Page 45 - Boiler Operator’s Handbook

30 Boiler Operator’s Handbook

automatic valves. Of course I should say that applies forming the owner that it was “just a puff” that occurred
to service engineers that worked for me at Power and as the burner started. Don’t ever let anyone convince
Combustion. In some instances a service engineer will you that a puff is anything other than an explosion. A
leave a job that doesn’t light off properly; as far as I puff is simply an explosion that did no or limited dam-
know we never did. age. Every puff you experience should be considered a
I always tell this story because it introduces another warning and is not be tolerated because sooner or later
term in a manner that operators understand. One of the whatever is causing the problem will get worse and you
reasons Power and Combustion provided quality boiler will experience an explosion that does some serious
and burner installations was the interaction between the damage.
design engineer (me) and the technicians in the service What causes explosions, including puffs? It is the
department who performed the work in the field. They direct result of an accumulation of a flammable mixture.
never hesitated to show me how I had screwed up or call Make no mistake about it, when you’re burning a fuel
when they had a problem they couldn’t resolve. In the you are creating an explosive mixture because there is
1980’s my service manager at Power and Combustion no difference between a mixture of fuel and air that will
was a gentleman named Elmer Sells. Elmer and I got burn and an explosive mixture. The reason we can safely
along well because we’re both hillbillies, natives of the fire a boiler is we burn the explosive mixture at the same
Appalachians, I grew up in western New York State and rate that we create it. It’s only when the mixture doesn’t
he grew up in West Virginia. We were into the start-up burn and accumulates that we have an explosion. We
phase of a project to convert three oil fired boilers at Fort control the combustion by controlling the rate of burn-
Detrick to gas firing. ing. When an accumulation ignites it burns at a rate
I got a call from Elmer asking that I come out to dictated by nature and that’s a lot faster than our normal
the plant to look at a problem they had. When he called fire, so fast that the products of combustion expanding
he used that West Virginia drawl that normally meant can create a pressure wave which will create a force of
he figured he had me, so I knew I was in trouble before 18 to 70 psig. The explosions we experience and call a
I even left. I arrived right after lunch time and found puff were simply small accumulations of an explosive
Elmer standing next to the largest boiler, a four burner mixture which did not produce pressure high enough to
unit rated at 140,000 pph. Working that WV drawl he in- rupture the furnace.
formed me they had just purged the boiler and he would It’s not always possible to avoid a puff or rough
like me to try to light off the bottom left burner. light off. They occur when burner systems fail to repeat
As I climbed up the ladder to the burner access the conditions established when they were set up. Mate-
platform I noticed the observation port on the burner rial can plug orifices, linkage can slip, regulator springs
was open so I stood off to the side of the burner while I can soften and many times a combination of minimal
started it. The gas-electric ignitor started fine but there factors can combine to prevent a smooth light off or
was a little delay after I opened the last main gas shut- burner operation. If you experience a puff you should
off valve. The burner ignited, the boiler shuddered, and consider it a warning sign that something is going
a tube of flame shot out of that observation port about wrong and do something about it. If your sense of what
six to nine feet long. I had my finger on the burner stop has been happening with your burner is sound, you may
button immediately but realized the burner was operat- be able to correct the problem yourself but you should
ing normally. Then I turned to look down at Elmer who keep in mind that more than 34% of boiler explosions
was standing there with his hands clasped behind his are attributed to operator error or poor maintenance;
back while rocking back and forth on his toes and heels. make adjustments only when you are confident that you
He dropped his broad smile and said, again with that understand what is causing the delayed ignition. If you
WV twang “little rough, ain’t it?” I agreed and realized aren’t certain, it’s much wiser to call for a service techni-
what I had done wrong so we set out to correct the prob- cian that has experience with burner adjustments.
lem. Today those burners light off quietly and smoothly. I think it’s important that a flame begin within
The lesson to be learned here is any roughness on light the throat of the burner where heat radiating from the
off is just another form of explosion and shouldn’t be refractory throat provides ignition energy. I normally
tolerated. don’t see a stable flame on a burner without a good
In recent years I’ve encountered facilities where refractory throat. A boiler just south of Baltimore had a
the contractor that placed the equipment in operation furnace explosion in 1993 that was due to the improper
couldn’t establish a smooth light off and left the job in- adjustment of the burner such that the UEL was estab-