Thermodynamic analysis and optimization of a biogas-powered trigeneration system to produce power, cooling and freshwater

Abstract

Despite all the efforts to reduce the consumption of fossil fuels worldwide, the majority of the global energy matrix continues to depend on them, leading to serious environmental impacts such as droughts, that heavily affect rural areas in arid and semi-arid regions. In this work, aiming to reduce environmental impacts, losses and instability associated with power lines and water scarcity, a computational model of a decentralized small-scale trigeneration system to produce power, cooling and freshwater was developed and operating conditions were optimized to maximize both Energy Utilization Factor (EUF) and exergetic efficiency. The trigeneration system consists of biogas-powered microturbines, an LiBr/H2O absorption refrigeration system and a humidification-dehumidification desalination system. The results obtained have shown that the system was able to produce 104.4 kW, 12 kW and 0.1231 kg·s−1 of power, refrigeration and freshwater mass flow rate, respectively, with an EUF of 1.024 and exergetic efficiency of 25.39%. The analysis of exergy destruction has revealed that the microturbines, particularly their combustion chambers, accounted for 78.23% of the total exergy destruction rate in the system which was 295.92 kW for the base case. Using Genetic Algorithm to maximize the EUF, it was possible to achieve a 12.12% increase in the EUF and a 16.25% increase in freshwater production when compared to the base case considered.