U.S. patent application number 13/288026 was filed with the patent office on 2012-02-23 for partial stroke testing system coupled with fuel control valve.
Invention is credited to Tareq Nasser AL-BUAIJAN.
Application Number | 20120042721 13/288026 |
Document ID | / |
Family ID | 45592993 |
Filed Date | 2012-02-23 |
United States Patent
Application |
20120042721 |
Kind Code |
A1 |
AL-BUAIJAN; Tareq Nasser |
February 23, 2012 |
PARTIAL STROKE TESTING SYSTEM COUPLED WITH FUEL CONTROL VALVE
Abstract
A system for on-line testing of an emergency shut-off valve
includes a first emergency shut-off valve (first valve) and a flow
control valve (second valve), with the system being configured to
allow the second valve to serve as a combination flow control and
second emergency shut-off valve. A subsystem is also provided for
testing the first valve without fully closing the first valve in
response to a signal from the control. In this subsystem, a
solenoid valve bleeds off pressurized fluid to move the first valve
from a fully opened to a partially closed position. A bypass around
the second valve allows it to be tested as the second emergency
shut-off valve, allowing the second valve to close completely
without shutting down the process. The use of the two emergency
shut-off valves in series wherein either valve can shut down the
process provides a level 3 safety integrity level.
Inventors: |
AL-BUAIJAN; Tareq Nasser;
(Yarmok, KW) |
Family ID: |
45592993 |
Appl. No.: |
13/288026 |
Filed: |
November 3, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12038830 |
Feb 28, 2008 |
8074512 |
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13288026 |
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Current U.S.
Class: |
73/168 |
Current CPC
Class: |
F15B 20/00 20130101;
F15B 19/005 20130101; F16K 37/0075 20130101 |
Class at
Publication: |
73/168 |
International
Class: |
G01L 19/00 20060101
G01L019/00 |
Claims
1. A partial stroke testing system coupled with fuel control valve,
comprising: a combustion gas delivery line; a selectively operable
gas shutoff valve disposed along the combustion gas delivery line;
a selectively operable combination gas control and shutoff valve
disposed along the combustion gas delivery line, the combination
gas control and shutoff valve being disposed in series with the gas
shutoff valve; a control system for selectively automatically or
manually substantially completely closing and reopening the gas
shutoff valve; a control system for selectively automatically or
manually partially closing and opening the gas shutoff valve; and a
control system for selectively automatically or manually
substantially completely closing and reopening the combination gas
control and shutoff valve.
2. The partial stroke testing system according to claim 1, further
comprising: a gas vent line extending from the gas delivery line
and between the gas shutoff valve and the combination gas control
and shutoff valve, the gas vent line having a distal end; and a gas
combustion port disposed at the distal end of the gas vent
line.
3. The partial stroke testing system according to claim 1, further
comprising: a combustion gas bypass line disposed in parallel about
the combination gas control and shutoff valve; and at least one
selectively openable and closable bypass line shutoff valve
disposed along the combustion gas bypass line.
4. The partial stroke testing system according to claim 1, further
comprising: a gas shutoff valve actuator communicating
pneumatically with the gas shutoff valve; a pneumatic pressure line
communicating pneumatically with the gas shutoff valve actuator; a
main solenoid valve disposed in the pneumatic pressure line, the
main solenoid valve selectively controlling pneumatic pressure to
the gas shutoff valve actuator; a pneumatic vent line communicating
pneumatically with the pneumatic pressure line; a second solenoid
valve disposed in the pneumatic vent line, the second solenoid
valve selectively controlling pneumatic pressure in the pneumatic
vent line; a combination gas control and shutoff valve actuator
communicating with the combination gas control and shutoff valve;
and a third solenoid valve communicating pneumatically with the
combination gas control and shutoff valve actuator; wherein closure
of any one of the main solenoid valve, second solenoid valve, and
third solenoid valve results in closure of one of the gas shutoff
valve and combination gas control and shutoff valve.
5. The partial stroke testing system according to claim 4, further
comprising: an emergency shut-off system controller communicating
electronically with the main solenoid valve, the second solenoid
valve, and the third solenoid valve; a computer communicating
electronically with the emergency shut-off system controller; and a
process control communicating pneumatically with the combination
gas control and shutoff valve actuator.
6. The partial stroke testing system according to claim 4, further
comprising a current to pressure converter communicating
pneumatically with the combination gas control and shutoff valve
actuator.
7. The partial stroke testing system according to claim 4, further
comprising: a first open limit switch, a first closure limit
switch, and a partial stroke limit switch, each of the switches
communicating with the gas shutoff valve and the emergency shut-off
system controller; and a second open limit switch and a second
closure limit switch, each of the second limit switches
communicating with the combination gas control and shutoff valve
and the emergency shut-off system controller.
8. A partial stroke testing system coupled with fuel control valve,
comprising: a combustion gas delivery line; a selectively operable
gas shutoff valve disposed along the combustion gas delivery line;
a selectively operable combination gas control and shutoff valve
disposed along the combustion gas delivery line, the combination
gas control and shutoff valve being disposed in series with the gas
shutoff valve; a control system for selectively automatically or
manually substantially completely closing and reopening the gas
shutoff valve; a control system for selectively automatically or
manually substantially completely closing and reopening the
combination gas control and shutoff valve; a gas vent line
extending from the gas delivery line and between the gas shutoff
valve and the combination gas control and shutoff valve, the gas
vent line having a distal end; and a gas combustion port disposed
at the distal end of the gas vent line.
