OXYGEN BLAST FURNACE PROCESS FOR SWEDISH CONDITIONS
Linda Bergman1, Mikael Larsson1, Jan-Olov Wikström1, Lena Sundqvist Ökvist1
Guangqing Zuo2, Björn Jansson3
1
MEFOS, Box 812, 971 25 Luleå, Sweden
2
LKAB, Box 952 Luleå, Sweden
3
SSAB, 971 88 Luleå, Sweden
Abstract
A new blast furnace process with cold oxygen replacing the hot blast, CO2-separation from
the top gas and recirculation of the reducing gases to the BF tuyeres and stack is being
developed within the joint European ULCOS-project. In this paper the global effects of
converting the existing blast furnace at SSAB Luleå Works to the new concept is analysed
from a process integration perspective. A study towards minimum cost, energy consumption
and environmental effects are analysed and discussed.
Introduction
Pulverized coal injection (PCI) into the blast furnace (BF) was developed in Japan and Europe
during the early 80’s. Initial results indicated that injection rates around 100 kg per tonne of
hot metal could be reached quite easily in many blast furnaces, but higher rates were more
problematic. The problem was, among other parameters, related to an insufficient combustion
of coal in the raceway area. As a way towards much higher injection rates several different
concepts for full oxygen blast furnace (OBF) were proposed [1-3].
When the hot blast is replaced with oxygen , the gas volume leaving the raceway area is too
small for heating of the burden. The different concepts for OBF showed different solutions to
this problem. One concept, that was tested in pilot plant scale, was the NKK process,
developed at Keihin Works. A part of the blast furnace off-gas was combusted outside of the
blast furnace and the waste gas was injected into the
middle part of the shaft. The purpose of the gas injection
Top gas
was only preheating of the burden. Reduction was still
Tail gas
CO
made by the gas being produced in the raceway. The result
removal
unit
CO2 rich
from pilot plant tests were promising and oxygen tuyeres
as well as shaft gas burners were also developed and
Injection gas
demonstrated in full scale on industrial blast furnaces.
CO rich
Still, no decision for commercial use of the process was
taken.
2
900 °C
Heater
1000 °C
Figure
1
Schematic
description of an oxygen blast
furnace
An OBF process has also been developed and
demonstrated in a small industrial BF in Tula, Russia
during the late 80’s [4]. CO2 was separated from the BF
gas and the remaining reducing gas was preheated to
1100°C and injected into the tuyeres together with pure
oxygen. No injection of fossil fuel was applied. In the
90’s, many blast furnaces reached very high pulverised
coal injection rates with only a small addition of oxygen,
which made the OBF concept less attractive. Nowadays
there is a strong focus on emission of green house gases from steel making. Within the joint
European project, ULCOS, the OBF is proposed to be one of the possible routes to cut CO2emissions from steel making by 50 %. In the ULCOS-concept, cold oxygen is blown together
with pulverised coal via coaxial lances into the tuyeres. CO2 is separated from the BF top gas
in a VPSA (vacuum pressure swing adsorption). The remaining reducing gas is preheated and
recirculated into the tuyeres (1200 C) and the lower stack (900° C) of the BF, see Figure 1.
The process has been demonstrated in the LKAB Experimental BF at MEFOS in Luleå during
a seven weeks campaign in 2007. In this paper the integration of a full OBF concept into an
existing steel making plant based on the successful trial results from demonstration of the
process in pilot scale is considered. A Process integration model is used to evaluate the effects
of the new process route with respect to CO2-emission, energy consumption and cost.
