solid fuels

1. Dr. Asif Ali Siyal
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Solid Fuels
Learn continually there's always one more thing to learn

2. Fossil Fuels
• The combustible substances
formed from the dead remains
of the animals and plants
• Found in the earth’s crust
• Combustion of fossil fuels
release heat energy
Release of various
gases during fossil fuel
combustion can
contribute to climate
change
Used various domestic and industrial
applications

3.  Coal is a complex mixture of substances.
 Better energy source (low %O, high %C)
and exists in many grades.
 Coal as a fossil fuel has long been used
for a variety of industrial and domestic
purposes
 The worldwide distribution and widespread availability of coal resources
have been a major contributor to the economic growth of many countries,
either directly through their own resources or indirectly through access to
the international coal trade.
 environmental concerns and changes in the political climate have begun
to give coal an unfavorable public image.
 coal remains the world's single largest power source,
generating 34% of global electricity in 2020

4. Coal Consumption

5. * Commercial solid fuels only, i.e. bituminous coal and anthracite (hard coal), and lignite and
brown (sub-bituminous) coal, and other commercial solid fuels. Includes coal produced for
coal-toliquids and coal-to-gas transformations.
† Less than 0.005.
◆ Less than 0.05%.

7. Coal Formation

8. Coal Ranking
 The process of conversion of lignite to anthracite is called coalification (or)
metamorphism of coal
 The coalification process gives rise to different types of coals with
increasing degrees of maturation or rank
 Coalification exhibits ample changes in the physical and chemical
properties of coals.
 The stages of the carbonfication process are:
Wood → Peat → lignite → sub-bituminous → bituminous coal → Anthracite coal
 Coal rank is useful in the market, because it is a quick and
convenient way to describe coal without a detailed analysis
sheet.

9. Figure. Physical and chemical changes in coal during coalification,
aromaticity fa = [(C/H) − Haliphatic∗/(Haliphatic/Caliphatic)]/(C/H), where C/H is
the atomic ratio of organic carbon/hydrogen, Haliphatic∗ = Haliphatic/Htotal.

11. Fuel types Nature Heating value
(MJ/kg)
Compositions
(%)
Applications
Peat Soft, crumbly and light
brown in colour
High Moisture (80-90%)
15 C = 57
H = 06
O = 35
Used for domestic heating
Lignite Fibrous, brown coloured
coal, high volatile content,
burns with long smoky
flame
17-18 C = 67
H = 05
O = 26
power generation used
largely by local utilities
and industries close to
sites where it is mined
Sub
bituminous
coal
Dark brown to black, soft
and brittle at the lower end
of the range, to bright jet-
black, hard, and relatively
strong at the upper end
18-23 C = 77
H = 05
O = 16
steam-electric power
generation
Can be liquefied and
converted into petroleum
and gas
Bituminous
coal
Black, brittle, burns with
yellow smoky flame
25-30 C = 83
H = 05
O = 10
Power
generation,
coke making,
domestic fuel
Anthracite Hard & most matured coal,
volatile, moisture and ash
contents are very less,
burns without smoke
30-33 C = >85
H = 03
O = 03
Power generation
Metal's smelting and
fabrication industries
Filtration and purification
of domestic water supply
and industrial feed water
Classification of solid fuels

12. Before using the coal……..clean the coal
A collection of methods to increase efficiency of coal fired power plants while
decreasing harmful emissions.
1. Coal washing
• to remove S and minerals before
combustion
2. Gasification
• Coal + H2O CO+H2 (water
gas; both components are fuels,
burns at lower T, no NOx)
Coal, to be made more usable as
a fuel needs a change of phase
to gas or liquid state.
3. Wet scrubbing
Remove SO2 (with limestone
+ water)
4. Carbon capture and
storage
climate change mitigation technology
where CO2 is captured from power plants
and other industrial processes instead of
being emitted to the atmosphere.

