TECHNICAL FIELD
Embodiments of the subject matter disclosed herein generally relate to methods
and devices and, more particularly, to mechanisms and techniques for testing a
stage of a multiple stage centrifugal compressor, and specifically testing the
portion of the performance curve associated with very low to zero resistance or
9 even a negative suction head.
BACKGROUND
Centrifugal compressors are utilized extensively in many industries today across a
wide variety of applications. An important requirement in the manufacture, sale
and delivery of centrifugal compressors is providing a performance curve for the
centrifugal compressor that is based on empirical data with as little extrapolation
as possible of the performance curve. Using current methods and systems for
generating a performance curve for a centrifugal compressor, a prior art test
system 100 is configured as shown in prior art figure 1. A centrifugal compressor
102 is connected to a gear box 104 and an electric motor 106. The gear box 104
and electric motor 106 are sized based on the requirements of the centrifugal
^ compressor 102. Continuing with the prior art test system 100 example, the outlet
108 of the centrifugal compressor is piped through a control valve 110 and then a
process fluid cooler 112 before returning to the centrifugal compressor inlet 114. It
should be noted in the prior art example that sensors for recording operating
parameters such as, but not limited to process fluid temperature and pressure are
placed proximate to the centrifugal compressor outlet 108 and inlet 114.
The centrifugal compressor 102 is then operated with the control valve 110 at
different positions such as, but not limited to ten percent to one hundred percent
open in increments of ten percent while data is collected from the sensors
associated with the prior art test system 100. The collected data is then used to
generate a performance curve for the centrifugal compressor as illustrated in prior
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art figure 2. Prior art figure 2 depicts a graph of Head versus Flow and shows the
performance curve 202 based on the data collected from the test procedure with
the control valve 110 in different positions of almost closed 204, partially open 206
and fully open 208. It should be noted in the prior art test system 100 that the
resistance experience by the compressor is at a maximum, based on this test,
when the control vale f 10 is in the almost closed 204 position and at the minimum
obtainable by this prior art test system when the control valve 110 is in the fully
open 208 position.
The unknown section 210 of the performance curve is only determinate based on
extrapolation with the prior art test system 100 and does not have a unique
^P method of extrapolation. It should be noted in the prior art system 100 that
although the control valve is fully open 208, there are still losses associated with
the design of the system based on the presence of the components, and their
associated losses, of the prior art test system 100. The combination of uncertainty
in the extrapolation methods and the errors associated with extrapolation at a
boundary condition have led to market pressure to provide empirically produced
specifications in the unknown section 210 of the performance and even beyond to
a negative head location on the centrifugal compressor performance curve.
Accordingly, it would be desirable to provide designs and methods that avoid the
afore-described problems and drawbacks.
SUMMARY
1 According to one exemplary embodiment, there is a system for testing a
compressor comprising one or more compressors connected together in series to
a test compressor. The exemplary embodiment continues with an output of the
test compressor connected to an input of the first compressor in the series,
forming an overall loop. Next in the exemplary embodiment, the overall loop
contains one or more process fluid coolers, one or more orifices and a control
valve in the overall loop. Continuing with the exemplary embodiment, a first
plurality of sensors is configured adjacent to the process fluid input of the test
compressor and a second plurality of sensors are configured adjacent to the
process fluid output of the test compressor.
According to another exemplary embodiment, there is a system for sizing an
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electric motor associated with a test compressor, for optimally meeting the test
compressor startup requirements. The exemplary embodiment comprises an
auxiliary compressor connected to the test compressor wherein the process fluid
output of the auxiliary compressor is connected to the process fluid input of the
test compressor and a process fluid output of the test compressor is connected to
a process fluid input of the auxiliary compressor, forming a test loop. Next in the
exemplary embodiment, one or more process fluid coolers and one or more
orifices are configured in the test loop. Continuing with the exemplary
embodiment, a control valve is configured in the test loop. Further in the
exemplary embodiment, a first plurality of sensors is configured adjacent to the
9 process fluid input of the test compressor and a second plurality of sensors is
configured adjacent to the process fluid output of the test compressor.
