Exergetic, exergoeconomic, and exergoenvironmental aspects of an industrial-scale molasses-based ethanol production plant

Abstract

An industrial-scale molasses-based bioethanol production system was modeled and studied by conducting exergy, exergoeconomic, and exergoenvironmental analyses. The entire process was represented by a control volume, and its exergoeconomic and exergoenvironmental parameters were determined using the specific exergy costing (SPECO) approach. These exergy-based analyses were carried out to measure the overall exergy dissipation, cost, and environmental impact of the bioethanol production process based on actual operational thermodynamic, economic, and environmental data. Natural gas showed the highest contribution to the total input exergy (61.1%) and total environmental impact rate (56.6%) of the process, while the highest contribution to its total cost rate (75.7%) was from molasses. The exergetic efficiency determined for the process was 35.9%, while the exergy dissipation accounted for 60.8% of its total input exergy. The unit exergoeconomic costs of the fuel and product were determined to be 6.2 and 20.9 USD/GJ, while the unit exergoenvironmental impacts of the fuel and product were 15.5 and 31.5 mPts/GJ, respectively. The exergoeconomic factor of the process was found to be 29.4%, while the exergoenvironmental factor was 0.74%. Overall, natural gas consumption was the most significant exergetic hotspot of the process, and hence more exergetically-sustainable alternatives should be considered to improve the process. Low-cost waste feedstocks need to be utilized to improve the economic viability of the process.