Abstract
We increase the power density of a reverse electrodialysis (RED) stack by blending the low salinity feed with a higher salinity stream before the stack entrance. This lowers the capital cost of the system and the resulting levelized cost of electricity, enhancing the viability of RED renewable energy generation. Blending increases the power density by decreasing the dominating electrical resistance in the diluate channel as well as the effective resistance caused by concentration polarization, but not without sacrificing some driving potential. To quantify this trade-off and to evaluate the power density improvement blending can provide, a one-dimensional RED stack model is employed and validated with experimental results from the literature. For a typical stack configured with a feed velocity of 1 cm/s, power density improvements of over 20% and levelized cost of energy reductions of over 40% are achievable, provided the salinity of the available river water is below 200 ppm. Additional cost reductions are realized through back-end blending, whereby the diluate exit stream is used as the higher salinity blend stream. Also, improvements from blending increase for higher feed velocities, shorter stack lengths, and larger channel heights.