Cleaver-Brooks CBH 40 - Page 30

Chapter 2- The Pressure Vessel
mal firing operation since the high temperature of
operation vaporizes any condensation. However,
proper boiler operation must be maintained,
especially with a hot water boiler, to prevent the
flue gases from falling below the dew point.
At the start of lay-up, thoroughly clean the fireside
by removing any soot or other products of com-
bustion from the tubes, tube sheets and other fire-
side surfaces. Brushing will generally suffice.
Sweep away or vacuum any accumulation. The
fireside surfaces may be flushed with water, how-
ever, all moisture must be eliminated after
flushing and the surfaces dried by blowing air or
applying some form of heat. It is good practice to
protect the cleaned surfaces by coating them with
an anti-corrosive material to prevent rust.
To prevent condensation from forming in the con-
trol cabinet, keep the control circuit energized.
Dry storage is generally employed when the boiler
will be out of service for some time or where
freezing temperatures may exist. In this method
the boiler must be thoroughly dried because any
moisture would cause corrosion. Both fireside and
waterside surfaces must be cleaned of all scale,
deposits, soot, etc. Steps must be taken to
eliminate moisture by placing moisture absorbing
materials such as quick lime (at 2 pounds for 3
2-10
cubic feet of volume) or silica gel (at 5 pounds for
30 cubic feet of volume) on trays inside the vessel.
Fireside surfaces may be coated with an anti-
corrosive material or grease or tar paint. Refrac-
tories should be brushed clean and wash coated.
All openings to the pressure vessel such as man-
hole and handholes should be shut tightly. Feed-
water and steam valves should be closed. Damper
and vents should be closed to prevent air from
reaching fireside surfaces. Periodic inspection
should be made and absorption materials renewed.
Wet storage is generally used for a boiler held in
stand-by condition or in cases where dry storage is
not practical. The possibility of freezing tempera-
tures must be considered. Care must again be
taken to protect metal surfaces. Variables preclude
definite recommendations, however, it is suggested
that the pressure vessel be drained, thoroughly
cleaned internally and re-filled to overflowing with
treated water. If deaerated water is not available,
the unit should be fired to boil the water for a
short period of time. Additional chemicals may be
suggested by the water consultant to minimize
corrosion. Internal water pressure should be main-
tained at greater than atmospheric pressure.
Nitrogen is often used to pressurize the vessel.
Fireside surfaces must be thoroughly cleaned and
refractory should be wash coated.