CO2 Emission Comparison between Coal-based Direct Reduction ...

International Symposium on Ironmaking for Sustainable Development, 28-29 January. 2010, Osaka, Japan
CO2 Emission Comparison between Coal-based Direct Reduction Process and
Conventional Blast Furnace Process
Kyoichiro FUJITA 1 , Takao HARADA 1 , Haruyasu MICHISHITA 1 and Hidetoshi TANAKA 2
1 Technology & Process Engineering Department, Technology Center, Iron Unit Division, Kobe Steel, LTD.
2 Iron Unit Division, Kobe Steel, LTD.
Abstract
In producing pig iron, the CO2 emissions from the
ITmk3 ® process are compared with those from conventional
blast furnace from the view point of LCA.
Also, in producing steel, the CO2 emissions from ITmk3-
EAF are compared with those from BF-BOF. Comparison
is made with the cases with scrap and without scrap usage.
Due to the significant CO2 reduction by higher scrap usage
ratio, steelmaking by EAF takes significant advantage of
CO2 emissions over BF-BOF, which can be enhanced by
the pure iron unit supplied by ITmk3.
Key words
Direct Reduction, ITmk3, Rotary Hearth Furnace,
Iron nuggets, EAF, carbon, CO2 emissions, global warming,
greenhouse gas
1. Introduction
World crude steel production has been increasing and
exceeded 1.3 billion tons in 2007. Although it slightly
decreased in 2008 due to the recession caused by the
financial crises originated in USA, sign of the recovery can
be observed in latter half of 2009. Furthermore considering
expectation of future increase of steel demand especially in
developing countries, it is expected that world crude steel
production will be steadily and continuously increased from
now on.
On the other hand, reduction of greenhouse gas emissions
including carbon dioxide (CO2) is being required worldwide
to prevent global warming. It was reported that industrial
output accounts for 21% of global CO2 emissions and steel
industry emits about 15% of emissions within the industrial
sector. 1) Therefore, diffusion of lower CO2 emission
steelmaking technologies will be necessary to achieve
sustainable steel industry in future.
The current mainstream ironmaking technology is the blast
furnace process which requires coke ovens and sintering
plants that consume a large amount of energy and place a
burden on the environment.
On the other hand, gas-based direct reduction processes
such as the MIDREX ® Process are one of the alternatives to
blast furnace ironmaking. The CO2 emissions from the
technologies are much less than those from BF. The locations
are, however, limited to where natural gas is economically
available.
On this background, demand is growing for new
ironmaking processes of following advantages.
-Lower production and capital cost
-Utilization of a wide variety of raw materials and fuels
-Lower energy consumption and environmental load
In response to this demand, the coal-based direct reduction
ironmaking process, ITmk3 (Ironmaking Technology mark
III), has been developed by Kobe Steel, LTD. The first
commercial plant is getting started its operation in USA.
In this paper, we estimate and compare the CO2 emissions
from ITmk3 and conventional blast furnace in the pig iron
producing process and the steel producing process.
2. Calculation basis of CO2 emissions from ITmk3
2.1 Process flow of ITmk3
Fig. 1 shows the process flow of the ITmk3 process. Iron
ore and coal are mixed and agglomerated by a pelletizer and
then the agglomerates are fed into a Rotary Hearth Furnace
(RHF) to be spread on the bed. In the RHF, the
agglomerates are heated up to approximately 1,450 degree
C. After reduction and melting, the iron and slag are
separated in the RHF. They are cooled and discharged as
the product of iron nuggets from the RHF. Iron nuggets
typically contain carbon of 2.5-3.0%, that is to say
equivalent to pig iron. Nearly all of the chemical energy of
the ingredient fossil fuel is consumed and no gas credit is
exported from the system. ITmk3 does not require coke
oven or sinter plant. Accordingly both of the energy
consumptions and the CO2 emissions can be lower in
comparison with blast furnace.
Fig. 1 Process flow of ITmk3
2.2 CO2 emissions from ITmk3
In this paper, the CO2 emissions from ITmk3 with iron
nuggets production capacity of 500,000 tpa (metric-ton) are
estimated, that is the present commercial standard capacity
and same as that of the first commercial plant in USA. The
CO2 emissions in case of producing steel are estimated
when electric arc furnace (EAF) uses only iron nuggets as
the feed material. Also the CO2 emissions are estimated
when EAF uses partially iron nuggets with scrap to dilute
tramp elements in the scrap. The calculation basis is
mentioned in this section, and the results are shown in and
after section 4.
