Use of membrane technology for producing electrical energy

• Published in: Thermal engineering 2015, Vol.62 (9), p.678-686
• Main Authors: Kondrateva, M. A., Lobanova, O. N., Orlov, K. A., Panteleev, A. A., Khoruzhiy, O. V.
• Format: Article
• Language: English
• Subjects: Energy Conservation; Engineering; Engineering Thermodynamics; Heat and Mass Transfer; New; Renewable Energy Sources
• ISSN: 0040-6015; 1555-6301
• DOI: 10.1134/S0040601515050067

The most promising renewable energy sources are described, which are based on membrane processes with the usage of a water-salinity gradient. The energy is produced owing to the osmotic pressure difference which arises when water molecules pass through a semipermeable membrane from a solution with a low salt concentration to the more concentrated solution, which can be observed, e.g., in mixing of the river water and seawater. As a result, the volume flowrate of water increases and the energy is generated by releasing the pressure via a water turbine. The theoretical estimation of the maximum possible performance of the plant with application of currently available membranes is carried out. The simplest scheme is presented for converting osmotic energy to electricity. Two fundamental problems are identified that have to be solved in order to create a highly effective osmotic machine: firstly, to reduce engineering losses associated with mechanical losses in the pump and turbine and the cost of pretreatment of the river water and seawater; and, secondly, to find the optimal ratio of “freshwater–saltwater” fluxes. The expression is derived for determining a water flux through a membrane depending on the seawater flux with the given osmotic and working pressures. A range of the optimum ratio of “freshwater–saltwater” fluxes is found by constructing a model of flows in the membrane element. The ranges of parameters are defined within which the maximum power will be produced. The calculation of economic efficiency of an osmotic power station is presented by example of a station built in Norway. The analysis of this station is performed, and methods for improving its efficiency are proposed.