Chapter7 ControlLoop


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Instrumentation
Documentation
To successfully work with (and design) control systems, it is essential to
understand the documents that are typi
cally used to illustrate process con-
trol and associated field instrument
ation. The documentation of process
control and associated field instrume
ntation is normally created by the
engineering firm th
at designs and constructs th
e plant. The company that
commissioned the plant may have an internal documentation standard the
engineering firm will be required to follow.
For an older installation, the plant
documentation may only exist as a
series of paper documents. Today the documentation created for a new or
upgraded plant is produced electronically using automated design tools
and software. The tools and software selected by the plant or engineering
firm for initial plant design or up
grade will influence the documentation
format and how documentation is main
tained at the plant site. Also, the
selection of the control sy
ROCESSES
In this chapter, we examine four ty
pes of drawings that are commonly
used to document process control and associated field instrumentation.
NSTRUMENTATION
OCUMENTATION
tem to the field devices; thus, it is a good idea to use the plot plan to get a
sense of the plant layout and a feel
for the location of process equipment
7.2Process Flow Diagram
DRAINAGE DITCH
OFFICE
POND
POND
TRUCK
LOADING/UNLOADING
AREAS
PROPERTY BOUNDARY
WATER
TREATMENT
PUMP
STATION
POWER
CONTROL
PACKAGING
REACTION
FILTRATION
PLOT PLAN
PLANT ( )
SHEET DRAWING NUMBER REV
1 OF 1 DA200023 1
ROCESSES
Process flow diagram
– Drawing that shows the general
CHAPTER 7 – C
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OCUMENTATION
Figure 7-2. Process Flow Diagram
222-C-401
SPLIT
RANGE
CONDENSATE
222-E-402A/B
60 PSIG STEAM
To 225-E-505
OFF_GAS TO
PLANT
OFF-GAS TO
FLARE
222-E-401
STEAM
STREAM ID 1 2 3 4 5
MOLE FRAC LIQUID 1.00 0.00 1.00
0.00 1.00
TEMPERATURE , Deg F 143.67 158.02 258.92 26
9.19 269.19
PRESSURE, PSIG 558.00 450.00 454.75 45
5.00 455.00
RATE, LB/HR 149996 55799 264204 31
46.17 3186.14
MOLECULAR WEIGHT 49.89 38.69 55.76 54
.38 58.19
Act. RATE, GAL/MIN
632.40 ----1315.46
-----443.03
DENSITY , LB/FT3 29.06 0.85 25.04
5.00 25.06
COMP. LB-MOL/HR
COMMENTS:
VALVE NORMALLY OPEN
VALVE NORMALLY CLOSED
REFERENCE DRAWINGS
TITLE DWG NO.
PFD PLANT/225/220 DA6502
DRAWING CONTROL DA6500
SYMBOLS & LEGEND DA6501
FEED FROM 220-E-350
AS…BUILT
BY _____________ DATE _______
1 CONSTRUCTION 9/12/-2020
REV ISSUED FOR DATE
PROCESS FLOW DIAGRAM
PLANT ( ), SUMMER CASE
SHEET DRAWING NUMBER REV
1 OF 1 DA6503 1
ROCESSES
into the control system, as well as
local pressure, temp
erature, or level
gauges that may be viewed in the field but are not brought into the control
system.
As mentioned earlier, the engineering company that is creating the P&ID
normally has standards that they follow in the creation of this document.
In some cases, the drawing includes
an overview of the closed loop and
manual control, calculations, and measurements that will be implemented
in the control system.
Closed loop control
- Automatic regula
tion of a process
inputs based on a measurement of process output.
Manual control
– Plant operator adjustment of a process
CHAPTER 7 – C
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OCUMENTATION
Figure 7-3. Piping and Instrumentation Diagram
PHOSPHATE INJECTION
DA-50220 SHT 1
TO/FROM DRW. DA-50228
NOTES:
1.LEAD/ LAG VALUES SHALL BE
TUNED FROM THE OPERATOR
CONSOLE.
2.WHEN LIC-301 IS CHANGED TO
REFERENCE DRAWINGS
TITLE DWG NO.
