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Characterisation and Utilisation of Fly ash -A Holistic Approach

Characterisation and Utilisation of Fly ash -A Holistic Approach. Prof.A Sarkar Department of Applied Chemistry Indian School Of Mines ,Dhanbad-826004. My Team. Dr.Ruma Rano Dr.H Banichul Ms.B Haldar Ms.S Vishwakarma Mr.G Mondol It is their effort ----. Introduction:

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Characterisation and Utilisation of Fly ash -A Holistic Approach

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  1. Characterisation and Utilisation of Fly ash -A Holistic Approach Prof.A Sarkar Department of Applied Chemistry Indian School Of Mines ,Dhanbad-826004

  2. My Team • Dr.Ruma Rano • Dr.H Banichul • Ms.B Haldar • Ms.S Vishwakarma • Mr.G Mondol It is their effort ----

  3. Introduction: • According to a rough estimate , annual production of coal ash worldwide is ~600 million tones{MT}. • 75-80 %{~500 MT}of the ash thus produced is FLY ASH[Joshi et al 1997]. • Meanwhile coal consumption has increased by 50%, mainly due to the economic growth in China [International Energy Statistics, US Energy Information Administration; 2011.]. • The updated estimate of annual CFA generation is 750 MT [ Blissett et al 2012.]

  4. CFA utilisation: • The global average had been estimated to close to 25% [Wang S , 2008]. • US ::: 39% ,Europe :::47% [ACAA, 2009 Coal Combustion Product (CCP) Production & Use Survey Report;2010. Production and Utilisation of CCPs in 2008 in Europe, European Coal Combustion Products Association; 2008.]. • India::: 25% of fly ash was used for cement production, construction of roads and brick manufacture [Bhattacharjee U, Kandpal TC.2002].

  5. The energy sector in India generated over 130 MT of FA annually [Burke M ,2007] • This amount may have increased with an annual increase in coal consumption by 2.2%. • It is evident that a proper planning is necessary for disposal of such huge amount of fly ash. • Traditionally, this is achieved by dumping the ash, in ash lagoons/used as landfills.

  6. Such activities are associated with several environmental/local problems. • It is apparent that stress should be more on utilisation of fly ash towards product development than disposal. • For such purpose, there should be greater utilisation of fly ash in cement production, concrete, brick making etc.where there is scope for bulk utilisation . • Additionally high value uses should be also encouraged.

  7. A Synergy exists between Characterisation & Utilisation of fly ash. • It is necessary to carry out thorough studies of the various characteristics of CFA, and its constituents. •  Characterization of fly ash and its constituents in terms of various physico-chemical, mineralogical and morphological properties is of fundamental importance in the development of various utilization potential of fly ash.

  8. CHARACTERISATION • 2.0. Characterization of Fly Ash and Its Constituents • Characterization of fly ash and its constituents in terms of various physico-chemical, mineralogical and morphological properties is of fundamental importance in the development of various utilization potential of fly ash. It was S V Vassilev who realized the importance of a thorough characterization of fly and its various constituents and subsequently reported various results of their investigations in a series of publication. A scheme of the separation procedures for the composite fly ash was proposed by Vassilev and coworkers (Scheme.1).

  9. Although it may not be always possible to characterize the different constituents of fly ash to that extent, it is always advisable to characterize the as received fly ash, non magnetic magnetic component of fly ash, cenospheres and water soluble residues

  10. CHARACTERISATION • 2.0.1: Collection and Sampling of Fly ash • Collection and sampling of fly ash is a very important step towards the characterization of ash. • Collection of ash chimney bag house • ash dump • ash pond • from the hoppers • of the fields of electrostatic precipitator

  11. Collection from ash pond :::not advisable always. • leaching in contact with water alter the size, shape and other mineralogical and morphological constituents. • Some amount of CaO which is so important for pozzolanic property may also be lost. • Some of the surface enriched elements may be also leached away. • Collection from chimney bag house, which is covered, is most advisable if highly specific end uses are not envisaged. • Fly ash is directly collected from mechanical hoppers attached to electrostatic precipitators where highly specific end use of fly ash is required.

  12. 2.0.3: Physico- chemical properties: • COLOUR • The colour of Fly ash varies widely depending upon it’s carbon/Fe content.

  13. In the attached Fig.,A represents As received Fly Ash from A Super Thermal Power Plant • B Non Magnetic Component • C Magnetic Component. • XRD as well as XRF Analysis Reveals that Fe content is Maximum in case of C ,less in A and least in B. • Distinct Colour changes occur in AB,C

  14. XRD OF AS RECEIVED FA(A)

  15. XRD OF NON MAGNETIC FA(B)

  16. XRD OF MAGNETIC FA(B)

  17. F HIGH CARBON ASH • G MAG.COMPONENT HEATED ~750 0C • H NON- MAG.COMPONENT HEATED ~500 0C

  18. I Mesoporous Material from Fly ash • J Kota Fly Ash • K Kasimpur Fly ash • Colour of the ash gives a preliminary information about it’s carbon /Fe content

  19. DENSITY • DENSITY:::::: Three types. • Bulk, Apparent and True . • Bulk density data is quite useful for bulk utilisation of Fly ash, like Road making,Landfill,Embankment etc. • For High value utilisation,Apparent and True Density data are more relevant. • Density of Non Magnetic Components are less than the Magnetic Components.

