coal mining conversion use

7/29/2019 Coal Mining Conversion Use

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COAL AVAILABILITY & ITS UTILIZATION IN INDIA

What is coal? Where in India are coal and lignite available? Give the utilization pattern

for coal in India? List the coal conversion processes. Name the products obtained.

Coal is a product of decay of plant debris formed over geological time scale,under sedimentary sequences in a stratified form. It is classified into peat, lignite,

bituminous and anthracite -based on the degree of advance in coalification process.

Besides the organic content it contains mineral matter in its matrix. It is an Organic

rock.

Approximate chemical formula of coal is (C3H4)nIt is a hydrogen deficient solid hydrocarbon probably consisting of many interlocked

aromatic rings.

Reserves ofCoal in India were estimated by the Geological Survey of India in1998-99

approximately as 79 billion tonnes and Lignite reserves as 29.36 billion

tonnes.

States having coal deposits in India: Bihar (including Jharkhand), Bengal,

Madhya Pradesh (including Chattisgarh), Maharashtra, Andhra and Orissa.

LIGNITE: Reserve available in Tamil Nadu (1999) = 26 billion tones,

Rest of the reserves is in Rajasthan and Gujarat.

Coal production in India: 1983-84: 138 million tonnes

2000-01: 300 ,, ,,

Lignite production in : 1997-98:23 million tonnes

Utilization Pattern for coal in India:Power Generation,

To manufacture coke and in Steel mills,Cement manufacture, Textile and Railways

Smaller use: As household fuel

Coal Conversion Processes & products:

1. Coke Manufacture (Coke, Coaltar, Gas)

2. Coal Tar Distillation (aromatics,pitch)

3. Coal Gasification (Synthesisgas, Fuel gas)

4. Liquefaction of Coal(hydrocarbons) F.T.

5. Coal Hydrogenation (liquidhydrocarbons)

6. Coal combustion (Steam forpower)

Refer: S. SARCAR, FUELS AND COMBUSTION, 2 ED. 1990, CH 3 & CH 4

Ch 3: Coal as solid fuel, ranking, origin, composition, analysis, action of heat, oxidationand hydrogenation of coal.

Ch 4: Coal preparation, storage, carbonization, briquetting, gasification and liquefaction.


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CHEMICALS FROM COKE OVEN DISTILLATE

When coal is heated in the absence of oxygen to a temperature of about 1000oC, coke

forms together with liquid and gaseous decomposition products. It is this distillate, also

called coal tar, which was a source of aromatics and many other chemicals for the early

chemical industry.

A typical coking operation produces 80% coke by weight, 12% coke oven gas, 3% tarand 1% light oil consisting of crude benzene, toluene and xylenes.

CHEMICALS: BENZENE, TOLUENE, XYLENES, INDENE, COUMARONE,

PHENOLS, CRESOLS, PYRIDINES, ANTHRACENE, PHENANTHRENE,

CARBAZOLE, and PITCH (60% 0F TAR).

FISCHER TROPSCH REACTION:

COAL SYNTHESIS GASMIXTURES OF ALKANES

(IRON, NICKEL, COBALT

CATALYST, 150-300oC)

This process is not economical now as a route from coal to hydrocarbons.COAL GASIFICATION PROCESSES:

Process Main characteristics

Texaco Pressurised entrained bed process involving the use of a watery slurry

of powdered coal. Less suited for lignite. Product gas low in methane,

and tar free. Low H2/CO ratio (~ 0.7).

Lurgi Pressurized moving bed process suitable for noncoking, granular coal.

Relatively high steam consumption. Product gas rich in methane,residual steam, and CO2 and contains tar, H2/CO ratio (~ 0.5)

Koppers-Totzek Atmospheric entrained bed process Powdered coal, high oxygen &

steam used. Suitable for Syn-gas for ammonia/methanol.Winkler Suitable for lignite, fluid bed process 800-1000 o C Atm. pressure.

High temp.Winkler

Pressurized stationary fluid bed process for lignite. Higher gasificationrates, better conversion than Winkler.

