Fly ashes from the Lansing and Ottumwa power plants in Iowa were agglomerated by means of a continuous pan agglomerator, a continuous auger and a batch turbine agglomerator. In order to compare agglomeration mechanisms the following parameters were determined: (a) particle size distributions of the untreated fly ashes; (b) particle size distributions of the agglomerated fly ashes; (c) pore size distribution of agglomerates; (d) crystalline hydration products by X-ray diffraction; and (e) morphological characterization by scanning electron microscopy.In the batch system coalescence mechanisms were favoured. The agglomerates were fairly irregular in shape and had a rough surface texture. As residence time in the system increased breakage of agglomerates occurred, reducing the average agglomerate size. In the continuous systems layering of the fine feed particles onto established agglomerates was the predominant growth mechanism. The agglomerates were smooth and spherical. The layer structure was observed by scanning electron microscopy. Agglomerates of widely varying size, strength, and pore matrix can be produced in both systems. It is envisaged that while agglomerates could be produced with characteristics essential for their proposed end use by either method, continuous pan agglomeration would be the most versatile system to utilize.
A major shift to coal as a fuel source has resulted in the generation of vast quantities of difficult to disnose of coal residues. Innovative utilization of such coal combustion bv-~ ~~ ~~ ~ ~ products i s es&al A procedure has been dcvclopcd by which by-produc~r from l o i a Power stations can be agglomerated into inert pellcts of high compressive strength. Evaluation of the lcachatc potential of such matcnals showed heavy metal concentrations to be well below the allowable limits of the EPA toxicity tcsls. The commercial utilization potential as artificial aggregates is very high.This oaoer focuses on the feasibilitv of usine the cementing nrooenies and aeelomeration -. . cha&t;nsucs of such coal conven~& by-pr&ucts to encaprulatc and immobil;& h d o u s waste materials Sludgec from the elcctroplat~ng indumer wcrc encapsulated in a fly ash matrix. Encapsulation is a novel approach t o treating toxic wastes and combines the principles of stabilizationlsolidification and agglomeration in containing the pollutants. The agglomerates were subjected to the EPA leaching test, x-ray diffraction analysis, and SEMEDXA. Compressive strengths of the agglomerates were also determined.Initial results indicate that encapsulation of sludges in such a matrix stabilizes the toxic and metallic elements in an insoluble form by encasement in a low porosity. solid matrix so that significant leaching does not occur.
A procedure has been developed for organizing and displaying the results of particle size distribution determinations on fly ash so as to promote simple and useful comparisons. The procedure involves comparative plots of histograms displayed on a logarithmic size basis, and is illustrated by selected data drawn from a larger suite of analyses of Indiana fly ashes.
One of the major problems currently restricting the utilization of high-calcium (ASTM Class C) fly ashes in Iowa is lack of adequate storage space. High-calcium fly ashes are self-cementitious and are generally not economically reclaimable once they have been exposed to water (i.e., the environment). Since the on-site silo storage capacity of a given power plant is normally only about one or two weeks of overall generating capacity (assuming nearly full load), the fly ash industry is hard-pressed to meet the demand for fly ash during the peak construction months.This paper presents some early research findings concerning the storage alternatives available for these high-calcium fly ashes. A simple pan agglomerator, requiring only the addition of a water spray was used to produce fly ash pellets. Since the method required minimal energy input the process would be expected to be economically feasible for field production. Laboratory produced pellets appeared strong and durable and would be expected to withstand field handling without significant degradation. The pelletization process did not appear to result in a loss of reactivity for either the air-dried or water-cured pellets. This is highly important for potential use in Portland cement concrete or soil stabilization.
Fluidized bed combustion (FBC) residues from four Iowa power plants were characterized to provide background with respect to chemical, physical, mineralogical and microstructural parameters that might affect their utilization potential. Methodologies used include: bulk chemical analysis; grain size analysis; specific gravity determination; mineralogical analysis by x-ray diffraction; scanning electron microscopy; and thermal analysis.Chemical analysis of the major components showed the separation of the constituents during combustion. The bottom ash is derived from the calcined and partly sulfated limestone, thus the concentration of calcium and sulfur compounds is greater. The fly ash however is derived mostly from the coal and therefore exhibits higher concentrations of coal ash components such as silica (SiO2), alumina (Al2O3), and ferric oxide (Fe2O3). The alkalis appear to be more concentrated in the fly ash.The measured particle size distributions of the bulk samples varied greatly, from extremely coarse (mean particle size ˜2000 μm) to fine (mean particle size ˜25 μm). The size distributions also varied in breadth. Specific gravities values recorded ranged from about 2.65 to about 3.05.X-ray diffraction analyses showed that most of the FBC by-products contain, as easily detectable crystalline components, only quartz, anhydrite and lime, and as is to be expected due to the low combustion temperatures, do not show broad peaks characteristic of glass in conventional fly ashes. Scanning electron microscopy revealed the FBC by-products to be extremely intricate mixtures of particles of complex and variable composition and internal structure.FBC by-products are shown to be extremely complex mixtures of particles of variable composition and internal structure. However, despite their local variation, useful results can be obtained by overall chemical and physico-chemical analyses of their composition. The exploitable properties of FBC residue include the somewhat cementitious nature and the granularity. However, their heterogeneous nature, lack of pozzolanic properties, and elevated sulfate content may limit their uses, especially in construction.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.