An injector comprises at least one injection nozzle, a dosing system to provide a dosed flow of reducing agent to the at least one or each injection nozzle, and an injection line fluidically connecting the dosing system to the at least one or each injection nozzle. The injection line comprises an upstream pipe fluidically connected to the dosing system, at least one downstream pipe fluidically connected to a respective injection nozzle, and at least one anti-backflow device to avoid or minimize fluidic flow from the at least one or each downstream pipe toward the upstream pipe.