Pilot light flame detection on hydrogen burn off stack

[TConnolly]

We have a number of hydrogen gas burn off stacks, each of which has a natural gas pilot light at the top of the stack. There is a flame detector which prevents the hydrogen gas valve from opening if the pilot light is out. However, there is nothing to shut off the natural gas to the pilot if the pilot flame goes out and this has been identified as a potential hazard - looking for a pilot control device that incorporates an electric igniter (the stacks are 12' tall and right now the operator has to shinny up to relight it) and a auto shut off if the pilot is not detected as well as a solenoid operated on/off valve, 1/4" natural gas line.

 

[Oakley]

Not sure of the solution here, but thinking residentially, gas water heaters have electric starters.

 

[Ron Beaufort]

back in another lifetime, I used to work on restaurant equipment ... I’d probably still be doing it if my knees hadn’t given out ...



anyway, Domino’s Pizza uses natural gas ovens from Middleby Marshall ...



when it’s time to heat, the pilot autolights and the burning gas of the pilot flame provides an electrical path (yes, through the gas flame) that rectifies an AC signal ... the current is on the order of microamps ... which is why I had to buy a Fluke 25 meter - with a DC microamp scale ... so ... if there’s no pilot flame (properly rectified, of course), the safety controls turn off the main burner really quick ...



next time you’re near a Domino’s, stop in and listen to the oven fire up ... you can hear it roar all the way out at the front counter ... the main gas flame (only one) comes out of a pipe about 4 inches in diameter ... the flame is a jet about two or three feet long ... think “flame thrower” and you’ve pretty much got the picture ...



if nothing else turns up, you might check into the brand of gas controls (I’m guessing Johnson - but not sure) that Middleby Marshall uses for this type of application ... it’s pretty much GOT to be safe and reliable to be used in a Pizza shop ...



gosh ... what a trip down memory lane ... to think - I used to have to WORK for a living ...

 

[Mickey]

Fireye Flame Safe-Guard was the standard for flare-stacks, boilers and various heaters in the natural gas storage fields I worked at. See link below


http://www.fireye.com/

 

[Brian123]

Honeywell also makes a line of burner control systems.

http://customer.honeywell.com/Honeywell/UI/Pages/Catalog/SystemCategory.aspx?Catalog=Buildings&Category=Burner+Controls_166&ChannelID=%7b02CD9124-96F3-4A04-8EA7-1777CCCAD5B3%7d

For your ignition system, a standard ignition transformer system can be used. This would connect to a spark plug or spark rod. I believe that there are hot surface ignition systems available that may be more reliable. I don't have experience with those, but the spark ignition has been very reliable for us (all of our stuff is indoors though, YMMV.) The solenoid would be just a standard gas type solenoid.

I would check into your current flame controller as it may be capable of doing what you need with just some wiring changes. If not, it would still be helpful to know what kind of sensor that system is using; it may be able to be used by a new controller, avoiding buying a new sensor and running the associated wiring. Model numbers would help.

Brian

 

[Brian123]

the current is on the order of microamps ... which is why I had to buy a Fluke 25 meter - with a DC microamp scale ... so ... if there’s no pilot flame (properly rectified, of course), the safety controls turn off the main burner really quick ...

As a side note, the newer Honeywell 7800 series controllers output a high level voltage signal that represents the microamp signal (1 V = 1 microamp) so that they can be read by a standard voltmeter. We also have about a dozen of the older RA890 flame safeguards that use the microamp readout.

 

[danw]

UV detectors work great but can "fail" unsafe, indicating flame, when there is none, when they get saturated. Hence the code requirements for flame detectors that run continuously to use a shutter-check mechanism that blanks out the UV from the flame and determines whether the UV tube stays on (failure mode) or turns off (OK). The applicable codes state that if the burner is not turned off at least once in a 24 period, then shutter check style flame detectors need to be used. Shutter check UVs are quite expensive $2-3,000.

An alternative is a pilot assembly with its own flame rod detection.

Look at Honeywell's Q179B, C or D Flame rectifier Gas pilot assemblies.
typical:
http://customer.honeywell.com/honeywell/ProductInfo.aspx/Q179B1042

The pilot assembly is a mechanical assembly, you'd still need a flame safeguard "flame switch" electronic unit that tells you whether you have flame or not, something like RM7823A1016 (115Vac),
http://customer.honeywell.com/honeywell/ProductInfo.aspx/RM7823A1016
with mounting subbase Q7800Axxxx,
http://customer.honeywell.com/honeywell/ProductInfo.aspx/Q7800A1005
a flame rod amplifier card, (just can't remember model number)
and an ignition transformer (can't recall a model #)

I always have an S7800A indicating display, because it
- saves a history of failures
- has a Modbus RTU (RS485) output
- moveable, can be moved from flame safeguard to flamesafeguard
http://customer.honeywell.com/honeywell/ProductInfo.aspx/S7800A1001

Dan

 

[TConnolly]

...the pilot autolights and the burning gas of the pilot flame provides an electrical path (yes, through the gas flame) that rectifies an AC signal ... the current is on the order of microamps ... which is why I had to buy a Fluke 25 meter - with a DC microamp scale ... so ... if there’s no pilot flame (properly rectified, of course), the safety controls turn off the main burner really quick ...

I was just reading about those. Sensors never cease to amaze me. I understood the principle as soon as I read it, but I'm still amazed that someone thought up the application in the first place.

I've learned more about flame sensors and burner control in the last three hours than I thought I would ever need to know - until this morning I never had to deal with it. A factory across town (just a couple of blocks from where another forum member, CroCop works) blew apart a couple of weeks ago (fortunately no one was killed but some were injured) and now almost the entire work force is out of a job. Safety is a process of continuous improvement and so we regularly evaluate our safety systems, but the event raised awareness in our minds and this time we uncovered a possible failure scenario.