Coal and Coal as Chemical Feedstock Chemical Engineering Notes | EduRev

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Coal and Coal as Chemical Feed Stock

Coal can serve a potential source of synthetic fuel, a source of power production, coke production and large number of chemicals which are now being derived from petroleum and natural gas. Coal is the largest source of energy all over the world. Some of the recent development in utilistation of coal are coal gasification, coal to synthesis gas, coal to oil through FT synthesis, coal to methanol, coal to plastic are some of the future technologies which are likely to play important role in providing alternate feed stock for chemical industries.

Coal Origin and Composition 

Coal is carbonaceous solid black or brownish black sedimentary rock matter vegetation, biological changes originated 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 noncombustible inorganic matter containing, silica, iron, calcium, magnesium, mercury etc. Coal has a wide range of composition. Typical composition of Indian coal and other countries are given in Table M-II 1.1. The composition, sulphur content, mercury content and calorific value of the coal vary widely from one coal reserve to another coal reserve. Coal may be hard or slightly softer depending on the source.  

Table M-II 1.1: Composition of Indian Coal and Other Countries

Details

Indian coal

Coal in other countries

Ash content

40-50%

1-16%

Sulphur

0.5%

As high as 1.8%

Carbon

25-30%

53-57%

Hydrogen

<3%

4-6%

Calorific value

2450-3000

5000-6400

 
Coal Resources: Category of coal resources are based on degree of assurance i.e (i) coal reserves- proved, indicated , inferred or  (ii) depth range.  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.

Coal Reserves 

Worlds proven coal reserves are estimated at about 860 billion tones which is expected to last up to 120 years at the current level of production. The global coal reserves consist of 53percent anthracite and bituminous coals, 30percent sub-bituminous and 17percent lignite . Largest coal reserves of coal are in China, USA, Russia, Australia and India. India has the fifth largest coal reserves in the world of the total reserves, nearly 88 percent are non-coking coal reserves while tertiary coals reserves account for a meager 0.5percent and the balance is coking coal. Coal resources in India as on April 1, 2011 is given in Table M-II 1.2. Coal reserves of India up to the depth of 1200meters have been estimated to be 276.81 billion tones as on April 1, 2010. Projected coal demands in upcoming year are mention in Table M-II 1.3.Coal deposits are chiefly located in Jharkhand, Orissa, Chhattisgarh, West Bengal, Madhya Pradesh, Andhra Pradesh and Maharashtra. Details of state wise coal resources in India are shown in Table M-II 1.4. Table M-II 1.5 gives detail of coal resources in sedimentary rocks. Lignite reserves in the country have been estimated around 39.90 billion tones as on March 31, 2010. Major deposits are in Tamil Nadu. Details of coal letter of assurance and status of CBM blocks are given in Table M-II 1.7 and Table M-II 1.8 respectively.   

Table M-II 1.2: Coal Resources in India  

Resources in

million tones

Proved

Indicated

Inferred

Total

Coking coal

17,669

13,703

2,102

33,474

Non- coking coal

95,739

12,368

31,488

250,895

Tertiary coals

594

99

799.49

1,493

Total

114,001

137,471

34,389

285,862

 
  
Table M-II 1.3: Coal Demand Projections (million tones)

Plan

Period

Power

Non-power

Total

11th

2011/12

436

164

627

 12th

2016/17

603

221

824

13th

2021/22

832

299

1131

 14th

2026/27

1109

408

1517

15th

2031/32

1475

562

2037

 

Table M-II 1.4: Distribution of Coal Resources (million tones) 

State

Proved

Indicated

Inferred

Total

Andhra Pradesh

9194

6738

2985

18927

Arunachal

Pradesh

31

40

19

90

Assam

348

36

3

387

Bihar

-

-

160

160

Chhattisgarh

10910

29192

4381

44483

Jharkhand

39480

30894

6338

76712

Madhya Pradesh

8041

10295

2645

20981

Maharashtra

5255

2907

1992

10154

Meghalaya

89

17

471

577

Nagaland

9

-

13

22

Orissa

19944

31484

13799

65227

Sikkim

-

58

43

101

Uttar Pradesh

866

196

-

1062

West Bengal

11653

11603

5071

28327

Total

105820

123470

37920

267210

Table M-II 1.5: Coal Resources in Sedimentary Rocks (million tones)  

