Current-voltage (I-V ) characteristics of a non-transferred DC arc plasma spray torch operated in argon at vacuum are reported. The arc voltage is of negative characteristics for a current below 200 A, flat for a current between 200 A to 250 A and positive for a current beyond 250 A. The voltage increases slowly with the increase in carrier gas of arc. The rate of change in voltage with currents is about 3∼4 V/100 A at a gas flow rate of about 1∼1.5 V/10 standard liter per minute (slpm). The I-V characteristics of the DC plasma torch are of a shape of hyperbola. Arc power increases with the argon flow rate, and the thermal efficiency of the torch acts in a similar way. The thermal efficiency of the non-transferred DC plasmatron is about 65∼78%.

The chemical therm0dynarni.c equilibrium of acetylene production by coal pyrolysis in hydrogen plasma was studied. The thermodynamic equilibrium is obtained by using the method of free energy. Calculated results show that the hydrogen concentration in the equilibrium system is very important for the acetylene production by coal conversion and the energy consumption for the production of acetylene per-kilogram strongly depends on the hydrogen concentration and the temperature.

This paper describes the equilibrium compositions of the typical medical waste under high temperature pyrolysis by a steam plasma torch using the NXSX CEX2 program. Various components from selected typical medical waste were input to the program along with the treatment temperature from 1000 K -4100 K. The program then performed the Gibbs free energy calculations and searched for the equilibrium composition with minimizing the total system Gibbs free energy. The calculation results indicate that, the equilibrium composition of a system C-H-0 at C/O = 1 in the temperature range of 1400 K -2000 K has demonstrated that gas composition are CO and Hz mainly. the other components (COz, CzH4. C2Hz. CH4 etc.) is less than 1% by volume and the degree of raw material transformation is about 100%. Comparison with air plasma, the steam plasma treatment will not produce nitrogen oxides, if the materials are free of nitrogen element.