Hi there, and welcome to this lecture on process flow diagrams, letter and number designations.
My name is Marina Miletic.
In this lecture, we'll look more closely at the letter and number representations for
equipment.
Let's go back to our original process flow diagram for the production of ethylene oxide.
You may have noticed that next to each piece of equipment, there's a unique letter followed
by a dash and a 3-digit number designation.
This is because for identification purposes, each piece of equipment is given a letter
and number.
As an example, let's look at heat exchanger E-101.
The letter is the abbreviation for the type of equipment, whether it's a compressor, tower,
heat exchanger, reactor, turbine, or furnace.
All heat exchangers are designated by the letter abbreviation E. Just to review, the
letter designations for all pieces of equipment are shown here.
As part of the letter and number designation, the letter must be followed by a dash, followed
by a 3 or sometimes 4 digit number.
This first digit represents the area of the plant where the equipment can be found.
Often times, it's based on the location of a process within a specific facility.
Let's take a look at an example of a plant or facility.
If in area 100 in our plant, we make ethylene oxide, then all pieces of equipment in that
area used in making ethylene oxide should be labeled 101, 102, 103, etc.
If in area 200 in our facility, we make propylene, then all equipment in that area associated
with the propylene process should be measured 201, 202, 203, etc.
So this first number relates this piece of equipment to a specific production process.
The last two digits of the number represent that piece of equipment as counted from the
start of the process.
Let's go back to our process flow diagram to see how these heat exchangers are sequentially
numbered.
This first heat exchanger is E-101.
The one below it is labeled E-102.
The third, which is downstream from the first two, is E-103, and the fourth, further downstream,
is E-104.
Notice there's a bit of a judgement call you must make when numbering some of these units,
since some of them may be parallel to each other.
The general protocol is to number units based on the path of the process from starting materials
to products.
Trace the path of the process and number units of the same type based on their sequence from
start to finish.
For units which are part of parallel paths, give priority to equipment shown above other
units in the diagram.
I'd like to make one last point about these letter and number labels.
If by chance there's an A/B next to the letter/number designation, this means there are actually
two of that unit in place.
There are either parallel units in place or a main unit and a backup.
Because showing these spares or backups would clutter the diagram, this label is often times
added to minimize confusion.
This labeling is most common for pumps and smaller pieces of equipment.
Going back to our process flow diagram, you may have noticed that at the top of the diagram,
each piece of equipment is given a unique, descriptive name.
These names are important because they're how engineers and operators will usually refer
to equipment when discussing anything related to that unit, especially to people not familiar
with the process.
It's your job when developing a process flow diagram to concisely yet descriptively name
each piece of equipment, and I suggest always thinking about the key role it has in the
process, or to the equipment around it.
For example, if the purpose of a piece of equipment is to cool down a stream to help
make the separation unit run more effectively, you might call it a pre-distillation cooler.
These names can be very important, because they'll probably be used thorughout the lifetime
of the process.
Students often ask me in what order they should arrange the names of the equipment in this
row.
I suggest that you try your best to place these names above their corresponding process
units, while keeping them in one row if possible.
If you cannot fit all of these names in one row because they would become unreadable,
then add another row.