fly ash main
TRANSCRIPT
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FLY ASH
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TABLE OF CONTENTS
WHAT IS FLYASH?
CLASSIFICATION OF FLY ASH
WHY IS FLYASH A PROBLEM?
PROBLEMS DUE TO FLY ASH
SOLUTION TO FLY ASH PROBLEM
CONCLUSION
REFERENCES
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WHAT IS FLY ASH?
Ash produced during combustion of coal
Captured by electrostaticprecipitators before the flue gases reach
the chimneys of coal-fired power plants
Contains mainly SiO2(both amorphous and crystalline) andCaO, Al2O3, Fe2O3
Fly ashes are generallyhighly heterogeneous
http://en.wikipedia.org/wiki/File:Fly_Ash_FHWA_dot_gov.jpg -
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Particles are spherical in shape
Particle size - 0.5 m to 100 m
Toxic constituents depend upon thespecific coal bed makeup
May include one or more of the followingelements or substances in quantities fromtrace amounts to several percent:
arsenic
beryllium boron
cadmium
chromium
cobalt
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CLASSIFICATION OF FLY ASH
Classified on the basis of ASTM C618
Chief difference between these classes is the amount ofcalcium, silica, alumina, and iron content in the ash
The chemical properties of the fly ash are largely influencedby the chemical content of the coal burned(i.e., anthracite, bituminous, and lignite).
The two types are:
Class F fly ash
Class C fly ash
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CLASS F FLY ASH
Produced by the burning of harder, older anthracite andbituminous coal
Pozzolanic in nature
Contains less than 20% lime (CaO).
A cementing agent, such as Portland cement, quicklime, orhydrated lime, in the presence of water and Class F Fly Ashproduces cementitious compounds
The addition of a chemical activator such as sodium silicate (waterglass) to a Class F ash can lead to the formation of a geopolymer.
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CLASS C FLY ASH
Produced from the burning of younger lignite or subbituminous coal, in
addition to having
It too has pozzolanic properties
It also has self-cementing properties.
In the presence of water, Class C fly ash will harden and gain strengthover time.
Class C fly ash generally contains more than 20% lime (CaO).
Class C fly ash does not require an activator.
Alkali and sulphate (SO4) contents are generally higher in Class C fly
ashes.
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WHY IS FLY ASH A PROBLEM?
In the past, fly ash was entrained in flue gases and dispersed into theatmosphere.
Currently laws exist which have reduced fly ash emissions to less than 1 percentof ash produced.
Worldwide, the production is more than 300 million tons per year.
Worldwide, more than 65% of fly ash is disposed of in landfills and ash ponds.
INDIAN SCENARIO
Nearly 73% of Indias total installed power generation capacity is thermal, of
which 90% is coal-based generation
150 million tonnes of fly ash was produced in India in the year 2000
80-odd utility thermal power stations in India use bituminous coal and producelarge quantities of fly ash
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PROBLEM DUE TO FLY ASH
GROUNDWATER CONTAMINATION
EXPOSURE CONCERNS
Crystalline silica and lime along with toxic chemicals are among
the exposure concerns. Ex - Udupi Power Corporation Limited (UPCL) plant in Nandikur
SPILLS OF BULK STORAGE
Ex- Tennessee Valley Authority Fly Ash containment failure on23 December 2008 in Kingston, Tennessee
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DISEASES CAUSED DUE TO HEAVYMETALS PRESENT IN FLY ASH
METAL CONTENT (PPM) DISEASES
Nickel (Ni) 77.6 Respiratory problem, lung cancer
Cadmium (Cd) 3.4 Anaemia, hepatic disorder
Antimony (Sb) 4.5 Gastroenteritis
Arsenic (As) 43.4 Skin cancer, dermatitis
Chromium (Cr) 136 Cancer
Lead (Pb) 56 Anaemia
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SOLUTION TO FLY ASH PROBLEM-
REUSE OF FLY ASH
Concrete production, as a substitute material for Portland cementand sand
1 ton of Portland cement produces 1 ton CO2
Fly ash has pozzolanic properties Pantheon in Rome made from volcanic ash
Embankments and other structural fills (usually for roadconstruction)
Large uniformity coefficient
Consists of clay sized particles
Mostly Class F fly ash is used
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Waste stabilization and solidification
Fly ash is alkaline due to presence of lime
High water absorvity Transforms sewage sludge to organic fertiliser
Rhenipal process
Stabilization of soft soils
Increases shear strength
Increases load bearing capacity of soil
Mineral filler in asphaltic concrete
Fills voids
Provides greater contact points for large particles.
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As Aggregate substitute material (e.g. for brickproduction)
Two ways to manufacture bricks:
Flyash+clay+firing in kiln at 1000oC
Flyash+POP+soil+water+drying
India- Pulverised fuel ash for lime-pozzolan mixture
Recent development by Henry Liu in USA
Manufacture of geopolymers
Landfilling Concrete production
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To produce RCC
Ex- Ghatghar dam Project in Maharashtra
Metal Matrix Composites
Mixed with molten metals to make composite Hollow fly ash can be infiltrated by molten metal to get
alumina encased spheres
Reduces density and weight of product
New research to incorporate fly ash in lead acidbatteries
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CONCLUSION
Fly ash must be reused as it has very severehealth and environmental impacts.
The largest usage of fly ash is in manufacture ofConcrete.
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REFERENCES
http://en.wikipedia.org/wiki/Fly_ash
http://www.ifandp.com/article/00306.html
http://edugreen.teri.res.in/explore/air/flyash.htm
http://www.smartplanet.com/blog/pure-genius/fly-ash-from-toxic-by-product-to-nearly-free-metal-replacement/5902
http://conservationreport.com/2009/06/14/clean-coal-is-a-myth/
http://flyashbricksinfo.com/construction/disadvantages-of-fly-
ashdiseases-caused-by-fly-ash.html
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THANK YOU!!!