Coal-based electric power generation remains the basic source of obtaining energy. With increasing pressure to reduce CO2 emissions, improving power unit efficiency has become an issue of utmost significance. The development of technologies related to coal-fired power units does not focus solely on the steam parameters ahead of the turbine. Increasing the live steam parameters usually constitutes the greatest contribution to the rise in the efficiency of a power unit, but the sum of efficiency gains related to the application of other solutions can also be significant and can, in some cases, exceed the effects related to raising the temperature and steam pressure values. A paper presents thermodynamic and economic analysis of various configurations of the ultra-supercritical coal-fired 900 MW power unit with the auxiliary steam turbine. Main subject of research was a power unit considered within the Strategic Research Programme – Advanced Technologies for Energy Generation with the parameters of live and reheat steam: 30 MPa/650°C/670°C. The base configuration of the power unit has single steam reheat and electric drive boiler feed pump. Analysis of ultra-supercritical 900 MW power unit involves configuration with a single and double reheat. The following configurations of the auxiliary steam turbine will be presented and compared:
• extraction-backpressure steam turbine fed with steam from cold reheat line with bleed and steam outlet directed to the feed water heaters;
• extraction-backpressure steam turbine fed with steam from cold reheat line with bleed and steam outlet directed to the feed water heaters; the auxiliary turbine drives the boiler feed pump;
• backpressure turbine fed with steam from a hot reheat steam line operating in parallel with the intermediate-pressure turbine; the auxiliary turbine drives the boiler feed pump.
The analysis of the operation of the 900 MW unit was carried out for three load levels: for the nominal mass flow of live steam, and for the partial mass flow of 75% and 50%. For all presented solutions thermodynamic and economic analysis was performed, which has taken into account the charge for CO2 emissions.