Chapter 7 - Hydrothermal Gasification of Biomass

Abstract

This chapter deals with hydrothermal gasification of biomass in supercritical water (SCW). It explains the properties of supercritical water and the biomass conversion process in it. It also presents the effects of different parameters on SCW gasification and design considerations for the SCW gasification plants. Hydrothermal gasification involves gasification in an aqueous medium at a very high temperature and pressure exceeding or close to its critical value. While subcritical water has been used effectively for hydrothermal reaction, supercritical water has attracted more attention owing to its unique features. Supercritical water offers rapid hydrolysis of biomass, high solubility of intermediate reaction products, including gases, and a high ion product near (but below) the critical point that helps ionic reaction. These features make SCW an excellent reaction medium for gasification, oxidation, and synthesis. The most important feature of SCW is that one can “manipulate” and control its properties around its critical point simply by adjusting the temperature and pressure. Supercritical water possesses a number of special properties that distinguish it from ordinary water.