Page 96 - Boiler_Operators_Handbook,_Second_Edition

Boiler Plant Operations 81

because the water is already cold and it won’t take much and operators will consider it a simple leak. If, however,
more to start freezing it. There’s been more than one boil- you fix all the leaks the pressure will eventually split the
er plant shut down in the winter because cold drafts froze pipe because expanding heated water can produce as
their city water line solid. Don’t take an indicating light’s much force as freezing ice.
operation as proof that electric tracing is on, put your The best example for this is a typical run of hy-
hand on the covering. If it isn’t warm slip a thermometer dronic piping where the temperature of the water
under the lagging and if necessary push it through the ranges from an installation temperature of 70°F to a
insulation to the pipe (be careful with pointed thermom- maximum operating temperature of 250°F, 100 feet of
eters that you don’t penetrate the tracing). the piping heated from 70 to 250 will increase in length
Salt storage tanks are usually idle but they can by 1.3 inches but the water in the piping will extend its
overflow at any time. Brine can also freeze. An idle length 67.44 inches. Since the water isn’t very compress-
softener can freeze if exposed to a cold draft and can ible it will try to stretch the pipe that far, with drastic
contribute to salt leaking into the effluent (another one results if that water doesn’t have anywhere to go.
of those engineering terms, it’s the treated water leaving The simple solution for idle systems is never isolate
the softeners) if it isn’t checked while it’s idle. them completely. If you have to, then install provisions
Idle condensate and boiler feed pumps can freeze for expansion or a relief valve on them that discharges
up. That’s why it’s important to rotate them regularly. the liquid to a safe location. A favorite spot for this prob-
That’s rotate, not bump. When you bump a pump you lem is the short length of piping between two fuel oil
simply push the electric motor’s start and stop buttons safety shut-off valves. The engineer’s solution is a relief
one after the other so the motor turns over. The problem valve connected to that piping and discharging to the oil
with bumping any rotating equipment is it tends to stop return line. If you don’t have one of those you should
turning right where it stopped last time. Any rotor sus- have a branch line with a small valve for leak testing
pended between bearings will tend to sag over time and closed with a nipple and pipe cap. Remove the cap and
if left in, or returned to, the same position every time the open the valve each time the boiler is shut down for an
sagging increases. extended period then close it back up after a little air has
To rotate a pump you should turn it by hand. gotten in. That little bit of air should not create a prob-
Sometimes that means temporarily removing a coupling lem at the burner because it should pass through while
guard or reaching under it. The final key is to turn it the ignitor is still operating.
1º turns so it’s 90 degrees off its last position. Rotate it Fuel oil in idle piping exposed to the heat of a
once a month and it will only be in the same position boiler room can gradually break down to form heavier
one fourth of the year. All rotating equipment, anything hydrocarbons and gases that produce the equivalent of
run by an electric motor, gas or diesel engine or steam air pockets in piping. That doesn’t necessarily create a
engine or turbine including the drives should be ro- problem for the piping but pumping that fuel with its
tated monthly. By maintaining a schedule of the rotating pocket of gas to a burner can create a flame out (there’s
equipment and rotating one a day or one a week (de- not enough energy in the gas to keep the flame going)
pending on how many you have) all the equipment in a and subsequent re-ignition of the fuel oil to produce a
facility can be rotated on that monthly schedule. furnace explosion. Always recirculate oil to eliminate
Idle piping systems also deserve some attention. any gases long before starting a burner on fuel oil. Fuel
The first lesson of idle liquid piping systems should be oil piping can also be a hazard if it is fully isolated
to ensure there is always one way for the liquid to ex- I have seen four-inch water piping reduced to less
pand out of the piping system. If you valve off a piping than 3-inch internal diameter in a matter of months be-
system to the extent that the liquid is trapped inside, the cause it was idle. Despite chlorination and other forms
piping will be exposed to considerable swings in pres- of water treatment microbes manage to survive. Given
sure as the liquid is heated and cooled. The liquids that stagnant water and a minimal source of nutrients (food to
enter a boiler plant are typically colder than the plant so eat) they can thrive. Not only do those microbes construct
it’s very easy to isolate a cold liquid which will expand rather solid homes on the inside of the pipes they also
when heated. If that liquid is completely trapped the generate waste that can be very acidic or caustic to cor-
only way it can expand is to stretch the pipe and you rode the piping. Just recently I have seen a large number
better believe that it can do it. of articles in engineering magazines on the problems of
Expanding liquid normally raises the pressure to MIC (microbe induced corrosion) which, in many cases,
the point of failure of a gasket or packing at a valve stem is comparable to oxygen pitting because the microbes