Gas turbine heat balance analysis uses plant measured data as input, and solves conservation of mass and energy plus chemical combustion equations to yield additional information about the current state of the gas turbine. The calculated heat balance data is information that can be directly inferred from the measured data, and is as accurate as the measured data that was input to the analysis. There is no assumption about the performance of the gas turbine in the heat balance analysis. The heat balance outputs include the impacts of any degradation that may exit.
Measured Data Needed for Gas Turbine Heat Balance
Ambient temperature, Pressure and Relative Humidity
Power (generator output)
Compressor Discharge Pressure
Compressor Discharge Temperature
Inlet and Outlet Pressure Losses
Fuel Flow and Heating Value (optional)
First Stage Nozzle Area (optional)
Gas Turbine Heat Balance Outputs
Fuel Energy Consumption
Air Inlet Flow
Turbine Inlet Temperature
First Stage Nozzle Area
Exhaust Flow Rate and Composition
MapEx calculates the hot gas path temperatures into and out of each nozzle (stator) and bucket (rotor) in the expander of the gas turbine as measured data changes. The average blade metal temperatures are determined by the hot gas temperature, the cooling air temperature and the cooling effectiveness.
The chart shows gas turbine firing temperature and exhaust temperature as a function of GT load. Firing temperature initially decreases as the GT goes to part-load, but then remains essentially constant while the exhaust temperature increases under guide vane control. When the maximum exhaust temperature is reached, the exhaust temperature remains constant and the firing temperature decreases with load.
Stage 3 rotor metal temperature increases at part-load due to the increase in exhaust temperature. The first stage nozzle temperature decreases as the engine goes to part-load. MapEx allows the operator to track the changes in blade temperatures over time to more accurately estimate the impact of operation of blade life consumption. This information can allow informed decisions about overhaul frequency and operational strategies.
Redundancy in Gas Turbine Measurements
•GT’s typically have more measurements than needed for heat balance
•Can choose to calculate one parameter from measured values of other parameters
–Fuel Heating Value
•GE default is to calculate fuel flow
•If measured fuel flow is accurate, can track nozzle area as degradation parameter
–Use Least-Squares to find the heat balance that matches all measurements as closely as possible
–Gives estimate of measurement accuracy
–Can identify a bad measurement