Safety in Hydrogen Applications - Vol 4 of 7, Gas detection
Industrial firms that utilize hydrogen can benefit from gas detectors and flame detectors working in tandem to swiftly pinpoint a gas leak or a subsequent flame. Given that hydrogen gas is invisible, odorless, and tasteless under normal conditions, it’s crucial to deploy a gas detection system to alert staff of a leak before it ignites. These systems can be seen as the primary defense against a hydrogen release. Quick detection can halt a leak before it leads to a fire or explosion.
Two prevalent technologies for detecting combustible gas are infrared (IR) and catalytic bead point gas detectors. An IR gas detector responds to gases that absorb IR radiation, such as methane and propane that are hydrocarbon-based. However, since hydrogen doesn’t absorb IR radiation, IR gas detectors won’t detect hydrogen and are thus not recommended. This makes catalytic bead detectors the preferred choice for detecting hydrogen at lower flammable limit (LFL) levels.
A catalytic bead sensor can detect any combustible gas that reacts with oxygen to generate heat. If the gas can combust in air, this sensor will detect it. The catalytic gas sensor typically comprises a matched pair of platinum wire-wound resistors, one of which is encased in a ceramic bead. The active catalytic bead is coated with a catalyst, while the reference catalytic bead remains untreated. This matched pair is then enclosed behind a flameproof sinter, or porous filter.
During operation, the beads are resistively heated. When a combustible gas contacts the catalytic bead surface, it is oxidized, and heat is released, causing the wire’s resistance to change. The reference (or passive) bead maintains the same electrical resistance in clean air as the active bead but does not catalyze the combustible gas. The sensor detects gas by comparing the currents. If they differ, the detector can trigger an alarm. If there is no gas cloud, both beads will have the same current, and no alarm will occur.
Catalytic bead detectors have limitations. They are vulnerable to poisoning, which can cause them to fail from exposure to silicones and other chemicals common in industrial environments. In these cases, the porous filter gets clogged, causing the active bead to behave similarly to the reference bead, which may affect the system’s accuracy or possibly prevent the detector from sensing gas. If the active bead in a catalytic detector cannot sense gas, the operator in the control room will be unaware of it. Therefore, periodic bump or proof testing with calibration gas is necessary to ensure proper sensor operation.
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When installing these gas detectors, users should remember that hydrogen, being the lightest gas, rises quickly and disperses. Therefore, installers should ensure the gas detector is positioned close to and above a location where a leak might occur or hydrogen gas might accumulate — just above a valve stem, for example. Consideration should also be given to potential pressure and direction of any leak.
Det-Tronics Catalytic Gas Sensor (CGS) provides for hydrogen detection at 0-100% (LFL/LEL). It utilizes established catalytic bead technology and is designed as a single unit with an integrated thermal barrier. The sensor features a sinter-bonded flame arrestor that offers excellent protection against electromagnetic interference (EMI).
The sensor’s housing is made of 316 stainless steel, providing excellent resistance to impact and vibration. It operates over an extended temperature range of -55oC to +125oC. The sensor comes with thread types of ?-inch NPT, 20 mm, or 25 mm, and wire lead lengths of 6 inches (150mm) or 30 inches (760mm). The CGS is compatible with all Det-Tronics combustible gas transmitters and controllers.
Det-Tronics transmitters are available equipped with digital LCD that displays the gas level and provides for maintenance. Options include features such as a backlit, heated, five-color display that allows for easy, non-intrusive configuration and calibration. These transmitters have 0-20mA and relay outputs, with selectable operation modes.
The device is certified to be explosion-proof. They offer 3-port, ?” NPT, M25, or M20 thread options and are available with aluminium or stainless steel.The CGS Model is specifically incorporated with a CGS conditioning board. The transmitter is capable of operating within a wide temperature range, from -55 degrees Celsius to +75 degrees Celsius.
Technology and Innovation Manager -India ,Middle East, Africa Bureau Veritas -Dubai Views and posts are my own.
4 个月Pravin useful insights but you need to add that the process of selection and distribution of the sensors ,its sensitivity ,nature and type is so very reliant on physical and chemical characteristics and also the pressure temp and location (mass) of potential release.,these are typically done via dispersion studies which in my opinion need to be specific to the vessel installation and demonstrated for compliance. Even in present day and time the yard has a proposal that gets accepted by class and if you follow the trail for this approval you will.notice that these specifics are missing ..so often I have seen leaks also of significant nature missed to be captured ,with hydrogen and its high velocity and physical attributes you have illustrated this is all the more important to have..