To achieve optimum flare reliability it is necessary to select the best equipment, and then to seek operational reliability of the system as a whole. The best place to start is the flare itself. If the flare is to be normally lit, then pilots should be considered a requirement in the majority of cases. Systems with critical flaring requirements (such as sour gas flares) must operate pilots, continuously monitor them and have a reliable ignition system – often with a suitable backup system.
Pilot gas supply should be stable and continuous. The number of and duty of the pilot burners should be determined by the size of the flare and its application. The pilot gas flow to achieve the required duty is dependant upon the composition of the available pilot gas.
The main components of a pilot burner comprise an inspirator assembly (which includes a venturi and inspirator jet nozzle) and a pilot nozzle. The flow of the pilot gas through the jet and into the venturi draws in air through the inspirator assembly. This air then mixes with the fuel gas and flows up to the burner nozzle where it is ignited and the resultant pilot flame is stabilised. Reliable operation of the pilot burner is governed by achieving the right air fuel ratio for the pilot gas being used. Too much air and the pilot will be unstable, too little air and the pilot will struggle to light unless enough secondary air is available around the pilot nozzle.
Generally pilot burners are ignited at the pilot nozzle, however more sophisticated designs ignite the fuel air mix above the venturi but before the pilot nozzle and the resulting flame travels up inside the pilot tube to the nozzle where it is stabilised. This type of design serves to protect the ignition components from damage caused by flame impingement and can therefore offer improved longevity.
Pilot burners have to be designed to withstand rain, wind and high temperatures along with direct flame impingement from the flare tip. As the pilot burner nozzle is typically subjected to thermal cycling by being frequently engulfed in flame from the flare itself, Argo Flare Services offer a material upgrade for the pilot nozzle in Alloy 556 material as standard (this has been shown to provide a demonstrable improvement to service life).
Although many flares are operated without pilot burners, it should be recognised that flare reliability is compromised where pilot burners are not fitted.