BoilerControl Engineering Basics ISA Expo.ppt

Boiler Control Systems Engineering

1. Standards
Certification
Education & Training
Publishing
Conferences & Exhibits
Automation Connections
ISA EXPO
2006

2. Standards
Certification
Education & Training
Publishing
Conferences & Exhibits
Boiler Control Systems
Engineering
Jerry Gilman

3. Control System Functions
•A boiler is a process
•Regardless of what control technology is used all boilers
require certain control functions.
–Furnace Draft
–Drum Level Feedwater
–Fuel Air
–Steam Temperature

4. Control System Considerations
•Draft
•Drum level feedwater
–Single element
–Two element
–Three element
•Fuel air ratio
•Final elements Valves etc
–Valve Sizing

5. Basic Diagram of a Boiler
WATER
FUEL
AIR
MIXINGOF
FUEL&AIR
HEAT
TRANSFER
SURFACE
FURNACE
STEAM/WATERSYSTEM
STEAM
BLOWDOWN
FLUEGAS
ASH

6. Steam & Mud Drum / Circulation
STEAM
STEAM
M UD
DRUM
FUEL
FURNACE
FLAM E
AIR
GAS BAFFLES
FLUE GAS
CIRCULAT ION
WAT ER
CIRCULAT ES
CLOCKW ISE

7. 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

8. 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.

9. SAMA Symbols (Table III)
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
X
n
VARIABLE SIGNAL
GENERATION
A
NON-LINEAR FUNCTION
f(x)
TRANSFER
T
TRI-STATE SIGNAL
(RAISE, HOLD, LOWER)

SIGNAL MONITOR H/, H/L, /L

10. SAMA Legend
TA
A
K∫
1. CONTROLLER
SET POINT
GENERATOR
PROPORTIONAL
RESET
MANUAL SIGNAL
GENERATOR
AUTO./MAN.
TRANSFER SWITCH
TA
A
2. AUTO MANUAL + BIAS STATION
BIAS
ADJUSTMENT
MANUAL SIGNAL
GENERATOR
AUTO./MAN.
TRANSFER SWITCH
±
Measuring or Readout
Automatic Signal Processing
Manual Signal Processing
Final Controlling
Signal Repeater
∑ Summing ∑/
h
Summing
d/
d1 Derivative ∆ Difference ∫ Integral
K
,
-K Proportional, Reverse Proportional
X Multiplying ÷ Dividing √ Root Extracting
f(x) Non Linear or Unspecified Function
f(t) Time Function
> High Selecting < Low Selecting
High Limiting Low Limiting
Velocity or Rate Limiter
+, -, ± Bias
T Transfer A Analog Signal Generator
>|
>
|
|

11. Simple Feedback Control
PRIMARYVARIABLE
XT
K
ATA
f(x)
SETPOINT
PROCESS
MANIPULATEDVARIABLE

12. Feedforward Plus Feedback Control
PRIMARYVARIABLE
XT
YT
SECONDARY
VARIABLE
A T A
f(x)
MANIPULATEDVARIABLE
PROCESS
SETPOINT
K

13. Cascade Control
PRIMARYVARIABLE
XT
ZT
K
K
SETPOINT
A AT
PROCESS
f(x)
MANIPULATEDVARIABLE
SECONDARY
VARIABLE

14. Ratio Control
A T A
f(x)
MANIPULATEDVARIABLE
K
RATIOSET
X
YT
UNCONTROLLEDVARIABLE
CONTROLLED
VARIABLE
XT
PROCESS

15. Block Diagram of Boiler Control
+INPUT OUTPUT
FIRING
RATE
DEMAND
FUELDEMAND
AIRDEMAND
FEEDWATERCONTROL
STEAMTEMPERATURE
CONTROL
BOILER

16. Furnace Pressure Control

17. Block Diagram of Boiler Control
+INPUT
BOILER
OUTPUT
FIRING
RATE
DEMAND
FUELDEMAND
AIRDEMAND
STEAMTEMPERATURE
CONTROL
FEEDWATER CONTROL

18. Boiler Steam Drum Swell / Shrink
STEAM
STEAM
SATURATED
WATER
WATER
FEEDWATER
WATER-MIXEDSTEAMBUBBLES

19. Single Element Feedwater Control
SETPOINT
K
T
f(x)
A
A
X
LT PT
f(x)
FINALCONTROLDEVICE
M/ACONTROLSTATION
PRESSURE
COMPENSATION
DRUMPRESSUREDRUMLEVEL


Typicalsingle-drivecontrolsystem.Forsimplicity,redun-
danttransmittershavenotbeenshownonthistypical
controldrawing.SeeFigure2AforANSI/ISA-S5.1-1984
format.

20. Single Element Control Action
*INTERACTIONWITHFIRINGRATECONTROLDUETOIMBALANCE
BETWEENSTEAMFLOWANDFEEDWATERFLOW.
%STEAMFLOW
FEEDWATERFLOW
STEAM
FLOW
*
*
TIME0
0
25
50
75
100
NWL
SHRINK
DRUMLEVEL
SWELL

21. Two Element Feedwater Control


f(x)
K
TA
A
X X
K
LTPT PT FT TE
f(x) f(x) f(x)
FINALCONTROLDEVICE
M/ACONTROLSTATION
SETPOINT
PRESSURE
COMPENSATION
TEMPERATURE
ANDPRESSURE
COMPENSATION
LEVEL
PRESSURE
STEAM
TEMPERATUREFLOWDRUM
PRESSURE
Typicalsingle-drivecontrolsystem.Forsimplicity,redundant
transmittershavenotbeenshownonthistypicalcontroldrawing.
SeeFigure3AforANSI/ISA-S5.1-1984format.

