Insight on electrical and thermal powers mix with a Gen2 PWR: Rankine cycle performances under low to high temperature grade cogeneration

Performances of a Rankine PCS exemplary of the Gen2 PWRs fleet, are mapped under heat cogeneration. In the considered scenarios, steam latent heat is provided in a 146–285 °C range and cogeneration load rates up to 20% of SGs power. THERMOFLEX commercial software and CYCLOP in-house code are applied to balance cycle performances with and without taking into account turbine thermodynamic irreversibilities that arise from part-load operation. Deviations between both approaches highlight that the original cycle designed for a 100% electrical duty, does not deserve to be revised for a low temperature cogeneration application. Instead, growing of part-load irreversibilities indicates optimization possibilities of its design for high temperature grade cogeneration. As such, the most stringent cogeneration case shows a cycle electrical efficiency drop of 2.7 points if one considers a constant cycle bottoming pressure. An exergetic analysis outlines that the turbine governing valve which controls steam admission, plays a key entropic role while degradation of turbine efficiency and impact of SG feed water temperature change, remain low. Shift of turbine expansion lines to lower pressures is the reason for a weakly changed turbine efficiency, by reducing stage losses contribution due to steam moisture content.