Topics: • Classification • Properties • Combustion • Carbonization • Liquefaction and gasification • Electricity generation from coal

2. COAL

CHEMICAL STRUCTURE OF COAL (Depending upon source, structure may be widely different)

Anthracite Coal Carbon 92-98%

Coal is a stored fossil fuel, occurring in the earth’s crust, which has been formed by the partial decay of plant materials accumulated millions of years ago and further altered by the action of heat and pressure.

Coal is a combustible black or brownish-black sedimentary rock normally occurring in rock strata in layers called coal beds or coal seams.

Coal is composed primarily of carbon along with variable quantities of other elements, chiefly hydrogen, with smaller quantities of sulfur, oxygen and nitrogen.

COAL: FEW FACTS

COAL FORMATION Over time, the chemical and physical properties of the plant remains were changed by geological action to create a solid material.

THEORIES OF COAL FORMATION IN SITU THEORY DRIFT THEORY - Flood /Tsunami type wave

(velocity 800 km/h) 300 million of years (earth is 4.6 billion years old) 15-20 m of plant material = 1 m of coal seam In INDIA 30 m seam of coal has been found

450-600 m of plant material might have accumulated at that place. (Burj Khalifa in Dubai, 828 m: tallest man made structure in world)

COALIFICATION

Coal % C C H O Heating

value (MJ/kg)

Cellulose 45 100 14 111 - Wood (Dry) 50 100 12 88 10-11 Peat 60 100 10 57 10-12 Lignite 62 100 8 54 16-24 Bituminous coal 79 100 6 21 26-30 Anthracite 91 100 5 5.2 32-34 Graphite 100 100 0 0 34

Time

1. Peat 2. Lignite 3. Bituminous coal 4. Anthracite 5. Graphite

COAL RANKS

Starting point of coal formation Does not come in

the category of coal Carbon: 60-64%;

Oxygen: 35-30%

PEAT

Also known as brown coal Mark the transition of peat

to coal Carbon: 60-75%; Oxygen:

30-20% Colour: black, brown, earthy Disintegrate very easily Briquetting is done

LIGNITES

Neyveli Lignite Corporation, Chennai, Tamilnadu possesses largest reserves of Lignite in India

Electricity generation: 2490 MW

BITUMINOUS COALS

A. Sub-bituminous: Between lignites and bituminous Carbon: 75-83%; Oxygen: 20-10% No caking power (Briquettes can not

be made)

B. Bituminous: Black and banded Industrial and domestic usage Carbon: 75-90%; Oxygen: 10-5%

C. Semi-bituminous: Also known as Steam Coal Between bituminous and anthracite Metallurgical coke formation Carbon: 90-93%; Oxygen: 4-1%

Highest rank of coal A harder, glossy and black

coal Extreme of metamorphosis

from the original plant material

Carbon: 93+%; Oxygen: 2-1% Caking power zero

ANTHRACITE

Technically the highest rank

Difficult to ignite

Not used as fuel

Mostly used in pencils and as a lubricant,

when powdered

GRAPHITE

UNUSUAL COALS

A. Cannels: Found rarely High hydrogen content Burn with smoke and bright

flame Does not fall in any category

B. Torbanites: Also known as boghead coal Named after torbane hill of

scotland Rich in paraffin oil Fine grained coal

Country Electricity Generation Country Electricity

Generation South Africa 93% Israel 63% Poland 92% Czech Rep 60% PR China 79% Morocco 55% Australia 77% Greece 52% Kazakhstan 70% USA 49% India 69% Germany 46%

COAL CONSUMPTION FOR ELECTRICITY GENERATION

TOP COAL PRODUCERS IN THE WORLD

Country Coal

Production (in MT)

Country Coal

Production (in MT)

PR China 2971 South Africa 247

USA 919 Russia 229 India 526 Kazakhstan 96

Australia 335 Poland 78 Indonesia 263 Colombia 73

TOP COAL EXPORTERS IN THE WORLD

COUNTRY STEAM (in MT)

