Comparison of energy efficiency assessment methods: Case Bio-SNG process

• Published in: Energy (Oxford) 2014-09, Vol.74, p.88-98
• Main Authors: Kohl, T., Laukkanen, T., Tuomaala, M., Niskanen, T., Siitonen, S., Järvinen, M.P., Ahtila, P.
• Format: Article
• Language: English
• Subjects: Applied sciences; AspenPlus; Assessments; Bio-SNG (synthetic natural gas); Energy; Energy management; Exact sciences and technology; Exergy; Exergy analysis; Fuels; Method assessment; Natural gas; Primary energy efficiency; Production methods; Thermal efficiency
• ISSN: 0360-5442
• DOI: 10.1016/j.energy.2014.03.107

The goal of biofuel production is to partially replace fossil fuels in energy generation and transport. For the evaluation of biofuel production processes different criteria are applied and usually they include costs, efficiency aspects and emissions. However, evaluation of the energy efficiency of biofuels production is difficult since no general standard method exists for that. This paper compares three different assessment methods of energy efficiency both qualitatively and quantitatively. The methods are: thermal efficiency, exergy analysis and primary energy analysis. The feasibility of the methods is tested on a Bio-SNG (synthetic natural gas) production process which was modelled in AspenPlus and MS Excel. The results show that the exergy analysis seems to be advantageous when it comes to detailed (sub-) process analysis whereas the primary energy analysis offers the advantage of showing how the system is influencing the global primary energy resources. The results obtained by the thermal efficiency analysis do not add any new information to the results obtained by exergy and primary energy analyses. Exergy and primary energy analyses should be the preferred means for process assessment. Especially a combination of the two methods could offer the chance to develop a more holistic energy efficiency indicator. •Evaluation of thermal, primary, and exergy efficiency assessment methods.•Thermal energy analysis does not give additional information.•Primary energy analysis is not a suitable tool for detailed process analysis.•Exergy analysis does not consider the global impact of an energy system.•Improved efficiency assessment should combine exergy and primary energy analysis.