Tuesday, April 1, 2008 - 5:30 AM

Potential Role of Exergy in Analysis of Hydrogen Infrastructure

Ali A. Jalalzadeh-Azar, National Renewable Energy Laboratory

The objective of this paper is to demonstrate the potential role of exergy (second-law) analysis, as a complementary tool for economic assessments of hydrogen infrastructures. Thermodynamic analysis is particularly valuable for evaluating hydrogen production technologies that are energy intensive and represent a key infrastructural component.

This study focuses on three selected distributed hydrogen production technologies: natural gas steam reforming, ethanol steam reforming, and electrolysis. The prospect of distributed systems for early market adoption in the absence of a well-developed hydrogen distribution network is a compelling reason for this selection. The thermodynamic performance of these systems are evaluated and discussed in conjunction with their energy costs as major contributors to the total hydrogen production costs. Analyses are also performed in the context of the source energy and feedstock.  For these systems operating under prescribed conditions, the differences between the energetic and exergetic efficiencies are found to be rather insignificant. In light of the calculated unused/destroyed exergies, the potential for hydrogen cost reduction via energy savings is discussed as well.