Note: Descriptions are shown in the official language in which they were submitted.
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METHOD AND APPARATUS FOR MONITORING
THE PERFORMANCE OF A COMPRESSOR
BACKGROUND OF THE INVENTION
1. Field of the Invention
This disclosure relates generally to devices used to monitor apparatus, and
more
particularly to systems and related methods for monitoring the operation of
compressors used
in pipeline operations, oil refineries, chemical plants, petrochemical plants
and in other
industries.
2. Discussion of Related Art
In the gas transmission industry, it has become ziecessary to operate large
reciprocating type compressors that drive the movement of gas within a
pipeline continuously
without interruption, with the goal of achieving one hundred percent
efficiency. Engine
driven compressors may operate at high speeds (e.g., 500-1000 rpm), and are
therefore
subject to failing due to normal wear and tear. In addition, since pipeline
compressors often
operate unattended for protracted periods of time in remote locations, it is
imperative that
compressors be monitored to ensure they are operating properly.
Pipeline compressors often operate unattended for protracted periods in remote
locations and may require a host of instrumentation to ensure failsafe
operation. Periodically,
the efficiency of the compressors may be measured to determine the operation
of the
compressor, as well as to measure performance characteristics of the
compressor.
To measure efficiency of the compressor, it may be necessary to determine the
work
performed by the compressor. Prior techniques have involved the calculation of
indicated
horsepower through the measurement of pressure in the cylinder head or at the
discharge and
suction sides of the compressor. Problems may exist with such methods,
however, in that
pressure sensors may be expensive, inherently produce signal errors, and have
limited
durability, thereby resulting in lost time and efficiency during replacement
of failed pressure
sensors. Accurate measurement of compressor cylinder pressure may be hampered
by the
acoustic distortion introduced by the measurement channel between the cylinder
and the
installed pressure sensor. This distortion is particularly severe on high-
speed compressors.
Moreover, measurement of cylinder pressure and the resulting calculated work
may not
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include the frictional costs of the piston riding on the cylinder walls. For
large compressors
in the range of 2000 HP to 10,000 HP, or above, these losses can be
significant.
One approach to measuring work performed by a compressor is disclosed in U.S.
Patent No. 7,186,094, which is incorporated herein by reference for all
purposes. U.S. Patent
No. 7,186,094 discloses an apparatus and method for monitoring key parameters
of a
reciprocating member of a reciprocating piston compressor. Specifically, an
apparatus for
directly measuring rod strain on a compressor is disclosed in this patent. The
data acquired
may then be used to calculate power and work performed by the compressor. U.
S. Patent No.
7,186,094 also discloses that other parameters of the reciprocating members,
such as the
temperature of the cross-head bushing, may be measured.
SUMMARY OF THE INVENTION
One aspect of the disclosure is directed to a method of monitoring the
operation of a
compressor. In one embodiment, the compressor has a housing and a
reciprocating member
disposed within the housing. In a certain embodiment, the method comprises:
sensing a
parameter on the housing from a device placed on the housing; generating a
representative
sensor signal in response to the sensed parameter; transmitting from the
device a data signal
related to the representative sensor signal; and receiving the data signal at
a location remote
from the housing.
Embodiments of the method may include, when sensing a parameter, monitoring a
load on the housing. Transmitting a signal may comprise manipulating the
representative
sensor signal. Generating a representative signal may comprise generating a
voltage signal,
and transmitting from the device a data signal may comprise manipulating the
voltage signal
to a frequency signal. Sensing a parameter may comprise mounting a plurality
of strain
gauges on a load cell mounted on the housing. The method may further coniprise
calculating
a load on the housing and/or calculating the power used by the compressor. In
one
embodiment, the compressor may have a pressure inlet and a pressure outlet,
and the method
further includes sensing the pressure at the pressure inlet and outlet.