British Gas-

Lurgi slagging

gasifier

Pressurized moving bed process- non-coking granular coal based. Less

steam consumption, smaller reaction volumes and pure product gas

than via Lurgi process.

Shell Pressurized entrained bedDry coal powder, lignite suitable. High

thermal efficiency, pure product gas like that of Koppers- Totzek

COAL HYDROGENATION:

In the F-T process, the hydrogen required to convert coal to aliphatic hydrocarbons is

ultimately derived from water. In Bergius process, coal, lignite or coal tar were

hydrogenated over an iron catalyst at 450o

C and 700 bar. Less drastic conditions weresufficient for coal hydrogenation when a solvent tetralin was used to hydrogenate the coal

in a liquid- solid phase process at about 200o

C and 65 bar.

Reference: Drydens OUTLINE OF CHEMICAL TECHNOLOGY, 3rd

Edition,1997, Ch.Coal & Coal Chemicals, pp 370-378.


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COAL UTILIZATION

What is coal and where in India is it available? Give the utilization pattern for coal in

India? List the coal conversion processes. Name the products obtained.

Approximate chemical formula of coal is (C3H4)nIt is a hydrogen deficient solid hydrocarbon probably consisting of many interlockedaromatic rings.

Reserves ofCoal in India were estimated by the Geological Survey of India in1998-

99 approximately as 79 billion tonnesandLignitereserves as 29.36

billion tonnes.

States having coal deposits in India: Bihar (including Jharkhand), Bengal,

Madhya Pradesh (including Chattisgarh), Maharashtra, Andhra and Orissa.

Lignite: Reserve available in Tamil Nadu (1999) = 26 billion tones,

Rest of the reserves is in Rajasthan and Gujarat.

Coal production in India: 1983-84: 138 million tonnes

2000-01: 300 ,, ,,Lignite production in : 1997-98:23 million tonnes

Utilization Pattern for coal in India:Power Generation,

To manufacture coke and in Steel mills,

Cement manufacture and RailwaysSmaller use: As household fuel

Coal Conversion Processes & products:

1. Coke Manufacture (Coke, Coal tar, Gas) 2. Coal Tar Distillation (aromatics, pitch)

3. Coal Gasification (Synthesis gas, Fuel gas) 4. Liquefaction of Coal (hydrocarbons)

5. Coal Hydrogenation (liquid hydrocarbons) 6. Coal combustion (Steam for power)

Refer: S. SARCAR, FUELS AND COMBUSTION, 2 ED. 1990, CH 3 & CH 4

Ch 3: Coal as solid fuel, ranking, origin, composition, analysis, action of heat,oxidation and hydrogenation of coal.

Ch 4: Coal preparation, storage, carbonization, briquetting, gasification andliquefaction.


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(Images 4 and 5)
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(Image 6)

(Image 7)

(Image 8 and 9)Explosives used inmining

(Image 10)Workers using a Continuous Miner
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(Image 11)(Image 12)Chris5of5.html

Workers over looking a cutting machine as it loosens coal from a "long wall"
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Technologies for Energy Conversion

There are many different ways of mining, but they are separated into two categories,

surface mining and underground mining. Surface mining is used when the coal is located

close to the surface or on hillsides.

Surface Mining

This method pretty much involves removing the earth and rock that are covering the coal

with heavy earth-moving equipment, removing the coal then replacing the excavated soiland reestablishing vegetation and plants.(webpage 6) The excavation usually on a

stepped or benched, side slopes and can reach depths as low as 1500 ft. The advantages

of surface mining is that it recovers 90% of the coal to be mined. (Book 2)

Underground Mining(Webpage 4)

This method is used to extract coal that lies deep beneath the Earth's surface. The coal isreached by drilling two openings into the coal bed to transport workers and equipment

and to send coal to the surface. (images at top of page).

Underground mining is broken up to 3 main methods:

Conventional Mining: The older practice of using explosives to break up a coal seam

Continuous Mining: Uses a huge machine with a large rotating steel drum equipped withtungsten carbide teeth, and it scrapes coal from a coal seam at high speeds.

