Performance evaluation of combined heat and power unit equipped with rear heating turbine and heat storage tank

Combined heat and power (CHP) units face two challenges: considerable exergy loss during heating and heat-power coupling. For this reason, this study proposes a new unit featuring a rear heating turbine (RHT) and a heat storage tank (HST). A numerical RHT & HST unit model was constructed to evaluate its performance improvements from thermodynamic and flexibility perspectives. To quantify the practical benefits of the RHT & HST unit, a modified genetic algorithm (GA) was developed to solve the HST daily dispatch model, with a backpropagation neural network introduced to improve the model’s objective function accuracy. The results indicate that the RHT & HST unit performed energy cascade utilization of heating extraction steam, demonstrating higher energy and exergy efficiencies, with an increase of 21.8 % in the heating process’s exergy efficiency. Furthermore, its flexibility surpasses traditional units, with a maximum heating capacity increase of 62 MW during deep peak shaving. Compared to conventional GA, the modified GA shows significant improvements in objective function accuracy and computational efficiency. After optimizing dispatch using this algorithm, HST can effectively perform peak shaving and valley filling for heat load, enabling the unit to operate within a more efficient economic range. During the heating season, the RHT & HST unit expects to save approximately 27,257 tons of coal, reduce carbon emissions by about 71,359 tons, and generate around 14.213 million CNY in additional revenue. This study offers guidance on flexibility and energy-saving retrofits for CHP units.