Valve operator including a fugitive emissions detector, and a method of detecting fugitive emissions from an industrial valve

Abstract

A valve operator for a valve includes a valve operator housing defining at least one cavity and positioned to be at least partially contiguous with a valve stem passage of the valve. The cavity has a fixed volume and is sealed from the exterior environment. The valve operator includes a fugitive emissions detector having at least one sensor for measuring the pressure and temperature of the fluid within the interior of the cavity. The detector also includes a processor having an input for receiving data from the at least one sensor, a processing unit connected to the input to receive the data from the input and monitor changes in the amount of substance within the cavity by comparison of changes in temperature and pressure within the cavity and an output for providing an indication of fugitive emissions when the processor indicates an increase in substance within the cavity.

Claims

1. A valve operator for a valve, the valve operator comprising: a valve operator housing including: at least one cavity defined within the valve operator housing and positioned to be at least partially contiguous, in use, with a valve stem passage of the valve, the cavity having a fixed volume and being sealed from the exterior environment; and a fugitive emissions detection arrangement, the arrangement including at least one sensor for measuring a pressure and temperature of any fluid within the interior of the cavity; and a processor including an input for receiving data from the at least one sensor; the processor being communicably connected to the input and configured to receive the data from the input and monitor the proportional change in the number of moles within the cavity by comparison of changes in temperature and pressure within the cavity; and an output for providing an indication of fugitive emissions when the processor indicates an increase in the number of moles within the cavity, wherein the processor determines the proportional change in the number of moles within the cavity by calculating: $\frac{n}{n}=\frac{P_1{T}_0}{P_0{T}_1}-1$ wherein $\frac{n}{n}$ is the proportional change in the number of moles; P.sub.0 is the original measured cavity pressure (datum pressure); P.sub.1 is the current measured cavity pressure; T.sub.0 is the original measured cavity temperature (datum temperature); and, T.sub.1 is the current measured cavity temperature; and wherein: $\frac{n}{n}=0$ indicates no leak, and, $\frac{n}{n}>0$ indicates the presence of fugitive emissions.

2. A valve operator as claimed in claim 1, wherein the valve is an industrial valve.

3. A valve operator as claimed in claim 1, wherein the at least one sensor is in direct communication with the interior of the cavity.

4. A valve operator as claimed in claim 1, wherein the at least one cavity is provided with an overpressure vent outlet.

5. A valve operator as claimed in claim 1, wherein the processor is local to the valve operator.

6. A valve operator as claimed in claim 1, wherein the valve operator further comprises a network module in the form of a transmitter connected to the processor to interface with a remote monitoring system.

7. A valve operator as claimed in claim 1, wherein the valve operator housing further comprises a sealing face configured, in use, to sealing engage a flange, the flange being provided on the valve and surrounding the valve stem passage, so as to isolate the cavity from the external environment when mounted to the flange.

8. A valve operator as claimed in claim 7, wherein the sealing face of the valve operator includes at least one resilient sealing member.

9. A valve operator as claimed in claim 1, wherein the processor is configured to determine a change by monitoring changes in pressure relative to changes of temperature within the cavity.

10. A valve operator as claimed in claim 1, further comprising additional sensor devices for detecting the operational status of the valve and/or valve operator.

11. A valve operator as claimed in claim 1, further comprising a motor for rotating a drive shaft in use and an output driven by the drive shaft and arranged for driving a valve stem of the valve in use.

12. A valve operator as claimed in claim 11, wherein the output comprises a gear, which may for example be driven by a worm associated with the drive shaft.

