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

Abstract

tThe supercritical water gasification (SCWG) of glucose as a model compound for H2production is studiedin term of process development at 25 MPa and 650◦C. Gasification has been investigated using a labora-tory scale continuous plant comprising a continuous down flow reactor with a volume of 200 cm3, a heatrecovery 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 extractedfrom the bottom. The reactor is equipped with various inlet points that allow to modify the inlet positionof reacting streams in order to study the effect of stream mixing on reaction performance. Moreover, inorder to obtain a description of the fluid flow inside the reactor, computational fluid dynamics (CFD) sim-ulations were carried out. The simulations were conducted by the ANSYS CFX 15 code which uses a finitevolume method. Simulation allowed not only to understand the complex fluid dynamics that describesthe 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 sec-tion 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 thetop-side of the reactor, so contributing to rapid initiation of reaction and down-flow of speciesthrough the chamber. Using the best reactor configuration in term of mixing and temperature dis-tribution allowed to maximize the gasification efficiency and H2yield up to 72% and 74% by mole,respectively.