HYDRODYNAMIC STUDY OF A NOVEL DUAL FLUIDIZED BED GASIFIER USING NUMERICAL SIMULATIONS
This paper presents a numerical study of gas-solid flow dynamics in a Dual fluidized bed gasifier (DFBG). A novel design of Dual fluidized bed (DFB) gasifier is proposed, comprising of a fast bed combustor and a bubbling fluidized bed gasifier coupled together with a provision of bed materials circulating between the reactors. DFBG does not need external heating source to generate heat for endothermic gasification reactions to produce nitrogen-free syngas. Heat required to sustain gasification reactions is supplied from the combustor where a part of fuel is burnt in air. Connection of fluidized bed reactor to combustor via a fluidized loop seal is achieved in such a way that optimal range of solids circulation rates can be obtained. Loop seal prevents direct contact between the syngas and the flue gas. To arrest momentum of gas-solid flow at the end of riser, a diffuser is used. DFBG system is designed such that it is readily scalable to pilot scale. To investigate the practicability of current DFBG assembly, 3D simulation of a laboratory-scale model has been conducted using commercial CFD software Ansys/Fluent. Optimum operational parameters recommended in literature are utilized. The Eulerian-Eulerian approach is employed to simulate two phase flow dynamics in which both phases are considered as interspersed continuum. Kinetic theory of granular flow is used to model particulate phase properties. Solid holdup profiles indicated stable solid circulation in the system. Numerical simulation results also confirm affirmative hydrodynamic results before the actual operation of the cold flow setup.