BACKGROUND
TECHNICAL FIELD
Embodiments of the subject matter disclosed herein generally relate to installations
using reciprocating compressors in oil and gas industry, and, more particularly, to
constructively using the pressure pulsations to enhance the volumetric efficiency of
the compressor, Le., achieving a pulse charging effect.
DISCUSSION OF THE BACKGROUND
Compressors used in oil and gas industry have to meet industry specific requirements
that take into consideration, for example, that the compressed gas is frequently
corrosive and flammable. American Petroleum Institute (API), the organization
setting the recognized industry standard for equipment used in oil and gas industry,
has issued a document, AP1618, listing a complete set of minimum requirements for
reciprocating compressors.
The compressors may be classified in positive displacement compressors (e.g.,
• reciprocating, screw, or vane compressors) and dynamic compressors (e.g.,
centrifugal or axial compressors). In the positive displacement compressors, the
compression is achieved by trapping the gas and then reducing volume in which the
gas is trapped. In the dynamic compressors, the compression is achieved by
transforming the kinetic energy (e.g., of a rotating element) into pressure energy at a
predetermined location inside the compressor.
An ideal compression cycle (graphically illustrated in Figure 1 by tracking evolution of
pressure versus volume) includes at least four phases: expansion, suction,
compression and discharge. When the compressed fluid is evacuated from a
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compression chamber at the end of a compression cycle, a small amount of fluid at
the delivery pressure P1 remains trapped in a clearance volume V1 (Le., the minimum
volume of the compression chamber). During the expansion phase 1 and the suction
phase 2 of the compression cycle, the piston moves to increase the volume of the
compression chamber. At the beginning of the expansion phase 1, the delivery valve
closes (the suction valve remaining closed), and then, the pressure of the trapped
fluid drops since the volume of the compression chamber available to the fluid
increases. The suction phase of the compression cycle begins when the pressure
inside the compression chamber becomes equal to the suction pressure P2, triggering
the suction valve to open at volume V2. During the suction phase 2, the compression
chamber volume and the amount of fluid to be compressed (at the pressure P2)
increase until a maximum volume of the compression chamber V3 is reached.
During the compression and discharge phases of the compression cycle, the piston
moves in a direction opposite to the direction of motion during the expansion and
suction phases, to decrease the volume of the compression chamber. During the
compression phase 3 both the suction and the delivery valves are closed (Le. the fluid
does not enter or exits the cylinder), the pressure of the fluid in the compression
chamber increasing (from the suction pressure P2 to the delivery pressure P1)
because the volume of the compression chamber decreases to V4• The delivery
phase 4 of the compression cycle begins when the pressure inside the compression
chamber becomes equal to the delivery pressure P1, triggering the delivery valve to
open. During the delivery phase 4 the fluid at the delivery pressure P2 is evacuated
from the compression chamber until the minimum (clearance) volume V1 of the
compression chamber is reached.
One measure of the efficiency of the compressor is the volumetric efficiency, which is
a ratio of the volume of the compression chamber swept by the piston of the
reciprocating compressor during the suction phase V3- V2 to the total volume V3- V1
swept by the piston during the compression cycle.
The phenomenon of pressure pulsations occurring outside the reciprocating
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compressor is due to the discontinued nature of the gas flow inside the reciprocating
compressor. These pressure pulsations may lead to large vibrations and fatigue
stresses, high noise level, and reduced compressor performance. API618 includes
the detailed requirements for an acoustical study that has to be undertaken when
designing an installation including a reciprocating compressor, for, among other
purposes, avoiding the damaging effect of the pressure pulsations. In order to
prevent these pulsations from propagating throughout the installation, volume bottles
are installed before the suction valves and after the discharge valves of the
compressors, buffering the reciprocating compressor from the rest of the installation.
For example, Figure 2 illustrates a simplified model of an interface between a
reciprocating compressor 10 and the rest of the installation. Here the term "interface"
designates all the components between a valve 20 of the reciprocating compressor
10 and a plant pipe 30 through which gas is channeled to or from a rest of the
installation (e.g., an oil and gas plant). The reciprocating compressor 10 has a piston
40, and is connected via a pipe 50 to a volume bottle 60. The volume bottle 60 is
then connected to the oil and gas plant via the plant pipe 30.
The volume bottle 60 filled with the gas to be compressed or the compressed gas
(depending on whether the volume bottle is located before the suction valve or after
the discharge valve or the reciprocating compressor 10 has a high acoustical
impedance and operates as a reflector of the pulsations, allowing only a small fraction
to be transmitted towards the plant pipe 30.