PFD BOILER-12 DA5450
STEAM GENERATION DA50230
FEEDWATER DA50228
UTILITY WATER DA50220
SYMBOLS & LEGEND DA6501
AS…BUILT
BY _____________ DATE _______
1 CONSTRUCTION 9/12/-2020
REV ISSUED FOR DATE
PIPING AND INSTRUMENTATION DIAGRAM
STEAM DRUM -BOILER -12
SHEET DRAWING NUMBER REV
1 OF 1 DA50229 1
STEAM
DRUM
301
301
301
301A
301A
301
FV301A
FV301B
FT301
332
332
332
301D
312
311
312
301B
301A
301E
301F
301G
301C
301B
301A
301J
301H
301I
301D
301C
336
FT302
OUTLET
STEAM
DRUM STEAM -1
DRUM STEAM -2
FEEDWATER
DA-50228 SHT 1
UTILITY WATER
DA-50220 SHT 1
336
336
301
ASME
ASME
LIMIT
ASME
1Ž 80-47-6A1
1Ž W-157-203
1/2Ž D-118-1A1
1/2Ž D-118-1A1
1/2Ž D-118-1A1
1Ž C-24-6A1
10Ž W-149-6A1
1/2Ž
1
1/2Ž
1/2Ž
1/2Ž
1 ½ Ž D16-1A1
1 Ž
1/2 Ž
1/2 Ž
1 Ž
110-E 30
SAMPLE
COOLER
DA-40230 SHT 1
LOG. DIAG 42A7
STM DRUM
MONITOR FAULT
DA-40230 SHT 1
LOG. DIAG 42A7
STM DRUM LVL
LOW ALARM
DA-40230 SHT 1
LOG. DIAG 42A7
STM DRUM LVL
HIGH ALARM
DA-40230 SHT 1
LOG. DIAG 42A7
STM DRUM LVL
HI HIALARM
DA-40230 SHT 1
LOG. DIAG 42A7
STM DRUM LVL
LO LOALARM
TO/FROM DRW. DA-50230
311
301B
301A
LEAD/LAG
NOTE 1
NOTE 2
OPERATION
SELECT
SET @
SET @
4Žx7Žx8Ž
SET @
763 PSIG
4Žx7Žx8Ž
SET @
770 PSIG
PZV
PZV
CONDUCTIVITY
ROCESSES
When you are doing a survey of an existing plant, obtaining a copy of the
plant P&IDs is a good st
NSTRUMENTATION
OCUMENTATION
company that is designing a process normally has standards that they fol-
low in the creation of a loop diag
mented by the creation of a master
template that illustrates how field
devices and nomenclature are used on the drawing.
The loop diagram typically contains a significant amount of detail. For
example, if a junction box is used as
an intermediate wiring point, the loop
diagram will contain information on the wiring junctions from the field
device to the control system. An exam
Figure 7-4.
As is illustrated in this
example, junction box connections are shown on
ROCESSES
Figure 7-4. Example Loop Diagram—Level Control
15
15
FIELD
RACK
DISPLAY
SCHEMATIC
PULP MILL RACK ROOM
PULP MILL CONTROL ROOM
TAG NO. SPEC NO. PO/REL/ITEM MFGR. MODEL NO. CALIB/RANGE REV ISS
UED FOR DATE
LT ITEM 2C. EC-1011
GOULD PD3000 -165.3 TO -156.6 IN H
O 0 CONFIGURATION 6/21/2009
LC EC-1010 FISHER CL7001-1 0-87 IN H20 51
1 ELECT. DESIGN 8/20/2009
NOTES & INTERLOCK DESCRIPTION
1. SP. GR. = 0.5
SHEET LOOP NO. REV
1 OF 1 P-311 -LS 15 2
LOOP TITLE
** LEVEL **
FIRST STAGE
FLASH TANK
REF DWGS/COMMENTS
P & ID DWG:
LOC DWG:
FCA ITEM 6A EC-1011 W & T 5120M12111 0-6 GPH
FCB ITEM 6A EC-1011 W & T 5120M12111 0-6 GPH
LV ITEM 1B EC„1011
KAMYR
LJMA16 ---------------------
I/P ITEM 6B EC-1011
FISHER 546
---------------------
CONSTR
UCTION 10/2/2009
15
15
15
0 …87 INCHES
1 13
2 14
3 15
4 16
5 17
6 18
7 19
8 20
9 21
10 22
11 23
12 24
+24 V
9
15
RACK: 311-FC-2
CARD FILE: 3
SLOT: 6
FLASH TANK
EQ.NO.022-01
15
+
A2
FLASH TANK
EQ.NO.023-00
1/2Ž PI
LOCATION:
COL. 4,5G, F
ELEV. 264-6Ž
LOCATION:
COL. 4,5G,
ELEV. 262-0Ž
A/O, F/L
15
15A
WATER
15B
WATER
LV15
-
LOCATION:
COL. 4,5G,
ELEV. 262-0Ž
TB-5
TB-5
311-015-T4
311-105-T5
4-20ma
4-20ma
DIRECT
3/8Ž M4
1/2Ž P2
1/4Ž CI
311-015-T7
311-105-T8
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OCUMENTATION
obvious when you are touring the plan
t site. For example, as was previ-
ously presented in Chapter 3 on measurement, there are
various ways to
measure temperature. In the case of
a temperature measur
ement, the loop
diagram will provide information on th
e temperature transmitter, as well
as the measurement element that is
used. Figure 7-5 shows the loop dia-
gram for a temperature measurement in which a three-wire RTD element
is used for the temperature measuremen
t. Details such as
the grounding of
the shield for the element wire and
for the twisted pair going from the
transmitter to the control system are noted on the loop diagram.
