U.S. patent application number 15/750024 was filed with the patent office on 2018-08-09 for pumping system with barrier fluid delivery circuit for dry gas seals.
The applicant listed for this patent is Nuovo Pignone Tecnologie Srl. Invention is credited to Alberto GRIMALDI, Fabrizio MILONE, Giuseppe VERONICO.
Application Number | 20180223857 15/750024 |
Document ID | / |
Family ID | 54347782 |
Filed Date | 2018-08-09 |
United States Patent
Application |
20180223857 |
Kind Code |
A1 |
MILONE; Fabrizio ; et
al. |
August 9, 2018 |
PUMPING SYSTEM WITH BARRIER FLUID DELIVERY CIRCUIT FOR DRY GAS
SEALS
Abstract
A pumping system for carbon dioxide applications comprises a
plurality of centrifugal pumps each provided with one or more dry
gas seals, and one or more barrier fluid delivery circuits for
fluidly connecting the pump discharge of a pump in a running
condition to at least one dry gas seal of another pump in standby
condition. The pumps of the pumping system may be switched between
a running condition and a standby condition through a control
unit.
Inventors: |
MILONE; Fabrizio; (Florence,
IT) ; GRIMALDI; Alberto; (Florence, IT) ;
VERONICO; Giuseppe; (Florence, IT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Nuovo Pignone Tecnologie Srl |
Florence |
|
IT |
|
|
Family ID: |
54347782 |
Appl. No.: |
15/750024 |
Filed: |
August 2, 2016 |
PCT Filed: |
August 2, 2016 |
PCT NO: |
PCT/EP2016/068407 |
371 Date: |
February 2, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F04D 23/003 20130101;
F04D 29/128 20130101; F04D 13/14 20130101; F04D 25/16 20130101;
F04D 29/102 20130101 |
International
Class: |
F04D 29/10 20060101
F04D029/10; F04D 23/00 20060101 F04D023/00; F04D 25/16 20060101
F04D025/16 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 4, 2015 |
IT |
102015000041608 |
Claims
1. A pumping system, comprising at least a first pump and a second
pump, each of said pumps being provided with one or more dry gas
seals and being switchable between a standby condition and a
running condition, each of said pumps comprising at least a pump
intake and a pump discharge, the pumping system further comprising
at least a shared process fluid delivery circuit fluidly connecting
the pump discharge each of said pumps to the dry gas seal of each
of said pumps.
2. A pumping system according to claim 1, wherein said shared
process fluid delivery circuit comprises a first barrier fluid
delivery circuit fluidly connecting the pump discharge of said
first pump to a shared line and a second barrier fluid delivery
circuit fluidly connecting the pump discharge of the second pump to
said shared line, said shared line being in turn fluidly connected
to the dry gas seals of said pumps.
3. A pumping system according to claim 1, wherein said shared line
is provided with at least a reduction valve apt to reduce the
pressure of the barrier fluid coming from the pump discharges, at
least a filter, at least an heater and at least a shared
header.
4. A pumping system according to claim 1, wherein downstream to
said shared header said shared branch of said shared process fluid
delivery circuit splits into a first return branch line fluidly
connecting said shared header to said one or more dry gas seals of
the first pump, and into a second return branch line fluidly
connecting said shared header to the dry gas seals of the second
pump.
5. A pumping system according to claim 1, wherein a first check
valve is provided on said first barrier fluid delivery duct, and a
second check valve is provided on said second barrier fluid
delivery duct.
6. A pumping system according to claim 1, wherein said pumps are
centrifugal pumps.
7. A pumping system according to claim 1, wherein said fluid
discharged from the pump discharge of said first and second pump is
carbon dioxide.
8. Pumping system according to claim 1, further comprising a
control unit configured to switch the operative conditions of said
pumps and to control the operative conditions of said shared
process fluid delivery circuit.
9. A method comprising the following steps: receiving a barrier
fluid from a discharge port of a first pump into a shared process
fluid recovery circuit coupled with the discharge port; reducing
pressure of the barrier fluid; and directing the reduced pressure
barrier fluid to a dry seal of a second pump coupled with the
shared process fluid recovery circuit.
