STUDY OF COALIFICATION

P M V Subbarao
Professor
Mechanical Engineering Department

An Extremely Slow Action in Nature...

True Quasi-static Process to Create
Permanent Entropy Vehicles…..
Coal : First Kind of Entropy Vehicle
Timing of Newton’s Law???
 A tree converts disorder to order with a
little help from the Sun
• The building materials are in a
highly disordered state - gases,
liquids and vapors.
• The tree takes in carbon dioxide
from the air, water from the earth
as well as a small amount from
water vapor in the air.
• From this disordered beginning, it
produces the highly ordered and
highly constrained sugar
molecules, like glucose.
The radiant energy from the Sun gets transferred to the bond energies of the
carbons and the other atoms in the glucose molecule.
In addition to making the sugars, the plants also release oxygen which is essential
for animal life.
 First Law Analysis of Photosynthesis :
SSSF
Q W
m m Oxygen
CO2

m vegetation
m water Q
The Global Reaction Equation:
6CO2  6 H 2O  CH 2O 6  6O2
   
Conservation of Mass: m CO 2  m H 2O  m vegetation  m O 2 0
First Laws for furnace in SSSF Mode:
 
   V2  
   V2 
Q CV  m h  
 gz  
 m h   gz   
  2   2 
  CO 2    H 2O

   V2  
   V2  
m h   gz    m h   gz    W CV
 2     2 
   veg    O 2
 Coalification

• Orgin of Coal : A complex mixture of plant substances altered in

varying degree by physical and chemical process.
• Reaction time : ~~ 365 million years.
• Mechanism of Formation:
• In Situ Theory : Coal seam occupies the same site where
original plants grew and accumulated.
• Drift Theory : Plants and trees were uprooted and drifted by
rivers to lakes and estuaries to get deposited.
• During the course of time they got buried underground. Indian
coals are formed according to drift theory.
 In Situ Theory

Carboniferous periods of the

Paleozoic when these areas
were covered with forests

The humid climate of the Carboniferous Period (360 to 286 million

years ago), which favoured the growth of huge tropical seed ferns
and giant nonflowering trees, created the vast swamp areas
Sequence of Actions in Coalification
 Steps in Formation of Coal

Plant Debris Peat Lignite Brown Coal

Diamond Sub-Bituminous

Anthracite Semi Anthracite Bituminous

 Bio - Chemical Degradation of Dead Plants

• As the plants died and fell into the boggy waters.

• These Boggy waters excluded sufficient oxygen.
• Bacteria could only partially decomposed but did not rot away the
dead plants.
• The absence of oxygen killed the bacteria.
• The vegetation was changed into peat, some of which was brown
and spongy, some black and compact, depending on the degree of
decomposition.
• Peat deposition is the first step in the formation of coal.

2C6 H10O5  C8 H10O5  2CH 4  2CO2  H 2O

 Formation of Peat
• Natural Rate of reaction : 3cm layer per 100 years.
• Light brown fibrous at the surface and colour becomes darker with
depth.
• Typical Composition: Moisture : 85%, Volatile Matter : 8 %,
Fixed Carbon : 4%, Ash : 3%.
• Calorifica Value : ~2730 kJ/kg.
• Occurrence of Peat : Nilgiri Hills and banks of Hooghly.
• Sun dried Peat is very useful as a fuel with following composition:
• Moisture : 20%, Volatile Matter : 50 %, Fixed Carbon : 25%, Ash :
5%
• Bulk density : 300 kg/m3 and low furnace temperature and
efficiency.
• Products from Peat: Charcoal, Producer gas.
 Molecular Structure of Peat

Structure of smallest molecule: C8 H10O5

First Law Analysis of Formation of Peat :SSSF

P=??
m Peat

m
Species Conservation Equation:vegetation
m CO2
Q
2C6 H10O5  C8 H10O5  2CH 4  2CO2  H 2O m CH4
   
Conservation of m vegetation  m peat  m CH 4  m CO 2 0
Mass:
First Laws for furnace in SSSF Mode:
 
   V2  
   V2 
Q CV  m h  
 gz  m h   gz   
  2   2 
  veg 
   peat

   V2  
   V2  
m h   gz    m h   gz    W CV
 2   2 
  CH 4   CO 2
Atmospheric CO2 Concentration at Peat Bogs

