1. CHAPTER 2 Description of Chemical Processes
CHEM2003/Dr. Ahmed J. Ali/

2. Objectives To be able to define different streams in a process.
To describe the meaning of standard abbreviations and symbols used on process flowsheets.
Write a description of a process flowsheet.
Draw a process flowsheet from a written description.

3. What is Process? A process is some operation carried out to modify input(s) to output(s) – based on physical and/or chemical changes
Outputs
Inputs
Process
“feeds”
“products”

4. Classification of Processes
An integrated series of operations through which materials and/or energy
are converted from one form to another.
Batch process:
Has a definite end
Material is put in, processed, and discharged
Applies to more than just reactors (washing machine for example)
Continuous process
Materials enter and leave in uninterrupted streams
Periodic shutdown is required
Semi-batch or Semi-continuous
Some materials are charged/discharged at intervals while some
enter/exit continuously
Biotechnology industry, to add nutrients

5. Process Variables
The variables that describe the condition of a process fall into two categories:
Extensive variables: which depend on the size of the system (mass, volume)
Intensive variables: do not depend on the size of the system (e.g. T, p, , mass and mole fractions)
Often on a process flowsheet, designers would like to specify process variables such as size, composition and temperature, etc.

6. Flowsheet conventions
Chemical processes often involve substances of:
1-high chemical reactivity,
2-high toxicity, &
3-high corrosivity operating at high pressures &
temperatures.
Thus, visual information is the clearest way to present material & is least likely to be misinterpreted. For these reasons, it is essential that chemical engineers be able to formulate appropriate process diagrams & be skilled in analyzing & interpreting diagrams prepared by others.

7. Flowsheet conventions
Flowsheet: is a Diagram for Understanding
Chemical Processes.
the commonly used by chemical engineers are:
Block Flow Diagram (BFD)
Process Flow Diagram (PFD)
Piping and Instrumentation Diagram (P&ID)
Plant Layout

8. Block Flow Diagram1/4
In the courses of material & energy balances, often the initial step was to convert a word problem into a simple visual block flow diagram.
This diagram is a series of blocks connected with input & output flow streams. It included operating conditions (temperature & pressure) & other important information such as conversion & recovery, given in the problem statement.
But, it did not provide details regarding what was involved within the blocks, but concentrated on the main flow of streams through the process

9. Block Flow Diagram2/4
A block diagram is the simplest form of presentation.
Each block represents a single piece of equipment or a complete stage in the process.

10. Block Flow Diagram3/4 Operations shown by blocks
Major flow lines shown with arrows giving direction of flow
Flow goes from left to right whenever possible
Light stream (gases) toward top with heavy stream (liquids and solids) toward bottom.
Critical information unique to process supplied.
If lines cross, then the horizontal line in continuous and the vertical line is broken.
Simplified material balance provided.

11. Block Flow Diagram4/4 Combiner and splitter:
Avoid crossing streams. If streams must cross, you need to indicate whether they mix or not.
streams combine and split
streams cross without mixing
Ambiguous

12. Example of a block flow process diagram is shown in Figure 1.1
Toluene & hydrogen are converted in a reactor to produce benzene & a methane. The reaction does not go to completion, & excess toluene is required. The non-condensable gases are separated & discharged. The benzene product & the unreacted toluene are then separated by distillation. The toluene is then recycled back to the reactor & the benzene removed in the product stream.

13. Example: Synthesis of Ammonia1/5
Type of process?
Reactor and condenser are continuous
Storage tank is semi-continuous
Reaction: N H2 2NH3

14. Example: Synthesis of Ammonia2/5
A mixture of hydrogen and nitrogen is fed to a catalytic reactor where some of the hydrogen and nitrogen is converted to ammonia. The reactor effluent is sent to a condenser where all of the ammonia is condensed. The condensed ammonia is sent to product storage. The uncondensed hydrogen and nitrogen are recycled by being mixed with a fresh feed of the same composition. The resulting mixture is fed to the reactor.
Step 1 is the feed to the reactor:
“feed” N2 H2
“effluent”
NH3 N2 H2
reactor