13. A valve monitoring system as claimed in claim 12, further comprising a wired or wireless network.

14. A method of detecting fugitive emissions from a valve, the method comprising: providing a housing, having a cavity with a fixed internal volume, the cavity being in fluid communication with a leak path from a valve stem passage of the valve, isolating the cavity from the external environment; using at least one sensor to measure a pressure and temperature of any fluid within the interior of the cavity; and monitoring for proportional changes in the number of moles in the cavity using the detected change in pressure and detected change in temperature within the cavity, wherein the step of monitoring the proportional charge in the number of moles in the cavity includes calculating: $\frac{n}{n}=\frac{P_1{T}_0}{P_0{T}_1}-1$ wherein $\frac{n}{n}$ is the proportional change in the number of moles; P.sub.0 is the original measured cavity pressure (datum pressure); P.sub.1 is the current measured cavity pressure; T.sub.0 is the original measured cavity temperature (datum temperature); and, T.sub.1 is the current measured cavity temperature; and wherein: $\frac{n}{n}=0$ indicates no leak, and, $\frac{n}{n}>0$ indicates the presence or fugitive emissions.

15. A valve comprising: a valve member; a valve actuation stem for moving the valve member in use; and a housing, at least partially enclosing the valve, and including a portion defining a valve stem passage; at least one cavity defined within the housing and positioned to be at least partially contiguous, in use, with the valve stem passage, the cavity having a fixed volume and being sealed from the exterior environment; and a fugitive emissions detection arrangement, the arrangement including at least one sensor for measuring a pressure and temperature of any fluid within the interior of the cavity; and a processor, the processor includes an input for receiving data from the at least one sensor; the processor being communicably connected to the input and configured to receive the data from the input and monitor the proportional change in the number of moles within the cavity by comparison of changes in temperature and pressure within the cavity; and an output for providing an indication of fugitive emissions when the processor indicates an increase in the number of moles within the cavity, wherein the processor determines the proportional change in the number of moles within the cavity by calculating: $\frac{n}{n}=\frac{P_1{T}_0}{P_0{T}_1}-1$ wherein $\frac{n}{n}$ is the proportional change in the number of moles; P.sub.0 is the original measured cavity pressure (datum pressure); P.sub.1 is the current measured cavity pressure; T.sub.0 is the original measured cavity temperature (datum temperature); and, T.sub.1 is the current measured cavity temperature; and wherein: $\frac{n}{n}=0$ indicates no leak, and, $\frac{n}{n}>0$ indicates the presence of fugitive emissions.

Description

DESCRIPTION OF THE DRAWINGS

(1) A specific embodiment of the invention will now be described in detail, by way of example only, and with reference to the accompanying drawings in which:

(2) FIG. 1 schematically illustrating a valve and valve operator in accordance with an embodiment of the invention; and

(3) FIG. 2 schematically illustrates a cross sectional view of a fugitive emission detection arrangement provided in a valve operator in accordance with an embodiment of the invention;

(4) FIG. 3 schematically illustrates a cross sectional view of a fugitive emission detection arrangement provided in a valve operator in accordance with an alternative embodiment of the invention.

DESCRIPTION OF AN EMBODIMENT

(5) FIG. 1 shows a typical industrial valve assembly 10 which may be used to control the flow of fluids in industrial applications. For example, the valve assembly 10 could be used oil and gas, water and waste water, power, marine, mining, food, pharmaceutical and chemical industries. The valve assembly comprises a valve having a valve member 12 connected to a valve actuation stem 14. The valve could for example be a quarter turn valve or a multi-turn valve arrangement.

(6) The valve member 12 and stem 14 are provided within a housing 16. The upper portion of the housing 16 comprises a valve stem passage 17 and terminates at a flange 18. At least one stem seal 15 is provided between the stem passage 17 and stem 14 and is intended to prevent the escape of fluid from the valve housing 16 in use. As the stem seal 15 is a non-static seal (as the stem 14 will generally rotate relative to the passage 17 during actuation) it provides a less reliable seal than static seals (for example those between the valve housing and the associated pipe or conduit. Thus, when a leakage occurs at the valve the stem seal 15 is the path of least resistance and fugitive emissions will be expected to pass beyond the seal 15 and out of the stem passage 17.

