Fuel contains mainly ‘C’ which undergoes combustion and liberates large amount of heat energy. C+ O 2 CO 2 + heat (Exothermic) Burning of a substance

Fuel contains mainly ‘C’ which undergoes combustion and liberates large amount of heat energy.

C+ O2 CO2 + heat (Exothermic)

Burning of a substance (in presence of O2) or oxidation of a compound is called combustion.

CHEMICAL FUELS

SECONDARY OR DERIVED

FUELSPRIMARY OR

NATURAL FUELS

SOLID:Wood,coal, lignite

LIQUID:Crude oil

GASEOUS:Natural gas

SOLID: coke,charcaol

,petroleum

GASEOUS:coal gas, water gas, biogas

LIQUID:Petrol,kerosene,diesel

.

CLASSIFICATION OF FUELS

Characteristics of a good fuel : HCV Moderate ignition temperature. Low moisture content Low non-combustible matter Combustion products should not be harmful Low cost Easy to transport Should undergo spontaneous combustion Should leave less carbon residue.

Primary solid fuels :1) Wood : Its C.V. depends on nature of wood, but now it is not

used as main fuel.2) Coal : Is a stratified rock contains organic material derived

from decay of plant material.mineral mater and moisture.

Mechanism of coal formation :Insitu theory : Coal formation takes place at the place of

vegetation itself.Transportation theory : Trees uprooted and carried to Delta

area and deposited under earth. When this wood burns at high temp, high press, in absence of air, cellulose material of wood decompose liberating CO2 and CH4 gases.

Classification of coal:WOOD ----- PEAT----- LIGNITE ----- BITUMINOUSCOAL------ ANTHRACITE COAL PEAT: Brown, fibrous, jelly like mass. It is the first stage of

coalification. Uneconomical fuel. Used if deficiency of high rank coal is prevailing. Contains

80-90% of H2O. Composition C = 57%, H= 6%, O = 35%, ash 2.5 to 6%. Calorific value = 5400 kcal/kg.

Lignite: (Brown coal) soft, brown, colored lowest rank coal moisture content is 20 to 60%. Used for steam generation inthermal power plants and for production of producer gas.Composition : C = 60%, O = 20%, Calorific value = 6,500 to 7,100 k.cal/kg

Bituminous coal : (common coal) Black colored. It has laminated structure.used in making coal gas and metallurgical coke.and also for steam generation inthermal plants and for domestic heating. it is sub classifiedbased on carbon content. 70 – 95% carbon, 8600 kcal/kg calorific value.

Anthracite: Highest rank of coal. Used in households and for steam raising.also used in metallurgical purposes where no smoke and high local heat is desired.% of C = 98 % has lowest volatile matter hardest, dense, lustrous. CV = 8650 to 8700 kg.

Coal analysis :Depending on data required there are two types of analysis.

Proximate analysis : Empirical analysis

Moisture, Volatile matter, ash, Fixed carbon content as % of original weight of coal sample are recorded.

1) Moisture : About 1 gram of finely powdered air-dried coal sample is weighed in a crucible. The crucible is placed inside an electric hot air-oven, maintained at 105 to 1100C. The crucible is allowed to remain in oven for 1 hour and then taken out, cooled in a desiccator and weighed. Loss in weight is reported as moisture.

% of moist = (Loss in weight/Weight of Coal) x 100

2) Volatile matter : The dried sample of coal left in the crucible in (1) is then covered with a lid and placed in an electric furnace or muffle furnace, maintained at 925 + 200C. The crucible is taken out of the oven after 7 minutes of heating. The crucible is cooled first in air, then inside desiccators and weighed again. Loss in weight is reported as volatile matter on percentage-basis.

% of volatile matter = loss in weight due to the removal of volatile matter/wt of dry coal taken

3.Ash: The residual coal in the crucible in (2) is then heated without lid in a muffle furnace at 700 + 500 C for ½ hour. The residue is reported as ash on percentage-basis.

Thus, % of Ash = (weight of ash left/weight of coal) x

100

4 )Fixed carbon : 100 – (% of moist + % of volatile matters) + % of ash)

Significance :Low moisture content, Low volatile matter, Low ash content, high

fixed carbon content are the features of good quality coal.Disadvantages of high ash content : Lower C.V. of fuel Disposal of ash is a problem Ultimate analysis :determines % of C, H,O… 1.Carbon and Hydrogen: About 1 to 2 gram of accurately

weighed coal sample is burnt in a current of oxygen in a combustion apparatus. C and H of the coal are converted into CO2 and H2O respectively. The gaseous products of combustion are absorbed respectively in KOH and CaCl2 tubes of known weights. The increase in weights of these are then determined. C+O2 CO2