CO2

CO2
Secondary Transformation : Geo-Chemical
Stage

• The decayed vegetation was subjected to extreme

temperature and crushing pressures.
• It took several hundred million years to transform the
soggy Peat into the solid mineral.
• 20 m of compacted vegetation was required to produce 1
m seam of coal.
• This is called as coalification or coal forming.
• The extent to which coalification has progressed
determines the rank of coal.
Secondary Transformation : Geo-Chemical
Stage
 Modeling of Combustible Coalification
Peat to Enriched peat: (mostly due to heating)
19C8 H10O5  8C19 H18O3  24O2  23H 2O
Enriched peat to lignite: (mostly due to pressure &heating)
xC19 H18O3  yC35 H16O4  zO2  pH 2O
lignite to Sub-bituminous: (mostly due to pressure &heating)
xC35 H16O4  yC49 H19O4  zO2  pH 2O
Sub-bituminous to High volatile Bituminous:

xC49 H19O4  yC57 H 23O3  zO2  pH 2O

 Modeling of High Rank Coalification

High Volatile Bituminous to Medium volatile Bituminous:

xC57 H 23O3  yC64 H 23O1  zO2  pH 2O  qCH 4

Medium Volatile Bituminous to Low volatile Bituminous:

xC64 H 23O1  yC66 H 21O0.5  zO2  pH 2O  qCH 4

Low Volatile Bituminous to semi Anthracite:

xC66 H 21O0.5  yC67 H16O0.5  zO2  pH 2O  qCH 4

Semi Anthracite to Anthracite:
xC67 H16O0.5  yC72 H11O0.25  zO2  pH 2O  qCH 4
Global Reaction Model for Coalification

• The application of basic kinetics to the real coalification

requires some algebraic manipulations
3500
dC 0. 2

Reaction Rate  50t e T
dt
Chemical Structure of Coal
 Composition of Coals

• The natural constituents of coal can be divided into two groups:

• (i) The organic fraction, which can be further subdivided into
microscopically identifiable macerals.
• (ii) The inorganic fraction, which is commonly identified as ash
subsequent to combustion.
• The organic fraction can be further subdivided on the basis of its
rank or maturity.
 Microscopic Structure of Coals

• On the microscopic level, coal is made up of organic particles

called macerals.
• Macerals are the altered remains and byproducts of the original
plant material from which the coal-forming peat originated.
• Macerals are to coal as sediment grains.
• Coal petrographers separate macerals into three groups, each of
which includes several maceral types.
• The groups are Inertinite, Liptinite, and Vitrinite.
• These groups were defined according to their grayness in
reflected light under a microscope.
 Origin of Maceral Groups

• Vitrinite is thought to be derived mainly from the original

woody tissue of trees in peat swamps.
• Exinite , which is derived from pollen, spores and leaf
epidermis, is technologically important, because it enhances
the fluidity of coal.
• The inertinite group of macerals derives its name from its
more or less non-reactive character shown during the
carbonization process.
• Whereas exinite and vitrinite melt, with an evolution of
volatiles, inertinites generally remain intact.
• Inertinite is derived from fungal remains, charcoal and
partly charred wood.
Parents of Microscopic Macerals.
Maceral Groups and Macerals in Coals
 Chemistry of Maceral Groups

• The maceral content and volatile-matter yield of a coal may

be considerably influenced by the post-depositional chemical
environment to which the normally acid peat is subjected.
• There exist a correlation between carbon content and
reflectance and this is used to precisely determine rank.
• Petrographers in use the mean maximum reflectance of
vitrinite in oil (Romax), at 546 µ, as the level of organic
maturity, or rank, of a coal sample.
Carbon Content in Macerals
 Vitrinite reflectance (Ro)

• Vitrinite reflectance is the proportion of incident light

reflected from a polished vitrinite surface.
 Coal Reactivity

• The reactivity parameter was calculated using the

following equation:
1 dm
RT 
minitial dt
Secrets of Coal Reactivity
Comprehensive Coal Characterization
Closing Remarks on Coal Knowledge

