Biomass gasification in supercritical water

The use of biomass is at the heart of questions about energy resources in the 21st century. xxi ^e century. It is one of the major challenges. The term biomass has a wide range of meanings, from noble biomass destined for food use, such as cereals, to biomass that can be assimilated to waste, such as vinasse from beet production or biological sludge from wastewater treatment plants. In the case of wet biomass, one recovery process of interest is supercritical water gasification. This process avoids the need for a drying stage and, given the right pressure and temperature conditions, produces an energy gas that can contain hydrogen, methane, carbon monoxide and/or light hydrocarbons. The interest aroused by this process is therefore part of the global issue of access to non-fossil energy sources, as well as the issue of greenhouse gases, since the use of biomass is part of a short carbon cycle. Supercritical water gasification is particularly suited to very moist biomass (over 70% moisture content), which does not need to be dried beforehand. Reaction temperatures are relatively low (maximum 700°C), compared with conventional or dry gasification processes (typically 900°C). This limits the production of polluting gases, such as dioxins or NO _x . Similarly, the aqueous solvating medium limits the formation of solids and tars. The gases targeted are mainly hydrogen, but also a mixture of hydrogen and carbon monoxide (mixture for Fisher Tropsch synthesis), or methane production. The influence of the main operating conditions on the nature and yields of conversion will be detailed in this article (pressure, temperature, initial biomass concentration, presence or absence of catalysts). As industrial development of this process has not yet taken place, the most important laboratory pilots (up to 100 kg.h- ¹ ) will be presented.