Method and apparatus for oxy-fuel heating with lowered NO.sub.x in high temperature corrosive environments

A system for heating a chamber to an elevated temperature comprising in combination:

• a precombustor adapted for attachment to or mounting in a wall of said chamber, said precombustor having at least two generally parallel faces with one of said faces exposed to the inner volume of said chamber, said precombustor containing a generally cylindrical passage extending through said precombustor between said generally parallel faces, said passage adapted to position an oxy-fuel burner having a longitudinal axis, the axis of said burner coincident to the longitudinal axis of said passage;
• and
• a generally cylindrical post mix oxy-fuel burner of the type having a front end containing a single central fluid aperture surrounded by one surrounding fluid aperture or a plurality of apertures disposed in a single circular array so that fluid exiting said surrounding fluid aperture surrounds said fluid exiting said central aperture as it exits said front of said burner disposed inside said passage in said precombustor so that said passage extends a distance beyond said front end of said burner, said distance being fixed by a ratio of between 2 and 6 determined by dividing the distance (length) between the front end of said burner and the end of said passage in said precombustor by the diameter of said front end of said burner where said burner is selected to have a firing rate of from 0.25 to 40 million Btu/hr.
• means to introduce oxygen gas into said surrounding fluid aperture and gaseous fuel into said central fluid aperture, said means adapted to limit the velocity of said oxygen and said fuel at the front end of said burner to a maximum of 600 feet per second, wherein a coaxial flame is created inside said precombustor, said flame having a generally cylindrical fuel-rich phase surrounded by an oxygen-rich precombustor wall, cooling annular sheath through the entire length of said cylindrical passage so that the flame is discharged into said heating chamber without combustion occurring on the walls forming the precombustor passage.