Reflectance Rank
0.50% - 1.12% High-volatile bituminous
1.12% - 1.51% Medium-volatile bituminous
1.51% - 1.92% Low-volatile bituminous
1.92% - 2.5% Semi-anthracite
> 2.5% Anthracite
Natural Thermodynamics for Creation of Permanent
of Entropy Vehicles
Chemical Structure of Combustible Coal
Coal Ranking vs Utilization
 Mineral-Matter Composition of Coals

• The ash of a coal is the uncombustible oxide residue which

remains after combustion.
• Mineral matter is the natural mineral assemblage of a coal
that contains syngenetic, diagenetic and epigenetic species.
• Mineral matter is identified more accurately by X-ray
diffraction analysis of low-temperature ash (LTA).
• The post-depositional chemical environment of a peat
swamp, is the major factor determining the amount and
kind of mineral species present in coal.
 Analysis of Coal

• Proximate Analysis & Ultimate Analysis.

• Proximate analysis - to determine the moisture,
ash, volatiles matter and fixed carbon
• Ultimate or elementary analysis - to determine
the elemental composition of the coal
• The Energy content -- CFRI Formulae --
• Low Moisture Coal(M < 2% ) -- CV (Kcal/kg) = 71.7 FC +
75.6 (VM-0.1 A) - 60 M
• High Moisture Coal(M > 2%) -- CV(kcal.kg) = 85.6 {100 -
(1.1A+M)} - 60 M
• Where, M, A, FC and VM denote moister, ash , fixed carbon
and Volatile mater (all in percent), respectively.
Fuel Model
Dictionary of Few Indian Coals
Ash Model
 Additional Characteristics of Coal

• Sulfur Content : Coal with sulfur > 5% is not recommended for

combustion.
• Weatherability : Weathering or Slacking Index -- An indication
of size stability -- Denotes the tendency to break on exposure to
alternate wet and dry periods.
• Grindability Index : A measure of relative ease of grinding coals
or the power required for grinding coals in a pulverizer.
• Burning Characteristics of Coal : Free burning coals and Caking
Coals -- Caking index -- Pulverulent, sintered, weakly caked,
caked and strongly caked.
• Ash Fusion temperature -- The temperature where the ash
becomes very plastic -- Design of ash handling system. -- Stoker
furnace cannot use low ash fusion temperature coals.
Biochar Production Process
 Biochar Production at IIT Delhi

Kiln Capacity:25 L, Efficiency:20-25% Feedstock: Leaf Waste,

Operating Temperature<450° C
 Analysis of Biochar

Biochar C H N S O O/C H/C Moistur Volatil Fixe Ash pH

samples (%) (%) (%) (%) (%) (%) (%) e e d C (%)
(%) matter (%)
(%)

LWB400 79.4 2.3 0.2 0.2 8.6 0.11 0.03 1.2 64.9 24.7 9.3 10.2

LWB300 71.3 3.1 0.9 0.5 12.6 0.18 0.04 1.6 67.5 20.3 10.6 9.8

LWB200 68.3 4.8 1.1 0.5 14.2 0.21 0.05 2.2 71.0 15.8 11.0 9.6
Maximum Extra-somatic Energy Content of
A Fuel
• Obtained only thru Combustion.
• Standard heat of combustion:
• The energy liberated when a substance X undergoes complete
combustion, with excess oxygen at standard conditions (25°C and
1 bar).
• The heat of combustion is utilised to quantify the performance of
a fuel in combustion systems such as furnaces, Combustion
engines and power plants.
• In industrial terminology it is identified as the Gross Heating
(calorific) Value or Higher Heating (calorific) value.
• In a general design calculations, only Net Heating (calorific)
Value or Lower Heating (calorific) value is used.
Measurement of Calorific Value : Bomb
Calorimeter : Control Mass
 Thermodynamic Description of Bomb
Calorimeter

• It is a combination of two closed systems.

• Bomb: Constant volume closed system: Interacts only with
calorimeter.
• Calorimeter: Outer constant volume closed system:
• Interacts only with bomb.
• Isolates entire system with ambience.
The Bomb & Fuel
Temperature of Water in the Jacket
 Energy Balance & Estimation of CV

Who all accepted the Thermal energy (heat) liberated due to

combustion?