5.0 FUEL

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 Introduction to Fuels

The various types of fuels like liquid, solid and gaseous fuels are available for firing in boilers, furnaces and other combustion equipment. The selection of right type of fuel depends on various factors such as availability, storage, handling, pollution and landed cost of fuel.

    The knowledge of the fuel properties helps in selecting the right fuel for the right purpose         and efficient use of the fuel. The following characteristics, determined by laboratory tests,         are generally used for assessing the nature and quality of fuels.

Types of Fuel:

Chemical fuels are divided in two ways. First, by their physical properties, as a solid, liquid or gas. Secondly, on the basis of their occurrence: primary (natural fuel) and secondary (artificial fuel). Thus, a general classification of chemical fuels is:

General types of chemical fuels

Primary (natural)

Secondary (artificial)

Solid fuels

wood, coal, peat, dung, etc.

coke, charcoal

Liquid fuels

Petroleum

diesel, gasoline, kerosene, LPG, coal tar, naphtha, ethanol

Gaseous fuels

natural gas

hydrogen, propane, methane, coal gas, water gas, blast furnace gas, coke oven gas, CNG

 

A.   SOLID FUEL:

 

CHARACTERISTICS OF SOME SOLID FUEL

Fuel Parameters

 

 

Rice Husk

Wood

Rice Straw

Bagasse

Sewage Waste

Mustered Stak

 

Indian Coal

Calorific Value

 

Kcal/Kg

3410

 

3500

2272

 

3450

 

3120

Bulk Density

 

Kg/m3

100-150

 

 

 

 

 

 

900-1000

Proximate Analysis

TM

%

7.4

25-60

 

 

20

 

 

 

 

VM

%

64.7

85

69.7

 

47.6

 

 

 

 

FC

%

15.7

13

11.1

 

5.5

 

 

 

 

Ash

%

19.6

2

19.2

 

26.9

 

 

 

Ultimate Analysis

C

%

38.7

48

37.7

46.3

37

42.22

 

34.20

 

H2

%

5

6.5

5

5.8

5.0

3.35

 

2.0

 

N2

%

0.5

0.5

0.6

0.3

1.5

0.7

 

0.6

 

O2

%

36

43

37.5

45.8

8.9

29.5

 

7.7

 

S

%

0.1

NA

NA

0

0.7

1

 

0.5

 

Ash

%

14.47

0.4

4.8

1.8

26.9

12.49

 

45.0

 

M

%

10.62

-

15.7

50

20.0

1074

 

10.0

 

 

 

 

 

 

 

 

 

 

 

Fly Ash Analysis

Al2O3

%

0.1-0.4

 

 

10-13

 

15-20

 

10-20

 

CaO

%

2-4

 

 

3-5

 

15-20

 

2-10

 

Fe2O3

%

0.5-1.5

 

 

10-12

 

1.5-4

 

6-10

 

K2O

%

0.1-0.2

 

 

4.5-6

 

10-20

 

1-2.5

 

MgO

%

0.5-1.0

 

 

3-4

 

0.5-2

 

1-3

 

MnO

%

Trace

 

 

Traces

 

Traces

 

Traces

 

Na2O

%

0.5-1.0

 

 

0.5-1.5

 

2-8

 

1-5

 

P2O5

%

0.5-1.5

 

 

1-2

 

1-3

 

0.25-0.75

 

SiO2

%

85-95

 

 

50-60

 

25-35

 

45-65

 

SO3

%

Trace

 

 

Traces

 

8-12

 

4-8

 

TiO2

%

,,

 

 

2-4

 

0.2-0.4

 

1-1.5

 

V2O5

%

,,

 

 

Traces

 

Traces

 

Traces

 

ZnO

%

,,

 

 

Traces

 

Traces

 

Traces

Bulk Density

Vol

Kg/m3

600

 

 

 

 

 

 

 

 

Wt.

