Patent Application
20070056354
This invention relates generally to gas detecting systems, and more particularly to systems for detecting gas, e.g., hydrogen, leakage from point of connection joints in gas transport and/or storage systems.
In systems for conveying and/or storing gas, the detection of leakage of that gas is of considerable importance, particularly for applications involving flammable, explosive or otherwise hazardous gases. For example, in cryogenic applications, where hydrogen gas may be stored in tanks or other vessels and conveyed through conduits as gas or liquid, one common source of potential hydrogen gas leakage is at any releasably securable joint connecting two components of the system, e.g., a gasketed joint between two flanged conduits. Such releasably securable joints are typically held together by means of bolts extending through aligned openings in the confronting flanges or by clamps or some other means. Since the bolts/clamps are typically located at spaced positions about the periphery of the confronting flanges, if one or more of the bolts/clamps should not be tightened appropriately to form a gas-tight seal, the hydrogen gas may leak out of the gasket adjacent to the improperly tightened bolt/clamp. Thus, the leakage point can be at any position(s) about the periphery of the joint. Moreover, even if the bolts/clamps are tightened appropriately, there may be one or more local breaks or defects in the gasket (O-ring or metal annular disk). Thus, the hydrogen gas can escape through that(those) break(s)/defect(s).
Past technology has used handheld flammable gas detectors to search for leaks. In another prior art technique, joints are encapsulated to capture all leakage and that gas is presented to one leak detector. However, such prior art systems are not without their drawbacks, e.g., false alarms could occur from other flammable gases in the area (e.g., gasoline and oil emissions from nearby autos). In addition, often times the leak can be missed by an operator not placing the gas leakage sensor close enough or in the right position relative to the source of the leak under the ambient weather conditions (temperature, wind direction and humidity). The low density of hydrogen exacerbates leak detection because leaked hydrogen gas may rise in non-intuitive ways compared to heavy hydrocarbons, which can sink. Leakage found in captured joints does not provide leak location, other than somewhere around the joint, and additional work needs to be performed to locate the leak. In addition, captured joints do not provide information on multiple leaks in the same joint.
The patent literature includes several systems for detecting gas leaks. See for example, EP1482292A2, which is assigned to the same assignee as this application. That application discloses an apparatus and process for measuring the concentration of hydrogen gas being transferred through a nozzle from a source container to a destination container and for providing an alert and/or taking action where hydrogen gas leaks may create an unsafe condition. Other gas sensor configurations are shown in U.S. Pat. No. 5,279,795 (Hughes et al.); U.S. Pat. No. 6,293,137 (Liu et al.); U.S. Pat. No. 5,012,672 (McKee); U.S. Pat. No. 4,782,302 (Bastasz), U.S. Pat. No. 5,834,627 (Ricco et al.); and U.S. Pat. No. 5,932,797 (Myneni) and in Japanese applications JP2003149071A2, JP11023403A2 and JP03035138. See also, a paper by Mendoza, Kempen, Menon, Durets, Pflanze, Lieberman and Kazemi entitled “Multipoint Fiber Optic Hydrogen Sensor System For Detection of Cryogenic Leaks in Aerospace Applications” in “Proceedings of SPIE—The International Society For Optical Engineering (2001), 4204 (Fiber Optic Sensor Technology II), 139-150 and a paper by Keding, Kruse and Rieling appearing in Technische Ueberwachung (Dusseldorf) (2000), 41(4), 32-37.
While the aforementioned prior art systems may be suitable for their intended purposes they nevertheless leave much to be desired from one or more of the standpoints of simplicity of construction, ease of use, molecular specificity (e.g., hydrogen) and ability to determine the precise location of a leak. With respect to the latter drawback of the prior art, since the gas leak can be anywhere around the circumference of the joint, locating the leak in any direction can be a hit or miss proposition. If no directionality can be made, then all the bolts holding the joint together will likely be tightened, which action can lead to over tightening and bolt/gasket failure.
Accordingly, a need exists to provide a system and method for determining where/when and how much (concentration of species per unit volume of air) a gas leakage is occurring in gas transport and/or gas storage areas that have multiple leak potentials, e.g., in one or more joints each formed by a pair of confronting flanges held together by multiple bolts/clamps where one bolt is not tightened enough and allows gas leakage in that small area, or where the gasket or other sealing means may have a local break or leak.