(12) (44)

H2 + ½ O2 H2O(2) (18)

2KOH+CO2 K2CO3 + H2OCaCl2+H2O CaCl2 .7 H2O

%C = increase in wt of KOH tube/ wt of coal sample taken X 12/44 X 100

%H2 = increase in wt of CaCl2 tube/ wt of coal taken X 2/18 X100

2) Nitrogen (Kjeldhal’s method) :

About 1 gram of accurately weighed powdered coal is heated with concentrated H2SO4 along with K2SO4 (catalyst) in a long-necked Kjeldahl’s flask. After the solution becomes clear, it is treated with excess of KOH and the liberated ammonia is distilled over and absorbed in a known volume of standard acid solution. The unused acid is then determined by back titration with standard NaOH solution. From the volume of acid used by ammonia liberated, the percentage of N in coal is calculated as follows:

42)

4(Heat

42Nitrogen SONHSOH

42)

4(

423

22

32

422

42)

4(

SONHSOHNH

OHNHSONaNaOHSONH

% of N2=Volume of acid used X Noramality of acid X 14

Weight of coal sample taken X 1000

Volume of acid X Noramality of acid

Weight of coal sample taken= X 1.4

X100

3) Sulphur : Sulphur is determined from the washings obtained from the

known mass of coal, used in bomb calorimeter for determination of a calorific value. During this determination, S is converted in to Sulphate. The washings are treated with Barium chloride solution, when Barium sulphate is precipitated. This precipitate is filtered, washed and heated to constant weight.

S+ O2 SO4-2 + BaCl2 BaSO4

(32) (233)% of Sulphur =

wt of BaSO4 / Wt of sample taken X 32/233 X 100.

4) Ash: ash determination is carried out as in proximate analysis.

5.Oxygen: Percentage of Oxygen = 100 – percentage of ( C + H + S + N + Ash)

LIQUID FUELS

The main source of liquid fuels is petroleum which on distillation gives several fractions.

Petroleum is a complexes mix. Of

paraffinic,olefinnic, aromatic hydrocarbons. C = 80 – 87 % H = 11.1to 15% S = 0.1 -

3.5% N = 0.4- 0.9% REFINING OF CRUDE OIL: The crude oil is separated into various

fractions by fractional distillation.

Stages in refining

A) Separation of water (Cottrell's process)

B) Removal of harmful sulphur compounds

C) Fractional distillation.

A) Separation of water(Demulsification): The crude oil coming out from the well, is in the

form of stable emulsion of oil and salt water, which is yellow to dark brown in colour.

The demulsification is achieved by Cottrell’s process, in which the water is removed from the oil by electrical process. The crude oil is subjected to an electrical field, when droplets of colloidal water coalesce to form large drops which separate out from the oil.

Removal of harmful Sulphur compounds:

Sulphur compounds are removed by treating the crude oil with copper oxide.

Treatments results in the formation of copper sulphide in solid from which can be removed by filtration.

What is fractional distillation?

Fractional distillation is the separation of a material into its separate fractions. The main use of this is in the distillation of crude oil into various substances such as petrol and diesel.

Fractional distillation:

The crude oil is heated to about 4000c in a pipe still where by all volatile constituents are evaporated.

The hot vapors are then passed through a tall cylindrical tower, known as fractionating column, containing a no. of horizontal stainless steel trays at short distances.

These trays are provided with individual chimneys which are covered.

What are the products?

The products of crude oil (and their boiling points) are as follows:

EGEE 102-Pisupati 23

Fractions of Fractions of PetroleumPetroleum

Fraction Boiling Range /C

No of carbon atoms per molecule

Uses

Petroleum Gas

Below 40 1 - 4 Fuel for cooking




Uses

Petrol (Gasoline)

40 - 75 5 -10 Fuel for car engines




Uses

Naphtha 75 - 150 7 - 14 Chemical feedstock




Uses

Kerosene 160 - 250 11 - 16 Fuel for jet engines, cooking

and heating




Uses

Diesel 250 - 300 16 - 20 Fuel for diesel

engines




Uses

Lubricants 300 - 350 20 - 35 Making waxes and lubricating

oils

Uses of the products

• Petrol- fuel for cars• Gases- keeping houses warm• Naphtha- making plastics• Kerosene- aeroplane fuel

SYNTHESIS OF PETROLFischer - Tropsch method:Water gas (CO+H2) produced by passing steam over heated

coke , is mixed with hydrogen.The gas is purified by passing through Fe2O3 & then into a

mix. Of Fe2O3,Na2CO3.The purified gas is compressed to 15 – 25 atm & then led

through a converter, mainted at about 200 – 300 c .A mix of satured & unsatured hydrocarbons result: nco + 2nH2 - CnHn + nH2O nco +(2n +1) H2 -- CnHn+2 + nH2OThe crude oil thus obtained is then fractionated to yield:A) Gasoline B) high boiling heavy oil

BERGIUS PROCESS

The low ash coal is finely powdered and made into a paste with heavy oil and than catalyst is incorporated.

