A carbon fiber production method includes a carbon fiber production step including an oxidation step and a carbonization step; and an exhaust gas processing step including a heat exchange step; an external air mixing step; and a mixed external air supplying step in which the mixed external air is supplied to at least one step that uses heated gas in the steps in the carbon fiber production step; and among the exhaust gases, a high heating value exhaust gas having a heating value of 250 kcal/Nm.sup.3 or higher is supplied to an inlet side of an exhaust gas combustion apparatus and a low heating value exhaust gas having a heating value lower than 150 kcal/Nm.sup.3 is supplied to an outlet side of the exhaust gas combustion apparatus, respectively.

A self-regenerative combustion system comprising a single burner, capable of operating both during the combustion step and the waste gas aspiration step, and a valve with four ways and three positions, capable of switching the regeneration and the on/off control (oxydizing agent end and waste gas end). The system is provided for obtaining the maximum efficiency, flexibility, minimum fuel consumption and minimum environmental impact with reduced NOx emissions.

A method includes combustion products from combustion of fuel with oxidant brought first through a first heat exchanging step (150;201), in which thermal energy is transferred from the combustion products to the fuel which is thereby preheated, and the cooled combustion products thereafter are brought through a second heat exchanging step (151;203), in which thermal energy is transferred from the cooled combustion products to the oxidant which is thereby also preheated. A related system for preheating the fuel and oxidant is also provided.

A carbon fiber production method includes a carbon fiber production step including an oxidation step and a carbonization step; and an exhaust gas processing step including a heat exchange step; an external air mixing step; and a mixed external air supplying step in which the mixed external air is supplied to at least one step that uses heated gas in the steps in the carbon fiber production step; and among the exhaust gases, a high heating value exhaust gas having a heating value of 250 kcal/Nm.sup.3 or higher is supplied to an inlet side of an exhaust gas combustion apparatus and a low heating value exhaust gas having a heating value lower than 150 kcal/Nm.sup.3 is supplied to an outlet side of the exhaust gas combustion apparatus, respectively.