Chemical Engineering April 2019 - 42

Feature Report
Field Performance
Testing for Centrifugal
Compressors
Determining the field performance of centrifugal compressors can benefit operation and
maintenance of the equipment. Presented here is an overview of the parameters that must be
measured and calculated for effective testing
Nathan Poerner,
Tim Allison and
Hector Delgado
Southwest Research
Institute
IN BRIEF
PERFORMANCE
PRINCIPLES
MEASURED AND
CALCULATED
PARAMETERS
CENTRIFUGAL
COMPRESSOR
OPERATION
FIELD PERFORMANCE
TESTING
CONCLUDING REMARKS
C
ompressors are used in
all areas of production
and in many different
sectors of the chemical
process industries (CPI). Production
facilities can have a number
of compressors of different types
and in a range of sizes. The three
main compressor types are centrifugal,
axial and reciprocating.
This article focuses on centrifugal
compressors (Figure 1) and how
field performance testing can
be carried out in this equipment
class to benefit the end-users,
manufacturers and maintenance personnel.
The benefits of field testing for existing units
include the ability to quantify performance
deterioration as a function of equipment
age, to determine if and when certain maintenance
tasks should be performed, and to
identify specific equipment components for
product improvement. For new units, field
testing helps validate product performance.
Performance principles
Regardless of compressor type, there are
certain terms and parameters that will be
used to define and quantify equipment performance.
Primary among these are energy,
head, work and flow. Energy is a parameter
of the fluid in question, and will most commonly
be defined as the total enthalpy of the
fluid. Enthalpy is a combination of the kinetic
(fluid velocity) and potential (static pressure)
energy of the fluid. Because enthalpy is a derived
term, there is no direct way to measure
the enthalpy of a fluid. Instead, it is common
practice to rely on equations of state
42
FIGURE 1. Performance tests on a multi-stage centrifugal
compressor, like the one shown here, will quantify the factors
of energy, head, work and flow
(EOS) that relate measurable parameters
(most commonly temperature and pressure)
to derived terms, such as enthalpy and entropy,
for a given fluid composition. A variety
of EOS are available, and each will be best
applicable for only a given set of fluid compositions
over a specific range of operating
conditions. Because of this, it is important
that all parties involved in a performance test
understand and accept the chosen EOS.
Head is a measure of the increase of energy
within a fluid, and is typically defined as
the change in enthalpy of the fluid between
the suction and discharge conditions. Work
is the mechanical means of transferring energy
into the fluid.
Flow can be defined in terms of mass or
volume, with volume taking one of two common
forms. The first is the capacity, or actual
flow, which considers the volume flow for
the actual pressure and temperature of the
fluid, usually at inlet conditions. The second
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