ME-161Introduction to Mechanical

Engineering LEVEL-1, TERM-I

Adib Bin RashidCaptInstructor Class CMechanical Engineering Department

Study of sources of energy: conventional and renewable

Adib Bin RashidCaptInstructor Class CMechanical Engineering Department

MILITARY INSTITUTE OF SCIENCE & TECHNOLOGYDEPARTMENT OF MECHANICAL ENGINEERING

Energy engineering• Energy engineering or Energy systems is a broad field of engineering dealing with

energy efficiency, energy services, facility management, plant engineering, environmental compliance and alternative energy technologies.

ENERGY: DIFFERENT FORMS

Mechanical Energy:

•Defined as energy which can be used to raise a weight. •Can be easily and efficiently converted into other energy forms.

Electrical Energy:

•Defined as that class of energy associated with the flow or accumulation of electrons.

•Large quantities of electrical energy are transferred over long distances with the use of high-voltage transmission lines.

•Can be converted into other energy forms.

Energy: Different forms Electromagnetic Energy:

•Defined as that form of energy associated with electromagnetic radiation. •Extensively employed in nuclear energy study.

Chemical Energy:

•Defined as energy that is released as the result of electron interactions in which two or more atoms and/or molecules combine to produce a more stable chemical compound. •Commonly reported in the units of energy per unit mass or “mole” of fuel reactant

Sources of energy :-

There are two main sources of energy. They are conventional and non conventional sources of energy.

i) Conventional sources of energy :- are wood, flowing water and fossil fuels (coal, petroleum, natural gas).

ii) Non conventional sources of energy :- are solar energy, wind energy, biomass energy, ocean energy (tidal energy, wave energy, ocean thermal energy), geothermal energy, nuclear energy etc.

Some sources of energy are renewable like sun, wind, flowing water, ocean, wood, biomass etc.

Some sources of energy are non renewable like coal, petroleum and natural gas.

Conventional sources of energy :-

Fossil fuels :- are fuels formed inside the earth from the remains of plants and animals after

millions of years. The fossil fuels are coal, petroleum and natural gas. Fossil fuels are non renewable sources of energy so they should be conserved and used judiciously.

Disadvantages of fossil fuels :-

i) Burning of fossil fuels release gases and harmful particles which causes air pollution. ii) Burning of fossil fuels release acidic oxides of sulphur and nitrogen which causes acid

rain which is harmful for living organisms, affects soil and water, causes damage to buildings, corrosion of metals etc.

iii) Burning of fossil fuels release a large amount of carbon dioxide gas which increases the temperature of the atmosphere and causes global warming (green house effect).

Fossil Fuels:

Fossil Fuels are formed from Living things millions of years ago. They are Hydrocarbons and are Finite Fuels ie. They will run out in the future and cannot be regenerated. There are three main Fossil Fuels:

Coal, Oil and Gas

Oil: This was formed by dead sea creatures falling to the sea-bed where they were subjected to chemical change by Bacteria.

Coal: This was formed by the decay of Vegetation which was subjected to heat and pressure over a very long period of time.

Gas was formed in much the same way as Oil. It is often collected when drilling for Oil.

Classification of Fuel

Fuels may be classified into the following general terms:

1. Solid Fuel2. Liquid Fuels3. Gaseous FuelEach of these fuels may be subdivided into the

following categories-4. Natural Fuels5. Prepared Fuels

Solid Fuel

• Wood: At one time it was an extensively used fuel. It consists of mainly carbon and hydrogen.

• Peat: It is a spongy humid substance and contains about 30% water. It has to be dried before use. It is the first stage in the formation of coal.

• Lignite or brown coal: It is the next stage of peat in the coal formation and an intermediate variety between bituminous coal and peat. It contains nearly 40% moisture and 60% of carbon.

Solid Fuel

• Bituminous Coal: It represents the next stage of lignite in the coal formation and contains very little moisture(4-6%) and 75 to 90% of carbon.

• Anthracite Coal: It represents the final stage of coal formation and contains 90% or more carbon.

Solid Fuel

• Wood Charcoal: It is made by heating wood with a limited supply of air to a temperature not less than 280˚C.

• Briquetted Coal: It is produced from finely ground coal by moulding under pressure with or without a binding material.

• Pulverised Coal: The low grade coal with high ash content is powdered to produce pulverised coal.

Coal composition and rank:

• All of the fossil fuels are produced from the fossilization of carbohydrate compounds.

• Coal, the most abundant fossil fuel, is thought to be fossilized vegetation.