COKING COAL (in MT)

TOTAL (in MT)

Australia 134 125 259 Indonesia 200 30 230

Russia 105 11 116 Colombia 69 - 69

South Africa 66 1 67 USA 20 33 53

Canada 7 21 28

TOP COAL IMPORTERS IN THE WORLD

COUNTRY STEAM (in MT)

COKING COAL (in MT)

TOTAL (in MT)

Japan 113 52 165 PR China 102 35 137 South Korea 82 21 103 India 44 23 67 Taiwan 57 3 60 Germany 32 6 38 UK 33 5 38

Coal Resource is the amount of coal that may be present in a deposit or coalfield. This does not take into account the feasibility of mining the coal economically. Not all resources are recoverable using current technology.

Coal Reserves can be defined in terms of proved (or measured) reserves, probable (or indicated) reserves and guessed (or inferred) reserve. • Proved Coal Reserve is that part of the total coal resource for which

quantity and quality can be estimated with a high level of confidence. • Indicated Coal Reserve is that part of the total coal resource for

which quantity and quality can be estimated with reasonable levels of confidence based on information gathered and supported by Interpretive Data.

• Inferred Coal Reserve is that part of the total coal resource estimate for which quantity and quality can only be estimated with low levels of confidence.

COAL RESOURCES AND RESERVE

TYPE OF COAL RESERVE (As on 1.4.2009 in MT)

PROVED INDICATED INFERRED TOTAL (A) Coking 17545 13766 2102 33413 • Prime Coking 4614 699 0 5313 • Medium Coking 12449 12064 1880 26393 • Semi-Coking 482 1003 222 1707 (B) Non-Coking:- 87798 109614 35312 232724 (C) Tertiary Coal 477 90 506 1073

Grand Total 105820 123470 37920 267210

Years to consume this coal with present rate: 600

Cokes are the solid carbonaceous material derived from destructive distillation of low-ash, low-sulfur bituminous coal. Tertiary Coals usually have high sulfur content (2-8%).

COAL RESERVES OF INDIA

STATEWISE COAL RESOURCES

State Geological Resources of Coal (As on 1.4.2009 in MT)

Proved Indicated Inferred Total Jharkhand 39480 30894 6338 76712 Orissa 19944 31484 13799 65227 Chhattisgarh 10910 29192 4381 44483 West Bengal 11653 11603 5071 28327 Madhya Pradesh 8041 10295 2645 20981 Andhra Pradesh 9194 6748 2985 18927 Maharashtra 5255 2907 1992 10154 Uttar Pradesh 866 196 0 1062 Meghalaya 89 17 471 577 Assam 348 36 3 387 Bihar 0 0 160 160 Sikkim 0 58 43 101 Arunachal Pradesh 31 40 19 90 Nagaland 9 0 13 22 Total 105820 123470 37920 267210

IMPORT OF COAL

YEAR COAL IMPORTED (IN MT)

COKING NON-COKING TOTAL

1991/92 5.27 0.66 5.93

1996/97 10.62 2.56 13.18

2000/01 11.06 9.87 19.70

2003/04 12.99 8.69 21.68

2005/06 16.89 21.70 38.59

2006/07 22.00 23.00 45.00

GRADING OF INDIAN COAL For coking coal Gradation is based on ash content

Non-coking coal Gradation is based on Useful Heat Value

(UHV)

For semi coking/weakly coking coal Gradation is based on ash plus moisture

content.

GRADING OF COKING COAL

GRADE ASH CONTENT Steel Grade-I Not exceeding 15%

Steel Grade-II Exceeding 15% but not exceeding 18%

Washery Grade-I Exceeding 18% but not exceeding 21%

Washery Grade-II Exceeding 21% but not exceeding 24%

Washery Grade-III Exceeding 24% but not exceeding 28%

Washery Grade-IV Exceeding 28% but not exceeding 35%

Steel Grade Coal is used in Steel Industries. Washery Grade Coal is used as fuel in thermal power plants.

