INDIAN INSTITUTE OF TECHNOLOGY ROORKEE

Characterization of coal
Prof. Shushil Kumar
Department of Chemical Engineering
IIT Roorkee
Contents

➢ Proximate analysis

➢ Ultimate analysis

➢ Heating value

2
Proximate analysis

➢ Moisture: Loss in weight of sample due to drying at 105oC for 24h.

➢ Volatile matter: Loss in weight of moisture-free sample heated in a muffle

furnace at 950 oC for 7 minutes in the absence of oxygen in a close crucible.

➢ Ash: Weight of residue left after combustion of dry sample in a muffle furnace
at 750 oC for half an hour in the presence of oxygen in an open crucible.

➢ Fixed carbon: Obtained by subtracting moisture, volatile matter, and ash

percent from 100.

Ref: Craig J. Donahue and Elizabeth A. Rais, 2009

3
Proximate analysis

Typical proximate analysis data for various types of coals

Type of coal Moisture (%) Volatiles (%) Fixed Carbon (%) Ash (%)
Peat 1.5 57.6 33.0 7.8
Lignite 7.6 36.8 47.7 7.9
Sub-Bituminous 1.4 38.5 52.4 7.7
Bituminous 0.1 34.4 55.3 10.2
Anthracite 0.2 2.7 88.6 8.5

4
Ultimate analysis

• Ultimate analysis or elemental analysis (CHNS) is determined by a CHNS

analyzer

• The CHNS Analyzer determine the percentages of Carbon, Hydrogen, Nitrogen,

Sulphur and Oxygen of organic compounds, based on the principle of "Dumas
method" which involves the complete and instantaneous oxidation of the
sample by "flash combustion".

• The combustion products (NO2,CO2, SO2, and H2O) are separated by a

chromatographic column and detected by the thermal conductivity detector
(T.C.D.), which gives an output signal proportional to the concentration of the
individual components of the mixture.

5
Ultimate analysis

• For analysis product gas mixture flows through a silica tube packed with copper
granules.

• This zone is held at about 500°C, and the remaining oxygen is trapped inside,
and nitric/nitrous oxides are reduced. The leaving gas stream includes the
analytically important species CO2, H2O and N2. Eventually SO2 is absorbed at
appropriate traps.

6
Ultimate analysis

Typical ultimate analysis data of various coal types

Type C H O N S Ash
Peat 23 10 59 1.5 0.5 6
Lignite 42 7 43 1 1 6
Sub-Bituminous 59 6 29.5 1 0.5 4
Bituminous 77 5 5 1.5 0.5 11
Anthracite 86.5 2.5 3 0.5 0.5 7

Ref: Speight, J. G. Handbook of Coal Analysis, 2005

7
Heating value

Heating value (or calorific value):

• It is the amount of heat released during the combustion of a specified amount

of it.

• It is measured in units of energy per unit of the substance, usually mass, such
as: kJ/kg, kJ/mol, kcal/kg, Btu/lb.

Higher heating value(HHV) or Gross calorific value (GCV):

• It is determined by bringing all the products of combustion back to the original

pre-combustion temperature, and in particular condensing any vapor produced.
Such measurements often use a standard temperature of 15 °C (59 °F; 288 K).

8
Heating value

Lower heating value (LHV or LCV) or Net calorific value (NCV):

• It is determined by subtracting the heat of vaporization of the water vapor from

the higher heating value.

• This treats any H2O formed as a vapor. The energy required to vaporize the
water therefore is not released as heat.

A common method of relating HHV to Where

Hv = Heat of vaporization of water
LHV is:
nH2O,out = moles of water vaporised
n, fuel = number of moles of fuel combusted
HHV = LHV + HV(nH2O, out/ n, fuel)

9
Heating value

Determination of heating value of solid and liquid fuel

• A known amount of solid fuel is burnt in a bomb.

• The generated heat is used to raise the temperature of a certain volume of

water kept in a bucket.

• Heat gained by the water is equivalent to the heat released by the fuel.

10
Heating value

• Empirical relations for heating value calculation based on proximate and

ultimate analysis data
Where,
Name of the author Correlation (HHV, MJ/kg)
VM – Volatile matter
Jimennez and Gonzalez HHV= -10.81408+ 0.3133 (VM+FC) FC – Fixed carbon
C – Carbon
Demirbas HHV= 0.196 FC+ 14.119 O – Oxygen
Demirbas HHV= 0.312 FC + 0.1708 VM N – Nitrogen
S – Sulfur
Cordero et al. HHV= 0.3543 FC+ 0.1708
Tillman HHV= 0.4373 C-1.6701
Boie HHV= 0.35C + 1.16H – 0.11O + 0.06N + 0.1S
Demirbas HHV= 0.33C + 1.42H – 0.15 O – 0.14N
Jenkins HHV= -0.76+0.30C+ 0.525H + 0.6 O

11
Reference:

• https://nptel.ac.in/courses/103107157

• Twidel, J. and Tony W., Renewable Energy Resources, Second Edition, Taylor &
Francis 2006

• Kreith F., Goswami D. Y., Energy Management and Conservation, CRC Press 2008

• Sukhatme S., J Nayak J., Solar Energy: Principles of Thermal Collection and
Storage, 3/ed, Tata McGraw-Hill Publishing Company Ltd 2008

12