4E assessment on a CCHP cogeneration Brayton system with dimensional design of PCHEs and turbomachinery

The supercritical carbon dioxide Brayton cycle is considered a promising solution for energy conversion due to its high efficiency, compactness, flexibility, and safety. However, the process design and optimization are challenging when relying on conventional empirical models for key components such as heat exchangers and turbomachinery. In this paper, a Brayton system based on metrics such as energy, exergy, economy, and environmental impact is assessed. To do this, one-dimensional models are developed for turbomachinery to evaluate process structure and internal performances. Results show that the artificial energy efficiency, artificial exergy efficiency, levelized cost of energy, and artificial environment emissions of the Brayton system are 0.51, 0.63, 30.3 USD/(MW·h), and 73.4 tons CO₂, respectively. Moreover, the passage losses within rotor and stator can account for over 68 % of the total losses in the turbomachinery. The turbomachinery can regulate the rotor speed to optimize the flow alignment between fluid and blades under varying operating conditions. Furthermore, increasing the waste heat temperature of the Brayton top cycle can enhance the heating and cooling performance of bottom cycles. Additionally, raising the initial pressure of evaporator in the heat pump cycle can optimize pinch heat transfer of both recuperator and evaporator in the heat pump cycle. Finally, decreasing the initial pressure of generator or increasing the waste heat temperature in the ammonia absorption refrigeration cycle can reduce dimensional calculation deviations of solution heat exchanger using the correlations proposed by Conde-Petit.