Determining Residual Ammonia in Flue Gas Conditioned Fly Ashes and Its Influence on the Pozzolanic Activity

ABSTRACTThis paper gives physical and chemical properties of some Canadian fly ashes. Specific surface area, magnetic fraction, water soluble fraction and fraction finer than 45 μm were determined as part of the physical tests. Thermo-gravimetric analyses (TGA) in oxygen and nitrogen were conducted on raw ash samples. The change of pH with time in suspensions of the different ashes in water was also determined. Pozzolanic activity of the ashes with lime for all the ashes was evaluated to measure ash reactivity.The ash activity seems to be related to fineness of the ash measured by the Blaine air permeability method, but not to the fineness measured by nitrogen sorption. Generally the greater the specific surface area, the higher the reactivity of the ash. The correlation was, however, not strong and no other physical or chemical parameter measured in this investigation seems to be related to pozzolanic activity.The results of pH and TGA tests indicated that the ashes differ in many respects from each other. The TGA data suggest that loss on-ignition in many of the ashes is not entirely due to the presence of unburned carbon. Specific surface area determined by various methods seems to provide different values. No characterization parameter was found that was uniquely related to coal type.

Download Full-text

Ammonia in Fly Ashes from Flue Gas Denitrification Process and its Impact on the Properties of Cement Composites

Buildings ◽

10.3390/buildings9110225 ◽

2019 ◽

Vol 9 (11) ◽

pp. 225 ◽

Cited By ~ 2

Author(s):

Agnieszka Michalik ◽

Joanna Babińska ◽

Filip Chyliński ◽

Artur Piekarczuk

Keyword(s):

Fly Ash ◽

Flue Gas ◽

Coal Combustion ◽

Catalytic Reduction ◽

Structural Features ◽

Cement Composites ◽

Fly Ashes ◽

Ammonia Content ◽

Denitrification Process ◽

Flue Gas Denitrification

The paper presents the results of research on the properties of fly ashes from the process of flue gas denitrification by selective non-catalytic reduction (SNCR), consisting of dosing urea into the coal combustion chamber. The research was carried out on two types of fly ash: Silica fly ash from flue gas denitrification and ash from a traditional boiler without the flue gas denitrification process. The scope of comparative studies included physicochemical and structural features of ashes, as well as slurries and mortars with the addition of ashes. Fly ash from denitrification, whose ammonia content at the time of sampling was 75 mg/kg at the maximum, was examined. Our own research has shown that fly ash from flue gas denitrification is characterized by a higher value of losses on ignition and ammonia content in comparison to ashes without denitrification. It was shown that the ammonia content in the analyzed range does not limit the use of fly ash as an additive to cement and concrete.

Download Full-text

An examination of the ASTM Lime Pozzolanic Activity Test for class C fly ashes

Cement and Concrete Research ◽

10.1016/0008-8846(84)90125-x ◽

1984 ◽

Vol 14 (4) ◽

pp. 499-504 ◽

Cited By ~ 5

Author(s):

S. Schlorholtz ◽

T. Demirel ◽

J.M. Pitt

Keyword(s):

Pozzolanic Activity ◽

Fly Ashes ◽

Activity Test ◽

Class C

Download Full-text

Fly ashes reactivity in relation to coal combustion under flue gas recycling conditions

Thermochimica Acta ◽

10.1016/s0040-6031(97)00067-1 ◽

1997 ◽

Vol 296 (1-2) ◽

pp. 67-74 ◽

Cited By ~ 4

Author(s):

L. Santoro ◽

S. Vaccaro ◽

A. Aldi ◽

R. Cioffi

Keyword(s):

Flue Gas ◽

Coal Combustion ◽

Fly Ashes ◽

Gas Recycling

Download Full-text

Modified Fly Ash-Based Adsorbents (MFA) for Mercury and Carbon Dioxide Removal from Coal-Fired Flue Gases

Energies ◽

10.3390/en14217101 ◽

2021 ◽

Vol 14 (21) ◽

pp. 7101

Author(s):

Marta Marczak-Grzesik ◽

Piotr Piersa ◽

Mateusz Karczewski ◽

Szymon Szufa ◽

Hilal Ünyay ◽

...

