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

Michael Papapetrou,Giorgio Micale,Alessandro Tamburini,Francesco Giacalone,Bartolomé Ortega-Delgado,Andrea Cipollina,George Kosmadakis

doi:10.3390/en12173206

Michael Papapetrou, Giorgio Micale + Show 5 more

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https://doi.org/10.3390/en12173206

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Abstract

In the examined heat engine, reverse electrodialysis (RED) is used to generate electricity from the salinity difference between two artificial solutions. The salinity gradient is restored through a multi-effect distillation system (MED) powered by low-temperature waste heat at 100 °C. The current work presents the first comprehensive economic and environmental analysis of this advanced concept, when varying the number of MED effects, the system sizing, the salt of the solutions, and other key parameters. The levelized cost of electricity (LCOE) has been calculated, showing that competitive solutions can be reached only when the system is at least medium to large scale. The lowest LCOE, at about 0.03 €/kWh, is achieved using potassium acetate salt and six MED effects while reheating the solutions. A similar analysis has been conducted when using the system in energy storage mode, where the two regenerated solutions are stored in reservoir tanks and the RED is operating for a few hours per day, supplying valuable peak power, resulting in a LCOE just below 0.10 €/kWh. A life-cycle assessment has been also carried out, showing that the case with the lowest environmental impact is the same as the one with the most attractive economic performance. Results indicate that the material manufacturing has the main impact; primarily the metallic parts of the MED. Overall, this study highlights the development efforts required in terms of both membrane performance and cost reduction, in order to make this technology cost effective in the future.

Highlights

There are very large amounts of waste heat that remain unexploited all over the world
For both cases 5 and 6, when using current commercial prices and without relying on any future cost reductions either for the reverse electrodialysis (RED) or for the multi-effect distillation system (MED) components, a levelized cost of electricity (LCOE) of 0.09 to 0.10 €/kWh can be reached. This reduces further to values of 0.06 €/kWh for large systems. These results indicate that future improvements in membrane performance are much more critical in the aim of reaching competitive LCOE compared to the cost of the components
By reducing the number of MED effects from 24 to six, the GWP and eutrophication potential are reduced by a factor of about four, while the acidification potential is reduced by a factor of six

Summary

Introduction

There are very large amounts of waste heat that remain unexploited all over the world. The main focus is on industrial waste heat that is mostly available at a temperature of over 100 ◦ C and represents a significant fraction of the total. Various technologies are developed to exploit this heat and convert it into useful energy, with the main concepts dealing with the production of power/electricity [2]. Energies 2019, 12, 3206 various heat engines developed that can exploit this low-temperature heat source and convert it into power [5]. The most common one is a heat engine based on the organic Rankine cycle (ORC), which has reached commercial level and is applied in various industries and temperature ranges [6]. Other heat engines have been developed, attempting to offer improved performances or lower costs than the ORC one

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