GE-7FA Total Efficiency

[sonckerr]

How can I calculate the GE-7FA's HRSG efficiency? Total unit efficiency (compressor+Turbine+HRSG)?

I have calculated the compressor efficiency and the thermal efficiency.

Also, how can I calculate the Steam adjusted heat rate? Or what resources should I use to figure this out?

I appreciate any input.

 

[pmover]

look within the ASME Power Test Codes - check online - and refer to your thermo textbook are a couple of references. Check in the GE website as I know they have several online documents available that may be of use for you.

good luck!
-pmover

 

[davefitz]

The 7 Fa is just the combustion gas turbine ( compressor + gas turbine , the HRSG and steam turbine are added by the site integrator / EPC contractor to result in a combined cycle plant.

The efficiencies are normally presented as an ISO efficiency ( 60 F at 1 atm )as % of LHV efficiency in marketing brochures and modified for site climate conditions.

On the simplest level, you can calculate the gas turbine efficiency from knowing the fuel flowrate ( from a calibrated flow element) and the net electrical output at the step-up transformer. Efficiency = {net elect output ( MWe)} / {fuel gas thermal input , MWth, LHV } * 100.

Official testing for cycle efficiency for purposes of meeting contract requirements is more complicated and requires use of an agreed test code ( ASME PTC ) , agreed test instrument accuracies, and an agreed method of accounting for inaccuracies. It becomes complicated partly due to differences in treating inaccuracies and also due to the dependence of the gas turbine efficiency due to site climate and elevation, and the need to clsoe the contract out expeditiously.

 

[ccfowler]

sonckerr,

What is (are) your purpose(s) for these efficiency estimates? Your original posting suggests an expectation of some relatively constant value for efficiency. If so, you will likely be greatly disappointed by reality.

There is nothing constant about the efficiencies of any combustion turbine system. In fact their efficiency is highly dependent upon loading. Rather than having a tendency toward somewhat constant efficiency over some significant loading range such as with naturally aspirated diesel engines, combustion turbines tend toward operating with relatively constant fuel consumption over fairly large loading range. In general, a simple cycle combustion turbine can be expected to consume fuel at approximately 80% to 90% of its full load rate (gpm or cuft/min) while operating at synchronous idle (NO LOAD).

Obviously, the "efficiency" of any engine with such a characteristic is very highly load dependent. Beyond this, the service life of critical components is highly dependent upon operating temperatures (very highly load dependent), and usually the advertised, most wonderful efficiency is produced at loadings that may significantly compromise the service life of the combustion turbine.

Highest possible efficiencies will be achieved at a loadings that will allow only a relatively few hours of operation before major maintenance and repair work will be necessary. Similarly, operation at suitably reduced loadings may permit operation for thousands or even tens of thousands of hours before any significant maintenance and repairs would become necessary.

Valuable advice from a professor many years ago: First, design for graceful failure. Everything we build will eventually fail, so we must strive to avoid injuries or secondary damage when that failure occurs. Only then can practicality and economics be properly considered.