Pilot status can be determined by several means including heat, ionised gas, light or sound. Trying to view the pilots from grade however is a very uncertain method. Operationally, on an offshore facility it may be feasible to use a burst of rich gas in the pilot line to produce a larger yellow flame to help see a pilot, but even this can pose difficulties. To give constant feedback of pilot status one of the following systems will need to be used:
- Heat – Thermocouples
- Ionised Gas – Flame ionisation detection
- Light – IR or UV systems
- Sound – Acoustic systems
Thermocouple flame detection is the most commonly used system and typically used in association with flame front and high energy ignited pilot burners. The pilot is considered to be ‘on’ when the thermocouple set point has been reached. Key to reliability of this system is protection of the thermocouple mounting in the pilot burner nozzle.
HT ignition systems generally use flame ionisation detection for flame monitoring as they can utilise the same cable for ignition and monitoring. The weak point of this type of monitoring is providing adequate protection of the ignition/detection cable.
Generally positioned at grade, and therefore serviceable whilst online, these units use a special camera lens aimed at the flare to detect infra red and/or ultra violet light from the flame. Whilst affective at determining flame presence, it is not always possible to confirm pilot flame presence over the flare flame. Additionally extreme weather conditions can obscure the line of slight.
Similar to optical monitoring in that the detection equipment is positioned away from the pilot, acoustic monitoring systems respond to the specific sound signature of a pilot burning that is transferred along the pipe work.
Where pilots are not used, typically on pellet driven ignition, or direct spark ignition systems, the issue of flame detection is much easier. Light based systems, or even a video link may be sufficient. To work effectively with ignition systems it may also be advisable to confirm the presence of hydrocarbon gas. This can best be done with the latest Ultrasonic Flare Gas Meters. If gas presence is confirmed, and the flare is out, then the ignition system needs to be operated, or alarm raised.
Although a large number of platforms and FPSOs operate without a fully functional pilot ignition system and still get good day to day flaring reliability using a ‘Very’ pistol/signal gun to ignite the flares, Argo advise the use of a continuous pilot and flame detection system in order to ensure flame stability at both high flow and low flow purge conditions for all normally lit flare tips. Argo supplied pilot and ignition systems are supplied with thermocouple flame monitoring as standard.