PERFORMANCE AND EMISSION LEVELS IN GAS-TURBINE PLANTS

The rise in gas turbine combustion chamber temperatures requires optim al choices to be made with regard not only to performance parameters b ut also with a view to resolving pollutant emission problems. For this reason, the authors have set up a gas turbine cycle model, which perf orms an accurate analysis of several processes, in terms of operating fluid chemical and thermodynamic properties. The model also enables pr ediction of NOx formation based upon chemical kinetics and is able to relate the amount of pollutants to a number of operating parameters (e .g., cycle pressure ratio, fuel-to-air equivalence ratio, residence ti me in combustion chamber, etc.). It can also predict the effect of mos t usual NOx reduction systems, such as water or steam injection. A com parison of several possible choices for the gas and combined cycles is then presented, in terms of thermodynamic performance (e.g., first an d second law analysis) and nitric and carbon dioxide emissions. In ord er to find the best compromise between performance improvement and lim itation of pollutant emission, enhanced gas cycles are also considered , such as STIG or intercooled-reheat cycles. Examples also refer to me dium or low Btu gases, obtained from coal gasification, in order to sh ow not only the possible advantages in terms of thermal NOx reduction, but also the significant amounts of ''fuel NOx'' that can arise from ammonia contained in the fuel.