In Situ Gasification (ISG)

ISG occurs when coal is heated underground, in-situ (being "on site" or "in position") through a highly controlled process, and transformed from its solid state into a range of valuable gases, collectively known as synthesis gas, or Syngas. 

Syngas is produced and extracted through wells drilled into the coal seam, by which air or oxygen are injected to heat the coal in-situ, and to produce the synthetic gas (“Syngas”) to the surface for further processing, transport, or manufacture.

The wells that extract the gas are called Production Wells, and Injection Wells supply the air or oxygen.

 

 

Once the Production Well is drilled vertically into the coal seam, it is cased in steel and concrete to ensure there is no gas leakage. 

This well is connected to the gas clean up plant above the ground. 

The Injection Well, located some distance away, is drilled horizontally in the coal seam to precisely intersect the Production Well.

The Injection Well is connected to surface facilities with the oxygen, air and nitrogen supply equipment. 

 

ISG Process

By creating the right process conditions (pressure, temperature and oxygen) in the coal seam, a series of chemical reactions occurs, which results in gasification of the solid coal. The high-pressure natural environment in deep coal seams (pressure increases with depth) is beneficial to the gasification process, resulting in more thorough and efficient conversion of coal into Syngas that is produced to the surface.   

Detailed planning is undertaken to locate and define the parameters of the ISG chamber.  The ISG chamber is formed within the coal itself, with the rock above forming the roof of the ISG chamber. 

The ISG process starts by heating the coal underground.  An Ignition Tool is fed through and to the end of the Injection Well, to provide heat to start the ISG process  and is then retracted and removed from the ISG chamber.

Oxygen or air is then injected from surface facilities through the Injection Well into the ISG chamber to commence and then maintain the gasification process.  As the solid coal changes to its gaseous form, a chamber bounded by coal forms.  That is, not all of the coal is gasified.  The outer boundaries of the chamber remain to hold the roof rock above.  Controlling the rate of gasification in the process ensures that the chamber’s integrity is not compromised.

As the coal is heated a chemical reaction (gasification) occurs inside the chamber which converts the solid coal into gas.  Put simply, the atoms in the coal, moisture present and oxygen supplied separate under high temperature and then recombine to form the different gases within Syngas.  Once heat and oxygen are applied to the coal, Syngas is produced. 

Importantly, as the ISG process operates in a highly controlled and constantly monitored environment, it can be stopped quickly and easily at any time by simply shutting off the oxygen supply.

Due to the differences in pressure in the ISG chamber and the Production Well, Syngas flows easily from the ISG chamber into the Production Well, and then to the surface, where it is cleaned and separated for gas distribution ahead of power generation or fertiliser manufacture.

 

Advantages of ISG

ISG is not a new technology or process, and because it has successfully operated in many demonstration sites and commercial operations in several countries over many decades, its benefits are well documented.  ISG has many advantages, including:

  1. Low capital and operating costs
    1. No surface gasification facilities are needed, hence, capital costs are substantially reduced;
    2. No coal is transported at the surface, reducing cost, emission control equipment, and costs associated with operating railways, coal shipping and stockpiling;
    3. The cost of producing ISG gas is lower than surface coal gasification and other non-conventional gas developments.
  2. Extracting energy from coal too deep or uneconomic to mine.
  3. Small surface disturbance
    1. Above ground facilities can be easily located away from sensitive areas without impacting access to targeted coal reserves.
    2. The need for above ground plant, production, or refinement facilities, or for solid waste handling and disposal operations is eliminated because ash, char, and other solid residual materials from the gasification process remain underground.
  4. Highly efficient gasification process - small physical footprint for very large amounts of energy extraction and produces energy (gas) efficiently relative to other coal extraction and natural gas production techniques.
  5. Safe working environment – only small amounts of equipment goes underground, not people and large machines.
  6. ISG can be conducted at depths well below fresh water, and in saline water.
  7. ISG eliminates much of the energy waste associated with moving waste rock as well as usable product from the ground to the surface.
  8. Produces less greenhouse gas than conventional mining.
  9. Has potential for geologic CO2 storage (known as carbon sequestration).
  10. ISG delivers significant benefits to regional areas through economic development and the creation of employment opportunities, many of which are long term and include skill advancement roles.