13. Analysis of Solid Fuels

14. Properties of Coal
1 • Physical Properties
2 • Chemical properties
Calorific value
• Gross or higher calorific
value
• Net or lower calorific
value
Proximate analysis
• Moisture content
• Volatile matter
• Fixed carbon
• Ash
Carbon Hydrogen
Sulphur Nitrogen
Ultimate analysis

15. Calorific Value
Definitions
• The quantity of heat obtained per kilogram
(solid or liquid) or per cubic metre (gas) when
burnt with an excess of oxygen in a calorimeter
• The amount of energy released or produced
when 1 kg of fuel burns or any other substance
is burnt in the presence of oxygen and the
products of combustion are cooled to STP
 The amount of heat given out by the
complete combustion of the 1 Kg of fuel.
kJ/kg
kCal/kg
kJ/m3
kCal/m3
• Units of measurement
For Solids or liquids fuels
For Gaseous Fuels
BTU/lb
BTU/ft3

16. Types of the Calorific Value
• the amount of heat released when one unit of fuel is burnt completely
and the products of its combustion are cooled down to the temperature
of the air supplied (usually taken as 15ºC)
• HHV is obtained when the water formed by combustion is completely
condensed
Gross or Higher heating value
Net or Lower heating value
the amount of heat released when one unit of fuel is burnt
completely and the products of its combustion are not
cooled down to the room temperature but allowed to escape
LHV is obtained when the water formed by combustion
exists completely in vapour phase.

17. Determination of heating value
• Chemical Analysis
1
• Laboratory Method
2
Dulong’s Formula
Bomb Calorimeter
Boys Gas Calorimeter
For solid and liquid
fuels
If the chemical analysis of
the fuel is available, then
the higher calorific value of
the fuel is determined by
HHV=33800 C + 144000 H2 +
9270S (KJ/Kg)
Dulong’s
Formula
Where C, H2, S represent the mass of carbon, Hydrogen, Sulfur in 1 kg of fuel,
and numerical value indicates their respective calorific values
For solid and liquid &
Gaseous fuels

18. Higher heating value
 Dulong suggested a formula for the calculation of the
calorific value the solid or liquid fuels from their chemical
composition
 If the fuel contains the oxygen (O2) then it is assumed
that the whole amount is combined with hydrogen having
mass equal to 1/8 of that oxygen.
 Therefore while finding the calorific value of fuel, this
amount of hydrogen should be subtracted, then

19. Lower heating value
If the higher calorific value is known, then the lower calorific value may be
obtained by subtracting the amount of heat carried away by product of
combustion (especially steam) from H.C.V.

20. Net calorific value or LHV is obtained from the difference between HHV
and the heat of vaporization (water vapor). The HHV is commonly
correlated to the LHV as
where,
ΔHvap = heat required to vaporize the water in kJ/kg
nH2O,out = number of moles of vaporized water
nfuel,in = moles of fuel combusted,
MWH2O,out = molecular weight of water
and MWfuel = molecular weight of fuel

21. Illustrative Example 1
Example:01
A fuel consists of 85% of carbon, 12.5% of hydrogen and 2.5% of ash
by mass. Find the higher and lower heating value of the fuel.
Data:
C = 85% = 0.85 kg
H = 12.5% = 0.125 kg
Ash = 2.5% = 0.025 kg
HHV =?
LHV =?
Solution: By Dulong`s formula:
HHV = 33800 C + 144000 (H − O/8) + 9270 S
HHV = 33800×0.85 + 144000 (0.125− 0) + 9270×0
HHV = 46730 kJ/ kg
LHV = HHV – 2466(9×H ) kJ/ kg
LHV = 46730 – 2466(9 x 0.125)
LHV = 43956 kJ/ kg.

22. Illustrative Example 2
The HHV of methane (CH4) at room temperature (21ºC) is measured as 55,533 kJ/kg.
Convert this HHV to LHV for a given heat of vaporization of water; ΔHvap,water=2454
kJ/kg at 21ºC.

23. 1. Calculate the higher and lower heating value of a coal
which analyses were C 74%, H 6%, N 1%, O 9%, S
0.8%, moisture 2.2% and ash 8%.
2. The ultimate analysis of a coal sample were C 77%, H
5.8%, N 1.7%, O 4.8%, S 2.5% and ash 9%. The
moisture content is 5 %. Calculate higher and lower
heating value of sample using Dulong’s formula.

24. Heating value of different fuels

25. Proximate analysis
• Fixed carbon, volatile matter,
moisture and ash percentages
Ultimate analysis
• Carbon, hydrogen, nitrogen,
sulpher, oxygen
Analysis of coal
The proximate analyses are performed
in accordance with related standards for
solid fuels (Proximate analyses
methods for solid bio-fuels, GB/T
28731-2012).
The elemental analyses (C, H, N and S) of samples are determined
using an elemental analyzer (Vario EL cube), while the O content
was obtained by difference (i.e. O=100-C-H-N-S-ash).
Very useful in deciding its utilization
for a particular industrial use.
Gives the elementary constituents of coal.
Useful to the designer of coal burning
equipment and auxiliaries.

