Thermal Plasma Gasification of Biomass

Since the 1980s applications of thermal plasmas experienced an important increase. In the 1990s fundamental research led to great progress in the understanding of the basic phenomena involved, and to a renewed interest in applying thermal plasmas to material processing and waste treatment. The application of plasma torches for environmental purposes is a relatively new process. Thermal plasma offers unique capability of carrying extremely high energy by small amount of plasma and ensures high heat transfer rates to treated materials. All materials can be decomposed if they are brought into contact with plasma. Generators of thermal plasma (plasma torches) operate simultaneously as a plasmachemical and a thermal apparatus. The electrical energy of the torches goes into the plasma which transfers its energy to the substances to be treated, thereby triggering a dual simultaneous reaction process in the plasmachemical reactor: the organic compounds are thermally decomposed into their constituent elements (syngas with more complete conversion of carbon into gas phase than in incinerators), and the inorganic materials are melted and converted into a dense, inert, non-leachable vitrified slag, that does not require controlled disposal. Therefore, it can be viewed as a totally closed treatment system. While decomposition of waste and dangerous materials in thermal plasmas has been intensively studied in the last decade and industrial scale systems for treatment of various types of waste has been installed, plasma gasification of biomass is newly appearing application. For this application, the principal goal of the technology is production of fuel gases, principally mixture of carbon monoxide and hydrogen, called syngas. Thermal plasma offers possibility of decomposition of biomass by pure pyrolysis in the absence of oxygen, or with steichiometric amount of oxygen (gasification) to produce high quality syngas, with high content of carbon monoxide and hydrogen and minimum presence of other components. As production of fuel gas is the main goal of the technology, an energy balance of the process is thus much more important than in case of waste treatment, where the principal goal is material decomposition. Gasification is a process by which either a solid or liquid carbonaceous material, containing mostly chemically bound carbon, hydrogen, oxygen, is reacted with air or oxygen. The reactions provide sufficient exothermic energy to produce a primary gaseous product containing mostly CO, H2, CO2, H2O(g), and small content of higher hydrocarbons. Heat