Biomass Gasification in Supercritical Water - A Review

Supercritical water possesses a number of important characteristics that make it suitable for oxidation, synthesis and gasification reactions. It is especially advantageous for very wet biomass whose gasification in this medium avoids the large expense of energy required for drying. Although the process is in laboratory scale it has a great potential for production of hydrogen and other gases from biomass. This paper reviews the present state of the art and summarizes major observations arrived at in small scale laboratory flow and batch reactors. Effects of operating parameters like, pressure, temperature, etc., on the yield and conversion are discussed. Catalysts appear to play an important role in increasing the conversion rate and decreasing the reaction temperature for gasification. Heat recovery from the product stream holds key to making the gasification process auto-thermal. Heat exchanger efficiency, therefore, plays an important role in this process. Several investigators have used the equilibrium model and exergy analysis for thermodynamic analysis of supercritical gasification plants. Energy efficiency of such a plant could be around 50%.