GRADING OF NON-COKING COAL

Grade Ash% + Moisture % (at

60% RH & 40o C) Useful Heat Value (UHV) (in Kcal/Kg) UHV= 8900-138(Ash% + Moisture % )

A Not exceeding 19.5 Exceeding 6200

B 19.6 to 23.8 Exceeding 5600 but not exceeding 6200

C 23.9 to 28.6 Exceeding 4940 but not exceeding 5600

D 28.7 to 34.0 Exceeding 4200 but not exceeding 4940

E 34.1 to 40.0 Exceeding 3360 but not exceeding 4200

F 40.1 to 47.0 Exceeding 2400 but not exceeding 3360

G 47.1 to 55.0 Exceeding 1300 but not exceeding 2400

GRADING OF SEMI-COKING AND WEAKLY-COKING COAL

GRADE ASH+MOISTURE

CONTENT Semi coking grade-I

Not exceeding 19%

Semi coking grade-II

Exceeding 19% but not exceeding 24%

ROYALITY TO STATES

Nationalization in 1971 Coal companies are paying the

royalty to states This varies from Rs 90-250/tonne The rate is dependent of coal

grade Rates are 16 August, 2002

onwards

ANALYSIS OF COAL

Proximate analysis

Ultimate analysis

Heating/calorific value

ANALYSIS Moisture content: 105 - 110 oC Volatiles: 925 ± 15 oC for 7 min time (with lid) Ash: 800 ± 15 oC (without lid) Fixed carbon by difference

PROXIMATE ANALYSIS Proximate analysis shall comply IS:1350-I (1984)

REPORTING As received basis, Moisture free /Dry basis Dry ash free basis

A sample of finely ground coal of mass 0.9945 g was placed in a crucible of 8.5506 g in an oven, maintained at 105 oC for 4.0 ks. The sample was then removed, cooled in a dessicator and reweighed; the procedure being repeated until a constant total mass of 9.5340 g was attained. A second sample of mass 1.0120 g in a crucible of mass 8.5685 g was heated with a lid in a furnace at 920 oC for 420 s. On cooling and reweighing, the total mass was 9.1921 g. This sample was then heated without lid in the same furnace maintained at 815 oC until a constant total mass of 8.6255 g was attained. Perform the proximate analysis of the sample and express the results on “as received” and “dry, ash-free” basis.

EXAMPLE OF PROXIMATE ANALYSIS

A sample of finely ground coal of mass 0.9945 g was placed in a crucible of 8.5506 g in an oven, maintained at 105 oC for 4.0 ks. The sample was then removed, cooled in a dessicator and reweighed; the procedure being repeated until a constant total mass of 9.5340 g was attained. Determination of Moisture from first sample: Mass of sample = 0.9945 g Mass of dry coal = (9.5340 - 8.5506) = 0.9834 g Mass of moisture = (0.9945 - 0.9834) = 0.0111 g % Moisture = 0.0111×100/0.9945 = 1.11%

EXAMPLE OF PROXIMATE ANALYSIS (contd…)

A second sample of mass 1.0120 g in a crucible of mass 8.5685 g was heated with a lid in a furnace at 920 oC for 420 s. On cooling and reweighing, the total mass was 9.1921 g. This sample was then heated without lid in the same furnace maintained at 815 oC until a constant total mass of 8.6255 g was attained. Heating up to 920ºC in absence of air removes volatile matters, subsequent heating up to 815ºC in presence of air burns all fixed carbon of the sample leaving behind ash in the crucible. Determination of Ash from second sample: Mass of sample = 1.0120 g Mass of crucible = 8.5685 g Mass of ash (remnant in crucible) = (8.6255 - 8.5685) = 0.0570 g % Ash = 0.0570 × 100/1.0120 = 5.63 %

EXAMPLE OF PROXIMATE ANALYSIS (contd…)

