Oxy-fuel reburn: a method for NO
View Patent ↗A method is disclosed for reducing the NO x emission of fossil fuel burners. The method creates fuel-rich and fuel-lean zones within the boiler to enhance the removal of NO x species by creating a plurality of NO x reducing precursors.
1. A method of reducing NO x emission consisting of the steps of:
creating a first combustion zone by combusting a first fuel with a first air stream, wherein the first combustion zone is provided with an excess of the first air stream to produce a fuel-lean combustion environment,
producing a plurality of NO x species in the first combustion zone,
creating a reburn zone downstream of the first combustion zone by combusting a second fuel with a oxygen stream, wherein the reburn zone is provided with an excess of the second fuel to produce a fuel-rich combustion environment having a stoichiometric ratio between about 0.6 and about 0.70,
increasing the local flame temperature and producing a plurality of NO x reducing precursors in the reburn zone during combustion, and
reacting the plurality of NO x reducing precursors with NO x produced in first combustion zone, wherein a substantial portion of the NO x is converted to molecular nitrogen.
2. A method of reducing NO x emission consisting of the steps of:
creating a first combustion zone by combusting a first fuel with a first air stream, wherein the first combustion zone is provided with an excess of the first air stream to produce a fuel-lean combustion environment,
producing a plurality of NO x species in the first combustion zone,
creating a reburn zone downstream of the first combustion zone by combusting a second fuel with a oxygen stream, wherein the reburn zone is provided with an excess of the second fuel to produce a fuel-rich combustion environment having a stoichiometric ratio between about 0.6 and about 0.70,
increasing the local flame temperature and producing a plurality of NO x reducing precursors in the reburn zone during combustion, and
reacting the plurality of NO x reducing precursors with NO x produced in first combustion zone, wherein a substantial portion of the NO x is converted to molecular nitrogen,
creating a burnout zone downstream of the reburn zone,
utilizing an overfire air port to provide a second air stream to burnout zone, and
combusting a substantial portion of the uncombusted second fuel with the second air stream in the burnout zone.
3. A method of reducing NO x emission consisting of the steps of:
creating a first combustion zone by combusting a first fuel with a first air stream, wherein the first combustion zone is provided with an excess of the first air stream to produce a fuel-lean combustion environment,
producing a plurality of NO x species in the first combustion zone,
creating a reburn zone downstream of the first combustion zone by combusting a second fuel with a oxygen stream, wherein the reburn zone is provided with an excess of the second fuel to produce a fuel-rich combustion environment having a stoichiometric ratio between about 0.6 and about 0.70,
increasing the local flame temperature and producing a plurality of NO x reducing precursors in the reburn zone during combustion, and
reacting the plurality of NO x reducing precursors with NO x produced in first combustion zone, wherein a substantial portion of the NO x is converted to molecular nitrogen,
creating a burnout zone downstream of the reburn zone,
utilizing an overfire air port to provide a second air stream to burnout zone, wherein the step of providing a second air stream creates a stoichiometric ratio between about 1.0 and 1.2 in the burnout zone, and combusting a substantial portion of the uncombusted second fuel with the second air stream in the burnout zone.