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LECTURE–4: COAL & CHEMICALS FROM COAL

CHEMICAL TECHNOLOGY (CH-206)Dr. Vimal KumarDepartment 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 of

synthetic fuel, a source of power production, coke production, and Fine chemicals which are now being derived from

petroleum and natural gas. Some of the alternate feed stocks for chemical

industries from coal are coal 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

temperature and pressure altered these deposits to coal. Coal is composed of chiefly carbon and other

elements like hydrogen, 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 US 1950 - 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

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 reserve

Proved reserve are those resources which has been reliably estimated and can be recovered economically.

Indicated reserves is the coal resource which is based on combination of direct measurement and reasonable geological assumptions.

Inferred coal resource 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

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 (LOA)

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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

gas was made administrative ministry. CBM gas production is about 2 lakhs cubic meter

per day [Annual Report 2011- 12 Govt. of India Ministry of Petroleum and Natural gas].

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TYPES OF COAL Coal are classified into various grades based on the

Composition calorific value Degree of coalification that has occurred during its formation.

Coal may be also classified as hard 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/coalclassification].

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CLASSIFICATION OF DIFFERENT TYPE OF COAL

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TYPICAL COAL CHARACTERISTICS

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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 sediments

Na, 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

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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CHEMISTRY 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

CmHn CH4 + (m-n)/4 C

Carbonization carried out at ~400 ˚C, products are H2 and CH4 Important 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 kJBut “hydrogasification” requires high temps, 800 0C 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 400 0C 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 kJCO + H2O = CO2 + H2 + 41.4 kJCO + 3 H2 = CH4 + H2O + 206.3 kJ2 C + 2 H2O = CH4 + CO2 - 15.1 kJ

Hence in theory can convert coal to methane with energy of only 15.1 kJBut exothermic reaction goes at 400 0C, endothermic one at 900 0CNeed to supply heat to endothermic one, to do so burn more coalRequires 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

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PRODUCTION AND USE OF COKEGasification breaks apart hydrocarbons–products are volatile gases and

carbonized coal Carbonized 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 industryAlthough 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–called tar

Tar contains low FW aromatic compounds distilled to produce benzene, toluene, xylenes,

and their corresponding alcohols, which are important petrochemical feedstocks

Secondary products that can be made from tars are synthetic dyes, antibiotics and anesthetics, flavoring agents, and perfumes

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COKE OVEN PLANTS For the production of chemicals from cokes and due to

increasing demand of iron and steel, there has been a considerable increase in the coke oven capacity.

Two types of coke manufacturing technologies use are: Coke making through by product recovery Coke making through non-recovery/ heat recovery

In India, building of coke oven batteries was initiated in the beginning of the 19th century,

There are about 3000 ovens are in operation/ construction in the coke oven plant.

In the year 2011-12 ,the world coking coal requirement was about 433 million metric tones in which India’s requirement is estimated to about 54 million tones.

By product from coal gasification plant includes coke, coal tar, sulphur, ammonia.

Coal tar distillation produces tar, benzol, cresol, phenol, creosote.

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COKING COALS Blast furnace requires coke of uniform size, high

mechanical strength, and porosity with minimum volatile matter and minimum ash.

Coking coal may be derived on the basis of their coking properties: prime coking coal, medium coking coal, semi coking coal. The prime coking coal produce strong metallurgical coke

while coals of other groups yield hard coke The moisture concentration of ash, sulphur and

sometime phosphorous and ash fusion temperature are important in determining the grade of coking coal since they influence the quality of coke produced.

Low moisture, ash, sulphur and phosphorous content in the coal are desirable for production of good quality coke.

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COKING COALS The desired analysis of typical coal charge to

coke oven is.Ash content : 16% ±0.5%Moisture : 6-7%Volatile matter : 22-25%Fixed carbon : 58-60%%Sulphur : 0.56%Phosphorous : 0.09%

Some of the other factors affecting quality of coke are rank of coal, particle size, bulk density, weathering of coal, coking temperature and coking rate, soaking time, quenching practice.

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COCK OVEN PLANTS: VARIOUS SECTIONS

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COCK OVEN PLANTS

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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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THANKS