Chemical Reaction Engineering (CRE) | PFR - Plug Flow Reactor
Chemical Reaction Engineering (CRE):
Chemical reaction engineering (CRE) is concerned with the exploitation of chemical reactions on a commercial scale. It's goal is the successful design and operation of chemical reactors. In other words: Chemical Reaction Engineering (CRE) is the field that studies the rates and mechanisms of chemical reactions and the design of the reactors in which they take place.
In chemical engineering fields, chemical reactors are vessels designed to contain chemical reactions. The design and manufacturing to produce a chemical reactor deals with multiple aspects of chemical engineering.
PFR - Plug Flow Reactor
In a PFR - Plug Flow Reactor , one or more fluid reagents are pumped through a pipe or tube. The chemical reaction proceeds as the reagents travel through the PFR.
Plug Flow Reactor (PFR)
The plug flow reactor (PFR) model is used to describe reactions in continuous, flowing systems. The PFR model is used to predict the behavior of reactors, so that key reactor variables, such as the dimensions of the reactor, can be estimated. PFRs are also generally called as Continuous Tubular Reactors (CTRs).
Modeling in PFR id done as follows:: Fluid going through a PFR may be modeled as flowing through the reactor as a series of infinitely thin coherent "plugs", each with a uniform composition, traveling in the axial direction of the reactor, with each plug having a different composition from the ones before and after it and the key assumption is that as a plug flows through a PFR, the fluid is mixed perfectly in the radial direction but not in the axial direction. Each plug of differential volume is considered as a separate entity, effectively an infinitesimally small batch reactor and limiting to zero volume. As it flows down the tubular PFR, the residence time of the plug is a function of its position in the reactor. In the ideal PFR, the residence time distribution is therefore a Dirac delta function and with a value equal to t.
CSTRs (Continuous Stirred Tank Reactor) and PFRs have fundamentally different equations, so the kinetics of the reaction being undertaken will to some extent determine which system should be used and though there are a few general comments that can be made with regards to PFRs compared to other reactor types including CSTR.
The main advantages are that Plug flow reactors have a high volumetric unit conversion, run for long periods of time without maintenance, and the heat transfer rate can be optimized by using more, thinner tubes or fewer, thicker tubes in parallel while disadvantages of plug flow reactors are that temperatures are hard to control and can result in undesirable temperature gradients and also its maintenance is more expensive than CSTR maintenance.
Through a recycle loop a PFR is able to approximate a CSTR in operation and this occurs due to decrease in the concentration change due to the smaller fraction of the flow determined by the feed. This takes place in the limiting case of total recycling, infinite recycle ratio, and the PFR perfectly mimics a CSTR.
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