ESE-800

Clean Coal Technologies

Part2:Clean Coal Gasification

Lecture-1
Coal Gasification Basics/Types

Presented By
Shahid Hussain Ansari
Assistant Professor
Centre for Energy Systems (CES)
National University of Sciences & Technology (NUST)
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 Clean Coal Technologies (CCTs)

 A new generation of coal-burning power plants with energy

processes that reduce air emissions and other pollutants

 Clean Coal Technologies (CCTs) are defined as ‘technologies

designed to enhance:
Efficiency of conversion
Environmental acceptability of coal extraction, preparation
and use
The key environmental challenges facing the coal industry are related to:
– Coal Mining
– Particulate emission
– Acid rain
– Ozone and Waste disposal
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 Components of CCTs

 Crushed coal is mixed with a liquid that allows the impurities to

separate and settle

 Wet Scrubbers: remove SO2 which helps to reduce acid rain

 Low NOx Burners: reduces nitrogen oxides

 Electrostatic Precipitators: removes particles that aggravate

asthma and other respiratory diseases

 Gasification: avoids burning coal altogether, more

environmentally friendly

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 Measures to achieve sustainable development

 Promoting CCTs, including carbon sequestration is essential

to a balanced cost effective climate change response

 Developing countries where coal combustion efficiencies are

low CCT promotion a need of the day

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 What is gasification

 Conversion of any carbonaceous fuel to a gaseous product with

a useable heating value

 The feed for Gasification can be

Gas (e.g., Natural gas)

Liquid (e.g., Light or Heavy oils)
Solid (e.g., Petroleum Coke, Coal, Lignite or
Biomass).

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 Principles of gasification

 Gasification technologies have been commercially applied for

more than a century for production of both fuels & chemicals

 Gasification is an incomplete combustion of coal

 The primary goal of gasification is to convert the entire non-

ash fraction of feed to syngas

 Syngas is used for power generation, clean fuels production and

basic chemicals manufacturing

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 Products flexibility from gasification
Power & Steam Carbon Source Iron Reduction

Naptha Fischer- Gasification Fuel/Town Gas

Tropsch
Waxes Liquids Synthesis Gas H2 Ammonia
& Urea
Diesel/Jet/Gas Fuels Methanol Dimethyl Ether

Synthetic Natural Gas

Ethylene
Methyl Acetate &
Acetic Acid Propylene
Acetate
Esters Oxo Chemicals

Acetic Anhydride Polyolefins

 Alternative features of gasification technology

 The ability to produce a consistent product

 To process a wide range of feed-stocks including coal, biomass,

petroleum coke, agricultural wastes and refinery wastes

 To convert low-value products into higher value products

 To minimize the amount of MSW requiring landfill disposal

 To remove the contaminants in the feed-stocks

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 History of gasification
Period Technology
Before 1700 Major fuels were Wood and Charcoal

1700-1750 Industrial revolution – Coal as fuel

1800-1900 Coal Pyrolysis – Town gas supply

Water gas, Producer Gas

1920 Cryogenic air separation – Oxygen replaces air

1926 Winkler Fluidized Bed Gasifier

1931 Lurgi Moving Bed Gasifier

1940 Koppers-Totzek Entrained Flow Gasifier

1950s Texaco and Shell develop Oil Gasification

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 History of gasification
Period Technology
1970s Oil crisis

1973 Texaco develops Slurry Process for Coal Gasification

1974 Shell and Koppers-Totzek Pressure Gasification JV

1981 High Temperature Winkler Gasification

1984 Lurgi Slagging Gasifier

1999 Shell/Krupp-Uhde develops Pressurised Entrained

Flow Gasifier

Beyond 2000 Shell Gasification, GE Quench,

Siemens, Chinese, Plasma

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Gasification Methods

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 Gasification vs. Combustion

 Both gasification and combustion processes convert

carbonaceous material to gases. Gasification processes operate
in the absence of oxygen or with a limited amount of oxygen,
while combustion processes operate with excess oxygen

 Objectives of combustion are to thermally destruct the feed

material to generate heat. In contrast, objective of gasification is
to convert feed material into more valuable, environmentally
friendly intermediate products

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 Gasification vs. Combustion

 Products of gasification is syngas consisting of CO, H2, CO2,

H2O, CH4, NH3, N2, S, HCl, COS, HCN, elemental carbon, and
traces of heavier hydrocarbon gases