10. The method according to claim 9, wherein it further comprises
the steps of: filtering and warming the barrier fluid in said
shared process fluid recovery circuit after reducing its pressure
and before directing the reduced pressure barrier fluid to the dry
seal of the second pump.
11. The method of claim 9, wherein when the first pump is in a
running condition and the second pump is in a standby condition,
and the barrier fluid coming from the running condition is provided
to the dry seal of the standby pump.
12. The method of claim 9, further comprising the step consisting
of switching the functioning conditions of the two pumps so that
the first pump reaches a standby condition and the second pump
reaches a running condition, the barrier fluid coming from the
running condition pump is provided to the dry seal of the standby
pump.
13. A pumping system according to claim 2, wherein said shared line
is provided with at least a reduction valve apt to reduce the
pressure of the barrier fluid coming from the pump discharges, at
least a filter, at least an heater and at least a shared
header.
14. A pumping system according to claim 2, wherein downstream to
said shared header said shared branch of said shared process fluid
delivery circuit splits into a first return branch line fluidly
connecting said shared header to said one or more dry gas seals of
the first pump, and into a second return branch line fluidly
connecting said shared header to the dry gas seals of the second
pump.
15. A pumping system according to claim 2, wherein a first check
valve is provided on said first barrier fluid delivery duct, and a
second check valve is provided on said second barrier fluid
delivery duct.
16. A pumping system according to claim 2, wherein said pumps are
centrifugal pumps.
17. A pumping system according to claim 2, wherein said fluid
discharged from the pump discharge of said first and second pump is
carbon dioxide.
18. Pumping system according to claim 2, further comprising a
control unit configured to switch the operative conditions of said
pumps and to control the operative conditions of said shared
process fluid delivery circuit.
19. The method of claim 10, wherein when the first pump is in a
running condition and the second pump is in a standby condition,
and the barrier fluid coming from the running condition is provided
to the dry seal of the standby pump.
20. The method of claim 10, further comprising the step consisting
of switching the functioning conditions of the two pumps so that
the first pump reaches a standby condition and the second pump
reaches a running condition, the barrier fluid coming from the
running condition pump is provided to the dry seal of the standby
pump
Description
BACKGROUND
[0001] The present disclosure relates to a fluid pumping system,
particularly but not exclusively for pumping carbon dioxide (CO2),
comprising a plurality of pumps and a dry gas seals protecting
apparatus for protecting the integrity of dry gas seals of said
pumps, in an embodiment centrifugal pumps, during standby
conditions.
[0002] More in particular, the present disclosure relates to a
pumping system which allows to protect the integrity of the dry gas
seals of a centrifugal pump during standby conditions of said pump
for CO.sub.2 applications, e.g. the re-injection, transportation
and sequestration of pure CO.sub.2 and CO.sub.2+hydrocarbons in oil
and gas recovery plants.
[0003] The application of dry gas seals to centrifugal pumps for
the shaft sealing instead of wet seals offers several benefits,
e.g. reducing power consumption, reducing seals system footprint,
increasing the reliability and eliminating maintenance costs
related to barrier fluid refilling.
[0004] The many benefits of dry gas seals at the running conditions
of centrifugal pumps hide problems associated with the use of dry
gas seals on centrifugal pumps at other operating conditions such
as in the standby condition, as it will be more clearly explained
in the following.
[0005] Gas, and in particular CO.sub.2, leakage across the primary
seal is normal because also in the standby condition the pump is
pressurized and ready to start.
[0006] Therefore, the gas pressure inside the pump is higher than
the external, atmospheric, pressure. Downstream of the primary seal
there is a pressure established by a buffer fluid, typically
nitrogen or air available at a pressure of four to six bar.
Further, the higher pressure and un-treated process gas permeates
the primary dry gas seal, transporting particulate and liquid
contamination.
