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CHAPTER -1

HISTORICAL PROFILE

1.1 Natural Occurrence

Magnesium oxide is a naturally-occurring white hygroscopic solid also known as magnesia (the name derives

probably from Magnesia, a district of Thessaly in Greece) and it is also the second most abundant compound in

the earth's crust. The majority of magnesium oxide produced today is obtained from the processing of naturally

occurring minerals such as magnesite (magnesium carbonate), magnesium chloride rich brine, and seawater.

Magnesite (MgCO3) is an ore for magnesium production and the source of a range of industrial minerals. Where

pure, magnesite contains 47.8% magnesium oxide and 52.2% carbon dioxide. [1, 2]

World magnesite reserves are shown in Table-1. In addition to those estimates shown, magnesite deposits occur

in Spain, Pakistan, and the Sudan. Deposits of less than 1 million metric tons (Mt) were reported in Mexico,

Iran, the Philippines, Australia, Egypt, and the Republic of South Africa. Small deposits also have been noted in

Cuba, Sweden, Norway, Poland, Scotland, France, Italy, Kenya, and Tanzania. [1]

Table-1: World magnesite reserves in million metric tons of contained Mg [1]

Country Reserves

China 750

Russia 650

North Korea 450

Other countries 420

Turkey 65

Brazil 45

India 30

Greece 30

Slovakia 20

Austria 15

Spain 10

United States 10

Serbia and Montenegro 05

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1.2 Traditional Applications

a) Magnesia cement uses in masonry construction is ancient. It was used primarily as a mortar component

and stabilizer for soil bricks. Magnesia has also been identified in the Great Wall of China and other

ancient landmarks and Roman cement is reported to have contained high levels of Magnesia.[3]

b) Ancient European artisans used a timber frame with magnesium oxide infill in constructing homes and no

gaps are visible in these 800 year old walls that still remain in use.[3]

c) Magnesium Oxide is widely used primarily as wallboard alternative to conventional gypsum-based drywall

but with much improved characteristics such as fire resistance, weather ability, strength, resistance to

mould.[3]

1.3 Manufacturers in India [4]

Elite Chemicals, Bhavnagar, Gujarat.

Magnesium Products (P) Ltd., Virgo Nagar, Bangalore.

Canton Laboratories P. Ltd., Mumbai.

Aroma Agencies, Okhla, New Delhi.

Bhavani Chemicals, Ahmedabad.

1.4 Early Industrial Applications [3]

Magnesium oxide has been used for many different things. Its applications include everything from being a

laxative to providing a protective coating in plasma displays. A list of its early industrial applications is given

below:

a) Cement production

b) Insulators in industrial cables

c) Laxatives

d) Desiccant

e) Refractory material

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CHAPTER -2

APPLICATIONS

2.1 Various grades of Products

The thermal decomposition of natural magnesite into magnesia and carbon dioxide gas in the temperature range

from 600 oC up to 3000 oC results in different forms or types of magnesium oxide being produced , and as a

result, the MgO produced may have different chemical properties. The various grades of Magnesium oxide are

discussed below and their properties are dependent on the mode of origin of the original magnesite, the

mineralogical composition of the natural magnesite and the calcination temperature chosen. [5-6]

a) Calcined Magnesia: It is used for agricultural and industrial applications, e.g., as a feed Supplement to cattle,

fertilisers, electrical insulations, industrial fillers, and in flue gas desulphurisation. [6]

b) Dead burned Magnesia: This is used almost exclusively for refractory applications in the form of basic bricks

and granular refractories. Dead burned magnesia has the highest melting point of all common refractory oxides

and is the most suitable heat containment material for high temperature processes in the steel industry. Basic

magnesia bricks are used in furnaces, ladles and secondary refining vessels and in cement and glass making

kilns. [6]

c) Fused Magnesia: Fused magnesia is superior to dead burned magnesia in strength, abrasion resistance and

chemical stability. Major applications are in refractory and electrical insulating markets. Producers of fused

magnesia commonly fall into one of two categories: those producing refractory grades and those producing

electrical grades. Few producers serve both markets on a mainstream basis. [6]

d) Refractory Grade Fused Magnesia: The addition of fused magnesia grains can greatly enhance the

performance and durability of basic refractories such as magcarbon bricks. This is a function of a higher bulk

specific gravity and large periclase crystal size, plus realignment of accessory silicates. Due to its excellent

corrosion resistance, refractory grade fused magnesia is used in high wear areas in steel making, e.g., basic

oxygen and electric arc furnaces, converters and ladles. [6]

e) Electrical Grade Fused Magnesia: Fused magnesia is also used as an electrical insulating material in heating

elements. Although electrical grades of fused magnesia have very tight specifications, they do not necessarily

require the highest MgO contents or densities. Impurities such as sulphur and iron are particularly undesirable,

but the product should contain sufficient silica to enhance its electrical properties. [6]

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Table-2: Properties of different Grades of Magnesium Oxide. [5]

Property Caustic Calcined

MgO

Hard Burned

MgO

Dead Burned

MgO

Fused MgO

Surface area 1-200 m2g-1 0.1 to 1.0 m2g-1 < 0.1 m2g-1 Extremely small

surface area.

Crystal Size 1-20 µm Characterized by

moderate crystalline

size.

Characterized by

large crystal size

(30 to 120 µm).

Extremely large

crystal size, single

crystal weighs 200

g and more.

Acid solubility Readily soluble in

dilute acids.

Readily soluble

only in

concentrated acids.

Reacts very slowly

with strong acids.

Reacts very slowly

with strong acids.

Hydration

Behavior

Readily absorbs

water vapor and

carbon dioxide from

the atmosphere to

form basic

magnesium

carbonate.

Hydrated rapidly in

cold water.

Coverts to

Mg(OH)2 upon

exposure to

moisture or water.

Hydrates very

slowly to form

magnesium

hydroxide.

Does not readily

hydrate or react

with CO2.

Does not readily

hydrate or react

with CO2.

Chemical

Reactivity

Moderate to high

chemical reactivity.

Characterized by

low chemical

reactivity.

Characterized by

very low chemical

reactivity.

Characterized by

very low chemical

reactivity.

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2.3 Applications

Table-3: Various uses of Magnesium Oxide. [8]

Fields Uses

Abrasives

As a binder in grinding wheels

Animal feed

supplement

Source of magnesium ions for chickens, cattle and other animals

Boiler (oil-fired)

additives

Raises melting point of ash generated to produce a friable material that is easily

removed; reduced corrosion of steel pipes holding steam as well as sulphur emissions

into the environment

Boiler feed water

treatment

Reduces iron, silica and solids

Chemicals Starting point for the production of other magnesium salts such as sulphate and nitrate

Coatings Pigment extender in paint and varnish

Construction Basic ingredient of oxychloride cements used for flooring, wallboard, fiber board, and

tile

Electrical Semi-conductors; heating elements insulating filler between wire and outer sheath

Fertilizers Source of essential magnesium for plant nutrition

Foundries Catalyst and water acceptor in shell molding

Glass manufacture Ingredient for specialty, scientific and decorative glassware and fiberglass

Insulation Light, flexible mats for insulating pipes

Lubricating oils Additive to neutralize acids

Pharmaceuticals Special grades of magnesium hydroxide, oxide and carbonate are used in antacids,

cosmetics, toothpaste, and ointments

Plastics manufacture Filler, acid acceptor, thickener catalyst and pigment extender

Refractory and

ceramics

Basic ingredient in product formulations for the steel industry

Rubber compounding Filler, acid acceptor, anti-scorch ingredient, curing aid, pigment

Steel industry Annealing process; coating for grain-oriented silicon steel used in electrical transformers

Sugar refining Reduces scale build-up when used in juice clarification and precipitation

Sulphite wood

pulping

Source of base for cooking liquors

Uranium, gallium &

boron

Precipitation initiator by acid neutralization processing

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CHAPTER -3

ECONOMIC SCENARIO

3.1 World Scenario

Until mid-2008 the global magnesium oxide market had been tightening, because of continued global growth in

the main consuming industry refractories for steel and cement production for dead-burned magnesia (DBM) and

fused magnesia (FM). In the same period Chinese exports, which had dominated the market in previous years,

started to decrease. In addition, environmental applications had gained ground for caustic-calcined magnesia

(CCM). Accordingly, companies around the world announced plans for capacity expansions, or a return to

production activities in dead-burned magnesia that had been given up years before, when inexpensive Chinese

imports had made these activities unattractive. However, as the economic downturn started in late 2008,

consumption started to decrease and projects were postponed or came under review. China dominated the global

market with its exports covering roughly one-fourth of the global market outside China.

