Thermodynamic Degradation and Life-Cycle Carbon Mitigation of a 350 MW Supercritical Coal-Fired Unit During Deep Peak Shaving to 20% Load

This study couples a plant-validated steady-state boiler–turbine model of a 350 MW supercritical unit with life-cycle carbon accounting, renewable-accommodation sensitivity analysis, entropy-weighted TOPSIS, and a constrained load-adaptive operating strategy over 100–20% load. Maximum deviations are below 3% for boiler working-fluid temperatures and 1% for turbine extraction-steam temperatures. From 100% to 20% load, boiler exergy efficiency falls from 61.31% to 48.35%, while net coal consumption and unit-level carbon intensity rise from 293.8 to 391.7 g/kWh and 925 to 1235 gCO2/kWh, respectively. At 20% load, system-level life-cycle carbon intensity decreases from 987.0 to 279.8 gCO2/kWh as the effective renewable-energy accommodation ratio rises from 0% to 100%, crossing below the full-load baseline only above approximately 8.8%. TOPSIS relative closeness decreases from 0.7547 to 0.2453, showing that carbon gains do not eliminate the thermodynamic sacrifice of deeper peak shaving. Excess-air and auxiliary-equipment coordination cuts 20%-load net coal consumption by 5.5 g/kWh but leaves off-design penalties. The framework establishes the renewable-accommodation threshold and recoverable efficiency loss, supporting operating optimization and flexibility compensation.