Thermoeconomic analysis of multi-stage recuperative Brayton cycles: Part II – Waste energy recovery using CO2 and organic Rankine power cycles

Abstract

Multi-stage gas turbine cycle configurations can greatly contribute to improve the economic and environmental aspects of gas turbine power plants. In the first part of this work, the hybridization of multi-stage recuperative Brayton power cycles with a solar power tower system that used a pressurized air receiver was evaluated. In this work, a detailed thermodynamic and economic analysis was conducted to evaluate the waste energy recovery from a non-solar multi-stage recuperative Brayton cycle configuration that showed the lowest levelized cost of electricity (LCOE) in the first part. A comparative analysis between different organic Rankine cycles (ORCs) and supercritical CO2 power cycles was conducted for waste energy recovery from both intercooling stages and the exhaust gas. After designing the systems, a transient analysis was conducted to consider the effect of off-design conditions on the cycles thermo-economic performance. The obtained results showed that waste energy recovery using an ORC is the most economical option. By recovering the available heat in intercooling and exhaust gas stages by ORCs that use Isobutane and Toluene as working fluids, respectively, an additional power of 3508 kW was generated. Also, thermal efficiency was increased from 53.6% to 59.9% and the LCOE was reduced from $57.80/MWh to $54.77/MWh. Overall, the results demonstrated that waste energy recovery from intercooling stages and exhaust gas of a multi-stage gas turbine power plant is an attractive option for improving its thermal and economic performance. Also, considering the high price of a solar power tower plant and the technological pressure and temperature limitation of a pressurized air receiver, waste energy recovery is a more practical and beneficial option at current time than hybridization with a solar power tower plant.