The majority of the magnesium oxide produced worldwide is consumed as refractory magnesia. The primary

use of refractory magnesia is in furnace linings in the iron and steel industry. The second major market for

refractory magnesia is in the production of cement. However, global cement production grew in the 2007–2009

period with Asia, and to a lesser extent Africa and the Middle East, making up for the losses in the European,

North American and CIS markets. [9]

According to a new market report published by Transparency Market Research "Magnesium Oxide Market-

Global Industry Analysis, Market Size, Share, Trends, Analysis, Growth and Forecast, 2012 - 2018," the global

magnesium oxide demand was worth USD 18.3 million in 2011 and is expected to reach USD 31.2 million in

2018, growing at a CAGR of about 8.7% from 2013 to 2018. Asia-Pacific dominates the global market in terms

of demand and is expected to be the most promising market in the near future. [10]

3.1.1 Plant Capacity and location

Present demand of Magnesia in India is 4,03,000 tons per annum as in 2010-2011 and expected to

reach a level of 6,22,000 tons in 2016 with a growth rate of 9%.Production of magnesia on the other

hand is much less as companies producing Magnesia in India can only produce 2,30,000 tons of

magnesia per year.

As a result of this demand and supply gap, India has to import high quality Magnesia from China,

Russia, North Korea and Turkey.

The Chemical plants which manufacture Magnesium Oxide from Magnesite ore have nearly the plant

capacity between 10,000 tons/yr to 70,000 tons/yr. So we decided to set the plant of Magnesium Oxide

with the plant capacity of 20,000 tons/yr.

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Figure-1 : World Consumption of Magnesium Chemicals 2009. [9]

The global demand for magnesium oxide has been surging owing to its application in furnace linings,

construction & ceramics and precision industries such as aerospace, advanced electronics and others.

Volatility in market prices, higher cost of raw material and health issues are major concerns for the

magnesium oxide industry.

The magnesium oxide market by application in terms of revenue is dominated by the refractory

material in the furnace linings segment. The refractory market by revenue is growing at a CAGR of

8.5% from 2013 to 2018. Following this, the market for construction & ceramics is also witnessing

significant growth. In terms of volume, the refractory market is growing with a CAGR of 7.3% for the

forecast period between 2013 and 2018. [9]

3.2 Asia-Pacific Scenario

Asia-Pacific is the market leader for magnesium oxide, growing at a CAGR of 8.9% by revenue and a

CAGR of 7.7% by volume, both from 2013 to 2018. Europe and North America although occupying a

smaller market share are growing steadily and growth is expected to be robust in these markets over the

next five years. In Asia-Pacific, China and India are the most attractive markets and are expected to

keep the region in the forefront in the magnesium oxide market. Some of the key players of the market

2% 2%

75%

5%

3% 8%

1%

4%

Others Asia / Oceania- 2%

Japan- 2%

China- 75%

Africa / Middle East- 5%

CIS- 3%

Europe- 8%

Central / South america- 1%

North America- 4%

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are Martin Marietta Magnesia Specialties Inc., American Elements Company, Sigma Aldrich, Sky

Spring Nanomaterials, Inframat, and others. [9]

Table-4: World MgO annual production capacity (×103 ton), year 2000. [1]

Country and company name Caustic Calcined

Magnesia

Dead Burned

Magnesia

Australia:

Causmag Ore Co. Pty. Ltd.

Queensland Magnesia Pty. Ltd.

(QMAG

18

30

-

120

China:

China Metallurgical Import &

Export Liaoning

Magnesite Co.

Dashiqiao Guantun Magnesite

Mine

Liaoning Magnesite and

Refractories Corp. of China

Yingkou Qinhua Magnesite Corp.

-

-

200

-

200

130

20

350

India:

Almora Magnesite Ltd.

Burn Standard Co. Ltd.

Dalmia Magnesite Corp.

Himilayan Magnesite Ltd.

Khaitan Hostombe Spinels

Magnesite & Minerals Ltd.

-

5

60

-

-

-

24

42

-

11

27

45

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CHAPTER -4

PROPERTIES OF MAGNESIA

4.1 Physical and Chemical Properties

Table-5: Various Properties of Magnesium oxide. [11-12]

4.2 Reactivities and Incompatibilities [13]

Violent reaction with halogens, chlorine trifluoride, bromine pentafluoride, phosphorous pentachloride, strong

acids. May ignite and explode when heated with sublimed sulphur, magnesium powder, or aluminium powder.

Phosphorus pentachloride and magnesium oxide react with brilliant incandescence.

Violent reaction or ignition on contact with inters halogens (e.g., bromine pentafluoride; chlorine trifluoride).

Chlorine trifluoride reacts violently, producing flame, with magnesium oxide.

Colour/Form White, very fine powder

Chemical Formula MgO

CAS 1309-48-4

Molecular Weight .0403044(kg/mole), 40.3044(g/mole)

Odor Odorless

Boiling Point 3,873 K , 3,600 oC

Melting Point 3,098 K, 2825 oC

Density 3600 kg/m3, 3.6 gm/cm3

pH 10.6 (saturated aqueous solution)

Solubility Soluble in acids and ammonium salt solutions.

Insoluble in ethanol.

In water,0.086 kg/m3 at 303 K

Heat of fusion 77.4 kJ/mol at 2915 K

Spectral Property Index of refraction: 1.7355 at 589×10-9m; 1.7283 at

750×10-9m

Heat of formation 601.7 kJ/mol at 298 K

Thermal Conductivity 45-60 W.m-1.K-1

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4.3 Bio-Environmental Characteristics

4.3.1 Human Exposure Studies [13]

Examination of 95 workers exposed to an unspecified concentration of MgO dust revealed slight irritation of the

eyes and nose, Conjunctivitis, nasal catarrh, and coughing up discoloured sputum was cited after industrial

exposures, but even when such exposures doubled serum magnesium as compared to normal concentrations, no

systematic effects were noted among these workers; however, serum calcium concentrations were elevated.

Four volunteers were exposed for 1-9 min to freshly generated magnesium oxide fume at 410, 420, 430, or 580

mg/cu.m. Although slight reactions were observed after less than10 min of exposure at these concentrations, it

was believed that increased exposures would lead to more severe reactions. Inhalation of magnesium oxide

produced a febrile reaction and a leukocytosis, similar to metal fume fever, in the exposed subjects analogous to

that caused by inhalation of zinc oxide.

4.3.2 Health hazard information [13]

Potential Health Effects:

Eye: Causes mild eye irritation.

Skin: Causes mild skin irritation.

Ingestion: May cause irritation of the digestive tract. May be harmful if swallowed.

Inhalation: May cause respiratory tract irritation. May be harmful if inhaled.

Acute health effects:

Breathing magnesium oxide can irritate the eyes and nose.

Exposure to magnesium oxide can cause mental fume fever. This is flu like illness with metallic taste in

the mouth.

Chronic health effects:

Cancer hazard

Reproductive hazard

4.4 Work place exposure limits [13]

OSHA: the legal airborne permissible exposure limit (PEL) is 15 mg/m3 averaged over an 8 hr work shift.

ACGIH: the recommended exposure limit is 10 mg/m3 averaged over an 8 hr work shift.

(OSHA - occupation safety and health administration)

(ACGIH – American conference of governmental industrial hygienist)

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4.4.1 Work place control practices [13]

The following workplace practices are recommended that can help to reduce hazardous exposures:

Where ever possible automatically transfer magnesium oxide from drums or storage tanks.

Wear protective work clothing.

Wash the clothing thoroughly immediately after exposure to magnesium oxide or just after the work shift.

Do not take contaminated clothes to home; family members might also get contaminated.

Eye wash fountains should be installed in the work place for emergency use.

Emergency shower facility for skin exposures.

Use a vacuum or wet method for cleaning up the work place, do not dry sweep.

4.5 Handling and storage [13]

Prior to working with magnesium oxide we should be trained on its proper handling and storage:

Magnesium oxide must be stored to avoid contact with Chlorine Triflouride, Phosphorous Pentachloride,

Performic Acid and Bromine Penta flouride since Violent Reactions Occur.

