lecture-5-coal and coal chemicals
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7/21/2019 Lecture-5-Coal and Coal Chemicals
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LECTURE–4:
COAL & CHEMICALS FROM COAL
CHEMICAL TECHNOLOGY (CH-206)
Dr. Vimal Kumar
Department of Chemical Engineering
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INTRODUCTION –COAL
Coal is the largest source of energy all over the world.
Coal can serve a potential source ofsynthetic fuel,
a source of power production,
coke production, andFine chemicals which are now being derived from petroleum
and natural gas.
Some of the alternate feed stocks for chemical
industries from coal arecoal gasification,
coal to synthesis gas,
coal to oil through FT synthesis,
coal to methanol,
coal to plastic
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COAL ORIGIN
Coal is carbonaceous solid black or brownish black
sedimentary rock matter
It is made from the accumulation of partially
decomposed vegetation.
Biological changes and subsequent effects of temperatureand pressure altered these deposits to coal.
Coal is composed of chieflycarbon and other elements
likehydrogen, sulphur, oxygen, nitrogen, moisture
and non-combustible inorganic matter containing,
silica, iron, calcium, magnesium, mercury etc.
The coal composition, sulphur content, mercury
content and calorific value of the coal vary widely from
one coal reserve to another coal reserve.
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COAL TIMELINE
200 BC- first published record of coal used for heating
(Greece)
300 AD- Coal adopted as heat source in China
900 AD - Coal mining begun in western Europe
1285 AD- Coal burning begins to pollute London
1600’s- Great Britain runs out of wood, switches to
coal, beginning of the industrial revolution
1800’s - US becomes leading producer of coal
1945 - coal is leading energy source in US1950 - USSR becomes leading producer of coal, coal
provides 60% of world energy sources
2000 - coal provides 30% of world energy sources as
dependence on petroleum grows
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GEOGRAPHICAL DISTRIBUTION OF
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http://www.eia.gov/countries/reports.cfm
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WORLD OIL/COAL RESERVES BY
REGION (%)
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COAL PRODUCTION AND
CONSUMPTION
The global coal production in 2011 was 7 billion
tones.
China accounted for approximately half of the
production and consumption.
Total coal production in India during 2009-10
was 532.29 million tones.
Lignite production in India in 2009-10 was 23.95
million tones
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COAL RESOURCES:
BASED OF DEGREE OF
ASSURANCE
Coal reserveProved reserveare those resources which has been
reliably estimated and can be recovered economically.
Indicated reservesis the coal resource which is
based on combination of direct measurement andreasonable geological assumptions.
Inferred coalresource is based on the assumed
continuity of coal beds.
Depth range determines the economy of
extraction and a cope of exploration.
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COAL RESOURCES IN INDIA
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COAL DEMAND PROJECTION(million tones)
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DISTRIBUTION OF COAL RESOURCES(MILLION TONES)
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COAL RESOURCES IN SEDIMENTARY
ROCKS(MILLION TONES)
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COAL LETTERS OF ASSURANCE
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COAL BED METHANE (CBM)
Coal bed methane is an environmentally friendly
clean fuel similar to natural gas.
Preliminary activities related to exploration of CBM
in India started in early 1990’s
Till 1997 the Ministry of Coal had allotted some coal
bearing areas for CBM exploration.
In India 33 CBM contracts were signed for
explorations of CBM gas.
In July 1997, Ministry of Petroleum and Natural gaswas made administrative ministry.
CBM gas production is about 2 lakhs cubic meter
per day[Annual Report 2011- 12 Govt. of India Ministry ofPetroleum and Natural gas].
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TYPES OF COAL
Coal are classified into various grades based on theComposition
calorific value
Degree of coalification that has occurred during its formation.
Coal may be also classified ashard or soft coal,
low sulphur or high sulphur coal.
Coal may be also classified in rock types based on
petrological components known as maceral:
clarain,durain,
fusain and
vitrain
[http://www.britannica.com/EBchecked/topic/1703417/coalclassifi
cation].
