OPTIMIZATION OF GAS-TURBINE COMBINED CYCLES

T.K. Mikiashvili,   N.G. Chagmelashvili
Georgia

At the current stage of development of energy industry, major challenge for gas-turbine combined cycle units is improvement of maneuverability, that requires optimization of their thermodynamic parameters, technological schemes, management and regulation systems according to the requirements of their operation modes. Optimization task is based on a multifaceted analysis, which depends on various factors.

The study is dedicated to thermodynamic analysis and optimization of the parameters of the gas-turbine combined cycle. It includes a formulation of the cycle’s thermal efficiency factor in using single and three-pressure steam loops as well as the cases with or without additional fuel combustion; the change of the efficiency factor depending on the changes of the efficiency factors of gas and steam cycles as well as heat recovery boilers and thermodynamic parameters is analyzed; key factors affecting the cycle efficiency are identified; the optimization task based on the decision of which the nature of the change of thermal efficiency factor of the combined cycle is determined is formulated - it increases significantly when initial parameters of the gas-turbine cycle increase and its increase is rather insignificant initial parameters of the steam-turbine cycle increase. Increase of the overheated steam pressure does not result in the significant increase of the efficiency factor of the combined cycle. It has an extreme point from where the increase of the initial pressure results in the reduction of the cycle’s efficiency factor. 

Specific properties of the heat recovery steam boiler as well as the change of the exhaust steam humidity as per initial parameters, etc. should be taken into consideration for optimization of the real cycle units. At this time, maximum values of the efficiency factor are achieved at the initial parameters that are different from the ideal cycles, and the optimization of the control and designing is conducted for specific conditions of the capacities and operation modes.