The whole is heated with H2 at 450oc , at pressure 200 – 250 atm for about 1.5 hrs during which H2 combines with coal to form saturaed hydrocarbons, which decompose at prevailing high liquid.

The issuing gases are led to condenser , where a liquid resembling crude oil is obtained , which is then fractioned to get:

A) Gasoline – 60% B) Middle oil & heavy oil

GASEOUS FUELS

The most imp gaseous fuels are Natural gas , producer gas , water gas ….

Natural gas: It is obtained from well dug in the oil bearing regions. It is mainly composed of methane , ethane & other gases. Composition of natural gas is: Methane: 88.5% ethane 5.5%, propane 3.7% butane 1.8%

pentane H2, CO, CO2 higher hydro carbons 0.5%. The calorific value of natural gas varies from 8000-14000

kcal/m3

Uses:

It can be conveyed over very large distances in pipelines, it is finding increasing use as domestic & industrial uses.

It is also used as a raw material for: i) The manufacture of carbon black & hydrogen

which in turn used as filler for rubber & ammonia synthesis respectively.

Methanol , formaldehyde & other chemicals. Methane on microbiological fermentation gives

synthetic proteins which are used as animal feed.

FLUE GAS ANNALYSIS BY ORSAT’S APPARATUS

Principle of analysis is that the gas to be analyzed is to be taken in burette which is connected to several pipettes containing suitable solutions.

The gas is forced through three pipettes one after the another.

The certain constituent get absorbed or volumes of the unabsorbed gases are found from which from the volume of the particular constituent is known.

Orsat’s apparatus: It consists a water – jacketed measuring burette,

connected in series to a set of three absorption bulbs, through stop cocks.

The other end is provided with a three way stop cock,the free end of which is further connected to a U – tube packed with glass wool (for avoiding the incoming of any smoke particles, etc.)

The graduated burette is surrounded by a water jacket to keep the temperature constant of gas during the experiment.

The lower end of the burette in connected to a waterreservoir by means of along rubber tubing.

The absorption bulbs are usually filled with glass tubes, sothat the surface area of contact between the gas and the solution is increased.

The absorption bulbs have solutions for the absorption of CO2, O2 and CO respectively.

First bulb has potassium hydroxide solution (250 g KOH in 500ml of boiled distilled water), and it absorbs only CO2.

The second bulb has solution of alkaline pyrogallic acid (25 g pyrogallic acid + 200g KOH in 500 ml ofdistilled water) and it can absorb CO2 and O2.

The third bulb contains ammonium cuprous chloride(100g cuprous chloride + 125ml liquor ammonia + 375 ml of water) and it can absorb CO2, O2 and CO.

It gives valuable information for regulating combustion in the furnace.

Presence of free CO shows in complete combustion & air supply to be increased.

If there is a large amount of free O2 if shows large excess of air.

41

Calorific value• Calorific value is the total quantity of heat

liberated when a unit mass of fuel burn completely.

• Measured at 25˚C.

• Heat or energy produced

• Gross calorific value (GCV): vapour is fully condensed

• Net calorific value (NCV): water is not fully condensed.

NCV = GCV – (mass %hydrogen)(9)(λv)kJ/kg

λv –latent heat of water vapour at reference temperature, normally at 298.15K.

λv at 298.15K = 2442.5kJ/kg.

42

Units of calorific values:

For solid and liquid calorific value are

Joules/kg [ in SI system]calori / gram [ in cgs system]kcalori/kg [ in mks system]B.T.U/lB [ British system ]

Relation 1kcal/kg = 1.8B.T.U/lB.

For gases; kcal/cubic meter. BTU/cubic feet.Relation 1kcal/cubic meter = 0.107BTU/IB.

Determination of calorific value by Junker’s gas calorimeter:

AIM :To determine calorific value of gaseous fuel by Junkers gas calorimeter

APPARATUS: The apparatus mainly consists of a cylindrical shell with copper coil arranged in two passage configuration with water inlet and outlet to circulate through the copper coil, a pressure regulator, a wet type gas flow meter & a gas Bunsen burner.

DESCRIPTION: Determination of calorific value (heat value) of combustible gases is essential to assess the amount of heat given away by the gas while burning a known amount of gas to heat a known amount of fluid (water) in a closed chamber.

PROCEDURE: Install the equipment on a flat rigid platform near an

uninterrupted continuous water source of ½” size and a drain pipe.

