Following are the types of fuels:

(A) Solid Fuels:

Dung coke Wood, Peat, Coal, Lignite, Anthracite Bri­quette fuel wood charcoal coke.

Advantages of solid fuels are:


(i) They are easy to transport

(ii) They are convenient to store without any risk of spontaneous explosion

(iii) Their cost of production is low-cheap

(iv) They possess moderate ignition temperature, Coal 150°C


Disadvantages solid fuels are:

(i) Their ash content is high

(ii) Their large proportion of heat is wasted during combustion. Combustion efficiency is low.

(iii)They burn with clinker form


(iv) Their combustion operation cannot be controlled easily

(v) Their cost handling is high.

(vi) Their calorific value is lower, 4000 K cal/Kg (wood)

(vii) -They require excess air for complete combustion


(viii) -They are dirty

(ix) Large space is required for storage

(x) Require huge chimney for the gases.

I. Dung Coke:


Calorific value 6-8 KJ/gm.

II. Wood:

On account of the large amount of oxygen present, less than 1 % of the H2 is available for combustion & the heat of combustion of wood is almost en entirely due to the carbon which it contains.

Ordinarily air- dried firewood usually contains about 20% of moisture, 40% C,H2=4.8%,02 = 33.6%, ash = 1.6% Calorific value 3300 K. Cal/Kg., 17 kJ/gm.


Newly feed wood contains from 25 to 50% of moisture.

When dry- wood is also a good fuel, but being lighter and more bulky than Coal it burns at a quieter rate. Does not yield the same quantity of clinker or ash.

III. Peat:

Peat consists of the fossil (water with) remains of vegetables matter generally mosses & aqueduct plants (growing in water). Perfect dried peat has composition C=58%, H2-6%, 02=30%, N=l%, Ash=5%. The calorific value of Peat is 3500K cal/Kg.

IV. Coal:

Coal is the product of vegetable matter which has, during the course 0f ages, been decomposed and solidified under great pressure.

The character of the coal depends on the length of time which has been occupied in its production & on the amount of pressure & heat to which it has been subjected in the strata layer) of the earth. The coal is the best and most is suitable solid fuel when be produced at a reasonable price.

The principle varieties of coal are as follows- .

(A) Lygnite or Brown Coal:

Lignite or Brown coal is intermediate in appearance and properties between Peat & coal. It burns with a very long smoky flame, & it is generally non- taking after drying in the air, lignite contains from 15 to 20% of moisture. If thoroughly dried in a stove & again exposed to the air if reabsorb the water which it Lost during the drying. The composition of lignite 65% C, 5% H2, 22% 02, 1 % N2,3.3%, Ash

The specific gravity is from 1.2 to 1.3

Low Grade fuel

(BI) Cannel or Long Flaming Coal-

This coal is highly valued for gas-making; it burns with a long flame & gives off large quantities of smoke. Specific gravity is 1.27 to 1.32.

(BII) Caking Bituminous Coal –

It softens & swells when heated, & aparts adhere together, forming a pasty It burns with a long flame & requires a careful continuous stoking to avoid smoke Specific gravity 1.26 to 1.36. Composition is 81% C, H2 8%, 02 1.5%, N2 1 CI Ash 3.5% calorific value 7500 Kcal/kg.

(BIII) Non- Caking or Dry Bituminous Coal-

It burns with shorter flame than that of caking coal & it gives off with or no smoke. Specific gravity 1.28 to 1.42. Compositions C = 78 to 90%, Volatile 20- 45%.

(C) Anthracite-

It burns without flame or smoke & with an intense local heat, but it requires a strong draught for its combustion. It is hard, brittle & most varieties to crack by heat considerable when it is heated, especially when the heat is applied suddenly, care has to be taken that the fuel is so managed that the small pieces do not fall between the fire bars & get lost.

The Moisture in coal, other than brown coals when brought to the surface may be from 5 to 10%. After exposure to the air the amount of moisture may be from 1 to 5%. Composition 91% C, 3% H2 2.5% 02,0.5 N,0.5%S, 2.5% Ash. HCV 8500 KCal/Kg.

Artificial Solid Fuels:

(a) Briquette Fuel:

It is usually made by mixing coal dust with pitch or some other binding then & formed into hard blocks of rectangular shape. Good briquette fuel contains 7% of ash, 3% of moisture in addition to the coal. Its calorific value is about 8ooo kcal/kg.

(B) Wood Charcoal:

It is made by heating wood out of contact with the atmosphere, or with only a limited supply of air to a temperature lower than 550° F (287.8°C), the higher the temperature the backer & harder is the charcoal produced.

