There are four main types of coal defined by their carbon content and heat value: anthracite, bituminous, subbituminous, and lignite. Coal is extracted through surface mining methods like strip mining, open-pit mining, and mountaintop removal mining, or through underground mining. After mining, coal is shipped by train or barge to power plants where it is pulverized and burned to produce electricity. Thermal decomposition of coal is a complex process that occurs in stages as temperature increases and involves the evolution of volatile matter and gases through physical and chemical changes to the coal substance.

2. Types of coal
• 4 Main Types of Coal
– Anthracite
• Carbon content between 86 and 98 percent. Heat value of about 15,000
BTUs/lb.
– Bituminous
• Carbon content between 45 and 86 percent. Heat value of 10,500 to 15,500
BTUs/lb.
– Subbituminous
• Carbon content between 35 and 45 percent. Heat value of 8,300 to 13,000
BTUs/lb.
– Lignite
• Carbon content between 25 and 35 percent. Heat value of 4,000 to 8,300
BTUs/lb.

3. How do we get coal out of the ground?
• Surface Mining:
– Typically occurs at depths above 180 ft.
– Most common form in Wyoming
• Underground Mining
– Typically occurs at depths below 300 ft.
– Accounts for 60% of world coal production

4. Surface mining
• 4 Main Types of Surface Mining
– Strip Mining
• Removal of large strips of overlying rock and soil to reveal coal.
– Open-Pit Mining
• Removal of rock and soil creating a vast pit where coal can be
extracted.
– Mountaintop Removal Mining
• Removal of mountain tops with explosives. Land made flat after
reclamation.
– Highwall Mining
• A continuous miner cuts holes horizontally into the coal formation.

5. Where does the coal go after it leaves
the mine?
• The coal is shipped by train or barge to its
destination.
• The coal may be refined before shipping
– Washing with water or a chemical bath to remove some impurities
• When the coal arrives at the power plant, it is
pulverized into a heavy powder that is suitable
for burning.

6. How is coal used at a power plant?

7. How is electricity Measured?
• Electricity is measured in units of power.
• The basic unit of power is the watt (W)
• W = J/s = (N x m)/s = (kg x m2)/s3
• Most power plants produce electricity in the
scale of megawatts (MW)

8. Power Plants Near Lander
• Beaver Creek Gas Plant
– Power generation – 5 MW
• Boysen Power Plant
– Power generation – 15 MW
• Pilot Butte Power Plant
– Power Generation – 1.6 MW
• The average household in Wyoming consumes
896 kWh. These 3 plants combined generate
enough electricity to run 17,360 homes

9. What is nanotechnology?
• The study of manipulating matter on an atomic or molecular
scale.
• Deals in the size range of 1 to 100 nanometers (nm).
• Applications in many fields such as energy production,
medicine, biomaterials, and electronics.

10. Coal Utilization
• Utilization of coal is referred to as the utilization of the organic constituents in the
coal.
• Conventionally, coal is used as the primary energy source through direct
combustion.
• The statistics data shows that nearly 47 percent of global electrical power plants
use coal as fuel.
• Another aspect in coal utilization is carbonization of coal to produce cokes.
• The coke production amount is 389 million tons in 1995. Cokes are mainly used in
metallurgical industry.
• In order to reduce production costs, many countries have set up jumbo coke-
ovens.
• But in recent years people have been interested in the development of coal
conversion technologies, including coal gasification and coal liquefaction, by which
coal will be converted into clean fluid fuels as the secondary energy source.
• Fluid fuels (gaseous or liquid fuels) are convenient not only for shipping but also
for utilization.

11. Coke
• Coke is what remains when the impurities in
coal, such as coal-tar and coal-gas, are
removed by high temperatures in an oxygen-
free furnace. The absence of oxygen during
the process prevents the coal from burning.
Unlike coal, coke can be burned with little or
no smoke.

12. Coal Utilization
• What is more attractive is that the utilization of fluid fuels can
effectively reduce environmental pollution.
• At present, there are several dozen technological processes, which
have been developed or are under development.
• Some of these can be commercialized in the near future.
• Apart from the utilization of coal as energy-source, through
carbonization, gasification or liquefaction, some chemicals can be
obtained.
• Therefore, coal is an important feedstock source for the organic
chemical industry.
• For example, synthesis gas, a mixture of CO and H2, produced by
coal gasification, is a feedstock for the synthesis of methane that is
used to produce a variety of chemicals.

