Reduction of the shadow spacer effect using reverse electrodeionization and its applications in water recycling for hydraulic fracturing operations

Abstract

Reverse electrodialysis (RED) is an electrically driven process for the extraction of usable energy from the Gibbs free energy of mixing. Past research efforts have focused on the improvement of power density through higher voltages, large cell numbers, and overall reduction of stack resistance, yet the process remains far from optimized. One of the principal problems is the shadow spacer effect where limited conductivity near the spacer decreases the amount of electrical transport. We have improved this technology by incorporating ion exchange wafers in each cell, shortening the diffusion pathways, limiting the shadow spacer effect, and obtaining net power densities of approximately 0.32 W/m 2 for reverse electrodeionization (REDI) compared to 0.01 W/m 2 for the RED case. Further, we have found that applying voltage to the system gives an increase in the overall power extraction efficiency due to wafer optimization and the non-ohmic behavior at low voltages. This is the first study incorporating electrodeionization techniques in RED systems. We also investigated the use of REDI in hydraulic fracturing and obtained a net power density of approximately 0.79 W/m 2 using produced water. This technology could be utilized for processing of produced water from hydraulic fracturing operations to provide some of the power used at the well site (when mixing with fresh water for re-fracking) with no greenhouse gas emissions. Using REDI at fracking sites, an industrial process that has been mired by environmental concerns can take positive steps toward developing and adopting sustainable practices.

Electrodialytic Processes: Market Overview, Membrane Phenomena, Recent Developments and Sustainable Strategies

“…Its huge advantage is a constant electricity generation, however current productivity is limited due to maximum power densities not exceeding 0.26 W/m² [ 276 ]. Other technological developments include reverse electrodeionization (REDI) showing a decreased system resistance compared to RED due to embedded IX resin in the dilute compartment, leading to 0.32–0.44 W/m² power densities [ 277 , 278 ]. Reverse electro-electrodialysis (REED) was also developed to mitigate RED’s shortcomings and produce hydrogen for energy.…”

Electrodialysis Applications in Wastewater Treatment for Environmental Protection and Resources Recovery: A Systematic Review on Progress and Perspectives

“…One study proposed reverse electrodeionisation (REDI) for simultaneous energy recovery and water reuse by controlled mixing between treated fracturing produced water and fresh water (needed for replenishment) [347]. The REDI diluate contained IXR-wafers to lessen the electrical resistance.…”

Improvement in the Power Output of a Reverse Electrodialysis System by the Addition of Poly(sodium 4-styrenesulfonate)

“…27,35 Therefore, it should be important to consider other methods for further power enhancement. 10,[31][32][33][34] In this research, the effect of a polyelectrolyte dissolved in the dilute solutions was evaluated. Polyelectrolytes can be retained in the aqueous phase using a dialysis membrane.…”

“…[27][28][29][30][31] Therefore, many research groups have improved the cell systems to reduce the electrical resistance of the compartments of dilute solutions. 27,29,[31][32][33][34][35] The simplest method would be to thin the compartments of dilute solutions, and a lot of attempts have improved the efficiency of the power outputs of the RED systems. 27,29,35 However, excessive thinning the solution…”