Predicting power consumption in continuous oscillatory baffled reactors

Abstract

Continuous oscillatory baffled reactors (COBRs) have been proven to intensify processes, use less energy and produce fewer wastes compared with stirred tanks. Prediction of power consumption in these devices has been based on simplistic models developed for pulsed columns with single orifice baffles several decades ago and are limited to certain flow conditions. This work explores the validity of existing models to estimate power consumption in a COBR using CFD simulation to analyse power density as a function of operating conditions (covering a range of net flow and oscillatory Reynolds numbers: !" #$% = 6 − 27 / !"-= 24 − 96) in a COBR with a single orifice baffle geometry. Comparison of computed power dissipation with that predicted by the empirical quasi-steady flow models shows that this model is not able to predict correctly the values when the flow is not fully turbulent, which is common when operating COBRs. It has been demonstrated that dimensionless power density is inversely proportional to the total flow Reynolds number in laminar flow and constant in turbulent flow, as is the case for flow in pipes and stirred tanks. For the geometry studied here (1/2) * = 330 !" 7 ⁄ in laminar flow and (1/2) * = 1.92 in turbulent flow.

Mixing performance in continuous oscillatory baffled reactors

“…It is evident from Fig. 3(a) that the velocity field is mesh independent using a 350 mm mesh, which is consistent with the observation made in our earlier work using ANSYS CFX (Avila et al, 2020). However, when using this mesh size, the concentrations are highly diffused.…”

“…As will be evident in the next section, extremely fine meshes are needed to avoid numerical diffusion of the high Schmidt number scalars. Our previous simulations to study the hydrodynamics (Avila et al, 2020) used ANSYS CFX, simulating a wedge of the true geometry. However, for the study of mass transfer it soon became evident that massively finer meshes are needed and that there would be significant benefits in using ANSYS Fluent for these sim ulations.…”

“…The 2D mesh was constructed in ANSYS Meshing using a paving algorithm, which used mostly quadrilateral cells whilst occasionally introduc ing triangular cells to fit geometric constraints. The starting point was a mesh size of 350 mm that was shown to give mesh indepen dent simulations for the hydrodynamics (Avila et al, 2020); this mesh was then progressively refined with the smallest cell size used being 30 mm.…”

Another Critical Look at Three-Phase Catalysis

“…Oscillatory amplitudes from half to one baffled cell length and oscillation frequency from 1 to 8 Hz can be employed, the latter is much higher than that in pulsed trickle bed reactors. The energy dissipation rate in OBR was developed by assessing inertial and frictional effects of the flow together with pressure drop due to a static head, [145][146][147][148] as in Equation 2:…”

“…Effect of energy density (P/V) on initial reaction rate (r 0 ) at different pressures in PARR and OBR. Working conditions: initial molar ratio 3-butyn-2-ol/Pd ¼ 1,360 and temperature ¼ 323 K 148. OBR, oscillatory baffled reactor.…”