Transcript Introduction to Flowsheets

Understanding Process Diagrams
Dr. AA
PiCS, UTM
Introduction to Flowsheeting
Now that I are an Inguneer, all I do is right!
Roughly speaking, communication is paramount ~ As an Engineer,
transfer the most amount of information with the least amount of effort
on the part of the reader.
Flowsheeting
Flowsheets are the pictorial representation of the
process.
CWS
Goal:
Transmit the most
amount of
information with the
least amount of effort
on the part of the
reader!
E-1
F-1
P -1A/B
T-1
CWS
STM
E-2
E-3
F-2
STM
E-4
Flowsheet
Is a diagrammatic model of the process
• Shows the arrangement of equipment selected to carry our the
process
• Includes
stream connections, names of streams, stream flow rates
compositions and operating conditions (temp., Pressure)
instruments
optional details of streams molar compositions
physical data (, ),code no. of streams,Enthalpies of streams
Brief description of stream
Type of Diagrams
Block Diagram
Material Flow Sheet
Energy Flow Sheet
Process Flow Diagram
Information Flow Diagram
Piping & Instrumentation Diagram
Type of Flowsheets
Block
Process
6
7
F CV
2 18
Piping and Instrumentation
Block Diagram
Conveys what is achieved in a given step, not how it is achieved
• Particularly useful in initial studies
• Useful for conveying information to management
• Useful to show inter-relation of streams
• Useful in conveying global, not detailed, material balance
Feed 1
Feed 2
Feed 3
Process
Product 1
Product 2
Product 3
This particular block flow could be used to obtain (assist) in the development
of an initial material balance for streams crossing the battery limits. You
might use it in your input/output structure development during synthesis.
Block Flow Diagram
Example:
Byproduct to
Refinery
Refinery
Gas
Low Temp
Clean-up
Compression
Reaction &
Cooling
Product
Purge
Air
Separation
Recycle
Compression
Oxygen
Major steps are conveyed but no equipment details. Sometimes the blocks
may be process flow diagram symbols. Sometimes steps may include
equipment if it is particularly important to the communication.
Block Flow Diagram
I find block flows to be particularly useful for setting up (identifying) the key streams
to solve the material balance around the major blocks. I subsequently solve the
material balance inside each block.
113
128
104
T-102
114
T-103
134
T-101
101
153
F-105
F-101
103
147
106
140
108
T-104
109
150
T-105
151
111
146
105
159
160
Material Flow Sheet
• Is drawn with standard symbols and labeled
and include all data obtained
• If no space available to label equipment, a
equipment key can be drawn at the bottom of
the flow sheet
• Following data should be shown on the flow
sheet in deferent ways
– flow rate of each component
– total stream flow rate
– percentage composition
N
P
C
1
Component Flow rate T
R2
Equipment key
C1
Column
R2
Reactor
N Component Flow rate T
P
Simplest method suitable for simple processes with few
equipments: tabulate the data in blocks alongside the process stream
Better method applicable for all complex processes: stream line is
numbered and the data tabulated at the top or bottom of the sheet
Energy Flowsheet
• Energy balance is to determine the energy
requirement of the process
• In energy flow sheet Inlet and outlet energy
flow rates should be shown separately for each
piece of equipment. Include:
– energy of each component in all (inlet and outlet)
streams
– process conditions of all (inlet and outlet) streams
– process conditions of the specific equipment
Energy Balance Sheet
Information Flow Diagram (IFD)
• Is used in simulation programs
• Is presented by blocks
• Each block represents a calculation module in the simulation
program, usually a process unit or part of a unit
• units in which no change of composition or temperature or
pressure occurs are omitted from IFD
• But other operations not shown on the process flow diagram as
actual pieces of equipment, but which can cause changes in the
stream composition must be shown.
• Flow of information should be shown with lines and arrow
Process Flow Diagrams
Dr. AA
PiCS, UTM
Process Flow Diagram
Conveys the major processing steps represented by the equipment
• Useful for conveying the heat and material balances
• Useful for conveying major pieces of equipment
• Useful for conveying processing conditions
• Useful for conveying utilities
There are no hard and fast rules but Howat Standards include
• essentially every major piece of equipment
• every flow
• every temperature
• every pressure
• auxiliary services (utility flows)
• equipment sizes
• process control
Standard symbols
BS 8888 ; BS 1553
Reactor
Sealed tank
Tray column
Fluid
contacting
column
Heat exchange
Material Flow Sheet
•
Is drawn with standard symbols and labeled and include all data obtained
If no space available to label equipment, a equipment key can be drawn at
the bottom of the flow sheet
Following data should be shown on the flow sheet in deferent ways
flow rate of each component
total stream flow rate
percentage composition
Simplest method suitable for simple processes with few equipments,
tabulate the data in blocks alongside the process stream
Slide 14
Better method applicable for all complex processes,
stream line is numbered and the data tabulated at the top or bottom of
the sheet (above and below the equipment layout)
Slide 15
Process Flow Diagram
The following diagrams are examples of class and
commercial process flow diagrams (PFD’s). The content
depends on the goals for the communication.
