ENERGY TECHNOLOGY

S.JITENDRA PAL Assistant Professor

Department of Chemical Engineering National Institute of Technology Karnataka

Surathkal-Karnataka.

Fundamentals of energy and its impact

on society and the environment.

What is energy? Energy :defined as the ability or capacity to do work.

Energy is measured in BTU (British Thermal Unit) or Joule

According to Max Planck, energy is defined as the ability of a system to cause external action.

The term energy carrier thus a carrier of the above defined energy is a substance that could be used to produce useful energy, either directly or by one or several conversion processes

In this respect the following forms of energy are distinguished: mechanical energy (i.e. potential or kinetic energy), thermal, electric and chemical energy, nuclear energy and solar energy etc.

Think about how you use energy every day. You wake up to an alarm clock. You take a shower with water warmed by a hot water heater. You listen to music on the radio as you dress , u eat breakfast.. And so on.

Food items, medicines, groceries, the accessories which we use, Cosmetics, electronic appliances, lighting, heating cooling,

Everything needs energy in direct or indirect way

Why Energy is needed ?

Why Energy is needed ? Various sectors of economy- Industry, residential,

commercial, transport Industry- Petroleum Refining , steel, cement,

chemical, metal, paper, pharmaceuticals, mining etc

Transportation,-automobile, commercial transport,-bus , truck, train, airplane , mass transits

Residential and commercial buildings use energy in for heating and cooling, lighting, heating water, and operating appliances.

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Non-Renewable Energy Sources

Conventional

Petroleum

Natural Gas

Coal

Nuclear

Unconventional (examples)

Oil Shale

Natural gas hydrates in marine sediment

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Renewable Energy Sources Solar photovoltaics Solar thermal power Passive solar air and water heating Wind Hydropower Biomass Ocean energy Geothermal Waste to Energy

World Energy Scenario

World primary energy demand grows by 1.6% per year on average between 2006 and 2030 an increase of 45%

The worlds energy needs would be well over 50% higher in 2030 than today. China and India together account for 45% of the increase in global primary energy demand in this scenario.

- World Energy Outlook ( www.iea.org )

Indian Energy Sector Some facts

India - one of the fastest growing economies in the world. It is poised to grow at around 7 percent on moderate term.

Indias Energy Consumption is 12.6 million btu. India energy intensity is higher compared to Japan, USA

and Asia as a whole by 3.7, 1.55 and 1.47 times respectively (energy consumption compared to GDP). This indicates inefficient use of energy but also substantial scope of energy savings.

Long term energy plan for India therefore should aim at a) Projecting the energy demand

b) Projecting the energy mix

c) Exploring the possibilities for alternative sources and

d) Suggesting measures for energy efficient uses

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Peak Production of Petroleum in US

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Projected World Peak Production of Petroleum

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1999 Regional Shares of Crude Oil Production (3445 Mt)

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World Total Primary Energy Supply in 1998 (9491 Mtoe)

**Other includes geothermal, solar, wind, heat, etc.

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World Energy Consumption

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World Energy Consumption

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World Total Energy Consumption 1990 -2020 (Quadrillion Btu)

Region/Country 1990 1997 2020

United States 84.0 94.2 120.9

Western Europe 59.9 64.0 78.4

Japan 18.1 21.3 25.4

China 27.0 36.7 97.3

Former Soviet Union 61.0 40.8 57.3

Total World 346.7 379.9 607.7

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U.S. Energy Flow, 1999

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U.S. Energy Consumption by Source, 1998

Primary Commercial Energy Mix (%)

World V/S India Resources World India

Oil 37.4 33.22

Natural Gas 24.3 9.34

Coal 25.5 53.54

Nuclear 6.5 1.04

Hydel 6.3 2.63 Source : www. planningcommission.gov.in

Indian Energy Sector Vision of Some Eminent Experts..

The energy scene in the 21st century is going to see a major shift. Very soon, oil and gas will see its finiteness. It is high time that we realize this factor and work towards the fuel of the future. - Dr. A P J Abdul Kalam, Former President of India, Address

at Energy Technology Conclave Technology for Sustainability

If we expect our economy to keep growing at 9-10% p.a., we need a commensurate growth in power supply. The power sector has made good progress over the past few years. It has also seen very significant changes. However we have not been able to make a decisive breakthrough in ensuring high and sustainable rates of growth of this sector and improving its financial health.

- Honble Prime Minister Dr. Manmohan Singh

Energy Potential Shape of Things to Come

India's energy potential is rated the third largest in the world, with annual installations of 875 mega watts (MW), only after Europe and the United States, exceeding forecasts of 500 MW - BTM Consult.

A recent study by the World Resources Institute (WRI) Indias energy demand is expected to more than double by 2030. The country is consequently in need of a huge amount of new power generation capacity. Considering the figures of the WRI, the cheapest generating capacity for India will no doubt be energy savings.

Per Capita Energy Consumption in Some Countries (kWh). How does it compare?

17179

13338

8076

6206

1379

631

Canada

USA

Japan

UK

China

India

India - Primary Energy Sources in India(%)

53%31%

9%6% 1% Coal

Oil

Gas

Hydro

Nuclear

Source :BP Statistical Review of World Energy, June 2009

India - Estimated Fuel Mix by 2020 (%)

25

16

8

5

16

30 Coal

Oil

Gas

Renewable

Nuclear

Traditional

Source : World Energy Statistics, 2009

India Potential for various Renewable Energy Technologies by 2020

Sources/System Approximate Potential

Biogas plants (in millions) 12

Improved woodstoves in

millions)

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Biogas (MW) 17000

Solar Energy (MW/KM2 ) 20

Wind Energy (MW) 20000

Small Hydropower (MW) 10000

Ocean Energy (MW) 50000

Source: India 2020 A Vision for the New Millennium by Dr. A P J Abdul Kalam & Y S Rajan, Page No. 254

Definitions of Energy terms

Primary energy carriers are substances which have not yet undergone any technical conversion,

whereby the term primary energy refers to the energy content of the primary energy carriers and the "primary" energy flows

Secondary energy carriers are energy carriers that are

produced from primary or other secondary energy carriers, either directly or by one or several technical conversion processes (e.g. gasoline, heating oil, electrical energy),

whereby the term secondary energy refers to the energy content of the secondary energy carrier and the corresponding energy flow

Final energy carrier and final energy respectively are energy streams directly consumed by the final user (e.g. light fuel oil inside the oil tank of the house owner, wood chips in front of the combustion oven, district heating at the building substation)

Useful energy refers to the energy available to the consumer after the last conversion step to satisfy the respective requirements or energy demands (e.g. space heating, food preparation, information, transportation).

It is produced from final energy carrier or final energy, reduced by losses of this last conversion (e.g. losses due to heat dissipation by a light bulb to generate light, losses of wood chip fired stove to provide heat)

Fossil energy resources are stocks of energy that have formed during ancient geologic ages by biologic and/or geologic processes.

They are further subdivided into fossil biogenous

energy resources (i.e. stocks of energy carrier of biological origin) and fossil mineral energy resources (i.e. stocks of energy carrier of mineral origin or non-biological origin).

The former include among others hard coal, natural gas and crude oil deposits, whereas the latter comprise for instance the energy contents of uranium deposits and resources to be used for nuclear fusion processes.

Conventional energy :Energy that has been used from ancient times is known as conventional energy. Coal, natural gas, oil, and firewood are examples of conventional energy sources. Basically A Fossil Fuel.

Non conventional energy sources are those energy

sources which are exposed to use from modern technological advancements; rather than the normal use of conventional fuels as energy sources like gas or

oil.

E.g. tidal energy, geothermal energy etc can be harnessed

now with new technology.

Renewable energy

These are the resources that can be generated continuously. Renewable energy is natural energy which does not have a

limited supply. Renewable energy can be used again and again, and will never run out. Renewable energy includes conventional energy sources

like: firewood, petrol plants, plant biomass, animal dung, water energy etc. These are mostly biomass based which are renewed over relatively short period of time and then available in unlimited amount in nature. Non-conventional energy sources like solar energy, wind

energy, tidal energy, geothermal energy and hydro thermal energy etc. These can reproduce themselves in nature and can be harvested continuously through a sustained planning and proper management

Non- renewable or exhaustible energy sources: These are available in limited amount and develop over a longer period of time. Hence, they cannot be replenished in the quantities they are being consumed in a given period of time.

This include Conventional sources like coal, petroleum etc and Non- Conventional energy sources like nuclear energy etc.

Why should we look for alternate energy sources?

Fossil fuels, which are the main source of energy, are getting depleted at a rapid rate. As a consequence the cost of fossil fuels are increasing.

Fossil fuel based systems produce detrimental effects on the environments. This in turn will affect our health. This means that indirectly, the medical bills will be rising the world over.

How long will fossil fuel last?

Consider a hypothetical case where in earth contains a thin core filled entirely with oil as shown in the previous slide. It turns out that the volume of the oil present is 1.0861021m3((4/3)(6378103)3).

The energy density of fuel is in the range of 10000Wh/Lt.

The energy content in the fuel within the earth is obtained as 1.11025KWh. Assuming that growth rate is maintained at 7% and the entire energy is supplied using fossil fuels.

