U.S. patent application number 10/628185 was filed with the patent office on 2004-07-08 for carbon scavenger fly ash pretreatment method.
Invention is credited to Boggs, Bruce E..
Application Number | 20040129180 10/628185 |
Document ID | / |
Family ID | 27616299 |
Filed Date | 2004-07-08 |
United States Patent
Application |
20040129180 |
Kind Code |
A1 |
Boggs, Bruce E. |
July 8, 2004 |
Carbon scavenger fly ash pretreatment method
Abstract
A method for pretreatment of a quantity of fly ash for use in a
cementitious composition containing an air entrainment agent. An
effective amount of an aromatic carboxylic acid or its salts is
added to the fly ash to satiate unburned carbon in the ash. The
treatment with the aromatic carboxylic acid (or hydroxy substituted
aromatic carboxylic acid or its salts) does not significantly
promote or retard the air entrainment functions of the air
entrainment agent.
Inventors: |
Boggs, Bruce E.; (Kennesaw,
GA) |
Correspondence
Address: |
JACKSON WALKER L.L.P.
Suite 2100
112 E. Pecan Street
San Antonio
TX
78205
US
|
Family ID: |
27616299 |
Appl. No.: |
10/628185 |
Filed: |
July 28, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10628185 |
Jul 28, 2003 |
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09804737 |
Mar 13, 2001 |
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6599358 |
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60188737 |
Mar 13, 2000 |
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Current U.S.
Class: |
106/705 ;
106/709 |
Current CPC
Class: |
Y10S 106/01 20130101;
Y02W 30/92 20150501; C04B 18/08 20130101; Y02W 30/91 20150501; C04B
18/08 20130101; C04B 20/023 20130101; C04B 18/08 20130101; C04B
20/1022 20130101 |
Class at
Publication: |
106/705 ;
106/709 |
International
Class: |
C04B 014/00; C04B
018/06 |
Claims
1. A method for pretreating fly ash for use in cementitious
compositions containing an air entrainment agent comprising the
steps of: applying an effective amount of benzoic acid to a
quantity of fly ash to satiate unburned carbon in said ash without
effecting the air entrainment functions of said air entrainment
agent.
2. A method for pretreating fly ash for use in cementitious
compositions containing an air entrainment agent comprising the
steps of: applying an effective amount of salicylic acid to a
quantity of fly ash to satiate unburned carbon in said ash without
effecting the air entrainment functions of said air entrainment
agent.
3. The method of claim 1 wherein said amount of benzoic acid is in
the range of about 0.01 g to about 100 g for each 100 g of said fly
ash.
4. The method of claim I wherein said amount of salicylic acid is
in the range of about 0.01 g to about 100 g for each 100 g of said
fly ash.
5. A method for pretreating fly ash for use in cementitious
compositions containing an air entrainment agent comprising the
steps of: applying an effective amount of lithium salicylate to a
quantity of fly ash to satiate unburned carbon in said ash without
effecting the air entrainment functions of said air entrainment
agent, said effective amount of lithium salicylate is about 0.07 g
for each 100 g of said fly ash.
Description
[0001] This application is a continuation of co-pending U.S. patent
application Ser. No. 09/804,737, filed Mar. 13, 2001, which claims
priority to U.S. Provisional Patent Application No. 60/188,737,
filed Mar. 13, 2000.
BACKGROUND OF THE INVENTION
[0002] Coal fired power plants generate fly ash from the combustion
of pulverized coal, or combinations of pulverized coal and other
carbonaceous supplemental fuels such as petroleum coke, woodbark,
charcoal, wood, residual fibers, etc. The fly ash is captured in
the power plant's emission control devices, such as by
electrostatic precipitators and baghouses. The principal
composition of fly ash includes an inert mineral fraction
consisting primarily of ferro-alumino-silicate glass and residual
unburned carbon from coal and/or other supplemental fuels.
[0003] The inert mineral fraction of fly ash is a pozzolan, which
makes fly ash an acceptable mineral admixture for use in Portland
cement concrete. The fly ash itself includes the devolatized
mineral matter which has been trapped or loosely associated with
the coal as well as incombustible components and elements of the
coal and/or of the supplemental fuels. In addition to such
incombustible components, the fly ash contains carbon rich
particles which have not been completely combusted, usually due to
the inefficiency of the boiler design or related conditions.
