Page 88 - Boiler plant and distribution system optimization manual
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Chapter 8
The Control of Boilers
Controlling boilers can be a complex subject. SAFETY CONTROLS
The intent here is to summarize, simplify and
clarify the subject of boiler controls. There are The purpose of the boiler safety control sys-
many very good companies specializing in boiler tem is to prevent explosions and other damage to
controls who have been continually improving the boiler. If an accumulation of unburned fuel
control system technology for many years. vapor suddenly ignites, explosive levels of ener-
The field of boiler controls is an advancing gy can be released and cause severe damage to
rapidly especially since the introduction of dis- the boiler and surrounding countryside.
tributed digital systems, the latest in a long string If the water level in the boiler drops below a
of advances. However, the basics of boiler control certain point, it could have a melt down. If there
are straight forward and subject to less change. are disruptive fuel pressure changes, the ensu-
ing flame instability could cause an explosion or
heavy smoking. These and several other condi-
STEAM PRESSURE CONTROL tions must, for the sake of safety, be controlled at
all times.
The steam pressure is the balance point be-
tween demand for energy in the distribution sys-
tem and the supply of fuel and air to the boiler for COMBUSTION CONTROL
combustion.
As energy is used by the steam system, pres- The energy is supplied to the boiler by the
sure drops, creating a demand for more energy. combustion process and the combustion control
Several interacting control loops are used to system regulates the firing rate by controlling
insure steam pressure is maintained and that the amount of air and fuel delivered to the burners.
flows of water, air and fuel are managed to insure Combustion control systems are regulated
safe, efficient and reliable operation. to maintain the desired steam pressure and they
These control loops are: must be able to respond the many dynamic as-
pects of the burner, fuel and air control sub-sys-
tems in a coordinated way to maintain the steam
————————————————————————
• Boiler Safety Controls pressure set point in spite of demands of the
steam distribution system.
• Combustion Control
• Feedwater Control
• Blowdown Control
FEEDWATER CONTROL
• Furnace Pressure Control
• Steam Temperature Control The purpose of the feedwater control system
• Cold End Temperature Control for air heat- is to maintain the correct water level in the boiler
ers and economizers during all load conditions.
——————————————————————— Feedwater control must be able to regulate
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