The energy requirement at any time, t can be calculated using 701012e0.07tKWh

t is obtained as 368 years. The fossil fuels will get depleted in about 368 years.

If we consider the real situation, the earth is not-completely filled with oil as assumed and further the annual energy consumption rate is continually growing. So the fuel may get exhausted in about 70-100 years.

If the reserves of fuels decrease there will be a sharp increase in the price of energy. This will lead to decrease in energy consumption through fossil fuels. If alternative sources are explored and utilized, then the fuel may be actually used for more number of years.

ENERGY for the future - Some Options

Clean Coal Technologies

Usage of renewable energy resource

Modernization of power transmission & distribution system

Alternative fuels for surface transportation- bio-fuels, electric vehicles, hydrogen and fuel cell vehicles.

Hydrogen has significant potential as a clean energy source

What is Conventional/ non conventional?

Non conventional energy sources are those energy sources which are exposed to use from modern technological advancements; rather than the normal use of conventional fuels

Conventional energy :Energy that has been used from ancient times is known as conventional energy.

Coal, natural gas, oil, and firewood are examples of conventional energy sources. Basically A Fossil Fuel.

E.g. tidal energy, geothermal energy

Fossil fuels

Fossils fuels (oil, coal, natural gas) are energy rich substances that have formed from the remains of organisms that lived 200 to 500 million years ago.

During the stage of the Earths evolution, large amount of dead organic matter had collected.

Over million of years, this matter was buried under layers of sediment and converted by heat and pressure into coal, oil and natural gas.

Coal is mostly used in the generation of electricity (thermal power).

Natural gas is used for commercial and domestic purposes like heating, air conditioning and as fuels for stoves and for other heating appliances.

Chemically, fossil fuels largely consist of hydrocarbons, which are compounds of hydrogen and carbon. Some fossils fuel also contains smaller quantities of other compounds.

Majority of fossil fuels are being used in transportation, industries heating and generation of electricity.

Crude petroleum is refined into gasoline; diesel and jet fuel that power the worlds transportation system.

Today, fossil fuels are considered to be non-renewable for the reason that their consumption rate is far in excess of the rate of their formation.

Oil

Crude oil, also called petroleum, is a thick liquid found in underground rock formations.

The petroleum industry extracts crude oil out of the ground and then refines it into products such as gasoline.

Crude oil contains a complex mixture of compounds made of carbon chains with hydrogen molecules attached to each link in the chain.

Oil Extracted crude oil also contains small amounts of

sulfur, oxygen, and nitrogen compounds mixed with the hydrocarbons.

The principle of oil refining is to remove crude oils impurities, that is, anything that is not a hydrocarbon.

The following nations hold the largest oil reserves, in order:

Saudi Arabia, Canada, Iran, Iraq, United Arab Emirates, Kuwait, Venezuela, Russia, Libya, and Nigeria.

Coals about 250 to 350 million years ago coal was formed on

earth in hot, damped regions. Almost 27350 billion metric tones of known coal

deposits occur on our planet. Out of which about 56% are located in Russia, 28% in USA and Canada. India has about 5% of worlds coal reserve and that too

not of vary good quality in term of heat capacity. West Bengal, Jharkhand, Orissa, Andhra Pradesh,

Madya Pradesh and Maharastra are the major coal producing states of India.

Mainly, there are three types of coal:

Anthracite or hard coal ( 90% carbon content)

Bituminous or soft coal (85% carbon content)

Lignite or brown coal (70% carbon content)

The present annual extraction rate of coal is about 3000 million metric tones, at this rate coal reserves may lasts for about 200 hundred years and if its use is increased by 2% per year then it will last for another 65 years.

Advantages and Disadvantage of Coal

Advantage Disadvantage

Ample supplies (225-900years)

Very high environmental impact

High net energy yield High land use (including mining)

Low cost (with huge substitutes)

Severe threat to human health

Mining and combustion technology well developed

High carbon dioxide emissions when burnt

Petroleum

Convenience of petroleum or mineral oil and its greater energy content as compared to coal on weight basis has made it the lifeline of global economy.

Petroleum is cleaner fuel when compared to wood or coal as it burns completely and leaves no residue.

Petroleum is unevenly distributed like any other mineral. There are 13 countries in the world having 67% of the petroleum reserves which together form the OPEC (Organisation of petroleum exporting countries)

Petroleum

Six regions in the world are rich in petroleum USA, Mexico, Russia and West Asian countries. Saudi Arabia oil producing has one fourth of the world oil reserves.

The oil bearing potential of India is estimated to be above one million square kilometers is about one third of the total geographic area.

Northern plains in the Ganga-Brahmaputra valley, the coastal strips together with their off-shore continental shelf (Bombay High), the plains of Gujarat, the Thar Desert and the area around Andaman and Nicobar Islands.

Advantages and Disadvantage of conventional oil

Advantage Disadvantage

Amply supply for 40-50years Need to find substitute within

High net energy yield Artificially low price encourages waste and discourages search for alternative

Low cost (with huge substitutes) Air pollution when burnt, Releases carbon dioxide

Easily transported within and between countries , Efficient distribution system

Moderate water pollution

Low land use

Technology is well developed

Natural Gas

Natural gas mainly consists of Methane (CH4) along with other inflammable gases like Ethane and propane.

Natural gas is least polluting due to its low Sulphur content and hence is clearest source of energy.

It is used both for domestic and industrial purposes.

Natural gas is used as a fuel in thermal plants for generating electricity, as a source of hydrogen gas in fertilizing industry and as a source of carbon in tyre industry

Natural Gas

The total natural gas reserves of the world is about 600 000 billion meters, out of this Russia has 34%, Middle East 18%, North America 17%, Africa and Europe 9% each and Asia 6%.

Annual production of natural gas is about 1250

billion cubic meters and hence it is expected to last for about 50-100 years.

In India gas reserves are found in Tripura,

Jaisalmer, off shore areas of Bombay and Krishna-Godavari Delta.

Advantages and Disadvantage of conventional Natural Gas

Advantage Disadvantage

Amply supply for 125 years Non renewable resources

High net energy yield Methane ( a green house gas) can leak from pipelines

Low cost (with huge substitutes) Air pollution when burnt, Releases carbon dioxide

Less air pollution than other fossil fuels

Shipped across ocean as highly explosive LNG

Moderate environmental impact Sometimes burnt off and wasted at wells because of low prices

Easily transported by pipelines Requires pipelines

Low land use

Environmental effects of Using Fossil Fuels:

Acid rain: When fossil fuels are buried, Sulphur, Nitrogen and Carbon combine with oxygen to form compounds known as oxide. These oxides when released into the atmosphere, they react with water form and result in the formation of Sulphuric acid, Nitric acid and Carbonic acid. These acids can harm biological quality of forests, soils, lakes and streams.

Ash particles: Ash particles are the un burnt fuel particles. However with strict imposition of Government regulations, some equipments are provided to trap these particles. Petro and natural gas generate less ash particles than coal, diesel or gasoline.

Environmental effects of Using Fossil Fuels:

Global warming: Carbon dioxide is a major by product of fossil combustion and this gas is known as green hour gas. Green hour gas absorbs solar heat reflected off the earths surface and retains this heat, keeping the Earth warm and habituate for living organisms.

Rapid industrialization between 19th and 20th centuries, however has resulted in increasing fossils fuel emissions, raining the percentage of carbon dioxide by about 28%. This drastic increase has led to global warming that could cause environmental problems, including disrupted weather patterns and polar ice cap melting.

Nuclear Energy Nuclear energy is non- renewable source of

energy, which is released during fission(disintegration) or fusion (union) of selected radioactive materials.

Nuclear power appears to be the only hope for large scale energy requirements when fossil fuels are exhausted. The reserves of nuclear fuels is about ten times more than fossil fuels and its major advantage is that even small quantities can produce enormous amounts of energy.

Nuclear Energy

For example, a ton of uranium 235 can produce an energy equivalent 3 million tones of coal or 12 million barrels of oil.

Nuclear energy has been successfully used in the generation of electricity in spaceships, marine vessels, chemical and food-processing industry.

Definitions

Fuels are substances which, when heated, undergo chemical reaction with an oxidizer, typically oxygen, to liberate heat.

Commercially important fuels contain carbon and hydrogen and their compounds, which provide heating value

Definitions (contd)

Fuels may be solid, liquid or gaseous

Fuels may be fossil (non-renewable) or biomass (renewable)

Fossil fuels may be coal, petroleum-crude derived or natural gas.

Biomass fuels may be wood, refuse or agricultural residues.

Definitions (contd)

World-wide production of fossil fuels in 1994:

Coal: 180 x 1015 kJ

Petroleum crude: 114 x 1015 kJ

Natural gas: 98 x 1015 kJ

Biomass fuels provide about 20 x 1015 kJ to world energy production

Fossil fuels provide about 85% of world energy production. Balance provided by hydroelectric, nuclear and biomass.

Some statistics

Middle East and Eastern Europe have 70% of worlds natural gas reserves

Middle East has 67% of worlds crude oil reserves

Canada has approx. 1 trillion barrels of oil in tar sands

North America, Eastern Europe and China have the largest coal reserves

Some statistics

The US with a small fraction of the worlds population consumes 25% of the worlds crude oil, 25% of the worlds natural gas and 21% of the worlds coal production. They also have a third of the worlds motor vehicles

Each American uses the same energy as 3 Japanese, 38 Indians and 531 Ethiopians!

