Studies of industrial high intensity gas combustors

Abstract

This paper describes theoretical and experimental studies of high intensity gas combustors, providing information from which practical combustors have been designed and applied in industrial furnaces and heating equipment. The combustors consist of combinations of an injector, in which low pressure air injects fuel gas, followed by a refractory-lined combustion chamber in which the air/gas mixture is burned, and the burned gases, at or near flame temperature, are accelerated through a refractory exit nozzle. The studies included investigations of the fluid dynamics of injection, the burner pressure loss characteristics, flame stability, completeness of combustion and combustion intensity. In designing a combustor of this type, the objective is to make the best possible use of the air supply pressure to obtain the highest exit velocity of the burned gases, or alternatively, the highest air/gas mixture velocity at the mixture nozzle (if a burner of wide stability range is required, i.e., high turndown). This necessitates minimizing the pressure losses in the whole burner, from fuel gas inlet to combustion exit. The pressure losses in the system may be characterized by defining a dimensionless pressure efficiency, i.e., the ratio of the dynamic pressure of combustion gases in the exit nozzle to the dynamic pressure of air in the injector air nozzle. Examples of the calculation of pressure efficiency have been given for both incompressible and compressible conditions. Experimental determinations of flashback rates have been carried out over a wide range of burner sizes and the results in the laminar flow range have correlated with the concept of a critical boundary velocity gradient. In the turbulent region no such correlation has been found. Compositions of combustion products at the burner exit have been determined experimentally and compared with the calculated equilibrium values to find the combustion chamber length required for complete combustion.