9. The partial stroke testing system according to claim 8, further
comprising a control system for selectively automatically or
manually partially closing and opening the gas shutoff valve.
10. The partial stroke testing system according to claim 8, further
comprising: a combustion gas bypass line disposed in parallel about
the combination gas control and shutoff valve; and at least one
selectively openable and closable bypass line shutoff valve
disposed along the combustion gas bypass line.
11. The partial stroke testing system according to claim 8, further
comprising: a gas shutoff valve actuator communicating
pneumatically with the gas shutoff valve; a pneumatic pressure line
communicating pneumatically with the gas shutoff valve actuator; a
main solenoid valve disposed in the pneumatic pressure line, the
main solenoid valve selectively controlling pneumatic pressure to
the gas shutoff valve actuator; a pneumatic vent line communicating
pneumatically with the pneumatic pressure line; a second solenoid
valve disposed in the pneumatic vent line, the second solenoid
valve selectively controlling pneumatic pressure in the pneumatic
vent line; a combination gas control and shutoff valve actuator
communicating with the combination gas control and shutoff valve;
and a third solenoid valve communicating pneumatically with the
combination gas control and shutoff valve actuator; wherein closure
of any one of the main solenoid valve, second solenoid valve, and
third solenoid valve results in closure of one of the gas shutoff
valve and combination gas control and shutoff valve.
12. The partial stroke testing system according to claim 11,
further comprising: an emergency shut-off system controller
communicating electronically with the main solenoid valve, the
second solenoid valve, and the third solenoid valve; a computer
communicating electronically with the emergency shut-off system
controller; and a process control communicating pneumatically with
the combination gas control and shutoff valve actuator.
13. The partial stroke testing system according to claim 11,
further comprising a current to pressure converter communicating
pneumatically with the combination gas control and shutoff valve
actuator.
14. The partial stroke testing system according to claim 11,
further comprising: a first open limit switch, a first closure
limit switch, and a partial stroke limit switch, each of the
switches communicating with the gas shutoff valve and the emergency
shut-off system controller; and a second open limit switch and a
second closure limit switch, each of the second switches
communicating with the combination gas control and shutoff valve
and the emergency shut-off system controller.
15. A partial stroke testing system coupled with fuel control
valve, comprising: a combustion gas delivery line; a selectively
operable gas shutoff valve disposed along the combustion gas
delivery line; a selectively operable combination gas control and
shutoff valve disposed along the combustion gas delivery line, the
combination gas control and shutoff valve being disposed in series
with the gas shutoff valve; a control system for selectively
automatically or manually substantially completely closing and
reopening the gas shutoff valve; a control system for selectively
automatically or manually substantially completely closing and
reopening the combination gas control and shutoff valve; a
combustion gas bypass line disposed in parallel about the
combination gas control and shutoff valve; and at least one
selectively openable and closable bypass line shutoff valve
disposed along the combustion gas bypass line.
16. The partial stroke testing system according to claim 15,
further comprising a control system for selectively automatically
or manually partially closing and opening the gas shutoff
valve.
17. The partial stroke testing system according to claim 15,
further comprising: a gas vent line extending from the gas delivery
line and between the gas shutoff valve and the combination gas
control and shutoff valve, the gas vent line having a distal end;
and a gas combustion port disposed at the distal end of the gas
vent line.
18. The partial stroke testing system according to claim 15,
further comprising: a gas shutoff valve actuator communicating
pneumatically with the gas shutoff valve; a pneumatic pressure line
communicating pneumatically with the gas shutoff valve actuator; a
main solenoid valve disposed in the pneumatic pressure line, the
main solenoid valve selectively controlling pneumatic pressure to
the gas shutoff valve actuator; a pneumatic vent line communicating
pneumatically with the pneumatic pressure line; a second solenoid
valve disposed in the pneumatic vent line, the second solenoid
valve selectively controlling pneumatic pressure in the pneumatic
vent line; a combination gas control and shutoff valve actuator
communicating with the combination gas control and shutoff valve;
and a third solenoid valve communicating pneumatically with the
combination gas control and shutoff valve actuator; wherein closure
of any one of the main solenoid valve, second solenoid valve, and
third solenoid valve results in closure of one of the gas shutoff
valve and combination gas control and shutoff valve.
19. The partial stroke testing system according to claim 18,
further comprising: an emergency shut-off system controller
communicating electronically with the main solenoid valve, the
second solenoid valve, and the third solenoid valve; a computer
communicating electronically with the emergency shut-off system
controller; a process control communicating pneumatically with the
combination gas control and shutoff valve actuator; and a
current-to-pressure converter communicating pneumatically with the
combination gas control and shutoff valve actuator.
20. The partial stroke testing system according to claim 18,
further comprising: a first open limit switch, a first closure
limit switch, and a partial stroke limit switch, each of the
switches communicating with the gas shutoff valve and the emergency
shut-off system controller; and a second open limit switch and a
second closure limit switch, each of the second switches
communicating with the combination gas control and shutoff valve
and the emergency shut-off system controller.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 12/038,830, filed on Feb. 28, 2008.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates to a system for improving the Safety
Integrity Level (SIL) rating of process heaters (e.g., industrial
heating systems) using partial stroke testing of an emergency
shut-off valve coupled to a supplementary fuel control valve.
