Energy saving optimization of 1000MW ultra-supercritical secondary reheat unit integrated with BEST

With the increase of steam parameters, exergy of secondary reheating units generally has problems such as higher superheat of extraction steam, temperature difference of heater heat exchange and greater loss of exergy, which hinder the further improvement of unit efficiency. In this paper, a 1000MW ultra-supercritical secondary reheat unit is taken as an example, and three optimization schemes are proposed. Scheme 1 with external steam cooler (OSC), the integration scheme 2 OSC and back pressure extraction turbine (BEST). The exergic economy of the three schemes was compared, and exergic loss of some units of the system was calculated by exergic analysis method. The results show that scheme 2 can effectively utilize the multi-stage superheat of RH1~RH7, and the thermal economy under higher load is higher than scheme 1 and original system. At 100%THA, the feed water temperature and cycle thermal efficiency of scheme 1 have increased by 6.24℃ and 0.48%, respectively, and the exergic loss of boiler, turbine and regenerator system has decreased. With the decrease of load, the exergic loss of scheme 2 on feed water temperature, cycle thermal efficiency and exergic loss decreased. The exergic loss of turbine with load below 50%THA was slightly higher than that of scheme 1 and original system. Therefore, compared with scheme 1 and original system, scheme 2 has higher thermal economy.