Experimental and numerical evaluation of the performance of the electrochemical reactor operated with static and dynamic electrodes in the reduction of hexavalent chromium

In this work, we assess two electrochemical reactor designs to reduce hexavalent chromium diluted in rinsing waters from the electroplating industry. One reactor has a dynamic electrode composed of rotating rings electrodes (RRE), and the other is a novel design that has static electrodes (SE) with two pitched blade turbines (PBT). The SE, named "Electro-Baffles", disrupts the tangential flow induced by impellers and promotes the electrochemical reactions. The hydrodynamic behavior of both designs was assessed by Computational Fluid Dynamic using the multiple reference frame approach. Experimental measurements of the mixing and treatment times to validate the results were performed. The rotational velocity of the RRE was150 rpm, the optimum rpm reported, while for the impellers of the other design, two speeds were tested; one, operated at the same rpm as for RRE and the other, at 362 rpm, to operate it at the same Reynolds Number (Re) as the RRE. The pumping effectiveness (eta(Q)) using SE increased up to 86% in comparison with the RRE design, due to the enhancement in the axial circulation generated by the impellers and the flow interactions with the "Electro-Baffles". Hydraulic SE system improvements reduced the mixing time by 16% with the PBT rotating at 150 rpm, while at the same Re, the reduction was 47%. The total specific energy had a reduction of 39% when the two PBT rotated at 362 rpm, whereas by about 21% at 150 rpm.