Integration of low-temperature transcritical CO_2 Rankine cycle in natural gas-fired combined cycle (NGCC) with post-combustion CO_2 capture

摘要

When integrating a natural gas-fired combined cycle (NGCC) with post-combustion CO_2 capture, an efficiency penalty is induced. In the current work the penalty was a reduction of net plant efficiency from 58.5% to 50.6%. The largest part of this penalty is related to the reduction of power output from the power plant due to steam consumption for CO_2 capture solvent regeneration. The potential of recovering low-temperature un-used thermal energy is limited as this low-grade energy is at a temperaturebelow the low-pressure pinch-point of the steam boiler. In this work, heat sources located in the CO_2 capture process and CO_2 compression process have been identified and integrated with a low-temperature Rankine cycle utilizing CO_2 as working fluid.The approach presented in this paper is novel in the sense that it has not been applied on power plants operating with post-combustion CO_2 capture. Results show that integration of the low-temperature CO_2 Rankine cycle can increase the net plant efficiency of a natural gas-fired Combined Cycle power plant by 1.6%-points (50.6-52.2%) when using a conventional Monoethanolamine (MEA)-based CO_2 capture process. Capture process modifications (Lean Vapour Recompression) in combination with application ofthe CO_2 Rankine cycle can increase the efficiency by 1.8%-points (50.6-52.4%). The contribution from the CO_2 Rankine cycle for the latter case is 0.9%-points.