Numerical simulation of hydrogen production by chemical looping reforming in a dual fluidized bed reactor

Although exploitation of Dual Fluidized Bed systems (DFB) is currently being explored in various fields, DFBs present some criticalities, mainly related to effective control of solids recirculation and to avoidance of gas leakage between the beds, extremely critical in Chemical Looping Reforming (CLR) for hydrogen production. For the latter, the choice of the degree of oxygen carrier oxidation/reduction, operation temperature and loop design makes the design even more challenging. This paper aims at the quantitative assessment of the influence of design variables by means of the numerical simulation of a DFB-CLR process operated at steady state conditions. The model couples a simple hydrodynamic simulation of a DFB system equipped with non-mechanical valves for bed solids circulation with a 1D, dynamic and non-isothermal CLR model developed to determine temperature and oxidation degree of solids and gaseous species concentration at the exit of both Air and Fuel Reactors. The DFB, consisting of a riser and of a bubbling fluidized bed (BFB) as Air and Fuel Reactors respectively, was modeled as a combination of interconnected blocks (riser, cyclone, L-valve, BFB, loop-seal) after selection of constitutive equations. Methane and Nickel (II) oxide were selected as fuel and oxygen carrier. Results corresponding to steady state operation are presented and the effects of operating conditions on the expected process performance are assessed. It is concluded that an appropriate choice of both operating temperature and amount of oxygen transported by oxygen carrier from AR to FR is an essential prerequisite in order to ensure process feasibility and good performances in terms of CH4 conversion and H2 selectivity.