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:
introducing a combustion feed material into a combustion zone to combust the combustion feed material; and
introducing a nitrogenous material into the combustion zone to reduce nitrogen oxide formed from combustion of the combustion feed material, wherein the combustion zone has a temperature ranging from about 1,400° F. to about 3,500° F.
2. The method of claim 1 , wherein the
combustion feed material is contacted with an additive to form a combined combustion feed material, the additive comprising the nitrogenous material, wherein the combined combustion feed material is introduced into the combustion zone in the introducing steps, and wherein
combustion of the combined combustion feed material to form an off-gas comprising the 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.
3. The method of claim 2 , 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 P 80 size ranging from about 6 to about 20 mesh (Tyler).
4. The method of claim 2 , wherein the combustion feed material comprises mercury, wherein combustion of the combined combustion feed material volatilizes elemental mercury, and wherein the additive comprises a halogen-containing material to oxidize the elemental mercury.
5. The method of claim 4 , wherein an amount of nitrogen added in a 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. % additive, and wherein the nitrogen content of the nitrogenous material:halogen in the additive ranges from about 1:1 to about 2400:1.
6. The method of claim 2 , 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 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.
7. The method of claim 2 , 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 nitrogenous material comprises a polymerized methylene urea.
8. The method of claim 2 , 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 the combustor.
9. The method of claim 2 , further comprising:
at a location remote from a combustor, contacting the additive with the combustion feed material to form a combined combustion feed material; and
transporting the combined combustion feed material to the combustor.
10. The method of claim 2 , further comprising:
monitoring at least one of the following parameters: rate of introduction of the additive to the combustor, concentration of gas phase molecular oxygen, combustor temperature, gas phase carbon monoxide, gas phase nitrogen dioxide concentration, gas phase nitric oxide concentration, limestone concentration, and 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.
11. The method of claim 1 , wherein the nitrogenous material is introduced into the combustion zone separately from the combustion feed material and after combustion of the combustion feed material.
12. The method of claim 11 , 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 amine.
13. The method of claim 1 , wherein the nitrogenous material forms ammonia when combusted and comprises a halogen-containing material that forms a gas phase halogen when combusted.
14. The method of claim 13 , wherein the nitrogenous material comprises one or more of an amine and amide.
15. The method of claim 14 , wherein the nitrogenous material comprises urea.
16. The method of claim 13 , wherein the halogen in the halogen-containing material is one or more of iodine and bromine.
17. The method of claim 13 , wherein a mass ratio of the nitrogen content of the nitrogenous material:halogen in the halogen-containing material commonly ranges from about 1:1 to about 2400:1.
18. The method of claim 13 , wherein the nitrogenous material is supported.
19. The method of claim 13 , wherein the nitrogenous material is unsupported and in the form of a free-flowing particulate.
20. The method of claim 13 , wherein the nitrogenous material and halogen-containing material are mixed with coal.
21. The method of claim 13 , wherein the nitrogenous material is in the form of a liquid.
22. The method of claim 13 , wherein the nitrogenous material comprises a coating to impede thermal degradation and/or decomposition of the nitrogenous material.
23. The method of claim 1 , wherein the combustion feed material is combined with the nitrogenous material, before introduction into the combustion zone, to form a combined combustion feed material.
24. The method of claim 23 , wherein the combined combustion feed material comprises from about 0.05 to about 1 wt. % additive, with the remainder being coal.
25. The method of claim 23 , 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.
26. The method of claim 23 , wherein the combined combustion feed material comprises a mass ratio of nitrogen:halogen from the additive commonly ranging from about 1:1 to about 2400:1.
27. A computer readable medium comprising microprocessor readable and executable instructions to perform the steps of claim 10 .