LIQUID FUELS

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1. Occurrence and Processing

The basic source of liquid fuels is crude oil, which occurs in strata of sedimentary rocks.

Gaseous, liquid and semi-solid materials are separated at the well head, but the liquid fuels which are burned in practice are first processed in a refinery.

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The most significant of the refinery processes is distillation.

The crude oil is flashed (i.e. it undergoes a sudden drop in pressure) into a column.

The main part of the column is at atmospheric pressure with a vacuum section producing the heavier products.

90

The vaporized oil travels up the column which has a vertical temperature gradient with the top of the column being the coolest part (Fig. 8.1, next slide).

The fraction of the oil which vaporizes in the column will condense out at the appropriate level in the column. A system of bubble caps and trays is used to facilitate this.

93

All the products which have been condensed in the column are grouped as distillate oils, whereas the component of the feedstock which did not evaporate forms residual fuel products.

Further processing will take place which enables heavier fractions to be cracked into lighter products or the lower molecular weight components reformed into larger molecules.

94

2. Properties of oil Fuels

Table 8.1 (next slide) gives some physical properties of the commercially important fuel oils.

Some explanatory notes about the properties in the table follow.

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Flash Point This gives an indication of the flammability of the fuel. Its significance is in the safety aspects of storing and handling the fuel.

Viscosity This is a measure of resistance to flow. It reflects the energy required to pump the oil through pipework and it has an important bearing on the atomization process in burners.

97

The usual method of quoting the viscosity of an oil is to give the value of the kinematic viscosity in centistokes (cs).

Kinematic viscosity is the dynamic viscosity divided by the density of the fluid. It is measured in a standard U-tube viscometer at 38.

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Pour Point This is complementary to viscosity in that it gives an indication of the temperature at which the oil will start to flow freely.

Calorific Value The calorific value of a liquid fuel is measured in a bomb calorimeter, which measure directly the gross calorific value at constant volume. It can be seen that the less volatile oils have lower calorific values.

99

Sulfur content Sulfur exists in all liquid fuels, but it is present to a significant degree in residual fuel oils. When burnt, sulfur forms SO2 and SO3 which are major sources of air pollution.

100

There are two important consequence of SOX for thermal plant installations: The flue must be designed to provide acceptable

concentrations of SOX at ground level;

It is particularly important to prevent condensation from the flue gases anywhere in the equipment, as both SO2 and SO3 are soluble in water, forming sulfurous and sulfuric acid respectively, and sulfuric acid vapor can be formed in the flue gas.

101

Specific Heat A knowledge of the specific heat of the liquid is important in handling liquid fuels since the residual oils all have to be heated before they can be atomized, and the heavier grades must be stored in a heated tank if they are to flow freely into the distribution pipework.

102

Relative Cost Although there is a clear price differential in favor of the residual oils, the capital investment in the storage system, handling and combustion equipment for residual fuel oils is significantly higher than that needed for distillate oils.

103

3. Combustion of Liquid Fuels

For efficient combustion, a liquid fuel must be broken up into a stream of droplets to maximize the surface area-to-volume ratio.

The various types of burner accomplish this in different ways, but the objective of all types of burner is to produce a spray of droplets which are small, and which have a narrow size distribution.

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The combustion process consists of evaporation of the droplet, driven by heat transfer from its surroundings, with the vapor subsequently burning in a diffusion flame.

A classical analysis of this situation where the heat transfer to the droplet is by convection shows that the rate of mass transfer (and hence the combustion rate of the droplet) is inversely proportional to the diameter.

105

Because evaporation of the droplet is the controlling influence on the combustion rate, liquids with low latent heats of evaporation will burn more quickly.

The combustion of a liquid fuel spray is more complex than is indicated above: in particular, heat transfer to the droplet will be by radiation as well as convection.

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The combustion of oil is a two phase process.

Intimate mixing of the fuel and air is an important requirement hence the fuel is broken up into a fine spray, or atomized.

Three common oil burners with different atomization methods are reviewed below.

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4. Pressure Jet Burners

The simplest form of pressure jet consists of a swirl chamber through which the fuel passes before issuing through the final orifice (Fig. 8.2, next slide).

Angular velocity is imparted to the liquid by tangential slots or ports.

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The fuel emerges from the jet as a conical sheet which subsequently breaks up into droplets of between 10 and 200 m diameter.

The oil supply pressure is usually greater than 500 kPa.

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The simplest and most common type of oil burner incorporates the pressure jet, and this is shown diagrammatically in Fig. 8.3 (next slide).

Pressure jet burners span a wide range of ratings, from domestic units of about 25 kW up to 2.5 MW. Classes C, D, and E oils can be burned.

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The control of the output of the burner depends on its size.

Units of less than 300 kW usually operate in on/off mode; larger units than this can incorporate continuous modulation of the air and oil supply flow rates, with reversion to on/off control at low loads.

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Pressure jet burners are not capable of modulating to accommodate a wide range of loads.

A maximum turndown ratio (max. firing rate/min. firing rate) of 2:1 can be achieved, but 1.5:1 is a more usual figure.

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5. Rotary Cup Burners

The supply of oil is fed onto a rotating surface (usually a cup or disk) and the atomization is achieved when the fluid is flung off the cup by centrifugal force (Fig. 8.4, next slide).

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These atomizers tend to give a narrow size range of droplets and are ideally suited to the more viscous liquid fuels, as pumping pressures are much lower than those for pressure jet burners.

The cup rotates at 4,000-6,000 rpm to atomize a class G residual fuel oil, although much higher speeds are used in some applications.

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The air supply to this type of burner is split into two streams: 15% is supplied as primary air around the atomizer itself, the remainder being admitted subsequently as secondary air.

Rotary cup atomizers are used to burn residual oils of classes E, F and G, and are rated between 150 kW and 5 MW.

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6. Twin-fluid Atomizers

A second fluid (typically air or steam) is used to produce the shear necessary to break up the oil into droplets.

The nozzle is essentially similar to that of the pressure jet burner with the addition of an extra set of tangential ports on the inside or outside of the oil flow passage.

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In an air-blast atomizer about 2-10% of the combustion air is supplied at a high pressure (20-100 kPa).

This type of atomizer is more expensive to operate than the other types but it is capable of much greater load modulation, achieving turndown ratios up to 5:1, which can make the extra expense worthwhile.

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7. Storage of Liquid Fuels

Tanks may be located inside or outside and are usually of the vertical or horizontal cylindrical type.

It is usual to allow for a storage capacity equivalent to 2-3 weeks full load running - this figure is easily obtained from the rating of the burner and the calorific value of the fuel.

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The oil tank itself must be vented and a bund wall must be provided which can hold the entire tank contents.

For distillate oil systems a single pipe system is adequate for delivery of the oil to the burner.

For residual fuel oil systems a ring main system is required and provision must be made to ensure that the oil is at the appropriate temperature, as summarized in Table 8.2 (next slide).

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Table 8.2 Storage and handling temperatures for liquid fuels

Class Min. temperature ()

Storage Outflow

E

F

G

10

25

40

10

30

50

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Additional heating is usually provided at the burner appropriate to the type of atomizer in use.

Where storage heating is required (classes F and G) the tank is insulated against heat loss.

Types of Fuels

Liquid Hydrocarbon fuels may be

1. Paraffins: straight chain compounds like methane, ethane, propane, etc. or branched chain compounds (isomers) like iso-butane, iso-heptane (like 2,2,3 tri-methyl butane or triptane) and iso-octane (like 2,2,4 tri-methyl pentane).

2. Olefins: Open chain unsaturated hydrocarbons with a double bond like ethene or propylene which also have straight and branched chain compounds.

3. Diolefins: These are olefins with 2 double bonds.

Both types of olefins produce gum when reacted with oxygen which can block fuel filters.

Types of Fuels (Continued)

4. Alkynes: Unsaturated hydrocarbons with a triple bond. A typical example is acetylene or ethyne.

5. Napthenes or Cycloparaffins: Have same general formula as monoolefins but are saturated compounds with a ring structure. Examples are cyclopropane, cyclobutane etc.

6. Aromatics: Ring structured unsaturated hydrocarbons with double bonds but more stable than the parafffinc double bond hydrocarbons. Examples are benzene, toluene, naphthalenes, and anthracenes.

The molecular weight of a hydrocarbon is given by: Mol. Wt.=12x + y

where x = carbon no. & y = no. of H atoms

Gasoline from Methanol

Gasoline from Methanol

General Formulas for Organic Compounds found in Crude Oil

Family Formula Structure

Paraffins (alkane) CnH2n+2 Straight and Branched

Paraffins (alkene) CnH2n Straight and Branched

Paraffins (alkyne) CnH2n-2 Straight and Branched

Naphthenes

(cyclanes) CnH2n Ring

Aromatics

(Benzenes) CnH2n-6 Ring

Aromatics

(naphthalene) CnH2n-12 Ring

Differences Between Coal and Petroleum

Coal Petroleum

Formed from land plants

decaying under mildly

reducing conditions

Formed mainly from sea

plants and animals decaying

under strongly reducing

conditions

Seams remain where

deposited, i.e., location of

existing deposits are usually

same as the location of

accumulation of debris

Can migrate under effects of

temperature and pressure,

i.e., location of existing

deposits may not be the

same as location of

accumulation of debris

Composition of typical crude oil

Carbon: 80-89%

Hydrogen: 12-14%

Nitrogen: 0.3-1.0%

Sulfur: 0.3-3.0%

Oxygen: 2.0-3.0%

Plus oxygenated compounds like phenols, fatty acids, ketones and metallic elements like vanadium and nickel.

