20-09-2017, 10:26 AM
Osmotic energy, salinity gradient power or blue energy is the energy available from the difference in salt concentration between sea water and river water. Two practical methods for this are reverse electrodialysis (RED) and pressure-delayed osmosis (PRO). Both processes are based on membrane osmosis. The main waste product is brackish water. This byproduct is the result of the natural forces that are being exploited: the flow of fresh water in seas that are composed of salt water.
In 1954 Pattle suggested that there was an unexplored source of energy when a river mixes with the sea in terms of lost osmotic pressure, however it was not until the mid-1970s that a practical method of exploiting it using membranes selectively permeable by Loeb was outlined.
The method of energy generation by pressure-delayed osmosis was invented by Prof. Sidney Loeb in 1973 at the Ben-Gurion University of the Negev, Beersheba, Israel. The idea came to prof. Loeb, in part, as he watched the Jordan River flowing into the Dead Sea. I wanted to reap the energy of the mixture of the two aqueous solutions (the Jordan River being one and the Dead Sea the other) that I was going to lose in this natural mixing process. In 1977, Prof. Loeb invented a method for producing energy by means of an inverse electrodialysis thermal motor.
The technologies have been confirmed under laboratory conditions. They are being developed for commercial use in the Netherlands (RED) and Norway (PRO). The cost of the membrane has been an obstacle. A new low-cost membrane, based on an electrically modified polyethylene plastic, made it suitable for potential commercial use. Other methods have been proposed and are currently being developed. Among them, a method based on double layer electric condenser technology and a method based on the vapor pressure difference.