Comprehensive analysis and optimization of a novel solar-driven two-stage condensation transcritical power system using CO2-based mixture for liquefied natural gas cold energy recovery

This research presented a novel solar-driven two-stage condensation transcritical power cycle integrated with a liquefied natural gas (LNG) direct expansion power cycle. The two-stage condensation process was introduced to enhance power generation efficiency, and five CO2-based mixtures (R1270/CO2, R290/CO2, R152a/CO2, R161/CO2, and R32/CO2) were investigated to optimize temperature matching in heat exchangers. Owing to the temperature glide effect, the exergy efficiency of the proposed solar-driven two-stage condensation transcritical power system (TCTPS) using R290/CO2 (0.3/0.7) increased by 15.64 %, while the levelized cost of energy decreased by 10.68 % compared to the system using pure CO2. In the critical two-stage condensation process, parametric analysis revealed that the optimal first-stage condensation temperature occurred near the CO2 triple point, while the optimal second-stage condensation temperature varied depending on the refrigerant and operating conditions. Finally, multi-objective optimization under different LNG usage scenarios revealed that R290/CO2 exhibited the best overall performance, followed by R1270/CO2, R152a/CO2, and R161/CO2. Compared with the basic regenerative solar-driven transcritical power system, the TCTPS achieves improvements in net power output (13.03 %–17.46 %), exergy efficiency (1.03 %–3.16 %), and CO2 emission reduction (13.02 %–17.46 %), along with a 1.42 %–3.13 % reduction in the levelized cost of energy.