Typical Refinery Products

Product Boiling Range, oC

Liquefied Petroleum Gas -40 to 0

Motor Gasoline 30-200

Kerosene, jet fuel (ATF) 170-270

Diesel Fuel 180-340

Furnace Oil 180-340

Lube Oils 340-540

Residual Fuel 340-650

Asphalt 540+

Petroleum Coke Solid

Products from Asphalt-based Crude

Products from Paraffin-based Crude

Refinery processes

1. Distillation: Continuous, Atmospheric, and Vacuum.

2. Cracking: Thermal, Catalytic and Hydro.

3. Reforming: Thermal, Catalytic and Hydro

4. Polymerization

5. Alkylation

6. Isomerization

7. Hydrogenation

Likely Fuels from Various Primary Energy Resources with Conversion Efficiencies

Primary Energy Resource

(Conversion Efficiency)

Fuels Obtainable

Petroleum Crude

(0.90-0.98)

Cleaned crude oil (water, solids,

and gases removed. Distillate fuel

(obtained from distillation)

Oil Shale

(0.63-75)

Hydrogenated shale oil. Distillate

fuel.

Coal

(0.37-0.95)

Powdered coal. Pulverized coal.

Solvent refined coal. Distillate fuel.

Fischer-Tropsch liquid HCs

Biomass

(0.25-0.35)

Ethanol. Liquid hydrocarbons.

Nuclear

(0.17-0.20)

Methanol, Fischer-Tropsch liquid

hydrocarbons

Petroleum Crude Conversion to Oil

Coal Conversion to Oil

Oil Shale Conversion to Oil

Liquid fuels

Liquid fuels are derived from 2 main sources :

From crude oil and from coal.

Liquid fuels can be divided into 2 classes,

Light oils /spirits, suitable for IC engines

Heavy oils, suitable mainly for burning in furnaces.

Petroleum

The approximate composition of petroleum is: carbon 80-89%, hydrogen 12-14%, nitrogen 0.3-1.0%, sulphur 0.3-3.0% and oxygen 2-3%.

Chemistry of petroleum: The main components of petroleum are hydrocarbons i.e, they contain only carbon and hydrogen. Carbon combines with hydrogen in various amounts to form a variety of compounds. Types of hydrocarbons found in petroleum are paraffins, iso-paraffins, olefins, naphthenes, and aromatics.

Paraffins:

They are given the suffix ane,eg.,methane, ethane propane etc.Their general formula is CnH2n+2.These compounds are quite stable and have a lower specific gravity.The compounds with lower molecular weight are gasses at room temperature and pressure

Iso-paraffins:

Iso-paraffins are isomers of normal paraffins.The chemical formula remains the same but the arrengement of atoms is modified. Eg.,2,2,4-trimethylpentane. Pentane indicates the five carbonatoms of a paraffin molecule,trimethyl indicates 3 methyl groups attached to main carbon chain,2,2,4 gives the number of carbon atoms in the main chain to which the methyl group is attached.

Olefins:

olefins are generally named with the suffixene,eg., pentene, octene etc.They have a straight carbon chain but with one or more carbon atoms doubly bonded together. They are unsaturated hydrocarbons. They are chemically active as compared to the other hydrocarbons and have good burning characteristics.

Naphthenes:

Naphthenes are designated by the termcyclo in their name because of the carbon ring in the molecule.They have general formula as for monolefins but they are saturated( CnH2n).

Aromatics:

Aromatics are those that have benzene rinfg in their molecular sructure.The banzene ring consists of 6 carbon atoms in a ring with alternative carbon atoms double bonded.This leaves the carbon atom with a single valence.An aromatic which has a single hydrogen atom in the benzene ring replaced by a normal alkyl group is called an alkylbenzene compound, eg.,n-propyl-bengene.

Fractional Distillation

Distillation is a process of separation on a molecular basis. The crude oil is first heated around 300c to 350c. These vapors are then condensed in a cylindrical tower called FRACTIONATING COLUMN. The column is kept at nearly atmospheric pressure. The uncondensed gases leave the tower from the top, and are sent for absorption.

Substances with high boiling points condense at the bottom and substances with low boiling points condense at the top.

Cracking

Cracking means the breaking of heavy molecules into lighter hydrocarbons. In this process, the temperature is around 500c. At this elevated temperature, heavy oils decompose to give lower hydrocarbons which have a low boiling range and a heavy residue of coke.

The cracking process is two types:

thermal

catalytic.

Thermal Cracking Initiation reactions, where a single molecule breaks apart into two free radicals. Only a

small fraction of the feed molecules actually undergo initiation, but these reactions are necessary to produce the free radicals that drive the rest of the reactions. In steam cracking, initiation usually involves breaking a chemical bond between two carbon atoms, rather than the bond between a carbon and a hydrogen atom..

CH3CH3 2 CH3 Hydrogen abstraction occurs where a free radical removes a hydrogen atom from another

molecule, turning the second molecule into a free radical.

CH3 + CH3CH3 CH4 + CH3CH2 Radical decomposition occurs where a free radical breaks apart into two molecules, one an

alkene, the other a free radical. This is the process that results in the alkene products of steam cracking.

CH3CH2 CH2=CH2 + H

Radical addition, the reverse of radical decomposition, occurs where a radical reacts with an alkene to form a single, larger free radical. These processes are involved in forming the aromatic products that result when heavier feedstocks are used.

CH3CH2 + CH2=CH2 CH3CH2CH2CH2 Termination reactions occur when two free radicals react with each other to produce

products that are not free radicals. Two common forms of termination are recombination, where the two radicals combine to form one larger molecule, and disproportionation, where one radical transfers a hydrogen atom to the other, giving an alkene and an alkane.

CH3 + CH3CH2 CH3CH2CH3 CH3CH2 + CH3CH2 CH2=CH2 + CH3CH3

catalytic cracking The feedstock to an FCC is usually that portion of the crude oil that has an initial boiling point of 340 C or higher at atmospheric pressure and an average molecular weight ranging from about 200 to 600 or higher. This portion of crude oil is often referred to as heavy gas oil. The FCC process vaporizes and breaks the long-chain molecules of the high-boiling hydrocarbon liquids into much shorter molecules by contacting the feedstock, at high temperature and moderate pressure, with a fluidized powdered catalyst.

Vacuum Distillation Process

The residue of processes can be refined to yield more gasoline by vacuum distillation. Due to high temperature and low pressure, heavy distillates are squeezed out of the residue. The remaining residue is called vacuum bottoms. The distillate is usually subjected to the catalytic cracking process.

These vacuum bottoms can be used as charge for the visbreaking process.

Some compounds have very high boiling points. To boil such compounds, it is often better to lower the pressure at which such compounds are boiled instead of increasing the temperature. Once the pressure is lowered to the vapor pressure of the compound (at the given temperature), boiling and the rest of the distillation process can commence. This technique is referred to as vacuum distillation and it is commonly found in the laboratory in the form of the rotary evaporator.

This technique is also very useful for compounds which boil beyond their decomposition temperature at atmospheric pressure and which would therefore be decomposed by any attempt to boil them under atmospheric pressure.

Visbreaking This process is similar to thermal cracking

except that the pressure and temperature used are lower. The purpose of this process is to obtain large volumes of distillate for catalytic cracking from vacuum bottoms.

A visbreaker thermally cracks large hydrocarbon molecules in the oil by heating in a furnace to reduce its viscosity and to produce small quantities of light hydrocarbons (LPG and gasoline)

Reforming Process

The purpose of the reforming process is to change the chemical nature of various hydrocarbons to give the desired physical properties. These include thermal and catalytic reforming.

The main difference between the refining and reforming processes is that the former is carried out on crude, residue, or heavy oils, while the latter is done on gasoline.

Catalytic reforming is a chemical process used to convert petroleum refinery naphthas, typically having low octane ratings, into high-octane liquid products called reformates which are components of high-octane gasoline (also known as petrol). The overall effect is that the product reformate contains hydrocarbons with more complex molecular shapes having higher octane values than the hydrocarbons in the naphtha feedstock. In so doing, the process separates hydrogen atoms from the hydrocarbon molecules and produces very significant amounts of byproduct hydrogen gas for use in a number of the other processes involved in a modern petroleum refinery.

Reforming

Thermal Reforming Catalytic Reforming Thermal reforming is similar to

thermal cracking. The temperature of around

500-600c and pressure of around 80 kg/cm.

The Extent of reforming is controlled by quenching the hot vapours with cold oil called quenching oil.

The quenched vapours are then passed in to a fractionate column to remove residual gases.