The yield of charcoal varies from 15 to 25% by weight of the wood from which it is produced, the yield being lower the higher the temperature.

Dry charcoal contain from 80 to 95% of C, 0.5 to 3% H, & 1 to 5% of ash, the remainder being N, combined 02& H, Charcoal which has been exposed to the air frequently contain from 5 to 12% of moisture. The calorific value of good peat char coal is about 7000 kcal/kg.

(C) Peat Charcoal:

It is prepared from peat in the same manner that wood charcoal is made from wood. Good charcoal when dry contains from 80 to 90% of C & 10 to 15% Ash. It is usually extremely friable (reduced to powder).

(D) Coke-

It is the solid carbonaceous material left after coal has been heated to a high temperature with a limited supply of air, or in the case of gas coke with no air at all Coke when dry is an excellent fuel.

The best coke for fuel is prepared from bituminous coals; it is hard, brittle, and Porous, of a dark grey colour and slightly metallic luster (Brightness).

The yield of coffee front bituminous coal is from 50 to 80% of the weight of the coal. The yield 30 to 40% volatile matter which is converted in to coal tar. Naphthenic, Benzyl as by products in coke ovens Anthracite yields from 80 to of coke, which is of a pulverulent or powdering nature and not valued as a fuel.


Good dry coke .contains from 85 to 95% of carbon, 0.25 to 2% of sulphur, and 4 to 6% ash. Exposed to the air it absorbs from 10 to 20% of moisture.

(B) Liquid Fuels:

Advantages of liquid fuels

(a)Low excess air is used

(b)It is possible to build high capacity plants for burning oils

(c)Storage space is small

(d)Handling during transportation is easy

(e)Fuels do not deteriorate during storage

(f) Change in load can be suitably met

(g) Ash & refuse are small; they burnt without forming ash & clinker.

(h) Banking & stand by losses small.

(i) Operational labour is less

(j) System is neat & clean.

(k) They have higher calorific value 10500 K cal/Kg Heavy fuel oil.

(I) Their firing is easy.

(m) Their flame can be controlled.

(n) Loss of heat to chimney is low in these cases.

Disadvantages of the liquid fuels –

(i) Heat produced is costly

(ii) The cost is high

(iii) Costly special storage tanks can needed.

(iv) Greater chances of fire hazards.

(v) They give bad odour.

(vi) Burners – chocking is possible. Following an liquid fuels –

(A) Petroleum (IC Engine):

For steam raising (steamship boilers, boilers in coastal and places away from Coal mines) the liquid fuel almost exclusively used is obtained from natural ore petroleum, on account of the high fuel value, much less spacing & transportable.


The crude Petroleum as it comes from the well usually con­tains from 83 to 87% of carbon, and from 11 to 14% of Hydrogen, together with small percentage of oxygen, nitrogen and sulphur.

Its specific gravity is from 0.8 to 0.95, and its calorific value is about 10,800 kcal/kg.

The crude petroleum is a mixture of many hydro carbons mixture having different densities and different boiling points.

The liquid fuel generally used for steam rising is the residual when the oil is subjected to partial distillation at temperature up to 300° C. during this partial distillation the light constituents evaporate at the lower temperatures.

Petrol consist of a mixture of aromatics like Benzene, toluene etc. Paraffins like pehtan Haptane etc. & naphenes like Hexahydro tolune etc.

(B) Petrol or Gasoline:

Comes off at temperature from 70°C to 80°C Boiling point is 33.3 to 190°C. specific gravity is 0.74. Composition is 85.4% carbon 14.6% Hydrogen. Higher calorific value is 12000 Kcal/Kg. mean molecular mass.

(C) Neptha:

The different grade of Neptha comes off at temperatures from 80 to 150°C.

(D) Paraffin Oil, Kerosene Oil:

It comes off at temperature from 150° to 300°C. Specific gravity is 0.79. The percentage composition is carbon 86.3% Hydrogen 13.6% sulphur 01%. Higher calorific value is 11000 Kcal/Kg. Boiling point is 140 to 280°C.

(E) Fuel Oil:

The fuel oil has specific gravity of 0.88 to 0.94 and calorific value 10100 to 10900 Kcal/Kg.

Flash point is about 150°C. The heavier fraction can be heated and distilled under high pressure known as cracking yield larger quantities of liquid oil.

Benzyl mixture obtained as a byproduct of coke oven.

It consists of aromatics like benzene, toluene and having well anti petroleum properties. It is genially mixed with petrol.