Magnesium oxide is not compatible with strong acids (such as Hydrochloric, Sulphuric and Nitric);

Oxidizing Agents and Powdered Metals.

Store in tightly closed containers in a cool, well-ventilated area away from moisture.

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CHAPTER -5

MANUFACTURING PROCESSES

5.1 Introduction to Manufacturing Processes [14]

The standard methods for producing MgO are described below:

1. Seawater and underground deposits of brine are important sources of MgO. The production of MgO

from seawater follows the same process as that used for a typical brine source. The sea or brine water is

treated with hydrated lime [Ca(OH)2] to precipitate magnesium hydroxide [Mg(OH)

2].

Reaction: Ca(OH)2

+ MgCl2

Mg(OH)2

+ CaCl2

2. A process, used worldwide, involves mining, crushing, sizing, and calcinations of natural magnesite.

MgO is produced by driving off carbon dioxide:

Reaction: MgCO3 heat MgO + CO

2

3. Another way to extract magnesium from brine is to mix brine with calcined dolime (CaO.MgO)

obtained from dolomitic limestone to produce an aqueous suspension containing magnesium hydroxide

[Mg(OH)2].

Reaction: CaCl2 + MgCl

2 + (CaO.MgO) + 2H

2O 2 Mg(OH)

2 + 2 CaCl

2 + H

2O

The magnesium hydroxide obtained is then precipitate, filtered, dried, and calcined to produce

magnesia (MgO).

Reaction: 2 Mg(OH)2 heat 2MgO + 2 H

2O (steam)

4. Dead Sea Periclase Ltd., on the Dead Sea uses yet another method for the production of Magnesium

Oxide. A concentrated brine stream from the Dead Sea is sprayed into the reactor at about 17000C. the

brine is thermally decomposed into Magnesium Oxide and Hydrochloric Acid.[15]

5.2 Brief Description of Processes

1) Manufacture of magnesium oxide from sea water by Premier Periclase [16]

The process involves formation of a magnesium compound from the reaction of dissolved magnesium salts in

sea water with calcium hydroxide, followed by further reactions. The process is continuous, with the raw

materials being fed in continuously and the magnesium oxide being continuously produced.

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Feedstock (raw materials, preparation)

The feedstock is slaked lime (calcium hydroxide) and purified sea water. These have to be produced from the

raw materials, which are limestone, fresh water and sea water. The limestone and fresh water are used to

produce the calcium hydroxide, which is then reacted with the purified sea water to produce magnesium

hydroxide.

Treatment of raw materials

About 6 million litres of fresh water are used each day. Sulphuric acid is used to lower the pH of the fresh water

to about 4. The water is then passed downwards through a tower against a rising current of air which strips off

carbon dioxide. About 1000 tonnes of limestone are used each day. The limestone is very pure calcium

carbonate (over 98%), and is crushed and washed before being heated in a lime kiln to form quicklime (calcium

oxide):

CaCO3 → CaO + CO2

This reaction is carried out in a rotary kiln at 1500 0C. Fresh water is then added to the quicklime to produce

slaked lime (calcium hydroxide):

CaO + H2O → Ca(OH)2

Rate and product yield (Temperature and Pressure variables, catalysts etc.)

Catalysts, or pressures other than atmospheric pressure, are not required for any of the reactions involved in the

Premier Periclase process. There are no reversible reactions involved, so no compromises in relation to striking

a balance between reaction rates and product yields are needed. In the reaction of sea water with calcium

hydroxide:

Reaction: MgCl2 + Ca(OH)2 → CaCl2 + Mg(OH)2

The conditions have to be chosen which will result in the production of large crystals of magnesium hydroxide,

which will settle and filter more easily. To do this, the following is done:

• Dilution of the incoming sea water with spent sea water.

• Seeding with heavy slurry of magnesium hydroxide.

The reaction in which magnesium hydroxide is converted into magnesium oxide is carried out in a Multiple

Hearth furnace. A high temperature (900oC), which favours a higher rate of reaction, is used. In the furnace,

there are three stages:

• Removal of the remaining water from the wet filter cake.

• Reaction to form MgO at 900oC

• Cooling

14 | P a g e

The yield of magnesium oxide is approximately 2 g from each litre of sea water, given that sea water contains

approximately 30 g of sodium chloride per litre, it is quite clear that sea water is an abundant source of

magnesium as well as of salt.

Co-products (Separation, Disposal)

The main co-product is calcium chloride, which is in solution in the spent sea water. This water also contains

excess calcium hydroxide, and therefore has to be neutralised before it is discharged to the sea. There are at

present no commercially profitable co-products from the Premier Periclase process.

Costs (fixed costs, variable costs, cost reduction by use of heat exchangers, catalysts, recycling and selling).

The fixed costs (i.e. those which have to be paid regardless of the rate of production) include labour costs, plant

maintenance and plant depreciation. The variable costs (i.e. those which depend on the rate of production)

include the cost of electricity, fuel and materials, and the costs of waste disposal. Manufacture of periclase is a

high-energy process. Apart from the heat needed to maintain high temperatures in the lime kiln, the multiple

hearth furnaces, and the sintering kilns, there are also the costs of pumping, lighting, transport, crushing etc.

Because catalysts are not used and there are no commercially profitable co-products, and recycling does not play

a part in the process, savings cannot be achieved in any of these ways. However, cost reduction can be achieved

in a number of other ways. For example, the kilns and furnaces are designed to allow a switch over between oil

and natural gas as price and other considerations dictate. Another cost reduction is achieved by reclaiming heat

from waste gases and using it to preheat the intake air to the lime kiln.

15 | P a g e

Process Outline

Fig-2: Block diagram of production of MgO from sea water

LIMESTONE CRUSHING

WASHING

LIME KILN – CaO

FORMED

SLAKING OF LIME

DEGASSED FRESH

WATER

SEA WATER INTAKE

SEA WATER RESERVOIR

DEGASSING

CLARIFICATION

REACTION OF SEA WATER WITH CALCIUM HYDROXIDE – MAGNESIUM HYDROXIDE FORMED

THICKNERS

FILTERATION AND WASHING

STORAGE AND SHIPPING

16 | P a g e

2) Manufacture of Magnesia through Calcination of Magnesite [17]

Conversion of Crude Magnesite into Burnt Magnesite

Most of the mined magnesite is converted directly into magnesium oxide by burning (calcining). This is done by

burning the lumps in horizontal rotary kilns, normally by direct firing with oil or gas. Grades with very low

sulphate content are obtained by burning with wood. The temperature and duration of the calcinations procedure

determines the respective reactive properties (grades) of the magnesium oxide.

Decomposition of magnesium carbonate to form magnesium oxide and carbon dioxide begins at a temperature

slightly above 400 °C.

Reaction: MgCO3 MgO+CO2 (temperature greater than 400oC)

Calcination temperatures of between 500 and 1,000°C produce magnesium oxide with a relatively high specific

surface area and remarkable reactivity.

Raw material

The raw materials are mined from open pit and underground mines and the first size reduction and preliminary

treatment is achieved during the mining operation. Standard processing units are used for the preparation of raw

materials such as crushing, grinding or milling and sieving plants. For preparing magnesite, heavy sludge

preparation is sometimes used. Raw materials are sometimes washed in order to exclude impurities.

Furthermore, permanent magnet separators are used for magnetic preparation tasks.

General process description

Magnesia is produced by firing the treated and prepared natural stone raw material in a multiple hearth furnace

(MHF), a shaft kiln or a rotary sintering kiln. The chemical reaction can be expressed as follows:

MgCO3 + Heat MgO + CO2

The chemical reaction is endothermic, depends on a high firing temperature and is very energy intensive. The

input of energy is high (ΔH = +113 kJ/mol). The process starts at a temperature of around 550 – 800 °C where

the magnesite is de-acidified and carbon dioxide is released. The result from this reaction is the product caustic

calcined magnesia (CCM). In the next process step, CCM is further heat treated at temperatures of between

1600 to 2200 °C in one or two phases to sintered or dead burned magnesia. The temperatures, along with the

duration of the treatment, are the decisive controlling factors in obtaining a product which is well crystallised

and which can achieve a high density.

