Thermal plasmas with a power of less than 400 kW: applications

Thermal plasmas cover a very wide range of applications: cutting or welding of metal parts, surface treatments and deposits, spheroidization and particle purification, chemical analysis, synthesis of nanometric or ultra-fine powders, manufacture of shaped parts, extractive metallurgy, metal remelting-purification, heating of casting tundishes, chemistry, waste treatment... Some applications are very well established (since the 1940s, but generally since the 1960s), but others are in the making.

Torch technology (see "Thermal plasmas: production" dossier) ) has made great strides over the past 25 years for a number of reasons:

• the need for industry to develop more efficient processes;

• the attractive cost of electricity in some countries (mainly for high-power applications (> 1 MW));

• the potential for developing new materials and corresponding technologies;

• greater cooperation between equipment manufacturers, researchers, industrialists involved in the various processes and electricity producers.

However, despite numerous technological advances over the past twenty-five years, and feasibility demonstrations in the laboratory or at prototype scale, the number of large-scale industrial applications is still relatively low. The reasons for this are

• an overestimation of the potential of plasmas, which has led to a certain disappointment among users;

• the lack of fundamental studies to support technical development, in particular to obtain reproducible operating conditions (up to 60 macroscopic parameters can condition the operation of a plasma process);

• natural electrode wear (for arc torches) that users don't always know how to compensate for;

• economic issues, all the more crucial when the plasma process is applied to a low value-added product. For example, the use of plasmas on blast furnaces is directly linked to the relative price of coke/kWh.

Numerous applications have been developed industrially in the power range from a few kilowatts to a few hundred kilowatts. Others seem promising at the laboratory level, but have not yet seen the light of day. If we consider the breakdown between arcs and RF (radio frequency) discharges, the vast majority of applications use the arc process. For power applications ranging from several hundred kilowatts to a hundred megawatts, apart from two pure chemistry applications, plasmas have made their breakthrough mainly in metallurgy, and more recently in waste destruction....