Additives for mercury oxidation in coal-fired power plants
First Claim
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1. A flue gas treatment method, comprising:
- (a) providing a coal feed, the coal feed having a Loss on Ignition (“
LOI”
) of at least about 10% and comprising mercury, alkali, and iron, wherein an iron content of the coal feed is less than about 10 wt. % (dry basis of the ash) as Fe2O3, the alkali content of the coal feed is at least about 20 wt. % (dry basis of the ash) alkali, and wherein the coal feed comprises no more than about 500 ppm halogens;
(b) contacting the coal feed, prior to combustion, with an additive, the additive comprising a transition metal and a halogen, wherein the additive promotes oxidation of elemental mercury wherein the additive comprises no more than about 1 wt. % carbon and no more than about 0.5 wt. % (dry basis) sulfur;
(c) combusting, by a wet bottom boiler, the coal feed to form a flue gas comprising elemental mercury derived from the mercury in the coal feed and fly ash; and
(d) collecting the oxidized mercury and fly ash to provide a treated flue gas, wherein;
the additive further comprises a mineralizer;
the mineralizer is zinc oxide; and
the additive comprises at least about 1 wt. % (dry basis) mineralizer.
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Abstract
The present invention is directed to an additive, primarily for combustion of low sulfur and high alkali coals, that includes a transition metal to impact positively bottom ash slag and optionally a halogen to effect mercury oxidation and collection in the flue gas.
368 Citations
23 Claims
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1. A flue gas treatment method, comprising:
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(a) providing a coal feed, the coal feed having a Loss on Ignition (“
LOI”
) of at least about 10% and comprising mercury, alkali, and iron, wherein an iron content of the coal feed is less than about 10 wt. % (dry basis of the ash) as Fe2O3, the alkali content of the coal feed is at least about 20 wt. % (dry basis of the ash) alkali, and wherein the coal feed comprises no more than about 500 ppm halogens;(b) contacting the coal feed, prior to combustion, with an additive, the additive comprising a transition metal and a halogen, wherein the additive promotes oxidation of elemental mercury wherein the additive comprises no more than about 1 wt. % carbon and no more than about 0.5 wt. % (dry basis) sulfur; (c) combusting, by a wet bottom boiler, the coal feed to form a flue gas comprising elemental mercury derived from the mercury in the coal feed and fly ash; and (d) collecting the oxidized mercury and fly ash to provide a treated flue gas, wherein; the additive further comprises a mineralizer; the mineralizer is zinc oxide; and the additive comprises at least about 1 wt. % (dry basis) mineralizer. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A flue gas treatment method, comprising:
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(a) providing a coal feed, the coal feed having a Loss on Ignition (“
LOI”
) of at least about 10% and comprising mercury and iron, wherein an iron content of the coal feed is less than about 10 wt. % (dry basis of the ash);(b) combusting the coal feed to form a flue gas comprising elemental mercury derived from the mercury in the coal feed and fly ash; (c) contacting an additive with (i) the coal feed, prior to step (b), and/or (ii) the flue gas resulting from step (b), the additive comprising a transition metal and at least one of a halogen, wherein the additive comprises no more than about 1 wt. % carbon, wherein the additive comprises no more than about 0.5 wt. % (dry basis) sulfur, wherein, in either option (i) or (ii), the additive promotes post-combustion oxidation of the elemental mercury; and (d) collecting the oxidized mercury and fly ash to provide a treated flue gas, wherein; the additive comprises; (a) at least about 50 wt. % (dry basis) iron; (b) at least about 1 wt. % (dry basis) halogens; and (c) a mineralizer. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23)
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Specification