17 | P a g e

Fig-3: Process diagram of magnesia production using dry process route

3) Production of Magnesia from Brine and Calcined Dolime [18]

First, naturally occurring brine is mixed with both calcined dolime and water to produce an aqueous suspension

containing magnesium hydroxide and calcium chloride:

Chemical Reaction:

CaCl2 + MgCl2 + CaO.MgO + 2H2O 2Mg (OH)2 + 2CaCl2 + H2O

Brine Dolime Magnesium Hydroxide Calcium Chloride

18 | P a g e

The magnesium hydroxide and calcium chloride produced from this reaction exist together but in two distinct

physical states: magnesium hydroxide is formed as solid particles while the calcium chloride is dissolved in the

liquid or watery phase .Gravity is used to separate the solids from the liquid in the aqueous suspension since

magnesium hydroxide is heavier than water. Milk of magnesia is another name for magnesium hydroxide.

Magnesium hydroxide slurry (white) is pumped over to another holding tank and allowed to settle. The blue

colour indicates the watery layer containing dissolved magnesium chloride that has formed above the settled

magnesium hydroxide particles. The bottom solids are then filtered to remove any remaining water and given a

series of water washes to remove chlorides from the material. This results in a damp filter cake which can be

seen dropping off the lower roller of the press about waist high to the operator. The washed filter cake is finally

directed to a source of heat, such as a rotary kiln where it is thermally decomposed (calcined) to produce

magnesium oxide.

Chemical Reaction: 2Mg(OH)2 + Heat 2MgO + 2H2O (steam)

Several types of kilns can be used in the calcination step. Calcination not only converts magnesium hydroxide to

magnesium oxide, but is also the most important step for determining how the final product will be used.

Fig-4: Block diagram of production of magnesia from brine and calcined dolime.

19 | P a g e

5.3 Comparison between different manufacturing processes

Table 6: Comparison between different manufacturing processes

Basis of comparison MgO from sea water MgO from magnesite MgO from Calcined

Dolime

Raw Materials Slaked lime

Purified Sea Water

Magnesite Ore Calcined Dolime

Brine

Catalyst No No No

Recycle No Yes Yes

Temperature Condition 9000C 500-10000C 10000C

By Product Non-Profitable - -

Purity Pure Pure (90 -98%) Purest

Advantage and

Disadvantage

Water needs to be

neutralized before

discharge.

High energy process.

MgO produced has

relatively high surface

area and remarkable

reactivity.

Co-incinerating waste

products can be used as

fuel.

Low Boron content.

High density (3.35-3.40 *

103 kg/m3)

Correct CaO/SiO2

content.

20 | P a g e

CHAPTER -6

SELECTED PROCESS

6.1 Manufacture of Magnesia by Calcination of Natural Magnesite (MgCO3) [17, 19]

6.1.1 Magnesite

The term ‘magnesite’ denotes natural magnesium carbonate (MgCO3). Magnesite is partially derived from rock

formation materials and it mostly occurs together with dolomite and forms deposits, which are generally very

old (>400 million years old). Generally, two types can be distinguished, differing mainly in their iron content as

follows:

Spar Magnesite (Type Veitsch, Iron Rich with 4 – 6 %)

Gel Magnesite (Type Kraubath, With A Low Iron Content of <0.5 %).

6.1.2 Fuels

In 2007, the following different types of fuels were mainly used in the firing process:

Natural gas

Petroleum coke (pet coke)

Heavy fuel oil.

However, depending on the availability and economics, other fuels are also used, such as anthracite or coal.

There is a good relationship between the efficiency and the price of petroleum coke. However, because of the

high thermal energy demand and the high temperatures required for the production process, it is necessary in

some cases to add other combustibles. Air is usually added to the combustion process, when high temperatures

are required for the sinter or dead burn process.

6.2 General description of the production process of magnesia from magnesite (naturally sintered/dead burned

magnesia)

Magnesia is produced by firing the treated and prepared natural stone raw material in a shaft kiln or a rotary

sintering kiln and further cooling the obtained stock in coolers. The chemical reaction can be expressed as

follows:

Chemical Reaction: MgCO3 MgO + CO2

The chemical reaction is endothermic, depends on a high firing temperature and is very energy intensive. The

input of energy is high (ΔH = + 118 kJ/mol).

21 | P a g e

Fig-5: Process scheme of the natural pathway for magnesia production

Production of DBM through Rotary Kiln

The magnesite lumps are reduced to the size of 4 cubic inches in primary crushers. To reduce this size further,

they are passed through secondary crushers where the magnesite is crushed to one cubic inch size. These pieces

shall then be screened to obtain uniform sizes of magnesite pieces which are put in the rotary kiln. This is

essential to facilitate the magnesite pieces to get uniform heating in the rotary kiln. In rotary kiln, one end is

called the 'feeder end. At this end almost uniform sizes of magnesite pieces are fed. The other end of the kiln is

called 'burning end' from where, with the help of furnace oil, heating is done. At this end, the heat will be at a

very high temperature, around 1500 0C to 1800 0C and it will go on slowly decreasing through the rotary

cylinder. The burning temperature depends on the purity of the magnesite concerned - high iron magnesite can

be sintered at close to 1500 0C but a very high pure magnesite must be sintered at temperatures in excess of

1800 0C. In order to reduce the cost of dead burning, sometimes, a small quantity of iron oxide is added as a

fluxing agent or the impurities present themselves form fluxing agents and dead burning is thus effected at a

lower temperature, about 1500 0C. The magnesite pieces coming from the feeder end get heated gradually

through their passage in the rotary cylinder towards the burning end. The passage time for the magnesite from

the feeder end to the burning end is normally six hours. This time can be altered depending upon the rotation of

the kiln, quality of the input, etc. The burned magnesite is collected from the burning end and cooled in coolers.

The production process flow chart of DBM through rotary kiln is given in Fig: 6.

22 | P a g e

Process Flow Sheet

Fig: 6 - Process flow diagram of manufacture of magnesia from MgCO3.

23 | P a g e

Production of DBM through Shaft Kiln

The process of DBM production in shaft kiln using furnace oil is the same as that of calcination in shaft kiln

with the only difference that enormous heating is used here. As a very high temperature is required for the

conversion of raw magnesite into DBM, heating is done from 6 points at the middle of the kiln instead of two as

in the case of calcination process.

Note: The DBM produced in shaft-kiln and rotary kiln vary in quality, chemical properties, reactivity, etc, also,

the cost of production differs in these two methods. Even though the cost of production of DBM in rotary kiln is

slightly higher than that of shaft kiln, due to the requirements of higher quality of the end product, the shaft kilns

are being replaced by rotary kilns in the Indian magnesite Industry.

Consumption of raw materials (unprocessed magnesite) and water

At high temperatures, magnesite (MgCO3) is thermally decomposed to magnesia (MgO) and carbon dioxide

(CO2). Taking as a basis the molecular weight of magnesite (84.31 g/mol), the following quantities of magnesia

and carbon dioxide result from the decomposition as shown in table-7.

Table 7: Amounts of magnesia and CO2 after decomposition.

Material Amount of Mg

(g/mol)

Amount of

C(g/mol)

Amount of O

(g/mol)

Total amount

Magnesite

(MgCO3)

24.31 12.01 48.00 84.31

CO2 - 12.01 32.00 44.01

Magnesia (MgO) 24.31 - 16.00 40.30

This result can also be presented in relative terms as a material share/composition from magnesite as shown in

table:

Table 8: Yield of Magnesia and Carbon dioxide in Magnesite

Material Share in magnesite (MgCO3) %

Magnesia 47.80

CO2 52.20

Total 100

24 | P a g e

Water consumption

The use of process water is high since a comparatively more quantity of water is used, e.g. for washing the raw

material (magnesite) in order to exclude impurities or to cool the magnesia product in the coolers and for the

heavy media separation process. There are some operations with exhaust gas washing systems, however, and the

emissions gases are washed with water.

Energy consumption

The manufacture of magnesia (dry process) is energy intensive as magnesia, mainly DBM, is manufactured by

very high temperatures. Magnesite (MgCO3) is thermally decomposed to magnesia (MgO) and carbon dioxide

(CO2). The process is highly endothermic and its theoretical reaction enthalpy is 2803 MJ/kg MgO. The

decomposition of magnesite begins at a temperature of 550 °C and is completed at a temperature of below 1000

°C if it contains significant amounts of other carbonates. Natural gas, petroleum coke and fuel oil are used for

the firing process. Table below shows the fuel requirement for the production of one tonne of sintered magnesia

by using a direct heat process. The higher values mentioned in this table are required for sintered or dead burned

magnesia production.