Table 1 shows the typical unit consumptions of the
ITmk3 process. Most of fuels are consumed by burners of

International Symposium on Ironmaking for Sustainable Development, 28-29 January. 2010, Osaka, Japan
RHF. The heat of exhaust gas can be utilized to preheat
burner air and dryer air through the heat exchanger. A
steam boiler/turbine package is also applied to generate
electric power. For estimating the CO2 emissions derived
from coal and LNG, we referred to unit heat value and
carbon emission factor of various fuels as shown in Table 2
which was defined by Ministry of the Environment of Japan
in 2007 2) as a guideline to assess CO2 emissions.
Table 1 Unit consumptions of ITmk3 process
Consumption
[Unit/t-Ng*]
CO2 emission
[kg-CO2/t-Ng*]
Reductant Coal 500 kg 1,298
Others ** -
100
Fuel (LNG) 4.6 GJ 230
Total -
1,627
Power 200 kWh -
Recovery Power -250 kWh -
* “t-Ng” stands for “ton iron nuggets”.
** Additives such as limestone.
Power 3%
Preheated air
19%
Fuel gas
20%
Coal
58%
× Power generation efficiency
ITmk3
Heat recovery for
preheated air
19%
RHF offgas loss 8%
Pellet drying process 8%
Power for ITmk3
9%
Heat recovery for power generation
11%
Ironmaking process
44%
Nugget/Slag cooling 7%
Heat Loss 3%
Fig. 2 Energy Balance of ITmk3
Power for others
2%
The electric-power-related CO2 emissions and credits
vary depending on the countries where the plant is located,
therefore we referred to data of the Federation of electric
power companies of Japan for the case installed in Japan,
and referred to “energy balance of OECD countries in
2005-2006” for the case installed in other countries. Each
carbon emission factor is shown in Table 3.
Table 2 : Unit heat value and carbon emission factor of
various fuels
Unit C emission
heat value factor
[MJ/kg] [g-C/MJ]
M etallurgical Coal 28.9 24.5
Pulverized Coal 28.9 24.5
Coke 30.1 29.4
Heavy Oil - C 41.7 19.5
[MJ/Nm3] [g-C/MJ]
LNG 54.5 13.5
COG 21.1 11.0
BFG 3.41 26.6
LDG 8.41 38.4
Unit consumptions shown in Table 4 3) were used to
estimate the CO2 emissions from EAF steelmaking. Iron
nuggets contain carbon of typically 2.5-3.0%, so its
combustion heat can be used in EAF to save its power
consumption. Calculations in this paper were made with
2.5% carbon contained in iron nuggets.
Table 3 : Carbon emission factor of electric power
Country France Canada Japan Italy UK Germany USA
CO2 emission factor
[kg-CO2/kWh]
0.08 0.19 0.39 0.44 0.50 0.54
Table 4 : Unit Consumption of EAF
Consuming items
Unit
Resource for EAF
Nugget 100% Scrap 100%
Electrode kg-C/t-steel 2.5 2.5
Recarburizer kg-C/t-steel 0.0 9.5
Lime (12% Carbon) kg-C/t-steel 3.6 3.6
Total 6.1 15.5
Oxygen * Nm3/t-s 20 26
Melting kWh/t-steel 388 388
Auxiliary kWh/t-steel 55 55
Oxygen * kWh/t-steel 10 13
Savings by carbon in nuggets kWh/t-steel -44 0
Total 409 456
Note) Unit consumptions of iron nuggets 100% case were partly revised
from the original considering property of iron nuggets.
3. Calculation basis of CO2 emissions from Blast furnace
Energy balance of blast furnace (BF) including coke oven,
sinter plant, and basic oxygen furnace (BOF) used in
estimation here is as shown in Table 5. These figures
referred to energy balance flow of the model complex iron
steel works in Japan of which steel production capacity is
6,000,000 tpa. Table 6 shows the mass balance calculated
by Table 2 and Table 5. IEA has reported that the energy
efficiency of the Japanese ironmaking industry is higher
than those of other countries. Accordingly estimated CO2
emissions from steel works in most of other countries must
be larger than the results in this paper.