Formation

Proved

Indicated

Inferred

Total

Gondwana

Coals

105343

123380

37414

266137

Tertiary Coals

477

90

506*

1073

Total

105820

123470

37920*

267210

  Table M-II 1.6: Coal Letters of Assurance (LOA)  

Name of sector

Number approved

Quantity approved(MTPA)

Power Utilities

15

57

Captive Power Plants Including Cement CPPs

224

42

Independent Power

Producers

12

24

Cement Plants

72

21

Sponge Iron Units

236

17

Total

559

161

  Source: Annual Report 2007-08 Ministry of Coal, GOI 
 
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 and 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. As of now about 250 BCM reserves have been established in 5 CBM blocks. CBM gas production is about 2 lakhs cubic meter per day [Annual Report 2011-12 Govt. of India Ministry of Petroleum and Natural gas].  

Table M-II 1.7: Status of CBM Blocks  

Block awarded

3

Under round I

5

Under round II

8

Under round III

10

Total

26

Area Awarded (sq. km)

13600

Total CBM resources (BCM)

1374

CBM Wells Drilled

210

Expected Production Potential(MMSCMD)

38

Approved Gas Sale Price($/MMBTU)

6.79

Sources: India Exploration and Production Activities 2007-08 

Coal Production and Consumption

The global coal production in 2011 was 7 billion tones of which 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 2009-10 was 23.95 million tones

Types of Coal

Coal are classified into various grades based on the composition and calorific value and 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 petro logical components known as maceral. Based on maceral content coal may be classified as clarain, durain, fusain and vitrain . Classification of different type of coal is mention in Table M-II 1.8.
Ultimate analysis of non-coking (Thermal) coal from three power stations (Kahalgaon, Simhadri, and Sipat) is shown in Table M-II 1.9 along with analysis of Ohio coal in the United States and Long Kou coal from China. 

Table M-II 1.8: Classification of Different Type of Coal 

Types of coal

Description

Peat

Peat is the precursor of coal formed

Lignite

With further increase in temperature during coal formation peat is converted

to lignite. Lignite is considered as immature coal. Lignite are brown coloured, soft, low calorific value coal. It is compact in texture.

Sub-bituminous

Sub-bituminous coals are black coloured and are more homogeneous in appearance and their properties range from lignite to that bituminous coal.

Bituminous coal

Bituminous coal is usually black, with higher carbon content and calorific value

Anthracite coal

Anthracite is highest rank coal is a harder, glassy black coal with highest

content of carbon and calorific value. Anthracite coal is best suited for making metallurgical coke, for gasification to produce synthesis gas and for combustion as fuel for power generation. The ash content is low.

Graphite

Graphite is the highest rank and is difficult to ignite

 
 
 
 Table M-II 1.9: Typical Coal Characteristics in selected Indian Power Plants, Compared to selected Chinese and U.S. Coals

Details, %

Kahalgaon

Simhadri

Sipat

US (Ohio)

China (Long Kou)

Carbon

25.07

29.00

30.72

64.2

62.8

Hydrogen

2.95

1.88

2.30

5.0

5.6

Nitrogen

0.50

0.52

0.60

1.3

1.4

Oxygen

6.71

6.96

5.35

11.8

21.7

Moisture

18.5

15.0

15.0

2.8

11.0

Sulphur

0.17

0.25

0.40

1.8

0.9

Ash

46.0

46.0

45.0

16.0

7.7

Calorific Value, kcal/kg

2450

2800

3000

6378

6087

 
 
Selection of coal for various applications depends on its composition and carbon content, calorific value, moisture content, ash content, composition of ash, fusion temperature of ash, coking quality, sulphur content.  

