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New Energy-Efficient Melting Process Saves Energy and Reduces Production Losses
Aluminum melting is an energy intensive process that exhibits a 2% to 3% loss rate due to the generally open heating method for melting. An immersion heating process, Isothermal Melting (ITM), has been developed by Apogee Technology, Inc., with support from AMO. The system uses immersion heaters in a closed loop multiple bay arrangement. Each bay contributes to an efficiency improvement. The pumping bay provides circulation that provides better mixing for purifying and alloying and more uniform temperature profiles throughout the molten pool. The heating bay is the major source of efficiency gain, where electricity is converted into heat through the immersion heaters and conducted directly to the molten metal. The heating bay raises the molten metal temperature (typically less than 90°F) just high enough to melt the solid metal being charged into the pool. Compact charging and treatment bays provide control and introduce solid charge or alloying and purifying elements in a more energy efficient manner compared with opening hearth doors and exposing the entire surface of the pool and refractory to the plant environment.
The challenge to developing the ITM system was the creation of immersion heaters that could provide the high heat flux and the chemical, thermal, and mechanical robustness required in an industrial molten aluminum environment. Apogee Technology’s research program developed new materials, fabrication techniques, and quality control systems to build immersion heaters with high heat flux (approximately 70,000 Btu/hr-ft2), approximately 5 to 10 times more than commercially available heaters. These new heater designs are based on highly thermally conductive, impact resistant ceramic coating on a metallic sheath and a highly conductive dielectric integral coupling medium between the sheath and the heat producing element. This allows heat transfer by conduction to be the dominant mode, rather than particle to particle radiation heat transfer that prevails in conventional processes. The composite refractory coating is resistant to corrosive attack by the molten aluminum, yet sufficiently thin enough to provide a high heat flux.
IMPACT OF COMMERCIALIZED TECHNOLOGY
|Energy Savings (Trillion Btu)||0.006||0.004||0||0||0.001||0.003||0.003|
- Developed by Apogee Technology, Inc.
- Installed at four facilities.
Can be used in aluminum melting processes and other metal melting processes.
- Can be retrofitted to existing furnaces.
- Applies to multiple types of molten metal heating operations.
Reduces metal lost to oxidation to <1%.
Environmental Emissions Reductions
Produces zero in-plant emissions compared with natural gas process heating.