Benefits of DRO Cascade Assisted
Aluminum Melting Furnaces
A case study was made for EMTEC. Here the Cascade e-ion was also used for melting as well as as dross reduction. The standard configuration however is with the cascade e-ion as an add on cover. Summary:
Highest melting rate and low dross was achieved in the report. Best energy efficiency and
best furnace loading
The aluminum industry is one of the most energy intensive industries
in the world. Compared with other competing materials such as steel,
copper, wood, glass, and plastics, etc., aluminum has the highest
energy content. The availability for the optimum furnaces for clean-aluminum
melting/casting and heat-treating will certainly improve the competitive
position of aluminum vs. other materials. Any DRO Cascade e-Ion Aluminum Furnace could bring several immediate benefits to the vast aluminum industry.
Reduced energy consumption will be the number one payoff.
U.S. primary aluminum production was about 3.6 million tons while
secondary aluminum recovery was about 3.3 million tons. The average
energy consumption for producing primary aluminum is about 16,500
kWh/ton, in which 5.5% (~908 kWh/ton) is consumed for melting/casting.
On the other hand, the average energy consumption for producing
secondary aluminum is about 6% of that required for primary aluminum.
The total energy consumed for melting/casting aluminum (both primary
and secondary) in the U. S. per year is thus approximately (3.6
x 106 tons x 908 kWh/ton + 3.3 x 106 tons
x 990 kWh/ton) = 6.5 x 109kWh (22.3 x 1012
No need for nitrogen cover A key benefit of using the cascade e-Ion ionic-source comes from the
elimination of nitrogen, argon or toxic flux covers normally used
for melting and holding aluminum. The DRO machine takes air and converts to a nitrogen-ion cover.
Small foot-print and no noise
High melting rates are thus achieved with a low foot-print of the
furnace. Noise and toxic materials normally used as fluxes are eliminated (except that from a blower).
The DRO Cascade e-ion is ~ 10kW device. In most instances the melting furnace power overpowers this and so the DRO is not primary for melting. However, for smaller furnaces an experiment was conducted that showed that DRO melting gives significant energy efficiency.
Over the years, the aluminum casting industry has been looking for
an clean energy efficient rapid melting furnace with reduced losses from
oxidation and contamination. To accomplish these goals combined
with energy efficiency, the furnace design must incorporate heating
systems, which allow directing highly concentrated heat on the aluminum
ingots, sprues, or scrap. The Plasma Aluminum Melting(PAM) furnace
is the answer to deal with the next generation melting problems,
allowing energy rates as low as 0.198 kWh/lb, as opposed to induction
melting energy rates of 0.345 kWh/lb. The PAM is an automated furnace
allows quick charging, rapid melting, pouring, and disposal of dross.
Combined effects of conduction from the hearth, forced convection
from Plasma , and radiation contribute to the concentrated heat
source. This furnace is developed for a variety of melting needs
ranging from ingot melting, sprue melting and scrap melting for
recycling. Several custom footprints are available. There
is no such furnace available elsewhere for aluminum melting. In
addition, there is no noise or foul burning gas smell.
For Aluminum a 23KW
Energy to melt
Dross/Total Metal Loss
~12.7 g/s (compare with 3g/s for conventional)
~1 Ton / day
Ingot, sprue and scrap melting
The furnace above was experimentally constructed to allow quick charging of ingots, sprues and scrap
for melting and pouring into holding furnace or to ladles for casting
1. The plasma provides a clean and oxidation-free
2. Energy efficient, as low as 0.198 kWh/lb, as opposed to the industry’s
clean and best energy efficient rate provided by the induction melting
practice at 0.345 kWh/lb.
3. No capital investment for creating induction melting facility.
4. Increased productivity is realized with increased rates of ingots
or sprue loading in to the furnace.
5. Direct utilization of clean molten alloy for die casting, permanent
mould, or sand moulds.
6. The key to success lies with the ability to reduce residence
time of sprue to prevent dissolution of the filter material.
7. Inexpensive, since no need to add expensive pure aluminum to
dilute iron content, unlike the current industrial practice.
How does the energy
density values of PAM furnace compare with conventional furnaces?
Does your conventional furnace manufacturer even talk about energy
density? A typical electric resistance melting furnace will have
an energy density concentration of 64,557 BTU/ft3 as
opposed to the new PAM with 269,146 BTU/ft3, for equal
volume of hot zones. The PAMF has 4 times higher energy per unit
volume compared to electric resistance furnace, thus making it a
unique furnace with highly concentrated power.
