Thermodynamic Analysis of a Regenerative Brayton Cycle Using H2, CH4 and H2/CH4 Blends as Fuel

Gontzal Lopez-Ruiz,Jesús María Blanco-Ilzarbe,Joseba Castresana-Larrauri

doi:10.3390/en15041508

Gontzal Lopez-Ruiz, Jesús María Blanco-Ilzarbe + Show 1 more

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https://doi.org/10.3390/en15041508

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Journal: Energies	Publication Date: Feb 17, 2022
Citations: 2	License type: CC BY 4.0

Affiliation: University of the Basque Country

Abstract

Considering a simple regenerative Brayton cycle, the impact of using different fuel blends containing a variable volumetric percentage of hydrogen in methane was analysed. Due to the potential of hydrogen combustion in gas turbines to reduce the overall CO2 emissions and the dependency on natural gas, further research is needed to understand the impact on the overall thermodynamic cycle. For that purpose, a qualitative thermodynamic analysis was carried out to assess the exergetic and energetic efficiencies of the cycle as well as the irreversibilities associated to a subsystem. A single step reaction was considered in the hypothesis of complete combustion of a generic H2/CH4 mixture, where the volumetric H2 percentage was represented by fH2, which was varied from 0 to 1, defining the amount of hydrogen in the fuel mixture. Energy and entropy balances were solved through the Engineering Equation Solver (EES) code. Results showed that global exergetic and energetic efficiencies increased by 5% and 2%, respectively, varying fH2 from 0 to 1. Higher hydrogen percentages resulted in lower exergy destruction in the chamber despite the higher air-excess levels. It was also observed that higher values of fH2 led to lower fuel mass flow rates in the chamber, showing that hydrogen can still be competitive even though its cost per unit mass is twice that of natural gas.

Highlights

IntroductionPublisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations
In order to face up this variable generation and following the so-called “Power to gas” (P2G) concept, hydrogen can be produced by electrolysis of water during the generation peaks [2,3]
The present study focuses on the use of hydrogen–methane blends as fuel in a regenerative Brayton cycle, aiming to qualitatively assess the global unsteady state such as the energetic and exergetic efficiencies of the cycle and the irreversibilities of each subsystem

Summary

Introduction

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. New solutions for the efficient generation of carbon-neutral electricity are essential to curb the climate crisis. In order to face up this variable generation and following the so-called “Power to gas” (P2G) concept, hydrogen can be produced by electrolysis of water during the generation peaks [2,3]. Green hydrogen is stored and distributed for a wide range of end uses (hydrogen to power). Different cost-benefit studies have concluded that green hydrogen will be a feasible and competitive energy carrier in the coming years, optimising the use of natural resources [4,5,6]

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