Note: Descriptions are shown in the official language in which they were submitted.
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ROTATIVE VALVES FOR RECIPROCATING COMPRESSORS
AND RELATED METHODS
Embodiments of the subject matter disclosed herein generally relate to
apparatuses and
methods for using a single actuator to control both intake and discharge of
fluid in a
compression chamber of a reciprocating compressor; more particularly, to
actuate a
rotative valve configured to close or open an intake flow path and a discharge
flow path
to/from a compression chamber.
Compressors may be classified as positive displacement compressors (e.g.,
reciprocating,
screw, or vane compressors) or dynamic compressors (e.g., centrifugal or axial
compressors). For positive displacement compressors, the compression is
achieved by
trapping the gas and then reducing its volume. For dynamic compressors, the
gas is
compressed by transferring kinetic energy, typically from a rotating element
such as an
impellor, to the gas being compressed by the compressor.
Figure 1 is an illustration of a conventional dual chamber reciprocal
compressor 10. The
fluid compression occurs inside a body 20, usually having a cylindrical shape.
A fluid to
be compressed (e.g., natural gas) is input into the body 20 via an inlet 30
and suction
valves 32 and 34, and, after the compression, the fluid is output via an
outlet 40 and
discharge valves 42 and 44. The compression is a cyclical process in which the
fluid is
compressed due to a movement of the piston 50 inside the body 20, between a
head end
26 and a crank end 28. The piston 50 divides the body 20 into two compression
chambers 22 and 24 that operate in different phases of the compression cycle,
the volume
of the compression chamber 22 being at its lowest value when the volume of the
compression chamber 24 is at its highest value and vice-versa.
Suction valves 32 and 34 are configured to open to allow the incoming fluid
(having a
first pressure Pi) to enter into the compression chambers 22 and 24,
respectively.
Discharge valves 42 and 44 are configured to open to allow the outgoing
compressed
fluid (having a second pressure P2> Pi) to be output from the compression
chambers 22
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and 24, respectively. The piston 50 moves due to energy transmitted from a
crankshaft
60 via a crosshead 70 and a piston rod 80. The valves 32, 34, 42, and 44 are
illustrated
on side walls of the body 20, but they can also be located on the head end 26
and the
crank end 28 of the body 20.
Conventionally, the suction and the discharge valves used in a reciprocating
compressor
are automatic valves that are switched between a closed state and an open
state due to a
differential pressure across the valve (i.e., between the pressure on one side
of a mobile
part of the valve and the pressure on the other side of the mobile part). The
automatic
valves have the disadvantage that they add significantly to the clearance
volume of the
compression chamber, the clearance volume (e.g., 25) being a volume that
cannot be
efficiently used in the compression cycle. The larger the clearance volume,
the smaller is
the compression efficiency.
Actuated rotary valves minimize the portion of the clearance volume of the
compression
chamber due to the valves, and increase the flow area. Figures 2A and 2B
illustrate a
conventional rotary valve 200 that may be placed opening or closing a flow
pathway
between the inlet 30 and the compression chamber 22. The valve 200 may be
considered
to be used instead any of the valves 32, 34, 42, and 44. The valve 200
includes a seat (or
stator) 210 and a rotor 220. The seat 210 and the rotor 220 are coaxial disks
with
openings spanning a sector of the same size around a stem 230. The rotor 220
may be
actuated to rotate around the stem 230 from a first position (Figure 2A) in
which the
rotor's opening 222 overlaps the seat's opening 212, to a second position
(Figure 2B) in
which the rotor's opening 222 and the seat's opening 212 (shown using dashed
line) span
different sectors. When the rotor 220 is in the first position, the rotary
valve 200 is in the
open state, allowing a fluid to flow through the valve. When the rotor 220 is
in the
second position, the rotary valve 200 is in the closed state, thus preventing
the fluid from
flowing through the valve.
The use of rotary valves is difficult if at all feasible for compressors used
in the oil and
gas industry. Compressors used in the oil and gas industry have to meet
industry-specific
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requirements that take into consideration, for example, that the compressed
fluid is
frequently corrosive and flammable.
American Petroleum Institute (API), the
organization setting the recognized industry standard for equipment used in
the oil and
gas industry, has issued a document, API618, listing a complete set of minimum
requirements for reciprocating compressors.