The frequency of the pressure pulsations generated by the reciprocating compressor
10 is the frequency of the compression process in the reciprocating compressor.
Resonance occurs when a natural frequency f of the pipe 30 equals the frequency of
the pressure pulsations generated by the reciprocating compressor. The natural
frequency f of the pipe 50 depends on the speed of sound in the gas c and the length
L of the pipe 50. In a first approximation, the following relationship exists between
these quantities: f=c/(2L). If stationary pressure waves are formed along the pipe 50,
orifices (Le., localized narrowing of the pipe) may be employed to reduce the
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amplitude of the stationary pressure waves.
Thus, conventionally, the pressure pulsations (that inherently occur due to
discontinued nature of the gas flow in a reciprocating compressor) are dissipated, not
used.
It would be desirable to provide methods and devices (included or performed in oil
and gas installations including a reciprocating compressor) that use constructively the
pressure pulsation to enhance the efficiency of the reciprocating compressor.
SUMMARY
Some of the embodiments have an actuated valve and a gas circulation device
configured to have a resonance frequency substantially equal to a frequency of
performing compression cycles in the reciprocating compressor. The valve is
actuated such as to enhance the volumetric efficiency of the compressor using
constructively the inherent pressure pulsations. This manner of using the pressure
pulses to enhance efficiency is known as the pulse charging effect.
According to one exemplary embodiment, an apparatus includes a gas circulation
device and a controller. The gas circulation device provides a path through which gas
(to be compressed or after being compressed) circulates between a reciprocating
compressor and a volume bottle buffering a gas flow connecting of the reciprocating
compressor to an oil and gas plant. The gas circulation device is configured to have
a resonance frequency substantially equal to a frequency of performing compression
cycles in the reciprocating compressor. The controller is configured to control timing
of switching a valve located between the reciprocating compressor and the gas
circulation device in order to use constructively pressure pulsations occurring in the
gas circulation device to enhance a volumetric efficiency of the reciprocating
compressor.
According to another exemplary embodiment, a method of using a pulse charging
effect to enhance a volumetric efficiency of a reciprocating compressor is provided.
The method includes providing a gas circulation device between a valve of the
reciprocating compressor and a volume bottle buffering the reciprocating compressor
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from an oil and gas plant, the gas circulation device being configured to have a
resonance frequency substantially equal to a frequency of performing compression
cycles in the reciprocating compressor. The method further includes controlling
timing of actuating the valve to use constructively pressure pulses inherently
occurring in the gas circulation device, to enhance the volumetric efficiency of the
reciprocating compressor.
According to another exemplary embodiment, a method for retrofitting a reciprocating
compressor installation is provided. A reciprocating compressor of the installation
has an output or an input thereof buffered by a volume bottle from the rest of the
installation. The reciprocating compressor installation is retrofitted to use a pulse
charging effect of the reciprocating compressor to enhance a volumetric efficiency
thereof. The method includes modifying a gas circulation device connecting an
output or an input of the reciprocating compressor to the volume bottle, by adding at
least one acoustic resonator to a pipe of the gas circulation device, to make the gas
circulation device to have a resonance frequency substantially equal to a frequency of
performing compression cycles in the reciprocating compressor. The method further
includes connecting a valve between the reciprocating compressor and the gas
circulation device, to a controller configured to control timing of actuating the valve in
order to use constructively pressure pulsations occurring in the gas circulation device,
to enhance a volumetric efficiency of the reciprocating compressor.
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 pressure versus volume graph illustrating an ideal compression cycle;
Figure 2 is a schematic diagram of a conventional interface between a reciprocating
compressor and an oil and gas plant;
Figure 3 is a schematic diagram of an interface between a reciprocating compressor
and an oil and gas plant, according to an exemplary embodiment;
6
•
Figure 4 is a schematic diagram of an interface between a reciprocating compressor
and an oil and gas plant, according to an exemplary embodiment;
Figure 5 is a schematic diagram of an interface between a reciprocating compressor
and an oil and gas plant, according to an exemplary embodiment;
Figure 6 is a schematic diagram of an interface between a reciprocating compressor
and an oil and gas plant, according to an exemplary embodiment;
Figure 7 is a schematic diagram of an interface between a reciprocating compressor
and an oil and gas plant, according to an exemplary embodiment;
Figure 8 is a schematic diagram of an interface between a reciprocating compressor
and an oil and gas plant, according to an exemplary embodiment;
Figure 9 is flow chart of a method of using pulsations inherently generated during
operation of a reciprocating compressor in order to enhance compressor's efficiency,
according to an exemplary embodiment; and
Figure 10 is a flow chart of a method for retrofitting a reciprocating compressor
installation, according to an exemplary embodiment.