Another aspect of the disclosure is directed to a method of monitoring a
machine. In
one embodiment, the machine has a housing and a reciprocating member disposed
within the
housing. In a certain embodiment, the method comprises: sensing at least one
parameter on
the housing of the machine from a device placed on the housing; generating a
representative
sensor signal in response to the at least one sensed parameter; transmitting
from the device on
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the housing a data signal related to the representative senor signal; and
receiving the data
signal at a location remote from the housing.
Embodiments of the method may include, when sensing at least one parameter,
monitoring a load on the housing. Transmitting a signal may comprise
manipulating the
representative sensor signal. Sensing at least one parameter may comprise
mounting a
plurality of strain gauges on a load cell mounted on the housing. The method
may further
comprise calculating a load on the housing and/or calculating the power used
by the
compressor. In one embodiment, the compressor may have a pressure inlet and a
pressure
outlet, and the method further includes sensing the pressure at the pressure
inlet and outlet.
Receiving the data signal may further comprise manipulating the data signal.
Transmitting
may be performed by a transmitter. Sensing at least one parameter may be
performed by at
least one sensor.
Yet another aspect of the disclosure may be directed to a compressor
comprising a
housing, a reciprocating member disposed in the housing, a motor coupled to
the
reciprocating member, and an apparatus. In one embodiment, the apparatus
includes a
mobile assembly attachable to the housing. The mobile assembly has a sensor, a
transmitter
and a power source. The sensor is operable to measure a parameter of the
housing and
generate a representative sensor signal. The representative sensor signal is
input to the
transmitter, with the transmitter being operable to transmit a data signal
related to the
representative sensor signal. The power source is operable to power the
transmitter and
sensor. The apparatus further includes a stationary assembly having a receiver
operable to
receive the data signal from the transmitter.
DESCRIPTION OF THE DRAWINGS
For a better understanding of the present disclosure, reference is made to the
drawing
figures which are incorporated herein by reference and in which:
FIG. 1 is a schematic view of a compressor and a monitoring system of the
disclosure;
and
FIG. 2 is a partial view of a compressor and the monitoring system shown in
FIG. 1.
DETAILED DESCRIPTION OF THE INVENTION
This disclosure is not limited in its application to the details of
construction and the
arrangement of components set forth in the following description or
illustrated in the
drawings. The disclosure is capable of other embodiments and of being
practiced or ofbeing
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carried out in various ways. Also, the phraseology and terminology used herein
is for the
purpose of description and should not be regarded as limiting. The use of
"including,"
"coniprising," or "having," "containing," "involving," and variations thereof
herein, is meant
to encompass the items listed thereafter and equivalents thereof as well as
additional items.
Directly measured parameters of components of a compressor are not readily
available because of the difficulties in directly accessing internal
components of the
compressor and transmitting the key sensor data from the internal
reciprocating member. The
rapid movement and resulting forces on a monitoring sensor and associated
devices make
direct monitoring very difficult and expensive when using a sensor mounted on
any of the
internal components of the compressor. For example, directly measured brake
horsepower
may not be readily available on compressors, such as those used in the gas
pipeline industry.
Typically compressors are controlled based on indirect measurements, such as
torque inferred
from fuel flow, suction pressure, discharge pressure, swept volume and
clearance. This may
lead to inaccuracies in the measurement of the load on the engine, limits the
ability to take
full advantage of the flexibility available and can result in overloading the
compressor and
parts, such as the frame, crankshaft, rods and bearings. Prior methods and
apparatus, such as
the approach disclosed in U.S. Patent No. 7,186,094, teach a system for
directly measuring
parameters of a reciprocating motor or compressor port. More specifically, as
disclosed in
the 7,186,094 patent, an apparatus for directly measuring rod strain on a
compressor is
provided The data acquired may then be used to calculate power and work
performed by the
compressor. Similarly, other parameters of the reciprocating members, such as
the
temperature of the cross-head bushing may be measured. The resulting
information can be
used to control and limit potential operating conditions leading to part
overloading, reducing
the likelihood of potentially catastrophic failures.
