1. INTRODUCTION

Origin of the report

The Mumbai universities have assigned the task of submitting report in

the subject presentation and communication techniques as a part of

curriculums.

Purpose

The purpose of the report is to know the students how the alumina is manufactured, which type of process is include in manufacture in alumina. And to find out the other alternative process to manufacturing alumina to reduce the cost of product.

Scope

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The scope of the report is to know the students how the alumina is

manufactured, which type of process is include in manufacture in

alumina. And to find out the other alternative process to manufacturing

alumina to reduce the cost of product.

Limitations

Due to lack of time the visit was not possible therefore the all data is secondary (got it from the internet and books).

Sources of Methods of collecting data

World wide web (w.w.w.) Direct Reference.

2. TRACING THE HISTORY OF THE ALUMINIUM MINING

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Aluminium came late into the world of major metals for the reason that

it was an electrolytic process product and required the electric furnace

at a high stage of development for its production. The Industry is only

half a century old and the principal producing countries have

developed the production of aluminium on the basis of one process and

one ore: .the process being the Hall-Héroult process, in which the oxide

of aluminium, alumina, produced by .chemical treatment of the bauxite

ore, is reduced electrolytic al ly; and the ore being high-grade bauxite,

which is a mixture of hydrated oxides of aluminium containing si l ica,

ferric oxide and other impurities.

2.1. Definition of Aluminium

Aluminium or aluminum is a si lvery white member of the boron

group of chemical elements. It has the symbol Al, and its atomic

number is 13. It is not soluble in water under normal circumstances.

Aluminium is the third most abundant element

(after oxygen and si l icon), and the most abundant metal , in

the Earth's crust. It makes up about 8% by weight of the Earth's solid

surface. Aluminium metal is too reactive chemically to occur natively.

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Instead, it is found combined in over 270 different minerals. [ 4 ]  The

chief ore of aluminium is bauxite.

2.2. History of Aluminium

Ancient Greeks and Romans used aluminium salts as dyeing mordants

and as astringents for dressing wounds;  alum is sti l l used as a styptic.

In 1761,Guyton de Morveau suggested call ing the base

alum alumine.  In 1808, Humphry Davy identif ied the existence of a

metal base of alum, which he at f irst termed alumium and

later aluminum (see etymology section, below).

The metal was first produced in 1825 (in an impure form)

by Danish physicist and chemist Hans Christian Ørsted. He

reacted anhydrous aluminium chloridewith potassium amalgam and

yielded a lump of metal looking similar to tin. [ 4 2 ]  Friedrich Wöhler was

aware of these experiments and cited them, but after redoing the

experiments of Ørsted he concluded that this metal was pure

potassium. He conducted a similar experiment in 1827 by mixing

anhydrous aluminium chloride with potassium and yielded

aluminium. Wöhler is generally credited with isolating aluminium

(Latin alumen, alum), but also orsted can be l isted as its

discoverer.  Further, Pierre Berthier discovered aluminium in bauxite

ore and successfully extracted it.  Frenchman Henri Etienne Sainte-

Claire Devil le  improved Wöhler's method in 1846, and described his

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improvements in a book in 1859, chief among these being the

substitution of sodium for the considerably more expensive

potassium. Devil le l ikely also conceived the idea of the  electrolysis of

aluminium oxide dissolved in cryolite;  Charles Martin Hall  and Paul

Héroult might have developed the more practical process after Devil le.

Before the Hall-Héroult process was developed in the late 1880s,

aluminium was exceedingly diff icult to extract from its various  ores.

This made pure aluminium more valuable than gold.  Bars of aluminium

were exhibited at the Exposition Universelle of 1855. [ 4 7 ]  Napoleon II I ,

Emperor of France, is reputed to have given a banquet where the most

honoured guests were given aluminium utensils, while the others made

do with gold.

Aluminium was selected as the material to be used for the 100 ounce

(2.8 kg) capstone of the Washington Monument in 1884, a time when

one ounce(30 grams) cost the daily wage of a common worker on the

project.  The capstone, which was set in place on December 6, 1884, in

an elaborate dedication ceremony, was the largest single piece of

aluminium cast at the time, when aluminium was as expensive as

si lver.

The Cowles companies supplied aluminium alloy in quantity in

the United States and England using smelters  l ike the furnace of  Carl

Wilhelm Siemens by 1886. Charles Martin Hall  of Ohio in the U.S.

and Paul Héroult  of France independently developed the Hall-Héroult

electrolytic process that made extracting aluminium from minerals

cheaper and is now the principal method used worldwide. Hall 's

process in 1888 with the financial backing of  Alfred E. Hunt, started the

Pittsburgh Reduction Company today known as  Alcoa. Héroult's process

was in production by 1889 in Switzerland at Aluminium Industrie,

now Alcan, and at Brit ish Aluminium, now Luxfer Group and Alcoa, by

1896 in Scotland.

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By 1895, the metal was being used as a building material as far away

as Sydney, Australia in the dome of the Chief Secretary's Building.

Many navies have used an aluminium superstructure for their vessels;

the 1975 fire aboard USS  Belknap that gutted her aluminium

superstructure, as well as observation of battle damage to Brit ish ships

during the Falklands War, led to many navies switching to

all  steel superstructures. The Arleigh Burke  class was the first such

U.S. ship, being constructed entirely of steel.

Aluminium wire was once widely used for domestic electrical wiring.

Owing to corrosion-induced failures, a number of f ires resulted. This

discontinuation thus i l lustrates one failed application of the otherwise

highly useful metal.

In 2008, the price of aluminium peaked at $1.45/lb in July but dropped

to $0.70/lb by December.

2.3. Old Method of Aluminium

Manufacturing

It has already been noted above that there are two essential stages in

the production of ingot aluminium from the ore which is normally

bauxite but may be alternatively clay, Lucite, alunite, nephelin or other

minerals giving rise to aluminium oxide. These two essential stages

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are the production of pure aluminium oxide from the ore and the

reduction, by fused electrolysis, of the oxide to yield pure aluminium.

In addition to these main processes there are ancil lary operations such

as the manufacture of synthetic cryolite for the molten electrolysis

bath and the production of anodes for the electrolysis cells.

Bayer Process(Old Process)

The Bayer process is the principal industrial means of refining bauxite to

produce alumina (aluminium oxide).

Bauxite, the most important ore of aluminium, contains only 30–54% alumina, Al2O3,

the rest being a mixture of silica, various iron oxides, and titanium dioxide.[1] The

alumina must be purified before it can be refined to aluminium metal. In the Bayer

process, bauxite is digested by washing with a hot solution of sodium, NaOH, at 175

°C. This converts the alumina to aluminium hydroxide, Al(OH)3, which dissolves in the

hydroxide solution according to the chemical equation:

Al2O3 + 2 OH− + 3 H2O → 2 [Al(OH)4]−

The other components of bauxite do not dissolve. The solution is clarified by filtering

off the solid impurities. The mixture of solid impurities is called red mud, and

presents a disposal problem. Next, the hydroxide solution is cooled, and the

dissolved aluminium hydroxide precipitates as a white, fluffy solid. Then, when

heated to 980°C (calcined), the aluminium hydroxide decomposes to alumina, giving

off water vapor in the process:

2 Al(OH)3 → Al2O3 + 3 H2O

A large amount of the alumina so produced is then subsequently smelted in the Hall–

Héroult process in order to produce aluminium.

