skip to main content

SciTech ConnectSciTech Connect

Title: Thermodynamic analysis of energy density in pressure retarded osmosis: The impact of solution volumes and costs

A general method was developed for estimating the volumetric energy efficiency of pressure retarded osmosis via pressure-volume analysis of a membrane process. The resulting model requires only the osmotic pressure, π, and mass fraction, w, of water in the concentrated and dilute feed solutions to estimate the maximum achievable specific energy density, uu, as a function of operating pressure. The model is independent of any membrane or module properties. This method utilizes equilibrium analysis to specify the volumetric mixing fraction of concentrated and dilute solution as a function of operating pressure, and provides results for the total volumetric energy density of similar order to more complex models for the mixing of seawater and riverwater. Within the framework of this analysis, the total volumetric energy density is maximized, for an idealized case, when the operating pressure is π/(1+√w⁻¹), which is lower than the maximum power density operating pressure, Δπ/2, derived elsewhere, and is a function of the solute osmotic pressure at a given mass fraction. It was also found that a minimum 1.45 kmol of ideal solute is required to produce 1 kWh of energy while a system operating at “maximum power density operating pressure” requires at least 2.9 kmol. Utilizingmore » this methodology, it is possible to examine the effects of volumetric solution cost, operation of a module at various pressure, and operation of a constant pressure module with various feed.« less
Authors:
 [1] ;  [1] ;  [2]
  1. Univ. of Connecticut, Storrs, CT (United States). Dept. of Chemical and Biomolecular Engineering
  2. Idaho National Lab. (INL), Idaho Falls, ID (United States)
Publication Date:
OSTI Identifier:
1184718
Report Number(s):
INL/JOU--15-34129
Journal ID: ISSN 0376-7388; TRN: US1500202
DOE Contract Number:
AC07-05ID14517
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Membrane Science; Journal Volume: 487; Journal Issue: C
Publisher:
Elsevier
Research Org:
Idaho National Laboratory (INL), Idaho Falls, ID (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; THERMODYNAMICS; SOLUTIONS; SEAWATER; ENERGY DENSITY; MATHEMATICAL MODELS; OSMOSIS; COST; PRESSURE DEPENDENCE; ENERGY EFFICIENCY; POWER DENSITY; MASS; MEMBRANES; MIXING; EQUILIBRIUM; VOLUME pressure retarded osmosis; thermodynamic analysis; osmotic heat engine; osmotic energy/storage generation; osmotically driven membrane process