[0004] Specifications for the use of fly ash in Portland cement
concrete are set out in ASTM #C618. This specification limits the
loss-on-ignition (LOI) content of fly ash pozzolan to less than 6%.
The LOI value of fly ash in generally equal to the percent by
weight of the unburned carbon content of the fly ash. This carbon
content can vary from as little as about 0.5% up to 20% or more of
the weight of the total fly ash product. However, for pozzolanic
activity, a good quality fly ash should contain less than 1% carbon
but, in any case, no more than 4% carbon.
[0005] A high carbon fly ash as a pozzolanic mixture has a
detrimental impact upon the quality of concrete. The presence of
carbon reduces air entrainment, which, in many locations, is the
only real protection that concrete has against freeze-thaw/wet-dry
conditions. Therefore, the lower the carbon content, the better the
concrete mix is from an air entrainment perspective. The presence
of carbon also increases water requirements, reduces pozzolanic
reactivity, and degrades the appearance of finished concrete
surface. Thus, carbon negatively affects the strength, durability,
and aesthetic appearance of concrete. Therefore, the lower the
carbon content in any fly ash, the better the fly ash as a concrete
admixture.
[0006] In many cases, air entrainment agents (AEA) are added to the
concrete mix in order to desirably increase the amount of small air
bubbles that are formed during mixing. In these cases, carbon
reduces the ability of these agents to operate efficiently.
SUMMARY OF THE INVENTION
[0007] The present invention is directed to a chemical treatment
that may be applied to the high carbon content fly ash either prior
to or concurrent with its mixing with the other concrete
components.
[0008] Specifically, aromatic carboxylic acid or hydroxy
substituted aromatic carboxylic acid is added to a quantity of fly
ash to reduce air entraining chemical demand. Such aromatic
carboxylic acids include benzoic, phthalic, isophthalic, and
terephthalic acids and their salts. Included in the hydroxy
substituted aromatic carboxylic acids found effective are salicylic
acid, m-hydroxybenzoic acid, and p-hydroxybenzoic acid and their
salts.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0009] Recent emphasis has been given to the removal of the carbon
from the fly ash before utilization (i.e. mixing) of the ash
component in the concrete, such as Portland cement concrete (PCC).
These chemical treatments or chemical carbon scavengers must
somehow satisfy the affinity of the carbon for the commonly used
air-entraining agents. At the same time, the use of just any
chemical is not acceptable since the chemical itself must not
entrain air when the ash is used in the PCC, nor must the chemical
inhibit the intended, desirable functions of the AEA.
[0010] Accordingly, "air neutral" agents must be used to improve
the air entrainment properties of the carbon containing ash. That
is, these chemical carbon scavengers should not significantly
promote air entrainment by themselves or retard air or bubble
formation. However, these scavengers should be adsorbed onto the
carbon, thus satisfying the affinity or appetite that the carbon
otherwise would have for the AEAs.
[0011] Pretreatment of the fly ash by the chemical carbon scavenger
may be performed simultaneously with other chemical treatments
applied to the ash, such as those that may be used to reduce the
NH.sub.3 content of the ash.
[0012] At present, exemplary chemical carbon scavengers have been
found to include the aromatic carboxylic acids such as benzoic,
phthalic, isophthalic, and terephthalic acids and their salts and
the hydroxy substituted aromatic carboxylic acids such as salicylic
acid, m-hydroxybenzoic acid and p-hydroxybenzoic acid and their
salts.
[0013] Based upon available preliminary test data, salicylic acid
and its salts may be preferred, with lithium salicylate perhaps the
most preferred at present. It has been noted that treatment of 100
g of ash with 0.07 g lithium salicylate has achieved at least 30%
reduction of air entraining chemical demand. Further, this
particular carbon scavenger did not exhibit either air entrainment
or suppression. It is anticipated that treatment dosages of these
scavengers will range from 0.01 g to 100 g chemical carbon
scavenger based on 100 g of fly ash.
[0014] Other additional candidate chemical carbon scavengers
include families of dyes and multi-ring aromatics as well as some
alkyl-aryl compounds.
[0015] Although the invention has been described with reference to
a specific embodiment, this description is not meant to be
construed in a limiting sense. On the contrary, various
modifications of the disclosed embodiments will become apparent to
those skilled in the art upon reference to the description of the
invention. It is therefore contemplated that the appended claims
will cover such modifications, alternatives, and equivalents that
fall within the true spirit and scope of the invention.
* * * * *