Table 9: Fuel requirements for the production of one tonne magnesia (MgO)

Fuels Minimum Maximum

Natural Gas 176 Nm3/t 310 Nm3/t

Petroleum Coke 240 kg/t 393 kg/t

Fuel Oil 190 kg/t 330 kg/t

The energy demand for magnesia production ranges between 6 and 12 GJ/t MgO and is determined by different

factors, such as the characteristics and moisture content (wet or very dry) of raw magnesite.

In order to achieve the very high combustion temperature of above 2000 °C that is required, oxygen can also be

used. The amount of oxygen required is between 15 and 150 Nm³/t sintered magnesia. It has to be noted that, if

special types of sintered magnesia with very high levels of purities or large crystal dimensions are to be

produced, the values can be significantly higher up to 150 Nm³/t.

Significantly more electrical energy (electric arc furnaces) in a range of 3500 – 4500 kWh/t is required for the

production of dead burned magnesia. However, for the production of very pure grade magnesia the value for the

energy requirement can be doubled or can even be above that.

Emissions

Emissions to air, water and land (process losses/waste) and also noise emissions arise during the manufacture of

magnesium oxide/magnesia using the dry process route. In this section, ranges of air pollutant emissions are

presented for the dry process of magnesium oxide/magnesia manufacture.

25 | P a g e

Emissions to air : The so-called ‘CO2 process emissions’ result from the decomposition of magnesite (MgCO3)

to magnesia (MgO) and around 1 ton CO2/ton magnesia may occur. Furthermore, CO2 emissions also result

from the fuel combustion process, e.g. by using natural gas or pet coke. Around 0.4 to 1.3 t CO2/t sintered

magnesia are contributed from the fuel combustion process to the CO2 emissions. Emissions to air do not only

occur during the firing process, but also during other manufacturing steps, such as:

Storage and handling of raw materials, fuels or products – dust emissions can arise

Grinding and milling processes – dust emissions can arise.

Process losses/waste

Process losses/waste originating from magnesia manufacture are different types of magnesium carbonate dusts

which are separated in off-gas cleaning units, e.g. the dust precipitator. The dust types are, e.g. magnesium

carbonate containing various proportions of caustic calcined and sintered magnesia. Packaging waste (plastic,

wood, metal, paper, etc.) arises from the packaging step.

Some of the dust types can be recycled and re-used within the process. Furthermore, collected dust can also be

used within other environmental applications, e.g. industrial waste water treatment, metal capture in land filling.

The techniques used for the dusts and other wastes at waste disposal facilities range from re-use in marketable

products and recycling through to disposal.

Washing fluids used for wet washing go through a phased sedimentation process to separate the solid materials.

The solids that are obtained in this process are stored at an intermediate storage site for later use within the

process while water is re-used and fed back into the system.

Emissions to water

Water is used in different stages of the process. Water for washing the raw materials (magnesite) and for the

heavy media separation process is re-used in the process after sludge decantation and clarification. Furthermore,

water is used to cool the product in the coolers. However, this water is evaporated because of the high process

temperatures. Water is also used for some operations with exhaust gas washing systems where emissions gases

are cleaned. No waste water is produced by the magnesia production processes using the dry process route.

26 | P a g e

CHAPTER -7

MASS AND ENERGY BALANCES

7.1 Introduction [20, 21]

Material Balance is an application of conservation of mass to the analysis of physical systems. By accounting

for material entering and leaving a system, mass flows can be identified which might have been unknown, or

difficult to measure without this technique. Therefore, mass balances are used widely in engineering and

environmental analyses. They are important first step when designing a new process or analyzing an existing

one. They are almost always perquisite to all other calculations in the solution of process engineering problems.

Material balances are nothing more than the application of the law of conservation of mass, which states that

mass can neither be created nor destroyed. They are used in industry to calculate mass flow rates of different

streams entering or leaving chemical or physical processes.

The general form quoted for a mass balance is the mass that enters a system must, by conservation of mass,

either leave the system or accumulate within the system .Mathematically the mass balance for a system is as

follow:

Rate of Input of Mass = Rate of Output of Mass + Accumulation ----------- (1)

And for steady state Accumulation is taken as zero. Thus the above equation reduces to:

Rate of Input of Mass = Rate of Output of Mass --------------------------------- (2)

INPUT OUTPUT

.

Fig-7: (Representing Block diagram of General Mass Balance Equation)

7.2 Mass Balance

Assumption:

- Plant capacity of Magnesia Production plant = 20,000 tonnes/annum

- No. of plant working days = 330 days

- Plant operating duration = 24 hours

PROCESS

27 | P a g e

- In one year total production = 20,000 tonnes

In 330 days = 20,000/330 = 60.606 tonnes/day = 60.606*1000 =60606 kg/day

For 24 hours = 60.606/24 = 2.525 tonnes/hr = 2.525*1000 = 2525 kg/hr

- Mol. Wt. of Magnesite(MgCO3) = 84 g/mole

- Mol. Wt. of Magnesia(MgO) = 40 g/mole

- Mol. Wt. of Carbon dioxide = 44 g/mole

Chemical Reaction taking place in rotary kiln:

MgCO3 MgO + CO2

1mole 1 mole 1 mole

Now, by application of backward integration method, we are doing mass balance:

7.2.1 Mass Balance in screen and during packing

Mass in: 2537.625 kg/hr Mass out: 2525 kg/hr

Fig-8: Mass balance in screen

As it is a mechanical operation the losses during are assumed to be 0.5 %.

Exiting product after screening (i.e. MgO) , Applying losses to it

We get 0.5% of 2525 = 12.625 kg/hr, as we are doing backward integration.

Mass entering in screen = 2525 +12.625 = 2537.625 kg/hr

7.2.2 Mass balance in rotary kiln

Assuming conversion = 99% (as the process is irreversible)

Reaction: MgCO3 MgO + CO2

As conversion is 99 % , product contains 99% MgO and 1% MgCO3

So, 2537.625 kg/hr product contains 99% MgO and 1% unconverted MgCO3

Mass of MgO coming out of kiln = 2512.24 kg/hr.

Mass of CO2 coming out of kiln = 2512.24 kg/hr

Mass of unconverted MgCO3 in the product = 25.376 kg/hr

28 | P a g e

Mass in: 5049.875 kg/hr Mass out = 2512.24 kg/hr (CO2)

Mass out = 2512.24 kg/hr (MgO)

Mass of unconverted MgCO3 =

25.376 kg/hr

Fig-9: Mass balance in rotary kiln

7.2.3 Mass balance in crushers and vibrating screen

As these are mechanical operation the losses are assumed to be 0.5 % in crushers and vibrating screen

collectively.

7.2.3.1 For Vibrating Screen

Mass of exiting stream after screening = 5049.875 kg/hr Applying losses to it which is 0.5 %.

We get 0.5% of 5049.875 kg/hr = 25.249 kg/hr, as we are doing backward integration.

Mass entering in screen = 5075.124 kg/hr

Mass in = 5075.124 Screen Mass out = 5049.875

Fig-10: (Mass balance in vibrating screen)

7.2.3.2 For Jaw Crusher and secondary crusher

Crushers which are available these days are loss free so taking 0% losses in crushing section we have:

Feed

Mass in = 5075.124 kg/hr Mass out = 5075.124 kg/hr

Fig-11: (Mass balance in Crushers)

7.2.4 Overall Mass Balance

Rotary

kiln

CRUSHER

29 | P a g e

Mass in = 5075.124 kg/hr

Mass out = 2525 kg/hr (MgO) and 2525 kg/hr (CO2)

Mass in = 5075.124 kg/hr Mass out (MgO)=2525 kg/hr

Mass out (CO2) = 2525 kg/hr

Mass of unconverted MgCO3

= 25.12 kg/hr

Fig-12: (Representing Block diagram of Overall Mass Balance)

Now, mathematically the mass balance for a process is

Total Mass entering into the system = Total Mass coming out the system

Mass In (MgCO3) = Mass Out(MgO) + Mass Out(CO2) + Mass of Unconverted MgCO3

5075.124 = 2525 + 2525 + 25.12

5075.124 kg/hr = 5075.12 kg/hr

7.3 Introduction to Energy Balance [21]

The Energy balance of a particular system can be achieved from the first law of thermodynamics which states

that the total energy of an isolated system and its surrounding remains constant. The conversion of one form of

energy into another is possible. When a system gains or losses energy, it must be exactly equal to the loss from

gain of energy by the surrounding. Thus, the first law of thermodynamics relates to conversation of energy. The

energy coming into a unit operation can be balanced with the energy coming out and the energy stored.

