• In Fired Heaters we have natural gas for pilot and fuel gas for main burner in BMS logic mentioned if pilot pressure goes low low heaters will get totally trip.why they give this logic because we have different media for pilot and burners?If heaters continue with main burner there is any harm?



  • JON Mical, ADNOK, 1147-15pt@imco.edu.om

    Thanks Jake. Also some fired heaters with BMS logic for each Pilot Burner and Main burner has flame scanner. If few burners losses their flame scanner it leads to trip the heater totally.



  • Jake Gotham, InSite Technical Services, jake.gotham@insitetechnical.com

    You are right to challenge this. I have seen this approach taken in several furnaces, but it is poorly thought through. The purpose of the pilot is to ensure a source of ignition remains in the firebox if the main burner flame is unstable. The worst thing you can do if the pilot is unstable (i.e. low pilot gas pressure) is to create an unstable main burner flame by tripping the main burner. If the main burner trip functions properly, the furnace will shutdown safely.  But if the main burner valve doesn’t seat, the trip you describe has created a hazardous situation, not prevented one.

    A better design trips the main burner on low main burner pressure, and trips the pilot on low pilot pressure. The only thing that should trip both is the emergency shutdown button.

    You wouldn’t want to operate the furnace in the long-term without the pilots, but there is no need for an immediate trip. I have seen a furnace with a delayed trip – i.e. if the pilot gas pressure isn’t restored within a number of hours, the main burner trips. But most furnaces don’t trip the main burner at all if the pilot pressure is low, and that’s the solution I would advocate.

    It is also worth bearing in mind that lighting a furnace is one of the most hazardous activities an operator has to do. Every time a furnace trips, somebody has to relight it. This is another reason to push back against unnecessary main burner trips.