A detailed presentation of various types of gaseous fuels

gaseous fuels

1. 1
Gaseous Fuels
Vellore Institute of Technology
August 2017

2. Importance of Gaseous Fuels
Gas fuels are the most convenient and requiring the least amount of handling and simplest and most maintenance free burner systems. Gas is delivered "on tap" via a distribution network and so is suited to a high
population or industrial density.
Advantages
Economy in engines and efficiency of engine

It is compressible and storage is easier

Lees air required for combustion

Less starting trouble in engines
Transportation is easier
High cleanliness
Less emission
Disadvantages
High capital & Purification cost
2

3. Gaseous Fuels
Natural Gas
Gasification & Town Gas
LPG
Hydrogen
Wobbe Number
3

4. 4

5. 5
2. Natural Gas
Natural gas is obtained from deposits in
sedimentary rock formations which are also
sources of oil.
Naturally occurring gas found in oil fields and
coal fields . Principal component is methane.
Other components include higher
Hydrocarbons which can be separated out as
a condensate. Some gases also contain
hydrogen sulphide

6. Hydraulic Fracturing

7. Types of Natural Gas
Dry or lean - high methane content (less
condensate)
Wet - high concentration of higher
hydrocarbons (C5
 - C10)

Sour - High concentration of H2S

Sweet - low conc. of H2S
7

8. 8
Natural Gas- Energy requirement
The initial processing, compression and
heating at governor installations uses the gas
as an energy source.
The total energy overhead of a natural gas is
about 6% of the extracted calorific value.

9. 9
Natural Gas – Composition
The characteristics of a typical natural gas are:
Composition (% vol)CH
4 92
other HC 5
inert gases 3
Density (kg/m
3
) 0.7
Gross calorific value (MJ/m
3
) 35-41
Approximately 1,000 Btu/cu.ft (22,500 Btu/lb)

10. 10
Natural Gas Reserves (Trillion Cu. Ft)
Far East and
Oceania, 375.4
Africa, 409.7
C. & S.
America, 227.9
North America,
261.3
W. Europe,
159.5
E. Europe and
FSU, 1947.6
Middle East,
1836.2
US - 167 T Cu. ft
World - 5210 T cu. ft

11. 11
US = 166 T. Cu. Ft / 21.7 T. Cu. Ft per year
(1999) = 7.6 years
World = 5240 T cu. Ft/84.2 T. Cu.ft per year
=62 years
How long can we depend on Natural
Gas?

12. 12

13. 13
4. Liquefied Petroleum Gas (LPG)
LPG is a petroleum-derived product
distributed and stored as a liquid in
pressurized containers.
LPG fuels have slightly variable properties,
but they are generally based on propane
(C
3H
8) or the less volatile butane (C
4H
10).

14. 14
LPG
Compared to the gaseous fuel described
above, commercial propane and butane have
higher calorific values (on a volumetric basis)
and higher densities.
Both these fuels are heavier than air, which
can have a bearing on safety precautions in
some circumstances.

15. LPG- PETROLEUM REFINERY
15

16. 16
Products,
wt%
Diesel Mode Gasoline Mode LPG Mode
Dry Gas 2 – 3 4-8 6-10
LPG 6-10 10-20 35-45
Naphtha 20-25 45-50 20-30
Light
Cycle Oil
40-45 15-20 10-15
Clarified
Oil
10-12 8-10 5-7
Coke 4-5 6-7 8-10
FCC Product Yield Pattern

17. 17
LPG-Properties
Typical properties of industrial LPG are given below:
Gas Propane Butane

Density (kg/m
3
) 1.8 2.4
Gross calorific value (MJ/m
3
) 96 122
Boiling point ( at 1 bar)
℃
-45 0

18. LPG- Specifications
18

19. 19

20. 20
Gasification is the transformation/ conversion
of any carbonaceous fuel to a gaseous
product with a useable heating value. It does
include the technologies of pyrolysis, partial
oxidation, and hydrogenation.
What is Gasification ?
Advantages:
1. Easy CO2 sequestration.
2. Removal of most pollutants from the gas
3. Low emission of SO2, NO2, and dust.

21. 21
Gasification

22. 22
Town Gas
This gas was produced by a cyclic process where the
reacting bed was alternately blown with air and
steam- the former exhibiting an exothermic, and the
latter an endothermic, reaction.
A typical town gas produced by this process has the
following properties:
Composition (% vol) H
2 48
CO 5
CH
4
34
CO
2
13
Density (kg/m
3
) 0.6
Gross calorific value (MJ/m
3
)20.2

23. Gasification Types
23
-Autothermal - The energy required for
the gasification is produced inside of the
reactor due to exothermic reactions
- Allothermal - The energy required for the
reaction is produced outside of the
reactor.

