The nature of product dervice

THE NATURE OF PROCESS DESIGN
A Creative Activity ！

[ Example ]
CH3
+
Toluene

Toluene
(10,000 kg/h)

Hydrogen
(820 kg/h)

H2

+

Hydrogen

Reactor

Benzene

CH4

Methane

Gas
Separator

• Block Flow Diagram (BFD)
• Process Flow Diagram (PFD)
• Piping and Instrumentation Diagram (P&ID)

Mixed Gas
(2,610 kg/h)

Benzene
(8,210 kg/h)
Conversion
75% Toluene

The most effective way of
communicating information about
a process is through the use of
flow diagrams.

Table 1.1 Conventions and Format Recommended for Laying out a
Block Flow Process Diagram

Mixed Liquids

Toluene
Reaction : C7H8

+ H2 = C6H6 + CH4

Figure 1.1 Block flow process diagram for the production of benzene
Toluene and hydrogen are converted in a reactor to produce benzene and methane.The

1. Operations shown by blocks.
2. Major flow lines shown with arrows giving direction of flow.
3. Flow goes from left to right whenever possible.
4. Light stream (gases) toward top with heavy stream (liquids and solids) toward
bottom.
5. Critical information unique to process supplied.
6. If lines cross, then the horizontal line is continuous and the vertical line is broken.
7. Simplified material balance provided.

reaction does not go to completion, and excess toluene is required. The noncondensable
gases are separated and discharged. The benzene product and the unreacted toluene are
then separated by distillation. The toluene is then recycled back to the reactor and the
benzene removed in the product stream.

Process Flow Diagram (PFD)
A PFD includes the following items:
1. major equipments;
2. principal flow route and control involved from raw
material feed to final product;
3. key temperature and pressure corresponding to
anticipated normal operation;
4. material flow rates and compositions;
5. design duties and sizes of major equipments.

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Table 1.2 Conventions Used for Identifying Process Equipment
Process Equipment

Supplemental Information

Table 1.3 Conventions for Identifying Process and Utility Streams
Process Streams
All conventions shown in Table 1.1 apply.
Diamond (square) symbol located in flow lines.
Numerical identification (unique for that stream) inserted in diamond (square).
Flow direction shown by arrows on flow lines.
lps
mps
hps
htm
cw
wr
rw
rb
cs
ss
el
ng
fg
fo
fw

Utility Streams
Low Pressure Steam: 3-5 barg (sat)‡
Medium Pressure Steam: 10-15 barg (sat)‡

High Pressure Steam: 40-50 barg (sat)‡
Heat Transfer Media (Organic): to 400°C
Cooling Water: From cooling tower 30°C returned at less than 45°C+
River Water: From river 25°C returned at less than 35°C
Refrigerated Water: In at 5°C returned at less than 15°C
Refrigerated Brine: In at -45°C returned at less than 0°C
Chemical Waste Water with high COD
Sanitary Waste Water with high BOD, etc.
Electric Heat (specify 220, 440, 660V service)
Natural Gas
Fuel Gas
Fuel Oil
Fuel Water

‡These

pressure are set during the preliminary design stages and typical values vary within the ranges
shown.
45°C, significant scaling occurs.

+Above

Table 1.6 Equipment Descriptions for PFD and P&IDs
Equipment Type
Description of Equipment
Towers
Size (height and diameter), Pressure, Temperature
Number and Type of Trays
Height and Type of Packing
Materials of Constructions

Heat Exchangers
Type: Gas-Gas, Gas-Liquid, Liquid-Liquid, Condenser, Vaporizer
Process: Duty, Area, Temperature, and Pressure for both streams.
No. of shell and Tube Passes
Materials of Construction: Tubes and Shell
Tanks
See vessels
Vessels
Hight, Diameter, Orientation, Pressure, Temperature, Materials of Construction
Pumps
Flow, Discharge Pressure, Temperature, rP, Driver Type, Shaft Power, Materials of Construction
Compressors
Actual Inlet Flow Rate, Temperature, Pressure, DrverType, Shaft Power,
Materials of Construction
Heaters (fired)
Type, Tube Pressure, Tube Temperature, Duty, Fuel, Material of Construction
Others
Provide Critical Information

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General Format XX-YZZ A/B
XX are the identification letters for the equipment
classification
C - Compressor or Turbine
E - Heat Exchanger
H - Fired Heater
P - Pump
R - Reactor
T - Tower

TK - Storage Tank
V - Vessel
Y designates an area within the plant
ZZ are the number designation for each item in an
equipment class
A/B identifies parallel units or backup units not
shown on a PFD
Additional description of equipment given on top
of PFD

Table 1.4 Information Provided in a Flow Summary
Essential Information
Stream Number
Temperature (°C)
Pressure (bar)
Vapor Fraction
Total Mass Flow Rate (kg/h)
Total Mole Flow Rate (kmol/h)
Individual Component Flow Rates (kmol/s)

Optional Information
Component Mole Fractions
Component Mass Fractions
Individual Component Flow Rates (kg/h)
Volumetric Flow Rates (m 3/h)
Significant Physical Properties
Density
Viscosity
Other
Thermodynamic Data

Heat Capacity
Stream Enthalpy
K-values
Stream Name

Piping and Instrumentation Diagram
(P&ID)
1. All process equipments and pipings required for start-up, shut-down, emergency and
normal operation of the plant, including valves, blinds, etc.
2. An id number, an identifier of the material of construction, diameter and insulation
requirements for each line.
3. Direction of flow.
4. Identification of main process and start-up lines.
5. All instrumentation, control and interlock facilities with indication of action on
instrument air failure.
6. Key dimensions or duties of all equipments.
7. Operating and design pressures and temperatures for vessels and reactors.
8. Equipment elevations.
9. Set pressure for relief valves.
10.Drainage requirements.
11.Special notes on piping configuration as necessary, e.g. “gravity drainage.”