op diagrams is made easier by the
fact that many components used to
represent measurement and control in
similar applications are often repeated. For example, the manner in which
the control valve, actuator, and as
sociated I/P transducer were repre-
sented in the loop diagram example for
a level application is duplicated in
other loop diagrams that depict a regula
ting (control) valve. This is illus-
trated in the loop diagram shown in
Figure 7-6 for a pressure application
in which a regulating valve
is used in the control of pressure. Also in this
example, the pressu
re measurement is made with a two-wire transmitter.
As will be noted by comparing Figure
7-4 and Figure 7-6, the wiring for
the pressure tran
smitter is similar to that us
ed for the level transmitter.
In some cases, the operator uses a pr
ocess measurement as
an indicator or
as an input to a calculation that is done in the control system. A loop dia-
gram may be developed for these type
s of measurement
ROCESSES
Figure 7-5. Example Loop Di
agram – Temperature Control
16
16
FIELD
RACK
DISPLAY
SCHEMATIC
PULP MILL RACK ROOM
PULP MILL CONTROL ROOM
TAG NO. SPEC NO. PO/REL/ITEM MFGR. MODEL NO. CALIB/RANGE REV ISS
UED FOR DATE
TE ITEM 5D EC-1032 GOULD T3000 200-400 Deg F
0 CONFIGURATION 6/21/2009
TT ITEM 5D EC-1032 GOULD T3000 200-400 Deg F
1 ELECT. DESIGN 8/20/2009
NOTES & INTERLOCK DESCRIPTION
SHEET LOOP NO. REV
1 OF 1 P-311 -LS 16 2
LOOP TITLE
** TEMPERATURE **
DIGESTER
EXTRACTION
REF DWGS/COMMENTS
P & ID DWG:
LOC DWG:
TI EC-1040 FISHER DM0321-1-82 200-400 Deg F 2
CONSTRUCTION 10/2/2009
16
16
200-400 Deg F
2
RACK: 311-FC-1
CARD FILE: 1
SLOT: 4
FLASH TANK
LOCATION:
COL. E-D/4-5
ELEV. 265-9Ž
LOCATION:
COL. 4,5G,
ELEV. 262-0Ž
TB-1
311-016-T1
311-016-T2
4-20ma
+24 VDC
FROM NO.1
DIGESTER
16
12
1 2 3 4
1 2 3
+ -
311-016-W1
311-016-W2
311-016-W3
CHAPTER 7 – C
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OCUMENTATION
101
Figure 7-6. Example Loop Diagram – Pressure Control
17
17
FIELD
RACK
DISPLAY
SCHEMATIC
PULP MILL RACK ROOM
PULP MILL CONTROL ROOM
TAG NO. SPEC NO. PO/REL/ITEM MFGR. MODEL NO. CALIB/RANGE REV ISS
UED FOR DATE
PT ITEM 4B EC-1020 GOULD LPG3040 0 -5 PSIG
0 CONFIGURATION 6/21/2009
PC EC-1040 FISHER CL7001-1 0-5 PSIG
1 ELECT. DESIGN 8/20/2009
NOTES & INTERLOCK DESCRIPTION
SHEET LOOP NO. REV
1 OF 1 P-311 -LS 17 2
LOOP TITLE
**PRESSURE**
SECOND STAGE
FLASH TANK
REF DWGS/COMMENTS
P & ID DWG:
LOC DWG:
PV ITEM 1B EC-1020
KAMYR
LJMA10 ---------------------
I/P ITEM 6B EC-1020
FISHER 546
---------------------
CONSTRUC
TION 10/2/2009
17
17
17
0 …5 PSIG
1 13
2 14
3 15
4 16
5 17
6 18
7 19
8 20
9 21
10 22
11 23
12 24
+24 V
6
17
RACK: 311-FC-2
CARD FILE: 3
SLOT: 6
17
+
A2
TURPENTINE
CONDENSER
LOCATION:
COL. 4,5G,
ELEV. 282-8Ž
A/O, FL
17
LV17
-
LOCATION:
COL. 4-5/G-H
ELEV. 281-6Ž
TB-1
TB-1
4-20ma
4-20ma
DIRECT
1/4Ž CI
311-017-C1
311-017-C2
1/2Ž
LOCATION:
COL. 4-5, G-H
ELEV. 281-6Ž
311-017-T1
311-017-T2
FROM
SECOND STAGE
FLASH TANK
ROCESSES
Figure 7-7. Example Loop Diagram – Flow Measurement
18
18
FIELD
RACK
DISPLAY
SCHEMATIC
PULP MILL RACK ROOM
PULP MILL CONTROL ROOM
TAG NO. SPEC NO. PO/REL/ITEM MFGR. MODEL NO. CALIB/RANGE REV ISS
UED FOR DATE