Keyword(s):

Carbon Dioxide ◽

Particle Size ◽

Fly Ash ◽

Chemical Composition ◽

Solid Waste ◽

Flue Gas ◽

Flue Gases ◽

Co2 Removal ◽

Fly Ashes ◽

Modified Fly Ash

One of the solid waste produced during the combustion of coal are fly ashes. Disposal challenges and environmental consequences are the results of significant process yield and atmospheric emission of fly ashes. The exact chemical composition of FA depends mainly on the type of utilised fuel and combustion conditions. It consists mainly of chemically stable metal oxides, such as Al2O3, Fe2O3, SiO2, CaO, MgO, K2O, Na2O and TiO2, but its toxicity is related to the possible presence of some trace elements, such as As, Hg, Cd, Se and Cr. The chemical and physical properties of fly ash (e.g., particle size distribution, porosity, and surface area) make it suitable as an adsorbent to remove various impurities from process flows such as flue gas stream. Its suitability for capturing mercury from flue gas was experimentally confirmed due to its abundant supply, particle size, bulk density, porosity, chemical composition and low cost. Hence, the use of fly ash as adsorbents and precursors for the production of heavy metal adsorbents is of great practical importance, as it reduces the cost of mercury capture and alleviates the problems associated with the disposal of solid waste. Studies showed that the chemical components present in fly ash additives could stimulate catalytic oxidative capacity, which increases the adsorption of Hg0 oxidation and adsorption of both Hg and CO2. The presented study analysed fly ashes from different zones of the electrostatic precipitator and verified their suitability for removing impurities from flue gases, i.e., mercury and carbon dioxide. The results outlined modified fly ash as having good Hg and CO2 removal capabilities. The adsorption efficiency of Hg reached 92% for Hg and 66% for CO2, while untreated fly ash reached 67% for Hg and 59% for CO2.

Download Full-text

Multivariate Statistical Analysis of the Wfarddc North American Fly Ash Database

MRS Proceedings ◽

10.1557/proc-245-3 ◽

1991 ◽

Vol 245 ◽

Author(s):

Hans S. Pietersen ◽

Simon P. Vriend ◽

Gregory J. Mccarthy

Keyword(s):

Compressive Strength ◽

Statistical Analysis ◽

Specific Gravity ◽

North American ◽

Activity Index ◽

Pozzolanic Activity ◽

Mineral Admixtures ◽

Fly Ashes ◽

Glass Chemistry ◽

Bulk Chemistry

ABSTRACTThe database of chemical, mineralogical and physical characteristics of North American Fly ashes, assembled by the WFARDDC in North Dakota, was analyzed using multivariate statistics. Prior to the multivariate analysis, the data were rearranged in subgroups containing information on bulk-chemistry, glass chemistry, mineralogy and ASTM physical test results. These groups were analyzed individually. The multivariate technique used was Fuzzy C-Means Cluster Analysis, combined with Non-Linear Mapping. Analysis of the data-set indicates a relation between glass network former and network modifier content. The database shows that a subdivision on the basis of bulk CaO (< 11%; 11–20%; >20%) correlates well with the ASTM C618 Σ(SiO2 +Al2O3 +Fe2O3) and/or specific gravity. Mineralogical data indicate a subdivision into clusters containing varying amounts of mullite, quartz and/or ferrite spinel and a variety of Ca-containing minerals; high CaO ashes usually have high Ca-mineral contents. Of the CaO containing minerals, only portlandite contributed slightly to the compressive strength as defined by ASTM C618. Analysis of glass chemistry reveals smaller differences in absolute amounts of major oxides than would be expected on the basis of bulk chemistry alone. Surprisingly, the total glass content does not contribute significantly to 28 day compressive strength; multiple regression analysis only indicates a significant relation of particle size and specific gravity with the ASTM Pozzolanic Activity Index (portland cement). The Pozzolanic Activity Index with lime seems to be of limited importance in evaluating the performance of fly ashes as mineral admixtures in concrete. On the basis of the statistical analysis, suggestions for selection of important classifying variables are made.

Download Full-text