Page 30 - Boiler plant and distribution system optimization manual
P. 30
Boiler Plant Orientation 15
different so the manufacturers technical manual accumulation of fuel in the furnace. The fuel oil
should be consulted. safety shut off valves will automatically shut
when flame can not be detected in the furnace.
FLAME SAFETY CONTROL
BOILER SAFETY VALVES
A furnace explosion is the ignition and al-
most instantaneous combustion of highly flam- Safety valves are devices that protect the
mable gasses in the boiler. It can cause great ex- steam and water circuits against accidental over
plosive force on the boiler, minor explosions, pressurization.
called puffs or blowbacks can blow flames from Safety valves are required on every pressure
doors and covers. Anyone in the flame path· can vessel. The boiler and pressure code also requires
be seriously burned. Major explosions can shatter that the safety valves have a total steam relieving
observation ports, blow off doors, and demolish capacity at least equal to the rated full load steam
boilers and buildings. flow of the boiler.
A safety valve setting table is supplied in the
instruction manual for each unit showing the pre-
THE MAIN CAUSES OF scribed valves and settings.
ExPLOSIONS ARE: There are a variety of safety valves installed
on systems from over pressurization.
1. Flame failure with no resulting fuel iso-
lation A. There are spring type safety valves supplied
with the boiler main steam and reheat steam
2. Faulty regulating controls
piping.
3. Failure to purge a boiler with at least 4
air volume changes after shutdown or B. There are drum safety valves connected di-
before each attempted light-off. rectly to the steam drum.
4. Fuel shut-off valve leakage C. Superheat safety valves are connected di-
5. Loss of furnace draft rectly to the main steam: line to the high
pressure turbine.
D. Safety valves are connected directly to the
AN OvER PRESSURE CONDITION reheat inlet piping.
CAN OCCUR IN ONE OF TWO WAyS:
E. Safety valves are connected directly to the
A gradual increase in pressure due to reheat outlet piping.
improper operation or malfunctioning
equipment. There are electrically or pilot operated pres-
sure relief valves located on the superheater out-
A sudden and rapid increase in pressure let lead downstream from the spring type safety
caused by an immediate loss of steam valves. These relief valves are not included in the
flow. total relieving capacity of the safety valves be-
cause they can be isolated from the boiler. They
are set to open at a pressure below the popping
The flame safety control is designed to pre- pressure of the lowest set superheater safety
vent any condition which could result in a boil- valve. This is to prevent the safety valves from
er explosion. Its basic function is to prevent the opening except on major over pressures.