15. Example: Synthesis of Ammonia3/5
A mixture of hydrogen and nitrogen is fed to a catalytic reactor where some of the hydrogen and nitrogen is converted to ammonia. The reactor effluent is sent to a condenser where all of the ammonia is condensed. The condensed ammonia is sent to product storage. The uncondensed hydrogen and nitrogen are recycled by being mixed with a fresh feed of the same composition. The resulting mixture is fed to the reactor.
Step 2 is to purify the product:
“feed” N2 H2
reactor
condenser
“effluent”
NH3 N2 H2
NH3
liquid

16. Example: Synthesis of Ammonia4/5
A mixture of hydrogen and nitrogen is fed to a catalytic reactor where some of the hydrogen and nitrogen is converted to ammonia. The reactor effluent is sent to a condenser where all of the ammonia is condensed. The condensed ammonia is sent to product storage. The uncondensed hydrogen and nitrogen are recycled by being mixed with a fresh feed of the same composition. The resulting mixture is fed to the reactor.
Step 3 is to send product to storage:
“feed” N2 H2
reactor
condenser
“effluent”
NH3 N2 H2
NH3
liquid
Storage tank

17. Example: Synthesis of Ammonia5/5
A mixture of hydrogen and nitrogen is fed to a catalytic reactor where some of the hydrogen and nitrogen is converted to ammonia. The reactor effluent is sent to a condenser where all of the ammonia is condensed. The condensed ammonia is sent to product storage. The uncondensed hydrogen and nitrogen are recycled by being mixed with a fresh feed of the same composition. The resulting mixture is fed to the reactor.
purge
Step 4 is to recycle unreacted feeds:
recycle
N2, H2
“feed” N2 H2
reactor
condenser
“effluent”
NH3 N2 H2
NH3
liquid
Storage tank

18. Block Flow Diagram of a Refinery

19. Petroleum Asphalt Block Flow Diagram

21. Process Flow Diagrams (PFD)1/3
Engineering flow diagram shows the sequence of equipment and unit operations in the overall process.
In drawing these flow sheets symbol which fairly resembles the actual equipment employ in the pilot plant are used.

22. Process Flow Diagram (PFD)2/3
All the major pieces of equipment in the process will be represented on the diagram along with a description of the equipment.
Each piece of equipment will have assigned a unique equipment number and a descriptive name.
All process flow streams will be shown and identified by a number.
A description of the process conditions and chemical composition of each stream will be included. These data will be displayed either directly on the PFD or included in an accompanying flow summary table.

23. Process Flow Diagram (PFD)3/3
The basic information provided by a PFD can be categorized into one of the following:
1. Process topology
2. Stream information
3. Equipment information

24. 1- Process Topology
The location of and interaction between equipment and process streams is referred to as process topology
Equipment is represented symbolically by
icons and is identified by a number
The number represents the location of the equipment
Figure in next slide is a skeleton process flow diagram for the production of benzene

26. Figure 1.3 shows that each major piece of process equipment is identified by a number on the diagram.
A list of the equipment numbers along with a brief descriptive name for the equipment is printed along the top of the diagram.
The location of these equipment numbers & names roughly corresponds to the horizontal location of the corresponding piece of equipment.
The convention for formatting & identifying the process equipment is given in Table 1.2.

28. Also identified in Figure 1. 3 are utility streams
Also identified in Figure 1.3 are utility streams. Utilities are needed services that are available at the plant. Chemical plants are provided with a range of central utilities that include:
Electricity, compressed air, cooling water, refrigerated water, steam, condensate return, inert gas for blanketing, chemical sewer, waste water treatment, & flares.
A list of the common services (utilities) is given in Table 1.3, which also provides a guide for the identification of process streams.

30. Equipment Numbering1/3 XX-YZZ A/B/…
XX represents a 1- or 2-letter designation for the equipment (P = pump)
Y is the 1 or 2 digit unit number (1-99)
ZZ designates the equipment number for the unit (1-99)
A/B/… represents the presence of spare equipment

31. Equipment Numbering2/3
1 . Number each process area, starting with 100, 200, 300, etc.
2. Number major pieces of process equipment in each area, starting with 110, 120, 130, etc.
3. Number supporting pieces of equipment associated with a major process unit by starting with the next higher number than the major process unit, e.g., 111, 112, 113, 114 for supporting pieces associated with 110.
4. Attach a prefix letter to each equipment number from the following list to designate type.
5. The first nine numbers in each area are reserved for equipment servicing the entire area, such as a packaged refrigerating unit (e.g., P-105). However, any packaged unit may be broken into its components and numbered as in steps 2 through 4.
6. Use letters following the equipment number to denote duplicates or spares (e.g. C-l0l A and C-l0lB denotes two identical compressors )

