HERTWICH ECOMELT melting furnaces are designed on the following principles:
 
  • 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 is not melted, as the temperature of the hot-gas-flow is at all times below the melting temperature.
  • Combustion and post combustion, due to the constant high of gasified organics takes place in all chambers of the furnace. The gasified hydro-carbons contribute to the energy input of 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 to assure the necessary melting energy supply. This method of melting results in the lowest metal 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 system ensures high combustion efficiency with low energy consumption. (< 600 kWh/ton)

Despite strategic design criteria, detailed furnace design is flexible to meet individual specifications and capacities.

Ecomelt PR (preheat ramp)

Ecomelt Preheat Ramp
The multi-chamber furnace with preheat ramp is best suited for scrap types with moderate contamination.

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 electromagnetic liquid metal pump circulates the melt between the furnace chambers, thereby providing necessary energy to melt the scrap.

The time to thoroughly preheat the entire scrap heap to approximately 500°C depends on scrap type and density.
For proper preheating of the charged scrap and gasification of organic compounds, the 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.

Furnace capacity: 30 - 120 tons
Melting rate: 3 - 6 tons/hour (60 - 120 tons/day)

Schematic view of furnace
Schematic view of furnace
 
Two Ecomelt PR-120 furnaces (120 tons/day)
Two Ecomelt PR-120 furnaces (120 tons/day)
 

Ecomelt PS (preheat shaft)

Ecomelt Preheat Shaft

This furnace type is well suited for efficient and economic melting of class 3 scrap including painted profiles with thermal break, baled litho sheets, UBC etc. with organic compounds up to 10% at high melt rates.

With Ecomelt PR and PC furnaces the production rate is limited to the scrap quantity of one batch load. The Ecomelt PS type furnace accepts several batch loads in the preheat compartment, thus a melting capacity of 12tons/hour (240tons/day) is achieved. Specific Energy consumption is as low as 370 - 450 kWh/ton.

Scrap is loaded with a payloader into bins. The charging crane takes one full bin at the time and charges the scrap  load. Hot air from the melt chamber is circulated through the scrap in upward direction and back to the melt chamber. 

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 gas is generated quite gradually, whereby gas generation can be regulated with the intensity of the re-circulating hot air flow (controlled by the fan speed).

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. 

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. 

An outstanding feature is the “foot”  of the scrap pile, which is at all times immersed during melting. The constant metal flow, generated by the  electromagnetic pump, ensures a steady melt rate. Due to the submersion melt process metal loss from oxidation is reduced to a minimum.

Schematic view of furnace
Schematic view of furnace
 
Ecomelt PS-160 furnace (160 tons/day)
Ecomelt PS-160 furnace (160 tons/day)
 

Ecomelt PC (preheat chamber)

Ecomelt Preheat ChamberThis furnace type has been developed particularly for efficient remelting of long, painted profile scrap containing plastic thermal break yet without prior shredding and grading of profiles.

 Savings come not only from avoiding shredding and separating, but significantly from thermal reclamation of the hydrocarbons in 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 370 to 450 kWh/ton of aluminium during continuous operation.

The gasification compartment is an elevated chamber across the furnace roof with the capacity to match the scrap load of one scrap bin. The charge is then compressed by a block integrated in the hood of the compartment.
A very intense flow of hot gases is forced through the scrap load from one end. The hot gases pass through the charge in longitudinal direction. On the entry side the temperature of the gases is marginally below melting point.

The heating and gasification starts at the hot gas entry side and during a period of 15 to 25 minutes the heat front gradually moves through the entire charge. Formation of pyrolysis gases is therefore not a sudden process, but gases are rather released gradually at a rate that permits controlled combustion.

Automatic charging of metal is performed with a number of scrap bins circulating on a two level bin conveyor and a bin elevator. This concept also serves as a buffer with a storage capacity of approximately 12 tons, equivalent to 2 hours of melting. Scrap loading is done in loading position by payloader or fork truck. An integrated scale takes the net weight of the scrap load. Typical load weight is 2 to 3 tons.

Full bins are moved onto an entry accumulator from where they are lifted by the elevator to the furnace top. Upon automatic opening of the two flaps which form the bottom of a bin, the scrap load drops  into the gasification compartment of the furnace.

Longitudinal section of gasification compartment
Longitudinal section of gasification compartment
 
Schematic view of furnace
Schematic view of furnace
 

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