Advanced Monitoring to Improve Combustion Turbine/Combined ...

The effects of humidity are a second order effect and as such have less of an impact on the data.
However, in an effort to remove all possible variations due to the effects of atmospheric
conditions, accounting for humidity is required. The presence of water vapor in dry air changes
the values of the gas properties, namely, CP (constant pressure specific heat), CV (constant
volume specific heat), R (gas constant), and γ (the ratio of CP/CV ), primarily due to the
molecular weight of water being far lower than that of dry air. Changing the gas properties can
have a significant effect on thermodynamic processes throughout the CT. The correction
algorithm utilizes generic exchange rates that are applied to the gas properties or specific gas
path parameters, which may be utilized for first-order accuracy, to predict the effects of humidity
on key performance parameters. 1
The ambient humidity correction method used to adjust the gas properties and select gas path
parameters to their corresponding values at ‘standard day’ relative humidity conditions employs
the generic exchange rates given in Figure 2-7 and 2-8, respectively. The humidity correction
process utilized first converts the desired value to its corresponding zero-moisture, ‘dry-air’
value if necessary by dividing the value by the exchange rate given for the current specific
humidity. A subsequent step is taken to further modify the property or parameter value to its
‘standard day’ value by multiplying the value by the exchange rate resultant of a specific
humidity value of 0.0064, corresponding to a relative humidity of 60 %.
Figure 2-7
Exchange Rates for Ambient
Humidity Correction of Gas
Properties 1
Figure 2-8
Exchange Rates for Ambient
Humidity Correction of Select Gas
Path Parameters 1
2-9