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
embodiments are discussed, for simplicity, with regard to the terminology and structure
of reciprocating compressors used in an oil and gas plant (Le., installation or
equipment). However, the embodiments to be discussed next are not limited to this
system, but may be applied to other similar technical conditions.
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
7
/
embodiment. Further, the particular features, structures or characteristics may be
combined in any suitable manner in one or more embodiments.
In some embodiments described below, a gas circulation device, which provides a path
through which gas (to be compressed or after being compressed) circulates between a
reciprocating compressor (Le., the compression chamber thereof) and a volume bottle.
The gas circulation device is configured to have a resonance frequency substantially
equal to a frequency of performing compression cycles in the reciprocating compressor.
Furthermore, a valve located between the compression chamber and the gas circulating
device is controlled to open relative to a phase of the pressure pulsations near the valve
in the gas circulation device such that to enhance efficiency of the compressor.
If one considers that the valve is the suction valve, an increased pressure in the gas
circulation device near the suction valve while the valve is open results in a larger
amount of gas entering the volume of the compression chamber to be compressed.
The suction taking place at a higher pressure P2+fjp, where fjp is due to the pulse
charging effect, is illustrated as a dashed line in Figure 1. Since the volume V2'
corresponding to the intersection of the dashed line with line representing the expansion
phase 1 is smaller than V2, the volumetric efficiency increases because the numerator of
the ratio defining the volumetric efficiency increases V.r V2'>V.r V2.
In fact, Lip is not a constant offset of the pressure as it varies in time, between a
maximum positive value and a maximum negative value. A controller may determine
the opening moment of the valve 20 to have a maximum pressure Lip (added or
subtracted) at the time of opening of the valve or achieve an overall pressure higher
pressure than the suction pressure during (or at the end of) the suction phase.
Figure 3 is a schematic diagram of an interface 100 (Le., an apparatus) between a
reciprocating compressor 10 and a volume bottle 60 providing a gas volume buffer to an
oil and gas plant according to an exemplary embodiment. The large volume of gas in
the volume bottle 60 prevents or substantially damps pressure pulses occurring in gas
outside the reciprocating compressor 10 due to flux variation in the reciprocating
compressor 10 (Le., due to the pulse charging effect). The interface 100 includes a gas
8
circulation device and a controller 110. The gas circulation device provides a path
through which the gas (to be compressed or after being compressed) circulates
between the reciprocating compressor 10 and the volume bottle 50. The gas circulation
device is configured to have a resonance frequency substantially equal to a frequency of
performing compression cycles in the reciprocating compressor. The gas circulation
device includes a pipe 130 and an in-line resonator 140 having an area larger than the
pipe area. The exact location of the in-line resonator 140 along the pipe 130 does not
affect the acoustic characteristics of the gas circulation device.
The controller 110 controls an actuator (not shown) actuating the valve 120. That is, the
controller 110 controls timing of actuating the valve 120 relative to the phase of the
pressure pulses (due to the pulse charging effect) near the valve such that to use the
pressure pulses to enhance the volumetric efficiency of the compressor. If the valve
120 is the suction valve, the controller 110 controls the timing of actuating the valve 120
to have a maximum pressure value 11p added to the suction pressure, while the valve
120 is open (Le., during the suction phase of the compressing cycle).
In another exemplary embodiment illustrated in Figure 4, the gas circulation device of an
interface 101 includes a side branch resonator 150 in addition to the in-line resonator
140. Optionally, the side-branch resonator 150 may be connected to the in-line
resonator 140 via a resonator valve 160. The resonator valve 160 may be switched to
connect or to disconnect the side-branch resonator 150 to/from the pipe 130, depending
on a composition of the gas (Which composition affects the speed of sound in the gas
and therefore the resonance frequency of the gas circulation device). The controller 110
may control the resonator valve 160.
In another exemplary embodiment illustrated in Figure 5, the gas circulation device of an
interface 102 includes a side-branch pipe 170 instead of the in-line resonator 140.
