42
December
2014
HYDROCARBON
ENGINEERING
one of the biggest challenges for plant management is
maximising the productivity of these assets,
implementing the best strategies to achieve
maximisation of machine availability and reducing
downtimes. In this context, it is evident that the
capability to detect early indicators of eventual
malfunctioning is extremely useful in minimising overall
operational costs due to the above mentioned causes.
One of the main problems for the analysis of
centrifugal compressors’ operational performance is
that this performance is usually graphically represented
in terms of discharge pressures, temperatures,
polytropic heads, efficiencies and absorbed power,
related to the design inlet conditions, e.g. gas mix
composition, inlet pressure and temperature. However,
actual performance is related to actual field inlet gas
conditions that often deviate from design conditions. In
this situation the comparison of field measurements to
expected values becomes complicated because the
expected performances need to be adjusted to the
actual field conditions.
The main purpose of this article is to present a
method and tools for the evaluation and comparison of
centrifugal compressor field performances. A case study
will be presented, in which this method has been
applied.
The execution of the method that is to be
elaborated is complex, and requires the availability of
calculation algorithms able to predict both machine
behaviour and thermodynamic gas properties under
different operating conditions. In contrast, current
practice relies on simplified theories. These simplified
theories are often completely neglected at plant/
machine level, causing a lack of analytical support for
evaluation of machine health and consequently a lack
of support for maintenance decision making.
Furthermore, these theories become progressively
more approximate when approaching the high pressure
range. Introduced errors inhibit the ability to make
accurate predictions about more severe applications. In
these cases more rigorous calculations and adequate
computational tools are in fact necessary to implement
the most modern thermodynamic theories and machine
models without limiting approximations.
In order to execute this advanced machine
performance analysis, the IPC research lab has
developed a dedicated software tool based on the
most recent gas theories and centrifugal machine
models.
Cmap is a Windows based software tool for PC,
designed to perform simple and easy centrifugal
compressor performance evaluations. The software also
allows some additional tasks useful to compare
centrifugal compressor expected/design performances
with field data measured ones.
Method
In order to compare performances obtained under
different inlet conditions it is necessary to adjust and
align performances to the same reference inlet
conditions.
When attempting to evaluate performance by
comparison between field measured parameters and
expected parameters, the trick is to remember that one
of the two performances needs to be manipulated and
adjusted to the inlet conditions of the second one. In
brief, inlet conditions need to be homogenous (Figure 1).
3
Paper for Oil&Field
2
Final review
1
Preliminary review
Tech. report.20/11
0
Prediction of centrifugal
compressor performances
Paganini Di Febo 13/05/2014
E
5/5
rev
description
prepared checked approved date
language sheets
As starting point we can consider that, for a centrifugal compressor, performances are
strictly linked to the inlet gas conditions. This consideration is valid both to the design
performances as for the field/actual performances.
It is the important to note also that performances referenced to different inlet conditions
cannot be in general compared. In order to compare performances obtained under
different inlet conditions it is necessary to adjust and align performances to the same
reference inlet conditions.
figure 1
When attempting to evaluating performances by comparison between field measured
parameters and expected parameters, the special trick is then remember that one of the
two performances need to be manipulated and adjusted to the inlet conditions of the
second one. In brief inlet conditions need to be homogeneous. (see below sketch for
concept flow)
Figure 1.
: Compressor performances can be
compared when obtained with the same inlet
conditions.
Project : Pro 250 - CMap
PREDICTION OF CENTRIFUGAL
COMPRESSORS PERFORMANCES
AND APPLICATIONS FOR TEST,
SURGE PROTECTION AND
MACHINERY DIAGNOSTIC
TR 20/11 Paper Cmap rev 3
3
Paper for Oil&Field
2
Final review
1
Preliminary review
Tech. report.20/11
0
Prediction of centrifugal
compressor performances
Paganini Di Febo 13/05/2014
E
7/7
rev
description
prepared checked approved date
language sheets
figure 3
3 SOFTWARE
This paragraph describes how to apply the software tool. In order to use Cmap, the
starting point is the availability of a centrifugal compressor performance curve, the relevant
gas mix composition and thermodynamic conditions (pressure and temperature). Having
this inputs data available, the software will perform all complex calculation in fully
automated way and will produce the expected compressor performances for inlet
pressures, inlet temperatures and gas mix compositions different for design / reference
ones. The software is easy and intuitive, and will provide also automatic storage of data in
a project archives for quick consultation and historic trends. Cmap is structured to allow to
analysts and engineers to build their own machinery database and to maintain records of
all executed calculations. Let us consider the case of availability of centrifugal compressor
performances (pressures and temperatures):
The input process offers many alternative ways to set up compressor reference data. The
most common way is to enter performances curves expressed in terms of delivery
pressure vs inlet flow rate, and delivery temperature vs inlet flow rate. As alternative, when
available, it is possible to input directly non dimensional data.
Data input process can be also executed in digital way picking data graphically directly on
pdf or jpeg files. In order to complete the data input process it will be necessary to input
the considered gas mix composition and the considered pressure and temperature.
Figure 2.
Design performances, adjusted o actu l
(field/test) performances can be used as reference
for me sured performance evalu ti n.
Project : Pro 250 - CMap
PREDICTION OF CENTRIFUGAL
COMPRESSORS PERFORMANCES
AND APPLICATIONS FOR TEST,
SURGE PROTECTION AND
MACHINERY DIAGNOSTIC
TR 20/11 Paper Cmap rev 3
3
Paper for Oil&Field
2
Final review
1
Preliminary review
Tech. report.20/11
0
Prediction of centrifugal
compressor performances
Paganini Di Febo 13/05/2014
E
9/9
rev
description
prepared checked approved date
language sheets
figure 4
figure 5
Figure 3.
Centrifugal compressor design
performances comparison to calculated
performances (discharge pressure).
