BOF Heat and Gas Recovery

The gas produced in the BOF has a temperature of approximately 1200°C and a flow rate of approximately 50-100 Nm3/t-steel. The gas contains approximately 70-80% CO when leaving the BOF and has a heating value of approximately 8.8 MJ/Nm(NEDO, 2008) or 0.84GJ/t-steel (IEA, 2007). Therefore, recovery of the sensible and latent heat from BOF presents the single most important opportuniy for energy efficiency in BOF. This can also  make the process a net energy producer.  However, the gas production in the BOF is intermittent, show high temperature and composition variations, and is dirty.  Consequently, in most plants this gas is still flared (IEA, 2007). 

Heat recovery processes are classified as combustion and non-combustion methods. In the combustion method, the CO leaving the furnace is allowed to combust by letting large amounts of air to enter the exhaust hood.  The resulting hot gas from the combustion is then used in a heat recovery boiler to produce high pressure steam.  

In the non-combustion method, conversion of CO to CO2 (i.e. combustion) is prevented.  The sensible heat of the CO-rich off-gas is first recovered in a waste heat boiler, generating high pressure steam. The gas is subsequently cleaned and stored and used as a fuel by mixing with other by-product gases (coke oven gas, blast furnace gas).  Non-combustion method recovers about 70% of the latent heat and sensible heat. 

Development Status Products
Commercial
steel

BOF Heat and Gas RecoveryCosts & Benefits

Parent Process: Basic Oxygen Furnace
Energy Savings Potential

With the combustion method 0.125 GJ/t-steel can be recovered (NEDO, 2008)

With the non-combustion method savings can be in the range of 0.54 and 0.92 GJ/t-steel, depending on how the steam is used.  

Energy reduction potential with the worldwide applicaiton of the BOG gas recovery is estimated to be 250 PJ. (IEA, 2007. p. 127)

 In an ArcelorMittal plant in Ghent, Belgium, BOF gases are recovered and used partly within the mill and partly for electricity production by a local generator. This is estimated to reduce mill's energy consumption by 3%. By using the BOF gases, the mill reduced its energy consumption by 0.7 GJ/t-steel (ArcelorMittal, 2013

CO2 Emission Reduction Potential

CO2 reductions can be reduced approximately by 50 kg/t-steel with this measure (US EPA, 2010. p. 22)

Worlfwide recovery of BOF gas can reduce CO2 reductions by 25 Mt/y. (IEA, 2007. p. 127). 

 With the use of BOF gases in the mill, a plant in Belgium is able to reduce CO2 emissions by 170 000 tonnes per year (ArcelorMittal, 2013). 

Costs

For a 110 t/charge capacity plant in Japan, the equipment costs for non-combustion technology was reported to be ¥600 to 1100 million.  For this plant the payback time is estimated to be 8.3 to 15 years. (NEDO, 2008) 

 

The capital cost of the recovery system is estimated at roughly $20/t-steel (or approximately $66 million for an average BOF shop with a production rate of 2.7 million t/. The payback period is estimated as 12 years (US EPA, 2010. p. 22)

Retrofit capital costs are $34.4/tonne steel. According to an experts opinion, the installation costs vary in a wide range depending on the scope of supply and the country of installation. Basically the Return of Investment is between 2,5 and 4 years. Payback is a strong function of the natural gas prize.

 In a plant in Belgium, a system to recover and utilize BOF gases was installed for a cost of €38 million. It is estimated that the investment will be recoverd within two years (ArcelorMittal, 2013)

BOF Heat and Gas RecoverySchematic

BOF Heat and Gas Recovery 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: 

89

Global Warming Countermeasures: Japanese Technologies for Energy Savings / GHG Emissions Reduction

This revised 2008 version of the publication from New Energy and Industrial Technology Development of Japan includes information on innovative Japanese technologies for energy efficiency and for the reduction of COemissions.  

Page Number: 

77