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Case Studies: Steel Reheating for Further Processing

Oxy-fuel burners can reduce steel furnace energy use by up to 45%.
Steel reheating is an energy-intensive process requiring uniform temperature distribution within reheating furnaces. Historically, "recuperators" have been used to preheat combustion air, thereby conserving energy. More recent innovations include oxygen enrichment and the use of regenerative burners, which provide higher preheat air temperatures than recuperators. These processes have limitations such as equipment deterioration, decreasing energy efficiency over time, high maintenance costs, and increased NOx emissions with increased air preheat temperature, unless special equipment is used.

Praxair, Inc., supplier of oxygen and other industrial gases to the steel industry, proposes to introduce an innovative oxy-fuel burner technology (using 100% oxygen) to the steel reheating industry. Oxy-fuel combustion reduces or eliminates nitrogen in combustion air and substantially reduces waste heat carried out with flue gas. Based on technology currently used in the glass, hazardous waste, and aluminum industries, Praxair has developed and patented low temperature, oxy-fuel burners that can be used in high temperature industrial furnaces where temperature uniformity is critical and extremely low NOx emissions are desired.

Benefits

  • Potential to reduce energy consumption by 30-45% per ton of steel
  • Potential to reduce NOx emissions by 60-90% per ton of steel
  • Annual projected energy savings: 112 billion Btu (one furnace)
  • Annual projected cost savings: $240,000 (one furnace)
  • Reduces waste heat
  • Eliminates recuperator
  • Eliminates installation of NOx removal equipment applications

The technical goal of the project, sponsored in part by DOE's NICE3 program, is to demonstrate the use of oxy-fuel burners in a slab reheat furnace while reducing energy consumption by 45% and NOx emissions by 90% within the converted furnace zones. Successful implementation of this technology also will eliminate the need to periodically replace recuperators and install NOx removal equipment.

The low NOx feature of this system is expected to be a general requirement of the steel industry of the future. Bethlehem Steel started up its system in May 1998.

Savings Potential for Steel Industry
Continuous furnaces, which are more fuel-efficient than batch furnaces, represent much of steel production. On average, reheating consumes 2.2 million Btu per ton of steel. Overall fuel savings with this technology are estimated at 35%, since there is less potential benefit in more fuel-efficient furnaces. Given 100 million tons of steel per year, the potential industry-wide annual fuel savings are 7.7 x 1013 Btu.

Applicability to Other Industries
This technology has been used in the glass industry, and in general can apply to any combustion system. However, fuel savings and economics favor higher temperature processes, such as steel and glass.

Estimated Energy Savings (BTU per Year)
Furnace with Conventional Burners: *250 billion
Furnace with Oxy-Fuel Burners: 138 billion
Savings: 112 billion

Estimated Annualized Utility Cost
Furnace with Conventional Burners: *$620,000
Furnace with Oxy-Fuel Burners: $380,000
Savings: $240,000

*Producing 120,000 tons of steel/year

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