Production of energy from concentrated brines by pressure-retarded osmosis : II. Experimental results and projected energy costs

Abstract

The osmotic region between ordinary osmosis and osmotic equilibrium has been examined up to osmotic pressure differences of 500 atm and hydraulic pressure differences of 90 atm. The process, called Pressure-Retarded Osmosis (PRO), appears appropriate for energy production if a high osmotic pressure solution, the permeate-receiver, and a low osmotic pressure solution, the permeate-donor, are simultaneously available, as at the Dead Sea or Great Salt Lake. The experimental work was carried out in short duration tests with “Minipermeators” containing asymmetric Du Pont Permasep B-10 hollow fibers (external skin) made at present for sea water desalination. Sodium chloride and magnesium chloride solutions were used as permeate-receivers and gave similar results at similar osmotic pressures. Dead Sea brine was extensively tested at various dilutions as a permeate-receiver. Filtered and distilled water, and solutions made from it were used as permeate-donors. p]The results could be generally correlated by assuming diffusional transport through both the skin and the porous substructure. For low osmotic pressures on the permeatedonor side (inside) of the fibers, asymmetry was as advantageous in PRO as in RO. p]From the data obtained, it was estimated that energy could be produced for about 0.07 dollars per kilowatt hour in a PRO power plant utilizing Dead Sea brine and water as permeate-receiver and donor, respectively.