 The products of combustion processes are CO2, H2O, SOx, Nox,

and HCl

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 Gasification vs. Combustion
Combustion Gasification
Operating temperature Lower Higher
Operating pressure Usually atmospheric Often high pressure
Ash condition Often dry Often slagging
Feed gases Air Steam, oxygen
Product gases CO2, H2O CO, H2, CH4, CO2, H2O
Gas cleanup Postscrubbing Intermediate scrubbing
Pollutants SO2, NO2 H2S, HCN, NH3, COS
Char reaction rate Fast (with O2) Slow (with CO2, H2O)
Oxidizer In excess (Oxidizing) Deficient (Reducing)
Tar production None Sometimes
Purpose High-temperature gas Fuel-rich gas
 Factors affecting quality of syngas

 Feedstock composition

 Feedstock preparation and particle size

 Reactor heating rate

 Residence time

 Plant configuration

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 Introduction of coal

 Coal is an extremely complex heterogeneous material that is

difficult to characterize. Coal is a rock formed by geological
processes and is composed of a number of distinct organic
entities called macerals and lesser amounts of inorganic
substances – minerals
 Coal is a chemically and physically heterogeneous, combustible,
sedimentary rock consisting of both organic and inorganic
material
 It is a readily combustible black or brownish-black sedimentary
rock
 Coal consists primarily of carbon, hydrogen & oxygen with
lesser amount of sulfur and nitrogen
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Coal
 Origin of coal

 Coal is found in deposits called seams that originated through

the accumulation of vegetation that has undergone physical and
chemical changes

 Two main theories for accumulation of vegetal matter that gives

rise to coal seams

1. Autochthonus Origin (Vegetation grew & fell)

2. Allochthonous Origin (Vegetation carried by streams and

deposited on the bottom of the sea or in the lakes)

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 Coalification

Peat  Burried peat is converted to coal when

Lignite high pressure and elevated temperature is
applied, is known as coalification
Sub-bituminous  Physical & chemical structure of coal
Bituminous changes over time
 Petrography
Anthracite  The depth, temperature, degree of acidity
and natural movement of water are
important factors in the formation of coal

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 Most commonly used terms

 As-received/As-fired: Data are expressed as percentages of the

coal with moisture

 Dry basis (db): Data are expressed as percentages of the coal

after moisture has been removed

 Dry ash free (daf): Data are expressed as percentages of the

coal with the moisture and ash removed

 Dry mineral matter free (dmmf): The coal is assumed to be free

of both moisture and mineral matter and data bases on the
organic portion of the coal
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 Most commonly used terms
 Moist ash free (maf): The coal is assumed to be free of ash but still
contains moisture

 Moist mineral matter free (mmmf): The coal is assumed to be free

of mineral matter but still contains moisture

 Caking /Coking coal: upon heating pass through a plastic state

during which the coal soften, swells and re-solidify into coherent
char residue

 Non-caking coal: do not become plastic when heated and produce

a weakly coherent char residue

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 Most commonly used terms
 Gross calorific value/Higher Heating Value (HHV):

 Net calorific value/ Lower Heating Value (LHV):

 Proximate analysis (moisture, volatiles, ash, fixed carbon, mineral)

 Ultimate analysis (elemental composition)

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 Rank of coal

 The degree of coal maturation

 It is an indication of the extent of metamorphism

 Rank is also a measure of carbon content

 Fixed carbon increases with extent of metamorphism

 Lignite and subbituminous (Low rank coal)

 Bituminous and anthracite (High rank coal)

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 Coal type

 The ultimate microscopic constituents of coal are called

macerals

 Three main groups are characterized by their appearance,

chemical composition and optical properties

1. Vitrinite (Derived from woody tissues, having higher oxygen)

2. Exinite/ Liptinite (Derived from plant resins, spores, algal

remains, having higher hydrogen content)

3. Inertinite (derived from woody tissues & fungal remains,

having high inherent carbon content)
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 Grade of coal

 The grade of coal refers to the amount of mineral matter that is

present in the coal and is a measure of coal quality

 Sulfur content, ash fusion temperatures (behavior of ash at high

temperature) and quantity of trace elements in coal are also
used to grade the coal

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Thank You

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