However, although the approach disclosed in U.S. Patent No. 7,186,094 provides
an
improvement over prior art methods and apparatus, applying sensors to the
reciprocating
member still provides design challenges. Specifically, since the reciprocating
member (i.e.,
the piston) is an internal component that operates at a rapid rate, a
tremendous amount of
wear and tear associated with normal operation of the compressor may
compromise the
reliability of such an approach. It is also much more difficult, more
expensive and less
practical to install sensors on internal compressor parts rather than on
external areas of the
compressor. The methods and apparatus of the instant disclosure improve on
monitoring the
performance and safety of the compressor. Specifically, the methods and
apparatus provide a
means for measuring parameters of the reciprocating member without having to
attach a
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device to the reciprocating member. Instead, a device may be attached to a
housing
(sometimes referred to as an "external casing") of the reciprocating member.
In one
embodiment, the device may be one or more strain sensors. The strain sensors
may be
configured to measure parameters of the compressor and generate signals that
are sent to a
computer or data analyzer to analyze the information to optimize the
performance and safety
of the compressor.
Using the presented methods and apparatus make it possible to operate the
compressor at maximized efficiency, and in combination with other
measurements, such as
compressor temperature or enthalpy rise, fuel flow, crank shaft angle and
other parameters, to
locate capacity and performance problems more accurately.
In one embodiment, the strain sensors may be comprised of full bridge strain
gauges
that are mounted externally on the housing that surrounds the piston assembly.
The strain
sensors may be configured to measure compressive, tensile and bending strain
on the external
wall of the housing. In a certain embodiment, data obtained by the bending
strain gauge may
be required to analyze data obtained by the tensile and conipression strain
gauges in order to
calculate the work performed by the compressor. The strain sensors may embody
load cells
that are mounted on a device that is located on an external surface of the
housing. These
sensors may be configured to isolate strain due to bending forces thereby
allowing accurate
calculation of strain due solely to axial loading. Each load cell may generate
a representative
strain gauge signal that is transmitted to a computer via a
transmitter/receiver system. The
strain sensors, also known as load cells, are temperature compensated in order
to offset fals
signals generated from thermal drift.
With reference to FIG. 1, a reciprocating piston compressor is generally
designated at
10. As shown, a motor 12 is configured to supply fuel from a line 14 that is
connected to the
same source as the gas to be compressed by the compressor 10, although fuel
could
alternately be provided by other means. The compressor 10 is constructed in
the typical
manner to include a crankshaft 16 rotated by the motor 12. This crankshaft 14
may be
connected to a slider 18, which is in turn may be connected to a connecting
rod 20 and a
piston rod 22. As shown, the piston rod 22 is configured to drive a piston 24.
The rotation of
the crankshaft 16 causes the piston 24 to reciprocate within a cylinder 26. A
typical
compressor 10 may employ the shown slider 18 and connecting rod 20, but this
arrangement
may be modified as is known in the art. As shown schematically in FIG. 1, a
housing or
external casing 28 is provided to house and protect the components of the
compressor 10.
These components are suitably coupled to the housing 28 as is known in the
art.
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The cylinder 26 may be provided with an inlet line 30, which is connected to a
source
of gas, such as the gas line 14. An inlet valve 32 may be provided to control
the flow of gas
from the inlet line 30 into the cylinder 26. The cylinder 26 may also be
provided with an
outlet line 34. An outlet valve 36 may be provided to control the flow of gas
from the
cylinder 26 to the outlet line 34. As is conventional in the art, operation of
the valves 32, 36
may be controlled by pressure differentials so that gas is drawn from the
inlet line 30 through
the inlet valve 32 into the cylinder 26. Once gas enters the cylinder 26, the
gas is compressed
by the piston 24, with the compressed gas flowing out of the cylinder through
the outlet valve
36 to the outlet line 34.
As discussed above, prior art devices, such as the apparatus disclosed in U.S.
