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Overview of Underground Coal Gasification

What is Gasification?
Gasification is the conversion of coal to a gas (called synthesis gas or syngas) through a series of reactions involving heat, pressure, coal and water.

Coal gasification is not new. It has been used since the 1800s to supply heating gas to cities and towns, generate electricity from gas turbine power stations and to produce synthetic liquid fuels.

Syngas can also be used for producing chemicals or other gases such as hydrogen, methane, ammonia, methanol and dimethyl ether.

What is Underground Coal Gasification?

Underground Coal Gasification is the process of gasifying coal in-situ, that is, where it lies in the ground.

This process eliminates the need for mining the coal and processing it through a surface gasification plant. It also removed the need for coal transportation and indeed, ash handling. UCG has been utilised in both commercial and trial scales since the early 1900s.

In its simplest form, the UCG process works like this:

1. Vertical wells are drilled into the coal and linked together horizontally through modern day horizontal drilling techniques;

2. The coal seam is injected with air (sometimes supplemented with oxygen) and is pumped into a well (the injection well) to allow for partial combustion of the coal;

3. Heat and syngas are produced through partial combustion of the coal;

4. Through a series of chemical reactions involving pressure, heat, steam (generated from water in the coal) and carbon from the coal, synthesis gas or “syngas” is produced;

5. The syngas flows from the gasification chamber through the horizontal connection in the coal seam and flows to the surface through another well (called a production well).

The quality and composition of the gas produced depends on many factors including coal type, operating pressure and temperature, coal depth, water ingress to the process and the type of oxidant used (air or oxygen).

Benefits of UCG

UCG offers the potential to use the energy stored in coal deposits that are uneconomic to mine by conventional methods. The use of UCG could potentially increase global coal reserves from 900 billion tonnes to 1.5 trillion tonnes.

Other benefits of UCG include:

• No need to mine the coal or build a surface plant for gasification;

• Elimination of the safety hazards associated with underground coal mining;

• The syngas product can be used in a variety of industrial processes including power generation, liquid fuel production and chemical manufacture;

• Significant environmental benefits, such as reduced surface disturbance and land use conflicts (compared with coal mining and oil and gas operations), a relatively small footprint area for large amounts of energy extraction and the technology is designed for carbon capture;

• With an approximate 25 per cent reduction in greenhouse gas emissions, UCG is a lower carbon dioxide emitting technology for power generation (compared to coal fired power stations);

• UCG sites often exist in areas where geological formations are suitable for the long term sequestration and storage of carbon dioxide (geo-sequestration).

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What is Gasification?
Gasification is the conversion of coal to a gas (called synthesis gas or syngas) through a series of reactions involving heat, pressure, coal and water.
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