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Comprehensive multivariable analysis of the possibility of an increase in the electrical efficiency of a modern combined cycle power plant with and without a CO2 capture and compression installations study

Kotowicz, Janusz, Brzęczek, Mateusz
Energy 2019 v.175 pp. 1100-1120
air, carbon dioxide, combustion, cooling, generators (equipment), greenhouse gas emissions, heat recovery, models, power plants, steam, temperature, transpiration
The main objective of the presentstudy is to determine whether the thermodynamic efficiency of a modern combined cycle power plant (CCPP) with steam reheating can be increased when using designs both with and without CO2 separation and compression installations. The relatively high costs of a steam cycle compared to a gas turbine (GT) have motivated the present direction of efficiency research in this area. Therefore, in all systems analyzed in this work, the same structure of heat recovery steam generator (HRSG) was assumed, producing fresh and secondary steam, with the parameters 600 °C/18 MPa and 600 °C/4 MPa, respectively, and a constant GT exhaust gas temperature of 630 °C. A methodology for modeling the operation of a GT within a wide range of compression ratios β (10 ≤ β ≤ 100) has been developed.Power plants that employ various types of open-air cooling (convective, film, or transpiration) in order to cool the air in a steam cycle (SC) were analyzed. These power plants were equipped with closed steam and closed air cooling, sequential combustion (reheat), and the ability to capture CO2from the flue gas.For all analyzed systems, a uniform methodology for determining the efficiency, the stream of coolant used in a GT, combustor outlet temperature (COT), and unitary CO2 emission was developed. These parameters were determined as a function of the pressure ratio, β.It is important to show the limitation of the efficiency increase that results from the COT, β level, the cooling method, and the structure of the CCPP. This paper shows that the power plant equipped with sequential combustion and steam cooling has the greatest potential for an increase in efficiency from ηel.n = 61.5% (β = 30) and ηel.n = 65.8% (β = 60) to ηel.n = 67.9% (β = 100), all at COT ≤ 1550 °C. Assuming COT = 1900 °C, the CCPP equipped with only closed-steam gas turbine cooling will reach the efficiency ηel.n = 65.5% at β = 76, and the system with film cooling will reach an efficiency ηel.n = 63.56% at β = 66. At β = 30, these CCPPs achieve efficiencies ηel.n = 61.7% (COT = 1550 °C) and ηel.n = 61.3% (COT = 1580 °C), respectively.