Compositions: coating or plastic – Coating or plastic compositions – Inorganic settable ingredient containing
Reexamination Certificate
2002-09-23
2004-09-14
Marcantoni, Paul (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Inorganic settable ingredient containing
C106SDIG001, C423S237000, C423S238000, C423S352000, C073S023200, C073S028010, C436S009000, C436S113000
Reexamination Certificate
active
06790264
ABSTRACT:
BACKGROUND OF THE INVENTION
Fly ash produced at coal fired power plants is commonly used in ready-mixed concrete as a pozzolanic admixture and for partial replacement for cement. Fly ash consists of alumino-silicate glass that reacts under the high alkaline condition in cementitious slurry to form additional cementitious compounds when the fly ash is added to the cementitious slurry. Fly ash is an essential component in high performance concrete. Fly ash contributes many beneficial characteristics to cementitious compounds including increased density, long term strength, decreased permeability, improved durability against chemical attack, and improved workability of freshly placed material.
Coal burning power stations commonly inject ammonia or ammonia based reagents into associated flue gas containing fly ash in an effort to: (1) enhance electrostatic precipitator (ESP) performance to reduce opacity and (2) remove nitrous oxide (NO
x
) using selective catalytic reduction (SCR) and selective non-catalytic reduction (SNCR) technologies to meet NO
x
emission regulations. Ammonia injection into the flue gas for ESP, SCR and SNCR performance enhancement commonly results in the deposition of ammonia on the fly ash. Also, gas phase reaction of SOx and NH
3
in the flue gas results in the deposition of ammonium salts on the fly ash in the form of ammonium sulfate—(NH
4
)
2
SO
4
and ammonium bisulfate—NH
4
HSO
4
. In both SCR and SNCR processes, NO
x
is reduced using ammonia to produce nitrogen gas (N
2
) and water (H
2
O) vapor according to the following reaction:
4NO+4NH
3
+O
2
→4N
2
+6H
2
O
2NO
2
+4NH
3
+O
2
→3N
2
+6H
2
O
The degree of ammonia contamination in the fly ash, and associated concentration levels, vary among power plants depending on the rate of ammonia injection, the performance of SCR or SNCR process, the amount of SO
3
in the flue gas and the associated operating conditions of the boiler and air pollution control devices. It has been observed that fly ash produced from high sulfur eastern bituminous coal (Class F fly ash) adsorbs more ammonia than fly ash produced from low sulfur western sub-bituminous coal (Class C fly ash). As previously mentioned, the presence of sulfur in the flue gases increases the associated deposition of ammonia in the form of (NH
4
)
2
SO
4
and NH
4
HSO
4
. The high alkaline condition of Class C ash inhibits ammonia cation (NH
4
+
) formation. Typical ammonia concentrations on fly ash, as a result of ammonia injection, ranges between 50-120 mg/kg for SCR generated fly ash, 250-600 mg/kg for SNCR generated fly ash, and 700-1200 mg/kg for ESP generated fly ash.
When ammonia-laden fly ash is used in cementitious slurry applications, the ammonium salts dissolve in water to form ammonia cations (NH
4
+
). Under the high pH (pH>12) condition created by cementitious alkali, ammonium cations (NH
4
+
) are converted to dissolved ammonia gas (NH
3
). Ammonia gas evolves from the fresh cementitious slurry into the air, exposing workers. The rate of ammonia gas evolution depends on ammonia concentration, mixing intensity, exposed surface, and ambient temperature. Ammonia has no measurable effect on concrete quality (strength, permeability, etc.). Ammonia gas odors could range from mildly unpleasant to a potential health hazard. Ammonia odors are detected by the human nose at 5 to 10 ppm levels. The OSHA threshold and permissible limits are set at 25 and 35 ppm for the time weighted average—eight-hour (TWA 8-hr) and the short term exposure limit—fifteen-minute (STEL 15-min), respectively. Ammonia gas concentration of 150-200 ppm can create a general discomfort. At concentrations between 400 and 700 ppm ammonia gas can cause pronounced irritation. At 500 ppm, and above, ammonia gas is immediately dangerous to health; at 2,000 ppm, death can occur within minutes.