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CLASSIFICATION OF DIFFERENT TYPE OF COAL
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TYPICAL COAL CHARACTERISTICS 8 /
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CHEMICAL COMPOSITION OF COAL
Model of coal
Inorganic constituents are from
original plant material, plus minerals
leached into the coal from
surrounding sedimentsNa, Ca, Mg, K salts,
Al, Si, Fe, S oxides
Coal also contains trace amounts of
Ga and Ge, both of which are
important for the modern electronics
industry
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Conclusion: Coal is a 3D cross-linked polymer of aromatic rings and
alkane linkers with a small amount of inorganic contaminants
Unlike petroleum, coal cannot be
separated into individual
products. It must be reformed
into smaller FW useful material
(synthetic fuels) or combusted to
capture the heat.
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CHEMISTR
Y OF COAL
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COAL GAS
Coal carbonization: coal is heated at moderate
temperature, thermal decomposition of the
organic material releases small amounts of
flammable gas
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CmHn → CH4 + (m-n)/4 C
Carbonization carried out at ~400 ̊C, products are H2 and CH4Important historically because this was the first large source of CH4 which
was used for lighting in the early 20th centuryNot a useful process anymore because of the large known reserves of CH4
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COAL GAS Coal gasification: conversion of coal into methane:
C + 2 H2 → CH4 + 74.9 kJ
But “hydrogasification” requires high temps, 8000C
Also is inefficient because it is exothermic and driven to left at high T
More efficient route to methane:
CO + 3 H2 → CH4 + H2O + 206.3 kJ
Reaction is more exothermic but operates at 4000C with Ni catalyst
Process can produce liquids by Fischer-Tropsch chemistry:
n CO + (2n+1)H2 → CnH2n+2 + nH2O
Production of methanol:
CO + 2 H2 = CH3OH
What is the feedstock for CO and H2?
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COAL GAS Steam reforming:
C + H2O→ CO + H2 - 131.4 kJ (1)
Produces equal amounts of CO and H2
If extra H2 is needed, perform “water-gas shift” reaction:
CO + H2O→ CO2 + H2 + 41.4 kJ (2)
This fulfil the needed CO and H2
So overall, use two equiv. of (1), add to (2) and methanation to get:
2 C + 2 H2O = 2 CO + 2 H2 - 262.8 kJ
CO + H2O = CO2 + H2 + 41.4 kJ
CO + 3 H2 = CH4 + H2O + 206.3 kJ
2 C + 2 H2O = CH4 + CO2 - 15.1 kJ
Hence in theory can convert coal to methane with energy of only 15.1 kJ
But exothermic reaction goes at 4000C, endothermic one at 9000C
Need to supply heat to endothermic one, to do so burn more coal
Requires 262.8 kJ/mole of methane, about 32% of energy content of methaneHence upper limit is 68%, lower in practice due to other losses
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COAL LIQUIDIFICATIONIndirect liquidification: Product of coal gasification (CO and H2 mixture, also called
synthetic gas or syngas) is reacted to form larger FW hydrocarbons 8 /
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PRODUCTION AND USE OF COKE
Gasification breaks apart hydrocarbons–products are volatile gases and
carbonized coalCarbonized coal is called coke - can be burned at high temperatures up to
1100 ̊C
If coal carbonization is carried out at high temperature:
Coke is used in blast furnaces in the steel industry
Although coke can support high combustion temperatures, some unburned
coke is carried out of the furnace as small particulate matter called smoke
Smoke is a major contributor to air pollution
If coal carbonization is carried out at low temperature:
Coke burned at temperatures lower than 750 ̊C combusts completely (no
smoke)
This is commonly used for small-scale industries that cannot afford the
scrubbers used to clean smoke
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PRODUCTION AND USE OF TAR
Coal carbonization also produces a small amount
of sticky, black liquid–calledtar
Tar contains low FW aromatic compoundsdistilled to produce benzene, toluene, xylenes, and
their corresponding alcohols, which are important
petrochemical feedstocks
Secondary products that can be made from tarsare synthetic dyes, antibiotics and anesthetics,
flavoring agents, and perfumes
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COKING OF COALBeehive oven
Byproduct oven (or coke oven plant)
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BEEHIVE OVEN
Beehive coke ovens were called that because they
were built in a beehive-like hemispherical shape,
and then covered with earth.
