SEMINAR PRESENTATION

FLY ASH : UTILIZATION AND DISPOSAL

Submitted by:Jyoti kumari

Environmental EngineeringNational Institute of Technology

Content:

IntroductionHistoryChemical compositionTypes of fly ashAsh generation and effectsProduction ProcessUtilisationDisposalEnvironmental considerationAdvantages & disadvantages ConclusionReferences

IntroductionFly ash is one of the residues created during the

combustion of coal in coal-fired power plants.

Fine particles rise with flue gasses and are collected with filter bags or electrostatic precipitators

Fly ash is a waste by-product material that must be disposed of or recycled

Fly Ash is considered as amorphous and mixture of Ferro- alluminosilicate minerals.

History

The Roman Colosseum Ghatghar Dam

Chemical CompositionBecause fly ash is a by-product material chemical

constituents can vary considerably but all fly includes:Silicon Dioxide (SiO2)Calcium Oxide (CaO) also known as LimeIron (III) Oxide (Fe2O3)Aluminum Oxide (Al2O3)

Depending on source coal may include one or more toxic chemicals in trace amounts:Arsenic, Beryllium, Boron, Cadmium,

Chromium, Cobalt, Lead, Manganese, Mercury, Molybdenum, Selenium, Strontium, Thallium, and Vanadium

Types of Fly ashASTM C618 Defines two classes of fly ash:

Class CClass F

ASTM C618 requirements:Loss of Ignition (LOI) < 4% 75% of ash must have fineness of 45 µm or less

Primary difference between Class C and Class F fly ash is the amount of calcium, silica, alumina, and iron content in the ash

Class FProduced from burning harder, older anthracite

and bituminous coal.Contains less than 20% limeRequires cementing agent like PC, quick lime , hydrated limeUsed in high sulfate exposure conditionsUsed for structural concretes, HP concretes, high sulfate exposure concretes Useful in high fly ash content concrete mixes

Class CProduced from burning younger lignite and

subbituminous coalHigher concentration of alkali and sulfateContains more than 20% limeSelf-cementing propertiesDoes not require activatorNot for use in high sulfate conditionsPrimarily residential constructionLimited to low fly ash content concrete mixes

Ash Generation and EffectsAsh is an inherited impurity of coal that will not burn.

Typical range is 5% to 40%Reduces handling and burning capacity.Increases handling costs.Affects combustion efficiency and boiler efficiencyCauses clinkering and slagging.

Ash is generated as the product of combustion of coalComprises of 80% Fly Ash and 20% Bottom Ash

Parameter Indian Coal

Indonesian Coal

South African Coal

Ash content (%)

38.63% 13.99% 17%

Scenario in India:

Production / Segregation process

UtilizationIn developed countries more than 80% Fly Ash is

used for the manufacturing following:-

In agricultureBuilding materialBricks constructionMine fillsMetallurgyUse of new materialEnvironmental controlEmbankment

Details on UtilizationAgriculture Indian Fly Ash is alkaline and as such improves soil quality. In a

research conducted by MSEB, it was found that with dose of 10MT per hectare and just 50% dose of chemical fertilizers there is increase of 20% yield in terms of grains and fodder

Mine Fills Utilization of Fly Ash in Mine fills has potential to consume large

quantity of Fly Ash. This single application of Fly Ash can utilise about 1/4th of total Fly Ash generation

• Metallurgy The Fly Ash contains about 20%-25% alumina. CPRI Bengaluru has

developed a process to extract alumina from Fly Ash. About 1 tonne of Fly Ash with 400 kg of other additives like lime and

gypsum can produce 150 kg of alumina and 1250 kg of pozzolanic cement, which is a good raw material for quality bricks

Precast Fly Ash concrete units

It can be used in production of various types of precast building units such as solid and hollow core slabs, doors and window frames

Clay Fly Ash Bricks

About 0.25 – 0.80 times of calay can be replaced by fly ash. Further, the residual carbon content in Fly Ash brings about an

economy in fuel consumption during firing of bricks.

Cement

Fly Ash being an artificial pozzolanic material can be used for manufacturing of Portland Pozzalona Cements (PPC), as partly replacement of cement in mortar and concrete

Building material

Fly Ash is a Pozzolanic material containing silica in good proportion. It has tremendous potential to be used as an alternative material for building construction

Road construction material

Utilization of Fly Ash in bulk quantities for road works depending on the intersection between Coal ash and sub-grade soil.