According to another exemplary embodiment, there is a method for obtaining nonextrapolated
empirical data associated with the performance characteristics of a
compressor at head values lower than head value losses associated with a test
loop connected to the compressor. Continuing with the exemplary embodiment,
the method connects an auxiliary compressor to a main compressor in a test loop
such that a process fluid output from the auxiliary compressor is connected to a
process fluid input of the main compressor and a process fluid output from the
main compressor is connected to a process fluid input of the auxiliary compressor.
Next in the exemplary embodiment, the method installs a control valve in the test
9 loop between the auxiliary compressor and the main compressor. Continuing with
the exemplary embodiment, the method installs one or more process fluid coolers
and one or more orifices in the test loop between the auxiliary compressor and the
main compressor. Next in the exemplary embodiment, the method installs a first
plurality of sensors in the test loop adjacent to the process fluid input of the main
compressor. Continuing with the exemplary embodiment, the method installs a
second plurality of sensors in the test loop adjacent to the process fluid output of
the main compressor. Further in the exemplary embodiment, the method collects
data from the first plurality of sensors and the second plurality of sensors while
operating the test loop at conditions such that the main compressor head is lower
than head value losses associated with the test loop.
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BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are incorporated in and constitute a part of the
specification, illustrate one or more embodiments and, together with the
description, explain these embodiments. In the drawings:
Figure 1 is a prior art exemplary embodiment depicting a centrifugal compressor
connected to a gear box and drive motor and configured with the outlet connected
to the inlet through a control valve and a process fluid cooler;
Figure 2 is a prior art exemplary embodiment graph of a performance curve of a
centrifugal compressor plotted on head versus flow axis through various
resistance loads based on the position of the control valve;
W Figure 3 is an exemplary embodiment depicting an auxiliary compressor loop and
a test compressor loop connected in series and configured to allowing
performance testing of the test compressor to a zero head and further to a
negative head condition;
Figure 4 is an exemplary embodiment depicting the flow path of the process fluid
in an overall test loop of an auxiliary compressor and a test compressor connected
in series and configured to allowing performance testing of the test compressor to
a zero head and further to a negative head condition
Figure 5 is an exemplary embodiment graph of a performance curve of a
centrifugal compressor plotted on head versus flow axis through various
resistance loads based on the position of the control valve through a negative
W head resistance condition based on an auxiliary and test centrifugal compressors
connected in series; and
Figure 6 is an exemplary method embodiment flowchart depicting a method for
obtaining non-extrapolated empirical data associated with performance
characteristics of a compressor at head values lower than the head value losses
associated with a test loop connected to the compressor.
DETAILED DESCRIPTION
The following description of the exemplary embodiments refers to the accompanying
drawings. The same reference numbers in different drawings identify the same or
similar elements. The following detailed description does not limit the invention.
Instead, the scope of the invention is defined by the appended claims. The following
5
embodiments are discussed, for simplicity, with regard to the terminology and
structure of turbo-machinery including but not limited to compressors and expanders.
Reference throughout the specification to "one embodiment" or "an embodiment"
means that a particular feature, structure, or characteristic described in connection
with an embodiment is included in at least one embodiment of the subject matter
disclosed. Thus, the appearance of the phrases "in one embodiment" or "in an
embodiment" in various places throughout the specification is not necessarily
referring to the same embodiment. Further, the particular features, structures or
characteristics may be combined in any suitable manner in one or more
embodiments.
W Turning now to Figure 3, an exemplary embodiment depicts a multi-centrifugal
compressor test system 300 comprising three independent test loops based on a
preconfigured multi-centrifugal compressor test system 300 configuration. The
first test loop in the multi-centrifugal compressor test system is the main test loop
and comprises main centrifugal compressor 302 connected to a gear box 304 and
a motor 306. Continuing with the exemplary embodiment, the process fluid output
from main centrifugal compressor 302 is connected to the process fluid input of
main centrifugal compressor 302 first through a control valve 308, then through a
process fluid cooler 310 and then through an orifice 330. It should be noted in the
exemplary embodiment that a bypass valve 312 is required for directing process
fluid flow based on whether the system is operating as a main test loop or an
W overall test loop.