Catalytic reforming is a chemical process used to convert petroleum refinery naphthas, typically having low octane ratings, into high-octane liquid products called reformates which are components of high-octane gasoline (also known as petrol). Basically, the process re-arranges or re-structures the hydrocarbon molecules in the naphtha feed stocks as well as breaking some of the molecules into smaller molecules

Polymerization

Light gases resulting from fractional distillation and cracking can be polymerized to give heavier hydrocarbons, thus increasing the yield of gasoline from the escaping gases.

Polymerization is the reverse of cracking.

Ethylene, propylene, butylene, etc. are quite reactive and can easily be polymerized in the presence of a catalyst at higher temperatures and pressures to give liquid hydrocarbons.

Isomerization

The process of changing one type of molecule to another type with the same molecular weight is known as isomerization.

It is usually carried out in the presence of a catalyst aluminium chloride(ALCL3) activated by anhydrous hydrochloric acid.

The temperature and pressure suitable for such reactions are 110c and 21kg/cm3 for butane isomerrization.

Flash point and Fire Point

Flash Point Fire Point

As fuel oils are heated, vapours are produced which at a certain temperature flash when ignited by an external flame. This temperature is called the flash point of the oil.

As fuel oil are heated, vapours are produced which at a certain temperature flash when ignited by an external flame. If heating is continued, sufficient vapours are finally driven off to produce continuous burning and not a single flash. This temperature is called the fire point.

Calorific value & Ash Content

Calorific value Ash Content

The calories or thermal units contained in one unit of a substance and released when the substance is burned.

The quantity of heat produced by the complete combustion of a given mass of a fuel, usually expressed in joules per kilogram

Ash is the inorganic residue remaining after the water and organic matter have been removed byheating in the presence of oxidizing agents, which provides a measure of the total amount of minerals.

Reid vapour pressure

This is a measure of vapour pressure of an oil at 38c expressed in kg/cm3 or in millimeters of mercury. The vapour pressure is a measure of tendency of gasoline to vapour lock or generate vapour bubbles in the oil line.

VARIOUS PETROLEUM PRODUCTS

Motor gasoline Aviation gasoline Aviation turbine fuels Kerosene Diesel fuels Fuel oils Oil shales

Motor gasoline: Motor gasoline is an ideal fuel for spark ignition engines. The main advantage of a gasoline engine is its light weight per B.H.P. developed. This makes it most suitable for automotive vehicles.

Aviation gasoline: The desired properties of aviation gasoline are slightly different than for motor gasoline. Various grades of aviation are gasolines are available. The grade number indicates its octane number or performance number.

Kerosene: It is extensively used for heating and lighting. Its boiling range is 150 to 300oc. It mainly consists of paraffins. Its viscosity should be less than 2.5 centistokes for easy flow of fuel through capillaries or the wick.

Diesel fuels: Diesel fuels are used in compression ignition engines. The normal boiling range for the diesel fuel is 200 to 370oc. High speed diesel may use oils with initial boiling point as low as 140oc.

SOLID FUELS

186

1. Introduction

Solid fuel embraces a wide variety of combustibles, ranging from wood, peat and lignite, through refuse and other low calorific value substances, to coal and other solid fuels derived from it.

Coal represents by far the largest component of the worlds fossil fuel reserves.

187

In thermal terms 90% of the known hydrocarbon fuel deposits are formed by coal.

The carbon: hydrogen ratio of coal is the highest of the fossil fuels, hence the calorific values of coals are principally determined by the carbon in the fuel.

188

It is usual to consider coals in terms of their rank: in general, a high ranking coal will have a high carbon content.

The other major coal constituent element, hydrogen, is present in hydrocarbons which are released as volatile matter when the coal is heated.

189

Coal is a sedimentary rock of vegetable origin. Vast deposits of plant material, formed approximately 80 million years ago, were consolidated by pressure, heat and earth movement.

The rank of a coal is related to its geological age and, generally, its depth in the earth.

190

The ranking sequence is: Wood Peat Lignite (brown coal) Bituminous Coal Anthracite

In general, deposits close to the surface which can be worked by strip mining produce a more economical fuel than deep mined coal.

191

Coal was the fuel which fired the Industrial Revolution, but it is no longer the cheapest option among the fossil fuels.

The cost of working the deposits and the investment in technology needed to meet increasingly stringent emissions standards have increased the cost of burning coal.

192

Recent developments in gasification processes have shown that it is possible to produce gas from coal at a viable thermal efficiency and to remove the sulfur from the fuel at the same time.

193

2. Coal Classification

As the rank of a coal increases, its carbon content increases from 75% to about 93% (by weight), the hydrogen content decreases from 6% to 3%, and the oxygen content decreases from 20% to 3%.

A useful method for analyzing a coal is the proximate process.

Proximate analyses of some common fuels are given in Table 9.1 (next slide).

194

Table 9.1 Composition of some typical solid fuels (% by mass)

Fuel Carbon Volatile

matter

Moisture

Ash

Peat

Lignite

Bituminous

Coal

Anthracite

44

57

82

90

65

50

25

4

20

15

2

1

4

4

5

3

195

The moisture in coal is made up of two components: surface moisture and inherent moisture.

The former is affected by the way in which the coal is stored, and is thus variable.

196

Coals are also analyzed in terms of their elemental constituents, giving the ultimate analysis which was used earlier in stoichiometric calculations.

Typical ultimate analyses of two types of solid fuels are given in Table 9.2 (next slide).

197

Table 9.2 Ultimate analyses (% by mass) of some coals

Coal Carbon Hydrogen Oxygen Nitrogen Sulfur

Anthracite

Bituminous

94.4

89.3

2.9

5.0

0.9

3.4

1.1

1.5

0.7

0.8

198

3. Coal Properties

There are a number of properties which are important in identifying the suitability of a coal for any given application:

Size Some common size groups, together with their rather picturesque names, are given in Table 9.3 (next slide).

199

Table 9.3 Size distribution for coals

Name Upper limit (mm) Lower limit (mm)

Large Cobbles

Cobbles

Trebles

Doubles

Singles

>150

100-150

63-100

38-63

25-38

75

50-100

38-63

25-38

13-18

200

Calorific value The ranking of a coal is not necessarily related to its calorific value.

Coal fuels generally have a range of values from 21 to 33 MJ/kg (gross).

The design rating of a coal-fired burner is usually based on an estimated calorific value of 26 MJ/kg (6,200 kcal/kg).

201

Ash Fusion Temperature The melting point of the ash left after combustion of the coal is of particular importance in terms of the combustion and ash disposal equipment.

If the ash fuses it produces a glassy, porous substance known as clinker (slag).

The combustion equipment will be designed to handle either clinker or unfused ash, and use of the wrong type of coal can have dire consequences.

202

Sulfur Content Many deep-mined coals have a fairly high sulfur content, typically around 1.5% by weight.

The same consideration apply to coal-fired installations as to oil-fired combustion equipment namely that condensation inside the plant must be avoided and that the design of the flue must ensure that ground concentration of sulfur oxides are controlled within acceptable limits.

203

4. Coal Combustion

Coal combustion is a two-phase process and the objective of the burner is, as always, to achieve complete combustion of the fuel with maximum energy efficiency.

Three common ways of burning solid fuels are currently in use and are briefly reviewed below.

204

Pulverized Fuel The coal is ground to a very fine size (about 0.08mm or more than 70% pass through #200 mesh) when it can be made to behave rather like a liquid if air is blown upwards through the powder.

The preparation and handling equipment is very expensive and pulverized fuel installations are generally only economically viable in very large scale applications, such as thermal power stations.

205

The fuel is injected in the form of a conical spray, inside a swirling conical primary air supply in a fashion analogous to that for an oil burner.

Fluidized Bed Combustors (FBC) The basic principle of operation is that the coal is mixed with an inert material (e.g. sand) and the bed is fluidized by an upwards flow of air (Fig. 9.1, next slide).

207

Although the fluidization requires more fan power than the conventional grate combustions (Figs. 9.3 & 9.4), there are a number of advantages in FBC: (1) The bed temperature can be kept cooler than in the case of grate combustion-fluidized bed temperatures are generally within the range 750-950. This means that ash fushion does not occur and the low temperatures produce less NOX.

208

(2) High rates of heat transfer can be attained between the bed and heat exchanger tubes immersed in it. (3) A wide range of fuel types can be burned efficiently. (4) additives (such as limestone) can be used which react with oxides of sulfur retaining the sulfur in the bed with consequent reduction in SOX emission.

209

Grate Combustion The simplest, and most common, way of burning coal is by igniting a bed of the fuel on a porous grate which allows air to rise through the bed, either by buoyancy in smaller equipment or with fan assistance in the larger, automatic stokers.

The combustion of a coal on a grate commences with heat transfer to the raw coal from the adjacent incandescent fuel.

The first effect that this has is to drive off the volatile matter from the coal.

210

The volatiles will then rise through the bed, partly reacting with the hot carbonaceous material above it, to burn as a yellow flame above the bed.

As the combustion process proceeds, the volatile matter decreases until there is only the carbonaceous residue left, which burns with the intense emission of radiation.

211

As the air enters the fuel bed from below, the initial reaction is the combustion of the carbon to carbon dioxide.

In the hot upper region of the gas this is reduced to carbon monoxide: CO2 + C 2CO Which burns in the secondary air above the bed.