[0004] 2. Description of the Related Art
[0005] In the oil, gas, petroleum and power industries, natural gas
or other combustible gas is often used to provide the required heat
or combustion motive power for the desired operation, more
generally referred to herein as a "process." Various conditions may
occur that necessitate immediate shut down or tripping of the
operations, process or plant. In those industries, a majority of
the final control elements of a shut-off system are implemented
with fast acting shut-off valves. In such industries, a majority of
the shut-off valves remain open while the process is in a safe and
controlled state. Such valves are closed only upon a plant trip,
i.e., actuation of the shutdown system of the plant, arising from
an out-of-control process or during a normal maintenance
outage.
[0006] In practice, the testing of emergency shut-off valves is
normally done during shut down of the process or plant operation.
However, there is a tendency for such valves to stick or freeze due
to corrosion or other reasons, which may lead to an unsafe
condition where the valve cannot be closed during an emergency
shutdown. This problem is exacerbated by economic conditions in the
operation of the factory or plant that have lead to a reduction in
the frequency of valve shut-offs for maintenance or testing
purposes. For example, in some operations a process or operation
may run continuously for one or more years without shutting down
the process for maintenance.
[0007] State of the art emergency shut-off systems, which control
the shut-off valves, have a number of features to detect plant or
process failures and typically include redundancies for added
reliability. However, such systems may not provide for the testing
of a shut-off valve itself other than stroking the valve. The
problem is that full stroking or completely closing the valve
causes an undesirable disruption in the process.
[0008] A number of patents have been issued in the past that relate
to the operation or stroking of industrial valves, and the increase
of reliability in such systems. An example of such is found in U.S.
Pat. No. 6,155,282, issued to Zachary et al., which discloses an
arrangement for testing solenoids individually without process
interruption. The arrangement operates in a two out of three manner
to provide relatively high safety, low spurious tripping and a
relatively low installation cost, while also enabling on-line
testing of each solenoid individually without process interruption.
Solenoid arrangements are preferably manifolded to facilitate
maintenance on any detected failure, and to simplify installation
and replacement.
[0009] A more recent U.S. Pat. No. 6,920,409, issued to Essam,
discloses an apparatus for testing the operation of an emergency
valve. As disclosed, the apparatus is for testing an emergency
valve in which a valve member is moveable by a fluid operated
actuator between a normally open or closed position and an
emergency position, closed or open respectively. The apparatus
comprises partial stroking means for the valve including means for
initiating emergency movement of the valve from its normal position
towards its emergency position, and means for returning it from a
predetermined position intermediate the normal and emergency
positions at its normal operating speed. The apparatus includes
means for detecting the loss of the controlling electrical signal
to the valve and a means for detecting the correct operation of the
valve and its associated operating components by measuring the
pressure of fluid being released from or being applied to the
actuator.
[0010] In addition, U.S. Pat. No. 7,010,450, issued to Law et al.,
discloses a combination of field device operations with overrides
and bypasses within a process control and safety system. The
process control or safety instrumented system uses function block
logic to coordinate the logic within the process control or safety
instrumented system with operational states of field devices, even
when these operational states are initiated externally to the
process control or safety system. Logic within input or voter
function blocks associated with field devices may monitor and
determine when the associated field devices are being put into
testing or calibration modes and may automatically initiate
appropriate bypass or override functionality in response to such
detected field device configuration states. Likewise, the function
block logic may automatically remove the bypass or override
functionality when the field devices are placed back into their
normal operational configuration states. This automatic initiation
of bypasses and overrides helps to prevent a safety system within a
process plant from initiating a shut-down procedure as a result of
a device test initiated manually by, for example, a handheld device
attached to a field device. Likewise, the automatic removal of
bypasses and overrides helps to prevent a safety system within a
process plant from failing to operate properly because a user
forgot to manually reset a bypass or override that was set up to
allow a device test.
[0011] Recognizing that the emergency shut-off valves can be
stroked or operated through the partial length or movement of their
full travel as a safeguard against frozen or stuck valves has lead
to a need for a simple, secure and reliable system for testing such
valves without adversely affecting production. This approach also
improves the safety of the operation.
[0012] The partial stroke testing system in accordance with my
earlier invention, described in my U.S. Pat. No. 6,435,022, which
is hereby incorporated by reference in its entirety, provides a low
cost, simple and reliable test for emergency shut-off valves in the
oil, gas, petrochemical and power industries. Such tests do not
adversely interrupt the plant or factory operation or process and
will minimize or almost eliminate the risk of a "frozen" emergency
shutoff valve in the event of an out-of-control process or
operation. Such a system is cost effective and has been designed to
utilize a shut-off valve with a fast acting piston actuator. The
system is also applicable to slow acting valves.
[0013] In processes in the oil, gas, petroleum, and power
industries, fuel to power the heaters, boilers, or the like, or
perhaps to provide fuel for a prime mover, is fed to the associated
burners or other components through a fuel control valve and a fuel
shut-off valve. The fuel control valve regulates pressure/flow to
the burners, whereas the shut-off valve is normally in a fully open
state. The shut-off valve closes to cut off fuel supply in the
event of an emergency.