The subject invention overcomes many of the drawbacks of the prior art by making use of a plurality of sensors located at positions, e.g., stationary or fixed, as close as possible to potential leak site(s) to provide signals indicative of a leak to a data acquisition unit which can then determine or identify the dominant leak direction, whereupon corrective action can be taken, e.g., tightening the bolt(s) closest to the leak. Moreover, the subject invention optionally enables one to monitor and/or track changes in the leakage rate. All of this is accomplished through the use of an array of small sensors which do not take up significant space and are readily adapted to be mounted adjacent the potential gas leak site(s).
A detection system for detecting gas, e.g., hydrogen, leaking out of a connecting joint having an interface formed of first and second confronting surfaces. The joint has a first outer surface, e.g., a flange, located adjacent the first confronting surface and a second outer surface, e.g., a flange, located adjacent the second confronting surface. The joint may form a portion of a gas transport and/or storage system wherein the confronting surfaces are held together by plural bolts, with a gasket located at the interface formed between the confronting surfaces.
The detection system 20 basically comprises a plurality, e.g., an array, of gas sensors and an associated data acquisition unit. The plural sensors are adapted for mounting at spaced locations with respect to one another about at least a portion of at least one of the first and second outer surfaces, e.g., the flanges, closely adjacent the interface. The data acquisition unit can be arranged to be located on the flange or remote from the interface. Each of the plural gas sensors comprises a base and a gas detecting element mounted on the base. The gas detecting element of each sensor is coupled, e.g., wired, to the data acquisition unit to provide a signal thereto.
The base of each sensor is configured, e.g., is a flexible base, or a small footprint base, etc., to enable the gas detecting element associated therewith to be readily mounted onto a portion of the first or second outer surface of the joint at a respective one of the spaced locations irrespective of the contour of the portion of the surface thereat. The data acquisition unit is arranged to receive signals from the sensors to provide an indication of leakage of gas at the interface of the joint and an indication of the location of the portion of the interface at which the leakage has occurred.
Referring now to the various figures of the drawing wherein like reference numbers refer to like parts, there is shown in
Before describing the gas leakage detection system 20, a brief description of the exemplary gas transport and/or storage system 10 is in order. To that end, as can be seen in
Notwithstanding the tightening of the bolts/nuts hydrogen gas, within the system shown may tend to leak out through one or more of the gaskets at the connecting joints in one or more locations about the periphery of that (those) gasket(s). To that end, the gas leakage detection system 20 is provided to rapidly detect any such leaks and to identify the location of such leaks to operating personnel or to take some automated action, e.g., shut down or isolate the portion of the system at which the leak is occurring.
The details of the leakage detection system 20 will be described later. Suffice it for now to state that the system 20 basically includes plural gas sensors 22, a data acquisition unit 24 and a remote computer/control system 26 (
It should be mentioned at this juncture that in the exemplary embodiment shown in
In the exemplary embodiment of
Various types of conventional sensors can be used in the subject invention. One particularly effective sensor is the H2SCAN flexible hydrogen sensor that is commercially available from H2Scan of Valencia, Calif. That sensor includes a detector element 22A mounted on a base or backing 22B formed of a Mylar type material for flexibility. The base or backing is quite thin, e.g., <2 mm thick. Accordingly, as best seen in
Since the base 22B of each sensor 22 is flexible and thin, each sensor 22 can be located and mounted on any shaped surface, e.g., the circular outer periphery of the flange 11B, adjacent a joint to be monitored, irrespective of the contour of that surface. In
Irrespective of the type of sensors utilized, e.g., whether a sensor of the type shown in
The output signal from the data acquisition unit is arranged to be provided to a remotely located computer/control system 26. One exemplary embodiment of the computer system 26 is shown in
In order to prevent or otherwise minimize the occurrence of the sensors 22 becoming fouled or otherwise degraded by dust, moisture or other adverse ambient conditions, each of the sensors 22 is preferably provided with a hollow cap 30 to protect the gas detecting element 22A of the sensor. The cap 28 can be of any suitable shape. In the exemplary embodiments each cap basically comprises an inverted cup-like member that is disposed over an associated gas detector 22A and base 22B of the sensor 22. The cap material of construction will be selected as not to restrict gas permeation to the sensor. The peripheral edge of the sidewall portion of each cap 28 is preferably in abutment with or immediately adjacent the underlying surface of the portion of the joint on which the sensor is mounted. Since any gas that will tend to leak out of the gasket (such as shown schematically by the arcuate arrows in
While the invention has been described in detail and with reference to specific examples thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.
