This document discusses the key objectives and performance indicators for boiler control systems. It provides an overview of boiler processes including elementary block diagrams of the steam/water system and combustion system. Expanded models are shown for the boiler process and heat conversion in the boiler. Basic control functions are outlined for drum level control, furnace pressure control, combustion control, and steam temperature control. Diagrams of common boiler types such as fire-tube, water-tube and fluidized bed designs are also included.

1. Practical Boiler Control and
Instrumentation for
Engineers and Technicians
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2. Performance objectives of Boiler Controls
Safety
OObbjjeeccttiivveess ooff BBooiilleerr CCoonnttrroollss
Know the hazards
Safety trip systems
Availability Performance
Burner safety
Regulatory
Reliable C & I
Robust controls
Trouble shooting
Secure software
Stable controls
Operability
Efficiency
Dynamic response
Testing Maintenance
Figure 1.1
Key objectives and performance indicators for boiler control systems
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3. Elementary block diagram of boiler processes
Fuel in / Steam out!
Flue Gas
Steam/Water system
Feed water Steam
Heating , Evaporation &
Superheating
Blow Down
Heat Transfer
Combustion system
Fuel
Air
Hot Gas
Ash removal
Mixing
and heating
Radiant
heat
Combustion furnace
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4. Boiler process model expansion
Feed Water
Drum
Sat. Steam
S/H 1
Steam to
Users
Flue Gas Heat
Economiser
Atmosphere
Air Heater
Heat to evaporation
Water Circulation
Wind box
S/H 2
De-S/H
Heat to
Superheaters
Combustion in furnace
Warm
Air
F D Fan
I D Fan
Burners
Fuel feeders
Figure 1.3
Expanded model for the boiler process
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5. Heat conversion in the boiler
Heat to raise water to
boiling temperature
Heat to evaporation to
convert to steam
Output superheated
steam: intensive energy
supply
Heat to atmosphere
Heat content
Heat to superheat the
steam
Temperature
Feedwater
Heat from
combustion of
fuel
Heat recovery to
incoming air and water
Figure 1.4
Heat input requirements for steam generation at atmospheric
pressure
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6. Interaction of variables in the boiler
processes
Interaction of variables in the boiler processes
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7. Typical Horizontal Return Tube Fire-Tube Boiler
Figure 1.6
Early type of firetube boiler
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8. Typical 3 or 4 pass Horizontal (Scotch Marine) Fire
Tube Boiler
Figure 1.7
Example of the firetube boiler
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9. Fundamentals of the water tube boiler
circulation and its superheater
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10. Section through typical industrial boiler
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11. Atmospheric fluidized bed boiler
Figure 1.10
Example of a fluidized bed boiler with gravimetric feeder for coal
or waste material
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12. Boiler (Drum) level control function
Set Point
+ -
Drum
(Water inventory)
MV ( Manipulated Variable)
Ref section 1.6 of manual
Boiler Control Functions
Feedwater
supply rate
Level control
+ -
Steam flow
LT
PV
(Process Variable)
Figure 1.11
Basic control function for drum level
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13. Furnace pressure control function
Ref section 1.6 of manual this set point?
Boiler Control Functions
SP
- +
What determines
MV PV
Furnace
ID Fan
extraction
rate
Draft control
PT
-
+
FD air flow
Difference will integrate to
change pressure over time
Figure 1.12
Basic control function for furnace draft
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14. Outline of the combustion control function
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15. Outline of the pressure and load control function Ref section 1.6 of manual
Boiler Control Functions
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16. Steam temperature control function
De-superheater
spray flow valve
Ref section 1.6 of manual
Boiler Control Functions
TT
PV
MV
SP
+ -
Temperature
control
Water flow to de-superhtr.
-
Steam temp from 1st stage
superhtr.
Heat flow to
1st stage
+
2nd stage superheater.
Heat flow to
2nd stage
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17. DO YOU WANT TO KNOW MORE?
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