To provide a method and a system for rendering dioxins in boiler ash harmless.

In a system where an incinerator 1 for incinerating refuse thrown into from a throw-in section 2 is coupled with a boiler 5 for recovering heat of exhaust gas from the incinerator 1, the boiler ash discharging section 5B of the boiler 5 is coupled trough a return path 6 with at least one of the throw-in section 2 and the incinerator 1 so that the boiler ash can be returned.