Gasification is a process that converts carbon-based materials like coal, biomass, and waste into a synthetic gas (syngas) through partial combustion with oxygen and steam. Underground coal gasification (UCG) uses the same chemical reactions as surface gasification but occurs directly in underground coal seams. UCG allows access to deeper or less accessible coal reserves and produces syngas with lower emissions and ash/tar content than surface gasification. While UCG has economic and environmental advantages over mining and surface gasification, challenges include potential groundwater contamination and subsidence if not properly managed through geological studies and process optimization.

1. Earth. Insight. Values.
What is Gasification?
8/29/2022 Slide 1
 Gasification is a form of incomplete combustion in which a fuel is burnt in an oxygen-deficient atmosphere. This technological
process that can convert any carbonaceous (carbon-based) raw material such as coal, biomass and some waste streams into fuel
gas, also known as synthesis gas (syngas for short) which can be further used in production of electricity and other useful products.
 The advantages of gasification in specific applications and conditions, particularly in clean generation of electricity from coal, may
make it an increasingly important part of the world's energy and industrial markets.
 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).
 Syngas is primarily composed of colorless, odorless, highly flammable gases carbon monoxide (CO) and hydrogen (H2), syngas
has a variety of uses.
 More importantly, hydrogen enriched syngas can be used to make gasoline and diesel fuel.

2. Earth. Insight. Values.
What is Underground Coal Gasification?
8/29/2022 Slide 2
 Underground Coal Gasification (UCG) takes advantage of the
same chemical reactions of coal to produce product gases, as
those occurring in conventional gasifier reactors. The main
difference is that in UCG the underground coal seam itself
becomes the reactor, so that the gasification of the coal takes
place underground instead of in a manufactured gasification
vessel at the surface.
 Underground coal gasification is the most prominent way to
harness unrecoverable reserves of coal.

3. Earth. Insight. Values.
Underground Coal Gasification
8/29/2022 Slide 3
 With increasing demand for natural gas and chemical products and increasing concerns over mining practices, interest in UCG has
revived around the world.

4. Earth. Insight. Values.
8/29/2022 Slide 4
The challenge of managing CO2 emissions creates a
strong drive towards pairing UCG with carbon capture
and sequestration (CCS).
The added potential of economically sequestering
greenhouse gas emissions in the combustion cavity or
adjacent strata gives UCG an especially important added
advantage over other clean coal technologies.

5. Earth. Insight. Values.
Advantages of UCG:
8/29/2022 Slide 5
 UCG eliminates the need for mining, and the dangers to miners and environmental degradation that are associated with it.
 It also makes deep or difficult to access coal seams into usable energy assets, as only one-sixth to one-eighth of the world's coal
reserves are economically mineable.
 UCG has been demonstrated on almost all types of coal, although coal with lower ash content is preferable.
 Compared to surface gasification, UCG requires much smaller gas cleanup equipment, because both the tar and ash content of
UCG-based syngas is substantially lower than that obtained from a surface gasifier. Because the processing of the coal is kept
underground, surface and air emissions of sulfur, nitrous oxides, and mercury are dramatically reduced.

6. Earth. Insight. Values.
Economic Advantages of UCG:
8/29/2022 Slide 6
 The economics of UCG appear extremely promising.
 The capital expenses of UCG plants appear to be substantially less than the equivalent plant fed by surface
gasifiers because purchase of a gasifier is not required.
 Similarly, operating expenses are likely to be much lower because of the lack of coal mining, coal
transportation, and significantly reduced ash management facilities.
 Even for configurations requiring a substantial environmental monitoring program and additional swing
facilities, UCG plants retain many economic advantages.

7. Earth. Insight. Values.
Disadvantages of UCG:
8/29/2022 Slide 7
 Challenges with underground coal gasification from the potential leaching of unwanted substances into groundwater. Controlling
leaching also requires extensive geological study.
 Subsidence, where the surface sinks as the deep seam is gasified, can also be an issue. Subsidence can be reduced or eliminated
through careful analysis of geology and selective gasification of seam areas, much like pillar and chamber underground mining
practices.
One approach demonstrated in Australia involves optimizing operating conditions such that the pressure in the gasifier is lower than
pressure in the coal seam and in the surrounding strata. As a result, there is no drive for groundwater flow from the gasifier chamber or
loss of product or contaminants into the surroundings.

8. Earth. Insight. Values.
8/29/2022 Slide 8
Thank You