Abstract
For engine exhaust gas heat recovery, the organic Rankine cycle (ORC) cannot be directly used due to the thermal stability and safety of organic fluids. Thus, a creative power system is given by integrating the supercritical CO2 Brayton cycle and transcritical ORC. This system can directly utilize the thermal energy of a high-temperature exhaust gas. The inefficiencies in the heat exchangers are highly reduced by using supercritical working fluid. The mathematical model of the system, covering both the thermodynamic and economic aspects, is built in detail. It is found that the highest irreversible loss takes place in the gas heater, taking 21.14% of the total exergy destruction. The ORC turbine and CO2 turbine have the priority for improvement, compared to the compressor and pump. The increase in CO2 turbine inlet pressure improves the system exergy efficiency and levelized cost of energy. Both the larger CO2 and ORC turbine inlet temperatures contribute to a decrease in levelized cost of energy and a rise in system exergy efficiency. There is a maximum value of system exergy efficiency and minimum value of levelized cost of energy by varying the ORC turbine inlet pressure. The determined exergy efficiency and levelized cost of energy in the proposed system are 54.63% and 36.95 USD/MWh after multi-objective optimization.
Highlights
The requirement for energy has experienced a substantial rise in the past few decades around the world, especially in developing nations that are expediting urbanization advancement
The increase in CO2 turbine inlet pressure improves the system exergy efficiency and levelized cost of energy. Both the larger CO2 and organic Rankine cycle (ORC) turbine inlet temperatures contribute to a decrease in levelized cost of energy and a rise in system exergy efficiency
There is a maximum value of system exergy efficiency and minimum value of levelized cost of energy by varying the ORC turbine inlet pressure
Summary
The requirement for energy has experienced a substantial rise in the past few decades around the world, especially in developing nations that are expediting urbanization advancement. Reported an impressive work in respect to the thermal characteristics of an ORC along with its economic performance This ORC was powered by the exhaust thermal gas of Sustainability 2022, 14, 1276. Proposed an integrated dual loop transcritical-subcritical ORC power system to efficiently recover the thermal energy from both the coolant as well as the engine exhaust gas. The thermal stability and safety of organic fluids highly restrains the power generation temperature of ORC, and there are large irreversible losses in the heat transfer action from exhaust gas to working fluid. This motivates researchers to seek hightemperature thermal power cycles to substitute for or coupled with ORC. It can beofobserved that the system arranged as thecycle bottom loop driven by the turbine of the CO2 Brayton The cycle.high‐te aisCO
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