Page 81 - Boiler Operator’s Handbook

66 Boiler Operator’s Handbook

ery time, once you have it set. lected procedure should be submitted to, and approved
Now that you can get a main flame it’s a good time by, the manufacturer.
to review the process. Open valves admitting fuel to the The contractor may say “we always did it that
furnace only after purge and low fire position interlocks way;” but that doesn’t make it right; insist on a written
are proven. Open the valves in the main fuel only after document. Be certain to remove brass, copper or bronze
a pilot (ignitor) flame is proven. Prove the purge limits parts exposed to the boiler water because the caustic
prevent completion of a purge cycle when combustion water can damage them. In many instances that includes
air is blocked by blocking it. Ensure the purge require- the safety valves. Replace them with overflow lines run
ments are not satisfied when the burner register(s) to a safe point of discharge where any liquid that passes
is(are) closed, when the fan inlet is blocked to the degree through can be collected and treated. Be prepared to
the required air flow cannot achieve the specified flow dispose of the boil-out chemicals after the process is
rate and when the boiler outlet is similarly blocked. En- completed. Sometimes it’s necessary to interrupt the
sure the burner start-up cannot continue after purging dry-out procedure to dump the boil-out chemicals,
until the low fire position is proven. Admit main fuel flush, and refill the boiler. Have a procedure in place for
only after observing a stable and adequate pilot flame re-establishing the dry-out. Be prepared to commence
exists and extinguishes at the end of the main flame trial normal water treatment immediately after the boil-out.
for ignition period (unless there are separate pilot and Don’t rush these steps, pushing activity along at
main flame sensors where you assure the main flame this point can damage the boiler in a manner that will
sensor does not detect the pilot flame). Purge the boiler last its lifetime. Have adequate personnel on hand for
completely according to the code after each test or fail- the maximum period required because it is not unusual
ure to produce a main flame. Don’t alter flame trial tim- to start and stop the boiler frequently during the initial
ing of the control. phase of a dry-out. It’s also possible for the procedure to
take much more than an eight hour shift. On any large
Boil-out and Complete Dry-out boiler it’s common for it to take more than a day.
This normally only applies to a new boiler. You Normally the dry-out and boil-out are performed
may have to boil-out a boiler after tube replacements or with controls in manual for minimal adjustments as
complete dry-out of some refractory repair so follow the necessary to obtain a clean burning fire. You started the
sequence when necessary. The entire process is skipped dry-out before beginning boil-out and will probably
for normal operation of a boiler. end up finishing boil-out before the dry-out is complete.
Some boilers will have pipe caps or plugs in casing That’s because you don’t produce any steam pressure to
drains where moisture can escape during dry-out. They speak of while boiling out so the temperature is only a
should be removed for this period of operation. little over 212°F when the boil-out is complete.
Normally the boiler is simply filled with treated You’ll have to let the boiler cool some before drain-
makeup water or feedwater before this stage. Once ing the boil-out chemicals and refilling it but there’s no
the process begins that will have to change. Boil-out harm in dropping them while the boiler is hot. There
chemicals should be as prescribed by your boiler water are two arguments about dropping boil-out water; one
treatment supplier or the boiler manufacturer. Be certain is solids will stick to the metal and bake on so allowing
you don’t have conflicting requirements. Handle those the water to cool is best, the other is they will retain the
chemicals with extreme care and using all the required solids while hot but drop them out if they’re allowed
protective clothing and equipment; they’re a lot tougher to cool so dumping the water hot is best. I happen to
than normal chemicals. They should be added right be- believe the second argument but always look for recom-
fore you start the boil-out and dry-out and removed as mendations of an appropriate temperature to drain the
soon as the boil-out is done. water from the boiler and chemical manufacturers.
Burner operating time should be limited until The boil-out water is considerably more caustic
the boiler is operational and you’ve completed refrac- than normal boiler blowdown so you should provide
tory dry-out and boiler boil-out. When it’s possible to for proper disposal of that water, neutralizing it before
operate the boiler on main flame, make the first step a dumping it in the sanitary sewer or employing a li-
combined refractory dry-out boiler boil-out procedure. censed hauler to dispose of it.
Neither function can be performed without having an Once the boil-out chemicals are drained the boiler
effect of the outcome of the other. Procedures supplied water must be treated. The boil-out removed all the
by the boiler manufacturer should be followed or the se- varnish and grease that was covering the inside of the