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Table 1.8 Exclusions from Piping and Instrumentation Diagram
1. Operating conditions T,P
2. Stream flows
3. Equipment locations

4. Pipe routing
a. Pipe lengths
b. Pipe fittings
5. Supports, structures, and foundations

Table 1.9 Conventions in Constructing Piping and Instrumentation Diagrams
For Equipment - Shown Every Piece Including
Spare units
Parallel units
Summary details of each unit
For Piping - Include All Lines Including Drains, Sample Connections and Specify
Size (use standard sizes)
Schedule (thickness)
Materials of construction
Insulation (thickness and type)
For Instruments - Identify
Indicators
Recorders
Controllers
Show instrument lines
For Utility - Indentify
Entrance utilities

Activities of Process Design
(1)Synthesis
The step where one conjectures the building blocks and their
interconnections to create a structure which can meet the stated design
requirements.
(2)Analysis (Simulation)
The activity of modeling and then solving the resulting equations to

predict how a selected structure should behave if it were constructed.
(3)Evaluation
The activity of placing a worth on the structure where the worth might
be its cost, its safety, or its net energy consumption.
(4)Optimization
The systematic searching over the allowed operating conditions to
improve the evaluation as much as possible.
Parameter
structure

Exit utilities
Exit to waste treatment facilities

Process Synthesis

IMPORTANCE OF PROCESS STRUCTURE
(1) Recycle？

A→P

Ｒ

A design task where one conjectures the
building blocks and their interconnections to
create a structure which can meet the stated
design requirements.

or

Ｒ

Ａ
Ｐ
Ａ
　　　　　　　　　　　　　　　　　　　

Ｓ

Ｐ

(2)separation Sequence ?
A (propane)
A

B (1-Butene)

A
AB

or

ABC
BC

C(n-Butane)

B

ABC

C

C

B
C

(3)Heat Recovery ?

or
H

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Feed
Streams

Product
Streams

PROCESS ?

(a) Process design starts with the synthesis of a process to convert raw

Figure 1.6 The “onion model” of
process design. A reactor design in

needed before the separation and recycle
system can be designed, and so on.
(From Smith and Linnhoff, Trans.
IChemE, ChERD, 66:195, 1988;
reproduced by permission of the
Institution of Chemical Engineers.)

materials into desired products.

Reactor
Feed
Streams

Product
Streams ?

PROCESS

Separation and
Recycle System
Heat Exchanger
Network

(b) Simulation predicts how a process would behave if it was constructed.

Figure 1.1 Synthesis is the creation of a process to transform feed streams
into product streams. Simulation predicts how it would behave if it was
constructed.

Utilities

A HIERARCHICAL APPROACH

Example Hydrodealkylation of Toluene
CH3

1

＋ CH4

＋ H2
Toluene

Benzene

2

＋ H2
Benzene

Toluene + H2 ® Benzene + CH4

Diphenyl

2 Benzene

Diphenyl + H2

1150 ° F ～ 1300 ° F
500 psia

Vapor Recovery System
H2 Feed

H2, CH4

Benzene
product

Flash
hh

FIGURE 1.2-2
Hydrodealkylation of toluene; maximum energy recovery.

ENERGY INTEGRATION

Stablizer

CW

Benzene Col.

Gas
recycle

Reactor

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Toluene
Recycle

Toluene Col.

furnace

Flash
Drum
Benzene

compressor
Diphenyl

Reactor

Toluene
Feed

Purge

Purge

compressor

Liquid
recycle

H2, feed

Toluene
feed

Diphenyl

Distillation Train

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ALTERNATIVES OF DISTILLATION TRAIN
(1) Recycle Diphenyl
H2, CH4

Benzene

(2)
Feed

ALTERNATIVES OF VAPOR RECOVERY
SYSTEM

Toluene
(recycle)

Diphenyl

(3)

H2
CH4

(1) Condensation;
Benzene

(2) Absorption;

Toluene
(recycle)

(3) Adsorption;
(4) Membrane.
Diphenyl

Gas recycle
Vapor recovery
system

H 2 , CH 4

H 2 , CH 4
H 2 , CH 4

Reactor
system

Purge
H 2 , CH 4

Purge

Phase
split

Toluene

Benzene
Reactor
system

Separation
system
Dipheny1

Toluene
Liquid separation
system

Benzene

Toluene recycle

Dipheny1

Simplified Flowsheet for the Separation System

Purge
H 2 , CH 4

Recycle Structure of the Flowsheet

Hierarchy of decisions
1. Batch versus continuous
2. Input-output structure of the flowsheet

H 2 , CH 4

Benzene

Toluene

Dipheny1

3. Recycle structure of the flowsheet
4. General structure of the separation system
a. Vapor recovery system
b. Liquid recovery system
5. Heat-exchanger network

Ch. 4
Ch.5

Ch.6, Ch.7, Ch.16

Input-Output Structure of the Flowsheet

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