ISA Boiler Control System Fundamentals

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© 2003, ISA
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ISA
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ES15w
Introduction to
Boiler Control
Systems
© 2003, ISA
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3
Seminar Logistics
• Seminar materials
− Downloadable presentation
− Question and Answer session (audio and email)
− Survey
− Earn 1 Professional Development Hour (PDH)
• Seminar length
− 60 minute presentation
− Three 10-minute question and answer sessions
4
Audio Instructions
• As a participant, you are in a “listen-only”
mode.
• You may ask questions via the internet, using
your keyboard, at any time during the
presentation. However, the presenter may
decide to wait to answer your question until
the next Q&A Session.
• If you have audio difficulties, press *0.
• If you have visual difficulties, call (866) 493-
2825.
© 2003, ISA
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Audio Instructions
• As a participant, you are in a “listen-only”
mode.
• You may ask questions via the internet, using
your keyboard, at any time during the
presentation. However, the presenter may
decide to wait to answer your question until
the next Q&A Session.
• If you have audio difficulties, press *0.
• If you have visual difficulties, call (866) 493-
2825.
6
Audio Instructions
• As a participant, you are in a “listen-only”
mode.
• You may ask questions via the internet, using
your keyboard, at any time during the
presentation. However, the presenter may
decide to wait to answer your question until
the next Q&A Session.
• If you have audio difficulties, press *0.
• If you have visual difficulties, call (866) 493-
2825.
© 2003, ISA
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Audio Instructions for Q&A Sessions
• Questions may be asked via your telephone line.
• Press the *1 key on your telephone key-pad.
• If there are no other callers on the line, the operator will
announce your name and affiliation to the audience and
then ask for your question.
• If other participants are asking questions, you will be
placed into a queue until you are first in line.
• While in the queue, you will be in a listen-only mode until
the operator indicates that your phone has been activated.
The operator will announce your name and affiliation and
then ask for your question.
8
Introduction of Presenter
• ISA Presenter
− Gerald F. Gilman, PE
− Consultant to companies for safety applications and
developer of training programs.
− He started consulting after 37 years at Proctor & Gamble as
a Control and Information Systems Manager in the Soap
Sector Engineering Department.
− He was responsible for the control and information systems
at three P&G sites, the coordinator for safety instrumented
systems and safety standards worldwide, and a key
resource for boiler control systems and boiler start-ups.
− Contact information: jgilman@cinci.rr.com or (513) 522-4154
© 2003, ISA
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Key Benefits of Seminar
• Understand control systems and instrumentation for boilers
• Understand process dynamics of a boiler and the process
control interactions
• Be able to describe
− boiler components and their function
− how the systems interact and how to set up the controls
− swell and shrink
• Be able to configure
− Furnace draft
− Drum level feed water control
− fuel air control
− steam temperature
10
Boiler Fuels
• Gas
• Oil
• Coal
• Fuel combinations
© 2003, ISA
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SAMA Symbols (Scientific Apparatus Makers Association)
ENCLOSURE SYMBOLS
Table 1
Function Symbol
Measuring or
Readout
Manual Signal
Processing
Automatic Signal
Processing
Final Controlling
Within a circle use a letter symbol from Table II
Within other enclosures us a symbol from Table III
12
SAMA Symbols (cont’d)
