A Review of Exergy Based Optimization and Control

Abstract

This work presents a critical review of the use of exergy based control and optimization for efficiency improvements in energy networks, with a background of exergy based analysis given for context. Over the past three decades, a number of studies using exergy were conducted to gain a performance advantage for high energy consumption systems and networks. Due to their complexity and the increased scale of the systems, the opportunity to misuse energy inevitability leads to inefficient operations. The studies accomplished in this area are grouped into either control or optimization to highlight each method's ability to minimize system irreversibilities that lead to exergy destruction. The exergy based optimization and control studies featured demonstrate substantial improvements (as high as 40%) over traditional methods based on the first law of thermodynamics. This paper reviews the work completed in the area of exergy based optimization and control as of the end of September 2019, outlines the progress made, and identifies specific areas where future work can advance this area of study. A relatively small amount of publications are available compared to other fields, with most work occurring in the area of exergy based multi-objective optimization.

Energy and Exergy Analyses of Rice Drying in a Novel Electric Stationary Bed Grain-Drying System with Internal Circulation of the Drying Medium

“…When the exergy analysis of the drying process was carried out, the exergy of the drying medium and grain was expressed in the form of exergy rate according to the basic state parameters [ 20 ]: …”

“…Zohrabi et al [ 19 ] studied the exergetic performance of a pilot-scale convective dryer with exhaust air recirculation by a wood-chip drying experiment, and found that increasing the drying temperature, air volume flow rate, and recycling fraction improved the overall functional exergetic efficiency of the drying system, while exhaust air recirculation profoundly improved the overall functional exergetic efficiency of the drying system. Exergy analysis has been an important analytical method for scholars seeking to optimize control and improve the energy efficiency of drying systems over the past three decades [ 20 , 21 ]. Because the energy consumption index is jointly determined by dryer performance and drying process optimization, for some grain-drying systems the optimization of the drying process plays an important role in the evaluation of the energy-saving index.…”

Conventional and Advanced Exergy-Based Analysis of Hybrid Geothermal–Solar Power Plant Based on ORC Cycle

“…For calculating the cost per exergy unit, the exergo-economic balance of each component should be obtained according to Equations (12) and (13) where c i is the cost of the streams, . C P is the cost rate of the equipment, .…”

“…However, this analysis alone fails to identify the quality of the dissipated energy and how much work potential is available. To assess both the quantity and the quality of the lost or gained energy, both the first and second laws of thermodynamics (SLT) must be used in conjunction with each other to provide a more thorough understanding of the conversion inefficiencies, termed exergy, James et al [13]. Exergy (Ex) is defined as the maximum theoretical work that a system can achieve when it comes into equilibrium with the environment or the dead state.…”

“…A conventional analysis of exergy describes the location, magnitude and causes of thermodynamic inefficiencies. This method of analysis appears to be growing in popularity and provides detailed information on the thermodynamic imperfections of the system, James et al [13]. These imperfections, termed exergy destruction (E D ), wasted work or wasted work potential, are the very inefficiencies that engineers spend their careers trying to avoid, minimize or eliminate.…”