Novel three-phase steam–air plasma torch for gasification of high-caloric waste

Highlights: • The steam–air plasma torch volt–ampere characteristics and efficiency were experimentally determined. • The increase in steam content of the plasma forming gas leads to voltage and power growth. • High efficiency of the plasma torch is experimentally confirmed. • The achieved levels of plasma energy content allow conversion of plastic waste into syngas virtually free from ballast gases. - Abstract: Research results are presented for an AC electric arc that burns a mixture of steam and air in a three-phase high-voltage plasma torch and can be implemented to produce plasma for plastic waste gasification. The dependences of electric parameters on the ratio of the steam to air mass flows (H2O/air ∼1–6) at an approximately constant total mass flow of the plasma-forming gas are obtained during several experiments. During the experiments, the arc parameters were as follows: voltage drop of 1.0–1.8 kV, current of ∼28.5 A and power of ∼52–86 kW. The thermal efficiency of the plasma torch was ∼94–95%. CCD cameras operating at 4000 fps were used to determine the average discharge length of ∼798 mm. Photography with a high shutter speed (1/8000 s) was used to determine the average arc diameter (∼4.47 mm). Arc temperatures were calculated (10,000–11,500 K) using the thermodynamic equilibrium approach. Experimental results indicate that increases in the steam content of the steam–air plasma lead to a reduction of the arc's temperature and electrical conductivity. Using an equilibrium approach, the main parameters of plasma gasification were estimated: syngas yield (3.62–3.48 m3/kg), composition (H2 – 55.5–62.5, CO – 32.8–34.1 vol.%) and energy consumption (11.0–12.3 MJ/kg)