Isothermal Melting: Reaching for the Peak of Efficiency in Aluminum Melting Operations

From the Spring 2008 issue of Energy Matters

It's called Isothermal Melting—and this new technology, developed with support from the U.S. Department of Energy's Industrial Technologies Program, could revolutionize the aluminum industry's melting capabilities.

Photo shows several vertical metal electrical components with tubes extending down and plugged into receptacles in an aluminum furnace.

Direct immersion high-efficiency heaters are a key energy-saving feature of the Isothermal Melting process.

How Does it Work?

This superior melting system offers many benefits to aluminum manufacturers:

Energy

70% higher efficiency than conventional furnaces
Near-zero in-plant emissions
Widespread, cross-cutting applications
Energy diversity: using traditional and renewable energy sources.

Cost and productivity

Low capital and operating costs
Dramatically reduced process time
Extended refractory life
Significantly reduced plant floor space
Portable
Retrofit to sidebays of conventional furnaces.

Quality

Less than 1% metal loss
Excellent metal quality
Improves plant environment by reducing noise and pollution.

Aluminum is a lightweight, high-strength, and recyclable metal, and in great demand as a versatile and sustainable material for transportation, construction, and packing products. However, the energy demands required for the aluminum melting process are also substantial, driving aluminum manufacturers to find ways to reduce costs.

Aluminum melting is an energy-intensive process that typically uses gas-fired, reverberatory furnaces. These furnaces are thermally inefficient, yield high metal oxidation rates and melt loss, and generate emissions. Faced with the high energy requirements of the melting process, rising natural gas prices, and growing demand, the aluminum industry is exploring energy-efficient ways to melt, hold, and transport aluminum.

Isothermal Melting Represents a Paradigm Shift

Dr. C. Edward Eckert of Apogee Technology, Inc., understood the need for a radical melting technology that could substantially reduce energy intensity and metal loss in large-scale aluminum melting and other molten metal processes. So, with support from DOE's Industrial Technologies Program (ITP), Apogee Technology assembled a project team to research, develop, and demonstrate a new melting technology.

The result? The Isothermal Melting process (PDF 48 KB), which offers a revolutionary, highly efficient aluminum melting alternative to conventional furnaces. Download Adobe Reader. The Isothermal Melting system employs high-efficiency, high-intensity electrical resistance heaters to melt aluminum, using less than one-third of the energy required by conventional gas-fired furnaces. The resulting potential savings in natural gas used by the aluminum industry for melting and molten metal processing is estimated at 63 trillion Btu per year, equal to a cost savings of $340 million per year.

"The key to the Isothermal Melting process was to develop a technology that was capable of using an energy conversion process that could operate at near 100% conversion efficiency, and then effectively and rapidly transfer the heat that was produced into the melt," says Dr. Eckert. "Once it was clear that we could begin to do that, it made sense to move forward with the project."

After 5 years of intensive R&D, the project moved into the commercial demonstration phase at Aleris International, Inc. at Newport, Ohio, and was christened during a kick-off event in April 2006.

The project partners are not the only ones who are excited about this technology. In 2006, the Isothermal Melting process was awarded a prestigious R&D 100 award. Most recently, the technology was named one of the top 10 technologies of 2008 by Industrial Heating magazine.

Technology Synergy Yields Energy Savings

The Isothermal Melting (ITM) project demonstrates that working together works. ITP partnered with Apogee Technology, Inc., Aleris International, Drexel University, the University of Pittsburgh, and Argonne National Laboratory to produce a technology breakthrough with significant energy savings impact and widespread potential commercial applications.

Unlike conventional gas-fired furnaces, ITM melts aluminum via conduction and convection using a multi-bay, continuous-flow system that features two independent heating sources. The first is an array of high-heat-flux, direct-immersion electric heaters that supply melting heat requirements. The second is a moderate-heat-flux refractory panel heating system that provides holding heat for the molten aluminum. Aluminum manufacturers can expect benefits such as excellent metal quality, highly efficient operations, zero in-plant emissions, less melt loss, and reduced plant floor space requirements. (See How Does It Work?")

Moving into Commercial Demonstration

Aleris International, Inc., is one of the world's largest recyclers of aluminum and one of North America's leading manufacturers of common-alloy sheet from recycled aluminum. In its 48 production facilities worldwide, the company looks for ways to increase energy efficiency and reduce costs in melting operations. In 2005, the first commercial-scale, 5,000 lb/hour isothermal melter was installed at the Aleris International aluminum plant in Newport, Ohio. The furnace operated continuously for 15 months with molten aluminum. In comprehensive melting tests, the furnace demonstrated a thermal efficiency of 87% (including holding losses), a melt energy performance of 552 Btu/lb, and less than 1% metal loss to oxidation.

"While conventional recycling of aluminum uses just 5% of the initial energy investment needed to produce aluminum from mined products, it still represents a large energy expenditure for Aleris when we are melting billions of pounds of aluminum," says Dr. Ray D. Peterson, Director of Technology at Aleris International. "We are very excited about the opportunity that Isothermal Melting may offer to replace our current melting technologies and provide us with both savings in melting cost and a reduction in metal lost due to oxidation."

The next phase of the project promises to boost energy savings even further, through direct delivery and dispensation of molten aluminum to the casting operations site.

Integrating Melting and Delivery System Optimizes Energy Savings

The second phase of R&D focuses on integrating the energy-efficient melting capabilities with advanced portable delivery and in-plant dispensation technology. The new process will be showcased at Aleris International's operations and GM's Powertrain Division in Saginaw, Michigan, beginning in 2009. This demonstration calls for melting to be done at Aleris in an Isothermal Melter, and then uses turbo-electric ladle (TeL) trucks to transfer and dispense the molten aluminum at GM's casting operations site.

The integrated delivery and dispensing system further reduces metal loss and contamination, provides the flexibility to change alloy chemistry, and eliminates the need for energy-intensive holding furnaces at the casting site. The overall energy savings of the integrated system could exceed 85%, compared with the current practice of conventional melting, gas-burner-preheated ladles, and the reliance on insulation and superheated metal that limit transport time and distance.

Energy Savings Potential Expands in Cross-Cutting Applications

The Isothermal Melting project exemplifies a successful collaboration between ITP, industry, and academia to develop a promising new technology with a significant impact on energy efficiency in melting and other molten metal processes. As Apogee, Aleris and GM move forward with the next phase of the project, they will expand the initial technology into advanced melting and delivery capabilities.

What's more, the potential cross-cutting applications for the technology will extend energy savings and environmental benefits beyond the aluminum industry. These include other molten metal processes such as those involving lead, zinc, magnesium, and copper-based alloys as well as the production of glass, chemicals, and forest products.

For more information on process heating systems, see this month's Ask an Energy Expert column, and the article on the new process heating sourcebook.

Isothermal Melting Project Partners

For more information, please contact Glenn Strahs, DOE Industrial Technologies Program, or call 202-586-2305.

How Does It Work?

View an animation of the isothermal melting technology. This animation is intended to represent a basic overview of the Isothermal Melting and transport and delivery process.

Text Version

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