Reverse electrodialysis
Encyclopedia
Reversed electrodialysis (RED) is the salinity gradient energy retrieved from the difference in the salt concentration
between seawater
and river water
.
In reversed electrodialysis
(RED) a salt solution and fresh water are let through a stack of alternating cathode and anode exchange membranes. The chemical potential difference between salt and fresh water generates a voltage over each membrane and the total potential of the system is the sum of the potential differences over all membranes. It is important to remember that the process works through difference in ion concentration instead of an electric field, which has implications for the type of membrane needed.
In RED, as in a fuel cell
, the cells are stacked. A module with a capacity of 250 kW has the size of a shipping container.
In the Netherlands
, for example, more than 3,300 m³ fresh water runs into the sea per second on average. The membrane halves the pressure differences which results in a water column of approximately 135 meters. The energy potential is therefore e=mgΔh=3.3*106 kg/s*10 m/s2*135 meters ca.= 4.5*109 Joule
per second, Power=4.5 gigawatts.
, the Netherlands, the focus is on prevention of biofouling
on the anode
, cathode
and membranes and increasing the membrane performance. In 2007 the Directorate for Public Works and Water Management, Redstack and ENECO signed a declaration of intent for development of a clean plant in Afsluitdijk
dam in Netherlands To start with, the conditions for the construction of an installation in or on the Afsluitdijk dam will be investigated. This study should be concluded by the middle of 2008. Subsequently a small 10-50 kilowatt installation will be built to test the RED technology under actual working conditions. These tests will run from mid 2008 until 2010. After that, the capacity will be expanded to 1000 kW and the system will be optimized. It is to be expected that after this phase the installation will be further expanded to a final capacity of 200 MW.
Concentration
In chemistry, concentration is defined as the abundance of a constituent divided by the total volume of a mixture. Four types can be distinguished: mass concentration, molar concentration, number concentration, and volume concentration...
between seawater
Seawater
Seawater is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5% . This means that every kilogram of seawater has approximately of dissolved salts . The average density of seawater at the ocean surface is 1.025 g/ml...
and river water
Fresh Water
Fresh Water is the debut album by Australian rock and blues singer Alison McCallum, released in 1972. Rare for an Australian artist at the time, it came in a gatefold sleeve...
.
In reversed electrodialysis
Electrodialysis
Electrodialysis is used to transport salt ions from one solution through ion-exchange membranes to another solution under the influence of an applied electric potential difference. This is done in a configuration called an electrodialysis cell...
(RED) a salt solution and fresh water are let through a stack of alternating cathode and anode exchange membranes. The chemical potential difference between salt and fresh water generates a voltage over each membrane and the total potential of the system is the sum of the potential differences over all membranes. It is important to remember that the process works through difference in ion concentration instead of an electric field, which has implications for the type of membrane needed.
In RED, as in a fuel cell
Fuel cell
A fuel cell is a device that converts the chemical energy from a fuel into electricity through a chemical reaction with oxygen or another oxidizing agent. Hydrogen is the most common fuel, but hydrocarbons such as natural gas and alcohols like methanol are sometimes used...
, the cells are stacked. A module with a capacity of 250 kW has the size of a shipping container.
In the Netherlands
Netherlands
The Netherlands is a constituent country of the Kingdom of the Netherlands, located mainly in North-West Europe and with several islands in the Caribbean. Mainland Netherlands borders the North Sea to the north and west, Belgium to the south, and Germany to the east, and shares maritime borders...
, for example, more than 3,300 m³ fresh water runs into the sea per second on average. The membrane halves the pressure differences which results in a water column of approximately 135 meters. The energy potential is therefore e=mgΔh=3.3*106 kg/s*10 m/s2*135 meters ca.= 4.5*109 Joule
Joule
The joule ; symbol J) is a derived unit of energy or work in the International System of Units. It is equal to the energy expended in applying a force of one newton through a distance of one metre , or in passing an electric current of one ampere through a resistance of one ohm for one second...
per second, Power=4.5 gigawatts.
Testing
In 2006 a 50 kW plant is planned located at a coastal test site in HarlingenHarlingen, Netherlands
Harlingen is a municipality and a city in the northern Netherlands, in the province of Friesland at the Wadden Sea. Harlingen is an old town with a long history of fishing and shipping....
, the Netherlands, the focus is on prevention of biofouling
Biofouling
Biofouling or biological fouling is the undesirable accumulation of microorganisms, plants, algae, or animals on wetted structures.-Impact:...
on the anode
Anode
An anode is an electrode through which electric current flows into a polarized electrical device. Mnemonic: ACID ....
, cathode
Cathode
A cathode is an electrode through which electric current flows out of a polarized electrical device. Mnemonic: CCD .Cathode polarity is not always negative...
and membranes and increasing the membrane performance. In 2007 the Directorate for Public Works and Water Management, Redstack and ENECO signed a declaration of intent for development of a clean plant in Afsluitdijk
Afsluitdijk
The Afsluitdijk is a major causeway in the Netherlands, constructed between 1927 and 1933 and running from Den Oever on Wieringen in North Holland province, to the village of Zurich in Friesland province, over a length of and a width of 90 m, at an initial height of 7.25 m above sea-level.It is...
dam in Netherlands To start with, the conditions for the construction of an installation in or on the Afsluitdijk dam will be investigated. This study should be concluded by the middle of 2008. Subsequently a small 10-50 kilowatt installation will be built to test the RED technology under actual working conditions. These tests will run from mid 2008 until 2010. After that, the capacity will be expanded to 1000 kW and the system will be optimized. It is to be expected that after this phase the installation will be further expanded to a final capacity of 200 MW.
See also
- Osmotic power
- Van 't Hoff factorVan 't Hoff factorThe van 't Hoff factor i is a measure of the effect of a solute upon colligative properties, such as vapor pressure, osmotic pressure and freezing point depression. The van 't Hoff factor is the ratio between the actual concentration of particles produced when the substance is dissolved, and the...
- Pressure retarded osmosisPressure retarded osmosisPressure retarded osmosis is the salinity gradient energy retrieved from the difference in the salt concentration between seawater and river water.In PRO, the water potential between fresh water and sea water corresponds to a pressure of 26 bars...
(PRO) - Electrodialysis reversal (EDR)
- Reverse osmosisReverse osmosisReverse osmosis is a membrane technical filtration method that removes many types of large molecules and ions from solutions by applying pressure to the solution when it is on one side of a selective membrane. The result is that the solute is retained on the pressurized side of the membrane and...
- Semipermeable membraneSemipermeable membraneA semipermeable membrane, also termed a selectively permeable membrane, a partially permeable membrane or a differentially permeable membrane, is a membrane that will allow certain molecules or ions to pass through it by diffusion and occasionally specialized "facilitated diffusion".The rate of...
- Green energy
- Renewable energyRenewable energyRenewable energy is energy which comes from natural resources such as sunlight, wind, rain, tides, and geothermal heat, which are renewable . About 16% of global final energy consumption comes from renewables, with 10% coming from traditional biomass, which is mainly used for heating, and 3.4% from...
External links
- Wetsus
- KEMAKEMAEstablished in 1927, KEMA is an independent knowledge leader and a global provider of high-quality services to the energy value chain, including business & technical consultancy, operational support, measurements & inspection, and testing & certification...
- KEMA
- Dutch Research Database
- Osmotic Energy (1995)
- Salinity Power UN Report
- Practical Potential of Reverse Electrodialysis, Environ. Sci. Technol., July 29, 2009
- Dutch water plan to turn green energy blue