In ebullating-bed reactors, a bed of catalyst particles is set in weak suspension by an upward flow of liquid and gas reactants. Comparing to fixed beds, the fluidization of the catalyst particles leads to better mixing degrees, which enhances the mass and heat transfer rates, and prevents the bed plugging and channeling due to the formation of coke in certain processes. In addition to better transport properties, the ebullating-bed technology can also grant operation in longer cycles on what catalyst deactivation is concerned: the fluidization allows for a continuous partial removal of deactivated catalyst particles from the reactor and addition of regenerated catalyst. The catalysts usually used in this kind of devices are extrudates with diameters of the order of 1 mm and length around 3-5 mm.
Catalysts in development for these kind of processes must be tested and screened beforehand in its commercial form in smaller pilot-scale units, which try to reproduce the conditions found under the industrial operation. The smaller size of these units allows for easier, faster and less expensive experimental testing by using a smaller amount of catalyst and reactants. However, these pilot-scale units must be quite versatile, enabling testing a large range of conditions: different fluids (gas and liquid charges) and catalysts, and under a large range of flow rates.
In this work, Computational Fluid Dynamics (CFD) has been used to design a new pilot unit based in an internal turbine for the liquid reactive charge recirculation and mixing, and promoting simultaneously the suspension of the catalyst particles. The reactor internal parts have been designed to avoid problems detected in previous existing testing units, such as the flooding of the pumping turbine and the erosion of the catalyst particles. Rapid prototyping of the internal parts of the new unit has been made for experimental validation using the innovative technique of 3D printing. The degree of fluidization of the particles has been quantified from visualization experiments. The degree of mixing in the reactor has been characterized by RTD and mixing time experiments, and from CFD simulations coupled with transport equations of the moments of the age of the fluid.