Kg/m3

1000

 

 

 

 

 

 

 

 Bio-fuel

Bio-fuel can be broadly defined as solid, liquid, or gas fuel consisting of, or derived from biomass. Biomass can also be used directly for heating or power—known as biomass fuel. Bio-fuel can be produced from any carbon source that can be replenished rapidly e.g. plants. Many different plants and plant-derived materials are used for bio-fuel manufacture.

Biomass Briquette

Biomass briquettes, mostly made of green waste and other organic materials, are commonly used for electricity generation, heat, and cooking fuel. These compressed compounds contain various organic materials, including rice husk, bagasse, ground nut shells, municipal solid waste and agricultural waste. The composition of the briquettes varies by area due to the availability of raw materials. The raw materials are gathered and compressed into briquette in order to burn longer and make transportation of the goods easier. These briquettes are very different from charcoal because they do not have large concentrations of carbonaceous substances and added materials. Compared to fossil fuels, the briquettes produce low net total greenhouse gas emissions because the materials used are already a part of the carbon cycle.



Proximate analysis of some Biomass Briquettes:

 

 

 

Saw dust

Groundnut Husk

Sawdust and Groundnut Husk

Sr. No.

Test Parameters

Unit

Results

Results

Results

1

Fixed Carbon

%

16.68

19.15

14.99

2

Volatile matter

%

71.10

67.32

65.68

3

Ash content

%

4.32

4.32

8.04

4

Moisture content

%

7.90

9.19

11.29

5

Gross calorific value (By BOMB calorimeter)

Kcal/Kg

4199

43.24

4177
 

B.     Liquid Fuel

Liquid fuel is classified according to the mode of procurement.

1.      Natural or crude oil – petrol, Benzene, petroleum spirit, kerosene, benzoyl, diesel, gas oil.

2.      Artificial oil - natural gas oil, Shale oil, tar oil, Coal Tar etc.

Factors are considered for the gradation of Petroleum

1.      Specific Gravity - It is the ratio of the weight of a given volume of petroleum to the weight of the same volume of water at fixed temperature 288 °K.

API - scale of measuring specific gravity introduced by American petroleum industry.

API = (141.5/Sp. Gravity at 200°K) – 131.5

2.      Viscosity – The force required to displace 1 m2 of imaginary plane surface of fluid at a rate of 1 m/s with respect to the second plane separated by 1 m distance from the 1st plane and parallel to it. Viscosity index scale is an arbitrary scale based on the viscosity temperature relationship of liquid fuel. (Unit – Ns/m2)

3.      Congealing point – It is the temperature at which crude become so pasty that it remains in place and does not flow out for one minute from e test glass inclined at 45°.

4.      Flash point – It is the temperature at which a liquid fuel gives off just sufficient vapour to create an explosive mixture that will flash if brought into contact a flame.

5.      Pour Point - The pour point of a fuel is the lowest temperature at which it will pour or flow when cooled under prescribed conditions. It is a very rough indication of the lowest temperature at which fuel oil is readily pumpable.

6.       Specific Heat - Specific heat is the amount of kCals needed to raise the temperature of 1 kg of oil by 1°C. The unit of specific heat is kCal/kg°C. It varies from 0.22 to 0.28 depending on the oil specif- ic gravity. The specific heat determines how much steam or electrical energy it takes to heat oil to a desired temperature. Light oils have a low specific heat, whereas heavier oils have a high- er specific heat.

7.     Calorific Value - The calorific value is the measurement of heat or energy produced, and is measured either as gross calorific value or net calorific value. The difference being the latent heat of condensation of the water vapour produced during the combustion process. Gross calorific value (GCV) assumes all vapour produced during the combustion process is fully condensed. Net calorific value (NCV) assumes the water leaves with the combustion products without fully being condensed. Fuels should be compared based on the net calorific value.

The calorific value of coal varies considerably depending on the ash, moisture content and the type of coal while calorific value of fuel oils are much more consistent.