SUMMARY OF THE INVENTION
[0014] This invention relates to a system for improving the Safety
Integrity Level (SIL) rating in processes or operations that employ
burners fed by a combustible gas or fuel line using partial stroke
testing of an emergency shut-off valve coupled to a supplementary
fuel control, i.e., a second valve with a bypass for enabling the
second valve to be fully closed for testing as a second emergency
shut-off valve without interrupting the process. Such systems are
particularly applicable in the oil, gas and petrochemical
industries.
[0015] From the safety point of view, the shutoff action of the
shutoff valve is of utmost importance in plant or factory
operations or processes. The operability of the shutoff valve can
be confirmed by means of the online valve partial stroke testing.
However, any failure in the internals of the shut-off valve may
lead to a fuel leakage to the heater or other component being
supplied by the combustible gas or fuel passing through the
valve(s). Introduction of a solenoid valve in the pneumatic circuit
of the fuel control valve, in which the solenoid is driven by an
emergency shut-off signal, is conceived as a means for
supplementing the fuel shutoff action and the redundancy to achieve
up to Safety Integrity Level Three (SIL-3) in plant or factory
operations.
[0016] In addition, the partial stroke testing system in accordance
with the present invention will not interfere with a plant trip,
i.e., a full shut down due to an emergency condition. Furthermore,
if a partial stroke test is being conducted at the time of a plant
trip, the partial stroke test will contribute to a more rapid
closing of the emergency shut-off valve. Thus, the partial stroking
design acts as a backup to the main trip mechanism.
[0017] Accordingly, such systems should reduce the cost of
insurance or risk coverage. In essence, the system partially closes
the emergency shut-off valve to a predetermined position to test
and confirm its ability to function and to ensure its availability
on demand in the event of a plant emergency.
[0018] The present system design can be applied to design loop
instrumentation (e.g., heater or boiler fuel loops, to piping
loops, or to any separation between high pressure loops and low
pressure loops) to achieve up to the Safety Integrity Level Three
(SIL-3) in the final element (shutoff valve) part by using a
regulator control valve as supplementary or second shutoff valve,
as required by IEC (International Electrical and Electronic
Commission)--61508 and ISA (Instrumentation, Systems, and
Automation Society)S 84.01 standards.
TABLE-US-00001 TABLE 1 IEC 61598 Safety Integrity Levels Safety
Integrity Average Probability of Failure to Perform its Design
Level Function on Demand SIL-1 >10.sup.-1 to .ltoreq.10.sup.-2
(One failure in 11 to 100 demands) SIL-2 >10.sup.-2 to
.ltoreq.10.sup.-3 (One failure in 101 to 1000 demands) SIL-3
>10.sup.-3 to .ltoreq.10.sup.-4 (One failure in 1001 to 10,000
demands)
[0019] There is also a widespread concern among process operators
about the Probability of Failure on Demand (PFD) of final shutdown
elements, such as shut-off valves used in safety applications.
Partial trip testing of the final shut-off valve coupled with the
supplementary emergency shut-off valve according to the present
invention will serve to improve the PFD rating of shut-off action
in such systems. In Table 2, the first column represents parameters
of interest, where MTTF is the mean time to failure, xv is the
shut-off valve, cv is the control valve, Ti is the test interval,
and PITT is partial instrument trip testing. The second column is
the test interval (in years), and the PFD in the third column is
the probability of failure on demand corresponding to the test
interval in the second column.
TABLE-US-00002 TABLE 2 Utilizing shut-off (XV) with the control
valve (CV) in 1oo2 configuration MTTF (xv) = 35 years Ti (CV) PFD
MTTF (cv) = 35 years 0.5 1.09E-4 Ti (XV) = 4 years 1 1.14E-4 Ti
(CV) = 0.5, 1, 2, 3 years 2 1.31E-4 Diagnostic Coverage (CV) = 85%
3 1.48E-4 Diagnostic Coverage (XV) = 80% T(PITT) = 1 week
[0020] A programmable logic scheme performs the function of
controlling the actuation of the partial stroke of the shutoff
valve system and the closing of the shutoff valve and the control
valve in the event of an emergency shut-off trip, to achieve up to
Safety Integrity Level Three (SIL-3).
[0021] The system is designed for implementation on an emergency
shut-off valve, which is normally movable between a fully opened
and a fully closed position, and a fuel control valve. The fuel
control valve regulates pressure/flow to the burners or other
component(s) using the gas, whereas the shut-off valve is normally
in a fully open state. The shut-off valve closes to cut off fuel
supply in the event of an emergency.
[0022] As contemplated by the preferred embodiment of the
invention, the fuel control valve will be in a position between
fully open and some regulated position and the emergency shut-off
valve will be in its fully opened position during normal operation
of a process or operation. Both valves will rapidly close to shut
down the process in the event of an emergency.
[0023] The system is designed for interfacing to the plant
emergency shut-off system controller for generating electrical
signals for initiating a test of the valves and to a source of
pressurized gas such as compressed air for driving the valve
shut-off system.
[0024] The essential control components of an emergency shut-off
valve are the main trip solenoid valve with manual reset, quick
exhaust valve and a fluid actuator. The control components of the
fuel control valve are a solenoid valve and a fluid signal from the
I/P converter to the actuator of the fuel control valve to
accomplish the fuel regulating function.
[0025] On a trip signal the solenoid valve de-energizes, signaling
the quick exhaust valve to vent the actuator and close the shut-off
valve.