[0007] This problem is emphasized with carbon dioxide (CO2) as the
process flow, and or with any other fluid which may change phase
(ice or liquid) due to the fluid expansion through the seal. The
carbon dioxide (CO2) expansion through the tight tolerances of the
dry gas seal rings can form ice on the seal rings. Subsequently,
when the pump returns to normal operating conditions, the
contamination between the dry gas seal rings results in premature
wear and failure of the dry gas seal.
[0008] With reference to FIGS. 1 to 3, a known configuration
comprising a single centrifugal pump utilizing a dry gas seal is
shown.
[0009] FIG. 1 discloses a detailed diagram of a related art
configuration of a dry gas seal (DGS) system 100 for a carbon
dioxide (CO2) pump. It should be noted in this configuration that
any fluid in a supercritical state can be used as a barrier fluid
in place of the exemplary carbon dioxide (CO2).
[0010] The configuration of FIG. 1 reflects the behavior of the dry
gas seal during operating conditions and includes a CO2 pump 102
with its associated area to be sealed, a primary (inboard) seal 104
of a dry gas seal, a secondary (outboard) seal 106 of the dry gas
seal, a process fluid filter 108, a process fluid heater 110, a
valve and control element 120 for controlling the flow to a
flare-safe area, an intermediate buffer gas filter 114,
intermediate buffer gas 116, barrier fluid 118, pressure reduction
valve 120, a primary dry gas seal chamber 122 and a secondary dry
gas seal chamber 124.
[0011] In the related art configuration of FIG. 1 is shown a
process fluid, e.g. carbon dioxide, from the pump discharge being
used as a barrier fluid. The pressure of the barrier fluid is
reduced by a valve 120 and heated by a heater 110. The barrier
fluid is then filtered by filters 108 and injected into the primary
dry gas seal chamber 122.
[0012] The pressure of the barrier fluid is higher than the suction
pressure of the pump and therefore it prevents the entry of any
untreated process gas into the primary seal 104.
[0013] The barrier fluid (carbon dioxide) flows partly into the
pump through the inner labyrinth and partly to the primary vent
through the primary dry gas seal. Next in the related art
configuration, the carbon dioxide (CO2) that flows into the pump
reaches a suction pressure that is higher than the critical
pressure for carbon dioxide (CO2) and accordingly no problems of
icing will occur. Further in the considered configuration, the
carbon dioxide (CO2) that flows through the primary seal to the
primary vent expands from P1 to a value established by the buffer
gas (typically N2/air at 4-6 bar). It should be noted that in the
known configuration the temperature of the carbon dioxide (CO2)
barrier fluid should be maintained, by a heater, to a value high
enough to avoid, during the expansion, the risk of icing.
[0014] An intermediate buffer gas 116, e.g. nitrogen or dry air is
filtered by filters 114 and injected into the secondary dry gas
seal chamber 124. It should be noted in the known configuration
that other gases than nitrogen or air can also be used as a buffer
gas. The pressure of the intermediate buffer gas 116 is higher than
the pressure of the barrier gas passing through the primary seal
104 and prevents the barrier gas from reaching the secondary seal
106.
[0015] In the known configuration, the mixture of barrier gas 118
and intermediate buffer gas 116 in the secondary dry gas seal
chamber 124 passes through a valve 112 and flows to a flare-safe
area.
[0016] FIG. 2 shows the same diagram of FIG. 1 when the pump is in
a standby condition. In this condition the discharge pressure from
the pump is equal to the pressure in the area to be sealed 102.
When the pump is in a standby condition, the pressure into the pump
reaches a uniform value very close to the suction pressure.
[0017] It should be noted that in the related art configuration the
result of the standby condition is the process fluid from the pump
discharge can no longer act as a barrier fluid to prevent the flow
of untreated process fluid, from the area to be sealed 102, into
the primary seal 104. Furthermore, the untreated process fluid is
not heated or filtered and therefore contaminates can enter the
primary seal 104 and icing can occur in the primary seal 104.
[0018] Due to the fact that the pump is pressurized also in the
standby condition, there is a natural carbon dioxide (CO2) leakage
across the primary seal when the pump is in standby condition.
[0019] According to the state of the art, the reference is to FIG.
