Underground coal gasification (UCG) involves drilling wells into a coal seam and injecting oxidants to gasify the coal in situ. The resulting syngas is brought to the surface through a second well. UCG allows exploitation of deep and unminable coal reserves. It produces syngas with lower emissions than conventional coal and leaves radioactive ash underground. Recent projects demonstrate renewed interest from China, India, South Africa, and Australia in commercializing UCG.

2. PRESENTATION TOPIC
UNDERGROUND COAL GASSIFICATION
PRESENTATION BY
ABDURRABB KHAN

3. COAL
COALGASSIFICATION
UNDERGROUND COALGASSIFICATION
THE BASIC UCG PROCESS
COMPLETE UCG PLANT OVERVIEW
PROCESS CONTROL
UCG PRODUCTS
WHY UCG IS IMPORTANT
UCGADVANTAGES
UCG DISADVANTAGES
DEVELOPMENTS, PROJECTSAND INTERESTS
CONTENTS

4. COAL
*Coal is a black or brown rock that can be
ignited and burned to produce energy in the
form of heat.

5. Coal Gasification-Controlled combustion
of coal and obtain syngas (H2, CO).
1) Underground coal gasification (UCG)
2) Surface coal gasification(SCG)
COAL GASIFICATION

6. Underground Coal Gasification
Underground coal gasification (UCG) is the in-situ
conversion of coal into combustible gases. In which
unmined coal seams are reacted underground, with
insufficient oxygen for complete combustion to
produce syngas(CO+H2)

7. TheBasicUCG
Process
Two wells drilled into the
coal, one for injection of
the oxidants, another to bring
the product gas to
the surface.

8. 8
Two boreholes are drilled into the coal seam and a path between these two
boreholes is established.
Borehole maximum depth 600m, Distance between two boreholes is about
50m.
UCG – 1st stage

9. 1. Fracture of the coal seam by air pressure or explosions
2. Reverse combustion technique
3. Modern directional drilling techniques(magnetic target, magnetic
detector)

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Coal is ignited, combustion is maintained by injecting air or oxygen and steam
–

11. 11
The resulting gases are brought to surface by the second bore hole
–

12. 12

13. Operator of an underground coal gasification plant has
following controls over the process.
Temperature
Pressure
Gas flow rate
Composition of gas at injection and production well
PROCESS CONTROL

14. Change in gas composition and temperature from the
injection well to the production well at 50meter
apart.
Flammable gases combust in the first ten meters, consuming all of the
available oxygen and causing a sharp rise in gas temperature.
At the end of the combustion zone, the gases primarily consist of hot,
non-flammable N2,CO2, and H2O. In the following 40 meters, steam
and CO2 react with char, so H2 and CO concentrations rise while
steam and CO2 levels fall.
The methanation reaction raises the concentration of methane. The
gas calorific value increases as the gas flows through the cavity.

15. The temperature falls due to the endothermic nature of
the steam and CO2 gasification reactions, as well as the
heat required to evaporate water seeping into the cavity.
By the time the gas reaches the production well at 50
meters, the temperature is barely sufficient to sustain a
significant rate of gasification.

16. 16
Coal
UCG - Products

17. Coal seam shallower then 150m is rejected.
Coal seam Deeper then 600m is rejected.
Coal Seams thinner then 10m are also rejected
Recovery factor is 65% and remaining 35% is left for
roof support.
LIMITATIONS FOR THE SELECTION
OF COAL DEPOSIT

18. Most known coal resources in the world are too deeply buried to be
economically mined out. Nearly 85% of known coal reserves are un-
mineable with surface mining. So, UCG is proposed for these reserves.
The costs of drilling air injection and syngas production wells are a
small fraction of the cost of a gasification complex, so deeply buried
coal seams may be gasified at a reasonable cost.
UCG is producing fuels and hydrocarbon feedstock today from
unrecoverable coal deposits.
Countries are turning to UCG to fully utilize their coal resources in an
economically viable and environmentally acceptable manner.
WHY UCG IS IMPORTANT?

19. 19
UCG - Utility

20. Composition of syngas:
syngas chemical composition can vary based on the raw
materials and the processes, the syngas from coal
gasification generally is a mixture of 30 to 60% carbon
monoxide, 25 to 30% hydrogen, 5 to 15% carbon dioxide,
and 0 to 5% methane.

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Facilitates exploitation of deep / unminable coal
reserves
Higher efficiency coupled with low capital costs
than conventional coal-fired station
Eliminates SO2 emission
Radio active ash remains deep down…
UCG - Advantage

22. 1. Environmentally friendly
2. Significant reduction in CO2, SOx, NOx emissions
3. No Waste disposal (Ash Trapped Underground)
4. Reduced emission of Green House Gases by CO2 Sequestration
5. Short Construction and Commissioning Time
22
UCG - Advantage

23. 1) Surface subsidence
2) Aquifer water contamination
3) Removal of the coal from coal seam can cause the
roof fall, when roof collapses the water from a shallow
freshwater aquifer mixed with the tar-contaminated
coal and rock and is contaminated.
UCG- DISADVANTAGES

24. In the last few years there has been significant renewed interest in UCG as
the technology has moved forward considerably.
China has about 30 projects in different phases of preparation that use
underground coal gasification.
India plans to use underground gasification to access an estimated 350
billion tones of coal.
SouthAfrican companies Sasol and Eskom both have UCG pilot facilities
that have been operating for some time, giving valuable information and
data.
InAustralia, Linc Energy has the Chinchilla site, which first started
operating in 2000. Carbon Energy has completed a successful 100 day
commercial scale study in Blood wood Creek in 2008.
DEVELOPMENTS, PROJECTS & INTEREST