EG-111 Auto CAD notes - Session 6 PDF

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College of Engineering Swansea University EG-111 Chemical Engineering Skills Course Notes PC Session 6: Introduction to Flow sheeting, and Tool palettes

Author: Dr R Butterfield Email: [email protected]

Table of Contents Introduction ............................................................................................................................................ 1 Learning Aims.......................................................................................................................................... 1 General Study Advice .............................................................................................................................. 1 What are Piping & Instrumentation Diagrams (P&ID) and Process Flow Diagrams (PFD) ..................... 2 Process Instrumentation Symbols ...................................................................................................... 4 Importing & Developing Your Own Symbol Library ................................................................................ 7 PFD and P&ID Layouts........................................................................................................................... 12 Self Assessment Questions ................................................................................................................... 14 Learning Outcomes ............................................................................................................................... 21

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Introduction In this session on the use of AutoCAD, you will be finding out how to produce basic Process Flow Diagrams (PFD) and Piping and Instrumentation Diagrams (P&ID). You will create a small set of the most common P&ID symbols as the basis for a symbols library to use in PFD and P&ID’s. You will then create a tool palette to allow you to “click and drop” these blocks into your PFD and P&ID drawings. You will also learn how to interpret a simple process description and present it as a PFD. This is only an introduction to the concept of PFD and P&ID drawings, you will be expected to develop these skills throughout the duration of your degree course. When you begin the Chemical and Environmental Design Project in the 3rd year of the course, you will be expected to be proficient in how to produce detailed P&ID’s and PFD’s.

Learning Aims At the end of this session, you will:  

Create of toolpalette from a Symbol Library for PFD’s and P&ID’s drawings. Translate a process description into an PFD



Draw a simple PFD which also presents some key process information.

General Study Advice You should ensure you have completed the section on Using Blocks in AutoCAD from the notes of previous PC session. You should also ensure you have downloaded copies of:   

BS EN ISO 10628-1:2015 Diagrams for the chemical and petrochemical industry – Part 1: Specification of diagrams. BS EN ISO 10628-2:2012 Diagrams for the chemical and petrochemical industry – Part 2: Graphical symbols. Parts 1 – 4 of BS 1646: Symbolic representation for process measurement control functions and instrumentation

I also refer you to Chapters 4 and 5 of the following text book: Sinnott, R., & Towler, G. (2009). Chemical Engineering Design (5th ed). Oxford: ButterworthHeinemamn This text gives a good introduction to understanding how to draw PFD’s and P&ID’s as well as provide a good guide on process control symbols and line types. The book also provides examples of commonly used control loops. Please note that this book uses the ISA-5.1-1984 (R1992) symbols and codes. Much of which are shared by BS 1646.

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What are Piping & Instrumentation Diagrams (P&ID) and Process Flow Diagrams (PFD) A typical site where you might work as a chemical or environmental engineer could look something like this.

A Piping and Instrumentation Diagram, or simply P&ID, is a “schematic” of your chemical processing plant. This diagram is used by field techs, engineers and operators to better understand the process and how the instrumentation is interconnected across the site. The P&ID shows details of instrumentation and control, and often lists pipe sizes, insulation, thermodynamic states of streams, operating pressures/temperature of equipment etc. In some P&ID drawings there is an indication of equipment elevation relative to one another, this is typically when your plant is distributed across a number of floors within a multi-story structure. The Supporting Material Folder in the module content section for the course on MyStudies contains an example P&ID for a Glacial Acetic Acid Plant. Please be aware this a P&ID drawn under a version of the Symbol Standards used in 1995 and many of the symbols have been superseded. You should also be aware that there are a number of other drawing standards used worldwide, such as “ANSI”. Process Flow Diagrams (PFD) are a simpler version of the P&ID. The PFD conveys less detail than the P&ID and is used general to understand how the process works at a glance. PFD’s are typically accompanied by a table which contains the mass and energy flows for each process stream. This pictorial representation of a Temperature Controlled process may be informative; however it is not practical or CAD friendly, especially in a multi-loop process.

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The P&ID will use symbols and circles to represent each instrument and how they are inter-connected in the process.

Tag “numbers” are letters and numbers placed within or near the instrument to identify the type and function of the device.

These tag descriptors can be explained as follows. Page | 3

So returning to the earlier example,

BS 1646 outlines all the “Identification Letters” that describe the type of instrument being represented. The most common are summarised in the following table.

Process Instrumentation Symbols The symbol that is used to represent the instrument also provides information on where the instrument is located, whether it shares a display or has shared control, and if it has computer control associated with it.

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Instrument location Instruments are generally denoted by a circle. The presence or absence of a line determines the location of the physical device. For example no lines means the instrument is installed in the field near the process e.g. A pressure gauge on top of a boiler.

Shared Displays/Shared Control Some instruments are part of a Distributed Control System (DCS) where a specific controller or indicator can be selected from many others but shown in one location (such as a terminal screen). This is indicated by a box being placed around the instrument symbol.

You can also have computer controlled instrumentation, this is represented by a hexagonal symbol. The symbols used to represent instrumentation are summarised as follows:

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There are different line types used to represent how instrumentation is interconnected. The most common are summarised below.