Patent
No. 7,186,094, may be used in conjunction with the compressor to measure
performance
parameters of the compressor. The apparatus may include a sensor assembly,
such as a rod
load monitor or temperature sensor, an encoder, a processor, a transmitter and
a power
source. The apparatus may be designed to measure one or more parameters of the
reciprocating parts of the compressor, such as the crankshaft cross-head or
bushing, the
connecting rods, slider or piston rods, and transmit data based on the sensed
parameters to a
receiver.
Contrary to the teachings of U.S. Patent No. 7,186,094, an apparatus of the
present
disclosure, which is generally designated at 40 in FIG. 1, measures a
parameter associated
with a non-moving member, such as the housing 28 of the compressor 10. Various
parameters may be measured, such as strain or load, axial and transverse
loading,
temperature, enthalpy, or other parameters considered relevant to monitoring
the performance
and efficiency of the compressor 10.
In one embodiment, the apparatus includes a mobile assembly generally
indicated at
42 and a stationary assembly generally indicated at 44. The mobile assembly 42
includes a
sensor 46 that may embody a strain monitor, preferably mounted to the housing
28 of the
compressor 10, for measuring the load or strain on the housing when the
compressor is in use.
It should be understood that the strain monitor may be mounted to other non-
moving parts of
the compressor, such as the outer wall of the cylinder 26. The sensor 46
generates a
representative sensor signa148. When attached to the housing 28 of the
compressor 10, the
sensor 46 may generate a strain signal representative of the strain on the
housing 28. In other
embodiments, a temperature sensor may be employed to measure the temperature
of the
housing 28. Temperature variations of the housing 28 may indicate certain
operating
conditions of the compressor 10.
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With reference to FIG. 2, in a certain embodiment, the sensor 46 may include
multiple
strain gauges, each indicated at 50, mounted on the outer surface of the
housing 28. The
strain gauges 50 may be mounted on the housing 28 to sense loads on or
movement of the
housing. In one embodiment, two pairs of strain gauges 50 may be employed,
with each pair
consisting of two strain gauges to measure strain in two separate directions
on the housing.
As discussed above, the sensor 46 (e.g., strain gauges 50) generates the
representative sensor
signal 48, which is transmitted to a computer or data analyzer 52. In one
embodiment, the
sensor 46 may be wired to the computer 52 (FIG. 2) via wire lines.
In certain embodiments, other sensor assemblies may be used with the present
apparatus to monitor other parameters of the compressor. For example, as
discussed above, a
temperature sensor (not shown) may be mounted to the housing to measure the
temperature
of the compressor housing. For example, an unexpected temperature rise may
indicate a
potential catastrophic failure of the compressor. Monitoring such a rise in
temperature would
allow the user to shut down the compressor for repair prior to such a failure.
In one
embodiment, the temperature sensor may be connected to the power source, for
powering the
sensor, and produces a temperature sensor signal which is transmitted to the
computer and
encoder, as necessary, so that the signal may be transmitted via a
transmitter.
The representative sensor signal 48, such as strain gauge signal or
temperature signal,
may be processed by the computer 52, which may include amplifiers, filters,
data storage
units, a CPU, gauge bridges, AC/DC and other converters, clocks, calculators,
software and
other devices as known in the art. For example, the computer 52 may include an
encoder 54
to convert analog signals to digital signals as necessary. Preferably the
computer 52 may
include a low noise amplifier to amplify to a more usable level the output of
the sensor signal
48. Similarly, the computer 52 may employ an electronic integrator as a
negative feedback
element in the amplifier to eliminate or reduce any static levels in the
representative signals.
The representative signals typically are output from the sensors as a voltage.
As discussed
below, the computer 52 may operate to generate a signal, such as a radio
frequency signal, for
transmission to a stationary assembly. The computer 52 may include an
electronic device,
such as a VCO, which outputs a continuous train of fixed width pulses whose
frequency is
proportional to the rod strain, as measured in voltage by the rod load
monitor. Further
circuitry may be used, such as for generating a static offset voltage to the
VCO so as to
establish a stable signal.
