Electrolyte Pumping Optimization in Already Manufactured Vanadium Redox Battery Based on Experimentally Determined Electrical and Hydrodynamic Losses

Abstract

Herein is presented an optimization of electrolyte pumping systems in industrial vanadium redox flow batteries (VRBs). The main advantages of the VRB relate to its prolonged service life, outstanding dynamic response, and flexible controllability during charge/discharge processes. In spite of their exceptional electrical parameters, VRBs suffer from significant energy requirements in the hydraulic pumping system needed for circulation of electrolyte from external tanks to battery cells. The industrial VRB equipped for this purpose with centrifugal driven by controllable electric motors hydraulic pumps were made from plastic components and able to work in the aggressive acid electrolyte. Electrolyte flow is carried out through the entire hydraulic system and battery cells containing carbon electrodes and providing electrochemical reduction-oxidation reactions of vanadium ions. Currently, electrodes in the VRB are made from carbon felt material because its porous structure possesses high specific surfaces which provide more reaction sites for the electrochemical reaction and thus a sufficient current (power). In spite of the significant electrode surface area, intensive electrolyte flow is required for eliminating effects of concentrated polarization of inactive vanadium ions in the vicinity of the electrodes’ surface causing a diminution of battery output power. However, carbon felt has significant hydrodynamic resistance, diminishing the overall efficiency of VRBs. This disadvantage could be significantly decreased by the correct selection (optimization) of electrolyte flow rate using as a criterion, a minimum energy surplus comprising hydrodynamic and electrical losses. In the already manufactured VRB, such optimization could be done by the appropriate control of the electrical motors driving electrolyte pumps. However, manufacturers do not inform end-users regarding all main battery components, and partly it looks as an aggregate is assembled from black-boxes. Therefore, this optimization problem seems a rather challenging task requiring a special approach. The present paper proposes an optimization of the available VRB hydraulic system including build-in centrifugal pumps and driving electrical motors based on experimentally determined battery internal electrical resistance and hydraulic losses. The purpose of this optimization is to obtain maximum VRB efficiency.