27 Nov Coupling Electrodialysis with bipolar membranes with renewable energies through advanced control strategies
Calogero Cassaro, Giovanni Virruso, Andrea Cipollina, Adriano Fagiolini, Alessandro Tamburini, Giorgio Micale.
Recently, EU is directing its priorities to the implementation of innovative strategies for waste valorisation and smart use of energy, pushing towards ecological transition. Powering water treatment technologies with renewable energies, using the process buffering capacity as a way to indirectly store energy, has been recently proposed as an effective strategy for smart energy use. With this respect, electrodialysis with bipolar membranes (EDBM) can be particularly suitable due to the high energy intensity, coupled with an extreme flexibility of its operational modes.
EDBM is an electro-membrane process able to convert saline wastewater into valuable products such as acids and bases, simply by supplying electric power. This work was focused on the development of advanced control systems allowing EDBM to operate under transitory regimes following the highly variable trend of renewable energy availability, adapting the operating conditions and the process targets according to the variable power input offered during a normal day.
To this aim, a pilot scale EDBM unit (provided by FuMA-Tech GmbH) was operated and tested in Lampedusa island (Italy) in feed and bleed configuration under two different scenarios (summer and winter) at a fixed concentration target of acids and base (0.5 M of NaOH and HCl). In the hours of the day with an available power higher than a minimum threshold value (2.0-6.5 kW), the controller was able to keep the outlet concentration at its target (0.5 M of NaOH and HCl) by letting the outlet flowrate of the product to vary from 0.5 up to 3 l min-1.
In these operating conditions, the controller was able to guarantee high product quality, still retaining high specific productivity (in the range of 0.1-0.2 kg h-1m-2) and low consumption (in the range of 1.3-1.9 kWh kg-1 of NaOH and 1.8-2.4 kWh kg-1 of HCl). In all cases, the parallel control logic allowed to tune the applied voltage in order to meet the electric power availability, while manipulating the outlet flowrate to meet the desired product specification. The obtained results demonstrate for the first time at the pilot scale how EDBM can be particularly suitable to valorise, in industrial relevant scenarios, available saline streams and unstable energy sources, thus pushing towards the industrial implementation according to sustainable and circular values approaches.
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