How does the quality of melt compare with conventional
furnaces? 1. Although, induction melting furnaces offer somewhat
a rapid melting, but because of its intense stirring activity, breaks
the oxide film from the molten alloy surface and promotes severe
oxidation process leading to generation of more of dross and dross
dispersed melt. As the density difference between the molten alloy
and that of dross is not significantly different, further deteriorates
the quality the cast material resulting in poor ductility, and poor
2. Gas or oil fired furnaces invariably produce nascent hydrogen
from their combustion processes, providing opportunity for excessive
dissolution of the gas leading to hydrogen embrittlement and poor
fracture toughness values. To remove the dissolved gases, an additional
step of de-gasification of molten metal must be employed which will
incur further expenses due to chemicals, tools, waste of energy,
3. The conventional electric sprue melting furnace will melt all
pieces of sprues and remain molten condition for a longer time until
it attains sufficient superheat to facilitate de-gasification treatment.
During this long waiting period of time the material of the filter
will have ample opportunity to dissolve in the melt, resulting in
iron rich aluminum. Large quantities of expensive virgin aluminum
ingots will be needed to dilute the iron, thus making a prohibitively
4. The PAM furnace melts at an extremely rapid rate of 13 g/s and
allows the molten alloy to drain out quickly leaving the steel filter
material behind. Further, the convective plasma provides protective
atmosphere while keeping the thin protective oxide film on the molten
surface intact, without causing it to break, preventing formation
of dross in the absence of turbulence or agitation. Molten aluminum
surrounds itself completely with a thin envelope of oxide film.
As long as this oxide layer remains unbroken, the rate at which
gas is absorbed by the melt is quite low, and further oxidation
5. The dross generated by the PAM is insignificantly low, typically
less than 1%, unparalleled to any known industrial melting practice.
6. Alloy chemistry adjustment is not frequently required using PAM or smooth melt surface
furnaces since the volatile elements such as Li, Mg, and Zn will
not vaporize due to rapid melting, smaller residence time, quick
pouring and faster disposal of filter materials.
Often a question is asked whether DRO machines should be used like a Intense Plasma Melter for scrap and spent dross.
DRO-PAM type furnaces were conceived as continuous melters but the aluminum industry has not really caught on to continuous melting operations. Conventional high [powered plasma furnaces are costly and may not be required.
Melting old spent dross mixed with something like aluminum chip-waste - such recovery methods include melting at a very high temperature e.g. a MHI batch furnace fitted with a DRO e.g. for old spent dross one could use:
In such a furnace a Kg 25 Kg crucible batch can be melted in about 2- 4hrs (depending on crucible temperature). So over a period of a day or so of continuous use 10 loads of 20-25 Kg equaling 250 kg can be melted and transferred to a holding furnace which could have a DRO attached if required.
The DRO provide a very useful ionic cover when used continuously over existing melting furnaces. THE DRO is not the right equipment like a high temperature furnace for oxide melting. The batch furnace above costs about 40 K FOB without any crucible handling devices (i.e. good for about 25 Kg crucible). Once a crucible load is melted, it can be transferred to a 250 Kg holding furnace with the DRO fitted on it if required.
So in summary. The DRO is a very useful add on to an existing furnace and melt holding and melting furnaces. To melt chips and dross, and affect a economic recovery it is perhaps best to melt in a smaller but very high temperature furnace with hard refractories.
Electric melting It is clearly noted from the chart above that electric
heating is the most efficient and clean method of heating. The following
is adapted from an EPRI report on electric heating. Melting, using
electric resistance heating (radiation heating to the crucible),
can be the low-cost choice, as well as provide complete freedom
from the noise and excessive heat of combustion processes. This
simplistic heating method also results in a high quality melt with
low oxidation losses. Resistance furnaces are often suitable for
smaller melting facilities where investment funds are limited and
high production rates are not necessary. Production electric resistance
melting furnaces are available in a range of sizes from 100 lb.
capacity to custom designed furnaces in excess of 20 tons. Crucible
furnaces are generally used in the 250 to 2500 lb. range, while
reverberatory furnaces are suited for higher production requirements.