[0026] The invention provides a test means for testing the
emergency shut-off valve without fully closing the emergency
shut-off valve in response to a signal from the plant emergency
shut-off system controller.
[0027] The test means includes a second solenoid valve for bleeding
off compressed air to thereby move the emergency shut-off valve
from a fully opened position to a partially closed position. Means
such as a closure limit switch which may be operable on the basis
of the movement of the shut-off valve, is provided.
[0028] Means such as a timer set to a predetermined time limit to
terminate the shut-off valve test in the event of the limit switch
failure is also provided.
[0029] In addition, means for initiating cyclic or periodic testing
and reporting of test results of the partial stroking of the
emergency shut-off valve is provided. During the partial stroke
testing, the status of shutoff valves is displayed on the monitor
of the Distribution Control System (DCS). Since the test loop is
part of the distribution control system, this provides the
opportunity to observe any changes, detect trends, set alarms, and
store this data in memory. This system may be used with any of the
facilities and with any of the capabilities provided by the
emergency shut-down (ESD) and distribution control center (DCS)
available in the control room. Also, this system will indicate the
positional change and movement of the valve and can be recorded and
used for maintenance as a diagnostic tool. The record may also be
used for insurance approval. Finally, if the test of the partial
stroke of the valve is correct, it will return to the same trend as
stored in control system memory.
[0030] These and other features of the present invention will
become readily apparent upon further review of the following
specification and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] FIG. 1 is a schematic illustration of a partial stroke
testing of a shutoff valve coupled with supplementary shutoff of a
fuel control valve in accordance with a preferred embodiment of the
invention.
[0032] FIG. 2 is a flowchart that illustrates the operation of the
partial stroke testing system software residing in the plant
emergency shut-off system controller, in accordance with the
present invention.
[0033] FIG. 3 is a flowchart that illustrates the operation of the
software residing in the plant emergency shut-off system
controller, controlling the partial stroking means in the event of
an emergency trip signal from the plant emergency shut-off system
controller in accordance with the present invention.
[0034] Similar reference characters denote corresponding features
consistently throughout the attached drawings.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0035] It is well known in the oil, gas and petrochemical
industries that emergency shut-off valves are susceptible to a
build-up of frictional forces which if undetected can cause failure
of the emergency shut-off valve during an out of control process or
operation. Accordingly, the various regulatory agencies concerned
with the safety of such operations mandate periodic shut-off valve
testing and inspection in order to ascertain shut-off valve
operability.
[0036] As disclosed herein, a partial stroke valve test system
tests an emergency shut-off valve on-line, i.e., without shutting
down the process, for free movement over a reduced portion of its
full stroke. Therefore, tests can be performed at frequent
intervals. By so doing, there is a high probability of ensuring the
emergency shut-off valve's operability, which reduces the
likelihood of failure of the emergency shut-off valve during
extended runs.
[0037] In the oil, gas and petrochemical industries, emergency
shut-off valves generally remain open while the operation or
process is in a safe and controlled state. These valves close only
upon a plant trip, i.e., the actuation of the emergency shutdown
system of the factory or plant, which arises from an out of control
process or operation. The emergency shut-off valve typically
includes a pneumatic cylinder that drives the emergency shut-off
valve into a fully closed position within about one second.
[0038] The partial stroke testing system 10, incorporated with a
shut-off valve for use in the oil, gas, petrochemical and power
industries, is illustrated schematically in FIG. 1. Such a system
includes an emergency shut-off valve 20 installed in series in a
supply or delivery line 21 for the combustible gas used for the
process(es) or operation(s) accomplished in the factory or plant.
The emergency shut-off valve 20 remains in a fully open position
during normal process conditions or operations. Compressed air or
other gas from a source 22, e.g., conventional compressor or
pressurized tank or container, etc., is used for maintaining the
valve 20 in an open position. The compressed air or gas maintains
the valve 20 in an open position by driving a spring biased piston
actuator 24. The compressed air or gas flows through a pneumatic
line or tubing 23 through a main solenoid valve 26 and line 25 to a
quick exhaust valve 28, thence to the actuator 24 through the line
27.
[0039] In the event of a plant trip, i.e., an out of control
process or operation, a signal as for example from the plant
emergency shut-off system controller 30 actuates a solenoid 32 that
closes the main solenoid valve 26 with respect to the pressurized
air from the source 22 and allows the air or gas from tubing or
line 25 to exhaust through an exhaust port 26A. The release of
pressure against the quick exhaust valve 28 opens the exhaust port
28A allowing the actuator 24 to bleed through tubing 27, quick
exhaust valve 28 and exhaust port 28A, thereby closing the shut-off
valve 20 to shut down the flow of combustion gas for the process or
operation of the plant or factory.
[0040] The partial stroke testing portion of the system 10 includes
a second solenoid 40 and second solenoid valve 42. That portion
also includes an isolation valve 44 that may be operated manually,
as indicated by the manual control extending to the right of the
isolation valve 44 in FIG. 1. The second solenoid valve 42 is
operatively connected to the actuator 24 through pneumatic line or
tubing 47, isolation valve 44, tubing or line 43 and "T" connection
45 through pneumatic line or tubing 27.
