This paper describes the fundamental performance of gas turbines and centrifugal compressors (known as "turbomachinery"), and how to model them for pipeline simulations. Previous P.S.I.G. papers have described very well how to model gas turbine driven centrifugal compressors, using somewhat laborious curve-fitting techniques and/or table lookups. However, since the advent of Excel, the process of curve-fitting has become much simpler. Presented in this paper is a straightforward, simple and accurate method of modeling turbomachinery performance, which is Not specific to any manufacturer's performance curve format Is easily input into your pipeline simulation model Includes factors for contamination and degradation to more realistically predict the performance And, this paper also presents a template model of a gas turbine driven centrifugal compressor, which will accept curve-fit coefficients of your turbomachinery to simulate it in your pipeline simulation software. This paper explains how to use gas turbine and centrifugal compressor performance curves for your specific unit(s) in a pipeline simulation model, to predict their performance under various pipeline conditions. The two questions that will be answered are:

  1. What is the flow and pressure ratio capability?

  2. What is the fuel consumption?

The methodology in this paper has been successfully used by Gordon Muster of El Paso Corporation to model several two-shaft gas turbine engines.


What a gas turbine driven compressor model should tell us:

There are three basic questions to ask of a turbomachinery model (at specified suction pressure and throughput):

  1. Will the compressor operate satisfactorily (is the desired operating condition on the curve)?

    • Is it over maximum continuous speed?

    • Is it on surge control recycle?

  2. Does the gas turbine driver have enough power available at the prevailing environmental conditions?

  3. What discharge pressure and/or throughput can be achieved at full power?

Once the above basic questions have been answered, and all the restraints of surge control, maximum speed, and power available have been satisfied, other information can be determined:

  • Compressor speed

  • Compressor efficiency, can the operating point be moved to a higher efficiency?

  • Surge margin

  • Discharge temperature

  • Gas turbine fuel consumption


Just how accurate is the modeling process?

There are several reasons why we must expect that the predictions of any turbomachinery model cannot be exact:

  1. The vendors' performance curves for both the gas turbine and the centrifugal compressor are predictions of the expected performance of an average unit, in new and clean condition, in the factory test. Generally, the actual performance of new-and-clean turbomachinery can be expected to deviate from their curves by as much as 4%.

  2. The actual performance of turbomachinery will deteriorate with time, so it will deviate even more from the prediction curves with accumulating operating hours.

  3. The process of measuring actual performance on site as less than exact, so some deviation due to testing and measurement uncertainty is to be expected.

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