Unless there are reasons to the contrary, the standard is:
• All major equipment
• All major process lines
• All major utility lines involving material flow
• All stream numbers, temperatures, pressures, flows
• All major process controls and valves
• All equipment sizes with relevant MEB information as
required
• All equipment names and numbers
Process Flow Diagram
The goal is to present the most amount of information with the
least amount of effort on the part of the reader.
• The flowsheet should generally flow from left to right.
• The flowsheet should not be cluttered - use multiple sheets.
• The flowsheet should be in landscape with the bound edge at top.
• The equipment should be drawn in approximately relative size, e.g.
towers larger than drums, exchangers larger than pumps etc.
• The major towers and reactors are generally on one, or nearly one,
level.
• The reader should be able to follow it with his or her eye.
• The streams should have the minimum of direction changes.
• The streams that enter across the battery limits should be on the left.
• The streams that leave across the battery limits should be on the right.
• The streams that move to the next sheet should leave on the right.
• The streams that recycle to earlier sheets should leave on the left.
153
Flowsheeting
140
T-104
109
146
105
160
The process flowsheet shown below is one
possible expansion of the block flow for T-104. When
this PFD was drawn, the process was not complete
as is evident by the missing equipment sizes, pump
discharge pressures etc. In this case, the process
control scheme was not included. It generally is,
however.
Process Flow Diagram
The following process flow is an approximate rendition of a refinery
alkylation unit. This is however not as complete as it is required in
industry practice
Note that equipment sizing is not included.
The material balance grid is included. Many companies require the
material balance to be imposed on the diagram. In those cases, the
stream numbering may not be as extensive as we typically use in
design. Or, only a limited number of streams are included in the
material balance grid.
Process Flow Diagram
Another example from design. This includes the equipment sizing and material balance
block. Note the symbol key is included. This is frequently necessary when client
standards differ.
Process Flow Diagram
The following two sheets are examples of a commercial PFD
developed prior to construction. Note that the content is, yet again,
different. In this case, the control scheme is included as is the legend
key. There are some differences. Note that there are three different
feed points shown on the diagram. It is typical to have multiple feed
points for a column but unusual to show them on the PFD. They were
shown here because it was critical for discussing different feedstocks
in the process design report. The process description which
accompanied the PFD described the reason for the multiple feeds.
On the second diagram, you will note the pressure control. This is a
split range controller with the primary control being a flooded
condenser and the secondary control being a vent. Note that the
pumps show operating and design conditions.
The process description
will sometimes dictate
the content of the
process flow diagram.
For most purposes, the
process control scheme
will be included in our
work. Multiple feed
points or side stream
points will not be shown
unless it is critical to the
process. We will
typically not be showing
the future equipment
such as the reboiler
shown on the left of the
column.
When you examine the
flowsheet, you should
be able to deduce the
type of equipment.
Tower type?
Repoiler type?
Pump type?
This is the other part of
the previous flowsheet.
Because of scan
limitations, I’ve broken
the flowsheet into two
parts. However, the
original is all one
flowsheet drawn in
landscape.
In this flowsheet, you
will not the original
reboiler is on flow
control reset by
temperature. The
primary measured
variable is steam flow,
the manipulated
variable is steam flow
and the controlled
variable is steam flow.
The secondary
measured variable is
temperature. What is
the temperature
indicative of? Why
above the bottom?
Process Flow Diagram
This process flow diagram is another commercial example. This client
standard had two PFD’s per page, each shown in landscape, one on
top of the other on the same page. I have taken the top PFD and split
in two. (This is the basis for the following EFD’s.)
This was a revamp. Shaded equipment is new, unshaded equipment
is existing. Note that the control scheme is included. There are
additional symbols which indicate that the controls are connected to a
digital distributed control system. The tags at the edge of the page
indicate connections to other PFD’s.
This is an extractive distillation tower. There are additional reboilers here (type?) that are in
place for heat recovery. The shaded equipment is new. The unshaded equipment was
existing. The equipment might be in a new service, however. We will generally not show
instrument connections to the DCS (distributed control system). The instruments will be
shown but the connection will be implied.
This is the overhead system for the extractive distillation column. Note that there is a vent
condenser from F-204. Why might we add a vent condenser? What is the purpose? Note
that the F-204 Reflux Drum has a ‘boot’. What might that be for? The circle symbol in the
center bottom is a professional stamp of a licensed engineer. He/she is signifying that the
engineering integrity of the process.
