Chemical fuels(ppt).ppt

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CHEMICAL FUELS

Definition

Chemical fuel is a combustible carbonaceous material which

on proper burning in air gives large amount of heat that can

be used economically for domestic and industrial purposes.

Eg.- wood, charcoal, coal, kerosene, petrol, diesel,

producer gas, water gas, natural gas, etc.,



During the process of combustion, C and H of the fuel

combine with oxygen of air to form C! and H!

respectively.

"ince the heat content of combustion products C!, H!,

etc. being lower than that of reactants #C, H, etc. of fuel$, the

chemical fuel release heat during their combustion process.

Classification

% &ased on their origin' 1) Primary (Natural) fuels

2) Secondary (Derived) fuels

% (hese are again subdivided into solid, li)uid and gaseous

according to the physical state.



Table-1. Classification of Fuels

*hysical state *rimary fuel "econdary fuel

"olid +ood, *eat, Charcoal, Coke

Coal, ignite

i)uid Crude petroleum *etrol, erosene,Diesel, "ynthetic

petrol

as /atural gas *roducer gas,

+ater gas, Coal gas,

&iogas, *



Characteristics of a Goo Fuel% High calorific value.

% 0oderate ignition temperature.% ow moisture content% ow content of non-combustible matter.% 1n case of solid fuel, the ash content should be

less and the si2e should be uniform.% 3eadily available in bulk at low cost.% *roducts of combustion should not be harmful.% Combustion should be easily controllable.% 1t should be safe, convenient and economical

for storage and transport.



Calorific !alue

1t is defined as 4the amount of heat liberated when

unit mass #or unit volume in the case of a gaseous

fuel$ of fuel is completely burnt in air or oxygen5Units

%"olid or i)uid fuels - cal6g or kcal6kg or 76kg%aseous fuels 8 kcal6m9 or 76m9

%Gross or Hi"her calorific !alue #GC$%

1t is defined as 4the amount of heat liberated when

unit mass 6 volume of the fuel is burnt completely

in air and the products of combustion are cooled

to room temperature5



% &et or Lo'er calorific !alue #&C$%

1t is defined as 4the amount of heat produced when

unit mass6volume of fuel is completely burnt in air and the products of combustion are allowed to escape into

the atmosphere5

% C: ; /C: < atent heat of condensation of steam

% /C: ; C: 8 = > 0ass of hydrogen > atent heat

of steam

%/C: ; C: 8 ?.?= > @ of hydrogen > atent heat

of steam



(rinci)le

A known mass of the fuel sample is burnt completely inexcess of oxygen.

(he liberated heat is absorbed by water and calorimeter.

(he heat lost by burning fuel is the heat gained by water

and calorimeter.

(he calorific value of the fuel is calculated from the

measured data.

Determination of calorific value using

&omb Calorimeter





*bser!ations an Calculations0ass of the fuel sample taken ; m g

0ass of water taken in the copper calorimeter ; + g

+ater e)uivalent of calorimeter ; w g1nitial temperature of water ; tB

? C

inal temperature of water ; t!? C

Heat liberated by burning of fuel ; Heat absorbed by waterand calorimeter

m x C: ; #+ < w$ #t! - tB$

C: ; #+ < w$ #t! - tB$ cal6g

m

C: ; #+ < w$ #t! - tB$ > .B > B?9 76kg

m



Calculation of /C:

1f H ; *ercentage of hydrogen in fuel, then

% +ater formed by combustion of Bg of fuel ; B x H

! B??

; ?.?=H g

% atent heat of water formed ; ?.?=H > FG cal6g

% /C: ; C: 8 atent heat of water formed

; C: 8 ?.?=H > FG cal6g



(he water e)uivalent of the calorimeter is determined by

burning a fuel of known calorific value and using the above

e)uation.(he fuels used for this purpose are ben2oic acidHC:; ,9!F kcal6kg and naphthalene HC:;=, kcal6kg

(roble+,% A solid fuel of ?.F g was burnt in a &omb calorimeter and

the temperature of B?? g of water raised from ! to

!.FoC. 1f the fuel contains G@H, calculate its /C: I C:.

