A gas re-use system for carbon fiber manufacturing processes based on hydrocarbon thermal decomposition. The system permits re-use of the output gas from the carbon fiber manufacturing process, a process based on the use of an industrial gas as the main raw material. The system can comprise a feedback pipeline provided with force and filtering means to raise the pressure from the reaction furnace output manifold to its input. There are also return and bleed lines operated separately to assure suitable pressure ranges at the same time both in the reaction furnace input area and extraction area.