Plug Flow Reactor

The plug flow reactor model (PFR) also known as continuous tubular reactor (CTR) is the model that is used in chemical engineering. PFR is basically used to describe chemical reactions in continuous, flowing systems of cylindrical geometry in chemical engineering. The PFR model is used to calculate the action of chemical reactors in tubular design. It is done to note the key reactor variables like estimating dimensions of the reactor.

In a Plug Flow reactor, fluid goes through the reactor in a serious of extremely thin coherent plugs. Each plug has a uniform composition for better flow. The plugs migrate in an axial direction through the reactor. Each plug is set up in a way that is has a different composition from the one before it and the one after it. This makes the fluid flow smoothly in plug through a PFR. The fluid is mixed in the fundamental direction and not in the upstream or downstream direction. Each plug is a separate unit that is an infinitely small batch of reactor that mixes the fluid well. As the plug flows down the PFR, the time taken by the plug element can be known from its position in the reactor.

PFR Modeling

The PFR is conducted by the simple ‘differential equations’ which can be calculated through appropriate boundary conditions. The PFR model works great with fluids like liquids, gases and slurries. The PFR model is convenient for these types of fluids.

In PFR model, several assumptions must be made to simplify the problem.

Note that not all of these assumptions are necessary, but if you remove these assumptions, it will not increase the complexity of the problem. The PFR model is used for multiple reactions as well as other reactions involving change in temperatures, pressures and densities of the flow. Although these complications are ignored in what follows, they are often relevant to industrial processes.

Some assumptions are outlined below

Plug Flow: Plug flow is a simple process of a fluid flowing in a pipe. The momentum of the fluid is assumed to be constant across any cross-section of the pipe

Steady State: In a steady state all the state variables are constant despite of the ongoing process that strive to change them

Constant Density: Is reasonable for some liquids but have a 20% error for polymerizations. Under ‘no pressure’ drop, they are valid for gases.

Single reaction: occurs in the bulk of fluid.