Considering that valves used in oil and gas compressors typically have an
actuation time
of about 5 ms, in order to actuate rotary valves for such compressors,
voluminous
(relative to available space) actuators would be necessary. Due to potential
danger of an
explosion, electrical valve actuators (that are capable of providing the
required actuation
time) are preferably placed such as not to be in contact with the flammable
gas, the
motion generated by these actuators being mechanically transmitted to the
valve's mobile
part that is in contact with the fluid. The space necessary to place an
actuator and a
mechanism for transmitting a displacement generated by the actuator to the
valve's
mobile part may not always be available. Additionally, the crank end side of a
dual
reciprocating compressor usually has less room than the head end side.
Accordingly, it would be desirable to provide alternative solutions to the
automated
valves for reciprocating compressors used in the oil and gas industry, meeting
the
requirements and taking into consideration the limited space.
Using rotative valves in reciprocating compressors has the advantage of
controlling both
suction and discharge flow pathways with a single actuator. Rotative valves
may be
mounted at the head end and at the crank end of a dual reciprocating
compressor. Two
rotative valves in a dual reciprocating compressor may be actuated using the
same
actuator.
According to an exemplary embodiment, a reciprocating compressor has (1) a
compression chamber configured to compress a fluid that has entered the
compression
chamber via an intake, and is discharged from the compression chamber, after
being
compressed, via a discharge, (2) an actuator configured to supply an angular
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displacement, and (3) a rotative valve configured to receive the angular
displacement and
to control whether the intake and the discharge are opened or closed depending
on the
angular displacement. The rotative valve includes a rotatable disk configured
to rotate
due to the angular displacement and having a first opening, allowing a suction
fluid flow
to enter the compression chamber when the first opening overlaps the intake,
and a
second opening allowing a discharge fluid flow to exit from the compression
chamber
when the second opening overlaps the discharge.
According to another exemplary embodiment, a dual reciprocating compressor has
(1) a
body divided into two compression chambers, each compression chamber being
configured to compress a fluid that has entered the compression chamber via an
intake,
and is discharged from the compression chamber via a discharge, (2) a piston
configured
to move along the body, thereby varying volumes of the two compression
chambers, (3)
an actuator configured to supply an angular displacement, and (4) two rotative
valves
located on opposite ends of the body and configured to receive the angular
displacement
and to control whether the intake and the discharge of a respective chamber
are opened or
closed depending on the angular displacement. Each rotative valve includes a
rotatable
disk configured to rotate due to the angular displacement and having (A) a
first opening
allowing a suction fluid flow to enter the respective compression chamber when
the first
opening overlaps the intake, and (B) a second opening allowing a discharge
fluid flow to
exit from the respective compression chamber when the second opening overlaps
the
discharge. The angular actuation of at least one of the two rotative valves is
caused by
the angular displacement.
According to another exemplary embodiment, a rotative valve useable at one end
of a
compression chamber having an end plate with a suction opening configured to
allow a
suction fluid flow to enter the compression chamber, and a discharge opening
configured
to allow a discharge fluid flow to exit the compression chamber. The rotative
valve
includes a rotatable disk having a first opening and a second opening
positioned at
different angular locations such that, when the first opening overlaps the
suction opening,
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the suction fluid flow passes there-through, and when the second opening
overlaps the
discharge opening, the discharge fluid flow passes there-through.
According to another exemplary embodiment, a method of retrofitting a
reciprocating
compressor initially having two automated valves located on an end plate of a
compression chamber of the reciprocating compressor is provided. The method
includes
(1) removing mobile parts of the valves, while leaving seats of the valves in
place, each
seat having an opening toward an inside of the compression chamber, (2)
providing an
actuator configured to supply an angular displacement, (3) mounting, outside
the end of
the compression chamber, a rotatable disk having two openings at different
angular
positions, such that one of the openings of the rotatable disk overlaps the
opening of one
of the seats at a first angular position, and another one of the openings of
the rotatable
disk overlaps the opening of another one of the seats at a second angular
position,
different from the first angular position. The method further includes (4)
connecting the
rotatable disk to the actuator to enable the rotatable disk to rotate due to
the angular
displacement to positions in which one of the openings of the rotatable disk
overlaps the
openings of one of the seats, respectively, allowing a fluid flow to pass
there-through
toward or from the compression chamber.
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 schematic diagram of a conventional dual chamber reciprocating
compressor;
Figures 2A and 2B illustrate a conventional actuated rotary valve in an open
state and in a
closed state, respectively;
Figure 3 is a schematic diagram of a single chamber reciprocating compressor
according
to an exemplary embodiment;
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Figure 4 is an illustration of a rotatable disk of a rotative valve according
to an exemplary
embodiment;
Figure 5 is a schematic diagram of a double chamber reciprocating compressor
according
to an exemplary embodiment;
Figure 6 is a schematic diagram of a double chamber reciprocating compressor
according
to an exemplary embodiment; and
Figure 7 is a flowchart of a method of retrofitting a reciprocating compressor
according
to an exemplary embodiment.
