Development of an innovative high-performance poly-generation plant for efficient multi-level heat recovery of a biogas-powered micro gas turbine: Environmental and Multi-criteria analysis

Abstract

Nowadays, the biogas-powered gas turbine cycles in poly-generation systems play a crucial role due to increasing fuel prices, declining renewable energy sources, and environmental concerns associated with fossil fuels. Concerning the high temperature of expanded gas, a novel high-performance poly-generation plant is achievable by intelligently selecting different subsystems. This paper presents a novel biogas-fueled poly-generation plant for producing electricity, refrigeration load, distilled water, and hydrogen simultaneously using multi-level heat recovery. An extended assessment of the devised plant output is performed based on energy-exergy, environmental, and exergoeconomic criteria, in which the plant’s gas turbine inlet temperature, preheated air temperature, air compressor pressure ratio, as well as turbine inlet pressure, are considered as variables. In the following, to demonstrate the advantages of using a Stirling engine, this study investigates two scenarios to reveal its superiority, and a bi-objective optimization is performed, where the objective functions comprise minimizing the poly-generation unit products cost and maximizing the sustainability index. When the plant is operated with a Stirling engine, the plant produces 986 kW of electricity, 137.5 kW of refrigeration load, 8.39 m3/h of distilled water, and 2.96 kg/h of hydrogen. In this case, the energetic and exergetic efficiencies of the proposed system are enhanced by 2.96% and 7.89%, respectively compared to non-Stirling engine mode. Also, the carbon dioxide emissions and sustainability index are ameliorated from 606.2 kg/MWh to 588.6 kg/MWh and from 1.47 to 1.5, respectively. In addition, the sensitivity analysis indicates that in a certain ratio of PRAC, the plant's performance reaches its optimal mode. Moreover, the unit cost of products and sustainability index are improved by 9.9% and 8%, respectively, compared to the base design case with the SE.