Feedwater repowering of 800 MW supercritical steam power plant

The paper presents concept of using hot exhaust gases from the gas turbine to heat up feedwater in supercritical power plant unit. The benefits of such solution are discussed and the factors to be taken into account are listed. Details are discussed criteria to be met by gas turbine, in order to be safely and optimally connected to the steam system. Reference unit model with 800 MW electric power was created, which was later supplemented with a gas turbine. The system with gas turbine in relation to “clean” steam system has greater power and efficiency. The power increase is due to the extra power generated by gas turbine and steam system higher output by increasing amount of steam flow through the turbine (closed extraction to "bypassed" high-pressure heat exchanger). System power is changed linearly with the steam flow and reaches the nominal point 20% higher than without an added gas turbine. The characteristics of the effciency of the whole system are flatter, having higher values. At the nominal point the difference is about 1% and rises from 43.5% to approximately 44.5%.