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 the oil and gas industry. However, the embodiments to be
discussed
next are not limited to these compressors, but may be applied to other systems
that require
the supply of force at a low price and with a reduced footprint.
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.
As discussed relative to the background art, one technical problem related to
the use of
actuated valves in reciprocating compressors is that an actuator capable of
providing an
angular displacement in a very short time (i.e., approximately 5 ms) is
relatively
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voluminous and electrical. Due to the flammable nature of the fluid in the oil
and gas
industry, the actuator is not to be in contact with the fluid, and the
actuation motion has
then to be transmitted to the valve's mobile part, which is in contact with
the fluid. The
space necessary to fit an actuator and the transmission mechanism for each
valve may not
be available in meaningful proximity to the reciprocating compressor's valves.
Some of
the embodiments described below use a single actuator for controlling (i.e.,
opening and
closing) two flow paths to/from a compression chamber. Moreover, in some
embodiments, the same actuator controls all four flow paths to/from two
compression
chambers of a dual reciprocating compressor.
According to an exemplary embodiment illustrated in Figure 3, a single chamber
reciprocating compressor 300 has a compression chamber 310 configured to
receive a
fluid via an intake 320, compress the fluid and then discharge it from the
compression
chamber 310 via a discharge 330. Whether the fluid flow pathways to the
compression
chamber 310 from the intake 320 and from the compression chamber 310 to the
discharge
330 are opened depends on the position of openings of a rotatable disk 340
which rotates
due to an angular displacement supplied by an actuator 350. The rotatable disk
340 is the
switching (moving) component of a rotative valve that controls whether the
fluid flows
toward and from the compression chamber 310. The openings of the rotatable
disk 340
are configured to match the intake 320 and the discharge 330 at certain
angular positions.
The intake 320 and the discharge 330 are formed in a head end 360 of the
compression
chamber 310. A cover 365 separates the ambient from the volume in which the
rotatable
disk 340 is located.
The fluid compression is performed cyclically due to a back-and-forth motion
of a piston
370 along an axis 375 correlated with timely opening or closing of the intake
320 and the
discharge 330 by the rotatable disk 340.
A frontal view of the rotatable disk 340 is illustrated in Figure 4. The
rotatable disk 340
has a first opening 342 through which the fluid flow enters the compression
chamber 310
when the first opening 342 overlaps the intake 320. The rotatable disk 340
also has a
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second opening 344 through which the fluid flow exits the compression chamber
310,
when the second opening 344 overlaps the discharge 330.
An angular displacement of the rotatable disk 340 is transmitted from the
actuator 350 via
a gear mechanism. The angular displacement may be a continuous rotation (one
direction) or an alternating (clockwise and counter-clockwise) rotation. The
actuator 350
is preferably placed outside the fluid for avoiding the danger of explosion
(given that
fluids are likely flammable). The gear mechanism includes a valve stem 380
penetrating
through the cover 365. A gear 382 is attached to the end of the valve stem 380
and
meshed with the rotatable disk 340 (i.e., teeth 382A of the gear 382 engage
teeth 340A of
the rotatable disk 340), inside the volume filled with fluid between the disk
340 and the
cover 365. Another gear 384 is attached to the other end of the valve stem
380. One end
of an actuator stem 390 is attached to the actuator 350, and the other end is
attached to a
gear 392, which is meshed with the gear 384 (i.e., teeth 384A of the gear 384
engage
teeth 392A of the gear 392). The valve stem 380 may have collars 386 and
bushings 388
on both sides of the cover 365 to enhance its stability in operation.
In Figure 3, the actuator 350 and the gear mechanism are illustrated to be
located closer
to the intake 320. However, in other embodiments it may be closer to the
discharge 330
or located at another location around the compression chamber 310. No relative
dimensional relationship between components should be inferred from Figure 3
or other
exemplary embodiments illustrated in the figures.
A dual chamber (or action) reciprocating compressor is more frequently
employed in the
oil and gas industry than the single chamber (or action) reciprocating
compressor. Figure
5 illustrates a dual chamber reciprocating compressor 500 according to another
exemplary embodiment. The fluid is compressed due to the back-and-forth
movement of
a piston 510 provided inside a body 520, between a head end plate 530 and a
crank end
plate 540. The piston 510 divides the body 520 into two compression chambers
522 and
524 that operate in different phases, the volume of compression chamber 522
being at its
lowest value when the volume of compression chamber 524 is at its highest
value and
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vice-versa. The piston 510 moves back and forth due to energy received, for
example,
from a crankshaft (not shown) via a crosshead (not shown) and a piston rod
512.
