Proposal and 3E (energy, exergy, and exergoeconomic) assessment of a cogeneration system using an organic Rankine cycle and an Absorption Refrigeration System in the Northeast Brazil: Thermodynamic investigation of a facility case study

Abstract

This paper proposes a cogeneration system to achieve the partial electric and thermal demands of a building in the public University. This proposed system comprises an Internal Combustion Engine (ICE), an organic Rankine cycle (ORC), and equipment that will operate as a sink. For the latter, two types of equipment were selected: a cooling tower and an Absorption Refrigeration System (ARS). The building selected to propose the cogeneration system is the Institute of Sustainable Energies (IES), located at the Federal University of Paraíba (UFPB), in the Northeast of Brazil. The performance of the system based on energetic and exergetic points of view operating under two distinct modes; ORC Simple (ORC-S) and ORC Combined (ORC-C), was compared. Both modes are based on the energy availability of the ICE exhaust gases. The thermodynamic models for both modes were developed based on the first and second laws of thermodynamic considering input parameters, such as inlet temperature, pressure ratio, and outlet temperature of the expander and the cold-water storage tank. For the exergoeconomic technique, the SPECO Method (Specific Exergy Costing) was used and implemented along with the Thermodynamic model. The ORC system studied uses a scroll expander and operates with R-134a as the working fluid and water/ammonia pair for the single-effect ARS. The results showed that the ORC-C mode can meet from 18.9% to 37.5% of the IES electricity demand, while the ORC-S mode can meet from 12.4% to 24.5%. The thermodynamic analysis reported that the ORC-C allowed a 33.6% increase in mechanical power production, an increase from approximately 4.5% to 34.5% in energy efficiency as well as exergy efficiencies around 40% and reduction of the total destroyed exergy. From the exergoeconomic point of view, the specific cost of the chilled water has a slight influence on the total cost of the products, while the specific cost of hot water has a strong influence on the total cost of the products (a variation of approximately 46% for a distinct heat source).