• It is estimated that at least 20 ft of compacted vegetation was necessary to produce a 1-ft-thick seam of coal.

• This compacted coal is then converted into peat, a low-grade fuel, then into brown, then into lignite, then into sub bituminous coal, then into bituminous coal, and finally into anthracitic coal.

• Aging process progresses, coal becomes harder, hydrogen and oxygen fractions decrease, moisture content decreases, and carbon fraction increases.

Coal composition and rank:

• Coal is an organic rock (as opposed to most other rocks in the earth's crust, such as clays and sandstone, which are inorganic).

• It contains mostly carbon (C), but it also has hydrogen (H), oxygen (O), sulfur (S) and nitrogen (N), as well as some inorganic constituents (minerals) and water (H2O).

Coal composition and rank:

It is estimated that at least 20 ft of compacted vegetation was necessary to produce a 1-ft-thick seam of coal .

Coal composition and rank: There are several different systems used for classifying coal, but the American Society for Testing Materials (ASTM) has developed a method for ranking coal into four major classifications: Class I Coals: Anthracitic coals Class II Coals: Bituminous coals Class III Coals: Sub bituminous coals Class IV Coals: Lignite coals

Liquid Fuels

• Almost all the commercial liquid fuels are derived from natural petroleum. The liquid fuels consist of hydrocarbons.

• The natural petroleum may be separated into petrol or gasoline, paraffin oil or kerosene, fuel oils and lubricating oil by boiling the crude oil at different temperature and subsequent fractional distillation.

• The following liquid fuels are important from the subjects point of view.

Liquid Fuels

1. Petrol or gasoline: It is the lightest and most volatile liquid fuel, mainly used for light petrol engines. It is distilled at a temperature from 65˚-220˚C.

2. Kerosene or Paraffin oil: It is the heavier and less volatile fuel than the petrol, and is used as heating and lighting fuel. It is distilled from 220˚-345˚C

3. Heavy Fuel oil: The liquid fuels distilled after petrol and kerosene are known as heavy fuel oil. These oils are used in diesel engines and oil fired boilers. They are distilled at a temperature from 345˚-470˚C.

Merits and Demerits of Liquid Fuel over Solid Fuel

Following are the merits and demerits Solid Fuel:

Merits:

1. Higher Calorific value.2. Lower storage capacity required.3. Better economy in handling.4. Better control of consumption by using valves.5. Practically no ashes.6. Non-deterioration in storage.7. Non-corrosion of boiler plants.8. Higher efficiency.

Merits and Demerits of Liquid Fuel over Solid Fuel

Demerits:

1. Higher cost2. Greater risk of fire.3. Costly containers are required for storage

and transport.

Gaseous FuelThe natural gas is, usually found in or near the petroleum fields,

under the earth’s surface. It essentially consists of marsh gas or methane(CH4) together with small amounts of other gases such as ethane(C2H6), carbon dioxide(CO2).

The following gaseous fuels are important from subject point of view.

1. Coal gas: It is obtained by carbonization of coal and consists mainly of H2,CO and various hydrocarbons.

2. Producer Gas: It is obtained by the partial combustion of coal, coke, anthracite coal or charcoal in a mixed air-steam blast.

Gaseous Fuel

• Water gas: It is a mixture of H2 and CO and is made by passing steam over incandescent coke.

• Mond Gas: It is produced by passing air and a large amount of steam over waste coal at about 650C.

• Blast Furnace Gas: It is a by-product in the production of pig iron in the blast furnace.

• Coke oven gas: It is by-product from coke oven and is obtained by the carbonization of bituminous coal.

Merits and Demerits of Gaseous Fuel:

Merits:1. The supply of fuel gas and hence the temperature of

furnace is easily and accurately controlled.2. The high temperature is obtained at a moderate cost

by pre-heating gas and air with heat of waste gases of combustion.

3. They are directly used in internal combustion engine.4. They do not produce ash or smoke.5. They undergo complete combustion with minimum air

supply.

Merits and Demerits of Gaseous Fuel

Demerits:1. They are readily inflammable.2. They require large storage capacity.

Requirements of Good Fuel

1. A good fuel should have low ignition point.2. It should have a high calorific value.3. It should freely burn with a high efficiency, one it

is ignited.4. It should not produce harmful gases.5. It should produce least quality of smoke and

gases.6. It should be economical, easy to store and

convenient for transportation.

Coal Analysis • Proximate Analysis: It gives the mass fractions of fixed carbon (FC), volatile matter (VM), ash (A), and moisture (M) in the coal.

