Process to reduce emissions of nitrogen oxides and mercury from coal-fired boilers
View Patent ↗A flue gas additive is provided that includes both a nitrogenous component to reduce gas phase nitrogen oxides and a halogen-containing component to oxidize gas phase elemental mercury.
1. A method, comprising:
contacting a combustion feed material with an additive to form a combined combustion feed material, the additive comprising a nitrogenous material; and
combusting the combined combustion feed material to form an off-gas comprising a nitrogen oxide and a derivative of the nitrogenous material, the derivative of the nitrogenous material causing removal of at least a portion of the nitrogen oxide, wherein the nitrogenous material comprises at least one of an amine and amide, wherein the derivative of the nitrogenous material comprises ammonia, and wherein the additive is a free flowing particulate composition having a P80 size ranging from about 6 to about 20 mesh (Tyler).
2. The method of claim 1 , wherein the nitrogenous material is supported by a particulate substrate, the particulate substrate being one or more of the combustion feed material, a zeolite, other porous metal silicate material, clay, activated carbon, char, graphite, (fly) ash, metal, and metal oxide.
3. The method of claim 1 , wherein an amount of nitrogen added in the nitrogenous material added to the off-gas is at least about 0.5% of a theoretical stoichiometric ratio based on an amount of nitrogen oxide present, wherein the combined combustion feed material comprises from about 0.05 to about 0.75 wt. % of the additive, wherein the additive comprises a halogen-containing material, and wherein a mass ratio of the nitrogen content of the nitrogenous material to the halogen content in the additive ranges from about 1:1 to about 2400:1.
4. The method of claim 1 , wherein a P80 particle size distribution of the additive is reduced from about 6 to 20 mesh (Tyler) to no more than about 200 mesh (Tyler) via in-line milling followed by introduction, without intermediate storage, to the combustor.
5. The method of claim 1 , further comprising:
at a location remote from a combustor, contacting the additive with the combustion feed material to form the combined combustion feed material; and
transporting the combined combustion feed material to the combustor.
6. The method of claim 1 , wherein the combusting is in a combustion zone of a combustor and wherein the combustion zone has a temperature ranging from about 1,400° F. to about 3,500° F.
7. The method of claim 6 , wherein the temperature ranges from about 1,400° F. to about 2,000° F.
8. The method of claim 1 , wherein the combustion feed material is a coal, and wherein the coal is at least one of a high alkali, high iron, and high sulfur coal.
9. The method of claim 1 , wherein the combined combustion feed material comprises a halogen-containing additive that forms a gas phase halogen when combusted.
10. The method of claim 9 , wherein the combined combustion feed material comprises a mass ratio of nitrogen:halogen from the halogen-containing additive ranging from about 1:1 to about 2400:1.
11. A flue gas additive, comprising:
a nitrogenous material that forms ammonia when combusted; and
a halogen-containing material that forms a gas phase halogen when combusted, wherein the flue gas additive comprises a coating to impede thermal degradation and/or decomposition of the nitrogenous material.
12. The flue gas additive of claim 11 , wherein the nitrogenous material comprises one or more of an amine and amide.
13. The flue gas additive of claim 11 , wherein the halogen in the halogen-containing material is one or more of iodine and bromine.
14. The flue gas additive of claim 11 , wherein a mass ratio of the nitrogen content of the nitrogenous material to the halogen content in the additive ranges from about 1:1 to about 2400:1.
15. The flue gas additive of claim 11 , wherein the additive is supported.
16. The flue gas additive of claim 11 , wherein the additive is unsupported and in the form of a free-flowing particulate.
17. The flue gas additive of claim 11 , wherein the flue gas additive is mixed with coal.
18. A combined combustion feed material comprising coal and a nitrogenous material for reducing nitrogen oxides, wherein the combined combustion feed material comprises from about 0.05 to about 1 wt. % of the additive, with the remainder being coal.
19. The combined combustion feed material of claim 18 , wherein the nitrogenous material is at least one of an amine and amide and wherein the coal is at least one of a high alkali, high iron, and high sulfur coal.
20. The combined combustion feed material of claim 19 , wherein the additive comprises a halogen-containing material and wherein the combined combustion feed material comprises a mass ratio of the nitrogen content of the nitrogenous material to the halogen content of the additive ranging from about 1:1 to about 2400:1.