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The following instructions for Flame Front generation are somewhat generic and prepared without regard to the specific details
introduced by the equipment supplier. They are intended as a practical guide and not as an official publication. Automatic systems, particularly, will be somewhat
specific to the manufacturer, but all will follow essentially the same principles and will probably need to be set up and commissioned in a manual mode.
A location known as an ignition panel is usually used to ignite the pilots, either manually or automatically.
Initial Preparation
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The flare must be free of an explosive gas/oxygen mixture (see purging) and will be either
- in a standby condition with the possibility of flammable relief or
- in a dormant condition with no process gas connections.
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For multiple flares in close proximity and in common structures, purging procedures of all flares must be coordinated prior to ignition of pilots. It
is not practical to separate commissioning or lighting of the flares.
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Ensure that all electrical hookups have been made to the panel.
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Check that all pipelines to the panel are in accordance with the supplier's drawing and that suitable pressure reducing valves and strainers are
installed in the upstream piping.
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Check that pilot fuel gas, ignition fuel gas and ignition air are available upstream of isolating valves or line blanks.
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All lines must be clean and scale free. It may be necessary to break piping unions to remove foreign matter.
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Operate all drain cocks and remove all condensate from piping upstream and downstream of the panel. Close all drain cocks after this exercise.
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Open the isolating block valve for the pilot fuel gas supply and set the pressure regulator according to the Pilot Burner manufacturer's instructions.
If you do not know the correct pressure, check it.
Most suppliers use pressures in the range of 5 - 15 psig with individual pilot gas flows providing a pilot flame in the range of 50,000 Btu/h - 250,000 Btu/h.
Contrary to the belief of many operators, as a general rule, use of a higher pressure than the recommended design is unlikely to solve persistent difficulties with
successful ignition. (see debugging).
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Allow sufficient time for the fuel gas to reach the pilot after displacing the air or purge gas from the pipe line. The length of time needed
will depend on the length and diameter of the fuel gas line to the top of the flare, as well as the number and style of pilot being supplied.
As a conservative estimate, estimate 1 second gas travel time per square inch of pipe internal area for every 1 ft length of pipe.
[1500 ft of 1" pipe could take up to 20 minutes][1000 ft of 3" pipe could take up to 2 hours]
Manual Operation of a Flame Front Generator
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Check that the flame front piping is dry, that all the drain valves have been closed.
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Open the isolating block valves on the ignition fuel gas and air supplies.
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If appropriate, turn any control panel selector switches to Manual mode.
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Determine which pilot is to be ignited. Open all the manual flame front diverter valves leading to the designated pilot and close the diverter
valves for any un-selected pilot(s). In some designs, all pilots are ignited concurrently using a single common flame-front line to the flare tip, which splits into
a distribution manifold at the tip. In some automatic systems, opening valves manually may involve partial activation of the controls. Become familiar with
your own equipment.
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Carefully note which is the gas train relative to the air train on the panel.
Set the ignition fuel gas and air pressure regulating valves to give the manufacturer's recommended setting. If this is not known use approximately 5 - 10 psig for
each, for the initial trials.
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Remember that the final settings of pressure for each supply will depend on the composition of the fuel gas at the time of pilot commissioning. Where
the fuel gas composition is not clearly defined, determining the correct relative fuel gas and air settings will be by trial and error method and could be time consuming.
(see item 9 below)
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Allow sufficient time for the gas and air mixture to fill the flame front pipe all the way to the pilot. Approximately 10 seconds per 100 feet of pipe
run should be adequate for a 1" pipe.
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Press the manual ignition pushbutton momentarily. This will activate the ignition unit (or ignition transformer), creating a spark at the ignition
point in the flame front line.
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Watch for ignition by observing the sight port (if provided) and/or by noting a marked vibration of the pressure gauges. Ignition may also be
accompanied by an audible sound ranging from a click to a loud bang. If the detonation is extremely loud, the mixture is air rich and requires that the gas pressure
regulator be adjusted so as to increase the gas pressure. If there is no detonation at all, the mixture is probably gas rich and requires that the gas regulator be
adjusted so as to reduce the gas pressure. Adjust gas pressure by 1/3 psig increments until proper ignition occurs.
For Natural draft units, try the gas at a constant pressure setting and make adjustments to the venturi air intake.
To save time, I always set the gas at a constant rate, say 5 psig, and gradually wind up the air flow slowly whilst holding down the ignition button. As soon
as the mixture runs into the flammable range it starts igniting. The pipe rattles and the gauges begin to jump. Don't keep doing this once you've found the
approximate range because the pipe starts to get hot and that's the fastest way to cause more problems . Make all final adjustments more cautiously taking note of
the guidelines above.
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The flame propagates at the appropriate flame speed (reaction speed) through the mixture and gets to the top after some time. Be patient waiting
for evidence of pilot ignition. It can sometimes take as long as one to two minutes to establish a pilot flame. Pilot flames are sometimes hard to see during daylight.
On just one or two occasions you will not notice the delay and the flame will seem to get to the top of the flare as quickly as you pressure start
button. Those occasions will also be accompanied by a really loud "BANG". That's because the mixture is much too close to stoichiometric
and you run to a detonation which travels at sonic velocity. This often occurs at the beginning of the ignition attempts when the mixture is still purging air
from the flame front line. Wait a few minutes, reduce the air flow and try again.
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Remember that, after the flame passage along the line, all that hot flue gas has to be purged out before you get back to the useable mixture so
patience is the order of the day.
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If there is a "Flame-In" indicator light, it should illuminate if the pilot flame is established. Otherwise, the "Flame-Out" light
will stay illuminated indicating unsuccessful lighting of the pilot in which case repeat previous steps (5) through (9).
If you need to visually highlight a pilot flame, turn off the air flow to the flame front generator. This allows the flame front tube to fill with raw gas and
gives a larger and more visible flame at the pilot. Bear in mind however that, if you do this whilst you are in the middle of an ignition procedure, the flame front
line needs to be refilled with air/gas mixture before you can resume.
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Note or mark permanently on the panel the established gas pressure at which ignition occurs for future use.
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Select another pilot and return to step 4.
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