Blast Furnace System

In a blast furnace (BF) the iron oxides are reduced and the resulting iron is melted. Approximately 70% of the global steel production involves the use of BFs. Sizes of BFs installed cover a very wide spectrum, ranging from less than 100 m3 to more than 5000 m3. Larger BFs have less heat losses and enable installation of heat recovery equipment more cost effectively (IEA, 2007.p. 116).

Cold blast blowers, and hot blast ovens are other important elements of the BF system. While the former provides the necessary air flow at 3 – 5 bar pressure, the latter increases the temperature of air to 900 – 1350 oC. Ore, sinter or pellets, coke and lime (that removes impurities and acts as flux) are added to the blast furnace from the top, whereas hot blast (compressed air) is introduced from tuyères at the lower part.  Auxiliary reductants/fuels – like coal, fuel oil, natural gas, or other alternative sources – can also be injected from the bottom of the furnace.  At lower parts of the furnace coke is gasified and the resulting CO reduces ironoxides as it ascends in the furnace. The molten iron trickles down and collects at the bottom. The impurities that are removed by the aid of CaO form a slag that floats on the molten iron. The hot gases leaving the blast furnace still maintain a pressure of 2 – 3 bar. In addition, a gas with low calorific value (~ 3 MJ/Nm3) is produced at a rate of 1300 – 2200 Nm3/t-pig iron. After cleaning, this gas can be used as fuel.(Worrell et al., 2010. pp. 12-13)

The pracitcal minumum energy use for a blast furnace is 10.4 GJ/t (IEA, 2007). However, based on information obtained from six efficienct hot blast stoves and blast stoves around the world, the average total primary energy requirement for a blast furnace system is reported to be 1.8 GJ/t-hot metal for the hot blast stoves and 11.6 GJ/t-hot metal for the blast furnace itself. (Worrell et al., 2010. p. 83). 

Chinese flag CO2 emissions in China can be reduced by 37 Mt/yr, if all furnaces were as efficient as the largest ones that are currently in operation (EIA, 2007. p.118).

Direct reduced iron (DRI) and smelting reduction technologies offer an alternative to blast furnaces for iron production, and are gaining importance day by day.

Blast Furnace SystemSchematic

Blast Furnace SystemTechnologies & Measures

Technology or MeasureEnergy Savings PotentialCO2 Emission Reduction Potential Based on LiteratureCostsDevelopment Status
Use of High Quality Ore

The use of high quality ore increases productivity and energy efficiency of of ironmaking process.

This technique will reduce CO2 emissions by 15-80 kg/t hot metal.

The economic benefits are connected with increased productivity, reduced energy consumption and decrease in demand of reducing agents.

Commercial
Pulverized Coal Injection

For every ton of coal injected, 0.85 to 0.95 ton of coke production can be avoided. Energy savings are estimated to be 3.76GJ/t-injected coal. (Worrell et al., 2010, pp. 83-84)

If the average pulverized coal injection rate at global level was 180 kg /t-hot metal, about 10 Mt CO2 could be saved.

Cost savings in the range of US $16 to 33/t-hot metal can be expected, lowering the hot metal production costs by approximately 4.6%. 

Investment of coal grinding equipment is estimated at $50-55/t Coal injected.

Commercial
Top Pressure Recovery Turbines

40–60 kWh of electricity can be produced per ton of hot metal (APP, 2010. p.40)

A dry-types TRT installed at a 1 Mt/y BF produced 55.4 GWh/y of electricity (NEDO, 200. p. 74)

If TRT were Installed Worldwide at all the Furnaces Working at Elevated Pressure, CO2 emissions can be reduced by 10 Mt/year.

For a 1 Mt/y blast furnace, the installation cost of a 7 MW dry type TRT was ¥400 million for equipment and ¥400 million for construction. The payback time for the whole investment was around 1.8 years. (NEDO, 2008. p. 74)

Commercial
Increased Blast Furnace Top Pressure (> 0.5 Bar Gauge)

This technology reduces coke rate and tuyere level injectants. Furnaces operating at high pressures can produce electricity in order of 0.35 GJ/t-HM if the system has recovery turbines installed

Lower emissions due to reduced energy consumption are expected.