Can be determined by weighing, heating and burning a small sample of powdered coal.

Procedures:

Coal sample is carefully weighed and then heated to 110ºC for 20 min. Sample is weighed again and mass loss is divided by the original mass to obtain the moisture fraction (M).

Remaining sample is heated to 954ºC in a closed container for 7 min. Sample is then reweighed and resulting mass loss is divided by the original mass to obtain the fraction of volatile matter (VM).

Sample is then heated to 732ºC in an open crucible until it is completely burned. Residue is then weighed and final weight is divided by original weight to obtain ash fraction (A).

Mass fraction of fixed carbon (FC) is obtained by subtracting the M, VM and A from unity.

Coal Analysis

Ultimate Analysis: o The chemical approach to characterizing coals is to determine the

amounts of the principal chemical elements in them.

o In the jargon of the coal business, this procedure is called the ultimate analysis of coal.

o It is a laboratory analysis that lists the mass fractions of carbon (C), hydrogen (H2), oxygen (O2), nitrogen (N2), and sulfur (S) in the coal along with higher heating value.

Calorific Value of Fuel:It is defined as the amount of heat produced when

unit quantity of fuel is completely burnt under standard conditions.

It is expressed as kcal per kg or kcal, per cubic meter of gaseous fuel.

Two ways: (i) Higher calorific value (HCV) and

(ii) Lower calorific value (LCV).

Calorific Value of Fuel:

(i) The higher or gross of calorific value is the total amount of heat produced when unit quantity of fuel is burnt completely and the products of combustion have been cooled to room temperature.

(ii) The lower calorific value is the net amount of heat produced when unit quantity of fuel is completely burnt and the products of combustion are not cooled to room temperature but are allowed to escape.

Calorific Value of Fuel:The higher or gross of calorific value

According to Dulong’s Formula,

HCV=33800C+144000H2+9270S kJ/kgor,

HCV=33800C+144000(H2 -O2/8) +9270S kJ/kg

The lower calorific value

L.C.V= H.C.V- (ms X 2466 kJ/kg)

Calorific Value of Fuel:Problem - 1. The percentage composition by weight of a sample of

coal is given as: C = 65.50%, H2 = 6.65%, O2 = 17.50%, S =1.80%. Using Dulong’s formula, calculate the calorific (heating) value of coal .

Problem - 2. A sample of coal has the composition by weight: C =

70%, H2 = 8%, O2 = 7%, N2 = 3%, S =2% and ash 10%. Using Dulong’s formula, calculate the calorific (heating) value of coal.

Thermal power plants :- • In thermal power plants the heat energy

produced by burning fossil fuels like coal, petroleum or natural gas is used to heat water and change it into steam which rotates the turbines of generators to produce electricity.

Thermal power plants :-

Thermal power plants :-

Thermal power plants :-

Hydro power plants :- • In hydro power plants water from rivers are

stored by constructing dams. The water from the dam flows down through pipes and rotates the turbines of generators to produce electricity.

Hydro power plants :-

Hydro power plants :-

Hydro power plants :- • Advantages :-

i) Flowing water is a renewable source of energy. ii) The electricity produced does not cause pollution. iii) The water stored in dams can also be used to control floods and for

irrigation.

• Disadvantages :-

i) The initial cost is high. ii) Large areas of land gets submerged and the decomposition of vegetation

produces methane gas which is a green house gas. iii) It causes displacement of people from large areas of land.

Non conventional sources of Energy :-

Non conventional sources of Energy :-

Biomass energy :- • The waste materials and dead parts of living

things are called biomass. Eg :- wood, animal dung, vegetable waste, agricultural waste, sewage etc. Biomass is decomposed by anaerobic microorganisms to produce biogas.

• Biogas is a mixture of gases containing methane, carbon dioxide, hydrogen and hydrogen sulphide.

Biogas plant :-

The biogas plant has a large underground tank made of bricks and cement. The lower part is the digester and the upper part has a dome with a gas outlet. On one side of the tank above the ground is a mixing tank and on the other side is an overflow tank. Animal dung is mixed with water in the mixing tank and the slurry is sent into the digester. In the digester the slurry is decomposed by anaerobic microorganisms and after a few days biogas is produced. The gas is taken out through the gas outlet and used for heating and lighting purposes. The slurry left behind is rich in nitrogen and phosphorus and is used as manure for crops.

FIXED DOME TYPE BIOGAS PLANT

Wind energy :- Wind energy is used in wind mills which converts the kinetic energy of the wind

into mechanical or electrical energy. The kinetic energy of wind can be used to do mechanical work like lifting water from wells or grinding grains in flour mills. It can also be used to rotate the turbines of generators to produce electricity.