212

The effect of this is to decrease the concentration of oxygen from 21% at entry, to zero at about 100 mm above the grate.

At this point, there is a peak in the carbon dioxide concentration which falls away as the reduction to carbon monoxide proceeds (Fig. 9.2, next slide).

214

Underfeed Stoker Next slide, Fig. 9.3, coal is fed into the retort by the action of a screw.

When combustion is completed at the top of the bed, a residue of ash and clinker remains which falls to the sides of the retort.

216

The de-ashing of underfeed stokers is generally a manual process, although some manufacturers offer automatic ash-handling facilities.

Bituminous singles with an ash fushion temperature of around 1,200 are an appropriate fuel for this type of device.

217

Chain Grate Stoker A diagram of a chain grate boiler is shown in Fig. 9.4 (next slide).

The coal is supplied by the travelling grate and the thickness of the bed controlled by the guillotine door.

The speed of the grate and an air damper setting control the firing rate.

219

The fuel for such boilers is usually smalls (about 13-25 mm) with a high ash fushion temperature.

The ash falls from the end of the grate into a pit, from where it can be removed by a conveyor belt or screw.

220

5. Coal Storage and Handling

Solid fuels are stored in bunkers-normally a quantity equivalent to 100 hours at peak firing rate is the target storage capacity, with a minimum amount of 20 tonnes.

Coal is usually conveyed into storage from the delivery vehicle by tipping or by pneumatic conveyance along pipes.

Forms of Fuels Natural Form Artificial Form

Wood Wood Charcoal

Peat Peat Charcoal

Lignite Lignite Briquettes

Lignite Coke

Hard Coal Sub-bituminous

Hard Coal bituminous

Hard coal anthracite

Coal Briquettes Carbonized

and Uncarbonized

Low, Medium & High Temp.

Coke

Solid Fuel Analysis

Proximate analysis: (ASTM D3172)

Sample of known mass, to determine:

Moisture dried at 105 to 110oC in an oven

Volatile combustible matter heated to 900oC in a covered crucible

Fixed carbon heated to 750oC in an open crucible

Ash the final residue

Solid Fuel Analysis

Ultimate Analysis: (ASTM D3176)

Provides the major elemental composition of the fuel, that is usually reported on dry, ash-free basis

Carbon includes organic carbon & carbon from mineral carbonates

Hydrogen includes organic hydrogen & hydrogen from moisture & mineral hydrates

Other elements include oxygen, nitrogen, sulfur and others like chlorine.

Wood

A Renewable Fuel

Typical Proximate Analysis of Wood compared to Coal

Fuel Moisture,

%

Volatile

Matter, %

Fixed

Carbon, %

Ash, %

Bituminous

Coal

2.5 37.6 52.9 7.0

Hard Wood

wet

45.6 48.58 5.52 0.3

Hard Wood

dry

0.0 89.31 10.14 0.56

Southern

pine wet

52.3 31.5 15.9 0.29

Southern

pine dry

0.0 66.0 33.4 0.6

Typical Ultimate Analysis of Some types of Wood in %

Type of Wood C H O N S Ash

California Red

Wood

53.5 5.9 40.3 0.1 Trace 0.2

Western

Hemlock

50.4 5.8 41.4 0.1 0.1 2.2

Douglas Fir 52.3 6.3 40.5 0.1 Trace 0.8

Pine (Sawdust) 51.8 6.3 41.3 0.1 Trace 0.5

Typical Ultimate Analysis of Some types of Bark Species in %

Types of Wood C H O N S Ash

Western Hemlock 53.0 6.2 39.3 0.0 Trace 1.5

Douglas Fir 51.2 5.2 39.2 0.1 Trace 3.7

Loblolly Pine 56.3 5.6 37.7 0.0 Trace 0.4

Long Leaf Pine 56.4 5.5 37.4 0.0 Trace 0.7

Short Leaf Pine 57.2 5.6 36.1 0.4 Trace 0.7

Flash Pine 56.2 5.4 37.3 0.4 Trace 0.7

Typical Values of Calorific Values in kJ/kg of Wood Fuels

Wood Variety Calorific Value, green Calorific Value, dry

Ash-white 10,300 12,550

Beech 9,165 12,465

Birch Yellow 8,850 12,150

Chestnut 6,125 13,440

Cotton Wood 7,035 13,950

Elm-white 8,350 13,280

Hickory 9,425 14,420

Maple, sugar 9,490 13,000

Maple, red 8,710 13,880

Oak, red 7,860 12,940

Oak, white 9,300 12,930

Willow 5,510 13,650

Wood Storage

Wood fuels undergo losses in net available energy as storage time increases due to

1. Moisture accumulation with time and reaches saturation.

2. Loss of volatiles due to evaporation: 15% of net available energy is lost this way.

The pH of wood is reduced making it acidic leading to corrosive effects

Last in, first out (LIFO) must be followed.

Wood Combustion

1. Surface undergoes thermal breakdown: vapors, gases, mists (combustibles) are evolved. Exists up to 200oC.

2. More gases are evolved. Heat liberation reactions occur but no flaming. Occurs from 200 to 280oC.

3. Gases continue to evolve and heat is liberated. Flaming starts. Occurs up to 500oC.

4. Above 500oC all gases and tar are driven off. Pure carbon (charcoal) remains. Further heating will result in combustion of charcoal.

Combustion Characteristics of Wood

1. It is easily ignited.

2. Does not burn in large pieces because layers of semi-fused ash forms on the surface.

3. Produces a long, non-smoky flame when burned in excess air. With limited air, it burns with a lot of smoke.

4. As saw dust it burns readily. Saw dust can be made into binderless briquettes at pressures of up to 8 kg/mm2.

Alternate fuels from Wood

1. Charcoal:

A carbonized form of wood. Involves the decomposition of the wood in the absence of air. Three methods are known:

a. An ancient process: in pits.

b. Low temperature carbonization: in metal retorts, at about 350oC.

c. High temperature carbonization: in retorts, at around 1000-1200oC.

Charcoal is easily ignited. Used as reducing agent for iron ore, domestic cooking and to manufacture producer gas.

Alternate fuels from Wood

1. Charcoal (Continued)

Typical Ultimate analysis on wet basis with ash:

Carbon: 85.2%

Hydrogen: 2.9%

Oxygen+Nitrogen: 3.5%

Ash: 2.5%

Moisture: 5.9%

Calorific Value: 31,400 kJ/kg

Alternate fuels from Wood

2. Substitute Natural Gas (SNG) and Methanol:

Obtained by gasifying wood to carbon monoxide and hydrogen after moisture is removed.

Wood has self generating water supply and low ash and sulfur, making its gasification superior to coal gasification.

CO and H2 are synthesized to form SNG over a catalyst or methanol. Methanol can be converted to gasoline by the MTG process.

Alternate fuels from Wood

3. Producer gas:

In India, producer gas from wood is used as a fuel. Yield from about 500 kg wood is about 7400 m3 and calorific value is about 5600 kJ/ m3.

Peat

Beginning of Fossilization

Peat

Peat is the first stage in the formation of coal.

It is regarded as the borderline between vegetation (biomass) and a fossil fuel.

It is a brown, fibrous mass of partially decayed plant material accumulated in situ under water-logged conditions.

Composition depends on type, depth of deposit and age. The oldest peats are about 1 million years old.

Peat is believed to have formed from wood. When wood is subjected to bacterial processes under nearly stagnant water, the cellulose, lignin and protein are decomposed. Residuals combine to form dopplerite.

Peat (Continued)

Contains 70-90% dopplerite and 5-30% resins and waxes.

Wet peat contains 95% moisture.

Reduces to 90% when cut.

Reduces to less than 25% when air dried.

Ash is about 3%.

Calorific value varies between 16,700 and 20,900 kJ/kg.

Peat (Continued) Ultimate Analysis

Element Moss Peat Forest Peat Old Peat

Carbon 51.1 55.5 59.5

Hydrogen 6.1 5.8 5.8

Nitrogen

1.8 1.5 2.3

Sulfur 0.6 0.8 1.0

Oxygen 40.4 36.4 31.4

Peat (Continued) Combustion Characteristics

1. Its low calorific value and high moisture content reduces furnace temperature and efficiency of combustion.

2. Its low bulk density (320 kg/m3) reduces capacity of furnace and increases storage and handling capacity due to its high volume.

3. Its friable nature (can be easily crumbled) causes appreciable loss in handling.

4. It may be used as a powder or may be briquetted without any binder.

Peat Carbonization

Like wood, it may be carbonized at low temperature in metal retorts. Yields:

Charcoal: 30%

Gases: 19-30%

Moisture: 30-40%

Tar: 6-7%

Gases used to provide heat for carbonization. Tar yields was and oil. Moisture yields ammonium sulfate, calcium acetate and methanol.

Ultimate Analysis of Peat on wet basis with ash:

Carbon: 84.2%

Hydrogen: 1.9%

Oxygen+Nitrogen: 7.8%

Ash: 3.1%

Moisture: 3.0%

Calorific Value 29,300 kJ/kg

Producer gas from Peat

Gives producer gas at an efficiency of 80-85%. No water needed as in case of coal. Gives high yield of gas and ammonia.

