Gas Turbine Handbook : Principles and Practices

Gas Turbine Inlet Treatment 129
ingested directly into the gas turbine compressor. This could result
in severe damage to the compressor and possibly the entire gas
turbine.
Another concern is foreign object damage (FOD) caused by a
loose or broken nozzle head. Some fog system manufacturers recognize
this potential and have provided a “tie” (made of plastic or
stainless steel wire) to retain the nozzle if it should separate from
the supply line. Each time the nozzle is removed and replaced this
“tie” must be cut off and a new one installed. Considering that the
inlet of the large gas turbines could have several hundred of these
nozzles and “ties,” the possibility of just one piece being left loose
in the inlet increases exponentially. A loose nozzle head would do
an enormous amount of damage to the gas turbine compressor
components and possibly also the turbine components. Other system
manufacturers have placed the wet compression nozzles far
enough up stream of the compressor inlet such that if a nozzle
should break loose it would fall to the bottom of the duct and
come to rest before getting close to the compressor inlet.
An ideal application would install an inlet fogger evaporation
system upstream of the inlet air filters and a wet compression
system upstream of the compressor inlet (either upstream or down
stream of the acoustic silencers, but downstream of the filters).
The fogger evaporation system would reduce the inlet temperature
and the wet compression would provide compressor intercooling.
An example is a study sponsored by the Electric Power Research
Institute (EPRI) and reported in 1995. 2 In this study a General
Electric MS7001 was used and a fogger evaporative cooling system
injected 23 gpm upstream of the inlet air filters. This alone
boosted power 10% (from 61 MW to 67.1 MW).
A wet compression system installed downstream of the acoustic
silencers injected 23 gpm of water directly into the compressor
inlet. The wet compression system increased power an additional
3.8% to 69.4 MW. Placing the fogger evaporative cooling nozzles
upstream of the inlet air filters eliminated the need for highly
treated water as the filters would “catch” any contaminants in the
water-air stream. This left only the wet compression water to be
highly treated.
A guide for estimating the affects of water fogging is provided
in detail in Appendix C-11.