(F) Diesel Oil:

Specific gravity 0.87. Percentage composition carbon 86.3% Hydrogen 12.8% sulphur 0.9%. Higher calorific value is 11000 Kcal/Kg. Boiling point is 182.2 to 290°C. Light & heavy diesel oil comes next leaving lubricating oils, paraffin wax, and petroleum jelly. Mean molecular mass 180-200.

(G) Heavy Fuel Oil:

Specific gravity 0.95. Composition 86% carbon Hydrogen 11.8% sulphur 2%. Higher calorific value 10500 Kcal/Kg. Boiling point is 250°C. & upward.

(H) Shale Oil:

Another source of natural fuel oil is Bituminous. Useless found in some coun­ties as natural deposit Crude shall oil can be obtained by distillation at high temperature as a residual & is a dark viscous liquid like crude petroleum as it comes for boilers. The products of distillation include petrol, paraffin & diesel oil. It is settable for boilers.

(I) Furnace Oil:

Calorific value 40800 KJ/Kg.

(J) Ethanol calorific value 30 kj/gm.

(c) Gaseous fuels:

Advantages of gaseous fuels:

(a) Higher calorific value 27800 Kcal/m3 LPG.

(b) Lighted at moment’s notice.

(c) Conveyed easily through pipe lines.

(d) Burn without smoke ashes the soot heat losses.

(e) Clean Lines in use.


(a) Very large storage tanks are needed.

(b) Highly inflammable.

(c) Costly

The natural sources, of gaseous fuels are fever than those of solid and liquid fuels. These fuels are mainly marsh gas or Methane, ethane and carbon monoxide. The following are the gaseous fuels available:-

(A) Natural Gas:

It is produced as a result of the decomposition of organic matter in marshy lands and can be collected by stirring up the bottom of stagnant (to cease to flow) pools. It consists of methane.

Methane is also produced in gassy coal miner mixed with other hydrocarbon and carbon mono oxide and may form a highly explosive mixture, if accidentally ignited. Its calorific value is 900 to 1000 BTU /ft3 (10850 to 125 00 kcal/m3)% volume . CO = 0.45,1 =182,0,= 0.35, N2 3.4 CH4= 93.33 C4H10 = 0.1-1 Heavy C2H6 = 0.17- 0.58 C3I=0.13-0.21 C02 = 0.22C2H4 = 0.25 H2S =0.18.

(B) Town or Coal Gas:

It is manufactured for town lighting, heating or combustion in gas engine.

Coal gas is obtained by the distillation or carbonization of Bituminous coal in closet} retorts out of contact with air and is stored in gas cylinder under pressure after purification of the gas. If made at 900°C. to 1000°C. & Yield is 200 – 260 m3 per tonne of coal.

Volumetric Composition of coal gas is H2 = 27%, CO = 7%, CH4 = 48%, C2H4= \ 3% C02 = 3%. N2 = 2% Higher calorific value & lower calorific value at NTP is >630 Kcal/m3. & 6920 Kcal/m3. Respectively.

(C) Coke Oven Gas:

It is manufactured as a byproduct in the manufac­ture of c0ke by the high temperature carbonization of Bituminous coking coal.

Volumetric composition H2, = 50/%C = 8% CH4 = 29% C2 H4 = 4% CO = 2% N, = 7,%. H’CV = 51 oo Kcal/m5 LCV = 4600 Kcal/m3 at NTP.

(D) Producer Gas:

It is manufactured in gas producer by the injection of air & steam in limited a red hot bed of charcoal coke or non flowing Coal, Anthracite containing the least volatile matter.

Volumetric composition is H, = 6% CO – 23% CH4 = 3% C2H4 0.2% CO, = 5 N, 62% some oxygen & other hydrocarbon HCV = 1200 Kcal/m3 LCV = 1150 kcal/m3 Depending upon carbon Value at NTP.

(E) Blast Furnace Gas:

This is manufactured in blast furnaces & is a by product in the manufacture of pig iron from the iron are. It is used in boilers by injecting incandescent (luminous with heat) bed of Coke breeze (gentle wind) to sit tight.

(F) Industrial Synthetic Gas:

Composition CH4 = 52%Heavy

HYDROCARBON = 34% C02 11 H2 = 9% N2 = 246%

LCV = 5300 Kcal/m3.

(G) Water Gas:

H2 = 51 % Co21 % CH41 % N2 4% Co2 = 4%. HCV 2800 Kcal/m3

(H) Bio Gas/Gobar Gas:

CH4 = 60-65% C02 = 25%- 30% H2 = 5% H2S = 1 % N2 = 5%

It is not poisons gas.