% J+ater e)uivalent of calorimeter ; F?.?g, atentheat of steam ; FG cal 6 degK



o/s Calori+eter



(rinci)le

% A known volume of gaseous fuel sample is burnt in thecombustion chamber of a &oyLs calorimeter.

%(he released heat is )uantitatively absorbed by cooling

water, circulated through copper coils surrounding the

combustion chamber.%(he mass of cooling water and its rise in temperature

are noted.%(he mass of water produced by condensation of steam

is calculated.

%(he calorific value of the fuel sample is then calculatedfrom these data.



*bser!ations an Calculations

:olume of fuel burnt at "(* in time, t ; : m9

0ass of cooling water circulated in time, t ; + kg

"teady temperature of incoming water ; tB? C

"teady temperature of outgoing water ; t!? C3ise in temperature ; #t! - tB$

? C

0ass of water produced from steam condensation ; m kg

Heat released by combustion of fuel ; Heat absorbed by water

: x C: ; + #t! - tB$



% C: ; + #t! - tB$ kcal6m9

: ; + #t! - tB$ > .B k76m9

:

% atent heat of steam per m9

of fuel sample ; m > FG kcal :

% /C: ; + #t! - tB$ - m >FG kcal

: : ; J+ #t! - tB$ - m >FG K .B k76m9

: :



Soli Fuels

+ood M*eat Mignite M&ituminous coal MAnthracite

Carbon content, calorific value and hardness

0oisture content, C,,/ and " content, volatile matter

Coal

Coal is a highly carbonaceous matter that has been formed as a result of alteration of vegetable matter #e.g., plants$

under certain favorable conditions.

%1t mainly composed of C, H, /, and , besides

non-combustible inorganic matter



Analsis of coal an its si"nificance

The )ro0i+ate analsis involves the determination ofmoisture, volatile matter, ash, and fixed carbon.

%(his gives )uick and valuable information regarding

commercial classification and determination of

suitability for a particular industrial use.

The ulti+ate analsis involves the determination of

carbon, hydrogen, sulphur, nitrogen, oxygen and ash.

%(he ultimate analysis is essential for calculating heat

balances in any process for which coal is employed

as a fuel.



*roximate analysis*roximate analysis

i% Moisture' An air-dried coal sample is weighed into a

dry silica crucible and heated for about one hour at

BB?? C in an electric hot air-oven. (he crucible is

cooled first in air then in a desiccator and then

weighed.

@ moisture ; oss in weight > B??

+t. of coal taken

% 0oisture in coal evaporates during the burning of coal and

it takes some of the liberated heat in the form of latent heatof evaporation.% 0oisture lowers the effective calorific value of coal.% esser the moisture content better is the )uality of coal as a

fuel.



ii% $olatile +atter ' (he dried sample of coal left in the

crucible in step #i$ is then covered with a lid and placed

in a muffle furnace, maintained at =F?? C. (he crucible

is taken out after G minutes of heating. 1t is cooled firstin air then in a desiccator and finally weighed.

@ :olatile matter ; oss in weight > B??

+t. of coal taken

% A high volatile matter content means that a high proportion

of fuel will distill over as vapour and a large portion of which

escapes unburnt. "o, higher @ of volatile matter in coal is undesirable.% A high volatile matter containing coal burns with a long flame,

high smoke and has low calorific value.% esser the volatile matter, better is the rank of coal.



iii% Ash, (he residual coal left in the crucible in step #ii$ is

then heated without lid in a muffle furnace at G??-GF?? C,

until a constant weight of residue is obtained.

@ Ash ; +t. of ash left > B??

+t. of coal taken

Ash-for+in" constituents in coal are unesirable

for the follo'in" reasons, % (he calorific value of the coal is decreased% (he removal and disposal of ash poses problems

% (he ash deposited in the fire bars interferes withcirculation of air

% 1f the ash fuses to form a clinker on the fire bars, it

hinders air circulation and also promotes corrosion

of the fire bars.



i!% Fi0e carbon, 1t is reported as the difference

between B?? and the sum of the percentages ofmoisture, volatile matter and ash content of a coal

sample.