A single wind mill produces only a small amount of electricity. So a large number of wind mills in a large area are coupled together to produce more electricity in wind energy farms.

Advantages :- i) It is a renewable source of energy. ii) It does not cause pollution. iii) The recurring cost is less. Disadvantages :- i) Wind is not available at all times. ii) It requires a large area of land. iii) A minimum wind speed of 15 km/h is required

Solar energy :- Solar energy is the energy obtained from the sun in the form of heat and light. The heat energy is

used in solar heating devices like solar cooker, solar water heater, solar furnaces etc. The light energy is used in solar cells.

i) Solar cooker :- The box type solar cooker has an insulated box painted black inside. It is covered by a glass plate which allows heat to enter inside but does not allow heat to escape out. It has a mirror to reflect more sunlight into the box. The food to be cooked is kept in containers inside the box It can produce a temperature of 100° to 140°.

Solar energy :- ii) Solar water heater :- A solar water heater has an insulated box painted black inside with a

system of copper tubes. It is covered with a glass plate which allows heat to enter inside but does not allow heat to escape out. When water flows through the copper tube it absorbs heat and becomes hot

Solar cells :- Solar cell is a device which converts solar energy into electrical energy. Solar cells are

made from semi conductors like silicon, germanium, gallium etc. A single solar cell produces a voltage of about 0.5 to 1 V and produces about 0.7 W electricity. So several solar cells are arranged in a solar panel to produce more electricity.

Solar cells :-Advantages :-

i) It uses renewable source of energy.

ii) It produces electricity which does not cause pollution.

iii) It can be used in remote areas where there is no power supply. Disadvantages :- ii) It uses a special grade of silicon which is expensive.

ii) Since silver is used for connecting the cells together it is more expensive.

iii) The current produced is DC and to convert it to AC increases the cost.

Energy from the sea :- Energy from the sea is obtained in three different forms. They are Tidal energy, Sea wave

energy and Ocean thermal energy.

i) Tidal energy :- The periodic rise and fall of sea level due to gravitational attraction of the moon causes

tides. A dam is constructed at a narrow opening between the land and sea. The movement of water during high tide and low tide can be used to rotate the turbines of generators to produce electricity.

Energy from the sea :-

ii) Sea wave energy :- When strong wind blows over the sea it produces huge waves. The kinetic

energy of the moving waves can be used to rotate the turbines of generators to produce electricity.

Energy from the sea :- iii) Ocean thermal energy :- There is a temperature difference between the warm surface water and the cold water at

the bottom of the oceans. This difference is about 20°C. The warm surface water is used to boil liquid ammonia and the vapour is used to rotate the turbines of generators to produce electricity. The cold water from the bottom is then pumped up to cool the vapour back to liquid .

Geothermal energy :- • The deeper regions of the earth’s crust is very hot. This heat melts rocks and

forms magma. The magma moves up and collects below at some places called Hot spots. The underground water in contact with hot spot gets heated into steam at high pressure. By drilling holes into hot spots the steam coming out can be used to rotate turbines of generators to produce electricity.

Nuclear energy :-Nuclear energy is the energy is the energy released during

nuclear reactions. During nuclear reactions some mass is converted into energy and so a very large amount of energy is produced during nuclear reactions. Nuclear reactions are of two types. They are Nuclear fission and nuclear fusion

Nuclear energy :-i) Nuclear fission :- is a nuclear reaction in which

the nucleus of a heavy atom like uranium, plutonium, etc. splits into smaller nuclei with the release of a large amount of energy. It is used to make atom bombs and to produce electricity. In a nuclear power plant the heat energy produced by a controlled nuclear fission chain reaction is used to produce steam which rotates the turbines of generators to produce electricity.

Nuclear energy :-

ii) Nuclear fusion :- is a nuclear reaction in which small nuclei fuse together to form a heavier nucleus with the release of a very large amount of energy. The energy of sun is produced by the fusion of hydrogen nuclei to form helium nucleus. It is also used to make the hydrogen bomb.

Nuclear energy :-

Advantages of nuclear energy :- i) It produces a very large amount of energy per unit

mass than any other source of energy. ii) If safety measures are taken, it is more

environment friendly than fossil fuels. Disadvantages of nuclear energy :- i) The cost of a nuclear reactor is very high. ii) The availability of nuclear fuel is limited. iii) Nuclear reactors produce harmful nuclear wastes

which is difficult to dispose.

Nuclear Power Plant