FE ITEM F18 EC-1021 FLUID TECH 120 0-500 IN H2O
0 CONFIGURATION 6/21/2009
FT ITEM 1B EC-1021 GOULD PDH3000 0-500 IN H2O 1
ELECT. DESIGN 8/20/2009
NOTES & INTERLOCK DESCRIPTION
SHEET LOOP NO. REV
1 OF 1 P-311 -LS 18 2
LOOP TITLE
** FLOW **
COUNTER WASH
REF DWGS/COMMENTS
P & ID DWG:
LOC DWG:
FI EC-1040 FISHER DM0321-1-82 0-750 GPM 2
CONSTRUCTION 10/2/2009
18
18
0-750 GPM
5
RACK: 311-FC-1
CARD FILE: 1
SLOT: 4
TO DIGESTER
OUTLET
LOCATION:
COL. 4/C
ELEV. 234-0Ž
TB-2
311-016-T4
311-016-T5
4-20ma
+24 VDC
FROM COLD
BLOW PUMP
18
12
18
+ -
FCA ITEM 6A EC-1021 W & T 5120M12111 0-6 GPH
FCB ITEM 6A EC-1021 W & T 5120M12111 0-6 GPH
LOCATION:
COL. 4/C
ELEV. 234-6Ž
18A
18A
WATER
WATER
1/2Ž
P2
18
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103
in North America has been developed through the efforts of ISA. The for-
mat of tags used to identify field devices is defined by ISA-5.1 - Instru-
mentation Symbols and Identification.
The ISA-5.1 standard defines a standard tag number convention for
valves, transmitters, other field devices, and calculation and control func-
tions. In addition, the standard defi
nes expanded tag number conventions
TYPICAL TAG NUMBER
TIC 103 -Instrument Identification or Tag Number
T 103 -Loop Identifier
103-Loop Number
TIC -Function Identification
T -First-letter
IC -Succeeding-Letters
EXPANDED TAG NUMBER
10-PAH-5A -Tag Number
10 -Optional Prefix
A-Optional Suffix
Note: Hyphens are optional as separators
ROCESSES
All the devices that are used together
to perform a specific function are
normally assigned the same loop nu
mber. For example, the flow transmit-
ter and regulating valve used to meas
ure and regulate the flow of a pro-
cess stream may be assigned loop number 101.
The loop number normally has only
three digits. Consequently, the num-
ber of field devices that can be uniquely identified using the standard tag
number convention is very limited. For this reason, an expanded tag num-
ber convention, defined by the ISA-5.1 standard, is used in the process
industry. The expanded tag number convention allows a number to be
inserted in front of the function, an
d that number is usually the process
area number. As discusse
d in Chapter 2, a plant is divided into process
areas that are assigned a number. The combination of the area number, the
function letters, and the loop nu
mber is unique within a plant.
In some cases, multiple field devices may be used to perform a similar
function. For example, in some boiler
applications the temperature of each
tube in the superheater section of
a boiler may have individual tempera-
ture measurements. Rather than assi
gning a loop number to each mea-
surement, the expanded tag number
convention assigns a common loop
number to all these measurements. When
this is done, one or more charac-
ters may be added after the loop numb
er to uniquely id
entify each mea-
surement. For the boiler example, loop
number 105 might be assigned to
all the superheater temperature meas
urements and the
surements may be identified by adding
an A after the loop number for the
first measurement, a B for the second
measurement, and a C for the third
measurement.