% Higher the percentage of fixed carbon, greater is its

calorific value and better is the )uality of coal. % reater the percentage of fixed carbon, smaller is the

percentage of volatile matter. 1t is the fixed carbon

which burns in the solid state.

% 1nformation regarding the percentage of fixed carbon

helps in designing of the furnace and the fire-box.



Ulti+ate Analsis

i% Carbon an Hro"en, An accurately weighed coal

sample #B-! g$ is burnt in a current of oxygen in combustionapparatus. As a result C and H of the coal are converted into

C! and H! respectively. (hese are absorbed respectively

in H and CaCl! tubes of known weights. (he increase in

the weights of H and CaCl! tubes corresponds to theamount of C! and H! formed respectively.

C < ! M C!

B!

! H < C! M !C9 < H!

H! < B6!! M H!



@ Carbon ; 1ncrease in wt .of H tube > B! > B??

+t. of coal taken >

@ Hydrogen ; 1ncrease in wt. of CaCl! tube > ! >B?? +t. of coal taken >B

% C and H in coal directly contribute towards the calorific value

of the coal.% Higher the percentage of C and H, better is the )uality of the

coal and higher is its calorific value.

ii% &itro"en, Determined by digesting a known )uantity #Bg$ of

powdered air-dried coal sample in a NeldhalLs flask with conc.H!" in the presence of !" as a catalyst. After the solution

becomes clear, it is treated with excess of /aH.



(he liberated ammonia is distilled into a known volume of

standard acid solution. (he volume of unused acid is then

determined by back titration with standard /aH solution.rom the volume of acid used by ammonia liberated, the

percentage of nitrogen is calculated.

@ /itrogen ; +t. of nitrogen > B??

+t. of coal taken

+here,

+t. of nitrogen ; :ol. of acid used > /acid > B

B???

(hus, &itro"en 2 $ol. of aci use 3 &aci 31.4

5t. of coal ta6en



% iii%Sul)hur, A known amount of coal

sample is burnt completely in a bomb

calorimeter. "ulphur present in coalis oxidi2ed to sulphates. (he ash left after

combustion from the bomb calorimeter is

extracted with dil. HCl. (he acid extract isthen treated with barium chloride solution

to precipitate sulphate as barium

sulphate. (he precipitate is filtered,washed, ignited and weighed.



Sul)hur 2 5t. of aS*4 obtaine 3 78 3 199

5t. of coal ta6en 3 877

% "ulphur containing coal is not suitable forthe preparation of metallurgical coke as it

adversely affects the properties of the

metal.% xides of sulphur pollutes the

environment and leads to corrosion.



#i!% Ash, (he ash content of coal sample is

determined as described under proximate

analysis.

#!% *0"en, *0"en 2 199 : #C ; H ; & ; S ; Ash%

(he lower the oxygen content, the more is thematurity of coal and greater is its calorific value

( t l fi i



(etroleu+ refinin"

(he various fractions condensed and collected

at different heights of the column are '

Gases #oilin" ran"e< belo' 799C%<

(etroleu+ ether #79-=99 C%<

Gasoline or )etrol #49-1899 C%< &a)htha #189-1>99 C%<

?erosene #1>9-8@99 C%<

Diesel or fuel oil or li"ht "as oil #8@9-7899C%< Hea! oil #789-4999 C%<

(araffin 'a0< As)halt< etc.< #abo!e 4999 C%.



Crac6in"

%Crac6in" is efine as the )rocess of eco+)osition of

hi"her +olecular 'ei"ht hrocarbons #hi"her boilin"%

into lo'er +olecular 'ei"ht hrocarbons #lo' boilin"%.

% Cracking process involves breaking of C-C and C-H bonds.% 1t produces low boiling alkanes and alkenes.% A small amount of carbon and hydrogen are also produced.



Cracking

Cracking

CB?H!! CFHB! < CFHB?

Decane *entane *entene

(hermal Cracking

JCarried out at high temperature

and pressure in the absence of

catalystK

Catalytic CrackingJCarried out in the presence of a

catalyst #Al!

9

< "i!

$ at a much

lower temperature and pressureK





A!anta"es of fluiie-be crac6in"

% A high degree of mixing is achieved and conse)uently

a good contact is established between the catalyst and

the feed stock vapours.