An intake 532 and a discharge 534, which communicate with the compression
chamber
522, are formed through the head end plate 530. Similarly, an intake 542 and a
discharge
544, which communicate with the compression chamber 524, are formed through
the
crank end plate 540. Outside the body 520, rotatable disks 550 and 560, are
disposed at
the head end and at the crank end, respectively. The rotatable disks 550 and
560 are
configured to rotate due to the angular displacement received from actuators
570 and 580,
respectively. Each of the rotatable disks 550 and 560 has a first opening
allowing a fluid
flow to enter the respective compression chamber, 522 or 524, when the first
opening
overlaps the intake 532 or 542, respectively. Further, each of the rotatable
disks 550 and
560 has a second opening allowing the fluid flow to exit from the respective
compression
chamber, 522 or 524, when the second opening overlaps the discharge, 534 or
544,
respectively. A structure of the rotatable disks 550 and 560 may be similar to
the
rotatable disk 340 shown in Figure 4. Some of the details at the crank-end
side (i.e.,
around the rotatable disk 560) are omitted to keep the relevant details clear.
Gear assemblies 575 and 585 are configured to transmit the angular
displacement from
the actuators 570 and 580, respectively, to the rotatable disks 550 and 560,
respectively.
Covers 555 and 565 separate a fluid volume from the ambient. A detailed
description of
each of the components of the gear assemblies is omitted because the gear
assemblies are
similar to the gear assembly described for the single chamber compressor 300.
Although in Figure 5, the dual chamber reciprocating compressor 500 is
illustrated as
having rotative valves (as defined by the rotatable disks) 550 and 560 at both
a head end
and at a crank end thereof, alternative embodiments may have a rotative valve
only at one
of the head end and the crank end, having other types of valves at the other
end of the
compression chambers.
Figure 6 illustrates a dual chamber reciprocating compressor 600 having
rotative valves
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at both the head end and at the crank end. The rotative disks 550 and 560 of
the
compressor 600 are actuated by the same single actuator 590 instead of two
actuators 570
and 580 in Figure 5. Description of the components of the reciprocating
compressor 600
similar to those of the reciprocating compressor 500 is not repeated.
Existing reciprocating compressors with automated valves can be retrofitted to
use
actuated rotative valve(s). A method 700 of retrofitting a reciprocating
compressor
initially having two automated valves located on an end plate of a compression
chamber
of the reciprocating compressor is illustrated in Figure 7. The method 700
includes
removing mobile parts of the automated valves, while leaving seats of the
automated
valves in place, each seat having an opening toward an inside of the
compression
chamber at S710. The seat of a suction valve may serve as the intake, and the
seat of the
discharge valve may serve as the discharge.
The method 700 further includes providing an actuator configured and connected
to
supply an angular displacement, at S720, and mounting, outside the end of the
compression chamber, a rotatable disk having two openings at different angular
positions,
at S730.
The method 700 also includes connecting the rotatable disk to the actuator to
enable the
disk to rotate due to the angular displacement to positions in which one of
the openings of
the disk overlaps the opening of one of the seats, respectively, allowing a
fluid flow to
pass there-through toward or from the compression chamber, at S740.
The method 700 may further include mounting a gear mechanism to transmit the
angular
displacement from the actuator to the rotatable disk. The gear mechanism may
be
configured to penetrate though a cover of the reciprocating compressor
separating a
volume filled with fluid from ambient, where the actuator is located.
If the retrofitted reciprocating compressor is a dual chamber reciprocating
compressor
having two back-to-back compression chambers in a body, and initially having
two other
automatic valves located on an opposite end of the body than the end on which
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automatic valves are located, the method 700 may further comprise steps to
replace the
two other automatic valves with another rotative valve. Thus, the method 700
may
further include (1) removing mobile parts of the other two valves while
leaving seats of
the other two valves in place, each seat having an opening toward an inside of
another
compression chamber, (2) mounting, outside the opposite end, another rotatable
disk
having two other openings at different angular positions, and (3) connecting
the other
rotatable disk to the actuator, to enable the other rotatable disk to rotate
due to the angular
displacement to positions in which one of the openings of the other rotatable
disk
overlaps one of the two other openings, respectively, allowing a fluid flow to
pass there-
through toward or from the other compression chamber.
The disclosed exemplary embodiments provide reciprocating compressors with at
least
one rotative valve and a method for retrofitting existing reciprocating
compressors to
have at least one rotative valve. 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.
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Such other examples are intended to be within the scope of the claims.
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