Classifying – separating – and assorting solids – Fluid suspension – Liquid
Reexamination Certificate
1999-03-26
2001-09-18
Lithgow, Thomas M. (Department: 1724)
Classifying, separating, and assorting solids
Fluid suspension
Liquid
C423S237000, C423S238000, C423S352000
Reexamination Certificate
active
06290066
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method for removing of ammonia and ammonia compounds from fly ash and other combustion byproducts.
In recent years, there has been increasing public and government concern over the environmental impact of nitrogen oxides (NO
x
) emissions, which contributes to the environmental impact of acid rain. Power plants and other industrial plants based on combustion processes are by far the largest producers of NO
x
pollution. In the United States, the Clean Air Act Amendment of 1990 called for a significant reduction in the NO
x
emissions from such plants.
It is known in the art that ammonia or ammonia compounds can be utilized to reduce nitrogen oxides emissions by selective catalytic or non-catalytic reduction. Ammonia or ammonia compounds react with and convert the nitrogen oxides to nitrogen. The following is an example of the reaction: NH
3
+4 NO+0
2
→4 N
2
+6 H
2
O.
However, while ammonia has been used successfully to reduce nitrogen oxide emissions, the ammonia is typically introduced in excess for the reaction and is not totally consumed. Therefore, residues from the combustion process such as fly ash and other combustion byproducts will contain ammonia and/or ammonia compounds (such as ammonia sulfates, ammonia chlorides, ammonia hydroxide, ammonia carbonates).
Ammonia has also been utilized to help reduce particulate emissions, which are closely regulated by the government. For example, ammonia can be added as a conditioning agent in electrostatic precipitators to modify the properties of fly ash for improved collection efficiency. In this process, ammonia and ammonia compounds are also deposited on fly ash. See J. R. Turner et al in 1994,(l .R. Turner, S. Chone and M. P. Dudukovic, “Ammonia/Fly ash Interaction and Their Impact on Flue Gas Treatment Technologies,”
Chemical Engineering Science
, V. 49,No. 24A, pp, 4315-4325, 1994.)
The deposition of ammonia and ammonia compounds on combustion by-products such as fly ash can cause problems for the utilization of the by-products. For example, about 10 million tons of fly ash are currently utilized annually in the United States for concrete applications. When ammonia-contaminated fly ash is used in such applications, hazardous levels of ammonia odor may be generated. Concentrations of ammonia as low as 100 ppm can be an odor irritant as well as an irritant to the eyes. In order to use the fly ash in concrete or other applications, the ammonia content of the fly ash should desirably be below 60-80 ppm (0.060-0.080 mg NH
3
/g fly ash). Accordingly, it is important to reduce or remove ammonia and ammonia compounds from combustion by-products such as fly ash prior to their utilization in other applications.
U.S. Pat. No. 4,288,420 teaches a method for the removal of nitrogen oxides and ash from a coal-fired boiler by treatment with ammonia in which the ammonia is separated from the coal ash by heating the exhaust gas at a temperature of 350 to 700° C. U.S. Pat. No. 4,911,900 describes the combination of various ammonia stripping and scrubbing processes to recover ammonia for nitrogen oxide reduction. However, these methods are focused on the recovery of ammonia for reuse in nitrogen oxides reduction, and do not provide a method for the removal of residual ammonia on fly ash which is to be used in other applications.
Many processes have been developed for the beneficiation of fly ash. For example, U.S. Pat. Nos. 5,227,047 and 5,456,363 describe wet processes including froth flotation, magnetic separation and others to separate various fly ash components, such as carbon, aluminum silicates, cenospheres, and iron oxides. However, these processes do not consider the effects of ammonia on the separated products. For example, when the ammonia contaminated fly ash is subjected to such beneficiation processes, ammonia and its compounds are dissolved in the process water. If the separated products are utilized while containing a portion of the process water, ammonia contaminants may still be present in the separated products, causing possible problems for their utilization. In addition, the process water is frequently filtered from the separated products and recirculated. Thus, the ammonia concentration in the process water can build up to very high concentrations.
Accordingly, there is still a need in the art for a method of reducing or removing ammonia and/or ammonia compounds from combustion by-products such as fly ash prior to their utilization.
SUMMARY OF THE INVENTION
The present invention meets that need by providing a method for removing ammonia from combustion by-products such as fly ash which utilizes treatment with water and/or heat to reduce the ammonia content of the fly ash to an acceptable level of less than about 60-80 ppm. By “ammonia”, hereinafter, it is meant ammonia and ammonia compounds such as ammonia sulfates, ammonia chlorides, ammonia hydroxide, ammonia carbonates.
According to one aspect of the present invention, a method for removing ammonia from fly ash in a wet beneficiation process is provided comprising the steps of mixing raw fly ash containing ammonia and other components with water to form an aqueous slurry, separating and collecting an amount of at least one of the other components from the slurry, and then filtering the slurry to separate the ammonia and water from the fly ash such that the filtered fly ash contains less than about 60-80 ppm ammonia.
The filtering step preferably includes the step of washing the filtered fly ash with water which contains no ammonia compounds, referred to herein as “wash water”. The method also preferably includes the step of heating the filtered fly ash at a temperature of at least 100° C. In this embodiment, the water in the slurry is preferably maintained at a pH of greater than about 9.The wash water is also preferably maintained at a pH of greater than about 9.
In another embodiment of the invention, a method for removing ammonia from fly ash is provided in which raw or processed fly ash containing ammonia is mixed with water to form a solution such that the ammonia is dissolved into the water. By “processed” fly ash, it is meant fly ash that has undergone a beneficiation process to separate one or more components such as carbon from the fly ash. The water in this embodiment is preferably used in amount of at least about 0.1 to 5% by weight of the total fly ash/water mixture, and more preferably, from about 50-70% by weight. In embodiments where the water is used in smaller amounts, e.g. about 5% or less, the water may be in the form of steam.
The solution is then filtered to remove the ammonia and water such that the fly ash has an ammonia content of less than about 60-80 ppm. This method may further include the step of drying the filtered fly ash by heating at a temperature of at least room temperature. More preferably, the drying step is conducted at a temperature of between about 80° C. to about 250° C.
In an alternative embodiment of the invention, the raw or processed fly ash is mixed with water and then dried at a temperature of at least room temperature, and more preferably, at a temperature of between about 80° C. to about 250° C. This method may optionally include a filtering step. In this embodiment, the water preferably comprises less than about 25% by weight of the total fly ash/water mixture. The water may also be in the form of steam.
In yet another embodiment of the invention, a method is provided for removing ammonia from ammonia-contaminated fly ash which does not utilize water. This method comprises the steps of providing an amount of raw or processed fly ash containing ammonia, and heating the fly ash at a temperature of between about 100° C. to about 500° C. for a time sufficient to reduce the ammonia content of said fly ash to less than about 60-80 ppm. More preferably, the fly ash is heated at a temperature between about 200° C. to about 400° C.
The resulting fly ash may be used in a number of applications including concrete, fillers, pozzolanic material, and
Board of Control for Michigan Technological University
Killworth, Gottman Hagan & Schaeff LLP
Lithgow Thomas M.
LandOfFree
Method for removal of ammonia from fly ash does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for removal of ammonia from fly ash, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for removal of ammonia from fly ash will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2488999