coal prepration

1. COAL PREPARATION, CARBONIZATION,
LIQUEFACTION &
GASIFICATION
PREPARED BY:
SANJAY SHARMA (16-MRE-001)
AKHIL SHARMA (16-MRE-003)
SHAIVYA MANHAS (16- MRE-005
AMAN SHARMA (16-MRE-007)
OSHIN CHATTA (16-MRE-009)
VASUNDHRA GUPTA (16-MRE-011)
AFSHAN RASHID (16-MRE-013)

2. COAL PREPARATION

3. What Is Coal Preparation?
• Coal preparation is the removal of undesirable material (ash,
Sulphur, moisture)from the Run-of-Mine (ROM) coal by
employing separation processes which are able to differentiate
between the physical and surface properties of the coal and the
impurities.
• Coal preparation is also called as Washing, Cleaning, Processing
of Coal.
• Coal processing technologies play an important role in the
electrical power supply chain by providing high-quality fuel for
coal-fired utilities and industrial boilers.

4. cont…
• The upgrading and cleaning of the coal is achieved by
using following separation process :
i) Low cost separation.
ii) Solid-solid separation.
iii) Solid-liquid separation
• The separation process removes waste rocks and water
from the mined coal.

5. Why is Coal Preparation Needed?
• Coal preparation is required because freshly mined coals contains:
i) Heterogeneous mixture of organic (carbonaceous) matter.
ii) Inorganic (mineral) matter.
• These impurities reduce coal heating value, leave behind an
undesirable ash residue.
• Increase the cost of transporting of coal to market.
• Reduces heating value and can lead to handling and freezing
issues for consumers.

6. Coal Separation Mechanism
• The coal separation mechanism includes:
 SCREENING.
 CLASSIFICATION.
 DENSE MEDIUM SEPRATION.
 GRAVITY SEPRATION..
 CENTRIFUGATION.
 FILTERATION.
 THICKENNG.

7. Coal Processing Operations
Particle Sizing:
• Run-of-mine coal produced by mechanized mining
operations can contain particles as small as fine powder
and as large as several hundred millimeters.
• There are different type of sizing equipments used to
produce desired size of coal which are as:
i)Vibrating screens
ii)Cyclones

8. Vibrating Screens
• Screening is used to separate different
sizes of crushed coal. In this process
coarse and fine coal is separated so to
accommodate for specific markets and
industrial usage.
• Screens are mechanical sizing devices
that use a mesh to sort particles into
fine (particles that pass through the
screen openings) and coarse (particles
that are retained on the screen surface).
• Vibrating screens, use a shaking rotating
mechanism to segregate particles and to
move material along the screen surface.
• High-frequency screens vibrate very
rapidly to enhance the passage of fine
particles and are normally used for
dewatering fine coal or rock.

9. Cyclones
• A cyclone is a conical vessel in which coal along with finely
ground magnetite is pumped tangentially to a tapered inlet and
short cylindrical section at a predetermined flow rate and pressure
followed by a conical section where the separation takes place.
• The higher specific gravity fractions being subject to greater
centrifugal forces pull away from the central core and descend
downwards towards the apex along the wall of cyclone body and
pass out as rejects.
• The lighter particles are caught in an upward stream and pass out
as clean coal through the cyclone overflow outlet.

10. Cont…

11. cont..
• Cyclones are used where conventional screening or sieving
becomes impractical.
• Classifying cyclones are commonly applied to size (cut) at 0.10 to
0.15 mm.
• And represent the only practical option for sizing ultrafine particles
(at a cut of 0.045 mm).
• This sizing device exploits differences in the settling rates of
particles of different size (i.e., smaller particles settle slower than
larger particles).

12. Solid - Solid Separation
The separation of valuable carbonaceous material from waste rock is
typically accomplished using low-cost processes that exploit
differences in physical properties that vary with mineral content.
The common properties that are used to separate coal and rock are
•Size
•Density
•Wet ability

13. What is Dense Medium Separation?
• Dense medium separation or heavy medium separation is used
in coal preparation to produce a commercially graded end
product ,clean coal being separated from heavier shale or high
ash coal.
• A popular process for cleaning coarse coal which is having a
size greater than 12.5 mm.

