Cooling apparatus of heating furnace

A heating furnace comprising a combustion burner which mixes a fuel supplied through a fuel supply pipe with a combustion air supplied through a combustion air supply pipe and burns the fuel in the inside of the furnace, wherein

• a cooling medium guiding pipe which guides a cooling air for cooling the fuel supply pipe to the inside of furnace is arranged on an outer peripheral side of the fuel supply pipe,
• a cooling water supply pipe for supplying a cooling water via a cooling water adjusting valve is connected to the cooling medium guiding pipe, and
• when the combustion burner mixes the fuel supplied through the fuel supply pipe with the combustion air supplied through the combustion air supply pipe and burns the fuel in the inside of furnace, the fuel supply pipe is cooled with the cooling air guided to the inside of furnace through the cooling medium guiding pipe arranged on the outer peripheral side of the fuel supply pipe, and when the inside of furnace is cooled, the combustion by the combustion burner is stopped while the cooling water adjusting valve is opened to guide the cooling water through the cooling water supply pipe into the cooling medium guiding pipe so that the cooling water is sprayed from the cooling medium guiding pipe to the inside of furnace.