Optionally, the side-branch pipe 170 may be connected to the pipe 130 via a resonator
valve 180. The resonator valve 180 may switched to connected or to disconnect the
side-branch pipe 170 to/from the pipe 130, for example, depending on a composition of
the gas (which composition affects the speed of sound in the gas and therefore the
9
resonance frequency of the gas circulation device). The controller 110 may control the
resonator valve 180.
Alternatively, in another exemplary embodiment illustrated in Figure 6, the gas
circulation device of an interface 103 includes a side-branch resonator 200 attached to
the pipe 130. Optionally, the side-branch resonator 200 may be connected to the pipe
130 via a resonator valve 210. The resonator valve 210 may be switched to connect or
to disconnect the side-branch resonator 200 to/from the pipe 130, for example,
depending on a composition of the gas (which composition affects the speed of sound in
the gas, and, therefore, the resonance frequency of the gas circulation device). The
controller 110 may control the resonator valve 210.
In another embodiment illustrated in Figure 7, a gas circulation device of an interface
104 includes an additional side-branch resonator 220 connected to the side-branch
resonator 200. Optionally, the side-branch resonator 200 and/or the additional sidebranch
resonator 220 may be connected to pipe 130 and to the side-branch resonator
200, respectively via resonator valves 210 and 230, respectively. The resonator valves
210 and 230 may be switched to connect or to disconnect the side-branch resonator
200 and the additional side-branch resonator 220, respectively, depending on a
composition of the gas (which affects the speed of sound in the gas, and, therefore, the
resonance frequency of the gas circulation device). The controller 110 may control the
resonator valve 210 and/or 230.
In another embodiment illustrated in Figure 8, the gas circulation device of the interface
105 has the side-branch resonator 200 connected to the volume bottle via a secondary
pipe 240. A resonator valve 250 located on the secondary pipe 240 is switched
depending on the composition of the gas.
In various embodiments illustrated in Figures 3-8 and other equivalent embodiments,
it is executed a method 300 of using pulsations inherently generated outside but due
to operating the reciprocating compressor, to enhance the volumetric efficiency of the
compressor. As illustrated in Figure 9, the method 300 includes providing a gas
circulation device between a valve of the reciprocating compressor and a volume
10
bottle buffering the reciprocating compressor from an oil and gas plant, the gas
circulation device being configured to have a resonance frequency substantially equal
to a frequency of performing compression cycles in the reciprocating compressor, at
8310. The method 300 further includes controlling the timing of actuating the valve to
use pressure pulses inherently occurring in the gas circulation device due to the pulse
charging effect, to enhance the volumetric efficiency of the reciprocating compressor,
at 8320.
In one embodiment, the providing 8310 of method 300 may include adding a sidebranch
resonator or a side-branch pipe to a pipe connecting the valve to the volume
bottle. In another embodiment, the providing 8310 of method 300 may include
switching one or more resonator valves connecting acoustic resonators to a pipe
connecting the valve to the volume bottle.
An existing reciprocating compressor installation may be retrofitted to become able to
use pulsations inherently generated during operation of the reciprocating compressor
to enhance compressor's efficiency. Figure 10 is a flow chart of a method 400 for
retrofitting the reciprocating compressor installation, according to an exemplary
embodiment. The method 400 includes modifying a gas circulation device connecting
an output or an input of the reciprocating compressor to the volume bottle, by adding
at least one acoustic resonator to a pipe of the gas circulation device, to make the
gas circulation device to have a resonance frequency substantially equal to a
frequency of performing compression cycles in the reciprocating compressor, at
8410. The method 400 further includes connecting a valve between the reciprocating
compressor and the gas circulation device, to a controller configured to control timing
of actuating the valve in order to use pressure pulsations occurring in the gas
circulation device due to a pulse charging effect of the reciprocating compressor, to
enhance a volumetric efficiency of the reciprocating compressor, at 8420.
In one embodiment of the method 400, the at least one acoustic resonator may
include an in-line acoustic resonator, a side-branch acoustic resonator or a sidebranch
pipe. In another embodiment, the method 400 may further include connecting
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the at least one acoustic resonator to the apparatus via a resonator valve.
The disclosed exemplary embodiments provide apparatuses (devices) and methods
for using constructively the pressure pulses (i.e., the pulse charging effect) occurring
around the reciprocating compressors due to the flow variation, to enhance the
volumetric efficiency of the 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 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 of the subject matter disclosed to enable any
person skilled in the art to practice the same, including making and using any devices or
systems and performing any incorporated methods. The patentable scope of the
subject matter is defined by the claims, and may include other examples that occur to
those skilled in the art. Such other examples are intended to be within the scope of the
claims.

