SITE PERFORMANCE TEST EVALUATION FOR GAS TURBINE AND ELECTRIC MOTOR DRIVEN COMPRESSORS

Centrifugal gas compressors are used in many applications in
the oil and gas industry, such as in pipelines, for gas gathering, gas
reinjection, gas lift, gas storage, in onshore as well as offshore
environments. The predominant driver for these compressors is
two shaft gas turbines, and, to some extent, variable speed electric
motors. Both types of drivers have in common that the speed of the
compressor can be varied easily over a large range. To some extent,
variable speed electric motors are used in similar tasks.
Performance testing of compressor packages is becoming increasingly
frequent because economic pressures demand that the
efficiency, power, fuel flow, capacity, and head of an installation be
verified to assure a project’s return on investment. Test results may
have significant financial implications for the compressor and gas
turbine manufacturers and their customers. They may be the basis
of future decisions on plant modifications or extensions, or may
serve as baseline data for monitoring purposes. Field tests also
provide the operator and the equipment manufacturers with information
complementary to the data collected during factory testing.
Thus, for the end user and the manufacturer, an accurate determination
of the package field performance is critical. This paper
discusses problems and challenges related to the field performance
testing of gas turbine or electric motor driven, variable speed compressor
sets.
Insights from over 100 field performance tests on centrifugal
compressors are described. Such field tests provide the user with
valuable operation and maintenance data and the manufacturer
with information complementary to the data gathered through
factory testing.
This paper also describes in detail how raw test data (i.e.,
measured pressures, temperatures, flows, and speeds) are
converted into meaningful data that can be used for evaluating the
performance of a gas turbine or a gas compressor. Details on
instrumentation will not be provided by this paper, but can be
found elsewhere (Kurz, et al., 1999). The data reduction is
explained based on the basic relationships of pressure, temperature,
flow, and head, as well as the operational characteristics of centrifugal gas compressors, with special consideration of test
uncertainties. Methods of data correction are explained. A few
remarks on general procedures, valid for any type of test, including
the application of test uncertainties are included.
Assume a performance test has just been concluded and columns
of pressures, temperatures, and speeds have been measured. Fuel
and process gas compositions are known. The test was conducted
using a reasonably accurate test protocol (ASME PTC 10, 1997;
Kurz, et al., 1999). The test was conducted to gain information
about the performance of the gas turbine driven centrifugal compressor
set. The question is now (actually, this question should
have been asked prior to the test), what to do with all that data? In
this paper, the authors want to review methods to reduce the raw
test data to information about the performance of the compression
system.

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