The effect of gas permeation through vertical membranes on chemical switching reforming (CSR) reactor performance

A novel membrane assisted fluidized bed reactor concept has been proposed for ultra-pure hydrogen production with integrated CO2 capture from steam methane reforming. The so-called Chemical Switching Reactor (CSR) concept combines the use of an oxygen carrier for supplying heat and catalysing the steam methane reforming reaction and hydrogen perm-selective membrane (thin Pd-membrane) for hydrogen recovery. However, extraction of gas through the membranes influences the hydrodynamics of the fluidized bed by altering the bubble behaviour and the extent of gas back mixing. Bubble properties (size, number and velocity) strongly influence the performance of fluidized bed reactors as they play a major role in heat and mass transfer phenomena. This work experimentally investigates the effects of gas extraction via vertical membranes on the bubble properties using Digital Image Analysis (DIA) technique and numerically using the Two Fluid Model approach (TFM) closed by the kinetic theory of granular flow. The simulation studies were extended to investigate real reactive conditions. A pseudo 2D experimental setup with a multi-chamber porous plate mounted at the bottom of the back plate was used to simulate vertical membranes. This setup allowed for gas extraction in specific locations from the back of the column, thus facilitating studies on the effect of gas extraction rates and locations on the bubble properties. Results show that variation of gas extraction flow rates slightly influences the bubble behaviour, whereas variation of gas extraction locations (varying the area) significantly influences bubble properties. Cold flow simulations showed a reasonable comparison to experimental measurements and reactive simulations revealed very similar hydrodynamic responses to changes in gas extraction rate (membrane permeability) and location. Shifting gas extraction towards the centre of the bed proved to be beneficial in reducing gas back-mixing. Specifically, reducing the number of vertical membranes from 7 to 5 by removing the outer two membranes showed a slight increase in hydrogen extraction performance.