WE CLAIM :
1. An apparatus, comprising:
a gas circulation device that provides a path through which a gas to be
compressed circulates between a reciprocating compressor and a volume bottle
buffering the reciprocating compressor from an installation, the gas circulation device
being configured to have a resonance frequency substantially equal to a frequency of
performing compression cycles in the reciprocating compressor; and
a controller configured to control timing of switching a valve located between
the reciprocating compressor and the gas circulation device in order to use
constructively pressure pulsations occurring in the gas circulation device, to enhance
a volumetric efficiency of the reciprocating compressor.
2. The apparatus of claim 1, wherein the gas circulation device comprises
a pipe and an in-line resonator having an area larger than the pipe area, the pipe and
the in-line resonator being arranged in-between the reciprocating compressor and the
volume bottle.
3. The apparatus of claim 2, wherein the gas circulation device further
comprises a side-branch resonator, arranged lateral to the in-line resonator wherein
the side-branch resonator is connected to the in-line resonator via a resonator valve,
the resonator valve being switched between being opened and being closed thereby
connecting or disconnecting the side-branch resonator to the in-line resonator
depending on a composition of the gas.
4. The apparatus of claim 1, wherein the gas circulation device comprises
a pipe arranged between the reciprocating compressor and the volume bottle, and a
side-branch pipe arranged lateral to the pipe, wherein the side-branch pipe is
connected to the pipe via a resonator valve, the resonator valve being switched
between being opened and being closed thereby connecting or disconnecting the
side-branch pipe to the pipe depending on a composition of the gas.
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5. The apparatus of claim 4, wherein the gas circulation device further
comprises an additional side-branch resonator connected to the side resonator.
6. The apparatus of claim 5, wherein at least one of the side-branch
resonator and the additional side-branch resonator is connected via a valve to the
pipe or to the side-branch resonator, respectively, the valve being switched between
being opened and being closed thereby connecting or disconnecting the side-branch
pipe or the additional side-branch resonator thereof depending on a composition of
the gas.
7. The apparatus of claim 1, wherein the gas circulation device comprises
a pipe arranged between the reciprocating compressor and the volume bottle, and a
side-branch pipe arranged lateral to the pipe, the side-branch pipe being connected to
the pipe via a resonator valve, the resonator valve being switched between being
opened and being closed thereby connecting or disconnecting the side-branch pipe to
the pipe depending on a composition of the gas.
8. The apparatus of claim 1, wherein the valve is a suction valve and the
controller controls the timing of actuating the valve to have a ~aximum pulsation
pressure added to a suction pressure while the valve is open.
9. A method of using a pulse charging effect to enhance a volumetric
efficiency of a reciprocating compressor, the method comprising:
providing a gas circulation device between a valve of the reciprocating
compressor and a volume bottle buffering the reciprocating compressor from an
instalation, the gas circulation device being configured to have a resonance frequency
substantially equal to a frequency of performing compression cycles in the
reciprocating compressor; and
controlling timing of actuating the valve to use constructively pressure pulses
inherently occurring in the gas circulation device, to enhance the volumetric efficiency
of the reciprocating compressor.
10. A method for retrofitting a reciprocating compressor installation in which
an output or an input of a reciprocating compressor is buffered by a volume bottle
14
from the rest of the installation, the installation being retrofitted to use a pulse
charging effect of the reciprocating compressor to enhance a volumetric efficiency
thereof, comprising:
modifying a gas circulation device connecting an output or an input of the
reciprocating compressor to the volume bottle, by adding at least one acoustic
resonator to a pipe of the gas circulation device, to make the gas circulation device to
have a resonance frequency substantially equal to a frequency of performing
compression cycles in the reciprocating compressor; and
connecting a valve between the reciprocating compressor and the gas
circulation device, to a controller configured to control timing of actuating the valve in
order to use constructively pressure pulsations occurring in the gas circulation device,
to enhance a volumetric efficiency of the reciprocating compressor.
(ADR/Pa)
~~~o~
MANISHA SINGH NAIR
Agent for the Applicant [IN/PA-740]
LEX ORBIS .
Intellectual Property PractIce
709/710, Tolstoy House,
15-17, Tolstoy Marg,
l'-l"ew Delhi-llOOO l