Is a pilot necessary?

[TravisWolfe]

When starting an industrial sized natural draft burner, is there a requirement to have a pilot? I start these via torch now, but to automate is a pilot required or is just an ignitor sufficient?

Thanks in advance

 

[Flareman]

Depending on where you are geographically and what industry you are in, there may indeed be regulations governing the use of pilots. However, you are not alone in the use of a hand ignitor.
The use of a hand ignitor or continuous pilot is really a security issue and depends, in large part, on the rest of the control scheme which you have in place. You need to think about what happens if the flame were to go out, perhaps due to a momentary interruption in the fuel flow because of a line blockage or valve failure. If your emergency shut down and start up procedures and safety controls are safe and worked around the use of a hand ignitor, then it's OK. If the flame fails and you have to run out and turn the valve off before the furnace fills up with fuel, it's not. It also depends on whether this is one burner in a furnace of 100 or a single burner furnace in critical service.
You could try the NFPA forum and ask a similar question, but please state your geographic residence so that others in the same part of the world can respond knowledgably.

David

 

[TravisWolfe]

Does anyone know of the requirement to have FM approved vent valves on multiple natural gas natural draft burner installations?

Block valves are required to be FM approved, however can't find info in vent valves case?

T

 

[EngineerBSME]

I can think of no application where a pilot is required. Continuously lit pilots are a lazy, hazardous, unreliable, cheap but expensive (inital cost is low, operating cost is not, safety features are defeated by heat generated when repeated attempts to light off fail). My opinion does not count but in my opinion, pilots should not be used and should not be approved for use.
A pilot is hazardous and can result in an inappropriate light off. Pilots were popular previous to reliable spark ignitors for lighters ie. what you call torches.

For automatic lightoff please consider using.
1. A high energy spark ignitor (HEI) to light off a lighter (torch). Styles include auto retract, permanent insert, manual removal, and manual lightoff (see

http://www.fps.com

for a good commercial grade lighter/ignitor/burner combination)Also see B&W, Cohen, Fireye, CE, GE, Fossil Power Systems
2. A lighter (torch) to light off the burner
Note: Design of the lighter and ignitor must comply with the appropriate ASME standard (Local, state, federal)for the fuel type, ambient temp, fuel flow, of the burner (and lighter) Basically, the lighter must provide adequate BTU to maintain combustion even if the burner fails to light. Likewise the sparker must maintain spark even if the lighter fails to light off. ie. safety first.
3. A flame scanning system is required during combustion to prove flame of the ignitor, lighter, and burner. To be of value and avoid fooling the operator, flame scanners must be able to discriminate between ignitor, lighter, and burner. Manual visual observation is one approved method of monitoring flames. Logic controls (x out of y flames lit) is another approved method of monitoring.

Due to the nature of your question, the complexity of the answer, the available options, and the potential for disastrous results possible from a minute mistake, please seek and obtain professional advise. The selected method of compliance must be approved and periodically monitored by the ASME approved state inspector.

 

[Flareman]

Excuse me jumping back in but I want to emphasize the High Energy aspect of EngineerBSME's response lest there be any confusion.
The HEI is a special device with a capacitance discharge and a special type of spark plug (similar to those used in Gas Turbines). Don't confuse the HEI with a High tension system like the one in most Automobiles and many existing burner ignition systems.
The High tension system relies on a spark being able to jump an air gap and is sensitive to gap size, grounding off and fouling up (don't we know it?!!). The HEI system uses a "timed" capacitance discharge to overload a continuous circuit through the plug and produce a bolt of electrical discharge at the tip. These systems do not foul, or ground off and are good for liquid or gas ignitions (I've even used one in a bucket of water). You absolutely need a full circuit back to the power pack because the power pack may not be fully grounded and you don't want 12 joule sparks leaping around at loose connections.

David

 

[op9]

For all these recommended means of ignition you have to get back to basics.......The idea of using a pilot before the main flame (I'm talking about interrupted pilots here), is to introduce a small controlled amount of fuel,(in conjunction with an automatic programmed control and flame scanning)so that at the end of the Ist safety time, that amount of fuel introduced if ignited right at the end of the safety time does not liberate energy which will cause structural damage, and/or danger to personnel. If still no flame at the end of this time, all fuel must be shut-off and another purge initiated before next attempt. This designated amount of fuel Vs Safety time is set by local regulations and is worked on the available furnace volume and hence how long till the fuel concentration would build up toward some percentage of the LEL. For example in Australia this is 50% LEL for natural gas.

Normally pilot fuel will light smoothly well before the end of the set safety time. However you will probably be familiar with the effect of a delayed ignition (when hand lighting)....if your lucky just a small blowback. This is because you are getting toward the "critical time" after which maybe a BIG bang. Obviously then trying to control this energy with the main flame volume flow is a lot more critical. So as you can see the progression...small spark (low energy) lights small flame (medium energy), which then lights main flame (larger energy).

If all this is set up correctly to the required standards, the use of an auto startup programmer, with flame scanning, and an auto interrupted pilot IS a tried and proved safe procedure.

Using a HESI (High energy spark ignitor) or HEI (as you call it) is also another method as it provides a high energy ( or medium energy when compared with the sequence above) reliable source of ignition BUT it must be related to the aforementioned critical times when lighting main fuel (ie the safety time will be a lot shorter). By the way the HESI system is related to a car ignition system...CDI (Capacitor discharge ignition). I know I had one back in the 70's and yes I saw a demo where it continued to operate with a distributer filled with water.

Hope this gives you an idea of the principles involved.
Rod Nissen.
Combustion & Engineering Diagnostics
canded@iprimus.com.au

http://www.canded.com.au