32. Equipment Numbering3/3
As an example of how to use this information, consider the unit operation P-101A/B & what each number or letter means.
P-101A/B identifies the equipment as a pump
P-101A/B indicates that the pump is located in area of the plant
P-101A/B indicates that this specific pump is number 01 in
unit 100.
P-101A/B indicates that a back-up pump is installed. Thus,
there are two identical pumps P-101A and P-101B.
One pump will be operating while the other is idle.

33. Equipments Symbols
The symbols used in process diagrams presented in this text is shown in Figure 1.4. A short list is presented.
This list covers over most of those needed in fluid (gas or liquid) processes.

38. LINE SYMBOLS

39. Stream Numbering and Drawing1/3
Number streams from left to right as much as possible
Horizontal lines are dominant
yes no no

40. Stream Numbering and Drawing2/3
Add arrows for
Change in direction
Inlet of equipment
Utility streams should use convention given in Table 1.3, lps, cw, fg, etc.

41. Stream Numbering and Drawing3/3
Referring back to Figure 1.3, it can be seen that each of the process streams is identified by a number in a diamond box located on the stream.
The direction of the stream is identified by one or more arrowheads.
The process stream numbers are used to identify streams on the PFD, & the type of information that is typically given for each stream.

42. Stream Information1/3
For small diagrams containing only a few operations, the characteristics of the streams such as:
1- Temperatures,
2- Pressures,
3- Compositions, and
4- Flowrates
can be shown directly on the figure, adjacent to the stream.

43. Stream Information2/3
This is not practical for a more complex diagram. In this case, only the stream number is provided on the diagram.
This indexes the stream to information on a flow summary or stream table, which is often provided below the process flow diagram. In this text the flow summary table is provided as a separate attachment to the PFD.

44. Stream Information3/3
The stream information that is normally given in a flow summary table is given in Table 1.4.
The flow summary table for the toluene benzene process, Figure 1.3, is given in Table 1.5 & contains all the required information listed in Table 1.4

46. Flow Summary Table (Toluene – Benzene Plant)

48. With information from the PFD
1- Figure 1.3 and
2- Flow summary Table (Table 1.5),
Problems regarding material balances & other problems are easily analyzed.
To start gaining experience in working with information from the PFD, the following examples are provided.

49. Example
Check the overall material balance for the benzene process shown in Figure 1.3. From the figure, we identify
1- the input streams as Stream 1 (toluene feed) & Stream 3
(hydrogen feed)
2- the output streams as Stream 15 (product benzene) & Stream
16 (fuel gas). From the flow summary table, these flows are
listed as (units are in (103 kg)/h):
Input: Output:
Stream Stream
Stream Stream
Total ×103 kg/h Total ×103 kg/h
Balance is achieved since Output = Input.

50. 3. Equipment Information
The final element of the PFD is the equipment summary. This summary provides the information necessary to estimate the costs of equipment & furnish the basis for the detailed design of equipment.
Table 1.6 provides the information needed for the equipment summary for most of the equipment encountered in fluid processes.

52. The information presented in Table 1
The information presented in Table 1.6 is used in preparing the equipment summary portion of the PFD for the benzene process.
The equipment summary for the benzene process is presented in Table 1.7.

55. Combining Topology, Stream Data to Give a PFD
Ex 4.4
Vol 6
P 150

56. PIPING & INSTRUMENTATION DIAGRAM (P&ID)
The piping & instrumentation diagram (P&ID) or mechanical flow diagram (MFD) provides information needed by engineers to begin planning for the construction of the plant (ie shows the engineering details of the equipment, instruments, piping, valves and fittings and their arrangement).
The general conventions used in drawing P&IDs are given in Table 1.9.