So, returning to the initial example. The temperature control for a heat exchange may appear as follows physically out on the plan, or in a laboratory setting.

But if drawn as a P&ID, the temperature control system would look like this.

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You will learn more regarding control systems in other modules as you progress through the degree course. These notes are just to introduce you to the concepts. If you wish to learn more, then I refer you to the information provided in the General Study Advice at the start of these notes.

Importing & Developing Your Own Symbol Library You will be expected to use the BS EN ISO 10628 parts 1 & 2 as the standards for all your PFD and P&ID drawings. To get you started I have produced a small symbol library of some of the more common symbols used. This takes the form of a drawing containing blocks and line types you will find useful to use. You are now going to import this library into AutoCAD and create a symbol library for the blocks. Download the following files from the Mystudies webpage for this sessions notes into the My Documents folder. PFD Symbols Library – student.dwg Shape files.zip In My Documents create a folder called shape files and extract the contents of shape files.zip into this folder. Start AutoCAD and open PFD Symbols Library – student.dwg You should see the following prompt asking for details of some shape files.

Click on specify shape files and navigate to the shape files folder you created in My Documents. Click on the L.shx file. This should now present you with a series of blocks and two new line types loaded. This is going to be the reference drawing where all your PFD and P&ID symbols should be stored. As you progress through the course you will need to expand this symbol library with new blocks to represent the equipment and plant items not already featured in the library. You learned how to create blocks in notes for Session 5.

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To utilize this library best, you are going to create a Tool Palette, from you can click and drop the symbols into your drawing. To do this you will need to access the Design Center, found on the Insert tab of the ribbon bar. Open a new drawing, but use the acadiso template. Once opened save this PFD Template.dwg to an accessible location. Navigate to the Insert Tab and click on Design Centre.

If the Design Centre is not visible on the Insert Tab, then you can navigate to the View Tab and select the Design Centre from there.

This will bring up a dialog box that looks similar to that shown below. With a folder list on the left and a window on the right for showing information.

Now, in the folder list navigate to the location where you have saved PFD Symbols Library – student.dwg. Expand the tree so you can see you can see all the blocks, dimstyles, layers, layouts etc. First you will add the linetypes to your drawing. So click on linetypes in the folder tree.

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In the window to the right, right click ELECTRICAL and select addlinetypes.

Now do the same for HYDRAULIC line type. This has now loaded those two line types into your drawing. As long as you keep the shapefiles folder you created earlier in the same location, AutoCAD will automatically load the relevant files. If not, you will have to go through the procedure of navigating and selecting the shapefiles again. Now left click on Blocks in the folder list. You should find that all the blocks stored in this drawing will appear in the right window, as shown below. You could add them all individually to your drawing, but it is better to create a toolpalette that will load every time you use AutoCAD.

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Right click on Blocks in the folder list and select Create Tool Palette. This will then load all the blocks into a tool palette that you can use, which should look something similar to that shown below.

If the tool palette isn’t visible, navigate to the View tab and click on Tool Palettes.

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You can now click and drop the symbols from the tool palette into your drawing. Save the your PFD Template.dwg file. This will ensure that every time you open the file it will load the line types added to it. Note: You must keep the PFD Symbols Library.dwg file in the same location. Otherwise the tool palette will not load when you next start AutoCAD. This should not be a problem on your home computers, but may be an issue for the University Network PC’s. In which case you may need to go through the procedure of saving the symbols library and shape files to the pc and load them back into AutoCAD in the same way you have just done.

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PFD and P&ID Layouts You will need to create A4, A3 and A1 Layouts in your PFD Template.dwg file. How to create layouts has been explained in notes for PC session 3. The only difference is that you do not need create any border on the lay outs, those you will create around the P&ID and PFD on the model space as required. But you will need to expand the view port on each layout to match the existing dotted lines that trace the margins of the paper. The conventions on how PFD’s and P&ID’s should be presented are found in BS EN ISO 10628 part 1. The following examples are taken from this standard. Process flow diagram with basic information

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Basic process flow diagram incorporating a mass balance.

Note: That in both cases the drawings are bordered and have a title block in the bottom right hand corner. Now try to complete self assessment question 1.

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Self Assessment Questions Question 1: A stream containing a mixture of 40 mol% Benzene, 35 mol% Toluene and 25 mol% O-xylene is fed to a distillation column. From the top the column almost all the Benzene and some Toluene leave as distillate. The remainder leaves the bottom of the column and is fed to a second distillation column. In the second distillation column all the remaining Benzene, almost all the Toluene and some O-xylene leave the top of the column. The bottoms leaving the reboiler of the second distillation column contains mainly O-xylene and some Toluene. For the 1st column: Recovery of Benzene in the distillate is 97.50%. Recovery of Toluene in the distillate is 1.13% For the 2nd Column Recovery of Toluene in the distillate is 92.52% Recovery of O-xylene in distillate is 1.33% 1) Complete the material balance for the system and determine the molar flows of Benzene, Toluene and O-xylene in all streams. Use a suitable basis to perform the calculations. 2) Draw in Autocad the flowsheet for the process. As part of the drawing, include a table showing the molar flows of each component in each stream. Include a suitable Title block and border. Hint: You should have covered or be in the process of covering Material Balances in EG-100. If you have not done this yet, then skip this part and reproduce the drawing shown in the solution. You can always go back and check the numbers at a later date. You may want to learn how to use the Table function found on the annotate tab.

