Hydrodynamics of inclined rotating fixed bed reactors

Periodic operation of trickle bed reactors is an academically established process intensification concept, especially in cases where the mass transfer of the gas phase to the catalyst surface dominates the overall reactor performance.
Further advantages such as damping hot spots and reducing maldistribution have been mentioned in many studies. However, the positive effect of the cycling feed at the inlet strongly decays along the reactor length. Furthermore, industrial implementation hurdles are caused by the complex transient reactor behavior and its control.

Operating a fixed bed reactor at quasi steady-state conditions while maintaining a periodic operation can be achieved by rotation of an inclined reactor: Inclination promotes the phase separation whereas the superimposed rotation induces a periodic wetting and draining of the fixed bed, resulting in alternating access of the gas and liquid reactants to the catalyst surface. This new reactor concept is illustrated in Figure 1.

To evaluate the new reactor concept, hydrodynamic studies were conducted to reveal the flow regimes and to elucidate the liquid saturation distribution. The latter is visualized by a noninvasive compact γ-ray computer tomography system (CompaCT) with a spatial in-plane resolution of 2 mm.
These hydrodynamic studies cover variations of reactor inclination (α = 15°-90°), rotational speed (up to 60 rpm) and gas and liquid superficial velocities (uL = 0.01 m/s – 0.05 m/s and uG = 0.025 – 0.05 m/s). Results for additional variations of particle size, liquid properties (deionized water, silicone oil, cumene) will be reported as well. Furthermore, the hydrodynamic behavior of the inclined rotating reactor is compared with the vertical non-rotating trickle bed reactor configuration.

The effect of reactor inclination and rotational speed on the liquid saturation distribution is exemplarily shown in Figure 2. The lower area of the depicted tomograms corresponds to the bottommost area of the counterclockwise rotating reactor. These experiments were conducted with deionized water and air at ambient pressure and room temperature (ϑL = 20 °C) in a tubular reactor (ID = 0.1 m, L = 1.2 m) packed with 4 mm glass spheres.

For the lowest rotational speed, the gas phase flows mainly in the upper region of the reactor cross-section (Figure 2 a, d) with a pronounced entrainment of the liquid phase for the lower inclination (Figure 2 a) and a clear phase separation for the higher inclination (Figure 2 d). Increased reactor rotation equalizes the liquid distribution for both inclinations (Figure 2 b, e) and results in a ring-like flow pattern (Figure 2 c, f) for the highest rotational speed.

The new reactor concept provides additional degrees of freedom for flow modulation: Reactor inclination and rotational speed. Their influence on the flow patterns and liquid saturation distribution has been investigated by noninvasive tomographic imaging. In combination with the gas and liquid flow rates, these new degrees of freedom allow for adjusting residence time and periodicity of wetting and draining, respectively.