57. PIPING & INSTRUMENTATION DIAGRAM (P&ID)
P&ID diagram includes every mechanical aspect of a plant except
Operating conditions T,P
Stream flows
Equipment locations
Pipe routing
Pipe lengths
Pipe fittings
Support, Structures and Foundations

59. Dimensions of Welded and Seamless Pipe Carbon, Alloy and Stainless Steel ANSI B36.10,B36.19

60. Control Instrumentation1/2
Instruments are used to sense process variables and drive control valves.
These are denoted on P&IDs by circles with letters:
Level control Flow recorder control
Valves are connected by solid lines to the point where variables are measured, and by dotted lines are connected to the equipment they control LC
FRC
FRC

61. Control Instrumentation2/2
First letter describes the variable sensed by the instrument:
Pressure (P), Temperature (T), Flow (F), level or liquid level (L), composition (A)
The second and third letters describe the action taken:
Record ( R), Indicate (I), Sound an alarm (A), or Control (C )
Explain the symbols (see next slide):
Level Indicator Pressure Indicator Control
Table 1.10 summarizes the conventions used to identify information related to instrumentation & control LI
PIC

62. INSTRUMENT SYMBOLS
Dr. Ahmed Zoromba

63. Conventions used for identifying instrumentation on P&IDs

64. PFD and P & ID Diagrams
Each PFD will require many P&IDs to provide the necessary data.
Figure 1.7 is a representative P&ID for the distillation section of the toluene - benzene process that shown in Figure 1.3.
The P&ID presented in Figure 1.7 provides information on the piping (this plot is included as a small part of the complete P & ID diagram.
As an alternative, each pipe can be numbered, and the specifics of every line can be provided in a separate table accompanying this diagram.

67. Other Common Diagrams1/4
Plot Plans (site plan) – plan or map drawn looking down on plant (drawn to scale with all major equipment identified)
Elevation Diagrams – show view from side and give information about equipments distance from ground

69. Other Common Diagrams2/4
Section of Elevation Diagram

70. Other Common Diagrams3/4
Piping Isometrics – show piping in 3-dimensions
Vessel Sketches – show key dimensions of equipment and locations of inlet and outlet, nozzles, etc.

74. Other Common Diagrams4/4
Process Layout: The sequence of the main equipment items shown symbolically on the flow-sheet follows that of the proposed plant layout.
Process Layout :To show the flow of material from stage to stage as it will occur, and to give a general impression of the layout of the actual process plant. The equipment should be drawn approximately to scale.
Good Layouts should Consider the followings:
Material handling equipment
Capacity and space requirements
Environment and aesthetics
Flows of information
Cost of moving between various work areas
CHEM2003/Dr. Ahmed J. Ali/

75. Process flow diagram and Floor plan (Layout diagram of equipments) for tomato-paste processing

76. Three-dimensional (3D) Diagram For Tomato Paste Line

78. Computer-Aided Design
Computing hardware & software have become indispensable tools in process & plant design. Capabilities provided by computers for rapid calculations, large storage, & logical decisions plus available technical & mathematical software permit design engineers to examine effect that various design variables will have on process or plant design & to be able to do this more rapidly than was required in past to complete a single design by hand calculation.

79. Process simulators are often useful in generating databases because of their extensive data banks of pure-component properties & physical property correlations for ideal & non ideal mixtures.
When such data are unavailable, simulation programs can regress experimental data obtained in laboratory or pilot plant for empirical or theoretical curve fitting. The computer-aided process simulator is also a useful tool in preparing material & energy balances.

83. End of Chapter 2

84. Acetaldehyde is a colorless liquid with pungent, fruity odor
Acetaldehyde is a colorless liquid with pungent, fruity odor. It is primarily used as a chemical intermediate, principally for the production of acetic acid. This is the description of process for Unit 100. Ethanol, an 85 wt% solution in water is combined with 85% ethanol recycle stream from Unit 200, is then pumped to 100 psia and heated to double heaters using low pressure steam at 6260F before being fed to an isothermal, catalytic, packed-bed reactor, where the ethanol is dehydrogenated to form acetaldehyde. The reactor effluent is then cooled to a double cooler using cooling water produce a two phase stream and fed to a flash vessel. The vapor is sent to an absorber where it is contact with water, which absorbs the acetaldehyde and ethanol from the vapor stream. The resulting vapor effluent, is then sent for further processing and recovery of valuable hydrogen. Alternatively, this stream could be used as fuel. The liquid is combined with the liquid effluent from the flash vessel and sent to Unit 200.

85. For the given processdescription
Draw a PFD
Name all the existing equipment for Unit 100
Number all stream lines