Production of energy from concentrated brines by pressure-retarded osmosis

In this, the first of two papers, preliminary technical and economic correlations have been made on the production of energy from concentrated brines by Pressure-Retarded Osmosis (PRO). p]In PRO, the hydraulic pressure is less than the osmotic pressure, so that water flux is against the hydraulic pressure gradient, this fact being the basis for energy production. It is visualized that a PRO power plant, operating continuously, would pump a concentrated brine such as Dead Sea brine on the outside of the fibers in hollow fiber modules at a high hydraulic pressure. Simultaneously, Jordan River water or brackish springs would be pumped through the inside of the fibers, and would permeate through the fiber wall into the pressurized brine. The permeate-enhanced brine would be depressurized through a hydroturbine, delivering net power equal to the high hydraulic pressure x the permeate rate, in the idealized case. p]A transport analysis indicated that an asymmetric membrane, with the brine on the skin side, is as desirable in PRO as it is in reverse osmosis from the standpoint of high water permeation flux. p]The mechanical efficiency of a PRO power plant was examined. The efficiency is very sensitive to V/Δ V, the ratio of concentrated brine rate to permeate rate, a low value of this ratio (less than 2) being desirable. p]A preliminary analysis was made of the unit cost of energy production from a PRO plant. The results are expressed as a function ofV/ΔV, the water flux, and the hydraulic pressure used. This analysis indicated the desired course of experimentation to obtain data for calculation of the minimum unit energy cost. p]In the second and concluding paper, experimental results will be given from which the validity of correlations given here can be estimated, and unit energy costs will also be given.