Experimental and fluid dynamic study of continuous supercritical water gasification of glucose

Abstract

The supercritical water gasification (SCWG) of glucose as a model compound for H2 production is studied in term of process development at 25MPa and 650°C. Gasification has been investigated using a laboratory scale continuous plant comprising a continuous down flow reactor with a volume of 200cm3, a heat recovery section and pre-heat of the biomass to simulate more closely an industrial design. Feed streams (pure water and glucose solution) are introduced at the top of the vessel and products are extracted from the bottom. The reactor is equipped with various inlet points that allow to modify the inlet position of reacting streams in order to study the effect of stream mixing on reaction performance. Moreover, in order to obtain a description of the fluid flow inside the reactor, computational fluid dynamics (CFD) simulations were carried out. The simulations were conducted by the ANSYS CFX 15 code which uses a finite volume method. Simulation allowed not only to understand the complex fluid dynamics that describes the system, but also to optimize the reactor configuration in order to attain good process performance.Experimental results coupled with CFD analysis, allowed to find that the reactor has the top section that behaves like a mixed reactor and the bottom section that behaves like a plug flow reactor. The two jet streams (water and glucose solution) entering the reactor cause back mixing in the top-side of the reactor, so contributing to rapid initiation of reaction and down-flow of species through the chamber. Using the best reactor configuration in term of mixing and temperature distribution allowed to maximize the gasification efficiency and H2 yield up to 72% and 74% by mole, respectively.