Continuing with the exemplary embodiment, the second test loop in the multicentrifugal
compressor test system 300 is the auxiliary test loop and comprises
auxiliary centrifugal compressor 314 connected to an auxiliary gear box 316 and
an auxiliary motor 318. Next in the exemplary embodiment, the process fluid
output from auxiliary compressor 314 is connected to the process fluid input of
auxiliary centrifugal compressor 314 first through an auxiliary valve 326, then
through an process fluid auxiliary cooler 324, then through an auxiliary control
valve 320 and then through an auxiliary orifice 328. It should be noted in the
exemplary embodiment that a bypass valve 332 is required for directing process
fluid flow based on whether the system is operating as a main test loop or an
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overall test loop.
Next in the exemplary embodiment, the third test loop in the multi-centrifugal
compressor system 300 is the overall test loop and comprises connecting the main
centrifugal compressor 302 and the auxiliary centrifugal compressor 314 in series.
It should be noted in the exemplary embodiment that the output of the auxiliary
centrifugal compressor 314 feeds the input of the main centrifugal compressor 302
and the output of the main centrifugal compressor 302 feeds the input of the
auxiliary centrifugal compressor 314. Continuing with the exemplary embodiment,
a connection is made from a branching connection in the auxiliary test loop,
between the auxiliary centrifugal compressor 314 and the auxiliary valve 326, to a
W branching connection in the main test loop, between the control valve 308 and the
process fluid cooler 310. Next in the exemplary embodiment, a connection is
made from a branching connection in the main test loop, between the main
centrifugal compressor 302 and the main control valve 308, to a branching
connection in the auxiliary test loop, between the auxiliary valve 326 and the
auxiliary cooler 324. It should be noted in the exemplary embodiment that other
piping arrangements are possible and that the branching locations can be placed
in different positions with respect to other system components.
Continuing with the exemplary embodiment, it should be noted that the multicentrifugal
compressor test system 300 can be operated as a test system for the
auxiliary centrifugal compressor 314, a test system for the main centrifugal
W compressor 302 and a test system for the main centrifugal compressor 302
wherein the auxiliary centrifugal compressor 314 and the main centrifugal
compressor 302 are operated in series allowing testing of the main centrifugal
compressor 302 with a zero or even a negative resistance. Next in the exemplary
embodiment, the auxiliary centrifugal compressor 314 test loop can be operated
by closing auxiliary bypass valve 322, closing main bypass valve 312 and opening
auxiliary valve 326. In the exemplary embodiment, process fluid flow is controlled
by auxiliary control valve 320 and cooled by auxiliary cooler 324. Further in the
exemplary embodiment, the main centrifugal compressor test loop can be
operated by closing auxiliary bypass valve 322 and closing main bypass valve
312. In the exemplary embodiment, process fluid flow is controlled by main control
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valve 308 and cooled by main cooler 310. Continuing with the exemplary
embodiment, the overall test loop, i.e., operating the auxiliary centrifugal
compressor and the main centrifugal compressor in series, can be operated by
closing auxiliary valve 326 and main control valve 308 and opening auxiliary
bypass valve 322 and main bypass valve 312. In the exemplary embodiment, the
process fluid flow is controlled by auxiliary control valve 320 and cooled by
auxiliary cooler 324. It should be noted in the exemplary embodiment that the
auxiliary centrifugal compressor is a larger capacity compressor than the main
centrifugal compressor. It should be noted in the exemplary embodiment that
when operating in the overall test loop, the auxiliary centrifugal compressor 314
W overcomes the losses of the overall test loop and allows the main centrifugal
compressor 302 to operate at vanishing or even negative heads allowing the
performance for the main centrifugal compressor to be measured directly at these
operating conditions. It should further be noted in the exemplary embodiment that
auxiliary orifice 328 and/or main orifice 330 are included in flow path of the overall
test loop.
