Giovanni Cataldi

Influence of High Fogging Systems on Gas Turbine Engine Operation and Performance

High fogging is a power augmentation device where water is sprayed upstream of the compressor inlet with higher mass flow than that which would be needed to saturate the intake air. The main focus of this paper is on applications of high fogging on the ALSTOM gas turbine engines of the family GT24/GT26. Engine operation and performance are illustrated based on test results obtained from four different engines that have meanwhile accumulated more than 12,000 operating hours (OH) in commercial operation with ALSTOMs ALFog® high fogging system. The effect of internal cooling (water evaporation inside the compressor) is investigated considering actual compressor boundaries matched within the complete engine. Changes in the secondary air system (SAS) and corresponding movement of the engine operating line have been taken into account. Power output gain as high as 7.1% was experimentally demonstrated for injected water mass fraction (f=m H2O /m air ) equal to 1% and considering internal cooling effects only. Higher figures can be obtained for operation at low ambient relative humidity and partial evaporation upstream of the compressor inlet.

A Model for the Simulation of Large-Size Single-Shaft Gas Turbine Start-Up Based on Operating Data Fitting

Start-up is an important aspect of gas turbine operation. In the last years plant operators have shown an ever increasing interest in this critical phase, with particular focus on start-up reliability and start-up time. Several issues should be considered in order to achieve optimal start-up behavior: operability issues (e.g. compressor aerodynamics, combustor light-off and light-around, shaft acceleration), impact of thermal stresses on cyclic life, proper sizing of external starting devices. Models for the simulation of gas turbine behavior during start-up are very useful both for the design of new gas turbines and for the analysis and improvement of engines already in operation. In this paper, a physics-based model for the simulation of the start-up phase of large-size single-shaft gas turbines is presented. The model is based on operating data fitting and covers machine operation from combustor light-off to compressor blow off valve closure. The model makes use of steady-state component characteristics, while dynamics is taken into account through shaft power balance. Special features are also included to properly model the effects of heat soakage, i.e. the dependence of the engine behavior on its thermal status before the start-up. The quality of the model has been proven by application to the gas turbine engine ALSTOM GT13E2 and by comparison between measured and simulated data.Copyright

Prediction of Evaporative Effects Within the Blading of an Industrial Axial Compressor

The results of a compressor flow-analysis code calibration study for estimating the effects of water evaporation within the blade rows of industrial axial compressors are presented. In this study, a mean-line code was chosen for the calibration tool due to its accepted use during preliminary design studies, at which time during the compressor design process one would logically consider power augmentation through wet compression. The calibrated code features a nonequilibrium thermodynamic single-droplet evaporation model augmented with an empirical splashing model, which, as input, uses measurements of droplet spectra data taken on water injection nozzles in an intake rig configured with realistic length scales. In addition, a wetted-airfoil-surface flow-angle deviation model is applied to predict changes in compressor stage characteristics, which, in turn, affect the inlet mass flow of the compressor. The test vehicle for calibration was a 50 Hz Alstom industrial gas turbine. Once calibrated, the code was successfully utilized to predict wet-compression effects for three additional like-family Alstom gas turbines operating at constant speed while under full load. The effects modeled by the code include bleed supply pressure suck-down and bleed temperature cool-down effects, as well as compressor inlet mass flow and power consumption effects.