Double Block and Vent for Fuel Gas Pipe To Burner Heater

[NickVil]

Hello,
I know, according to NFPA 86 (Ovens and Furnaces) that we need to install a double block and vent on-off valves in the pipe of fuel gas that will be burned in the heater. That is what we have for Fuel Gas.
But, in adittion, we also burn some sour gas (independent pipe to burner) from the amine regenerator and from sour gas stripping unit. In this case we have just one on-off valve and one on-off vent that opens to flare. Is that enough or for this kind of service we to install an additional on-off block valve?

Best Regards

 

[JLSeagull]

The sour gas especially needs the double block for positive shutoff. Positive shutoff prevents gas from entering the firebox thus an explosion hazard. Toxic gas entering an unlighted firebox could also kill people without an explosion.

 

[CJKruger]

NickVil, we route vacuum off gas to a heater and had to put in two shut off valves. We did not put a vent between them, as the upstream gas is vented to flare anyway (but it took a long time to convince the local regulators).

The rules that applies to these situations are not always consistent. In our case, the rules strictly only apply to a stream that contains hydrocarbon (even though H2S also burns).

 

[NickVil]

Ok. Thanks for your comments. I think that given the small flow of vacuum off-gas is enough to put one block and one vent valve.
Also, what about the fuel gas that goes to the pilots (ignitor)? Is it valid to put the double block and vent valves up stream the interconection between the main fuel gas pipe and the pilot fuel gas piepe in order to avoid to install additional double block and vent valves in the fuel gas pipe that goes to pilots?

Regards