Scale-Up Oscillatory Helical-Baffled Reactor for Multiphase Reactions

Scale-up oscillatory helical-baffled reactor for multiphase reactions

Anh N. Phan and Adam P. Harvey

School of Chemical Engineering & Advanced Materials (CEAM), Newcastle University, NE1 7RU, UK

Corresponding to anh.phan@ncl.ac.uk

Mesoscale oscillatory helical-baffled reactor (MOHB), a helical wire embedded inside a smooth tube without modification to the tube, was constructed and characterised at very low net flow rates (net flow Reynolds numbers, Re_n≤10) over a wide range of oscillation conditions. The fluid mixing is controlled by the oscillatory flow and is thus independent of net flow. The flow becomes chaotic at high oscillatory Reynolds numbers and the secondary flow (swirling) becomes active, which imposes an axial velocity component. The coupled effect of the vortex flow and the swirling flow in the presence of helical baffles augments the significant radial mixing and greatly broadens the operating/design window of these reactors. Plug flow performance can be achieved at a ratio of oscillatory Reynolds number to net flow Reynolds number of approximately 10-250 and a helical turn to tube diameter ratio in a range of 0.2-0.6. The highest degree of plug flow was achieved at Strouhal number 0.2<St≤0.1 and Re_o=400-700 with the number of tanks in series equal to the number of helical turns. At a scale of 5mm inner diameter, the MOHB is considered to be effective and robust in scale-down production of high added value products, decreasing the reagents requirements and waste.

Is there a correlation between this mesoscale and a conventional scale? We scaled the mesoscale reactor up to 13 times and 130 times in volume by maintaining geometrical parameters (opened cross-sectional area and helical turn to tube diameter ratio) and oscillatory conditions.  It was found that the same mixing behaviour in terms of residence time distribution profiles of tracers was obtained in the large scales as in the mesoscale.

Keywords: scale-up, helical-baffled reactor, oscillatory flow, plug flow