Nowadays, transferred type arc plasma torches have been widely present in industrial applications, in particular, using melting pool of electrically conducting materials such as arc furnace, welding and volume reduction of radioactive wastes. In these applications, the melting pools are normally employed as an anode, thus, heat flux distributions on anode melting pool need to be characterized for optimum design of melting pool system. For this purpose, we revisited the one-dimensional model of the anode boundary layer of arcs and solved governing equations numerically by using Runge-Kutta method. In addition, the direct melting process of non-combustible wastes in the crucibles were discussed with the calculation results.

In this work, we report test results for direct melting of non-combustible wastes by using a 100 kW class transferred type plasma torch. For this purpose, non-combustible wastes consisting of metals and sands were prepared, weighed and melted by a transferred arc in a ceramic crucible with inner diameter of 150 mm. Test results reveal that 75wt% M6 iron bolts mixed with 25wt% sands were completely melted down within 140 seconds at the plasma power level of 83.8 kW, producing melting speed of 100 kg/hr and volume reduction rate of 62.8%. In addition, for simulated wastes consisting of 77.3wt% metal chips and 22.7wt% sands, the volume reduction rate high than 88% was achieved at 50 kW plasma power. These results indicate that non-combustible wastes can be treated efficiently when directly melting them by using transferred type plasma torch.

We developed a 100 kW Class Transferred Type Plasma Torch applicable for melting of noncombustible metal wastes. By employing reverse polarity discharge structures for hollow electrode plasma torch, a transferred type arc plasma was generated stably with long arc length higher than 10 cm at the arc currents of ~400 A and gas (N2) flow rate of ~50 lpm. High arc currents and high arc voltages caused by the increased arc length could input high power level of ~100 kW to the noncombustible metal wastes, enabling quick melting. In addition, relatively long arc length and low gas flow rates can help reduce the deposition of melted materials on the exit surface of the torch. Thanks to these features, the developed plasma torch is expected to be suitable for small-scaled and portable melting system.