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
Coal in other countries
As high as 1.8%
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
Non- coking coal
Table M-II 1.4: Distribution of Coal Resources (million tones)
Name of sector
Captive Power Plants Including Cement CPPs
Sponge Iron Units
Table M-II 1.7: Status of CBM Blocks
Under round I
Under round II
Under round III
Area Awarded (sq. km)
Total CBM resources (BCM)
CBM Wells Drilled
Expected Production Potential(MMSCMD)
Approved Gas Sale Price($/MMBTU)
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
Peat is the precursor of coal formed
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 coals are black coloured and are more homogeneous in appearance and their properties range from lignite to that bituminous coal.
Bituminous coal is usually black, with higher carbon content and calorific value
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 is the highest rank and is difficult to ignite
China (Long Kou)
Calorific Value, kcal/kg
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
Iron and Steel
Small and Isolated
Ultra Mega Power Project
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 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.
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.