This option to add letters after the
loop number allows unique tag num-
ent, even when a large number of
similar measurements is made in a pr
ocess area. A hyphen may be option-
ally used in the tag number to sepa
rate the area number or characters
added after the loop number. However, in general, the use of a hyphen in
the tag number is not recommended since in many control systems, the
length of a tag number is limited
to a maximum number of characters
(e.g., 12 or 16 characters).
As defined by ISA-5.1, the identificati
NSTRUMENTATION
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105
ROCESSES
measurement used only for indication
would be identified as TI, “temper-
ature indication.” A positi
on transmitter would be
identified using the let-
In the ISA-5.1 standard, several examples are provided that illustrate the
correct use of the indication letters
within a tag number. Also, the stan-
Instrument supply
or connection to process
Pneumatic Signal
Electric Variable or Binary
CommunicationLink
NSTRUMENTATION
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107
only be accessed by control or calculation functions in the control system
and thus would not be shown in the documentation as being directly
accessed by the operator. However, th
e associated control or calculation
function that is accessed by the operator would include a horizontal line.
As illustrated in Figure 7-11, one of the conventions advocated in ISA-5.1
rcle if the associated function is
accessed by an operator through a vi
deo display of a distributed control
system (DCS). However, in practice, th
is convention is often not followed.
It is common practice to illustrate the
valve body, as well as the valve actu-
ator and positioner function in control system documentation. The ISA-5.1
standard addresses the re
presentation of a valve body. Most types of
valves are addressed by this standard. However, the engineering firm that
is designing a process plant may have adopted some variation of what is
shown in ISA-5.1. In such cases, it is common practice for the engineering
firm to provide a drawing that explai
ns the symbol functions included in
their documentation. Also, in some cases, a general valve representation is
used rather than different representa
tions for a rotary valve or sliding
stem valve. [5] Generally, a damper w
ill be shown rather than the general
valve symbol to indicate the regulation
of air or gas flow to a boiler or a
similar process such as a kiln or heater. An excerpt from ISA-5.1 Valve
Body and Damper Symbols are
illustrated in Figure 7-12.
Since the type of actuator used with
a valve body may impact the opera-
tion and failure mode of the valve, th
e type of actuator is normally indi-
cated in control system documentatio
n. The representation of common
types of actuators as defined by ISA-5.1 is shown in Figure 7-13. A com-
ROCESSES
When a positioner is used with a va
lve, the diaphragm
representation may
be combined with a representation of
the actuator and the valve body, as
is illustrated in Figures 7-16 to 7-19.
The failure mode of
open or fail closed) is often indicate
d by the valve symbol in control sys-
tem documentation.
A special actuator symbol is defined by the standard for motorized actua-
tors. Motorized actuators are used in
some industry segments because
upon loss of power, the last valve po
sition is maintained. Also, better reso-
lution may be achieved using a motori
zed actuator for a specific applica-
tion, such as the basis weight valve that
is used to regulate the thick stock
flow to a paper machine in paper ma
nufacturing. [6] Solenoid actuators
that are used to automate valves used in on-off service are shown using a
special symbol.
General Symbol
BallValve
Globe Valve
NSTRUMENTATION
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109
7.7Equipment Representation
A representation of major pieces
of process equipment is normally
included in control system documentat
ion. This allows the field instru-
mentation installation to be shown in relationship to the process equip-
ment. Example process eq
s are illustrated in
Figure 7-15.
A general vessel representation may be appropriate for vessels, agitators,
heat exchangers, and pumps that do not play an important role in the con-
trol system. For example, an agitator on a tank may not directly impact the
control associated with the tank level.
A special representation is provided
Figure 7-13. Excerpt from ISA-5.1 Actuator Symbols
Figure 7-14. Excerpt from ISA-5.1 Symbols for Other Devices
Generic actuator,
Spring-diaphragm
Spring-diaphragm with
Linear piston actuator
Rotary motor operated
actuator
Solenoid actuator for
on-off valve
Restriction Orifice, With
Flow Transmitter
Hand Valve
Inline Measurement
Measurement Element
ROCESSES
Vessel, Jacketed Vessel,
Reactor
Atmospheric Tank, Storage
Heat Exchange
Agitator
Pump
NSTRUMENTATION
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111
process are shown in this piping an
d instrumentation diagram illustrated
in Figure 7-16.
After reviewing this diagram, cons
ider the following questions and
answers.
