Improving low-grade heat utilization in the heat recovery steam generator (HRSG) is crucial for enhancing the efficiency of gas turbine combined cycle (GTCC) power plants. This study proposes a dual heat source plan (DHSP)for the fuel gas heater, in which low-temperature hot water from the low-pressure economizer is first used to preheat the fuel in the primary fuel gas heater, followed by further heating in the secondary fuel gas heater using high-temperature water from the intermediate-pressure economizer. A thermodynamic model of the bottoming steam cycle and fuel heating system was developed to investigate the mechanisms by which the DHSP improves operational performance. Results show that, compared with the conventional single-heat-source heating strategy (SHSP) which uses high-temperature hot water extracted from the intermediate-pressure economizer to heat natural gas through two fuel gas heaters arranged in series, the DHSP reduces the extraction flow from the intermediate-pressure economizer, increasing both reheat and low-pressure steam flows, thereby enhancing power output and lowering the HRSG stack temperature. More importantly, the proposed DHSP represents a system-level optimization of heat distribution within the HRSG by shifting heat extraction from high-temperature to low-temperature sources, enabling more effective utilization of low-grade thermal energy without modifying gas turbine operation. Performance improvements vary with operating conditions: lower unit loads weaken the DHSP’s effect, while lower ambient temperatures strengthen it. The DHSP requires larger heat transfer area for the fuel gas heater, increasing investment costs; however, for a typical F-class GTCC unit with 3,000 annual full-load hours and an average ambient temperature of 21.7 °C, it can generate approximately 0.6 million CNY in annual revenue with a payback period of around 5.5 years, demonstrating its technical and economic feasibility for GTCC power plants. • A system-level dual-heat-source plan (DHSP) for the fuel heating system is proposed to enhance low-grade heat utilization in GTCC power plants. • DHSP’s performance enhancement and its variation with unit load and ambient temperature are analyzed. • DHSP improves GTCC performance and delivers favorable economic benefits with a short payback period, demonstrating its economic viability for GTCC power plants.
Xiao et al. (Fri,) studied this question.