8.      Moisture and sediment contents

9.      Sulphur content – The amount of sulphur in the fuel oil depends mainly on the source of the crude oil and to a lesser extent on the refining process. The normal sulfur content for the residual fuel oil (furnace oil) is in the order of 2-4 %. Higher sulphur content of oil leads to corrosion problem.

For example – Fuel oil gun tip made of tungsten carbide, during partial oxidation reaction in gasifier, converts in tungsten sulfide which is a brittle material and breaks off the gun tip.

S + O2 -->SO2

WC + SO2 ==> WS +CO2

Example – Furnace Oil

Definition:

A dark viscous residual fuel obtained by blending mainly heavier components from crude distillation unit, short residue and clarified oil from fluidized catalytic cracker unit.

Nomenclature:

Bunker fuel, furnace oil, Fuel oil are other names for the same product. Though Fuel oil is a general term applied to any oil used for generation of power or heat, Fuel oil can included distillates and blends of distillates and residue such as Light Diesel Oil.

Specification:

Furnace oil in the current marketing range meets Bureau of Indian Standards Specification IS : 1593 - 1982 for fuel oils, grade MV2.

Viscosity:

Viscosity is the most important characteristic in the furnace oil specification. It influences the degree of pre-heat required for handling, storage and satisfactory atomization. If the oil is too viscous it may become difficult to pump, burner may be hard to light and operation may be erratic. Poor atomization may result in the carbon deposits on the burner tips or on the walls. The upper viscosity limit for furnace oil is such that it can be handled without heating in the storage tank is excepting under server cold conditions. Pre-heating is necessary for proper atomization.

Flash Point:

As per the Controller of Explosives classification, Furnace oil falls in the class "C" category with minimum flash point standard of 66 deg. C. Since Penskey Martens Closed Cup method is used, it is apparent that a small quantity of low boiling point hydrocarbons is sufficient to lower the flash point drastically.

Pour Point:

It is a very rough indication of the lowest temperature at which Furnace Oil is readily pump able. In the specification the pour point of Furnace oil is not stipulated. However, for Furnace oil manufactured indigenously and for imported parcels, the pour point is such that current supplies normally can be handled without heating the fuel oil handling installation.

Water:

Water may be present in free or emulsified form and can on combustion cause damage to the inside furnace surfaces especially if it contains dissolved salts. It can also cause sputtering of the flame at the burner tip. Water content of furnace oil when supplied is normally very low as the product at refinery site is handled hot and maximum limit of 1% is specified in the standard.

Sediment:

Furnace oil being a blend of residues contains some quantity of sediments. These have adverse effect on the burners and cause blockage of filters etc. However, the typical values are normally much lower than the stipulated value of maximum 0.25 percent, by mass.

Ash:

Ash is incombustible component of the furnace oil and is expressed as a percentage mass of the furnace oil sample. Ash consists of extraneous solids, residues of organ metallic compounds in solution and salts dissolved in water present in the fuel. These salts may be compounds of sodium, vanadium, calcium magnesium, silicon, iron etc.

Ash has erosive effect on the burner tips, causes damage to the refractories at high temperatures and gives rise to high temperature corrosion and fouling of equipments.

Sulphur:

Sulphur determination includes burning of known quantity of oil, treating the sulphur oxidation products formed during combustion and weighing of sulphur in the form of sulphate.

The sulphur di-oxide may come in direct contact with the product during the combustion process and may create adverse quality effects in the product.

Calorific Value:

Calorific value of a fuel is the quantity of heat generated in kilocalories by complete burning of one kilogram weight of fuel. Gross calorific value is higher than net calorific value to the extent of heat required to change water formed by combustion into water vapours.

 


 

CHARACTERISTICS OF SOME FUEL OIL

 

 

 

Low Density Oil

FURNACE OIL (Special Grade)

Low Sulphur Heavy Stock

Sl.No.