%(his results in a higher yield.

% (he regeneration of the inactive catalyst can be

carried out continuously without interrupting the

production of gasoline unlike in fixed-bed catalytic

cracking.

Befor+in" of )etrol



Befor+in" of )etrol

Cataltic Befor+in", 1t is the process of upgrading gasoline

#increasing its octane number$ in presence of a catalyst

%(he increase in octane number of straight run gasoline occurs

through structural modifications such as conversions of straight

hydrocarbons into branched, cyclic and aromatic hydrocarbons.

% Befor+in" (rocess, (he feed stock #straight run gasoline$ is

preheated to remove " and / content to acceptable limits to

avoid platinum catalyst being poisoned. (he vapours of thefeed stock is mixed with hydrogen and preheated to F??? C.

(he mixture is compressed #BF-F? atmosphere$ and then fed

into a series of three cylindrical reactors containing the

platinum catalyst supported on alumina-silica base. (he

reformed products are fractionated to get stabili2ed gasoline.

Befor+in" reactions



Befor+in" reactions% Iso+erisation, (he conversion of straight chain

hydrocarbons into branched chain hydrocarbons.

% Dehro"enation, Dehydrogenation of Cycloalkanes toproduce aromatic compounds.

CH9

#CH!$D CH9

CH9

CH

CH9

CH!

CH9

CH!

!-methyl petanen-hexane

CH9

CH9

< 9 H!

Cyclohexane &e2ene

< 9H!

0ethyl cycloheane (oluene



% Cclisation an ehro"enation' Cyclisation of straight

chain hydrocarbons followed by dehydrogenation to

produce aromatic hydrocarbons.

CH9 CH9#CH!$D H!<

n-Hexane Cyclohexane

< 9H!

Cyclohexane &en2ene

% Hro crac6in", Hydro cracking of n-*araffins to produce

light gases that are removed from gasoline fraction.

CH9 #CH

!$E CH

9 CH9 #CH

!$9 CH

9< H!

Cat!

n-Decane n-*entane



?noc6in"

(he explosive violent noise coming out from the 1C engines

due to instataneous burning of the last portion of the fuel rapily

is known as knocking

% (he efficiency of power production in spark ignited

internal combustion #1C$ engines is related to the

compression ratio #C3$.% (he C3 is the ratio of the cylinder volume #:B$ at the

end of the suction stroke to the volume #:!$ at the

end of the compression stroke of the piston.

% (his ratio is always greater than one, since :B being

greater than :!.

%



(he tendency to knock decreases as

follows'

n-alkanes> mono substituted alkanes >

cycloalkanes > alkenes > poly substituted

alkanes > aromatics.



A!erse effects of "asoline 6noc6

% 1t increases the fuel consumption.

% 1t results in decreased power output.% 1t causes mechanical damage by overheating of the

cylinder parts.% (he driving becomes rather unpleasant.

The 6noc6in" in IC en"ines can be +ini+ie throu"h

the follo'in" +easures,

% &y a suitable change in engine design.% &y using high rating gasoline.% &y using anti-knocking agents.



*ctane &u+ber % Among alkanes, n-heptane knocks severely,

while under identical conditions, !,!,-trimethyl pentane

#iso-octane$has a high resistance to knocking.% or the scale proposed to indicate the anti-

knock properties of gasoline, n-heptane was

arbitrarily assigned an octane number of 2ero

and iso-octane was arbitrarily assigned a

value of B??.%



*ctane nu+ber is efine as the )ercenta"e

b !olu+e of iso-octane in a +i0ture of iso-

octane an n-he)tane blen<'hich has the sa+e 6noc6in" characteristics

as the "asoline sa+)le< uner the sa+e set

of conitions.

% (hus a gasoline with an octane number of=?, has the same knocking characteristics as a

mixture of iso-octane and n-heptane containing

=?@ by volume of iso-octane. "ince iso-octanehas good anti-knock properties, it is clear that

greater the octane number, greater is the

resistance to knocking.



Anti-6noc6in" A"ents

(he octane rating of gasoline samples

can be increased by the addition ofcertain organometallic compounds

called anti-knocking agents and the

process is called 4doping5. An extensively used anti-knocking

agent is tetraethyl lead #(E$,

*b#C!HF$.



