Hertwich Ecomelt Melting Furnaces are generally based on integrated scrap preheating / delaquering and submerged melting process. They are designed for remelting of scrap with impurities like oil, paint, and plastic. Total non-metallic organic substances may reach 10% of charge weight, subject to calorific value.
Savings come not only from avoiding shredding and separating, but significantly from thermal reclamation of the hydrocarbons from paint and plastic. During preheating of such scrap, up to 80% of the gas consumption is substituted by the inherent energy of the gasified hydrocarbons.
The specific fuel gas consumption varies from 350 to 550 kWh/ton of aluminium during continuous operation subject to the quantity of organic impurities.
Hertwich Ecomelt furnaces for scrap type I - III are designed on the following principels:
- 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 aluminium does not start to melt, as the temperature of the hot-gas-flow is at all times below the melting temperature.
- Combustion and post combustion of gasified organics takes place in all chambers of the furnace. The gasified hydro-carbons contribute to the energy input for the melting process. The main chamber of the furnace is well suited for post combustion because of the constant high furnace chamber temperature (> 900°C) and the controlled furnace atmosphere.
- Melting of preheated scrap is exclusively by contact with liquid melt (submerged melting process). An electromagnetic liquid metal pump transports sufficient melt to the scrap. This method of melting results in the lowest achievable melt loss.
- Near continuous heating - charging and melting activities do not interrupt main burner operation.
- The majority of the melting energy is introduced to the melt in the main chamber in the form of radiant heat. The use of a regenerator ensures high combustion efficiency with low energy consumption.
Functional principle multi chamber melting furnaces
Ecomelt PS (Preheat Shaft)
The Ecomelt PS melting furnace is well suited for efficient and economic melting of type III scrap including painted profiles with thermal break, baled litho sheets, UBC etc. In fact it is the most versatile melting device in terms of scrap grades and categories.
The Ecomelt PS unlike Ecomelt PR furnace is not limited to a single batch, rather is the melting process continuous. The Ecomelt PS multi chamber furnace accepts several batch loads in the preheat compartment.
Most stringent environmental and emission regulations are met due to the combination of closed charging unit and high efficiently combustion equipment.
With the development of the preheat shaft furnace a melting capacity of 12 tons/hour (250 tons/day) is achieved. Specific energy consumption is as low as 350 - 550 kWh/ton subject to organic impurities.
Scrap is loaded via a payloader into containers. The charging crane takes one full container at the time and charges the scrap load via a material lock at the top of the preheat shaft. Hot gases are circulated through the scrap in upward direction. The long retention time of scrap inside the preheat shaft ensures adequate preheating and thorough gasification of organic compounds even for problematic (baled) scrap.
Pyrolysis gases are ducted to the main chamber of the furnace for combustion whereby the inherent energy of volatile hydrocarbons is thermally reclaimed, to contribute to the energy needed for melting. Through an opening in the partitioning wall hot air flows from the main chamber to the melting chamber to supply energy for scrap preheating. All organics are properly gasified prior to scrap being submerged.
Melting of scrap is started by raising of the melt bath level at the preheating/melting chamber with the liquid metal pump, thereby flooding the chamber. The melt rate is controlled over the melt flow speed and melt level in the chamber. An outstanding feature is the "foot" of the scrap pile, which is at all times immersed during melting. The constant melt flow, generated by the electromagnetic pump, ensures the steady melt rate. Due to the submersion melt process metal loss from oxidation is reduced to a minimum.
Ecomelt PR (Preheat Ramp)
The multi-chamber furnace with preheat ramp is best suited for loose scrap with moderate organic content.
The scrap rate is up to 200 tons per day.
Scrap is charged with a charging machine onto the dry hearth ramp for preheating and gasification of organics. Thereafter the scrap heap is pushed into the melt bath by the charging machine or an integrated scrap pusher.
An electromagmetic liquid metal pump circulates the melt between the furnace chambers, thereby providing necessary energy to melt the scrap. The time to thorougly preheat the entire scrap heap to approximately 500°C depends on scrap type and density.
For proper preheating of the charged scrap and gasification the Hertwich furnace design includes provisions 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. A furnace with 6 tons/hour melt rate (120 tons/day) therefore requires two charging cycles of 3 tons each, per hour.
The capacity of the charging machine is approximately 13 m³ with a maximum load of 5 tons. Before opening the furnace door for charging the attached hood docks to the furnace to extract escaping fumes. Preheated scrap on the ramp is pushed into the melt bath with the charging machine front shield and the new scrap load is deposited onto the ramp in turn.
As an alternative to the rail bound charging machine Hertwich offers a top-charging concept. Full scrap containers are lifted to a position above the furnace to dock onto a material lock in the furnace roof. An overhead crane is integrated for automated scrap container manipulation. After unloading and preheating on the dry hearth scrap is pushed into the melt by a scrap shield in furnace side wall.