Description of studied system
The SSAB Tunnplåt AB steel plant in Luleå, Sweden, is a BF/BOF route based system. The
BF is operated with 100% pellets, and is equipped with pulverised coal injection (PCI). The
PCI capacity is in the range of 160-180 kg per tonne of hot metal, depending on production
level. A coke plant produces the majority of the coke used in the BF. Since the introduction of
olivine pellets from LKAB in the mid 80’s, the slag volume has been low, in the range of 150170 kg per tonne hot metal, and the reductant rate among the lowest in the world. In plant
fines are recirculated to the BF as cement bounded briquettes, at a rate of ~50 kg per tonne of
hot metal. There are two basic oxygen furnaces (BOF converters) in the system, operated with
hot metal from the BF and a small amount of scrap. The crude steel is further treated in the
CAS-OB and RH degassing units. Two continuous casters produces slabs that are transported
1000 km by train to the rolling mill located in Borlänge. In 2006 the slab production was
2020 ktonnes.
The distribution of process gases is shown in Figure 2. Since the rolling mill for the plant is
located at another site, a surplus of process off-gases arises (coke oven gas - COG, Blast
furnace gas -BFG and steelmaking gas - BOFG). The BF hot stoves uses BFG with addition
of COG as fuel. The coke oven is fired with pure COG. Other usage of the COG is in lime
kiln and burners in the steel plant. The recovered BOFG together with the surplus of BFG and
COG is used as primary fuel in a near by heat and power plant (CHP). The CHP plant
produces hot water for district heating for the community, electricity for the steel plant and
the waste gases are used for drying in a wood pellet production facility.
Production chain
Raw material
Gas distribution
Raw material
Coke oven
BF
BOF
CC
Slabs
CHP plant
Figure 2 A schematic description of gas- and energy distribution within and between the
processes
Method
Process integration
Process integration is a generic term for structured methods used in analysis of industrial
energy systems. These methods are applied for the design of integrated production systems
and treats complex systems with different inner and outer requests. They have special
emphasis on the efficient use of energy and reducing environmental effects. The methods can
be used in analysis- and decision making to achieve over all solutions that gives more
effective industrial systems in environment-, energy- and cost point of view.
In the analysis of converting No 3 BF at SSAB Luleå Works to the OBF process
mathematical linear programming (MILP) was used. The mathematical programming method
refers to a process system modelled with mathematical relationships. The optimisation
problem is defined by a mathematic description of the system and an objective function
defining the goal to be optimised in the system. The optimisation is defined as maximisation
or minimisation of the goal.
Model description
The process integration model for the SSAB system is based on previous modelling work [5].
The core of the model is a mass- and energy balance for the production chain. Separate subbalances for the main processes provide the possibility to do an over all analysis over the steel
plant and calculate the effects of a change in the operation practice for the processes. The
driving force of the model is the production of slabs. Each step of the process is linked to the
next by the primary product from each process; coke, hot metal and liquid steel. The steel
demand in the continuous casting decides the level of production in the BOF, which in turns
leads to a certain amount of production in the BF. The electricity demand is included as
normalised electricity consumption per tonne of cast product.
Coke plant
The model calculates the production of coke and by-products (coke oven gas, benzene,
sulphur and tar) based on the ingoing coal properties. The rate of production in the coke plant
is set to 84 t coke/h. There is a possibility to buy or sell coke if the demand from the BF is
higher or lower than the actual production.
Blast furnace
Ferrous materials and additives are together with coke charged through the top of the BF. Hot
blast or oxygen is blown through the tuyeres, where pulverised coal is also injected. The
reductants are combusted by oxygen in the hot blast and its main task is to reduce and heat up
the descending burden. A need of power, oxygen, COG and steam/heat are included in the
description of the process.
The chemical reactions in the process are too complex to describe mathematically. A separate
BF simulation tool is used to create the different cases of operation to be included in the
overall optimisation model. The model divides chemical and thermal reactions in the furnace
into different sections, above and below the reserve zone. The off-line BF simulation model
has been extended to model also the OBF. Modelling results have been validated by results
from OBF operation with top gas recycling at the LKAB Experimental Blast Furnace. The
model results were then applied on the SSAB No 3 BF at Luleå Works. The estimated process
data are shown in Table 1.
