Exxon Testing
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Luck saved the day when the flare
gas/air mixture flashed back, but you can NOT count on luck.
You need to have a proper, safe design and
installation.
NAO built the arrestors to
replace the aluminum units. We tested a similar piping arrangement
make up
of flanged sections of pipe 250' (76 meters) of 24" (610 mm) pipe (PART OF NAO
RENTAL FLEET
-- flares, stacks, trailers and piping). The piping was
filled with a mixture (near stoichiometric - fastest,
most explosive mixture) of
propane & air to simulate the vapors from the crude storage.
The arrestors proved that they
stopped the flames. The 24" (610 mm) pipes which weighted 29,000 Lbs
(13
Metric Tons) would vibrate and rumble like a freight training was coming down
the rails.
NAO also added other accelerators
(trail of diesel oil, gasoline to simulate dirty pipes as in the field)
in the
piping system to further prove our design. The trail of liquid hydrocarbon was
sprayed on the
walls and floor of the pipe header for the entire length to get
the worst case. The vapors from the
liquid hydrocarbon did greatly
accelerate the flamefront speed. The NAO arrestor stopped the flame.
We wanted to further prove the
NAO design, so we replaced the arrestor grid with an orifice plate
of equal flow
area (one large hole vs. thousands of small tunnels). We were looking for
a failure
to prove that the grid was working and that some other variable was
not throwing off our testing.
When we ignited the mixture the
flame rumbled down the pipe and through the orifice plate
producing a flashback
flame 40' (12 meters) long about 3' (1 meter) in diameter. The shockwave
from the flashback broke fluorescent lights bulbs in workshop about 150' (45
meters) away.