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 combustion feed material comprises mercury, wherein the combustion of the combined combustion feed material volatizes elemental mercury, and wherein the additive further comprises a halogen-containing material to oxidize the volatilized elemental mercury.
2. The method of claim 1 , wherein the nitrogenous material comprises at least one of an amine and an amide, wherein the derivative of the nitrogenous material comprises ammonia, and wherein the additive is a free flowing particulate composition having a P 80 size ranging from about 6 to about 20 mesh (Tyler).
3. The method of claim 1 , wherein the nitrogenous material comprises at least one of an amine and an amide, wherein the derivative of the nitrogenous material comprises ammonia, and wherein the nitrogenous material is supported by a particulate substrate, the particulate substrate being one or more of the combustion feed material, a zeolite, another porous metal silicate material, a clay, an activated carbon, char, graphite, (fly) ash, a metal, and a metal oxide.
4. The method of claim 1 , wherein the nitrogenous material comprises at least one of an amine and an amide, wherein the derivative of the nitrogenous material comprises ammonia, and wherein the nitrogenous material comprises a polymerized methylene urea.
5. The method of claim 1 , wherein an amount of nitrogen 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 the nitrogen oxide present, wherein the combined combustion feed material comprises from about 0.05 to about 0.75 wt.% of the additive, and wherein a ratio of a nitrogen content- of the nitrogenous material to a halogen in the additive ranges from about 1:1 to about 2400:1.
6. The method of claim 1 , wherein a P 80 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 a combustor.
7. 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.
8. The method of claim 1 , further comprising:
monitoring at least one of the following parameters: a rate of introduction of the additive to the combustor, a concentration of gas phase molecular oxygen, a combustor temperature, a gas phase carbon monoxide concentration, a gas phase nitrogen dioxide concentration, a gas phase nitric oxide concentration, a limestone concentration, and a gas phase SO 2 concentration; and
when a selected change in the at least one of the parameters occurs, changing at least one of the parameters.
9. A computer readable medium comprising microprocessor readable and executable instructions to perform the steps of claim 8 .
10. A combustor feed material, comprising:
coal; and
an additive comprising a nitrogenous material that forms ammonia when combusted, wherein the nitrogenous material comprises a coating to impede thermal degradation and/or decomposition of the nitrogenous material, and a halogen-containing material that forms a gas phase halogen when combusted.
11. The combustor feed material of claim 10 , wherein the nitrogenous material comprises one or more of an amine and an amide.
12. The combustor feed material of claim 11 , wherein the nitrogenous material comprises urea.
13. The combustor feed material of claim 10 , wherein a halogen in the halogen-containing material is one or more of iodine and bromine.
14. The combustor feed material of claim 10 , wherein a mass ratio of a nitrogen content of the nitrogenous material to a halogen content of the halogen-containing material ranges from about 1:1 to about 2400:1.
15. The combustor feed material of claim 10 , wherein the additive is supported.
16. The combustor feed material of claim 10 , wherein the additive is unsupported and in the form of a free-flowing particulate.
17. The combustor feed material of claim 10 , wherein the coating is one or more of a silane, a siloxane, an organosilane, an amorphous silica, and clay.
18. The combustor feed material of claim 10 , wherein the coating impedes thermal degradation and/or decomposition of the nitrogenous material during combustion in a combustor.
19. A method, comprises:
(a) combusting a combustion feed material having a coating to impede thermal degradation and/or decomposition of a nitrogenous material in a combustion zone of a combustor, thereby generating a nitrogen oxide; and
(b) introducing the nitrogenous material into the combustion zone to reduce the nitrogen oxide, wherein the combustion zone has a temperature ranging from about 1,400° F. to about 3,500° F.
20. The method of claim 19 , wherein the temperature ranges from about 1,400° F. to about 2,000° F. and wherein the nitrogenous material comprises one or more of an amide and an amine.
21. A combined combustion feed material comprising coal and an additive comprising 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.
22. The combined combustion feed material of claim 21 , wherein the nitrogenous material is at least one of an amine and an amide and wherein the coal is at least one of a high alkali, high iron, and high sulfur coal.
23. The combined combustion feed material of claim 21 , wherein the combined combustion feed material comprises a mass ratio of nitrogen:halogen from the additive ranges from about 1:1 to about 2400:1.
24. A combustor feed material, comprising:
coal particles;
a flue gas additive comprising a nitrogenous material that forms ammonia when combusted, wherein the nitrogenous material is absorbed into a matrix of the coal particles;
a halogen-containing material that forms a gas phase halogen when combusted,
wherein the flue gas additive is applied to the coal in the form of a liquid.
25. The combustor feed material of claim 24 , wherein the nitrogenous material comprises one or more of an amine and an amide and further comprising a binder to adhere or bind the nitrogenous material to the coal particles.
26. The combustor feed material of claim 25 , wherein the nitrogenous material comprises urea.
27. The combustor feed material of claim 25 , wherein the binder is one or more of a wax, a wax derivative, a gum, and a gum derivative.
28. The combustor feed material of claim 24 , wherein a halogen in the halogen-containing material is one or more of iodine and bromine.
29. The combustor feed material of claim 24 , wherein a mass ratio of the nitrogen content of the nitrogenous material to a halogen of the halogen-containing material ranges from about 1:1 to about 2400:1.
30. The combustor feed material of claim 24 , wherein the additive is supported.
31. The combustor feed material of claim 24 , wherein the additive is unsupported and in the form of a free-flowing particulate.