Temporary CO2 Capture Shut Down: Implications on Low Pressure Steam Turbine Design and Efficiency

The Natural gas Combined Cycle (NGCC) with post combustion capture using liquid solvents may in some cases be of interest to design with a flexible steam bottoming cycle, so that it can operate both with and without CO2 capture. It is then important that the choice of the low pressure (LP) steam turbine exhaust size is made accordingly. The paper describes why a flexible NGCC requires a LP steam turbine with smaller exhaust than the corresponding NGCC without CO2 capture, and how this will affect the LP turbine exhaust loss and NGCC process efficiency. Handling large variations in LP steam flow is in fact well- known technology in combined heat and power (CHP) plants, and the use of 3D simulation tools can further help making the best LP steam turbine design choice.