••• Advanced Heating
Isothermal Melting (ITM) is a very high energy efficiency electrical resistance melting process that produces zero in-plant emissions. The ITM process uses a continuous flow system where molten metal is re-circulated through separate heating and charge bays. Two innovative and patented heating processes were developed to enable ITM. These are high watt-density Direct Immersion Heaters, and precision cast heated refractory panels known as Baffle and Side Pocket Panel, or BSPP for short.
The initial proof of concept ITM to the right exhibited the following performance: | |||
|---|---|---|---|
Metric |
Baseline |
Proposed |
Demonstrated |
Melt Energy (BTU/lb) |
2100 |
<750 |
617 (w/ holding losses) |
Melt Loss |
5% |
1% |
0.41% (Mg Alloy) |
Spatial Efficiency |
65lb/hr/ft² |
>300 |
385 |
Both BSPP and Direct Immersion Heaters, while serving different heating purposes in the system, share one thing in common that is fundamental. Primary heat transfer via conduction, where the aluminum is in intimate contact with the heat source, is used as the ideal means to add thermal energy directly to the melt and in fact, making the melt itself the conduit for heat transfer to incoming cold charge. Forced circulation within the ITM assures excellent heating of this charge.
A 7,000lb commercial prototype ITM was commissioned for Aleris Rolled Products at their Newport, OH facility. This cost-shared unit is capable of a 5,000lb/hr output when melting light weight scrap (edge trim), and up to 7,000lb/hr solid charge. Preliminary melt tests showed this unit to be capable of a 550btu/lb energy requirement with a heating area no larger than 15 square feet.
In addition to high energy efficiency and zero in-plant emissions, the commercial prototype also enjoys considerably less floor space than traditional units of similar output. Measuring only 10 foot by 15, an ITM of 7,000lb/hr output makes planning efforts for integrating a new ITM in existing operations simple. Sophisticated closed-loop control systems provide a melt manager with easy operation via touch screen interfaces, operational data logging, and internet-enabled remote surveillance or even direct control. ITM automatically adjusts its energy input to maintain molten metal inventories within plus or minus 2 degrees Fahrenheit of set point. That’s only a little more than one tenth of one percent variation no matter what the circumstances- a changed plant environment, or all out melting of cold metal. Holding heat and melting heat in the ITM are controlled by two distinct systems. That means that only enough heat required for a given charge rate is used- automatically- by the ITM and no more. As the charge rate changes, the heat input rate is automatically adjusted.