Table 5 Energy balance of BF-BOF [MJ/ton-steel]
Coke Oven Sinter Blast Furnace BOF
Coal 22,324 Coke 1,144 Coke 13,018 Pig Iron 10,277
Fuel 1,490 Fuel 1,301 PCI 3,955 Fuel 165
Power 160 Lime * (189kg) Power 1,259 Lime * (59kg)
Fuel 2,207
Ore 7
Sinter 399
Lime * (2.3kg)
In Total 23,974 In Total 2,445 In Total 20,845 In Total 10,442
Coke 14,162 Sinter 399 Pig Iron 10,227 Steel 8,476
COG 5,276 Steam 231 Pig for sale 788 LDG 1,095
Chemicals 2,613 Waste heat 1,884 Slag 513 Slag 113
CDQ steam 843 BFG 5,974 Steam 37
Waste heat 1,174 Condense 1019 Waste heat 716
TRT 127
Waste heat 2,242
Out Total 24,068 Out Total 2,514 Out Total 20,890 Out Total 10,437
Consumed Consumed Consumed Consumed
Power 160 Power * 576 Power 1,259 Power * 728
Source) With symbol of “*” : The iron and steel institute of Japan *3)
Without symbol of “*” : The iron and steel institute of Japan *4)
IN
OUT
The CO2 emissions derived from fuel and power
consumptions in BF were estimated with Table 2 and Table 3.
Efficiency of 35% was used for calculating kWh power
generated by CDQ, TRT, steam and surplus by-product gas.
In the referred energy balance flow, 8% of pig iron
discharged from blast furnace is not fed into BOF but goes
0.56

International Symposium on Ironmaking for Sustainable Development, 28-29 January. 2010, Osaka, Japan
outside of the total balance, for outside usage, therefore each
figure except BOF in Table 5 multiplied by 0.92 were used to
calculate the CO2 emissions for steelmaking.
Table 6
Mass balance of blast furnace
Coke Oven Sinter Blast Furnace
BOF
Coal 772 kg Coke 38 kg Coke 432 kg LDG 2 20 Nm3
COG 1 31 Nm3 BFG 2 382 Nm3 PCI 137 kg Lime 59 kg
BFG 1 234 Nm3 Lime 189 kg COG 1 26 Nm3
LDG 1 4Nm3 BFG 1 436 Nm3
LDG 1 20 Nm3
Lime 2 kg
Coke 470 kg BFG 1,752 Nm3 LDG 130 Nm3
COG 250 Nm3
Chemicals 3 63 kg
Note)
1 Ratios of COG, BFG and LDG are referred to Reference * 3).
2 Type of fuel gas is assumed.
3 Chemicals are assumed to be heavy-oil of class-C (fuel oil).
OUT IN
4. Comparison between ITmk3 and Blast furnace in
producing pig iron
4.1 Simple comparison between ITmk3 and BF
Table 7 shows the CO2 emissions from ITmk3 and BF to
produce pig iron in various countries, which have different
carbon emission factors of electric power (CO2 emissions per
kWh) as shown in Table 3. The CO2 emissions from BF
include those from coke oven and sinter plant. The CO2
emissions from ITmk3 are less than those from BF in all of
these countries by 8 - 17 %. Considering that the product
capacity of ITmk3 is much smaller than that of blast furnace,
it is comprehended that the ITmk3 process is significantly
efficient and environmental friendly.
Table 7 : CO2 emission from ITmk3 and BF in producing
pig iron
Blast Furnace
ITmk3
[kg-CO2/t-pig]
[kg-CO2/t-pig]
ITmk3
Source of CO2
Source of CO2
Consumed Recovered
Fuels*
Fuels*
Consumed
/BF
Sum
Recovered Sum
Power Power**
Power Power
France 1,995 14 -51 1,957 1,627 16 -20 1,623 -17%
Canada 1,995 33 -122 1,906 1,627 38 -47 1,618 -15%
Japan 1,995 67 -250 1,812 1,627 78 -98 1,608 -11%
Italy 1,995 75 -282 1,788 1,627 88 -110 1,605 -10%
UK 1,995 86 -320 1,760 1,627 100 -125 1,602 -9%
German 1,995 93 -346 1,742 1,627 108 -135 1,600 -8%
USA 1,995 96 -358 1,732 1,627 112 -140 1,599 -8%
* CO2 emissions by consumed coal, fuel and additives, considering CO2 credit by
recovered chemicals
** It was assumed that all of surplus by-product gas and generated steam are used for
power generation with 35% efficiency.