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(Fig 2.2.1) Bayer Process

2.4. Modern Method of Aluminium

Manufacturing

There are two stages of Aluminium Manufacturing

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STAGE 1- Converting Bauxite to Alumina

STAGE 2- Converting Alumina to Aluminium

STAGE 1- Converting Bauxite to Alumina

STEP 1- Crushing and Grinding:   Alumina recovery begins by passing

the bauxite through screens to sort it by size. It is then crushed to

produce relatively uniformly sized material. The ore is then fed into

large grinding mil ls and mixed with a caustic soda solution ( sodium

hydroxide) at high temperature and pressure. The grinding mil l rotates

l ike a huge drum while steel rods - rol l ing around loose inside the mil l -

grind the ore to an even finer consistency. The process is a lot l ike a

kitchen blender only much slower and much larger. The material f inally

discharged from the mil l is called slurry. The resulting l iquor contains a

solution of sodium aluminate and undissolved bauxite residues

containing iron, si l icon, and titanium. These residues - commonly

referred to as "red mud" - gradually sink to the bottom of the tank and

are removed .

(Fig 2.3.1) Crushing of Aluminium

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STEP 2-Digesting:  The slurry is pumped to a digester where the

chemical reaction to dissolve the alumina takes place. In the digester

the slurry - under 50 pounds per square inch pressure - is heated to

300 °Fahrenheit (145 °Celsius). It remains in the digester under those

conditions from 30 minutes to several hours.

More caustic soda is added to dissolve aluminum containing compounds

in the slurry. Undesirable compounds either don't dissolve in the

caustic soda, or combine with other compounds to create a scale on

equipment which must be periodically cleaned. The digestion process

produces a sodium aluminate solution. Because all of this takes place

in a pressure cooker, the slurry is pumped into a series of " flash tanks"

to reduce the pressure and heat before it is transferred into " settl ing

tanks."

(Fig 2.3.2) Digestion of Aluminium

STEP 3-Settling:  Settl ing is achieved primarily by using gravity,

although some chemicals are added to aid the process. Just as a glass

of sugar water with fine sand suspended in it wil l separate out over

time, the impurities in the slurry - things l ike sand and iron and other

trace elements that do not dissolve - wil l eventually settle to the

bottom.

The l iquor at the top of the tank (which looks l ike coffee) is now

directed through a series of f i lters. After washing to recover alumina

and caustic soda, the remaining red mud is pumped into large storage

ponds where it is dried by evaporation.

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The alumina in the sti l l warm liquor consists of t iny, suspended

crystals. However there are sti l l some very fine, solid impurities that

must be removed. Just as coffee fi lters keep the grounds out of your

cup, the fi lters here work the same way.

The giant-sized fi lters consist of a series of "leaves" - big cloth fi lters

over steel frames - and remove much of the remaining solids in the

l iquor. The material caught by the fi lters is known as a " fi lter cake" and

is washed to remove alumina and caustic soda. The fi ltered l iquor - a

sodium aluminate solution - is then cooled and pumped to the

"precipitators."

(Fig 2.3.3) Settl ing of Aluminium

STEP 4-Precipitation:   Imagine a tank as tall as a six-story building.

Now imagine row after row of those tanks called  precipitators. The

clear sodium aluminate from the settl ing and fi ltering operation is

pumped into these precipitators. Fine particles of alumina - called

"seed crystals" (alumina hydrate) - are added to start the precipitation

of pure alumina particles as the l iquor cools. Alumina crystals begin to

grow around the seeds, then settle to the bottom of the tank where

they are removed and transferred to " thickening tanks." Finally, it is

f i ltered again then transferred by conveyor to the "calcination kilns." 

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(Fig 2.3.4) Precipitation of Aluminium

STEP 5-Calcination:  Calcination is a heating process to remove the

chemically combined water from the alumina hydrate. That's why, once

the hydrated alumina is calcined, it is referred to as  anhydrous

alumina. "Anhydrous" means "without water."

From precipitation, the hydrate is f i ltered and washed to rinse away

impurities and remove moisture. A continuous conveyor system delivers

the hydrate into the calcining kiln. The calcining kiln is brick-l ined

inside and gas-fired to a temperature of 2,000 °F or 1,100 °C. It slowly

rotates (to make sure the alumina dries evenly) and is mounted on a

ti lted foundation which allows the alumina to move through it to

cooling eqipment. (Newer plants use a method called fluid bed

calcining where alumina particles are suspended above a screen by hot

air and calcined.)

The result is a white powder l ike that shown below: pure alumina. The

caustic soda is returned to the beginning of the process and used

again.

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(Fig 2.3.5) Calcination of Aluminium

STAGE 2- Converting Alumina to Aluminium

Smelting:   In 1886, two 22-year-old scientists on opposite sides of the

Atlantic,  Charles Hall  of the USA and Paul L.T. Heroult  of France, made

the same discovery - molten cryolite (a sodium aluminum fluoride

mineral) could be used to dissolve alumina and the resulting chemical

reaction would produce metall ic aluminum.  The Hall-Heroult

process remains in use today.

The Hall-Heroult process takes place in a large carbon or graphite l ined

steel container called a " reduction pot". In most plants, the pots are

l ined up in long rows, called potl ines.

The key to the chemical reaction necessary to convert the alumina to

metall ic aluminum is the running of an electrical current through the

cryolite/alumina mixture.  The process requires the use of direct current

(DC) - not the alternating current (AC) used in homes. The immense

amounts of power required to produce aluminum is the reason why

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aluminum plants are almost always located in areas where affordable

electrical power is readily available. Some experts maintain that  one

percent of al l the energy used in the United States is used in the

making of aluminum.

The electrical voltage used in a typical reduction pot is only  5.25 volts,

but the amperage is  VERY high - generally in the range of  100,000 to

150,000 amperes or more. The current f lows between a

carbon anode(positively charged), made of petroleum coke and pitch,

and a cathode (negatively charged), formed by the thick carbon or

graphite l ining of the pot.

When the electric current passes through the mixture, the carbon of

the anode combines with the oxygen in the alumina. The chemical

reaction produces metall ic aluminum and carbon dioxide. The molten

aluminum settles to the bottom of the pot where it is periodically

syphoned off into crucibles while the carbon dioxide - a gas - escapes.

Very l itt le cryolite is lost in the process, and the alumina is constantly

replenished from storage containers above the reduction pots.

The metal is now ready to be forged, turned into alloys, or extruded

into the shapes and forms necessary to make appliances, electronics,

automobiles, airplanes cans and hundreds of other familiar, useful

items.

Aluminum is formed at about 900 °C, but once formed has a melting

point of only 660 °C. In some smelters this spare heat is used to melt

recycled metal, which is then blended with the new metal.  Recycled

metal requires only 5 per cent of the energy required to make new

metal. Blending recycled metal with new metal al lows considerable

energy savings, as well as the efficient use of the extra heat available.

When it comes to quality, there is no difference between primary metal

and recycled metal.

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The smelting process required to produce aluminum from the alumina is

continuous the potl ine is usually kept in production 24 hours a day

year-round. A smelter cannot easily be stopped and restarted. If

production is interrupted by a power supply fai lure of more than four

hours, the metal in the pots wil l solidify, often requiring an expensive

rebuilding process. The cost of building a typical, modern smelter is

about $1.6 bil l ion.