7.3.1 Energy Balance Equation

Energy In = Energy Out + Energy Stored

ΣER = ΣE

P + ΣE

W + ΣE

L + ΣE

S

Where

ΣER

= ER1

+ ER2

+ ER3 + ……. = Total Energy Entering

ΣEp = E

P1 + E

P2 + E

P3 + ……. = Total Energy Leaving with Products

PROCESS

30 | P a g e

ΣEW

= EW1

+ EW2

+ EW3 + … = Total Energy Leaving with Waste Materials

ΣEL

= EL1

+ EL2

+ EL3 + ……. = Total Energy Lost to Surroundings

ΣES

= ES1

+ ES2

+ ES3 + ……. = Total Energy Stored

7.3.2 Calculation of Ideal Gas Heat Capacity

The method of JOBACK can be applied to calculate the ideal gas heat capacities. It is based on the method of

group contributions and is the easiest to apply amongst other methods so, we shall proceed by incorporating the

values of A, B, C, and D that are furnished in the book because this provides the most accurate values for the

calculation of ideal gas heat capacities.

The formula used is:

Cp (ideal) = A + B*T + C*(T2) + D*(T

3)

Where A, B, C and D are constants which have different values for different compounds and T is temperature in

Kelvin.

ΔH = ṁ *ʃ cp * dt ------------------ (a)

Where:

H - Enthalpy

ṁ – Mass flow rate

cp – specific heat of compound in J/mol.K

Now the formula becomes :

H = ṁ *ʃ (A + BT + CT2 + DT3 + ET4)*dt -------------- (b)

Where: A, B, C, D, E are the various constants for individual compounds.

7.4 Energy Balance

Q = (- Heat of reactants) + ( Heat of products) + ( Heat of reaction) ------------- (c)

Heat of reactants = ṁ×cp×∆t ----------------------------------------------------------(d)

Where,

ṁ = mass flow rate

cp = specific heat capacity

∆t = change in temperature

Heat of products = ṁ×cp×∆t

31 | P a g e

Heat of reaction = Positive, if endothermic reaction.

= Negative, if exothermic reaction.

Energy requirement for size reduction can be calculated by Bond’s Law. [22]

-------------------------------------------- (e)

Where, P = Power required for size reduction in kilowatts.

ṁ = mass flow rate in kg per hours.

Kb = 0.3162 Wi (Wi is the work index for material being crushed)

Dp = Diameter of particle in millimetres.

Work index is defined as the gross energy requirement in kilowatt hours per ton of feed needed to

reduce a very large feed to such a size that 80% of product passes a 100 µm screen. So, Work index

for magnesite ore in 16.84 kWh.

Bond’s law for power requirement when size of both feed and product are known, [22]

----------- (f)

Where, P = Power required for size reduction in kilowatts.

ṁ = mass flow rate in kg per hours.

Wi = is the work index for material being crushed

Dp = Diameter of product particle in millimetres.

Df = Diameter of feed particle in millimetres.

7.4.1 Energy Balance in Jaw Crusher

Feed of Unknown size Product Size = 4 inch3

Fig-13: Energy Balance in Jaw Crusher

ṁ ( feed rate ) = 5075.124 kg/hr

= 5.075124 ton/hr

Kb = 0.3162 * Wi ------------------------------- (g)

= 0.3162 * 16.84

= 5.3245 kWh/ton

Jaw Crusher

32 | P a g e

Volume of product particle = 4 inch3

Considering particle shape to be spherical we have,

4 = 4πr3

r = 0.68278 inch

= 0.0173427 m

= 17.3427 mm

So, Dp = 34.6854 mm

Now applying the Bond’s law for power requirement,

Putting the values in equation –

P =

= 4.576 kW

= 4.576* (1000/746) = 6.134 hp

7.4.2 Secondary Crusher

Feed size = 4 inch3 Product size = 1 inch3

Fig-14: Energy Balance in Secondary Crusher

Data

ṁ = 5.075124

Kb = 5.3245 kWh/ton (0.3162*Wi)

Dp = 34.6854 mm (Calculated above)

Now calculating Df,

Volume of product particle = 1 inch3

Secondary

Crusher

33 | P a g e

Considering particle shape to be spherical we have,

1 = 4πr3

r = 0.430127 inch

= 0.010925 m

=10.925 mm

So, Dp = 21.84 mm

Now applying the Bond’s law for power requirement,

Putting the values in the equation –

P = 5.075124 * 5.3245 (

= 1.194 kW

= 1.6 hp

7.2.3 Rotary Kiln

CO2 exiting at 1773 K

MgCO3 entering at 298 K MgO exiting at 1773 K

Fig-15: Energy Balance in Rotary Kiln

Enthalpy of feed = ṁ×cp×∆t , where

ṁ = mass flow rate

cp = specific heat capacity

∆t = change in temperature

34 | P a g e

Q = - Heat of reactants + Heat of products + Heat of reaction

Taking reference temperature as 273 K and temperature inside the kiln is 1773 K.

Enthalpy of Reactant

Reactant Enthalpy = 0, because MgCO3 is entering at room temperature only.

Enthalpy of product Calculation

1. For MgO (Magnesium Oxide)

Q =

= ṁ*

Now, cp for MgO can be calculated by following equation:

cp = 10.86 + 0.001197 *T – (208700/T2) cal/(mol K)

Applying the value of cp in equation,

∆H = ṁ

------ (h)

Integrating above equation (h) we get:

∆H = ṁ* [10.86 (1773-298) + ((0.001197/2)(11732-2982)) + (208700/(1773-298))]

ṁ = 2537.625 kg/hr

∆H = 4578113 kJ/hr

= 1271.704 kW

2. For CO2 (Carbon Di-oxide)

∆H =

= ṁ

ṁ = 2512.24 kg/hr

35 | P a g e

Now, cp for CO2 can be calculated by following equation:

cp = A + B*T + C*T2 + D*T3 +E*T4 (J/mole.K) -------- (i)

Hence,

∆H =ṁ*

--- ( j )

∆H = ṁ *[A*(1773-298) + (B*(1773-298)2/2) + (C*(1773-298)3/3) + (D*(1773-298)4/4) + (E*(1773-298)5/5)]

Table-10: Values of Constant for cp calculation of CO2 [23]

A B C D E

27.473 0.042315

-0.000019555

3.9968E-09

-2.9872E-13

Putting the values in above equation ( j) we get –

∆H = 4936640 kJ/hr

= 1371.289 kW

Now, Total Enthalpy of products = Enthalpy of MgO + Enthalpy of CO2

= 4578113 + 4936640

= 9514753 kJ/hr

Heat of reaction = +118 kJ/mol

Total moles of MgCO3 reacted = 63.44065 kmol/hr

So, Enthalpy of reaction = 118 * 63.44065 * 1000

= 7845996.7 kJ/hr

We know, Q = - Heat of reactants + Heat of products + Heat of reaction

So, Q = 0 + 9514753 + 7845996.7

= 17360749.7 kJ/hr (Endothermic)

7.2.4 Cooler

36 | P a g e

MgO entering at 373K MgO leaving at 333 K for storage

Fig-16: Energy Balance in cooler

Enthalpy of MgO in cooler :

Tin = 373 K

Tout = 333 K

∆H =

ṁ = 2537.625 kg/hr

now, ∆H = ṁ*

Now, cp for MgO can be calculated by following equation:

cp = 10.86 + 0.001197 T – (208700/T2) cal/(mole K)

Applying the value of cp in equation,

∆H = ṁ *

Integrating above equation we get –

∆H = ṁ [10.86 (373-333) + ((0.001197/2)(3732-3332)) + (208700/(373-333))]

∆H = 150326.2924 kJ/hr

7.2.5 Utility required: Cooling Air ,Power & Fuel Requirement

Cooler

37 | P a g e

Q = ṁ×cp×∆t (For cooler)

150326.2924 = ṁ * 1.006 * 31

ṁ = 4820.31 kg/hr (Flow rate of cooling air used in cooler)

Fuel Requirement in Rotary Kiln:

Calorific Value of Fuel Oil = 9800 Kcal/kg

Q= 17360749.7 kJ/hr (For Rotary Kiln)

= 4149318.762 kcal/hr

Now, Fuel requirement = 4149318.762/9800

= 423.399 kg/hr

So,

Power requirement for Jaw Crusher = 4.939 kW

Power requirement for Secondary Crusher = 1.2849 kW

Flow rate of air required for cooling MgO = 4820.31 kg/hr

Fuel Oil requirement in Rotary Kiln = 423.399 kg/hr

38 | P a g e

7.5 Control Strategy

Fig: 17 – Control strategy for rotary kiln reactor

The following figure illustrates a typical kiln process and instrumentation.