HCV = 5300 Kcal/Kg. 35-40 KJ/gm.

(i) H2 – Explosive inflammable not safer to store, cost of production high, calorific value 15 KJ/gm.

(J) Methane HCV:

3000 Kcal/m3

(K) Butane:

Gas burn readily calorific value 55 KJ/gm.

(L) LPG:

Liquefied petroleum gases are usually classified as commercial butane, propane & butane propane mixtures. LPG marketed in India is a mixture of propane and butane.

For identification of gas leakage LPG is mixed with smelling gas dehydrated desulpurired traces of organic sulphites. By product of oil refinery during the cracking of heavy oils from well.

1.5 to 2 times heavier than air. For this reason ground level of kitchen should ventilated at floor level.

LPG in cylinder 30 Kn./cm2 (2.942 Kv/m2 Gas inlet pressure 2.452 – 3.432 KN/m2 LPG is liquefied under moderate pressure & is the supplied as at pressure gas.

Advantage of L.P.G. are:

(i) High efficiency and heating rate

(ii) Calorific value = 2 x natural gas calorific value

= 6 x coal gas calorific value

(iii) Complete combustion. No smoke

(iv) Needs little care.

(v) Clean.

(vi) Flexible.

(vii) Portable.

(viii) Less health hazard.

(ix) Cheaper than gasoline.

(x) Residue & oil Contamination is small.

Dis-advantage of LPG:

(i) Faint odours

(ii) Leakage detection difficult.

To operate LPG cylinder valve is first opened and the lighted match/lighter is applied to the burner while appliance valve is opened simultaneously. The gas ignites in an instant and the flame can be adjusted by turning the nob. To extin­guish the flame the nob is turned off. When not in use the cylinder valve is kept closed and this ensures safety.

L.P.G. can exist as gas under atmospheric pressure but can be readily liquefied under pressure.


Gas taps:

The appliance has a tap for each burner On & OFF.

Taper plug tap-spring loaded to maintain gas tight.

Screw down valve injector jets shall be fixed calibrated type.


Draught divert or:

Where an appliance is to be ventilated to outside air. Flue outlet an appliance in which the burner is enclosed in a chamber e.g. a hot food cabinet shall be provided with a fuel outlet.

All pilot flames & weep terminals shall be protected as far as possible by design & position against diminution or extinction by draught product of combustion by overheating, by condensation, falling from above.

Ignition of the main burner from the pilot flame shall be smooth & no pilot flame shall left soar or length sufficiently to cause discoration on any external surface soot deposition or smell at working pressure between 2.452 & 3.432 KN/ nr (25 & 35 kg/Cm2).

Flame failure device:

Shall prevent gas from being supplied to burner

The main burner until the pilot flame is established.

Shall after flame failure stop all gas flow to main burner.

Shall be actuated only by a pilot flame site to ignite the main burner without failure or delay.

The mixer head carrier has a air shutter and an opening for the gas orifice. The horizontal pipe through which gas flows from the fuel line to the different orifices is called the manifold. Attached to the manifold are burner valve handles which direct the gas through orifice and mixer head into the burner.

Forced through the orifice at a velocity of 30 to 50m/Sec. The gas develops sufficient suction to draw air through the partly open shutter, Primary air mixes with the gas in a venture meter, gives a clean sharp flame. The gas air mixture flows through the ignition part on the side of the burner head.

Openings in the burner are drilled horizontally on the outer rim and vertical or at 45° angle in the centre. The inner parts (4 or 5) heat the central portion of the utensil bottom frequently from the simmer section of the burner.

Flame from the horizontal ports projects outward from an 2.5 to 5 cm. it is then lifted upward against the utensil bottom. Flame failure device-shall prevent gas from being supplied to the main burner. The pilot flame is established.

Wall floor or ceiling should be not being in excess of 65° C above the room temperature after 2 hours operation.

No portion of the surface of the appliance other than working surface (pan support, oven flue outlet grill covers, and plate racks) likely to be accidentally touched shall not exceed 120°C.

Tap handle & synthetic rubber with raglan should not have a temperature exceeding 60° C.

Ignite each burner in turn and maintain the flame in the mixing tube.

(D) Electricity:

Advantages are:

(i) Easily controllable

(ii) Heat adjustment is very easy

(iii) No storage is needed

(iv) Large amount is available

Disadvantages are:

(i) A gas burner can produce more heat/unit area than an electric burner.

(ii) Power cuts/interruptions are there

(iii) Installation cost is higher.