Fly Ash Main

7/31/2019 Fly Ash Main

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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!!!

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