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Remanufacturing and Advanced Machining
In high-pressure (p > 10 kPa), direct-current (DC), and radio-frequency inductively coupled plasma (ICP) devices operating with common plasma gases (Ar, N 2 ,
H 2 , He) at flow rates of 100–300 lpm, the torch input power can be up to 150 kW.
For the same arc current, the anode heat flux for the CO 2 /CH 4 plasma is significantly
up to three times higher and the overall thermal efficiency of the CO 2 /CH 4 mixture
is much better (65–75%) than of Ar (<50%), despite the higher heat losses. Thus,
at a given current, the CO 2 /CH 4 mixture generates a much higher power than the
argon mixture does. For example, the torch is capable of operating at a power of up
to 70 kW at arc currents of less than 400 A when the plasma-forming gas consists
of a mixture containing 70% CO 2 and 30% CH 4 . The arc power is limited by the
maximum heat flux withstandable by the channel wall, which is ca. 2·10 5 kW/m 2
(Mostaghimi et al., 2017).
The plasma process is governed by a large number of parameters from input power
to furnace configuration and can be generated using various types of plasma reactors.
Thermal plasma has found its application in coating technologies, synthesis of fine
powders, spheroidization with densification of powders, slag metallurgy, a wide range
of laboratory and industrial processes, and at various stages of product life cycle until
waste destruction and recycling (Samal, 2017). It is especially useful in the case of
metal-containing waste and new wastes and has a great potential in recycling. Plasma
methods prove to be an efficient and environmentally friendly way for processing of
various metal-containing waste types, such as printed circuit boards, red mud, galvanic sludge, zircon, aluminum dross, and incinerated ash. plasma methods, which
include DC extended transferred arc plasma reactor, DC non-transferred arc plasma
torch, RF thermal plasma reactor, as well as argon and argon–hydrogen plasma jet are
particularly useful. In addition, the plasma arc melting technology has a better purification effect on the extraction of useful metals from metal-containing waste, provides
a substantial volume reduction of waste materials, and ensures a low leaching toxicity
of solid slag. Plasma processing can be applied to all kinds of metal waste materials
(Du et al., 2018). Moreover, plasma-assisted pyrolysis and gasification of different
sorts of waste can be performed (Sikarwar et al., 2020):
• Using DC plasmatrons: medical waste, wood, municipal solid waste (ca.
2.1 billion tons per year are produced), carpet waste, solid waste, used old
tires, polypropylene, agricultural residue, granulated metal powder, C coating from CH 4 , vanadium ore
• Using DC-RF hybrid fixed bed reactor: charcoal deformed after treatment
• Using RF plasmatrons: MSW with raw wood, tire powder, rice straw, polyethylene, polypropylene, heavy oils
• Using microwave (MW) plasmatrons: spirulina algae, polyethylene, glycerol
From the industrial perspective, the main advantages of plasma processes compared
to other methods are as follows (Vandenabeele and Lucas, 2020):
• Plasma techniques are environmentally clean, require very small quantities
of chemicals, and produce little waste.
Remanufacturing and Advanced Machining
In high-pressure (p > 10 kPa), direct-current (DC), and radio-frequency inductively coupled plasma (ICP) devices operating with common plasma gases (Ar, N 2 ,
H 2 , He) at flow rates of 100–300 lpm, the torch input power can be up to 150 kW.
For the same arc current, the anode heat flux for the CO 2 /CH 4 plasma is significantly
up to three times higher and the overall thermal efficiency of the CO 2 /CH 4 mixture
is much better (65–75%) than of Ar (<50%), despite the higher heat losses. Thus,
at a given current, the CO 2 /CH 4 mixture generates a much higher power than the
argon mixture does. For example, the torch is capable of operating at a power of up
to 70 kW at arc currents of less than 400 A when the plasma-forming gas consists
of a mixture containing 70% CO 2 and 30% CH 4 . The arc power is limited by the
maximum heat flux withstandable by the channel wall, which is ca. 2·10 5 kW/m 2
(Mostaghimi et al., 2017).
The plasma process is governed by a large number of parameters from input power
to furnace configuration and can be generated using various types of plasma reactors.
Thermal plasma has found its application in coating technologies, synthesis of fine
powders, spheroidization with densification of powders, slag metallurgy, a wide range
of laboratory and industrial processes, and at various stages of product life cycle until
waste destruction and recycling (Samal, 2017). It is especially useful in the case of
metal-containing waste and new wastes and has a great potential in recycling. Plasma
methods prove to be an efficient and environmentally friendly way for processing of
various metal-containing waste types, such as printed circuit boards, red mud, galvanic sludge, zircon, aluminum dross, and incinerated ash. plasma methods, which
include DC extended transferred arc plasma reactor, DC non-transferred arc plasma
torch, RF thermal plasma reactor, as well as argon and argon–hydrogen plasma jet are
particularly useful. In addition, the plasma arc melting technology has a better purification effect on the extraction of useful metals from metal-containing waste, provides
a substantial volume reduction of waste materials, and ensures a low leaching toxicity
of solid slag. Plasma processing can be applied to all kinds of metal waste materials
(Du et al., 2018). Moreover, plasma-assisted pyrolysis and gasification of different
sorts of waste can be performed (Sikarwar et al., 2020):
• Using DC plasmatrons: medical waste, wood, municipal solid waste (ca.
2.1 billion tons per year are produced), carpet waste, solid waste, used old
tires, polypropylene, agricultural residue, granulated metal powder, C coating from CH 4 , vanadium ore
• Using DC-RF hybrid fixed bed reactor: charcoal deformed after treatment
• Using RF plasmatrons: MSW with raw wood, tire powder, rice straw, polyethylene, polypropylene, heavy oils
• Using microwave (MW) plasmatrons: spirulina algae, polyethylene, glycerol
From the industrial perspective, the main advantages of plasma processes compared
to other methods are as follows (Vandenabeele and Lucas, 2020):
• Plasma techniques are environmentally clean, require very small quantities
of chemicals, and produce little waste.