The lower carbon emission factor of power is, the more
advantages ITmk3 takes. Recently, especially in advanced
countries like Europe, the power generation process emitting
less CO2 by using nuclear power or renewable energy is
preferred due to CO2 issue. As this trend spreads worldwide
and such process replaces existing coal or gas fired power
plant, the average unit CO2 emissions per kWh will decrease.
It is supposed that the CO2 emissions from ITmk3 will be
getting even lower than BF as this happens all over the world
in future.
4.2 Comparison between ITmk3 and BF from the
viewpoint of LCA (life cycle assessment)
One of advantageous business structures of ITmk3 is that
ITmk3 is located in a mining site and steel mills import iron
nuggets from there. In this structure, the CO2 emissions
derived from transportation of raw materials can be highly
decreased compared with blast furnace route, because slag
and ash content as well as moisture and oxygen in ore and
coal are removed at a mining site through ITmk3.
Consequently fuel consumption for transportation can be
decreased. We therefore compared CO2 emissions from each
process from the view point of LCA (life cycle assessment).
In this paper following two cases were compared as shown in
Fig. 3. One is that Japanese steel mills receive iron nuggets
from ITmk3 in USA mining site to produce steel in Japan.
The other is that Japanese BF steel mills import all of ore and
coal. It shows that ITmk3 can reduce CO2 emissions by as
much as 15%.
Coal
Ore
CO2 : 8 kg/t-Ng
Coal
Ore
Mining Site
CO2 : 35 kg/t-pig
CO2 : 68 kg/t-pig
CO2:1599kg/t-Ng
ITmk3
Iron Nugget
Custommer Site
CO2:1812kg/t-pig
Coke Oven
Sinter
Blast Furnace
Total CO2 emission = 1915 kg-CO2/ts
CO2:25kg/ts
BOF
Customer
(EAF)
Total CO2 emission = 1632 kg-CO2/Nugget
Fig. 3 CO2 emission comparison considering LCA
5. Comparison between ITmk3 and Blast furnace in
producing steel
5.1 Steelmaking without scrap
It is most likely that iron nuggets produced by ITmk3 will
be used together with scrap in EAF. Although it is not the
usual practice, we have calculated the CO2 emissions from
ITmk3-EAF based on 100% iron nuggets feeding to EAF, as
the comparison with BF-BOF. Table 8 shows the result. In
France and Canada where carbon emission factors are low,
the CO2 emissions from ITmk3 are less than those from BF-
BOF by 12 – 17%. In other countries CO2 emissions from
ITmk3-EAF are almost equivalent to those from BF-BOF.
5.2 Steelmaking with scrap and iron nuggets as pure
iron unit in EAF
For the discussion of EAF steelmaking we need to address
the issue of tramp elements contained in scrap. This is
especially important when EAF aims at high grade steel
product or when good quality scrap is not available.
Impurities such as copper and tin in scrap cannot be removed
through processing at EAF. Therefore, it is common practice
to dilute tramp elements by using pure iron unit such as pig
iron or direct reduced iron together with scarp in EAF.
ITmk3 iron nuggets can be used in the same way, because of
the similar chemical composition to pig iron.
The usage ratio of pure iron unit varies depending on the
target product quality and the available scrap quality at each
EAF. To our best knowledge on the typical operation practice
in Japan and USA, the most efficient usage ratio of iron
nuggets is in the range of 20-40% as pure iron unit, and then
the rest is scrap (80-60%).
On the other hand, it is known that the applicable scrap
usage ratio at BF-BOF is 20% at highest, according to the

International Symposium on Ironmaking for Sustainable Development, 28-29 January. 2010, Osaka, Japan
restriction of raw material charging system configuration at
BF and excess heat available at BOF.
The CO2 emissions from ITmk3-EAF in producing steel
with scrap and iron nuggets have been estimated. Fig. 4
shows the comparison between the CO2 emissions from
ITmk3-EAF and those from BF-BOF, where the applicable
range of scrap usage ratio is 0-20% for BF-BOF and 60-80%
for ITmk3-EAF. It shows the CO2 emissions from ITmk3-
EAF are around 50% of those from BF-BOF, thanks to the
higher scrap usage ratio applicable to EAF. Further, similar
tendency is observed regardless of the plant location or
carbon emission factor of electric power.
