Gas turbine power augmentation systems such as inlet fogging, evaporative cooling and wet compression have been applied to many units over the past several years. The ability to generate additional power output during periods of high demand or to maintain rated power output levels when ambient temperatures are high can translate into significant economic benefits.
These benefits, however, can be lessened if the treatment systems result in damage to turbine blades or combustion system hardware. Many operators express concerns about if, and to what extent, the presence of water droplets will lead to excessive erosion, wear, and premature failure. The results of a recent gas turbine inspection at Cardinal Cogeneration in Stanford, California indicate that power augmentation systems can be operated effectively with little appreciable damage.
During a one-week outage in March 2002 at the Cardinal plant, a GE Frame 6B combustion turbine was retrofitted with Caldwell Energy and Environmental’s (CE&E) PowerFog and Caldwell Wet Compression Technology (CWCT). The retrofit included a redesign of the inlet air filtration systems that included the removal and replacement of inertial separators and media based evaporation systems with new pleated inlet air filter elements and fogging system. The resulting inlet system modifications reduced inlet pressure losses by more than two inches of water, resulting in a permanent improvement in power plant performance and efficiency.
One year later – in March of 2003 – an inspection was performed in conjunction with a planned combustion system maintenance outage. Each of the augmentation systems had operated for more than 1,100 hours since installation and the combustion turbine had accumulated more than 124,500 total hours of operation since commissioning. A borescope examination revealed that the compressor exhibited similar wear patterns as experienced with other combustion turbines that have been equipped with wet compression. Specifically, the observed erosion was primarily on the leading edge of the row 1 compressor blade, and the vane segments and downstream stages were not as affected as row 1 by the system operation.
The turbine inspection showed that the compressor and combustion system were in good condition and that fogging and wet compression system operation could resume. The systems and engine were returned to service with the recommendation to continue use of the fogging and wet compression systems for power augmentation.