Next Article in Journal
Analysis of Entropy Generation Rate in an Unsteady Porous Channel Flow with Navier Slip and Convective Cooling
Previous Article in Journal
Reliability of Inference of Directed Climate Networks Using Conditional Mutual Information
Article Menu

Export Article

Open AccessArticle
Entropy 2013, 15(6), 2046-2080; doi:10.3390/e15062046

Generalized Least Energy of Separation for Desalination and Other Chemical Separation Processes

Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
*
Author to whom correspondence should be addressed.
Received: 22 April 2013 / Revised: 14 May 2013 / Accepted: 22 May 2013 / Published: 27 May 2013
View Full-Text   |   Download PDF [705 KB, uploaded 24 February 2015]   |  

Abstract

Increasing global demand for fresh water is driving the development and implementation of a wide variety of seawater desalination technologies driven by different combinations of heat, work, and chemical energy. This paper develops a consistent basis for comparing the energy consumption of such technologies using Second Law efficiency. The Second Law efficiency for a chemical separation process is defined in terms of the useful exergy output, which is the minimum least work of separation required to extract a unit of product from a feed stream of a given composition. For a desalination process, this is the minimum least work of separation for producing one kilogram of product water from feed of a given salinity. While definitions in terms of work and heat input have been proposed before, this work generalizes the Second Law efficiency to allow for systems that operate on a combination of energy inputs, including fuel. The generalized equation is then evaluated through a parametric study considering work input, heat inputs at various temperatures, and various chemical fuel inputs. Further, since most modern, large-scale desalination plants operate in cogeneration schemes, a methodology for correctly evaluating Second Law efficiency for the desalination plant based on primary energy inputs is demonstrated. It is shown that, from a strictly energetic point of view and based on currently available technology, cogeneration using electricity to power a reverse osmosis system is energetically superior to thermal systems such as multiple effect distillation and multistage flash distillation, despite the very low grade heat input normally applied in those systems. View Full-Text
Keywords: least work of separation; Second Law efficiency; cogeneration; power production; exergy least work of separation; Second Law efficiency; cogeneration; power production; exergy
This is an open access article distributed under the Creative Commons Attribution License (CC BY 3.0).

Scifeed alert for new publications

Never miss any articles matching your research from any publisher
  • Get alerts for new papers matching your research
  • Find out the new papers from selected authors
  • Updated daily for 49'000+ journals and 6000+ publishers
  • Define your Scifeed now

SciFeed Share & Cite This Article

MDPI and ACS Style

Mistry, K.H.; Lienhard, J.H., V. Generalized Least Energy of Separation for Desalination and Other Chemical Separation Processes. Entropy 2013, 15, 2046-2080.

Show more citation formats Show less citations formats

Related Articles

Article Metrics

Article Access Statistics

1

Comments

[Return to top]
Entropy EISSN 1099-4300 Published by MDPI AG, Basel, Switzerland RSS E-Mail Table of Contents Alert
Back to Top