Investigation of the Bottoming Cycle for High Efficiency Combined Cycle Gas Turbine System With Supercritical Carbon Dioxide Power Cycle

The supercritical CO₂ (S-CO₂) power cycle has been receiving attention as one of the future power cycle technology because of its compact configuration and high thermal efficiency at relatively low turbine inlet temperature ranges (450∼750°C). Thus, this low turbine inlet temperature can be suitable for the bottoming cycle of a combined cycle gas turbine because its exhaust temperature range is approximately 500∼600°C. The natural gas combined cycle power plant utilizes mainly steam Rankine cycle as a bottoming cycle to recover waste heat from a gas turbine. To improve the current situation with the S-CO₂ power cycle technology, the research team collected various S-CO₂ cycle layouts and compared each performance. Finally, seven cycle layouts were selected as a bottoming power system. In terms of the net work, each cycle was evaluated while the mass flow rate, the split flow rate and the minimum pressure were changed.

The existing well-known S-CO₂ cycle layouts are unsuitable for the purpose of a waste heat recovery system because it is specialized for a nuclear application. Therefore, the concept to combine two S-CO₂ cycles was suggested in this paper. Also the complex single S-CO₂ cycles are included in the study to explore its potential. As a result, the net work of the concept to combine two S-CO₂ cycles was lower than that of the performance of the reference steam cycle. On the other hand, the cascade S-CO₂ Brayton cycle 3 which is one of the complex single cycles was the only cycle to be superior to the reference steam cycle. This result shows the possibility of the S-CO₂ bottoming cycle if component technologies become mature enough to realize the assumptions in this paper.