MEASURING/READOUT LETTERS
Table II
Process Variable Function
A = Analysis**
C = Conductivity
D = Density
F = Flow
L = Level
M = Moisture
P = Pressure
S = Speed
T = Temperature
V = Viscosity
W = Weight
Z = Position
R = Recording
I = Indicating
T = Transmitter
RT = Recording
 Transmitter
IT = Indicating 
 Transmitter
FRT
FR
**Self-defining symbols such as O 2, pH, etc., can be used in place of A.
© 2003, ISA
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SAMA Symbols (cont’d)
SIGNAL SIGNAL
FUNCTION PROCESSING
SYMBOL
FUNCTION PROCESSING
SYMBOL
SUMMING ∑ or + INTEGRATE OR TOTALIZE Q
AVERAGING ∑/n HIGH SELECTING
DIFFERENCE ∆ or - LOW SELECTING
PROPORTIONAL K or P HIGH LIMITING
INTEGRAL ∫ or I LOW LIMITING
DERIVATIVE d/dt or D REVERSE PROPORTIONAL -K or -P
MULTIPLYING X VELOCITY LIMITING V
DIVIDING ÷ BIAS ±
ROOT EXTRACTION √ TIME FUNCTION f(t)
EXPONENTIAL Xn VARIABLE SIGNAL
GENERATION
A
NON-LINEAR FUNCTION f(x) TRANSFER T
TRI-STATE SIGNAL
(RAISE, HOLD, LOWER)
b SIGNAL MONITOR H/, H/L, /L
14
Simple Feedback Control
PRIMARY VARIABLE
XT
K
A T A
f(x)
SET POINT
PROCESS
MANIPULATED VARIABLE
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Feedforward Plus Feedback Control
PRIMARY VARIABLE
XT
YT
SECONDARY
VARIABLE
A T A
f(x)
MANIPULATED VARIABLE
PROCESS
SET POINT
K
16
Cascade Control
PRIMARY VARIABLE
XT
ZT
K
K
SET POINT
A AT
PROCESS
f(x)
MANIPULATED VARIABLE
SECONDARY
VARIABLE
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Ratio Control
A T A
f(x)
MANIPULATED VARIABLE
K
RATIO SET
X
YT
UNCONTROLLED VARIABLE
CONTROLLED
VARIABLE
XT
PROCESS
18
Audio Instructions for Q&A Sessions
• Questions may be asked via your telephone line.
• Press the *1 key on your telephone key-pad.
• If there are no other callers on the line, the operator will
announce your name and affiliation to the audience and then
ask for your question.
• If other participants are asking questions, you will be placed
into a queue until you are first in line.
• While in the queue, you will be in a listen-only mode until the
operator indicates that your phone has been activated. The
operator will announce your name and affiliation and then ask
for your question.
© 2003, ISA
ES15w (1.0) 
19
Live Question and Answer Session
• During Q&A, questions may be asked via your telephone line.
• Press the *1 key on your telephone key-pad.
• If there are no other callers on the line, the operator will announce
your name and affiliation to the audience and then ask for your
question.
• If other participants are asking questions, you will be placed into a
queue until you are first in line.
• While in the queue, you will be in a listen-only mode until the
operator indicates that your phone has been activated. The
operator will announce your name and affiliation and then ask for
your question.
20
Basic Control Functions
• Regardless of the
hardware and software
used certain control
functions are required
• These controls are
− Furnace Draft
− Drum Level Feedwater
− Fuel Air
− Steam Temperature
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Boiler Components
COLD AIR
SUPERHEATER
DESUPERHEATER
STEAM DRUM
STEAM
FROM
SECOND
BOILER
STEAM
FROM
THIRD
BOILER
STEAM TO
THE PROCESSSTEAM HEADER
COLD AIR
FEED WATER
FLUE GASES
AMBIENT
AIR
F.D. FAN
INLET
VANES
I.D. FAN INLET DAMPER
TOTAL
AIR
AIR HEATER
SPRAY WATER FROM
FE DWATER PUMP
HOT AIR
DAMPER
HOT AIR
PULVERIZED
COAL WITH
PRIMARY AIR
(P.A.)
PULVERIZED
FEEDER
P.A. CONTROL
DAMPER
P.A. FAN
FROM OTHER
PULVERIZERS
COLD
AIR
DAMPER
SECONDARY
AIR
E
22
Block Diagram of Boiler Control
+INPUT OUTPUT
FIRING
RATE
DEMAND
FUEL DEMAND
AIR DEMAND
FEEDWATER CONTROL
STEAM TEMPERATURE
CONTROL
BOILER
© 2003, ISA
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Furnace Pressure Control
24
System Reliability & Availability ISA-77.41
• Field transmitter device redundancy should be
provided to the extent necessary to achieve desired
system reliability. The following conditions apply:
− When two transmitters are employed, excessive deviation
between the transmitters shall be alarmed and the associated
control loop shall be transferred to manual
− When three transmitters are employed, excessive deviationbetween the transmitters shall be alarmed
• A transmitter select scheme shall be used for control
purposes
• Furnace pressure shall be measured with three
furnace pressure transmitters, each on a separate
measurement tap.
© 2003, ISA
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Block Diagram of Boiler Control
+INPUT OUTPUT
FIRING
RATE
DEMAND
FUEL DEMAND
AIR DEMAND
FEEDWATER CONTROL
STEAM TEMPERATURE
CONTROL
BOILER
26
Boiler Steam Drum/Swell Shrink
STEAM
STEAM
SATURATED
WATER
WATER
FEEDWATER
WATER-MIXED STEAM BUBBLES
© 2003, ISA
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Single Element Feedwater Control
SET POINT
K
T
f(x)
A
A
X
LT PT
f(x)
FINAL CONTROL DEVICE
M/A CONTROL STATION
PRESSURE
COMPENSATION
DRUM PRESSUREDRUM LEVEL
∫
∆
Typical single-drive control system. For simplicity, redundant transmitters have not been
shown on this typical control drawing. See Figure 2A for ANSI/ISA-5.1-1984 format.