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Solution to Q1

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Question 2 Add the following symbols from BS EN ISO 10628-2 to your PFD Symbol library – student.dwg file as blocks. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17.

Vessel with dished ends and support brackets. Vessel with dished ends and electrical heating Vessel with dished ends and thermal insulation Heat exchanger with straight tubes (fixed-tube plates) Heat exchanger of plate type. Evaporator, re-boiler Pump, centrifugal type Pump, gear type Pump, screw type Compressor, vacuum pump liquid ring type Compressor, ejector type, vacuum pump jet type Valve, globe type Valve, angle globe type Valve, three way globe type Valve, ball type Valve, angle ball type Valve, three way ball type

Once you have created these symbols and added them to your library file. Create a new tool palette that incorporates the new symbol library.

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Question 3: Process Description: Thermal De-Alkylation of Toluene Note: This question is very challenging at this stage of your degree, but is something you as a chemical engineer will be expected to do. Feel free to challenge yourself by doing this question. Brief Process Description This petrochemical plant produces the valuable chemical benzene (C6H6) from the less valuable chemical toluene (C7H8) by heating toluene in the presence of hydrogen to remove the methyl (CH3) group. The methyl group combines with hydrogen to form methane (CH4). After the reaction, the products (unreacted hydrogen and toluene, methane, biphenyl and benzene) are cooled to condense the unreacted toluene, and the biphenyl and benzene, in order to separate them from the gaseous hydrogen and methane. Some of the gas mixture is recycled and the remainder is sold as a fuel for synthesis gas. The liquids are distilled to separate them into the benzene product, unreacted toluene (which is recycled to the reactor) and biphenyl which is sold as fuel oil. Detailed Process and Equipment Description Paragraph 1 We can describe the process in greater detail to show how each piece of equipment is used. Fresh toluene is pumped from a Feed tank and mixed in a pipe line with recycled toluene from the toluene column (see paragraphs 13 & 14) and recycle gas from the compressor. The mixture is pre-heated in the feed-effluent heat exchangers by cooling the hot mixture from the liquid quench tank. There are two exchangers here because the area required is greater than that commercially available in one unit. Equal sized units are used for the convenience in construction an maintenance. These are part of the heat input section. Paragraph 2 The heated feed mixture then goes to a fired heater or furnace to raise it to the final temperature needed (about 650 °C). The heater burns fuel gas, produced in part by the process. The furnace completes the heat input section. Waste gases pass through a waste heat boiler (which raises steam) to a chimney stack. Paragraph 3 From the fired heater, the mixture goes to an insulated reactor vessel in which the desired reaction occurs, releasing heat so that the effluent stream is about 720 °C. Paragraph 4 This hot stream must be cooled so that the components can be separated. It loses part of its heat to the cold feed in the feed-effluent exchanger already mentioned in paragraph 1. However to avoid using such high temperatures in the exchanger (metallic alloys get structurally weak at very high temperatures) some cold liquid from the phase separator (see Paragraph 6) is added to the stream before the feed-effluent exchangers in a unit called the liquid quench.

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Paragraph 5 The combined quench and effluent stream leaving the feed-effluent heat exchangers is still at about 150 °C and so must be cooled further. This is accomplished in the two effluent coolers, using cold water to remove the heat. Here again there are two units because one would have to be too large. This completes the heat removal section. Paragraph 6 Now the effluent mixture is at about 40 °C and consists of some liquid and some gas (mostly unreacted hydrogen, with methane formed in the reaction). This mix is fed to a vessel called the phase separator in which the liquid and the gas separate because of the difference in density. Paragraph 7 Some of the gas (CH4 and H2) is sent to the fuel system, and used in the fired heater or elsewhere in the refinery. Some more pure hydrogen from a storage vessel is mixed with the remainder and this is then compressed and recycled to the feed. Some of the liquid from the separator is pumped to the quench tank to cool the hot gases from the reactor. The balance is fed to the first distillation column, called the stabilizer. Paragraph 8 We now encounter a series of distillation columns. These separate compounds according to diffence in boiling points. Every distillation involves: a) a means of contacting liquid and vapour, called the column, in which special trays or oddly shaped packings are used to promote intimate mixing and then separation of phases; the feed is introduced somewhere in the middle of the column; b) a reboiler, or heat exchanger in which the liquid from the bottom of the column is converted to vapour by heating with steam; c) a condenser, or heat exchanger in which vapour from the top of the column is converted to liquid by cooling with either water or refrigerant; d) a reflux accumulator or drum, a vessel in which liquid from the condenser is collected. Some of the collected liquid from the reflux accumulator is pumped to the top of the column because liquid is needed to run down through the column, contacting with the vapour; the rest of the condense liquid is the overhead product. Similarly, some of the liquid flowing from the bottom of the column mus...