The following list covers those typical problems with Flame Front generation which are largely responsible for many problems and
unsatisfactory reports of Flame Front generator usage.
Water in the line:
The passage of the ignition flame through the flame front line is a progressive combustion process which consumes the mixture in the line as the flame travels along the
pipe. Excessive moisture in the pipe can quench the flame by making the local mixture non-flammable. This is particularly the case if there are pockets in the line which
allow standing pools of water.
In many locations, particularly in warm sunny climates, a high daytime relative humidity allows moist air to enter a dormant or un-used flame front line where it cools
slightly and drops some of its water content into the line. This can cause significant liquid build up even over the short period.
Some water can also remain in the line as a product of combustion after repeated ignition attempts.
If this problem is suspected, blow through the flame front line with dry air to remove all traces of moisture and correct any pocketing as soon as possible. In some cases,
prolonged blowing with dry air for 8 - 12 hours may be necessary to adequately dry a wet flame front line. In cases of a persistent problem, a permanent flow of air or
air/gas may be needed to maintain a dry internal atmosphere.
Incorrect Mixture:
The pressure requirements for Gas and Air sometimes change due to variations in gas composition or even due to changes in ambient temperature and pressure. If problems
are experienced using gas and air pressures which have been previously successful, return to the original set up procedure of the
instructions and find a new mixture.
Impatience of the Operator:
The flame travel through the flame front line and the time taken to fill, purge and refill the line during ignition attempts are all time consuming. Trying to start a flame
front too frequently will only lead to extinguishing of previous attempts before the flame front has had time to complete its run to the pilot.
Instrument Response Time:
For pilots with thermocouples, be sure to wait for an adequate instrument response before attempting re-ignition as this can sometimes destabilize an established flame which
is heating the thermocouple.
Blocked Flame Front Lines:
Un-drained flame front lines or old scaled piping can cause restrictions in the piping and prevent the satisfactory passage of flame. This is usually detected when some
pilots ignite well but the blocked line always stops the flame front.
Blocked Pilot Gas Jet:
Line scale, tar or sulfur deposits can sometimes plug pilot jets and prevent gas flow. Even successful flame front passage will not be able to ignite this pilot. This may be
suspected when pilots seem to fail or clear sporadically after de-pressuring the fuel gas header. If caused by tars, the blockage can sometimes be successfully removed by
steaming the line with medium pressure steam for several hours. Failing this, the jet must be cleaned out physically by dismantling at the pilot and physically cleaning the
parts. Blow out the lines before re-assembling the pilot jet. If choosing to install a strainer ahead of the gas jet, ensure that there is adequate excess flow area in
the strainer and that the mesh size is smaller than the gas jet.
Unsuitable Flame Front Piping:
Flame front generation works best when the flame front lines are of constant diameter and free from constrictions or enlargements, which permit turbulent eddies to establish
in the pipe. Lines of one inch (1") diameter with long radius elbows are most commonly successful. Heavy fittings with reduced ports or Tees can be troublesome. Pipe
expansions into drain pots or to different line sizes, almost always, will prevent passage of a flame or will make pressure settings extremely sensitive and critical. Where
drains are fitted try to minimize the drain leg and use the stem of a tee, using the clear run for the flame front line.
Flame in the Line:
If a flame front line design is unsatisfactory in some way, it is possible that a flame may establish in the line and burn permanently at one point as long as gas is flowing.
The line will become hot and eventually the external paint will begin to char and blacken. Turn off the gas and allow air only to flow until the line cools down. When
retrying ignition do not use the same gas and air pressures as before but increase all settings to provide a greater flow and try to prevent a recurrence of the problem.
Cold Climate:
During severe winter conditions, an ultra-cold flame front line can quench the flame by cooling the flammable mixture as it flows to the tip. This may create narrower
flammable limits within the line than those which exist at the ignition panel. Thus a flame may ignite at the panel but be quenched as it progresses further along the
pipe. Flammable characteristics may also change in the line if cooling causes dew-point fall out of heavy components.
To resolve this problem,
- increase all settings to provide a greater flow rate and try to minimize heat transfer;
- if possible, change fuel gas to a composition with minimal dew-point concerns;
- in the extreme case, heat tracing and insulation of lines may be needed.
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