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The apparatus 40 may also include a transmitter 56, which is coupled to the
computer
52. The transmitter 56 transmits a signa158 to a receiver 60 of the stationary
assembly 44.
The signa158 may be an analog, digital, optical, or an RF-based signal.
Power for the operation of the various components of the mobile assembly 42 of
the
apparatus 40 is provided with a power source 64. In one embodiment, the power
necessary to
operate various electrical components of the apparatus 40 may be supplied
through the
operation of the compressor itself. In one particular embodiment, the power
source 64 may
be a battery or other source capable of being mounted to the housing 28 of the
compressor 10.
However, a power generator, such as an inductive coil assembly, may be
preferred since the
power generator would eliminate the need for frequent replacement.
In addition to the receiver 60 and the antenna 62, the stationary assembly 44
may
include another computer or data analyzer 66. The antenna 62 may be configured
to receive
the signa158 from the transmitter 56 of the mobile assembly 42. The signal 58
may then be
manipulated as necessary by the computer 66, which can include decoders,
clocks, pulse
generators, stabilizers, a CPU, software, programs and other devices. The
circuitry may be
powered by the power source 64 of the mobile assembly 42, such as a battery,
by direct
wiring to an electrical supply or other source, such as a solar power
generator.
The transmitter 56 of the mobile assembly 42 and the receiver 60 of the
stationary
assembly 44 eliminates the need for a wire connection between the two
assemblies for
transmission of the signals.
As shown, FIG. 2 illustrates the slider 18, connected to the crankshaft at
cross-head
bushing or connector (not shown). The slide 18 moves linearly along a channel
70. A back
cover 72 of the housing 28 is shown and typically a similar front cover (not
shown) encloses
the slider 18 and piston rod 22.
The apparatus 40 of the disclosure used in conjunction with the compressor 10
may
also include pressure sensors, such as a suction pressure sensor 74 fixed in
the inlet line 30 so
as to measure the suction pressure of gas entering the compressor 10.
Appropriate pressure
sensors are well known and are readily available. Such a sensor 74 may
generate a suction
pressure signal 76 representative of the suction pressure of the gas entering
the compressor
10. The apparatus 40 may further comprise a discharge pressure sensor 78 fixed
in the outlet
line 34 so as to measure the pressure in this line, which is the discharge
pressure of gas
leaving the compressor 10. The discharge pressure sensor 78 generates a
discharge pressure
signal 80 representative of the discharge pressure.
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The apparatus 40 is designed to reduce dependence on pressure sensors provided
on
the inlet and outlet lines 30, 34 of the compressor 10. However, the apparatus
40 maybe
used in conjunction with such sensors. The pressure and strain data may be
used in
conjunction or as comparative data. For example, the function of the remaining
sensors, such
as a crank angle indicator, may be to provide the remaining data necessary to
determine the
work performed by the compressor.
Other sensors, such as a fuel consumption flow rate sensor may be used as
well.
The apparatus may also include a rod location sensor 82 as is known in the
art. The
rod location sensor 82 serves a similar function as the crank angle indicator
and will not be
described in detail. The rod location sensor 82 provides a generated rod
location signal 84
representative of the location of the rod in its travel along its function
path such that the user
has an indication of the location of the rod.
The representative signals from the stationary assembly 44, pressure sensors
74, 78,
crank angle encoder and/or rod member location sensor 82 are sent by
respective lines to a
sensor controller 86. The stationary assembly 44 is connected to the
controller 86 by line 88.
The pressure sensors 74, 78 are connected to the controller 86 by line 90. The
rod member
location sensor 82 is connected to the controller 86 by line 92. The sensor
controller 86 is
designed to receive the representative signals from the various indicators.
The controller 86
may include amplifiers, band pass filters, data storage units, a CPU, gauge
bridges, A/D
converters and other devices as are known in the art. For example, the
processor may convert
analog signals to digital signals as necessary. The controller 86 may include
a calculator,
timing and other circuitry, converter soflware, storage capacity and
cumulative mathematical
calculations.