Table 1 BF No. 3 reference data and OBF data
Parameter
Burden
Pellet
Limestone
BOF slag
Briquettes
Reducing agents
Coke
PCI
Gas inj. tuyeres
Temperature
Gas inj. shaft
Temperature
Tuyere parameters
Blast volume
Oxygen
Blast temperature
Flame temperature
Bosh gas volume
Normalised
Top gas
Volume
Temperature
CO
CO2
H2
N2
ηCO
Heat value
Shaft efficiency
Direct reduction rate
a
b
Unit
Ref 2006
OBF
kg/tHM
kg/tHM
kg/tHM
kg/tHM
1362
26
46
59
1366
20
42
59
kg/tHM
kg/tHM
Nm3/tHM
°C
Nm3/tHM
°C
318
142
0
206
170
284
1000
244
900
Nm3/tHM
%
°C
°C
Nm3/tHM
976
24
1100
2086
1308
1.0
216a
b
100a
b
25a
b
2283
808
1.7
Nm3/tHM
°C
%
%
%
%
1471
120
20.5
24.7
3.5
51.3
0.547
2.97
0.97
0.32
1088
100
44.2
40.6
10.5
4.7
0.479
6.7
0.96
0.14
MJ/Nm3
0
based on oxygen flow to blast tuyeres
based on total flow to blast tuyeres
One
difference
between
the
conventional BF and the OBF is the
recirculation of reducing gases. After
cleaning, the top gas enters a CO2
removal unit in order to separate the
CO2. In the modelling a VPSA has
been used for CO2 separation. After
preheating, the injected gas is
distributed into the furnace at two
levels; the normal tuyeres and a new set
of tuyers in the shaft. The specific
energy consumption for VPSA,
including cryogenics and compression
enabling long-range transport and
storage of CO2, is included.
Aiming for the same production rate for
the OBF case as for the reference case
will result in lower bosh gas volume.
The comparison of the bosh gas volume
for the OBF case with the reference
case indicates that the production rate
could be significantly increased. To
avoid low top gas temperatures causing
condensation of water in the BF top
and at the same time keep the flame
temperature below 2300 °C, the blast
parameters have to be adjusted. As can
be seen from Table 1, a tuyere gas
temperature of 1000 °C will result in a
top gas temperature of 100°C and a
flame temperature of 2280 °C. A
decreased tuyere gas temperature
decreases the energy demand of the hot
stoves.
Basic oxygen furnace
The hot metal produced in the BF passes the sulphur refining process and enters the BOF. The
BOF model is based on a heat and mass balance determining the amount of different ingoing
materials. The oxygen demand is calculated on the basis of the total carbon content oxidised
and the metals oxidised in the slag. The post combustion ratio defined as the ratio CO2/CO in
the BOFG is set to 0.3. Scrap is used as a cooling agent in the converter due to the large
amount of energy released. The properties of the slag are controlled by addition of fluxes. The
slag basicity practice of CaO/SiO2=4 is used in the calculation.
Continuous casting
The liquid steel is treated in a secondary metallurgy process before entering the continuous
casting. The secondary metallurgy is not considered in the model and the liquid steel is
directly introduced to the continuous casting from the BOF shop.
A liquid exchange efficiency, ηLS=0.95 is used as a ratio between the liquid steel and the cast
product. The recoverable losses are brought back to the BOF shop as cooling agent.
The surrounding system and CHP plant
The off-gases from the steel plant are collected in gas holders for COG, BOFG and mixed gas
(BF-, BOF- and COG). Some of the gas is brought back to the processes as fuel and some is
used as the primary fuel in the CHP.
The CHP plant has two modes of operation, the pure back-pressure mode or the partly
condensing mode. In the 100 % back-pressure mode of operation, the district heating demand
of the city of Luleå is used as a heat sink. For this operation the ratio between the power and
the heat generation, is set to 0.44. In the completely condensing mode of operation, all the
heat is cooled by an external cooling circuit. The steam is expanded further in an extra turbine
stage in the steam turbine. This results in extra power generation. The energy efficiency for
the electricity generation is set to 0.32.
