Leigh Creek Energy (LCK) plans to produce energy from coal using a process known as in situ gasification (ISG) at the Leigh Creek Coalfield in northern South Australia.
The ISG process converts coal from its solid state into a gaseous form, resulting in the generation of synthesis gas (syngas) containing methane, hydrogen and other valuable components. The syngas can be either used to produce electricity directly or further refined into a variety of products including synthetic methane and ammonia.
Both locally and internationally ISG is also known as underground coal gasification (UCG), however the terms ‘in situ gasification’ or ‘ISG’ are used in South Australia to describe the process, which is consistent with the legislation governing ISG in South Australia.
For the ISG reactions to commence, air is introduced through the inlet well and an initiation device is used to create very high temperatures. As the temperature and oxygen concentration reach optimum levels, a series of reactions convert the solid fuel into syngas, which is then extracted through the outlet well.
The ISG process is a chemical conversion from solid coal to gas rather than a combustible conversion (‘burning’) which would create heat and carbon dioxide rather than syngas.
The area in the coal seam where the gasification takes place is referred to as the gasifier chamber, and the reactions that form syngas typically occur at temperatures of between 900°C and 1200°C.
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:
Small surface disturbance: above ground facilities can be easily located away from sensitive areas without impacting access to targeted reserves. 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.
Safe working environment: only small amounts of equipment goes underground, not people and large machines.
Groundwater protection: ISG can be conducted at depths well below fresh water and in saline water.
Waste minimisation: ISG eliminates much of the energy waste associated with moving waste rock as well as usable product from the ground to the surface.
Reduction in greenhouse emissions: ISG produces less greenhouse gas than conventional mining and has the potential for subsurface geologic CO2 storage.
Low capital and operating costs: no surface gasification facilities are needed; hence, capital costs are substantially reduced. No coal is transported at the surface, reducing cost, emission control equipment, and costs associated with operating railways, coal shipping and stockpiling. The cost of producing ISG gas is lower than surface coal gasification and other non-conventional gas developments.
Optimising resources: able to extract energy from coal too deep or uneconomic to mine.
Highly efficient process: small physical footprint for very large amounts of energy extraction and produces energy (synthesis gas) efficiently relative to other coal extraction and natural gas production techniques.