Most smelters produce aluminum that is 99.7% pure - acceptable for

most applications. However, super pure aluminum (99.99%) is required

for some special applications, typically those where high ducti l ity or

conductivity is required. It should be noted that what may appear to be

marginal differences in the purities of smelter grade aluminum and

super purity aluminum can result in significant changes in the

properties of the metal.

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(Fig 2.3.6) Smelting of Aluminium

3. RESOURCES USED IN

ALUMINIUM

MANUFACTURING

There have been essential ly no fundamental changes in process or

equipment since the beginning of the industry, although great

improvements have been made in the design of the furnaces and in the

electrodes.

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3.1. Raw Materials

The aluminium industry has been oriented with reference to the raw

materials bauxite, electric power, coal and caustic soda used in the

preparation of alumina for electrolysis, and carbon for the manufacture

of electrodes.

One metric ton of aluminium requires three to four horse-power years

(roughly equivalent to 20,000-25,000 kWh) of electrical energy, four to

f ive tons of bauxite, four to f ive tons of coal, a substantial amount of

water, about one ton of caustic soda (of .which the greater part is,

however, recoverable) and 0.5-0.6 tons carbon electrodes--that is to

say, in all more than ten tons of material plus a large quantity of

power. These are optimum figures under the best production conditions

with the best materials.

Labour requirements depend upon the scale of operations, in the

largest plants being about 5 to 6 man-hours per ton of alumina

produced and about 30 man-hours per ton of aluminium produced from

alumina. In smaller plants the labour may work out as high as double

this f igure.

With the above starting point it is apparent that aluminium can be

produced at the cheapest rate where the combination of cheap power,

good bauxite and cheap coal exist: since there is, however, no region

in the world where these three raw materials are coincident--in other

words, since no one country enjoys sufficient preferential advantages

to grant it a monopoly--the process of aluminium production based on

the Hall-Héroult process and on bauxite has involved one main

dichotomy, it having been found more economical to produce the

alumina for reduction dose to coal rather than to bauxite, whilst the

electrolytic reduction plants must, of course, be located close to the

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source of power. This dichotomy immediately introduces the factor of

transport, which becomes a further vital "raw material."

3.1.1. Availability of Power

In the early days of the aluminium industry power was almost

universally construed in terms of water power; hydro-electric energy

was then becoming an important factor in industrial economy and

strenuous efforts were made by the major industrial nations to secure

favorable locations and development of water power. At that time the

modern conception of electric power stations with alternative sources

of energy based on alternative fuels such as powdered coal, mineral

oi l , or even peat on a large scale (as used in certain regions of the

U.S.S.R.) was non-existent and hydraulic power represented a unique

advantage in the newly developing electrolytic process industries in

which aluminium was one of the major products. Capital investment in

hydraulic power stations varied greatly with the natural resources but

viewed as a long-term project it was always a good economic

proposition and in favorable instances . it provided remarkably cheap

power, as for instance, on the Saguenay river or at Niagara. In Europe,

conditions were, of course, at their best in Switzerland and Norway.

Since the situation of the source of power is nearly always unfavorable

for the location of a major industrial undertaking, power derived from

hydraulic stations was commonly relayed to selected centers which

could serve as the loci for assembly of the other raw materials and for

the erection of works and their concomitant towns and satell ite

industries.

These factors, with their geographic and economic background, are

complementary to the technical aspects of the use of water power in

the cheapest manner. An important consideration in all electrolytic

processing is the necessity for a continuous supply of electric energy

(in contrast with part-time uti l ization for engineering and municipal

requirements, e.g., for l ighting and heating) which implies a very high

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load factor. From this angle the needs of an electrolytic industry such

as aluminiumare both favorable and unfavorable as regards power

consumption: on the one hand, the power undertaking can count on

disposing of an otherwise unused capacity and on the other hand, it is

essential that the production .cost of the energy shall be low and the

power supply steady. A hydro-electric system normally expects to

provide for commitments for a certain amount of f irm power which has

to be based upon the lowest level of water during the year, taking into

account normal storage provision. Due to irregular volume of water

f low, both annual and seasonal, the minimum may be exceeded during

certain years and for certain months in every year and this excess

power, known as secondary power, has been uti l ized successfully in the

electrolytic industry and to some extent in the aluminium industry. In

this industry, however, most of the big producers have their own power

undertakings or own at least a controll ing interest in them.

3.1.2. Coal & Fuel

Fuel is one of the most important materials consumed in the production

of aluminium, being essential to f ire the kilns in the production of

alumina. Unti l the outbreak of the second world war, the only fuel used

in the manufacture of alumina was coal; but during the war years and

particularly in America, some shift has taken place towards other fuel

sources, for example, natural gas, oi l or electricity may also be used in

the production processes according to the situation of the works

relative to a supply at a favorable cost.

In Europe the most favorably situated countries from the angle of coal

supply for alumina production were Germany and England, with Italy as

a runner-up. In the United States a good supply of high-quality coal is

available in the State of Washington and there is plenty of lower grade

bituminous coal for most of the plants producing alumina, although oil

was substituted for coal at four or f ive plants distributed through the

States in recent years.

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(f ig 3.1) Coal

3.1.3. Caustic Soda

In general the aluminium industry has concerned itself only with the

mining of bauxite and the manufacture of alumina and metall ic

aluminium and has not entered into the production of the caustic soda

uti l ized in the alumina process. Both the processes used on a large

scale for the production of caustic soda, namely the soda-ammonia and

the electrolytic process,. Belong essential ly to the heavy chemical

industry and large quantities are available at a low price. The raw

material for caustic soda production, which is chiefly soda ash, is

available in abundant supply. This material also enters directly into the

process of alumina production by the Bayer method in some instances.

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(f ig 3.2) Caustic Soda

3.1.4. Electrode Carbon

The anodes used in the electrolysis cells are prepared from a mixture

of petroleum coke and ordinary pitch, roughly in 70-30 ratio, but this

f igure varies according to the quality of the coke. Petroleum coke is a

by-product of petroleum refining, being actually the residue after the

volati le and fuel oi ls have been withdrawn. Before it is ready for

service for the production of anodes. The crude materials from the

petroleum sti l ls have to be calcined and this process requires special

plant and consumes one-fifth to one-quarter of the weight of crude

coke processed in fuel supply.

(f ig 3.3) Electrode Carbon

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3.1.5. Bauxite

Chemically, bauxite consists of hydrated aluminium oxide together with

oxides of iron si l icon, t itanium and other elements, and varying small

percentages of clay and other si l icates. Physically, bauxite can be as

hard as rock or as soft as mud. Its colour may be buff, pink, yellow,

red, white or various combinations of colours.

Bauxite is the ore that is converted to alumina and then to aluminium.

Australia is the world's leading producer of bauxite, producing 33% of

the world’s bauxite production in 2007 (63 MT). Its deposits are among

the largest in the world (estimated at more than seven bil l ion tones of

commercial grade ore),

Second only to Guinea. Bauxite is mined by open cut methods in the

Northern Territory, Queensland and in Western Australia.

(f ig 3.4) Bauxite

3.1.6. Alumina

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Alumina is made from bauxite at refineries in the Northern Territory,

Queensland and Western Australia. Around two and a half tonnes of

bauxite are needed to produce one tonne of alumina. Australia is the

world's leading producer of alumina, producing 30% of global output.