: What tag number conven
tion is shown in this
example?
convention, defined by
the ISA-5.1 standard, is not us
ed in this ex
ample since the
tag only contains function
Static Mixer
Discharge
Reagent
Stage 1
Reagent
Stage 2
Feedforward
Signal
Characterizer
101
101
102
103
103
103
104
104
105
105
101
103
106
105
ROCESSES
actuator is also tied to this
box. Therefore, we can assume
that these valves
are installed with a valve positioner.
: What type of valve is being used to regulate
: The general valve body sy
the type of valve is not
: Is the plant operator able to access the control
functions indicated by AC103, AC104, FC101, and FC105?
: Yes, the circle indicating these control functions
contains a horizontal line that indicates the operator may
access this function.
: Can the operator acce
ss flow measurements
FT101, FT102, and FT105, as well as analytic (pH) measure-
ments AT103 and AT104?
: No, the circle indicating
these measurement func-
tions does not include a horizontal line. In this case, these
measurements are not directly accessed by the operator.
: Are any on-off (blocking)
valves used in this
: Yes, two blocking valves
: What function is provided by AC103?
: The function letters of
the tag number indicate
that the function is analytic control.
: What measurement is used by AC103 in per-
forming its control function?
: Since an electric signal line is shown from AT103
to AC103, then control must be based on the measurement
AT103 (pH).
: What is the purpose
NSTRUMENTATION
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113
: Does the vessel have an agitator?
: Yes, the figure shows an agitator impeller in the
vessel, powered by a motor on top of the vessel.
: Is the pump fixed speed or variable speed?
: Since control of the proc
ess is done using a regu-
lating valve, then it may be
assumed that the pump is fixed
speed.
: How could the liquid in the vessel be heated?
: A heat exchanger is shown in the recirculation line
and could be used to heat (or
cool) the liquid in the vessel.
: How is the pH of the incoming stream adjusted?
: The output of AC103 and AC104 go to a valve and
flow loop, respectively, that regulates the flow of reagent to
the inlet stream and recirculation line. Thus, it may be
assumed that reagent is used to adjust pH.
7.8.2 Example – Basic Column Control
The basic column control system shown in Figure 7-17 is somewhat more
complicated than the basic neutrali
zer control system. However, after
studying this example, it will become
clear that many of the components
that make up the column control system are similar to those used in the
basic neutralizer control
system. As we have seen, what is learned by
working with one process may be ofte
n applied to another process. Once
you become familiar with a few processes, it becomes easier to work with
other processes.
7.8.3 Example – Batc
Batch processing plays an important ro
le in some indust
ries. In a batch
process, a vessel is charged with feed
material that is processed in the ves-
sel through mechanical or chemical means (or both). At the end of the pro-
cess, the product—which may be a fini
shed product or an intermediate
product for use in another process—is
removed from the vessel. The batch
reactor example illustrated in Figure 7-18 is known as “continuous feed
batch,” in which feed material is
continuously added to the vessel
throughout part or all of the batch
processing. The reaction takes place,
mparing the basic
components to those seen in the prev
ious two examples,
the only new ele-
ment introduced by this example is
an eductor (a device that produces
vacuum by means of the Venturi effect
) that is used to remove gases cre-
ated by the batch reaction.
ROCESSES
Figure 7-17. Basic Column Control System
Figure 7-18. Example – Batch Reactor Control
Receiver
Overheads
Reflux
Vent
Storage Tank
Feed Tank
RTD
FT111
FT111
Feedforward
Feedforward
110
110
111
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Figure 7-18
Coolant
Discharge
Coolant
Vent System
Anti-Foam
Batch Reactor
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NSTRUMENTATION
OCUMENTATION
115
7.8.4 Example – Continuous Feed and Recycle Tank
In studying the example of a continuo
us feed and recycle tank shown in
Figure 7-19, you will note that the only new function that was not con-
tained in a previous example is FFC13
3. The function letters of the tag
number indicate that this new functi
on is ratio control. The line connec-
the ratio control is implem
ented using two feed streams
to Reactor 1.
d symbols on a P&ID is the first step in under-
standing which measurement and control functions have been installed on
the process. As the examples shown in
Figure 7-16 to 7-19 illustrate, a
process is possible if you are famil-
iar with the tag number and symbols on the P&ID. Later chapters on con-
trol implementation will address ho
w the control functions shown on the
P&ID and loops sheet are implemented.
Figure 7-19. Example – Continuous Feed and Recycle Tank
Feed Tank
Reactor 1
Reactor 2
Recycle Tank
Makeup
Reactor 1
Recycle
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ROCESSES

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