28
Two Element Feedwater Control
∆
∫
f(x)
K
TA
A
X X
K
LTPT PT FT TE
f(x) f(x) f(x)
FINAL CONTROL DEVICE
M/A CONTROL STATION
SET POINT
PRESSURE
COMPENSATION
TEMPERATURE
AND PRESSURE
COMPENSATION
LEVEL
PRESSURE
STEAM
TEMPERATUREFLOWDRUM
PRESSURE
Typical single-drive control system. For simplicity, redundant transmitters have not been
shown on this typical control drawing. See Figure 3A for ANSI/ISA-5.1-1984 format.
© 2003, ISA
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Three Element Feedwater Control
PRESSURE
COMPENSATION
f(x)
A
X
PT FT TE
f(x) f(x)
X
LT PT
f(x)
X
FT TE
f(x)
K
K
∆
∆
T A
FINAL
CONTROL
DEVICE
M/A CONTROL
STATION
SET POINT
PRESSURE AND
TEMPERATURE
COMPENSATION
STEAM
TEMPERATUREFLOWPRESSURE
Typical single-drive control system. For simplicity, redundant
transmitters have not been shown on this typical control drawing.
See Figure 4A for ANSI/ISA-S5.1-1984 format.
LEVEL PRESSURE
DRUM
TEMPERATURE
CONDENSATION
FLOW TEMPERATURE
FEEDWATER
Typical single-drive control system. For simplicity, redundant
transmitters have not been shown on this typical control drawing. See
Figure 4A for ANSI/ISA-5.1-1984 format.
30
Block Diagram of Boiler Control
+INPUT
BOILER
OUTPUT
FEEDWATER CONTROL
STEAM TEMPERATURE
CONTROL
FUEL DEMAND
AIR DEMAND
FIRING
RATE
DEMAND
© 2003, ISA
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Firing Single Fuel/Cross Limiting
AIR CONTROL
FT PT FT
A
A T
P I
A T
P I
A T
P I
f(x)
f(x)
Fuel FLOW
STEAM
HEADER PRESSURE AIR FLOW
SP SP
LO SELECT HI SELECT
Fuel CONTROL
Fuel Feed
AIR DAMPER
32
Dual Fuel O2 Trim
P I
TA
X
Y
X
X
C
Z Y
Y
Y
Y
X X
Y
B
SP
A X
P I
TA
X
P I
TA
X
P I
TA
X
X
P I
A T
P I
A T
A
GAS FLOW
0-90,000 SCFH
FT FT
OIL FLOW
0-10,000 PPH
0-30” WC
FUEL
SUMMER
YX
FUEL
CONTROL
SP
STEAM HEADER
PRESSURE
PT
0-850 PSI
PV
SP SP
GAS CONTROL OIL CONTROL
LOW SELECT HIGH SELECT
GAS VALVE OIL VALVE
FAN DAMPER
AIR CONTROL
PV
SUB
MASTER
HEADER
PRESSURE
CONTROL
AIR FLOW
CHARACT...
f(x)
AIR FLOW
FT AT0-5” WC
BOILER O2
O2 10%
f(x)
O2 TRIM
CONTROL
SP
STEAM
FLOW
© 2003, ISA
ES15w (1.0) 
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Audio Instructions for Q&A Sessions
• Questions may be asked via your telephone line.
• Press the *1 key on your telephone key-pad.
• If there are no other callers on the line, the operator will
announce your name and affiliation to the audience and
then ask for your question.
• If other participants are asking questions, you will be
placed into a queue until you are first in line.
• While in the queue, you will be in a listen-only mode until
the operator indicates that your phone has been activated.
The operator will announce your name and affiliation and
then ask for your question.
34
Live Question and Answer Session
• During Q&A, questions may be asked via your telephone line.
• Press the *1 key on your telephone key-pad.
• If there are no other callers on the line, the operator will announce
your name and affiliation to the audience and then ask for your
question.
• If other participants are asking questions, you will be placed into a
queue until you are first in line.
• While in the queue, you will be in a listen-only mode until the
operator indicates that your phone has been activated. The
operator will announce your name and affiliation and then ask for
your question.