*roposed 0echanism'

*b#C!HF$ <! *bO! <ther products

3CH!O < ! 3CH < HO!

*b < H O *b#H$*bO! < 3CH! *b <3CH!O

HO! < *b HO < *b!

*b#H$ < HO *b! <H!

(etraethyl lead helps to cut self ignition broughtabout by compression by generating a smooth

supply of free radicals



Unleae (etrol

*etrol wherein the enhancement of octane rating is

accomplished without the addition of lead compounds isreferred to as unleaded petrol.

% (o improve its octane number, Concentration of high octane

components #like isopentane isooctane et!ylben"ene

isopropyl ben"ene etc$ is increased by the process of

reforming.% Compounds like met!yl tertiary butylet!er (#$%&) can also

be added to improve octane number of unleaded petrol.

0(&E provides oxygen #of ether group$ for combustion of

petrol in 1C engines, thereby reducing considerably the

formation of peroxy compounds #which causes knocking$.



A!anta"es of unleae )etrol

% (he harmful effects of discharge of poisonous lead and its

compounds through the exhaust of automobiles is avoided.% ne of the maNor advantages of using unleaded petrol

is that it permits the attachment of a catalytic converter to

the exhaust pipe in automobiles.

Cataltic con!erter contains rhoiu+ catalst.% 1t converts the toxic gases such as C and / to harmless

C! and /!.

% 1t also oxidi2es hydrocarbons into C! and H!.

eaded petrol cannot be used in automobiles e)uipped with

catalytic converter as the lead present poisons the catalyst

thus destroying the active sites.



Gaseous Fuels

Liuefie )etroleu+ "as #L(G% or bottled gas or refinery gas

% 1t is obtained as a byproduct, during the cracking of heavy oils

or from natural gas.% * is dehydrated, desulphurised and traces of odorous

organic sulphides #mercaptans$ are added to give warning of

gas leak. 1t is supplied under pressure in containers under the

trade name like 1ndane, &harat gas, etc.% 1t has the calorific value of about !F??? kcal 6m9.% * consists of hydrocarbons of such volatility that they can

exist as gas under atmospheric pressure, but can be readily li)uefied under pressure.% (he main constituents of * are n-butane, isobutene,

butylenes and propene.

* i id l d d ti f l P d



% * is widely used as a domestic fuel. Psed as an

alternative fuel for 1C engines, since it permits the

attainment of high compression ratios without producing

knocking

A!anta"es of L(G o!er "asoline as a +otor fuel% 1t is cheaper than gasoline.% 1t readily mix with air.

% 1t is highly knock resistant,% 3esidue and oil contamination is less, as it burns cleanly.

Disa!anta"es of L(G o!er "asoline as a +otor fuel

% Handling has to be done under pressure.% * is advantageous only in engines working under

high compression ratio.% 1ts octane number is )uite low.% 1ts response to blending is very poor.

5 t



5ater "as

% 1t is essentially a mixture of combustible gases, C and H!.

% 1t is also known as blue gas because it burns with a blue flame

due to the combustion of carbon monoxide.% (he calorific value of water gas is about B???? -BB??? 76m9.% (he average composition of water gas is as follows'

C' ? 8 F@ Q H! ' F 8 F?@ Q C! ' @ Q /! ' @

Manufacture, 1t is produced by passing alternatively steam

and little air through a bed of red hot coke maintained atB???? C.

(rinci)le, +hen steam is blown through a bed of hot coke

#B???? C$ water gas is produced.

C < H! #steam$ M C < H! RH ; B9B. 7% (he reaction being endothermic in nature, the temperature

of the coke bed gradually decreases with continuous passage

of steam and the drop in temperature must be prevented. or

this the steam supply is temporarily cut off and air is blown in.



(he over all reaction during air blow is the formation of C.

!C < ! M !C RH ; - !!B.= 7

(his reaction being exothermic increases the temperature of

the coke bed to about B???? C. (hus by blowing steam and

air alternatively, the temperature of the coke bed can be

maintained at B????

C.

