undefined | unit 3 fuels

CHEM

Unit 3

Fuels

Q1) Write a short note on classification of fuels?

A1) Chemical fuels are classified on the basis of occurrence into :-

Primary ( natural )

Secondary ( derived ) types / manmade .

The secondary fuels are obtained from primary fuel by processing or they are manmade. e.g.:- charcoal is obtained from wood by partial combustion of wood , ethyl alcohol is obtained by fermentation of carbohydrates .

Both the primary and secondary fuels are further classified on the basis of physical state into solid liquid and gaseous fuels.

Extra definitions :-

1] fuels :-

Fuels are defined as materials that create usable energy through chemical nuclear or electrochemical reaction.

2] chemical fuel :-

The fossil fuels , wood vegetal oils etc. . which produce heat on burning are known as chemical fuels.

Q2) What do you mean by Calorific value?

A2) Calorific value :- efficiency of combustible fuels can be measured in terms of their calorific value . it is the heat evolved on combustion of a unit quantity of fuel.

Definition of calorific value :-

It is defined as the amount of heat obtained on complete combustion of unit mass of a solid or liquid fuel or unit volume of a gaseous fuel at STP.

Q3) Write a brief deception about G.C.V. and N.C.V?

A3) Usually fuel contains some hydrogen . the hydrogen atoms are bonded to carbon atoms in the fuel when the fuel is burnt , hydrogen forms water vapors . the water vapors if cooled , we get certain amount of heat as the water has high latent heat of 2450 joules / gm or 587 Cal / gm.

Thus, during the study of calorific value of a fuel we get some heat directly by combustion of fuel and in addition we get certain amount of heat by cooling the products of combustion to 15-degree c.

Gross calorific value :-

Gross calorifia value of a fuel can be defined as the total amount of heat obtained on complete combustion of unit mass of a solid or liquid fuel or unit volume of a gaseous fuel ( S T P ) and on cooling the products of combustion to 15 degree c . the gross calorific value is also called as higher calorific value.

The G.V.C is of only theoretical importance because in actual practice we do not have any provision of cooling the products of combustion during combustion of fuel in an engine , furnace or any other fuel burning device.

Net calorific value :-

A fuel contain hydrogen produces water heat and actually less heat is available for heating.

There is not any furnace , engine or device designed to collect the heat being taken away by the water vapors . therefore, practically we get lower calorific value than the theoretical expected.

Net calorific value :-

Net calorific value is defined as the amount of heat obtained practically on complete combustion of unit mass of solid or liquid fuel or unit mass of solid or liquid fuel or unit volume of a gaseous fuel at step and the products of combustion are allowed to escape with some heat N.C.V is also called as lower calorific value.

The N.C.V and G.C.V are related as under

G.C.V = N.C.V + )

Where h is the percentage of hydrogen in the fuel.

It should be noted that the unit of latent heat of water and unit of G.V.C , N.C.V should be same .

Units of calorific value :-

System	Solid or liquid fuel	Gaseous fuel
CGS	Cal / gm	Cal / liter
MKS	Kcal / kg	Kcal /
S.I	Joules / kg	Joules /

Q4) Explain what do you mean by solid fuels?

A4) Solid fuels :- coal

Coal is highly carbeanous matter formed vegetable matter buried in geomorphic changes , under pressure , by action of aerobic and anaerobic bacteria for long time.

Peat :-

Peat is brown and fibrous in texture .

Freshly mined out peat contains large quantity of water as it is found in waterlogged areas.

Air dried peat contains 15 – 25 percent moisture and it crumbles into powder during air drying.

Calorific value of peat is about 5400 Cal / gm.

It has low density

It contains 57 percent c , 61 percent c .

Lignite :-

It is intermediate stage between peat and black coal.

It is brownish black and more compact than peat.

It contains 45 – 50 percent volatile matter and burns with log flame.

Its C.V id about 6000- 6700 Cal / gm and c percent it is 65 – 70 percent .

It contains 5 percent H 20 percent O.

Bituminous coal :-

This type of coal burn with smoky yellow flame and are dark – grey to black they contain 70 – 90 percent c and therefore they are classified as

Anthracite coal :-

This is highest rank or grade coal

It has C.V about 8700 coal / gm and 92 – 98-degree c.

It is highly lustrous black and hard coal.

It burns with non – smoky short blue flame of high temperature.

Q5) Write a short note on the analysis of coal?

A5)

Calculate C , N , H , S from the following observation for a sample of coal.

2.05 gms of the coal is burnt in combustion tube. The increase in weight of any hydrous Cacl2 is 0.55 gm and increase in weight of KoH tube is 5.75gm.

0.75 of the coal is kjaldahl experiment released NH3 which is passed in 50ml 0.12 N NaoH to neutralize in back titration.

Washings of the bomb pot when 1.8 gm.

Given data :-

Increase in weight of any hydrous calcl2 = 0.55

Mass of coal = 0.75gms

Volume of 0.12 NHCL consumed by NH3 = 50 – 41

= 9 ml

Mass of coal = 1.8gms

Weight of Baso4 = 0.31 gm

Weight of CO 2 formed = increase in wt. OfKoH

Therefore ,

C percent ) = **100 = 76.5 percent .

