Plasma Flame Sustained by Microwaves and Burning Hydrocarbon Fuel: Its Applications

Abstract

Thermal plasma torches have been developed for various industrial applications. Industries require them to be high power, contaminant-free, low-maintenance, low-cost, and largevolume. Principally, the plasma torch is a device to produce an arc plasma column between two electrodes. There are several kinds of plasma torches, including dc arc torch, induction torch, and high-frequency capacitive torch. The dc arc torch is operated by the dc electric field between two electrodes at a severe environment of high arc current in the range from several tens to thousands of amperes. Therefore, their electrodes are replaced often due to their limited lifetime, in particular an oxidative environment. Almost all radio frequency torches are inductively coupled discharges. Their typical thermal efficiencies (% of power effectively dissipated in the plasma forming gas) are in the range of 40-50% (Fauchais & Vardelle, 1997). These conventional torches also have a small volume of plasma, high operational cost and require many expensive additional systems for operation. Although the conventional plasma torches are used in many industrial applications, the wide acceptance of these processes is limited by economic, competitive, reliability, and other concerns. From the reason above-mentioned, they may not be useful in environmental applications. In order to overcome problems related with the conventional plasma torch, an electrodeless microwave plasma torch at atmospheric pressure was developed (Hong et al., 2003; Kim et al., 2003). Microwave plasmas operated at the atmospheric pressure, especially waveguidebased plasma, have been subject of increased attention during the last decade (Margot, 2001; Moisan et al., 2001). Such an interest comes from their potential and actual use in various applications, including excitation sources for elemental analysis, lighting, and purification or remediation of gas effluents detrimental to the environment (Hartz et al., 1998; Woskov & Haddi, 1999). The microwave plasma torch can easily be made by modifying typical household microwave ovens as inexpensive method (Kim et al., 2003). Therefore, the microwave plasma torch is simple, compact and economical. Furthermore, in previous works, the microwave plasma torch has been investigated in various applications such as the abatement of CF4, NF3 and SF6, the elimination of chemical and biological warfare agents, and synthesis of carbon nanotube, titanium dioxide, titanium nitride, and zinc oxide (Hong et al., 2004; Kim et al., 2007). Although the microwave plasma torch in air discharge 10