[0041] A combination flow control and shut-off valve 57 is also
installed in the combustible gas supply line 21, in series with the
previously discussed emergency shut-off valve 20. The valve 57 is
shown to the lower left portion of FIG. 1. A valve actuator 57A
operates the valve 57, controlling the valve 57 and thus regulates
the flow of combustible gas therethrough for the plant or factory
operation. A trip event will also actuate a third solenoid 69 (left
portion of FIG. 1) by means of an electrical signal 60 from the
system controller 30, which opens solenoid valve 68 to release the
air pressure from the actuator 57A of the control valve 57, causing
it to close the valve 57 completely as an emergency shut-off. The
trip event or electrical signal 70 (lower portion of FIG. 1) from
the emergency shut-off control 30 also actuates a fourth solenoid
62, which opens solenoid valve 61 to bleed the gas trapped between
the control valve 57 and the shutoff valve 20 if there is any
remote possibility of a leak from the control valve 57. Such
combustible gas leakage (if any) is vented to the flare system 63,
with the system terminating in a gas combustion port at the top or
distal outlet end of the system 63 for any vented combustible gas.
A manual reset 64 is provided to prevent an auto start before reset
of the system, permitting operators of the system check it prior to
restart.
[0042] Closure limit switch (ZSL) 77 and open limit switch (ZSH) 78
indicate the opening and closing of the control valve 57. During
the trip event, closure limit switch 77 will be on, i.e.,
electrically closed or activated, and open limit switch 78 will be
off, i.e., electrically open or inactive.
[0043] Isolation valves 59 and 66 provide isolation for solenoid
valves 61 and 68, respectively, for maintenance requirements. The
valves 59 and 61 are connected in series to the vent 63 and its
distal gas combustion port to the atmosphere.
[0044] Valves 75, 76, and 73 are components of the bypass system to
be used for any required maintenance of the control valve actuator
57A and control valve 57 or during a full stroke test of the valve
57. The control valve 57 also serves as a second emergency shut-off
valve, as noted further above.
[0045] Process control (PC) 71, current to pressure converter (FP)
74, and pressure transmitter (PT) 72 are part of the control
process loop used in the petrochemical and power plant
industries.
[0046] A key feature of the present invention resides in the use of
the control valve 57 as a second emergency shut-off valve. A bypass
571 extends around the valve 57 in order to enable this function.
In practice, the control valve 57 is provided in the combustible
gas supply or delivery line 21 and is in series with the first
emergency shut-off valve 20. The control valve 57 can be isolated
from the system by the bypass 571 for fully stroking the control
valve 57 for testing or to allow the control valve 57 to act as a
second emergency shut-off valve. Valves 73, 75 and 76 are used to
bypass the combination control valve and second emergency shutoff
valve 57 so that the second emergency shutoff valve 57 can be fully
stroked without shutting down the system. In such cases, the first
emergency shutoff valve 20 fully protects the system in the event
of an emergency. However, when the first emergency shut-off valve
20 is being tested, the control valve 57 serves as a second
emergency shut-off valve to protect the plant or system in the
event of a true emergency.
[0047] For a partial stroke test of the emergency shut-off valve
20, a signal from the plant emergency shut-off system controller 30
actuates the second solenoid 40, which opens the second solenoid
valve 42 to bleed off compressed air from the actuator 24 and
associated pneumatic lines or tubes so that the spring biased
actuator 24 partially closes the shut down valve 20. This partial
closing is limited by partial stroke limit switch 52, which sends a
signal to plant emergency shut-off system controller 30 in a
conventional manner. The plant emergency shut-off system controller
30 deactivates the solenoid 40 to thereby close the second solenoid
valve 42 and the shut-off valve 20 returns to a fully open state.
By limiting the movement of the shut down valve 20 by time or
stroke, there is no interruption of the flow of gas through the
supply or delivery line 21. Nevertheless the open limit switch 53
and partial stroke limit switch 52 provide signals to the plant
emergency shut-off system controller 30 that the valve 20 actually
moved, which indicate that it is not frozen or stuck. Suitable
sensing means such as a conventional linear variable transducer can
also be used to check that the valve 20 has in fact been displaced
in response to the signal from the plant emergency shut-off system
controller 30. If the linear variable transducer indicates that a
preselected degree of deflection has occurred, the valve tested has
been shown to be free to move.
[0048] However, if the sensing means indicates that the deflection
has not occurred, a signal is sent to the plant emergency shut-off
system controller 30 indicative of the fact. A suitable alarm is
provided to indicate that the valve 20 is stuck and that corrective
action should be initiated.
[0049] The magnitude of the displacement of the valve 20 may be any
suitable degree to positively indicate that the valve movement is
possible, but must not be of such magnitude as to disrupt the
process or the plant operation and will ordinarily be accomplished
in a few seconds or less.
[0050] The plant emergency shut-off system controller 30 may be
interfaced to a computer 54 to initiate periodic partial stroking
of the shut-off valve 20. The computer 54 is also used to record
the results of each test, which may be printed out on a printer 56.
The manually operated isolation valve 44 is used to isolate the
second solenoid valve 42 from the shut-off valve system for
maintenance without affecting the operation of the shut-off valve
20.
[0051] The manual latch facility 37 of the solenoid 32 of the main
solenoid valve 26 allows the operators to manually open the
shut-off valve 20, after field verification, subsequent to a trip
and reset of the trip signal.