A second sample of mass 1.0120 g in a crucible of mass 8.5685 g was heated with a lid in a furnace at 920 oC for 420 s. On cooling and reweighing, the total mass was 9.1921 g. This sample was then heated without lid in the same furnace maintained at 815 oC until a constant total mass of 8.6255 g was attained. Determination of Volatile matters from second sample: Initial mass of sample + crucible = 1.0120 + 8.5685 = 9.5805 g Final mass after heating up to 920ºC (without air) = 9.1921 g Mass of volatile matter + moisture = Initial – Final mass = (9.5805-9.1921) g = 0.3884 g % Moisture + Volatiles matters = 0.3884 x 100/1.0120 = 38.3794 % % Volatile matters = 38.3794 – 1.11 (% Moisture) = 37.26 %

EXAMPLE OF PROXIMATE ANALYSIS (contd…)

% Moisture (M) = 1.11%

% Ash (A) = 5.63 %

% Volatile matters (VM) = 37.26 %

% Fixed carbon (FC) = 100 – (%M + %A + %VM)

= 100 – (1.11+ 5.63+ 37.26)

= 56.0 %

EXAMPLE OF PROXIMATE ANALYSIS (contd…)

Proximate analysis as received basis Moisture : 1.11 % Ash : 5.63 % Volatile matter : 37.26 % Fixed carbon : 56.00 %

Proximate analysis on dry, ash free basis Moisture + Ash : 1.11 + 5.63 = 6.74% Fixed carbon : 56.0 x 100/(100-6.74) = 60.04 % Volatile matter : 37.26 x 100/(100-6.74) = 39.95 %

REPORTING OF PROXIMATE ANALYSIS

1. Carbon

2. Hydrogen

3. Oxygen

4. Sulfur : 0.5-2.50 %

5. Nitrogen : 1.0-2.25 %

6. Phosphorus : 0.1%; Blast Furnace: < 0.01 %

7. Chlorine

ULTIMATE ANALYSIS Ultimate analysis shall comply IS:1350- IV (1974)

Mercury: A big problem from NTPC plants (up to 0.3mg/kg)

1. Calculated from proximate analysis

2. Calculated from ultimate analysis

3. Experimental determination

HEATING VALUE OF COAL

1. Gross/High heating value (accounts for water in the exhaust leaving as vapor and includes liquid water in the fuel prior to combustion)

2. Useful/low heating value (determined by subtracting the heat of vaporization of the water vapor from the higher heating value)

Hydrogen Water (gas/vapor or liquid phase) Carbon Carbon Dioxide (gas phase) Latent heat of vaporization of water: 2.26 MJ/kg

HEATING VALUE FROM PROXIMATE ANALYSIS

TAYLOR AND PATTERSON RELATIONSHIP HV = 4.19 (82FC + a VM) kJ/kg Where FC and VM are the %age values on dry ash free basis and a is an empirical constant which depends on the VM content of coal.

VM 5 10 15 20 25 30 35 38 40

a 145 130 117 109 103 98 94 85 80 60

80

100

120

140

160

0 10 20 30 40

a

VM

DULONG FORMULA

HV = 338.2C + 1442.8(H - O/8) + 94.2 S kJ/kg Where C, H, O and S are the % of these elements on dry ash free basis.

HEATING VALUE FROM ULTIMATE ANALYSIS

This experiment shall comply IS:1350- II (1970) Solid /liquid samples can be analyzed 1 g air dried sample is burnt in a bomb in oxygen

atmosphere Rise in temperature gives the heat liberated and

heating value is determined after doing the corrections for resistance wire and thread

Microprocessor based bomb calorimeters are now available

EXPERIMENTAL DETERMINATION OF HEATING VALUE

BOMB OF CALORIEMETER

VARIOUS COMPONENTS OF BOMB CALORIMETERIC EQUIPMENT

ROUTES OF GENERATION OF HEAT AND POWER FROM COAL

1. Direct use as thermal energy in heating processes, furnaces and domestic heating by open fires

2. Transfer of the heat to a thermal fluid and application of the latter for heating and power e.g., steam for heating in process industry, central heating and electricity generation by steam turbines