The majority of the world's alumina production is made by a process

known as the “Bayer Process”, which was developed in 1889 by German

scientist, Karl Bayer. This complex refining process produces a fine

white anhydrous aluminium oxide powder, known as alumina AL203.

The “Bayer Process” begins by grinding the bauxite and mixing it with

caustic soda to form slurry. The aluminium component is dissolved out

of the bauxite in a series of steam-heated digesters. The l iquid passes

into large settl ing tanks where the impurities, including sand and iron

oxide, settle out. The aluminate l iquor is f i ltered, cooled and “seeded”

with crystals of aluminium hydroxide to aid precipitations of alumina

hydrate. The hydrate is then fi ltered, washed and passed through

rotating calcinating kilns operating at high temperatures to produce

the white powder known as alumina.

More than 90% of the world's alumina production is used to make

aluminium. Small quantities are also used as an abrasive, absorptive

and refractory in the chemical ceramics and glass-making industries.

(f ig 3.5) Alumina

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3.2. Main Chemical & Mineralogical

Constituents of Bauxite

TAA (Total Available Alumina – 42-43%)

This is very much important for cost effective production in Alumina

Refinery.

Gibbsite (Al203 3H20- 32-34%)

Gibbsite is crystall ine euhedral with variable grain sizes. It is more

easily soluble in Caustic Soda (< 135 oC) and the most preferred

bauxite. % Gibbsite of TAA should be 80-82%. When the bauxite is

predominantly Gibbsitic, the digestion can be carried out at relatively

low temperature i.e. Atmospheric Digestion (A.D.) at 105 oC and Low

Pressure Digestion (L.P.D.) at 140-145 oC, Energy consumption is less in

case of A.D. or L.P.D.

Boehmite (Al203 H20 – 9-11%)

It is soluble in Caustic Soda at higher temperature and pressure. %

Boehmite of TAA should be 18-20%. For boehmite bauxite high

temperature digestion at 240-245 oC is preferred. Energy consumption

in alumina refinery is higher in case of such bauxite. It is tough to

digest and result in low extraction efficiency.

Diaspore (0.8-1.2%)

It is soluble in caustic soda at very high temperature (greater than

300oC) and pressure. It is not preferred.

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Silica (3-4%)

Caustic loss in alumina refinery is basically due to reaction of si l ica,

alumina and caustic leading to formation of desil icated product (DSP,

Sodalite or Can crinite) which is insoluble during digestion process.

Kaolinite (Al4 (Si4O10) OH)

It is reactive part of si l ica causes loss of both alumina and caustic soda

as well contaminate product and forms scales.

Quartz (SiO2 – 1.0%)

Non reactive part of si l ica but at high temperature a certain amount of

quartz can also dissolve in the l iquor.

Iron (15 – 18%)

Iron in bauxite is essential ly insoluble during digestion process and

increases mud load. Iron is distributed in 60:40 proportions as

Hematite and Goethite in most of Indian Bauxite.

Goethite (Fe203 H20- 5-7%)

Goethite in Iron should be 30-35%. Goethite causes settl ing problem

and alumina locked in Fe-minerals is diff icult to extract. Unreacted

Goethite can be colloidal in nature and result in settl ing trouble. It

also acts as an active seed for auto precipitation in the mud circuit.

Higher Goethite/Hematite ratio wil l result in higher potential for this

problem.

Hematite (Fe203 – 9-10%)

Higher proportion of hematite in iron is good for settl ing.

Vanadium (V205 – 0.25-0.30)

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It is a valuable by product from bayers alumina refinery. More

vanadium dissolves at high temperature digestion and if not removed

forms harmful Vandate compound.

Gallium (Ga)

Found in traces (15 to 150 ppm) Bayer l iquor has been found world

richest source of gall ium.

Organic Matters (0.02-0.5%)

increases impurity level and affect alumina precipitation. Organic

matter as organics is highly soluble in Bayer l iquor and forms sodium

oxalate.

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4. PROCESSES WHICH TAKES

PLACE IN THE

MANUFACTURING OF

ALUMINIUM

4.1. Hammer Mill

The purpose of Hammer Mil l area is to reclaim and grind 3” – 4”

Bauxite to ½” size (95%) by Hammer Mil l and transport it to Bauxite

day bin.

There are three Hammer Mil l circuits each containing two

Hammer Mil ls namely: -

Hammer Mil l # 1 & 2 - Sweetening Bauxite

Hammer Mil l # 3 & 4 - Normal Bauxite

Hammer Mil l # 5 & 6 - Normal Bauxite

Hammer Mil l # 7 - Normal Bauxite

Page | 27

Equipment provided in each circuit are Bauxite Feeder (Reclaim &

Emergency) 2 No’s, Hammer Mil l Feed Conveyor, Magnet & Metal

detector on Conveyor, Vibrating Screen, Hammer Mil l , Hammer Mil l

discharge Conveyor, Sump Pump in Conveyor Pits, Dust collection

system (Bag Filters), Weight-o-meter on Hammer Mil l discharge

Conveyor (Old circuit only), Air Blasters.

Hammer Mil l Description: It contains a high-speed rotor turning a

cylindrical body. The shaft is horizontal. Here the bauxite is dropped

into the top of the casing and gets broken by set of swing hammers

pinned to a rotor disk. Bauxite shatters into pieces, which fly against a

l iner inside the casing and breaks into small fragments. This in turn is

further crushed by the hammers and pushed through cage bars, which

covers the discharge opening.

The crit icality of the operation is to maintain the size of the hammer

mil l discharge, it should be +1/2” up to 5%. But in the raining season it

increases to 10%.

For health and safety purpose chemicals and water are spread in the

unloading area at the Wagoner end, for suppressing the fine dust of

bauxite.

Trouble shooting practices are for oversize product, abnormal sound

coming from Hammer Mil l , abnormal vibration in Hammer Mil l , bauxite

not coming through feeders to feed end conveyor of Hammer Mil l ,

misalignment of Conveyors and hammer Mil l tripping frequency.

Page | 28

(f ig 4.1) Hammer Mil l

4.1.1. Specification of Hammer Mill

Motor capacity-270 hp

No. of hammer -80

Grinding capacity-150 t/h

Load current-47.7 amp

Type – f lood coupling

4.1.2. Operation of Hammer mill During Rainy Season

Due to wet, bauxite operation becomes diff icult as plugging of feed and

discharge chute, etc. occurs.

To avoid diff iculty fol lowing steps are taken-

1\2’’cage bars are replaced by 1’’.

1\2’’ bypass screen is replaced by 1’’.

Feed rate is reduced

Page | 29

There are eight numbers of ball mil ls, which operate at different

capacities. The 1/2" size of bauxite from the hammer mil l is stored in

the day bin. Then with the help of belt conveyor it is feed into the ball

mil l . The load shell of belt conveyor takes care of feed rate of the ball

mil l . Out of eight ball mil ls, seven ball mil ls always remain in l ine. Here

wet grinding with the spent l iquor in the ball mil l is not done. For wet

grinding maximum speed of ball mil l should be 70-75% of its crit ical

speed.

4.1.3. Critical Speed

The crit ical speed is the theoretical speed at which the centrifugal

force acting on a ball mil l in contact the mil l shell at the height of its

path equals the force on it due to gravity.

The expression for crit ical speed is-

NC = 76.6/D1 / 2

Where NC = Crit ical Speed, D = Diameter of ball mil l in feet.

