Page 89 - Boiler_Operators_Handbook,_Second_Edition

74 Boiler Operator’s Handbook

pressure switch should trip before the fire becomes boiler is taken off line and left to cool.
unstable. The final step in a normal boiler start-up is to
establish its manual firing rate or place it in automatic
• Decrease oil pressure to the burner while watching control. Since you should still be at low fire, this can
the fire, again at minimum fire. The low oil pres- require increasing the firing rate manually until the
sure switch should trip before the fire becomes desired firing rate is reached. If you intend to place it in
unstable. automatic you should increase the firing rate until you
notice that it’s about the same as the same sized boiler
• If the oil is heated at the boiler you can check op- that’s already on automatic before switching to auto.
eration of high and low oil temperature switches Simply throwing the switch to auto isn’t the appropriate
(if present) by adjusting the oil temperature while way to do things because the boiler controls could swing
observing the fire. This takes time due to the ther- for some time before they are stable again.
mal inertia of the system so be prepared for that.
If the fuel is heated at a common supply point the
testing should only be done when you will not in- EMERGENCY BOILER START-UP
terrupt the operation of other boilers.
Emergencies come in two forms, instantaneous
What happens if the burner doesn’t trip on low and impending. If you’ve done your job as far as ob-
water cutoff, flame failure, or high pressure limit? You serving the equipment is concerned, regardless of who
secure it, note the failure in the log, and notify your maintains it, you shouldn’t face too many of either.
superiors that it isn’t working properly. A boiler with There are some emergency situations that are beyond
malfunctioning safety controls should not be placed in our control, such as power failures, but we should have
operation. plans for them; right? Instantaneous emergencies in-
Open the boiler isolating valve on a heating boiler volve an immediate shutdown of the plant or an operat-
when the boiler pressure is reasonably close to the ing boiler such that you can’t supply steam to the facility
header pressure. It’s best to open the second stop valve served by the boiler plant. Impending emergencies are
on high pressure boilers when the pressure in the boiler the ones where you know it’s only a matter of time until
is within twenty pounds of header pressure. The mini- you can’t supply that steam.
mal difference in pressure limits steam wire drawing the Impending emergencies involve things like the
second stop valve seats and makes it easier to open the severe squeal of a fan belt or motor bearing on operating
valve. When there’s a bypass built into, or around, the equipment that tells you it’s bound to fail very soon. It
second stop valve you can use it to pressurize the boiler can also be clouds on the horizon and the sound of thun-
header. The normal way is to open the non-return valve der when you know the power is going to fail because
when ready to put the boiler on line to build up pressure you never seem to make it through a thunderstorm
in the boiler header. In either case, always be certain without a power failure. Natural occurrences from flood
the free blow drain valve is open and blowing steam to to excessive heat to deep snow and forest fires seldom
ensure yourself there’s no condensate in the header that come without a warning so they should be impending
would suddenly enter the plant steam header. emergencies, something you know is coming.
After steam is flowing to the header, as indicated With your disaster plan in mind you can take ap-
by a steam flow recorder or a drop in boiler pressure as propriate action. And that’s why you make the plans, so
the non-return valve lifts, close the free blow drain of a you don’t have to stop and think about it. The less time
high pressure boiler. you take to act the more time is allowed for warming
Once the boiler is “on-line” which means it is de- up a boiler and other things that you don’t want to rush
livering heat to the facility, record the fuel and steam or unless you have to. If you’ve actually rehearsed those
other output meter readings. It’s one of the little things disaster plans you will find yourself surprisingly com-
I ask operators for that I never get an answer to—“how fortable with what’s going on.
much fuel does it take to bring that boiler up and onto Steam may be such a precious commodity in your
the line?” If yours is one of those plants that change plant that you maintain a boiler on hot standby. In that
boilers frequently it may be a very important question case, start the standby boiler so it can be brought on
because there’s considerable amount of fuel used to do line. Once the problem with the boiler that tripped is re-
that and an associated amount of energy lost when a solved you can put it on standby or restore it to service.