Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture – Nitrogen or nitrogenous component
Reexamination Certificate
2002-12-04
2004-06-08
Green, Anthony J. (Department: 1755)
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
Nitrogen or nitrogenous component
C106S705000, C106SDIG001, C209S011000, C423S238000, C423S352000, C423S356000
Reexamination Certificate
active
06746654
ABSTRACT:
FIELD OF THE INVENTION
The herein disclosed invention finds applicability in the field of coal combustion flue gas purification and more particularly in the field of fly ash purification.
BACKGROUND OF THE INVENTION
Ammonia vapor comes into contact with fly ash in connection with several processes for NOx reduction or particulate capture in pulverized coal combustion, including selective catalytic reduction (SCR), selective non-catalytic reduction (SNCR), and electrostatic precipitator conditioning [Castle, 1980, Golden, 2001]. Typically some portion of the vapor phase ammonia adsorbs or deposits on fly ash with the potential to cause problems in ash utilization, handling, and disposal [Larrimore, 2000]. Of particular concern for disposal is the possibility for high ammonia contents in surface and groundwater near ash ponds [Golden, 2001] and at landfill sites in runoff, leachate and surrounding atmosphere [Lowe et al., 1989; Golden, D., 2001]. Problems in utilization arise not from degradation of concrete properties [Novak and Rych, 1989; Golden, 2001] but rather from worker exposure to odor, especially during enclosed concrete pours. Ammonia odors are perceived as a sufficiently serious nuisance that levels of 300 ppm or more by weight in ash (not uncommon in untreated fly ash streams from units with SCR systems), can effectively destroy the ash utilization market. Acceptable ammonia levels to avoid problems in utilization and disposal have been cited by different sources as less than 50, 60, or 100 ppm [Novak and Rych, 1989; Necker, 1989].
There are few publications in the archival scientific literature on ash/ammonia interactions, exceptions being the work of Janssen et al. [1986] which focused on catalysis of the NO/NH
3
reaction and most notably the work of Turner et al. [1994], which focused on the mechanism of adsorption and its potential impact on the operation of flue gas treatment technologies. Recently, however, there has been a flurry of applied studies reported in the conference literature, patent literature, and in industry reports, motivated by current projections of widespread SCR unit installation in the U.S. in the coming years [Muzio et al., 1995; Hinton, 1999; Larrimore, 2000; Golden, 2001; Brendel et al., 2001; Levy et al., 201; Rubel et al., 2001; Ramme and Fischer, 2001; Bittner et al., 2001]. These sources discuss many aspects of the ammonia/ash problem and present a number of new ideas for remediation processes. The factors governing the extent of ammonia contamination are not fully understood, but are believed to depend on the concentration of unreacted ammonia leaving the SCR unit (the “ammonia slip”), duct temperatures/time history, ash composition [Muzio et al., 1995], and SO
3
concentration in the flue gas [Larrimore, 2000, Turner et al., 1994, Muzio et al., 1995]. Ammonia associated with fly ash can be in the form of ammonium sulfate or more commonly bisulfate particles [Golden, 2001; Rubel et al., 2001], or ammonia species adsorbed on carbon sites [Rubel, 2001], likely on carbon surface oxides, or mineral surfaces [Turner, et al. 1994]. Ammonia is well known to chemisorb on acidic surface sites [Sahu, et al., 1998], and indeed is extensively used as a titrant to characterize surface acidity [Gedeon et al., 2001].
Relevant Patents
1. U.S. Pat. No. 6,136,089, “Apparatus and Method for Deactivating Carbon in Fly Ash”. This patent describes the use of ozone to improve the air entrainment behavior of fly ash by modifying the surface chemistry of unburned carbon, e.g., carbon passivation vs. ammonia reduction.
2. U.S. Pat. No. 6,077,494, “Method for Removing Ammonia from Ammonia Contaminated Fly Ash”. This recent patent covers the use of very small amounts of water (<5%), in the so-called semi-dry state. The patent makes no mention of method of water addition, requires intense mechanical agitation of the ash, and does not mention humid air, or ozone.
3. Japanese patent JP8187484A describes a process for removing ammonia that involves a humidifier. The process involves intense mechanical agitation and there is no mention of using warm humid air, which holds sufficient moisture that upon cooling in contact with co-flowing ash will deliver a uniform and controlled moisture level.
4. U.S. Pat. No. 5,069,720, U.S. Pat. No. 5,211,926, International patent 99/48563 describe the use of water to remove ammonia, but in large amounts that classify these as truly “wet” techniques.
Experimental Background
There is almost no information in the archival scientific literature on methods of ammonia removal from fly ash, despite great commercial interest in a variety of competing techniques [Larrimore, 2000, Golden, 2001], including thermal methods [Levy et al., 2001], combustion-based methods [Giampa, 2001], and water-based methods [Gasiorowski and Hrach, 2000; Katsuya et al., 1996; Hwang, 1999]. An objective of the present invention is to investigate the chemistry of room temperature methods for ammonia removal from fly ash using moisture and oxidizing agents, alone or in combination. In a study, special emphasis was placed on controlled addition of small amounts of moisture to avoid wet ash handling, so-called “semi-dry processing”, which is the basis for several industrial patents [Gasiorowski and Hrach, 2000; Katsuya et al., 1996], and on the use of ozone, which has recently been found to passivate unburned carbon surfaces in fly ash and thus improve air entrainment properties of problem ash streams [Gao et al., 2001].
Objects of the Invention
A main object of this invention is to remove ammonia from fly ash employing a minimum amount of water.
An important object of this invention is to remove ammonia from fly ash without sensibly wetting the fly ash with water.
A further object of the invention is to effectively use ozone for ammonia removal from fly ash, alone or in combination with moisture.
A still further object of this invention is to carry out the process of ammonia removal at temperatures under 150° C.
These and other objects of the present invention will become apparent from a reading of the following specification taken in conjunction with the enclosed drawings.
BRIEF SUMMARY OF THE INVENTION
The herein disclosed invention involves a process for ridding fly ash of ammonia that avoids the use of sensible moisture; but instead uses a water fog (water mist) or warm humid air.
The terms water fog and water mist are used interchangeably in this disclosure.
Also, disclosed by the invention is the use of ozone to rid the fly ash of ammonia.
A method of this invention for removing ammonia from fly ash comprises subjecting ammonia containing fly ash to a water mist wherein the water mist contacts the ammonia containing fly-ash and removes the ammonia from the fly ash. The water mist can be applied to the fly ash in a warm air environment or the mist can be applied in humid air. In a specific method of the invention, the fly ash is a basic fly ash and/or the water mist has a high pH. In another specific method for removing ammonia from fly ash, a water mist is applied to a co-flowing fly ash stream in controlled amounts to produce fly ash with uniform 1-5 wt-% moisture with water droplets being fine enough to remain suspended as an aerosol for uniform wetting of the dispersed ash after mist/ash mixing and afterwards the co-flowing suspension is subjected to gas/particle separation to yield a reduced-ammonia ash suitable for disposal/utilization and an ammonia-laden waste gas stream.
Another method for removing ammonia from fly ash comprises subjecting ammonia containing fly ash to a water fog (water mist) wherein the water fog or mist contacts the ammonia containing fly ash and removes the ammonia from the fly ash. The water fog can be applied in a warm environment. As a further embodiment, the fog is produced with an ultrasonic nebulizer i
Chen Xu
Gao Yuming
Hurt Robert H.
Mehta Arun K.
Suuberg Eric M.
Armstrong Kratz Quintos Hanson & Brooks, LLP
Brown University Research Foundation
Green Anthony J.
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