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

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 x 350 MWe coal-fired power plant. With the same heat supply amount of 237.56 MWth, 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.

Automated summary

The new energy-saving scheme for combined heat and power (CHP) retrofitting in coal-fired power plants combines high back-pressure (HBP), absorption heat pump (AHP) and absorption heat exchanger (AHE) to reduce exergy losses and waste heat, resulting in increased power output and efficiency. By effectively applying this scheme in dual unit systems, additional power loss due to off-design conditions can be reduced or eliminated, leading to overall performance improvement. Thermodynamic, exergy, and techno-economic analyses show a 3.55% increase in power efficiency with a dynamic payback period of 1.59 years and a net present value increase of 48,805 thousand USD over a 25-year lifespan.