Commercial
Improved Hot Stove Process Control

Energy savings typically range between 5 and 12%, and may reach 17%. Typically, this may equate to 0.037 GJ/t-HM (US EPA, 2010. p.20). 

US flag Emissions can be reduced by 22.6 Kg CO2/t-HM (US EPA, 2010. p.9).

US flag Retrofit capital cost is estimated to be US $0.47/t-HM. The payback times are around 4 months (US EPA, 2010. p.20).  

Commercial
Blast Furnace Process Control

By implementing this technology, coke consumption was reduced to approximately 0.458 ton/t-HM in an Austrian steel plant in 2001 (Worrell et. al., 2010, p.87).

US flagEmissions reduction potential of the technology is 24.4 Kg CO2/t-HM (US EPA, 2010. p.9).

Commercial
Heat Recuperation from Hot Blast Stoves

This technology can reduce the energy demand by 0.24 GJ/t-HM. Its global application has 0.2 EJ/y energy reduction potential (EIA, 2007. p.126).

Energy savings can be as much as 0.3 GJ/t-pig iron (Worrell, 2010. et al., p. 87)

Various systems allowing fuel savings between 80 to 85 MJ/t-HM have been installed. (US EPA, 2010. p. 20)

Japanese flag By recovering 40-50% of the sensible heat from the stove flue gases, 0.125GJ/t-pig iron saving has been realized in a 1 Mt/y BF system in Japan (NEDO, 2008. p. 72)

With global application of this technology, CO2 emissions could potentially be reduced by 20 Mt annually (EIA, 2007. p.126)

Commercial
Increased Hot Blast Temperature (>1 000 oC)

The total energy savings possible by a combination of techniques is of the order of 0.5 GJ/t-HM (APP, 2010. p.48)

Energy savings will result in reduced emissions.

Lower operating costs because coke ratio reduces by 2.8% per 100°C rise in blast temperature when it is maintained between 1000°C to 1200°C (Yiwei, et al., 2008).

Commercial
Improved Combustion in Hot Stoves

Energy savings can be around 0.04 GJ/t-HM (Worrell, et al., 2010.p. 87). 

Commercial
Injection of Coke Oven Gas

The replacement rate of COG is about 1.0 ton of gas for 0.98 ton of coke.

EU Flag Since 2002, a plan in Austria has operated their small blast furnaces with a simultaneous injection of reduction gas and heavy fuel oil as standard operational procedure with a replacement of 70 % of the heavy fuel oil by COG. In 2004, these furnaces averaged an oil injection rate of 45.5 kg/t-HM and a COG rate of 46.9 kg/t-hot metal with a total equivalent coke rate of 477.8 kg/t hot metal.

EU Flag Emission reductions due to replaced coke (0.98t-coke/t-COG) and reduced flaring of COG will arise.

EU Flag The investment at the Austrian plant for the gas injection plant was about €10 million for a production of about 5000 t-HM/day. The total specific operational costs are: €1.3/t-HM or €12/1000 m3 COG (€2 400 000/year and 200 million m3 COG/year).Commercial
Improved Recovery of Blast Furnace Gas

Energy savings of 35 MJ/t-HM (Worrell et al, 2010. p. 86) to 66 MJ/t-HM (US EPA, 2010. p.19) are reported. 

US flag Emissions can be reduced by 4.0 Kg CO2/t hot metal.

EU Flag Retrofit capital costs are $0.47/t-HM have been reported from a plant in Netherlands.  Payback time was estimated to be 2.3 years (US EPA, 2010. p.19).

Commercial
Bell Less Top Charging System

An increased fuel efficiency is reported.

Operating costs will be lower thanks to reduced coke consumption and high attainable Pulverized Coal Injection (PCI) rates.

Commercial
Injection of Oil

Every ton of oil used can reduce the coke demand by 1.2 tons (Worrell, et al., 2010. p. 84).

CO2 reductions will vary depending on the composition of oil, and in particular Carbon and Hydrogen contents.  

Commercial
Natural Gas Injection

Fuel savings are estimated to be 0.9 GJ/t-HM.

US flag Savings of 54.9 Kg CO2/tHM are estimated by the injection of 140 kg natural gas/t-HM (US EPA, 2010. p.9).

