Page 87 - Boiler_Operators_Handbook,_Second_Edition

72 Boiler Operator’s Handbook

admitting steam and gradually open the steam supply Record the start-up activity in the log and begin
to the deaerator only after there is a constant flow of monitoring the plant as required for normal operation.
water to the boiler. Any sudden surges in water flow It’s very important to note all problems that came up,
could rapidly produce a vacuum in the deaerator. Also changes in operating procedures that were required to
avoid any rapid changes in facility steam consumption accomplish the start-up or correct problems, and the
that could cause a drop in steam pressure. If a vacuum is conditions at various times during the process with the
formed the deaerator and its storage tank could be dam- times noted. That data can be used to compare with the
aged. Once the deaerator pressure is up to normal, open original SOP for dead plant start-up and modify it to
the isolating valves wide so the steam pressure regulator improve the process.
can function and close the vent valve to its normal throt- Notice that I didn’t say shorten the process. Usual-
tling position. ly when starting up a dead plant you have time because
Test the low water cutoff before reaching normal many other operations won’t even be contemplated un-
operating pressure and after the pressure is high enough til you have steam or hot water flowing normally. A slow
for the boiler to return to firing. That’s normally when start-up ensures minimal stress from thermal shock and
pressure exceeds 6 psig for heating boilers, 30 psig for avoids the pitfalls of rushing to get the job done.
power boilers. Lift test the safety valves when the pres- On the other hand, when the plant is being re-
sure is above 75% of the safety valve set pressure. They stored after an unscheduled interruption, you can take
could have corroded shut during the shutdown period. the shortest reasonable time based on experience with
At some point low fire will not be adequate for prior start-ups. If called upon to rush you should al-
pressure to continue to rise. Increase the firing rate ready know which boiler to select for it—the one that
manually in small increments (less than 10%) and al- needs the most refractory repairs anyway. Selectively
low the pressure to stabilize before increasing it again. damaging the plant under emergency conditions, such
Initially all the condensate will stay in a steam system as restoring heat to a hospital or nursing home where
because the pressure will be below atmospheric wher- it’s critical, is part of a well prepared disaster plan.
ever automatic vents aren’t operating properly or don’t
exist. Condensate will not return until there is enough
pressure differential to push it back to the boiler plant. NORMAL BOILER START-UP
At several points during the start-up the pressure dif-
ferential will accelerate condensate returning; the slow After that initial plant start-up we begin to relax
steps will limit the rate at which that happens. Wait until and, regretfully, can get too casual about a boiler start-
the pressure is at, or slightly above, normal operating up. We tend to forget that the equipment deteriorates
pressure to switch control to automatic. with age and use to the degree that something could go
After an hour or so of automatic boiler operation wrong. A certain amount of that should be addressed
the normal operating levels of the condensate tank and each year right after the annual inspection when, be-
deaerator may be restored if they were lowered for the cause we had the boiler apart, we should start it up as
start-up. Increase the level gradually to avoid any dam- if it were new. We should also pick up a few other good
age associated with a rush of cold inlet water. If your habits that take that wear and age into consideration.
timing is right you shouldn’t have an inrush because the Close circuit breakers as needed to apply power to
vessels will be filled by the condensate stored in the sys- the burner management control at least 24 hours prior to
tem. Make a point of noting the amount of condensate starting a fire in the boiler. Flame sensors can deteriorate
returned to provide better guidance in an SOP for the and provide false flame signals but may operate nor-
next dead plant start-up. mally when they are first energized. The long warm-up
With steam generation stabilized, draw water ensures the sensors are properly checked by the burner
analysis and determine setup of chemical feed and management system during start-up.
blowdown controls. Open cooling water valves to any A normal boiler start-up assumes other boilers in
quench system. Open valves to put the continuous the plant are operating and the boiler to be started has
blowdown heat recovery system into operation. Vent not had maintenance or other work performed on it. If
the flash tank until steam has been flowing out the vent there was work performed, review the recommenda-
for ten to fifteen minutes so you don’t push air into the tions for new plant and dead plant start-up to determine
deaerator. Alternatively, leave the deaerator vent wide if there’s anything you should check or test before pro-
open until the blowdown system is in normal operation. ceeding. Make sure the vent valve is open. If the stop