A novel Reverse Electrodialysis application to generate power from low-grade heat

A novel idea for the conversion of low-temperature heat into electricity is based on the generation of electricity from salinity gradients using a Reverse Electrodialysis (RED) device in a closed-loop system. In this concept a limited amount of artificial saline solutions can be used as the working fluids in a closed-loop. The solutions exiting from the RED unit are then regenerated, in order to restore the original salinity gradient, by means of a separation step, which uses low-temperature heat (40-100°C) as its energy source. A theoretical analysis of potentials of this technology is illustrated in the present work.

NH4HCO3–water solutions regeneration in RED closed loop applications

Reverse Electrodialysis (RED) in closed loop arrangement (Reverse Electrodialysis Heat Engine - REDHE) is a promising technology to convert low-grade waste heat into electricity. RED is a membrane process exploiting the salinity gradient between a concentrated and a diluted solution to generate electrical current. Due to the transfer phenomena occurring in the RED unit, the two exiting solutions are partially mixed. Thermal regeneration processes can be used to restore the initial conditions of the two solutions, thus closing the loop. In this regard, ammonium hydrogen carbonate (NH4HCO3) salt solutions are suitable for such applications, being able to decompose at temperatures above 40-45 …

Magnesium recovery from exhausted brine

abstractita

Magnesium recovery from concentrated brines

Reactive crystallisation process for magnesium recovery from concentrated brines

Seawater brines, generated either by natural or anthropic processes, often cause significant environmental issues related to their disposal. A clear example is the case of brines from desalination plants, which can have severe environmental impacts on the receiving water body. On the other side, brines can represent a rich and appealing source of raw materials, especially when they are very concentrated, as it happens with bitterns (i.e. exhausted brines) produced in saltworks. In particular, magnesium concentration can reach values up to 30-40 kg/m3 of brine, which is 20-30 times that of typical seawater. An experimental campaign has been carried out in the present work for assessing the p…

Reverse electrodialysis with NH4HCO3-water systems for heat-to-power conversion

Abstract A Reverse ElectroDialysis Heat Engine (REDHE) system operating with “thermolytic” ammonium hydrogen-carbonate (NH4HCO3) aqueous solutions as working fluids is studied. The engine is constituted by (i) a RED unit to produce electric power by mixing the solutions at different salinity and (ii) a thermally-driven regeneration unit including a stripping and an absorption column to restore the initial salinity gradient thus closing the cycle. In the present work only the RED unit and the stripping column are taken into account. In particular, a simplified integrated process model for the whole cycle was developed: it consists of (i) a lumped parameter model for the RED unit validated wi…

RED Heat-to-Power: conversione di calore di scarto in energia elettrica mediante elettrodialisi inversa a ciclo chiuso

La produzione di energia da gradienti salini si sta affermando come una valida alternativa alle tradizionali fonti di energia rinnovabili. In particolare l’elettrodialisi inversa (RED) è di certo tra le tecnologie più promettenti per effettuare la conversione di gradienti salini in energia utile. Un recente sviluppo è l’utilizzo del processo RED a ciclo chiuso con soluzioni saline artificiali, nel quale le soluzioni in uscita dall’unità RED vengono rigenerate all’interno di un’unità di rigenerazione termica, che ripristina il gradiente salino iniziale. L’utilizzo del sistema a ciclo chiuso premette dunque di convertire calore a bassa temperatura (e.g. calore di scarto a T <70-100°C) in e…

SELECTIVE CRYSTALLISATION OF MAGNESIUM AND CALCIUM HYDROXIDES FROM INDUSTRIAL WASTE BRINES: A PILOT STUDY

In the last years, a rising interest has been focused on the valorization of waste brines from industrial processes, such as desalination plants. In most current scenarios, waste brines are disposed directly, or after being treated, into a receiving water bodies, often causing environmental concerns and, more importantly, renouncing to the possibility of using such a waste as source of valuable raw materials. In fact, these brines are typically rich in useful salts and minerals, whose recovery can increase the environmental and economical sustainability of the industrial process [1-2]. The ZERO BRINE EU-H2020 project aims at the development of technologies for the recovery of salts, mineral…

Performance of a RED system with ammonium hydrogen carbonate solutions

The use of closed-loop salinity gradient power (SGP) technologies has been recently presented as a viable option to generate power using low-grade heat, by coupling a SGP unit with a thermally-driven regeneration process in a closed loop where artificial solutions can be adopted for the conversion of heat into power. Among these, the closed-loop reverse electrodialysis (RED) process presents a number of advantages such as the direct production of electricity, the extreme flexibility in operating conditions and the recently demonstrated large potentials for industrial scale-up. Ammonium hydrogen carbonate (NH4HCO3) is a salt suitable for such closed-loop RED process thanks to its particular …

A pilot-plant for the selective recovery of magnesium and calcium from waste brines

Abstract The problem of brines disposal has raised great interest towards new strategies for their valorisation through the recovery of minerals or energy. As an example, the spent brine from ion exchange resins regeneration is often discharged into rivers or lakes, thus impacting on the process sustainability. However, such brines can be effectively reconcentrated, after removal of bivalent cations, and reused for the resins regeneration. This work focuses on developing and testing a pilot plant for selective recovery of magnesium and calcium from spent brines exploiting a novel proprietary crystallization unit. This is part of a larger treatment chain for the complete regeneration of the …

Effect of different aqueous solutions of pure salts and salt mixtures in reverse electrodialysis systems for closed-loop applications

Abstract Reverse Electrodialysis (RED) in a closed-loop arrangement is a viable way to convert low-grade heat into electric power. The present work experimentally investigates the use of pure salt- and equimolar two salts-water solutions as feeds in a lab-scale RED unit. RED performances were analysed in terms of Open Circuit Voltage (OCV), stack resistance and corrected power density. The pure salts and the mixtures employed were chosen via a computational analysis. Effect of feed solution velocity and concentration was investigated. Results concerning the pure salt-water experiments show that NH4Cl is the most performing salt in the concentration range probed, while higher power density v…

Thermal regeneration of ammonium bi-carbonate solutions for closed-loop reverse electrodialysis

Reverse electrodialysis is a novel technology that exploits a salinity gradient to generate electrical energy. The salinity gradient can be available from natural waters such as seawater and river water or they can be artificially generated and used within closed-loop applications. This last option has been recently investigated leading to the development of the RED heat engine concept. In this case, the deployed salinity gradient exiting the RED unit is regenerated in a thermally-driven unit using low-temperature heat, thus being able to convert heat to power within an integrated system. Among the different regeneration alternatives, the use of thermolytic salts has been presented as a pro…