Analysis of CO2 emissions, energy conversion and cost
Raw materials and products are analysed with respect to possible CO2- and energy sources in
the system. The objective function coefficients for CO2-emissions, energy conversion and
costs are shown in Table 2. The costs considered in the model are raw material costs and the
main investment costs.
The investment cost is estimated from
Table 2 Coefficients included in the
rebuilding the existing BF.
objective function
Resource
Coking coal
PCI coal
External coke
Pellets
Limestone
Raw dolomite
Dolomite
FeSi
Scrap
Oil
Power
Credits
Power
Coke
Benzene
Sulphur
Tar
Unit
ton
ton
ton
ton
ton
ton
ton
ton
ton
ton
MWh
MWh
ton
ton
ton
ton
CO2
objective
(tonne/unit)
[2.49-3.07]
2.92
3.69
Energy
objective
(GJ/ unit)
[27.0-35.9]
28.2
42.2
0.43
0.47
3.05
0.60
40.2
3.6
-0.60
-3.69
-3.29
-3.6
-42.2
Cost
objective
(€/unit)
[54.7-88.0]
125
271
93
51
31
98
428
266
681
0.043
-0.043
-271
-170
-4
-138
•
•
•
To clean CO2 from the top gas a
CO2 removal unit is needed. In the
analysis costs for a VPSA unit was
considered.
The existing silica refractories in
the hot stoves have to be replaced
with alumina bricks due to
carburization.
New piping for shaft- and tuyere
gas injection has to be installed.
The existing oxygen plant is too small to
handle the demand of oxygen for the new
-3.35
process. The investment cost of a new
oxygen plant is not estimated. Instead the
unit price of oxygen is included. The estimated cost to rebuild SSAB BF No 3 to an OBF is
1000 MSEK. The investment calculation is made according to an annual repayment according
to:
r
Annual repayment =
(1)
*G
−n
1 − (1 + r )
r = interest
n = Economical endurance
G = Investment
The calculation is made with an interest of 15 % and an economical endurance of 15 years. In
the evaluation, the annual repayment cost is converted into an hourly cost based on the hourly
production set in the system.
Results
Seasonal variations of the district heating in the CHP plant are defining three cases; an
average level of 80 MWh/h as well as a cold winter day and a warm summer day of 140 and
25 MWh/h respectively. In the model oil is set as back up resource if the energy content in the
mixed gas is not sufficient for the energy demand in the CHP. Based on the estimated data for
the new BF process, the integration of a full OBF was examined in a process integration
model for the SSAB Luleå Works. The modelling work was evaluated for three OBF cases as
well as a reference case of the SSAB BF No 3 with respect to CO2-emissions, energy
conversion and costs.
Table 3 Material consumption
parameters for the modelled cases
OBF
Ref. Summer
Coke Plant
Coke prod.