Increase in weight of any hydrous Cacl2

= weight of H2O formed

Mass of coal = 2.05gm

H ( percent ) = **100

= 2.98 ( percent )

2. N ( percent ) =

= 2.02 ( percent )

3. S ( percent ) = *100

= 2.36 ( percent )

Theoretical calorific values

A] gouthal formula :-

Theoretically calorific value of coal can be calculated from proximate analysis data by using gouthal formula .

G.C.V Cal / gm = 82fc + a.VM

The values of constant are as under

Q6) What is the classification of petroleum?

A6) Petroleum :-

Petroleum or crude oil is a dark greenish brown viscous liquid in earth crust at the depth of few meters to 7kms.

Crude oil is the most important source of various liquid fuels used now and a large number of petrochemicals can be manufactured ( plastics , rubber , fibers , medicine ) from the crude oil fractions.

Origin of petroleum :-

As per modern theory petroleum is formed from buried debris of plants and animals ( organic matter ) under favorable conditions.

The burial of the organic matter during volcano upheavals. In earth surface should take place along with large quantity of water and under a dome of hard , impervious rock.

An aerobic bacteria , higher temperature , radioactive matter makes the degradation of organic matter , in the presence of water , under the dome to highly alkanes rich matter as crude oil.

The anaerobic bacteria take out oxygen atoms from cellulose protein oil molecules and forms alkenes rich crude oil

E.g. –

Prolonged action of higher temperature and action of radioactive substances cause the breaking very long hydrocarbon molecules to smaller during the ages of time , the hydrocarbon molecule.

Crude oil is always deposited on the layer of salty water and above crude oil layer there is natural gas consisting of C1 TO C4 hydrocarbons and NH3 , H2S , CO , moisture.

Composition of petroleum :-

Average elemental composition of petroleum crude oil is,

C = 80 -87 percent

H= 11 to 15 percent

O = 0.1 to 0.9 percent

S = 0.1 to 3 percent

N = 0.4 to 0.9 percent

Petroleum contains following type of compounds :-

1) Open chain alkanes

2) Cycloalkanes

3) Aromatics

4) Asphaltenes

5) Resins

Open chain alkenes :-

Both straight chain and branched alkanes are present in crude oil. In some crude oil such alkenes are major part.

Aromatics :-

In all the crude oils benzene and alkyl substituted benzenes are up to 2 percent.

Asphaltenes :-

All the crude oil contains small amount of poly condensed aromatic solid as colloidal dispersion in crude oil .the asphaltenes also contain N ,S , O atoms.

Resins :-

These are polymeric substances .they are gummy and are lower molecular weight polymers . they are also containing N , S , O atoms .

All the crude oil contain little amount of emulsified water is rich with dissolved salts.

The number of carbon atoms in hydrocarbon molecules range from C1 TO C70 in crude oil.

Refining of petroleum :-

Crude oil cannot be directly used for any purpose .refining or fractionation is the processes of separation of various fraction from crude oil , on the basis of fractional distillation .

The crude oil contains a large number of hydrocarbon but by the processes of refining they are divided into few groups of mol.wt or boiling point ranges.

Q7) What is the process for Refining of petroleum?

A7) The various petroleum fraction has calorific value about 1100 Cal / gm .their composition, boiling range and uses are given.

Name of fraction	Boiling range	Composition of HC	uses
Uncondensed gases	Below 40 ° c	C1 to c4	Domestic and industrial fuel under lpg name
2. Petroleum ether	40-70° c	C5 to c7	Fuel for Aeroplan helicopter as solvent
3. Petrol or gasoline	60-120° c	C5 to c8	Fuel for petrol engines dry cleaning as solvent.
4. Naphtha or solvent spirit	120 -180 ° c	C7 to C10	For dry cleaning for chemicals
5. Kerosene	180-250° c	C10 TO C16	For domestic fuel for oil gas.
6. Diesels	250 - 320° c	C15 to c18	Diesel engine fuel
7. Heavy oil	320-400° c	C18 – c20	Lubricating purpose
8. residue		Above C30	Road making water proofing

Q8) Short note power alcohol.

A8) Power alcohol

Definition :-

When ethyl alcohol is used as fuel internal combustion engine .it is called as power alcohol . combustion engine it is called as power alcohol generally , ethyl alcohol is used as its 5 – 25 percent mixture with petrol.

India has started mixing 5 percent ethyl alcohol in petrol from year 2003 but countries like brazil use 25 percent .ethyl alcohol in petrol from 1970.

Use of ethyl alcohol is petrol reduces our dependence for petrol on foreign reserves by about rs 5000 annum. Further it gives boost to the indigenous manufactures of ethyl alcohol and farmers get better price of their grain produce .

Ethyl alcohol is mainly manufactured by fermentation of molasessstretch .carbohydrates on a large scale and cheaply . it can also be obtained from synthesis of gas ( co , H2 ).