3, in order to avoid risks of damages and icing when the pump is in
standby condition additional boosters, not shown in the drawing,
are provided for the barrier fluid 118 to maintain the barrier gas
at the conditions provided during running condition of the pump.
This solution requires the similar treatment of the process fluid
with respect to filtering and heating to prevent contamination of
the dry gas seal.
[0020] Plants for carbon dioxide (CO.sub.2) applications, e.g. the
re-injection, transportation and sequestration of pure carbon
dioxide and carbon dioxide+hydrocarbons in oil and gas recovery
plants, are here considered.
[0021] In said plants, at least one centrifugal pump is provided,
in an embodiment at least two centrifugal pumps working
alternatively are provided, so that when a first pump is in an
operative/running condition the second pump is in a standby
condition.
[0022] Switching between the pumps allows reduction in the
maintenance costs due to replacing the barrier fluid and increase
in the MTBF (Mean Time Between Failures).
[0023] Having more centrifugal pumps, each pump may work for less
time, lengthening the expected time between a fault and the other
(MTBF).
[0024] Furthermore, the use of more centrifugal pumps avoids the
plant shutdown, being able to operate a second pump when it is
necessary to perform maintenance on a first pump.
[0025] The object of the present disclosure is to provide a pumping
system suitable to achieve, among others, the advantages listed
above.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] Further details and specific embodiments will refer to the
attached drawing, in which:
[0027] FIG. 1 is a schematic view of a dry gas seal and the
associated gas support system when the pump is in an
operating/running condition;
[0028] FIG. 2 is a schematic view of a dry gas seal and the
associated gas support system when the pump is in a dangerous
standby condition (risk of damages and icing);
[0029] FIG. 3 is a schematic view of a dry gas seal and the
associated gas support system when the pump is in a safe standby
condition (no risk of damages and icing);
[0030] FIG. 4 is a schematic view of the pumping system according
to the present disclosure;
[0031] FIG. 5 represents a flowchart of the steps of the method
according to the present disclosure.
DETAILED DESCRIPTION
[0032] The following description of exemplary embodiments refers to
the accompanying drawings. The following detailed description does
not limit the disclosure. Instead, the scope of embodiments
disclosed herein are defined by the appended claims.
[0033] The present disclosure relates the oil and gas recovery
plants, i.e. on off-shore oil and gas implants. More in details,
the present disclosure concerns industrial plants for carbon
dioxide (CO2) applications.
[0034] Some of the most shared applications of carbon dioxide, are
the re-injection, transportation and sequestration of pure carbon
dioxide and carbon dioxide+hydrocarbons in oil and gas recovery
plants.
[0035] In said plants, at least one centrifugal pump is provided,
in an embodiment at least two centrifugal pumps working
alternatively are provided, so that when a first pump is in an
operative/running condition the second pump is in a standby
condition.
[0036] Switching between the pumps allows reduction in the
maintenance costs due to replacing the barrier fluid and increase
in the MTBF (Mean Time Between Failures).
[0037] Having more centrifugal pumps, each pump may work for less
time, lengthening the expected time between a fault and the other
(MTBF).
[0038] Furthermore, the use of more centrifugal pumps avoids the
plant shutdown, being able to operate a second pump when it is
necessary to perform maintenance on a first pump.
[0039] The object of the present disclosure is to provide a pumping
system suitable to achieve, among others, the advantages listed
above.
[0040] The pumping system 200 according to the present disclosure
comprises at least a first pump 300 and a second pump 400, in an
embodiment the first and the second pump are centrifugal pumps, at
least one dry gas seal being associated to each of the first and
second pump.
[0041] The pumping system 200 according to the present application
comprises a process shared fluid delivery circuit 150 in turn
comprising a first barrier fluid delivery circuit 301 which fluidly
connects the pump discharge 330 of the first pump 300 to at least
one dry gas seal of the second pump 400 to deliver a barrier fluid
to said at least one dry gas seal of the second pump 400.
[0042] The shared process fluid delivery circuit 150 according to
the present application comprises a second barrier fluid delivery
circuit 401 which fluidly connects the pump discharge 430 of the
second pump 400 to at least one dry gas seal of the first pump 300
to deliver a barrier fluid to said at least one dry gas seal of
said first pump.