The three control selectors, and eight dynamic elements. A decoupling network addresses the

interaction between the hot and cold end temperature control. Constraints on O2 and draft are provided

as overrides on gas flow and ID fan speed adjustment. Output is maximized based on the ID fan being

the limiting factor on production.

39 | P a g e

CHAPTER -9

PRELIMINARY EQUIPMENT DESIGN

9.1 Jaw Crusher

Maximum Feeding Size = 200 mm

Discharge size = 15- 50 mm

Capacity = 5-20 ton/hr

Motor Power = 5-10 kW

9.2 Screen

Particle Form Particle Size

Coarse > 50 mm

Medium 15-50mm

Fine 3- 15 mm

Straining < 3 mm

Table-11: Details of screen

Item Manually Cleaned Mechanically Cleaned

Bar Size: Width (mm) 5-15 5-15

Depth (mm) 25-80 25-80

Aperture (mm) 20-50 5-80

Slope to Flow (Deg) 450-600 18o-90o

Velocity Through Screen (m/s) 0.3-0.6 0.6-1.0

9.3 Feed Hopper

Production of MgO (product) = 2550.25 kg/hr = 61206 kg/day = 61.206 ton/day

Production of CO2 = 60.60 ton/day

40 | P a g e

Feed rate of MgCO3 = 5075.124 kg/hr =121802.976 kg/day = 121.803 ton/day

Design of feeder is done on the basis of ratio control and definite ratio has to be maintained between each other.

Considering water in place of feed: Processed Volume of feed =

=

=121.803 m

3/day.

9.4 Storage Vessel

Total production of Magnesium Oxide = 2550.25 kg/hr

Assumption: Storage is taken as 1 day.

Total production combined with storage in a day = 2550.25*24 kg/day = 61206 kg/day

Total volume storage in a day:

Volumetric flow rate =

Density of Magnesium Oxide = 3600 kg/m3

=

= 17 m3/day

Calculation of diameter of storage tank:

=> 17 = π* 2*h

Let: h/d =1.218.026= π *(d/2)2*(

)

17= π* (d3/4)* 1.2 => d = 2.622 m

h/d = 1.2 => h = 3.147 m

Volume of cylinder = *r2*h

41 | P a g e

CHAPTER -10

DETAILED EQUIPMENT DESIGN

10.1 Rotary Cooler

Process design of Rotary Cooler

Let the diameter of cooler be 2.75 m

Air is passed in counter current with respect to solid.

Air is heated from 44ºC to 75 ºC.

MgO powder is cooled from 100 ºC to 60 ºC and the moisture content in it ranges from 1.5-2 % (by mass).

In a rotary cooler the moisture content of product is reduced by 0.5 mass %.

Overall Heat Balance

Average Temperature of air =

= 59.5oC = 332.65 K

Molar volume of air at STP (T=273 K, P=1atm) =22.4136 L

Molar volume of air at 332.65 K =

= 27.296 m3/kmol

Density of air (ρg) =

= 1.061 kg/m3

Moisture Removal of Magnesium Oxide = 2525*(0.015-.005) =25.25 kg/hr

Total heat load of product in rotary cooler (Φ1) = 2525*0.877*(100-60) + 25.25*2644

= 88577 + 66761 = 155338 kJ/hr = 43.1494 kW

Average heat capacity of air (Cpa) at 59.5 0C = 1.005 kJ/(kg .oC)

Air is heated from 44oC to 75oC.

Mass flow rate of air (qma) =

= 4985.97 kg/hr

Volumetric flow rate of air (qva) =

= 4699.311 m3/hr

Assuming diameter of rotary cooler (D) = 2.75 m

Air is passed in countercurrent fashion to solids flow.

Cross sectional area of cooler (A) =

= 5.93957 m

2

42 | P a g e

Velocity of air =

= 0.21977 m/s

It is a low velocity, normally in a cooler velocity of 1.5 m/s is preferred. Hence, we have assumed a velocity of

1.5 m/s.

Calculation of Length of Rotary Cooler

L = Nt * Ht

L = Rotary cooler length (in m)

Nt = Number of transfer units

Ht = Height (length) of transfer unit (in m)

Nt = Δ

Δ where, Δ = tg,out – tg,in ,

oC

ΔTlm =

= 20.17 oC

Nt =

= 1.537 ( Nt is preferred in range of 1.5 -2.5)

Ht =

G = Mass flow rate per unit area of air (in kg/m2 * s)

Ca = Heat capacity of air = 1.005 kJ/(kg * s)

U = Overall volumetric heat transfer coefficient = 237*G0.67 / D

D = Rotary cooler diameter, m

G =

= 0.2331 kg/m2 * s

U = [237* (0.2331)0.67]/(2.75) = 32.483 kJ/( m3 * s * oC )

Ht =

=

= 7.211 m

L = 1.537 *7.211 = 11.083 m

Hence,

=

= 4.030 (Value should remain between 4 to 10)

Mechanical design of cooler

Cooler at any point of Temperature should be designed for a Temperature up to 200 oC.

Material of Construction: Carbon Steel

Working Pressure in cooler = 101.325 kPa

43 | P a g e

Design Pressure, P = 1.1 * working pressure = 1.1 * 101.325 = 111.4575 kPa = 0.11145 N/mm2

Permissible stress of material used, f = 140 N/mm2

J =0.85 (spot radiography)

Internal Diameter = 2.75 m (Assumed)

Thickness of Shell, t =

=

= 1.288 mm, considering a corrosion allowance of 2mm and

adding it to 1.2888 mm. We get, t = 3.288 mm.

Length of cooler = 11.083 m

10.2 Cyclone Separator

Fig-17: Schematic of Cyclone Separator

Process design of Cyclone Separator

DP=

Dp= particle size of MgCO3 = 10 micron = 10*10-6m

Inlet velocity of gas, V = 24m/sec

NT=no. of turns made by gas in vessel = {[0.1079-(0.00077*V)-(1.94*10-6*V2)]*V}

44 | P a g e

= 2.17 ≈ 2 turns

ρ = density of MgCO3 = 2960 kg/m3

ρg = density of air = 1.225 kg/m3

µ = viscosity of air = 1.73*10-5 NS/m2

Putting all these values in the above equation,

10*10-6 =

= 8.728624*10-11

Dc = 1.14565 m

Length of cyclone, L = 4*1.14565 = 4.582623 m

Diameter of cyclone, Dc= 1.14565 m

Cyclone inlet diameter, Bc =Dc/4= 0.28641 m

Cyclone gas outlet diameter, De=Dc/2 = 0.572825 m

Cyclone inlet height, Hc= Dc/2=0.572825 m

Cyclone cylinder length, Lc=2*Dc=2.2913 m

Width, Sc=Dc/8 = 0.143206 m

Cyclone cone length, Zc= 2*Dc= 2.2913 m

Cyclone outlet diameter, Jc=Dc/4= 0.28641 m

Cyclone gas outlet duct length, S = Hc + Sc = 0.716031 m

Pressure Drop = 0.03* ρf*Vi2*NH

ρf = 1.225 kg/m3

Vi=24 m/sec

NH= 7.5*

= 1.0740

Putting all these values in equation of pressure drop we get,

Pressure drop = 0.003*1.225*(242)*1.0740

= 2.273 N/m2

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Mechanical design of Cyclone Separator

P = maximum allowable working pressure in psig

r = Cyclone inside radius before corrosion allowance in inch

d = Cyclone inside diameter before corrosion allowance in inch

S = maximum allowable stress value in psi = 140 N/mm2

E = Joint efficiency = 0.85 (spot radiography)

α = ½ apex of the cone (Considering it 90o)

Material of Construction is Stainless Steel.