Process Flow Diagram
Unless stated otherwise, the target content for
PFD’s is:
All major process equipment
All major process and utility streams – all
numbered
All major process controls necessary to
operate the process
All operating temperatures
All operating pressures
All operating flows
All equipment sizes
Piping and Instrumentation
Diagram
Dr. AA
PiCS, UTM
Piping and Instrumentation Diagram
• Similarly to electrical schemas, the control industry (especially
the chemical and process industry) describes its plants and their
instrumentation by a
• P&ID (pronounce P.N.I.D.) (Piping and Instrumentation Diagram),
sometimes called P&WD (Piping and wiring diagrams)
• The P&ID shows the flows in a plant (in the chemical or process
industry) and the corresponding sensors or actors.
• At the same time, the P&ID gives a name ("tag") to each sensor
and actor, along with additional parameters.
• This tag identifies a "point" not only on the screens and
controllers, but also on the objects in the field.
Piping & Instrumentation Diagram (P & I)
• P & I should be included with
– All process equipment identified by equipment number
– All pipes identified by a line number. Pipe size and material of
construction should be shown (material may include as a part
of the identification number)
– All valves with an identification no. along with their type & size
should be shown
– Ancillary fittings that are part of piping system such as inline
sight glasses, strainers and stream traps with an identification
no.
– Pumps identified by a suitable code no.
– All control loops and instruments with identification
Instrument Identification
Measured Variable
Type of Conditioner
Type of Component
F = Flow
R = Recorder
T = Transmitter
L = Level
I = Indicator
M = Modifier
P = Pressure
C = Controller
E = Element
Q = Quantity
A = Alarm
T = Temperature
P&ID
The P&ID mixes pneumatic / hydraulic elements, electrical elements
and instruments on the same diagram
It uses a set of symbols defined in the ISA S5.1 standard.
Examples of pneumatic / hydraulic symbols:
pipe
350 kW
heater
valve
one-way valve (diode)
vessel / reactor
binary (or solenoid) valve (on/off)
analog valve (continuous)
heat exchanger
pump, also
Instrumentation identification
The first letter defines the measured or initiating variables such as Analysis (A), Flow (F),
Temperature (T), etc. with succeeding letters defining readout, passive, or output functions
such as Indicator (I), Record (R), Transmit (T), and so forth
FIC
V1528
tag name of the
corresponding
variable
mover
(here: solenoid)
S
function
(here: valve)
ISA S5.1 General instrument or function symbols
Primary location
accessible to
operator
Field mounted
Auxiliary location
accessible to
operator
Discrete
instruments
Shared
display,
shared
control
Computer
function
Programmabl
e logic control
1. Symbol size may vary according to the user's needs and the type of document.
2. Abbreviations of the user's choice may be used when necessary to specify location.
3. Inaccessible (behind the panel) devices may be depicted using the same symbol but with a
dashed horizontal bar.
Source: Control Engineering with data from ISA S5.1 standard
Example of P&ID
The output of FIC 101 is an electrical signal to TY 101
located in an inaccessible or behind-the-panel-board location.
Square root extraction of the
input signal is part of FIC
101’s functionality.
FT101 is a field-mounted flow
transmitter connected via
electrical signals (dotted line)
to flow indicating controller
FIC 101 located in a shared
control/display device
The output signal from TY
101 is a pneumatic signal
(line with double forward
slash marks)
making TY 101 an I/P (current
to pneumatic transducer)
TIC 101’s output is
connected via an internal
software or data link (line
with bubbles) to the setpoint
(SP) of FIC 101 to form a
cascade control strategy
TT 101 and TIC 101 are
similar to FT 101 and FIC
101
but are measuring,
indicating, and controlling
temperature
The ISA code for instrument type
First letter
Measured or initiating variable
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
Q
R
S
T
U
V
W
X
Y
Z
Analysis
Burner, combustion
User's choice
User's choice
Voltage
Flow rate
User's choice
Hand
Current (electrical)
Power
Time, time schedule
Level
User's choice
User's choice
User's choice
Pressure, vacuum
Quantity
Radiation
Speed, frequency
Temperature
Multivariable
Vibration, mechanical analysis
Weight, force
Unclassified
Event, state, or presence
Position, dimension
Modifier
Differential
Ration (fraction)
Scan
Time rate of change
Momentary
Integrate, totalizer
Safety
X axis
Y axis
Z axis
Common connecting lines
Connection to process, or
instrument supply
Pneumatic signal
Electric signal
Capillary tubing (filled
system)
Hydraulic signal
Electromagnetic or sonic
signal (guided)
Internal system link
(software or data link)
Source: Control Engineering with data from ISA S5.1
standard
Many Standards
• DIN
• ISA
• etc