Multi-chamber furnaceMelting furnaces
These are the key principles we apply to design HERTWICH ECOMELT melting furnaces:
These principles remain the same, yet we adapt the detail engineering to meet your specific requirements.
- Automatic scrap charging
- Thermal gasification of organic content by heating the scrap in a hot gas flow to approx. 400 - 500 °C. During this phase, the aluminum does not melt because the temperature of the hot gas flow remains below its melting temperature.
- Combustion and post-combustion. The constantly high level of organics gasification induces combustion in all the furnace chambers. Here, the gasified hydrocarbons contribute to the energy input of the melting process. As it maintains a constantly high temperature (>900 °C) and a controlled furnace atmosphere, the main chamber of the furnace is ideal for post-combustion.
- The preheated scrap melts exclusively due to contact with liquid melt (submerged melting process). Crucial here is an electromagnetic liquid-metal pump that transports sufficient melt to the scrap to ensure the necessary melting energy. This method results in the lowest metal loss.
- Near-continuous heating. That means the charging and melting activities do not interrupt the main burner operation.
- Most of the melting energy is introduced to the melt in the main chamber in the form of radiant heat. Using a regenerator system ensures high combustion efficiency at low energy consumption (< 600 kWh/ton).
If you use scrap types with moderate contamination, the best option for you is a multi-chamber furnace with a preheat ramp.
Here is how it works: First, a charging machine feeds the scrap onto the dry hearth ramp for preheating and gasification of the organic substances. Then the charger or an integrated scrap pusher pushes the scrap heap into the melt bath.
To generate the energy needed to melt the scrap, an electromagnetic liquid metal pump circulates the melt between the furnace chambers.
How long it takes to thoroughly preheat the entire scrap heap to approximately 500 °C depends on the scrap type and density. Essential to the process is thorough preheating of the charged scrap and gasification of the organic compounds. That's why the furnace design includes elements for intense hot gas circulation as well as additional hot gas nozzles in the furnace roof.
The average scrap preheat time is 30 minutes per charge. This means a furnace with a melt rate of 6 tons per hour (120 tons per day) requires two charging cycles of 3 tons each per hour.
Furnace capacity: 30 - 120 tons
Melting rate: 3 - 6 tons/hour (60 - 120 tons/day)
Here is a furnace type that efficiently and cost-effectively melts class-3 scrap at high melt rates. Included in this type of material are painted profiles with thermal break, baled litho sheets, UBC, etc. containing up to 10% organic compounds.
The production rate of Ecomelt PR and PC furnaces is limited to the scrap from one batch load. So it's a huge advantage of the Ecomelt PS that you can charge the preheat compartment with several batch loads. This results in a melting capacity of 12 tons per hour (240 tons per day). Equally impressive is the low specific energy consumption of as little as 370 - 450 kWh per ton.
Right at the start of the process, a pay loader loads the scrap into bins. Then a crane picks up one full bin at a time and charges the scrap into the furnace. Hot air from the melt chamber circulates up through the scrap and back into the melt chamber.
The long retention time of the scrap inside the preheat shaft ensures effective preheating and thorough gasification of organic compounds - even if you charge difficult (baled) scrap. Gradually, pyrolysis gas forms. It's easy to regulate the gas generation by varying the intensity of the recirculating hot air flow (controlled by the fan speed).
Next, the pyrolysis gases flow through ducts into the main chamber of the furnace for combustion. That's another example of our green technology, because the inherent energy of the volatile hydrocarbons is thermally reclaimed and added to the energy for melting. Now scrap melting itself starts. A liquid metal pump raises the melt bath level next to the preheating/melting chamber, flooding the chamber.
Significant here is that the foot of the scrap pile is at all times immersed during melting. The constant metal flow generated by the electromagnetic pump ensures a steady melt rate. This submersion melt process achieves an extremely low metal loss from oxidation.
What this furnace type excels at is remelting long, painted profile scrap containing plastic thermal break - even without prior shredding and grading.
Savings come not only from avoiding shredding and separating, but especially from thermally reclaiming the hydrocarbons in paint and plastic. During preheating, up to 80% of the gas consumption is substituted by the inherent energy of the gasified hydrocarbons. As a result, the specific fuel gas consumption varies from 370 to 450 kWh per ton of aluminum during continuous operation.
This configuration features a gasification compartment in the form of an elevated chamber across the furnace roof. It accommodates the scrap load from one scrap bin. Next, a block integrated in the hood of the compartment compresses the charge. An intense flow of hot gases is forced through the scrap load from one end. These gases pass through the charge in longitudinal direction at a temperature on the entry side marginally below melting point.
Heating and gasification starts at the hot gas entry side. It takes around 15 to 25 minutes for the heat front to move through the entire charge. This means pyrolysis gases do not form suddenly, but are released gradually at a rate that permits controlled combustion.
A number of scrap bins circulating on a two-level bin conveyor plus a bin elevator ensure automatic metal charging. Yet there is another important function of this system, because it provides a buffer with a storage capacity of approximately 12 tons. That's equivalent to 2 hours of melting. A pay loader or fork-lift truck loads the scrap when the bins are in the right position. Here, an integrated scale measures the net weight of the scrap load. A typical load weight is 2 to 3 tons
Once a bin is full, it moves onto an entry accumulator. Then the elevator lifts the bin to the furnace top. Finally, the two flaps which form the bottom of a bin open automatically, and the scrap drops into the gasification compartment of the furnace.