Performance assessment of new energy-saving schemes for combined heat and power plants

Highlights: • A combination of AHP, AHE and HBP is proposed in CHP retrofitting. • New scheme is applied in dual unit systems for better performance. • Thermodynamic, exergy and techno-economic performance is evaluated. A new energy-saving scheme is proposed for the combined heat and power (CHP) retrofitting in a coal-fired power plant by combining the high back-pressure (HBP), the absorption heat pump (AHP) and the absorption heat exchanger (AHE). Compared to the conventional CHP retrofitting scheme, the proposed new scheme reduces the exergy loss during heat transfer and the waste heat to environment, enabling more power output with the same heat supply amount. When the proposed new scheme is effectively applied in dual unit systems by system integration, the additional power loss caused by the off-design condition of the low-pressure turbine could be reduced or even eliminated, which further improves the overall performance. Detailed thermodynamic, exergy and techno-economic analyses are conducted to compare the proposed new scheme with the conventional scheme in a 2 × 350 MW_e coal-fired power plant. With the same heat supply amount of 237.56 MW_th, the power efficiency is increased by 3.55% in total. Techno-economic analysis results show that the dynamic payback period (DPP) to offset the total investment increase of the proposed new scheme is 1.59 years, and the net present value (NPV) increase for a 25-year lifespan can reach 48,805 thousand USD.