Reactions :-

4. The starch or sucrose in molasses is converted into ethyl alcohol by fermentation as in above reactions the ethyl alcohol obtained contains 95.5 percent alcohol is separated by use of suitable dehydration agent or by distilling it along with benzene .

Advantages of power alcohol :-

Ethyl alcohol has very good anti knocking property and its octane number is go , while the octane number of petrol is about 65 ( percent ).

Therefore, addition of ethyl alcohol to petrol increases its octane number.

2. Alcohol has property of absorbing any traces of water if present in petrol.

3. If a specially designed engine with higher compression ratio is used, then the disadvantage of lower c.v of ethyl alcohol can be overcome.

4. Ethyl alcohol contains O atoms which help for complete combustion of power alcohol and the polluting emissions of co , hydrocarbon is reduced largely.

5. Use of ethyl alcohol in petrol reduces our dependence on foreign countries for petrol and saves foreign currency considerably.

6. Power alcohol is cheaper than petrol.

Disadvantages :-

Ethyl alcohol has c.v 7000cal /gm . use of power alcohol reduces power output up to 35 ( percent )

2. Ethyl alcohol has high surface tension and its atomization especially at lower temperature is difficult causing starting trouble.

3. Ethyl alcohol may undergo oxidation to form acetic acid which corrodes engine parts .

4. Ethyl alcohol obtained by fermentation processes directlycannot be mixed with petrol, but it has to be dehydrated first.

5. Prepare sodium methoxide from sodium metal and methanol .add the sodium methoxide about 2 percent by weight to vegetable oil or fat.

6. Add methanol about 20 percent by volume to the mixture .

7. Heat the mixture with stirring for 30 min

8. Cool and mix sufficient water stir well the glycerol and soap dissolve in water phase .

9. Separate the water insoluble phase from water phase

10. Add antioxidant to the biodiesel to avoid it to become gumany due to oxidation and polymerization.

Q9) What do you mean by Biodiesel?

A9) Biodiesel can be obtained from various vegetable oils like soya beenoil ,palm oil , groundnut oil , cottonseed oil , mustard oil , flower oil , etc. . and also, from the animal fats .

The product is given name biodiesel on account of that it is obtained from biological product and It is biodegradable material.

Advantages of biodiesel:-

Biodiesel can be used as a good fuel for diesel engine but generally it is used as its 20 percent mixture with diesel.

Biodiesel is cheaper

2. It has high c.v of about 40 kg / gm

3. It is regenerative and environmentally friendly .

4. It does not give out particulate and CO pollutants .

5. It has certain extent of lubricity

6. It uses provided good market to vegetable oils and reduces our dependence on biodiesel onforeign countries , saving currency.

7. It is clean to use biodiesel in diesel engine.

Q10) What do you mean by gaseous fuel? Explain it briefly?

A10) Natural Gas is a fossil fuel. It occurs naturally and approximately consists of 95% hydrocarbon methane, the other 5% consists of nitrogen, carbon dioxide, helium or hydrogen sulfide. It takes millions of years for it to form.The gas is formed when layers of decaying plants and animals are buried under the earth’s surface and are exposed to intense heat and pressure for millions of years. Plants originally obtain energy from the sun and store in the form of chemical bonds in the gas. And thus, the formation of this gas occurs.

Properties:

The state of matter of this gas is gaseous.

It doesn’t have any color and is a tasteless gas.

It is free of any kind of toxic, there is no smoke on burning and it has high calorific value.

The gas is odourless. However, a chemical called mercaptan is added to it in small amounts to give it distinctive smell of eggs. This helps to find out any gas leaks.

It is a combustible gas and a fossil fuel.

Its a mixture of simple hydrocarbon compounds.

It contains primarily methane, along with small amounts of ethane, butane, pentane, and propane.

The by-products of this gas are water vapor and carbon dioxide.

Air is 60% heavier than natural gas.

It has a low flammability range and a high ignition temperature.

Generally, it is transported through pipes.

It occurs naturally in the rocks beneath the earth’s surface, in sedimentary rocks that are porous.

Applications

It is used in vehicles in the form of CNG (Compressed Natural Gas).

It is also used to manufacture a few chemicals and fertilizers.

The gas is used as a source of energy for cooking, heating, and electricity generation.

It is used as chemical feedstock for manufacturing plastic and other commercially important organic chemicals.

The gas is also useful in the production of fabrics, glass, paint, plastic, steel, etc.

Hydrogen can also be produced with the help of it.

Protein-rich animal and fish feed is produced by feeding this gas on a commercial scale.

Hydrogen gas as a future fuel

The main purposes to produce green hydrogen is to add it to the natural gas system, because the natural gas system is seen as a seasonal and large energy storage and necessary for balancing the intermittent electricity production from renewable wind and solar. When hydrogen is mixed with natural gas, the hydrogen content can vary in a wide range. Gas engines have the capability to burn gases with a wide range of hydrogen content, but there are also some challenges with a potentially high fluctuation of the hydrogen content or fast rate of change.

The two technology areas, traffic decarbonisation and long-term energy storage, depend on H2. As H2 will be transported in pipelines, the need for flexible H2-tolerant gas engines will rise.

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