14. PRINCIPLE
It is the simplest of all gravity processes and has long
been a standard laboratory method for separating
minerals of different specific gravity.
Heavy coal particles of suitable density are used ,so
that those minerals lighter than the heavy particles will
float, while those denser will sink to bottom .

15. Water-Based Density Separators
• Water-Based Density Separators is a variety of density-based separators
available for separating coal and rock in the particle size range between 0.2 and
1.0 mm.
• The most common methods include water-only cyclones and spirals.
• A water-only cyclone (WOC) is similar to a classifying cyclone, but typically
has a broad wide angled conical bottom .
• Separation of coal and rock occurs because of the formation of dense
suspension created by the natural fines already in the feed slurry.

16. • A spiral consists of a corkscrew-shaped device that sorts coal from rock by
selective segregation that occurs as particles move in the flowing film
along the helical trough.
• Because of the low unit capacity (two to four tons per hour), spirals are
usually arranged in groups that are fed by an overhead distributor. WOCs
and spirals are often employed in two stages or in combination with other
water-based separators to improve performance.
Cont…

17. Banks of spirals used to separate coal
from rocks

18. Solid-Liquid Separation
• Solid-liquid separators are used downstream of coal cleaning processes to
remove unwanted surface moisture that lowers heating value, leads to
handling/freezing problems, and increases transportation costs.
• Several different types of mechanical dewatering methods are required,
depending on the size of particles to be treated.
• The removal of water from the surfaces of coarser (> 5 mm) coal is
predominantly carried out using simple screens.
• Fine particles, which have a higher surface area and tend to have
correspondingly higher moisture content, are typically dewatered using
centrifugal methods or filtration system.

19. Centrifugal Dewatering
• Centrifugal dewatering systems, which use centrifugal force to pull water
away from the surfaces of coal particles, operate in much the same fashion
as the spin cycle in a home washing machine.
• For coarse particles, centrifugal dryers that use either a rotating scroll or
vibratory action to transport solids are commonly used.
• For fine particles (< 1 mm), another popular design, known as a screen-
bowl centrifuge, may be used.
• These units are capable of providing low moisture products, although some
ultrafine solids can be lost as waste effluent with the bulk of the water.

20. Filtration Dewatering
• Filtration processes may be used to dewater fine coal in cases where high
coal recovery is desirable.
• Filtration involves the entrapment of fine solids as a cake against a porous
filtering medium.
• Traditionally, flotation concentrates have been dewatered using some form
of vacuum filtration.
• These units are capable of maintaining high coal recoveries (greater than 97
percent) while generating product moisture contents of approximately 20 to
30 percent.
• The most popular type of vacuum filter used in the United States is the disc
filter.

21. CARBONISATION

22. Carbonization
• The process of converting coal into coke is called as
carbonization of coal.
• When a coking coal is heated in the absence of air, the
porous , hard and strong residue left is called coke.
• Coke making process is multistep complex process and
variety of solid liquids and gaseous products are produced
which contain many valuable products.

23. Contd…
• Coke is white , lustrous, dense porous mass.
Depending on the behavior of coal , when heated in
the absence of air, the coal is classified into:
1. Non-coking coal which undergoes practically no
fusing effect and also called as free burning coal.
2. Coking coal which gives porous , hard and strong
residue after heating in the absence of air. The
residue is used for metallurgical purposes and is
known as coke.

25. Types of coal
• Depending upon the extent of carbonization , coal can
be classified into four types as follows:
Classification of coal
• Peat 11%
• Lignite 38% (soft coal/ brown coal)
• Bituminous 65% (household coal)
• Anthracite 90% (hard coal)

27. Carbonization at various
temperature
• Low temperature carbonization is used to produce liquid fuels
while high temperature carbonization is used to produce
gaseous products.
• Low temperature carbonization (450-7500 C): In low
temperature carbonization quantity of gaseous product is less
while liquid products are large.
• High temperature carbonization (above 9000 C): In high
temperature carbonization, the yield of gaseous product is more
than liquid products with production of tar relatively low.

