. More recently, the hydrogen narrative was launched.
» Each KET can be deployed in parallel. There is It promotes the radical change away from carbon to
no risk for carbon lock-in by starting with one hydrogen produced with renewables. Although the
technology. On the contrary, the combination costs of the transition are very high in case only
of 2 KET is creating additional synergy gains renewables are considered, it is believed that banning
which will accelerate the deployment. carbon feedstock is the most desirable abatement
» All technologies are scaled related to realistic option.
supply constraints. Both narratives however have the same issues: lack
of robustness and increasing costs with scaling up.
There are beliefs in a deterministic world with only
A New Narrative for Carbon-Neutral Steel- one endgame (e.g., “continue storage of fossil CO2”;
making — Until now, two narratives for carbon- “green hydrogen economy”). There is no flexibility to
neutral steelmaking were launched: the CCS narrative adapt the path for future “black swans.” An example
is the belief in hydrogen fuel cells for future transport
I IRON & STEEL TECHNOLOGY I AIST.ORG
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Fig. 30 Integrating five key enabling technologies allows to move existing BF and DRI plants to move to carbon neutral.65
Fig. 31 T
he traditional CCS (point A) and Hydrogen (point B) narratives result in high cost and low flexibility (thus risks). The novel
Smart carbon narrative is flexible and combines five strategies at their lowest cost point.
until recently the battery technology popped up as a recently in the U.S., no significant progress was made
game changer. One clear black swan that occurred related to CCS.
after the ULCOS project is the gasfermentation of The same risks happen with the hydrogen narrative.
steel waste gas, which suddenly makes large-scale The EU is allocating massive amounts of money to
CCU possible. support the initial investments in hydrogen, but this
Both narratives are suffering from the law of will be not enough. Limited potential to deploy locally
diminishing returns. This means that the first abate- renewable power will result in high costs. All experts
ment steps can be relatively cheap, but the larger the believe that the hydrogen narrative will be more cost-
deployment, the higher the costs and the lower the ly compared to the CCS narrative and will require
returns. Green hydrogen production on-site for flex- financial support during decades. The result is loss
ible injection can be relatively cheap for the first 50 of competitiveness and jobs and higher contributions
or 100 MW, but in order to run 3-GW electrolyzers from taxpayers (directly through taxes or indirect-
24/7 with renewable power, long-distance transport ly through contract for differences, carbon border
of power and hydrogen with intermediate (seasonal) adjustments, etc.). The lack of justness risks creating
storage will be required. The same is true for CCS: a resistance against the whole climate transition plan.
fraction of the CO2 can be captured at a low cost and The two conflicting narratives are paralyzing the
can be stored or used locally. But 100% capture of climate actions in the steel industry and are block-
all CO2 and storage during decades will result in an ing the necessary investments to move to carbon
exponential increase of the marginal storage costs. neutrality.
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Although IPCC confirms that without CCS the CO2 Steelmakers need to develop a new, compelling
abatement costs, 2015–2100 will be 138% higher ver- narrative based on the Smart Carbon pathway (point
I IRON & STEEL TECHNOLOGY I AIST.ORG
sus solutions with CCS,41 CCS never got the necessary C in Fig. 30). The steel sector can be at the center of
incentives and political will due to the two aforemen- the future ecosystem guided by values as zero waste,
tioned reasons. The lack of flexibility created the fear cradle to cradle and high returns thanks to optimal
that supporting CCS would lead to carbon lock-in specialization. The optimum is not only carbon or
(for example by keeping the coal-fired power plants). only hydrogen, but the combination of both. This
Financing CCS risked making the deployment of results in lower costs for CO2 capture (the red curve),
renewable power more expensive and thus policymak- more flexibility to support variable renewables, higher
ers feared to have to pay twice. Since 2005, except added value thanks to the production of chemicals,66
higher return to society by promoting circular econo- 8. T. Okosun et al., “On the Impacts of Pre-Heated Natural Gas
Injection in Blast Furnaces,” Processes 2020, Vol. 8, p. 771.
my and job creation.