Other than OSHA exposure limits, there are no regulatory, industry or ASTM standards or guidelines for acceptable levels of ammonia in fly ash. However, based on industry experience, fly ash with ammonia concentration at less than 100 mg/kg does not appear to produce a noticeable odor in ready-mix concrete. Depending on site and weather conditions, fly ash with ammonia concentration ranging between 100-200 mg/kg could result in unpleasant or unsafe concrete placement and finishing work environment. Fly ash with ammonia concentration exceeding 200 mg/kg produces unacceptable odor when used in ready-mixed concrete applications.
In addition to the risk of human exposure to ammonia gas evolving from cementitious slurry produced using ammonia-laden ash, the disposal of the ammonia-laden fly ash in landfills and ponds at coal burning power stations also creates potential risks to humans and the environment. Ammonium salt compounds in fly ash are extremely soluble. Upon contact with water, the ammonium salts leach into the water and are carried to ground water and nearby rivers and streams causing potential environmental damage such as ground water contamination, fish kill and eutrophication. Ammonia gas could also evolve upon wetting of alkaline fly ashes, such as those generated from the combustion of western sub-bituminous coal. Water conditioning and wet disposal of alkaline, ammonia-laden, fly ash exposes power plant workers to ammonia gas.
SUMMARY OF THE INVENTION
The present invention relates to the addition of a chemical oxidizing agent to dry fly ash containing concentrations of ammonia. The chemical can be added and blended with the dry fly ash at any point between the fly ash collection system at the power plant and final delivery to the ready-mixed customer, or at the point of use at the ready-mixed customer site. The pre-blended chemical oxidizing agent does not react with ammonia in the dry fly ash; the chemical oxidizing agent is released during the wet slurry mixing process. Once the ammonia-laden fly ash is introduced in the cementitious slurry, ammonium salts from the ammonia-laden fly ash dissolve. The high alkaline (high pH) condition of the cementitious slurry converts the ammonium cations (NH
4
+
) to dissolved ammonia gas (NH
3
). Without the chemical oxidizing agent, ammonia gas (NH
3
) evolves from the cementitious slurry during mixing, transportation, pouring and placement.
More specifically, this invention relates to pre-treated ammonia-laden fly ash and to methods of treating the ammonia-laden fly ash. Addition of the chemical oxidizing agent with the dry ammonia-laden fly ash prior to incorporating the fly ash into cementitious slurries results in chemical conversion, via oxidation, of ammonia into harmless products. Thereby, the exposure risk of the ammonia gases (NH
3
) is limited.
The preferred chemical treatment reagents are strong oxidizers such as hypochlorites (OCl
−
) commonly found in the form of Ca(OCl)
2
, NaOCl, LiOCl, trichloro-s-triazinetrione (trichlor), etc. and are added to the ammonia-laden fly ash. Preferably, the oxidizers are added in dry form to the fly ash, but it is also possible to spray a dilute solution (containing up to about 30% oxidizer) onto the fly ash. At present, calcium hypochlorite is preferred. The reagent is activated upon water addition and reacts with dissolved ammonia in the ash or concrete slurry to form primarily monochloramine (NH
2
Cl). An overdose of the hypochlorite reagent would further oxidize monochloramine to form nitrogen gas (NH
2
) and chlorides.
As used herein, the phrase hypochlorite containing oxidizer is used to denote compounds that include the hypochlorite moiety or form such moiety upon addition of water. For example, the trichor compound forms hypochlorous acid and cyanuric acid upon water addition. At elevated pHs, the hypochlorous acid ionizes to the hypochlorite ion.
The basic aqueous phase ammonia oxidation reaction using hypochlorite is as follows:
NH
4
+
+OCl
−
→NH
2
Cl+H
2
O
The rate of ammonia oxidation by hypochlorite depends upon pH, temperature, time, initial dosage and the presence of competing reduci
ISG Resources, Inc.
Wegman Hessler & Vanderburg
LandOfFree
Control of ammonia emission from ammonia laden fly ash in... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Control of ammonia emission from ammonia laden fly ash in..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Control of ammonia emission from ammonia laden fly ash in... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3264809