Commercial
Dry Dedusting of Blast Furnace Gas

Dry dedusting will reduce water consumption by 7-9 Nm3/tHM. It may also increase the power generated by TRT systems by 30% compared to wet-type dedusting. 

Indirect GHG reductions will arise due to increased power generation in the TRT - if installed. 

Investment costs are 70% compared to wet-type dedusting equipment cost.

Commercial
Plastic Waste Injection

The energetic value of the 0.4 Mt plastic used in Japanese steel plants yearly is equal to 20 PJ. (IEA, 2007. p.121)

For every ton of plastic waste used, coke use can be reduced by 750 kg. (IPPC, 2009. p.355)

For every ton of plastics used CO2 emissions linked to the production of 750 kg of coke will be avoided. 

The investment for the plastics injection plant in Austria was about €20 million for an injection capacity of up to 220 000 t/y. Additional costs were projected for unit's maintenance (IPPC, 2009. p.356)

Commercial
Oxy-Oil Injection

Up to 130 kg/t hot metal Oxy-Oil Injection is applied. The savings of coke is thus about 15 kg/t hot metal.

Reduction in CO2 emissions is roughly 50 kg/t hot metal.

Additonal costs will arise for air enrichment to provide constant huge amounts of Oxygen and additional requirement of injection unit maintenance.

Commercial
Residue Injection

A system that provided a BF with 2.5 t-HM/day capacity with 12 kg-residue/t-HM was installed at a cost of €4 - 6 million in Austria. 

Commercial
Improvement of Hearth Drainage Efficiency and Refractory Life

This technology increases blast furnace productivity.

This technology prolongs blast furnace life. Repairs and Relining are as Late as possible and as early as necessary.

Commercial
Biomass use in BF

PCI can be substituted fully by charcoal in large BFs i.e approximately 40% of the carbon input. 

Biomass is CO2 neutral if strict conditions are met in producing it.

Total production costs for charcoal may range from $355 to $474 depending on type of wood

Demonstration
Charging Carbon Composite Agglomerates

On charging 30% CCB, coke rate and the total reducing agents rate are reduced by 30.2% and 6.3% respectively.

Reductions in coke input rate may ultimately reduce BF emissions.

Demonstration
COURSE 50The goal is to cut total CO2 emissions by about 30%.The tentative total cost of project Phase 1 Step 1 is about ¥10 billion.Research
Charcoal Use

The most efficient Charcoal-fired BF at Acesita used 16.2 GJ charcoal/t pig iron. However it does not result in significant energy efficiency gains.

In Brazil, CO2 emissions from charcoal-based steelmaking was 0.30-0.55 t CO2/t steel in 2005, as compared to 0.92 t CO2/t-steel of coal based production (IEA, 2007. p.123)

Charcoal accounts for 40% of Pig-Iron costs in charcoal based BFs.

Commercial
Top Gas Recycling Blast Furnace

A 26% coke saving/ton Hot Metal from the current BF coke consumption is feasible by the application of this technology.

A 15% reduction of CO2/t-HRC is expected to be feasible without CCS. Upto 50% CO2 Reduction is possible with CCS.

Investment and/or operational costs are not available because technology is still in research.

Research
Slag Heat Recovery

Associated energy savings would be approximately 0.35 GJ/t-HM (Worrell et al., 2010. p. 86)

There will be a reduction in CO2 emissions if the recovered heat is adequately utilized.

Total cost of slag heat recovery including capital and operational expenses is estimated at around $2.5/GJ (Rodd, et al., 2010)

Research
Extended Universal Fuel Gas Measuring DeviceResearch

Blast Furnace System Publications

Energy Efficiency Improvement and Cost Saving Opportunities for the U.S. Iron and Steel Industry

The U.S. Environmental Protection Agency’s (EPA) energy guide, Energy Efficiency Improvement and Cost Saving Opportunities for the U.S. Iron and Steel Industry, discusses energy efficiency practices and technologies that can be implemented in iron and steel manufacturing plants. This guide provides current real world examples of iron and steel plants saving energy and reducing cost and carbon dioxide emissions.

Page Number: 

12-13

Page Number: 

9, 18-21