Looking now to figure 4, an exemplary embodiment of a process fluid flow path for
an overall test loop 400 is depicted. Continuing with the exemplary embodiment, a
test compressor 402 is connected in series to an auxiliary compressor 412. Next
in the exemplary embodiment, the process fluid output from the main compressor
flows through an auxiliary cooler 420 then through a control valve 418 before
W entering as input process fluid to auxiliary compressor 412. Continuing with the
exemplary embodiment, the process fluid output from auxiliary compressor 412
flows through a process fluid cooler 408 and an orifice 410 before entering as
input to test compressor 402. It should be noted in the exemplary embodiment
that auxiliary compressor 412 is connected to an auxiliary gear box 414 and
auxiliary motor 416 and test compressor 402 is connected to a gear box 404 and a
motor 406. It should further be noted in the exemplary embodiment that auxiliary
compressor 412 and test compressor 402 can be centrifugal compressors. It
should also be noted that an additional orifice can be configured in the overall test
loop between the auxiliary cooler 420 and the auxiliary compressor 412.
Looking now to figure 5, a graph 500 depicts Head versus Flow for a main
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centrifugal compressor and shows the performance curve 502 based on the data
collected from an overall test loop procedure with the auxiliary control valve 418 in
the fully open position 504 and the auxiliary centrifugal compressor 412 delivering
compressed process fluid flow 506 to the main centrifugal compressor 402 inlet
and reducing the resistance to the main centrifugal compressor 402 allowing the
collection of empirical data related to the performance characteristics of the main
centrifugal compressor 402 zero resistance or even negative head operating
conditions. It should be noted in the exemplary embodiment that operation of the
multi-centrifugal compressor test system 300, 400 and the data collected and
graphed as represented by graph 500 can be used to size an electric motor for a
9 centrifugal compressor such that it is the appropriate size based on centrifugal
compressor startup requirements, i.e., a smaller motor can be specified based on
non-extrapolated empirical data from a zero head, or even a negative head,
condition.
Looking now to figure 6, a flowchart 600 of an exemplary method embodiment for
obtaining non-extrapolated empirical data associated with the performance
characteristics of a compressor at head values lower than the head value losses
associated with a test loop connected to the compressor is depicted. First at step
602 of the exemplary embodiment, an auxiliary compressor is connected to a main
compressor, the test compressor, in a test loop. It should be noted in the
exemplary method embodiment that the process fluid output of the auxiliary
W compressor is connected to the process fluid input of the main compressor and the
process fluid output of the main compressor is connected to the process fluid input
of the auxiliary compressor. It should also be noted in the exemplary method
embodiment that the auxiliary compressor has a greater output capacity than the
main compressor under test.
Next at step 604 of the exemplary method embodiment, a control valve is installed
in the test loop between the auxiliary compressor and the main compressor.
Continuing with the exemplary embodiment, the control valve allows the test loop
resistance to be changed for different runs of the test loop providing the capability
to collect data and develop a test compressor performance curve. It should be
noted in the exemplary embodiment that when the control valve is fully open, the
9
test compressor can be operated, allowing the collection of performance data, at
test compressor heads approaching zero or even under a negative condition.
Next at step 606 of the exemplary method embodiment, a process fluid cooler is
installed in the test loop between the auxiliary compressor and the main
compressor. It should be noted in the exemplary embodiment that the location of
the process fluid cooler can have an optimal installation location, such as in the
test loop portion flowing from the main compressor to the auxiliary compressor,
based on the configuration of the test being performed and the auxiliary
compressor and main compressor installed in the test loop.
Continuing with step 608 of the exemplary method embodiment, sensors are
W installed in the control loop adjacent to the process fluid input connection on the
main compressor. It should be noted in the exemplary method embodiment, that
the sensors can, but are not limited to, measuring temperature, pressure,
volumetric flow, mass flow, etc. It should further be noted in the exemplary
method embodiment that the data collected from these sensors is included in
generating a performance curve for the main compressor. Next, at step 610 of the
exemplary method embodiment, sensors are installed in the control loop adjacent
to the process fluid output connection on the main compressor. It should be noted
in the exemplary method embodiment, that the sensors can, but are not limited to,
measuring temperature, pressure, volumetric flow, mass flow, etc. It should
further be noted in the exemplary method embodiment that the data collected from
W these sensors is included in generating a performance curve for the main
compressor.
Continuing at step 612 of the exemplary embodiment, data is collected from the
sensors installed in the control loop while the compressors are operating at
various resistance conditions dictated by the position of the control valve. It
should be noted in the exemplary embodiment that when the control valve is in the
fully open position, the main compressor head at the process fluid input
approaches zero and can even reach a negative head value. These
circumstances of the exemplary method embodiment allow the collection of data
for generating a main compressor performance curve without having to resort to
extrapolation of data in this region important to startup procedures for a
10
i
compressor.
