Lexington Stack Melter
An innovative stack melter has been demonstrated at Lexington Die Casting of New York. Scrap aluminum, mostly ingots but also in-house scrap, is fed to the top of the melter. A burner fires through the scrap which melts the lower portion and preheats the upper portion. As the lower portion is melted, it is drawn out and the upper preheated scrap falls to a lower level where it in turn melts.
The throughput is 2500 pounds per hour at a burner firing rate of 3 MMBtu/hr, yielding a specific energy use of 1,400 Btu/lbm. Compared to a conventional furnace of 3,000 Btu/lbm, this results in a 47% energy savings. This energy savings is brought about primarily because the flue gases preheat the scrap and the gas temperature is dropped to under 500oF and can be as low as 300oF.
The advantages of the stack melter are as follows:
- Low Use of Energy - Only 1,600 Btu/lbm is used, for a thermal efficiency of 35%. This results in an energy reduction of 47% compared to conventional furnaces, or 11,732 MMBtu annually.
- Emission reduction - NOx would be quite low due to the low flue temperature. Also, all gaseous emissions would be reduced by 47%, compared to conventional furnaces, due to the reduction in firing rate.
- Increase in Production - If the firing rate is fixed, then a production increase of 47% would occur.
- Quick Payback - From the energy savings alone, a simple payback of 3.2 years results. If the production increase is used, then the payback would be well under one year. Also, the emission benefits would relieve Lexington of having to buy pollution prevention equipment that would add to the savings.