28. LIQUEFaCTION

29. Conversion of Coal to Liquid
(CTL) Fuels
• Several very old processes… since WWII
• Same general theme: increase H/C ratio
• Can make a wide variety of hydrocarbon products (e.g.
synthetic crude or synfuel)
• Two basic methods: direct and indirect

30. Advantages
• CTL Improves national and economic security
• Lessens dependence on foreign oil
• Uses domestic resources and produces more jobs for
Americans
• Provides environmental benefits
- Cleaner fuels that reduce NOx and particulate emissions
- Enables use of higher efficiency engines
• Is capable of capturing CO2 emissions
• Provides geographic diversity as energy source

31. Coal Liquefaction
• Very expensive
• Liquefaction attractive for transportation fuel
• Indirect liquefaction commercially proven (>50 years)
• Acid gas removal by amines (CO2, H2S)
• S removal by Claus Process
H2S + O2 = H2O + SO2
H2S + SO2 = S + H2O

32. Direct Liquefaction Features
• Low transportation cost
• Less chemical transformation required
• Higher efficiency than high Btu gas production
• Easy to store
• Less water required for manufacture
However, processing slurries at high temperature and pressure
presents difficulties with equipment life and solid/liquid separation
(still not commercial)

33. SASOL in South Africa
• South Africa’s SASOL Co. developed a commercial coal
liquids industry (fuel plus chemicals)
• The plant produces about 150,000 barrels daily at its second
plant
Indirect Coal liquefaction is proven technology

34. Conversion Approaches
1. Direct Liquefaction:
• Dissolves coal in a solvent at elevated temperature and
pressure
• Combined with hydrogen gas and a catalyst
2. Indirect Liquefaction:
• Involves first gasifying coal, followed by reacting carbon
monoxide and hydrogen together
nCO + (2n+1)H2 = CnH2n+2 + nH2O

35.  Adds hydrogen to break down the
coal
 Dissolves in a solvent followed by
hydrocracking
 Operates at 450 C and 170 bars
 Light products are distilled
 Medium and heavy distillates
obtained from vacuum distillation
 Liquid yields of 70% of the dry
weight of coal feed
 Further upgrade is needed for use
as transportation fuels
 Complete breakdown of coal with
steam and oxygen
 Sulfur is removed from the syngas
 Syngas reacted over catalyst at
300 C and 20 bars
 Produces a lighter suite of
products; high quality gasoline and
petrochemicals
 Oxygenated chemicals
Comparison of Processes
Direct
Liquefaction
Indirect
Liquefaction

36. Indirect Liquefaction
• Fischer-Tropsch Indirect Liquefaction Process
- Yields high quality transportation fuels plus other
products

37. • Coal-based liquid fuel becomes viable when the per-barrel price of oil is
expected to exceed the $70-100 range for 20+ years.
• CTL has high front-end capital cost
- A 50,000 barrel-a-day plant would cost over $3 billion to construct.
• The product refinement process is three to four times more expensive than
refining an equivalent amount of oil.
• The cost of sequestering the captured CO2 would increase the price of the end
product by $10-20 a barrel.
• The imposition of a carbon cap and trade policy would also raise the cost of
fuel produced with CTL technology
CTL Costs

38. Liquids Fuels Summary….
• Proven technologies
• All processes require adding hydrogen
• All processes remove sulfur and ash
• Product include liquid, gas, and combustible solid(char)
• Several long-standing commercial processes (e.g., S. Africa -
SASOL)
• So far no large-scale use without government support

39. Coal to Liquids Summary….
• Good promise because of very large coal deposits in the world
• Numerous processes that can generate a wide variety of
products
• Environmental issues include some hazardous wastes and
byproducts
• Does not yet effectively compete with natural gas or oil
production … requires some form of subsidy