The disclosed exemplary embodiments provide a system and a method for
reducing the size of a centrifugal compressor while maintaining the performance
characteristic of the larger centrifugal compressor. It should be understood that
this description is not intended to limit the invention. On the contrary, the
exemplary embodiments are intended to cover alternatives, modifications and
equivalents, which are included in the spirit and scope of the invention as defined
by the appended claims. Further, in the detailed description of the exemplary
embodiments, numerous specific details are set forth in order to provide a
comprehensive understanding of the claimed invention. However, one skilled in
W the art would understand that various embodiments may be practiced without such
specific details.
Although the features and elements of the present exemplary embodiments are
described in the embodiments in particular combinations, each feature or element
can be used alone without the other features and elements of the embodiments or in
various combinations with or without other features and elements disclosed herein.
This written description uses examples to disclose the invention, including the best
mode, and also to enable any person skilled in the art to practice the invention,
including making and using any devices or systems and performing any incorporated
methods. The patentable scope of the invention is defined by the claims, and may
include other examples that occur to those skilled in the art. Such other examples
W are intended to be within the scope of the claims if they have structural elements that
do not differ from the literal language of the claims, or if they include equivalent
structural elements to those recited in the literal languages of the claims.

WE CLAIM :
1. A system for testing a compressor, said system comprising:
one or more compressors connected together in series to a test compressor
wherein an output of said test compressor is connected to an input of a first
compressor in said series, forming an overall loop;
one or more process fluid coolers in said overall loop;
one or more orifices in said overall loop;
a control valve in said overall loop; and
a first plurality of sensors configured adjacent to a process fluid input of said test
compressor and a second plurality of sensors configured adjacent to a process
W fluid output of said test compressor.
2. The system of claim 1, wherein said test compressor is a centrifugal
compressor.
3. The system of claim 2, wherein said one or more compressors are centrifugal
compressors.
4. The system of claim 1, wherein said one or more compressors have a
cumulative output capacity greater than said test compressor.
5. The system of claim 4, wherein said cumulative output capacity is sufficient to
overcome head value losses associated with said overall loop.
6. The system of claim 5, wherein said testing is associated with generating a test
compressor performance curve based on non-extrapolated empirical data for said
W test compressor at head values lower than said head value losses associated with
operating conditions of said overall loop.
7. The system of claim 1, further comprising connecting a separate motor and gear
box to each of said one or more compressors and to said test compressor.
8. The system of claim 1, further comprising a plurality of valves configured in said
overall loop such that each of said compressors and said test compressor can be
isolated and operate as an independent test loop.
9. A method for obtaining non-extrapolated empirical data associated with
performance characteristics of a compressor at head values lower than head value
losses associated with a test loop connected to said compressor, said method
comprising:
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connecting an auxiliary compressor to a main compressor in a test loop such that
a process fluid output from said auxiliary compressor is connected to a process
fluid input of said main compressor and a process fluid output from said main
compressor is connected to a process fluid input of said auxiliary compressor;
installing a control valve in said test loop between said auxiliary compressor and
said main compressor;
installing one or more process fluid coolers and one or more orifices in said test
loop between said auxiliary compressor and said main compressor;
installing a first plurality of sensors in said test loop adjacent to said process fluid
input of said main compressor;
^ installing a second plurality of sensors in said test loop adjacent to said process
fluid output of said main compressor; and
collecting data from said first plurality of sensors and said second plurality of
sensors while operating said test loop at conditions such that said main
compressor head is lower than head value losses associated with said test loop.
10. A method for sizing an electric motor associated with a single or multistage
compressor, for optimally meeting said compressor startup requirements, said
method comprising:
obtaining, using the method of claim 13, non-extrapolated empirical data for each
stage of said compressor;
calculating an overall performance map of said compressor using the non-
W extrapolated empirical data for each stage of said compressor; and
calculating the absorbed power of said compressor at startup using said overall
performance map of said compressor to size the electric motor.