Use of new material

In order to maintain the present rate of technological development some alternative materials viz., fly ash, fibre glass, reinforced plastics and glass, reinforced gypsum are used as building materials.

Embankment

Lower unit weight reduces dead loads and induced settlement of sub-soil High shear strength compared with its low unit weight for good bearing

support Ease of placement and compaction can reduce construction time and cost

Soil Stabilization

A sheep’s foot roller is commonly used to add the fly ash to the soil.Also specialized equipment can be utilized to pump fly ash or other stabilizers into the soil.Class C fly ash is used in soil stabilization

Flowable Fill

Fly ash generally supplements the Portland cement in greater volume The fine particulate of the fly ash acts as ball bearings allowing it to flow freely. Generally Class C fly ash is used for flowable fill.

Fly ash use

Let us see what fly ash achieves in totality: -It delays the heat of hydration and hence reduces the

thermal cracks in concreteIt improves the workability of concreteIt makes the mix homogeneous and hence reduces

segregation and bleeding

The concrete finish is improved due to perfectly spherical fly ash particles

The concrete permeability is substantially reduced which enhances the life of the structure

Fly ash contributes to the long term strength in concrete

Examples of fly ash utilization

Reclamation of saline soils using fly ash (75% savings in Gypsum)

First fly ash embankment in the country (Okhla fly over, New Delhi)

Examples of fly ash utilization

Upper dam of Ghatghar Pumped Storage Scheme constructed with RCC ( 65% replacement of cement with fly ash)

Use of Fly ash for Road Embankment

Disposal

In the past fly ash produced from coal power plants was simply entrained in flue gasses and released into the environment. Now in the U.S., EPA regulations requires greater than 99% of total fly ash produced in a plant to be captured and either stored, recycled, or disposed.

Worldwide, more than 65% of fly ash produced in the world is disposed of in landfills or ash ponds.

In India alone fly ash landfills comprise 65,000 acres of land.

Modes of disposalDry Fly Ash Disposal

Fly Ash once collected in Electrostatic Precipitator gets transported to Fly Ash Bunkers using pressurized air and then gets transported via truck or conveyers at the site and disposed by constructing a dry embankment.

Wet Fly Ash Disposal

Fly Ash once collected in ESP is mixed with water to form slurry and then this slurry is transported through pipe to the ash ponds or dumping areas near the plants.

Environmental Consideration of DisposalThe environmental aspect of Fly Ash disposal aims at

minimizing air and water pollution.The Fly Ash produced by thermal power plants can

cause all three environmental risks-Air : Air pollution is caused by direct emissions of toxic

gases from the power plants as well as wind-blown ash dust from ash mound/pond.

surface water: The wet system of disposal in most power plants causes discharge of particulate ash directly into the nearby surface water system

ground water pollution. The long storage of ash in pond can cause leaching of toxic metals from ash and contaminate the underlying soil and ultimately the groundwater system

Schematically pathways of pollutant movement around Fly Ash disposal.

Advantages of fly ash utilizationSaving of space for disposalSaving of scare of natural resourcesEnergy saving, firstly because the material

is automatically produced as a by-product and no energy is consumed for its generation and secondly because it can replace material which otherwise would need to be produced by consuming energy.

Protection of environment, as in construction it can partly replace cement, production of which entails energy consumption and CO2 emissions.

Disadvantages of fly ash utilizationGroundwater contamination due to runoffs carrying

ill-treated fly ash.

Cannot be used for structures requiring shorter setting time, a demand which is expected by most of the engineers and builders.

It is very difficult to use in winter season due to further increase in already longer setting time.

Difficult to control colour of cement containing flyash. Hence, a bit problematic to use where cosmetic quality plays a significant role.

ConclusionFlyash can be proclaimed as one of the most

advantageous waste material.Using it as a construction material will not only

help in its disposal but will also add strength and durablity of structures.

Since, the current usage of flyash in India is still around 25% and below 45% even in the developed countries like United States, there is a huge scope for flyash in upcoming years.

So let us harness a billion dollar resource that has been wasted so far.

Referenceshttp://www.flyash.com1st International Conference on Fly Ash Utilization,

NDCC Convention Centre, New Delhi held during November 24-25, 2011.

Use of Fly Ash in Mine Filling- cbri enviwww.cbrienvis.nic.in/mine_filling.htm

Fly Ash Technologies- National Metallurgical Laboratory (A constituent establishment of (CSIR)

2nd Annual International Summit on Fly Ash Utilization, NDCC Convention Centre, New Delhi held during January 17-18, 2013.

 

Thank You