Table 8 : CO2 emissions from ITmk3-EAF and BF-BOF
in producing steel without scrap
BF-BOF
ITmk3
[kg-CO2/t-steel]
[kg-CO2/t-steel]
ITmk3
Source of CO2
Source of CO2
Fuels*
Consumed
/BF
Recovered Sum Fuels Consumed Recovered Sum
Power Power**
* Power Power
France 2,103 20 -61 2,062 1,691 49 -20 1,720 -17%
Canada 2,103 47 -144 2,006 1,691 117 -49 1,759 -12%
Japan 2,103 97 -297 1,904 1,691 240 -100 1,831 -4%
Italy 2,103 110 -335 1,878 1,691 270 -113 1,849 -2%
UK 2,103 125 -380 1,848 1,691 307 -128 1,870 1%
German 2,103 135 -411 1,827 1,691 332 -138 1,885 3%
USA 2,103 140 -426 1,817 1,691 344 -144 1,892 4%
* CO2 emissions by consumed coal, fuel and additives, considering CO2 credit by
recovered chemicals
** It was assumed that all of surplus by-product gas and generated steam are used for
power generation with 35% efficiency.
CO2 emissions [kg-CO2/t-molten iron]
2,000
1,800
1,600
1,400
1,200
1,000
800
600
400
200
0
Applicable scrap
usage range for
BF-BOF
BF-BOF
ITmk3-EAF
0 10 20 30 40 50 60 70 80 90 100
Ratio of scrap [%]
Efficient iron nugget usage
range as pure iron unit for EAF
ITmk3 : Located in USA
EAF : Located in Japan
BF-BOF : Located in Japan
Fig. 4 : CO2 emissions in steelmaking with applicable
scrap usage ratio
Fig 5 shows the comparison in Japan and USA. Since the
CO2 emissions per kWh in USA is 40% higher than those in
Japan according to the carbon emission factor in Table 3, the
CO2 credit of electric power made by surplus energy at BF-
BOF becomes bigger in USA than Japan. It gives lower CO2
emissions from BF-BOF than ITmk3-EAF with 100% iron
nuggets in USA. The impact by scarp usage, however, is
much bigger than location factor. As fundamental approach,
higher scrap usage will be the key to reduce CO2 emissions
at steelmaking.
CO2 emission [kg-CO2/t-steel]
2000
1500
1000
500
0
1,904 1,817
1,831 1,892
182 251
1,904 1,817
873 944
Japan
BF-BOF
USA
1,649
1,640
ITmk3-EAF
Nugget 100% use
EAF
ITmk3
214 288
660 656
ITmk3-EAF
Nugget 40% use
554 628
224 300
330 328
Japan USA Japan USA Japan USA
ITmk3-EAF
Nugget 20% use
Fig. 5 : CO2 emissions in steelmaking in various case
6. Conclusion
According to above, it is concluded as follows.
1) In producing pig iron, ITmk3 has advantage over large
scale BF in Japan of which energy efficiency is the highest in
the world. The advantage will be even bigger over small
scale BF typically being operated in inland areas of Asian
countries such as China and India. So, the significant CO2
reduction is expected by replacing the small BF with ITmk3
in such areas, where it is difficult to apply large BF due to the
logistics and infrastructure problem.
2) In producing steel, the CO2 emissions from ITmk3-EAF
can be significantly reduced with the higher scrap usage ratio
applicable at EAF. This is because amount of consumed
energy and CO2 emissions to convert scrap to steel is much
less than those to convert iron ore to steel. Iron nuggets
produced by ITmk3 enable EAF to produce higher quality
steel by diluting the tramp elements derived from scrap.
ITmk3 promotes the dynamic shift of steelmaking process
from BF-BOF to scrap based EAF, which achieves the
dramatic CO2 reduction as much as 50%.
3) CO2 reduction in the electric power generation industry
is desired and supposed to be enhanced in near future by
using nuclear power and renewable energy. It will be more
preferable to use the electric power generated by such
efficient power plants than to use electric power generated by
their surplus energy from the CO2 emissions point of view.
The ITmk3-EAF process will take advantage of the trend in
steelmaking, since it dose not generate surplus energy.
References
1) T.Smith:Steel Times International (Nov/Dec 2007),
p.56.
2) Ministry of the Environment of Japan : Accounting
guideline of greenhouse gas emissions, (2007), P.11-
12
3) ISIJ Basic research group : Inhibition of carbon
dioxide gas and the future of ironmaking process
(1993).
4) ISIJ Heat economy technology committee : Research
of next generation CO2 reduction technologies (2007),
p.97-99