THERMODYNAMIC ANALYSIS OF TRIGENERATION SYSTEM

Abstract

Energy is essential for sustaining human life and is a key indicator of a society's prosperity and development. However, rapid population growth and industrialization have significantly increased global energy demand for electricity, heating, and cooling, leading to energy crises. To meet this demand, excessive use of fossil fuels, which are already limited in availability, has become prevalent. Consequently, burning these fuels, particularly the emission of greenhouse gases like CO2, has contributed to severe environmental issues such as global warming and climate change. Addressing these challenges requires adopting advanced technologies to reduce global warming and enhance energy system efficiency. Various nations have proposed and implemented solutions to mitigate environmental impact. One promising approach is the use of trigeneration systems, which can meet rising energy needs in a cleaner, more sustainable and cost-effective manner. Trigeneration systems utilize waste heat recovery to produce electricity, heating, and cooling simultaneously from a single fuel source. Notably, helium turbine-based trigeneration systems, combined with efficient waste heat recovery through organic Rankine cycles, are widely employed in industrial applications, particularly in process industries. These systems offer high efficiency, low pollution, reduced capital costs, flexibility, and the capability to generate multiple forms of energy. This thesis proposes novel helium turbine-based trigeneration systems (Combined Cooling, Heating, and Power systems) for the simultaneous generation of electricity, chilled water, and hot water. A solar power tower (SPT) system is a promising option to harness solar energy for solar thermal electricity generation via power cycles. These days, combined cycles, especially those based on the supercritical helium Brayton cycle, are very popular. The performance of different configurations of helium Brayton cycles (HBC) driven with SPT has been further investigated in this thesis work. Apart from this, organic Rankine cycle (ORC), ejector refrigeration system (ERC), cascaded vapour absorption refrigeration-vapour compression refrigeration (VAR-VCR) system, and cascaded ejector refrigeration-vapour compression refrigeration (ERS-VRS) system were used as bottoming waste heat recovery cycles. Also, a short analysis has been performed with a combined Rankine power and vapour absorption refrigeration (VAR) cycle, a CCHP system driven by a low-temperature heat source using various eco-friendly refrigerants for cooling, heating, and power vi generation. Simultaneously, the effects of the working fluids on the system performance were investigated. First, the output of the SPT-based combined HBC and ORC with an ejector refrigeration integrated system for combined heating, cooling, power generation, and waste heat recovery was investigated. The trigeneration system comprises a Brayton cycle using helium as the working fluid and an organic Rankine cycle (ORC) integrated with an ejector refrigeration system (ERS) to recover waste heat from the Brayton cycle. The Brayton cycle and ORC generate power, while the evaporator and condenser provide simultaneous cooling and heating, respectively. The heating and cooling effects were generated at 50°C and 10°C for building applications such as hospitals and hostels. Finally, when all the studied parameters are considered, the optimal system exhibits exergy and energy efficiency of 25.12% and 23.3%, respectively. This study evaluates the performance of a combined helium Brayton cycle (HBC) and organic Rankine cycle (ORC) system, which incorporates a cascade vapour absorption refrigeration (VAR) and vapour compression-refrigeration (VCR) system as the bottoming cycle. By using the ultra-low GWP working fluid R410a, the system aims to minimize global warming and ozone depletion. Designed for solar power tower (SPT) plants, this trigeneration system efficiently produces electricity, heat, and cooling at low temperatures using a high temperature SPT heat source. It integrates cascaded VAR-VCR refrigeration technology with the helium Brayton cycle to deliver power, heating, and low-temperature cooling (-20°C) for applications like food preservation. The SPT plant achieves a power output of 14,865 kW, an exergy efficiency of 39.53%, and an energy efficiency of 28.82%. The coefficients of performance for cooling and heating are 0.5391 and 1.539, respectively. Exergy analysis indicates that the solar subsystem contributes to 78.18% of the total energy destruction in the plant. Key factors affecting performance include the temperatures of the evaporator, generator, helium turbine inlet, heliostat, and receiver efficiencies. This system outperforms configurations using supercritical CO2 and Rankine cycles compared to prior studies. Moreover, parametric analysis of the SPT-based combined HBC and ORC with cascade ERS-VRS integrated system was investigated. Effects of topping cycle parameters on combined cycle and ORC performance were also investigated. The organic Rankine (ORC) cycle, cascaded ejector refrigeration system (ERS), and vapour compression refrigeration (VCR) system have been implemented in the solar power tower (SPT)-based conventional helium Brayton cycle (HBC) to enhance the performance of the solar-based energy vii generation system. It was concluded that the overall proposed solar plant (SPT-HBC-ORC ERS-VCR) obtained energy efficiency, exergy efficiency, and network output of 60.66%, 35.55%, and 15585 kW, respectively. The study’s fourth phase involved a thermodynamic analysis of integrated systems combining rankine-absorption power and refrigeration cycles designed to simultaneously produce cooling and power. The system generates both outputs from a single heat source using a binary liquid mixture of water and ammonia as the working fluid. Key parameters influencing net power output, refrigeration output, and exergy efficiency include the heat source temperature, ambient temperature, refrigeration temperature, turbine intake pressure, turbine inlet temperature, and ammonia concentration in the solution. Results show that increasing the turbine inlet pressure improves the cycle's energy and exergy efficiencies. Energy dissipation primarily occurs in the heat exchanger exhaust, followed by losses in the heat exchanger, boiler, turbine, superheater, absorber, condenser, and rectifier. The system's energy and exergy efficiencies were evaluated and compared with energy loss distributions. This integrated cycle is well-suited for solar thermal power generation using cost-effective concentrating collectors, which can lower initial investment costs for solar thermal facilities. Finally, a study of a combined power, heating, and cooling integrated system driven by a low-temperature heat source was examined using six ultra-low GWP eco-friendly refrigerants as working fluids. This study describes an integrated power, cooling, and heating cycle incorporating an ejector refrigeration system, an ORC, and condenser heating with a low-temperature heat source. Thermodynamics' first and second laws were used to analyze the performances of six distinct alternative refrigerants on the combined cycle. The influence of the most important parameters, including evaporator temperature, turbine entering temperature, heat source temperature, refrigeration output, exergy efficiency, entrainment ratio, thermal efficiency, total exergy destruction, and thermal efficiency of the stated system using different environmentally friendly working fluids (R-123, R-124, R-141b, R-290, R 134a, and R-152a), was studied. Out of all the working fluids employed in this study, R-152a and R-134a are the most appropriate from an energy efficiency and environmental perspective for the suggested combined cycle. Energy efficiency drops as evaporator temperature rises and increases as turbine inlet temperature rises, respectively. Conversely, if the heat fluid temperature of the heat source and turbine entering temperature rises, the viii cycle's thermal efficiency also rises. Furthermore, studies have found that as evaporator temperature rises, the ejector's entrainment ratio drops and refrigeration output rises. The findings of this study are expected to offer significant insights into helium turbine-based trigeneration systems, contributing to the advancement of energy solutions that are efficient, clean, sustainable, and economically viable. By addressing critical aspects of system performance and efficiency, the results can serve as a valuable resource for researchers, engineers, and policymakers aiming to develop and implement cutting-edge energy technologies. These advancements have the potential to support global efforts in reducing greenhouse gas emissions and promoting the widespread use of renewable energy sources, thereby fostering a transition to a more sustainable energy future.