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Waste heat is one of the major problems associated with the energy system. This paper discusses an energy, exergy, and emissions approach for the hybrid system by utilizing waste heat to the maximum extent. A thermoelectric generator (TEG) is incorporated to utilize the low-temperature waste heat from a hybrid model of a solid oxide fuel cell (SOFC) and a combined heat and power (CHP) system. SOFC is an electrochemical cell that generates power at high temperatures through an electrochemical reaction. The high-temperature, unutilized fuel leaves the SOFC, which is burned in the afterburner. The afterburner temperature controls the operating temperature of SOFC. Here, three recuperators are used to utilize this high-temperature waste heat to improve the performance of SOFC and simultaneously generate heat power from the water or gas recuperator. TEG is an auxiliary power production technology that converts waste heat into energy. A novel integration of TEG with SOFC–CHP hybrid system to utilize the low temperature waste heat, is employed. The main goal of this study is to analyze a novel SOFC–CHP-TEG hybrid system in terms of its thermodynamics and emissions. A Two stage TEG is integrated with the SOFC–CHP hybrid system. The simulation model of high temperature fuel cell (SOFC) is developed on MATLAB and validated with published results. This study analyses the impact of pressure ratio and afterburner temperature on the performance of SOFC–CHP-TEG. To do this, perform energy and exergy assessments using the principles of the first and second laws of thermodynamics. A novel exergy-based sustainability index with emissions analysis for the proposed SOFC–CHP is presented. The achieved overall energy efficiency is 62.54% at a pressure ratio of 12 and an afterburner temperature of 1000 K. With an increase in pressure ratio and temperature, the level of CO emissions reduces significantly. [Display omitted] • A novel energy exergy for SOFC–CHP-TEG system is presented. • Exergy based performance is compared and achieve 56.62. • Utilization of waste heat via TEG. • Energy efficiency of SOFC–CHP-TEG is 62.54% at rp = 12 and afterburner temperature of 900 K. [ABSTRACT FROM AUTHOR]

This paper contributes a novel sustainability index and modified exergy indicators for conventional gas turbines and solid oxide fuel cell integrated gas turbine (SOFC-GT) hybrid power cycles. In this work, an intercooled gas turbine (Ic-GT) cycle is considered as a base cycle, which gives an additive advantage in lowering the power required for the compressor. Moreover, on SOFC integration with Ic-GT, the qualitative and quantitative performance are examined. Numerical modeling is done using MATLAB and an exclusive comparison has been made based on energy-exergy and sustainability analysis for the system and its components. On comparing the first law efficiency at turbine inlet temperature, TIT 1250K and rp = 18 for Ic-GT, intercooled recuperated gas turbine (Ic-RGT), and Ic–SOFC–RGT, it is 25.82%, 36.04%, and 64.78%, respectively. Similarly, second law efficiency is 11.43%, 22.33%, and 61.11% and the overall sustainability index is 1.12, 1.28, and 2.57 for Ic-GT, Ic-RGT, and Ic–SOFC–RGT, respectively. Nine other modified exergy-based parameters are used to identify the role of fuel and product exergy and then compare the most affected component in three configurations. [Display omitted] • Gas turbine exhaust waste heat has been examined to power fuel cell. • Two typical intercooled gas turbines and a fuel-cell hybrid system are compared. • Energy efficiency, exergy efficiency, sustainability index are compared. • Configurations are compared using nine modified exergetic performance indicators. [ABSTRACT FROM AUTHOR]

In this paper, six novel modified exergy relations are explored to determine the precise estimation of exergy destruction and to identify which component has the most improvement potential. For this, three power generation cycles are considered, i.e., simple gas turbine (SGT), recuperated gas turbine (RGT), are compared with a novel hybrid system (SOFC-RGT: Solid Oxide Fuel Cell-RGT), which operates with fuel flexibility as well as enhanced work-output and thermal efficiency. For energy, exergy, and sustainability studies, numerical modeling is conducted using MATLAB. At r p = 4, TIT = 1250 K, an exclusive comparison has been made between proposed configurations based on thermodynamic modeling and exergy-based sustainability index. It is found that with the inclusion of a recuperator and a fuel cell in the proposed cycles, the thermal and sustainability performance tend to increase significantly. Whereas, exergy destruction increases but has minimal impact on comparing thermal performance and sustainability index. In terms of sustainability, RGT is 30.76% more sustainable than SGT, while SOFC-GT is 63.39% more sustainable than RGT. [Display omitted] • The gas turbine exhaust waste heat generated has been examined for powering the fuel cell. • A comparative sustainable, qualitative and quantitative performance comparison has been made between SGT, RGT and SOFC-RGT. • As per sustainability index the performance order is SGT < RGT < SOFC-RGT (lower to higher). • 6-Modified exergy indicator is used for performance comparison. • A novel performance map has been drawn for SGT, RGT and SOFC-RGT. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel comparison of pine sawdust, poplar sawdust and almond shell for SOFC-GT hybrid system. • Exergy analysis for each component is compared with the three proposed biomass. • Eight modified dimensionless exergy indicator is used for performance comparison. • Pine sawdust has the maximum thermal efficiency of 63.12% at rp = 6 and TIT = 1250 K. Conventional gas turbines (GT) are working with limited fuels and exhibit thermal efficiency between 30 and 40%. This restriction with the fuels and its efficiency range can be improved by adding an electrochemical fuel cell, i.e; a Solid Oxide Fuel Cell (SOFC). This paper proposes three different types of biomasses, including pine sawdust, poplar sawdust, and almond shell, which may all be used to power the novel biomass-fueled solid oxide fuel cell gas turbine (SOFC-GT) presented herein. MATLAB based simulation is used to validate the results of this fuel cell based hybrid cycle performance. Three performance parameters are considered namely, current density (i d), turbine input temperature (TIT), and pressure ratio (rp) to evaluate the performance of the proposed system. For this, energy-exergy approaches based on the first and second law of thermodynamics are used to assess each cycle component as well as the entire system. The sustainability index and environmental impact factor of each component are evaluated using dimensionless modified exergy indicators. With all three of the suggested biomass fuels, the SOFC-GT hybrid system runs most effectively at pressure-ratio of 6 and TIT 1250 K. Pine sawdust (Case-1) exhibits the largest levels of exergy destruction (2653.14 kW), environmental effect (0.91), and the lowest sustainability index (2.09) but it also has the highest levels of thermal efficiency (63.12%). [ABSTRACT FROM AUTHOR]