[0052] The control sequence for conducting the partial stroke test
of the first shut-off valve 20 (FIG. 1), programmed into the plant
emergency shut-off system controller 30 (FIG. 1), is illustrated in
FIG. 2. The Partial Instrument Trip Testing (PITT) or partial
stroking of the shut-off valve 20 is initiated by the plant
emergency shut-off system controller 30 (FIG. 1) by initiating the
execution of the program sequence illustrated in FIG. 2. Starting
at step 160 the plant emergency shut-off system controller 30 (FIG.
1) energizes power supply to the solenoid 40 (FIG. 1) of the
solenoid valve 42 (FIG. 1) and starts an internal timer as
indicated in step 161. On energizing the solenoid 40 (in FIG. 1),
the solenoid valve 42 (FIG. 1) opens and bleeds the actuator air
supply, causing the actuator 24 (in FIG. 1) to move the shut-off
valve 20 (FIG. 1) towards the closed position.
[0053] The shut-off valve movement to partial limit is checked in
step 164. If the shut-off valve 20 (FIG. 1) has reached the partial
limit, the program sequence proceeds to step 166 to de-energize the
solenoid 40 (in FIG. 1) to close the solenoid valve 42 (FIG. 1) and
to stop the timer. The actuator 24 (FIG. 1) on closure of the
solenoid valve 42 (in FIG. 1) gets full air supply and drives the
shut-off valve 20 (in FIG. 1) to its fully open position. The
program sequence then proceeds to step 168 to indicate the status
of the test as pass and to step 170 for generating a test report
and archiving the test data. After generating the test report and
archiving the test data (valve tag no., test status, test duration,
and/or other data), the test control sequence is terminated at step
172 and diverted to other applications in the plant emergency
shut-off system controller 30 (FIG. 1).
[0054] In the event that the shut-off valve 20 has not closed to
its partial limit in step 164 and the test timer (PITT timer) has
not timed out as in step 171, the control sequence returns to step
162 and loops through steps 164 and 171 until the valve 20 reaches
the partial limit or the PITT timer times out.
[0055] In the event that the shut-off valve 20 has not closed to
its partial limit in step 164 and the test timer (PITT timer) has
timed out as in step 171, the control sequence goes to step 173 to
de-energize the solenoid 40 (FIG. 1) to close the solenoid valve 42
(FIG. 1). The actuator 24 (FIG. 1) on closure of the solenoid valve
42 (FIG. 1) gets full air supply and drives the shut-off valve 20
(FIG. 1) to its fully open position. The program sequence then
proceeds to step 175 to indicate the status of the test as fail and
to step 170 for generating a test report and archiving the test
data. After generating the test report and archiving the test data
(valve tag no., test status, test duration, etc.), the test control
sequence is terminated at step 172 and diverted to other
applications in the plant emergency shut-off system controller 30
(FIG. 1).
[0056] The PITT solenoid valve 42 (FIG. 1) will remain energized,
i.e., open, until the trip is reset. The additional bleed
introduced by the solenoid valve 42 (FIG. 1) will enhance the
shut-off performance of the shut-off valve 20.
[0057] A partial stroke testing system for on line testing of
emergency shut off valves can also be implemented as a portable
self contained test apparatus for conducting partial stroke tests
on shut off valves which are controlled by non-programmable
shut-off systems.
[0058] FIG. 3 of the drawings provides a flow chart that somewhat
resembles that of FIG. 2. However, the flow chart of FIG. 3
encompasses the closure of both the shut-off valve 20 and the
control or regulating valve 57, as would occur in a complete system
shutdown. Following the initial start point 300 in FIG. 3, the
three solenoid valves most critical to the operation of the
shut-off valve 20 and the control or gas flow regulating valve,
i.e., valves 26, 42, 68, and 61, are actuated, as indicated in the
first step 302 of FIG. 3. This results in the loss of pneumatic
pressure to the main shut-off valve actuator 24 as the main
solenoid valve 26 closes, and the venting of pressure from the
pressurized pneumatic line 27 to the actuator 24 as the Partial
Instrument Trip Testing (PITT) valve 42 opens. The regulator
solenoid valve 68 also opens to release pneumatic pressure from the
control or regulator valve actuator 57A, thus resulting in the
closure of the control or regulator valve 57. The vent solenoid 62
is also actuated to open the vent solenoid valve 61, in order to
vent any residual gas and/or gas leakage in the main gas supply
line 21 between the shutdown valve 20 and the control valve 57. The
timer (included with the plant emergency shutdown system controller
30 of FIG. 1) is also started at this point, as indicated in step
302 of FIG. 3.
[0059] The operation continues as indicated in the following step
304 of the flow chart of FIG. 3 until the main shutdown valve 20
and the control or regulator valve 57 are completely closed (step
306 of FIG. 3). If the valves do not fully close within the period
allotted by the timer, the system continues to attempt to close the
valves, as indicated by the flow chart looping back from step 306
to step 304 in FIG. 3. Assuming that the two valves 20 and 57 do
close completely, thereby shutting down the system, the stroke
timer is stopped (step 308 of FIG. 3) and a report is generated
(step 310 of FIG. 3). This terminates the shutdown program, as
indicated by the final step 312 of FIG. 3.