  20. Variation in Apparent Density with LOI

  21. PARTICLE SIZE • Particle size of FAs are very important consideration in variety of Applications. • Particle size can be on the basis of sieve analysis OR Laser based Particle Size Analysis. • Sieve Analysis has its own limitations. • Dry Analysis is sometimes erroneous due to comminution of the particles. • Wet Analysis has agglomeration problem.

  22. Laser based Particle size analysis is a good approximation of the real size provided the particles are spherical. • Since Laser Based Analysers measure the volume , converts it into an equivalent sphere and reports the particle diameter the irregularly shaped particles ‘ size is not a true representation.

  23. The particle size of fly ash varies widely depending upon the source. • Super thermal power plants produce ash having arithmetic mean diameter of 6-30µm.

  24. ULTRAFINE FLY ASH(UFFA) • Fly ash particles with particle diameter,5 µm are termed asUFFA.These are most useful candidates for variety of applications like polymer filler, high performance concrete, paints etc. • Fly ash particles with particle diameter<10 µm are also quite useful for high value uses. • Fly ash particles with particle diameter>45 µm are not very useful for use in concrete[ Mehta]

  25. Vol% Of FA Particleswith diameter<5µm

  26. Grain Size Distributions • Grain size distributions (Figs) provide some useful information regarding the distribution of the particle size. • Grain size distributions are normally grouped as • ( a) Normal-Gaussian grain size distribution. • (b)Asymmetric grain size distributions • (c) Wide to bimodal grain size distributions

  27. Normal Gaussian grain size distributions are characterized by an uniform bell shaped distribution curve with mode equidistant from both the ends . • Asymmetric distribution as the term implies is not symmetric around a mode. • The extent of asymmetry in an asymmetric distribution is measured by skewness. • Skew are of two types(a) negative skew or left skewed(b) positive skew or right skewed. • Negative skew has a longer left tail and the mass of the distribution is concentrated to the right of the figure. It has relatively few low values.

  28. Positive skew has a longer right tail ,the mass distribution being concentrated on the left of the figure and have relatively low high values. • Bimodal grain size distributions have two modes and represents uneven distribution patterns.

  29. Chemical Composition • The properties of the feed coal and combustion conditions have direct bearing on the chemical composition of fly ash. • Basically, the major chemical constituents of fly ash are silica, alumina, iron oxide, magnesium oxide and calcium oxides. • Along with these, other minor and trace elements may be present (Table1).

  30. Table 1a:Elemental Composition Of As received FA ,Ib Magnetic component

  31. Mineralogical Analysis • 2.0.4: Mineralogical Composition • Mineralogical analyses of various fly ash have revealed the presence of quartz, mullite, anhydrite, hematite and magnetite as the main mineralogical phases. • The type and content of the phases present in the ashes also depend upon the nature of the feed coal as well as the combustion conditions. • Nonmagnetic and Magnetic components of FA are distinctly different.

  32. XRD of Non Magnetic Component of Fly ash

  33. XRD of Non Magnetic Component of Fly ash

  34. The Nature of Carbon Present in the High Carbon Ash can also be determined using XRD. Fig: XRD patterns of non-magnetic fractions fly ash.

  35. XRD patterns of demineralised samples

  36. Morphological Analysis • 2.0.5: Morphological analysis of fly ash: • Scanning and Transmission Electron Microscopy are very useful Tools for Morphological analysis of Fly Ash. • The shape,pores,deposits on the surface can be easily determined. SEM of non magnetic component of FlyAsh.

  37. SEM OF MAGNETIC COMPONENT OF FA

  38. The Chemical Composition of the Fe-bearing particles on the surface can be determined by EDX/EPM. • These materials are soft magnetic materials as revealed by Hysteresis Diagram. • These materials have been found to have super paramagnetic properties and has been used as catalyst for DEEp Oxidation Of Methane.

  39. Microphotograph of High Carbon Ash

  40. CHARACTERISATION & UTILISATION • Having discussed threadbare about the various aspects of characterisation of fly ash, let us see how characterisation and utilisation go hand in hand. • Use of Fly Ash In Concrete: • FA can be used as partial replacement of sand.However,high carbon ash are not good replacement of sand,as the following examples reveal.

  41. Use as Fillers in Polymers • Ash used: Non-Magnetic component Of Fly Ash from 7th Field of Rihand Super Thermal Power Station. • Processed FA was used as Fillers 5,10,12.5, 15%Ash was mixed with polypropylene and composite prepared. • Mechanical properties studied: • Tensile strength • Percent elongation • Stress at maximum load • Strain at maximum load

  42. Particle Size Analysis.

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