Uses % 1t is used for the production of hydrogen.% 1t is extensively used for the manufacture of methyl alcohol

and synthetic petrol.% 1t is used as a fuel in glass and ceramic industries.% Enriched water gas #mixed with hydrocarbons$, which

burns with luminous flame is used as illuminating agent.



(roucer "as



(roucer "as% 1t is essentially a mixture of carbon monoxide and nitrogen.% 1t is prepared by passing air mixed with little steam over a

red hot coal or coke bed maintained at aboutBB??

?

C.% (he average composition of producer gas is as follows'

C' !F-9?@ Q /! ' F?-FF@ Q H! ' B?@ Q C! ' F@Q

Hydrocarbons ' !-9@.% (he calorific value of producer gas is ??? - F??? 76m9.

Manufacture, (he producer is charged with coke from the

top and the charge is heated to about BB??? C. A mixture of

air and steam is passed over red hot coke bed through the

inlet at the bottom. (he producer gas goes out through theoutlet at the top.



Beactions that ta6es )lace in ifferent ones of the fuel be



Beactions that ta6es )lace in ifferent ones of the fuel be

% *0iation one, (his is the lowest part of the coke bed.

Here, the carbon of the coke burns in presence of excess of

air to give carbon dioxide.

!C < ! M !C! RH ; - 9=9.F 7

% Beuction one, Carbon dioxide produced in the oxidation

2one then rises through the hot bed and is reduced by coke to C.

!C! < C M !C RH ; - BG9.F 7

(he over all reaction in the formation of carbon monoxide

being exothermic, the fuel bed gets heated up beyond BB??? C. At high temperature'

- the ash forms clinkers or slag which are rather difficult to

remove.

- the grate bars and refractory lining get distorted.



1n order to avoid these problems in the producer, a

reduction in temperature is achieved by passing air saturated

with steam instead of air alone.

1n the reduction 2one, steam gets reduced to water gas.

C < H!

#steam$ M C < H!

RH ; B9B. 7

(his endothermic reaction brings down the temperature to

the

optimum level.

% Distillation one, (his is the upper most part of the fuel bed,

where the distillation of volatile matter of coke 6 coal occurs.

Uses,- 1t is used as a fuel in the manufacture of steel, glass,

A!anta"es of cataltic crac6in"



A!anta"es of cataltic crac6in"

% (he octane number of gasoline produced is high.

% (he yield of gasoline is also high.% (he process can be better controlled.% (he product contains a very little amount of undesirable

sulphur.% (here is a saving in production costs since high temper-

atures and high pressures are not needed.% 1n catalytic cracking, external fuel is not re)uired.

(he necessary heat is obtained by burning off the coke

deposited on the catalyst itself, during the regeneration

process.% (he gasoline formed contains much less gum and gum

forming compounds.% Catalysts are selective in their action, and therefore, they

permit cracking of only high boiling hydrocarbons.

%Fluiie #+o!in"% be cataltic crac6in",



Fluiie #+o!in"% be cataltic crac6in",

(he finely divided catalyst bed #Al!9 < "i!$ is fluidi2ed by the

upward passage of feed stock vapours #Heavy oil, gas oil, etc$

in a cracking chamber #called 3eactor$ maintained at FF?

?

C./ear the top of the reactor, there is a centrifugal separator

#called cyclone$, which allows only the cracked oil vapours to

pass onto the fractionating column but retains the catalyst

powder in the reactor itself. (he catalyst powder gradually

becomes heavier due to the deposition of carbon and settles tothe bottom, from where it is forced by an air blast to the

regenerator #maintained at ??? C$. After cracking, the products

are fractionated into gases, gasoline, gas oils and residual oils.

(he heavier oil fractions may be cracked in a second-stagecracking.

1n regenerator, the spent catalyst is stripped of the adsorbed

oil by passing steam and then decarboni2ed by a hot air blast,

under controlled conditions. (he heat liberated during this

regeneration is used to raise steam and to preheat the catalyst.



% H. 3. 3icardo, with the help of a variablecompression engine

% showed that in actual practice, the power

increases to a% maximum and then falls rapidly with furtherincrease in the

% C3. (he C3, corresponding to the maximum

power output, is% known as highest useful compression ratio

#HPC3$.