In normal electric heating, conduction through the walls of the
crucible ultimately melts its contents. The walls of the crucible
are heated radiatively. This is normally efficient for copper and
steel which melt at high temperatures but is not as efficient for
aluminum or zinc. Notwithstanding this issue, the efficiency is
high because using such a construction, there is little heat loss
due by convection or radiation to the outside. Using resistance
elements for heating results in reasonable uniformity and control
than is often possible with gas burners. However indirect gas burners
give better uniformity at low temperatures (such as that used for
aluminum). This uniformity impacts on crucible life. The advent
of the PAM furnace has shown to give the best of all systems i.e.
take advantage of electric heating efficiencies and control and
utilize the same for the benefits of convection heating which is
available from combustion systems.
Such furnaces are often of the reverberatory type. Reverberatory
furnaces are normally used for continuous melting operations. The
wet-bath reverberatory furnace is one of the most popular systems
for melting aluminum. With this type of furnace, raw materials are
introduced at a charging well into a molten bath at one end of the
furnace. The center holding portion of the furnace is sealed off
from the charging and delivery ends by a submerged blade or gate
rendering this section isolated and free of turbulence and fluing.
In the case of dry hearth reverberatory furnaces, scrap and/ or
ingot is placed in a “dry” sloped hearth where the melted
metal continuously runs off into the holding chamber. These furnaces
have lost favor, however, due to higher than average metal losses.
Basin type reverberatory furnaces are usually used in foundries
with medium to low production levels, and are generally designed
for melt loads of 300 to 1000 lb., but can be designed for heat
sizes in excess of 20 tons.
The principal advantage of this furnace is the extremely low energy
required for holding. For example, to hold 1500 lb. of aluminum
at 1380°F requires only 4 to 5 kW compared to 15 to 20 kW for
conventional furnaces. When high capacity furnaces are used, melting
can be during off-peak periods and pouring can be during on-peak
In radiant rod furnaces, electric currents of 4000 to 5000 amperes
are commonly used to heat graphite or silicon carbide resistance
elements which radiate to the furnace load and walls (note however
as described above such elements are not the most optimal). These
furnaces are made to oscillate, thereby facilitating conduction
to the melt from the furnace walls. Radiant rod furnaces require
relatively low investment cost, but are primarily being used as
Environmental (waste) savings
In addition to this, the DRO-Cascade e-Ion many other non-measurable savings,
such as elimination of harmful emissions and noise (no noise), and
increase of productivity. One could anticipate that by going electric many of the harmful emissions
(e.g. CO, CO2, NOx, etc.) associated with existing gas/oil-fired
furnaces will be totally eliminated.
Economic Analysis of Various Types of Furnaces
The factors to be taken into account are: (1) The cost of equipment
and installation. (2) Operating costs, which depend on (a) the utility
costs in the area (b) The energy efficiency of the equipment chosen
(c) The quality requirements of the finished casting (d) The metal
losses (dross) to be expected as a result of the melting process.
In additions there is a cost associated with (a) Regulation and
comfort factors, such as EPA considerations, heat, noise, and air
pollution and (b) The casting size range and the weight of metal
required per day and associated storage and manpower costs.
Installation costs of electric resistance and fossil-fuel-fired
furnaces are comparable. It is not practical to hypothesize a specific
example, as there are too many possibilities to take into account.
In general, fossil-fuel-fired furnaces require fluing, blower equipment,
and in some cases heat exchangers (for preheating combustion fuels);
however, on balance, power controls often result in a slightly higher
investment for electric operations. Another widely used method for
melting is the induction furnace. While induction furnaces cost
more than resistance furnaces their production rates are generally
much higher. An operating cost comparison is presented
in this table to illustrate the relative expenses for a hypothetical
aluminum melting operation. Metal loss includes dross plus flue
loss. The most significant operating cost consideration is not only
in the relative cost of the utilities, i.e., gas, oil, electric,
etc., but the relative metal losses to be expected and the reliability
index. Electric resistance melting yields are high, while metal
losses from fossil-fuel operations may be as high as 8 percent.
When taking into account the metal loss, the current as well as
the projected metal cost at the spout should be used in making investment
plans. Utility costs vary widely in different localities. For example,
gas prices can range from $2.50 to $4.86 per MCF, while electric
costs can range from $0.032/kWhr at off-peak times to $0.13/kWhr
If you are using an electrical furnace then the 10 Kw delivered by the respective Cascade-e-ion model is also saved in the original furnace energy use as this amount is efficiently added by the cascade e-ion.
Energy Efficient Device.