Long wall Mining: Uses a cutting machine with a large rotating steel drum that isdragged back and forth across a long wall or a seam of coal. The loosened coal then falls

onto a conveyer belt and is taken out of the mine to the surface.

Uses of Coal(webpage 7)

According to the World Coal Institute, coal has many uses such as transportation, steel

industry, domestic and agriculture uses and power generation. Most of the coal is being

used for generating electricity.
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1. Power Generation 62%

2. Domestic 5%

3. Steel Industry 16%

4.Non-Metallic Industry,

Cement5%

5. Other 2%

6.Commerce, public services,

transportation10%

Heavy Users of Coal around the World(1998)

Poland 86%

South

Africa90%

Australia 86%

China 81%

India 75%

CzechRepublic

74%

Greece 70%

Denmark 59%

USA 56%


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Steel Production(Website 8)

Around 67% of the steel that is produced world wide is made in a blast furnace where

coke is used. Iron occurs in nature in chemical compounds, ores, Fe2O3, hematite. Cokeis used to supply enough carbon as a reducing agent for the smelting of iron ore. Coal

was first used in the 17th century because of over timbering. Also, iron can dissolve andreact with H2S that is given off from coal. (Class notes)

Gasification(Class notes)

Gases are easier to handle, clean to burn and can be implemented into Natural Gas

Coal Gas: a good flue gas from the volatile matter of heated coal (H2, CH4).

Pros: Burns Clean, Cons: Low Yields, Produces Tars/Pollutants

Producer Gas: Low calorific fuel gas from incomplete coal combustion (CO)

Pros: Easy to produce, all coal goes to gaseous products and good for industrialprocesses

Water Gas: formed from reacting coal with water at high temperature yielding a gas

stream of H and CO

Pros: high calorific value Cons: Endothermic, takes a lot of energy
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Integrated Gasification Combined Cycle (IGCC)

Electric Power Generation

Coal based electric power generation (i.e., direct combustion of coal

in stoker fired and pulverised coal fired boilers) has historically been

the backbone of the electric utility industry and this technology is well

proven. But the technology has reached a plateau of maximum

efficiency with only marginal potential for further improvements due to

technical limitations.

In addition to this limitation on efficiencies, tightening of

environmental control requirements have resulted in substantial

increase in both capital and operating costs to reduce emissions from

conventional coalfired power plants and also in lowering plant

efficiency and reliability, on the otherhand coal gasification

technology has emerged as the most environmentally benign and

competitive way of coal utilisation. Thus it would be of enormous

benefit to the electric utility industry to find some practical means for

combining the high efficiency of combined cycle system with the

clean coal gasification-process for utilising coal which is a low cost

and abundantly available fossil fuel. This has led to the development

of IGCC Power system.IGCC is the technology designed to meet the higher efficiency and

stringent environmental regulations required in the 21st century.

IGCC systems have the potential to compete economically with

conventional coalfired steam plants and have lowest possible level of


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pollution. As environmental control requirements increase, the

economic advantages of IGCC would correspondingly increase.

Similarly with further developments in coal gasification and gas

turbine technologies taking place, the economic and performance

benefits of IGCC would increase significantly. The efficiency of IGCC

which is now around 40-45% is likely to increase to 55-60%. The

capital cost of large and mature technology IGCC plants and PC

plants with FGD are projected to be nearly same. IGCC is the most

economical system when compared to the conventional pulverised

coal fired plant for removal of sulfur and nitrogen. With high sulfur

coals the efficiency difference between the two plants is higher since

the auxiliary power consumption for the sulfur removal is up to 3% in

the flue gas desulfurisation (FGD) unit of coalfired plant and

negligible in the IGCC plant.

IGCC plants require less water than coal fired plant as approximately

60% of power is generated from gas turbine. IGCC plants also

require less land. IGCC systems are highly modular which enable

phased construction and higher plants availability up to 85% or about

7400 hours per year of plant operation [7] and economy at smaller

capacities of the order of 250 MW. Introduction of IGCC technology to

utilities can create new business opportunities in the co-production of

electricity with chemicals, liquid fuels etc.

