Page 79 - Boiler_Operators_Handbook,_Second_Edition

64 Boiler Operator’s Handbook

detected the valves should shut and the Burner Manage- keep the ignitor going.
ment should “lock out.” When you’re satisfied that the Operating on ignitor will provide a very slow
system passed the spark test check the timing and make warming of the boiler, so slow that it may seem like it’s
sure that the system locks out. doing nothing; give it a day if you do it. Only when it’s
Open the ignitor manual valves when the spark apparent that the ignitor can’t bring the temperature up
test and check of PTFI is complete. Then see if you anymore remove any temporary wiring to restore nor-
can establish a proven ignitor flame. Once the ignitor mal ignitor operation and allow main burner operation.
is proven the Burner Management allows at least ten A critical temperature during refractory dry-out is 212°F
seconds for main flame trial for ignition (MFTI) before because at that point you start making steam out of any
shutting down and we can use that period to check the water that’s in the refractory. The steam, expanding
ignitor fire and do some other things. You don’t have rapidly, can erode the refractory as it seeps out into the
to do this every time you start the burner, only after furnace. If you raise the temperature rapidly through
maintenance or adjustments have been made that could that temperature the steam generation can be so great
allow the scanner to see a spark as a flame. That includes that it creates pressure pockets in the refractory to force
a change in scanner alignment or simply removing and it apart, creating voids and cracks that will be repair
replacing the burner; you can’t be certain it’s back in items for years to come. That’s why long-term operation
exactly the same place. on ignitor can be beneficial to a new boiler, drying out
You should be satisfied that the ignitor lights that refractory so slowly that erosion, cracks and voids
quickly (not just before the end of its ten second trial) are dramatically minimized.
and burns with a clean and stable fire. If the ignitor isn’t Of course, all of this is a waste for boilers with
stable you can’t expect it to do a good job of lighting refractory that’s already been fired, right? Wrong! How
the main fire. It should be bright and ragged looking do you know what weather conditions that boiler was in
because there’s lots of excess air there. You don’t want it traveling to your site? Treat your new boiler as if the re-
snapping and breaking up like fire from a machine gun fractory was soaking wet and you’ll never regret it. Treat
where there are bursts of fire. it as if you should be able to run it to high fire right away
An ignitor gives us an opportunity to check op- and plan on a lifetime of refractory repairs. Once you’ve
eration of the boiler safeties and, during initial start-up, reached the limits of ignitor operation you’re ready to
maintain a minimum input into the furnace to slowly establish a main flame and prepare for a combination of
dry-out the refractory. Drain the water from the low refractory dry-out and boiler boil-out.
water cutoffs during the main flame trial period without Repeat the operation to dry-out any major refrac-
pressing any bypass push-buttons to be certain the cut- tory repairs as well. Refractory is one of those things
offs shut the burner down; I have encountered systems that can’t be guaranteed because the manufacturer and
that do an excellent job of alarming a low water cutoff installer have no way of knowing how the dry-out was
but didn’t trip the burner. handled. You want it to remain intact so give it the ten-
Use the cycling of the fuel safety shut-off valves der loving care it deserves.
to check fuel safeties as well (see the chapter on setting
safety switches). Every safety and limit switch should Establish Main Flame
be operated to ensure they will actually shut the burner Having spent a day or two on initially drying the
down. refractory and testing ignitor operation we’re ready to
light that main burner. This is not a time to be faint of
Start Refractory Dry-out heart or careless and quick. Although most small boilers
The life of refractory in a boiler is almost entirely come factory tested so you have some reason to believe
dependent on how it was treated on the initial start-up. it’s set right for main flame ignition that’s no guaran-
By performing a controlled, slow warm-up of the boiler tee. On many boilers you’ll find that particular burner
you can ensure a long life for the refractory. Slam the arrangement is being fired for the first time ever, so
fire to it and you can count on repairing refractory every nobody knows what the right settings are. I frequently
time you open it until you break down and do a com- see operators slowly opening the burner manual shut-
plete refractory replacement. I like to use the ignitor to off valve after the automatic valves open as a burner
begin a dry-out. It requires some temporary wiring and starts; that’s because they saw the technician do the
a relay in most cases (you simply energize the ignitor same thing on the initial start-up. I’ll explain later why
fuel valves (not the spark) in place of the main fuel to you shouldn’t do that but now, on initial start-up, that’s