Page 247 - Boiler_Operators_Handbook,_Second_Edition

232 Boiler Operator’s Handbook

where the oil is heated and a technician passes a stan- mess eliminated any profit we expected to make on the
dard match over the top of the cup containing the oil. entire job. Today an oil leak can cost tens of thousands
When the oil is so hot that it generates enough flam- of dollars to clean up so you should always seek to keep
mable vapor to be ignited by the match the temperature any leak contained.
of the oil is the flash point. Oil can be supplied directly to the plant via a pipe-
It’s called flash point because the flame starts and line. In such cases you’re relying on the supplier just like
extinguishes rapidly, flashing rather than continuing to you would for natural gas. Most plants could not justify
burn. When you’re burning oil with a low flash point a pipeline directly from a supplier so they have fuel oil
any leak should be a concern. Temperatures in a boiler delivered by truck and have to store the fuel on the plant
plant are frequently higher than 100°F, especially in site. Storage doesn’t have to be in tanks but potential
the summer, and steam and hot water piping is so hot hazards of leaks has eliminated use of open pits, old
that they can generate flammable vapors if the oil leaks mines, and similar measures.
onto them. What about gas you say? Natural gas has Tanks are generally one of three types, under-
a comparable flash point and it’s around 500°F. When ground, above-ground horizontal, and above-ground
we started converting boiler plants to natural gas in vertical. Underground storage tanks are now labeled
the 1960’s there were a number of concerned people “UST’s” for underground storage tanks and are a lot
expressing a common phrase “go gas—go boom!” But different than fifty years ago. Above-ground horizon-
the truth is gas requires more energy to ignite than oil tal tanks are common for small plants and include the
and it isn’t as hazardous. Of the boiler explosions I’ve ones enclosed in concrete vaults for physical protection
investigated the worse were always light oil fired. as well as fire safety. They’re called horizontal because
In addition to the normal grades of fuel oil there the tank is formed around a horizontal (parallel to the
are several sources of waste oils that can be burned in a ground) centerline. Larger ones may exist but the typi-
boiler as fuel. A common one used in small installations cal horizontal tank is limited to around 90,000 gallons
is waste lubricating oil. If you are firing waste lubricat- capacity. Vertical tanks are formed around a vertical
ing oils you’re firing a very dangerous product because centerline and can range in size from a few hundred to
it can be tainted by gasoline. In one army base I visited hundreds of thousands of gallons.
the waste lube oil was from helicopters and it could con- UST’s became a hassle when it was discovered
tain a considerable fraction of jet fuel. how many of them were leaking. From tanks at gasoline
Usually waste oils are burned as a second fuel filling stations to those at every boiler plant more tanks
to limit the effect of their variable heating content and were leaking than were intact. Much of it was due to a
air requirements. Some systems use density meters to lack of understanding of how the tank and soil interacts
measure the waste oil flow to get a concept of air re- as the fuel was added and removed. For years there was
quirements and energy content according to its density. a standard procedure for installing an underground tank
To date there isn’t an economical means of obtaining in- that consisted of pouring a concrete base then resting the
stantaneous measurements of higher heating value and tank in the concrete. Only after several years did we
air requirements for waste oils. discover that the tanks changed shape, becoming more
Typical problems with waste oil firing include dirt elliptical as they were filled and compressed the soil.
and grit in the oil. There’s also a concern for lead from The point between where the tank metal was trapped in
bearings oxidizing in the furnace to produce high ground concrete and bearing only on the soil provided a sharp
level concentrations of lead oxide around the plant. corner that the tank was always bending around and
Any grade of fuel oil is a hazardous waste if it that’s where they cracked and leaked. There were other
escapes the normal containers and piping to leak into problems, mainly corrosion due to electrolytic action in
the ground or sewers. Of particular concern is any floor the soil, that provoked leaks in those steel tanks.
drain in the plant. The wise operator should know The initial solution to the UST leakage problem
where the floor drains in the plant discharge. I remem- was their replacement with fiberglass tanks properly
ber years ago when we were converting a major uni- installed so they could flex with the soil. It hasn’t proven
versity from coal to oil and a line leaking at the fuel oil itself a wise decision. If you have a UST and it’s to be
pump and heater set ran away to a floor drain that dis- replaced with another one, it should be fiberglass resin
charged into a small creek right outside the boiler plant. encased steel to get the best of both worlds. All installa-
No more than four or five gallons of oil escaped before tions since the early 1990’s are required to have means
the leak was discovered but the cost of cleaning up the for testing the tank and connected buried piping for