Typical composition: Carbon monoxide: 17.% Hydrogen: 10.9% Methane: 2.5% Nitrogen: 55.7% Carbon dioxide 13.3% Gas yield: 2550 m3/tonne of peat Calorific value 4100 kJ/m3 Ammonium Sulfate 55 kg/tonne of peat

Lignite

Lignite

Forms the first phase of fossilization of vegetable matter.

It is an immature form of coal.

Believed to be between 10 and 40 million years old.

It is intermediate in composition between peat and bituminous coal.

Most immature lignites are chemically similar to most mature peats.

Composition of typical lignites

Carbon: 64.5-78.5%

Oxygen+nitrogen+sulfur 16.5-30%

Water (as mined) 20-75%

Water (dried) 12-20%

Ash 3-30%

Volatile matter 40-50%

Sulfur 1-12%

Calorific value (dry) 20,900-29,300 kJ/kg

Used raw or dried in furnaces

Pulverized and used in mills

May be used in briquetted forms as well

Coal

A Fully Fossilized Fuel

Coal A Heterogeneous Mineral

Consists principally of carbon, hydrogen, and oxygen, with lesser amounts of sulfur and nitrogen.

Other constituents are the ash-forming inorganic compounds distributed throughout the coal.

Coal originated through accumulation of wood and other biomass that was later covered, compacted and transformed into rock over a period of millions of years.

Coal Classification

There are a number ways to classify coals.

One way is to Rank the coal. It indicates the degree or extent of maturation.

It is a qualitative measure of carbon content.

Thus lignites and sub-bituminous are low rank coals

While bituminous and anthracite are high rank coals.

Rank is not synonymous with grade which implies quality.

Low rank coals may not be suitable for some applications as the higher ranked ones

Although they may be superior to them in other applications

Rank of Coal

With increasing Rank, the following characteristics are noticed:

1. Age of coal is increased. This increases with increase in depth of deposit.

2. A progressive loss of oxygen, hydrogen and in some cases sulfur, with a corresponding increase in carbon.

3. A progressive decrease in equilibrium moisture content.

4. A progressive loss of volatile matter.

5. Generally, a progressive increase in calorific value.

6. In some cases, a progressive increase of ash content.

Proximate Analysis of some typical anthracite coals

Class and group

Fixed

Carbon

%

Volatile

Matter

%

Age in

million

years

Cal.

value

kJ/kg

Meta-anthracite >98

Proximate Analysis of some typical bituminous coals

Class and group Fixed

Carbon,

%

Volatile

Matter,

%

Age in

million

years

Calorific

Value

kJ/kg

Low volatile 78-86 14-22 100 36520

Medium volatile 69-78 22-31 To -do-

High volatile: A,B,C 31 180 -do-

Proximate Analysis of some typical sub-bituminous coals

Class and group Fixed

Carbon,

%

Volatile

Matter,

%

Age in

million

years

Calorific

Value

kJ/kg

Sub-bituminous A 69-72 28-31 40 36050

Sub-bituminous B 64-69 31-36 To 35000

Sub-bituminous C 36 100 -do-

Proximate Analysis of some typical Lignites

Class and group Fixed

Carbon,

%

Volatile

Matter,

%

Age in

million

years

Calorific

Value

kJ/kg

Lignite A 58-64 36-42 1 36050

Lignite B 51-57 42-49 To 35000

Lignite C 41-51 49-59 40 -do-

Typical oxygen, water and ash content in solid fuels

Fuel Oxygen

(dry, ash-

free) %

Moisture

(ash-free)

%

Ash

(dry) %

Wood 45 15-50 0.-1.0

Peat 35 90 0.1-10

Lignite 25 30 >5

Bituminous coal 5 5 >5

Anthracite coal 2 4 >5

Refuse-derived fuel 40 24 10-15

Ultimate Analysis of some typical anthracite coals

Fuel C H O N+S Ash %

Moisture

%

Anthracite 93-95 3-4 1-2 1-2 ~2 ~2

Typical

Anthracite

90.27 3.0 2.32 1.44 2.97 1.0

Typical

Anthracite

93.7 2.0 2.2 Balance (Data not

available)

Ultimate Analysis of some typical Carbonaceous and Bituminous coals

Fuel Type C H O N+S Ash Mois-

ture

Carbonaceous 91-93 4.0-4.5 Data not given

Bituminous 80-91 4.5-6.0 Data not given

Typical Bituminous 82.9 5.7 9.9 Data not given

Sub- Bituminous 75-80 5.0-5.1 Data not given

Typical Sub-bitumin-

ous (dry, ash-free)

78 5 13 4 - -

Typical Sub-

bituminous

74.0 5.9 13.01 2.26 4.75 2.1

Typical Sub-

bituminous

73.3 5.1 18.4 Data not given

Ultimate Analysis of Some Typical Lignite, Peat and Wood

Fuel Type C H O N+S Ash Moisture

Lignite 60-75 5.0-5.7 Data not given

Typical Lignite 68.8 4.7 25.5 Data not given

Typical Lignite 68 5 25 2 Dry, ash-free

Typical Lignite 56.52 5.72 31.89 1.62 4.25 15.0

Typical Peat 60.5 5.6 33.8 Data not given

Typical Peat 55 6 38 1 Dry, ash-free

Typical Wood 50 6 44 Tr Dry, ash-free

Typical Wood 49.3 6.7 44 Data not given

Mineral Elements and Chlorine in Pine and Bituminous Coals

Element Pine (Ave. values)

(ppm)

Illinois Coal (ppm)

Ca 760 >5000

Na 28 200-5000

K 39 200-5000

Mg 110 200-5000

Mn 97 6-210

Fe 10 >5000

P 40 10-340

Si - >5000

Al 6 >5000

Cl 48 200-1000

More on coal

Coal may be banded or non-banded.

A banded coal is not homogeneous but consists of alternate layers or bands of bright-black, dull-black and gray vegetal matter. Exists in all types of coal.

Attributed to different kinds of wood and plant substances in various stages of decay.

Non-banded coals are uniform and compact in structure.

Co-existence of coal and petroleum

Where coal and petroleum co-exist, increasing temperature affect in opposite ways.

Coal gradually loses its volatility and goes deeper whereas petroleum becomes progressively lighter as it cracks and rises.

Thus the best coals are deeper in the ground whereas the best petroleum are nearer the ground level.

Coal Combustion

When heated to progressively higher temperatures in inert atmosphere (very little oxygen present), coal decomposes.

Evolves water, tar and gas, and leaves a solid residue whose composition and properties depend on heat treatment temperature.

Temperature range in which volatilization proceeds very rapidly is 350-500oC.

But thermal decomposition begins at a much lower temperature.

Can be divided into 3 stages.

Stages of Coal Decomposition

1. Below 200oC decomposition is slow. Release of small quantities of chemically combined water, oxides of carbon and hydrogen sulfide.

2. Begins between 350 and 400oC and ends around 550oC. About 75% of all volatile matter is released, including all the tar.

3. Termed secondary degasification, is characterized by gradual elimination of hetero-atoms, and ends when the char is transformed into a graphitic solid. Principal products include water, oxides of carbon, hydrogen, methane, and traces of C2 hydrocarbons.

As carbon content increases, active thermal decomposition occurs at progressively higher temperature.

In this stage, there is progressive aromatization of the char, i.e., increasingly large hexagonal carbon platelets.

Where residue is a coke, heat treatment up to 1000oC also leads to marked increase in mechanical strength.

Solid fuels from Coal

Coal can be used as mined or after treatment.

Coal can be briquetted or converted to coke.

1. Briquetting. Done because:

(i) to convert cheap and waste coal dust to lump fuel.

(ii) to use coal more effectively on the grate of furnace, and

(iii) to produce smokeless fuel from fine coal.

Briquetting (Continued)

Briquetting may be done as follows:

1. Without binder for sub-bituminous coal, lignite or peat.

2. With binder like pitch for bituminous, carbonaceous and anthracite coals.

Other inorganic binders like sodium silicate, magnesium oxychloride and lime silica may be used.

Cereal binders like starch and ground maize may also be used.

Inorganic binders are easy to use but will increase the ash content when burned.

Solid fuels from Coal (Continued)

2. Coke. Formed by the carbonization of coal.

Yields benzole, oils and tar. Gaseous products include coal gas.

Yield and chemical nature of the products depend on rank of coal carbonized and duration of carbonization.

Coke (Continued)

Two commercial processes are available:

1. Low temperature carbonization at about 600oC and

2. High temperature carbonization at temperatures above 900oC.

Coal is heated in retorts. Evolves gases like carbon monoxide, methane, unsaturated hydrocarbons, and hydrogen.

Tar forms up to about 500-600oC.

Coals for converting to coke must have carbon content from 83 to 90%.

Coke is used in iron and steel industries (metallurgical coke), foundries, and as a domestic (smokeless) fuel.

Coal Liquefaction

Coal can be converted into a clean liquid fuel by reducing its molecular weight with a substantial reduction in the C/H ratio. Four methods are possible:

1. Pyrolysis. 2. Direct Liquefaction. Examples are the SRC (Solvent Refined

Coal), the Synthoil and H-coal processes. 3. Indirect Liquefaction. The Fischer-Tropsch synthesis.

