Abstract.  Water vapour plasma technologies could be used for the conversion of biomass to hydrogen rich synthetic gas and for the neutralization and utilization of hazardous wastes. Formation of water vapour plasma has been investigated using a linear direct current plasma torch with stair stepped anode. A new device with an unique structure, operating at atmospheric pressure has been designed and tested at Lithuanian Energy Institute, Plasma Processing Laboratory for the innovative and environmental friendly plasma treatment of organic materials. The main operating conditions of plasma torch and main parameters of water vapour plasma jet were investigated. The power of plasma torch was 25–45kW; arc current was 140–180 A, the arc voltage was 172–231 V, the efficiency was 0.5–0.78. The average temperature of water vapour plasma jet in exhaust nozzle was 2600–3500 K, and the plasma jet velocity was 200–310 m/s.

Emission lines, registered by the optical emission spectrometer AOS4-1, are analyzed to observe the chemical composition of water vapour plasma jet. The optical emission spectrum measurement shows that the water molecule in the plasma is decomposed into H, OH and O radicals. Hydrogen is very desirable in the formation of high caloric synthetic gas (CO+H₂) during thermal plasma gasification of organic materials.

The summarized results can help to calculate and design gasification systems of biomass, to establish optimal parameters for stable operation of plasma generator and regulate the process parameters.