Burning Off a Hydrogen Process Stream 1

[rjw57]

I am in the midst of designing a furnace which will use hydrogen as a process gas. I am attempting to locate a supplier of a system to burn off said hydrogen during the process. My problem is that I am required to burn off both a steady stream of hydrogen (1-10 SCFM) as well as a surge of hydrogen which can be a maximum of 150 SCFM decaying to zero in approximately 5 minutes (this flow represents the exhaust from the 2" exhaust line of a vacuum pump while it removes the hydrogen within the vessel at the end of the process cycle). I would like to be able to use a common burn off system to accomplish the burn off of both process streams. I have located a "glow-plug" igniter type system for the 1-10 SCFM process requirement, but my problem is that I am inexperienced in locating burn off systems that are capable of 150 SCFM. Can anyone suggest any companies that can engineer systems with integrated flame / igniter safety controls to handle these flow rates? (Even better if they have one on the shelf!) It can be either the glow plug igniter or piloted flame types. The Hydrogen stream will be at a maximum of 250F.

 

[ash9144]

John Zink does a lot of furnace design.

 

[dtlb26]

John zink or similar RTOs will do fine

 

[Compositepro]

Hydrogen is not an air pollutant so it may be safer and easier to dilute it and vent it without burning it.

 

[MortenA]

the lel/uel band is very broad for H2 - so you need to dillute very much in order for it not to be explosive.

Best regards

Morten

 

[rjw57]

Thanks everyone for your replies. I have checked with John Zink. The rep started me at 50K and told me that the system is way too small for them to economically create, to look for somebody else (all very nicely). As far as this being done via dilution, this is a safety issue for the customer and burn-off, whether via piloted burner or glow plug, is required by their contract. I am looking for small systems, not flares for oil rigs. A list of potential vendors is really all I'm looking to score at this point, even if it is a dead end. Any and all input is appreciated.

 

[ScottyUK]

You could consider a catalytic burner rather than an open flame design. The hydrogen-atmosphere belt furnace I was loosely involved with in the thick film hybrid industry used this type of exhaust burner and it seemed fairly effective. Our hydrogen stream was very clean - beware of oil carryover in the vac pump exhaust stream, it might upset the catalytic burner. From memory I think the manufacturer was BTU International if they are still in business - t'was a long time ago.



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If we learn from our mistakes I'm getting a great education!

 

[ash9144]

The chlorine electrolysis units that replaced the old mercury cells generate a small hydrogen stream. You may want to check with some of those vendors for their combustion units.

 

[StewPad]

Why Burning when you can make electricity - google Fuel Cell Energy

 

[moltenmetal]

A fuelcell will be no better able to deal with that turn-down range than a burner would be.

Your problem is the turn-down range. The range is too large for a device to be optimally sized. What you probably need is a small shielded flare. The smallest one you can buy will probably have a pilot burner requiring a fuel gas flow larger than your normal flow.

If you find the right unit, let me know and I'll keep it in mind for the next time I need that particular problem solved. It's one that comes up frequently in the small plants we do.

 

[dcasto]

10 small fuel cells will give you all the turndown you need

 

[rjw57]

@ moltenmetal

Thanks for your reply. I did manage to get in touch with a vendor who sells "small shielded flares" as you have suggested. Your response is spot on with the conversation I had with them. The immediate focus was on the turndown ratio. I hope the pricing comes in at a reasonable figure. Anyhow, thanks for your input. Everyone else, thanks for trying to be green, but a fuel cell system for this turndown ratio would be amazingly expensive. If the customer wants to go green, it wil have to be on their dime.

 

[rjw57]

@moltenmetal

I will probably not be using these folks due to cost only (still looking for an alternate supplier), but NAO in Philadelphia looks like a potential player in the small shielded flame market and the owner is a really interesting guy whom is willing to talk tech with you any time you want. Just an all around good guy to deal with from my experience. I've attached a quote for you to look at.

 

[chemebabak]

RJW57, consider adding a buffer vessel with a pressure reducing valve. This arrangement can be designed to limit H2 flow to the range that you are specifying.

 

[chemebabak]

An even more cost effective method is to use a restriction orifice instead of a pressure reducing valve. Since you are dealing with such a low flow rate, the "buffer vessel" could simply be a section of oversized pipe. For example, you may design your pipe for, let us say, 1.5" schedule 40. You could include a, let us say, 5 ft section of 6" schedule 80 pipe as a "buffer vessel". On the inlet to your furnace from the "buffer vessel" you could insert a, let us say, 1/8" RO to limit the flow of H2 to 10 SCFM.