Patent ID: 8459986

Claim:
A method of modifying operation of a burner, comprising (A) providing a burner having at least two concentric conduits, wherein a stream of air mixed with particulate solid carbonaceous fuel can be conveyed through an innermost conduit of said burner, and wherein one or more streams of air other than the air mixed with said fuel can be conveyed through a central conduit surrounding the innermost conduit, and wherein said fuel and air can be combusted in a stable flame at said burner, but wherein maintaining said stable flame at said burner when air provided in said streams is the only source of oxygen for said combustion requires that the fuel satisfy one or more conditions in that one or more of (1) the mass flow rate of the fuel through said burner, (2) the fuel-to-air ratio of the stream of air mixed with fuel that is fed through the burner, (3) the content of combustible matter in the fuel, and (4) the specific energy value of the fuel, must be at least sufficient for said stable flame to be maintained at said burner, (B) inserting through said burner a lance the outlet end of which is positioned to eject gas into the base of a flame at said burner, (C) feeding through said innermost conduit a stream of air mixed with particulate solid fuel which does not satisfy at least one of said conditions and therefore cannot be combusted in a stable flame at said burner in air as the only source of oxygen for combustion, and feeding through said central conduit said one or more streams of air other than the air mixed with said fuel, (D) feeding gaseous oxidant comprising more than 21 vol. % oxygen through the outlet end of said lance, and (E) combusting said fuel and air fed in step (C) with said oxidant fed in step (D) in a stable flame at said burner, wherein said oxidant is fed into the base of said flame at a mass flow rate that maintains said stable flame.