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http://patheoldminer.rootsweb.ancestry.com/coke2.html
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BY-PRODUCT COKE OVEN
PROCEDURE
The carefully blended coal charge is heated on bothside so that heat travels towards the center and thus
produces shorter and more solid pieces of coke (no
air is introduced, to avoid burning of coal).
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BY-PRODUCT COKE OVEN PROCEDURE(KOPPER-BECKER UNDERJET LOW-DIFFERENTIAL
COMBINATION COKE OVEN WITH WASTE GAS RECIRCULATION) 8 /
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COKING COALS:COAL ANALYSIS BEFORE CHARGING INTO THE COKE
OVEN
The average temperature in the center of the coal
is 9800C.
The flue gas temperature is 12900C.
The temperature varies withthe condition of operations
The coking time
The width of the oven, and
The type of coal, its moisture contents and its
fineness of division.
The typical coking time is ~17 h.
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BY-PRODUCT COKE OVEN
PROCEDURE
Process is divided into following sequences:
1. Coal is transferred, crushed and screened,
2. Coal is charged to hot empty oven,
3. Coal is chemically transformed to coke and volatiles by
pyrolysis,
4. Hot coke is pushed out of the oven, quenched and
transported,
5. Condensable product of distillation are liquefied and
collected in the hydraulic main,
6. Foul gas is cooled, and tar extracted
7. Ammonia is removed from gas as ammonium sulfate
8. Gas is cooled and subjected to benzene and toluene removal
by absorption in straw oil,
9. Hydrogen sulfide is removed,
10.Purified gas is metered and transferred to consumers.
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COAL TAR CONTINUOUS
DISTILLATION 8 /
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CONTINUOUS TAR DISTILLATION
PRODUCTS
Streams Product Boiling point (oC)
Side stream 1 Light oil to 170
Side stream 2 Carbolic oil 170−205
Side stream 3 Naphthalene oil 205−204
Side stream 4 Creosote or wash oil 240−280
Residue 5 The residue or anthracene 280−340
Pitch 6 Residuum or pitch 340−400
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RECOVERY OF COAL CHEMICALS 8 /
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BYPRODUCTCOKEOVEN
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BY-PRODUCT COKE OVEN
PROCEDURE
AN AMMONIA STILL 8 /
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BY-PRODUCT COKE OVEN
PROCEDURE
The following materials are required in order to
produce:Gas 0.28–0.35 Mm3 of 20.5 MJ/m3,
Coke 700 kg, 38 L tar;
Ammonium sulfate 11.4 kgLight oil 7.6 – 15.2 L
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Bituminous coal 1 t Steam 200 – 600 kg
Sulfuric acid (60o
Be’) 12.5 kg Electricity 25 MJ
Lime 0.75 – 1 kg Direct labor 0.8 – 1.3 work-h
Water 4150 – 8000 L
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APPROXIMATE YIELDS PER METRIC
TON OF COAL CARBONIZED
High Temperature
kg
Low temperature
kg
Furnace coke 715 −
Coke breeze 46.5 −
Semicoke (12% volatiles) − 720
Tar 39 75
Ammonium sulfate 10 9
Light oil (removed fromgas by oil scrubbing)
10 8
Gas 1750 125
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VARIATION OF GAS FROM LOW− AND HIGH−
TEMPERATURE COAL CARBONIZATION
Gas Coking temperature,
500OC,
%
Coking temperature,
1000OC,
%
CO2 9.0 2.5
CnHm 8.0 3.5
CO 5.5 8.0
H2 10.0 50.0
CH4 and homologs 65.0 34.0
N2 2.5 2.0
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CONTINUE………
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ACKNOWLEDGEMENT
Slides are developed from the following references: Austin G. T., "Shreve’s Chemical Process Industries",
Fifth edition, Tata McGraw Hill, NY.
Kent J.A., "Riegel's Handbook of Industrial
Chemistry,”CBS Publishers.Gopala Rao M. & Marshall Sittig, "Dryden’s Outlines of
Chemical Technology for the 21st Century", Affiliated
East –West Press, New Delhi.
Mall I. D., "Petrochemical Process Technology",
Macmillan India Ltd., New Delhi.NPTEL (online)
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