40. COAL GASIFICATION

41. Introduction :--
 Gasification – conversion of carbonaceous fuel to gaseous product.
 Dominant chemical process – partial oxidation.
 Coal gasification – process for producing syngas.
PRE –
TREATMENT OF
COAL
GASIFICATION GAS CLEANING
3 steps of coal gasification process :--

42. SELECTION OF SUITBLE COAL FOR
GASIFICATION
 Lignite, bituminous, sub-bituminous, anthracite – different
applications
Factors Recommended specification
Coal rank Sub-bituminous, bituminous
Ash content <(8-12)% & max. 25%
Volatile content No limit
Coal reactivity Moderate - high
Ash viscosity < 250 poise at operating temp.
 4 ranks of coal – based on the carbon content

43. Gasification process
PRE –
TREATMENT OF
COAL
 Gasification - coal - properly preheated
 High moisture coal - drying required
 Caking coals - partial oxidation required
 Fluid or entrained bed gasifier - crushing &
pulverizing required
 Fixed bed gasifier - briqueting of fines coal
particle required

44. Gasification process
GASIFICATION
 Pretreated coal – charged in gasification reactor
 Temp. :- 800-1900 °C & Pressure :- 10 MPa
 Combustion reaction :-
C + 0.5O2 CO
C + O2 CO2
 Gasification reaction :-
C + CO2 2CO
C + H2O CO + H2
 Water – gas shift reaction :-
CO + H2O CO2 + H2
 Methanol production :-
CO2 + 3H2 CH3OH + H2O

45. Gasification process
 Low heat content product gas – coal
burning - < stoichiometric quantity of air
with or without steam
 Medium heat content product gas –
oxygen replaced by air
 Water-gas shift conversion – additional
hydrogen
 Ash – removed in dry condition
 Main product – synthesis gas – 1:2 =
CO : H2

46. Gasification process
GAS CLEANING
 Gas products – CO, CO2, H2, CH4, H2S, other organic
vapour, etc. - Impurities – particulate matters - Gas
product purification – prior to combustion –removal
of impurities
 Tar & oil removal – quenching method
 Ammonia removal – scrubbing process - either
aqueous or organic liquid
 Acid gases removal – solvent treatment technology
 Water-gas shift conversion process – CO2 removal -
passing through absorber – carbon capture
technology

47. Different gasification technique
 Updraft moving bed gasifier – coal from the top & oxidants
from the bottom
Downdraft moving bed gasifier – coal from the top & air from
the side
Entrained flow gasifier – reaction between fined coal particles &
oxygen & steam
Fluidized bed gasifier - for low rank coals like lignite

48. Underground coal gasification
 Process – under ground – within the coal
seam - 2 vertical walls drilled to the coal
seam – horizontally linked – combustion
process & syngas formation – same as
above ground gasification
 Economic benefits - no need to mine the
coal - no need for coal handling - no
need to prepare the coal to be fed into a
reactor
 Environmental benefits - minimum land
use - coal seams below the fresh
drinking water supplies - no landfill
disposal required for ash or slag

49. Applications
Synthesis gas production – electricity generation, transportation
fuels (e.g. gasoline & diesel)
Methanol production
Hydrogen formation – ammonia, powering hydrogen economy,
upgrading fossil fuels
Ammonia - fertilizer
Hydrocarbon – methane, natural gas from coal gasification –
liquefied natural gas – can replaced gasoline & diesel

50. Current Scenario
INDIA OTHER
 Rising population – increasing
energy demand – CO2 emitted from
gasification – released in atmosphere
– green house effect - research on
carbon capture technique – capture &
compression – transportation –
storage
 China - Recent development in
converting coal to clean fuels –
advance domestic gasification
technology – energy efficient –
Fischer – tropsch synthesis combined
– moving bed gasification – high
efficiency
 USA - Transport Integrated
Gasification (TRIG) technology – low
rank coals can also used – power
generation