Efficient furnace operation with medium-purity oxygen

A method of operating a furnace containing a charge to heat the charge, comprising:

• (A) providing gaseous oxidant comprising 60 vol. % to 85 vol. % oxygen;
• (B) passing the gaseous oxidant through a heated regenerator and out of an oxidant port into a furnace, to heat the oxidant in the regenerator so that it emerges from the oxidant port at a temperature of 500° C. to 1400° C., and to thereby cool said regenerator;
• and feeding gaseous fuel into said furnace through two or more fuel ports and combusting the fuel in the furnace with heated oxidant emerging from said oxidant port to produce gaseous hot products of said combustion which heat the charge;
• (C) discontinuing the flow of oxidant through the regenerator into the furnace, and passing said combustion products into said oxidant port and through and out of said cooled regenerator to heat said regenerator, wherein the temperature of the combustion products that pass out of said regenerator is at least 500° C.;
• and
• (D) alternating steps (B) and (C),
• wherein said oxidant port and said fuel ports are located above the top surface of said charge in said furnace;
• wherein at least one of said fuel ports is located on each side of a vertical line passing through the center of said oxidant port and said fuel ports are located 10 to 60 fuel port diameters from said oxidant port;
• and
• wherein the fuel that is combusted with oxidant from a given oxidant port is fed into the furnace from two or more fuel ports at velocities of 40 to 350 m/sec, and the oxidant is fed into the furnace from the oxidant port at a velocity of 2 to 20 m/sec, wherein the fuel fed from said fuel ports entrains gaseous combustion products in said furnace before combusting with the high temperature oxidant stream.