Ball changed inside a ball is 50% of its volume that is called bed

height which gives maximum capacity. The discharge of the ball mil l is

solid 50% with –200 mesh size (60-65%). From the discharge point of

view ball mil ls are of two types. In the first type the discharge of ball

mil l is passed through the simple sieve of –200 mesh size. The

underflow goes to the desil ication unit where as overflow again goes

into the ball mil l . In the other type the discharge of the ball mil l is

passed through the sump tank to the primary cyclone. The overflow of

the PC goes to secondary cyclone feed tank (SCFT) & underflow goes to

the ball mil l . From the SCFT slurry is feed to the secondary cyclone.

The overflow of the SC goes to the sump tank. The density of the

Page | 30

discharged slurry is maintained at1.82 kg/l. The description of

different ball mil ls is given below.

BALL

MILL NO

BAUXITE

RATE(T/HR)

LIQUOR

RATE

MOTOR

H.P.

TYPE

1 15 9-10 350 Overflow

2 30-32 16-18 900 Internal Grate

3 30-32 16-18 900 Internal Grate

4 40 17-19 1400 Overflow

5 50 23-25 1400 Overflow

6 50 23-25 1400 Overflow

7 70 28-30 2000 Overflow

8 50 25 1400 Overflow

(Chart 4.1)

The product quality of ball mil l plays an important role in the digestion

process. So the size of the ball & speed of the mil l is very crit ical. Lots

of sound pollution is there in ball mil l area. The level of sound isnearly

105 dB. Some of the area of troubleshooting is slurry density, which

becomes sometimes low. This can be removed by regular monitoring of

the ball mil l discharge.

Page | 31

4.2. Desilication

The product of the ball mil l (bauxite slurry) of al l ball mil ls is passed

through a desil ication heater where slurry is preheated up to 98°C by

means of steam of 2.4 kg/cm 2 pressure & temperature of 130 °C. This

slurry is passed through six no of desil ication tanks to provide holding

time of 10-12 hrs. Ball mil l no 4, 5, 6, 7&8 are used for normal bauxite

grinding & ball mil l 1, 2& 3 for the grinding of Gibbsitic bauxite. The

main reaction-taking place in the tank is

5[Al2O3 .2SiO2 .2H2O]+2Al(OH)3+12NaOH

2[3Na2O.3Al2O3 .5SiO2 .5H2O] + 9H2O

The temperature maintained for this reaction is nearly 98 °C. The slurry

first comes in the desil ication tank no 1, and then it is passed through

two heaters.

After passing through heater it goes to desil ication tank number 2, 3,

4, 5 & 6, where temp maintained is around 98°C and holding time is

12hrs to 14hrs. The maintained temperature and holding time is the

crit ical parameters for the desil ication tank. The main problem of the

desil ication area is the scaling in desil ication heaters. Life of heater is

30 days. After every 30 days heater is being cleaned with chemicals.

Efficiency of heater is around 60 % & level maintained in desil ication

tank is 90%. We can increase the service l ife of heater by using some

other metal instead of mild steel, l ike Al al loys, which are less

corrosive than mild steel. Also the speed of the slurry which passes

through heater is important parameter to be governed. The desil ication

product gets stick to the tank wall, which are removed after every 5 to

6 months. The main problem of desil ication area is the low pick up of

desil ication heater temperature.

Page | 32

4.3. Digestion

Two methods are in use for the digestion of bauxite-

Namely “One stream” and “Two stream” process.

One Stream: bauxite-l iquor slurry is heated indirectly to the digestion

temperature by passing through in series connected autoclaves .

Two Stream: the digesting l iquor is divided into two unequal stream.

The main stream (80-85%) is heated step-by-step in tubular heat-

exchangers with steam from flash tanks. The remaining l iquor is led to

the wet grinding of bauxite and fed.

LTD DIGESTION: In old technology 3 units of digestion are used to

digest alumina in caustic And each units are high temp type digestion

but in modern technology two type of digestion is used. First one is low

temp digestion and second is high temp digestion. This modification in

process is done on the basis that try hydrated alumina digests at lower

temp and pressure in caustic at 145 oC and12 bar while in high temp

digestion it digests at 245 oC and 36kg/cm2.

In this preheated slurry is fed to low temp digestion where it mixed

with 600psi and 290 gpl caustic and temp and pressure is maintained

Page | 33

at 145 oC and 12 bar and digested slurry is fed to pressure decanter

where we use flocculant to increase settl ing rate .and overflow of P D is

fed to flash tank while under f low is fed to 3 units of high temp

digestion using geho pumps.

(f ig 4.2) HTD Circuit Diagram

Page | 34

240-242OC

TO SAND CLASSIFIER

230 - 240 M3/Hr

DILUTION FROM

WASHER

70-80M3/Hr

190-205 M 3/Hr

80-82 o C

GEHO PUMPBOOSTER PUMP

LIQUOR HEATER

40% BAUXITE SLURRY FROM BALL MILLS

45-55 M3/Hr

TO BOILER 14-15 TPH

CONDENSATE FLASHING

30 psi STEAM TO WASHER 1.4-2.4 TPH100 psi 3.4-3.6 TPH

104-105OC 40% BAUXUITE

SLURRY DENSITY 189

TEMP. 95-96OC

DESILICATOR HEATER

78-80OC

CAUSTIC LIQUOR FROM EVAPORATION C255-

258gpl

155-165 M3/Hr

64-66 o C

CONDENSATE PUMP

BLOW OFF PUMP

106-108 OC

FLASH VAPORS FLASH TANKS

SLURRY HEATERS

CONDENSATE POTS

260-270 OC STEAM

42.5 Kg/Cm2

#2

DIGESTION FEED TANK

DIGESTER

ISH

ISH COND. POT

123

CONDENSATE TO BOILER

45 - 50 M 3/Hr

DISILICATOR TANK

8

9 268 7 5 4 3 1

6 5 4 3 2 17

BLOW OFF

TANK

#2 #2 #2 #2 #2 #2#1 #3 #4 #6 #7#5

240-242OC

Crea ted by : PANKAJ PANDEYH T D CIRCUIT DIAGRAM

HTD Digestion

Underflow of P D of LTD is pumped into the H T digestion having two

streams and direct heating system through slurry heaters where

Alumina content of bauxite is dissolved into caustic solution at 242 oC

temperature and 36 Kg per sq. cm pressure, in digestion I and II .

Digestion I I I is of single stream and indirect steam reaction occurring in

digestion is

Al2O3.3H2O + 2NaOH 2420C & 36Kg/cm2 2NaAlO2 + 4H2O

The above reaction is an endothermic reaction and requires heat for

reaction to take place. Two methods are in use for the digestion of

bauxite, namely “two stream” and “one stream” process.

Two streams is a process in which the digesting l iquor is divided into

two unequal streams. The main stream (80-85%) is heated step-by-step

in tubular heat exchangers with steam from flash tanks. The remaining

l iquor is led to the wet grinding of bauxite and fed finally to the

digesters. This method is used in digester I & I I . In one stream method

bauxite l iquor slurry is heated indirectly to the digestion temperature

by passing through in series connected autoclaves. This method is used

in digestion I I I .

To push the bauxite slurry into the mixing tee Geho pump is used. The

Geho pump has a diaphragm, which sucks and creates the adequate

pressure. Geho pump is used for high pressure and low flow. The

capacity of the Geho pump of digestion area I I and I is 17.75-35.5

M3 /Hr. and 133.8-153.9M 3 /Hr. respectively.

