Plug Flow Reactor A plug flow reactor (PFR) is a type of chemical reactor that is used in the chemical and biochemical industries for continuous production of chemicals or biochemicals. In a PER, the reactants flow through the reactor as a plug, with no mixing between the different sections of the reactor. In a PFR, the reactants are continuously fed into the reactor at one end, while the product is continuously removed from the other end of the reactor. The reaction proceeds as the reactants fl