(7) The valve assembly 10 also includes a valve operator 20. The valve operator 20 drivingly engages an upper drive portion of the valve stem 14 and provides a means for controlling and actuating the valve member 12 in use. The valve operator 20 is provided within a valve operator housing 22 which is arranged to be connected to the valve housing 16 via the flange 18. The box designated 21 defines a motor for rotating a driveshaft in use and an output driven by the driveshaft and arranged for driving the valve stem 14 in use. The output comprises a gear, which may for example be driven by a worm associated with the driveshaft. In its simplest form the valve operator could be a manual operator such as a hand-wheel (which may include an associated gearing arrangement). In the example of FIG. 1 the valve operator represents an electrical valve actuator (for example one of the IQ actuator range available form Rotork Controls Limited). In some embodiments the valve operator may also be an intermediate component in a valve actuation system; for example a gearbox or adaptor which is connected to the valve flange 18 to drivingly engage the stem 14 but which in turn receives a further actuator to power and or control the intermediate component.

(8) As best seen in the schematic partial cross section of FIG. 2, in accordance with embodiments of the invention, the valve operator 20 is provided with an integral fugitive emissions detection arrangement 45 (the components and operation of which will be described below).

(9) The valve operator 20 is connected to the valve flange 18 in any conventional manner. The mating surface of the valve operator housing 22 provides a sealing face 23 which abuts the corresponding upper face of the valve flange. The sealing face is provided with at least one sealing member 24, for example an O-ring received in a recess 25. With the valve operator 20 mounted on the valve housing 16, the sealing arrangement effectively forms a seal around the upper end of the valve stem passage 17.

(10) The valve operator 20 is provided with a cavity 30 which is defined within the interior of the housing 22. The cavity 30 may have any convenient shape or profile. The cavity 30 shape will depend upon the particular valve operator 20 and may for example be formed of a plurality of interlinked sub-cavities or chambers. However, regardless of the particular profile, at least a portion 32 of the cavity 30 must be contiguous with the valve stem passage 17 when the valve operator has been installed on the valve. Due to the sealing around flange 18 and the sealing surface 23 (which is a static seal so can be considered to allow a nominally perfect seal), the cavity 30 defined by the housing 22 is the only outlet (via the contiguous portion 32) from the stem passage 17 if fugitive emissions escape beyond the stem seal 15.

(11) To prevent dangerous pressure levels developing within the cavity 30, an overpressure outlet 34 is provided to enable venting of the, normally sealed, cavity 30 to the external atmosphere. A pressure controller 35 such as a valve or rupture diaphragm closes the overpressure outlet 34 during normal operation such that venting only occurs at a predetermined pressure based upon a nominal safety value for the pressure within the housing 22 of the operator 20. The operation of the fugitive emissions arrangement will, during normal operation, be unaffected by the presence of the overpressure outlet 34 as the sensitivity of the fugitive emissions detection can be selected to be significantly below the level of fugitive emissions which would be required to result in an overpressure situation.

(12) A temperature 42 and pressure 44 sensor are provided within the valve operator 20 and configured to allow direct monitoring of the fluid within the cavity 30. The temperature 42 and pressure 44 sensors provide information on the conditions within the cavity 30 to a processor 40 (which may for example be a logic solver). In the illustrated embodiment the processor 40 is locally provided integral to the valve operator 20. It will, however, be appreciated that alternatively raw data could be transmitted to a remote control or monitoring location which could include the processor. The valve operator may optionally be provided with additional status sensors such as a valve position sensor 46, which may be connected to an encoder device 47.

(13) To allow for monitoring of multiple valve devices, and preferable live and continuous monitoring, the processor 40 may be provided with a network module or transmitter 48 to interface with a remote monitoring system 50. For example the processor may connect via a field network 55 which could be either a wired or wireless system.

(14) Once the valve operator 20 in accordance with an embodiment has been installed on a valve the pressure and temperature information provided by the sensors 42, 44 may be utilised by the processor 40 to detect fugitive emissions.

(15) The processor utilises the Ideal Gas Law:
PV=nRT Where: P Pressure (Pa) V Volume (m3) n Chemical Amount (mol) R Ideal Gas Constant T Temperature (K)

(16) On the valve operator 20, the Volume V of the cavity 30 is constant. Further, the fugitive emissions detection is only required to determine a proportional change in the number of moles (i.e. not the absolute number) in order to detect a leak. Thus, the following equation can be derived:

(17) $\frac{n}{n}=\frac{P_1{T}_0}{P_0{T}_1}-1$
Where:

(18) $\frac{n}{n}$ is the proportional change in the number of moles; P.sub.0 is the original cavity pressure (i.e. a datum pressure); P.sub.1 is the current (measured) cavity pressure; T.sub.0 is the original cavity temperature (i.e. a datum temperature); and T.sub.1 is the current cavity temperature. if

(19) $\frac{n}{n}=0,$ there is no leak.