Power Efficiency Savings:
Savings per year:
In the estimates with 2% dross reduction the ROI happens within 6 months. Sometimes much faster or slower but this has to be discussed on a case by case basis for every use. It is a good deal. A key benefit of using the cascade e-ion plasma source comes from the elimination of nitrogen, argon or toxic flux covers normally used during melting of aluminum or silver. The plasma takes air and converts to a nitrogen ion cover. Many other non-measurable savings, such as elimination of harmful emissions and noise (no noise), and increase of productivity. Since gas/oil burners are also partially replaced by the Cascade-e-ion we anticipate that the harmful emissions (e.g. CO, CO2, NOx, etc.) associated with existing gas/oil-fired furnaces will be reduced. This is a good benefit. The comparison is shown below which is focused on greenhouse gas reduction. Although this is a complex question and very dependent on the comparison, a general rule of thumb is that 10 kW DRO additions are useful.
Cascade e-ion systems
Emissions, Health & Environment
Likely to produce CO2, SO2 and soot
Uses combustion gas inputs of fuel and air, commonly requiring plumbing
Typical 20,000 BTU/hr (5.858kW) burners produce about 22 moles of greenhouse gasses per hour
Fossil fuel powered combustion often leads to toxic by products such as Carbon Monoxide
Surfaces impacted by flame may be contaminated with small size soot-like particles
The CleanElectricFlame™ technology produces no CO2, SO2 or soot as a by product
No toxic emissions. Air is typical input.
Electricity powered, no plumbing or piping needed
No venting required
Uses only air input, no other gasses
No greenhouse gasses
Air to Air. It's like changing your combustion flame to an electric flame
Highly efficient, saving on energy costs
No residues left because of process
May improve shelf life and quality of products
Narrow area impact when requiring intense flame, non-uniform heat application
Uniformity requirements may require multiple burners
User configured width of plume
Requires less monitoring, saving on labor costs
Highly combustible, volatile
Incomplete combustion may be a down-stream fire hazard
No combustible gasses used as inputs
Flames are energy inefficient, with only around 10% of their energy able to be utilized for heat as quantized radiation may dissipate heat
Over 90% energy efficient
Realized energy savings may approach 80%. (A 30kW combustible flame may be replaced by a 6kW plasma plume)
Lack of precise control
Frequent quality control issues
Available built-in safety controls including an over-temperature shut-off
Noisy combustion process
Noxious odor is often noted from combustion by products
Cost of Operations
Consumes expensive reactant gasses
Frequent downtime leads to lost revenues and costs of repair
Higher insurance and other costs because of emissions and other flame hazards
Uses air and electricity
No reliance on supply of combustibles
Less downtime, less lost revenues, less cost of repairs
Possibility of lower insurance premiums from improved safety
General aluminum melt furnace comparisons from published article http://mhi-inc.com/one/heat_transfer.html and http://www.scientific.net/KEM.380.209 and other publications.
Energy used (kWh/lb)
Metal loss dross
Indirect fixed crucible
low cost of capital equipment
easy to maintain
gas is cheap
3,300 BTU/lb (0.9969 kWh/lb)
Low pot life
High energy loss
Leave a heel
Direct fixed (open flame)
easy to maintain
gas is cheap
4,000 BTU/lb (1.172 kWh/lb)
Low pot life
Very high energy loss
High uncontrolled emission
Very high noise
Leave a heel
Sloping dry hearth
3,000-5,000 BTU/lb (0.879-1.465 kWh/lb)
Very high melt loss
High energy loss
Improve flame impingement
Charge better scrap
Wet bath reverboratory
3,000 BTU/lb (0.879 kWh/lb)
High energy loss
Electric radiant reverboratory
cold start possible
820 BTU/lb (0.2403 kWh/lb)
Very high currents
Very small sizes
High cost of electricity
Pot life suspect if one element burns
Electric induction channel type
cold start possible
Too much of mixing of dross
Very expensive equipment & large space
Only for holding furnace
Non-metallics in channels
Use only when holding furnace needed
Coreless induction melting
cold start possible
Very expensive equipment
Large space needed
Use fluxing covering salts extensively
Please note this is an add-on to the furnaces above
extremely rapid melting
highly energy efficient
excellent for ingot, sprue and scrap melting
least iron contamination with sprue melting
no chemistry adjustmentsince Zn, Mg, Li will not have time to vaporize
Insignificantly low, < 1%.
No significant drawback
This is a prototype only. Melting furnace
is not for sale, only the Plasma Source and/or the technologies.
Please contact us for more details.
furnaces are unable to create heat on the charge and their efficiency
falls off. DRO Cascade e-ion assisted furnaces have high power
densities and heat transfers directly to the part. Melt rates are estimates that depend on the heat transfer coeffcient and overall power of the melting energy.