3. Gas turbine route to electricity generation 4. Conversion to gas/liquid fuels and subsequent usage

in IC engines/turbines (gas/steam)

Domestic cooking (Chulha at Tea stalls, Dhaba,

Bakery)

Space heating (Fireplace)

Lime and brick kilns (Direct heating of stack)

Ceramic industry (Oven/Furnace)

ROUTE I (DIRECT HEATING)

Generation of steam in a boiler Space heating by transferring heat of steam to air Process industry: Cogeneration is employed Utility services: steam turbines used

GOVERNMENT ALLOWED ELECTRICITY GENERATION BY PRIVATE DEVELOPERS Tariff Wheeling Banking

SUPERCRITICAL BOILERS: A RECENT CONCEPT Critical pressure: 218 bar (21.8 MPa), Critical temperature: 374oC Mark Benson, in 1922 patent was granted 22 MPa pressure ; η= 1-T1/T2 ≈ 0.53

ROUTE II (THERMAL FLUID)

ROUTE II (contd…)

COAL HOT AIR FOR SPACE HEATING

CO

ND

ENSA

TE

STEAM

ELECTRICITY TO GRID

CO

ND

ENSA

TE

STEA

M AIR

TO GRID

COGENERATION

ALTERNATOR STEAM TURBINE

HEAT EXCHANGER BOILER

ELEC

TRIC

ITY

STEA

M

PROCESS PLANT

STEAM TURBINE

ALTERNATOR STEA

M

ROUTE III (GAS TURBINE)

VENT

TUR

BIN

E EX

AH

AU

ST

ELECTRICITY TO GRID

AIR

ALTERNATOR GAS

TURBINE

HEAT EXCHANGER

COMPRESSOR

PULVERIZER

COAL

COMBUSTION CHAMBER

AIR

PREHEATED AIR

ROUTE III (contd…)

VENT

TUR

BIN

E EX

AH

AU

ST

ELECTRICITY TO GRID

AIR

ALTERNATOR GAS

TURBINE

HEAT EXCHANGER

COMPRESSOR COMBUSTION

CHAMBER

AIR

PREHEATED AIR

GASIFIER AND GAS CLEANING

UNIT

COAL

ROUTE IV (PYROLYSIS/GASIFICATION)

1. Partial gasification or pyrolysis/coking/ carbonization/destructive distillation (heating in the absence of air) Solid Liquid Gas

2. Complete gasification with air/oxygen Gas

PYROLYSIS

Medium temperature carbonization (700-900 oC) Liquid fraction for chemicals recovery/liquid fuel

High temperature carbonization > 900 oC Coke for metallurgical furnaces; gas yield high;

liquid low

Low temperature carbonization (500-700 oC) Coke (solid fuel) maximum; Classical domestic smokeless fuel production

PYROLYSIS (contd…)

PYROLYSER

COAL

WATER IN

WATER OUT

GAS FOR IC ENGINES/

GAS TURBINES/ THERMAL

APPLICATIONS COKE

FLUE GAS

PRETREATMENT UNIT LIQUID FRACTION

COAL TAR LIQUID FUELS CHEMICALS

CONDENSER

GAS FOR HEATING OF PYROLYSER

3

12x3 = 36 kg 1k mole = 1000 R.T/P (m3) ≈ 18 Liter

GASIFICATION

(Air Separation Unit)

ROUTE IV

1. Bergius process Friedrich Karl Rudolf Bergius (Germany) in 1913, Nobel Prize in 1931 (Shared with Carl Bosch) By end of World War II – most of the fuel for German

army was produced by this method. Hydrogenation of vegetable oils

2. Fischer-Tropsch process Franz Fischer and Hans Tropsch in 1926, Germany

Coal is hydrogen starved/hydrogen needs to be added to make it liquid (directly or indirectly)