PARAMETER

STADARD METHOD

SPECIFICATION

TYPICAL QUALITY

SPECIFICATION

TYPICAL QUALITY

SPECIFICATION

TYPICAL QUALITY

1

Density @ 15 deg. C g/ml

IS 1448 (P: 16)

 

 

0.96

0.96

 

 

2

Relative Density @ 15 °C, g/ml

IS 1448 (P: 32)

Report

0.855

 

 

Report

0.926

3

Pour Point, °C

IS 1448 (P: 10)

12°C for Winter, Max 21°C for Summer, Max

Minus 3

+27 Max.

3

66 (Max)

33

4

Flash Point (PMC), deg. C

IS 1448 (P: 21)

66 Min.

74

66 Min.

75

76 Min

85

5

Kinematic Viscosity, 50 deg.C, cSt

IS 1448 (P: 25)

2.5 to 15.7 Max.

5

165 Max.

160

 

 

6

Kinematic Viscosity, 100 deg.C, cSt

IS 1448 (P: 25)

 

 

 

 

50 Max

45

7

Gross Calorific Value, Cal/g

IS 1448 (P: 6)

 

 

Report

10350

Report

10550

8

Water content % vol.

IS 1448 (P: 40)

1.0 Max.

<0.05

1 Max.

< 0.05

1.0 Max

< 0.05

9

Ash % wt.

IS 1448 (P: 4)

0.02 Max

0.01

0.1 Max

0.04

0.10 Max

0.03

10

Sulphur, Total % wt.

IS 1448 (P: 33&35)

1.8 Max

1.2

2.8 Max

2.7

1.0 Max

0.95

11

Sediment % wt.

IS 1448 (P: 30)

0.10 Max.

0.04

0.25 Max.

0.02

0.25 Max

0.03

12

Acidity, Inorganic mgKOH/gm

IS 1448 (P: 2)

NIL

Nil

Nil

Nil

Nil

Nil

13

Asphaltene content, % wt.

IP 143

 

 

7.0 Max

5

 

 

14

Accelerated Dry Sludge % by Mass

IP 390 (Chemical ageing)

 

 

 

 

0.10 Max

0.03

15

Ramsbottom Carbon Residue (RCR)

IS 1448 (P: 8)

1.50 Max

1.3

 

 

 

 

16

Copper Strip Corrosion, 3 hrs at    100°C

IS 1448 (P: 15)

Not Worse than No. 2

No.1

 

 

 

 

17

Micro Carbon Residue, %wt

ASTM 4530

 

 

16.0 Max

15.5

 

 

18

Cleanliness spot Rating

ASTM D 4740

 

 

No 2 (Faint or poorly defined inner ring)

No. 1

No 2 (Faint or poorly defined inner ring)

No. 1

 


C.    GASEOUS FUEL:

 

Classified  

1.     Natural Gas

2.     Manufactured

 

 

-       Coal gas, Producer gas, Water gas, Oil gas, Town gas, Blast furnace gas

Liquid Natural Gas (LNG)

It is mixture of most volatile paraffin’s and methane to pentane.

Heat at combustion – 33.5 to 40 MJ/m3

Specific Gravity – 0.63 relative to air

Critical Temperature – 83 °C

CNG – Compressed Natural Gas

LPG – Liquid Petroleum Gas

( Cryogenic temperature are required to maintain gas as a liquid form at 36 bar pressure and 100 °C temperature.  

Coal Gas

It is the gaseous product of carbonization of coal. ( Methane, Hydrogen and Carbon monoxide)

Producer Gas

It is resulting from the complete gasification of the combustible material in solid fuels by air –steam mixture.

C + O2 → CO2

CO2 + C ↔ 2CO

Water Gas

It is resulting from the complete gasification of the combustible material in solid fuels by superheated steam.

C + H2O ↔ CO + H2

 

 


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