Assesment of Coal Quality 

Coal quality plays an important role in its efficient utilization as fuel and for gasification. It should have high calorific value, high carbon content with low ash content, low sulphur, low moisture, low cost. The quality of coal depends upon it rank. The coal rank is arranged in ascending order 

Lignite→  Sub-bituminous coal → bituminous coal→  anthracite 

Coal quality can be assessed by proximate, ultimate analysis and calorific value of the coal. Proximate analysis involves determination of moisture, volatile matter, ash and fixed carbon. Ultimate analysis involves determination of carbon and hydrogen,, nitrogen, sulphur, oxygen  Calorific value is represented as higher calorific value (HCV) or Gross calorific value (GCV) and Lower calorific value (LCV) or Net calorific value (NCV). Another term used to express energy content is Useful heating value (UHV).UHV is defined as UHV kcal/kg=[8900-138x( percentage of ash content+ percentage of moisture content)] 

Coal as Fuel 

Coal accounts for 53 percent of the commercial energy sources in India which is high compared to the world average of 30percent. The 11th plan projected India’s coal demand to grow at 975 per annum against 5.7 percent during 10thplan almost two-fold increase. The commercial coal consumed by India 72 percent for power, 14 percent for steel, 9percent for cement and 9 percent for others. Allocation of coal blocks to private companies are given in Table M-II 1.10.

Table M-II 1.10: Allocation of Coal Blocks to Private Companies  

Sector/End use

Blocks

Geological Reserves(MT)

Power

20

2702

Iron and Steel

47

6703

Small and Isolated

2

9

Cement

3

232

Ultra Mega Power Project

7

2607

Total

79

12254

 
 Coal as Chemical Feed Stock  

Coal originally was utilized as fuel. Many of the petrochemicals now derived from petroleum and natural gas was referred as coal chemicals. With starting of coke oven plants it became source of organic and some inorganic chemicals. Coal tar from coke-oven plants continues to be a source of aromatics, naphthalene and other valuable aromatics like pyridine, picoline, quinolene. Before the coming of petrochemical production a large number of organic chemicals was produced from acetylene produced from calcium carbide route in which coal was a important feed. Various coal chemicals derived from coal is given in Figure M-II 1.1

China has come in a big way for production of chemicals from coal because of the huge coal reserves. With the rising cost of crude oil and dwindling crude oil reserves, coal has again received attention all over the world to utilize coal as an alternative source of chemical feedstock. Various routes for production of organic and inorganic chemicals from coal are

  • Coal carbonization and coal tar distillation
  • Coal gasification and use of synthesis gas as feed stock for ammonia production
  • Coal liquefaction by hydrogenation
  •  Coal to methanol technology
  • Coal to olefin technology  
  • Coal to plastic technology
  • Acetylene from calcium carbide made from lime and coal 

Coal Carbonization and Coal Tar Distillation 

 Coal carbonization and coal tar distillation is integral part of coke oven nits in steel plant for production of coke where large number of chemicals like ammonia, naphtha, aromatics etc are produced benzene, toluene, xylenes were earlier produced from coal tar distillation obtained from coke oven plant.

Coal Based Power Generation 

Coal Gasification and Use of Synthesis Gas as Feed Stock for Ammonia Production: Partial oxidation of coal is used for production of synthesis and ammonia. CO from partial oxidation is converted to CO2which is used for Urea manufacture. Synthesis gas CO+H2 is used as chemical feedstock for production of large number chemicals.

Coal Liquefaction by Hydrogenation 

Coal can be converted to naphtha by direct or indirect liquefaction. Coal can be also converted into naphtha via FT process. 

Coal and Coal as Chemical Feedstock Chemical Engineering Notes | EduRev

 Figure M-II 1.1: Coal as Chemical Feed Stock

Coal to Methanol Technology The process involves the production of synthesis gas from coal via partial oxidation followed by conversion of synthesis gas to methanol 

Coal to Olefin Technology Methanol can be converted to dimethyl ether, which can be used as a gasoline blend or converted to olefin through olefin synthesis reactions. 

Coal to Plastic Technology

Olefin produced from the coal route can be use for the manufacture of plastic. Coal gasification and production of fuel from FT process getting significant attention. Coal gasification and production of synthesis gas is now considered to be a major potential on purpose source of commodity petrochemicals. The cost of coal and higher cost of chemicals derived from coal has been major constraint in its utilization as a substitute for petroleum and natural gas. 

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