[0043] According to a preferred embodiment of the present
disclosure shown in FIG. 4, the first 301 and second 401 barrier
fluid delivery circuits of said shared delivery circuit 150 merge
in a shared branch line 500 on which a reduction valve 512 suitable
to reduce the pressure of the barrier fluid coming from the pump
discharges 330, 430, a filter 514 and a heater 513 are
provided.
[0044] A shared header 515 is further provided on said shared
branch 500 downstream to said heater 513 with respect to the flow
direction. From said shared header 515, the shared branch 500
splits into two return branch lines: a first return branch line 517
which fluidly connects said shared header 515 to the dry gas seals
of the first pump 300, said first return line 517 in turn
comprising a first 517a and a second 517b barrier fluid delivery
sections, each of said sections of said first return line 517 being
fluidly connected to one of said dry gas seals of the first pump
300, and a second return branch line 518 which fluidly connects
said shared header 515 to the dry gas seals of the second pump 400,
said second return branch line 518 in turn comprising a first 518a
and a second 518b barrier fluid delivery sections, each of said
first 518a and second sections 518b of said second return line 518
being fluidly connected to one of the dry gas seals of the second
pump 400.
[0045] With reference to FIG. 4, the process fluid, e.g. carbon
dioxide (CO2), coming to the shared header 515 from the first pump
discharge 330 of the first pump 300 is used as a barrier fluid for
the dry gas seals of the second pump 400 when, in an operative
condition, said first pump 300 is in a running condition and said
second pump 400 is in a standby condition.
[0046] In the same way, the process fluid coming to the shared
header 515 from the second pump discharge 430 of the second pump
400 is used as a barrier fluid for the dry gas seals of the first
pump 300 when, in an operative condition, said second pump 400 is
in a running condition and said first pump 300 is in a standby
condition.
[0047] The pressure of the barrier fluid is reduced by the
reduction valve 512 and filtered by the filter 514 and then heated
by the heater 513. The barrier fluid is then injected into the dry
gas seal chamber of the pump in the standby condition.
[0048] To give an example, when the first pump 300 in in a running
condition, the process fluid is bled from the discharge 330 of the
first pump 300 through the first barrier fluid delivery circuit 301
and enters the shared branch line 500.
[0049] The pressure of the process fluid is then reduced in the
shared branch 500 by the reduction valve 512, and then the fluid is
filtered by the filter 514 and heated by the shared heater 513.
[0050] The process fluid, ready to be used as barrier fluid for the
gas seals, then flows into the shared header 515 where all the
fluctuations, due to discontinuous operations, are smoothed and the
fluid properties are stabilized. In this way the most fragile
components of the dry gas seals, that are the sealing faces, are
protected from abrupt pressure changes.
[0051] Downstream to the shared header 515 the process fluid flows
through the second return branch line 518 to the dry gas seals of
the second pump 400, which is in a standby condition.
[0052] A first check valve 302 is provided on said first barrier
fluid delivery duct 301, and a second check valve 402 is provided
on said second barrier fluid delivery duct 401.
[0053] The pumping system 200 according to the present disclosure
as above described, is therefore adapt to feed a flow of fluid, for
example carbon dioxide (CO2), from the pump discharge of a first
running pump 300 and to flush the dry gas seal or seals of the
second pump 400 when said second pump is in standby condition.
[0054] In the same way, when the first pump 300 is switched to a
standby condition and the second pump 400 to a running condition,
the pumping system 200 according to the present disclosure is apt
to feed a flow of process fluid from the pump discharge of the
second pump 400 ant to flush the dry gas seal or seals of the first
pump 300.
[0055] Thanks to the pumping system according to the present
disclosure, it is not necessary to provide highly reliable, and
therefore also highly expensive, auxiliary booster compressors to
provide barrier fluid to the dry gas seals of the pump which is in
a standby condition the whole time the pump is in a standby
condition. Eventually, in case that the pumping system comprises
only two pumps and both of them are in a standby condition at the
same time, it may be enough to provide the system with simpler and
cheaper boosters. In fact, with the pumping system according to the
present disclosure, said booster compressors will be switched on
only in the rare case and for the short period of time in which all
the pumps of the pumping system are simultaneously in a standby
condition.