9. ArcelorMittal, Carbon Action Report 1, June 2019.
10. IEA, “The Future of Hydrogen,” 2019.
Summary 11. IEA, “Net Zero by 2050,” 2021.
12. F. Patisson et al., “Hydrogen Ironmaking: How It Works,”
Metals, Vol. 10, 2020, p. 922.
This article gave an overview of the challenges and 13. Nippon Steel Carbon Neutral Vision 205, “A Challenge of
opportunities to transform the steel sector to car- Zero Carbon Steel,” March 2021.
bon neutrality. The main technological steps were 14. Primetals Technologies press release, London, U.K., June
described and the constraints for implementation in 2019.
a 2050 carbon-neutral world were identified. 15. J. Madias et al., “The Influence of Metallics and EAF Design,”
Steel Times International, December 2017.
Starting from the traditional and conflicting nar-
16. thyssenkrupp press release, Düsseldorf, Germany, August
ratives for carbon neutral steelmaking, which are 2020.
the CCS narrative and the hydrogen narrative, it 17. U. Bossel et al., “Energy and the Hydrogen Economy.”
was shown that steelmakers need to develop the new 18. S. Timmerberg et al., “Hydrogen and Hydrogen-Derived
compelling the Smart Carbon based on a flexible Fuels Through Methane Decomposition of Natural Gas
combination of carbon and hydrogen inputs from – GHG Emissions and Costs,” Energy Conversion and
Management: X, Vol. 7, 2020.
renewables and from waste resources at the entry
19. Westinghouse Plasma Corp.
and production of high valuable chemicals with CCU
20. J. Borlée, “European Steel Industry Main Pathways Toward
(carbon capture and use), CCE (carbon capture and the Smart, Low Carbon Industry of the Future,” ESTEP
export) and BECCS (bio-energy CCS). Workshop, February 2018.
The Smart Carbon narrative will bring the steel 21. M. Sukhram, “The Use of Plasma Torches in Blast Furnace
sector at the center of the carbon-neutral ecosystem Ironmaking,” ECIC2016, Linz, Austria.
with a more “ just transition” which creates jobs and 22. Monolith Materials, https://monolithmaterials.com.
prosperity for our society. 23. http://www.thyssenkruppsteel.com.
24. ISPT.EU, S2C Steel2Chemicals projected.
25. C. De Maré, “Carbon Neutral Steelmaking at ArcelorMittal:
Acknowledgments A Key Enabler for the Circular Economy,” VARIO Colloquium,
December 2019.
26. http://www.steelanol.eu.
I would like to thank my friends who nominated me 27. K. Wing, et al., “Combustibility of Charcoal for Direct
and the AIST Awards and Recognition Committee to Injection in Blast Furnace Ironmaking,” CanmetENERGY,
give me the honor to present the 2021 Howe Memorial Canada.
Lecture. I am especially thankful to ArcelorMittal and 28. S. Nannoni, “Valorizing Wood Waste for Energy and Material
in Europe,” November 2019.
all colleagues who supported me during all those
29. http://www.torero.eu.
years to develop new solutions for one of the most
30. http://www.valmet.com.
challenging problems. I would also like to thank
31. “The Known Unknowns of Plastic Pollution,” The Economist,
the many business partners (suppliers, technology 3 March 2018.
providers, researchers, etc.) who contributed to the 32. http://www.3d-ccus.com.
developments described. Finally, a special thank-you 33. “Shipping CO2 — UK Cost Estimation Study,” Final Report
to Jennifer Holmgren for the inspiring journey we for BEIS, elementenergy, November 2018.
could walk together over the last 10 years. 34. “Shipping Sun and Wind to Belgium Is Key in Climate
Neutral Economy,” Hydrogen Import Coalition Final Report,
January 2021.
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I IRON & STEEL TECHNOLOGY I AIST.ORG
1. “Our World in Data,” https://ourworldindata.org. 36. M. Xylia et al., “Worldwide Resource Efficient Steel
2. Carl De Maré’s own analysis. Production,” KTH Stockholm, VITO Belgium.
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— A Review,” Steel Research International, Vol. 90, 2019.You can also read