13. Coal Utilization
• A comprehensive utilization of coal can be realized by
adoption of combined technological processes in
different industries. These combinations are:
• Coal mining—Electricity generation—Construction
material—Chemical Industry
• Coal mining—Electricity generation—Town Gas—
Chemical Industry
• Steel Industry—Coke Manufacture—Chemical
Industry—Gas—Construction
• Material
• Coke manufactures—Gas—Chemical Industry

14. • The adoption of combination of processes is
another approach to comprehensive
utilization of coal.
• The combinations can be:
– Carbonization—Gasification—Liquefaction
– Thermal pyrolysis—Gasification—Electricity
generation
– Gasification—Synthesis

15. Coal Combustion and Combustion
Products
• 2.1 Fundamentals of Coal Combustion
• Coal combustion is an old and most extensively employed method
in the utilization of coal; it can generally be classified as either fixed
bed combustion and fluidized bed combustion.
• The final products from combustion mainly are CO2 and H2O, with
some amount of pollutants such as SO2, NOx, and particles. For the
reduction in SO2 emission, coal with a low sulfur content is
preferred in the combustion.
• If it is carried out in a cycle fluidized bed combustion, the relatively
low temperatures can decrease the amount of NOx formed during
combustion. But for the coal containing high sulfur content,
removal of SO2 is usually carried out in the post-combustion unit,
i.e. waste gas effluent treatment.

16. The Effect of Coal Rank on
Combustion
• Coal rank, the degree of coalification, determines the heat
value, reactivity, and major character in combustion.
• In general, coals of low coal rank, such as lignite and
bituminous coals with high volatility, are more reactive but
have lower heat value than the coals with high coal rank,
such as anthracite and bituminous coals with low volatility.
• Anthracite is obviously more difficult to burn than
bituminous coals.
• Coals desirable for combustion are expected to have low
content of moisture and ash with high slagging
temperatures, possess high reactivity and to be easily
crushed.

17. Mechanisms of Combustion
• The exact mechanism of coal combustion is still uncertain and it is difficult to
clarify.
• It is, anyhow, quite certain that combustion is a process of degradation of carbon,
i.e. when coal is heated, moisture and the volatile matter will first come off,
meanwhile the water gas shift reaction (CO2 + H2O → CO + H2), produces CO and
H2.
• The gas combines together with the volatile matter at the start to burn over the
coal particles.
• A simple model in describing the combustion process explains that de-
volatilization is the first step, followed by ignition of the volatility; the fast
combustion causes the ignition of coal particles, thus, combustion starts.
• It is understandable, in practice, that coal has already started to burn before de-
volatilization becomes complete, and in turn, devolatilization is accelerated, the
time needed to complete de-volatilization reduces.
• Once the combustion starts, it can be visualized that hydrocarbons surrounding
the coal particle are burning as they diffuse.
• On the other hand, oxygen proceeds to diffuse into the coal particles and is
absorbed on the inter-surface of the coal.
• The complicated intermediate products are formed; the gas product desorbs and
through diffusion out of carbon particles, finally returns to the bulk gas flow.

18. • dioxide and water respectively, and so, the chemical energy stored in coal is
converted to heat energy. In combustion, many reactions can proceed
simultaneously.
• They are, for example, parallel reactions, consecutive reactions, and reversible
reactions, which are related to the equilibrium of the system.
• Furthermore, the coal particle will be subject to the change in structure, both
chemically and physically.
• The residue from combustion is clinker, mainly containing SiO2, Al2O3, Fe2O3,
CaO, and MgO.
• The softening point of clinkers depends on its composition. Low softening point
means the easy occurrence of slagging. Fe2O3, as a mineral matter in coal, under
the reduction atmosphere of CO and H2, can be reduced to FeO, consequently, in
the coal fuel layer, slagging readily occurs, boiler thus is fouled.
• Another factor related to slagging is the content of alkaline metals.
• For example, the clinker is easy to remove if the content is below 5 percent by
weight; otherwise, the removal of clinkers becomes difficult.
• When coal is burning at high temperatures, the reaction favors the formation of
CO, from consideration of chemical equilibrium; excessive air causes CO to convert
into CO2.
• But in practical operation, residence time of coal particles is so short and the heat
transfer rate is so fast that the process in such a reaction temperature is a non
equilibrium one.
• The excessive amount of air needed is determined by a lot of factors, such as the
highest temperature of flame, moisture content in coal, the air temperature and
the complete combustion of fuel. As a rule of practice, the excessive amount of air
ranges from 15 to 20 percent.

