Gasification is a process for the conversion of waste into usable form and for energy production.

1. GASIFICATION
Prepared by Ayesha Ashraf
FUUAST
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2. INTRODUCTION
 Gasification is a technological process that can
convert any carbonaceous (carbon-based) raw
material such as coal into fuel gas, also known as
synthesis gas (syngas for short). Gasification
occurs in a gasifier, generally a high
temperature/pressure vessel where oxygen (or
air) and steam are directly contacted with the
coal or other feed material causing a series of
chemical reactions to occur that convert the feed
to syngas and ash/slag (mineral residues).
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3. FUNDAMENTALS OF GASIFICATION
 Gasification is a partial oxidation process.The term partial
oxidation simply means that less oxygen is used in gasification
than would be required for combustion (i.e., burning or complete
oxidation) of the same amount of fuel.
 Gasification typically uses only 25 to 40 percent of the
theoretical oxidant (either pure oxygen or air) to generate
enough heat to gasify the remaining unoxidized fuel, producing
syngas.
 The major combustible products of gasification are carbon
monoxide (CO) and hydrogen (H2), with only a minor amount of
the carbon completely oxidized to carbon dioxide (CO2) and
water.
 The heat released by partial oxidation provides most of the
energy needed to break up the chemical bonds in the feedstock,
to drive the other endothermic gasification reactions, and to
increase the temperature of the final gasification products.
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4. REACTIONS & TRANSFORMATIONS
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5. REACTIONS & TRANSFORMATIONS
. The chemistry of gasification is quite complex and is accomplished
through a series of physical transformations and chemical
reactions within the gasifier.
 Dehydration – Any free water content of the feedstock
evaporates, leaving dry material and evolving water vapor which
may enter into later chemical reactions.
 Pyrolysis –This occurs as the feedstock is exposed to rising
temperature in the gasifier. Devolatization and breaking of the
weaker chemical bonds occurs, releasing volatile gases such as
tar vapors, methane, and hydrogen, along with producing a high
molecular weight char which will undergo gasification reactions.
 Combustion –The volatile products and some of the char react
with limited oxygen to form carbon dioxide (CO2), carbon
monoxide (CO), and in doing so, provide the heat needed for
subsequent gasification reactions.
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6.  Gasification –The remaining char reacts with
CO2 and steam to produceCO and hydrogen (H2).
 Water-gas-shift and Methanation –These are
separate reversible gas phase reactions taking place
simultaneously based on gasifier conditions.These
are minor reactions which play a small role within in
the gasifier. Depending on the desired product, the
syngas may undergo further water-gas-
shift and methanation processing downstream from
the gasifiers.
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7. In the low-oxygen, reducing environment of the gasifier,
most of the feedstock’s sulfur coverts to hydrogen sulfide
(H2S), with a small amount forming carbonyl sulfide (COS).
Nitrogen chemically bound in the feed generally converts
to gaseous nitrogen (N2), with some ammonia (NH3), and a
small amount forming hydrogen cyanide (HCN).Chlorine is
primary converted to hydrogen chloride (HCl). In general,
the quantities of sulfur, nitrogen, and chloride in the fuel
are sufficiently small that they have a negligible effect on
the main syngas components of H2 and CO.Trace elements
associated with both organic and inorganic components in
the feed, such as mercury, arsenic and other heavy metals,
appear in the various ash and slag fractions, as well as in
gaseous emissions, and need to be removed from the
syngas prior to further use.
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8. SYNGAS
 Syngas is Composed primarily of the colorless,
odorless, highly flammable gases such as carbon
monoxide (CO) and hydrogen (H2).
 Syngas has a variety of uses.
 It act as an intermediate in the production
of synthetic natural gas.
 It can be converted (or shifted) to hydrogen and
carbon dioxide (CO2) by adding steam and
reacting over a catalyst in a water-gas-shift
reactor.
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9.  Furthermore, hydrogen made from coal or other
solid fuels can be used to refine oil, or to make
products such as ammonia and fertilizer. More
importantly, hydrogen enriched syngas can be used
to make gasoline and diesel fuel. Polygeneration
plants that produce multiple products are uniquely
possible with gasification technologies. Carbon
dioxide can be efficiently captured from syngas,
preventing its greenhouse gas emission to the
atmosphere and enabling its utilization (such as
for Enhanced Oil Recovery) or safe storage.
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10. SYNGAS COMPOSITION
 The composition can vary significantly
depending on the feedstock and the gasification
process involved; however typically syngas is 30
to 60% carbon monoxide (CO), 25 to 30%
hydrogen (H2), 0 to 5% methane (CH4), 5 to 15%
carbon dioxide (CO2), plus a lesser or greater
amount of water vapor, smaller amounts of the
sulfur compounds hydrogen sulfide (H2S),
carbonyl sulfide (COS), and finally some
ammonia and other trace contaminants.
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11.  The discussion of syngas composition is of
considerable importance considering the
varying requirements on composition and
impurities demanded according to final uses
of the syngas.The following table shows the
widely varying characteristics desirable for
the principal uses of syngas, including use as
fuel gas to fire boilers or turbines
in power cycles, use of syngas as feedstock
for production of synthetic fuels such
as gasoline, use as feedstock
for methanol synthesis, and use as feedstock
for production of hydrogen.
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12. Types of Gasifiers
Although there are various types of gasifers
(gasification reactors), different in design and
operational characteristics, there are three
main gasifier classifications into which most
of the commercially available gasifiers fall.
These categories are as follows:
 Fixed-bed gasifiers (also referred as moving-
bed gasifiers)
 Entrained-flow gasifiers
 Fluidized-bed gasifiers
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13. IGCC

14.  The syngas can, after cleaning, be combusted in
a gas engine resulting in an electrical efficiency
in the range of 22–35%. Another option is to
combust the syngas in a gas turbine, which gives
an electrical efficiency of up to 40.The syngas
can also be further upgraded into methane in
a methanation process.This product is often
referred to as substitute or synthetic natural gas
(SNG).The SNG could be fed into the natural gas
grid and be used in conventional stationary gas
utilities, or alternatively, as fuel in the
transportation sector. As indicated, also liquid
transport biofuels can be produced from the
syngas, including, for example, Fischer–Tropsch
diesel and methanol.
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15.  https://www.netl.doe.gov/research/coal/energy-
systems/gasification/gasifipedia/gasification-
chemistry
 https://www.slideshare.net/AdityaBose12/gasific
ation-and-gasifiers
 https://netl.doe.gov/research/Coal/energy-
systems/gasification/gasifipedia
 https://www.sciencedirect.com/topics/earth-
and-planetary-
sciences/gasification#:~:text=Gasification%20is
%20a%20process%20in,among%20other%20co
mponents%2C%20is%20produced.
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