Hi there, and welcome to this lecture on process flow diagrams: equipment symbol representations.
My name is Marina Miletic.
Here we have an equipment type which is critical to almost any chemical process.
See if you know what these are.
These are all reactors, and they have the letter abbreviation R. There are quite a few
choices amount reactors, including continuous stirred tank reactors, batch reactors, plug
flow reactors, packed bed reactors, fluidized bed reactors, moving bed reactors, and others.
There are also many different symbols to represent them.
Let's look at some of these reactors and how they're represented on a process flow diagram.
This is the symbol for a continuous stirred tank reactor.
It's called that because it features continuous flow of liquid in and out of a tank, and the
contents are mechanically agitated using a stirrer and motor.
This type of reactor is best for liquids which need to be well mixed.
Because of size and residence time limitations, it's not usually used in large processes that
make hundreds of tons of product per day.
Instead, this reactor is usually used in the food and personal care industries.
A batch reactor is related to the CSTR in that it's also liquid phase, and it's usually
filled and emptied once, so product is made in batches.
This type of reactor can feature agitation or not, and it's usually used when product
quality is critical, or when a very long residence time is required.
For example, this type of reactor is typically used to create fermented beverages such as
beer, but is also used to make pharmaceuticals and vaccines.
This generic symbol is commonly used to represent a plug flow reactor, or almost any kind of
non-agitated reactor where reactants flow through a cylindrical space.
Plug flow reactors are typically well mixed in the radial direction, which is within the
cross sectional plane, but are not mixed axially.
Notice that flow can occur through a large space such as this, or also through a narrower
tube, which helps facilitate a longer residence time, or many tubes running in parallel.
This type of reactor can be used for liquids or gases, and usually for high flowrate, larger
processes, and when a more consistent and longer residence time is needed compared to
a CSTR.
PFRs are typically used in large chemical production processes, when large amounts of
basic commodity chemicals need to be produced.
This reactor is directly related to a PFR because it's commonly considered a type of
plug flow reactor.
These are packed bed reactors.
Notice these symbols have large X's through them.
Whenever you see a large X on a process unit, whether it's on a reactor or separator, this
represents some volume filled with packing.
Packing can be a catalyst, or an inert solid such as ceramics, metals or glass.
So this reactor is a horizontal packed bed with fluid flowing from one end to the other
horizontally.
These are vertical packed columns, with packing most likely dumped in from the top, and supported
on mesh-like trays.
This type of reactor can be used for liquids and gases, and is ideal for large or fragile
catalysts, usually over 3 mm in diameter.
Let's look at two additional types of reactors and their symbols.
For catalyst particles that are smaller than 3 mm, it's a good idea to consider using this
type of reactor, a fluidized bed.
This reactor has a Q-tip like shape and may have a heating element at the bottom.
A fluidized bed reactor gets its name from the way catalyst is suspended in the vessel.
Catalyst is fluidized upward by gas or liquid going up into the vessel.
These solid catalyst particles mix with the reactants in this expansion volume.
The shape of this reactor helps facilitate the suspended mixing and even temperature
distribution.
For this to occur effectively, the catalyst particles must be traveling at greater than
a minimum velocity, but less than the maximum fluidizing velocity.
This type of reactor can accommodate liquids and gases, and is best to use on smaller catalyst
particles, in the range of 0.1 mm.
This type of reactor is very common in oil refineries, or plastic manufacturing processes.
Fluidized bed reactors are sometimes the only reactor in an entire crude oil refining process,
and there's usually no spare or backup.
It's one of the most important pieces of equipment in a refinery, because it's used to break
hydrocarbons into smaller molecules, but it can also be used for other reactions as well.
A moving bed reactor is related to both a plug flow and fluidized bed, in that it features
a stream of well-mixed catalyst that's continuously moving into and out of the reactor, as is
the process stream.
This reactant and catalyst flow can be cocurrent like this, or countercurrent.
The reason why the catalyst is continuously removed is that they type used in this reactor
requires regeneration.
The catalyst is usually removed, separated, and send to a kiln, where it's heated and
regenerated, and then sent back into the process unit.
This type of reactor can accommodate liquids or gases, and are typically used in large
commodity chemical processes, where the catalyst is prone to fouling and decay.
Let's next look at some common CHEMCAD and Aspen reactor symbols.
These two reactors are the most common representations you'll find in CHEMCAD.
This first one is a continuous stirred tank reactor, and the second is a packed bed reactor,
but it's also commonly used to designate a plug flow reactor.
These are the three most common reactor representations you'll see in Aspen.
The first is a CSTR.
The second is probably the most commonly used reactor you'll see in Aspen.
It represents plug flow and packed bed reactors, but can be used to represent almost any non-agitated
reactor.
This last one is another representation of a packed bed reactor.
In CHEMCAD or Aspen, almost all these reactors can be designed to run under adiabatic or
isothermal temperature control, and for isothermal conditions, you might see cooling water, high,
medium, or low pressure steam, refrigerated water, electric heat at 220, 440, or 660 V,
or any one of a number of utilities.
Something to keep in mind with all of these reactors is that these symbols are very general
representations of what these reactors really look like.
They actually come in a wide variety of sizes and shapes, and I encourage you to search
for and look at pictures of actual process reactors.