The sensor controller 86 may include many members and be located on or off-
site or
partially off-site. That is, the controller 86 is not limited to a single
physical location. The
controller 86 may compute or monitor certain parameters on-site while
transmitting these or
other parameters to an off-site control room. On-site monitoring and control
may, for
example, include emergency shut-down control in the case of an actual or
impending failure.
The controller 86 may be used to control the compressor operation. Typically,
at least some
of the controller function is remote to the compressor site.
The sensor controller 86 may function as the central processing unit carrying
out the
logic functions of the apparatus 40. The controller 86 may comprise a single
computer or a
multiplicity of computers or other calculator devices. The controller 86 may
be located on
site or remote from the compressor 10. It is anticipated that the controller
86 may most likely
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be remote from the compressor 10 and will receive data from a plurality of
compressors
spread over a wide geographic area. The controller 86 may contain a
microprocessor, digital
input and output subsystems, memory capacity in which is stored various
mathematical and
analytical programs and software and constant data regarding the compressor
being analyzed.
One of the primary functions of the controller 86 is to compute, using the
representative data
signals, the work performed by the compressor 10 during a predetermined time
interval. The
controller 86 may include the necessary formulas for repetitive calculations
of performance
parameters. Preferably the controller 86, in conjunction with the rod load
monitor, other
sensors and transmitter/receiver pair, permits continuous real-time monitoring
of the
compressor. Real-time and continuous work calculations can then be performed
and
monitored.
Other calculations may be made as well, such as the computation of work and
power
based on pressure measurements. The measurements and results of the
calculation can then
be used for optimization of the efficiency and use of the compressor 10. That
is, the resulting
data from the computer 86 may be used to regulate the operation of the
compressor 10 to
maximize the efficiency of the unit. Where several compressor units are being
monitored
simultaneously, the compressors can each be regulated to maximize the
efficiency of the
pipeline operation as a whole. The compressor utilization, health and
integrity is then used
by the compressor controllers (either human or software based) to affect
operation in an
optimized fashion. The optimization and regulation of the compressor units can
be done
manually, by remote transmission or direct manipulation, or automatically
through the use of
computer optimization software.
Optimization can also include automatic shut-downs where the measured
parameters
indicate a failure or danger of catastrophic failure. For example, the
temperature sensor may
be an indicator of impending failure. A sharp temperature rise may indicate a
need to turn off
the compressor.
In one embodiment, the controller may include many members and be located on
or
off-site or partially off-site with respect to the compressor. Specifically,
the controller may
not be limited to a single physical location. The controller may compute or
monitor certain
parameters on-site while transmitting these or other parameters to an off-site
control room.
On-site monitoring and control may, for example, include emergency shut-down
control in
the case of an actual or impending failure. The controller will be used to
control the
compressor operation. Typically at least some of the controller function is
remote to the
compressor site. The unit controller may function as the central processing
unit carrying out
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the logic functions of the device. The controller may comprise a single
computer or multiple
computers or other calculator devices. The controller may be located on site
or remote from
the compressor. The controller may contain a microprocessor, digital input and
output
subsystems, memory capacity in which is stored various mathematical and
analytical
programs and software and constant data regarding the compressor being
analyzed. One of
the primary functions of the controller is to compute, using the
representative data signals, the
work performed by the compressor during a predetermined time interval. The
controller may
include the necessary formulas for repetitive calculations of performance
parameters.
Preferably the controller, in conjunction with the rod load monitor, other
sensors and
transmitter/receiver pair, permits continuous real-time monitoring of the
compressor. Real-
time and continuous work calculations can then be performed and monitored.
Having thus described several aspects of at least one embodiment of this
disclosure, it
is to be appreciated various alterations, modifications, and improvements will
readily occur to
those skilled in the art. Such alterations, modifications, and improvements
are intended to be
part of this disclosure, and are intended to be within the spirit and scope of
the disclosure.
Accordingly, the foregoing description and drawings are by way of example
only.
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