Example is the SASOL process developed in South Africa. 4. Chemical Synthesis. Liquefaction entails use of large quantities of water and there is

the problem of ash disposal and slag removal plus elimination of sulfur dioxide emissions if the coal contains large quantities of sulfur.

Wood, Peat, Coal, Charcoal, Coke, etc. are few solid fuels

They supply about 33% of the total energy requirements globally.

COAL: Is of plant origin(converted because of the prolonged

action of bacteria, fungi, temperature, and pressure)

It is firm, brittle, sedimentary, Combustible rock

It consists mainly C,H,O with minor proportions of N,S

It occurs in two types

4 mts thick sequence deposits of coal streams

10 to 20 mts and sometimes of even 300mts thick more isolated deposits.

Wood contains Cellulose 45-65%

Lignin 25-35%

Water and proteins in solution 10-15%

These are partially decomposed to humus called humic acid

It occurs as a thick jelly called dopplerite, which is present in peat(70-90% resins and waxes 5-30%)

However there is no clear demarcation between them.

Anthracite is the oldest coal from geological perspective. It is a hard coal composed mainly of carbon with little volatile content and practically no moisture. Bituminous coal or black coal is a relatively soft coal containing a tarlike substance called bitumen. It is of higher quality than lignite coal but of poorer quality than Anthracite. It was usually formed as a result of high pressure on lignite.Bituminous coal is an organic sedimentary rock formed by diagenetic and sub metamorphic compression of peat bog material. Lignite is the youngest coal from geological perspective. It is a soft coal composed mainly of volatile matter and moisture content with low fixed carbon.

Fixed carbon refers to carbon in its free state, not combined with other elements. Volatile matter refers to those combustible constituents of coal that vaporize when coal is heated.

Normally D,E and F coal grades are available to Indian Industry

Heating Value:

The heating value of coal varies from coal field to coal field.

Measurement of Moisture Determination of moisture is carried out by placing a sample of powdered raw coal of size 200-micron size in an uncovered crucible and it is placed in the oven kept at 108+2 oC along with the lid. Then the sample is cooled to room temperature and weighed again. The loss in weight represents moisture.

Measurement of Volatile Matter Fresh sample of crushed coal is weighed, placed in a covered crucible, and heated in a furnace at 900 + 15 oC. For the methodologies including that for carbon and ash, refer to IS 1350 part I:1984, part III, IV. The sample is cooled and weighed. Loss of weight represents moisture and volatile matter. The remainder is coke (fixed carbon and ash).

Measurement of Carbon and Ash The cover from the crucible used in the last test is removed and the crucible is heated over the Bunsen burner until all the carbon is burned. The residue is weighed, which is the incombustible ash. The difference in weight from the previous weighing is the fixed carbon. In actual practice Fixed Carbon or FC derived by subtracting from 100 the value of moisture, volatile matter and ash.

The calorific value of a fuel is the quantity of heat produced by its combustion - at constant pressure and under "normal" conditions (i.e. to 0oC and under a pressure of 1,013 mbar).

The combustion process generates water vapor and certain techniques may be used to recover the quantity of heat contained in this water vapor by condensing it.

The Higher Calorific Value (or Gross Calorific Value - GCV) suppose that the water of combustion is entirely condensed and that the heat contained in the water vapor is recovered.

The Lower Calorific Value (or Net Calorific Value - NCV) suppose that the products of combustion contains the water vapor and that the heat in the water vapor is not recovered.

Fuel

Higher Calorific Value

(Gross Calorific Value - GCV)

kJ/kg Btu/lb

Acetone 29,000

Alcohol, 96% 30,000

Anthracite 32,500 - 34,000 14,000 - 14,500

Bituminous coal 17,000 - 23,250 7,300 - 10,000

Butane 49,510 20,900

Carbon 34,080

Charcoal 29,600 12,800

Coal 15,000 - 27,000 8,000 - 14,000

Coke 28,000 - 31,000 12,000 - 13,500

Diesel 44,800 19,300

Ethanol 29,700 12,800

Ether 43,000

Gasoline 47,300 20,400

Glycerin 19,000

Hydrogen 141,790 61,000

Lignite 16,300 7,000

Methane 55,530

Oils, vegetable 39,000 - 48,000

Peat 13,800 - 20,500 5,500 - 8,800

Petrol 48,000

Petroleum 43,000

Propane 50,350

Semi anthracite 26,700 - 32,500 11,500 - 14,000

Sulfur 9,200

Tar 36,000

Turpentine 44,000

Wood (dry) 14,400 - 17,400 6,200 - 7,500

kJ/m3 Btu/ft3

Acetylene 56,000

Butane C4H10 133,000 3200

Hydrogen 13,000

Natural gas 43,000 950 - 1150

Methane CH4 39,820

Propane C3H8 101,000 2550

Town gas 18,000

kJ/l Btu/Imp gal

Gas oil 38,000 164,000

Heavy fuel oil 41,200 177,000

Kerosene 35,000 154,000

1 kJ/kg = 1 J/g = 0.4299 Btu/ lbm = 0.23884 kcal/kg 1 Btu/lbm = 2.326 kJ/kg = 0.55 kcal/kg 1 kcal/kg = 4.1868 kJ/kg = 1.8 Btu/lbm 1 dm3 (Liter) = 10-3 m3 = 0.03532 ft3 = 1.308x10-3 yd3 = 0.220 Imp gal (UK) = 0.2642 Gallons (US)

Proximate analysis: The "proximate" analysis gives moisture content, volatile content, consisting of gases and vapours driven off during pyrolysis (when heated to 950 C), the fixed carbon and the ash, the inorganic residue remaining after combustion in the sample and the high heating value (HHV) based on the complete combustion of the sample to carbon dioxide and liquid water. Proximate analysis is the most often used analysis for characterizing coals in connection with their utilization. The proximate analysis determines only the fixed carbon, volatile matter, moisture and ash percentages. proximate analysis can be determined with a simple apparatus

Proximate analysis indicates the percentage by weight of the Fixed Carbon, Volatiles, Ash, and Moisture Content in coal. The amounts of fixed carbon and volatile combustible matter directly contribute to the heating value of coal. Fixed carbon acts as a main heat generator during burning. High volatile matter content indicates easy ignition of fuel. The ash content is important in the design of the furnace grate, combustion volume, pollution control equipment and ash handling systems of a furnace. A typical proximate analysis of various coal is given in the Table

Significance of Various Parameters in Proximate Analysis

Fixed carbon: Fixed carbon is the solid fuel left in the furnace after volatile matter is distilled off. It consists mostly of carbon but also contains some hydrogen, oxygen, sulphur and nitrogen not driven off with the gases. Fixed carbon gives a rough estimate of heating value of coal Volatile Matter: Volatile matters are the methane, hydrocarbons, hydrogen and carbon monoxide, and incombustible gases like carbon dioxide and nitrogen found in coal. Thus the volatile matter is an index of the gaseous fuels present. Typical range of volatile matter is 20 to 35%. Volatile Matter

Proportionately increases flame length, and helps in easier ignition of coal. Sets minimum limit on the furnace height and volume. Influences secondary air requirement and distribution aspects. Influences secondary oil support

Ash Content: Ash is an impurity that will not burn. Typical range is 5 to 40% Ash

Reduces handling and burning capacity. Increases handling costs. Affects combustion efficiency and boiler efficiency Causes clinkering and slagging.

Moisture Content: Moisture in coal must be transported, handled and stored. Since it replaces combustible matter, it decreases the heat content per kg of coal. Typical range is 0.5 to 10% Moisture

Increases heat loss, due to evaporation and superheating of vapour Helps, to a limit, in binding fines. Aids radiation heat transfer.

Sulphur Content: Typical range is 0.5 to 0.8% normally. Sulphur

Affects clinkering and slagging tendencies Corrodes chimney and other equipment such as air heaters and economisers Limits exit flue gas temperature.

Ultimate Analysis: The "ultimate" analysis" gives the composition of the biomass in wt% of carbon, hydrogen and oxygen (the major components) as well as sulfur and nitrogen (if any). The carbon determination includes that present in the organic coal substance and any originally present as mineral carbonate. The hydrogen determination includes that in the organic materials in coal and in all water associated with the coal. All nitrogen determined is assumed to be part of the organic materials in coal. The ultimate analysis determines all coal component elements, solid or gaseous. The ultimate analysis is determined in a properly equipped laboratory by a skilled chemist

The ultimate analysis indicates the various elemental chemical constituents such as Carbon, Hydrogen, Oxygen, Sulphur, etc. It is useful in determining the quantity of air required for combustion and the volume and composition of the combustion gases. This information is required for the calculation of flame temperature and the flue duct design etc. Typical ultimate analyses of various coals are given in the Table

The above equation is valid for coal containing greater than 15% Moisture content

SWELLING AND CAKING TEST: ASTM D-720

1gm of air dried coal, freshly ground to pass a 72 mesh is rapidly heated in a crucible above a burner flame, to 820o C

After the flame from the burning the volatile matter has dried out or after 24 minutes, which ever is greater period of time the crucible is cooled. the coke button is opened is removed and compared with standard numbered profiles from 1-9 in half minute.

The result is recorded as swelling number or free swelling Index.

Ash Fusibility test: ASTM D-1857 Molded cone( with dextrin binder