Mechanis+ of ?noc6in"



Mechanis+ of ?noc6in"% 1n 1C engines, the gasoline and air drawn into the cylinder is

compressed by the piston and ignited by an electric spark.

% As the flame front travels towards feed end of the combustion

chamber, rapidly expanding combustion gases, compress the

remaining un-burnt fuel ahead of flame front and raise its

temperature.% 1f the flame front travels rapidly at optimum speed, the

combustion of un-burnt fuel takes place but smoothly.% 1f the flame front travels too slowly, the entire last portion of

the fuel-air mixture may get heated up beyond its ignition

temp. and undergo instantaneous explosive combustion.

(his produces thermal shock wave which hits cylinder walls

and piston. (his result in emitting of characteristic rattling

sound called knocking or pinking.

Liui Fuels



Liui Fuels

(etroleu+ #Crue oil%

% An important primary li)uid fuel.% 1t is a dark colored viscous oil found deep in the earthLs

crust.% 1t is believed to have been formed millions of years ago by

anaerobic decay of marine plant and animal life under the

influence of high temperature and pressure.% 1t is mainly a complex mixture of hydrocarbons #like straight-

chain paraffins, cycloparaffins, olefins and aromatics$ with

small amounts of other organic compounds containing /, and ", and traces of inorganic compounds.

% (he average composition of crude oil is'

C' 9 - G@Q H' BB - BF @Q ", / and ' ?.B- F@.

(h h i f th h i l ti th t l d t



% (he mechanism of the chemical reactions that lead to

knocking is not clear.% 1t is believed that chemical reactions that are of importance

are cracking and the oxidation of the hydrocarbons.% *robably the reactions proceed by a chain reaction.% 1t was recogni2ed that the structures of the fuel

hydrocarbons determines largely their knocking tendency.

% (he tendency to knock decreases as follows'

n-alkanesS mono substituted alkanes S cycloalkanes S

alkenes S poly substituted alkanes S aromatics.

% (he tendency to knock depends not only on the fuel usedbut also on the engine design, shape of head, location of

plug, etc., and also upon the running conditions.



% Automobile gasolineTs have octane number ranging from GF% to =F. Aviation gasolineTs have a greater knock resistance% and their octane numbers are greater than B??. 1n such cases% the octane numbers are computed using the relationship,

% ctane number ; J *ower number 8B?? K < B??% 9% where, power number is an arbitrary number proportional to% the power being extracted by the engine.



% About ?.F ml of (E per liter is added for motor fuel and about

B ml of (E per liter is generally added for aviation petrol.% 1t is believed that during combustion of gasoline, (E forms

*b and *b.% (hese species act as free-radical chain inhibitors and thus

curtail the propagation of the explosive chain reaction and

thereby minimi2ing knocking.

% 1f (E alone is used, the species *b and *b may getdeposited on engine parts and cause mechanical damage.% (he vapours of *b and *b may pollute the air.% 1n order to minimi2e the air pollution and damage to engine

parts, (E is always used along with ethylene dibromide

or ethylene dichloride.% (he functions of these ethylene derivatives is to convert the

less volatile *b and *b into more volatile *b&r ! or *bCl!

which escapes into air along with exhaust gases.

Cataltic Crac6in" +ethos



Cataltic Crac6in" +ethos

% Fi0e-be cataltic crac6in", (he catalyst #Al!9 < "i!$

in the form of powder or pellets is placed on the grid in thecatalytic chamber. (he vapours of the feed stocks #Heavy oil,

gas oil, etc.$ are passed through the bed of catalyst main-

tained at F?-F??? C. About F?@ of the feed stock is

converted into gasoline together with elemental carbon

which gets deposited on the surface of the catalyst. Cracked

vapours are next subNected to fractionation in a fractionating

column wherein gasoline is separated from un-cracked heavy

oil. (he catalyst loses its activity because of the deposition

of carbon and also due to the adsorption of oil vapours. Accordingly, the catalyst re)uires regeneration after -B?

hours. During regeneration time, the cracking process is

interrupted and the adsorbed oil is stripped off by passing

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Chemical fuels(ppt).ppt