Page | 35

Caustic addition (290gpl)

67-70 oC

Bxt-Slurry

(f ig 4.3) Caustic Addition

The spent l iquor comes in the test tank where the concentration of the

caustic is maintained at 290 gpl by the addition of fresh caustic 900

gpl. Then with the help of pumps it is sent to the low-pressure heater

and medium pressure heater, before it comes to the mixing tee. From

the mixing tee it (Bxt-slurry l iquor) goes to the process slurry heater

where temperature is increased to 193 oC. Then it goes to ISH, where

Page | 36

Test tankPrimary

Booster

Charge Pump 20-22Kg/m3 Low Pressure

Heater

Booster

PumpMedium Pressure

Injection

Pump 69Kg/cm2Mixing Tee

Process Slurry

Indirect Steam Heater

193oC

Live Steam

Digesters 35 kg/cm2

230oCLive steam from Boiler at 42 bars

Tail Valve 35Kg/cm2

Flash Tank 1 to 7Blow OffBlow Off

PumpCLARIFICATIO

l ive steam is used to raise the temperature up to 230 oC. And finally the

mixture is passed through the digesters at 242 oC and 36Kg/cm 2

pressure. Holding time in digesters is 2hrs. The digested boehmite

bauxite slurry is f lashed in successive stages of f lash tanks and finally

the pressure is brought down near to atmosphere.

Sweetening is done in f lash tank 2, 3 or 4 at temp. 150 oC. in

sweetening process slurry is heated from 65 oC to 100oC by means of

2.4Kg/cm2 steam. And this slurry is fed to desired flash tank inlet l ine

in digestion unit I , I I , I I I through centrifugal pumps where it mixes with

the digester normal bauxite slurry. The Gibbsitic bauxite has higher

solubil ity at lower temperature (140 oC) resulting in increasing the

finished A/C ratio and enhanced rate of alumina dissolution. The main

advantages of this process are in increased rate of alumina dissolution

only through marginal addition steam requirement and higher l iquor

productivity.

The major operating parameters are steam temp., digestion temp.,

slurry flow, digestion pressure, steam pressure, back pressure

(pressure of control valve), heater temp. The main crit icality of the

operation is scaling in the heater pipe, vessel and pipelines, leakage

through joint, vent, pipeline, gaskets and welding joints. Scaling in the

pipe is removed by caustic cleaning. And crit ical equipments are

charging pump, booster pump, injection pump, Geho pump, heater and

agitator.

The heat recovery system of the digestion area is heater temp. Pick-up,

l ine and vessel insulation, steam line safety valve and use of steam

trap system. The safety equipment is pressure safety valve; if pressure

wil l increase it wil l open to release the pressure. Other arrangements

are facil it ies for tripping of booster pump, Geho pump, digestion slurry

control valve and injection pump.

Page | 37

Condensate generated from the process slurry flashing in series of

f lash tanks is pumped to boiler house for its heat recovery and

returned back to clear water header, used in refinery in pump gland

sealing and cooling tower make up.

The condensate management includes flash tank level to control. Some

of the preventions require during the operation are restricting moisture

to enter into the air, no choking of valve, smooth air supply, restricting

flow of wrong signals from control room, condensate contamination,

slurry leakage and slurry coming out from relief tank bottom. The whole

process of digestion area is DCS controlled. We can see and control al l

parameters through DCS.

4.4. Clarification

Purpose: To efficiently separate sand contents and red mud from

Pregnant Liquor, to remove maximum fine suspended mud solid

particles from Pregnant Liquor, to recover physical soda of red mud by

counter current washing and maximum possible economical recovery of

bound soda of mud by means of causticization process, f i ltration of red

mud slurry Techno-economically and environmentally viable disposal of

red mud.

Page | 38

4.4.1. HRD(High Rate Decanter)

Inside HRD sedimentation process takes place where separation of mud

and pregnant l iquor take place.

In HRD, the feed slurry is admitted tangential ly into the unit (feed well)

at a depth of 2 – 3 feet below the surface of l iquid. On entrance, the

slurry spread rapidly through the cross section of the settler. Liquor

than flows upward to be withdrawn at the overflow launder, and the

solid settles down to the bottom. The flocculent used for the settl ing of

solid particles are polymers (Flomina Al99F).The upper zone is free

from particles and increases sl ightly in solid below the entrance of the

feed. Particles settle in this zone by free settl ing. Below the dilute

zone is a compression zone in which the concentration of solids

increases rapidly with distance from the boundary between the zones.

The rakes, which operate in the bottom of the compression zone, tend

to break the flock’s structure and compact the underflow to a solid

contact. The main purpose of the rake is to keep mud pump able, to

bring mud towards pumping end and to remove trapped l iquor between

mud portable (underflow). In practice a clear overflow can be obtained

if the upward velocity of the l iquid in the dilute zone is less than the

minimum terminal velocity of the solid at al l point in the zone. Upward

velocity of the l iquid is directly proportional to the overflow rate. If

solid wil l be more then load on the rake wil l increase and in that case

dosing of f locculent is to be reduced.

Components of HRD are drive assembly, feed well, cable torque

mechanism and overflow launder.

Flocculants: It consolidates the underflow mud slurries. It neutralizes

the charges on the slurry, which in turn agglomerates to form flocs

each containing many particles.

Page | 39

4.4.2. Sand Classifier

The sand from the pregnant l iquor separates in cyclone by cyclonic

effect and comes in screw conveyor where the leaching of soda from

sand takes place and the sand collected in hopper is disposed off

through dumpers. The overflow of f irst screw conveyor is collected in

1 s t wash tank from where it is pumped in one of the settler in l ine. The

overflow of second screw goes either in settler or washer.

4.4.3. Washer

This system leaches out caustic from mud slurry and disposes l iquor

free mud. There are 7 Washers in one series. HRD underflow is

introduced into the 1 s t Washer feed tank. Polymer is added with the

feed. A counter current washing by the hot water takes place here.

The overflow of Washer # 1 is the final product of washing operation

and contains recovered caustic. Dilution is pumped to digestion area in

order to maintain L to P concentration. Wash water temperature is

maintained around 90 oC into last washer for effective leaching of soda.

Mud from last washer is pumped to drum fi lter directly. The other

streams received in washer circuit are drum fi ltrate l iquor, f ine seed

wash caustic zed l iquor, sand classif ier drained l iquor & fi lter press

washed cake.

The diameter of the washer is 125’ and they are 7 in number. Other

equipment associated with the washer is overflow pump, wash water

tank & underflow pump, dilution tank & dilution pumps and drum fi lter

heater (3 in nos).

Page | 40

4.4.4. Drum Filter

Filtration is the removal of solid particles from a fluid by passing the

fluid through a fi ltering medium or septum on which the solids are

deposited.

Drum fi lter is a continuous vacuum fi lter i .e. f i ltration is done under

vacuum. Drum fi lter is a drum rotating about a horizontal axis with a

portion of drum submerged in the slurry to be fi ltered in a vat.

Agitators in the vat keep the slurry thoroughly mixed. The drum

surface is divided into number of longitudinal sections comparatively

shallow in depth, each of which is connected by pipes to a common

stationery fi lter valve mounted on the end of one of the trunions on

which the drum rotates. The fi lter valve is connected to a vacuum

system. The drum suction is equipped with a perforated plate, which

forms the outer cylindrical surface of the drum and supports the fi lter

medium. The drum is then covered with a suitable fi lter cloth by

lateral caulking.