19. Thermal Decomposition Reactions
• Coal, when heated in the condition of isolation from air, will decompose to produce gas, coal tar,
and char.
• This process is termed pyrolysis, or thermal decomposition of coal. Based on very high
temperatures, this process can fall into one of the three types: low temperature destructive
distillation from 500–600°C, medium temperature distillation from 700–900°C, high temperature
distillation (conventionally termed as carbonization) from 900–1100°C.
• Flash pyrolysis of coal is a promising process for producing synthetic natural gas, liquid fuels, and
other chemicals.
• This offers a third method of coal conversion in addition to gasification and liquefaction.
• Studies of flash de-volatilization are also important for understanding the mechanism of coal
thermal conversion, such as combustion and gasification, since it is the preliminary step in these
thermal conversion processes.
• Despite extensive research, there are generally contradictory results reported, and various views
are offered as to the best approach to take, to express the kinetics of this process owing to
complicated coal structure and different experiment techniques.
• The phenomenological models have been successful in correlating experimental data and are
relatively easy to handle.
• Unfortunately, the kinetic parameters of those models vary with coal type and heating conditions.
The chemical reactions of coal are very complex in thermal decomposition processes. Main
chemical reactions of thermal decomposition are as follows:

20. Fundamentals of Thermal
Decomposition of Coal• There arise physical and chemical changes when coal is heated to the temperature at which thermal decomposition occurs. However, some changes may be noted before the
• onset of what is often referred to as the “thermal decomposition proper,” and may
• manifest themselves as the formation of low molecular weight species. During the
• thermal decomposition of coal a substantial weight loss occurs because of the evolution
• of volatile matter. The amount and composition of volatile products depends on coal
• type, coal size, and the conditions prevailing in the apparatus. After the decomposition a
• series of consecutive and parallel reactions, which involve both the residual solid char
• and the gaseous products of the primary decomposition stage, take place.
• 2.1 The Patterns of Thermal Decomposition
• Thermogravimetric measurements that follow the progress of decomposition by
• recording weight losses that accompany coal pyrolysis suggest that there is little change
• below a temperature Td. The temperature Td increases with coal rank from about 620K
• to 670K and that substantial breakdown of the coal substance occurs only beyond that
• temperature. Td is therefore commonly identified as the decomposition temperature of
• coal. It is more appropriate to associate Td with the onset of active thermal
• decomposition (which causes weight loss), and to view the overall decomposition
• process as composed of three successive stages, viz.
• (a) Limited thermal alteration of the original molecular structures (mostly by
• condensation reactions) at temperatures below Td;
• (b) Active decomposition at the temperature between Td and about 820K, leading to
• generation and discharge of bulk of volatile matter, primary in the form of tars and
• light oils;
• (c) Secondary degasification, resulting in formation and evolution of a variety of
• hydrocarbon gases, elemental hydrogen and oxides of carbon over an extended
• temperature range beyond 820 K.
• When coal is heated to temperatures below 473 K, water and adsorbed gas such as
• methane and carbon dioxide on the inner surface of the coal lump, will appear as
• products of the thermal treatment. On other hand, a lower rank coal such as lignite
• containing many carboxylic functional groups as part of the coal structure, will evolve
• carbon dioxide by thermal decarboxylation: Rh-COOH = R-H + CO2
• Such changes are usually noted to occur at temperature just in excess of 373 K. More
• than 50 percent of the carboxylic functional groups can lose carbon dioxide over the
• temperature range from 373K to 473K.
• As the temperature of the thermal treatment rises to the range of 473K to 643K, coal
• loses a variety of lower molecular weight organic species (especially aliphatic
• compounds). Some of the lower molecular aromatic species and sulfur compounds may
• also be obtained. At temperatures above 643K, methane, polynuclear aromatics, phenol,
• and nitrogen compounds are produced. With respect to the volatile matter produced by
• the thermal decomposition of coal, rapid thermal decomposition enables the yields of