Fluidized bed reactor assisted by Oxygen Transport Membranes: Numerical simulation and experimental hydrodynamic study

Abstract

In the near future, H2 is bound to become an important energy carrier used for surplus power storage and for sustainable transportation. An innovative technology for the production of a H2 rich gas is the Sorption Enhanced Reforming (SER) of hydrocarbons: a solid CaO-based sorbent is used to capture CO2 produced by reforming and water gas shift, enhancing the equilibrium. CaCO3 is decomposed in a fluidized bed oxy-combustion calciner and the sorbent recycled. In this work, the interest is focused on the Calcium Looping (CaL) cycle, more specifically on the combustor/calciner fluidized bed reactor of the pilot scale platform ZECOMIX (ENEA – 5 kmol/h of H2). The feasibility to feed O2 to a bubbling fluidized bed calciner by means of Oxygen Transport Membranes (OTM) is studied using a simulation model. The fluidizing flow rate is made of CO2 and CH4, preliminarily heated up to 700–850 °C by heat exchange with the output gas stream (above 900 °C); overall gas flow rate and methane content are enough to reach vigorous bubbling fluidization (u ≈ 10 umf) and temperature required by calcination, respectively. Cold model experimental tests with a cylindrical bubbling fluidized bed reactor with internals (vertical rods mimicking the OTM system) are carried out to support the design of the calciner unit in the ZECOMIX experimental platform. The hydrodynamic study is performed under ambient conditions to simulate fluidized bed expansion and to evaluate bubbles behavior in the calciner, in presence of vertical, tubular membranes for oxygen transfer.