BERGIUS PROCESS

PULVERIZER

COAL PASTING UNIT

HYDROGEN COAL

BERGIUS REACTOR

HEAVY FRACTION

HCS

T = 400 - 500 oC P = 20 - 70 MPA CATALYST = TIN η = 97%

FRACTIONATING COLUMN

FISCHER-TROPSCH (F-T) PROCESS

GASIFICATION UNIT

SYN GAS CLEANING

COAL

F-T REACTOR

HCS

T = 150 - 200 oC P = 1 - 25 MPA CATALYST = IRON OR COBALT BASED

FRACTIONATING COLUMN SYN GAS

(Large number of patents worldwide)

F-T PROCESS (COMMERCIAL PLANTS)

SASOL • Afrikaans: Suid Afrikaanse

Steenkool en Olie, • English: South African Coal and

Oil Established in 1950 Oldest plant producing petrol

and diesel profitably from coal and natural gas using Fischer-Tropsch (F-T) process

Presently engaged in Qatar, Iran and Nigeria in similar projects

F-T PROCESS (COMMERCIAL PLANTS) (cont…)

Players in this area of Gas To Liquid (GTL)

1. GE 2. Exxon 3. Shell 4. BP 5. Chevron 6. Sasol

With crude touching the $145+, these two technologies would be economically viable.

F-T PROCESS

Global warming Green house gases: water vapor, carbon dioxide,

methane, nitrous oxide, HFCs (hydrofluorocarbons), PFCs (perfluorocarbons), SF6 (Sulphur Hexafluoride)

SF6 is 22,200 more potential than CO2 Carbon dioxide gas: main culprit from fossil fuels; not

from biomass Intergovernmental Panel on Climate Change (IPCC) Nobel Peace Prize 2007: R. K. Pauchari and Al Gore Reduction in Carbon Dioxide emissions G8 meeting in Japan in July 2008

COAL COMBUSTION AND ENVIORNMENT

CO2 EMISSIONS AND CONCENTRATIONS (1751-2004)

Present CO2 level: 483 PPM

GLOBAL CARBON CYCLE (All values are in Billion Metric Tons Carbon)

GLOBAL CARBON CYCLE (contd…)

Carbon capture and storage, alternatively referred to as carbon capture and sequestration, is a means of mitigating the contribution of fossil fuel emissions to global warming

The process is based on capturing CO2 from large point sources, such as fossil fuel power plants, and storing it in such a way that it does not enter the atmosphere.

CO2 CAPTURE AND SEQUESTRATION

Sequestration 1. Gaseous storage in various deep geological formations

(including saline formations and exhausted gas fields)

2. Liquid storage in the ocean

3. Solid storage by reaction of carbon dioxide with metal oxides to produce stable carbonates

Capture Proven technology being used in process industries

and power plants

BUT THE COST IS DECIDING FACTOR

CO2 CAPTURE AND SEQUESTRATION (contd…)

CO2 CAPTURE AND SEQUESTRATION (contd…)

A process applied to the non-mined coal seams Injection and production wells are drilled End gas mix depends on type of coal seam Air/oxygen can be used for gasification Syn gas can be used for power generation in

combined cycle Syn gas can be converted to chemicals/fuel by F-T

process

UNDERGROUND/IN SITU COAL GASIFICATION

Source: World Coal Institute

UNDERGROUND/IN SITU COAL GASIFICATION (contd…)

• Methane Clathrate is also called as methane hydrate, hydromethane, methane ice, fire ice, buring ice and natural gas hydrate

• It is a solid clathrate compound in which a large amount of methane (CH4) is trapped within a crystal structure of water, forming a solid similar to ice

• 1 mole methane in 5.75 mole of H2O

• Available in Deep sea (methane from trench + cold water + high pressure) and at the lower ice layer in Antarctica

A NEW GENERATION OF SOLID FUEL?

ULTIMATE SOLUTIONS

Solar: Photovoltaic

Fuel cells: Chemical to electrical conversion

Hybrid vehicles: Honda introduced in India