22. Performance Two Element (Ideal Conditions)
NWL
100
75
50
25
0
0 TIME
STEAM
FLOW FEEDWATERFLOW
%STEAMFLOW
SWELL
SHRINK
DRUMLEVEL
FEEDWATERPRESSURE

23. Performance Two Element (Effect of Feedwater Variation)
NWL
SWELL
SHRINK
DRUMLEVEL
100
75
50
STEAM
FLOW
25
0
0 TIME
FEEDWATERFLOW
%STEAMFLOW
FEEDWATERPRESSURE

24. 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


TA
FINAL
CONTROL
DEVICE
M/ACONTROL
STATION
SETPOINT
PRESSUREAND
TEMPERATURE
COMPENSATION
STEAM
TEMPERATUREFLOWPRESSURE
Typicalsingle-drivecontrolsystem.Forsimplicity,redundant
transmittershavenotbeenshownonthistypicalcontroldrawing.
SeeFigure4AforANSI/ISA-S5.1-1984format.
LEVELPRESSURE
DRUM
TEMPERATURE
CONDENSATION
FLOWTEMPERATURE
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.
(K) (a) +K (b) + K (c) etc. + bias = output

25. Performance Three Element

26. Block Diagram of Boiler Control
+INPUT
BOILER
OUTPUT
FEEDWATERCONTROL
STEAMTEMPERATURE
CONTROL
FUEL DEMAND
AIR DEMAND
FIRING
RATE
DEMAND

27. Firing Single Fuel/Cross Limiting
AIR CONTROL
FT PT FT
A
AT
PI
AT
PI
AT
PI
f(x)
f(x)
Fuel FLOW
STEAM
HEADER PRESSURE AIR FLOW
SP SP
LO SELECT HI SELECT
Fuel CONTROL
Fuel Feed
AIR DAMPER

28. Cross Limit Control With O
2 Trim
G A S F L O W
S T E A M
F L O W
A IR C O N T R O LG A S C O N T R O L
H I S E L E C TL O S E L E C T
S P S P
S T E A M
H E A D E R P R E S S U R E A IR F L O W O
2
A IR D A M P E RG A S VA LV E
FT P T FT AT
P
P P
T
T
A
A
A A
I
I I
P
TA
I
f(x)
f(x)

29. Flow Characteristics
100
50
%FUELAND
AIRFLOW
0
0 50 100
%CONTROLRANGE
A,B–BASICFLOWCHARACTERISTICSOFCONTROLLEDDEVICES
C,D–CHARACTERISTICSAFTERLINEARIZATIONANDALIGNMENT
AIR
FUEL
FUEL
AIR
(B)
(A)
(D)
(C)

30. 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

31. 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

32. Characterization
0 10 20 30 40 50 60 70 80OUT
0 7.5 15 22.5 30 37.5 45 52.5 60IN
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
Series1
Series2

33. Control Valve Sizing Calculations
•C
v = Number of US gallons of water at 60
o
F that
flows through a valve in one minute when the
pressure differential across the valve is one pound
per square inch
–Valve sizing water no density consideration:
–The term C
v is generally used in industry for calculating the
relative flow capacity in valves
valverop acrosspressure dΔP
ravityspecific gSG
gpmQ




34. Control Valve Sizing Calculations (cont’d)
•Valve sizing water no density consideration:
P = pressure drop across valve typical third of drop
600,000 pph water = 600,000  8.34 lb/gal = 1200 gpm
P = pressure drop across valve, typical a third of drop
Pump pressure = 2000 psi,
Drum pressure = 1400 psi
2000  1400 = 600
600  1/3 = 200 valve drop
ΔPSGGPMCv 

35. Control Valve Sizing Calculations (cont’d)
•The calculation 600,000 pph is:
•The calculation for 250,000 pph is:
84.85 200 1.0 1200 C
P G S GPM C
v
v


24.49 150 1.0300 Cv 

36. Control Valve Sizing Calculations (cont’d)
•Valve sizing water 450
o
F, SG = 0.827
•The calculation 600,000 pph is:
C
v at 60
o
= 84.85
C
v
at 450
o
= 77.16
77.16 200 0.827 1200 C
P G S GPM C
v
v



37. Control Valve Sizing Calculations (cont’d)
•Valve sizing steam:
92.3
1083
100,000

17.2 63
100,000
C
17.2 0.44956 133 133, 400 of thirdOne
4001000 1400 ΔP
0.44956 lbs 1000at Steam volume,specific V
V P 63
pph
C
v
v









38. Control Valve Sizing Calculations (cont’d)
•Valve sizing steam:
114.1
876.6
100,000

13.9 63
100,000
C
13.9 0.6875 133 133, 400 of thirdOne
400
1000 - 1400 P
0.6875
lbs 1000at steam dsuperheate F
o
800 volume,specific V
V P 63
pph
C
v
v











39. Summary
•Regardless of the hardware and or software used certain
control functions are required.
•These controls are
–Furnace Draft
–Drum Level Feedwater
–Fuel Air
–Steam Temperature
•Measurement / transmitter specifications
–Calibration
–Calibration span
•Final elements Valves etc
–Valve Sizing

40. Questions and Discussion

41. Related Resources from ISA
Phone: [phone]
E-mail Address: [email protected]
•Boiler Control Systems Engineering Jerry Gilman
•The Control of Boilers Sam G. Dukelow
•ISA Courses
•ES15 Boiler Control System Engineering
–Three day course
–One day overview
–WEB introduction course
•ES16 Burner Management System Engineering
–Three day course
–One day overview