Page 221 - Boiler_Operators_Handbook,_Second_Edition

206 Boiler Operator’s Handbook

ness” is another unacceptable argument; put something cause no manufacturer will absolutely guarantee their
thicker on it! The energy lost in the month or more it material will remain intact. Materials exposed to the
takes someone to get around to ordering the right thick- high temperatures of a furnace are also subject to com-
ness will pay for the additional thickness. ponents of the fuel that become very caustic or acidic at
Speaking of various thicknesses, it doesn’t pay to the high operating temperatures. Some components of
maintain an inventory of multiple thicknesses, get pipe fuels produce considerable damage with vanadium be-
insulation in one inch increments, one, two, and three (if ing particularly offensive.
you need three inch) etc., and layer it for greater thick- Vanadium is common in many of the heavy fuel
nesses. Limit your stock of one-inch thickness to pipes oils and has a particular means to damage refractory.
two inches and smaller. For flat and large diameter sur- Vanadium pentoxide is molten at flame temperatures
face insulation all I would keep is two-inch thicknesses. and as low as 1200°F. It remains molten at the refrac-
Your inventory should also be limited to the insulated tory walls and soaks into the refractory during boiler
pipe diameters you actually have in the plant. operation. When the burner shuts down the materials
Be cautious with insulation on or near piping con- cool and the pentoxide solidifies. Being a metal oxide it
taining flammable liquids such as fuel oil. The insula- shrinks at a different rate than the refractory. The differ-
tion can absorb it like a wick to become a fire problem ence in thermal expansion, where the pentoxide soaked
later. Insulation in the area of fuel oil pumps, strainers, layer shrinks more than the regular refractory, creates a
burners and such other places that could be splashed shear plane between the two materials where they pull
by a leak should have full aluminum jacketing over a apart. The result is breaking off of a layer of the refrac-
mastic impregnated covering to prevent a leak or splash tory from one quarter to two inches thick, a process we
soaking in. call spalling. The damage is very evident on inspection
Insulation for refrigerant piping, chilled water, and of the furnace because the pentoxide soaked layer has
some ductwork has the added requirement that it be a glossy black appearance and is spotted with light tan
properly sealed. If there is an open path for water vapor areas where the pieces of refractory spalled off.
to flow through the insulation to reach the cold surface Yes, refractory does expand and contract with
of the equipment, piping, or duct it can condense there, changes in temperature. It’s nowhere near as much as it
soaking the insulation to reduce its effectiveness, cor- is for metal but it does grow and shrink and that must be
rode the metal, and occasionally harbor mold growth. accounted for. I’ve known operators to try repairing ev-
Cellular glass and foam insulations are inherently vapor ery crack that appears in the refractory in their boiler’s
proof but they only work if their seams are sealed tight. furnace on each annual outage and, as a result, acceler-
When you observe damage to vapor-tight insulation try ate the damage.
to take the system out of service for a while to allow any I have a rule that says any crack that is smaller
condensate to evaporate before restoring the vapor-tight than a number 2 pencil, where you can’t put a sharp-
seal. ened pencil in up to the yellow paint, should be left
Re-evaluate your insulation once in a while. The alone. Those are expansion cracks and will close up as
old rule that says it should be insulated if you can’t hold the boiler heats up. Plugging larger cracks, as much as
your hand on it still applies. The only thing you should three-quarters of an inch, with hard refractory materials
not add insulation to is any part of a boiler casing. isn’t recommended. Today we have access to ceramic fi-
The wise operator maintains the insulation in his bers rated at temperatures as high as 3200°F that should
plant. The argument that the owner won’t buy any be used to fill those cracks. The ceramic fibers shouldn’t
insulation is easily covered. Explain to the owner that be packed into the crack to the extent that they’re solid,
you’re paid to be there anyway so the cost of material leave it soft so there’s room for the major pieces of mate-
for repairing or even adding insulation is recovered in rial to expand into the crack.
fuel cost in a couple of months. The owner might even In my days of operating we used asbestos for such
consider boosting your salary a little with what is saved repairs and you could encounter asbestos in joints and
after that. cracks of refractory in an older boiler. If you have good
maintenance records you’ll know what you’re getting
into but, lacking data, treat any fibrous material as as-
REFRACTORY bestos until such time that it’s proven it isn’t.
One important location for providing thermal ex-
Refractory is unique material in one regard be- pansion is around the burner throat on oil and gas fired