Power production from coal-mine brine utilizing reversed electrodialysis

The present work was aimed at electric energy obtaining by mixing coal-mine brine with low-salinity water utilizing reversed electrodialysis (RED). The electrodialytic unit equipped with alternatively arranged cation and anion exchange membranes, was mounted in-between two Pt-coated electrodes. The number of the anion and cation-exchange membranes was set to achieve 4 brine and 4 low-salinity water compartments. The relatively thin, of 0.19 mm thickness, ED stack spacer enabled low membrane to membrane distance and resulted in relatively low ohmic voltage loss. The electrodialytic system was fed with brine, containing 111 g NaCl/L, simulating coal-mine brine and low-salinity water of 0.56 g/L NaCl content, as a fresh water. In order to estimate the possible electric charge and electric power produced in the proposed system, the current–voltage curves were analyzed at different linear flow velocities. Also the cost estimation based on the electric resistances was done. Thus the feasibility of electric energy obtaining in the considered way was discussed.

Utilizing reversed electrodialysis (RED) to generate electric energy by mixing coal-mine brine with low-salinity water in electrodialysis stack was examined in laboratory. The relatively thin, of 0.19 mm thickness, ED stack spacer enabled low membrane to membrane distance and resulted in relatively low ohmic voltage loss, that was desired. The electrodialytic system was fed with brine, containing 111 g NaCl/L, which was stimulating coal-mine brine and low-salinity water of 0.56 g/L NaCl content, as a fresh water. Analysis of our experiments results indicated that the maximum effective unit power depends on: electric current density, flow velocity and membrane resistance (type). The maximum effective unit power of 0.72 W/m2 was observed for AMX and CMX membranes at 20 A/m2 and 0.58 cm/s flow velocity and 1.040 W/m2 for low resistance membranes at 30 A/m2 and 0.58 cm/s linear flow velocity. The detailed cost estimation showed that the minimum energy obtaining investment cost, of $3.0/kWh) may be achieved using low resistance membranes. High unit price of low-resistance membrane, however, increase the energy obtaining cost to a great extent. We also concluded that high energy obtaining investment cost seems to prevent the application of RED technique at a large scale. Cost of equipment (e.g. pumps, pipes), and high cost of low resistance ion-exchange membranes are the origins of the above shortage in RED application. Since the membrane cost is the major component of the RED energy production cost, one may also conclude that aprox. a hundred time decrease in the membrane price would make the considered technology economically feasible.