Detonation of process gases when burner restarts

[gregsippel]

I am building a fume incinerator which destructs flammable gases which will be generated inside a muffle during a continuous process. The muffle is just a pipe that is heated externally by electric heaters. Our product (a powder) is pushed thru the pipe, and it is heated in a nitrogen atmosphere. The powder offgases hydrogen, ammonia, carbon monoxide, all of which are flammable. These gases are sent to a fume incinerator, which is fired by a natural gas burner. If the burner shuts off accidentally, my process gases will continue to be generated for many hours thereafter (thermal momentum). There is no way to stop them. These gases are still being sent to the fume incinerator even though its burner has shut down. When the burner is reignited, we would have to begin a purge, which introduces air, which I assume would cause an explosion inside the fume incinerator since it is filled with process fumes that are at approximately 1200F to 1400F (above auto ignition temp). How do I prevent an explosion when the burner is relit? Should I purge the entire furnace with large volumes of nitrogen gas anytime we lose the burner? I'm not sure this will help.

 

[ElwoodGreen]

Seems like you would have an explosion hazard if you don't divert the incoming gas as soon as the incinerator shuts down. After the gases are diverted to a safe area, then you could go through a purge and re-lite of the incinerator. Be aware of air quality permit issues on this one. Such a release would likely cause a Title V permit deviation in the US with potential enforcement action by local or federal authorities.

There are several companies that make flares for landfill gas, sewage treatment plant gas, and petroleum and other processing plant gases. I would contact them for possible solutions. You shouldn't have to "reinvent the wheel," so try a google search. Callidus made the fully enclosed LFG flare at the site I am near. The control system (Honeywell) includes an autodialer function to notify responsible persons that the flare shut down.

Just my thoughts on the subject, hope they are useful.

 

[25362]

Do you have the possibilities of installing a pilot burner supplied from an independent reliable source ? Do you have snuffing steam ?

 

[gregsippel]

We do not have a steam supply, but do have nitrogen. The idea of adding an independent pilot burner would solve the detonation issue since it would ensure that there was always combustion occurring inside the incinerator. I suppose I would have to have it ON all the time, otherwise the atmosphere could (quickly?) become an explosion hazard, since its internal volume is only 9ft3, and the process gas generation is estimated to be approx 25scfm. But I'd rather not have it on all the time and I'd rather not even have to add another burner, if I don't have to. But it is a new option. If the existing burner was protected by an UPS, this would cover me for the time period until the back-up emergency generator comes online, unless the burner went out for some other reason, which is exactly what happened in the past on a somewhat similar system (which did not explode). The pilot burner idea would provide redundancy, and I think it would solve the concern with any accidental environmental release, provided that it is instantly brought online. Thank you, 25362, for your idea. As for the idea of a flare, I don't have any experience with flares, and haven't done a search yet to educate myself. I will do this.

 

[thermicatech]

gregsippel,
IMHO you are operating an unsafe system!!
The waste gases should be diverted from the incinerator feed to another system designed to accept the stream on a temporally basis. The application of an igniter burner does NOT solve your particular problem.
For further information on safety of incinerators please feel free to email me
thermicatech@yahoo.com
I will forward a paper that I presented a few years ago at the International Conference of Incineration and Thermal Threatment Technologies, aka, IT3, about safety and process control of incinerators. The ignitor burner application is widely covered.