Heat–power decoupling technologies for coal-fired CHP plants: Operation flexibility and thermodynamic performance

Heat–power decoupling is important for combined heat and power (CHP) plants because it improves their operational flexibility. In this study, off-design and thermodynamic analysis models are developed to examine and compare the operational flexibility improvement and thermodynamic performance of heat–power decoupling technologies. Quantitative analyses are then conducted on a 350 MW reference CHP plant. Results show that feasible operation domains are enlarged by heat–power decoupling technologies. Low-pressure turbine (LPT) renovations, such as zero output renovation and that with a bladeless shaft, have the most potential for reducing the feasible minimum power load, followed by electric boilers. Under a heating load of 300 MW, the feasible minimum power loads can be reduced by 71.6, 124.2, 42.4, and 157.7 MW with a heat pump, an electric boiler, a heat storage tank, and LPT renovations, respectively. However, the heating load of LPT renovations is completely coupled with power load, and its feasible operation domain is limited. Moreover, electric boilers decrease the energy and exergy efficiencies of CHP plants. Therefore, the heat storage tank decoupling technology is the preferable energy-saving option, followed by the heat pump decoupling technology.