REVERSE ELECTRODIALYSIS FOR POWER PRODUCTION FROM OILFIELD WASTEWATERS

Abstract

Produced waters (PWs) are wastewaters generated by crude-oil extraction processes. They can present very different characteristics depending on the field location and production process. Dispersed oil, dissolved organics and solid particles are usually the main components. Moreover, PWs can contain a very high quantity of dissolved salts 1, with a total dissolved solid (TDS) concentration up to 300 g/L. Each barrel of extracted oil requires the simultaneous extraction of 3 barrels of produced water2 on average. PWs are often discharged into the sea, or sent in evaporation ponds thus leading to a dramatic environment impact3. Reinjection in the extraction well is currently the most common and safest option. With this respect, the high salt solution concentration of such solutions may be used in salinity gradient power (SGP) technologies in order to valorize them before the reinjection by producing clean energy. Reverse Electrodialysis (RED) is one of the most promising SGP technology, and has attracted the attention of research especially when natural solutions are involved. RED units are composed of several repetitive units, consisting of two channels, an anion exchange membrane (AEM) and a cation exchange membrane (CEM). When fed by two solutions with different salt concentrations, a potential difference is generated by a salinity gradient across each membrane, leading to an ionic flux between the two solutions. At the ends of the stack, two electrodes are inserted, rinsed by a solution containing redox couples, allowing the conversion of the ionic flux into electric current when an external load is connected to the RED unit. In the present work, the possibility to generate power, from real oil-industry brines via RED is investigated. An experimental campaign was performed by testing a 10 cm x 10 cm unit in long-run continuous operations, monitoring its performance for more than 25 days. Several anti-fouling strategies were adopted in order to prevent the system channels from clogging issues. As a result, a positive net power density was obtained for more than 18 days of continuous operations. A maximum power density of about 2.5 W/m2 was observed, demonstrating how the RED technology could be a strategy to harvest energy from produced waters.