kg/t slabs
to BF/OBF
kg/t HM
deficit / surplus
kg/t HM
Coke oven gas
nm3/t Coke
BF/OBF
Total HM prod
kg/t slabs
BF Slag
kg/t HM
Material consumptions
Pellet
kg/t HM
Coke
kg/t HM
PCI
kg/t HM
C
kg/t HM
Mn ore
kg/t HM
Lime stone
kg/t HM
By prod. Briquette kg/t HM
BOF slag
kg/t HM
Injected gas
Tuyers
nm3/t RJ
Shaft
nm3/t RJ
Oxygen
nm3/t RJ
Hot blast
nm3/t RJ
Top gas
Volume
nm3/t HM
Heat value
MJ/nm3
VPSA
Feed gas
nm3/t RJ
Inj. Gas
nm3/t RJ
Tail gas
nm3/t RJ
CO2 tailgas
kg/t HM
Excess
nm3/t HM
Power
BF/OBF
kWh/t HM
BOF shop
HM input
kg/t LS
BOF Slag
kg/t LS
Total scrap
kg/t LS
CaO/SiO2
Oxygen
nm3/t LS
CC
Casted slabs
Mt/y
CHP plant
Total Fuel
TWh/y
Mixed gas
TWh/y
Oil
TWh/y
364
302
-16
433
364
208
95
435
1115
162
1110
150
1362
318
141
400
4
30
59
46
1364
208
170
328
0
17
59
47
--39
931
process In Table 3 the material consumption
of the main processes in the modelled
system are shown. The reference case
OBF
OBF
Average Winter
(Ref.) represents the modelled data of
BF No 3 with an average district heat
364
364
208
208
demand of 80 MW. Each of the
95
95
modelled cases for the OBF; OBF
435
435
average, OBF summer and OBF
1110
1110
winter, has a specific hot water
150
150
demand of 80, 25 and 140 MW
1364
1364
respectively.
208
208
and
170
328
0
17
59
47
170
328
0
17
59
47
283
243
211
--
283
243
211
--
283
243
211
--
1446
2.98
1088
6.70
1088
6.70
1088
6.70
------
1088
526
503
232
60
1088
526
503
232
60
1088
526
503
232
60
91
116
116
116
936
90
137
4.9
51
932
71
137
4.9
50
932
71
137
4.9
50
932
71
137
4.9
50
2.02
2.02
2.02
2.02
2.278
2.278
0.000
1.193
1.193
0.000
1.254
1.193
0.062
2.095
1.193
0.903
In the reference case, external
purchase of coke is needed. For the
OBF cases the coke demand from the
BF is lower, resulting in an excess of
coke. The total demand of reducing
agents is lowered from 400 to 328 kg
C, in total 18% reduction, in the OBF
cases. Furthermore, due to the
decreased reductant rate the slag
amount is decreased and thus a lower
amount of additives are needed.
The top gas volume from the OBF is
lower than for the BF, but has a
higher heat value. Before recycling,
the top gas content of CO2 is
separated in a tail gas, totally 232 kg.
The silicon content of the OBF hot
metal is estimated to be reduced from
0.35 to 0.26 %. The reason is the
higher partial pressure of carbon
monoxide, which will limit the
gasification of SiO. This will result in
less demand of additives in the BOF, to reach the set point of slag basicity. The BOF slag
amount is thus 21 % lower than in the reference case.
Depending on seasonal variations, the demand of district heat will vary. In the OBF cases the
total amount of fuel gases available within the system is 597 kWh/t slabs. Depending on the
district heat demand the need of additional fuel (i.e. oil) will vary. This will also influence the
power generation
Effects on Energy, CO2 emission and Costs
The change from traditional BF operation to OBF will influence the gas distribution within
the site and to the external users. The gas- and energy distribution of the reference case is
shown in Figure 3. The COG is used internally at the coke plant, BF hot stoves heating, lime
kiln and for various burners at the BOF shop. The generated BFG is used together with the
COG in the hot stoves. The BOFG is primarily sent together with the surplus of BFG and
COG to the CHP. In total, the CHP plant receives 1128 kWh/t slabs while 265 kWh/t slab is
flared. No external power is needed to fulfil the requirements of the plant.
[kWh/t slabs]
Coke plant
122
419
273
1128
1005
Blast Furnace
1'
Gas holder
CHP plant
2'
3'
42
329
BOF
Drying gas Boiler
1'
45
DH
2'
347
Electricity production
3'
299
Electricity from grid
0
265
265
Figure 3 Gas- and energy distribution for the modelled reference case
The corresponding gas- and energy distribution of the OBF average case is shown in Figure 4.
The internal energy use of the coke oven is the same as in the reference case. The OBF
utilises the energy within the system together with some addition of COG to reach the
requirement of the hot stove firing. No external BFG is sent to the CHP.