(20) As a result, the processor 40 may calculate any proportional change in n within the cavity 30 using the readings for P and T provided by the sensors 42 and 44 within the valve operator 20. As the cavity is sealed in normal operation, any detected change in n will be indicative of fugitive emissions entering the cavity 30 from the valve stem passage 17.

(21) It is important to note that by assuming the volume of the cavity is constant the implementation of embodiments of the invention on different valve and valve operators is greatly simplified since the processor 40 need only measure changes in pressure and temperature.

(22) An alternate embodiment of the invention is shown in FIG. 3. In this embodiment the cavity 30 is formed below the flange 18 by providing a pair of spaced apart sealing arrangements on the shaft 14. It will be appreciated that the shaft 14 may be an output extending from an actuator and connected in use to the valve stem. The shaft 14 may be integral with the valve stem. The skilled person will appreciate that the shaft 14 may be considered to be a valve operator in the context of the present invention.

(23) The shaft 14 is contained within a shaft housing 22 which is contiguous with the valve stem passage of the valve. A cavity 30 is formed around the shaft 14 by the shaft housing 22 and a pair of sealing elements spaced axially apart along the length of the shaft 14. In the illustrated embodiment the sealing elements comprise a primary seal formed by a pack 19 and a secondary seal (which may be a conventional shaft seal) 15. The pack 19 is positioned below the shaft seal 15, but it will be appreciated that depending upon the particular arrangement of the housing 22 and shaft 14 the order/type of seals may be reversed. Thus an annular cavity 30 having a fixed volume is defined between the shaft 14, housing 22 and seals 15 and 19.

(24) Sensors 42 and 44 are provided and measure the temperature and pressure within the cavity 30 (although it will be appreciated that alternatively a single sensor may be arranged to sense both pressure and temperature). Data from the sensor(s) relating to pressure and temperature of within the chamber is provided to a processor as in the preceding embodiment and the change in pressure and change in temperature may be used to indicate a change in the substance (i.e. the amount of fluid) within the cavity and provide an indication of fugitive emissions.

(25) It will be appreciated that other features of the first embodiment may be incorporated into the second embodiment without departing from the scope of the invention. For example the cavity 30 may be provided with an overpressure vent to allow for controlled evacuation in the event of excess fugitive emissions. Further it will be appreciated that the housing 22 may be either formed integrally with the valve housing or may be attached to the housing in any convenient manner (with appropriate sealing provided).

(26) It will be appreciated from the above description that embodiments of the invention may provide an advantageous arrangement in which the valve operator include an integrated fugitive emissions detection arrangement. Advantages of embodiments may include one or more of the following: No labour input being required after commissioninformation is relayed via a field network (wired or wireless) to appropriate personnel. This information will be live and continuous. Direct detection of leaking fluid. Embodiments may be used as a diagnostic tool which can lead to improved and more effective asset management. Embodiments may aid in reducing volume of fluid released to the environment by fugitive emissions via prompt notification to appropriate personnel. This could lead to significant reductions in the severity of any leaks and the timely repair or replacement of leaking equipment. The detection does not rely on previous empirical data. Minimises the need for preventative maintenance. Does not require specific knowledge of the valve. Not affected by external noise. Can be used for a variety of fluids. Does not interfere with valve operation (i.e. has no effect on the production process).

(27) Although the invention has been described above with reference to a preferred embodiment, it will be appreciated that various changes or modifications may be made without departing from the scope of the invention as defined in the appended claims. For example, whilst the described embodiment utilises a single cavity to detect fugitive emissions, the skilled person could readily envisage that in a system requiring redundancy it may be possible to define a plurality of cavities and to apply the methodology of the invention to each cavity independently.