Exhaust gas recirculation on twin shaft gas turbines - A study to improve part load performance

Abstract: By recirculating exhaust gases to the gas turbine inlet a temperature rise and hence, a density reduction, is achieved at the compressor inlet. For a constant volume flow this results in a reduced mass flow, ultimately affecting the temperature of the flame, and the emissions, at part load. This study is conducted by creating a model of the Siemens twin shaft gas turbine SGT-750 in the software IPSEpro. The model is based on characteristics which are read from a text file. With the model, different cases of exhaust gas recirculation, EGR, are examined and the calculations are carried out for a simple as well as a combined cycle. Both cycles are examined with standard and tropical ambient conditions and matching. Depending on the case studied the results yield a 3 – 5 percentage point increase in total cycle efficiency at 50% load compared to the method of bleed used today. Furthermore, the gas turbine performance is better at normal conditions comparatively and the limitations of temperature and rotational speed is reached at higher loads for the tropical match. Although negative effects such as influence on lifing and practical issues of implementation are present, EGR is recommended based on the positive results and the general improvement of the gas turbine performance with the method.