 Current Technology - The Problem
 Flammable gas sensors are used extensively in offshore and onshore oil and gas installations to detect and give warning of the build-up of explosive levels of combustible gases, most typically methane.
Conventionally this detection has been carried out using the so called Pellistor or catalytic sensor. This detects flammable gases by burning the target gas on a heated filament, surrounded by a reaction enhancing catalyst, inside an explosion proof Exd enclosure.
The burning gas causes the resistance of the heater filament to rise and this change of resistance is remotely sensed in a Wheatstone Bridge circuit in comparison with a reference heated filament in the Pellistor enclosure that does not have the catalytic enhancement. These sensors are installed at strategic points in the hazardous installation area and are wired back to remote control and monitoring equipment with three core armoured cables connected to the Pellistor through a junction box.
The problem is that Pellistor sensors have been found to be unreliable. Pellistor sensors are subject to a number of effects from the environment; |
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They are prone to calibration drift. |
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In high gas concentrations they will provide false and unsafe readings. |
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Pellistors are 'poisoned' by contaminating chemicals. |
Poisonous chemicals react with the catalyst during the burning process and causing an inert layer to be built upon its surface. This build-up severely degrades the Pellistor's ability to detect gas, but is not evident at all during normal operation.
Typical poisons are;
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Silicones |
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Sulphur compounds |
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Chlorine compounds |
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Heavy Metals |
As a result Pellistors need regular maintenance, typically every 3 months. This high maintenance regime when coupled with regular sensor replacements and multiple sensor point arrays all adds up to a high cost of ownership.
To view the AMGas Solution click here. |
