Second law thermodynamic analysis of syngas premixed flames

The exergy loss in laminar premixed flames of syngas is investigated numerically by analyzing the local entropy generation. The effects of the change in the H-2 molar ratio in H-2-CO mixture at different temperature values (from 300 to 600 K), at atmospheric and high pressure (10 and 50 atm) conditions and for different equivalence ratios (0.5, 1 and 2) are studied identifying both the mainly responsible process for exergy loss and the factors that can positively affect the performance of the syngas combustion. It is found that the chemical reactions are not always the main contribution to the total entropy generation (i.e. to exergy loss) and that the roles of the chemical reactions and heat conduction are strongly affected by pressure. Furthermore, it is underlined that the hydrogen content in syngas worsens the exergy loss due to entropy generation by the combustion process, whereas pressure increase has positive effects. However, these beneficial effects are counterbalanced by an increase of the chemical exergy content in the flue gases (mostly due to unreacted species or incomplete combustion). Therefore, a careful selection of the combustion process conditions is required to meet efficiency constraints if exhaust exergy is not meant to be afterward exploited. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.