[0056] Therefore, the pumping system according to the present
disclosure allows installing more economical booster compressors
and, because said booster compressors are rarely switched on, the
system is very reliable and energy efficient.
[0057] The pumping system 200 according to the present application
allows switching of the pump function from a running condition to a
standby condition.
[0058] When the first pump 300 is in a running condition, the pump
discharge 330 supplies the barrier fluid through the first barrier
fluid delivery circuit 301 to the shared header 515 and, finally,
to the dry gas seals of the second pump 400, which is in standby
condition.
[0059] When it is required by the circumstances, for example when
maintenance operations are necessary on the first pump, or when it
ma advantageous to operate the two pumps alternatively for shorter
periods, e.g. to increase the MTBF of the pumps, the first pump 300
is turned in a standby condition, while the second pump 400 is
turned in an operative condition. The pumping system according to
the present disclosure is highly versatile with respect to the
possibility to switch the operative conditions of the two pumps, so
that the end user has a high number of possibilities to operate the
pumps in the best way in view of the circumstances and of the
results to be achieved. Thanks to the second barrier fluid delivery
circuit 401, the second pump 400, which now is the running pump
supplies the barrier fluid through the second barrier fluid
delivery circuit 401 to the first pump, which is in standby
condition.
[0060] It will be obvious to those skilled in the art that the
pumping system may comprise more than two pumps, e.g. three or four
pumps. In these possible configurations, the pumping system will
comprise a corresponding number of barrier fluid delivery
circuits.
[0061] The pumping system 200 according to the present application
may comprise a control unit configured to switch the operative
conditions of the pumps and to control the operative conditions of
the devices provided on the barrier fluid delivery circuits.
[0062] Among the others, the pumping system according to the
present disclosure achieves the results consisting of reduction of
maintainability costs, increase of MTBF and cost reduction of
booster compressors, which are no longer necessary.
[0063] The present disclosure also concerns a method for providing
a barrier fluid to a dry seal of a pump.
[0064] The method according to the present disclosure allows to
provide barrier fluid to a dry seal of a pump when said pump is in
a standby condition and without the need to provide additional
boosters. In order to achieve this result, a first running pump is
fluidly connected, by means of a shared process fluid circuit, to
said standby pump.
[0065] The method comprises at least the following steps, disclosed
in the flowchart of FIG. 5.
[0066] A first step 1 consisting of receiving a barrier fluid from
a discharge port of a first pump into a shared process fluid
recovery circuit coupled with the discharge port.
[0067] A second step 2 consisting of reducing pressure of the
barrier fluid;
[0068] A third step 3 consisting of directing the reduced pressure
barrier fluid to a dry seal of a second pump coupled with the
shared process fluid recovery circuit.
[0069] The method here above described further comprises a further
step 2a consisting of filtering and warming the barrier fluid in
said shared process fluid recovery circuit after reducing its
pressure and before directing the reduced pressure barrier fluid to
the dry seal of the second pump.
[0070] According to the method herein disclosed, when the first
pump is in a running condition and the second pump is in a standby
condition, and the barrier fluid coming from the running condition
pump is provided to the dry seal of the standby pump.
[0071] At any time, the functioning conditions of the two pumps can
be switched so that the first pump is switched to a standby
condition and the second pump is switched to a running condition.
Thanks to the shared process fluid recovery circuit, the barrier
fluid coming from the second pump, now in a running condition, is
provided to the dry seal of the first pump, now in standby
condition.
[0072] 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.
[0073] This written description uses examples to disclose the
application, including the preferred embodiments, and also to
enable any person skilled in the art to practice the application,
including making and using any devices or systems and performing
any incorporated methods. The patentable scope of the application
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 if they have structural elements
that do not differ from the literal language of the claims, or if
they include equivalent structural elements with insubstantial
differences from the literal languages of the claims.
* * * * *