[0060] Normally, the two solenoids 40 and 69 respectively for the
main solenoid valve 26 and the regulator solenoid valve 68 receive
continuous electrical power to hold the main solenoid valve 26 open
and the regulator solenoid valve 68 closed. Cutting the electrical
power to these two solenoids 40 and 69 will result in a reversal of
state for their two valves, with the main solenoid valve 26 closing
and the regulator solenoid valve 68 opening. However, no electrical
power is normally supplied to the solenoids 40 and 62 respectively
for the Partial Instrument Trip Testing (PITT) valve 42 and the
vent solenoid valve 61, with those valves normally remaining
closed. Transmittal of appropriate electrical power to actuate
their two solenoids 40 and 62 results in the opening of the two
valves 42 and 61, thereby venting pneumatic pressure from the
shutdown valve actuator system and gas pressure from the combustion
gas supply line 21 between the shutdown valve 20 and the control or
regulator valve 57 to the vent 63 and its gas combustion port or
flare. However, the system may be revised to obviate the need for
electrical power to the two solenoids 40 and 69 and to require
electrical power to the solenoids 40 and 62 for normal operation,
if so desired.
[0061] Analysis of the above-described system as illustrated in the
schematic drawing of FIG. 1 will demonstrate the redundancy of the
valve system and the reliability thus provided for the system. It
is not necessary for all three of the system valves, 26, 42, and 68
to operate in order to shut down the gas flow through the
combustion gas delivery line 21. (As the vent or relief valve 61
does not actually control either the shutdown valve 20 or the
combination control and shutdown valve 57 directly, it is not
included in the discussion of the redundancy and reliability of the
system.) Rather, the operation (closure or opening, as appropriate)
of any one of the main solenoid valve 26, PITT or second solenoid
valve 42, and regulator or third solenoid valve 68 will result in
the closure of either the main shutdown valve 20 or the combination
control (regulator) and shutdown valve 57. The table below
illustrates the redundancy and corresponding reliability of the
system.
TABLE-US-00003 TABLE 3 System Reliability Shutdown Signal in Demand
From Emergency Shutdown Controller System Valve 26 Valve 42 Valve
68 Shutdown Status 0 0 0 0 1 0 0 1 0 1 0 1 1 1 0 1 0 0 1 1 1 0 1 1
0 1 1 1 1 1 1 1
[0062] The above Table 3 illustrates the operation of the three
valves 26, 42, and 68, and the resulting system shutdown when the
valves operate. The number "1" indicates valve operation in each of
the valve columns and corresponding system shutdown in the right
hand "status" column. The character "0" indicates failure of valve
operation and corresponding failure of the system to shut down,
with system shutdown failure occurring only in the situation of the
top row when all three valves fail to operate.
[0063] As an example of the above, consider the second row of
binary characters. In this row, the main shutoff solenoid valve 26
has operated (closed), as indicated by the 1 in the Valve 26
column. However, the remaining two valves, i.e., the Partial
Instrument Trip Testing (PITT) valve 42 and the control or
regulator solenoid valve 68 are shown to be inoperative, i.e.,
remaining closed as indicated by the 0 character in their
respective columns. In such a situation the control or regulator
valve 57 would remain open, as the solenoid valve 68 controlling
pneumatic pressure in this part of the system would remain closed,
thus failing to vent the control pressure for the actuator 57A. The
actuator 57A would thus continue to hold the control or regulator
valve 57 open to allow gas flow therethrough. Also, the PITT valve
42 would not relieve the pneumatic pressure to the actuator 24 of
the shutdown valve 20. However, the closure of the main solenoid
valve 26 results in a loss of pneumatic pressure to the actuator
24, thus causing the actuator 24 to close the shutdown valve
20.
[0064] It will be seen that similar scenarios occur when any one of
the three valves 26, 42, or 68 operate on demand to shut down the
system, even though the other two valves fail to operate. This
redundancy results in the desired system shutdown in 2.sup.3-1
scenarios, or seven out of eight scenarios, as can be seen in Table
3. The reliability provided thus meets or exceeds the standards
required by Safety Integrity Level (SIL)-3, requiring no more than
one failure in 1,001 to 10,000 demands.
[0065] In fact, the system reliability is even greater than that
described above due to the operation of the vent control solenoid
valve 61, serving to vent combustion gas from the portion of the
gas delivery line 21 between the shutdown valve 20 and the control
or regulator valve 57. When the vent control solenoid valve 61
operates according to demand, combustible gas in the delivery line
21 is vented through the vent 63 where it is discharged at the
distal combustion port or flare of the vent line 63. While this per
se is not sufficient to divert all combustion gas from the delivery
line 21 if both the shutdown valve 20 and the control valve 57
remain open, the reduction of differential combustion gas pressure
across the shutdown valve 20 relieves much of the stress on this
valve, thus allowing it to operate more freely and more reliably.
In addition, the opening of the vent control solenoid valve 61
serves to vent any combustion gas leakage past the control or
regulator valve 57, in the event that this valve 57 has been
signaled to close but remains slightly open to allow some of the
combustion gas to pass therethrough. The venting of such residual
combustion gas results in the control or regulator valve 57 serving
as a supplementary or secondary shutdown valve, as practically no
combustion gas will continue to flow past the vent control solenoid
valve 61 even when the shutdown valve 20 remains open. Thus, it
will be seen that the system of the present invention greatly
enhances the reliability of gas delivery control and emergency
shutdown systems as installed in various plants, factories, and
similar facilities.
[0066] It is to be understood that the present invention is not
limited to the embodiments described above, but encompasses any and
all embodiments within the scope of the following claims.
* * * * *