Gasification of aqueous biomass in supercritical water: A thermodynamic equilibrium analysis

Abstract

The aim of this work is to give insights into the gasification of aqueous biomass in supercritical water. More precisely, a mathematical model based on the thermodynamical equilibrium assumption is derived in this study. This model allows the computation of the solid, liquid and gas phases produced in a process composed of a gasification reactor and a separator. The composition of these three phases is computed in terms of fractions of CH 4, H 2, H 2O, CO, CO 2, H 2S, NH 3, C 6H 5OH, CH 3COOH, CH 3CHO, C (s) and minerals. In the reactor, this composition is computed according to the derivation of balance equations on atoms and to the derivation of equations translating chemical equilibrium between species. Because of the specific conditions prevailing in this device (above the critical point of pure water), the computation of the activity of chemical species in the reacting media is performed using Peng–Robinson equation of state. The modelling of the separator is performed using mass balances as well as equations translating physical equilibrium of species between liquid and gaseous phases. The numerical predictions of this mathematical model are compared to experimental results obtained in the case of gasification of methanol and glucose in supercritical water. The gasification of sewage sludge is also investigated in this study.