As the drum rotates through the slurry in the tank, the l iquid is sucked

through the cloth into the drum piping and out through the fi lter valve.

The solids are trapped on the surface of the fi lter cloth, forming what is

known as fi lter cake and deposit on the outer surface of the rotating

drum, where it is subjected to water spray (Temp. is 90 oC). Air is then

passed through the cake by the suction as the rotation cycle

progresses, to remove residual cake moisture as much as possible.

As the fi lter section rotates towards the cake discharge point the fi lter

valve shuts off the vacuum on that particular section ready to

discharge. Mud cake is f inally discharged to hopper after being led off

the drum over a small rol ler and scarped by a string scrapper. When

the mud hopper gets full , the mud is emptied out in dumper stationed

below the hopper. The mud is then disposed off in Mud Yard. The

product of the drum fi lter should be of below specifications:

Solid after f i ltration - 70%

Page | 41

Leachable Soda - 1.0%

4.5. Precipitation

Precipitation of alumina tri-hydrate from seeded caustic aluminate

l iquor is an important step of the Bayer’s process for production of

alumina from bauxite. The importance of precipitation step arise from

the fact that by and large it determines the ultimate characteristics of

the product (calcined alumina) and much of the success of the plant’s

performance depends on this aspect.

During precipitation precipitate of alumina tri hydrate gets deposited

on seed crystals as well as on new nuclei that get formed during the

precipitation cycle. The new nuclei also grow by fresh deposition of

precipitate. There are four main mechanisms taking place during a

precipitation process. They are nucleation, crystal growth,

agglomeration and crystal breakage.

Nucleation is a special condition characteristic by the spontaneous

generation of very fine crystals, of submicron sizes and as a

consequence there is a rapid increase in the production of sub sieve

particles. Controlled nucleation is very necessary to produce just the

required quantity of new seed crystals for maintaining the precipitation

Page | 42

process in a balanced state. Uncontrolled nucleation along with in

sufficient agglomeration and /or crystal growth would lead to seed

balance getting disturbed and this can’t be tolerated especially in a

plant that produces coarse sandy alumina.

Growth is the mechanisms by which particles are enlarge by the

addition or deposition of newly precipitated alumina tri hydrate into the

original crystals. The conditions required here are more or less similar

to what are required to favor agglomeration, which is also a process of

enlargement of particles. Large particles are produce predominately by

growth are dense and strong and distinct from those produced by

agglomeration, which are generally weak.

Agglomeration is also a mechanism whereby larger particles are

produced. But as distinct from the mechanism of straight growth, in

this case the enlargement is achieved by smaller particles coll iding and

then getting cemented together by precipitation of hydrate between

the coll iding particles that is by interstit ial deposition of hydrate.

In addition to the above mentioned mechanisms there is yet a forth

one, crystal breakage which could occur at any stage in a precipitation

process. It is a mechanism not directly caused by the precipitation

process but all the same influences the end results of the process. Due

to the shear forces created by agitation and turbulence, either the

newly deposited particles are sheared-off or the particles are

continuously created. Thus during a precipitation process two opposing

mechanisms must proceed in such a way as to permit the circuit to

remain in balanced state, that is, just the amount of coarse particles to

yield a final product of acceptable granulometry and just the amount of

f ine particles to provide adequate surface area for further

precipitation, while achieving maximum possible yield from the l iquor.

And also it is equally important for the operator to ensure that as the

particles are enlarged the final material attains adequate strength to

withstand breakdown during subsequent operations.

Page | 43

Our aim in alumina plant precipitation area is to achieve maximum

yield with coarse aluminum tri-hydrate particles and lesser f inishing

A/C ratio. Amount of alumina tri-hydrate extracted per l iter of pregnant

l iquor in nothing but yield. Yield=L to P caustic (L to P A/C- Spent A/C)

4.5.1. Hydrocyclones

There are three batteries of cyclones: Product cyclone, Coarse cyclone

and Swing cyclones. The Swing cyclone is the stand by for both Product

and Coarse. One battery consists of 24 cyclones with feeding

arrangement, under f low and over f low piping. The product cyclone

under flow is collected in Product cyclone under flow tank and then

pumped to product deliquoring fi lter. The coarse cyclone under flow is

collected in coarse cyclone under flow tank and PT under flow is also

pumped into the tank. The slurry from this tank is pumped to coarse

deliquoring fi lter Mts and a volume of 1440 Cu.mts. The feed to all PT’s

are fed from cyclone over f low tanks and is controlled and adjusted by

online flow meters and C/V. The overflow goes to associated ST’s.

PT Under flow is pumped by PT Under flow pumps to coarse seed

cyclone under flow tank. There are three sets, each set contain two

pumps.

(f ig 4.4) Cyclone Separator

Page | 44

4.5.2. Secondary Thickeners

There are four ST’s in plant. Normally three are inl ine and one is in

stand by mode. The tank diameter of ST’s is 12.8 Mts and volume of

1560 Cu.mts. The overflow of all ST’s goes to TT. ST Underflow is

pumped by ST Under flow pumps to Fine seed slurry tanks. There are

four sets, each set contain two pumps.

(f ig 4.5) Thickener

4.5.3. Terminal Thickeners

There are two TTs installed in plant, normally one in l ine and one is

stand by. The thickeners have diameter of 38 Mts and operating volume

of 6700 Cu. Mts. The TT feed is combined overflow from the three ST’s

in l ine and spent l iquor from fi ltration area. The over f low is collected

in a collection box, Where flocculent is added to achieve good settl ing

and low over f low solids. The TT’s are equipped with a rake mechanism.

The torque and motor current are monitored on a regular basis. The

over f low of TT goes to spent l iquor tank.

Page | 45

4.6. Calcinations

Calcination is another important step in the Bayer’s process, where

alumina tri-hydrate is calcined to the final form, alumina possessing

certain desired characteristics. This step is essential because for the

conduct of electrolysis al l material added to the cells must be

completely free from water whether chemically bound or absorbed on

the surface.

Thermal dehydration of alumina tri-hydrate starts at 180-290 0C and is

practically over at about 600 0C. However, alumina produced at these

temperatures has a highly activated surface and as such tends to

absorb considerable amounts of moisture when in contact with the

atmosphere. Hence the dehydration step has to be followed by

energetic heating to temperature of more than 1100 0C at which its

property of absorbing moisture from the atmosphere is reduced to a

level considered safe enough for the operation of electrolytic cells.

In HINDALCO there are two types of calciner. These are as fol lows:

1. Gas Suspension Calciner (GSC) 2. Flash Calciner

The main components in the G.S.C.System comprises of:

Page | 46

Hydrate Feed System

Ventury Type Flash Drier

2-Stage Cyclone Pre-heater(P01-P10&P02)

Gas Suspension CalcinersPO4.

Disengaging Cyclone or Separating Cyclone (PO3).

4-stage Cyclone Cooler (C01, C02, C03 &C04).

Secondary Fluid Bed Cooler (K01&K02).

Oil Heating System

Dedusting and Dust Recycling System.

Gas suspension Calciner

Preheated and partly calcined alumina at 300-400 0C enters the reactor

in a direction parallel to the conical bottom. Preheated air for

combustion is introduced at about 800 0C through a single pipe in the

bottom of the reactor. The velocity of the air at the inlet is sufficient to

ensure proper suspension of the particles over the entire cross-section

of the reactor at ful l and partial capacity.

