Thermoeconomic and life cycle assessments for a trigeneration system: A case study

ABSTRACT

The current need to diversify the global energy matrix implies introducing renewable energy sources and evaluating commercially available solutions. This study assesses a trigeneration system from thermoeconomic and environmental viewpoints, employing the Theory of Exergy Cost and Life Cycle Assessment. The location of the theoretical study case is the state of Pernambuco, Northeast Brazil. The trigeneration system operates on biogas and is comprised of four subsystems: biogas purification, molted carbon fuel cell, combined cycle, and absorption refrigeration system. The energy services produced are electricity, heat (hot water), and cooling. The results of the thermoeconomic analysis revealed that the energy system requires an electricity tariff of at least US$ 106.76/MWh to generate revenue due to the high costs associated with the purchase of biogas and capital costs of the equipment for biogas purification and fuel cell. The life cycle assessment identified that the biogas purification step presented the highest environmental impacts due to the material composition of the absorption and regeneration columns, which is interesting as this is the most critical step of the process. LCA results indicate that although methane is a vital energy vector for energy transition, further studies are required on the technical and environmental aspects of its use in energy systems.

KEYWORDS:

• Biogas
• carbon footprint
• combined cooling
• environmental impacts
• greenhouse gas emissions
• heat and power

List of symbols

Symbol	=	Description
${\dot{m}}_i$	=	mass flow
$h_i$	=	Specific enthalpy
$s_i$	=	Specific entropy
$\text{mathop {{Q\_i}}limits^}$	=	Heat transfer rate
$W_i$	=	Work transfer rate
$E_i$	=	Energy rate
${\dot{B}}_i$	=	Exergy rate
$T_0$	=	Reference temperature
$h_0$	=	Reference state enthalpy
$s_0$	=	Reference state entropy
${B^{\ast }}_i$	=	Exergy cost
$k$	=	Unit exergy cost
$c_i$	=	Monetary cost per unit of exergy
$P{c}_i$	=	Monetary cost per unit of time

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes

1. A season encompasses the period from sowing to harvest, with a duration of 12 months. It starts on one year, and ends on the following year. Therefore the 2021/2022 season refers to the season that started in 2021 with sowing, and ended in 2022 after harvest in 2022.

Additional information

Funding

The authors wish to acknowledge the financial support of Coordination for the Improvement of Higher Education - Capes [project nº 88887.628663/2021-00], Brazilian National Council for Scientific and Technological Development – CNPq [productivity grant 309452/2021-0], and Foundation for the Support of Science and Technology of Pernambuco - FACEPE [IBPG-0542-3.05/19].

Notes on contributors

Elias Gabriel Magalhães Silva

Elias Gabriel Magalhaes Silva holds a bachelor's degree in Mechatronics Engineering from the Federal Institute of Education, Science and Technology of Southeast Minas Gerais, Brazil. Master in Bioenergy from the Federal University of Paraná, Brazil, with research in thermochemical transformation processes. He is currently a Doctoral student at the Graduate Program in Energy and Nuclear Technologies at the Federal University of Pernambuco.

Maria Helena de Sousa

Maria Helena de Sousa Graduated in Energy Engineering and Master's in Mechanical Engineering from the Federal University of Pernambuco (UFPE), Brazil. She is currently a doctoral student at the Graduate Program in Energy and Nuclear Technologies at UFPE, with an emphasis on energy use from biomass sources.

Monica Carvalho

Monica Carvalho is a Full Professor at the Department of Renewable Energy Engineering, Federal University of Paraíba, Northeast Brazil. She holds a BEng in Electrical Engineering (UFCG, Brazil), an MSc in Mechanical Engineering (UFPB, Brazil), and PhD in Mechanical Engineering (University of Zaragoza, Spain) with European Doctorate mention. She received a Natural Sciences and Engineering Research Council of Canada (NSERC) Industrial R&D Fellowship Award and is also a collaborating Professor at the Mining Engineering Department at the Laurentian University (Sudbury, Canada). Her research interests include thermal engineering and energy integration, optimisation of energy systems, thermoeconomics, and life cycle assessment.

Adriano da Silva Marques

Adriano da Silva Marques is a Professor at the Department of Renewable Energy Engineering, Federal University of Paraíba, Northeast Brazil. He is also a Professor at the Graduate Program in Renewable Energy Engineering, at the same university. He holds a BEng in Mechanical Engineering (UFPB, Brazil), MSc in Mechanical Engineering (UFPB, Brazil), and PhDin Mechanical Engineering (UFPB, Brazil). He has been conducting research in thermal engineering and energy efficiency, exergy, thermoeconomics and exergoenvironmental analysis.