Analysis of the GT26 single-shaft gas turbine performance and emissions

The progressive developments in terms of gas turbine materials as well as blade cooling systems have led to a continuous growth in the turbine inlet temperature (TIT) and the overall pressure ratio (OPR). This means higher thermal efficiency and power output. Other techniques to achieve better performance can be the adoption of a heat recovery system, an intercooler system or the reheat, as well as a combined cycle application. Furthermore, the higher the TIT and OPR the higher the NOx emissions. Nowadays, with an always stricter emissions legislation, it is particularly important to keep emission levels as low as possible. In the present work, a performance analysis has been conducted with the in-house modular tool ESMS (Equation Solver Modular System). The software simply represents the engine with separate blocks, solving the energy and the continuity equations. Firstly, the design process has been performed on the Ansaldo Energia GT26 machine, equipped with reheat, based on the manufacturer datasheet. Secondly, off-design simulations have been done, changing respectively the fuel mass flow in the 1st burner (EV) and in the 2nd burner (SEV). Therefore, both TIT and power output change. A sensitivity analysis of the thermal efficiency η and the power output with respect to both fuel flows shows how, for part load operations with a half of the design power output, it is better to change the SEV fuel flow only. It can also demonstrate that the high-pressure turbine (HPT) power output is more insensitive to SEV fuel flow than the low-pressure turbine (LPT) one. EV fuel flow variations affect both the HPT and the LPT behaviour. Eventually, a correlation for the NOx emissions has been characterized and results illustrate that NOx emissions are strictly related to the EV fuel flow: in fact, the O2 level in the SEV burner is sensibly lower than in the first one, thus contributing to lower emissions.