After a few seconds’ exposure to 1100-1250 0C, the calcined alumina is

entrained from the reactor by the gaseous mixture of water vapor and

combustion products.

Page | 47

(f ig 4.6) Calciner

4.7. Evaporation Unit

Evaporation Technology: Evaporation is the process in which the

change of state from liquid to gas can occur at any temperature up to

boil ing point. At any one time, a variable population of molecules in a

l iquid wil l have sufficient energy to escape into the atmospheric. The

rate of evaporation rises with increased temp. Because as the mean

kinetic energy of the l iquid’s molecules rises and so wil l and so wil l be

the number of molecules possessing enough energy to escape. In

Page | 48

general,the lower the boil ing points, the faster the rate of evaporation,

though this also depends on the latent heat.

The Economy of Evaporation Unit depends upon the number of factors:

Mass Flow Specific Heat T 60

Evaporation Rate(TPH) =

Latent Heat 1000

Working of Evaporation Unit

In the plant during process water is directly added to Caustic or

indirectly as steam. So the Caustic concentration goes down. To

increase the concentration of Caustic, the water content inside the

Caustic should be removed, so three Evaporation Units are set. In all

Evaporation units, process is almost similar. Diluted Caustic comes to

unit, and goes to Barometric Condenser in which it creates vacuum,

then goes to preheater in which caustic is heated. This heated caustic

goes in f irst evaporator. In evaporators barometric condenser already

creates vacuum. From first to last evaporator caustic goes in the same

fashion and in last evaporator steam is used to heat the caustic, this

caustic then travels in reveres manner means from last to f irst

evaporator and vacuum is also goes on increasing from last to f irst

evaporator. Due to these effect caustic f lashes inside evaporator and

produces hot condensate and it is then cool down. The hot condensate,

which is formed inside evaporator, is used to heat incoming caustic

from first to last evaporator. So in this manner the consumption of

steam is less as compared to the evaporation rate achieved.

Page | 49

(f ig 4.7) Evaporator

Page | 50

5. GENERAL USE OF

ALUMINIUM

Auminium is the most widely used non-ferrous metal . Global production

of aluminium in 2005 was 31.9 mill ion tonnes. It exceeded that of any

other metal except  iron (837.5 mil l ion tonnes). Forecast for 2012 is 42–

45 mil l ion tons, driven by rising Chinese output.

Aluminium is almost always alloyed, which markedly improves its

mechanical properties, especially when tempered. For example, the

common aluminium foils  and beverage cans are alloys of 92% to 99%

aluminium. The main alloying agents are

copper, zinc, magnesium, manganese, and si l icon (e.g.,  duralumin) and

the levels of these other metals are in the range of a few percent by

weight.

Some of the many uses for aluminium metal are in:

Transportation (automobiles, aircraft,  trucks, rai lway cars,

marine vessels,  bicycles, etc.) as sheet, tube, castings, etc.

Packaging (cans, foi l , etc.)

Construction (windows, doors, siding, building wire, etc.)

A wide range of household items, from cooking

utensils to baseball bats, watches.

Street l ighting poles, sail ing ship  masts, walking poles, etc.

Outer shells of consumer electronics, also cases for equipment

e.g. photographic equipment.

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Electrical transmission l ines for power distribution

MKM steel and Alnico magnets

Super purity aluminium (SPA, 99.980% to 99.999% Al), used in

electronics and CDs.

Heat sinks for electronic appliances such as transistors and CPUs.

Substrate material of  metal-core copper clad laminates used in

high brightness LED l ighting.

Powdered aluminium is used in  paint, and in pyrotechnics such

as solid rocket fuels and termite.

Aluminium can be reacted with hydrochloric acid or with  sodium

hydroxide to produce hydrogen gas.

A variety of countries,

including France,  Italy, Poland, Finland, Romania,  Israel, and the

former Yugoslavia, have issued coins struck in aluminium or

aluminium-copper alloys.

Some guitar models sports aluminium diamond plates on the

surface of the instruments, usually either chrome or

black. Kramer Guitars and Travis Beanare both known for having

produced guitars with necks made of aluminium, which gives the

instrument a very distinct sound.

Sustainabil ity of Aluminium in Buildings

6. SUMMARY

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Although it can be seen that the environmental impact of Aluminium

production is far from negligible,  the impact of bil l ions of people

constantly burning fossil fuels as a means of power and transport is far

more serious.

As long as every effort is made to replace / replant any environment

destroyed as a result of Bauxite mining, the biggest ecological cost of

Aluminium production is creating the power needed to refine it.   Indeed

the Aluminium Oxide which the Hydrogen generator produces could be

turned back into Aluminium.  Hopefully in the near future the energy to

do this wil l come from an environmentally friendly process (i .e. not

nuclear or fossil fuel power).   Methods already exist to extract energy

from the sea and the wind.   Methods may already exist (although not

publicly) to tap into the vast abundances of energy which exist

everywhere - after al l there is far more energy in one gram of matter

than all the power stations in the world produce in a year!

So the water / aluminum engine is not an ideal solution while we sti l l

produce electricity by non environmentally friendly means, but it is an

essential design which can give us some breathing (l iterally!) space

unti l our scientists come up with a method of tapping into the abundant

energy which surrounds us everywhere.

If you have the intell igence and knowledge to tackle these and other

crit ical problems then it is your duty to do so.   After al l what is the

point in l iving out your l i fe ignoring the bigger picture, only for your

descendants and species to die out when the planet that supports them

is poisoned beyond repair.  

7. GLOSSARY

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Agglomerate To from or collect in to rounded mass.

Air Blasters A strong gust or Air gust of wind.

Autoclave A strong Pressurized steam treated vessel.

Anthracite A dense shiny cold that has high carbon Content.

Barometric An instrument for measuring atmospheric Pressure.

Boster A device for increasing power or effectiveness.

Contaminates To make pure or under contact of mixture.

Colloidal A particulate matter so dispersed

Coarse A rough, especially to the touch

Cyclones A violet rotating windstorm

Condensate A substance formed by condensation

Clarification To make clear by removing impurities

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Calcinations To heat all substance of high temperature but

below melting point

Decanter A vessel used for decanting

Draft A current of air in enclosed area

Dilution Process of making weaker or less concentrated

Dehydration The process of removing water

Digestion The process of breaking down

Flomia Very aggressive solvent

Flashes To move or proceed rapidly

Gibbsite A mineral consisting of Hydrated alumina oxide.

Gheo Pump Piston Pump

Goethite A mineral consisting of hydrated alumina oxide

Hematite A brick- Red mineral that is ore of iron

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Hopper A funnel shape Container

Quartz A very hard mineral compound of si l ica

Sieve A utensil of wire mesh

Torque A turning or twisting force

Wagon A l ight Automotive transport vehicle.

8. References

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Professional or Personal web site

Aluminium Production Procedure- Oct 6, 2011-

http://anon99.tripod.com/water_engine/aluminium_production2.html

Features of Aluminium Oct 7, 2011-

http://www.rocksandminerals.com/aluminum/process.htm

Aluminium properties & Information Oct 7, 2011-

http://en.wikipedia.org/wiki/Aluminium

Aluminium Manufactures , Dealers, Exports Oct 8, 2011-

http://www.maharashtradirectory.com/catalogue/Alumina.htm

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