[kWh/t slabs]
Coke plant
329
419
Oil
30
76
621
0
Oxygen Blast
Furnace
1'
Gas holder
CHP plant
2'
3'
42
2247
BOF
6
268
Figure 4 Energy distributions for the OBF average case
Drying gas Boiler
1'
45
DH
2'
347
Electricity production
3'
Electricity from grid
153
269
The recovered gas energy sent to the CHP is 597 kWh/t slabs. The decrease is mainly due to
the lack of BFG, however the COG available within the system is increasing due to less
consumption in the BF hot stoves to heat up the injected gas, compared to the traditional
system. The energy requirements in the CHP plant is not fulfilled by steel plant gases, so
additional oil is required. The external power increases due to decreased power generation at
the CHP plant as a consequence of decreased energy input from the steel plant.
Figure 5a shows an evaluation of the energy conversion for the different cases. The energy
requirement for the reference case is 20.4 GJ/t slabs. In the three OBF cases the energy
conversion is 16.3 GJ/ t slabs within the process. This is a decrease of the energy demand of
20.3 %. External power and oil increases the energy demand for the total system, still
resulting in lower energy demand than for the reference case. The total decrease is 8.5 –
15.5% compared to the reference case.
Process
25
External power
Oil DH
Process
2.00
CO2 CCS
External
1.80
15
20.41
10
16.27
16.27
16.27
5
t CO2/t slabs
GJ/t slabs
20
1.60
0.16
0.17
0.21
1.40
0.26
0.26
0.26
1.20
1.00
1.83
0.80
0.60
1.22
1.22
1.22
Summer
Average
Winter
0.40
0.20
0
0.00
Summer
Average
Winter
Reference
Reference
Figure 5 a) Energy conversions for the calculated cases of the total system
b) The total CO2-emissions from the modelled system
The calculated CO2 emissions for the system are shown in Figure 5b. In the reference case the
specific emission within the system is 1.83 ton CO2/ton of slabs. In the OBF cases the
calculated emission varies between 1.64-1.69, of which the site emission corresponds to 1.22 t
CO2/t slabs. In the winter case with higher district heat demand, more power will be generated
in the back pressure operation mode.
The relative change in costs for raw material and energy for the average and summer case will
decrease 7-8 %, mainly due to less coke demand. However, due to the need for oil in the
winter case, the cost will increase with 7 %. The calculated investment cost is increasing the
relative costs with 2.7 %, however for the average case still less than for the reference system
(4 %).
Discussion
A process integration model for the material and energy system at SSAB Tunnplåt AB has
been used to examine the effects of changing the existing BF to an OBF with regards to
material flows, CO2 emissions, energy conversion and costs.
Calculation of operational data for converting the BF to an OBF operated on the same raw
materials shows that it is possible to decrease the coke consumption with 110 kg/t HM. This
is achieved by increasing the PCI rate (+28 kg/t HM) and recirculation of the top gas. The
OBF operation has several other positive effects on the system. The generated slag will be
less, due to the decreased coke rate in the blast furnace. Furthermore, the reduction of silicon
content in the hot metal will influence the production practice in the BOF, thus lower silicon
content decreases the chemical energy released from the oxidisation of Si to SiO2. This results
in less scrap melting capacity for the converter, and higher amount of hot metal or less iron
ore needed for cooling. However from the positive side this also effects the amount of slag
additives and the amount of slag generated. The decrease in generated slag (BF and BOF) will
be significant (-69.7 kton/y).
The decrease in coke rate in the OBF will result in a surplus of coke in the system, 214
kton/y. The excess coke can either be used within the SSAB Company at another site, or be
sold on the market. The evaluation has not considered the possibility to decrease the
production of coke.
