Lecture-5-Coal and Coal Chemicals

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

COAL RESERVES 8 /

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http://www.eia.gov/countries/reports.cfm



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)



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



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



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



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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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




PROCEDURE

AN AMMONIA STILL 8 /

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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



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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