Prototype Isothermal Melter Launched

Action has been "heating up" on the isothermal melting (ITM) front in recent months, with the installation of a commercial prototype unit at Aleris Rolled Products’ Newport, Ohio, facility and plans afoot to introduce the technology into General Motors’ Saginaw, Mich., metalcasting operations. (Aluminum Now magazine, Oct-Nov, 2006).

The isothermal melting process was developed by Verona, Pa.-based Apogee Technology Inc. through a four-year $5 million cost-share project sponsored by the Office of Energy Efficiency and Renewable Energy (EERE) of the U.S. Department of Energy (DOE). Under this project (“Energy-Efficient Isothermal Melting of Aluminumâ€), Apogee constructed and operated a 300 lb./hr. melt rate proof-of-concept unit in December 2003.

With the unit, Apogee set out to demonstrate a scalable electric melting process with total energy use of less than 750 BTU/lb. and 1 percent melt loss without direct in-plant greenhouse gas emissions. The resulting proof-of-concept process demonstrated 300 lb./hr. melt performance of 666 BTU/lb., and melt loss of approximately 0.4 percent. Compared to conventional methods such as gas reverbatory furnaces at more than 2,100 BTU/lb. and 2 to 8 percent melt loss, Apogee said ITM has “leapfrogged†current best practices.

In an extension to the original project, a commercial prototype unit was designed and commissioned in October 2005 for Aleris Rolled Products at its Newport, Ohio, facility. The unit is capable of up to 7,000 lb./hr. depending on the type of material to be melted.

Apogee and Aleris in July received a 2006 R&D 100 Award from R&D magazine for the project.

The Technology
According to Apogee Technology, the key breakthrough in ITM is the development of durable, high-intensity heaters, or “direct immersion heaters,†that impart heat directly to the melt pool via an efficient electrical process. These heaters use a thermally conductive, metallic core that efficiently transfers heat to a durable outer sheath that can withstand the aggressive melting environment. Compared to conventional gas-fired melting, the ITM process requires one-third of the energy input and is more than twice as efficient.

According to Apogee, if all of the aluminum melting in the U.S. were to switch to ITM technology, the resulting annual energy savings would be 63 trillion BTU—or $630 million in natural gas savings at $10/therm. Put another way, that is enough energy to power the city of Pittsburgh for four years.

“The direct immersion heaters convert 98 percent of electrical energy to heat,†said Ed Eckert, president of Apogee Technology. “Our industry partners understand the opportunity this technology provides to dramatically reduce energy waste. We hope that government recognizes the significant national impact of this reduction, as well.â€

Measuring 10’ x 15’ x 5’, isothermal melters are self-contained units that are approximately one-third the size of gas-fired reverbatory furnaces. This smaller size permits them to occupy far less space on plant floors, which allows them to be used in both new and retrofit applications, and to be trucked from one location to another.

Because they do not rely on combustion, isothermal melters can take advantage of electricity produced in any of a number of ways. Eckert explains: “Unlike fossil-fueled melting processes that are committed to one form of energy, an isothermal melter is energy diverse and can use any current or future cost-effective means to produce electrical energy."

By using an efficient electrical process rather than combustion, isothermal melters also reduce melt loss and eliminate the in-plant emissions released by conventional gas-fired melters.

Scrap-to-Caster System Under Development
Apogee is currently developing an advanced over-the-road heated-delivery and in-plant dispensation technology that will extend the capabilities of isothermal melting and result in the elimination of in-plant holding furnaces. This work is being supported by a new four-year DOE/EERE-sponsored project ("Energy-Efficient Melting and Direct Delivery of High-Quality Molten Aluminum"), with General Motors and Aleris International as major industrial partners. Additional project participants include the Argonne National Laboratory and the University of Pittsburgh.

Consistent with priorities outlined in the 2003 Aluminum Industry Technology Roadmap (to order, please visit www.aluminum.org/bookstore), the program aims to demonstrate the feasibility of supplying high-quality molten aluminum directly to the casting process using an off-site, high-efficiency isothermal melter and advanced heated delivery logistics that keep molten metal on-grade and at precisely controlled temperatures all the way to the caster.

These advanced delivery logistics include the development of a turboelectric ladle ("TeL") and conductive trough. In conjunction with an ITM, a TeL can provide similar benefits of thermal efficiency and control of metal temperature at capacities of 30,000 lbs. over the road in transit.

Apogee says the same baffle-and-side-pocket-panel (BSPP) heating technology applied to the ITM will provide a thermal efficiency profile six times better than conventional gas-burner hot top ladle designs with significantly reduced metal loss. When fitted to a docking station for direct dispensation to a delivery trough, the TeL can eliminate the need for a holding furnace.

BSPP heating will also be applied to intra-plant troughing. Rather than using radiant "glow bar" style launders, BSPP-powered troughing will heat the metal via conduction - avoiding the use of less-efficient radiation modes that often experience chemical and mechanical failure associated with exposed heating elements.

According to Apogee, the potential impact of the successful completion of the project would be a paradigm shift in current industry practices—namely, the outsourcing of aluminum melting and holding operations from the casting facility. Ready-for-use molten metal would be produced with the highest quality and lowest cost at single-purpose centralized facilities that use the best available technology. Apogee says the intrinsically high thermal efficiencies, process control, metal quality, and absence of plant emissions would qualify this paradigm as a "factory of the future".

DOE says the commercial potential for the integrated ITM/TeL metal supply system is widespread. According to the agency, in the aluminum industry both the wrought alloy and engineered castings sectors would have a “compelling†need for the system.

According to DOE, the benefits of developing the integrated system include:

• Potential energy savings of about 12.7 trillion BTU per year by 2020;
• Potential cost savings of about $45.7 million per year by 2020;
• Elimination of on-site generation of combustion gases, including carbon dioxide, sulfur oxide, nitrogen oxide, and particulates; and
• Reduction of dross formation.

 

isothermal melting,Aleris Rolled Products