The energy system at a steel plant is very complex. The generated off-gases are used as fuel in
other processes. In the SSAB case the main user is a power plant supplying the community
with district heat as well as producing power for the steel plant. The main idea with the OBF
process is to recirculate the off-gas and in that way decreasing the amount of gases out from
the system. Today, the BFG stands for 65% of the fuel supplied to the power plant. There is a
gas surplus in the system which is seen as flaring of gases (20%). In the OBF case, the fuel to
the CHP is decreased significantly as no BFG is available. This results in a demand for an
additional fuel, e.g. oil. Depending on seasonal variations the amount is varying. More oil is
needed in the winter case than in the summer case. Interestingly to notice is that the amount
of available COG will increase and can be used to replace some of the BFG at the CHP. The
reason for the increased availability of COG is mainly due to the fact that less energy is
needed to heat up the injection gas compared to heating up conventional hot blast. The
injection gas volume is 40 % less than that of conventional blast, furthermore has the injection
gas lower temperature.
The power demand for the system is increasing due to the fact that the OBF process has a
higher specific power demand compared to the conventional BF system. This is an effect of
the choice of CO2 removal unit and the increased oxygen demand for the system. With less
fuel gas to the CHP, less internal power will be generated and there will be a demand for
external electrical power. This will be influenced by the seasonal variations. In the winter case
more fuel is supplied and hence more power will be produced.
The specific energy use for the steel plant with an OBF will decrease with 15.5%. If the effect
of external energy sources is taken into consideration the decrease is 8-15%, depending on the
seasonal variations. The main reason for the decreased energy use is the decrease in coke
consumption, however the effect of improved gas management, i.e decreased flaring due to
gas deficit will also have an impact.
From the CO2 emission point of view, the analysis is more complex. If considering the system
without storage of the removed CO2 and including the emissions from external power the CO2
emission is decreased by 10% (totally 25%). If CO2 storage could be utilised additional 15%
reduction could be achieved. If the emissions from external power or oil are excluded the site
emissions would decrease 33% compared to the reference. Thus it is of great importance to be
able to store the captured CO2 as well as having a CO2 lean fuel alternative for the CHP.
The cost for rebuilding the SSAB BF to an OBF has been estimated to 1000 MSEK. From a
cost perspective the OBF will decrease the costs for raw material and energy with 8% manly
due to the less demand for coke. Increased coke price on the market will result in even further
advantages for the OBF. Penalties for CO2 emissions have not been included in the
evaluation. The costs for CO2 permits is varying and is at present 21 €/ton CO2 [6]. Based on
the assumption of investment cost, the increase of the relative cost is 3%. The cost for
emitting CO2 is likely to increase in the future, however with the level of today’s prices, the
benefit from reduced CO2 emissions in the order of 10% would result in reduced cost with
2%. If CO2 could be stored the cost reduction would be as high as 7%.
Conclusion
The implementation of the OBF concept, with recycling of BF top gas after CO2 removal with
a VPSA, has been analysed for SSAB Luleå Works. The analysis is based on successful
results from demonstration of the process in pilot scale. Under the assumption that the process
can be scaled up successfully to production rate and size of BF No. 3, following will be valid;
The coke demand for the system is decreasing when replacing the BF with an OBF. The coke
saving from the system is significant and can either be supplied to other sites within the SSAB
company, or be sold externally. With increasing coal and coke prices this might be of great
importance
Integration of the OBF in an existing system is restricted by the existing infra structure and
energy users. The fuel for the CHP will be decreased and a need for additional fuels will arise.
The potential reduction of CO2 emissions is due to this reason not fully utilized.
Acknowledgement
We are grateful to Centre for Process Integration in Steelmaking (PRISMA) for the possibility
to prepare this paper. PRISMA is an Institute Excellence Centre (IEC) at MEFOS,
Metallurgical Research Institute AB, supported by the Swedish Agency for Innovation
Systems, The Knowledge Foundation, the Foundation for Strategic Research, and by the
industrial participants Luossavaara-Kiirunavaara AB, SSAB Tunnplåt AB and Rautaruukki
Oyj.
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