Why and how are recycle reactors used?

Recycle reactors return portion of exit stream to inlet, combining PFR advantages with better temperature control. Recycle ratio R = recycle flow / fresh feed flow. At R=0, pure PFR; as R increases, approaches CSTR behavior. Benefits: dilutes inlet concentration for exothermic reactions (temperature control), converts unused reactants (improves overall yield), and allows steady-state operation with deactivating catalysts (maintain conversion). Used in ammonia synthesis (high recycle ratio due to limited per-pass conversion).