Wall thickness of cylindrical shell, ts =

=

= 5.28*10-3 inch

= 0.1341 mm

Wall thickness of Ellipsoidal Head, th =

=

= 5.28*10-3 inch

= 0.1341 mm

Wall thickness of Cone, tc =

=

= 0.0105 inch

= 0.268 mm

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CHAPTER -11

COST ESTIMATION

EQUIPMENTS:-

1. Jaw Crusher

2. Roll Crusher

3. Screen

4. Hopper

5. Rotary Kiln

6. Cyclone Separator

7. Cooler

8. Storage Tank

Table 12: CEPCI Index of various years.

YEAR CEPCI Index

2002 395.6

2007 525.4

2013 564.3

2014 588.6

(Ref:-capci_2014_py.pdf) [13]

11.1 Capital Cost

11.1.1 Jaw Crusher

By Graph: (Pg , Fig , Timmerhaus)

Flow rate = 1.517 kg/sec

Cost of Jaw Crusher in 2002 = $60,000

Using formula:

=

C1/C2 = (

)

60000/C2 = (395.6/588.6)

C2 = $89271.99 (2014)

CEPCI (2002) --- 395.6

CEPCI (2014) --- 588.6

Now according to conversion rate

1$ = Rs. 60

Cost = 89271.99*60

= Rs 5356319.515

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11.1.2 Roll Crusher

Flow rate = 1.517 kg/sec

Cost of Roll Crusher in 2002 = $18000 (from Graph)

Using formula:

=

C1/C2 = (

)

18000/c2 = (395.6/588.6)

C2 = $26781.59 (2014)

CEPCI (2002) --- 395.6

CEPCI (2014) --- 588.6

Now according to conversion rate

1$ = Rs. 60

Cost = 26781.59*60

= Rs 1606895.85

11.1.3 Screen

Cost of screen in 2007 in $ =20800 (from graph)

C=20,800 (588.6/525.4) *60

=Rs 1398121.02 (2014)

11.1.4 Hopper

Volume of Hopper = 430.181 ft3

Material of Construction = Carbon steel

So, Cost of Hopper in 2014 = $ 10800 (from Matche.com)

$1 = Rs 60

So, 10800 * 60 = Rs 648000

11.1.5 Rotary Kiln

Total Heat Duty = 16Million BTU/hr

Flow rate = 2.5 tons/hr

Inclination = 3%

Heat input = 1371.289 kW = 4679030.048 =4*106 Btu/hr

From graph:

Cost = $ 424060 (1987)

Now, Cost Index in 1987 = 320

So, applying the formula we get;

C1/C2 = (

)

424060 / C2 = (320 / 588.6)

Cost of Kiln in 2014 = $ 780000

$1 = Rs 60

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So, Cost of Kiln = Rs 46800000

11.1.6 Cyclone Separator

Q = 3156.476 ft3/sec = 189388.5621 ft3/min

From graph

Cost = $38000 (1987)

Now, Cost Index in 1987 = 320

So, applying the formula we get;

C1/C2 = (

)

38000 / C2 = (320 / 588.6)

Cost of Cooler in 2014 = $ 70000

$1 = Rs 60

So, Cost of Cooler = Rs 4200000

11.1.7 Cooler

Area = 63.9268 ft3

Working pressure = 16.1695 psig

Cost in 2002 =$ 7500

Cost in 2014 = $ 11158.99 = Rs 669539.4

11.1.8 Storage Tank

Volume of Storage Tank = 18.026 m3

(Assuming storage for 1 day.)

Cost in 2002 = $ 15000

Now, applying the formula =

=

C1/C2 = (

)

15000/c2 = (395.6/588.6)

= $ 22,295.4545

$1 = Rs 60

So, Cost of Storage Tank = Rs 1337727.27

Total purchased cost = Rs 62016601.67

11.2 Total Capital Investment

TCI = Fixed Capital Investment + Working Capital + Start up.

FCI = Total direct cost + Total indirect cost

Total direct cost = Total offsite cost + Total onsite cost.

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Table 13: Estimation of Direct and Indirect Cost.

Direct cost Fraction of delivered

equipment

Cost(Rs)

Purchased equipment Rs. 62016601.67

a. Onsite Cost

Land 20000m2 (Rs 250/m2) Rs. 5000000

Delivery(% of PEC) 0.10 Rs. 6201660.167

Delivered Equipment

cost

PEC + (0.10 *PEC) Rs. 68218261.84

Purchase Installation 0.45 DEC Rs. 30698217.83

IPC 0.18 DEC Rs. 12279287.13

Piping 0.16 DEC Rs. 10914921.89

Electric system 0.10 DEC Rs. 6821826.184

b. Offsite cost

Building 0.25 DEC Rs. 17054565.46

Yard 0.15 DEC Rs. 10232739.28

Service Facilities 0.40 DEC Rs. 27287304.74

Total Direct Cost Rs. 189308784.5

Indirect Cost

Engg. & Supervision 0.33 DEC Rs. 22512026.41

Cost expansion 0.41 DEC Rs. 27969487.35

Legal expansion 0.04 DEC Rs. 2728730.47

Contractor’s fees 0.22 DEC Rs. 15008017.6

Contingent cost 0.35 DEC Rs. 23876391.64

Total Indirect Cost Rs. 92094653.47

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FCI = Total Direct Cost + Indirect Cost

= Rs.189308784.5 + 92094653.47

= Rs. 281403438

Working Capital = 0.70 of DEC

= Rs. 47752783.29

Start up = 0.10 * FCI

= Rs. 28140343.8

Total Capital Investment = FCI + WC + Start up

=Rs 357296565.1

11.3 Estimation of Total Product Cost

Total Product Cost = Manufacturing Cost + General Expenses

Now,

MC=Direct production cost + Fixed charges + Plant overheads

Now, 1st we need to find cost of RM used

Table 14: Raw material requirement calculation.

Raw Material

Qty.

(kg/yr)

Price

(Rs/kg)

Cost per year(Rs)

MgCO3 43269345.5 (kg/yr) 36 1557696438

According to mass balance,

MgCO3 = 5463.27 kg/hr * 330 * 24

= 43269345.5 kg/yr

Cost = Rs. 36 / kg

= Rs. 1557696438

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Now, Raw Material Cost is 20 - 70 % of Total Production Cost, considering Raw material cost to be 60% of

total production cost we have:

TPC = 1557696438/0.60 = Rs. 2596160730

Direct Production Cost:

Table 15: Estimation of Direct Production Cost.

Parameters % Factor Cost(Rs)

Operating Labour(OL) 10% of TPC Rs. 259616073

Direct Supervision & clerical labour 10% of RM Rs. 155769643.8

Utilities 10% of TPC Rs. 259616073

Maintenance 2% FC Rs. 5628068.76

Labour charge 5% of OL Rs. 12980803.65

Total direct production cost = Rs. 690910662.2

Table 16: Fixed Charges Estimation.

Fixed charges % Factor Cost (Rs)

Local Tax 1% of FCI Rs. 2814034.38

Prof. Tax 4% of FCI Rs. 11256137.52

Financial tax 10% of TCI Rs. 35729656.51

Depreciation 10% of FCI + 2% of Building Cost Rs. 28481435.11

Total Rs. 78281263.52

Plant Overheads

40% of Operating Labour = Rs. 103846429.2

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General expenses

Table 17: General expenses estimation.

Administrative Cost 10% of Operating Labour Rs. 25961607.3

Distribution & Marketing Cost 2% of TPC Rs. 51923214.6

R&D 1% of TPC Rs. 25961607.3

Total Rs. 103846429.2

Manufacturing Cost = Rs. 873038354.9

Total Product Cost = Rs 873038354.9 + 103846429.2

= Rs. 976884784.1

11.4 Profitability Analysis

Total Revenue = Total production * cost/kg of MgO

= (20* 106) kg * Rs 60/kg = = Rs. 1200000000

PBT = Revenue - Total Product Cost

= Rs. 1200000000 - Rs. 976884784.1

= Rs. 223115215.9

Tax rate = 33.9 %

Profit after Tax = (1-0.339) * PBT

= 0.661 * 223115215.9

Net Profit = 147479157.7

Rate of Return = Net Profit / Total Capital Investment

= 147479157.7/ 357296565.1

= 0.41276 = 41.28%

Payback Period = Total Capital Investment / Net profit

= 357296565.1 / 147479157.7

= 2.42 years