As the global demand for coal increases, worldwide carbon emissions

will also increase. It is estimated that if all power producers were to

use the most efficient clean coal technologies, IGCC being one of

them, global carbon dioxide emissions could be cut by more than

half, compared with the levels that would be emitted by the existing


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power plant technologies, i.e. pulverised coalfired [8].

The expert group on IGCC technology appointed by Govt. of India

has prepared a Techno-Economic Feasibility Report (TEFR) in the

year 1991 comparing the operational performance and economics of

IGCC and PC based power generation for a 600 MW capacity plant

with 35% ash coal. According to the results of the study given in

Table 3 IGCC is more efficient, pollution is very less and capital and

generation costs are comparable with PC plant [7].

IGCC technology is now moving from drawing board to commercial

scale. A 250 MW IGCC plant of Tampa Electric Co. USA has

successfully completed one year of commercial operation. The

wabash project in USA of 262 MW IGCC plant began its commercial

operation in November 1995. Sierra pacific pinion pine IGCC project,

USA of 107 MW capacity is undergoing operation trials. A 250 MW

IGCC plant at Buggenum, Netherlands has entered its final

demonstration year. The capital cost of IGCC plant now is around

$2000/kW which is likely to come down to $1500/kW. The global

market for IGCC is expected to be 41 GW by 2004 [9].

3.4 Integrated Gasification Fuel Cell

Fuel cell is the most efficient and the least polluting system of power

generation. Out of the 3 fuel cell systems based on the type of

electrolyte used i.e. Phosphoric Acid Fuel Cell (PAFC) Molten

Carbonate Fuel Cell (MCFC) and Solid Oxide Fuel Cell (SOFC), the

latter two are suitable to utilise coal gas which resulted in the

development of Integrated Gasification Fuel Cell (IGFC) System.

PAFC is nearly commercial and the other two (MCFC and SOFC) are

at development stage.


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IGFC can attain efficiencies up to 60% and are cool enough to

prevent NOx formation. Sulfur and particulate present in the coal are

removed during the gasification process before feeding the fuel gas

to the fuel cell. A comparison between the emissions of a coalfired

conventional power plant and IGFC system is given in the table 4

which shows that fuel cell generates extremely clean power [10].

There are two major challenges with respect to commercialisation of

fuel cell: initial cost and reliable life. The two problems have to be

solved to improve the economics of fuel cell.

3.5 Other Technologies

In addition to IGCC, two other relevant technologies for power

generation are : Pressurised Fluidised Bed Combustion (PFBC) and

High Concentration Coal Water Slurry (HCCWS). The PFBC

technology is demonstrated in 80-100 MW scale abroad. The PFBC

is dependant on hot gas cleaning for the removal of particulate from

the flue gases or on a heavy duty gas turbine which can tolerate

particulate matter in the flue gases. Both hot gas cleanup and heavy

duty gas turbine are under development. IGCC also incorporates a

hot gas cleanup system which increases the overall efficiency, but

wet scrubbing by water can be employed in place of hot gas cleanup

with some loss in efficiency. Thus PFBC compared to IGCC is

constrained by availability of hot gas cleanup technology. Another

major disadvantage with PFBC is that more power is generated from

steam turbine which is less efficient compared to gas turbine.

Whereas in IGCC, more power is generated from the gas turbine and
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hence is more efficient. Continuous developments are taking place in

the gas turbine technology which could result in higher efficiencies in

IGCC beyond 50%. Such improvements in the steam turbine are

limited.

HCCWS consisting of 70% solids and 30% water is used for power

generation either through combustion or gasification route. High ash

content in the coal thermally penalises the conversion processes of

coal slurry resulting in lower and uneconomical efficiencies. Therefore

the coals have to be necessarily washed to bring down the ash

content to around 15% to improve the efficiency and economics. But

the cost of preparation of slurry itself depends upon the techno-

economics of washing which are at present unattractive for high ash

coals. Thus application of HCCWS technology to high ash coal

mainly depends on technoeconomics of washing the coal.

coal mining conversion use

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