Connect the gas source to the pressure regulator, gas flow meter and the burner respectively in series

Insert the thermometer / temperature sensors, into their respective places to measure water inlet and outlet temperatures and a thermometer to measure the flue gas temperature at the flue gas outlet

Start the water flow through the calorimeter at a study constant flow rate and allow it to drain through over flow.

Start the gas flow slowly and light the burner out side the calorimeter

Regulate the flow of gas at a steady rate to any designed flow (Volume)

Insert the burner into the calorimeter and allow the out let water temperature to attain a steady state

Swing the out let to a 1000 ml jar and start. The stop watch simultaneously, record the initial gas flow meter reading at the same time

Note down the time taken to fill 1000ml and at the same time the final gas flow reading recorded by the gas flow meter

Tabulate all the reading and calculate the calorific valve of the gas under test

Repeat the experiment by varying the water flow rate or gas flow for different conditions.

After the experiment is over stop the gas flow, water flow, and drain the water from the calorimeter, keep the equipment clean & dry.

Calculations:

Let V = volume of gas burnt in certain time ‘t’ at S.T.P

W = weight of water collected in ‘t’

T1 = temp of incoming water T2 = temp of outgoing water HCV =W(T2-T1)/V K.cal /m3

Suppose m= mass of steam condensed in certain time ‘t’ in graduated cylinder from Vm3 of gas . The latent heat of steam= 587 K.cal/kg. thus the lower calorific value (LCV) is given as:

LCV= [HCV- m/v X 587] K.cal/m3.

COMBUSTION Combustion reactions are exothermic reactions accompanied by evolution of heat and light and the temperature rises considerably. The amount of oxygen or air required for combustion of a given sample of fuel can be calculated.

Calculation of Air Quantities To determine the amount of oxygen and hence the amount of air required for combustion for a unit quantity of fuel, the following chemical principles are applied.(1) Substances always combine in definite proportions given by molecular mass. C + O2 → Co2

12 32 4412 g of carbon requires 32 g of oxygen and 44 g of CO2 is formed.

Cracking: Is defined as “the decomposition of bigger hydrocarbon molecules into simpler ,low boiling hydrocarbons of lower molecular weight”.

Gasoline is the most imp fraction of crude petroleum. The yield of this fraction is only 20% of the crude oil. The yield of heavier petroleum fraction is quite high. Therefore, heavier fractions are converted into more useful fraction, gasoline.

This is achieved by a technique called cracking.

Cracking is the process by which heavier fractions are converted into lighter fractions by the application of heat, with or without catalyst. Cracking involves the rupture of C-C and C-H bonds in the chains of high molecular weight hydrocarbons.

e.g:

6H

3C

12H

5CCracking

18H

8C

Cο36B.Pt Cο174B.Ptpentene pentane-n Decane

10H

5C

12H

5CCracking

22H

10C

Nearly 50% of today’s gasoline is obtained by cracking. The gasoline obtained by cracking is far more superior than straight run gasoline.

The process of cracking involves the full chemical changes:

•Higher hydrocarbons are converted to lower

hydrocarbons by C-C cleavage. The product obtained on cracking have low boiling points than initial reactant.

•Formation of branched chain hydrocarbons takes place from straight chain alkanes.

•Unsaturated hydrocarbons are obtained from saturated hydrocarbons.

•Cyclization may takes place.

Cracking can also be used for the production of olefins from naphthas, oil gas from kerosene.

KNOCKING

The instantaneous combustion causes a shock wave to set up. This is known as ‘ knocking’ ‘pinkinf’ ‘detonation’. It depends on the characteristics of the fuel , besides design factors. This ratting noise produced in he internal combustion engine is called knocking.

In a spark-ignition petrol engine, a phenomenon that occurs when unburned fuel-air mixture explodes in the combustion chamber before being ignited by the spark. The resulting shock waves produce a metallic knocking sound. Loss of power occurs, which can be prevented by reducing the compression ratio, re-designing the geometry of the combustion chamber, or increasing the octane number of the petrol.(formerly by the use of tetraethyl lead anti-knock additives, but now increasingly by MTBE – methyl tertiary butyl ether in unleaded petrol.

An antiknock agent is a gasoline additive used to reduce engine knocking and increase the fuel's octane rating.

The typical antiknock agents in use are: Tetra-ethyl lead (phased out) Methyl cyclo pentadienyl manganese

tricarbonyl (MMT) Ferrocene, Iron pentacarbonyl, Toluene,

Isooctane

Documents

Fuel contains mainly ‘C’ which undergoes combustion and liberates large amount of heat energy. C+ O 2 CO 2 + heat (Exothermic) Burning of a substance