According to the present invention, in a heating furnace in which a fuel is burned by mixing the fuel supplied through a fuel supply pipe with combustion air supplied through a combustion air supply pipe by a combustion burner, a cooling medium guiding pipe through which cooling air for cooling the fuel supply pipe is guided into the furnace is provided to the outer peripheral side of the fuel supply pipe, and a cooling water supply pipe through which cooling water is supplied via a cooling water adjusting valve is connected to the cooling medium guiding pipe.

Described herein is a method of combusting fuel with reduced emissions comprising the steps of: a. introducing a fuel inside of a liner wall without premixing in a pressurized air stream prior to ignition; b. producing a flowing stream of combustion products by igniting the fuel and air; and c. introducing no additional pressurized air inside and adjacent said liner wall for film cooling said liner wall, for reducing CO.

In one embodiment of the disclosure, a method (300) for predicting physical parameters of a combustion fuel system (100) includes causing water injection in at least one combustor. The water injection is associated with at least one time and performed during gaseous fuel operations or after liquid fuel operations. The method (300) includes measuring exhaust spread data associated with the water injection and allows correlating the exhaust spread data to at least one physical parameter associated with a nozzle (12) or a valve of the fuel system (100). The method (300) further includes storing the exhaust spread data, the at least one physical parameter, and the at least one time to a database. The method (300) further provides stored historical data from the database to an analytical model. The analytical model is operable to predict, based at least partially on the stored historical data, at least one future physical parameter associated with a future time.