26. Proximate analysis of a fuel provides the percentage of the
material that burns
Proximate Analysis
In a gaseous state (volatile matter)
In a solid state (fixed carbon), and
the percentage of inorganic waste
material (ash)
Proximate analysis has a fundamental importance
for effective use of any fuel

27. Determination of Moisture
Analytical Balance
Oven
Moisture
content (%)
EN ISO 18134-1
Analytical balance
(ME104E, Metler
Toledo, Switzerland)
Oven (DHG-914OA,
Shanghai, Yiheng
Scientific instrument
Co.)
About 1 gm of powdered, air dried
coal sample is heated in silica
crucible at 100 to 105 °C for one
hour. Percentage of moisture can
be calculated from the loss in
weight of the coal sample as
Moisture (%) = loss in
weight due to MC/Initial
weight of sample

28. Significance of Moisture content
Higher moisture is
undesirable in solid fuels
Higher the moisture, lower is the
heating value of fuel.
It takes away the appreciable
amount of liberated heat in the form
of latent heat of vaporization (Heat
is lost)
Higher moisture may
quenches fire in the furnace
Transport cost of fuel
increases if it contains higher
moisture
Excessive surface moisture
may cause difficulty in
handling of solid fuels
Moisture usually refers to inherent moisture plus surface moisture
Higher moisture may result in bacterial
and fungal growth, leading to biomass
degradation and self-heating, even
unprompted ignition
Hence fuel with lower moisture is desirable for efficient combustion

29. Determination of Volatile matter
Volatile matter is basically the percentage loss in the
mass of coal sample when it burnt
1 g of sample is placed into a lidded crucible
(to prevent ingress of air), which is placed in
a furnace at 950±20 °C for 7 min
Muffle Furnace
Crucible with lid
Volatile matters are those components of fuel which
are readily burnt in the presence of oxygen. This is
usually a mixture of aromatic hydrocarbons, short and
long-chain hydrocarbons, and sulfur. (Transform into
vapor

31.  High volatile matter represents high
reactivity, easier ignition, gasification and
oxidation (Anukam et al., 2016).
 Meanwhile, high volatile matter results in
more smoke and tar production, and less
mass yield
Significance of Volatile matter
A high % of VM
indicates that a large
proportion of fuel is
burnt as a gas
Higher VM gives long
flame, high smoke and
relatively low heating
value
Forms smoke and
produces pollution

32. Determination of Ash
 Inorganic residue remaining after ignition of combustible substances is
called ash.
 Ash is an impurity that will not burn
 After the analysis of volatile matter the crucible with residual coal
sample is heated without lid at 700 ± 50 °C for 30 minutes in a muffle
furnace
 Percentage of ash content can be calculated from the loss in weight
of the coal sample as

33. Ash contents are related to reactor performance (e.g. ash melting),
pollutant emissions (e.g. particulate matter), ash utilization and/or
disposal when biomass pellets are used for combustion.
Ash behavior and ash-related issues, such as slagging and fouling, are the challenges
in co-firing technology, which can reduce combustion efficiency and even lead to the
failure of the operation
Significance of Ash
• Reduces handling and burning
capacity
• Increases handling costs
• Affects combustion efficiency
and boiler efficiency
• Causes clinkering and slagging
• Large heat losses and leads to
formation of ash lumps
• Fuel with higher ash content has
lower heating value

34. Fixed carbon
 Fixed carbon is the carbon found in the material which is left after volatile
materials are driven off
 Fixed carbon can be determined as
 Fixed carbon gives a rough estimate of heating value of coal
Higher the fixed carbon content of the coal, higher will be
its heating value Value.

35. Data given
Mass of coal given = 2.5 g
Mass of moisture in coal sample = 2.415 g
Residue weight = 1.528 g
Mass of residue = 0.245 g
To Determine
Moisture, VM, Ash and Fixed carbon

37. iv. Determination of Fixed carbon
FC = 100-(3.4+35.48+9.8)
FC = 51.2%