Research On The Influence Factors Of Harvesting Energy By Pressure Retarded Osmosis

Fossil fuel accounts for about 80 percent of the world energy structure, being the most important substance of energy source. Unfortunately, the fossil fuel is nonrenewable with limited reserves. It is estimated by United States Geological Survey that the petroleμm can be supplied for another 200 years while the natural gas will be depleted in 80 years. Meanwhile, the overuse of fossil fuel has very bad effects on the environment, resulting environmental problems like globe warming, acid rain and haze weather. To solve the problems mentioned above, it’s urgent to research and develop new green renewable alternations for fossil fuel. Osmotic energy, which produced from mixing solutions with different concentration, is less affected by meteorological and geographical condition when compared with solar energy and wind energy. With the ability of continuously generating power and it’s huge reverse in the ocean, osmotic energy are attracting more and more attention.Pressure retarded osmosis(PRO) is a new membrane technology harvesting osmotic energy with a semipermeable membrane being its core part. In the first part of this paper, a variety of detection technologies were applied to characterize the CTA-NW membrane used in PRO, and its surface topography, cross-sectional morphology, chemical groups, hydrophilic property and pore diameter were studied to demonstrate the possibility of using CTA-NW membrane in PRO process. Then the separation capability and bearing capability of the membrane were tested in RO mode to acquire its water permeability coefficient(A) and salt permeability coefficient(B) as well as the rule of membrane’s state change under different hydraulic pressure, providing basis for the following theoretical research and the determination of test parameters. At last, based on the similarity with forward osmosis(FO), the PRO model was derived from FO model and the effect of concentration polarization on PRO was analyzed theoretically.In the second part of present research, sodiμm chloride solutions of different concentration were used as feed solution and draw solution to study the factors affecting PRO performance. The PRO performance was improved by orientating the membrane with active layer facing draw solution(AL-DS), increasing the feed solution concentration, decreasing the feed solution concentration, and increasing the flow rate and temperature. The effects of the influence factors on PRO performance lied on their effects on internal concentration polarization(ICP) which could be reflected by structure parameter(S). A larger value of S meant a larger mass transfer resistance resulting smaller water flux(JW) and power density(W). S was deduced from diffusion coefficient(D) which was calculated by a theoretical formula and used as criterion for mass transfer resistance. In addition, the specific reverse solute flux(JS /JW) was found to increase with increasing the applied hydraulic pressure, but the increase of experimental results was much more drastic than the theoretical prediction especially under higher hydraulic pressure, probably due to the increased solute permeability caused by membrane deformation.