Towards the first proof of the concept of a Reverse ElectroDialysis - Membrane Distillation Heat Engine

Abstract

The coupling of Reverse Electrodialysis with Membrane Distillation is a promising option for the conversion of waste heat into electricity. This study evaluates the performances of the integrated system under different operating conditions, employing validated model and correlations. This work provides a detailed description of the behaviour of a real RED-MD heat engine and indicates the set of inlet concentrations, velocities and equipment size which returns the highest cycle exergy efficiency. These operating conditions were selected for the pilot plant developed within the EU-funded project RED Heat to Power. For the first time, a perspective analysis was also included, considering highly performing RED membranes and future MD module. Relevant results indicate that technological improvements may lead to interesting system performance enhancement, up to an exergy efficiency of 16.5%, which is considerably higher than the values reported in literature so far.

Evaluation of the Economic and Environmental Performance of Low-Temperature Heat to Power Conversion using a Reverse Electrodialysis – Multi-Effect Distillation System

“…The use of improved IEMs in the RED stack, referred to as "high-performing" membranes, whose properties are reported in Table 1 and are in line with several high-performing IEMs available in the market [16].…”

“…This issue has been examined in [14], developing a detailed correlation to estimate the MED capital cost, including various parameters that are of use here. Except for MED, other separation technologies suitable for the RED heat engine are based on membrane distillation (MD) [12] or distillation columns with thermolytic salts [15], which show a lower potential due to their higher thermal energy consumption and specific capital cost [16,17].…”

“…Most of the works reported in the literature relevant to SGP-HE have focused on the use of sodium chloride salt-solutions [16,18,19]. However, the adoption of alternative salts, such as lithium chloride or potassium and cesium acetate has the potential to increase the performance of the RED-MED thanks to their high solubility [20].…”

“…The economics of the RED-MD system were examined in Ref. [16] and it was shown that if high-performing ion exchange membranes (IEMs) were developed, the levelized cost of electricity (LCOE) would be around 0.40 €/kWh. This could be further reduced to values in the range of 0.10 to 0.25 €/kWh, assuming important reductions in membrane and MD costs in the future in the case of industrial-scale production.…”

“…The safe conclusion reached here is that the RED-MED system is suitable only for at least medium-scale systems (as defined in this study), revealing the full technology potential as the capacity increases. For smaller systems, the RED-MD combination seems to be more suitable [16].…”