Application of thermoelectric generators and organic Rankine cycle combined system for cold exergy recovery from liquefied natural gas

As thermoelectric generators (TEGs) improve in techno-economic performance, their role in energy recovery becomes increasingly significant. This research evaluates the integration of TEG modules into three conventional liquefied natural gas (LNG) cold exergy recovery systems: direct expansion (DE), organic Rankine cycle (ORC)-DE combined, and double ORC-DE combined system. And the TEG condenser-TEG-double ORC DE combined system is proposed. The influences of key design parameters, including working fluid selection, ORC condensation temperature, LNG high-pressure, TEG installation position, and the number of TEG modules, on cold exergy recovery efficiency and levelized cost of electricity (LCOE) are assessed. The results reveal that to achieve the highest efficiency, R290 is the optimal working fluid for the single ORC system, and a combination of R1150 and R290 is best for the double ORC system; the optimal condensation temperature of working fluids is 169 K for R1150 and 231 K for R290; optimal LNG pressure is 120 bar for the DE and TEG-DE systems and 75 bar for the others; installing TEG as the ORC condenser yields higher efficiency. Besides, multi-objective optimization results reveal that the TEG-DE system has the lowest LCOE of 0.161 $/kWh with exergy efficiency of 15.0 %, the TEG condenser-TEG-double ORC-DE system achieves the highest exergy efficiency of 29.1 % with LCOE of 0.169 $/kWh.