© 2003, ISA
ES15w (1.0) 
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Excess Air vs. Boiler Load
EXCESS AIR
(% o2)
BOILER LOAD
(%)
0 50 100
5
4
3
2
1
36
Non Linear Flow
0 10 20 30 40 50 60 70 80 90 100
0 1 4 9 16 25 36 49 64 81 100
Flow in %
0
10
20
30
40
50
60
70
80
90
100
0 1
4
9
16
25
36
49
64
81
100
0
20
40
60
80
100
120
1 2 3 4 5 6 7 8 9 10 11
Series1
Series2
© 2003, ISA
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Characterization
0 10 20 30 40 50 60 7 0 80 O U T
0 7 .5 15 22 .5 30 37 .5 45 52 .5 60 IN
0
10
20
30
40
50
60
70
80
0
7 .5
15
22 .5
30
37 .5
45
52 .5
60
0
10
20
30
40
50
60
70
80
90
1 2 3 4 5 6 7 8 9
38
Block Diagram of Boiler Control
+INPUT
BOILER
OUTPUT
FIRING
RATE
DEMAND
FUEL DEMAND
AIR DEMAND
FEEDWATER CONTROL
STEAM TEMPERATURE
CONTROL
© 2003, ISA
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Water Side Control Mechanisms
DESUPERHEATER
SUPER-
HEATER
SECTIONS
PURE WATER SPRAYED INTO THE SUPERHEATED STEAM
VAPORIZES; DEGREE OF SUPERHEAT IS REDUCED HEAT
OF VAPORIZATION.
From Power magazine Special
Report, “Steam Generation,”
by R.J. Bender, Associate Ed.
McGraw Hill, NY
40
Typical Single Element Superheat Control
OPEN
CLOSE
K ∫
f(x)
TA
A
T T
A
A A
TT
SPRAY CONTROL VALVE SPRAY CONTROL VALVE
SPRAY
INTERLOCK
SET POINT
0%
0%
100%
M / A CONTROL
STATION
FINAL STEAM
TEMPERATURE
∆
© 2003, ISA
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Typical Two-Element Superheat Control
Open
Close
Final Steam
Temperature
Feedforward
Calculation
f(x)
TA
T T
A
A A
Spray Control Valve Spray Block Valve
Spray
Interlock
0%
0%
100%
M / A Control
Station
K
∆
∫
A
TT
Setpoint
ΣLoad
Index(es)
Transient
Correction
Signal(s)
42
Typical Three-Element Superheat Control
Note: 1. Attemperator Outlet
 Temperature or Spray Flow
Open
Close
Final Steam
Temperature
Transmitter
Feedback (Note 1)
Feedforward
Calculation
f(x)
TA
T T
A
A A
Spray Control Valve Spray Block Valve
Spray
Interlock
0%
0%
100%
M / A Control
Station
K
K
∆
∆
∫
∫
A
TT
TT/
FT
Set Point
ΣLoad
Index(es)
Transient
Correction
Signal(s)
© 2003, ISA
ES15w (1.0) 
43
Audio Instructions for Q&A Sessions
• Questions may be asked via your telephone line.
• Press the *1 key on your telephone key-pad.
• If there are no other callers on the line, the operator will
announce your name and affiliation to the audience and
then ask for your question.
• If other participants are asking questions, you will be
placed into a queue until you are first in line.
• While in the queue, you will be in a listen-only mode until
the operator indicates that your phone has been activated.
The operator will announce your name and affiliation and
then ask for your question.
44
Live Question and Answer Session
• During Q&A, questions may be asked via your telephone line.
• Press the *1 key on your telephone key-pad.
• If there are no other callers on the line, the operator will announce
your name and affiliation to the audience and then ask for your
question.
• If other participants are asking questions, you will be placed into a
queue until you are first in line.
• While in the queue, you will be in a listen-only mode until the
operator indicates that your phone has been activated. The
operator will announce your name and affiliation and then ask for
your question.
© 2003, ISA
ES15w (1.0) 
45
Related Resources from ISA
• Complete, hands-on course on this topic
available through ISA Training Institute online
at www.isa.org/training
− Boiler Control Systems Engineering (ES15)
− Burner Management Systems Engineering (ES16)
− Available any time as on-site training
• Books, software, videotapes, interactive
multimedia
• Standards, journals, membership services
Phone: (919) 549-8411
E-mail Address: info@isa.org
46
Additional ISA Resource Materials
• Fossil fuelpower plant standards
− Boiler Combustion Control ANSI/ISA-77.41-1992
− Feedwater Control System ANSI/ISA-77.42.01-1999
− Plant Demand Development ANSI/ISA-77.43-1994
− Steam Temperature Control System ANSI/ISA-77.44-
1995
− Fossil Fuel Power Plant Instrument Piping Installation
ANSI/ISA-77.70-1994
© 2003, ISA
ES15w (1.0) 
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Seminar Survey
• Web-based Seminar Surveys are tools to help ISA
maintain the quality of our training programs.
• Please complete the following four slides of the
survey and fax to ISA when it is complete.
Please fax completed survey pages to (919) 549-8288.
48
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3. How was registration process?
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Please fax completed survey pages to (919) 549-8288.
© 2003, ISA
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Seminar Survey (cont’d)
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