24. Gasification –Methods & Scale
24
Methods of
gasification
Scale of Operation
Fixed bed Small
Fluidized bed Small, Medium
Entrained flow Large

25. 25
Gasification –Methods

26. Gasification –Important Reactions
26

27. Types of Gases from Gasification
27

28. Shell- Integrated Gasification of Coal
28

29. 29

30. Hydrogen: Introduction
- Hydrogen is the lightest of all gases
-Hydrogen gas (dihydrogen or molecular
hydrogen)
 is highly flammable and will burn in
air at a very wide range of concentrations
between 4% and 75% by volume.
- The
 enthalpy of combustion is −286 kJ/mol
-CV = 13MJ/ m
3
&
 = 0.019 kg/m
3
at STP

31. 31
Upgrading of fossil fuels
Production of
 ammonia
Petrochemical ; hydrodealkylation,
 hydrodesulphurization,
and
 Hydrocracking)
Hydrogenating agent, particularly in increasing the level of
saturation of unsaturated fats and
 oils (found in items such
as margarine),
Production of
 methanol.
Manufacture of
 hydrochloric acid. 
Reducing agent
 of metallic ores.
Hydrogen: Uses

32. 32
Steam reforming of
 natural gas/Methane referred to
as steam methane reforming (SMR) - is the most
common method of producing commercial bulk
hydrogen at about 95% of the world production
At high temperatures (700 – 1100
 °C) and in the
presence of a
 metal-based catalyst (nickel), steam
reacts with methane to yield
 carbon monoxide and
hydrogen
CH
4
 
+ H
2
O
  CO + 3 H⇌
2 ,
ΔH
r
= 206 kJ/mol
CO + H
2
O
 CO⇌
2
 
+ H
2,
ΔH
r
= -41 kJ/mol
Steam Methane reforming

33. 33
Steam Methane Reforming –Flow sheet

34. 34
Hydrogen: Chemical Looping
Lavoisier produced hydrogen by reacting a mixture of steam with
metallic
 
iron 
through an incandescent iron tube heated in a fire.
Anaerobic oxidation of iron by the protons of water at high temperature
can be schematically represented by the set of following reactions:
Fe +
   H
2O → FeO + H
2
2 Fe + 3 H
2O → Fe
2O
3 
+ 3 H
2
3 Fe + 4 H
2O → Fe
3O
4 
+ 4 H
2
zirconium 
also undergoes a similar reaction with water leading to the
production of hydrogen.
These reactions are slightly exothermic, The process is made cyclic by
performing reduction of these metals using fuels such as CH4.

35. 35
Hydrogen: Chemical Looping

36. 36
Wobbe Number
This characteristic concerns the
interchangeability of one gaseous fuel with
another in the same equipment.
In very basic terms, a burner can be viewed
in terms of the gas being supplied through a
restricted orifice into a zone where ignition
and combustion take place.
Wobbe Number

37. 37
Wobbe Number
The three important variables affecting the
performance of this system are the size of the
orifice, the pressure across it (or the supply
pressure if the combustion zone is at ambient
pressure) and the calorific value of the fuel,
which determines the heat release rate.
If two gaseous fuels are to be
interchangeable, the same supply pressure
should produce the same heat release rate.

38. 38
Wobbe Number
The heat release rate, Q, will be obtained by
multiplying the volume flow rate by the volumetric
calorific value of the fuel:
If we have two fuels denoted as 1 and 2, we would
expect the same heat release from the same orifice
and the same pressure drop p, if
△
0.5
0
2
d
P
Q CVC A

 

 
 
0.5 0.5
1 0 2 0
1 2
1 2
0.5 0.5
1 2
2 2
. .
d d
p p
CVC A CV C A
CV CV
i e
 
 
    
   
   


39. 39
Wobbe Number
This ratio is known as the Wobbe number of a
gaseous fuel and is defined as:
Some typical Wobbe numbers are:
Fuel Wobbe number (MJ/m
3
)
Methane 55
Propane 78
Natural gas 50
Town gas 27
 
3
0.5
Gross calorific value (MJ/m )
Relative density (air=1)

40. 40
Wobbe Number
The significant difference between the values for natural gas and
town gas illustrates why appliance conversions were necessary
when the UK changed its mains-distributed fuel in 1966.
Example 1:
Calculate the Wobbe number for a by-product gas from an
industrial process which has the following composition by
volume:
H
2 12%
CO 29%
CH
4 3%
N
2 52%
CO
2 4%

41. 41
Wobbe Number
Solution:
The gross calorific values are:
CO 11.85 MJ/m
3
CH
4
37.07 MJ/m
3
H
2 11.92 MJ/m
3
The calorific value of the mixture:
CV=(0.12×11.92)+(0.29×11.85)+(0.03×37.07)=5.98
MJ/m
3

42. 42
Wobbe Number
The relative density of the mixture is
calculated by dividing the mean molecular
weight of the gas by the corresponding value
for air (28.84).
The mean molecular weight of this mixture is:
(0.12×2)+(0.29×28)+(0.03×16)+(0.52×28)+(0.04×44)=25.16

43. 43
Wobbe Number
The relative density is thus
25.16÷28.84=0.872.
The Wobbe number is then:
5.98/(0.872)
0.5
=6.36

The Wobbe number of a fuel is not the only
factor in determining the suitability of a fuel
for a particular burner.
The burning velocity of a fuel is also
important.

44. Thank You